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M.SC. (FINAL) CHEMISTRY
PAPER –III : ENVIRONMENTAL CHEMISTRY
BLOCK-I
Unit -1 : Environment
Unit-2 : Hydrosphere
Unit – 3 : Water Quality Parameters
Author – Dr. Purushottam B. Chakrawarti
Dr. Aruna Chakrawarti
Editor – Dr. Anuradha Mishra
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BLOCK SUMMARY
Environment is the totality of all social, biological and physical
factors individually as well as collectively that compose the nature
and manmade surroundings. Man is a part of environmental system.
The environment consists of four components atmosphere,
hydrosphere, lithosphere and biosphere. The temperature variation in
these components is the basis of heat budget of the earth. While the
elements (C, N, P, O etc.) and compounds that sustain us cycle
endlessly through living things and the environment.
Hydrosphere includes various water resources water is essential
for the sustenance of human life and activities. Human activities
pollute it. The pollutant include inorganic, organic, agricultural and
industrial effluents all.
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UNIT-1 ENVIRONMENT
STRUCTURE
1.1 Introduction
1.2 Objectives
1.3 Composition of Atmosphere
1.4 Vertical temperature, Heat budget of the earth.
1.5 Vertical Stability of Atmosphere
1.6 Biochemical Cycles of C, N, P and O
1.7 Biodistribution of elements.
1.8 Let Us Sum Up
1.9 Check Your Progress : The key
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1.1 INTRODUCTION
Environment (from the French environment: to encircle or surround) can
be defined as the circumstances and conditions that surround an organism or
group of organisms
We inhabit two worlds. One is the natural world of plants animals, soil,
air, and water that preceded us by billions of years and of which we are a part.
The other is the world of social institutions and artifacts that we create for
ourselves using science technology and political organization. Both worlds are
essential to our lives, but integrating them successfully enduring tensions.
Thus environment is a complex of so many things (light, temperature,
water, air, soil etc.) which surrounds an organism. The green fields, trees,
shrubs, ponds, tanks, lakes, rivers, forests, blue sky and the various systems
existing in the nature – all constitute the so called environment. Environment
creates favourable conditions for the existence and development of creatures.
The land is used for meeting the food and raw material supplies, while water is
used for drinking, irrigation and power etc. The air is an important part for
living creatures as no body can pass even few minutes without air.
'Environment' is considered as a composite term for the conditions in
which organism lives. It includes both biotic and abiotic substances, energy and
forces e.g., temperature, light, water, air, soil and other organisms. In nut shell
environment is the totality of all social, biological and physical or chemical
factors individually as well as collectively that compose the nature and man
made surroundings. Man is a part of Environmental system.
Thus 'Environment' is a very wide term. It includes total physical and
biotic world. in which biological beings live, grow, get nourished, and develop
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their natural characteristics. In other words, it concerns with the 'Biosphere',
which includes all biotic parts of hydrosphere lithosphere and atmosphere.
Environment is the source of life. It has not only given shelter to human
and all the other biotic world, but has also been the very basis for their
existence on the earth since their evolution to their development this date. The
future life is also dependent on it. Consider the extraordinary natural world that
we inherited and that we hope to pass on to future generations. In this beautiful,
bountiful planet, we live in a remarkably prolific and hospitable world that is as
far as we know, unique in our solar system. The mild and relatively constant
temperature along with plentiful supplies of clean air, fresh water, and fertile
soils, which are regenerated endlessly and spontaneously by biogeochemical
cycles.
Perhaps the most amazing feature of our planet is its rich diversity of life.
Millions of beautiful and intriguing species populate the earth and help sustain a
habitable environment. This vast multitude of life creates complex, interrelated
communities where towering trees and huge animals live together with, and
depend upon, such tiny life-forms as viruses. bacteria, and fungi, Together, all
these organisms make up delightfully diverse, self-sustaining communities,
including dense, moist forests; vast, sunny savannas; and richly colorful coral
reefs. No living being can live altogether solitary or isolated life. Different
living beings on this earth are in such a large quantity that, in its habitat one has
to live essentially in cooperation with many other living beings. This type of
cooperative living has serious effects on the way of life in a habitat. In this
respect the physical environment is also important; as the maximum energy of a
living being is consumed in adopting itself according to the physical conditions
of the environment. This underlines the interrelation between environment and
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biotic life and we can not imagine existence of any being devoid of
environment.
All animals for their food depend directly or indirectly on plants; while
many plants for the same depend on animals. For example plants need insects
for their pollination. Although some green plants can survive for some time
with the help of solar energy and the nourishing elements of soil but as soon as
germination starts competitive relations become evident. As, in the environment
of every living being other being are essentially and unavoidably present study
of the effects of environment on human life and vice versa is important. It is
also important in the light of various adaptations (Morphological, physiological,
behavioural and pertaining to social relations) which one has to take due to his
or her interactions with the environment.
As a matter of fact, the existence of life basically depends upon the
environment. All living beings including human being get various things useful
to their life from the environment. In the abscence of sustainable environment
many adverse and harmful effects are seen and the present conditions are such
that many countries of the world are suffering due to environmental pollutions.
To produce the goods and services needed to improve life for every one without
overtaxing the environmental systems and natural resources, on which we all
depend, understanding of our environment is necessary. Then only one, whether
a professional scientist or a concerned citizen, can apply his knowledge in
enjoyable and useful ways.
The geographers divide the environment into two parts – (i) Macro
Environment – a general environment to which an individual is exposed, for
example air, water, soil, noise etc. while (ii) Micro Environment – is a
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personal environment of an individual which is attached with his life style and
living for example house, garden, park, agricultural field, occupation, health,
education, family structure etc. So micro environment can be defined as the
specific environment of an individual in which he lives or an immediate
environment of an individual. in which he lives or an immediate environment of
an individual.
According to an anthropologist, the social environment is a micro
environment for a human being while according to medical geographer the
micro environment consists of physical and cultural phenomenon in which all
animals and human beings live together. Bio-scientists are of the view that
organic and inorganic phenomena can also be included in the micro
environment as they play a vital role in man and animal life. The wind,
humidity, temperature, soil, water, air and trace elements are called inorganic
materials while micro-organisms, food and agricultural materials including men
and animal life fall under the heading of organic materials. The environmental
health can be defined as that aspect of public health which is related with
inorganic and organic materials as they exert an influence on man's health,
because man is surrounded by both type of materials.
So micro environment can be defined as the environment involving air,
water, soil, food, sound etc. In fact it can be called an external environment to
which man is exposed. It has direct impact on physical and mental state of a
men.
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1.2 OBJECTIVES
The main objective of this unit is to discuss environment and its
components. After going through this unit you will be able to :
describe what is the significance of 'environment' and its components,
discuss composition of atmosphere,
describe vertical temperature and heat budget of the earth,
work out significance of biochemical cycles of C, N, P and O, and
describe biodistribution of elements.
1.3 COMPOSITION OF ATMOSPHERE
As has been pointed out, the environment can be described as the
physical surroundings and conditions affecting the lives of people and animals.
The environment consists of four components – (i) atmosphere,
(ii) hydrosphere, (iii) lithosphere and (iv) biosphere.
We live at the bottom of a virtual ocean of air that extends upward about
500Km. This thick layer around the earth is called the atmosphere. It is the part
full of gases. It absorbs sun rays, cosmic rays and man made gases etc., and
plays important role in keeping the heat balance of the earth through absorption
of rays and reemitting back from earth. This balance is maintained with the help
of major gases such as nitrogen and oxygen, along with traces of water vapours,
carbon dioxide, neon, helium, argon, xenon and many other gases.
The atmosphere consists of nitrogen 78.09% and oxygen 20.94% by
volume as its major components. The minor components are argon 0.34 X 10-
1%, Carbon dioxide 3.25 x 10
-2 % by volume (Table – 1.1), apart from trace of
inertgases and other gaseous substances.
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Table 1.1 : Minor Components of the atmosphere
Trace Components % by Volume
1. Helium 5.24x10-4
2. Neon 1.82x10-3
3. Krypton 1.14x10-4
4. Hydrogen 5x10-5
5. Ozone trace
6. Ammonia 1x106
7. Carbon monoxide 1.2x10-5
8. Iodine trace
9 Sulphur dioxide 2x10-8
10. Xenon 8.710-6
11. Nitrous oxide 2.5x10-5
12. Methane 2x10-4
13. Nitrogen dioxide 1x10-5
The total mass of the atmosphere is nearly 5 x 1013
tons and the density
of the atmosphere indicates a decrease with increase of altitude while
temperature varies from – 92ºC to about 1200ºC.
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Structure of atmosphere- The whole atmosphere can be divided into
four regions with altitude from 0 km to 500 km, temperature ranging from -
92ºC to 1200ºC. The chemical species present in different regions of
troposphere; stratosphere; mesosphere and thermosphere are H2O, N2, O2, CO2,
O3, NO+, O
+2 and O
+. Regions with change of altitude, temperature and species
are summarised in Table 1.2.
Table 1.2 – Regions of atmosphere with temperature change and chemical
species.
No. Region Altitude in
km.
Temperature
change in ºC
Chemical species
1. Troposphere 0-11 15 to -56 N2, H2O, CO2, O2
2. Stratosphere 11-50 -56 to -2 Ozone
3. Mesosphere 50-85 -2 to -92 NO+, O
2
4. Thermosphere 85-500 -92 to 1200 NO+, O
+, O
2
1. Troposphere – This is a region of atmosphere having an altitude
between 0-11 km, temperature changes 15ºC to – 56ºC and chemical species are
oxygen, carbon dioxide, nitrogen and water vapour. In fact this region contains
70% mass of the atmosphere where water content changes due to hydrological
cycle. The lower level near the earth has high temperature due to radiation from
earth while the top part is cold and has a temperature of about – 56ºC. This top
part is also known as tropopause. The word 'tropo' means change. In this
region action of winds keep the troposphere in motion continuously.
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2. Stratosphere – This region lies above the troposphere. The height ranges
from 11km. to 50km. while temperature changes from -2ºC to -56ºC. The main
chemical species of this region is the valuable compound ozone- a gas which is
very essential protective layer to check ultraviolet rays of the sun which are
harmful for man's life. As the temperature of this region is very low hence it
contains no clouds, dust or water vapour.
3. Mesosphere – The upper part of this region is known as mesopause
where the maximum temperature is – 92ºC. This sphere is situated at a height
between 50km. to 85 km. with a starting temperature of -2º due to absorption of
ultraviolet radiations by ozone. The important species are positively charged
particles or ions known as O
2 and NO+.
4. Thermosphere or Ionosphere – This region is situated at height
between 85 km. to 500 km. above the earth surface. As this region is situated
above the mesosphere hence the temperature range lies between – 92ºC to
1200ºC. As this region is under heavy exposure of ultraviolet rays which
influences the charged particles like O
2 , O+ and NO
+. In fact in this region
nitric oxide and oxygen first absorb ultra violet-radiations from solar rays then
split into positively charged particles as mentioned above.
1.4 VERTICAL TEMPERATURE : HEAT BUDGET OF THE EARTH
As has been mentioned above clean, dry air is mostly nitrogen and
oxygen. Water vapor concentrations vary from near zero to 4 percent,
depending on air temperature and available moisture. Minute particles and
liquid droplets – collectively called aerosol also are suspended in the air.
Atmospheric aerosols play important roles in the earth's energy budget and in
producing rain.
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The atmosphere has four distinct zones of contrasting temperature, due to
differences in absorption of solar energy (fig. 1.1). The layer of air immediately
adjacent to the earth's surface is called the troposphere (tropein means to turn or
change in Greek). Within the troposphere air circulates in great vertical and
horizontal convection currents, constantly redistributing heat and moisture
around the globe. The troposphere ranges in depth from about 18 km (11mi)
over the equator to about 8 km (5mi) over the poles, where air is cold and
dense. Because gravity holds most air molecules close to the earth's surface, the
troposphere is much more dense than the other layers; it contains about 75
percent of the total mass of the atmosphere. Air temperature drops rapidly with
increasing altitude in this layer, reaching about – 60ºC (-76ºF) at the top of the
troposphere. A sudden reversal of this temperature gradient creates a sharp
boundary called the tropopause, which limits mixing between the troposphere
and upper zones.
The stratosphere extends from the tropopause up to about 50km (31 mi).
It is vastly more dilute than the troposphere, but it has similar composition-
except that it has almost no water vapor and nearly 1,000 times more ozone
(O3). This ozone absorbs ultraviolet (UV) solar radiation, producing warmer
temperatures toward the top of the stratosphere. Since UV radiation damages
living tissues, this UV absorption in the stratosphere also protects life on the
surface. Recently discovered depletion of stratospheric ozone, especially over
Antarctica, is allowing increased amounts of UV radiation to reach the earth's
surface. If observed trends continue, this radiation could cause higher rates of
skin cancer, genetic mutations, crop failures, and disruption of important
biological communities.
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Fig 1.1 four distinct zones of the atmosphere
Above the stratosphere, the temperature diminishes again, creating the
mesosphere, or middle layer. The thermosphere (heated layer) begins at about
50 km. This is a region of highly ionized (electrically charged) gases, heated by
a steady flow of high-energy solar and cosmic radiation. In the lower part of the
thermosphere, intense pulses of high-energy radiation cause electrically charged
particles (ions) to glow.
Thus, in the lowest, 10 to 12 km, the layer known as the troposphere, the
air moves ceaselessly, flowing and swirling, and continually redistributing heat
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and moisture from one part of the globe to another. The composition and
behavior of the troposphere and other layers control our weather (temperature
and moisture conditions in a place) and our climate (long-term weather
patterns).
The sun supplies the earth with an enormous amount of energy, but that
energy is not evenly distributed over the globe. Incoming solar radiation
(insolation) is much stronger near the equator than at high latitudes. Of the solar
energy that reaches the outer atmosphere, about one-quarter is reflected by
clouds and atmospheric gases, and another quarter is absorbed by carbon
dioxide, water vapor, ozone, methane, and a few other gases. This energy
absorption warms the atmosphere slightly. About half of incoming solar
radiation (insolation) reaches the earth's surface. Most of this energy is in the
form of light or infrared (heat) energy. Some of this energy is reflected by
bright surfaces, such as snow, ice, and sand. The rest is absorbed by the earth's
surface and by water. Surfaces that reflect energy have a high albedo
(reflectivity). Most of these surfaces appear bright to us because they reflect
light as well as other forms of radioactive energy. Surfaces that absorb energy
have a low albedo and generally appear dark. Black soil, asphalt pavement, and
dark green vegetation, for example, have low albedos.
Absorbed energy heats the absorbing surface (such as an asphalt parking
lot in summer), evaporates water, or provides the energy for photosynthesis in
plants. Following the second law of thermodynamics, absorbed energy is
gradually reemitted as lower quality heat energy. A brick building, for example,
absorbs energy in the form of heat.
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The change in energy quality is very important because the atmosphere
selectively absorbs longer wavelengths. Most solar energy comes in the form of
intense, high-energy light or near infrared wavelengths. This short-wavelength
energy passes relatively easily through the atmosphere to reach the earth's
surface. Reemitted energy from the earth's warmed surface is lower-intensity,
longer-wavelength energy in the far-infrared part of the spectrum. Atmospheric
gases, especially carbon dioxide and water vapor, block much of this long-
wavelength energy, holding it in the lower atmosphere and letting it leak out to
space only slowly. This reemitted, or terrestrial, energy provides most of the
heat in the lower atmosphere. If the atmosphere were as transparent to infrared
radiation as it is to visible light, the earth's average surface temperature would
be about – 18ºC (0ºF) – 33ºC (59ºF) colder than it is now.
This phenomenon is called the "greenhouse effect" because the
atmosphere, loosely comparable to the glass of a greenhouse, transmits sunlight
while trapping heat inside. The greenhouse effect is a natural atmospheric
process that is necessary for life as we know it. However, too much greenhouse
effect, caused by burning of fossil fuels and deforestation, may cause harmful
environmental change.
Much of the incoming solar energy is used to evaporate water. Every
gram of evaporating water absorbs 580 calories of energy as it transforms from
liquid to gas. Globally, water vapor contains a huge amount of stored energy,
known as latent heat. When water vapor condenses, returning from a gas to a
liquid form, the 580 calories of heat energy are released. Imagine the sun
shining on the Gulf of Mexico in the winter. Warm sunshine and plenty of
water allow continuous evaporation that converts an immense amount of solar
(light) energy into latent heat stored in evaporated water. Now imagine a wind
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blowing the humid air north from the Gulf toward Canada. The air cools as it
moves north (especially if it encounters cold air moving south). Cooling causes
the water vapor to condense. Rain (or snow) falls as a consequence. Note that it
is not only water that has moved from the Gulf to the Midwest: 580 calories of
heat have also moved with every gram of moisture. The heat and water have
moved from a place with strong incoming solar energy to a place with much
less solar energy and much less water. The redistribution of heat and water
around the globe are essential to life on earth.
Uneven heating, with warm air close to the equator and colder air at high
latitudes, also produces pressure differences that cause wind, rain, storms, and
every thing else we know as weather. As the sun warms the earth's surface, the
air nearest the surface warms and expands, becoming less dense than the air
above it. The warm air must then rise above the denser air. Vertical convection
currents result, which circulate air from warm latitudes to cool latitudes and
vice versa.
Check Your Progress – 1
Note: (1) Write Your answers in the space given below
(2) Compare your answers with those given at the end of the unit.
(a) (i) Environment may be defined as –
---------------------------------------------------------------------------------
(ii) The four components of the environment are -
(a) ------------------------------
(b) -----------------------------
(c) -----------------------------
(d) -----------------------------
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(iii) The four regions of atmosphere have following characteristics :
Region
(Name)
Altidude in
Km
Temeprature
change in ºC
Chemical
species
1. ------------------ ----------------- ----------------- -----------------
2. ------------------ ----------------- ----------------- -----------------
3. ------------------ ----------------- ----------------- -----------------
4. ------------------ ----------------- ----------------- -----------------
(b) (i) Atmospheric ------------------------ play important roles in the
earth's ----------------------- and producing ---------------.
(ii) The composition and behaviour of the ------------------- and other
layers control our ------------------- and our -------------------.
(iii) the atmosphere, loosely comparable to the glass of a green house,
transmits ---------------- while trapping ---------------------------. This
phenomenon is called ----------------------------.
1.6 Biochemical Cycles of C, N, P, S and O.
The elements and compounds that sustain us cycle endlessly through
living things and the environment. Substances can move quickly or slowly: you
might store carbon for hours or days, while carbon is stored in the earth for
millions of years. When human activity alters flow rates of storage times in
these natural cycles, overwhelming the environment's ability to process these
substances, they can become pollutants.
1.6.1 Carbon Cycle
Carbon is the building material of all living organisms. All the organic
compounds have carbon as the basic component. It is present in food materials
as carbohydrates, proteins, fats and amino acids. The basic movement of carbon
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is from atmospheric reservoir to producers, to consumers and from both these
groups to decomposers and then back to atmosphere. The main source of all
carbon found in living organisms is carbon dioxide and dissolved carbon
dioxide in water. In atmosphere the concentration of carbon dioxide should be
0.03-0.04% in natural way but due to industries and other sources this
percentage is increasing.
During phototynthesis plants utilize carbon dioxide to form carbohydrate
and release oxygen in presence of sun light. This oxygen in utilized by animals.
26126Sunlight22 O6OHCOH6CO6esisPhotosynth
All the organic compounds are also oxidised to water and carbon dioxide
in different processes where CO2 is utilized by plants while H2O is absorbed by
soil for use of plants and in this way the process of photosynthesis by plants and
decompositon of organic compounds continues in nature to release carbon
dioxide.
OH6CO6O6OHC 2226126
and in this way the cycle of carbon continues in nature.
The aquatic carbon dioxide reacts with water in soil to form carbonic acid
(H2CO3) which dissociates into bicarbonate (HCO
3 ) and hydrogen (H+) ions.
As all the processes are reversible hence carbonate or bicarbonate ions on
combination with hydrogen ions lead to the formation of atmospheric carbon
dioxide.
Atmospheric
CO2 Dissolved CO2 + H2O H2CO3 H+ + HCO
3 H+ + CO
3
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By the activities of bacteria and fungi the carbon which is locked up in
animal wastes and in protoplasm of animals and plants is also released in the
atmosphere.
Carbon serves a dual purpose for organisms : (1) it is a structural
component of organic molecules, and (2) chemical bonds in carbon compounds
provide metabolic energy. The carbon cycle begins with photosynthetic
organisms taking up carbon dioxide (CO2) (Fig. 1.2). Once a carbon atom is
incorporated into organic compounds, its path to recycling may be very quick or
extremely slow. Imagine for a moment what happens to a simple sugar
molecule you swallow in a glass of fruit juice. The sugar molecule is absorbed
into your bloodstream, where it is made available to your cells for cellular
respiration or for making more complex biomolecules. If it is used in
respiration, you may exhale the same carbon atom as CO2 in an hour or less,
and a plant could take up that exhaled CO2 the same afternoon.
Alternatively, your body may use that sugar molecule to make larger
organic molecules that become part of your cellular structure. The carbon atoms
in the sugar molecule could remain a part of your body until it decays after
death. Similarly, carbon in the wood of a thousand-year-old tree will be
released only when fungi and bacteria digest the wood and release carbon
dioxide as a by-product of their respiration.
CombustionCoal Atmosphere
CO2
SeaWater
CalciumCarbonate
Aquaticbeings
Resp
iration
Dec
ay
Decay
Com
bustion
PlantsVegetables
Animals
Combustion
Fig.1.2 Carbon Cycle
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Sometimes, recycling takes a very long time. Coal and oil are the
compressed, chemically altered remains of plants or microorganisms that lived
millions of years ago. Their carbon atoms (and hydrogen, oxygen, nitrogen,
sulfur, etc.) are not released until the coal and oil are burned. Enormous
amounts of carbon also are locked up as calcium carbonate (CaCO3), used to
build shells and skeletons of marine organisms from tiny protozoans to corals.
The world's extensive surface limestone deposits are biologically formed
calcium carbonate from ancient oceans, exposed by geological events. The
carbon in limestone has been locked away for millennia, which is probably the
fate of carbon currently being deposited in ocean sediments. Eventually, even
the deep ocean deposits are recycled as they are drawn into deep molten layers
and released via volcanic activity. Geologists estimate that every carbon atom
on the earth has made about 30 such round trips over the last 4 billion years.
Materials that store carbon, including geologic formations and standing
forests, are known as carbon sinks. When carbon is released from these sinks,
as when we burn fossil fuels and inject CO2 into the atmosphere, or when we
clear extensive forests, natural recycling systems may not be able to keep up.
This is the root of the global warming problem.
1.6.2 Nitrogen Cycle
Organisms cannot exist without amino acids, peptides, and proteins, all
of which are organic molecules that contain nitrogen. Nitrogen is therefore an
extremely important nutrient for living things. (Nitrogen is a primary
component of many hosehold and agricultural fertilizers.) Even though nitrogen
makes up about 78 percent of the air around us, plants cannot use N2, the stable
diatomic (two-atom) molecule in the air.
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Plants acquire nitrogen through an extremely complex nitrogen cycle
(Fig. 1.3). The key to this cycle is nitrogen-fixing bacteria (including some
blue-green algae or cyanobacteria). These organisms have a highly specialized
ability to "fix" nitrogen, or combine gaseous N2 with hydrogen to make
ammonia (NH3).
Other bacteria then combine ammonia with oxygen to form nitrites (NO2)
Another group of bacteria converts nitrites to nitrates (NO3), which green plants
can absorb and use. After plant cells absorb nitrates, the nitrates are reduced to
ammonium (NH4), which cells use to build amino acids that become the
building blocks for peptides and proteins.
The reactions involved in this cycle can be summarised below:
3222
22
22
HNO4OOH2NO4
NO2ONO2
NO2ON
OH)NO(CaHNO2CaO
NONHNHHNO
2233
3433
2432
3222
NONHNHHNO
HNOHNOOHNO2
the amino acids are converted into ammonium compounds such as
ammonia, urea and uric acid by some micro-organisms present in the soil. The
ammonia and its salts in the soil are oxidised to nitrites by nitrosifying bacteria
present in the soil. The nitrites are further converted into nitrates by nitrifying
bacteria as follows :
OH2HNO2Bacteria
O3NH2 22
ngNitrosifyi
23
3
Nitrifying
22 HNO2Bacteria
OHNO2
22
Lightening , rain
HNO
+ H
NO
3
2
Atmosphere(N )
2
Denitri fying
bacteria
Dea
th, d
ecay
,
Excr
eti on
Nitr
ifying
Bac
teri a
Animals
Proteins
Plants
Symbio
tic
bacte
ria
Fig. 1.3 Nitrogen Cycle
Members of the bean family (legumes) and a few other kinds of plants
are especially useful in agriculture because nitrogen-fixing bacteria actually live
in their root tissues. Legumes and their associated bacteria add nitrogen to the
soil, so interplanting and rotating legumes with crops such as corn that use but
cannot replace soil nitrates are beneficial farming practices that take practical
advantage of this relationship.
Nitrogen reenters the environment in several ways. The most obvious
path is through the death of organisms. Fungi and bacteria decompose dead
organisms, releasing ammonia and ammonium ions, which then are available
for nitrate formation. Organisms don't have to die to donate proteins to the
environment, however, plants shed their leaves, needles, flowers, fruits, and
cones; animals shed hair, feathers, skin, exoskeletons, pupal eases, and silk.
Animals also produce excrement and urinary wastes that contain nitrogenous
compounds. Urine is especially high in nitrogen because it contains the
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detoxified wastes of protein metabolism. All of these by products of living
organisms decompose, replenishing soil fertility.
How does nitrogen reenter the atmosphere, completing the cycle?
Denitrifying bacteria break down nitrates into N2 and nitrous oxide (N2O), gases
that return to the atmosphere; thus, denitrifying bacteria compete with plant
roots for available nitrates. However, denitrification occurs mainly in
waterlogged soils that have low oxygen availability and a high amount of
decomposable organic matter. These are suitable growing conditions for many
wild plant species in swamps and marshes, but not for most cultivated crop
species, except for rice, a domesticated wetland grass.
In recent years, humans have profoundly altered the nitrogen cycle. By
using synthetic fertilizers, cultivating nitrogen-fixing crops, and burning fossil
fuels, we now convert more nitrogen to ammonia and nitrates than all natural
land processes combined. This excess nitrogen input is causing serious loss of
soil nutrients such as calcium and potassium, acidification of rivers and lakes,
and rising atmospheric concentrations of nitrous oxide, a greenhouse gas. It also
encourages the spread of weeds into areas such as prairies, where native plants
are adapted to nitrogen-poor environments. Blooms of toxic algae and
dinoflagellates in coastal areas also may be linked to excess nitrogen carried by
rivers.
1.6.3 Phosphorus Cycle
Plants consume nitrogen and phosphorus through fertilizers from the soil
which on reaction with glucose forms proteins and other useful organic
products. Bacteria and fungi also act upon dead matter to release phosphates
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and phosphoric acid. Phosphates are also released through urine of animals into
the soil which are utilized by plants in the formation of proteins etc.
Phosphates are also found in rocks etc and from these sources they pass
into fresh water ecosystems and terrestrial ecosystems. In mineral cycle,
phosphate is transferred to consumers and decomposers as organic phosphate
and thus becomes available for recycling. In photosynthetic zone, this
phosphorus is consumed by photoplankton. Thus zooplankton plays a key role
in phosphorus cycle.
Phosphorus is essential for life as it is involved in the metabolic process
of energy transfer and in encoding information in the genes.
Minerals become available to organisms after they are released from
rocks. Two mineral cycles of particular significance to organisms are
phosphorus and sulfur.
Death, decay
Phosphates,Plants
AnimalsDeath, decay
Bone ash
SuperPhosphate,(Fertilizers)Rock Phsophate
Soil
Fig. 1.4 Phosphorous cycle.
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The phosphorus cycle begins when phosphorus compounds leach from
rocks and minerals over long periods of time Fig 1.4. Because phosphorous has
no atmospheric form, it is usually transported in water. Producer organisms take
in inorganic phosphorus, incorporate it into organic molecules, and then pass it
on to consumers. Phosphorus returns to the environment by decomposition. An
important aspect of the phosphorus cycle is the very long time it takes for
phosphorus atoms to pass through it. Deep ocean sediments are significant
phosphorus sinks of extreme longevity. Phosphate ores that now are mined to
make detergents and inorganic fertilizers represent exposed ocean sediments
that are millennia old. You could think of our present use of phosphates, which
are washed out into the river systems and eventually the oceans, as an
accelerated mobilization of phosphorus from source to sink. Aquatic
ecosystems often are dramatically affected in the process because excess
phosphates can stimulate explosive growth of algae and photosynthetic bacteria
populations ("algae blooms"), upsetting ecosystem stability.
1.6.4. Sulphur Cycle
Sulfur plays a vital role in organisms, especially as a minor but essential
component of proteins. Sulfur compounds are important determinants of the
acidity of rainfall, surface water, and soil. In addition, sulfur in particles and
tiny airborne droplets may act as critical regulators of global climate. Most of
the earth's sulfur is tied up underground in rocks and minerals such as iron
disulfide (pyrite) or calcium sulfate (gypsum). Weathering, emissions from
deep seafloor vents, and volcanic eruptions release this inorganic sulfur into the
air and water (Fig. 1.5).
26
Atmosphere SO2 Acid rain
(Sulphates)
O O
SO2 H2S Plants
Decomposition
Reduction Decay
Oxidation
Combustion
SOIL
Sulphur in fossil fuels, sulphates and
sulphide sediments, inorganic sulphur, iron sulphide
Fig. 1.5 Sulphur Cycle
The sulfur cycle is complicated by the large number of oxidation states
the element can assume, producing hydrogen sulfide (H2S), sulfur dioxide
(SO2), sulfate ion (SO42-
), among others. Inorganic processes are responsible for
many of these transformations, but living oganisms, especially bacteria, also
sequester sulfur in biogenic deposits or release it into the environment. Which
of the several kinds of sulphur bacteria prerails in any given situation depends
on oxygen concentrations, pH, and light levels.
Human activities also release large quantities of sulfur, primarily through
burning fossil fuels. Total yearly anthropogenic sulfur emissions rival those of
27
natural processes, and acid rain (caused by sulfuric acid produced as a result of
fossil fuel use) is a serious problem in many areas. Sulfur dioxide and sulfate
aerosols cause human health problems, damage buildings and vegetation, and
reduce visibility. They also absorb ultraviolet (UV) radiation and create cloud
cover that cools cities and may be offsetting greenhouse effects of rising CO2
concentrations.
Interestingly, the biogenic sulfur emissions of oceanic phytoplankton
may play a role in global climate regulation. When dimethylsulfide (DMS),
which is oxidized to SO2 and then SO42-
in the atmosphere. Acting as cloud
droplet condensation nuclei, these sulfate aerosols increase the earth's albedo
(reflectivity) and cool the earth. As ocean temperatures drop because less
sunlight gets through, phytoplankton activity decreases, DMS production falls,
and clouds disappear. Thus, DMS, which may account for half of all biogenic
sulfur emissions, could be a feed back mechanism that keeps temperature
within a suitable range for all life.
1.6.5 Oxygen Cycle
As we know that 21% oxygen is present in the atmosphere. It is also
present in dissolved water in ponds, lakes, rivers, oceans etc. Animals utilize
this oxygen in respiration and return to atmosphere and water in form of carbon
dioxide. This carbon dioxide is taken up by plants during day time for
photosynthesis to form carbohydrates. Thus cycle of oxygen is maintained in
the ecosystem.
28
Atmosphere
(O2)
02
Plants Respiration
Respiration
CO2
Animals
Fig 1.6 Oxygen Cycle
1.7 Biodistribution of elements
We know that each ecosystem has two fundamental properties : (a) flow
of energy and (b) cycling of materials. Both of these are carried through food
chains. There are about 33 to 40 elements which plants and animals require for
their growth and development. These elements are generally called Biogenic
salts and are of two types :macronutrients and micronutrients. The macro-
nutrients are required in large quantities by plants and animals. They are
oxygen, nitrogen, carbon, phosphorus, calcium, magnesium, potassium etc. The
micro nutrients such as boron, cobalt, strontium, zinc, copper, molybdenum etc.
are very essential for animals and plants but needed in trace or very small
quantities. Their movement is cyclic one. These biogenic salts flow from non-
living to living and back to the non-living in almost circular path and hence
called biogeochemical cycle 'bio for living, geo' for rocks, soil and chemical for
the chemical reaction involved).
As a matter fact, different biological being, i.e. plants and animal's body,
are composed of mainly organic compounds and some metallic salts. Out of
29
these compounds, important one, are water, carbohydrotes, proteins, fats,
vitamins, hormones, enzymes and some inorganic salts. The principal elements
composing these compounds are C, H, O, N and P, in addition to the bulk
elements of body, Na, k, Ca and Mg. The trace elements, Cu, Co, Fe, Zn, Mn
and Mo, are necessary for healthy activity of various enzymes in our body. The
quantities of different elements present in our body weight (per 70 Kg) are as
follows :
O - 45.5 Kg.
C - 12.6 "
H - 7.0 "
N - 2.1 "
P - 2.1 "
Ca - 1.7 "
K - 0.25 "
Na - 0.07 "
Mg - 0.042 "
Fe - 0.005 "
Zn - 0.003 "
Check Your Progress -2
Notes:(1) Write your answers in the space given below
(2) Compare your answers with those given at the end of the unit.
(a) (i) During photosynthesis plants utilise .............................. to form
....................................... and release ................................ in
presence of ...............................
30
(ii) During lightning and rains atmospheric ....................is converted in
to .................... and ....................... and give ...................................
and ........................... in the soil.
(iii) The amino acids are converted into ............................., compounds
such as ........................., .................. and uric acid by some
................................ present in the soil.
(b) (i) Dead matter is converted to release ....................................... and
........................ by the action of ........................ and .........................
(ii) Sulphur cycle is complicated by the large number of oxidation
states of the element, can produce. ...................., ...................,
................. and others.
(iii) Bulk elements of body are .............., ................, ..............., and
............ while the trace elements, necessary for the activities of
enzymes are .................., ..................., .................., ....................
and .......................
1.8 LET US SUM UP
By going through this unit you must have achieved the objectives stated
in the start of the unit. Let us recall what we have discussed so far :
In nut shell environment is the totality of all social, biological and
physical or chemical factors individually a well as collectively that
compose the nature and man made surroundings. Man is a part of
environmental system.
As a matter of fact, the existence of life basically depends upon the
environment. All living beings, including human being, get various
things useful to their life from the environment.
31
The geographers divide the environment into two parts (i) Macro
environment and (ii) Micro environment.
Macro environment is the general environment to which an individual is
exposed (air, water, soil etc), while micro environment is a personal
environment of an individual which is attached with his life-style.
The environment consists of four components. (i) atmosphere, (ii)
hydrosphere, (iii) lithosphere and (iv) biosphere.
The atmosphere consists of 78.09% nitrogen and 20.94% oxygen by
volume, along with traces of other gases (inert gases, CO, CO2, NO2,
NO, SO2, H2S etc.).
The whole atmosphere is divided in to four zones :
Altitude in Km Temp., ºC Chemical species
(i) Troposphere 0-11 15 to -56 N2, H2O, CO2, O2
(ii) Stratosphere 11-50 -56 to -2 O3
(iii) Mesosphere 50-85 -2 to -92 NO+, O2
+
(iv) Thermosphere 85-500 -92 to 1200 NO+, O
+, O
+2
In the lowest layer, troposphere, the air moves ceaselessly, flowing and
swirling and continually redistributing heat and moisture from one part
of the globe to another. The composition and behaviour of the
troposphere and other layers control our weather and our climate.
The sun supplies the earth an enormous amount of energy. Most of this
is in the form light or infrared (heat) energy. Some of this is reflected by
bright surfaces (snow, ice and sand) ; while the rest is absorbed by the
earth's surface and water.
32
Absorbed energy heats the absorbing surface, evaporates water or
provides the energy for photosynthesis in plants.
Uneven heating with warm air close to the equator and colder air at the
latitudes, produces pressure differences that causes wind, rain, storm and
everything else we know as weather.
The elements and compounds that sustain us cycle endlessly through
living things and the environment. Important biochemical cycles are
carbon-cycle, nitrogen-cycle, phosphorous cycle, sulphur-cycle and
oxygen cycle.
Biogenic salts are of two types : macro nutrients and the micro nutrients.
As a matter of fact different biological beings (plants and animals) body
are composed of mainly organic compounds and some metallic salts. Out
of these compounds, important ones are water, carbohydrates, proteins,
fats, vitamins, hormones, enzymes and some inorganic salts.
The principal elements composing these compounds are carbon,
hydrogen, oxygen, nitrogen and phosphorous, in addition to the bulk
elements sodium, potassium, calcium and magnesium. The trace
elements copper, cobalt, iron, zinc, manganse and molybdenum are
necessary for healthy activity of various enzymes in our body.
1.9 CHECK YOUR PROGRESS : THE KEY
1. (a) (i) The circumstances and conditions that surround an organism
or group of organism.
(ii) (a) Atmosphere
(b) Hydrosphere
(c) Lithosphere
(d) Biosphere
33
(iii) Altitude Temp., Chemical
(a) Troposphere 0-11 15 to -56 N2, H2O, CO2, O2
(b) Stratosphere 11-50 -56 to -2 O3
(c) Mesosphere 50-85 -2 to -92 NO+, O2
+
(d) Thermosphere 85-500 -92 to 1200 NO+, O
+, O
+2
(b) (i) aerosols
energy budget
rain
(ii) troposphere
weather
climate
(iii) Sunlight
heat inside
the green house effect
2. (a) (i) Carbon dioxide
Carbohydrates
oxygen
sunlight
(ii) nitrogen
nitric acid
nitrous acid
nitrates
nitrites
34
(iii) ammonium
ammonia
urea
uric acid
(b) (i) phosphate
phosphoric acid
bacteria
fungi
(ii) hydrogen sulphide
sulphur dioxide
sulphates
(iii) Na, k, Ca and Mg
Cu, Fe, Co, Zn, Mn and Mo
35
UNIT-2 HYDROSPHERE
STRUCTURE
2.1 Introduction
2.2 Objectives
2.3 Chemical Composition of Water Bodies
2.3.1 Lakes
2.3.2 Streams
2.3.3 Rivers
2.3.4 Wet lands
2.3.5 Ground Water
2.4 Hydrological Cycle
2.5 Aquatic Pollution
2.5.1 Inorganic Pollutants
2.5.2 Organic Pollutants
2.5.3 Pesticides Pollutants
2.5.4 Agricultural Pollutants
2.5.5 Detergents Pollutants
2.5.6 Oil Spills and Oil pollutants
2.5.7 Industrial Pollutants and Sewage
2.6 Let Us Sum Up
2.7 Check Your Progress : The Key
36
2.1 INTRODUCTION
Hydrosphere includes various water resources such as rivers, seas, lakes,
oceans, glaciers, ground water, streams etc.
Water is essential not only for the sustenance of human life and activities
but for the quality of life as well. It is the essence of life on earth and totally
dominates the chemical composition of all organisms. The ubiquity of water is
biota as the fulorum of biochemical metabolism rests on its unique physical and
chemical properties. It provides both food and drink and has been used for
recreation transport, cooling, waste disposal and more besides.
Water is marvelous substance- flowing, swirling, seeping, constantly
moving from sea to land and back again. It shapes the earth's surface and
moderates our climate. Water is essential for our life. It is the medium in which
all living processes occur. Water dissolves nutrients and distributes them to
cells, regulates body temperature supports structures and removes waste
products. About 60 percent of our body is water. We can survive for weeks
without food but only a few days without water.
The water we use cycles endlessly through the environment. The total
amount of water on our planet is immense- more than 1404 million Km.
About 97% available water in oceans is not fit for drinking as it is salty.
Out of the remaining 3%, 2% is available in glaciers in green land etc. and on
the poles, the remaining 1% is available as fresh water (surface water-lakes,
rivers, ground water etc.) used for human beings for drinking, bathing,
irrigation and other purposes. Alas this 1% water is also polluted due to man
made activities by use of garbage, metals, chemicals as fertilizers and
pesticides, etc.
37
2.2 OBJECTIVES
The main aim of this unit is to discuss various aspects of hydrosphere.
After going through this unit you will be able to :
identify the composition of various water bodies.
discuss hydrological- cycle and
describe the various sources, which pollute our water bodies.
2.3 CHEMICAL COMPOSITION OF WATER BODIES
Water is an important part of our environment. All the living creatures
depend upon water in one way or the other but there are instances that
civilizations have disappeared due to shortage of water or due to water borns
diseases. Today water has became essential commodity for the development of
industries and agriculture. The quality of water is now the concern of scientists
in all countries of the world.
The earth is the only place that we know of where water exists in liquid
form in any appreciable quantity. Liquid water covers nearly three-fourths of
the earth's surface, and during the winter, snow and ice cover a good deal of the
rest. Not only is water essential for cell structure and metabolism, but water's
unique physical and chemical properties directly affect the earth's surface
temperatures, its atmosphere, and the interactions of life-forms with their
environments.
As has been pointed out only 3% of the world's total water supply is fresh
water; the rest is seawater. Much of the world's fresh water exists as glaciers
and polar ice, sources that are largely unavailable for human use-the exception
38
is the Inuit who cuts ice from a coastal iceberg and carts it home by snowmobile
to be melted for drinking water. Similarly much of the world's groundwater is
locked away in deep rock formations, out of the reach of conventional human
technology. Although it makes up only a tiny fraction of the world's water, the
planetary supply of accessible fresh water is more than enough to sustain the
growing world population.
The distribution of water often is described in terms of interacting
compartments in which water resides, sometimes briefly and sometimes for
eons (table 2.1) The length of time water typically stays in a compartment is its
residence time. On average a water molecule stays in the ocean for about 3000
years, for example, before it evaporates and starts through the hydrologic cycle
again. Nearly all the world's water is in the oceans. Oceans play a crucial role in
moderating the earth's temperature, and over 90 percent of the world' living
biomass is contained in the oceans. What we mainly need, though, is fresh
water. Of the 2.4 percent that is fresh. most is locked up in glaciers or in
groundwater. Amazingly, only about 0.1 percent of the world's water is in a
form accessible to us and to other organisms that rely on fresh water.
Water resources are broadly classified in to two groups :
1. External Water-Resources : This group includes water resources
existing out side the lithosphere e.g. oceans, sea, and bays. Nearly all the
world's water is in the oceans. Oceans play a crucial role in moderating the
earth's temperature and over 90 percent of the world's living biomass is
contained in the oceans. Sea and atmosphere affect each other.
2. Internal Water Resources : In this group rivers, lakes and ground water
are included. These sources are present in the lithosphere.
39
Table 2.1 : Fresh Water Distribution in the world
Water Quantity in Km3
1. Ice and Glaciars 24,000,000
2. Lakes and Reservoirs 280,000
3. Rivers and Streams 1,200
4. Soil Moisture 85,000
5. Ground Water 60,000,000
Rain Water
Rain is the main source of water for most plants and living beings. In
India 'Monsoon' mainly comes from Bay of Bengal and Arabian sea. This
causes heavy rains in south-western ghats and Bengal, Asam and Meghalaya
regions. The quantity of rain gradually decreases on moving from Bihar to
Rajasthan, through U.P., M.P., Delhi and Hariyana.
Although rain and snow bless us for only 3-4 months in the year but
forests hold back the monsoon waters and release slowly and slowly into
ground water, rivers, streams and wetlands etc. Besides this, people also keep
themselves in store the rain water in ponds, tanks, dams and other designed
sources for months together during summer season.
In its natural state rain water is purest of all the water bodies, but this is
also contaminated with dissolved gases of the atmosphere, e.g. oxygen,
nitrogen, inert gases, carbon di-oxide and acidic nitrogen and sulphur oxides,
along with the foul smelling gases present in city air.
40
2.3.1 Lakes
The volume of water that fills the lakes is just 0.03% of the earth's total
water in transport and held back in lakes. In the global scheme of things, water
flowing in rivers and streams and stored in lakes, reservours and ponds
constitute only 0.0091% of the total water on earth. Add to this 2% of water
locked in snow and ice.
Lakes contain nearly 100 times as much water as all rivers and streams
combined, but much of this water is in a few of the world's largest lakes. Lake
Baikal in Siberia, the Great Lakes of North America, the Great Rift Lakes of
Africa, and a few other lakes contain vast amounts of water, not all of it fresh.
Worldwide, lakes are almost as important as rivers in terms of water supplies,
food, transportation, and settlement.
Water in Lakes in also contaminated with the minerals present in the soil,
along with organic material and the dissolved gases. CO2, O2, chlorine, and
many gases which are essential for life are soluble in water to a slight or great
extent. Oxygen is very important for living organisms in water. The saturation
concentration of oxygen in water varies by temperature and salinity. It has been
found that if the temperature of the water is low and less saline the solubility of
oxygen increases to a great extent, while with high temperature and high
salinity the solubility of oxygen decreases depending upon the concentration of
various saline ions. Because of this reason the upper layers of water have high
oxygen content while deepest layers of water have low oxygen concentration.
The oxygen any how reaches to deeper layers by diffusion or through
circulation or movement of water.
41
2.3.2 Streams
Streams are generated from aquifers geologic layers that contains water
are known as aquifers. Aquifers may consist of porous layers of sand or gravel,
or of cracked or porous rock. Below an aquifer, relatively impermeable layers
of rock or clay keep water from seeping out at the bottom. Instead water seeps
more or less horizontally through the porous layer. Depending on geology, it
can take anywhere from a few hours to several years for water to move a few
hundred meters through an aquifer. If impermeable layers lie above an aquifer,
pressure can develop within the water-bearing layer. A well or conduit
puncturing the aquifer flows freely at the surface and is called an artesian well
or spring.
Areas where surface water filters into an aquifer are recharge zones. Most
aquifers recharge extremely slowly, and road and house construction or water
use at the surface can further slow recharge rates. Contaminants can also enter
aquifers through recharge zones. Urban or agricultural runoff in recharge zones
is often a serious problem.
The presence of various ions and radicals such as K+, Na
+, Mg
++, Ca
++,
3334 CO,HCO,NO,SO,Cl etc. in natural waters are responsible for salinity of
water. The salinity of water is the total amount of solid material in gms
contained in 1 kilogram of water.
The water is of two types : Soft water and hard water. When
334 CO,HCO,SO,Cl are absent in water they make it soft, while their presence
cause the water to be hard. The marine environment is mainly due to hard
water, while soft water constitutes fresh water environment. In both types of
environment the unique properties of water play a key role in the ecology of the
42
aquatic world. Due to dissolved minerals, often stream-water in number of
places, is used as medicine. Sulphur streams of himalian region are important in
this respect.
2.3.3 Rivers
Fresh flowing surface water is one of our most precious resources. Rivers
contain a minute amount of water at any one time. Most rivers would begin to
dry up in weeks or days if they were not constantly replenished by precipitation,
snowmelt or groundwater seepage.
As a rough estimate, the annual rainfall over the whole country would be
equivalent to about 3700 billion cubic meters. Of this around 1250 billion cubic
meters is lost by evapotranspiration and another 790 billion cubic meter by
seepage into the soil, thus leaving 1660 billion cubic meters as surface flow into
the river systems.
The volume of water carried by a river is its discharge, or the amount of
water that passes a fixed point in a given amount of time. This is usually
expressed as liters or cubic feet of water per second. The 16 largest rivers in the
world carry nearly half of all surface runoff on the earth.
The Indian rivers, which together carry to the oceans 16,45,000 million
m3 of water annually, have understandably very small sustained flow during
nine dry months in a year. An appropriate strategy for gainful utilization of
surface water flowing down rivers and streams is therefore needed. Fourteen
major river system share 83 percent of the drainage basin, accounts for 85
percent of the surface flow and serve 80 percent of the total population of the
country. There are other 434 medium and 55 minor rivers which are mostly
seasonal in nature (Table 2.2).
43
Table 2.2 : Average Annual flow in major Rivers of India (Central water
corporation report)
River Average
Annual flow,
M.Ha.M.
Useful flow,
M.HaM. (Million
Hactare Meter)
1. Ganga 51.01 25.0
2. Brahmaputra (including Barak) 54.00 20.4
3. Rivers flowing towards cast from
southern part of Tapti
21.80 03.1
4. Narmada and Tapti 06.20 04.9
5. Sindhu 07.70 04.6
6. Mahanadi & associates 12.30 09.1
7. Godawari, Krishna and associates 22.50 19.1
8. Rivers flowing from east of
Narmada to West
02.50 02.0
Total 178.04 70.2
In river-water also, sufficient amount of organic and inorganic substances
remain dissolved. However, as compared to still water of ponds and lackes,
river water is quite pure due to its flow. But its is largely contaminated with the
minerals and inorganic and organic salts of the rocks and soil through which it
flows. In addition human activities also pollute it.
2.3.4 Wet-Lands
Wetlands- bogs, swamps, wet meadows, and marshes- play a vital and
often unappreciated role in the hydrological cycle. Their lush plant growth
stabilizes soil and holds back surface runoff, allowing time for infiltration into
44
aquifers and producing even, year-long stream flow. In the United States, about
20 percent of the 1 billion ha of land area was once wetland. When wetlands are
disturbed, their natural water-absorbing capacity is reduced, and surface waters
run off quickly, resulting in floods and erosion during the rainy season and low
stream flow the rest of the year.
Water in these Wet lands are sufficiently contaminated with, largely the
organic material and dissolved salts, along with dissolved gases.
2.3.5 Ground Water
Ground water is one of our most important freshwater resource.
Originating as precipitation that percolates into layers of soil and rock,
groundwater makes up the largest compartment of liquid, fresh water. The
groundwater within 1 km of the surface is more than 30 times the volume of all
the freshwater lakes, rivers and reserviors combined.
It has been estimated that out of about 790 billion cubic meter of water
that seeps into the soil about 430 billion cubic meter remains in the top-soils
layers and produces soil moisture which is essential for growth of vegetation.
The remaining 360 billion cubic meter percolates into the porous strata and
represents the actual enrichment of underground water. Out of this the water
that can be estracted economically is only about 255 cubic billion. Ground
Water, likewise, is contaminated with organic matter and mineral salts. Water
leaking into mines shafts also dissolves metals and other toxic material. When
this water is allowed to seep into ground water aquifers, it pollutes ground
water.
45
2.4 HYDROLOGICAL CYCLE
Water is widely distributed on earth. More than 70 percent of the land is
surrounded by water in the form of sea. On earth it is present in the form of
river, lakes, ponds and other reservoirs. At the top of the hills and on poles it is
present in the form of ice and in air and clouds it is present in the form of
vapours.
The water cycles endlessly through the environment. The total amount of
water on our planet is immense, more than 1404 million km3. This water
evaporates from moist surfaces. falls as rain or snow, passes through living
organisms and returns to the ocean in a process known as the hydrologic cycle
(Fig. 2.1). Plants play an important role in the hydrologic cycle, absorbing
ground water and pumping it into the atmosphere by transpiration (transport and
evaporation). In tropical forests as much as 75 percent of annual precipitation is
returned to the atmosphere by plants.
Fig. 2.2 Hydrologic (Water) Cycle
46
Solar energy drives the hydrologic cycle by evaporating surface water,
which becomes rain and snow. Because water and sun-light are unevenly
distributed around the globe, water resources are very uneven. At Iquique in the
Chilcan desert, for instance. no rain has felled in recorded history. At the other
end of the scale 22 m (72 ft) of rain was recorded in a single year at Cherrapunji
in India. Most of the world's rainiest regions are tropical where heavy rainy
seasons occur or in coastal mountain regions. Most of the driest areas are in the
high-pressure bands of deserts.
Mountains also influence moisture distribution. The wind-ward sides of
mountain ranges including. The Pacific Northwest and the flanks of the
Himalayas are typically wet and have large rivers, on the leeward sides of
mountains in areas known as the rain shadow dry conditions dominate and
water can be very scarce.
Thus, the principal supply mechanism of fresh water is the global
hydrological cycle. The water evaporates from oceans results in the formation
of clouds. Under suitable conditions these clouds are responsible for
precipitation and water supply through hydrological cycle. The latent of water
plays an important role in the evaporation of water and condensation as rain. In
summer or hot days, snow melts, the melted water goes to rivers, forests,
irrigates lands etc. and surplus water goes to oceans. The oceans water is again
evaporated to form clouds and rainfall. Thus water cycle is continued in
environment. Precipitation is the result of gravitational pull on the vapour in
atmosphere. Precipitation occurs in various forms. These are, drizzle, rain,
snow, dew and frost, sleet and hail. Drizzle involves minute drops appearing as
to float in air. Rain is drops of liquid water, which are larger than drizzle and
also heavier. Snow is the moisture as solid state, and dew and frost are formed
47
due to condensation of moisture directly on the surfaces of objects, plants,
animals, soil etc. Sleet is in the form of small grains or pellets of ice, whereas
hail consists of balls or lumps of ice. Snow is injurious to plants, breaks tender
branches, flowers and fruits. Hail and sleet also cause similar damage. In India
mansoon mainly comes from bay of Bengal and Arabian sea. This causes heavy
rains in south-western ghats and Bengal, Asam and Meghalaya regions. The
quantity of rains decreases on moving from Bihar to Rajasthan, through U.P.,
M.P., Delhi and Hariyana.
The annual precipitation in India (leaving South America) is higher than
other continents. Thus India can be said as one of the richest countries in the
world so far as water resources or annual rainfall is concerned but alas that in
spite of abundance of this heavy rainfall people in this country are thirsty for
water and about one third population quench their thirst from polluted lakes,
ponds and other dirty sources.
Check Your Progress – 1
Note : (1) Write your answers in the space given below.
(2) Compare your answers with those given at the end of the unit.
(a) (i) Hydrosphere includes various ............................................ such as
........................., ....................., ................., .....................,
.............................. and ........................
(ii) Only ........................ of the world's total supply is ...........................
the rest is sea water.
(iii) The principal supply mechanism of ........................... is the global
........................
48
(b) (i) Water in lakes is contaiminated with the .....................................
present in the soil, along with ........................... material and the
dissolved ......................
(ii) Salinity of natural water is due to ions and radical such as
..................................................
(iii) Along with the organic and mineral salts ground water contain
........................ and other ........................... materials.
2.5 AQUATIC POLLUTION
Any physical, biological, or chemical change in water quality that
adversely affects living organisms or makes water unsuitable for desired uses
can be considered 'water pollution'. There are natural sources of water
contamination, such as poison springs, oil seeps, and sedimentation from
erosion, but here we will focus primarily on human-caused changes that affect
water quality or usability.
Pollution control standards and regulations usually distinguish between
point and nonpoint pollution sources. Factories, power plants, sewage treatment
plants, underground coal mines, and oil wells are classified as point sources
because they discharge pollution from specific locations, such as drain pipes,
ditches, or sewer outfalls. These sources are discrete and identificable, so they
are relatively easy to monitor and regulate. It is generally possible to divert
effluent from the waste streams of these sources and treat it before it enters the
environment.
In contrast, nonpoint sources of water pollution are scattered or diffuse,
having no specific location where they discharge into a particular body of
49
water. They are much harder to monitor and regulate than point sources because
their sources are had to identify. Nonpoint sources include runoff from farm
fields and feedlots, golf courses, lawns and gardens, construction sites, logging
areas, roads, streets, and parking lots. Whereas point sources may be fairly
uniform and predictable throughout the year, nonpoint sources are often highly
episodic. The first heavy rainfall after a dry period may flush high
concentrations of gasoline, lead, oil, and rubber residues off city streets, for
instance, while subsequent runoff may be much cleaner.
Perhaps the ultimate in diffuse, nonpoint pollution is atmospheric
deposition of contaminants carried by air currents and precipitated into
watersheds or directly onto surface waters as rain, snow, or dry particles. The
Great Lakes, for examples, have been found to be accumulating industrial
chemicals, such as PCBs (polychlorinated biphenyls) and dioxins, as well as
agricultural toxins, such as the insecticide toxaphene, that cannot be accounted
for by local sources alone. The nearest sources for many of these chemicals are
sometimes thousands of kilometers away.
Water system includes rivers, lakes, oceans and ground water all. Due to
its great solvent power, the water is used in washing, irrigation, flushing away
wastes, cooling, making paper. For centuries rivers and lakes have been used as
dumping grounds for human sewage and industrial waste of every conceivable
kind. Many of them been highly toxic and result in pollution of water.
The term water pollution denotes to the addition of an excess material (or
heat) that harmful to human, animals or desirable aquatic life. It otherwise
causes significant departures from the normal activities of various living
communities in or near bodies of water.
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In other words we can say that mixing of undesirable external substance
(s) in to water affecting and degrading its quality may be called water pollution.
Although the types, sources, and effects of water pollutants are often
interrelated, it is convenient to divide them into major categories for discussion
(Table 2.3)
Table 2.3
Water Pollution Contaminants and their Impact
Source or type of Contaminant Impact/pathological effects
1. Degradable wastes
Domestic and municipal sewage
and other oxygen demanding
industrial wastes. They are acted
upon by the bacteria and oxygen
dissolved in water and reduced to
inorganic form as also in quantity
Depletion of dissolved oxygen in
water harmful for fish and other
aquatic life. Many infectious diseases
eg. typhoid cholera dysentery polio
malaria filariasis etc.
2. Plant Nutrients
Phosphatic and nitrogenous
compounds dissolved in water from
industrial wastes or due to washing
away of fertilizers due to heavy
rains from fields.
Stimulate growth of algae/plankton
and other plants resulting in clogging
of water ways and rendering the
water unfit for human use.
3. Infectious Agents
Polluted stagnant water breeding
grounds for parasites bacteria
viruses of all kinds.
Cause water-borne disease and
outbreak of epidemics such as
amcobiosis dysentery cholera
typhoid etc.
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4. Synthetic Organic compounds
Such as pesticides agricultural
chemicals detergents industrial
wastes DDT etc.
Instance of cadmium lead and
mercury poisoning in human beings.
Cause neaurological impairment and
even death.
5. Inorganic Minerals & other
chemicals Asbestos and acids etc.
Asbestos produces lung cancer.
Acids cause allergies, uleers, skin
diseases. Also have catastrophic
impact on fish and aquatic life.
6. Radio-active Elements
Wastes from nuclear power plants
& nuclear fuel reprocessing plants
are packaged and buried under
water/ oceans.
Potentially hazardous in the event of
leakages and induce radiation-related
illness.
7. Sediments
Soil and mineral particles washed
into streams or water.
Reduce amount of sun-light available
for marine plants, cause clogging of
filter plants.
8. Thermal Pollution
Water used for cooling in electric,
thermal, nuclear power plants, when
recirculated in water bodies.
Can raise lake water temperature by
70-100ºC aggravate diminution of
dissolved oxygen, kills marine fish
and plant life.
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9. Metal Pollution
Mercury
Abdominal pain, headache,
diarrhoca, hemolysis chest pain.
Minimata diseases of Japan is a
burning example.
Lead Anaemia, vomiting, loss of appetite,
convulsions, damage of brain, liver
and kidney.
Arsenic Disturbed peripheral circulation,
mental disturbance, liver cirrhosis,
hyperkeratosis, lung cancer, ulcers in
gastrointestinal tract, kidney damage.
Cadmium Diarrhea, growth retardation, bone
deformation, kidney damage,
testicular atrophy, anemia, injury of
central nervous system and liver,
hypertension.
Copper Hypertension, uremia, coma,
sporadic fever.
Barium excessive salivation, vomiting,
diarrhoca, paralysis colic pain.
Zinc Vomiting, renal damage, cramps
Selenium Damage of liver, Kidney and spleen,
fever, nervousness, vomiting, low
blood pressure, blindness and even
death.
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Hexavalent chromium Nephritis, gastro-intestinal
ulceration, diseases in central
nervous system, cancer. Diarrhoca,
low blood pressure, lung irritation,
bone deformities, paralysis.
A water pollution source may be either natural or may be due to human
activity.
(a) Natural sources of water pollution : Natural sources of water-pollution
are soil-erosion, minerals, leaves, humus etc. But generally it is so small
that it is not harmful. However sometimes if dissolved toxic matter
exceeds a limit, then pollution becomes harmful and even dangerous
especially if some poisonous minerals such as nickel, beryllium, lead,
mercury etc. are present.
(b) Human sources of water pollution : There is no doubt that water
pollution is the result of human activities. The rapid growth of
population, urbanization, industrialization and increasing use of
chemicals have resulted in water pollution and this problem is increasing
day by day in spite of several measures taken in this direction.
The various water pollutants may be divided in to following six
categories :
1. Inorganic Pollutants
2. Organic Pollutants
3. Pesticides Pollutants
4. Agricultural Pollutants
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5. Detergents Pollutants
6. Oil Spills and Oil Pollutants
2.5.1 Inorganic Pollutants
Some toxic inorganic chemicals are naturally released into water from
rocks by weathering processes. Humans accelerate the transfer rates in these
cycles thousands of times above natural background levels through the mining,
processing, using, and discarding of minerals.
Among the chemicals of greatest concern are heavy metals, such as
mercury, lead, tin, and cadmium. Supertoxic elements, such as selenium and
arsenic, also have reached hazardous levels in some waters. Other inorganic
materials, such as acids, salts, nitrates, and chlorine, that are nontoxic at low
concentrations may become concentrated enough to lower water quality and
adversely affect biological communities.
There are many industrial units which discharge sulphides, nitrites,
sulphates, phosphates etc. in river waters making them unfit for drinking. These
inorganic substances decompose slowly and slowly into the water releasing foul
gases and produce several byeproducts which change the basic properties of
water and also pH. The reduction of pH to 4 or 5 makes the water acidic and
becomes responsible for the killing of aquatic life. The acceptable pH for
drinking water is 7-8.5. The nitrites and nitrates are responsible for number of
diseases in human beings and even and even death of infants. The inorganic
pollutants change chemical oxygen demand of water and thus make it unfit for
human health.
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Metals
Many metals, such as mercury, lead, cadmium, and nickel, are highly
toxic in even minute concentrations. Because metals are highly persistent, they
accumulate in food chains and have a cumulative effect in humans.
A mercury-poisoning disaster appears to be in process now in Brazil.
Ecuador, and Bolivia. Since the 1980s, thousands of garimperios, or
prospectors, have invaded the jungles along the Amazon River and its
tributaries to pan for gold. They use mercury to trap the gold and separate it
from sediments, and then boil off the mercury with a blowtorch. Miners and
their families suffer nerve damage from breathing the toxic fumes. Estimates
are that 130 tons of mercury per year are deposited in the Amazon, which will
be impossible to clean up.
Lead poisoning has been known since Roman times to be dangerous to
human health. Lead pipes are a serious source of drinking water pollution,
especially in older homes or in areas where water is acidic and, therefore,
leaches more lead from pipes. Even lead solder in pipe joints and metal
containers can be hazardous.
Mine drainage and leaching of mining wastes are serious sources of
metal pollution in water. A survey of water quality in eastern Tennessee found
that 43 percent of all surface streams and lakes and more than half of all
groundwater used for drinking supplies was contaminated by acides and metals
from mines drainage. In some cases, metal levels were 200 times higher than
what is considered safe for drinking water.
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Nonmetallic Salts
Desert soils often contain high concentrations of soluble salts, including
toxic selenium and arsenic. You have probably heard of poison springs and
seeps in the desert, where percolating ground water brings these compounds to
the surface. Irrigation and drainage of desert soils mobilize these materials on a
larger scale and can result in serious pollution problems, as in Kesterson Marsh
in California, where selenium poisoning killed thousands of migratory birds in
the 1980s.
Salts such as sodium chloride (table salt) that are nontoxic at low
concentrations also can be mobilized by irrigation and concentrated by
evaporation, reaching levels that are toxic for plants and animals. Salinity levels
in the Colorado River and surrounding farm fields have become so high in
recent years that millions of hectares of valuable croplands have had to be
abandoned. In northern states, millions of tons of sodium chloride and calcium
chloride are used to melt road ice in the winter. Leaching of road salts into
surface waters has a devastating effect on some aquatic ecosystems.
Acids and Bases
Acids are released as by-products of industrial processes, such as leather
tanning, metal smelting and plating, petroleum distillation, and organic
chemical synthesis. Coal mining is an especially important source of acid water
pollution. Sulfur compounds in coal react with oxygen and water to make
sulfuric acid. Thousands of kilometers of streams in the United States have been
acidified by acid mine drainage, some so severely that they are essentially
lifeless.
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Acid precipitation also acidifies surface water systems. In addition to
damaging living organisms directly, these acids leach aluminum and other
elements from soil and rock, further destabilizing ecosystems.
2.5.2 Organic Pollutants
The organic compounds which are discharged from industries and other
sources change pH of water drastically and also change dissolved oxygen, bio-
chemical oxygen demand and produce several byproducts which pollute the
water or water sources.
The pesticides, fungicides, bactericides etc. are the organic substances
which are mainly used for killing of small insects etc. but they persist in nature
for a longtime and due to their non-biodegradable nature, they create serious
water pollution complications and enhance bio-chemical oxygen demand to the
order of even 30,000 mg/l while in drinking water this value should be zero.
Thus these non-biodegradable substances make the water unfit for human
beings permanently or for a very long time.
The bio-degradable substances such as proteins, oils, carbohydrates,
starch, sugars, fats, food materials etc. also pollute the water although their
effects are temporary in nature.
Thousands of different natural and synthetic organic chemicals are used
in the chemical industry to make pesticides, plastics, pharmaceuticals,
pigments, and other products that we use in everyday life. Many of these
chemicals are highly toxic. Exposure to very low concentrations (perhaps even
parts per quadrillion in the case of dioxins) can cause birth defects, genetic
disorders, and cancer. Some can persist in the environment because they are
resistant to degradation and toxic to organisms that ingest them.
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The two principal sources of toxic organic chemicals in water are (1)
improper, disposal of industrial and household wastes, and (2) pesticide runoff
from farm fields, forests, road- sides, golf courses, and private lawns. The EPA
estimates that about-500,000 metric tons of pesticides are used in the United
States each year. Much of this material washes into the nearest waterway,
where it passes through ecosystems and may accumulate in high levels in
nontarget organisms. The bioaccumulation of DDT in aquatic ecosystems was
one of the first of these pathways to be understood. Dioxins and other
chlorinated hydrocarbons (hydrocarbon molecules that contain chlorine atoms)
have been shown to accumulate to dangerous levels in the fat of salmon, fish-
eating birds, and humans and to cause health problems similar to those resulting
from toxic metal compounds.
Hundreds of millions of tons of hazardous organic wastes are thought to
be stored in dumps, landfills, lagoons, and underground tanks. Many, perhaps
most, of these sites have leaked toxic chemicals into surface waters or
groundwater or both. The EPA estimates that about 26,000 hazardous waste
sites will require cleanup because they pose an imminent threat to public health,
mostly through water pollution.
2.5.3. Pesticides Pollutants
The use of pesticides has increased all over the world due to man's desire
to increase the production of grains and other agricultural products. These
compounds when sprayed on plants to kill harmful pests and weeds, percolate
through soil and get dissolved in soil water thus polluting it. The compounds
like D.D.T., B.H.C., endrin, heptachlor and toxaphene are also washed down
with rain water and find their way to sea through rivers and streams. The
compounds accumulate in the bodies of aquatic plants and animals. Some
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amounts of pesticides is also found in the milk of cow etc., in the vegetables
and in eggs besides other eatable things.
Pesticide is an all inclusive term of pesticides, herbicides, weedicides etc.
The pesticides include a variety of organic and inorganic compounds. The
modern pesticides consist of five following groups :
(1) Chlorohydro carbons (e.g. DDT, Aldrin, Endrin etc.).
(2) Carbamates (e.g., Sevin)
(3) Organo phosphorus compounds (e.g., Parathion and Malathion).
(4) Inorganic pesticides include compounds of lead, arsenic, mercury,
chlorine, HCN, lead-arsenate, sodium arsenite etc.
(5) Naturally occurring pesticides are rolenone, nicotine and petroleum
derivatives.
The characteristics of wastes from a DDT manufacturing factory. They
increase B.O.D., C.O.D., Cr. etc. of rivers and pollute them.
2.5.4 Agricultural Pollutants
Agricultural water pollution is caused by fertilizers, insecticides and
pesticides, farm animal wastes and sediments. In recent years, use of chemical
fertilizers has increased manifold.
The green revolution of India is a reflection of the increased use of
fertilizers. The chemicals used in fertilizers enter the ground water by leaching
and the surface waters by run-off. The nitrates, when mixed with water may
cause methemoglobinemia in infants Incidences of nitrate poisoning are also
there in livestock. The plant nutrients, nitrogen and phosphorus are reported to
stimulate the growth of algae and other aquatic plants.
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The use of various types of pesticides and insecticides in agriculture is
also one of the causes of water pollution. Their presence in water is highly toxic
to man and animals, because all these have a high persistence capacity, i.e.,
their residues remain for long periods.
The farm animal wastes often pose serious problems of odours and water
pollution. These wastes also contain pathogenic organisms which get
transmitted to humans. Sediments of soil and mineral particles washed out,
from fields also cause water pollution. They fill stream channels and reservoirs
and reduce the sunlight available to aquatic plants.
This agricultural pollution may be broadly classified into two heads :
(a) Livestock Waste Run off : According to Department of Agriculture the
production of waste by livestock was as follows :
Species Population/in million Solid waste
million tons
Liquid waste
million tons
Cattle 107 1004 390
Horses 3 17.5 4.4
Dogs 53 57.3 33.9
Sheeps 26 11.8 7.1
Chickens 375 27.4 -
Donkeys 104 19.0 -
Ducks 11 1.6 -
The human beings contribute about 50 Kg. of solid faecal matter and 440
litres of urine per person annually.
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The nature of the constituents present in the solid and liquid waste vary
from species to species depending upon their food and the digestive system.
However, it stands to reason that unless special precautions are taken a certain
of this waste may alongwith the eroded soils which find their way into the
streams because in rural areas soil is considered to be a pit for dumping all
wastes.
(b) Fertilizers and other Amendments Added to the Soil – According
to Indian Council of Agricultural Research, the total use of fertilizers in India in
1982-83 was as follows :
Fertilizer type Total use in 1982-83 in 1,000 tos 729
(as nitrogen)
Nitrogen (as urea, (NH4)2SO4,
Phosphorous (as super phosphate,
bone meal etc.)
297.53 (as P2O5)
Potassium (as KCl, K2SO4) 3039.86
Apart from these fertilizers, organic materials like oil cakes (groundnut,
castor, linseed etc.), manures etc. are used. It is obvious that during heavy
downpour some of the material may be physically carried away along with the
soluble decomposition products to the steams.
Normal drainage waters from irrigated fields also find their way into the
streams. They are generally more saline than the irrigation water employed and
may also carry down with them part of the soil amendments added to the
agricultural fields.
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2.5.5 Detergent Pollutants
The detergents cause serious pollution in water resources as they contain
phosphates. The phosphates are responsible for the growth of algae which
deplete the dissolved oxygen. When algae die, they release their components
inorganic and organic substances back into water and so become pollutants
themselves. Generally they give amino acids and ammonia in water.
2.5.6 Oil Spills and Oil Pollutants
The spread of oil in the sea has become a common feature nowadays. Oil
is transported across oceans through tankers and either due to some accident or
leakage, oil spills onto the water and causes the degradation of aquatic and
marine environment. Between 1968 and 1983, there were more than 500 tanker
accidents that involved oil spills.
The pollution in water by oil is called oil pollution. This generally
happens when oil is transported from one place to another place or from one
country to other through sea, when oil tankers either explode due to enemy's
attack or due to leakage in ports and docks. In a recent report of Department of
ocean, there are more than 50 heavily polluted places of oil pollution along the
Indian coast. In 1985 on one fine morning a long distance of Hazi port was full
of dead fishes due to oil pollution. Sometimes back in Gulf war the oil tankers
and other sources of Kuwait were destroyed by Iraq with the result that a layer
of oil spreaded all over the coast and aquatic animals died on the spot due to
non availability of oxygen and sun rays. The recent report of National Institute
of Oceanography indicates that fish field of Kerala decreased by 35% because
of coastal pollution in recent five years. Similar decrease in fish yield has been
reported in Tamil Nadu, Karnataka, Andhra Pradesh, Orissa and Gujarat.
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The oil is made up of about 40 components. The upper components like
petrol and kerosene evaporate causing air pollution in nearby areas while lower
components like naphtha etc. destroy the plant and animal kingdom of the sea
being thicker in nature thus neither allowing sun light to enter into the lower
portion of sea nor allowing oxygen to enter into lower portion of sea. Thus oil
in water is responsible for-
1. Reducing light penetration- Oil slick from a layer upto 2 meters below
the surface of water checks the light to reach into the lower part of sea needed
for photosynthesis of aquatic plants.
2. Reducing dissolved oxygen – They (oils) reduce the percentage of
dissolved oxygen in sea with the result that aquatic animals die due to lack of
oxygen necessary for respiration.
According to Ministry of Health, Govt. of India the maximum
permissible limit of oil in water is 0.3 mg/l. Any higher amount than this
prescribed value causes oil pollution. The oil pollution can be controlled by
checking spillage of oil. International laws be formulated to check the
bombardment of oil tankers.
Effects of oil pollution – (1) The crude oil contains small amount of
saturated hydrocarbons, nitrogen, sulphur compounds, metals like iron, nickel,
vanadium etc. which cause paralysis. This crude oil also contains carbonyl
sulphide which breaks up into hydrogen sulphide- a poisonous gas which
affects the respiratory system.
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(2) Aromatic compounds like mercaptans, thiophenes and
benzothiophenes are toxic in nature and damage kidney, lever and create mental
disorders.
(3) The saturated hydrocarbons like methane, ethane, propane cause
suffocation and respiration ailments. Liquid paraffins can cause pneumonia in
lung and can destroy the tissues of kidney.
(4) The animals also suffer due to damage of kidney and lever. The
oily furs of animals lose insulation resulting in death finally.
2.5.7 Industrial Pollutants
Industrial activities generate a wide variety of waste products which are
discharged n to water sources. Major contributors are the pulp and paper,
chemicals, petrochemicals and refining, metal-working, food processing,
textile, distillery etc. The wastes, broadly categorized as heavy metals or
synthetic organic compounds, reach bodies of water cither through direct
discharge or by leaching from waste dumps. All the Indian rivers have been
polluted by industrial effluents.
The important industries are – (1) Paper and Pulp, (2) Distillery, (3)
Potassic Fertiliser, (4) Electroplating Plant, (5) Asbestos, (6) Silt, (7) Alcohol,
(8) Detergents, (9) Steel, (10) Tanning, (11) Cane Sugar, (12) Oils, (13)
pesticides and Herbicides, (14) Radioactive wastes.
1. Paper and pulp industries : Effluents from paper and pulp industry
include wood chips, bits of bark, cellulose fibers and dissolved lignin in
addition to a mixture of chemicals. All these produce a sludge which
blankets fish spawning grounds and destroys certain types of aquatic life.
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The effluents contains chlorine, sulfur dioxide, methyl mercaptan etc.,
which are considered to be highly poisonous to fish.
Precautions– 1. The lignin should not be allowed to discharge as it
completely destroys the fauna and flora and impairs the productivity.
2. Heavy suspended material should be brought to minimum level
through settling tanks which reduce B.O.D.
3. The taste and odour producing substances can be removed by treating
waste water with activated carbon.
(2) Distillery – The Bengal distilleries near Hooghly produce approx.
0.145 mgd of wastes which are directly disposed into the river Hooghly.
In India, annual distillery discharge figures approximate between 100-
110 million litres and this can afford to produce 10-250 tonnes nitrogen, 1000-
2500 tonnes potash and 50-100 tonnes phosphorus, besides aminoacids, nitrate
and micro organisms like Phyto plankton and Zoo plankton.
3. Textile industries, effluents are alkaline in nature and have a higher
demand for oxygen.
4. Food processing industries include dairies, breweries, distilleries,
meatpacking etc. where the waste products include fats, proteins and
organic wastes. These industries, discharge wastes containing
nitrogen, sugar, proteins, etc. All these wastes have a higher BOD and
are responsible for water pollution.
5. Chemical industries include acid manufacturing industries, alkali
manufacturing, fertilizer, pesticides and several other industries. The
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effluents from these industries contain acids which have corrosive
effects. The effluents from fertilizer industries contain phosphorus,
fluorine, silica, and large amounts of suspended solids.
6. Metal industries usually discharge effluents containing copper, lead,
chromium, cadmium, zinc, etc., which are toxic to man as well to
aquatic life. These wastes also contain acids, greases and cleansing
agents.
7. Petrolcum industries include oil refineries and petrochemical plants.
The effluents include hydrocarbons, phenolic compounds and other
organic and inorganic sulphur compounds.
8. Other industries which pollute water are alcohol, Oil, tanneries,
soaps and detergent pesticides industries, electroplating, bleaching,
atomic plants, explosive factories etc.
9. Mining operations can result in metals leaching into the acidic
effluents, thus adding to the metal load in rivers, lakes and ground
water. Discharge of mercury from gold mining activities has polluted
some streams in Brazil and Ecuador and created serious health
problems.
10. Radioactive Wastes : Radioactive elements such as uranium and
radium possess highly unstable atomic nuclei. Their disintegration
results in radiation emission, which may be highly injurious. During
nuclear tests, radioactive dust may envelope the globe at altitudes of
3,000 metres or more, the same often comes down to the earth as rain
Eventually, some of the radioactive material, such as Strontium 90
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(which can cause bone cancer), percolates down through the soil into
ground water reservoirs or is carried out into streams and rivers. In
both cases public water supplies may be contaminated.
11. Thermal Pollution : Most of the thermal and electric power plants
also discharge considerable quantities (about 99%) of hot
effluent/water into nearby streams or rivers. This has resulted in
thermal pollution of our water courses. Thermal pollution is
undesirable for several reasons. Warm water does not have the same
oxygen holding capacity as cold water. Therefore, fishes like black
bass, trout and walleyes etc., which require a minimal oxygen
concentration of about 4 ppm, would either have to emigrate from the
polluted area or die in large numbers.
12. Noise Pollution : Every industry produce pressure variations audible
to the ear, constituting a noise. Mechanised industry is the most
serious of all large scale noise producers.
Sewage :
Man for his various domestic purposes such as drinking, preparation of
food, bathing, cleaning the house, cooling etc., uses on an average 135 litres of
water per day. About 70 to 80 per cent of this is discharged and drained out,
which through municipal drains poured into, in many cases, a river, tank or
lake. This water is known as domestic waste water in which when other waste
material such as paper, plastic, detergents, cloth, are mixed is known as
municipal waste or sewage. The domestic waste and sewage is the main source
of the water pollution. This is the inevitable and unfortunate fallout of
68
urbanization. As it decays, this organic waste depletes the oxygen from water
and upsets the natural balance of the aquatic ecosystem.
Municipal sewage is considered to be the main pollutant of water. Most
of the sewage receives no treatment before discharge, specially in developing
countries like India.
The typical constituents of domestic sewage according to Metcalf and
Eddy Inc. (1999) may be total dissolved solids, suspended solids, nitrogen,
organic nitrogen free ammonia, phosphorous (organic as well as inorganic),
chlorides, alkalinity as CaCO3. grease etc. Synthetic detergents and bacteria
also find their way into the river water. The natural purification action of the
flowing water tends to oxidize the organic matter and much of the bacteria also
die but if excess organic matter is present it may result in anaerobic conditions
and results in production of H2S.
Domestic sewage is very serious pollutant of wells and rivers which are
important sources of our drinking water. These rivers and wells are polluted
with our own excreta besides that of animals and birds. The drinking water
from these sources contains high amount of (1) Nitrite, (2) Nitrate, (3) B.O.D.
(4) C.O.D., (5) Chloride, (6) Sulphate and (7) Total dissolved solids. These
effluents in high concentrations are toxic and destroy fish and plant life.
The most serious water pollutants in terms of human health worldwide
are pathogenic organisms. Among the most important waterborne diseases are
typhoid, cholera, bacterial and amoebic dysentery, enteritis, polio, infectious
hepatitis, and schistosomiasis. Malaria, yellow fever, and filariasis are
transmitted by insects that have aquatic larvae. Altogether, at least 25 million
deaths each year are blamed on these water-related diseases. Nearly two-thirds
69
of the mortalities of children under 5 years old are associated with waterborne
diseases.
The main source of these pathogens is untreated or improperly treated
human wastes. Animal wastes from feedlots or fields near waterways and food
processing factories with inadequate waste treatment facilities also are sources
of disease-causing organisms.
Detecting specific pathogens in water is difficult, time consuming, and
costly, so water quality is usually described in terms of concentrations of
coliform bacteria – any of the many types that live in the colon or intestines of
humans and other animals. The most common of these is Eschericha coli (or E.
coli), which lives symbiotically in many animals, but other bacteria, such as
Shigella, Salmonella, or Lysteria, can cause fatal diseases. If any coliform
bacteria are present in a water sample, infectious pathogens are usually assumed
to be present also. Therefore, the Environmental Protection Agency (EPA)
considers water with any coliform bacteria at all to be unsafe for drinking.
Check Your Progress- 2
Note : (1) Write Your answers in the space given below
(2) Compare your answers with those given at the end of the unit.
(a) (i) The mixing of ..................... external ....................... in to water
affecting and ...................... its .................... may be called water
pollution.
(ii) The various pollutants may be divided into following six
categories.
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1. .........................
2. ........................
3. ........................
4. .......................
5. ......................
6. .......................
(iii) Organic pollutants include-
(a) ......................................
(b) .......................................
(b) (i) Agricultural pollutants may be classified into
(a) ...................................
(b) ...................................
(ii) Industrial Pollutants come from mainly –
1. .......................... 5. ..........................
2. .......................... 6. ..........................
3. .......................... 7. ..........................
4. .......................... 8. ..........................
(iii) Thermal, ........................ and .................... pollutions are also
included amongst industrial pollution.
2.6 LET US SUM UP
After going through this unit you must have achieved the objectives
discussed in the start of this unit. Let us recall what we have discussed in this
unit :
Hydrosphere includes various water resources such as rivers, seas, lakes,
oceans, glaciers, ground water, streams etc.
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Water is essential not only for the sustenance of human life and activities,
but also for the quality of life as well.
About 97% available water in oceans is not fit for drinking as it is salty.
Out of the remaining 3%, 2% is available in glaciers in greenlands etc.,
and on the poles, the remaining 1% is available as fresh water (Surface
water – lakes, rivers, ground water etc.).
Water resources are broadly classified into two groups :
(a) External Water resources i.e. those existing out side the
lithosphere, e.g. Oceans, Sea and bay, and
(b) Internal water resources, which constitute rivers, lakes and ground
water.
Rain is the main source of water for most plants and living beings. In its
natural state rain water is purest of all the water-bodies, but this is also
contaminated with dissolved gases of the atmosphere (O2, N2, CO2, inert
gases, oxides of N and S).
Waters of lakes, streams, rivers and ground water are always
contaminated with varying amounts of inorganic salts and organic
material.
Wet-lands are largely contaminated with organic material and inorganic
salts, alongwith the toxic material.
The principal supply mechanism of fresh water is the global hydrological
cycle.
72
The water cycles endlessly through the environment. Solar energy drives
the hydrologic cycle by evaporating surface water, which becomes rain
and snow and falls filling natural reservoirs (lakes, rivers, ground water
wells) and returns to the ocean in a process called the hydrologic cycle.
Any physical, biological or chemical change in water quality that
adversely affects living organisms or makes water unsuitable for desired
uses can be considered 'Aquatic Pollution'.
Due to its great solvent power, the water is used in washing, irrigation,
flushing away wastes, cooling, making paper. Further, for centuries
rivers and lakes have been used dumping grounds for human sewage and
industrial waste of every conceivable kind, many of them been highly
toxic. This results in pollution of water.
Although the types, sources, and effects of water pollutants are often
interrelated, it is generally convenient to divide them into major
categories.
These include :
1. Inorganic Pollutants
2. Organic Pollutants
3. Pesticides Pollutants
4. Agricultural Pollutants
5. Detergents Pollutants, and
6. Oil spills and oil pollutants
Industrial activities generate a wide variety of waste products which
generally discharged in to water sources. The major contributors are
73
(a) Paper and Pulp industries.
(b) Distilleries
(c) Electroplating plants
(d) Asbestos industry
(e) Detergent industry
(f) Steel industry
(g) Mining industry
(h) Tanning industry
(i) Cansugar industry
(j) Oils industries
(k) Pesticides industries
(l) Atomic energy industry
(m) heavy chemical industries
2.7 CHECK YOUR PROGRESS : THE KEY
1. (a) (i) Water resources
rivers, seas, lakes, oceans, glaciers and ground water.
(ii) 3%
fresh water
(iii) fresh water
hydrological cycle
(b) (i) mineral
organic
gases
(ii) K+, Na
+, Mg
++, Ca
++, Cl
-, SO4
--, NO3
- HCO3
- and CO3
--
(iii) metals
toxic
74
2. (i) Undisirable
substances
degrading
quality
(ii) 1. Inorganic 5. Detergents
2. Organic 6. Oil Spills and Oil
3. Pesticides Pollutants
4. Agricultural
(iii) 1. Industrial and household wastes
2. Pesticides run off.
(b) (i) (x) Livestock waste run off
(y) Fertilizers and other amendments added to soil
(ii) 1. Paper and pulp industries
2. Distilleries
3. Textile industries
4. Food processing industries
5. Chemical industries
6. Metal industries
7. Petroleum industry, and
8. Mining industry
(iii) radio activity
noise
75
UNIT-3 WATER QUALITY PARAMETERS
STRUCTURE
3.1 Introduction
3.2 Objectives
3.3 Dissolved Oxygen
3.4 Biochemical Oxygen Demand
3.5 Solid
3.6 Metals
3.7 Contents of Chloride, Sulphates, Phosphates, Nitrate and Micro-
Organisms.
3.8 Water Quality Standards
3.9 Analytical Methods for Measuring
3.9.1 Biochemical Oxygen Demand
3.9.2 Dissolved Oxygen
3.9.3 Chemical Oxygen Demand
3.9.4 Fluoride
3.9.5 Oils
3.9.6 Metals
3.9.7 Residual Chloride and Chlorine Demand.
3.10 Purification and Treatment of Water
3.11 Let us Sum Up
3.12 Check Your Progress : The Key
76
3.1 INTRODUCTION
The aquatic environment is the reservoir of industrial domestic and
agricultural wastes, Since 90% of the hazardous wastes are placed in the soil
and water, the organisms present in this environment are found to be affected
by these toxicants.
Water quality is a relative property dependent on the use to which the
water is put. Generally, it is a function of dissolved oxygen, dissolved solids,
biochemical oxygen demand (BOD), suspended sediments, acidity, and
temperature.
Dissolved oxygen is required by all aquatic plant and animal life. Fish
require the highest levels, vertebrates next and bacteria the least. Figure 3.1
shows how the solubility of oxygen varies with temperature; it drops from a
high of 15 ppm at 0ºC to about 6 ppm at 40ºC. Levels saturation arise from
decay of oxygen-demanding wastes. Most of these are organic. If we represent
them as carbon, we can write.
COg32
O
g12
C 2
which indicates that a 9-ppm level of dissolved oxygen would be totally
exhausted by 32
12 (9), or about 3 ppm of carbon waste. This is equivalent to
about a drop of oil in 10 liters of water.
What happens as dissolved oxygen gets depleted? Plant and animal life
disappear, Bacterial decomposition shifts from aerobic (O2- requiring) to
anaerobic (not requiring O2). The products of metabolism change. Under
aerobic conditions, C goes to CO2, N to NH3 + HNO3, S to H2SO4, and P to
H3PO4; however, under anaerobic conditions, C goes to CH4, C2H4, etc. : N to
NH3 + amines; S to H2S; and P to lower-valent phosphorus compounds. The
77
point to note is that under anaerobic conditions, the decomposition products
tend to stink and are more likely to be toxic.
Organic water pollutants include protein (domestic sewage, waste from
creameries, slaughterhouses), fat (sewage, soap production, food processing),
carbohydrates (sewage, paper mills), resin, coal, and oil, Inorganic pollutants
might be acids, alkalies, heavy-metal cations, and certain anions. Acid mine
drainage is a primary source of stream pollution, especially in coal-producing
regions. The actual pollutants are H2SO4 and soluble iron salts formed by
reaction of air and water on pyrites present in the coal seams. Certain types of
bacteria also appear to be involved, but their role is not understood. It is
estimated that about 4 X 109 kg of H2SO4 per year goes into streams, 60 percent
of which originates in abandoned mines. Acid stream pollution is one of the
primary causes of fish kills.
Water plants are also indispensable part of all aquatic populations due to
their high adaptability. Aquatic life includes benthic organisms inhabiting the
bottom sludge, plankton living in the water bulk, and organisms developing in
the surface layer of water (neuston). Underwater part of plants, bottom stones
and other objects are covered with growth in the form of crusts, pads, and
bushes, whose colour varies depending on the composition. Water plants form
"underwater meadows" in water bodies rich in soluble salts of calcium.
The density of plankton organisms is close to that of water. Heavy
organisms develop the ability to hover in water. They accumulate oils to form
mucilage, gas vacuoles (pseudovacuoles), claims, spirals. This increases their
volume and reduces their weight. The growth of water weeds is often very
intense and the water is said to "bloom".
Thus biological pollution of water may include bacteria, viruses,
protozoa, parasites, and plant toxins. Infections of the intestinal tract (e.g.,
78
cholera, typhoid, and dysentery), polio and infectious hepatitis have frequently
been traced to contaminated water supplies. Generally, no check is made for
these pathogenic contaminants because it is a 24-h problem to detect them, and
that is usually too late. Instead, one looks for a benign indicator such as
coliform bacteria, the presence of which alerts to fecal contamination.
Physiological pollution of water comes from bad taste and objectionable
odor. These usually go together, and the most frequent, contaminants sulfur
compounds and nitrogen compounds.
For a complete study of a water body, it is necessary to determine
different types of parameters, the most important ones are physical, chemical
and biochemical parameters.
Physical properties of any water body, generally depend on the ecology,
weather conditions and chemical properties of the place concerned. The
parameters included in such study are generally colour, odour, temperature, heat
budget, light transparancy etc.
While, during water-analysis, study of chemical properties is very
important, the important chemical parameters include determination of acidity
and alkalinity, pH, conductivity, redox potential, soluble solid, free oxygen,
dissolved oxygen, salts, hardness, N., P, Na, K, BOD, COD, metals, Chloride,
Sulphate, phosphate etc.
Amongst biochemical parameters, determination of specific pathogens in
water is difficult, time consuming and costly, so water quality is described in
terms of concentrations of coliform bacteria.
3.2 OBJECTIVES
79
The main objective of this unit is to study water quality parameters and
the methods of their determination. By going through this unit you will be able
to :
describe meaning and significance of dissolved oxygen, and biochemical
oxygen demand,.
discuss contamination of solids and metals and their consiquences.
describe the sources of chloride, sulphates, phosphates, nitrate and micro
organism contamination and their effects,
discuss water quality standards,
describe analytical methods for measuring BOD, DO, COD, fluoride,
oils, metals, residual clouride and chlorine demand; and
discuss purification and treatment of water.
3.3 DISSOLVED OXYGEN
The types and quantities of life in an aquatic system is determined by
oxygen. While the deficiency of oxygen has a adverse effect on most of the
aquatic beings , the excess of oxygen has also harmful effect on certain
anaerobic bacteria. The quantity of dissolved oxygen (DO) is an important
parameter, amongst the specificities studied for the first time.
Dissolved oxygen (Do) is one of the most important parameter in water
quality assessment and reflected the physical and biological processes
prevailing in the natural waters. The main sources of dissolved oxygen to the
waters are directly obtained from the atmosphere through the exposed surface
and from the photosynthesis of chlorophyll bearing plants. The diffusion of
oxygen from air is a physical phenomenon. This depends up on the temperature,
80
salinity and water currents. The photosynthesis reactions taking place in water
are biological processes. These reactions, taking place by the aquatic
autotrophy, depend upon the availability of light, number of autotrophs,
quantity of available gases and the rate of redox reactions The quantities of
oxygen in autotroph aquatic systems are not stable. The quantity of dissolved
oxygen on pollution free water surface is maximum. With the increasing depth
this quantity decreases rapidly. On the other hand, in oligotropic aquatic
systems the quantity of dissolved oxygen gradually increases from the surface
to increasing depth.
The amount of oxygen dissolved in water is a good indicator of water
quality and of the kinds of life it will support. An oxygen content above 6 parts
per million (ppm) will support game fish and other desirable forms of aquatic
life. At oxygen levels below 2 ppm, water will support mainly worms, bacteria,
fungi, and other detritus feeders and decomposers. Oxygen is added to water by
diffusion from the air, especially when turbulence and mixing rates are high,
and by photosynthesis of green plants, algae, and cyanobacteria. Therefore,
turbulent, repidly flowing water is constantly aerated so it often recovers
quickly from oxygen-depleting processes. Oxygen is removed from water by
respiration and chemical processes that consume oxygen.
3.4 BIOCHEMICAL OXYGEN DEMAND
Biochemical Oxygen demand (BOD) is the amount of oxygen utilized by
microorganisms in stabilizing the organic matter. It gives a qualitative index of
the organic substance degraded, quickly in a short period of time. BOD is an
important parameter to study intensity of pollution power of sewage, industrial
waste.
81
BOD is expressed as 'the miligrams of oxygen, per liter of water,
necessary for the fixation of biodegradable organic substance present in a
sample by microorganisms, of a given time under oxyconditions'. In other
words BOD indicates the fraction of soluble organic matter which is readily
degraded and assimilated by bacteria. BOD is an important index of organic
pollution and determine suitability of water for different purposes. Greater is
the amount of oxydisable organic matter present in the water, greater will be the
amount of oxygen needed for its bio-degradation and greater will be the value
of BOD.
3.4 SOLIDS
The principal sources of solids in water bodies may be either natural or
due to human activities. Amongst the natural sources, soil erosion, minerals,
leaves, humus etc. are important. While the human sources include domestic
effluents and sewage, industrial effluents and agricultural effluents.
The solids in the water bodies are present in all the three states, soluble,
suspended (and colloidal) and as sediments, and are both organic and inorganic
in nature. While minerals and industries are responsible for contamination of
inorganic solids, organic solids in water come from animal wastes and
industrial effluents. In Indian cities like Delhi, Kanpur, Bombay and Calcutta,
most of the garbage is dumped into nearby ponds or rivers.
The total solids quantify all the solids (organic and inorganic) suspended
and/or dissolved in water. When present in excess they create imbalance for
aquatic life for various reasons. According to Hart at. al. excessive total solids
present in water cause imbalance of osmotic regulation and suffocation even in
the presence of high dissolved oxygen.
82
Water clarity (transparency) is affected by sediments, chemicals, and the
abundance of plankton organisms, and is a useful measure of water quality and
water pollution. Rivers and lakes that have clear water and low biological
productivity are said to be oligotrophic (oligo = little + trophic = nutrition). By
contrast, eutrophic (eu + trophic = well nourished) waters are rich in organisms
and organic materials. Eutrophication, an increase in nutrient levels and
biological productivity, often accompanies successional changes in lakes.
Tributary streams bring in sediments and nutrients that stimulate plant growth.
Human activities can greatly accelerate eutrophication, an effect called
cultural eutrophication. Cultural eutrophication is mainly caused by increased
nutrient input into a water body however, eutrophication produces "blooms" of
algae or thick growths of aquatic plants stimulated by elevated phosphorus or
nitrogen levels. Bacterial populations then increase, fed by larger amounts of
organic matter. The water often becomes cloudy or turbid, and has unpleasant
tastes and odors. Cultural eutrophication can accelerate the "aging" of a water
body enormously over natural rates. Lakes and reservoirs that normally might
exist for hundreds or thousands of years can be filled in a matter of decades.
3.6 METALS
The major sources of metal pollution in water bodies are rock minerals
and industrial effluents. Many metallic salts are naturally released into water
from rocks by weathering processes. Humans accelerate the transfer rates in
these cycles thousands of time above natural back ground levels through the
mining, processing, using and discarding of minerals. Thus, mine drainage and
leaching of mining wastes are serious sources of metal pollution in water.
One category of materials which has attracted considerable attention due
to its wide use and listed as toxic and hazardous waste is heavy metals. This
83
includes mercury, lead, tin and cadmium. Supertoxic elements, such as
selenium and arsenic are also hazardous. Metals such as mercury, lead cadmium
and nickel are highly toxic, even in minute concentrations. Because these
metals are highly persistent, they accumulate in food chains and have
cumulative effect in human. Many industries such as nonferrous metallurgy,
pigments, storage batteries, metal processing, finishing and plating discharge
heavy metals with their effluents. All these metals when used as raw materials
or process chemicals are likely to find their way to the environment in the form
of solid, liquid and gaseous waste in various concentrations depending upon
industry and process.
Some of the metals are essential for biological activity of all living
organisms. However, when concentration levels of these essential metals
exceed those required for correct nutritional response by factors which vary
between 40 and 200 folds. depending on the metal and organisms, they become
toxic.
The discharge of heavy metal wastes into receiving waters may result in
numerous physical, chemical and biological response. These can be separated
into two broad categories :
(i) Effect of the environment on the metals, and
(ii) Effect of the metals on the environment.
The first category emphasises that conditions in receiving waters may
lead to a change in the specification and toxicity of metals. Such conditions
include differential input of anthropogenic and geochemical material, quality of
industrial effluents and concentration of suspended solid. Biological responses
under the second category are often equally diverse. Depending on
environmental conditions, there may be a change in density, diversity,
community structure and species composition of population. The nature and
84
extent of change depend largely on the concentration of heavy metals species in
the water and sediment. Hence, physico-chemical processes within efflents and
natural waters have a major, indirect effect on biological responses.
Heavy metals are recognised as serious pollutants of the aquatic
environment and heavy metal toxicity is often encountered in connection with
experimental work, commercial fish farming and the management of
recreational fisheries.
Heavy metals and their salts constitute the most widely distributed group
of highly toxic and long retained substances. Their salts are simple inorganic
compounds, the toxicity of which is caused by anions, cations or physico-
chemical properties of salts. Some salts of heavy matels are precipitated in a
weak alkaline medium and thereby enlarge the salt deposits of water body.
The presence of heavy metals in aquatic ecosystem is predominantly due
to increase in waste discharge from agricultural chemicals, dying and textile
processing industries.
Elemental mercury, the only liquid metal at 25ºC is the third member of
the group II-B triad of the periodic table. The chemical behaviour of mercury is
significantly different from that of the other two members of the same triad,
zinc and cadmium.
Mercury is an enzyme and protein inhibitor whereas zinc plays an active
role in protein, lipid and carbohydrate metabolism in a variety of organisms.
From the toxicological point of view, mercurials are classified into several
groups such as elemental mercury, short chain alkyl mercurials and other
organomercury compounds.
As a result of man's utilisation and exploitation of mercury and mercury
related technology, many forms of mercury have been released directly or
indirectly into the environment. Since mercury is purposely incorporated into
85
many industrial or consumer products such as paints, pharmaceuticals, paper
products, fluorescent lamps, mercury batterries and many other products too
numerous to list, the indiscriminate disposal of these products by a population
represents an important environmental mercury contamination route, especially
of our nation's rivers, streams and lakes.
Lead is the member of group IV of periodic table. It comes in this group
with C, Si, Ce and Sn. Lead is truely metallic as compared to carbon and
silicon. It resembles calcium in deposition and remobilisation from the skeletal
compartment of the body. Lead is one of the oldest metal known to man and
since medieval times has been used in piping, building materials, soldering,
paints, type metal, ammunition and castings. In more recent times lead has been
used mainly in storage batteries, metal products, chemicals and pigments and
has numerous commercial applications due to its physical properties and
relative chemical inertness. Unfortunately, it is highly toxic both as an inorganic
and an organic compound.
Presence of iron and calcium in water bodies is important. Iron presents
an important field of research due to its characteristic water-chemistry, viz. its
redox behaviour, complexation, bacterial-redox reaction and iron-exchange
reaction between iron and its carbonates, hydroxides and sulphides in solid
solutions.
In ground water it is mainly present as ferrous iron, as the ground water
has no contact with atmospheric oxygen. However when it is pumped out
ferrous iron readily gets oxidised by atmospheric oxidation in to ferric state. In
aerated water it is present as a suspension of hydrated ferric oxide or as a
complex with organic molecules. In Alkaline water it is present as Fe (OH)+ ,
while in an acidic water (mine-water or industrial discharge) we may have both
ferrous and ferric iron.
86
Amongst cations present in water bodies, Ca++
, ions are present in the
largest quantity. It primary sources are minerals (Gypsum, dolomite, Calcite,
lime-stone or marble). Waters rich in carbondioxide dissolve it forming
bicarbonate :
CaCO3 + CO2 + H2 O Ca (HCO3)2
The water in which degradation of organic-matter by microorganism is
high, quantities of carbonate and bicarbonate of calcium are also very high.
3.7 CONTENTS OF CHLORIDE, SULPHATES PHOSPHATES,
NITRATES AND MICRO-ORGANISMS
Common ions such as chloride, nitrates, sulphates and phosphates are
important components of total dissolved solids (TDS) present in water bodies.
However concentrations of chloride and sulphate ions are sufficiently high in
hard water. While, domestic and industrial effluents and in stream uses also add
to the pollutional loads of these common ions, agricultural return waters are
considered to be the most significant polluters for this category, and are
believed to raise the salinity of a river as it flows down its cultivated valley.
Domestic, industrial and agricultural, all these three classes are implied to
involve discharge of pollutant bearing waste waters that reach the river and
pollute it. The sulphur, nitrogen and phosphorous cycles in nature also
contribute contamination of SO4--, NO3
- and PO4
3- ions in water-sources.
Nitrogenous and phosphatic fertilizers also contribute to Nitrate and phosphate
contamination.
Nitrate Pollution
Every year around two million tons of nitrates penetrate in to subsoil and
flow towards the phreatic levels, for this reason we are 'drinking' 50 mg of
nitrates per day. Nitrates are not directly toxic for man, nitrates get converted in
87
our body in to nitrites. These in high doses lead to blood poisoning. Some
studies have also shown that nitrites then react in our organism to form well
known cancer provoking components, nitrosamines,. It is in lakes and rivers
that we observe the first sign of nitrate pollution. Nitrates accumulate in our
environment and they make up the first link in a chain of biological and
chemical conversions which lead to the formation of toxic compounds in our
body.
Nitrate to nitrite and on to nitrosamines
The nitrate (NO3-) ion is extremely stable and very slightly oxidant. In the
body it can only be transformed into nitrite by an enzyme, nitrate reductase,
which is present in certain bacteria in the buccal flora. Nitrite (NO2-) ion is
extremely reactive and very unstable. It can play the role of oxidant or reducer.
In an acid medium the nitrite ion forms nitrous acid. In the presence of a
halide ion, this latter can rapidly converts into a nitrosyl halide which then
reacts slowly with an amine (brought with food or medicine) and form
nitrosamine. The simplest nitrosamine is dimethyl nitrosamine.
Micro organisms
The most serious water pollutants in terms of human health world wide
are pathogenic microorganisms. Among the most important water borne
diseases are typhoid, cholera, bacterial and amoebic dysentery, enteritis, polio,
infectious hepatitis and schistosomiasis. Malaria, yellow fever, and filariasis are
transmitted by insects that have aquatic larvae.
The main source of these microorganisms (pathogens) is untreated or
improperly treated human wastes. Animal wastes from feedlots or fields near
waterways and food processing factories with inadequate waste treatment
88
facilities also are sources of disease causing organisms, i.e. this type of
pollution comes only from human and animal wastes, domestic and in-stream
uses are the major contributors, through agricultural and industrial waste waters
may also add small quantities.
Detecting specific micro organisms (pathogens) in water is difficult, time
consuming, and costly, so water quality is usually described in terms of
concentrations of coliform bacteria – any of the many types that live in the
colon or intestines of humans and other animals. The most common of these is
E. Coli, which lives symbiotically in many animals, but other bacteria, such as
Shigella Salmonella or Lysteria can cause fatal diseases. If any coliform
bacteria are present in a water sample, infectious pathogens are usually assumed
to be present also.
In presence of nitrate ion, phosphates accelarates eutrophication.
Check Your Progress-1
Notes:(1) Write Your answers in the space given below.
(2) Compare your answers with those given at the end of the unit.
(a) (i) Water quality is a .................. property dependent on the use to
which the water is put. Generally, it is a function of –
(a) .....................................
(b) .....................................
(c) .....................................
(d) .....................................
(e) .....................................
(f) .....................................
89
(ii) The amount of dissolved oxygen in water is a ..........................
of water. .................... and of the ...................... it will support.
(iii) BOD is an ............................... of organic ..................... and
determines ............................... for different purposes.
(b) (i) The tool solids quantity all ......................., ................... and
................, suspended and/or ......................... in water. When
present in excess they create ...................... for ......................
for various reasons.
(ii) Some of the metals are essential for .........................................
of all organism, while metal such as ..............., ....................,
........................, and ................ are highly ...................., even in
minute concentrations.
(iii) Nitrate ion in the body is converted into ................, which in
presence of ................. ion forms highly toxic ...........................
with amines. While phosphate ions in presence of ......................
ion, accelarate .............................................
3.8 WATER QUALITY STANDARDS
Rapid deterioration of aquatic environments as a result of different ways
of their utilization has led to the development of standards of quality of water.
The standards for quality of drinking water laid down by U.S. Public
Health Service are as follows :
(a) Physical Characteristics – The drinking water should be free from such
impurities which would cause offensive taste, smell and sense of sight.
90
Following physical limits should not be exceeded otherwise water will become
unfit for drinking (Table 3.1)
Characteristic Acceptable Case of rejection
(i) Turbidity (on J.T.U. scale)
(ii) Temperature
(iii) Taste
(iv) Odour
(v) Colour (on Platinum cobalt scale).
2.5
10ºC to 15.6ºC
Unobjectionable
Unobjectionable
5.0
10
Unobjectionable
Unobjectionable
25.0
(b) Chemical characteristics – The concentration of metals and other
chemical substances in potable water should not be exceeded by the amount
given in the following table 3.2
Characteristic Acceptable Cause of rejection
1. pH value
2. Total dissolved solids
3. Total Hardness (as CaCO3) in mg/l
4. Chlorides (mg/l)
5. Sulphates (mg/l)
6. Fluorides (mg/l)
7. Nitrates (mg/l)
8. Calcium (mg/l)
9. Magnesium (mg/l)
7.0-8.5
500
200
200
200
1.0
45
75
30
6.5-9.2
1500
600
1000
400
1.5
45
200
150
(If there are 250 mg/l of sulphates, Mg content can increased to a maximum of 125 mg/l with
the reduction of sulphates at the rate of one unit perery 2.5 units of sulphates).
10. Iron
11. Manganese
12. Copper
13. Zinc
14. Phenolic compounds
15. Anionic detergents
0.1
0.05
0.05
5.0
0.001
0.2
1.0
0.5
1.5
15.0
0.002
1.0
91
Characteristic Acceptable Cause of rejection
16. Mineral oil
Toxic Materials
17. Arsenic
18. Cadmium
19. Chromium
20. Cyanide
21. Lead
22. Selenium
23. Mercury
24. Poly-nuclear aromatic hydrocarbons
Radioactivity
25. Gross Alpha activity
26. Gross Beta activity
When pcu= pico curie unit.
nil
0.05
0.01
0.05
0.05
0.1
0.01
0.001
0.2 hg/l
3pcu
30pcu
nil
0.05
0.01
0.05
0.05
0.1
0.01
0.001
0.2 hg/l
3 pcu
30 pcu
Bactereological Standards :
(i) Water entering the distribution system – Coliform count in any sample
of 100 ml should be zero. A sample of the water entering the distribution
system that does not conform to this standard calls for an immediate
investigation into both the efficiency of the purification process and the method
of sampling.
(ii) Water in the distribution – Water in distribution system shall satisfy all
the three criteria indicated below :
(A) E-coli count in 100 ml sample should be zero.
(B) Coliform organisms not more than 10 per 100 ml shall be present in
any sample.
(C) Coloform organisms should not be detectable in 100ml of any two
consecutive samples or more than 50% of the samples collected for
the year.
92
In the inland surface waters for bathing GHATS, no viable floating
matter of sewage or industrial waste origin, and no unpleasant odour shall be
present (Table 3.3)
Table 3.3 Tolerance limits for inland surface waters for use as raw water supply and for bathing
Sl.N. Characteristic Tolerance Limit Method of Test, Ref. to CL No. in
IS : 1622
1964*
IS :
3025
1964+
IS:2488
(Part I)
1966+
IS :2488
(Part III)
1968$
(1) (2) (3) (4) (5) (6) (7)
(i) Coliform organisms (monthly
average MPN per 100 ml)
Not more than 5000, with less
than 5 percent of the samples
with value > 20,000, and less
than 20 percent of the samples
with value > 5000
3.2 - - -
(ii) pH value 6.0 to 9.0 - 8 - -
(iii) Flourides (as F), mg/l, Max 1.5 - 23 - -
(iv) Chlorides (as Cl), mg/l, Max 600 - 24 - -
(v) Cyanides (as CN), mg/l, Max 0.1 - 27 - -
(vi) Selenium (as Se), mg/l, Max 0.05 - 28 - -
(vii) Lead (as Pb), mg/l, Max 0.1 - 37 - -
(viii) Total chromium (as Cr), Mg/l,
Max
0.05 - 38 - -
(ix) Arsenic (as As), mg/l Max 0.2 - - - -
(x) Dissolved oxygen 40 percent saturation value of
3 mg/l whichever is higher
(xi) Biochemical oxygen demand
(5 day at 20ºC), mg/!, Max
3 - 53 - -
(xii) Phenolic compounds (as
C6H5OH), mg/l, Max
0.005 - 54 - -
(xiii) Alpha emitters, c/ml Max 10-9 - 58 - -
(xiv) Beta emitter, c/ml Max 10-8 - 58 - -
(xv) Nitrates (as NO3), Mg/l, Max 50 - 48 - -
(xvi) Oils and grease, mg/l, Max 0.1 - - 13 -
(xvii) Insecticides absent - - - 8
Table 3.4 records the limits of pollutants metallic cations and anions
commended By U.S. Public Health Service and as observed on a national
93
average in public water supplies. The limits are quoted in milligrams per liter,
which is essentially the same as parts per million by weight. For radium and
strontium, units are picocuries per liter, where one curie is the radiation
equivalent of one gram of radium (that is, 3.7 X 1010
disintegrations per
second). Phosphate, which is not included in the listing, has not been considered
a water pollutant in the same way as the toxic materials mentioned, but
increasing runoff from fertilizer and detergent use greatly affects biological
activity in streams and lakes. The problem is that phosphates are important
nutrients for growth, and their excessive presence in domestic waste water can
nourish biological processes beyond desirable rates. This phenomenon, known
as eutrophication (from the Greek word eutrophos, meaning "well nourished"),
can quickly choke an aquatic environment.
Physical pollution of water generally comes from turbidity, elevated
temperature (i.e., thermal pollution), and suspended matter. Turbidity, which
arises from soil erosion and colloidal wastes, can be corrected by addition of
coagulants such as FeCl3, alum or Fe2(SO4)3. Colloid particles (e.g., clay in
nutural waters, and proteins, fats, and carbohydrates in waste waters) are
usually stabilized by having negative charges at their surfaces, and these can be
neutralized by addition of ions. Thermal pollution usually arises when
manufacturing and power plants use streams for cooling. The result is decreased
dissolved oxygen and increased rate of biochemical activity.
94
Table 3.4 : Water Pollutant Limits, mg/liter
Substance Recommended
PHS
Observed
average
Remarks
Ag 0.05 0.008 Limit set for cosmetic reasons, leads to
discoloration of tissue.
As 0.01 0.0001 Serious systemic poison, cumultive
Ba 1.0 0.034 Not common, serious toxic effect on heart
Cd 0.01 0.003 Seepage from electroplating, 15 ppm in food causes
illness
Cr 0.05 0.0023 Not natural, suggests plating or tannery pollution
Cu 1 0.13 Essential and beneficial, adult needs 1 mg/day,
detectable taste at 1-5 ppm, large doses may cause
liver damage, used for algae control
Pb 0.05 0.013 Serious, cumulative body poison
226Ra 3* 2.2* Bone-seeking emitter, destroys bone marrow
90Sr 10* <1.0* Bone-seeking emitter
Zn 5 0.19 Essential and beneficial, milky at 30 ppm. matallic
taste at 40 ppm
Cl 250 27.6 Limit set for taste reasons, salty if too much
CN 0.01 0.00009 Rapid fatal poison, safety factor 100
F 1.2 0.32 Prevents dental caries in small amounts, mottling of
enamel above 1.2 ppm.
NO3 45 6.3 Fertilizer runoff, can cause methemoglobinemia in
infants.
SO4 250 46 Laxative effect above 750 mg/liter, often the cause
of traveler's diarrhea
* Picocuries per liter.
Similarly, the standards set for different industries for various parameters are
given in Table 3.5
95
Table 3.5 : Standards for Industries
S.N. Industry Parameter Standards
1 2 3 4
1. Caustic Soda Industry Concentration not to exceed milli gramme
per litre (except for pH and flow)
Total concentration of mercury in
the final effluent*
0.01
Mercury bearing waste water
generation (flow) pH
10 Kiloliters/tonne of caustic soda
produced 5.5 to 9.0
* Final effluent is the combined from (a) cell house, (b) brine plant, (c), chlorine
handling, (d) hydrogen handling, (e) hydrochloric acid plant
2. Man-made fibres
(synthetic)
Concentration not to exceed milligramme
per litre (except for pH)
Suspended solids Bio-chemical
oxygen demand, 5 days 20ºC pH
100
- 30
5.5 to 9.0
3. Oil refinery industry Concentration, not to exceed,
milligramme per litre (except for
pH)
Oil and grease
Phenol
Slphide
Bio-chemical oxygeri demand, 5 day
20ºC suspended solids
pH
Quantum, Kg/100 tonnes crude processed
10 7
0.5 0.35
15 10.5
20 14
4. Sugar industry Concentration not to exceed milligramme
per litre
Biochemical oxygen demand, 5 day
20ºC
100 for disposal on land 30 for disposal in
surface waters.
5. Thermal power plants Maximum limiting concentration,
milligramme per litre (except for pH and
temperature).
Condenser cooling
waters (one through
colling system)
pH
Temperature
6.5-8.5
Note more than 5ºC higher than the intake
water temperature.
96
S.N. Industry Parameter Standards
Boiler blowdowns Free available chlorine 0.5
Suspended solids 100
Oil and grease 20
Copper (total) 10
Cooling towar
blowdown
Free available chlorine 0.5
Zinc 1.0
Chromium (total) 0.2
Phosphate 5.0
Other corrosion inhibiting material Limit to be established on case by case
basis by Central Board in case of Union
territories State boards in case of States
Ash pond effluent pH
Suspended solids
Oil and grease
6.5-8.5
100
20
6. Cotton textile indstries
(composite and
processing)
Concentration not to exceed, milligramme
per litre (except for pH and bio-assay)
Common
pH
Suspended solids
Bio-chemical oxygen demand, 5 day
20ºC
Oil and grease
Bio-assay test
Special :
Total chromium (as Cr)
Sulphide (as S)
Phenoloic compounds (as C6H5OH)
5.5 to 9
100
150
10
90% survival of fish after 96 hours
2
2
5
7. Composite woolen mills Concentration not to exceed.
milligramme per litre (except for pH and
bio-assay)
Common : Suspended solids
Bio-Chemical oxygen demand, 5 day 20º
Oil and grease
Bio-assay
100
5.5 to 9.0
100
10
90% survival of fish after 96 hours
97
S.N. Industry Parameter Standards
Special :
Total chromim (as Cr.) 2
Sulphide (as S) 2
Phenolic compounds (as C6H5OH) 5
8. Dye and Dye
Intermediate Industries
Concentration not to exceed
milligrammes per litre (except for pH
temperature and bio-assay)
Supended Solids
pH
Temperature
Merucry (as Hg)
Hexavalent
Chromium
Total Chromium (as Cr)
Copper (as Cu)
Zinc (as Zn)
Nickel (as Ni)
Cadmium (as Cd)
Chloride (as Cl)
Sulphate (as SO4)
Phenolic Compounds (as C6H5OH)
Oil and Grease
Bio-assay Test (with 1:8 dilution of
effluents)
100
6 to 8.5
Shall not exceed 5ºC above the ambient
temperature of the receiving body.
0.01
0.1
2.0
3.0
5.0
3.0
2.0
1000
1000
1.0
10
90% survival of Test animals after 96
hours
9. Electroplating Industries Concentration not to exceed
milligrammes per litre (except for pH and
temperature) 6.0 to 9.0 shall not exceed.
98
S.N. Industry Parameter Standards
pH
Temperature
Oil and Grease
Suspended Solids
Cyanides (as CN)
Ammonical Nitrogen (as N)
Total Residual
Chloride (as Cl)
Cadmium (as Cd)
5ºC above the ambient
temperatures of the receiving body.
10
100
0.2
50
1.0
2.0
Nickel (as Ni)
Zinc (as Zn)
Hexavalent
Chromium (as Cr0
Total Chromium (as Cr)
Copper (as Cu)
Lead (as Pb)
Iron (as Fe)
Total Metal
3.0
5.0
0.1
2.0
3.0
0.1
3.0
10.0
10. Cement Plants Plant
capacity 2000 tonnes per
day Greater than 200
tonnes per day.
Total dust
(All Sections) Total dust
(All Sections)
Not to eceed milligrammes per normal
cubic metter
400
250
Carbon monoxide from coke over 3 kilogramme per tonne of coke
produced)
8[11 Stone crushing unit Suspended particulate matter The suspended particulate matter
measured between 3 meters and 10 metres
from any process equipment of a stone
crushing unit shall not exceed 600
microgrammes per cubic metre.
9[12 Coke ovens Concentrations in the effluents when
discharged into inland surface waters not
to exceed milligramme per litre (except
for pH)
pH 5.5-9.0
Bio-chemical Oxygen demand
(20ºC for 5 days)
30
99
S.N. Industry Parameter Standards
Suspended Solids
Phenolic Compounds
(As C6H5OH)
Cyanides (as CN)
Oil and Grease
Ammonical Nitrogen (as N)
100
5
0.2
10
50
13. Synthetic Rubber Concentration in the effluents when
discharged into inland surface waters not
to exceed milligramme per litre (except
for colour, and pH)
Colour Absent
pH 5.5-9.0
Bio-chemical oxygen demand 50
(20ºC for 5 days)
Chemical oxygen demand 250
Oil and Grease
Oil and Grease 10.0
14. Small Pulp and Paper
Industry
*Discharge into
inland surface
water
Disposal on land
pH
Suspended Solids
BOD
Suspended Solid
BOD
Concentration not to exceed milligramme
per litre (except for pH and sodium
absorption ratio)
5.5-9.0
100
30
100
100
Sodium Absorption Ratio 26
15. Fermentation Industry
(Distilleries, Maltries
and Breweries)
Concentration in the effluents not to
exceed milligramme per litre (except for
pH and colour and Odour)
pH
Colour and Odour
Suspended Solids BOD (5 days at
20ºC)
Disposal into inland surface water
Disposal on land
5.5-9.0
Absent
100
30
100
16. Leather Tanneries Concentration in the effluents not to
exceed milligramme per litre (except for
pH and per cent sodium)
100
S.N. Industry Parameter Standards
Suspended Solids
BOD-5 days at 20ºC
pH
Chlorides (as Cl)
Hexavalent
Chromium (Cr6+
) Total
Chromium (as Cr)
Sulphides (as S)
Sodium, percent
Boron (as B)
Oil and Greases
Inland
Surface
Waters
Public
Sewers
Land for
Irrigation
Marine
Coastal
areas
(a) (b) (c) (d)
100 100 200 100
30 350 100 100
6.0-9.0 6.0-9.9 6.0-9.0 6.0-9.0
1000 1000 100 -
0.1 0.2 0.1 1.0
2.0 2.0 2.0 2.0
2.0 5.0 5.0
- 60 60 -
2.0 2.0 2.0 -
10 20 10 20
17. Fertilizer Industry Concentration in the effluents not to
exceed milligramme per litre (except for
pH)
Effluents Straight Nitrogenous Fertilizers, excluding the
Calcium Ammonium Nitrate and Ammonium Nitrate Fertilizer
Plants
Commissioned
January 1, 1982
onwards
Plants
Commissioned
prior to January
1, 1982
(A) (b)
6.5-8.0 6.5-8.0
50 75
100 150
4 4
10 10
0.2 0.2
0.2 0.2
0.2 0.2
100 100
10 10
0.1 0.1
2.0 2.0
pH
Ammonical Nitrogen
Total Kjeldahl Nitrogen
Free Ammonical Nitrogen
Nitrate Nitrogen
Cyanide as CN
Vanadium As V
Arsenic as As
Suspended Solids
Oil and Grease
*Hexavalent
Chromium as Cr
*Total Chromium as Cr
Complex Nitrogenous Plants commissioned Plants commissioned
101
S.N. Industry Parameter Standards
Fertilizers
including Calcium
Ammonium Nitrate
and Ammonium
Nitrophosphate
Fertilizers
Complex Nitrogenous
Fertilizers
including Calcium
Ammonium Nitrate
and Ammonium
Nitrophosphate
Fertilizers
prior to
January 1, 1982 January 1, 1982
pH
Ammonical Nitrogen
Free Ammonical Nitrogen
Total Kjeldahl Nitrogen
Nitrate Nitrogen
Cyanide as CN
Vanadium as V
Arsenic as As
Phosphate as P
Oil and Grease
Suspended Solids
*Fluoride as F
**Hexavalent
Chromium as Cr
** Total Chromium as Cr
pH
Ammonical Nitrogen
Free Ammonical Nitrogen
Nitrate Nitrogen
Cyanide as CN
Vandium as V
(a) (b)
6.5-8.0 75 6.5-8.0
50 150
100
4 4
20 20
0.2 0.2
0.2 0.2
9.2 0.2
100 100
10 10
0.1 0.1
2.0 2.0
Plants
commissioned Jan.
1, 1982 onward
Plants
commissioned prior
to Jan. 1, 1982
(a) (b)
6.5-8.0 6.5-8.0
50 75
4 4
100 150
10 10
0.2 0.2
0.2 0.2
0.2 0.2
5 5
10 10
100 100
10 10
0.1 0.1
2.0 2.0
Plants
commissioned
January 1, 1982
Plants
Commissioned prior
to January, 1, 1982
(a) (b)
102
S.N. Industry Parameter Standards
6.5-8.0 6.5-8.0
50 75
100 100
20 20
0.2 0.2
0.2 0.2
Arsenic as As
Phosphate as P
Oil and Grease
Suspended solids
* Fluoride as F
**Hexavalent
Chromium as Cr
** Total Chromim as Cr
0.2 0.2
5 5
10 10
100 100
10 10
0.1 0.1
2.0 2.0
Stright Phosphatic
Fertilizers
pH
Phosphate as P
Oil and Grease
Suspended Solids
* Floride as F
**Hexavalent Chromim as Cr
**Total Chromium as Cr
5 7.0-9.0
5
10
100
10
0.1
2.0
Emissions
- Phosphatic
Fertilizers (Fluoride and
particulate matter
emission)
- Urea (Particulate
matter emission)
Phosphoric acid manufacturing unit
Granulation, mixing and grinding of
rock-phosphate
Prilling Tower
Commissioner prior to 1.1.1982
Commissioned after 1.1.1982
25 milligramms per normal cubic metre as total
Fluoride normal cubic metre of perticulate matter
150 milli gramme per normal cubic metre or 2
kilogramme per tonne of product
50 millgramme per normal cubic metre or 0.5
kilogramme per tonne of product
18. Aluminium Particulate Matter Emissions
- Calcination
- Smelting
250 milligramme per normal cubic metre of
particulate
150 milligramme per normal cubic metre of
particulate matter.
19. Calcium Carbide Particulate Matter Emission
250 milligramme per normal cubic metre
103
S.N. Industry Parameter Standards
- Kiln
- Are Funace
150 milligramme per normal cubic metre
20. Carbon Black Particulate Matter Emission 150 milligramme per normal cubic metre
21. Copper, Lead and Zinc
Smelting
Particulate Matter
Emission in concentrator
Emission of Oxides of sulphur in
Smelter and Convertor
150 milligramme per normal cubic metre
Off-gases must be utilised for sulphuric acid
manufacture. The limits of sulphur dioxide emission
from stock shall not exceed 4 kilogramme per tonne
of concentrated (on hundred per cent) acid produced.
22. Nitric Acid (emission of
oxide of nitrogen)
Emission of Oxides of Nitrogen 3 kilogramme of oxides of nitrogen per tonne of
weak acid (before concentration) produced.
23. Sulphuric Acid
(emission of sullphur
dioxide)
Sulphur dioxide Emissions 4 kilogramme per tonne of concentrated (on hundred
per cent) acid and acid mist) produced.
24. Iron and Steel
(Integrated)
Acid mist
Particulate Matter Emission
50 milligramme per normal cubic metre
- Sintering Plant
- Steel making
- during normal operation
- during oxygen normal
- Rolling Mill
Carbon monoxide form coke
oven
150 milligramme per normal cubic metre
150 milligramme per normal cubic metre
400 milligramme per lancing cubic metre
150 milligramme per normal cubic metre
3 kilogramme per tonne of coke produced
*To be complied with at the outlet of fluoride removal unit. If the recipient
system so demands, fluorides as F shall be limited to 1.5 mg/l.
**To be complied with at the outlet of chromate removal nit.
7. Ins by S.O. 82 (E). dt. 16.2.1987 (1987 CCL-III 600).
8. Ins by S.O. 393 (E), dt. 16.4.1987 (1987 CCL-III)
9. Ins. by S.O. 64 (E), dated 18.1.1988, published in the Gazette of India, Extra,
Part II, Section 3 (ii), dated 18.01.1988.
3.9 ANALYTICAL METHODS OF ANALYSIS
In the study of natural and waste water, chemical study has a special
importance, as for a better understanding of the aquatic environment,
104
knowledge of its components, pollutants and other chemicals present is
necessary.
The various sources of water can be classified into (1) surface waters and
(2) subsurface waters. The surface waters include streams, lakes and reservoirs
while sub-surface waters generally include waters from shallow and deep wells.
Characteristics of water – The characteristics of water from various
sources depend on :
(i) the nature of material with which it is in contact,
(ii) the time of year
(iii) the effect of other substances, and
(iv) the rainfall.
The different characteristics can be summarised below :
Type Radioactive
matter
Organic matter Inorganic
matter
Microbial count
Deep well
Shallow well
Surface
Nil
very low
variable
low
variable
high
high
low
low
low
variable
generally contaminated
The analysis of water involve three steps :
1. Sampling of water
2. Preservation of the sample, and
3. Analysis of the sample
1. Sampling
For a physico-chemical and biological examination of water, a proper
sampling procedure must be adopted.
There are two types of samples :
(1) Grab sample, and (2) Composite sample
105
(1) Grab sample- A grab sample is a manually collected single portion of
sample of water or waste water.
(2) Composite sample – When a grab sample is collected at regular intervals
for a certain period, for example 12 hrs, or 18 hrs, and mixed, then this
mixed water or waste water sample is called composite sample.
Quantity of sample – In general, about 2 litres of sample is taken for physical
and chemical examination of water.
Sample container – Ordinarily stoppered Winchester Qart bottle of 2.5 litres
capacity is sufficient. Generally glass containers are preferred over polythene
materials. All sample containers before use must be cleaned thoroughly to
remove all extraneous matter. Soda lime glass bottles are not recommended as
sample containers. Glass stoppers or new cork stoppers that have been
throughly washed or plastic caps with suitable liners are recommended.
Frequency of sampling – For water having sewage contamination, individual
samples at frequent intervals such as biweekly or monthly are to be taken for
analysis work. If samples are taken from river then they may be taken at short
intervals, for instance daily. If there are greater variations, samples should be
taken at hourly intervals.
Sampling potable waters – The sample should be taken from the tap directly.
Before collecting the sample, the inside and outside of tap should thoroughly be
cleaned.
Well – If water from a well is collected, then well has to be pumped for a longer
time so that sample represents ground water that feeds the well.
106
Sampling in larger rivers and streams – Three or four samples are taken at mid
point of equal cross sectional areas of such rivers and streams. The samples are
then combined together to obtain a composite sample, If only a grab sample is
taken, it is better to collect in the middle of the stream and at mid depth.
When a river is mixing with a sewage then sample is taken down stream
sufficiently away to allow thorough mixing. Generally a distance of 1 to 3 or 4
km below the tributary is advisable.
Sampling sewage – For collection of sewage samples, a composite sample over
24 hrs. period been suggested. The different grab samples should be combined
in a container of 2.3 litres.
Sampling industrial effluents – As industrial samples are subject to rapid
change within a few minutes due to breakdowns, spill overs, floor washing etc.
hence it is necessary to collect individual samples at uniform intervals, say 10
or 20 minutes. In fact the degree of variation in rate of flow will determine the
time interval for sampling.
Polythene containers are used for collection of raw sewage, activated
sludge etc. Cleaning procedure of these containers was to soak the jars in 2%
HNO3 solution for 24 hours, followed by multiple rinses with doubly distilled
water. The collected samples should be stored at 4ºC in surface of polythene.
Samples should be collected from different points after different treatments.
Preservation of samples – Generally samples should be kept in dark at low
temperature. However some specific preservation methods are as follows :
(1) Oxygen demand : Samples should be preserved at 4ºC.
(2) Total organic Carbon : Add conc. HCL to lower down the pH
below2
107
(3) Nitrogen balance : Add 1ml conc. H2SO4 per litre and refrigerate.
(4) C.O.D.: Add conc. H2SO4 to being pH about 3.
(5) Sulphides : Add 0.2 ml zinc acetate solution per 100 ml sample.
(6) Metals : Adjust pH below 2 by adding conc. HCL or Conc. HNO3.
Labelling of sample
The containers are labelled with the following information :
(i) Date and Time
(ii) Sample number
(iii) Source of sample
(iv) Exact point of sample
(v) wind speed, pressure and speed of river
(vi) Name and signature
3. Types of Examination
(A) Physics Examination includes-
(i) Colour (ii) Odour and taste, and (iii) Turbidity.
(B) Chemical Examination-
(i) Total solids, (ii) Organic matter, (iii) Alkalinity, (iv) Hardness,
(v) pH, (vi) Acidity, (vii) (a) Nitrogen as nitrites; (b) as nitrates; (c) as free
ammonia, and (d) as albuminoid ammonia, (viii) Sulphates (ix) Calorides, (x)
Dissolved oxygen, (xi) Bio-chemical oxygen demand (B.O.D.), (xii) Chemical
oxygen demand (C.O.D.), (xiii) Free CO2, (xiv) Free available and combined
available chlorine (xv) Chlorine demand, and (xvi) Chlorine dosage.
(c) Microbiological Examination includes-
(i) Total count and coliform MPN
(ii) Straptococci
(iii) Clostridium Welchii
108
3.9.1 Analytical Method for Measuring Bio-Chemical Oxygen Demand
(BOD)
Biochemical Oxygen Demand (BOD) indicates the presence of
biodegradable organic matter in water quantitatively, which consumer dissolved
oxygen from water, hence it is an index of organic pollution and indicates
suitability of water for a particular consumption.
The B.O.D. is the amount of oxygen required by bacteria while
stabilizing decomposable organic matter under aerobic conditions. The
decomposition of organic impurities in presence of bacteria results in utilisation
of a part of the dissolved oxygen by the bacteria during their respiratory and
metabolic activities. This depletion of oxygen is considered as a measure of the
strength of water.
OHCOnutrients
OxygenOrganics 22
bacteria
All organic constituents of sewage degrade under aerobic conditions.
The organics in sewage can be divided into three major groups :
(1) Carbohydrates (starches, sugars and cellulose), (2) Proteins and (3)
Fats.
The approximate distribution or organics being 40 to 50% Carbohydrates,
40 to 50%. Protein and Fat is 5 to 10%. The starches and sugars are easily
metabolized by microorganisms while cellulose decomposes at a slower rate.
OHCOacidsFattyAlcoholstesCarbohydra 22
sroorganismEnzymermic
The proteins are complexes of amino acids which form major source of
microbial nutrients.
1. Amino acids + ammonia Nitrite Nitrate
2. H2SH2SO4
109
3. Alcohols + Organic acids CO2+H2O
Proteins and other nitrogen containing organic compounds organismsmicro
orEnzyme
Fats are degrated by microorganisms at very slow rate
Fats ismsmicroorgan
Enzymesor Fatty acids + Glycerol + Alcohols + Lower Fatty
acidsCO2+H2O
The biochemical oxidation of organic matter in sewage can be considered
as a monomolecular reaction, given by linear rate equation :
Y = L [1 – 10-kt
]
when Y = BOD at time t
L = the ultimte BOD and
k = the reaction rate constant
The L and D both serve as an effective means of gauging the qualitative
and quantitative changes in the decomposable material in unchlorinated and
chlorinated samples.
A reduction in k implies that as a result of chlorination, a quantitative
change in the character of sewage constituents had taken place so that they had
become less readily decomposable by aerobic organisms. Thus a k value of 0.2
will exert 90% of its ultimate first stage BOD in 5 days at 20ºC while a k value
of 0.15 will have exerted only 32% of its BOD in the same 5 days at 20ºC.
The chlorination of sewage always reslts in the reduction of L value
which indicates that there is a quantitative change in the decomposable fraction
of the sewage.
Reagents :
(1) Conc. H2SO4.
(2) 48% MnSO4 solution in water.
110
(3) Alkaline KI-Add 700 gm of KOH and 150 gms of KI in 1 litre.
(4) 0.0125 N standard sodium thiosulphate solution.
(5) Starch indicator.
(6) Sodium sulphite.
If the sample of sewage or water is alkaline or acidic then neutralize at
pH 7 with 1 N N2SO4 or 1 N NaOH using pH meter. Excess of chlorine will be
removed in sample is allowed to stand for 1 to 2 hrs. in open. If residual
chlorine is too high titrate it with this solution and add the required amount of
sodium sulphate.
Now take three bottles, A, B and C of 500ml capacity and fill the bottles
with aerated water and stopper without leaving any air bubble. Determine the
dissolved oxygen in A immediately by adding 1ml of MnSO4 + 2ml of conc.
H2SO4 (Avoid air passage).
In bottles B and C, take 1 ml of MnSO4 solution and 2ml of conc. H2SO4
solution. In bottle C, add 2 ml of sewage sample. Incubate both the bottles at
room temperature for 5 days, find dissolved oxygen of both the bottles B (black
bottle) and C (sample bottle) by the same method as described above.
Calculation – 1 ml of 0.0125N Na2S2S3 soln. = 0.1 mg of O2
Oxygen content in A, mg/litre = bottleinwaterVolume
01.01000Titre
For B and C, BOD, mg/litre = takensamplewasteofml
1000)CB( or ppm
The (A-B) suggests loss of oxygen during incubation.
111
3.9.2 Dissolved Oxygen
The low values of dissolved oxygen affect the potability of water and can
cause killing of fish and other animals of sea kingdom. It is a test which
indicates the sanitary status of a water. The dissolved oxygen also suggests
whether the process undergoing a change are aerobic or anaerobic. A good
water should have solubility of oxygen about 15 mg/litre at 0ºC and 7 mg/litre
at 30ºC.
Reagents :
(1) Alkaline Potassim iodide – Dissolve 100 gm of KOH and 150 gm of
KI in 1 litre of water.
(2) 48% MnSO4 solution.
(3) 0.0125 N Sodium thiosulpahte solution.
(4) Starch indicator
(5) Conc. Sulphuric acid.
Procedure – Take 200 ml of sample in a conical flask. Add 1ml of MnSO4
solution (by pipette dipping the end below the surface) and 1ml of alkaline KI.
Put the stopper and mix the solution thoroughly (avoid passage of air). After
10-15 minutes when the precipitate settles down, add 2ml conc. H2SO4.
Dissolve the precipitate by shaking. Now titrate the solution with sodium
thiosulphate using starch as indicator. Note the ml of titrant used in getting the
end point. Perform the blank titration, the difference of the two should be
regarded as ml of sample titre.
Calculation – ml of 0.0125N Na2S2O3 solution = 0.1 mg of O2
ml of sample titre x Normality of Na2S2O3x8x1000
Dissolved oxygen, mg/litre
Volume of water in the conical flask
112
Chemical reactions involved are as follows :
4MnSO Mn++
+
4SO
Alk KI K+ + I
- + OH
-
Mn++
+ 2OH- Mn (OH)2
white Ppt
Mn++
+ 2OH- +
2
1O2 MnO2 + H2O
Brown Ppt (Oxygen present)
MnO2 + 4H+ + 2I- I2 + Mn
++ + 2H2O
I2 + 2Na2S2O3 Na2S4O6 + 2NaI
It indicates the organic pollution in water. It is a measure of the strength
of sewage or polluted water.
3.9.3 Chemical Oxygen Demand
Chemical oxygen demand is used for measuring the pollutional strength
of waste water. Most of the organic compounds can be oxidised to carbon
dioxide and water by the action of strong oxidising agents regardless of the
biological assimilability of the substances.
It is generally obtained by potassium dichromate reflux method.
Reagents :
(1) Standard ferrous ammonium sulphate solution.
(2) Standard potassium dichromate N/4.
(3) Sulphuric acid (with 1 gm of silver sulphate in every 75ml acid).
(4) Ferroin indicator.
Procedure – Take 50 ml of the sample (A) in a conical flask. Add 100 ml of
distilled water and 15ml of standard potassium dichromate solution slowly and
slowly and add 75 ml. conc. H2SO4. Reflux the mixture for 2 hours, cool and
wash down the condensate with distilled water.
113
Transfer the contents to 500 ml. flask. Dilute the mixture to about 300
ml. Titrate the excess dichromate with standard ferrous ammonium sulphate
using ferroin indicator.
Now perform the blank experiment (B) by taking 100 ml distilled water,
75ml acid and 25ml potassium dichromate solution. Reflux for 2 hours and
titrate the excess dichromate with ferrous ammonium sulphate.
Calculations – C.O.D. mg/litre = sampleofml
10008C)BA(
when A = ml. of ferrous ammonium sulphate used with sample.
B = ml. of ferrous ammonium sulphate used with distilled water,
C = Normality of ferrous ammonium sulphate.
3.9.4 Fluoride Estimation
It can be estimated by iodometric titration. When KI and acetic acid are
added in fluoride solution, it liberates iodine which can be titrated with sodium
thiosulphate using starch as indicator. The minimum detectable concentration is
approximately 0.04 mg of chlorine per litre. The reaction is mostly carried out
at pH 3 to 4 in absence of light.
Reagents :
(1) KI
(2) Acetic acid (glacial)
(3) Starch indicator
(4) 0.005 N Na2S2O3 solution. A few drops of chloroform are added to
increase the storage life for more than a month.
114
Procedure – Avoid the presence of direct sunlight when performing the
experiment.
Take 200 ml of the sample. Add 5 ml of glacial acetic acid to reduce the
pH between 3 and 4. Add about 1gm of KI in the sample and titrate with 0.005
N thiosulphate solution from burette until yellow colour of liberated iodine is
almost discharged. Now add 1 ml of starch solution and titrate until the blue
colour is discharged.
Blank titration – Perform the experiment with blank titration (without
fluoride water) by mixing KI in acetic acid and distilled water with same
quantity of the sample.
The actual titre value = (Titrate value with sample – titre value with
blank).
Calculation – Fluoride in water, mg/litre, mg/litre = Actual titre sampleofml
1000127thioofnormality
3.9.5 Oil
The greatest damage to water is inflicted by petroleum and its products.
This generally happens when oil is transported from one place to another place
or from one contry to other through sea.
Oil can be removed by using absorbents such as moss, saw beat dust,
pine bark and straw etc.
The other method is emulsification.
It can also remove by using floating Booms.
Using chemical additives oil is solidifies. Mechanical methods are also
used to remove oil slick from marine water.
115
3.9.6 Metals
Samples of water, for determination of heavy metals are collected in the
plastic bottles. The sample container are thoroughly washed and rinsed with
dilute HNO3 and then with the distilled water before being reused.
Samples for dissolved metals are filtered through 0.45m pore diameter
filter paper. The filtrate is then acidified to pH 2 with concentrated HNO3 and
analysed directly using the Atomic Absorption Spectrophotometer (Model
2380).
3.9.7 Residual Chlorine and Chlorine Demand
(A) Total Residual Chlorine
The chlorine present in water as Cl2, HOCl, OCl-,H2OCl+, Cl
3 is called
as free available chlorine Residual chlorine. When chlorine in water combines
with ammonia to form chloramines and other chloroderivatives then the mixture
of chloramines and other derivatives is called available chlorine. Both free and
combined chlorine may be present simultaneously in the chlorinated water.
Orthotolidine : Arsenite method – This method is used in the
determination of free available and combined available chlorine and colour due
to interferring substances. Orthotolidine gives yellow color in presence of
chlorine.
The most important point is that all the experiments must be performed at
low temperature (preferably 1ºC) as at room temperature. Some of combined
available chlorine can react with orthotolidine giving a high free available
chlorine value.
116
Reagents-
(1) Sodium arsenite reagent – Dissolve 5gm of sodium arsenite in 1 litre
distilled water.
(2) Orthotolidine reagent – Dissolve 1.35 gm of orthotolidine
dihydrochloride in 500 ml distilled water. Now add in this solution,
350ml of distilled water and 150ml of conc. HCl. The total solution is
1 litre. Keep it in ambered bottle. The solution is stable for 6 months.
(3) 0.5 M phosphate buffer solution – Take 22.86 gm of Na2HPO4 and
46.16gm of KH2PO4 in 1 litre flask and make up with distilled water.
(4) Permanent chlorine standard using chromate dichromate stock
solution-Add 1.55 gm of K2Cr2O7 and 4.65 gm of K2CrO4 in a litre
flask and make up with 0.1M standard buffer solution. The colour
produced will be equal to 20 mg of chlorine per litre (10 mg/litre)
For getting the range between 0.01-1.0 mg of chlorine per litre, take 100
ml of chromate- dichromate stock solution to 1 litre with 0.1 M phosphate
buffer. The colour develops is equal to 1 mg/litre. Take out
1,3,5,7,10,15,20,40,50,60,70,80,90 and 100 ml. of chromate-dichromate stock
solution to 100ml flask and make up with 0.1 M phosphate buffer to get the
required range (between 0.01 and 1 mg chlorine per litre) of standards.
The whole analysis can be summarised in the following way:
117
Take three comparator cells A, B and C and perform the experiment as follows:
Free available chlorine + Total residual chlorine + Interfering colour present in
interfering colour interfering colour the immediate reading and
after 5 min.
A B C
Add 0.5 ml orthotolidine Add 0.5 ml orthotolidine Add 0.5 ml. of arsenite reagent
reagent reagent
Add 10 ml of sample Add 10 ml of sample Add 10 ml of sample
Add 0.5 ml of arsenite reagentCompare the colour with the Add 0.5 ml. of othotolidine
within 10 secs and compare standard after 5 minutes reagent and compare the
the colour with the standard colours with the standards
(immediately) immediately (say C1)
Compare the colour again
after 5 minutes (say C2)
Calculation-
The free available chlorine = A-C1
The total available (residual) chlorine = B- C2
3.10 PURIFICATION AND TREATMENT OF WATER
The raw water available from various sources is contaminated or contains
impurities and hence it is made safe for the purposes for which it is to be used.
All the impurities cannot be fully eliminated but they are reduced to such an
extent that water becomes suitable for intended use.
118
Generally water contains many impurities such as minerals and organics as
given in table 3.6. They should be removed.
Table 3.6 Impurities in Water
Class of
Impurity
Cause of Impurity Result of Impurity
(A) Mineral
(a) Suspended
(b) Dissolved
(b) Organic
(a) Suspended
(i) Vegetable
(ii) Animal
(b) Dissolved
(i) Vegetable
(ii) Animal
Particles of sand, clay, silt etc.
Carbonates, bicarbonates of Ca
and Mg.
Ca and Mg sulphates
Ca and Mg chlorides
Na carbonates and bicarbonates
Na chlorides
Na fluorides
Iron oxide
Manganese
Decayed leaves, Algae, peat,
pollen, fungi etc.
Dead animals, hair, insects, skin,
scales etc.
Large amount of albuminoid
ammonia with a little free
ammonia and chlorides.
Large amount of albuminoid
ammonia with large quantity of
free ammonia and chloride.
Turbidity
Hardness and alkalinity
Hardness
Hardness, corrosion of boilers.
Alkalinity and softness
Brackish taste.
Excess over 1.5 ppm causes teeth
staining.
Red color, taste, hardness.
Brown colour and taste.
Green or brown colour, taste, acidity,
water suspicious.
Bacteria, water dangerous to health.
Bacteria, water suspicious.
Disease producing type bacteria,
sewage pollution, water dangerous.
119
The main object of treatment processes is to remove all the undersirable
impurities, to that extent where they do not cause any trouble and water is
available to the consumers as per health standards. Following may be the
objects.
(i) To remove objectionable taste and odour from the water.
(ii) To remove colour, dissolved gases and murkiness of water.
(iii) To kill the troublesome bacteria, algae and fungi.
(iv) To elminate the corrosive and tuberculation properties of water.
(v) To make water safe for drinking, bathing, domestic purposes and for
various industrial purposes like brewing, dyeing, steam boilers etc.
Various treatment processes are given below. It is not essential that all
these processes will have to be employed at all the places, but it depends upon
the quality of raw water.
Removal of Dissolved Gases :
It has been found that some of the gases if present in water are dissolved
from may cause certain difficulties. Dissolved carbon dioxide corrodes the
pipes. Similarly oxygen, chlorine, and other gases, if in dissolved form, are
present in excess amounts, also cause difficulties.
Many dissolved gases can be removed by boiling, decompression or by
means of chemical treatment, except oxygen and nitrogen all other gases can be
reduced by aeration. Aeration process removes carbon dioxide, hydrogen
sulphide, and odours very rapidly. Following are some of the methods of
aeration.
(i) By mechanically agitating water.
(ii) By diffusing compressed air inside the water.
(iii) Mixing air in water under pressure.
120
(iv) By spraying water into the atmosphere through nozzles 1 to 2.3
metres.
(v) Flowing water through perforated trays and coke beds, so that the
water filters through them.
(vi) By flowing water over weire, steps etc. so that water is exposed to sun
as much as possible.
Removal of Iron and Manganese:
Manganese and iron are generally found together, in raw waters. Iron is
found in the form of ferrous sulphate and ferrous bicarbonates. The presence of
iron and manganese in excess of 0.3 ppm renders water objectionable due to
following reasons:
(i) They cause corrosion to plumbing works.
(ii) They cause taste and odour.
(iii) They cause troubles in various manufacturing processes and make
them uneconomical.
(iv) They cause spots on clothes during washing or during their use in
textile.
(v) They may make water reddish due to presence of iron bacteria.
Removal of iron and managanese can also be done by any one of the
following methods :
(i) By base-exchange processes.
(ii) By chlorination
(iii) By aeration of water.
Iron alone in the absence of organic matter can usually be removed by
aeration of any type, followed by sedimentation and filteration. Combination of
iron and manganese or iron alone loosely bound to organic matter may require
121
aeration in multiple coke trays containing coke, gravel or crushed pyroluste
(pyrolusite is a negative manganese dioxide).
It has been revealed that mataphosphates may be used to prevent
precipitation of iron or manganese. Their use is generally applicable when the
iron concentration is less than 1 ppm.
Removal of Silica :
The following are the methods which may be used for silica removal.
(i) By using magnesium hydroxide with carbon dioxide, calcium
bicarbonate or magnesium bicarbonate which produce magnesium
carbonate absorbing silica.
(ii) Apply ferric sulphate and lime to develop ferric hydroxide which
absorbs silica.
Removal of Taste, Odour and Colour :
Coagulation followed by filtration, prechlorination, superchlorination
followed by dechlorination and use of chlorine dioxide are the methods which
help in the removal of taste, odour and colour.
Conversion of Saline Water :
Sea water contains about 35000 ppm of dissolved solids. No single
process of treatment can be suitable for making such water safe. Vapour-
compression method, ion exchange method, solar distillation, freezing, osmotic
processes and ultrasonics are the methods which may be employed for
purification of such waters.
Ion exchange method is more promising when the concentration of
dissolved material is below 4000 to 5000 ppm. Several plants of applying this
method have been constructed recently in U.S.A.
122
Removal of Radio-activity from Water :
Radio-active materials may pollute the sources of water supply which is
used for drinking purposes. Dangerous materials may be mixed with water due
to nuclear blasts, wastes from atomic energy installations, are use in research,
industry or medicine. The wastes from atomic energy installations are so
controlled that an appreciable health hazards is unlikely.
Radio-active materials may be partly removed from water by ordinary
methods of coagulation. Removals up to 80 to 90% can be expected. No other
feasible method have been devised so far.
Removal of Dissolved Minerals :
Kenzelite and Zepholite proprietary, base-exchange compounds, have
been used successfully in the removal of lead, zinc, dissolved solids from 1000
to 3000 ppm may be demineralized successfully be the application of a direct
electric current is specially designed cells with canvas or similar diaphragms.
Removal of Oils :
It may be removed by absorption by passing the water through containers
of excelsior.
Hardness of Water or Softening of Water :
Hard water has the following bad effects : (1) It develops bad taste. (2) It
develops corrosion and incrustations in pipes (3) It also influences the working
of dyeing (4) It develops scales in the boilers. (5) It consumes more of soap.
The hard water has to be made soft by certain methods before it is
supplies to the consumers.
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Types of hardness : Temporary hardness is caused due to the presence
of bicarbonates of calcium and magnesium.
The permanent hardness is caused by the presence of sulphates, chlorides
and nitrates of calcium and magnesium. This is also called non-carbonate
hardness.
Removal of temporary hardness : This hardness of water can be
removed by either boiling or by adding lime. Chemical reaction may be as
follows :
Ca (HCO3)2 + Heating CaCO3 + H2O + CO2
Ca (HCO3)2 + Ca (OH)2 2CaCO3 + 2H2O
Mg (HCO)2 + Ca(OH)2 CaCO3 + MgCO3 + 2H2O
Removal of permanent hardness : The following three methods may be
adopted for this purpose.
1. Zeolite process.
2. Demineralization process
3. Lime soda process
Lime soda process : Hydrated lime removes permanent hardness due to
magnesium sulphate, magnesium chloride and calcium chloride and magnesium
chloride. Chemical reactions are given here.
CO2 + Ca(OH)2 CaCO3 + H2O
MgSO4 + Ca(OH)2 Mg (OH)2 + CaSO4
CaSO4 + Na2CO3 CaCO3 + Na2SO4
MgCl2+Ca(OH)2Mg(OH)2 + CaCl2
CaCl2+Na2CO3 CaCO3 + 2NaCl
MgCl2+Na2CO3MgCO3+2NaCl
Mg(HCO3)2 + Ca(OH)2 CaCO3 + MgCO3+H2O
124
Municipal Sewage Treatment
Sanitary engineers have developed ingenious and effective municipal
wastewater treatment systems to protect human health, ecosystem stability and
water quality. This involves following steps :
Primary treatment physically separates large solids from the waste stream with
screens and settling tanks (fig 3.2a). Settling tanks allow grit and some
dissolved (suspended) organic solids to fall out as sludge. Water drained from
the top of settling tanks still carries up to 75 percent of the organic matter,
including many pathogens. These are treated by secondary treatment, in which
aerobic bacteria break down dissolved organic compounds. In secondary
treatment effluent is aerated, often with sprayers or in an aeration tank, in which
air is pumped through the microorganism-rich slurry (Fig 3.2b). Fluids can also
be stored in a sewage lagoon, where sunlight, algae, and air process waste more
cheaply but more slowly. Effluent from secondary treatment processes is
usually disinfected with chlorine, UV light, or ozone to kill harmful bacteria
before it is released to a nearby waterway.
Tertiary treatment removes dissolved metals and nutrients, especially
nitrates and phosphates, from the secondary effluent Although wastewater is
usually free of pathogens and organic material after secondary treatment, it still
contains high levels of these inorganic nutrients. If discharged into surface
waters. these nutrients stimulate algal blooms and eutrophication. Allowing
effluent to flow through a wetland or lagoon can remove nitrates and
phosphates. Alternatively, chemicals often are used to bind and precipitate
nutrients (fig. 3.2)
125
Figure 3.2
Sewage sludge would be valuable fertilizer if it were not contaminated by
metals, toxic chemicals, and pathogenic organisms. The toxic content of most
sewer sludge necessitates disposal by burial in a landfill or incineration. Sludge
disposal is a major cost in most municipal sewer budgets.
In many cities, sanitary sewers are connected to storm sewers, which
carry runoff from streams and parking lots. Storm sewers are routed to the
treatment plant rather than discharged into surface waters because runoff from
streets, yards, and industrial sites generally contains a variety of refuse,
fertilizers, pesticides, oils, rubber, tars, lead (from gasoline) and other
undsirable chemicals. Unfortunately heavy storms often overload the system,
126
especially where the system is old and already overtaxed. As a result large
volumes of raw sewage and toxic surface runoff are dumped directly into
receiving waters. To prevent this overflow, cities are spending hundreds of
millions of dollars to separate storm and sanitary sewers.
Waste Water Treatment :
Waste water treatment can be classified into three successive stages
primary, secondary and tertiary. In primary treatment the waste water is passed
(i) through screens, to take out the large solids, (2) Successively into grit and
sedimentation tanks, where the smaller sediments are allowed to settle, and then
(3) through a chlorine treatment, to destroy the bacteria. Most of the solids,
about one-third of the BOD and a few percent of the persstent organic
compounds are removed in this way. In secondary treatment, further pollutant
redction is achieved by adding one of two possible processes : trickling filter or
activated-sludge treatment. For trickling filter, a bed of gravel and rocks is
provided through which the sewage is passed slowly enough that bacteria
multiply on the stones and consume most of the organic matter. The process is
about 75 percent effective. In the activated-sludge method, incoming sewage is
inoculated with activated sludge from recirculation), passed into an aeration
tank, then into a sedimentation tank, and finally on to chlorine treatment. The
process takes several hours but is 90 percent effective at removing organic
wastes.
Tertiary treatments, because of their expense are used only when
drinking-quality water needs to be produced in a completely recycled system or
from naturally contaminated sources. They are also used when it is necessary to
remove organic compounds that do not yield to secondary treatment. One such
method is to treat the nearly purified water with activated charcoal, filter off the
127
charcoal after it has adsorbed the impurities, and then regenerate it with steam
distillation. To remove phosphate, precipitation of the highly in-soluble
phosphates can be achieved by adding CaO, Fe(OH)3, or Al(OH)3, Other
inorganic salts, such as nitrates, are very difficult to remove.
One promising technique for waste-water recovery is reverse osmosis.
Instead of taking the waste out of the water, the water is squeezed out of the
waste. Figure 3.3 shows a schematic representation of the setup. Salt water is
fed into the top of the cell, the bottom part of which is blocked off by a
semipermeable membrane.
Normally, fresh water tends to move toward the salty side, but by putting
a sufficiently large pressure on the inflowing saline water the normal osmotic
flow can be reversed and fresh water literally squeezed through the membrane
so as to come out the bottom pipe.
Fig. 3.3 : Reverse – Osmosis cell for getting fresh water from salt water.
The above process is not very cheap, but in certain installations it may be
of value. One hopeful application for the future might be removal of nitrate ion.
128
Recent generous use of nitrate fertilizers has raised NO
3 levels in some ground
waters to dangerous levels. The danger appears to be particularly great for very
young infants who are prticlarly susceptible to methemoglobinemia (blue-baby
syndrome). This comes from oxidation by nitrite, NO
2 , of the iron in
hemoglobin so it can no longer carry oxygen. Water intake by infants is
disproportionately large and the infant's digestive equipment is likely to harbor
the wrong kind of bacteria, which reduce nitrate to nitrite. Nitrate removal
remains an unsolved problem.
Check Your Progress – 2
Notes : (1) Write your answers in the space given below.
(2) Compare your answers with those given in the end of the unit.
(a) (i) The quality of drinking water should be free from such impurities
which cause ......................, .................... and ......................... The
concentrations of metals and other ..................... should not exceed
the ........................... while all the three criteria given below for
bactereological standards should be satisfied :
(a) ...................................
(b) ...................................
(c) ...................................
(ii) Physical pollution of water comes from –
(a) .............................
(b) .............................
(c) .............................
129
(iii) Water analysis involve the following three steps :
(a) ...............................
(b) ..............................
(c) ..............................
(b) (i) BOD is the amount of oxygen required by ....................... while
stabilising .............................. under ........................... conditions. It
is determined by ......................... titration method.
(ii) DO suggests whether the processes undergoing change are
........................ or ....................... It is determined by .......................
titration.
(iii) COD is used for measuring the .......................... of .......................
It is generally obtained by ............................. method.
(iv) The residual chlorine is the chlorine present in water as
..................., ........., ............., ...................., and .....................
(v) Sewage treatment involves three steps :
In primary step large solids are physically separated with
........................ and .............................. In the secondary step
effluent is ......................... while in the tertiary step
........................... and .......................... especially ..........................
and ........................ from the secondary effluent are removed.
3.11 LET US SUM UP
By going through this unit you would have achieved the objectives laid
down at the beginning of this unit. Let us recall what we have discussed so far :
The aquatic environment is the reservoir of industrial, domestic and
agricultural wastes. Since 90% of the hazardous wastes are placed in the
130
soil and water, the organisms present in this environment are found to be
affected by these toxicants.
Dissolved oxygen is required by all aquatic plant and animal life. Fish
require the highest levels, vertebrates next, and bacteria the least. When
dissolved oxygen gets depleted, plant and animal life disappear.
Organic water pollutants include protein (domestic sewage, waste from
creamaries, slaughter houses), fat (sewage, soap production, food
processing), carbohydrates (sewage, paper mills), resin, coal, and oil.
Inorganic pollutants might be acids, alkalies, heavy metal- cations and
certain anions. While biological pollution of water may include bacteria,
viruses, protozoa, parasites and plant toxins.
For a complete study of a water body, it is necessary to determine
different type of parameters, the most important ones are physical,
chemical and biochemical parameters.
Physical properties of any water body generally depend on the ecology,
weather conditions, and chemical properties of the place concerned. The
parameters included are generally, colour, odour, temperature, heat
budget, light transparancy etc.
During water analysis, study of chemical properties is very important, the
important chemical parameters include determination of acidity and
alkalinity, pH, conductivity, redox potential, soluble solid, free oxygen,
dissolved oxygen, salts, hardness, N, P, Na, K, BOD, COD, metals,
chloride, sulphate etc.
Amongst biochemical parameters, determination of specific pathogens in
water is difficult, time consuming and costly, so water quality is
described in terms of concentrations of coliform bacteria.
131
Dissolved oxygen is one of the most important parameter in water quality
assesment and reflects the physical and biological processes prevailing in
the natural waters.
The amount of oxygen dissolved in water is a good indicator of water
quality and of the kinds of life it will support.
Biochemical oxygen demand is the amount of oxygen utilised by micro
organisms in stabilising the organic matter. It gives a qualitative index of
the organic substance degraded, quick in a short period of time.
The principal sources of solids in water bodies may be either natural or
due to human activities. Amongst the natural sources soil erosion,
minerals, leaves, humus etc. are important while the human sources
include domestic effluents and sewage, industrial effluents and
agricultural effluents. The total solids quantity all the solids (organic and
inorganic), suspended and/or dissolved in water. When present in excess
they create imbalance for aquatic life for various reasons.
Metal contamination in water mainly comes from rock minerals and
industrial effluents.
The hazardous metals include mercury, lead, tin and cadmium.
Supertoxic elements such as selenium and arsenic are also hazardous.
Heavy metals are recognised as serious pollutants of the aquatic
environment and heavy metal toxicity is often encountered in connection
with experimental work, commercial fish farming and the management of
recreational fisheries.
Common ion such as chloride, nitrates, sulphates and phosphates are
important components of total dissolved solids (TDS) present in water
bodies. However, concentrations of Cl- and SO4
— - ions are sufficiently
132
high in hard-water. While, domestic and industrial effluents and in stream
uses also add to pollutional load of these common ions, agricultural
return waters are considered to be the most significant polluters.
Nitrate pollulation becomes dangeous, since in the body it can be
transformed into nitrosamine, said to be the source of cancer in the body.
The most serious water pollutants in terms of human health would wide
are pathogenic microorganisms. Among the most important water borne
diseases are typhoid, cholera, bacterial and amoebic dysentry, enterritis
polio, infectious hepatitis and schisto somiasis. Maleria, yellow fever and
filariasis are transmitted by insects that have aquatic larvae.
The main source of these pathogens is untreated or improperly treated
human and animal wastes.
Rapid diterioration of aquatic environments as a result of different ways
of their utilisation has led to the development of standards of quality of
water by Public health services. These sandards incarporate physical,
chemical, industrial and biological parameter all.
In the study of natural and waste water, chemical study has a special
important, as for a better understanding of the quatic envioronment,
knowledge) of its components, pollutants and other chemicals present is
necessary.
The analysis of water involve three steps :
1. Sampling of water
2. Preservation of the sample, and
3. Analysis of the sample.
The examination of water samples involve all the three, physical
examination, chemical examination and microbiological examination.
133
Physical examination includes study of colour, odour and taste, along
with the turbidity present in the sample water.
While the chemical examination includes determination of (i) total solids
(ii) organic matter (iii) alkalinity (iv) hardness, (v) pH, (vi) acidity, (vii)
nitrogen as nitrates, nitrites and free ammonia (viii) sulphates (ix)
chloride (x) dissolved oxygen (xi) biochemical oxygen demand, (xii)
chemica oxygen demand, (xiii) free CO2 (xiv) free available chlorine and
(xv) chlorine demand.
Microbiological examination involve determination of atleast total count and
coliform MPN.
BOD and DO are estimated by using iodometric titrations, while COD by
using potassium dichromate reflux method generally.
Metals are estimated using atomic absorption spectroscopy.
The raw water available from various sources is contaminated or contains
impurities and hence it is made safe for the purposes for which it is to be
used using the standard methods for its purification.
During munisipal sewage treatment three steps are involved. In the
primary treatment large solids are separated from the waste stream with
screens and settling tanks. The secondary treatment involves areation of
the effluent While in the tertiary treatment dissolved metals, nutrients are
removed, especially nitrates and phosphates from the secondary effluent.
134
3.12 CHECK YOUR PROGRESS : THE KEY
1. (a) (i) relative
(a) DO
(b) Dissolved solids
(c) BOD
(d) Suspended sediments
(e) Acidity
(ii) good indicator
quality
kind of life
(iii) important index
pollution
suitability of water
(b) (i) the solids
organic
inorganic
dissolved
imbalance
quality of life
(ii) biological activity
mercury
lead
cadmium
nickel
toxic
(iii) nitrite
chloride
nitrosamine
entrophication
135
2. (a) (i) Offensive taste
smell
sense of light
acceptable limits
(a) E. coli count should be zero
(b) Coliform should be below 10 % per 100 ml
(c) Coliform should not be detectable in 100ml. of any
two successive samples
(ii) (a) turbidity
(b) elevated temperature
(c) suspended material
(iii) (a) sampling
(b) Preservation
(c) Physical, Chemical and biological examination
(b) (i) bacteria
decomposable organic matter
iodometric
(ii) aerobic or anaerobic
iodometric titration
(iii) pollution strength
waste water
potassium dichromate reflux method.
(iv) Cl2, HOCl, OCl-, H2OCl
+, and Cl3
-
(v) Screen and settling tanks
aerated
dissolved metals
nutrients
nitrates
phosphates
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M.SC. (FINAL) CHEMISTRY
PAPER –III : ENVIRONMENTAL CHEMISTRY
BLOCK-II
Unit-4 : Soil
Unit-5 : Atmosphere
Unit-6 : Air Pollution Control
Author – Dr. Purushottam B. Chakrawarti
Dr. Aruna Chakrawarti
Editor – Dr. Anuradha Mishra
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BLOCK SUMMARY
Soil is an unique and valuable gift of nature to human society. The macro
and micro nutrients of soil which norish us and the waste material which pollute
our land and its treatment both are discussed in unit IV. While the chemical
composition and the chemical and photo-chemical reactions taking place in the
atmosphere are described in unit v. It also deals with atmospheric pollution by
chemicals and their effects such as green house effect and acid rain. In unit VI
air pollution control measures and their chemistry has been discussed. It also
gives analytical methods for measuring air pollutants such as chromotography
(HPLC, GC, GLC), nmr, ir, flame photometry, absorption spectroscopy,
polarography, voltametry, fluorimetry, non-dispersive, UV. Visible absorption
spectroscopy, coulometry, laser technique etc. In addition, continuous
monitoring instruments, for atmospheric pollution have also been described.
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UNIT-IV SOIL
Structure
4.1 Introduction
4.2 Objectives
4.3 Composition of Soil
4.4 Micro and Macro Nutrients of Soil
4.5 Pollution of Soil
4.5.1 Fertilizers Pollution
4.5.2 Pesticides Pollution
4.5.3 Plastics Pollution
4.5.4 Metal Pollution
4.6 Waste Treatment
4.7 Let Us Sum Up
4.8 Check Your Progress : The Key
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4.1 INTRODUCTION
Land is an unique and a valuable gift of nature to human society. It has
the capability to produce and to nourish life. It is because of this, land is
regarded the basis for the existence of all living being and is honoured as
'Mother'. The geographical area of India constitutes 2-4 percent of the total area
of the world and is a valuable treasure of biological diversity (8% of the world's
total diversity).
Land is an important component of the life support system. Unfortunately
land has been overused and even abused over the centuries. This is not simply
an environmental problem but one which is basic to the future of our country. In
a predominantly agricultural country like ours land comes first. Due to
exploding population soil is used increasingly which poses threat to its
productivity. Carelessuse damages soil that results into reduction in quality and
quantity of woodland. grassland cropland and soil erosion and degradation of
watersheds and catchments, deforestation and desertification. Due to
demographic pressures land is under stress due to sprawl in agriculture industry
and urbanisation. Cropland is losing fast fertile top soil.
Soil is a marvelous substance a living resource of astonishing beauty
complexity and frailty. It is a complex mixture of weathered mineral from rocks
partially docomposed organic molecules and a host of living organisms. It can
be considered an ecosystem by itself. Soil is an essential component of the
biosphere and it can be used sustainably or even enhanced under careful
management.
Of all the earth's crustal resources the one we take most for granted is
soil. We are terrestrial animals and depend on soil for life yet most of us think
of it only in negative terms. English is mischievously unique in using "soil" as
an interchangeable word for "Earth" and excrement.
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To understand the potential for feeding the world on a sustainable basis,
we need to know how soil forms, how it is lost, and what we can do to protect
and rebuild good agricultural soil. With careful husbandry, soil can be
replenished and renewed indefinitely. Many farming techniques deplete soil
nutrients, however, and expose the soil to the erosive forces of wind and
moving water. As a result, in many places we are essentially "mining" this
resource and using it much faster than it is being replaced.
Building good soil is a slow process. Under the best circmstances, good
topsoil accumulates at a rate of about 10 tons per ha (2.5 acres) per year –
enough soil to make a layer about 1 mm deep when spread over a hectare.
Under poor conditions, it can take thousands of years to build that much soil.
Perhaps one-third to one-half of the world's current croplands are losing topsoil
faster than it is being replaced. In some of the worst spots, erosion carries away
about 2.5 cm (1 in) of topsoil per year. With losses like that, agricultural
production has already begun to fall in many areas.
The importance of soil can be underlined in the following points
1. It is the basis of whole vegetation
2. It is the store of all essential nutrients for plants
3. It provides medium for physical, chemical and biological reactions
necessary for animals and plants.
4. It also function as medium in the biological cycle of nutritional
elements
5. It is natural-habitat for wild animals.
6. It is the place for the formation of number of types of organic
chemicals of soil.
7. In soil, organic compounds from animals and rocks are converted into
simple inorganic componds.
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The culture of the nation or state depends upon the soil present there. For
example persons living in dry and desert area differ in their life style and
culture from those of living in hilly regions. While persons living in regions of
very fertile lands differ in their occupation and culture from those living in
areas in areas described earlier.
4.2 OBJECTIVES
The main objective of this unit is to discuss characteristics of different
types of soils and the nature of their pollution. After going through this unit,
you will be able to :
describe compositions of soil,
discuss micro and macro neutrients of soil,
describe different types of soil pollutants, and
discuss waste material treatment.
4.3 COMPOSITION OF SOIL
There are at least 20,000 different soil types in the country and many
thousands more worldwide. They vary because of the influences of parent
material, time, topography, climate, and organisms on soil formation. There are
young soils that, because they have not weathered much, are rich in soluble
nutrients. There are old soils, like the red soils of the Tropics, from which
rainwater has washed away most of the soluble minerals and organic matter,
leaving behind clay and rust-colored oxides.
Most soils are stratified into horizontal layers called soil horizons that
reveal much about the soil's history and usefulness. The thickness, color,
texture, and composition of each horizon are used to classify the soil. A cross-
sectional view of the horizons in a soil is called a soil profile. Figure 4.1 shows
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the series of horizons generally seen in a soil profile. Soil scientists give each
horizon a letter or descriptive name. Soils usually have one to seven or more
horizons with different properties, depending on the soil type and history of a
specific area.
Fig. 4.1 Soil profile showing possible soil horizons. The actual number,
composition, and thickness of these layers vary in different soil types.
The soil surface is often covered with a layer of leaf litter, crop residues,
or other fresh or partially decomposed organic material (O horizon). Under this
organic layer is the surface horizon, usually an A horizon or topsoil, composed
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of mineral particles mixed with organic material. The A horizon ranges from a
thickness of several meters under virgin prairie to zero in some deserts. The
surface horizon contains most of the living organisms and organic material in
the soil, and it is in this layer that most plants spread their roots to absorb water
and nutrients. The surface horizon often blends into another horizon (the E
horizon), which is subject to leaching (removal of soluble nutrients) by water
percolating through it. This zone of leaching may have a very different
appearance and composition from horizons above or below it.
Beneath the surface horizons, the subsurface horizons, or subsoil, usually
have a lower organic content and higher concentrations of mineral particles.
Under the subsoil is the parent material, of C horizon, made of weathered rock
fragments with very little organic material. Weathering of this layer produces
new soil particles and allows downward expansion of the horizons above.
About 70 percent of all the parent horizon material in the United States was
transported to its present site by geologic forces (glaciers, wind, and water) and
is not directly related to the bedrock below it.
Without soil organisms, the earth would be covered with sterile mineral
particles far different from the rich, living soil ecosystems on which we depend
for most of our food. The activity of the myriad organisms living in the soil
helps to create structure, fertility, and tilth (condition suitable for tilling or
cultivation).
Soil organisms usually stay close to the surface, but that thin living layer
can contain thousands of species and billions of individual organisms per
hectare. Algae live on the surface, while bacteria and fungi flourish in the top
few centimeters of soil A.
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Single gram of soil (about one-half teaspoon) can contain hundreds of
millions of these microscopic cells. Worms and nematodes process plant roots
and litter. Bacteria and fungi decompose organic detritus and recycle nutrients
that plants can use for additional growth. The sweet aroma of freshly turned soil
is caused by actino-mycetes. bacteria that grow in fungus-like strands and give
us the antibiotics streptomycin and tetracycline.
Soils are classified according to their structure and composition into
orders, suborders, great groups, subgroups, families, and series. The richest
farming soils are the mollisols (formed under grasslands) and alfisols (formed
under moist, deciduous forests) is fortunate to have extensive areas of these
fertile soils.
Soil consists of a mixture of particles of different shapes and sizes
obtained due to degradation of rocks. The type of soil is determined on the basis
of percentage of different particles present in it. This also determines the
physical properties and water retantion power of soil. The particle sizes present
in different types of soil are given in table 4.1
Soil has pores in sufficient quantities which occupy about 50% volume of
it. These pores are occupied by water and air. Soil does not contain pure sand
clay or silt it is always contaminated with 0.4 to 1.1 percent decomposed
organic material 0.1 percent (by weight) of it comes from the living species and
micro organisms present in it.
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Table 4.1 Sizes of particles in different Soils
Soil Type Diameter of particles (mm)
1. Clay < 0.0002
2. Silt 0.002 to 0.05
3. Very Fine Sand 0.05 to 0.1
4. Small Sand 0.1 to 0.25
5. Medium Sand 0.25 to 0.5
6. Large Sand 0.5 to 1.0
7. Very large Sand 1.0 to 2.0
The Physical properties of soil depend upon the percentages of clay, silt
and sand particles in it. Large quantities of clay and silt give soil slippery nature
while large quantities of sand results in large quantities of air pores in it, hence
its water retention power will be high. Clay particles are very small hence it is
colloidal in nature. Such soil retain water to form mud which is harmful to
plants. When particles of different size are in equal quantities we get loam soil
which is very good for cultivation. Soil with clay and that which does not retain
water is best suitted for cultivation of wheat. Clay and humus particles bear
negative charge which attracts positive ions (Ca'', K', Na', Mg'' etc) and makes
available to plants. pH of soils is also important because it determines the type
of crop to be cultivated. Neutral soils have pH=7, while acidic soils have pH
less than 7 (0 to 6) and alkaline soils have pH higher than 7*8( to 14). Soils
with pH 5 to 8 are suitable for agriculture.
Most soils are startified into horizontal layers called Soil horizons that
reveal much about the soil's history and usefulness. The thickness colour texture
and composition of each horizon are used to classify the soil.
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The main factors affecting properties of a soil are
(i) Component substances
(ii) Climate
(iii) Geography
(iv) Vegetation
(v) Presence of micro organism and other living being and
(vi) Human-use
Types of Soil in India
In India the soil (of about 265 million hectares of cultivated land) can be
divided mainly into four groups.
1. Red soil 2. Black soil 3. Lateriti soil 4. Alluvial soil
1. Red soil : Maximum parts of the country have red-soil e.g. Bengal.
Orissa, MP, AP, Tamilnadu and Karnataka. This type of soil is derived from
granite rocks. The colour of this soil may be red brown-red or yellow. Red soil
has large percentage of iron. It contains less amounts of calcium phosphate and
nitrogen (humus), but potash is in sufficient quantity. In India the total area
covered by this type of soil is about 7 crore 20 lac hectares. It is sceptible to
sheet and rill erosion
2. Black soil : As regards its distribution it is second in the country. It is
found in Maharashtra, Madhya Pradesh and some parts of Andhra Pradesh,
Tamilanadu and Karnataka. It comprises total 6 crore 40 lac hectares of land.
Black soil is quite slippery and on wetting forms viscous mud. On drying it
cracks. This type of soil is very fertile and is best for cotton-cultivation. It is
more prone to water erosion.
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3. Lateriti soil : In this type of soil, process of soil formation remains
incomplete. Upper surface with small depth has some soil beneth it are rocks,
which gradually convert into soil. This type of soil is not fertile and is
suceptible to sheet and rill erosion like red soil. The principal areas of the
country containing this type of soil are Bengal, Asam, Karnataka and
Tamilnadu, which make total 1 crore 30 lac hectare area of the country.
4. Alluvial Soil : This type of soil is present in the planes of the principal
rivers in eastern and southern part of the country. It is also found in forests of
Himalayan region and on slopes of Himalayan range of the height of 15000
feet. This type of soil is very fertile and most suited for cultivation.
4.4 MICRO AND MACRO NUTRIENTS OF SOIL
4.4.1 Macro Nutrients for Plants – Plants require carbon, hydrogen and
oxygen to synthesise starch which they require as their food. In addition, the
plants also require phosphorus, potassium, nitrogen, sulphur, calcium, Iron and
magnesium, besides traces of a few other elements such as copper, boron, zinc,
manganese, molybdenum and cobalt.
Carbon, hydrogen and oxygen they get from air and water. The rest of the
essential elements are generally present in the soil to more of less exent in the
form of minerals or otherwise. However, after a few years of continuous
cropping, the soil becomes poorer and poorer in these materials and there is
need to put back what has been taken out from the soil by successive crops. If
the soil is not replenished by what it has lost, in time, it would become less
productive and, in extreme cases, may become even infertile. In order to keep
up soil fertility and to get good yields of various crops, it is necessary to add, at
least, materials containing nitrogen, phosphors and potassium, in the form of
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manures which may be natural of artificial. The artificial manures are called
chemical fertilizers. Nitrogen, phosphorus and potassium are regarded as
essential plant nutrients.
Plants get sufficient amount of calcium during treatment of acidic soil by
liming. The deficiency of calcium in soil results due to preserve of organic acid
which bind 2+ further, in presence of high acidity H
2 hinder the availability of
calcium to the plants.
In earth-crust about 1.2% magnesium is present with Maximum is
present, but maximum quantity of it is bound with minerals strongly. However
ion exchangeable magnesium should be available to plants, but this too depends
on Ca/Mg ratio. If its value is too high then because of low concentration of
magnesium compared to that of calcium, magnesium is not available to the
plants.
Sulphur is taken by plants in the form of sulphates. Leaves of the plants
do absorb sulphur dioxide from the atmosphere rich in sulphur di oxide,
Required amount of sulphur helps Gaps in proper development of plants as it is
an important component of essential amino acids, thymine and biotine.
Functions of Essential Nutrients
1. Nitrogen : Nitrogen is highly essential for rapid growth of plants and
hence it improves the yields of crops. It also raises protein content of the crops
and thus adds to their food value.
Plants take nitrogen in the form of nitrates. Although some rice plants do
assimilate ammonia, for other plants it may be toxic. When nitrogen is mixed in
the soil in the form of ammonium compounds. nitrifing bacteria convert
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ammonium ion into nitrate. Some nitrogen is fixed directly from the atmosphere
by nitrogen- fixing bacteria, which live on the roots of legminous plants, such
as clover. They convert nitrogen to proteins and other nitrogen compounds.
2. Phosphorus: Phosphates are highly valuable fertilizers. Experiments
have shown that phosphates promote early growth as well as early maturity of
plants. The addition of phosphates also increases resistance of plants to frost
and disease and helps in formation of high yielding seeds.
3. Potassium. Potassium develops a healthy root system which helps the
plants to get regular supply of nutrients from the soil. As a result, we get a
healthy plant which develops sufficient resistance towards various diseases. It
helps in the formation of albuminoids and carbohydrates in the various plants.
Potassium compounds are generally used in mixed fertilizers containing
introgen and phosphorus as well. Such materials are commonly referred to as
N.P.K. Fertilizers.
4.4.2 Micronutrients of Soil
Boron, chlorine, copper, iron, manganese, molybdenum, sodium,
vanadium and zinc are considered essential micro-nutrients for plants. These
elements are needed only in micro-quantities and play important part in the
activities of essential enzymes. While Mn, Fe, Cl, Zn and V also take part in
photosynthesis phenomenon.
Thus, micronutrients are important component of soil health, which
generally receives inadequate attention and most of the farmers in rural areas
are not aware of their vital role in crop production. Farmers often misconstrue it
to disease when dificiency symptoms are visible on plants and due to their
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ignorance to identify the particular deficiency. they go for some fungicidal
sprayings for its control, such sprayings for wrong purposes do not give any
good results further it costs the farmers time, energy, money. It may also affect
the plants growth and reduces the crop yields if further neglected. Therefore,
there is a need to educate the farming community about the importance of
micronutrients, their identification of deficiency symptoms on various plants
and the ways to correct it effectively. Mr. S.N. Ranande during 1960's was the
pioneer in our country to realise the importance of micronutrients in plant
nutrition and was instrmental in bringing many agroproducts.
Micronutrients or minor or trace elements are very small quantities of
certain elements, and shortage of one of more of these elements usually affects
the appearance of the plant, giving the leaves a chlorotic, bronzed or mottled
colour or altering its habit or causing the death of the growing plant. The
essential micronutrients for crop production are boron, copper, iron, manganese,
zinc, molybdenum, chlorine and sodium. Each of the micronutrient plays a
specific role in growth and development of plants as mentioned below :
- Boron helps in development of root and shoot growing points, cell
division, cell wall development, pollen germination and growth, fruit
development, carbohydrate metabolism, protein synthesis.
- Copper aids several enzymes for their catalytic activity and
involvement in protein and carbohydrate metabolism, symbiotic
nitrogen fixation, lignin formation, etc.
- Iron activates several enzymes and is involved in synthesis of
chlorophyll, respiration, carbohydrate production, nitrate and sulphate
reduction and in N assimilation.
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- Manganese has a direct role in photosynthesis, splitting of water and
in activation of several enzymes.
- Zinc plays a role in several enzyme systems, N-metabolism, protein
synthesis, auxins synthesis, starch formation, etc.
- Molybdenum functions in enzymes like reductase which is involved
in protein synthesis of the plants and nitrogenase which helps in
biological fixation by legumes. It is required in smaller quantities than
the other micronutrients.
Micronutrient Deficiency :
Soil Factors : Some soils are inherently poor in fertility status like sandy loam
etc. or soils having too high or too low soil reaction or with high amounts of
calcium carbonate deposits or with higher clay content.
Crop Factors : The introduction of high yielding varieties of crops and its
intensive cropping systems necessitated the use of high doses of major nutrient
elements viz., nitrogen, phosphorus and potassium and this has resulted in the
manifestation of a number of micronutrient deficiencies, more so in the soils
with marginal content of micronutrient.
Management Practices : (a) During the land levelling operations the surface
soil is removed which is rich in micronutrient contents and the sub-soils are
variably poor in micronutrients.
(b) Intensive use of complex fertilizers restricting mainly to nitrogen,
phosphrous and potassic fertilizers causes micronutrient deficiency.
(c) Lack of a adequate quantities of organic manures to cope with the
heavy N, P and K demand for new and high yielding crop varieties.
(d) Mono cropping systems removes a particular fraction of
micronutrients from the soil.
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Deficiency Symptoms :
Boron : The symptoms of boron deficiency vary with the kind and age of
the plant, the condition of the growth and severity of the deficiency. In many
plants the growing point or the terminal growth is severely affected. The
terminal growth shows rosetting, failure to grow or elongate, die back,
discolouration, stimulation of lateral bud development, various abnormalities in
the leaves such as thickening, brittleness, curling, wrinkling, wilting and
chlorotic spots mottling or pigment formation may be seen. The petioles
become thick and corky, cracked or may show watery soaked dead areas,
hollow and rough brownish flecks, necrososis, cracks or dry rot, deformed fruits
and hollow central portions.
As foliar spray, 500 to 1000 gms of boric acid per 500 litres of water per
one hectare is recommended.Borax may be applied to soils @ 10 kgs/ha. Boron
sprays are beneficial, however, its soil application remains effective for longer
period.
Copper : Terminal growth is first effected in plants, Die back of twigs or
growing points is most common. Rosetting of terminal leaves often precedes
dieback, terminal leaves may or may not show chlorosis spotting or other
abnormalities. In small grain crops the younger leaves lose colour, leaves break,
tips die and become twisted and have a greyish appearance. In fruit trees young
shoots wither after the leaves turn yellow and fall off later.
Both soil and foliar application are effective to control copper deficiency.
Soil application @ 5 to 25 kg of copper sulphate/ha is recommended for pasture
and field crops. When symptoms of copper deficiency are observed, the plants
quickly respond to foliar sprays of copper compounds like Bordeax mixture.
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For spray, application of copper sulphate can also be used @ 1 to 1.5 kg of
copper sulphate/500 litres of water neutralized with 0.5 to 0.75 kg of lime. In
general, copper application produces better colour, increases sugar content and
improves flavour of most vegetable crops.
Iron : The deficiency results in intervenial chlorosis in the younger
leaves of plants. In later stages burning of the chlorotic leaves start from tips
and margin spread inwards, growth is reduced in severe cases, the chlorotic
leaves may become white and the leaf tissue devoid of chlorophyll, die. Iron
deficiency inhibits normal growth of the root system also.
Application of 5 to 10 kg/ha of iron chelates to the soil is suggested.
Spray application of 3% solution of ferrous sulphate (neutralized with half of
the quantity of the ferrous sulphate with lime) @ 450 lit/acre can be effective.
Soil application of ferrous or ferric sulphate or ferrous ammonium sulphate or
spray application of ferric citric or iron chelates are effective correctives but are
costly.
Manganese : Common symptom of this deficiency is interveinal
chlorosis with light yellow green colour in between the veins and dark green in
remaining part of the leaf. This resembles iron chlorosis and the difference
being the darker green chlorotic pattern between the leaf veins which are darker
green. It deficiency appears first in the younger leaves and the plants become
stunted and the leaves tend to turn under (out-curling) at the margins. Loss of
chlorophyll, mottling, nacrosis, marginal scorching and rolling or cupping of
the leaves are the characteristic deficiency symptoms.
Manganese deficiency can be corrected by appling manganese sulphate.
Foliar application of 2.2 kgs of manganese sulphate + 1.1 kgs. lime/450 lit. of
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water is recommended when deficiency symptoms are observed. Manganese
sulphate of about 50-100 kgs is applied to slightly acid to neutral soils, 100-200
kgs to neutral to slightly alkaline soils and 200-400 kgs to strongly alkaline
soils.
Zinc : Zinc is associated with fertilization and development of embryo
and synthesis of indole acetic acid. The terminal growth is first effected,
reduced leaf size, little leaf and malformation of leaves, shortened internodes
giving rosette appearance of whorling of leaves, intervenal chlorosis and often
with necrosis are symptoms of zinc deficiency, yellowing and bronze colours
on older leaves first and progress to younger leaves if deficiency is severe.
Both foliar and soil application of zinc sulphate is effective. Soil
application leaves considerable residual effect for many years besides being
effective and can be preferred. Application of 50 kgs/zinc sulphate/ha to soil is
recommended and where symptoms have already been observed, a spray of zinc
sulphate @ 0.2% concentration is recommended 3 to 4 times at weekly intervals
till the deficiency symptoms disappear.
Molybdenm : It is an essential component of major enzyme ammonium
reductase in plants. However, the deficiency of this element is not common
since the reqirements, which are very small, are usually met from the manures,
fertilizers are irrigation waters. Its deficiency reduces the activities of the
symbiotic and non-symbiotic N-fixing micro-organism. Its deficiency produces
'whip tail' in cauliflower, broccoli and other brassica crops. Soil application of
ammonium molybdenum or sodium molybdenum @ 500-1000gm/ha is
recommended, on need basis. Spray apllication of 25-30 gms ammonium
molybdate in 500 litres of water is also useful. Chlorine and sodium chlorine
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deficiency is characterised by wilting of the leaflets blade tip followed by
chlorosis. It activates the oxygen producing enzymes of photosynthesis and it
regulates the osmotic pressure and acid-base balance in the plants. Sodium is
not an essential element for plant growth, but some crops such as beens, celery,
cabbage, knol-knol, radish, turnip etc. benefit greatly by application of sodium
salts, especially if the soil is deficient in potassium.
Results of several experiments carried out amply proved the necessity of
use of micronutrients for maximising crop productivity as well as helped in
improving efficiency of applied major nutrients and other inputs. Each of the
micronutrient has a significant role in growth and development of plant and its
requirement of a particular crop depends on the nature of the soil, type of soil,
past crop history, fertilizer dose and climatic conditions. Therefore, soil and
plant analysis is necessary for correct diagnoss of deficiency. Micronutrients are
essential as macro nutrients, but excessive use can be deliterious to crop
growth. Therefore, before their application, it is better to consult a specialist in
the field. Micronutrient deficiency is likely to occur in sandy soils, highly
weathered and leached soils, highly acidic, alkaline or calcarious soils and soils
with low organic matter content.
Use of multimicronutrients fertilizers for increasing the quantitative
production of foodgrains and other agricultural produce in our country is
gaining much importance and further it is bound to increase in times to come
and its role cannot be overlooked as its importance is being realised and for
attaining the desired results at field level, the government, manufacturing
industries, scientists and extension agency must work in close association to
benefit the farming community by supplying good quality micronutrient
fertilizers in time of need and imparting the technical know-how about the
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importance of micronutrients by the way of conducting field demonstration at
farmer's level in villages and helping them in identification of deficiencies, and
ways to overcome the deficiencies and for the benefit of farmers for increasing
productivity.
Check Your Progress -1
Notes: (1) Write your answers in the space given below.
(2) Compare your answers with those given at the end of the unit.
(a) (i) Soil is a complex mixture of .................................... materials from
......................................, partially decomposed ...............................
and a host of ................................................
(ii) Soil profile shows four possible soil horizons, namely –
(a) --------------------------------------
(b) -------------------------------------
(c) -------------------------------------
(d) -------------------------------------
(iii) Sizes of particles in different soils vary as :
....................... < ........................... <
(b) (i) The macro nutrients of soil are :
..............., .................., ..............., ......................, ...................,
................, ................... and ....................
(ii) The micronutrients of soil are ............, .........., .............., ..............,
................, ................., ................., .................., and ..................
(iii) While N, P, K are necessary for ..................................... of the
plants, micronutrients are needed for ............................. of
.............................
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4.5 POLLUTION OF SOIL
Soil has been an important resource for mankind since his birth, as not
only ours but also the lives of other living being depend upon it. It has been
providing us the shelter as well as our food. Due to large quantity of pollution
and soil erosion it is becoming more and more toxic. If affects not only our
crops, but also our health. Soil pollution is also the principal cause of soil
degradation.
Definition
When various physical and chemical substances mix with soil to make it
unfit in respect of agriculture, it is supposed to be polluted. Pollution in soil also
reduces living capacity of trees. In other words the unwanted changes in
physical, chemical or biological properties of soil which affect humans and
other living being or due to which natural quality and use of soil is diminished
is called soil pollution.
As a matter of fact problem of soil pollution may be regarded as the
problem of disposal of solid-waste. In a broader sense land-pollution includes
soil degradation its chemical pollution by different sources, soil erosion
volcano-explosion and other natural changes making effective change in the
fundamental properties of soil.
The principal sources of soil pollution are-
1. Domestic wastes
2. Municipal wastes
3. Industrial wastes
4. Agricultural wastes
The soil pollution has been mainly caused by solid wastes and
chemicals. One of the major pollution problems of large cities has been the
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disposal of solid waste material including farm and animal manure crop
residues (agricultural wastes), industrial wastes like chemicals, fly ash and
cinders which have been residues of combustion of solid fuels garbagae, paper,
cardboard, plastics, rubber, cloth, leather, construction rubbish, brick, sand,
metal and glass resulting from demolition of buildings, dead animals like
cattles, dogs, cats, birds, containers, discarded manufactured products like old
refrigerators, washing machines and autos.
Huge quantities of unwanted material bring about serious disposal
problems. The simplest method has been crude tipping or open dumping a
common method which finds use in most Indian cities.
The main sources of land pollution have been the industries like pulp
and paper mills, oil refineries, power and heating plants, chemicals and
fertilizer manufactures iron and steel plants, plastic and rubber producing
complexes and so on. Thousands and thousands of solid wastes have been either
dumped or burnt or emptied into rivers. Most Industrial furnaces give rise to a
grey powder residue of unburnt material called fly ash and important pollutant
besides huge mounds of solid wastes. These waste products are the source of
many diseases.
Recently increase of industrial waste, metals, metal oxides, acids,
alkalies, aromatic compounds, phenols and pesticides etc. have made the soil
infertile. The overgrazing of fields, construction of dams, mine industries and
construction of roads have also destroyed the fertility of many fields due to
wastage of top soil. Hence it has become necessary that the industrialization and
modernization should be done with the careful planning.
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The tanneries, synthetic drug factories and distilleries discharge lot of
suspended and dissolved solids which pollute the soil. The antibiotic factories
release lot of toxic organic compounds which change rate of mutation in plants.
Besides this antibiotic factories are also responsible for adding alkalies in soil
which also produce somatic and genetic disorders in plants. The soil also
becomes infertile in a long time. The fertiliser factories add continuously
sodium, potassium, fluoride, phosphate, nitrate etc in the soil thus destroying
not only grasses and plants but making the soil useless for cultivation or
converting it into wasteland. The growth of rubber industries in India in last 20
years has also added lot of suspended and dissolved solids, high BOD, grease,
zinc, carbon and sulphate etc. which in cumulative way are sufficient to convert
fertile land into waste land. The presence of all these substances also retards
growth of plants, retards reproduction process and also fruit production.
Further, many of the chemicals suspended out into the air like
radioactive minerals, sulphur and lead eventually come to earth to pollute the
soil. Many pesticides and herbicides applied by aerosol spray and enter into the
soil. These chemicals may significant effects on plants and animals. bringing
about a disrption in species composition of commnities in forest ecosystems.
These chemical pollutants may be able to inhibit processes of soil formation
and reduce the capacity of the forest to maintain fertility of the soil.
4.5.1 Fertilizers - Pollution
Modern agriculture is mainly responsible for polluting soil through the
non-judicious use of chemical fertilizers, herbicides, insecticides and fumigants.
Most of these have been cummulative effect. The chemical such as calcium
carbonate, bicarbonates, calcium sulphate, and soluble salts etc. from eroded
sediments pollute the soil. It is estimated that 85% of phosphorus and about
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70% of nitrogen loading of surface water are brought from eroded soils from
hills or other places. According to a report of United Nations Food and
Agricultre Organisation deposited on the upper layer of the irrigated lands of
the world are affected by the soluble salts which get deposited on the upper
layer of the soil making it infertile. The rain water (which contains lot of natural
chemicals) in deep soils also causes salty soil or usar soil as on keeping the
water for a long time the water evaporates and salts or chemicals get deposited
on the upper layer and make harder and unfit for cultivation. Besides this, the
chemicals such as fertilisers, pesticides etc. also destroy the fertility of the soil.
Fertilisers add phosphorus, nitrogen, sodium, potassium, sulphate, nitrate
etc. in the soil. When they are added in the soil to increase crop production,
they are retained by the soil. The nitrates are very harmful for human beings
and have been claimed as cancer generating chemical present in nature. The
high concentration of nitrates and phosphates also cause eutrophication,
choking the whole aquatic ecosystem in nature. According to a report more than
11 million tonnes of fertilisers are being used in India per year.
4.5.2 Pesticide Pollution
Pollution caused by pesticides has been among the greatest cause of
concern in the field of agricultural pollution. Pesticides residues occur in soil air
and water as well as in living organisms. Besides killing the living organism
present on the surface of the soil, they reach even the deeper layers through
tilling and irrigation on the land, killing still more living forms. With the
continuous use the soil microorganisms lose their capacity of nitrogen fixation.
Pesticides include, insecticides, herbicides, bactericides, fungicides,
nematicides, rodenticides and defobiants. Most of the synthetic pesticides are
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organohalogenated compounds, DDT, aldrin, gammexane, malthion, parathion
etc. which have toxic effects on human liver, heart, central nervous system,
kidney, bones and fatty tissues.
Although the use of DDT has been banned in all developed countries but
developing countries are still using it freely to kill insects. The reason for
banning this chemical is that it does not degrade in nature upto very long time
and so enter into food chain of human beings through crops, water, eggs, milk
etc. causing many diseases. Besides this the other chlorinated hydrocarbons like
BHC, endrin, aldrin, dieldrin, heptachlor, chlordane, lindane are also used
freely. The resides of these get absorbed by soil particles which in a slow rate
contaminate root crops. The organo-phosphates like parathion, malathion,
phosdrin, trithion, ethion, fenthion etc. also disturb the functioning of roots in
the soil. At present there are more than 35000 chemicals present in the market
with different names used to kill pests have not only polluted water and air, but
soil also. It is said that today 30% diseases in human beings are due to presence
of fungicides, isecticides, rodenticides, herbicides, nematicides and
molluscicides.
However, some effects of pesticides are mentioned below :
(1) Through soil, pesticides which adhere to soil particles reach to maize,
grain, wheat, rice, pulses, fruits, vegetables, grasses etc.
(2) Polychlorinated biphenyls have been proved to be very dangerous for
human beings and cattle. The kinetic studies have shown that
polychlorinated biphenyls have generally half life periods of 24 to 30
years in soil and hence once they adhere in the soil remain there for very
long time. When they reach to human food chain through vegetables,
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cereals etc. they create nervous disorders, destroy liver functioning,
create stomach cancer, skin cancer and deformities in bones.
(3) From soil, pesticides reach in atmosphere with wind, storm and other
sources. They also mix up in ponds, rivers and other water bodies thus
pollute the drinking and ground water. So through atmosphere and water
pesticides like DDT, BHC, organochloro pesticides affect tissues and
also affect metabolic activities of human beings and animals.
(4) In a report published by Vietnam, it has been mentioned that during
ecological destruction programme of U.S.A. to Vietnam, the following
effects were noticed :
(i) Heavy increase in soil erosion.
(ii) Destruction of forests upto 45%, cultivated land upto 40%, mangrove
forests about 70%, rubber plants about 40% and rice crop about 30%.
(iii) Loss of birds, cows and other useful and wild animals.
(iv) Increase in diarrhoea, dysentry, maleria, typhoid and other. disease
including skin diseases
4.5.3 Plastics - Pollution
Innovative and appropriate use of plasticulture assumes great significance
at this critical juncture when productivity of certain crops in the country has
reached a plateau because of inherent technological constraints, feels
agriculturist A.N. Sarkar.
Plastics could be used in a number of ways. As a matter of fact it is used
for different purposes and has become an essential part of our daily life.
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With the overall consumption of plastics in the country going up to five
lakh tonnes, advent of plastics and development of appropriate plasticulture
technologies pollution of soil and watershed management, pisciculture and
livestock among others continues to offer a threat to ecology.
In the last 20 years, plastic has affected the health and life of a human
being very badly. Some incidents have attracted the whole world and put a
question mark about the use of plastic in daily life.
As we know plastic is a big group of different chemical substances in
which mainly there is a substance having a high molecular weight which
ultimately changes into solid state in the last. In the middle stage, it is very
flexible and can be given any shape depending on temperature and pressure. In
practices, urea formaldehyde, polyethylene, polystyrene, polyvinylchloride,
phenolic compounds and other substances are used in the preparation of
plastics.
Now-a-days the most popular plastic is polyvinyl chloride (P.V.C.) When
any food material or blood is stored in the said plastic containers then gradually
the soluble chemical gets dissolved in them causing death, cancer and other skin
diseases. Polyvinyl chloride has also been found to destroy the fertility of the
animals and their respiratory systems. When mixed with water, it causes
paralysis and also damages bones and causes irritation to the skin.
Recently U.S.A. has banned the use of P.V.C. plastic in space apparatus
and in food containers (as chemicals get dissolved in the food). India should
immediately ban the use of P.V.C.
The raw materials (known as plastic polltants) used in the manufacture of
plastics can be summarised as follows :
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(1) Caprolactum (2) Sebacic acid
(3) Hexamethylene diamine (4) Formaldehyde
(5) Melamine formaldehyde (6) Trimethylol melamine
(7) Benzoyl peroxide (8) Vinyl acetate
(9) Hydrochloric acid (10) Urea
(11) Nitric acid (12) Ethyl and Methyl alcohols
(13) Acetone (14) Butanediol
(15) Terephthalic acid (16) Organo silicon dichloride
(17) Tetrafluoro ethylene (18) Trifluoro chloroethylene etc.
Hazards to Human Health :
These chemicals in one way or in other have been identified in the plastic
industries besides plastics which have become main sources of pollution in
nearby vicinity and ultimately fall in ponds or rivers. It has been noticed that
industry owners do not care to collect the materials or have no method for the
treatment or removal of pollutants which cause neurotroubles, abnormality in
stomach, itching of skin, lung diseases and cancer.
The problem of these toxic substances requires the attention of research
workers, Public Health authorities and Government as these hazardous
substances are not only harmful for human health, animals, fruits and
vegetables but to the economy as a whole.
Moreover the plastics formed from these chemicals are non degradable in
nature and hence are responsible for choking of underground pipes, sewage
system and small water bodies. Today they have greatest sources of choking of
water in drainage systems. Early solution is necessary to save humanity from
plastics and their products.
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4.5.4 Metal Pollution
Areas surrounding smelting and mining complexes are generally soiled
by metals like cadmium zinc lead, copper, arsenic and nickel. These act as
phytotoxic even in small quantities. They also make plants unsafe for human
and animal consumption. Zinc along with cadmium has been released into the
environment during the use or breakdown of lubricating oils, vehicle tyres,
galvanized metals and fertilizers. The metallic pollutants from copper, steel,
cadmium, zinc factories pollute the soil due to excess of Cu, iron, Cd and zinc.
Besides this, the presence of Co, Ni, Pb, Ba, Hg, Mo, Mn, Al, sodium,
potassium, Sr, silicon, Ca etc. are added to the soil from various industries in
combined form also pollute the soil. Such pollution by metals is called metallic
pollution. In super phosphate fertilizers, Pb, Cd, As etc. are found as trace
metals which pollute the soil and decrease the fertility of the soil forever. The
selenium, manganese and nickel in iron rich soils form insoluble basic
compounds while sulphur present in iron rich soils make it acidic. The synthetic
chemicals also liberate toxic metallic species in the soil which form oxides or
hydroxides due to combination with water thus making the soil alkaline in
nature. The excess of sulphur is released in nature by chemicals as sulphur
dioxide. This sulphur dioxide reacts with H2O to form sulphurous and sulphuric
acids which damage the plants and make the soil highly acidic. A list of some
industries and their pollutants in water and soil are shown in Table 4.2
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Table 4.2 Some Industries and their pollutants in soil and water.
No Industry Pollutants No. Industry Pollutants
1. Galvanising Zinc 12. Dye Cr, Ni, Co, Fe, Cd
2. Chrome tanning Chromium 13. Silver ornaments Zn, Ag, Cd, CN
3. Paint Lead 14. Gold ornaments Cu, Cd, Ag
4. Textile Mineral acids fats,
oils etc.
15. Rayon Zn, Na2SO4
5. Viscose rayon Zinc, sulphides 16. Paper and Pulp Sodium salts, Ligno
sulphonate
6. Wood Processing Zinc, sulphide 17. Ayurvedic medicine
(Metallic) Preparation
Zn, Ag, Au, Cu etc.
7. Steel Mills Iron, As, CN etc. 18. Metal Plating Zn, Cu, Al, Cr, Cd
cyanides and low pH
8. Fertilizers Pb, Cd As as
tracementals, NH3,
CaSO4
19. Iron foundry Iron and suspended
solids
9. Battery Pb, Cd, Ni, etc. 20. Photographic Products Silver, organic and
inorganic reducing
agents, alkalies.
10. Electroplasting Chromium, Nickel 21. Thermal Power Plants Heavy metals,
inorganic compounds
11. Dyestuffs Potassium, and
sodium hydroxides
4.6 Waste Treatment
Waste is everyone's business. We all produce unwanted by products and
residues in nearly everything we do. According to the Environmental Protection
Agency (EPA), the United States produces 11 billion tons of solid waste each
year. Nearly half of that amount consists of agricultural waste, such as crop
residues and animal manure, which are generally recycled into the soil on the
farms where they are produced. They represent a valuable resource as ground
cover to reduce erosion and as fertilizer to nourish new crops, but they also
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constitute the single largest source of nonpoint air and water pollution in the
country. About one-third of all solid wastes are mine tailings, overburden from
strip mines, smelter slag, and other residues produced by mining and primary
metal processing. Much of this material is stored in or near its source of
production and isn't mixed with other kinds of wastes. Improper disposal
practices, however, can result in serious and widespread pollution.
The major amount of solid rubbish has been provided by our households
in the form of domestic wastes. Some common examples include groceries,
food scraps, vegetable remains, packing materials, paper, remainants of used
coal, ash, wood, metals, plastics, ceramics, glass etc. Many of these are non-
reusable. All these form heaps of municipal refuse. If it is not properly disposed
off this can prove perilous. Such places often become a dwelling place for rats,
flies, bacteria, mosquitoes and a large number of other vectors, having the
potential of causing many human diseases.
Municipal waste, a combination of household and commercial refuse,
amounts to about 180 million metric tons per year. That's approximately two-
thirds of a ton for each man, woman, and child every year- twice as much per
capita as Europe or Japan, and five to ten times as much as most developing
countries.
Industrial waste- other than mining and mineral production- amounts to
some 400 million metric tons per year. Most of this material is recycled,
converted to other forms, destroyed, or disposed of in private landfills or deep
injection wells About 60 million metric tons of industrial waste fall in a special
category of hazardous and toxic waste.
Thus the sources of solid wastes have been
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1. Municipal : Street sweepings, sewage treatment plant wastes, wastes
from schools and other institutions.
2. Domestic : Garbage, rubbish and occasional large wastes from homes
3. Commercial : from stores and offices
4. Industrial : from manufacturing plants
5. Mining : from coal raining, strip mining and
6. Agriculture :
The solid wastes from these sources include-
(i) Garbage : Putrescible (decomposable) wastes food slaughter houses, can
ning and freezing industries etc.
(ii) Rubbish : Non decomposable wastes, either combustible or non
combustible Combustible wastes would include paper, wood, cloth,
rubber, leather and garden wastes. Non combustible would include
metals, glass, ceramics, stones, dirt, masonry and some chemicals.
(iii) Ashes : Res due e.g. cinders and fly ash of the combustion of solid fuels
or the incineration of solid waste by municipal, industrial and apartment
house incinerators.
(iv) Large wastes : Demolition and construction rubble, automobiles,
furniture, refrigerators and other home appliances, trees, tires etc.
(v) Dead animals : House hold pets, birds, rodents, zoo animals etc. In
addition anatomical and pathological wastes from hospitals.
(vi) Sewage treatment process solids : Screenings settled solids, sluge.
(vii) Industrial solid wastes : Chemicals, paints, sand, explosives etc.
(viii) Mining wastes : 'Tailings' slag heaps, etc.
(ix) Agricultural wastes : Farm animal manure, crop residues etc.
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The Waste Stream
Does it surprise us to learn that we generate that much garbage? Think for a
moment about how much we discard every year. There are organic materials,
such as yard and garden wastes, food wastes, and sewage sludge from treatment
plants, junked cars; worn-out furniture; and consumer products of all types.
Newspapers, magazines, advertisements, and office refuse make paper one of
our major wastes. In spite of recent progress in recycling, many of the 200
billion metal, glass, and plastic food and beverage containers used every year.
Wood, concrete, bricks and glass come from construction and demolition sites,
dust and rubble from land-scaping and road building. All of this varied and
voluminous waste has to arrive at a final resting place somewhere.
The waste stream is a term that describes the steady flow of varied wastes
that we all produce, from domestic garbage and yard wastes to industrial,
commercial, and construction refuse. Many of the materials in our waste stream
would be valuable resources if they were not mixed with other garbage.
Unfortunately our collecting and dumping processes mix and crush everything
together, making separation an expensive and sometimes impossible task. In a
dump or incinerator, much of the value of recyclable materials is lost.
Another problem with refuse mixing is that hazardous materials in the
waste stream get dispersed through thousands of tons of miscellaneous garbage.
This mixing makes the disposal or burning of what might have been rather
innocuous stuff a difficult, expensive, and risky business. Spray-paint cans,
pesticides, batteries (zinc, lead, or mercury), cleaning solvents, smoke detectors
containing radioactive material, and plastics that produce dioxins and PCBs
(polychlorinated biphenyls) when burned are mixed willy-nilly with paper,
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table scraps, and other nontoxic materials. The best thing to do with household
toxic and hazardous materials is to separate them for safe disposal or recycling.
WASTE-DISPOSAL METHODS
Traditional Methods :
Where do our wastes go now? In this section, we will examine some
historic method of waste disposal, as well as some future options. Notice that
our presentation begins with the least desirable- but most commonly used –
measures and proceeds to discuss some preferable options. Keep in mind as you
read this that modern waste management reverses this order and stresses the
"three Rs." of reduction, reuse, and recycling before destruction or, finally,
secure storage of wastes.
Open Dumps
For many people, the way to dispose of waste is to simply drop it
someplace. Open, unregulated dumps are still the predominant method of waste
disposal in most developing countries. The giant Third World megacities have
enormous garbage problems. Mexico City, the largest city in the world,
generates some 10,000 tons of trash each day. Until recently, most of this
torrent of waste was left in giant piles, exposed to the wind and rain, as well as
rats, flies, and other vermin. Manila, in the Philippines, has at least ten huge
open dumps. The most notorious is called "Smoky Mountain" because of its
constant smoldering fires. Thousands of people live and work on this 30-m-high
heap of refuse. They spend their days sorting through the garbage for edible or
recyclable materials. Health conditions are abysmal, but these people have
nowhere else to go.
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The problem of illegal dumping likely to become worse as acceptable
sites for waste disposal become more scarce and costs for legal dumping
escalate. We clearly need better enforcement of antilittering laws, as well as a
change in our attitudes and behavior.
Ocean Dumping
The oceans are vast, but not so large that we can continue to treat them as
carelessly as has been our habit. Every year some 25,000 metric tons (55
million lbs) of packaging, including half a million bottles, cans, and plastic
containers, are dumped at sea. Beaches, even in remote regions, are littered with
the nondegradable flotsam and jetsam of industrial society. About 150,000 tons
(330 million lbs) of fishing gear- including more than 1000 km (660 ml) of
nets- are lost or discarded at sea each year. Environmental groups estimate that
50,000 northern fur seals are entangled in this refuse and drown or starve to
death every year in the North Pacific alone.
Until recently, many cities dumped municipal refuse, industrial waste,
sewage and sewage sludge in the ocean. Federal legislation now prohibits this
dumping.
Some people claim that the deep abyssal ocean plain is the most remote,
stable, and innocuous place to dump our wastes. Others argue that we know too
little about the values of these remote places or the rare species that live there to
smother them with sludge and debris.
Landfills
Over the past 50 years, most cities have recognized the health and
environmental hazards of open dumps. Increasingly cities have turned to
sanitary landfills, where solid waste disposal is regulated and controlled. To
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decrease smells and litter and to discourage insect and rodent populations,
landfill operators are required to compact the refuse and cover it every day with
a layer of dirt. This method helps control pollution, but the dirt fill also takes up
as much as 20 percent of landfill space. Since 1994, all operating landfills have
been required to control such hazardous substances as oil, chemical compounds,
toxic metals, and contaminated rainwater that seep through piles of waste An
impermeable clay and/or plastic lining underlies and encloses the storage area.
Drainage and to help monitor chemicals that may be leaking. Modern municipal
solid-waste landfills now have many of the safeguards of hazardous waste
repositories.
More careful attention is now paid to the sitting of new landfills. Sites
located on highly permeable or faulted rock formations are passed over in favor
of sites with less leaky geologic foundations. Landfills are being built away
from rivers, lakes, floodplains, and aquifer recharge zones, rather than near
them, as was often done in the past.
Exporting Waste:
Although most industrialized nations in the world have agreed to stop
shipping hazardous and toxic waste to less developed countries, the practice
still continues. In 1999, for example, 3,000 tons of incinerator waste from a
plastics factory in Taiwan were unloaded from a ship in the middle of the night
and dumped in a field near the small coastal Cambodian village of Bet Trang.
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Modern Methods
Incineration and Resource Recovery
Landfilling is still the disposal method for the majority of municipal
waste. Faced with growing piles of garbage and a lack of available landfills at
any price, however, public officials are investigating other disposal methods.
The method to which they frequently turn is burning. Another term commonly
used for this technology is energy recovery, or waste-to-energy, because the
heat derived from incinerated refuse is a useful resource. Burning garbage can
produce steam used directly for heating buildings or generating electricity.
Internationally, well over 1,000 waste-to-energy plants in Brazil, Japan, and
Western Europe generate much-needed energy while also reducing the amount
that needs to be landfilled.
Muncipal incinerators are specially designed burning plants capable of
burning thousands of tons of waste per day. In some plants, refuse is sorted as it
comes in to remove unburnable or recyclable materials before combustion. This
is called refuse-derived fuel because the enriched burnable fraction has a higher
energy content than the raw trash. Another approach, called mass burn, is to
dump everything smaller than sofas and refrigerators into a giant furnace and
burn as much as possible. This technique avoids the expensive and unpleasant
job of sorting through the garbage for nonburnable materials, but it often causes
greater problems with air pollution and corrosion of burner grates and
chimneys.
Recycling
The term recycling has two meanings in common usage, Sometimes, we
say we are recycling when we really are reusing something, such as refillable
beverage containers. In terms of solid waste management, however, recycling is
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the reprocessing of discarded materials into new, useful products. Some
recycling processes reuse materials for the same purposes; for instance, old
aluminum cans and glass bottles are usually melted and recast into new cans
and bottles. Other recycling processes turn old materials into entirely new
products. Old tires, for instance, are shredded and turned into rubberized road
surfacing. Newspapers become cellulose insulation, kitchen wastes become a
valuable soil amendment and steel cans become new automobiles and
construction materials.
Benefits of Recycling
Recycling is usually a better alternative to either dumping or burning
wastes. It saves money, energy, raw materials, and land space while also
reducing pollution. Recycling also encourages individual awareness and
responsibility for the refuse produce recycling lowers our demand for raw
resources.
Recycling also reduces energy consumption and air pollution. Plastic
bottle recycling could save 50 to 60 percent of the energy needed to make new
ones. Making new steel from old scrap offers up to 75 percent energy savings.
Producing aluminum from scrap instead of bauxite ore cuts energy use by 95
percent, yet we still throw away more than a million tons of aluminum every
year. If aluminum recovery were doubled worldwide, more than a million tons
of air pollutants would be eliminated every year.
Reducing litter is an important benefit of recycling. Ever since disposable
paper, glass, metal, foam, and plastic packaging began to accompany nearly
everything we buy, these discarded wrappings have collected on our roadsides
and in our lakes, rivers, and oceans. Without incentives to properly dispose of
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beverage cans, bottles, and papers, it often seems easier to just toss them aside
when we have finished using them.
Energy from Waste
Every year, we throw away the energy equivalent of 80 million barrels of
oil in organic waste. In developing countries up to 85 percent of the waste
stream is food, textiles, vegetable matter and other biodegradable materials.
Worldwide, at least one-fifth of municipal waste is organic kitchen and garden
refuse. In a landfill, much of this matter is decomposed by microorganisms
generating billions of cubic meters of methane ("natural gas"), which
contributes to global warming if allowed to escape into the atmosphere. Many
cities are drilling methane wells in their landfills to capture this valuable
resource. Fuel cells are a good way to use this methane.
Composting
Pressed for landfill space, many cities have banned yard waste from
municipal garbage. Rather than bury this valuable organic material, they are
turning it into a useful product through composting : biological degradation or
breakdown or breakdown of organic matter under aerobic (oxygen-rich)
conditions. The organic compost resulting from this process makes a nutrient-
rich soil amendment that aids water retention, slows soil erosion, and improves
crop yields. A home compost pile is an easy and inexpensive way to dispose of
organic waste in an interesting and environmentally friendly way. All you need
to do is to pile up lawn clippings, vegetable waste, fallen leaves, wood chips, or
other organic matter in an out-of-the way place, keep it moist, and turn it over
every week or so. If you have a high percentage of carbon-rich material, such as
dry leaves or wood chips, add manure or nitrogen-containing fertilizer. Within a
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few months, naturally-occurring microorganisms will decompose the organic
material into a rich, pleasant-smelling compost that you can use as a soil
amendment.
Demanufacturing
Demanufacturing is the disassembly and recycling of obsolete consumer
products, such as television sets, personal computers, refrigerators, washing
machines, and air conditioners, Together with deconstruction of houses, it is a
good way to recover valuable materials. It also can be especially suited to inner
cities, where there is a large supply of materials to be demanufactured and a
pool of skilled and unskilled laborers who need jobs. There are about 300
million televisions and personal computers in use. Televisions often are
discarded after only about five years and computers, play stations, and other
electronics become obsolite even faster. Stoves, refrigerators, and other "white
goods" have a much longer lifetime- typically about 12 years – but the EPA
estimates that Americans dispose of 54 million of these household appliances
every year. Many of these consumer products contain both valuable materials
and toxins that must be kept out of the environment. Older refrigerators and air
conditioners, for example, have chloroflurocarbons (CFCs) that destroy
stratospheric ozone and cannot be released into the air.
Similarly, computers and other electronic equipment contain both toxic
metals (mercury, lead, gallium, germanium, nickel, palladium, beryllium,
selenium, arsenic) as well as valuable one, such as gold, silver, and copper, A
typical personal computer, for instance, has about $6 orth of gold, & 5 of
copper and $ 1 of silver It is estimated that 90 percent of the cadmium, lead,
and mercury contamination in our solid waste stream comes from consumer
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electronics, batteries, mercury lamps, and switches. Small entrepreneurial firms
are emerging in many urban centers to take advantage of this valuable resource.
Reuse
Even better than recycling or composting is cleaning and reusing
materials in their present form, thus saving the cost and energy of remaking
them into something else. We do this already with some specialized items. Auto
parts are regularly sold from jnkyards, especially for older car models. In some
areas stained-glass windows, brass fittings, fine woodwork, and bricks salvages
from old houses bring high prices. Some communities sort and reuse a variety
of materials received in their dumps.
In many cities glass and plastic bottles are routinely returned to beverage
producers for washing and refilling. The reusable, refillable bottle is the most
efficient beverage container we have. It is better for the environment than
remelting and more profitable for local communities. A reusable glass container
makes an average of 15 round-trips between factory and customer before it
becomes so scratched and chipped that it has to be recycled. Reusable
containers also favor local bottling companies and help preserve regional
differences.
Minimum Packaging
Excess packaging of food and consumer products is one of our greatest
sources of unnecessary waster. Paper, plastic, glass and metal packaging
material make up 50% of our domestic trash by volume. Much of that
packaging is primarily for marketing and has little to do with product
protection. Manufacturers and retailers might be persuaded to reduce these
wasteful practices if consumer ask for product without excess packaging. Thus
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we may have four categories : (1) No packaging (2) Minimal packaging (3)
Reusable packaging and (4) Recyclable packaging.
This plan set a target of 50% reduction in excess packaging.
Hazardous and toxic wastes
The most dangerous aspect of the waste stream we have described is that
it often contains highly toxic and hazardous materials that are injurious to both
human health and environmental quality. We now produce and use a vast array
of flammable, explosive, caustic, and highly toxic chemical substances for
industrial, agricultural, and domestic purposes.
Legally, a hazardous waste is any discarded material liquid or solid, that
contains substances known to be (1) fatal to humans or laboratory animals in
low doses; (2) toxic, carcinogenic, mutagenic, or teratogenic to humans or other
life-forms; (3) ignitable with a flash point less than 60ºC; (4) corrosive; or (5)
explosive or highly reactive (undergoes violent chemical reactions either by
itself or when mixed with other materials).
Most hazardous waste is recycled, converted to nonhazardous forms,
stored, or otherwise disposed of on-site by the generators- chemical companies,
petroleum refiners, and other large industrial facilities- so that it doesn't become
a public problem. Still, the hazardous waste that does enter the waste stream or
the environment represents a serious environmental problem. For years little
attention was paid to this material. Wastes stored on private property, buried, or
allowed to soak into the ground were considered of little concern to the public.
The Comprehensive Environmental Response Compensation and
Liability Act (CERCLA or Superfund Act), passed in 1980 and modified in
1984 by the Superfund Amendments and Reauthorization Act (SARA), is
179
aimed at rapid containment, cleanup, or remediation of abandoned toxic waste
sites. This statute authorizes the EPA to undertake emergency actions when a
threat exists that toxic material will leak into the environment. The EPA is
empowered to bring suit for the recovery of its costs from potentially
responsible parties, such as site owners, operators, waste generators, or
transporters.
Check Your Progress-2
Notes : (1) Write your answers in the space given below.
(2) Compare your answers with those given in the end of the
unit.
a (i) Principal sources of soil pollution are :
(a) ----------------------------------
(b) ---------------------------------
(c) --------------------------------
(d) --------------------------------
(ii) Modern agriculture is mainly responsible for polluting soil
through non judicious use of –
(a) --------------------------------
(b) --------------------------------
(c) --------------------------------
(d) --------------------------------
(iii) Metallic Pollutants (column one) come from the industries:
Metal Industry
Chromium
Lead
Iron
Nickel
------------------------------
------------------------------
------------------------------
------------------------------
180
(b) (i) Principal Sources of solid waste are
(a) -------------------------------
(b) -------------------------------
(c) -------------------------------
(d) -------------------------------
(ii) Modern methods of waste disposal are
(a) -------------------------------
(b) -------------------------------
(c) -------------------------------
(d) -------------------------------
(iii) Excess ....................... of food and consumer products is our
greatest sources of ........................... It can be reduced by
making for categories of packing viz .........................,
................., .................... and ...........................
4.7 LET US SUM UP
By going through this unit, you would have achieved the objectives
discussed at the start of this unit. Let us recall what we have discussed so far :
Land is an unique and valuable gift of nature to human society. It has
capability to produce and to nourish life.
Soil is the top most layer of the land, a living resource of astonishing
beauty, complexity and facility. It is complex mixture of weathered
minerals from rocks, partially decomposed organic molecules and a host
of living organisms. It can be considered an ecosystem by itself.
There are at least 20,000 different soil types and many thousands more
worldwide. Most soils are stratified into horizontal layers called soil
181
horizons, the actual number, composition and thickness of these layers
vary in different soil types.
However, the possible soil horizons may be five : Surface litter, top soil,
zone of leaching sub soil, and weathered parent material.
Soil consists of a mixture of particles of different shapes and sizes
obtained due to degradation of rocks. It has pores in sufficient quantities
which occupy about 50% volume of it and are occupied by water and air.
The physical properties of soil depend upon the percentages of clay, silt
and sand particles. Large quantities of clay and silt give soil slipery
nature. While large quantities of sand results in a large quantities of air
pores in it, hence its water-re-tention power will be high.
Main factors affecting properties of soil are :
(i) Component substances
(ii) Climate
(iii) Geography
(iv) Vegetation
(v) Presence of microorganism and other living being, and
(vi) human use
In India soil can be divided into four groups mainly – (1) Red Soil (2)
Black soil, (3) Lateriti soil and (4) Alluvial soil
Macronutrients for plants are C, H, and O. In addition, the plants also
require P, K, N, S, Ca, Fe and Mg, besides traces of a few others such as
Cu, B, Zn, Mn, Mo and Co. These are supplied by soil. While C, H and
O are obtained from air and Water.
182
For healthy growth of the plants three elements, N, P and K are essential.
In soil these are supplemented by using fertilizers.
Amongst micronutrients, B, Cl, Cu, Fe, Mn, Mo, Na, V and Zn are
important. These are required by plants in very small quantities for a
healthy functioning of different enzyme systems.
The unwanted changes in physical, chemical and biological properties of
soil, which affect human and other living being is called soil pollution.
The principal sources of soil pollution are;
(a) Domestic Wastes
(b) Municipal Wastes
(c) Industrial Wastes, and
(d) Agricultural wastes.
These also include fertilizer, pesticide, plastic, and metal
pollutants.
Municipal, domestic, commercial and industrial solid- waste disposal
has been a great problem to be solved.
The traditional method of waste disposal has been open dumping, ocean
dumping and landfills which resulted as a great source of pollution.
Amongst the modern methods of solid waste disposal are included – (i)
Incineration and resource recovery, (ii) Recycling, (iii) Production of
energy from waste, (iv) composting, (v) Demanufacturing and (vi)
Reuse.
However, best way is to minimise packaging and reusing.
183
4.8 Check your progress : The key
1 (a) (i) Weathered mineral
rocks
organic molecules
living organisms
(ii) (a) surface litter
(b) top soil
(c) sub soil
(d) Weathered parent material
(iii) Sizes of particles in different soils vary as :
Clay < Silt < sand
(b) (i) C, H, O, N, P, K, S, Ca, Fe and Mg.
(ii) B, Cl, Cu, Fe, Mn, Mo, Na, V and Zn
(iii) healthy growth of the plants
healthy activities of essential enzymes
2. (a) (i) 1. Domestic wastes
2. Municipal Wastes
3. Industrial Wastes
4. Agricultural wastes
(ii) (a) Chemical fertilizers
(b) Herbicides
(c) Insecticides
(d) Fumigants
(iii) Chrome-tanning
Paint
Steel Mills
Electroplasting
184
(b) (i) a. Domestic
b. Municipal
c. Industrial
d. Commercial
(ii) (a) Incineration
(b) Recycling
(c) Composting
(d) Getting energy from waste
(iii) Packaging
Unnecessary waste
no packaging, minimal packaging, reusable packaging and
recyclable packaging.
185
UNIT-V ATMOSPHERE
Structure
5.1 Introduction
5.2 Objectives
5.3 Chemical Composition of Atmosphere
5.4 Chemical and Photo Chemical Reactions of atmosphere
5.5 Oxides of N, C, S, O and their Effects
5.6 Pollution by Chemicals
5.6.1 Petroleum
5.6.2 Minerals
5.6.3 Chlorofluorohydrocarbons
5.6.4 Green House Effect
5.6.5 Acid Rain
5.7 Let Us Sum Up
5.8 Check Your Progress : The Key
186
5.1 INTRODUCTION
We live at the bottom of a virtual ocean of air that extends upward about
500 km (300ml) commonly called the atmosphere. Atmosphere is divided in to
four regions : troposphere, stratosphere, mesosphere and thermosphere. In the
lowest 10 to 12 km, a layer known as the troposphere, the air moves ceaselessly
flowing and swirling and continually redistributing heat and moisture from one
part of the globe to another. The composition and behavior of the troposphere
and other layers control our weather (temperature and moisture conditions in a
place) and our climate (long-term weather patterns).
Clean dry air is mostly nitrogen and oxygen. Water vapour
concentrations vary from near zero to 4 percent depending on air temperature
and available moisture. Minute particles and liquid droplets-collectively called
aerosols-also are suspended in the air. Atmospheric aerosols play important
roles in the earth's energy budget and in producing rain. However in 20th
century and especially the last few decades air pollution arising from burning of
fossil fuel and other human activities resulted in reduction in sunshine
morbidity and of materials. In addition, global warming, acid-rains and El-
Nino-effects have made air pollution most dangerous and a common kind of
environmental pollution that has been reported in most industrial towns and
metropolitans of India.
Control of atmosphere pollution is utmost necessary to save our plant
earth from the foreseen hazards of global warming and unpredicted climate and
weather-changes, such as El-Nino effect etc. Not only this a continuous
monitoring of atmospheric pollution is also necessary.
In this unit we shall discuss all these aspects of atmosphere and its
degradation.
187
5.2 OBJECTIVES
The main aim of this unit is to discuss chemical composition of
atmosphere, causes of its detoriation due to pollution, measures to check its
pollution and the methods of measuring it. After going through this unit you
would be able to :
understand chemical composition of the atmosphere,
discuss chemical and photochemical reaction taking place in the
atmosphere,
describe the sources of oxides of N,C,S,O in the atmosphere and their
effects,
discuss atmospheric pollution by chemicals (petroleum, minerals, CFC),
green house effect and acid rain,
underline air-pollution control measures and their chemistry.
discuss analytical methods for measuring air pollutants, and
identify continuous monitoring instruments for atmospheric pollution.
5.3 CHEMICAL COMPOSITION OF ATMOSPHERE
The atmosphere consists of nitrogen 78.09% and oxygen 20.94% by
volume as its major components. The minor components are argon 0.34 x 10 -
1%. carbon dioxide 3.25 x 10
-2% by volume in addition to the trace components
(by volume) summarised in Table 5.1
188
Table 5.1 Presence of trace components in air
Trace Components % of Volume Trace Components % of Volume
(1) Helium 5.24 x 10-4
(8) Iodine trace
(2) Neon 1.82 x 10-3
(9) Sulphur dioxide 2 x 108
(3) Krypton 1.14 x 10-4
(10) Xenon 8.7 x 10-6
(4) Hydrogen 5 x 10-5
(11) Nitrous oxid 2.5 x 10-5
(5) Ozone trace (12) Methane 2 x 10-4
(6) Ammonia 1 x 10-6
(13) Nitrogen dioxide 1 x 10-5
(7) Carbon monoxide 1.2 x 10-5
The total mass of the atmosphere is nearly 5 x 1015
tons and the density
of the atmosphere indicates a decrease with increase of altitude while
temperature veries from -92ºC to about 1200ºC.
The whole atmosphere is divided into four regions with altitude from 0
km, temperature ranging from -92ºC to 1200ºC. The chemical species present in
different regions of troposphere; stratosphere; mesophere and thermosphere are
H2O, N2, O2, CO2, O3, NO+, O
2 and O
2 . Regions with change of altitude,
temperature and species are summarised in Table 5.2
No. Region Altitude in km. Temperature change in ºC Chemical species
1. Troposphere 0-11 15 to -56 N2, H2O, CO2, O2
2. Stratosphere 11-50 -56 to -2 Ozone
3. Mesophere 50-85 -2 to -92 NO+ ; O
2
4. Thermosphere 85-500 -92 to 1200 NO+, O
+, O
2
The chemical species present in troposphere region of atmosphere are
oxygen, carbondioxide, nitrogen and water vapour. In fact this region contains
70% mass of the atmosphere where water content changes due to hydrological
cycle.
189
The main chemical species of stratosphere region is the valuable
compound ozone (O3) – a gas which is very essential protective layer to check-
ultra violet ray of the sun, which are harmful for man's life. As the temperature
of this region is very low (-2ºC to -56ºC) hence it contains no clouds, dust or
water vapour.
Mesosphere is situated at a height between 50km to 85 km. At this
height, due to absorption of ultra violet radiations by ozone, the important
species present in this region are positively charged particles or ions, viz, O
2
and NO+.
Similarly in thermosphere (the region above mesosphere at height
between 85km to 500 km) the temperature is very high (up to 1200ºC). As this
region is under heavy exposure of ultraviolet rays which influences charged
particles like O
2 , O+ and NO
+. As a matter of fact in this region NO and O2 first
absorb ultraviolet radiations from solar energy then split into positively charged
particles, mentioned above.
As air is always contaminated with gases like CO2, CO, oxides of
nitrogen, sulphur etc, hence atmosphere is a place of various chemical and
photo-chemical reactions. The particulate matter also plays important part in
these reaction. Particulate matter is released in the atmosphere in hundreds of
tons each month from thermal power plants (as ash) and chemical industries
like fertilizers, iron and steel, rolling mills etc.
190
5.4 CHEMICAL & PHOTOCHEMICAL REACTIONS OF ATMOSPHERE
Our knowledge about chemical and photochemical reactions of
atmosphere is limited, due to large number of difficulties encountered during
their study (e.g. small quantities of gases, other than N2 and O2, and the drastic
conditions of high altitude, solar energy and third body very much separated);
hence they could not be studies in the laboratory.
Further there are many reactions which do not take place in the absence
of sun light even at high temperatures. On the contrary, in presence of sun light
they take place at much lower temperature than expected. As a matter of fact
these photo-chemical reactions are catalysed by strong solar radiations.
The reactions of formation of ozone in the stratosphere and
photochemical dissociation and ionisation in the upper part of atmosphere are
important reactions.
The formation of ozone by photochemical reaction can be represented as
follows.
OOhvO nm240
2
O+O2 + N2 (third body) O3 + N2
O + O2 + N2 (third body) O3 + N2
While, the ultraviolet radiations cause photo-chemical ionisation,
dissociation etc. as follower :
2
nm308
3 OO*hvO
OOhvO2
eOhvO eOhvO 22
191
The atomic oxygen reacts with O3. OH+ radical or oxide of nitrogen
leading into formation of oxygen, thus oxygen becomes available in sufficient
amount in environment :
O + O3 2 O2
O + NO2 NO + O2
NO + O2 NO2 + O
NO + O3 NO2 + O2
O + HO* HOO*
O + HOO* HO* + O2
Another important reaction of stratosphere is the photochemical depletion
of ozone by chlorofluoro carbons (used in refrigeration and air conditioning) :
ClCFClCFCl 2
UV
3
or ClClCFClCF 2
UV
22
2
UV
3 OCLOClO
O2- 0.2UV
ClO- + O Cl
- + O2
In troposphere, the oxygen is used by aerobic organisms in the
decomposition of organic matter to liberate CO2.
OH2CO2organisms
O3CHOCH 22
aerobic
23
OHCOorganisms
OHCHO 22
aerobic
2
OH6CO4OOHHC2 22
organisms
252
OH4CO2O4OHCH2 22
organisms
23
Oxygen is also utilized in the burning of fossil fuels or oils to produce
carbondioxide and water.
22 COOC
OH2COO2CH 2224
192
Other important reactions taking place in the atmosphere are due to
release of pollutants as a result of human activities. These include the reaction
causing acid-rain and photochemical smog formation.
(A) Acid Rain
Among air pollutants, oxides of sulphur and nitrogen are significant
compounds, released from variety of sources. These oxides when washed away
with rain, form sulphuric and nitric acids, the main constituents of acid-rains :
Formation of H2SO4
*
22 SOhvSO
OSOOSO 32
*
2
32 SOOSO
SOSOSOSO 32
*
2
SSOSOSO 32
4223 SOHOHSO
sulphuric acid
Formation of HNO3
NO + hv NO *
2
NO *
2 + O2 NO3 + O
NO2 + O NO3
NO *
2 + NO2 NO3 + NO
NO2 + NO3 N2O5
N2O5 + H2O 2HNO3
Nitric acid
NO2 + H2O HNO3 + Nitrous acid HNO2
(B) Photochemical Smog
Acidic gases like SO2, NO2, H2S etc. when present in the atmosphere,
combine with aldehyde, ketones and particulate matter present in the
atmosphere resulting in formation of photochemical smog :
ONONOhV
2
193
HCOOHCO
OHCOCHOCHOCH
2
33
H 2
M
2 HOO
OHNONOHO 22
32 NOONO
52
M
33 ONNONO
3252 HNO2OHON
So photochemical smog gives a variety of noxious products in the air.
The study of this subject is very helpful as it tells how secondary
pollutants are produced from interactions among primary emissions. Most of
the secondary pollutants are new compounds unique to photochemical smog
process. The smog conditions are produced by the combination of concentrated
emissions, limited air volume and strong isolation.
The extreme form of atmospheric pollution resulting from the internal
combustion engine is the phenomenon of photo chemical smog : a visibility-
reducing haze with acid smell and taste, that is very irritating to the eyes and
has a decidedly unpleasant effect on the lungs. Photochemical smog is found
where the following conditions coincide : a high concentration of the primary
pollutants hydrocarbons and oxides of nitrogen); strong sunlight; and a
relatively stable air mass resulting from local geography. The greater Los
Angeles basin of U.S.A.; Tokyo of Japan; Brussel of Belgium; London of
England' Copenhagen of Denmark; Colon of Germany, Bombay and Calcutta of
India exhibit a classic conjunction of these factors.
Smog is an example of branched chain reactions. The main features of
typical day's smog, though some important components such as aerosols are
194
excluded. Researchers have shown that the major stages in the developing smog
are probably:
(i) Emission of hydrocarbons and nitrogen oxides from morning traffic,
which reaches a peak during 'rush hour'.
(ii) Absorption of sunlight by nitrogen dioxide, which increases as the
concentration of oxide and the sun's intensity increases.
(iii) A series of reactions in which nitric oxide is converted to nitrogen oxide,
with simultaneous reactions yielding oxidants such as ozone and
aldehydes.
(iv) Oxidation of hydrocarbons to products including eye irritants like PAN
(peroxyacyl nitrates) and haze-forming aerosols.
(v) The end of oxidation reactions and dispersal of products.
The stages overlap considerably and each represents the overall results of
many reactions which are not fully understood.
A complete chain of photochemical model can be represented in the
following 15 reactions :
223
32
2
ONONOO.3
MOMOO.2
ONOhvNO.1
cycle,No
4.
3OH23
2323
HNO2NoNO
ONONOO
2
nitric acid
5 SOSOSOSO 32
*
2
6. 2OH2 HNO2NONO2
7. OHNOhvHNO2 nitrous acid
8. 22 HOCOOHCO CO effect produces an OH chain
195
9. OHNONOHO 2
O
22
10. 2ROOHC
11. RCHOROOHC 23
12. RCHOROOHHC 2 aldehyde and peroxy radicals
13. RCHOROROHC 22
14. OHNONORO 22
15. RO2 + NO PAN (Peroxy aceyl nitrate)
Here M = a body which absorbs energy of the reaction
HC = hydrocarbons
2RO = Peroxy redical
5.5 OXIDES OF N, C, S, O, AN THEIR EFFECTS
Most conventional pollutants are produced primarily from burning fossil
fuels, especially in coal-powered electric plants and in cars and trucks, as well
as in processing natural gas and oil. Others, especially sulfur and metals, are by-
products of mining and manufacturing processes. Table 5.3 gives the sources
and effects of these principal air pollutants
Table : 5.3 : Principal Pollutants of Atmosphere
Pollutant Principal
Forms
Main
anthropocenic
sources
Natural
sources
Effects
Sulfur
Sulfur dioxide SO2 (also H2
SO4, sulfuric
acid)
Electric utilities
(oil, gas coal),
metal ore smelting
Sea spray,
volcanoses,
biogenic H2S
Damage materials and
properties due to
formation of acid Fads
fabrics, leather, paper
etc. Bronchial
diseases. Narcosis
(tissue destroying) and
chlorosis (yellowing
of leaves) in plants.
196
Carbon
Carbon-
monoside
CO Transportation
(incomplete fuel
burning)
Plant
metabolism
Toxic, combines with
haemoglobin may
cause death, resulting
in anoxia impair
mental performance
and visual acuity, may
cause death.
Carbon
dioxide
CO2 Fossil fuel
combustion
Cellular
respiration
Respiratory illness,
intrinsic
Nitrogen
Nitrogen –
oxides
NO, NO2, N2O,
NO3
(conllectively,
NON)
Transporation,
power plants,
industry, other fuel
uses, fertilizer
Lightning
soil microbes
Photochemical smog;
fading of textiles,
dyes; deterioration of
cotton and nylon,
corrosion of metals,
illness.
Secondary
Pollutants
Photochemical
oxidants
O, N2O, PAN
(peroyacetyl
nitrate)
Reactions among
VOCs and other
pollutants imitated
by sunlight
Lightning
forest fires
Irritation in eyes;
affects lungs, harms
plants and human
skin.
5.5.1 Oxides of Carbon
Carbon monoxide (CO) is less common than the principal form of
atmospheric carbon, carbon dioxide (CO2) but more dangerous, CO is a
colorless, odourless, but highly toxic gas produced mainly by incomplete
combustion of fuel (coal, oil, charcoal, wood, or gas). CO inhibits respiration in
animals by binding irreversibly to hermoglobin. In the United States, two-thirds
of the CO emissions are created by internal combustion engines in
transportation. Land-clearing fires and cooking fires also are major sources.
About 90 percent of the CO in the air is consumed in photochemical reactions
that produce ozone.
197
(A) Carbon Monoxide :
The source are automobiles, though other involving a combustion process
as stoves, furnances, open fires, forests and bush fires, burning coal mines,
factories power plants etc. also give off CO. The principal sources of this
pollutant are the exhust products from motor vehicles in common busy routes
and intercrossing in cities like Delhi, Kolkata, Mumbai etc. In Delhi during a
peak traffic hour as much as 692 Kg. of CO is emitted in the air. The smoke of
atomobiles and thermal power and hotmix plants, stone crushers etc. also
contribute to CO level in air. CO comprises for as much as 80% of all major
pollutants added to the atmosphere. In U.S.A. during 1965. 66 million tonnes of
CO was emitted from atomobile exhaust, roughly 91% of this gas from all
sources.
In air its concentration is from traces to 0.5 ppm; CO levels in urban
areas range from 5 to 50 ppm. Incomplete combustion of domestic fuels give
out CO. Natural sources of this gas are various plants and animals. Higher
animals produce some CO from haemoglobin breakdown. Some CO is also
liberated from bile jice. Breakdown of photosynthetic pigments in algae also
releases some CO. Plants on an average produce 108 tonnes of CO every year.
Carbon monoxide is very harmful to those persons exposed to congested
highways to a level of about 100 ppm. Thus drivers are the most affected
people. CO causes difficulty in breathing, causes headache, and irritation of
mucous membranes. It combines with haemoglobin of blood, reducing its O2 –
carrying capacity. The gas is fatal over 1000 ppm. causing unconsciousness in
an hour and death in four hours. If this gas is inhaled for few hours at even a
low concentration of 200 ppm., it causes symptoms of poisoning. Inhaled CO
combines with blood haemoglobin to form carboxyhaemoglobin about 210
198
times faster than O2 does. Formation of caboxyhaemoglobin decreases the
overal O2 – carrying capacity of blood to cells resulting into oxygen deficiency
hypoxi. At about 200 ppm for 6-8 hours, there begins headache, and reduced
mental acuity; above 300 ppm, there begins throbbing headache followed by
vomiting and collapse; at above 500 ppm, man reaches into coma and at 1000
ppm, there is death. The accepted maximum allowable concentration (MCA)
for occupational exposure is 50 ppm for 8 hors. The increase in
carboxyhaemoglobin level form 1-2% to 3-4% may cause cerebral anoxia
resulting into impairing of vision and psychomotor activity. Sub-lethal
concentrations of this gas may be injurious due to prolonged expossure. In
smokers, prolonged exposures may cause an adaptive response. even producing
more haemoglobin, as high as 8%. At 10% carboxyhaemoglobin in blood due to
smoking there may be lowered tolerance to CO. Cigarette smokers have
increased hematocrit (per cent volume of red blood cells), within minutes of
smoking. In developed countries cigaretts are linked to at least 80% of all
deaths from lung cancer. According to some, however, smoking provides
immunity to Parkinson's disease, affecting nervous system and characterised
by tremors, muscular rigidity and emaciation. Pyridine is released into body
while smoking and it provides protection against this disease, probably by
competing with other toxic substances and blocking the impact on neuro-
receptors. Most plants are not affected by CO levels known to affect man. At
higher levels (100 to 10,000 ppm), the gas affects leaf drop, leaf curling,
reduction in leaf size, premature aging etc. It inhibits cellular respiration in
plants.
(B) Carbon Di Oxide : Major amount of carbon dioxide is released in the
atmosphere from burning of fossil fuel (coal, oil etc.) for domestic cooking,
heating etc. and the fuel consumed in furnaces of power plants, industries, hot-
199
mix plants etc. From fossil fuels alone more than 18 x 1012
tonnes of CO2 is
being released into atmosphere each year. In our country, on an average,
thermal power plants are likely to release around 50 million tonnes of CO2 is
being released into atmosphere each year. Indian coals are notorious for their
high ash content (20-30% and 45% in some cases) and for very bad ash
quantities. The projected annual coal consumption for the four NTPC super
thermal power plants is eight million tonnes at Korba (high grade), 8.7 million
tonnes at Ramagundam and nearly five million tonnes at Farakka (high grade).
The coal we burn was produced 250 million years ago over a period of millions
of years. If eight million tonnes of coal burnt at Singrauli, is mined over an area
of 10 Sq. Km then the deposit formation period will be roughly 500 years and if
mined over an area of 1 Sq. Km. it would be 5000 years. Can one afford this
foolish act with nature? CO2 is also emitted during volcanic eruptions. On a
global time scale, the known amounts of CO2 in lime stone and fossil sediments
suggest that normal persistance period of CO2 in the atmosphere is around
100,000 years.
To some extent an increase in CO2 level in atmosphere increases the
photosynthesis rate and consequently plant growth, acting as fertiliser
especially in hot tropical climates. This potential of fertiliser effect may be
exploited by using modified crop varieties and agricultural practices. However,
an increase in CO2 concentration in atmosphere may result into disatrous effects
also i.e. effect, causing major threat to the planet earth of global warming.
5.5.2 Oxides of Nitrogen
Nitrogen oxides (NOx) are highly reactive gases formed when nitrogen-
bearing fuel is burned in a car or a furnace. The initial product, nitric oxide
(NO), oxidizes further in the atmosphere to nitrogen dioxide (NO2), a reddish
200
brown gas that gives photochemical smog its distinctive color. Because these
gases convert readily from one form to the other, the general term NOx is used
to describe these gases. Nitrogen oxides combine with water to form nitric acid
(HNO3), which is also a major component of acid precipitation. Excess nitrogen
in water is causing eutrophication of inland waters and coastal seas. It may also
encourage growth of weedy species that crowd out native plants.
Even in unpolluted atmosphere, there are present measurable amounts of
nitrous oxide, nitric oxide and nitrogen dioxide. Of these nitric oxide (NO) is
the main compound. It is produced by combustion as O2 and N2 during
lightning discharges and by bacterial oxidation of NH3 in soil. NO contacts with
air and combines with O2 or even more readily with O3 to form the more
poisonous nitrogen dioxide (NO2). NO2 may react with water vapour in air to
form HNO3. This acid combines with NH3 to form ammonium nitrate. Fossil
fuel combustion also contributes to oxides of nitrogen. About 95% of the
nitrogen oxide is emitted as NO and remaining 5% from electric generation and
the rest from other sources. In metropolitan cities, vehicular exhaust is the most
important source of nitrogen oxides.
(A) Nitrous oxide (N2O) : In atmosphere maximum N2O levels are about 0.5
ppm, whereas average global level is estimated to be nearly 0.25 ppm. This gas
has so far not been implicated in air pollution problems.
(B) Nitric oxide (NO) : The chief source of this gas are the industries
manufacturing HNO3 and other chemicals, and the automobile exhausts. At
high temperature, combustion of gasoline produces this gas. A large amount of
this is readily converted to more toxic NO2 in the atmosphere by a series of
chemical reactions.
201
NO is responsible for several photochemical reactions in the atmosphere,
particularly in the formation of several secondary pollutants like PAN. O3,
carbonyl compounds etc. in the presence of other organic substances. There is
little evidence of the direct role of this gas is causing a health hazard at the
levels found in urban air.
(C) Nitrogen dioxide (NO2) : A deep reddish brown gas, which is the only
widely prevalent coloured pollutant gas. This gas is the chief constituent of
photochemical smog in metropolitan areas. NO2 causes irritation of alveoli,
leading to symptoms resembling emphysema (inflammation) upon prolonged
exposure to 1 ppm level. Lung inflammation may be followed by edema and
final death. The MAC for occupational exposure are set at 5 ppm for an 8 hour
period. Smokers may readily develop lung diseases as the cigaretts and cigars
contain 330-1,500 ppm nitrogen oxides. NO2 is highly injurious to plants. Their
growth is suppressed when exposed to 0.3-0.5ppm for 10-20 days. Sensitive
plants show visible leaf injury when exposed to 4 to 8 ppm for 1-4 hours.
5.5.3 Oxides of Sulphur
Sulfur dioxide (SO2) is a colorless, corrosive gas that damages both
plants and animals. Once in the atmosphere, it can be further oxidized to sulfur
troxide (SO3), which reacts with water vapor or dissolves in water droplets to
form sulfuric acid (H2SO4), a major component of acid rain. Sulfur dioxide and
sulfate ions are probably second only to smoking as causes of air-pollution-
related health damage. Sulfate particles and droplets also reduce visibility in the
United States by as much as much as 80 percent.
The major source of SO2 emission are burning of fossil fuels (coal) in
thermal power plants. smelting industries (smelting sulphur containing metal
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ores) and other processes as manufacture of sulphuric acid and fertilisers. These
account for about 75% of the total SO2 emission. Most of the rest 25%
emission is from petroleum refineries and automobiles. In U.S.A. in 1970 there
was emitted 37 million tonnes of SO2, which is likely to go up over 125 million
tonnes by 2010. It is believed that about 109 million tonnes of SO2 are added
each year into the global environment.
In our country, also SO2 emission is on the increase over the years and
the projections are that by 2000 A.D. it would reach around 13.19 million
tonnes as against 6.76 million tonnes in 1979. This is due to a corresponding in
coal consumption in the country. NTPC has been spreading its network. In
India, coal production in 1950 was 35 million metric tonnes which increased to
150 million Mt in 1980 and is expected to touch 240 million Mt by 2000 A.D.
SO2 causes intense irritation to eyes and respiratory tract. It is absorbed in
the moist passage of upper respiratory tract leading to swelling and stimulated
mucus secretion. Exposure to 1 ppm level of SO2 causes a constriction of the air
passage and causes significant broncho-constriction in asthmatics at even low
(0.25 – 0.50 ppm) concentratons Moist air and fogs increase the SO2 dangers
due to formation of H2SO4 and sulphate ions. H2SO4 is a strong irritant (4-20
times) than SO2.
This gas causes damage to higher plants forming necrotic areas on leaf.
Plants are relatively more sensitive to SO2 than are animals and man. Thus
threshold levels of SO2 injury in plants are quite low as compared to animals
and man.
In most plants leaf area collapses under intense exposure to SO2. There is
bleaching of leaf pigments due to conversion of Chl-a to phaeophytin-a. Thus
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SO2 exposure has an impact on plant productivity. High concentration of SO2 in
air reduced the pH of leaf tissue of some trees, increasing the total sulphur
content of leaves and trees bark. There is also increased sulphur content of soil
in the area adjacent to a thermal power plant. In wheat, exposure to 0.5 ppm of
SO2 with coal smoke for 2 hours daily 60 days resulted in the reduction of root
and shoot lengths, number of leaves per plant, biomass productivity, number of
grains per spike and in yield.
Some plants like Nerium indicum in Delhi serve a indicators of SO2
pollution SO2 affects stomatal pores, stomatal frequency and trichomes as well
as chloroplast structure. The gas is absorbed after passing through stomata and
oxidised to H2SO4 or sulphate ions. SO2 itself may also be toxic to plants,
Sulphuric acid aerosols are generally toxic to plants.
SO2 is also involved in the erosion of building materials as limestone
marble, the slate used in roofing, mortar and deterioration of states. Petroleum
refineries, smellers, kraft paper mills deteriorate the adjoining historic
monuments.
5.5.4 Oxide of Oxygen : Ozone
It is universally accepted that the ozone layer in the stratosphere protects
us from the harmful UV radiations from sun. The depletion of this O3 layer by
human activities may have serious implications and this has become a subject
of much concern over the last few years. On the other hand, ozone is also
formed in the atmosphere through chemical reactions involving certain
pollutants (SO2, NO2 aldehydes) on absorption of UV-radiations. The
atmospheric ozone is now being regarded as potential danger to human health
and crop growth. The temperature decreases with increasing altitude in the
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troposphere (8 to 16 km. from earth surface), while it increases with increasing
altitude in the stratosphere (above 16km. up to 50 km). This rise in temperature
in stratosphere is caused by the ozone layer. The ozone layer has two important
and interrelated effects. Firstly, it absorbs UV light and thus protects all life on
earth from harmful effects of radiation. Second, by absorbing the UV radiation
the ozone layer heats stratosphere, causing temperature inversion. The effect of
this temperature inversion is very interesting. It limits the vertical mixing of
pollutants, thereby causing the dispersal of pollutants over larger areas and near
the earth's surface. That is why a dense cloud of pollutants usually hangs over
the atmosphere in highly industrialised areas causing several unpleasant effects.
The ozone problem is thus global in scope. Inspite of slow vertical
mixing, some of the pollutants (CFCs) enter the stratosphere and remain there
for years until transported back to the stratosphere. The stratosphere could be
regarded as a sink, but unfortunately, these pollutants (CFCs) react with the
ozone and deplete it. We will refer to these pollutants later in this section.
The ozone near the earth's surface in the troposphere creates pollution
problems. Ozone and other oxidants such as peroxyacetyl nitrate (PAN) and
hydrogen peroxide are formed by light dependent reactions between NO2 and
hydrocarbons. Ozone may also be formed by NO2 under UV-radiations effects.
These pollutants cause photochemical smog.
Increase in O3 concentration near the earth's surface reduces crop yields
significantly. It also has adverse effect on human health. Thus, while higher
levels of O3 in the atmosphere protects us, it is harmful when it comes in direct
contact with us and plants at earth's surface.
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In plants, O3 enters through stomata. It produces visible damage to
leaves, and thus a decrease in yield and quality of plant products. O3 may
dispose plants to insects. At 0.02 ppm. it damages tobacco, tomato, bean, pine
and other plants. In pipe seedlings it cause tip burn.
Ozone alone and in combination with other pollutants like SO2 and NOx,
is causing crop losses of over 50% in several European countries.
Ozone also reacts with may fibres especially cotton, nylon and polyster,
and dyes. The extent of damage appear to be affected by light and humidity.
ozone hardens rubber.
5.6 POLLUTION BY CHEMICALS
Both natural and human sources are responsible for air pollution. Natural
sources are valcano explosion and marshy soil. Valcano explosion release lac of
tons of dust, ashes particles, carbon monoxide, sulphur and other toxic gases.
While marsh soil releases different gases particularly hydrogen sulphide,
methane etc.
Human sources include combustion process, industrial manufacture
processes, matellurgical processes, agricultural work, atomic power plants, use
of solvents, social activities and personal habits. Combustion may be for house
hold works or combustion process used in automobiles or the process of
thermal power plants.
Burning of wood and coal for cooking is the common source of air
pollution in rural and urban areas. This harms the environment in two ways. On
one side it promotes cutting of forests for wood and on the other side releases
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most dangerous air pollutants i.e. carbon monoxide and carbon dioxide. Cutting
of trees disturbs O2-CO2 balance in the atmosphere.
Modern means of transportation, airplanes, ships, diesel-railengines,
trucks, buses, cars, two and three- wheel automobiles, all use petrol or diesel as
fuel. These fossil fuels on combustion release carbon particles, hydrocarbons,
nitrogen and sulphur oxides, causing air pollution. Out of several hundred tons
of pollutants in the atmosphere. 50% of them are created by automobiles.
Thermal power plants use coal burning for generating high temperature
and release carbon dioxide, sulphur oxides and other gases along with the fly-
ash. The thermal power plant at Delhi alone releases daily 45 tons of soot. 60
tons of sulphur dioxide, 85 tons of fly ash etc. in the atmosphere.
Industrialization has tremendously increased use of fossil fuel for
generating energy. Industries manufacturing fertilizers, cement, acids, steel,
petrochemical etc. all add tons of pollutants to the atmosphere. The major air
pollutants from industries are particulate matter, vapour, fumes, soot etc. along
with large number of gases such as hydrogen sulphide, sulphur oxides, carbon
oxides, arsenic, fluorides, dust, lead, asbestos, hydrocarbons etc.
5.6.1 Petroleum
Petroleum is also formed under the rocky strata of earth crust like coal. It
is originated from organic material like the bodies of fish or other aquatic
animals and plants, which remained buried for millions of years in the strata of
earth crust, under the effect of high temperature and pressure. Often there is an
accumulation of gas (Natural gas) above the oil and salt water under-neath.
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Crude petroleum oil contains varying amounts of sulphur. Petroleum thus
is also a source of oxides of sulphur and particulate matter pollution of air.
Petroleum is called 'Black Gold'. Crude petroleum is a black viscous
liquid. It is found in the layered rocks of sea, which originated during cambrian
and plyosine ages. However in India it is found in the tetiary rocks in large
quantities. By far the largest supply of proven in place oil in Saudi Arabia.
Which has 250 billion bbl, about one fourth of the total proven world reserve.
The countries of Middle East control nearly two thirds of all known oil
reserves.
Petroleum is brought to the surface by drilling wells Initially the gas
pressure may be enough to force some of the oil to the surface but later it has to
be pumped. The oil so obtained is known as crude oil. It is to be refined (in oil
refineries) to get different useful products from it e.g. petrol, diesel, kerosine,
paraffin wax, asphalt etc. Petrol is used as automobile fuel, while Kerosine is
used as domestic fuel and also for lighting. Grease is an important lubricant and
asphalt is used in road covering.
Petroleum is used in the manufacture of large number of petro-chemicals,
including fertilizers insecticides, pesticides, explosives, industrial ink, plastic,
artificial rubber dyes, perfumes, creams, fibres etc.
The geological distribution of oil and natural gas in the country is given
in Table 5.4. In the country two oil companies in the public sector i.e. Oil and
Natural Gas Commission (ONG) and 'Oil India Limited' (OIL) and many
companies in private and corporate sector are working to search and explore
production of oil and natural gas. During the year 98-99 the crude oil
production of the country was about 329 lac tons (Table 5.5)
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Crude oil is found along with natural gas. Natural gas is a very valuable
gift of nature. It has both domestic and industrial use as energy. During refining
of oil large quantities of natural gas is produced, but in the absence of proper
storing facilities and pipeline network this is being burnt. Thus about 17 million
cubic meter of this valuable resource is burnt every day, and causes air
pollution.
Table : 5.4 Oil and Natural gas fields India
State Place Resource
1. Andhra Pradesh Kaikaloor, Chintalpalli and
Mandpetta, Krishna-Godavari
basin (Offshore)
Natural gas
Narsapur and Kaza fields Oil and Natural gas
2. Arunachal Pradesh Ningru and Damdama Oil and Natural gas
3. Asam Digboi, Moran, Dudru sagar,
Changai gaon
Oil and Natural gas
Lakava and Sonani Adamtilla Natural gas
4. Gujrat Ankaleshwar, Kalol, Navagaon,
Balal Cambey basin, Kactcha
Basin
Oil and Natural gas
5. Rajasthan Jaisalmer Natural gas
6. Tamilnadu Kaveri basin Oil and Natural gas
7. Bombay Hai
(Off shore)
B-74, D-18, B-178 Panna East etc. Oil and Natural gas
8. Andaman and Daman P, -3 Basin Oil
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Table 5.5 Oil and Natural gas Resources in India
State Petrolium (in million tons) Natural gas, in
Billion Cubic meters
(a) On-shre
1- Asam etc. 156.22 151.68
2. Gujarat 158.26 93.99
3. Rajasthan - 1.22
(b) Off-shore
Bombay Hai 491.67 483.50
Total 806.16 729.79
The main refinaries in India are located at Barauni, Digboi, Gauhati
Haldia, Asam, Mathura, Chennai, Kochchi and Vishakhapatanam. Drilling,
refining, and use as a valuable fuel in automobiles, petroleum is one of the
major source of air-pollution. Mainly oxide of sulphur, hydrocarbons and
particulate matter.
Crude Oil contains varying amounts of sulphur. The sulphur content of
residual fuel oil can be 4 to 7 times that of crude oil. The overage sulphur
content of residual fuel oil produced from domestic crude oil is 1.76%. It has
been found that the amount of sulphur also depends on the type of oil of
differen countries (Table 5.6 and 5.7)
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Table 5.6 Crude Oil Production and Sulphur Contents in U.S.A.
Area Crude Oil
Production %
of U.S.
Annual Crude Oil Production, 106 bbl
Sulphur weight %
0.00-0.25 0.26-0.50 0.51-1.00
1. Michigan 0.47 12.0 0.9 1.2
2. Alaska 0.47 14.3
3. Golf Coast 29.52 568.4
4. Rocky Mountain 9.08 140.4 23.1 47.7
Table 5.7 Average sulphur content from fuel of different countries 1999
Country Average
Sulphur Present
Country Average
sulphur Present
Mexico 4.4 Canada 2.95
Italy 2.8 Venezuela 2.2
Argentina 1.0 West Indies 1.93
England 3.5 India 2.7
Combustion of petroleum products in automobile engines is also an
important source of air pollution. It throws large, amounts of CO, CO2, oxides
of nitrogen and sulphur along with particulate matter.
Air pollution due to petroleum causes skin ailments in man and checks
the growth of some plants. Oil is very harmful for sea kingdom and kills the
fish. Similarly natural gas (which contains methane and low sulphur content)
also affects skin, throat and lung. It retards the growth of plants and helps in
reducing the production of fruits.
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5.6.2 Minerals
A mineral is a naturally occuring, inorganic solid with a definite chemical
composition and a specific crystal structure. A rock is a solid cohesive
aggregate of one of more minerals. Within the rock, individual mineral crystals
(or grains) are mixed together and held in the solid mass.
Minerals are world's most precious natural resources, which have been
useful to mankind in different ways. Amongst common examples, salt, iodine,
chlorine, etc. are important part of our food and they keep our body healthy. All
the machines, which represent our present day civilisation have come into
existence due to metallic minerals and are using mineral fuels. The wealth of
the nation is measured in terms of the mineral resources of the country.
The history of use and development of mineral run parallel with the
history of human civilisation. The relation between these two is so deep that
periods of the civilisation are named (as they are known to day also) after
metals eg. copper age, bronze age, iron age etc. From ancient age to the present
age of science and technology minerals have played important role in the
development of civilisation Primitive man was using different minerals for
different purposes eg. flint for producing fire, quartz for the preparation of
arms, soil for preparation of utensiles etc. Even Palcolithic man was knowing
the use of a number of minerals in Neolithic age he became aquinted with
metals like gold and copper. Some non-metallic materials were also used in
their native form at that time. As early as, 8 lac years ago primitive man had
started using flint and quartz for preparation of tools. This was a long age of
lacks of years and it was named as stone age. About 20 thousand year ago the
age of metals started when the man had started using metals. First came copper
age; which was followed by Bronze age and about 6000 years ago man started
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using iron (called Iron age). This has continued to the present age of Machines.
It is called Machine age. Not only the machines are prepared using mineral
fuel. I t is because of this, some person call present civilisation as the age of
'Mineral Civlisation'.
Thus from the ancient times the man was knowing the use of various
minerals. In the start minerals were used in their native form only. Crystals and
jade were used for the preparation of arms, iron and manganese minerals were
used for color and painting, while the coloured stones like garnate and amethyst
were used in ornaments. Metals like gold, silver and copper were used for the
preparation of utensils.
The distribution of minerals in nature is quite different from that of plants
and animals. Contrary to the distribution of plants and animals, distribution of
minerals does not depend on the climate. but is the result of geological changes
taken place in the ancient past. Generally metallic minerals are found in the
places where there has been changes in tectonic plates of earth. On contrary
chemical minerals (coal, petroleum etc.) are found mainly in such places where
layers of the earth-crust have not reshuffled. The mineral resources are
generated so slowly that once they are exhausted they will not be re-generated
during the life span of a generation. It is because of this fact conservation and
sustainable usage of mineral resources (particularly coal and petroleum etc.) is
the thought of the time.
World industry depends on about 80 minerals and metals some of which
exist in plentiful supplies. Three fourth of these resources are abundant enough
to meet and all our anticipated needs or they have readily available substitutes.
At least 18 metals, however, including tin, platinum, gold, silver and lead, are in
short supply. Of these 80 metals and minerals between one half and two third
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are considered 'strategic resources' (those which a country uses but can not
produce itself and hence may cripple the country's economy) (Table 5.8)
Table 5.8 Metal Resources of the world
Metal Deposits,
in Crore
metric
Tons
Source Mineral
Ore
Main Producer
1. Iron 10.90 Haematite Russia
Magnetile USA
Siderite Canada
2. Aluminium 29.50 Bauxite Australia, Gini
3. Titanium 4.40 Ilmenite Canada
4. Copper 3.10 Chalocopyrite America, Chili, Canada,
Russia, Zambia
5. Zinc 1.20 Sulphatirite Canada, America, Russia
6. Lead 0.85 Galena America, Canada, Australia
7. Tin 0.05 Cassiterite Thiland, Malasia
8. Manganese 8.0 Pyrolusite South Africa
9. Chromium 7.80 Chromite South Africa
10. Nickel 0.70 Pentlandite Cuba, Russia, Canada
11. Molybdenum 0.05 Molybdenite America, Russia
12. Cobalt 0.03 Cobalt Sulphide Congo, Zambia
13. Tungsten 0.02 Scheelite,
Wolframite
China
14. Mercury 1.0 Cinnabar Spain, Italy
15. Indium India, Canada, Peru
16. Silver 7000 tons Argentite -do-
17. Gold 400 tons Gold Telluride South Africa, Russia
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Mineral Resources of India
As regards the mineral resources, India is not poor. If we look at the total
mineral resources available in India we find, they are not less, seeing the area of
the country (Table 5.10). It has, in more or less quantities, all those minerals
which a modern, self sufficient industrial country needs. The country has
sufficient quantities of iron, aluminum and titanium ores and in mica also it is
quite rich. However, other economically important minerals are not present in
sufficient quantities. New techniques are being used to search new reservoirs as
a part of economic development of the country.
At present more than 4000 mines are operating (except atomic minerals)
in the country and more than fifty minerals are produced. The mines of mineral
fuel, gold, silver, diamond, lead, copper and phosphorite are under public
sector, while other minerals are produced in mines under private sector.
Distribution and Availability of Mineral Resources in India
The natural distribution of minerals in Indian soil like in the world is
quite irregular. While there is derth of the mines of economically important
minerals minerals in northen planes made by alluvial soil. Bihar and Orissa are
very rich in mineral wealth, the mines here are quite old. This part of the
country has maximum number of reservoirs of metallic minerals eg iron,
manganese, copper, uranium, aluminium and chromium Industrial minerals like
mica silimanite and phosphates are also found in this region in abundance. In
addition to these about three fourth of the nation's coal is also located here. A
few districts of Bihar and neighbouring regions of Orissa are included amongst
the richest sources of coal in the world (about 81.28 Crore tons). This region of
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the country also has the largest store of manganese while Gaya region Bihar
gives about 50% of world's best quality of mica.
As regards the mineral wealth of the country, Madhya Pradesh and
Chhattisgarh stand the second. There are large stores of iron and manganese
ores and coal lime and bauxite are also found in large quantities. The total
quantity of gold of the nation comes from Karnataka. Large quantities of iron
clay and chrome ore are also found here Andhra Pradesh stores good
concentrates of second-grade coal and many minerals of industrial importance.
Keral is the good source of alluvial sand consisting metals. Malabar cost can
give 2.03 Crore tons of 9 lmanite and large quantities of monazite, zircon, rutile
and garnet.
Uttar Pradesh and Punjab have no important contribution in the minerals
of industrial importance. Rajasthan produces copper, lead, zinc, uranium, mica,
beryllium stirite, sapphire and emerald. Gujarat and Assam produce large
quantities of petroleum. Assam has large concentrates of tertiary coal. In West
Bengal mainly iron and coal are found (1.6 Crore tons of coal annually)
Himalayan region gives a very few minerals. Some regions of Kashmir store
coal aluminum ore and sapphire. Kumayun and Sikkim regions have some
concentrates of magnesite and iron ores
Thus, the nation is self-dependent in the production of some minerals e.g.
iron ores, bauxite, chromite, manganese ores, lime stone, magnesite and ferro-
alloys. But we are unable to fulfil the need of copper, lead, zinc, borax sulphur,
asbestos and rock phosphates. The shortage of sulphur, borax and asbestos is
about 80% and that of copper lead and zinc is nearly 45 to 75 percent (Table
5.9)
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Table 5.9 Mineral Production of India
Name of the Mineral Total production, in Tuns
1. Coal and Lignite 133178.000
2. Petroleum and Natural-gas 19734.000
+ 2861 m cu m +
3. Bauxite 1920,000
4. Chromite 264, 204
5. Copper Ore 2478.935
6. Gold 2244 kg
7. Iron ore 42721000
8. Lead (Concentrate) 21747
9. Zinc (Zinc Concentrate) 52839
10. Manganese ore 34274000
11. Lime 34274000
12. Mica 8766
13. Silver 14403 kg
14. Pyrites 56438
15. Diamond 13022 Caratt
16. Magnesite 418909
Classification of Minerals
Minerals are generally classified into three groups
(a) Non-metallic Mineral
(b) Metallic Minerals
(c) Mineral fuels
(a) Non-metallic Mineral- These are further divided on the basis of their
properties in to –
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1. Ceramic Minerals : e.g. Felspar, different soils
2. Infusable Minerals :
(i) Soil group – e.g. Kaolin, fire clay etc.
(ii) Sand group – e.g. Quartz etc.
(iii) Sylmanite group – e.g. Sylmanite, Kainite, etc.
(iv) Magnessium group – e.g. Magnesite, Dolamite etc.
(v) Chrome group – e.g. Chromite etc.
(vi) Other groups – e.g. Graphite, Rutete, Zircon, Talc, Pyrollusite, etc.
3. Insulating Minerals : e.g. Mica, Asbestos, Gypsum etc.
4. Industrial Minerals : e.g. Red Ochre, Barite, Witherite, Florite,
Cryolite, Anhydrite, Bentomite, Lime stone, Serpantine, Apatitic,
Cellastite, Pyrophillite salts Sulphur (Constalline), Borax, Borate,
Epsemite, Monazite, Phosphorite, Ballestonite, Itmanite, Pyrite etc.
5. Abrassive Group :
(i) Silicious Abrassive e.g. Quartz, Sand, diatmite, Flint etc.
(ii) High grade Abrassive e.g. Dimond Garnet etc.
(iii) Others- Bauxite, Magnesite, Calcite, Dolamite, Pyrophillite etc.
6. Building stones : Cynite, Dolerite, Belsalt, Phyllite, Sand stone,
Quartzite, State-stone, Lime stone etc.
7. Precious stones : Diamond Ruby, Sapphire, Emarald, Amechyst etc.
8. Semi precious stones: Topaz, Amethyst, Beryl, Criso-Beryl, Garnet,
peridote. Spinel Onex, Aqua marine, Amber, Diopside, Spodumene,
Rebellite, Bluestorm Alexandrite, Aventrine, Lapis Lazuli,
Zednephrite, Opal, Tourmallin etc.
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(b) Metallic Minerals
Most of the naturally occuring elements are metals. Many metals occur in
native state e.g. silver, gold, platinum etc. Other metals occur in combined state.
Out of the metallic minerals, the metal used in large quantities is only
iron. Other common metals are copper, zinc lead, aluminium etc.
Metallic minerals are divided into three groups
(i) Iron and Ferro-alloys
(ii) Non ferrous metals or Semi precious metals
(iii) Precious metals
(i) Iron and Ferro-alloys :
Iron deposits are found in the form of ballistic rocks and bedded
boulders.
These ores contain oxygen and contaiminated with silica, alumina,
sulphur and phosphorous. Ferrous-alloys contain iron along with chromium.
Manganese, Cobalt, Molybdenum. Tungston or Vanadium in varying quantities.
(ii) Non-ferrous or Semi precious metals :
These metals include copper, lead, aluminium, magnessium, titanium,
antimony, tin, mercury, arsenic, beryllium, bismuth, cadmium, radium,
uranium, selenium, tellurium, tantalum, columbium, zirconium, boron,
germanium, Indium, cesium, lithium, cerium, thorium, barium, calcium,
strontium etc.
(iii) Precious Metals :
The precious metals are : God, Silver & Platinum.
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(c) Mineral-fuel
Mineral fuels (or fossil fuels) are important sources of energy in the
present age of mechanical culture. These include coal and mineral oil
(Petrolium and diesel).
Pollution
Geologic materials are extracted by several different techniques,
depending on the accessibility of the resource and the content or concentration
of the material sought. All of these methods have environmental hazards.
Native metals deposited in the gravel of streambeds can be washed out
hydraulically in a process called 'placer mining'. This not only destroys
streambeds but fills the water with suspended solids that smother aquatic life.
Larger or deeper ore beds are extracted by strip mining or open pit mining,
where overlying material is removed by large earth moving equipment. Even
deeper deposits are reached by underground tunneling, an extremely dangerous
process for mine workers. Further in coal mines natural gas poses dangers of
explosion.
Mine wastes cause considerable environmental damage. Coal bearing
scrap heaps in or near coal mines can burn uncontrollably for years, producing
noxious smoke and gases, Surface waste deposits called tailings can cause
acidic or otherwise toxic run off when rainwater percolates through piles of
stored material. Trailings from uranium mines produce windborne radioactive
dust.
Water leaking in to mine shafts also dissolves metals and other toxic
material. When this water is pumped out or allowed to seep into ground water
aquifers, it pollutes ground water or stream.
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Huge strip-mines, in which vegetation, soil, and rock layers are stripped
from the surface to expose minerals, this material is replaced into the mine as
spoil blanks, which are very susceptible to erosion and chemical weathering.
This causes chemical and sediment runoff pollution.
Metals are extracted from ores by heating or with chemical solvents.
Both processes release large quantities of toxic materials that can be even more
environmentally hazardous than mining. Smelting, roasting ore to release metal,
is a major source of air pollution. One of the most notorious examples of
ecological devastation from smelting is a wasteland near Duck town Tennessee,
where smelting of sulphide ore of copper has in creased sulphur emmission
hazard, similarly, smelting, of copper-nickel ore in Sudbury, Ontario, caused
wide spread ecological destruction. Chemical extraction is used to dissolve or
mobilize pulverised ore, but it uses and pollutes great deal of water. A widely
used method is heap-leach extraction, which involves piling crushed ore in huge
heaps and spraying it with a dilute alkalive cynide solution. Once all the gold is
recovered, mine operator may simply walk away from the operation, leaving
vast amount of toxic effluent in open ponds behind earthen dams. In 2000 this
has poisoned millions of fish and threatened drinking water supply along about
640 Km near Baiamare in Romania.
Toxic metals and halogens are chemical, that are toxic when concentrated
and released in the environment. Principal metals of concern are lead, mercury,
arsenic, nickel, beryllim, cadmium, thallium, uranium, cesium and plutonium.
Halegens are highly reactive toxic elements. Most of these materials are mined
and used in manufacturing. Lead and mercury are wide-spread neurotoxins that
damage the nervous system.
221
Further, particulate materials (dust, ash, soot, smoke etc) often are the
most apparent form of air pollution. Breathable particles smaller than 2.5m
are among the most dangerous of this group because they can damage lung
tissues. Asbestos fibres and cigarette smoke are among the most dangerous
respirable particles in urban air because they are carcinogenic.
5.6.3 Chloro Fluorohydrocarbons
Chlorofluorocarbons (CFCs) are a group of synthetic chemicals. They
were developed in 1930 by the American scientist Dr. Thomas Midgley for Du
Point- General Motors combine for applications in refrigeration by these two
industrial giants. Before the arrival of CFCs, they were using ammonia or
sulphur dioxide which are both toxic and corrosive. On the other hand, the
CFCs marketed by the, chemicals company Du Pont under the trade name
"Freons" were non-toxic and inert CFC-11 and CF-12 were used as coolants in
refrigerators and air-conditioners, as aerosol propellants and in plastic forms.
Later on CF-113, another synthetic chemical belonging to the same group, was
found to be very useful as a solvent in the semiconductor industry.
The fluorocarbons are derived from hydrocarbons by the substitution of
fluorine for some or all of the hydrogen atoms in them. Hydrocarbons in which
some of the hydrogen atoms are replaced by chlorine in addition to those
replaced by fluorine, are known as chlorfluorocarbons (CFCs)
The most widely used CFCs tricholorofluoromethane (CCl3F) and
dichlorodifluoro methane (CCl2F2) are produced by the reaction of hydrofluoric
acid with carbon tetrachloride in the presence of a chlorofluoroantimony
catalyst. The CFCs are used as a refrigerants, aerosol propellants, solvents,
foam-blowing agents, fire extinguishants, anaesthetics and polymer
222
intermediates. The current uses of some important CFCs are shown in Table
5.10. The use of CFCs is quite wide-spread in industry, and also in products for
domestic use. For example, the annual consumption of CFCs in European
Economic Community (EEC) alone is about 903,000 tonnes (Fryatt, 1990).
Apart from their principal use in refrigeration and airconditioning
equipment, they are also employed as propellants in aerosols, as foam-blowing
agents for packaging and insulating boards, as solvents in the electronics
industry, and as sterilisers in the production and use of medical products.
Table 5.10 Ozone depleting substances and their control programme.
Ozone
depleting
gases
Uses Damage
to Ozone
related to
CFC
Control
under
Montreal
Protocol 1987
New controls
after
amendments in
London 1990
CFCs Refrigeration, air
conditioning, rigid
and flexible plastic
forms, solvent in
electronics industry
aerosols
1 50% cut on
1989 level by
1999
Complete phase
out by 2,000 AD
Halons Fire extinguishers (in
ships, air crafts and
computer control
rooms)
3 to 10 Freeze on
production at
1992 level
Total phase out by
2,000 AD except
for essential uses.
HCFs Replacement for
CFCs in
refrigeration, foam
blowing & aerosols
0.09 to 0.1 No controls No legal control
but informed
understanding that
they should be
used carefully by
industry.
223
Carbon Chemical feedstock
for CFCs, solvent in
pharmaceuticals
1 No controls 85% cut by 1995
phase out by 2000
AD
methyl
Chloroform
Solvent for precision
metal working and
electronics industry
0.1 No controls 70% cut by 2,000
and phase out
20,00-05 AD.
CFCs are also used in the processing of spices and nuts, in gaseous
dielectrics for the electrical power industry, in fire extinguishers, and as feed
stocks in the chemical process industry of the fluorination of polymers.
In addition to all the industrial applications mentioned above, the CFCs
also play an important role in scientific applications as modelling fluids for
two-phase flow studies.
Health Hazards : (1) In general, chlorinated hydrocarbons are higher in
toxicity than other fluorocarbons not having chlorine (or bromine) atoms in
their molecules. The lower toxicity of such fluorocarbons may be due to the
greater stability of the C-F bond, and perhaps also due to the lower lipoid
solubility of the more highly fluorinated compounds.
(2) It has been possible to select CFCs which are safe for their
intended uses. because of the history of safe use of CFCS,
therefore there is a poplar belief that they are completely safe
under all conditions of exposure. This, however, is not correct.
(3) To some extent, the volatile CFCs possess narcotic properties. For
example dichlorodifluoromethane (CCl2F2) if inhaled at 5%
concentration (by volume), however, loss of consciousness occurs.
224
At the threshold limit value (TLV) of 1,000 ppm (parts per
million), narcotic effects of CCl2F2 are not experienced by man.
(4) Toxic effects from repeated exposure (such as liver or kidney
damage) have not been produced by the fluoromethanes or
fluoroethanes. On the other hand, the fluoroalkenes, such as
chlorotrifluoroethylene CCIF : CF2), can produce liver and kidney
damage in experimental animals after prolonged and repeated
exposure to appropriate concentration.
(5) The exposure limits of some industrially important CFCs are given
in Table 5.11. This table shows the time-weighted averages of
threshold limit values (TLVs) as well as short term exposure limits
(STELs) recommended the American Conference of Governmental
Industrial Hygienists (ACGIH). The TLVs given in Table 5.11
have beer adopted by the ACGIH for a normal 8-hour workday and
40 hours workweek. The STELs, adopted again by the ACGIH, are
the maximum concentrations of CFCs to which industrial workers
can be exposed for a period of up to 15 minutes continuosly,
provided that no more than four such exposures per day are
permitted with at least 60 minutes between consecutive exposure
periods, and provided that daily TLV is not exceeded.
225
Table 5.11 Threshold limit values (TLVs) and short-term exposure limits
(STELs) of some chlorofluorocarbons (Zapp. 1983)
Chlorofluorocarbon TLV STEL
ppm mg/m3 ppm mg/m
3
CCl2F 1,000 5,600 1,260 7,000
CCl2F2 1,000 4,950 1,250 6,200
CHCl2F 10 40 - -
CHClF2 1,000 3,500 1,250 4,375
CCl2FCCIF 1,000 3,500 1,250 9,500
(CCIF2)2 1,000 7,000 1,250 8,750
(6) Like many other solvent vapours and surgical anaesthetics, the volatile
CFCs may also produce cardiac arrhythmia or arrest under circumstances
where an abnormally large amount of adrenaline is secreted exogenously
(Flowers et.al., 1975). The concentrations of CFCs required to produce
this effect are, however, well above those normally encountered during
the industrial use of these substances.
(7) All CFCs undergo thermal decomposition when exposed to a flame or
red-hot metal. Decomposition products of CFCs include hydrofluoric and
hydrochloric acid along with smaller amounts of phosgene and carbonyl
fluoride. The last compound is very unstable to hydrolysis and quickly
changes to hydrofluoric acid and carbondioxide in the presence of
atmospheric moisture.
226
(8) The three commercially most important CFCs (CCl3F, CCl2F2 and
CCl2FCCIF2) have been tested for mutgenicity and teratogenicity with
negative results (Epstein et.al, 1972; Greim et al, 1977). On the other
hand, CHCIF2 (a refrigerant and a possible propellant) was tested by the
Due Pont as well as the imperial Chemical Industries, and was found by
both to be mutagenic and teratogenic in a battery of tests. Their results,
though not published in scientific journals, point to caution when
delaying with CFCs that are not fully halogenated. After these tests, no
further consideration was given to CHCIF2 After these tests, no further
consideration was given to CHCIF2 as a propellant in areosols.
The chlorofluoro carbons diffuse slowly in stratosphere where UV-
radiation is between 1740 A to 2200 A as follows :
2
hv
3 CFCl*ClA22001740
CFCl
*ClCFClCFClhv
2
)or(min*FCClFCFClhv
22
hvClCFFCFCl
ClClCFClCF 2
hv
23
*FCFClClCFhv
2
The free radicals F* or Cl* act abruptly in the stratosphere with ozone.
Each chlorine atom reacts with about 1 lakh (100,000) molecules of ozone
converting it into oxygen and other chloro compounds. The chlorine which is
released by volcanic eruptions or other sources also reach at stratosphere and is
responsible for the destruction of ozone as follows:
227
*ClClCFClCF 222
Cl*+O3 Cl – O* + O2
Cl- O*+O Cl* – O2
O
CL-O+NO2 CL-O-N
O
Chlorine nitrate
Cl* + O3 ClO* + O2
ClO* + O Cl* +O2
5.6.4 Green House Effect
The name "Green House feects", was first coined by J. Fourier in 1827.
Later on the names – 'Atmospheric Effect', 'Heating effect of Earth', 'Global
warming' were given to this effect by various scientists because of increase of
CO2 level in atmosphere.
The green house effect can be defined as the progressive warming up of
the earth's surface due to blanketing effect of man made with CO2 in the
atmosphere.
Since CO2 is confined exclusively to the troposphere, its higher
concentration may act a serious pollutant. Under normal conditions (with
normal CO2 concentration) the temperature at the surface of the earth is
maintained by the energy balance of the sun rays that strike the planet and heat
that is radiated back into space. However, when there is an increase in CO2
concentration, the thick layer of this gas prevents the heat from being re-
radiated out. This thick CO2 layer thus functions like the glass panels of a
greenhouse (or the glass windows of a motor car), allowing the sunlight to filter
through but preventing the heat from being re-radiated in outer space. This is
228
the so-called greenhouse effect. Thus most heat is absorbed by CO2 layer and
water vapoures in the atmosphere, which adds to the heat that is already present.
The net result is the heating up of the earth's atmosphere. Thus increasing CO2
levels tend to warm the air in the lower layers of atmosphere on a global scale.
Nearly 100 years ago the CO2 level was 275 ppm. Today it is 350 ppm and by
the year 2035 and 2040 it is expected to reach 450 ppm. Imagine the earth's
temperature. CO2 increases the earth temperature by 50%, while CFCs are
responsible for another 20% increase. There are enough CFCs up there to last
120 years. What will be if we do not stop CFC release?
The heat trap provided by atmospheric CO2 probably helped to create the
conditions necessary for the evolution of life and the greening of earth
Compared to moderately warm planet, Mars, with too little CO2 in its
atmosphere is frozen cold and Venus with too much is a dry furnace. The
excess CO2 to some extent is absorbed by the oceans, But with the
industrialization of West and increased consumption of energy, CO2 was
released into atmosphere at a faster rate than the capacity of oceans to absorb it.
Thus its concentration increased. According to some estimates CO2 in air may
have risen by 25% since the middle of 19th century. It may even be doubled by
2030 A.D.
There are some differences of opinions however, about the extent of rise
in earth's temperature due to increasing CO2 levels. According to some,
computerised models, doubling the CO2 level will increase the global mean
temperature (15ºC) by 2 degrees C. But some others say that this will be less
than one quarter of a degree. There are other gases also which contribute to
greenhouse effect. These are SO2, NOx, CFCs discharged by industry and
agriculture. Even a change of two degree may disrupt the earth's heat budget,
causing catstrophic consequences (Table 5.12)
229
Some analysts believe that changes in the earth's mean temperature will
be apparent by 2050, when the temperature would increase by 1.5 to 4.5ºC.
According to one projection, changes will be the least in the tropics and the
most at the poles. So Greenland, Iceland, Norway, Sweden, Finland. Siberia and
Alaska will be among the most affected. The polar icecaps would melt. The
floating Western Antarctica ice sheet could begin to melt. A rise of five degrees
would raise the sea level by five meters within a few decades, threatening all
the densely populated coastal cities from Shanghai to Francisco. It is suggested
that North America would be warmer and drier. The U.S. would produce less
grains. On the other hand. North and East Africa the Middle East India, West
Australia and Mexico would be warmer and wetter, enabling them to produce
more grain. Rice-growing season as well as area under rice cultivation could
increase. However, this may not happen as higher surface temperature will
increase the evaporation of winter thus reducing grain yield. According to US.
Scientist, George Woodwell, India's annual monsoon rain may even cease
altogether.
Table 5.12 : Green House Gases
Green house gases Atmosphere concentration
(ppb v/v)
Annual rate of increase (%)
Carbon dioxide
Methane
Nitrous oxide
Methyl Chloroform
Ozone
CFC 11
CFC 12
Carbon tetrachloride
Carbon monoxide
344,000
1,650
304
0.13
variable
0.23
0.4
1.25
variable
0.4
1.0
0.25
7.0
-
5.0
5.0
1.0
0.2
230
According to an estimate, if all the ice on the earth should melt 200 feet
of water world be added to surface of all oceans, and low-lying coastal cities
like Bangkok and Venice would be inundated. A rise in sea level of 50-100 cm
caused by ocean warming would flood low-lying lands in Bangladesh and West
Bengal. Due to greenhouse effect, there may occur more hurricanes and
cyclones and early snow melts on mountains causing more floods during
monsoon, According to some, within next 25 years or so, there will be rise in
sea level by 1.5 to 3.5 meters and in Bangladesh alone 15 million people will
have to move or drown. Low-lying cities of Dhaka and Kolkata may be
inundated.
If the present trend continues, a global warming by a few degrees
centigrade will be invitable before the middle of the century. CO2 from the
burning of fossil fuels is rapidly accumulating in the atmosphere. So also the
gases like chloroflrocarbon (CFC3), which are far less abundant but equally
devastating. CO2, CFC3 and other gases came almost entirely from a variety of
man made sources like vehicles, exhausts, and industrial solvents. Only a
modest amount derives from natural sources like microbes in the soil.
Besides, the five emerging environmental issues (new technologies, red
tides, diesel pollution, acid rain and threals to Antarctica), that the UNEP has
been able to identify, the one that has proved the most vexatious, and
disquieting is the greenhouse effect of global warming. It is caused by the
build-up in the atmosphere of CO2 and other toxic gases discharged by industry
and agriculture. If unchecked, it could alter temperatures, rainfall and sea levels
of the earth. The UNEP has appropriately chosen the slogan "Glabal Warming:
Global Warning" to alert the people on World Environment Day. The cost of
defense (reduction of gas emissions and research to identify the hardest hit
emissions and plan of coastal defense) would be enormous in the region of $100
231
billion or more for a one meter rise in sea level. The problem is far most
vulnerable areas in developing world do not have economic resources. The
hardest hit may be developing world, which discharge 2/5ths of the global
carbon emissions each year which itself is increasing by over 100 million
tonnes a year.
Impacts of green house effect : The green house effect will disturb the climate
of the planet changing such critical variables as rain fall, wind, cloud cover,
ocean currents and the extent of the polar icecaps. The global impact of these
changes could be very large. Although the general direction and over all
magnitude of the global impacts can be predicted today, the precise regional
distribution of the effect cannot.
Climate change is now given the highest priority in the list of global
environmental problem. Current theory suggests that if the concentration of
carbondioxide reaches twice the pre-industrial level, the atmosphere will be
committed to a warming of 1.5 to 4.5 C, relative to average pre-industrial
temperature. A warming of this magnitude will directly affect many physical
aspects of the earth's global system.
It is said that the green house effect upon the climate will not be uniform
everywhere. Warming at the poles is likely to be two to three times the global
average, while warming in the tropics may be only 50 to 100 percent of the
average. The increased warming at the poles will reduce the thermal gradient
between the equator and the high latitude regions, decreasing the energy
available to the "heat engine" that drives the global weather machine. As the
thermal gradient is reduced, global patterns of wind and ocean currents, as well
as timing and distribution of rainfall, will change.
232
The global hydrological cycle is expected to intensify by 5 to 10 percent
if the world warms by 1.5 to 4.5 degree centigrade. Global rainfall will
probably increase by an estimated 7-11% a year, but the timing and distribution
of the regional rainfall is likely to change substantially. Temperate winters
might be wetter and summer drier. The tropics would also become wetter but
the sub tropics, already dry, could become drier still.
The most major change that would occur to ecosystem is that they would
be shifted in space. In the high latitudes of the northern hemisphere, for
example, the northern forest limit would shift polewards. As already mentioned
the rise in sea level due to the melting of polar caps and thermal expansion of
ocean, would cause flooding in many low-lying coastal areas. The result is that
many fresh water ecosystems become saline and many species may migrate or
be totally destroyed. This may also destroy coral reefs, the spawning grounds of
fishes and other aquatic organisms. The increase in the frequency of tropical
cyclones and other storms due to the increased surface temperature would cause
stresses on tropical animals, the loss of substantial amount of corals, and
decreased biological diversity among marine organisms.
5.6.5 Acid Rain
We have seen that the oxides of sulphur and nitrogen are important
gaseous pollutants of air. These oxides are produced mainly by combustion of
fossil fuels, smelters, power plants, automobile exhausts, domestic atmosphere
and can travel thousands of kilometers. The longer they stay in the atmosphere,
the more likely they stay in the atmosphere, the more likely they are to be
oxidised into acids. Sulphuric acids and nitric acid are the two main acids,
which then dissolve in the water in the atmosphere and fall to the ground as acid
rain or may remain in atmosphere in clouds and fogs.
233
The acid rain has been divided into two parts (i) Wet and (3) Dry. In fact
acid rain, fog, frost, mist and snow are termed wet form of deposition while
dust or other dry particles containing nitrite, nitrate, sulphite, sulphate are
termed dry form of deposition. As Wet form is very common so it is discussed
here.
Acidification of environment is a man-made phenomenon. The acid rain
is infact a cocktail of H2SO4 and HNO3 and the ratio of the two may vary
depending on the relative quantities of oxides of sulphur and nitrogen emitted.
On an average 60-70% of the acidity is ascribed to H2SO4 and 39-40% to
HNO3. The acid rain problem has dramatically increased due to
industrialisation. Burning of fossil fuels for power generation contributes to
almost 60-70% of total SO2 emitted globally. Emission of NOx from
anthropogenic sources ranges between 20-90 million tonnes annually over the
globe. Acid rains have assumed global ecological problem, because oxides
travel a long distance and during their journey in atmosphere they may undergo
physical and chemical transformations to produce more hazardous products.
The reactions pertaining to the formation of H2SO4 and HNO3 in the
atmosphere are given below :
H2SO4 formation :
42222 SOHO2
1SOOH
Formation of O2 and other products can be explained below :
SO2 (g) + H2O SO2 (aq)
SO2 (aq) + H2O H2SO3
H2SO3 + H2O HSO
3 + H3O+
HSO
3 + H2O – 2e HSO
4 + 2H+
O2 + 4H+ + 4e 2H2O
2HSO
3 + O2 2HSO4
234
HNO3 Formation :
H2O + 2NO2 HNO3 + HNO2
Formation of other products can be explained below :
NO2 (g) + H2O NO2 (aq)
2No2 (aq) + H2O HNO2 + HNO3
NO2 + O2 NO3 + O2
NO3 +NO2 N2O5
N2O5 + H2 2 HNO3
Acid rains create complex problems and their impacts are far reaching.
They increase soil acidity, thus affecting land flora and fauna; cause
acidification of lakes and streams thus affecting aquatic life, affects crop
productivity and human health. Besides these they also corrodes buildings,
monuments, statues, bridges, fences, railings etc. British parliament building
also suffered damage due to H2SO4 rains. Due to acidity, levels of heavy metals
as aluminium, manganese, zinc, cadmium, lead and copper in water increases
beyond the safe limits. Over 10,000 lakes in Sweden have become acidified.
Thousands of lakes in U.S.A., Canada, Norway have become unproductive due
to acidity. Fish population has decreased tremendously, and there are deaths of
salman trout etc. The fishless areas (lakes) are now fish graveyards.
Many bacteria and blue green algae are killed due to acidification, thus
disrupting the ecological balance. In West Germany nearly 8% of the forests
died and nearly 18 million acres of forests are critically afflicted by acid rains.
Forests in Switzerland, Netherlands and Czechoslovakia have also been
damaged by acid rains. Nutrients such as calcium, magnesium, potassium have
been leached away from soil by acids.
235
Acid rains are great threat to British environment as to Central Europe
and Southern Scandinavia. In 1974 acid rains over Scotland were found to be
more sour than vinegar (pH2.4). This H2SO4 shower, 500 times more acidic
than rain should naturally be stood as a world record for four years. Much of the
falling snow in Britain is now highly acidic. If it does not kelt it may turn into a
pollution time bomb. Several rivers as Twy are acidic.
Acid rains are carried away by prevailing winds to elsewhere where
precipitation takes places. Thus oxides may be produced at one place, and these
affect elsewhere by turning into acids. The two such victims are Canada and
Sweden. Canada gets acid rains from petrochemical units in North America.
Heavy winds pick up acid rain from factories in Britain and France to Sweden.
Equally grim are the acid rain in Norway, Denmark and W. Germany. It is said
that 90% of the acid rain of Norway and 75% of Sweden are due to drifted acid
rain oxides. Acid rains are thus becoming a major political issue.
Though acidity of rain water is yet to be adequately monitored,
developing countries like ours may soon have to face the acid rain problem. The
acid rain is fast spreading to developing world where tropical soils are even
more vulnerable than those of Europe. It appears that acid rain problem is on
the avil in India. Industrial areas with the pH value of rain water below or close
to the critical value have been recorded in Delhi, Nagpur, Pune, Mumbai and
Kolkata. This is due to sulphur dioxide from coal-based power plants and
petroleum refinery. According to a study made by B.A.R.C. Air Monitoring
Section; the average pH value of acid rain at Kolkatta is 5.80, Hyderabad 5.73,
Chennai 5.85, Delhi 6.21 and Mumbai 4.80. The situation may even worsen in
future due to increased installation of thermal power plants by NTPC, and
consequent increase in coal consumption. According to one estimate total
236
emission of SO2 in India from fossil fuel burning has increased from 1.38
million tonnes in 1966 to 3.20 million tonnes in 1979, a 21% increase as
compared to corresponding increase of only 8.4% in U.S.A. during the same
period. There is urgent need for proper regular monitoring to provide timely
warnings about acidification of our environment.
Check Your Progress -1
(a) (i) The reactions responsible for (a) formation and (b) depletion of
ozone in the atmosphere are :
(a) ...........................................
(b) ............................................
(ii) Acid rain is due to washing of .................. and ..................... by
rain.
(iii) The primary sources of atmospheric pollutants
(a) SO2, (b) CO and (c) CO2 are
(a) ..............................................
(b) ..............................................
(b) (i) Drilling refining and as a valuable fuel in Automobiles,
.................... throws large amounts of ..................., .................,
....................... and ...................... along with ............... matter.
(ii) .......................... and ...................... of ores to release ................. are
major source of air pollution.
(iii) .................... diffuses in ......................... under ............... radiations.
237
5.7 LET S SOME UP
After going through this unit you must have achieved the objectives
stated at the start of the unit. Let us recall what we have discussed so far :
The atmosphere consists of nitrogen (78.9%) and oxygen (20.94%) by
volume in addition to traces of inertgases CO2, Ozone, ammonia and
hydrogen.
The reactions of formation of ozone in the stratosphere and
photochemical dissociation, and ionisation in the upper part of
atmosphere are important reactions.
The formation of ozone by photochemical reaction can be represented as
follows:
3
Thirdbody
2
nm240
2
OOO
00hVO
The atomic oxygen reacts with O3, OH radical or oxide of nitrogen
leading into formation of oxygen, thus oxygen becomes available in sufficient
amount in
environment
Another important reaction of stratosphere is the photochemical depletion
of ozone by CFC :
2
UV
3
2
UV
22
OCLOClO
ClClCFClCF
Among air pollutants, oxides of sulphur and nitrogen are significant
compounds released from variety of sources. These oxides when washed
away with rain form sulphuric and nitric acids, the main constituents of
acid rain:
223
22
23
ONOONO
ONoNOO
O2OO
238
2322
42
OH
32
HNOHNOOHNO2
SOHSOOSO
Acidic gases like SO2, NO2, H2S etc. when present in the atmosphere,
combine with aldehyde, Ketones and particulate matter present in the
atmosphere resulting in formation of photo chemical smog. Photo
Chemical smog gives a variety of noxious products in the air.
Carbon monoxide is less common than the principal form of atmospheric
carbon, carbon dioxide, but is more dangerous. This highly toxic gas
produced mainly by incomplete combustion of fuel (Coal, Oil, Charcoal,
Wood or gas). Co inhibits respiration in animals by binding irreversibly
to hemoglobin.
Major amount of CO2 is released in the atmosphere from burning of
fossil fuel (Coal, Oil etc.) for domestic cooking, heating etc. and the fuel
consumed in furnaces of power plants, Industries, hot mix plants etc. An
increase in CO2 concentration in atmosphere may result into disastrous
effect of global warming.
Nitrogen Oxides (NOx) are highly reactive gases formed when nitrogen
bearing fuel is burned in a car or a furnace. NO2 is not only give
photochemical smog, but is also responsible for HNO3, a major
component of acid rain.
SO2 is a colourless gas that damages both plants and animals. Once in the
atmosphere, it can be further oxidised to SO3, which reacts with water
vapour or dissolves in water to form H2SO4 an another component of acid
rain.
239
Ozone layer in the stratosphere protects us from the harmful UV
radiations from sun. The depletion of this O3 layer by human activities
may have serious implications and this has become a subject of much
concern over the last few years.
During refining of oil large quantities of natural gas is produced, but in
the absence of proper storing facilities and pipeline network this is being
burnt.
Combustion of petroleum products in automobile engines is also an
important source of our pollution. It throws large amounts of CO, CO2,
Oxides of nitrogen and sulphur along with particulate matter.
A mineral is a naturally occurring inorganic solid with a definite
chemical composition and a specific structure. World industry depends
on about on about 80 minerals and metals.
Geologic materials are extracted by several different techniques,
depending on accessibility of the resource and the content or
concentration of the material sought. All of these methods have
environmental hazards, eg. mine wastes cause considerable
environmental damage, water leaking into mine shafts also dissolves
metals and other toxic material and pollutes ground water or stream.
Metals are extracted from ores by heating or with chemical solvents.
Both processes release large quantities of toxic materials that can be even
more environmentally hazardous than mining.
240
While smelting of sulphide ore creats sulphur-emmission hazard,
leaching of gold ore with alkali cyanide solution causes pollution of dams by
toxic effluent.
Chlorofluorocarbons are a group of synthetic chemicals used in
refrigeration, and are responsible for ozone depletion.
The green house effect i.e. global warming is due to blanketing effects of
man made with CO2 in the atmosphere.
The oxides of sulphur and nitrogen responsible for acid rain, are
produced mainly by combustion of fossil fuels, smelters, power plants,
automobile exhausts, domestic fires etc.
5.8 CHECK YOUR PROGRESS : THE KEY
1. (a) (i) (a) o2OhV
2
3
N
2 OOO 2
(b) 3
N
2 OOO 2
23 OClOOCl
(ii) NO2
SO2 + O
(iii) (a) Oil, gas, coal burning and ore smelting
(b) Automobiles
(c) Fossil fuel burning
(b) (i) petroleum
CO, CO2, NOx
SO2,
Particulate matter.
(ii) Smelting
roasting
metal
(iii) CFC
Stratosphere
UV
241
UNIT-VI ATMOSPHERE
Structure
6.1 Introduction
6.2 Objectives
6.3 Air Pollution Control
6.4 Analytical Methods for Measuring Pollutants.
6.4.1 High Pressure Liquid Chromatography
6.4.2 Optical Particle Counters for Air Quality Monitoring.
6.4.3 Determination of Polycyclic Aromatic Hydrocarbons (PAH)
6.4.4 Polarography
6.4.5 Voltrametry and Chronopotentiometry
6.4.6 Chemiluminescent System for O3 and NOx
6.4.7 Non-Dispersive IR Photometric system for CO.
6.4.8 Conductometric Analyser for SO2
6.5 Continuous Monitoring Instruments
6.5.1 Controlling Particulate Emissions
6.5.2 Monitoring of SO2. Oxides of Nitrogen, CO etc.
6.5.3 Correlation Spectroscopy
6.5.4 Pulsed Fluorescence Technique
6.5.5 Paper Tape Analyser
6.5.6 Chemical Sensing Electrodes
6.5.7 Mercury Substitution UV Absorption Analyser
6.5.8 Laser Techniques
6.5.9 Non-Dispersive UV- Visible Absorption
6.6 Let Us Sum Up
6.7 Check Your Progress : The Key
242
6.1 INTRODUCTION
Due to population explosion and industrialisation excessive deforestation
has made problem of air pollution an eye-sore for whole of the world. Although
there seems no way out to get rid of this menace the following measures,
however may help in controlling air pollution to great extent.
"Dilution is the solution to pollution" was one of the early approaches to
air pollution control. Tall smokestacks were built to send emissions far from the
source, where they became unidentifiable and largely untraceable. But
dispersed and diluted pollutants are now the source of some of our most serious
pollution problems. We are finding that there is no "away" to which we can
throw or waste products.
In this unit we shall discuss various methods of controlling pollution and
monitoring it.
6.2 OBJECTIVES
The main aim of this unit is to discuss various analytical methods for
measuring air pollutants and instruments used for its continuous monitoring.
After going through this unit you would be able to :
describe various analytical methods for measuring air pollutants such as
optical particle counter, pollarography, voltametry, IR photometry,
conductometry, correlation spectroscopy etc.
discuss control of particulate emission and
identify instruments for continues monitoring of air pollutants e.g.
mercury substitution ultra-violet absorption analyser, Laser techniques,
chemical sensing electrodes etc.
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6.3 AIR POLLUTION CONTROL
The most effective strategy for controlling pollution is to minimize
polluting activities. Since most air pollution in the developed world is
associated with transportation and energy production, the most effective
strategy would be conservation : reducing electricity consumption, insulating
homes and offices, and developing better public transportation could all greatly
reduce air pollution in the United States, Canada, and Europe. Alternative
energy sources, such as wind and solar power, produce energy with little or no
pollution, and these and other technologies are becoming economically
competitive. In addition to conservation, pollution can be controlled by
technological innovation.
Particulate removal involves filtering air emissions. Filters trap
particulates in a mesh of cotton cloth, spun glass fibers, or asbestos-cellulose.
Industrial air filters are generally giant bags 10 to 15m. long and 2 to 3 m wide.
Effluent gas is blown through the bag, much like the bag on a vacuum cleaner.
Every few days or weeks, the bags are opened to remove the dust cake.
Electrostatic precipitators are the most common particulate controls in power
plants. Ash particles pick up an electrostatic surface charge as they pass
between large electrodes in the effluent stream. Charged particles then collect
on an oppositely charged collecting plate.
These precipitators consume a large amount of electricity, but
maintenance is relatively simple, and collection efficiency can be as high as 99
percent. The ash collected by both of these techniques is a solid waste (often
hazardous due to the heavy metals and other trace components of coal or other
ash source) and must be buried in landfills or other solid-waste disposal sites.
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Sulfur removal is important because sulfur oxides are among the most
damaging of all air pollutants in terms of human health and ecosystem viability.
Switching from soft coal with a high sulfur content to low-sulfur coal is the
surest way to reduce sulfur emissions. High-sulfur coal is frequently politically
or economically expedient, however. In the United States, Appalachia, a region
of chronic economic depression, produces most high-sulfur coal. In China,
much domestic coal is rich in sulfur. Switching to cleaner oil or gas would
eliminate metal effluents as well as sulfur. Cleaning fuels is an alternative to
switching. Coal can be crushed, washed, and gasified to remove sulfur and
metals before combustion. This improves heat content and firing properties, but
may replace air pollution with solid-waste and water pollution problems;
furthermore, these steps are expensive.
Sulfur can also be removed to yield a usable product instead of simply a
waste disposal problem. Elemental sulfur, sulfuric acid, or ammonium sulfate
can all be produced using catalytic converters to oxidize or reduce sulfur.
markets have to be reasonably close and fly ash contamination must be reduced
as much as possible for this procedure to be economically feasible.
Nitrogen oxides (NOx) can be reduced in both internal combustion
engines and industrial boilers by as much as 50 percent by carefully controlling
the flow of air and fuel. Staged burners, for example, control burning
temperatures and oxygen flow to prevent formation of NOx. The catalytic
converter on your car uses platinum-palladium and rhodium catalysts to remove
up to 90 percent of NOx, hydrocarbons, and carbon monoxide at the same time.
Hydrocarbon controls mainly involve complete combustion or
controlling evaporation. Hydrocarbons and volatile organic compounds are
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produced by incomplete combustion of fuels or by solvent evaporation from
chemical factories, paints, dry cleaning, plastic manufacturing, printing, and
other industrial processes. Closed systems that prevent escape of fugitive gases
can reduce many of these emissions. In automobiles, for instance, positive
crankcase ventilation (PCV) systems collect oil that escapes from around the
pistons and unburned fuel and channels them back to the engine for
combustion. Controls on fugitive losses from industrial valves, pipes, and
storage tanks can have a significant impact on air quality. Afterburners are often
the best method for destroying volatile organic chemicals in industrial exhaust
stacks.
Thus for control of air pollution following measures may be helpful :
1. Use of soot free fuel should be encouraged. This may involve use of
electric appliances for cooking purposes as far as possible.
2. Filters and after-burner type appliances should be used in all automobiles
to check emission of soot.
3. To reduce pollution due to combustion of diesel anti-tibs should be
mixed with it while lead and sulphur free petrol should be used in all
automobiles.
4. Structures of internal combustion engines should be modified so that
there is complete combustion of fuel.
5. The vehicles in usage should be maintained in their best condition, so
that there is least pollution by them. The automobiles unfit according to
the pollution parameters should not be allowed to run on roads.
6. The rail engines running by coal should be completely banned.
7. The chimney of different industries and chemical factories should have
sufficient height and should be fitted with suitable filters and electric
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precipitants.
8. As such the technology liberating less or least pollution should be used in
the industries. The designs of the factories and the production methods
should be modified in such a manner that there is check on generation of
pollutants.
9. There should be strict monitoring of all anti pollution measurements.
10. There should be excessive plantation of trees along road side, near
factories and in open places.
11. There should be complete check on atomic tests and atomic power plants
should be free from leakage of radiations.
12. The decaying animals and other substances should be immediately
disposed off.
13. The dirty nallah's should be regularly cleaned.
14. As far as possible electric cremation should be encouraged.
15. Use of fossil fuels should be decreased to minimum and use of solar
energy should be encouraged.
16. Use of fertilizers, pesticides and insecticides should be proper. Excess
use of these chemicals should be avoided.
However the effective check will be through excessive plantation of
trees. Just abiding by the teachings of our Rishis and Philosophers, and
adopting Vedic culture of nature-love we can reduce this menace of pollution to
sufficient extent. Further, reaching these goals will require substantial lifestyle
changes. Aerosol hair sprays, deodorants, charcoal lighter fluid, gasoline-
powered lawnmowers, and drive through burger stands could be banned. More
than 3,000 consumer products, including automotive polishes, spot removers,
herbicides, lubricants, and floor-wax strippers, would need to meet new
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pollution limits. Paints and cleaning solutions would have to contain fewer
volatile solvents.
6.4 ANALYTICAL METHODS FOR MEASURING AIR POLLUTANTS
For the separation of various pollutants of air, gas chromatography, gas-
liquid chromatography or high presence liquid chromatography are used. Once
the pollutants are separated, they can be identified by the techniques of nuclear
magnetic resonance, i.r., flame photometry coupled with GC, atomic absorption
spectroscopy, polarography, voltammetry, tensammetry, fluorimetry, non-
dispersive-UV-visible absorption technique, coulometry, correlation
spectroscopy, Laser techniques, mercury substitution ultraviolet absorption
analyser, paper tape analyser, chemical sensing electrodes, conductometric
analyser, non-dispersive infrared photometric system, pulsed fluorescence
technique, chemiluminescent system, chromopotentiometry etc. The
instruments or techniques along with species to be separated, identified and
estimated are given in Table 6.1
Table :6.1 Instruments or techniques used for the detection and estimation
of air pollutants.
S.No. Instruments Species
1. Non-dispersive-UV-visible absorption
technique
Organic compounds
2. Fluorimetry Compounds in cigarette smoke,
automobile exhaust, heavy air pollutants
and trace nitrates.
3. Coulometry Petroleum Products, minerals etc.
4. High Pressure liquid chromatography For separation of toxic compounds.
Pesticides, Polyaromatic hydrocarbons
(PAH) etc.
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S.No. Instruments Species
5. Correlation spectroscopy NOx, SOx
6. Laser techniques Air Pollutants
7. Mercury substitution ultraviolet absorption
analyser
SO2
8. Paper Tape analyser SO2, NOx, CO
9. Chemical sensing electrodes SO2, NOx, CO
10. Condctometric analyser SO2
11. Non-dispersive Infra red Photometric
System
CO
12. Pulsed fluorescence technique SO2, H2S
13. Chemiluminescent System O3, NOx
14. Chronopotentiometry Air Pollutants
15. Tensammetry V, Cr, W, Ni, Cobalt etc.
16. Voltammetry Cr, Ni, Co, Zn, Cd etc.
17. Polarography Cr, Ni, Cd, Al, Ba, Sr, As, Sb
18. Atomic absorption spectroscopy Zn, Cd, As, Fe, Ni, Co, Zr. etc.
19. Flame Photometry coupled with GC Metals in Environment.
6.4.1 High Pressure liquid chromatography (HPLC) :
This is a type of chromatography through which rapid and efficient
separations can be made 550 psi is sufficient to handle most separations.
Through this technique, we can easily detect the nanogram quantities of phenol
in order to monitor the quality of water. Analysis of trace organic water is
another application area of HPLC. the technique is also employed to detect
toxic side effect due to decomposition of medicines.
Aflatoxins are extremely toxic materials sometimes found on peanuts,
wheat, corn, and other grain crops. They are produced by a fungus on the grain
and are considered to be dangerous to human health when their concentration
exceeds 20 ppb in any food product. It is extremely important to be able to
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monitor trace amounts of aflatoxins in foods. HPLC give a rapid separation of
aflatoxin from peanut butter. The peak for aflatoxin B-1 represents 12 ng of that
aflatoxin.
Analysis of trace organic matter is another application area of HPLC.
Now when sample is introduced, it immediately gives chromatograms
and from them the concentration of unknown sample is determined.
6.4.2 Optical particle counters for air quality monitoring :
The Air Quality in a wide range of environments has been a matter of
concern for many years. Gaseous and particulate emissions into the atmosphere
have increased as the rate of industrial and agricultural activities, along with
land use modifications, has risen. Aside from the obvious problem of
degradation of atmospheric visibility, there is concern over both short and long-
term deleterious health effects due to contaminants released into the atmosphere
from stationary and mobile sources. In order to maintain suitable control over
the quality of air, pollutant emission rate information, control device
effectiveness, and ambient air all should be monitored.
Instruments and techniques are now sufficiently developed for use with
most gaseous pollutants. However, advanced particulate pollutant measurement
techniques are still being developed for practical use. For many years,
requirements for defining the particle quantity in the air were based upon air
sample monitoring techniques that produced data on particle mass
measurements. The general term for mass loading in ambient air is "total
suspended particulate" (TSP). TSP levels usually are determined by weighing a
filter before and after a relatively large (TSP). TSP levels usually are
determined by weighing a filter before and after a relatively large volume of
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ambient air has passed through. Stationary source emission rates are stated as
grain loadings, or grains of dust per cubic foot of air sampled from the emission
source. Again, dust collector weight before and after air sample passage is the
means of measurement.
For ambient air samples the air passageway through the filter housing
was defined so as to discriminate against particles larger than approximately 20
m aerodynamic diameter. By sampling at a rate of approximately 1.5 m3/min.,
the mass loading even in relatively clean ambient air can be defined if the
sample acquisition time is long enough.
Optical particle countries can provide detailed particle size and
concentration data in real time.
Particle concentrations can be measured with good accuracy from
essentially zero to several thousand particles per cubic centimeter. Particles in
sizes from tenths of micrometers to nearly a hundred micrometers can be
defined with good accuracy. Any single measurement usually will cover
approximately one and one half decades. The data that are produced directly are
in the format of number of particles (pulse)/unit time in as many particle size
ranges as desired and justified by the sizing revolution of the particular particle
counter. Data processing can produce differential or cumulative number or
volume distributions and concentrations. Averaging time, depending upon
adequate particle concentration, can approach a fraction of a second, thus
permitting real-time data production and transmission from remote locations.
In short, for comparison with other measurement a basis methods is
needed. Next, optical particle counter packaging and reliability must be
improved to permit operation in environments more hostile than the normal
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laboratory and instrument shelter. Finally, a standard data format and data
procurement protocol must be developed and accepted.
Both ground based and airborne optical particle counters have been used
to observe concentration and particles size distribution of airborne particles
both in ambient air and in emission source plumes. The University of
Minnesota aerosol analyzing system is a mobile ground-based assembly of
instruments including optical particle counters for measurement of atmospheric
parameters. Research studies have been performed with airborne aerosol
sampling systems that have included optical particle counters. For example,
measurement and analysis of airborne plumes from power plants and
measurements of cloud and fog nuclei and particles are routine, it has been
found that optical counters are particularly well-suited for this type of work.
Suitable shock mounting must be used, however, since vibration levels over
approximately 1g will cause erroneous information to be developed by the
optical and electronic systems. It is also necessary that the instruments be
protected from extremes of temperature. The counters operate best in the range
of 0º to 50ºC. With these precautions testing can be carried out quite
satisfactorily.
A second type of application is the measurement of control device
performance. Operation of cold-side electrostatic precipitators for power plant
use has been observed with an optical particle counter by organizations such as
the Southern Research Institute. However, the particle concentration must not
exceed the limits beyond which more than one particle will be present in the
sensing volume at any one time. For practical purposes, these limits are in the
area of several thousand particles per cubic centimeter of sampled air or
approximately one milligram per cubic meter of air sample. For clean side
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operation these limits are satisfactory. However, if the control device has any
failure or problems, then the particle concentration limit will be overwhelmed
and erroneous data will be produced. Furthermore, the sample-gas temperature
must be less than 150ºC so as to avoid degradation of system performance. To
date, no commercially available optical particle counter has been routinely used
for higher temperatures. Where the control device is a high-efficiency
particulate air filter then optical particle counter is the only means of ensuring
adequate cleanliness of the air flows being monitored.
6.4.3 Determination of Polycyclic aromatic hydrocarbons :
Detection of PAH in the organic fraction of the particulate matter can be
done by any of the following techniques : (i) Column chromatography (ii) Thin-
Layer chromatography (TLC) or (iii) paper chromatography.
Out of these three, the TLC technique is the most convenient and widely
accepted. The various instrumental techniques that have been adopted by
different authors for the analysis of PAH in the enriched fraction are : (i) UV-
visible spectrometry, (ii) Fluorescence spectrometry (iii) Gas-Liquid
chromatography (GLC) and (iv) a combined GLC and Mass spectrometry GLC
has been found to be very suitable and hence largely used in the case of routine
analysis of these compounds, because of its accuracy, ease is handling, less time
requirement etc. The combined GLC and Mass spectrometry is also very
suitable and accurate means for this analysis but it requires special laboratory
facility.
The samples of suspended particulate matter are collected 24 hourly by a
high volume air sampler at a rate of 1-2 M3/Min. during winter months (Nov.-
Mar.), from different regions in a coal mining area where intensive coal mining
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and coal processing activities were prevalent and also from the area where no
such activities were present. The dust so collected is used as the basic material
for extraction of 'organic fraction' and its enrichment for the PAH by using TLC
technique with thin-layer coating material Silica gel G.
Gas-Liquid Chromatography (GLC) :
The cyclohexane extract of the enriched PAH obtained by TLC operation
with a solvent mixture of Cyclohexane : Benzene in the ratio of 1:1.5 ml. by
bubbling nitrogen gas through it under pressure. The solution, thus obtained are
taken in a Pye series 104 chromatograph (PYE NICAM) for analysis. The
analysis is carried out under the standard conditions. Chromatograms of the
individual compounds and their mixture are obtained with different
concentrations for use as standards for quantitative work. The peaks in the
chromatograms obtained with the unknown samples were identified by
comparing the retention times with those of the standards and then quantified
by comparing the integrated peak areas (Fig. 6.1)
Fig. 6.1 Typical Standard GLC curve of Benzo (a) Pyrene.
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6.4.4 Polarography :
Introduction : Polarography is a technique concerned with electrode
reactions at the indicator or microelectrode, i.e. with reactions involving
transfer of electrons between the electrode and the components of the solutions.
The components are called reductants when they can lose electrons and
oxidants when they can accept electrons. The electrode is cathode when
reduction takes place at its surface and an anode when oxidation takes place at
its surface.
Polarography deals with the relationship among current, electrode
potential and solution composition in a cell of which one electrode is a dropping
mercury electrode (cathode) and other is a pool of mercury (anode). The current
voltage curves can be interpreted to give both qualitative and quantitative
composition of the solution. As the curve obtained with the instrument is a
graphical representation of the polarisation of dropping electrode, the apparatus
is called a polarograph. A polarogram is a plot of the current flowing through a
polarographic cell against the potential of dropping electrode.
Polarographic methods are those methods of analysis in which advantage
is taken of polarization processes at mercury or other cathode. In 1922
Heyrovsky the inventor of polarography suggested these methods of analysis
for qualitative and quantitative determination of the substances present in
environment.
The metallic air pollutants of minute concentrations can easily be
detected and estimated by this techniques.
The current-voltage curve known as polarogram thus will obtained have
the limiting current, which is given by the height of the wave, is proportional to
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the concentration of electroactive species. The potential at the centre of the
rising part of the wave, referred as half wave potential is characteristic of
species being discharged and is independent of its concentration. The half wave
potential is used to identify the particular species.
Thus from polarogram, the relative amounts of various cations in the
mixture can be calculated.
The great advantage of polarographc method of analysis is that a mixture
consisting of a large number of reducible substances can be estimated in one
solution and in a single operation. thus if a solution containing Cu++
, Pb++
, Cd++
,
Cd++
, Zn++
, Mn++
and Ba++
subjected to polarographic analysis, a composite
polarogram is obtained for qualitative and quantitative determinations.
(1) Qualitative determinations : As half wave potential is independent
of the concentration of the electroactive species in solution hence can be used
for identification of the unknown species. The half wave potentials are
compared with the standard values and thus identification is made.
(2) Qualitative determinations : The polarographic method is employed
to determine concentrations in the range of 10-4
to 10-2
M. Sometimes the
concentration as low as 10-6
M can be detected. Since concentration is
proportional to diffusion current, the main problem is to measure this current
very accurately. There are various methods to obtain concentration values from
diffusion currents. Inorganic species and organic compounds can be
quantitatively determined.
Wave Height Concentration Plots (a calibration curve) prepared by
measuring the diffusion currents of standard solutions. The curve is a straight
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line. The diffusion current of an unknown solution is measured and
concentration of the solution can then be read from the calibrated graph (Fig.
6.2)
Fig. 6.2 Wave height- concentration plot
6.4.5 Voltammetry and chronopotentiometry :
Voltammetry : The voltametry involves an indicator electrode and a
reference electrode. A potential difference is created between these two
electrodes and the current flows because of electro-chemical reactions. Here the
current versus voltage curves are recorded when a gradually changing voltage is
applied to a cell. Generally the voltage is increased linearly with time. Such
curves are called voltammograms.
The concentration of unknown metals in solution is determined by
knowing the diffusion current as in case of polarography.
Tensammetry : In this technique, the capacity current is derived from
the process of adsorption/desorption or the oscillatory movements of dipoles
and the ions at the electrode surfaces, the technique is known as tensammetry.
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This technique is used in the detection of V., Cr, W etc. metals in solution from
the environment.
6.4.6 A Chemiluminescent System for O3 And NOx :
It is sensitive and specific system for determining ambient levels of O3
and is based on chemiluminescent reaction between O3 and disc coated with
Rhodamin B-absorbed on silica gel. The total resultant emission is detected by
phototube. The resulting current is directly related to the mass of O3 glowing
over the dye in unit time. Silicon resin is combine with Rhodamin B to avoid
the effect of moisture and extends the disc life and permits continuous
monitoring of O3. It can be used in the Range 10 ppb to 3.5 ppm.
The technique has also been used successfully for the detection of nitric
oxides and NOx. The chemiluminescent reaction of nitric oxide and ozone is
used as given here.
NO + O3 = NO2* + O2
NO2* = NO2 + hv – Detected by photomultiplier tube.
A pulsed ozone generator gives directly AC singal (proportional to NO
concentration) which can be easily amplified. This is unaffected by interference
from SO2, H2O, CO, CO2 and HC and so the technique can be used in presence
of SO2 and H2O.
6.4.7 Non-dispersive infra red photometric system for CO :
Carbon monoxide as an air contaminant is uniquely suited to this method
of analysis, as its absorption characteristics and typical concentration make
possible direct sampling.
A typical analyser consists of a sampling system-two infra red sources,
sample and references gas cells, detector, control unit and amplifier along with
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recorder. The reference cell contains a non-infra red absorbing gas, while the
sample cell is continuously flushed with the sample atmosphere. The detector
system consists of a 2 compartment gas cell (both filled with carbon monoxide
under pressure) separated by a diaphragm whose movement causes a change of
electrical capacitance in an external circuit, and ultimately gives an amplified
electrical signal which is detected by the detector.
In the analysis part, the reference and sample cell is exposed to the
infrared sources. At the frequency imposed by the chopper, a constant amount
of infrared energy passed through the reference cell to the compartment of the
detector cell, while a varying amount of infrared energy, invesersely
proportional to the carbon monoxide concentration in the sample cell, reaches
the other detector cell compartment. These unequal amounts of residual infrared
energy reaching the two compartments of the detector cell cause unequal
expansion of the detector gas. This unequal expansion causes variation in the
detector cell diaphragm movement resulting in the electrical signal described
above. It is a simple technique used for the detection of CO directly by the
digital instrument.
6.5 CONDUCTOMETRIC ANALYSER FOR SO2
This technique measures the conductance of an absorbing solution into
which SO2 from the sample has been dissolved by contact of the solution with
the sample. As we know that an increase in conductance is caused by ions
formed as SO2 combines with the solution. The two kinds of solutions used are
deionised or distilled water and dilute acidified hydrogen peroxide solution. The
observed increase in the conductivity is proportional to the SO2 concentration in
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the air if there are no interferences. So with the help of digital instrument, we
can read directly the SO2 concentration.
6.5 CONTINUOUS MONITORING INSTRUMENTS
The major objective of any air quality management strategy is to achieve
pollutant levels in a designated area that do not constitute a threat to human
health nor to animal life, vegetation, monuments, or property. The availability
and cost of technology that will reduce emissions into the atmosphere is a
crucial determinant in the degree of success that can be expected.
Any strategy to manage air quality has to be based on a knowledge of the
current situation, and preferably a time series showing the trends in the ambient
levels of specific pollutants in the air. The setting up of an adequate system for
monitoring is thus an early necessary step in any control scheme. Even though
many countries in the region had not yet established ambient air quality
standards, they already had operational systems for monitoring specific
pollutants in a number of cities.
In addition to the measurements to monitor air quality at a particular
time, the trends in pollutant levels need to be known, so that the effectiveness of
pollution control measures can be determined. From data it can be seen that the
Japanese have had considerable success in reducing sulfur dioxide levels in the
atmosphere during the last 15 years, but that the levels of nitrogen oxide
actually increased during the 1970s.
For the surveillance of air quality, it is necessary to establish a national
monitoring network and data-bases in order to determine the status of air
quality and compliance with standards, as well as to establish zones that depend
upon pollution levels. Ambient air quality and meterological monitoring should
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be carried out to achieve proper enforcement to control strategies, and also for
the feedback necessary to properly locate industries.
(i) It is also necessary to establish and adopt standard methods, statistical
techniques, and instrument types for measurement and monitoring of
air pollutants.
(ii) Emphasis should be placed on the development of low cost, easy to
operate, and reliable instruments for measurements of pollutants in
different situations including occupational, agricultural and domestic
settings, stack emissions and ambient locations.
(iii) Attempts should be made to gradually establish pollutant monitoring
stations that are appropriate. The highly developed areas and
industrialized areas may need monitoring, using automatic equipment,
for many pollutants.
(iv) Coordinated, national and perhaps international crosschecking should
be undertaken to ensure accuracy in air quality and emissions
monitoring techniques and equipment.
(v) To achieve quality control in the operation and application of
monitoring instruments :
(a) Training programs should be expanded or established to
provide sufficient personnel;
(b) Propagation of knowledge and technologies by exchange
programs and on the job training should be promoted.
(vi) In general, continuous emission monitoring will not be required
except in particularly critical areas. In such locations it may also be
desirable to establish a real time monitoring program, to provide
warning of oncoming serious air pollution episodes.
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The technology for controlling emissions from coal-fired power plants is
quite important, since these are frequently the largest industrial sources of
emission for particulates, sulfur oxides and nitrogen oxides. While the
transportation system is frequently the largest contributor to emissions of
carbon monoxide, and hydrocarbons, as well as a major contributor to nitrogen
oxide emissions.
6.5.1 Controlling Particulate Emissions : There was a general consensus that
particulate emissions could be substantially controlled through the use of
electrostatic precipitators, however, routine monitoring can be carried out in
stationary or mobile optical particle counters. An air quality monitoring
program can be designed to provide data on size and number concentration of
airborne particles for general record purposes and to provide information on
particle loading in the atmposphere so as to permit rapid correlations with
visibility. It can be used to link ambient air quality with source effects if
correlations with sample location and wind directions are made; it is possible to
identify source performance. These data are obtained on number and size of
particles in urban, rural, and industrial environments. Another example of
application of optical particle counters for routine monitoring purposes can also
be prepared. The relationship between particle concentrations inside and outside
a building and the typical diurnal variations in particle concentration seen in
urban environments is demonstrated.
In conclusion, it can be seen that optical particle counters, which are
being used for air quality monitoring, will find increasing areas of application.
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6.5.2 Monitoring of SO2, Oxides of nitrogen, CO etc. :
Monitoring of SO2, H2S, CO and Oxides of nitrogen is done using
various instruments such as correlation spectroscope, pulsed fluorescence
recorder, chemical sensing electrodes or mercury substitution UV absorption
analyser. Remote monitoring of air pollutants is done using laser photon-
counters, while for the monitoring of various oxidants presence in the
atmosphere non dispersive UV-visible absorption recorder is used.
6.5.3 Correlation Spectroscopy
The technique is generally used for the monitoring NOx, and SO2 from
air. Is thus technique, we use either skylight or artificial light for measurement
of SO2 or NOx. Accorrelation spectrometer for remote sensing collects skylight
by a telescope which is then collimated and dispersed by a prism or grating and
focussed into a correlation mask. The patterns of the mask are formed by
depositing aluminium on glass and then removing slits of aluminium
corresponding to absorption lines of the incident spectrum, then the
photomultiplier tube will observe a minimum when the mask is shifted off. The
difference in the light intensities seen by the photomultiplier is a measure of the
SO3 or NO2 concentration between the light source and the instrument.
Artificial source like Quartz Iodine or Zenon lamp with a defined distance is
used. This technique is used in open labs for the analysis of air samples.
6.5.4 Pulsed fluorescence technique :
This is a technique used for the monitoring of SO2 and H2S from air
samples. A given gas sample is placed to a source of pulsed ultraviolet (UV)
through a monochromatic filter. The SO2 molecules energised by the high
intensity pulsed light source emit an SO2 specific illumination which through a
narrow band filter impinges upon the photomultiplier tube. The emitted light is
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linearly proportional to concentration of SO2 molecules in the sample. The
signal is amplified and recorded by the recorder. Now-a-days digital pulsed
fluorescence technique gives the direct results.
The technique can also be used successfully for H2S monitoring. In this,
the sample is first scrubbed to remove the SO2 content and then passed through
a converter which converts H2S molecules into SO2 which is measured directly
by the digital arrangement.
6.5.5 Paper tape analyser :
This is a technique used for the monitoring of SO2, Nox, or CO based a
chemical reaction which takes place on test paper which has been impregnated
with suitable chemicals to obtain specificity for the concern pollutant. The
result of this reaction is coloured stain which is monitored photo-electrically.
The test paper is in form of a continuous motor driven reel of paper tape which
allows continuous monitoring. This is an easy technique and is used in mobile
label for monitoring gas parameters.
6.5.6 Chemical sensing electrodes :
The technique is used for monitoring of SO2, NOx and CO. Here a
known volume of air is sampled with a pH buffered absorbing solution. The
solution containing the dissolved gas pollutant (SO2 or NOx) then passed to an
ion selective electrode where the ion concentration proportional to the pollutant
concentration is measured potentiometrically.
Electro-chemical cell analysers avoid the use of wet chemistry of
traditional conductometric colorimetric and amperometric analysers by using
sealed modules-the electro-chemical cells inside which all chemical reactions
occur. The gas pollutant to be detected diffuses through a semi-permeable
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membrane into the cell. The rate of diffusion and hence cell current is
proportional to the pollutant concentration and hence the concentration on an
known species is measured within no time.
6.5.7 A mercury substitution ultraviolet absorption analyser :
The principle of UV-Fluorescence analyser for SO2 monitoring is based
on the measurement of intensity of the fluorescence in the ultraviolet of SO2
which is excited by Zn 213.8nm or Cd 228.8 nm line.
This is based on the generation mercury vapor from mercuric oxide after
reacting with CO. The generated vapour is detected by UV absorption-Hg
analyser.
6.5.8 Laser techniques :
These techniques are mainly used for the remote monitoring of air
pollutants. Raman scattering and resonance scattering have a great promise for
monitoring air pollutants.
Here sample is 'excited' by an intense monochromatic light source such
as laser and frequency is analysed with a grating monochromator. The detection
system uses a highly sensitive photon-counting technique.
6.5.9 Non-dispersive-UV-visible absorption :
This technique is mainly utilized for the monitoring of various oxidants
present in environment. The ultraviolet region is important for qualitative and
quantitative determination of organic compounds.
The common terms are chromophore, auxochrome, bathochromic effect
and hypsochromic effect.
265
Identification of compounds can be done by comparing absorption
spectrum with known compounds. A curve is plotted between wavelengths ( )
and degree of absorption ( ).
The quantitative analysis of compounds is based on Beer's Law:
clI
IlogA
t
O
where = extinction coefficient. It is independent of concentration of
absorbing species.
c = concentration and
l = length of the cell used in UV spectrophotometer.
In the determination of concentration of an unknown compound,
wavelength of maximum absorption for compound is selected. Then optical
densities are measured for some known compounds. Now the optical density is
plotted against concentration of solute over a range of concentrations. A straight
line is obtained and form this graph, the concentration of unknown is evaluated.
Check Your Progress
Notes : 1. Write your answer in the space given below
2. Compare your answers with these given at the end of the
unit.
(i) The instruments and techniques used for detection and estimations of
following air pollutants are
Pollutants Technique
(a) Oxides of N, S and C ..................................................
(b) Poly aromatic Hydrocarbon .................................................
(c) Metals ..................................................
(ii) Particle size and concentration data can be obtain by .........................
(iii) Monitoring of SO2 and NOx is generally done by using
266
5.10 LET US SOME UP
After going through this unit you must have achieved the objectives
stated at the start of the unit. Let us recall what we have discussed so far :
Dilution is the solution to pollution was one of the early approaches to air
pollution control. However, the most effective strategy for controlling
pollution is to minimize pollution activities for control of air pollution the
measures to be taken are as follows : 1 to 16 (from page 5 and 6)
For the separation of various pollutants of air, gas chromatography, gas
liquid chromatography, gas liquid chromatography or high presence
chromatography are used. Once the pollutants are separated they can be
identified by the techniques of nmr, ir, flame photometry coupled with
GC, atomic absorption spectroscopy, polarography, voltametry,
tensammetry, fluorimetry, non dispersive- UV-visible absorption
technique, coulometry, correlation spectroscopy, laser techniques,
mercury substitution. UV-absorption analyser, paper tape analyser,
chemical sensing electrodes, conductometric analyser, non dispersive
infrared photometric system, pulsed florescence technique,
chemiluminescent system, chromopotentiometry etc. The following
instruments or techniques for their identification and estimations are
used:
While for organic pollutants HPLC is used, particulate matter is
monitored using optical particle counters. Similarly for oxides of
nitrogen, sulphur and carbon chemical sensing electrodes (or paper tape
267
analysers) are used, the contents of metals are estimated using atomic
absorption spectroscopy (and polarography or voltametry).
The monitoring of particulate matter is done using optical particle
counters and that of oxides of nitrogen, sulphur and carbon is done by
using chemical sensing electrodes or the UV-fluorescence analyser.
The monitoring of various oxidants present in the environment is done by
using non dispersive- UV-Visible absorption and the remote monitoring
of our pollutants is done using laser – techniques.
6.7 CHECK YOUR PROGRESS : THE KEY
(i) (a) Chemical Sensing electrodes
(b) HPLC
(c) Atomic absorption spectroscopy
(ii) Optical particle counters
(iii) Correlation spectroscope.
268
M.SC. (FINAL) CHEMISTRY
PAPER –III : ENVIRONMENTAL CHEMISTRY
BLOCK-III
Unit-7 : Industrial Pollution
Unit-8 : Environmental Toxicology
Author – Dr. Purushottam B. Chakrawarti
Dr. Aruna Chakrawarti
Editor – Dr. Anuradha Mishra
269
BLOCK SUMMARY
National development and insutrialisation go hand in hand. However, the
indiscriminate and mushrooming growth of industries in all around residential
colonies has complicated the scenario of environmental pollution. Unit-III
describes the sources of environmental pollution from different industries. It
also discusses methods of disposal of wastes and their management.
Dangerous chemical agents are divided into two broad categories;
hazardous and toxic. Unit-III discusses different types of toxic substances. It
also describes chemical solution to the environmental problems bio-
degradability and principles of decomposition.
Better industrial processes are those which use such technology which
liberate least pollution and have design of the production methods which
generate least pollutants. All the end of the unit are discussed some more
important chemical industrial hazards viz. Bhopal Gas Tragedy, Chernobyl
disaster, Three mile Island accident and Minamata tragedy.
270
UNIT-VII INDUSTRIAL POLLUTION
Structure
7.1 Introduction
7.2 Objectives
7.3 Cement
7.4 Sugar
7.5 Distillery
7.6 Drugs
7.7 Paper and Pulp
7.8 Thermal Power Plants
7.9 Metallurgy
7.10 Polymers
7.11 Noise
7.12 Radioactive nuclide
7.13 Disposal of Waste and their Management.
7.14 Let Us Sum Up
7.15 Check Your Progress : The Key
271
7.1 INTRODUCTION
The indiscriminate and mushrooming growth of industries in all around
residential colonies complicated the scenario. The smoke from chimneys and
gases from burning of fossil fuel started polluting our environment, resulting in
menace like 'acid-rain', 'green house effect', smog formation and 'ozone-hole'.
Similarly disposal of sewage and effluents from industrial factories started
polluting surface and ground water. Water pollution affects both terrestrial and
aquatic ecosystems, and causing incidence of life threatening infectious
diseases. Thus pollutants accumulate slowly and circulate through the
atmosphere, hydrosphere and lithosphere and affects biotic communities as
well. They also change the climate usually and result in 'alnino effect'.
As a matter of fact, industrialisation has tremendously increased use of
fossil fuel for generating energy. Industries manufacturing fertilizers cement,
acids, steel, petrochemical etc. all add tons of pollutants to the atmosphere. The
major air pollutants from industries are particulate matter, vapours, fumes, soot
etc. along with large number of gases such as hydrogen sulphide, sulphur
dioxides, carbon oxides, arsenic, fluorides, dust, lead, asbestos, hydrocarbons
etc. Primary pollutants are released as smokestacks in a harmful form.
Secondary pollutants, by contrast, become hazardous after reaction in the
air. Photochemical oxidants (compounds formed with solar energy) and
atmospheric acids are probably the most important secondary pollutants.
Fugitive emissions are those that do not go through a smokestack.
Conventional or "criteria" pollutants are group of seven major pollutants
(sulfur dioxide, carbon monoxide, particulates, hydrocarbons, nitrogen oxides,
photochemical oxidants, and lead) that contribute the largest volume of air-
272
quality degradation and also are considered the most serious threat of all air
pollutants to human health and welfare.
The EPA also monitors unconventional pollutants, compounds that are
produced in less volume than conventional pollutants but that are especially
toxic or hazardous. Among these are asbestos, benzene, byryllium, mercury,
polychlorinated biphenyls (PCBs), and vinyl chloride. Most of these materials
have no natural source in the environment (to any great extent) and are,
therefore, only anthropogenic in origin.
Aesthetic degradation is another important form of pollution. Noise,
odors, and light pollution may not be life threatening, but they reduce the
quality of our lives.
7.2 OBJECTIVES
The main aim of this unit is to discuss pollution due to industrial
effluents. After going through this unit you will be able to :
describe sources of environmental pollution from different industries,
discuss effects of different effluents obtained from industries, and
describe methods of 'disposal of waste and its management.
7.3 CEMENT
Cement is one of the most important building materials at the present
time. Cement, is a complex aluminium silicate and is made by sintering lime-
stone and clay at high temperature and grinding the product to a fine powder.
The raw materials, limestone and clay, are first crushed separately in a
suitable machine. They are then mixed together in the required protions and
273
ground together finely. This grinding is done either by the wet process or by the
dry process. In the dry process much less fuel is needed in burning the materials
subsequently in a rotary Kiln. In the wet process, the clay is first washed with
water in wash mill to remove the foreign material and then lime is added and
the two ingredients are finely ground and homogenised.
Thus the main pollutants released from cement industry are carbon
dioxide (due to decomposition of lime stone into lime) and the particulate
matter. However, washings (in the wet process) of clay also releases many
pollutants in varying quantities.
An increase in CO2 has considerable potential for changing the earth's
energy balance. Carbon dioxide is partially responsible for the 'Greenhouse
Effect' of the atmosphere as it is transparent to solar radiation but quite opaque
to infrared radiation. Earth's radiation is concentrated in the infrared band from
7 to 20 micrometers. Carbon dioxide is absorbent of radiant energy in the
wavelengths in which the earth radiates heat away from the surface, and it is in
the 15 to 20 micrometer range where most of the absorption takes place. If CO2
absorbs earth radiation and the amount of CO2 in the atmosphere is increasing,
then more earth energy should be absorbed by the atmosphere. This absorption
and reradiation back to the surface shift the energy balance toward increased
storage of energy, hence rasing the temperature of the earth's surface and
atmosphere.
Cement factories emit plenty of dust, which is potential health hazard.
The crushers and hot mix plants create the menace. The SPM (Suspended
particulate matter) levels in such areas are five times the industrial safety limits.
Consequences of breathing this dirty air increased probability of heart attacks,
respiratory diseases and lung cancer. Of course the intensity and duration of
274
exposure, as well as age and general health are extremely important. The
persons are much more likely to beat risk if they are young, very old or already
suffering from some respiratory or cardio-vascular disease. Bronchitis and
emphysema are. common chronic conditions resulting from air pollution. Fine
suspended particulate matters penetrate deep into the lungs, causing irritation,
scarring and even tumor growth. Heart stress results from impaired lung
functions.
7.4 SUGAR
The sugar industry in Indian is playing an important role in the economic
development of the country. The industry is of a seasonal nature and operates
for about 200 days in a year. The effluents are discharged during manufacture
of sugar. They contain high polluted contents. As generally the sugar mills are
in rural areas where effluents pollute small rivers and give foul smell in the
nearly places of the mills. The following are the characteristics of the effluents
(Table 7.1)
Table 7.1 Characteristics of Cane Sugar Industry
Characteristics Analysis
1. Total solid 870 to 3500 mg/l
2. Suspended solid 220 to 800 mg/l
3. Volatile solid 400 to 2200 mg/l
4. pH 4.6 to 7.1
5. B.O.D. (5 days at 20ºC) 300 to 2000 mg/l
6. C.O.D. 500 to 4380 mg/l
7. Total nitrogen 10 to 40 mg/l
8. Colour Light brown (not specified)
275
Characteristics Analysis
9. Sugar and other carbohydrates Depend on mill (not specified)
10. Sulphur Depends on mill (not specified)
*I.S. 4903 (1968)
As the effluent contains a high degree of organic pollution hence if
effluent stagnates in an area for a few hours, biological action starts and septic
condition gives H2S gas imparting black colour to the effluent. Moreover the
oxygen is also exhausted (high value of BOD) giving death of fish and other
aquatic life. The water is extremely harmful to the plants.
To get rid of this pollution, the effluent should be treated with trickling
filter.
7.5 DISTILLERY
The fermentation reaction of carbohydrates in alcohol industries is the
source of release of carbon monoxide and carbon dioxide We know carbon
monoxide is a toxic gas, while carbon di oxide, which is the major release, is
responsible for green house effect.
In the fermentation of molasses besides alcohol glycerine, succinic, acid,
acetaldehyde, alkyl alcohol, acetic acid and fuse oil are also obtained. Thus they
also become source of air pollution. Amongst food processing industries
breweries and distilleries. These industries discharge wastes containing sugar
and nitrogen. These wastes have high BOD and are responsible for water
pollution.
In India, annual distillery discharge figures approximate between 100-
110 million litres and this can afford to produce 10-250 tonnes nitrogen, 1000-
276
2500 tonnes potash and 50-100 tonnes phosphorus, besides aminoacids, nitrates
and microorganisms like Phytoplankton and Zoo plankton.
Table 7.2 Characteristics of distillery waste
Paramenter March-June
(Summer)
July-August
(Rains)
Nov.-Feb.
(Winter)
Tolerance
limit
1. Temp. of water 38.5-50.2 32.0-42.1 38.0-46.0 -
2. Turbidity (ppm) 385>1000 365>1000 1000>1000 100
3. pH 4.6-6.9 5.0-6.9 4.8-6.9 5.5 to 9.0
4. Colour Brown-Deep
Brown
Brown-Deep
Brown
Brown Deep
Brown
-
5. D.O. (ppm) nil-nil Nil-0.2 nil-nil -
6. C.O.D. (ppm) 3826-52000 654-11200 1080-27200 -
7. B.O.d. at 20ºC (ppm) 16000-2100 14,100 5760-14850 30
8. Alkalinity (ppm) 308-4140 290-3600 490-9440 -
9 Sp. conductivity
x 10-6 mhos at 25ºC
1028-14399 4235-13199 6041-8999 -
The distillery wastes are highly organic in nature and because of its high
biochemical oxygen demand (B.O.D.) quickly removes the oxygen from the
water and unless waste is diluted can produce pollution hazards in the aquatic
ecosystem. Both BOD and COD were indicating high values as a result of
which oxygen was mostly absent (Table 7.2)
The diluted distillery effluent (1:200 dilution) gives birth to number of
green (Chlorella, scenedesmus, chlorogonium) and blue algae (oscillatria,
Phormidium, Anthrospria and Anacystis).
277
7.6 DRUGS
Drug industry is also one of the great source of pollution. Not only during
manufacture, but also during quality control tests. Further dumping of expired
drugs also cause pollution due to toxic chemicals.
Drugs industries can be classified into three groups :
(i) Antibiotics (ii) Natural drugs and (iii) Synthetic drugs.
The composition of waste water from a synthetic drug factory producing
anti-pyritics, sulphur drugs, antitubercular drugs and vitamins, is given in Table
7.3
Table 7.3 Characteristics of a Drug Factory
Characteristics Range
pH
Total solids
Total volatile solids
Chloride as Cl
Sulphate as SO4
Total nitrogen as N
Phosphate as P
COD
BOD
TLM*
Mineral acidity as CaCO3
0.8
8.6%
5.0%
18,500 mg/l
23000 mg/l
6100 mg/l
Nil
19700 mg/l
13000 mg/l
0.29% (by vol.)
28000 mg/l
TLM* Medium tolerance limit 48 hrs. at combined; wastes adjusted to pH 7.00
was 0.29% volume.
The main source of pollution from drugs- industries include micro
organisms, and toxic organic chemicals both in suspended and dissolved states.
These also include vitamins.
278
7.7 PAPER AND PULP
Effluents from paper and pulp industry include wood chips, bits of bark,
cellulose fibers and dissolved lignin in addition to a mixture of chemicals. All
these produce a sludge which blankers fish spawning grounds and destroys
certain types of aquatic life. The effluents contains chlorine, sulfur dioxide.
methyl mercaptan etc., which are considered to be highly poisonous to fish.
The chemicals used in the factory are : (1) Alum (2-3 tonnes), (2) Talc
(0-10 t), (3) Rosin (1-1.25 t), (4) Chlorine (1.5-3.5 t), (5) Caustic soda (150-250
kg), (6) Soda ash (150-180 kg), (7) Dyes (2-50kg), (8) Magnesium bisulphite
and sulphurous acid, besides clay (2-15 t). The characteristics of a paper factory
are given in Table 7.4
Table 7.4 Characteristics of combined effluents from Sulphite pulp and paper
industry located on the bank of Hooghly estuary.
Parameters Pulp Unit Bleaching operation unit
Max Min. Max. Min.
Temp. of effluent
colour
Turbidity
Specific conductivity at 25ºC x 10-6
mohs
Total alkalinity as CaCO3 (mg/l)
D.O. (mg/l)
KMnO4 demand (mg/l) 2
1hr. at 100ºC
3 min. at ambient temp.
B.O.D. at 20ºC 1ºC (mg/l)
Available chorine (mg/l)
39.0
Brownish
yellow
730
7.5
1000
2.9
5320
2000
1920
-
28.2
<85
5.0
44
0.0
140
11
400
-
32.8
Milky white
>1000
10.5
1134
0.0
6
0
133
1704
27.8
140
9.0
84
0.0
1
0
84
16
279
The data indicates that
1. The lignin should not be allowed to discharge as it completely
destroys the fauna and flora and impairs the productivity.
2. Heavy suspended material should be brought to minimum level
through settling tanks which reduce B.O.D.
3. The taste and odour producing substances can be removed by treating
waste water with activated carbon.
7.8 THERMAL POWER PLANTS
There are a number of thermal power stations and super thermal power
stations in the country. The National Thermal Power Corporation (NTPC) is
setting up four mammoth coal-powered power stations to augment the energy
generation. These are at Singrauli in U.P., Korba in M.P., Ramagundam in
Andhra Pradesh and Farakka in W. Bengal. The coal consumption of thermal
plants & several million tonnes. The chief pollutants are fly ash, SO2 and other
gases and hydrocarbons. Table 7.5 shows various gaseous pollutants from a 300
MW thermal power plant.
The three thermal power stations at the Indraprastha Estate, Rajghat and
Badarpur in Delhi as the main source of air pollution. The Indraprastha plant
daily consumes 3,500 to 4,000 tonnes of coal when all the five units function.
Badarpur, the largest consumes daily about 10,000 tonnes of coal.
280
Table 7.5 Gaseous pollutants from a 200 MW thermal power plant (Coal
consumed 6.67 x 200 = 1334, i.e., 1400 tonnes a day).
Components Emission factor
Kg/tonnes of coal
Emitted quantity
(tonnes a day)
Aldehydes 0.0025 0.0035
Carbon monoxide 0.25 0.35
Hydrocarbons 0.10 0.14
NOx 10.00 14.00
Oxides of sulphur (0.5% S) 19(S) 13.30
Particulate matter (33% ash) 8(A) 369.60
Ash 2(A) 92.40
(A) Ash content in coal in per cent
(B) Sulphur content in coal in per cent.
Most of the thermal and electric power plants also discharge considerable
quantities (about 99%) of hot effluent/water into nearby streams or rivers. This
has resulted in thermal pollution of our water courses. Thermal pollution is
undersirable for several reasons. Warm water does not have the same oxygen
holding capacity as cold water. Therefore, fishes like black bass trout and
walleyes etc. which require a minimal oxygen concentration of about 4 ppm.
would either have to emigrate from the polluted area or die in large numbers.
Further, various Industrial processes may utilize water for cooling and
resultant warm water is often discharged in to streams or lakes and cause
thermal pollution.
281
Sources of Thermal-Pollution
The main sources of thermal pollution are as follows
(i) Electricity generation constitute the major source of the thermal
pollution of rivers and lakes.
(ii) The thermal furnaces of electricity production through their cooling
systems discharge sufficient quantity of heat into a river a large lake
or an ocean.
(iii) Atomic power plants are also, similarly high sources of thermal
pollution.
(iv) A cooling tower has been another way of sending waste heat into the
atmosphere; which by evaporation process pollutes the atmosphere
with heat.
(v) Similarly in dry type cooling towers, cooling is done with the help of
air, casing atmospheric thermal pollution.
(vi) In tropical regions sun-radiations cause thermal-pollution
Effects of thermal pollution :
Thermal pollution alone poses no direct health risks to people. Where
thermal pollution raises temperatures of rivers of lakes water quality and
aquatic life are affected. amerous effects of temperature on living organisms
have been reported in the biological literature.
1. Each type of fish has its own fatal temperature, the temperature at
which it will suffer heat death. For sockeye salman fry, heat death
occurs at only 72ºF. whereas large-month bass can withstand
temperatures up to 79ºF.
282
2. Rapid temperature changes produce thermal shock and sometimes
almost immediate death, a sudden temperature rise of 16.7ºC (30ºF)
has been found to kill stickleback in 35 s and chum salmon in 10s.
3. If the body of water contains chemical pollutants, extra warmth
increase their toxicity to fish.
4. Temperature has been of course of vital importance to physiology
controlling reproductive cycles. digestion rates, respiration rates and
the many chemical activities taking place in the body. Higher
temperatures generally correspond to increased chemical reaction
rates and the behaviour of physiological processes.
5. Thermal discharges to a waterway may result in the growth of blue-
green algae with resulting damage to the ecosystem. Bluegreen algae
are a poorer food source and thought in some cases to be toxic to fish
Thermal discharges have been generally favourable to bacteria and
pathogens as well.
6. Higher temperatures also influence the physical and chemical
properties of water. As higher temperatures favour bacterial growth
and increase the rates of physiological processes the decomposition of
organic and other oxygen demanding wastes will get speeded up
increasing the rate of oxygen depletion and further aggravating the
dissolved oxygen problem.
7. Higher temperatures also result in faster growth rates and shorter life-
spans
8. In plants water absorption photosynthesis, respiration etc. all
physiological processes are affected by increase of temperature.
9. The growth, flowering and fruit formation all activities are adversely
affected by rise in the temperature in case of many plants.
283
10. Due to stratification and vernalisation at higher temperature
germination of plants is also affected.
11. Hibernaton and Aestivation both of the animals are affected due to to
rise in temperature.
12. Increase in temperature also affects the migration of animals such as
Flamingo, Great Crested, Grebe, Swan, Grey lag Goose. Barred
Heade Goose Pin tail. Teal, Ruddy Sheldrake, Quail etc.
13. The growth and preproduction of animals is also affected by thermal
pollution, which disturbs sex-ratio.
14. Metabolism is also affected due to increase in temperature e.g. in
Mytilus edulis.
Control of Thermal Pollution :
The problem of thermal pollution can be alleviated by using artificial
cooling lakes and ponds and cooling towers. Further, this problem can be
alleviated by improvements in efficiencies of electric generating plants.
Thermal pollution could be drastically reduced by direct conversion of
the heat into electricity. The thermal efficiency of fusion reactors might
approach 96% if combined with an efficient thermal electric plant.
Another method to reduce thermal pollution is to use waste heat for a
number of purposes which will simultaneous help to conserve our fuel
resources.
(i) Heating of Buildings
(ii) Heating of swimming pools
(iii) Deicing of waterways
(iv) Desalination
(v) Aquaculture
(vi) Warm water irrigation
284
Any net increase in the quantity of heat released into the atmosphere
must bring about an increase in the average temperature of the earth-atmosphere
system, however miniscule the change may be. In any use of nuclear or fossil
fuel all the heat content eventually gets released into the environment. Even if
some of the heat content is first made into electricity, eventually electrical
resistance heating and friction will change all the electricity to heat. Geothermal
energy releases some small quantity of heat
CHECK YOUR PROGRESS-1
Note : (1) Write your answers in the space given below.
(2) Compare your answers with those given at the end of the unit.
(a) (i) Pollutants accmulate slowly and circulate through the atmosphere,
................... and ................., and affect ....................... community.
They also change ..................... and result in ........................
(ii) Cement factories emit plenty of ................., which is potential
health hazard ..................... and ........................ are common
chronic conditions resulting from this pollution.
(iii) From sugar industries, effluents contain high degree of ...............
pollution, hence if effluent stagnates in an area for a few hrs,
...................... starts and ....................... condition gives
......................... gas importing ......................... to the effluent.
(iv) In India annual distillery discharge figures approximate
....................... million literes and this can afford to produce 10-250
tonnes .................., 1000-2500 tonnes ....................... and 50-100
285
tonnes ......................., beside................., ............. and ..................
organisms.
(b) (i) The main source of pollution from drugs industries include
.................... and ....................... both in suspended and dissolved
state.
(ii) Effluents from paper and pulp industries include ......................,
..........................., and dissolved ........................., in addition to a
.............................. of .......................
(iii) Thermal power planto discharge considerable qantities of
................. in to near by ........................ or .....................
7.9 METALLURGY
Metal industries usually discharge effluents containing copper, lead,
chromium, cadmium, zinc. etc., which are toxic to man as well to aquatic life.
These wastes also contain acids, oils, greases and cleansing agents.
These toxic metals (and halogens) when concentrated are released in the
environment. Principal metals of concern are lead, mercury, arsenic, nickel,
beryllium, cadmium, thallium, uranium, cesium, and plutonium. Halogens
(fluorine, chlorine, bromine, and iodine) are highly reactive toxic elements.
Most of these materials are mined and used in manufacturing. Mining
operations can result in metals leaching into the acidic effluents thus adding to
the metal load in rivers, lakes and ground water. Discharge of mercury from
gold mining activities has polluted some streams in Brazil and Ecuador and
created serious health problems.
The toxic effects of various metals are summarised in Table 7.6
286
Table 7.6 : Toxic Metals
Metal Effects
Mercury Abdominal pain, headache, diarrhoea, hemolysis chest pain.
Minamata diseases of Japan is a burning example.
Lead Anemia, vomiting, loss of appetite, convulsions, damage of
brain, liver and kidney.
Arsenic Disturbed peripheral circulation, mental disturbance, liver
cirrhosis, hyperkeratosis, lung cancer, ulcers in
gastrointestinal tract, kidney damage.
Cadmium Diarrohea, growth retardation, bone deformation, kidney
damage, testicular atrophy, anemia, injury of central nervous
system and liver, hypertension.
Copper Hypertension, uremia, coma, sporadic fever.
Barium Excessive salivation, vomiting, diarrhoea, paralysis colic
pain.
Zinc Vomiting, renal damage, cramps
Selienium Damage of liver, Kidney and spleen, fever, nervousness,
vomiting low blood pressure, blindness, and even death
Hexavalent
chromium
Nephritis, gastro-intestinal ulceration, diseases in central
nervous system, cancer.
Cobalt Diarrhoea, low blood pressure, lung irritation. bone
deformities, paralysis
Further the roasting, calcinations and smelting (of ores) processes release
main atmospheric pollutants such as carbon dioxide and sulphur dioxide.
Similarly refining operations release highly toxic chemicals like cyanide,
thiosulphate etc in the effluents.
287
7.10 POLYMERS
We are living in the plastic age. Metals, wooden articles and paper are
being replaced by plastic items. All of us are very well acquainted with natural
rubber, polythene bags, polystyrene use and throw tea cups and plates,
melamine crockery, acrylic paints and acrylic wool. We find it more convenient
to use the plastic chairs, table and plastic doors instead of wooden ones. They
are lighter and more durable. Nylon, terelyne and terecot clothes have also
replaced the cottonclothes. All these items are made of polymer organic
molecules. The term 'Polymer' is a greek word meaning combination of many
molecules ('Poly' mens many and 'mer' means part, molecule or a unit). Hence
polymerisation is defined as the combination of many molecules and polymer is
a compound of high molecular mass formed by the combination of large
number of small molecules. The small molecules which form the repeating
units are called monomer units. For example, polythene is a polymer obtained
by the combination of many units of ethene or ethylene. Thus in polythene,
ethylene is the monomer.
tionPolymerisa
22 )CHCH(n
H
C(
H
H
C
H
-) n
Polystyrene is obtained by the polymerisation of styrene units.
Such polymers which are obtained only from one type of monomer
molecules are called homopolymers. There are many examples of polymers
which are obtained by the polymerisation of two different type of monomer
units. Nylon and terylene are such examples. Such polymer in which the repeat
units are made up of two different monomer are called copelymers or mixed
Ethylene (Monomer) Polythene (Polymer)
288
polymers. Polymers are also called macromolecules as they are the big or giant
molecules.
Broadly speaking, polymes have been classified into two categories
namely natural and synthetic polymers. There are many common examples of
natural polymers. Starch, celllulose, proteins, nucleaic acids and natural rubber
are some of the examples of natural polymers. Starch and cellulose are made up
of glucose units. Cellulose is made by plants from glucose produced during
photosyntheses, Proteins are the polymers of -amino acids. Wool, natural silk,
hair, leather and skin contain proteins, natural rubber is made up of isoprene
units (2-Methyl -1 3-butadiene)
These days many polymers are being synthesised in the laboratories.
These are called synthetic or man made polymers.
We come across polymers with different type of properties like elasticity,
toughness, density etc. This is due to difference in the intermoleculer force of
attraction in the polymers.
Based upon the type of linkage of the monomeric units, polymers may be
classified as;
(i) Linear chain polymers (Polythene, polystyrene, nylon etc.)
(ii) Branched chain polymers (Polythene, glycogen etc. and
(iii) Cross linked polymers (Backetite, melamine etc.). Thus we may have
Elastomers : Thus we may have the polymer chains are held together by the
weak intermolecular forces. Due to weak forces, such polymers can be
stretched); Fibres have strong intermolecular forces and hence high tensile
strength); Thermoplastics (polymers which can be easily moulded on heating
and cooling to room temperature) and Thermosetting polymers contain cross
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linked monomeric units. On heating, cross linkages are accelerated forming
three dimensional network bonds. Such polymers on heating become hard and
infusible.
Addition polymers (polyolefins, polyhalo ethylene polyvinyl chloride
etc.) and condensation polymers (Polyesters, glyptal, polymids etc.) both have
variety of uses. However, most of the synthetic polymers are dangerous sources
of pollution, as they are bio-nondegradable.
In the last twenty years, or more, plastics has affected the health and life
of human being very badly. Some incidents have attracted the whole world and
put a question mark about the use of plastic in daily life. The most popular
polymer used for various purposes is PVC (Poly vinyl chloride). When this
plastic is used as containers then gradually the soluble chemicals get dissolved
in then gradually the soluble chemicals get dissolved in them causing death,
cancer and other skin diseases. PVC has also been found to destroy the fertility
of animals and their respiratory systems. When mixed with water, it causes
paralysis and also damages bones and causes irritation to the skin. It is because
of this, demand to ban use of PVC in water, pipes, food and medicine
containers has been raised.
7.11 NOISE
Sound of high intensity level and or produced by an irregular succession
of disturbances becomes discordant, unpleasant and unwanted and is said to
constitute noise. It can be produced through various natural processes but is
mainly a man-made by product of unbriddled technological development.
Environmental pollution by noise is a relatively new problem in India to
the assortment of occupational and other hazards. Although awareness about
this problem including the introduction of the various legislative and control
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measures came to other countries of the world a few decades back in India
noise pollution became an offence only recently through the promulgation of
the comprehensive Air Act of 1986.
Noise may be best defined as 'wrong sound' in wrong place' and at the
wrong time the word noise is derived from the Latin ward nausea.
Noise is generally defined as 'sound without value' or 'any sound that is
undesired by the recipient
The noise pollution is an unwanted sound which gets dumped into the
atmosphere without regard to the adverse effect it may have. In the electronic
communication system the term noise pollution may refer to perturbations that
get interfered with communications. Such noise tend to increase with
complexity and information content of systems of all kinds.
Every industry trade, occupation, transport and process using
equipments, apparatus materials, means and modes that produce pressure
variations audible to the ear constitutes a noise source. These noise sources may
be point line or plane generating spherical cylindrical or plane waves
respectively.
Industrialisation and urbanization has resulted in a number of causes of
noise, eg.-
(a) Industrial noise, and
(b) Transportation noise
(a) Industrial noise : Mechanized industry is the most serious of all large-
scale noise producers in industrial areas, noise usually emanates from a wide
variety of machines making it very complex in nature. The characteristics of
noise in the immediate neighborhood may, however, depend many a times on
the specific equipment's or machines used in any particular industry.
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(b) Transportation noise: The road vehicles (automobiles) used for
transportation of industrial goods are another extensive source of noise
pollution. This noise is mainly generated from the engine the born and the
frictional contact between the vehicle, ground and air. The level of traffic noise
in general depends on traffic flow rate speed of the vehicles, change in engine
speed and power and the proportion of heavy vehicles including motor cycles
on road.
Harmful effects of Noise
Noise not only affects human health but it also affects his working capacity
e.g.-
1. The major harmful effect of noise is to impair hearing, sometimes with a
lasting damage.
An examination of Burns and Robinson's data shows that this hearing
impairment is caused by noise levels above 80 dB.
2. Noise intrusion has also been reported to cause difficulty in falling asleep
and to awaken people who are already asleep. Detailed laboratory studies
have shown that disturbance of sleep become increasingly apparent as
ambient noise levels exceed dB.
3. There are many other physiological and psychological effects which have
been observed to occur due to noise exposure. Noise interferes with
speech communication. It has been found that for good speech
intelligibility indoors background noise levels of less than 45 dB (A) Leq
are needed while general daytime outdoor noise levels of less than 55 dB
(A) Leq and night time noise levels of 45 dB (A) Leq are needed.
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4. Noise annoyance can also cause nervous irritability and accidents. Noise
breeds fatique which may lessen efficiency. Noise can also cause blood
circulatory, digestive and metabolic difficulties.
Control of Noise Pollution :
As a general rule noise abatement and control measures shall necessarily
be based on the following concepts for their effective implementation.
(i) Noise abatement measures must start at the source by applying the
best practicable noise abatement technology. According to the
principle the emission standards for all kinds of industrial machines,
motor vehicles, domestic machines, aircrafts, trains etc. have to be
reduced gradually to compel manufacturers to apply all modern
technically and economically feasible noise abatement measures.
(ii) In cases where noise abatement at the source is not sufficient to limit
noise impact to an acceptable degree, additional measures like sound
proofing, traffic management, urban planning, design and construction
of buildings to isolate noise sources from vulnerable areas plant
installations and layout to keep noise at the work place to acceptable
levels, may be applied to prevent noise propagation.
7.12 RADIOACTIVE NUCLIDE
Radioactive elements such as uranium and radium possess highly
unstable atomic nuclei. This disintegration results in radiation emission which
may be highly injurious. During nuclear tests, radioactive dust may envelope
the globe at altitudes of 3,000 metres or more the same often comes down to the
earth as rain. Eventually, some of the radioactive material, such as Strontium 90
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(which can cause bone cancer), percolates down through the soil into ground
water reservoirs or is carried out into streams and rivers. In both cases public
water supplies may be contaminated.
Thus the gretest worry about nuclear power is the danger of accidents and
also tests that release hazardous materials into the environment. Several
accidents most notably the meltdown at the Chernobyl plant in Soviet Ukraine
in 1986 have convinced many people that this technology is too risky to pursue.
Other major worries about nuclear power include where to put the waste
products of the nuclear fuel cycle and how to ensure that the wastes will remain
safely contained for thousands of year required for 'decay' of the radio isotopes
to nonhazardous levels. As an example of nuclear hazard one can not forget.
Heroshima and Nagasaki where atom bomb was exploded in 1945 and
survivors are still suffering from its nuclear hazards.
The harmful effects of ionising-rediations from radioactive substances on
bio-eco-system is known as nuclear-pollution.
Sources of Nuclear Pollution
Sources of nuclear pollution are both, the natural and human generated.
Natural Source
Amongst natural source of nuclear pollution important examples are –
(i) Decay of naturally occuring radio-active isotopes e.g. Radium-226.
Uranium-238 and 235. Thorium-232 etc. which have very long life.
These isotopes naturally and spontaneously are liberating radiations.
(ii) Cosmic radiations, which contain ionic particles (mainly protons) and
are obtained from extra terrestrial sources.
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Artificial or Man-made sources :
(a) Radiations from Medical and Dental Exposures
Use of X'ray is common for different medical check-ups and also for
dental x-rays
(b) Radiations from Television Sets
For a person viewing television at a distance of 6-7 feet according to
Morgan the average dose of radiations to the overies is as high as 1.1
milirad/year (with out the glass) and to testes is 7.5 mlirad/year.
(c) Nuclear Power Plants
At present more than 31 countries in the world have about 440 reactors.
The accidents in the reactors are the greatest danger for mankind. Two
major accidents have at ready taken place one at Miles Island (America)
in 1979 and the other at Chernobyl (Soviet Ukraine) in 1986.
(d) Atomic fall-out
Radio active fall-out from nuclear weapons tests has been of grave
concern. Although local fall to of radio-active fission products takes
place for about a day or two but then world wide tropospheric fall out
continues for about a month from fission products released in to
troposphere and stratosphere fall world wide continues for many years
there after.
(e) Nuclear Wastes
Other major source of nuclear pollution is the nuclear waste obtained
from nuclear-power plants. The usual methods of dumping is either
ocean dumping or the land disposal. But both are dangerous in the long
term.
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Effects of Nuclear Pollution
The burning example of nuclear hazards are Hiroshima and Nagasaki.
The survivors of 1945 bomb-explosion are still suffering from genetic and other
cancerous diseases. The exposure of the radiation starts the ionisation-trail in
the body, resulting in damage to DNA structure. This mutation ultimately
results in cancerous formation.
1. If the radiation is of 500 rem its exposure causes death during 4-5 days. If
the radiation is low, exposure brings blisters on the skin and then blood
vomiting. This follows, the effect on other parts of the body.
2. The site in a living cell is most vulnerable to ionising radiation. It has its
nucleus in the genetic material DNA.
3. If the radiation is having affected germ-plasm, the flaws may eventually
give rise to permanent genetic damage to the offspring if the damage has
been in somatic tissue, they may give rise to leukemia (i.e. blood cancer)
4. Radiations into the pelvic region of a pregnant women may cause
damage to the fetus.
5. Radiations entering the body on airborne radioactive dusts and gases or
in food results into lung cancer.
6. Out of the various isotopes in the fall out most dangerous is strontium
because it is a bone-socket. It affects both somatic and genetic cells.
somatic effects have been on the body, but genetic effects have been
those involving mutations of the gene in these cells.
7. Radio active radiations also affect capability of animals and humans.
They produce antitoxins of bacterial and virus diseases.
8. Genetic changes results in the birth of disabled and undeveloped child
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Control of Nuclear Pollution
It is a big problem the, effective measure may be a complete check on
atomic-tests and closing of atomic reactors and power-plants.
However we know that the great pressure for energy will not allow
countries to close-down their atomic power plants. Effective disposal-methods
have to be searched for nuclear wastes. In no case nuclear wastes should be
dumped into sea without prior treatment or burried deep in the earth.
Certainly we can completely check use of nuclear weapons during wars.
7.13 DISPOSAL OF WASTE AND ITS MANAGEMENT
Waste is everyone's business. We all produce unwanted by-products and
residues in nearly everything we do According to the Environmental Protection
Agency (EPA) the United States produces 11 billion tons of solid waste each
year. Nearly half of the amount consists of agricultural waste such as crop
residues and animal manure which are generally recycled into the soil on the
farms where they are produced.
Solid waste, often called the third pollution after air and water pollution,
is that material which arises from various human activities and which is
normally discarded as useless or unwanted. It consists of the highly
heterogeneous mass of discarded materials from the urban community as well
as the more homogeneous accumulation of agricultural industrial and mining
wastes.
The metro-cities in India produce more then 3,00,000 tons of waste every
day.
sources of solid wastes have been:.
1. Municipal : Street sweepings, sewage treatment plant wastes, wastes
from schools and other institutions.
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2. Domestic : Garbage, rubbish and occasional large wastes from homes
3. Commercial : from stores and offices
4. Industrial : from manufacturing plants.
5. Mining : from coal mining strip mining and
6. Agriculture :
The solid wastes from these sources include-
(i) Garbage : Putreseible (decomposable) wastes from food slaughter
houses canning and freezing industries etc. These wastes have moisture content
of about 70% and heating valve around 6x106 J/kg.
(ii) Rubbish : Non decomposable wastes, either combustible or non
combustible. Combustible wastes would include paper, wood, cloth, rubber,
leather and garden waste. Non combustible would include metals, glass
ceramics, stones dirt, masonry and some chemicals (Moisture contents about
25% and heating value around 15x106 J/kg)
(iii) Pathological Wastes : Dead animals, human waste, etc. (The moisture
content is 85% and there are 5% non-combustible solids. The heating value is
around 2.5X106 J/kg.)
eg –
Ashes : Residue e.g. cinders and fly ash of the combustion of solid fuels or the
incineration of solid waste by municipal, industrial and apartment house
incinerators.
Large wastes : Demolition and construction rubble, automobiles, furniture
refrigerators and other home appliances, trees, tires etc.
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Dead animals : House hold pets, birds, rodents, zoo animals etc. in addition
anatomical and pathological wastes from hospitals.
(iv) Industrial solid wastes : Chemicals, paints, sand, explosives etc.
(v) Mining wastes : Tailings, slag heaps etc.
(vi) Agricultural wastes : Farm animal manure, crop residues etc.
Think for a moment about how much we discard every year. There are
organic materials, such as yard and garden wastes and sewage sludge from
treatment plants, junked cars, worn-out furniture and consumer products of all
types. Newspapers, maganzings advertisements and office refuse make paper
one of our major Wastes.
The waste stream is a term that describes the steady flow of varied
wastes that we all produce, from domestic garbage and yard wastes to industrial
commercial and construction refuse. Many of the materials in our waste stream
would be valuable resources if they were not mixed with other garbage.
Thus, the principal sources of solid wastes are domestic, commercial,
industrial and agricultural activities. Many times domestic and commercial
wastes are considered together as the so-called urban wastes. The main
constituents of urban wastes are similar throughout the world, but the weight
generated, the density and the proportion of constituents vary widely from
country to country, and from town to town within a country according to the
level of economic development, geographic location, weather and social
conditions. In general, it has been found that as the personal income rises,
kitchen wastes decline but the paper, metals and glass wastes increase; the total
weight generated rises but the density of the wastes declines.
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In India authentic information regarding the composition of the urban
wastes is not generally available as regular analysis of the refuse is not carried
out by the municipalities. In fact, refuse is very heterogeneous in composition
and the geographical, temporal and seasonal variations in its composition make
it difficult to define a "typical refuse". The solid refuse generated in urban areas
contains articles of various sizes and types and consists of dust, vegetable
leaves, waste paper, large paper-board cartons, glass bottles, worn out tyres,
carcasses of animals and night soil. Table 7.7 gives the composition of refuse in
various cities of India and a comparison is made with the urban refuse from a
typical European city. As is seen from Table 7.7. The average paper content in
the refuse of Indian cities is about
Table 7.7 Composition of city refuse (refs. 1, 2) (percentage by weight)
Kanpur Delhi Calcutta Bangalore Bombay Typical
European city
Paper 1.35 5.88 0.14 1.5 3.20 27
Vegetable-
putrescible matter
53.34 57.71 47.25 75.2 59.37 30
Dust, ash, etc. 25.93 22.95 33.58 12.0 15.90 16
Metals 0.18 0.59 0.66 0.1 0.13 7
Glass 0.38 0.31 0.24 0.2 0.52 11
Textiles 1.57 3.56 0.28 3.1 3.26 3
Plastics, leather,
rubber, etc.
0.66 1.46 1.54 0.9 - 3
Other (stones,
wooden matter,
etc.)
18.59 6.4 16.98 18.9 16.4 3
Density, kg/m3 500 - 540 578 - 132
2 to 3 percent as compared with about 27% for a typical european city,
Similarly, the density of refuse in India is much higher than that of the refuse
generated in the cities of western countries because of the inclusion in it of the
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street sweepings. The amount of refuse collected from urban areas in India is of
the order of 0.3 kg to 0.5kg per person per day excluding night soil.
Manufacturing industries produce wastes which are solid or semi-solid.
These wastes can be pyrophoric (self-igniting), explosive, toxic or radio-active.
Chemical process industries (CPI) generate a variety of wastes, both organic
and inorganic, which are mixtures with a wide range of component
concentrations.
Most of the industrial wastes generated in cities come from small scale
operations and these are usually disposed off along with the city refuse. Larger
industries are often located outside the cities and the disposal of their wastes is
primarily the responsibility of the industries themselves. Some of the industrial
wastes are often recycled (scrap metal and paper) while others can be utilized as
an energy source for specific processing plants in some regions. Energy can be
recovered from solid wastes by numerous thermal routes as well as by
biochemical conversion. The toxic and radioactive wastes, often classified as
hazardous wastes, need special consideration before their disposal.
Agricultural wastes comprise both crop residues and animal wastes such
as manure and urine. Whereas urban wastes amount to between 0.3 and 0.5 kg
per person per day in India, agricultural wastes amount to around 2 kg per
person per day. Animal and vegetable wastes contain valuable minerals and
nutrients. Humus from agricultural wastes contains nitrogen, phosphorus,
potash and trace elements which are vital to the fertility of the soil and optimum
plant growth. Burning of wastes as fuel in the conventional manner makes poor
use of the leaf content of the fuel burnt and, further, leads to loss of valuable
nutrients.
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The relationship between solid wastes and human disease is difficult to
prove, Nevertheless, improper handling of solid wastes is a health hazard and
causes damage to the environment. The main risks to human health arise from
the breeding of disease vectors, primarily flies and rats. A common
transmission route of bacillary dysentery and diarrhoeal disease in India is from
human faeces by flies to food or water and thence to humans. It has been
estimated that in warm climates, exposed garbage produces as many as 70,000
flies per 0.03 m3 in a week.
The refuse dumps also serve as a source of food for rats and small
rodents which quickly proliferate and spread to neighbouring areas. Rats
destroy property, infect by direct bite and spread various diseases like plague,
endemic typhus, salmonellosis, trichinosis, etc. Apart from diseases for which
insects and rats are carriers, the handling and transfer of bio-logical wastes
poses a threat to the worker and those he contacts. Disease transmission may
occur through direct contact with the waste, through infection of open sores or
through vectors.
The hazardous wastes are injurious to human health; some have acute
effects while others pose a health hazard after prolonged period of exposure.
Improper disposal of such wastes has resulted in the death of humans and
animals through contamination of crops of water supplies.
The environmental damage caused by solid wastes is mostly aesthtic in
nature. Uncontrolled dumping of urban wastes destroys the beauty of the
countryside; also, there is the danger of water pollution when the leachate from
a refuse dump enters surface water or ground water resources. In addition
uncontrolled burning of open dumps can cause air pollution.
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SOLID WASTE DISPOSAL AND ITS MANAGEMENT
Efficient collection and transportation are essential parts of the overall
solid waste management programme since these two activities constitute about
75% of the total cost. The basic mode of refuse collection in India is from
communal storage points. The refuse is delivered to fixed storage bins usually
built from concrete blocks, having capacities between 100 and 500 litres and
placed at intervals of 50 to 200 metres. The refuse is stored is the bins till it is
collected for disposal by a vehicle. Daily collection is essential because the
organic matter in the refuse tends to decompose rapidly in the hot climate.
Other methods of refuse collection like block collection and kerbside
collection are practised in developed countries. In block collection the waste is
brought in containers by individuals to a waiting vehicle which travels a regular
route twice or thrice a week.
In a relay system the collection can be made in trailers employing a lesser
number of tractors, or two vehicles can be employed for one unit of crew (2:1
relay). In the second alternative, the crew stays at the collection site and the
unloading at the disposal site is done mechanically.
Transportation of the collected refuse constitutes a key stage in the
overall waste management system. In India, no single mode of transport can
prove effective, economical and efficient due to congested and narrow lanes
and streets in towns and cities. Hence, various types of vehicles from hand carts
to modern mechanized vehicles are used. Hand cart collection is the best mode
of transport from congested and narrow places; the refuse is usually transferred
from the carts to a waiting trailer for final transport and disposal.
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Transfer Station
A transfer station may be described simply as a place for receiving refuse
from a number of small collection vehicles such as hand carts and transferring it
to larger line-haul type vehicles capable of undertaking a longer journey more
economically. the best construction for a transfer station is a ramp leading to a
concrete platform where the smaller vehicles discharge.
The process of selection of the right solid waste disposal method is a
complex one due to the heterogeneity of the urban refuse, but an appropriate
selection can save thousands of rupees and avoid future problems for the
average municipality. The disposal method should be selected in such a way
that the present requirements are fulfilled and future situations are anticipated.
The method should also provide opportunities for recycling of materials, if
possible, and should not pollute the air, the ground water, the surface water or
the land.
Several disposal methods are being used in the various parts of the world.
Traditional methods :
(i) Open Dumps : For many people the way to dispose of waste is to simply
drop is someplace. Open unreglated dumps are still the predominant method of
waste disposal in most developing countries. The giant Third World megacities
have enormous garbage problems.
(ii) Ocean Dumping: The oceans are vast but not so large that we can
continue to treat them as carelessly as has been our habit. Every year some
25,000 metric tons (55 million lbs) of packaging including half a million
bottles, cans and plastic containers, are dumped at sea.
(iii) Sanitary Landfill : Sanitary landfilling is an engineered operation,
designed operated according to acceptable standards. It may be defined as a
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method of disposing refuse on land without creating nuisances or hazards to
public health or safety. The operation is carried out without environmental
damage and in areas already spoiled or in need of restoration.
In sanitary landfill operation, refuse is spread and compacted in thin
layers within a small area. This layered structure is usually referred to as a cell.
To allow for proper compaction, the cell depth should not exceed about 2
metres. The cell is then covered with a layer of soil which is spread uniformly
and then compacted. To provide an adequate seal the 'cover' should normally be
at least 20 cm thick. If the refuse includes large irregular objects it may be
necessary to increase the thickness of the cover. On the other hand, a cover
thickness of less than 15 cm may be satisfactory if the refuse has been
pulverized. When a number of cells reach the final desired elevation, a final
cover of about one metre of earth is placed and it is again compacted. This final
cover is necessary to prevent rodents from burrowing into the refuse.
(iv) Exporting Waste : Although most industrialized nations in the world
have agreed to stop shipping hazardous and toxic waste to less developed
countries the practice still continues. In 1999 for example 3000 tons of
incinerator waste from a plastics factory in Taiwan were unloaded from a ship
in the middle of the night and dumped in field near the small coastal
Cambodian village of Bet Trang.
Modern Methods
(a) Incineration and Resource Recovery
Incineration involves the burning of solid wastes at high temperatures;
leftover ashes, glass, metals and unburned combustibles amount to perhaps 25%
of the original waste. This residue must still be disposed of in some manner.
Incineration leads to air pollution unless the plant is designed, equipped and
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operated to comply with air pollution standards. Typical air pollutants from
incineration are flyash SO2. hydrogen chloride, and organic acids. New
techniques of handling the waste have been developed. Thus, materials which
are not combustible are removed from the waste by gravity or magnetic
separation. Many of the separated materials like glass or metals can be recycled.
Air pollution can be controlled by installation of proper control equipment.
Industrial solid wastes that are incinerated are mostly cellulose type, and
more often industries have to handle certain kinds of chemical wastes in the
form of either solids or sludges. In the chemical process industries, incineration
is most frequently used to dispose of tarry and gummy petroleum and plastic
intermediate wastes and general refuse. The waste combustibility is an
important factor in determining the applicable incineration process industries,
incineration is most frequently used to dispose of tarry and gummy petroleum
and plastic intermediate wastes and general refuse. The waste combustibility is
an important factor in determining the applicable incineration process. Waste
combustibility is characterized by flammability limits, flash point, and ignition
temperature.
If incineration is to become an economical method for solid waste
disposal, useful material and energy must be recovered by the process. Heat can
be recovered by putting a waste heat boiler or some other recovery device on an
existing solid waste incinerator. The heat so recovered can be utilized for
generating electricity or for space heating purpose. The solid waste has about
one-third the heating value of coal, but unlike coal it has a very low sulphur
content.
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(b) Recycling
The term recycling has two meanings in common usage. Sometimes we
say we are recycling when we really are reusing something such as refillable
beverage containers. In terms of solid waste management, however recycling is
the reprocessing of discarded materials into new useful products. Some
recycling processes reuse materials for the same purposes for instance old
aluminm cans and glass bottles are usually melted and recast into new cans and
bottles Other recycling processes turn old materials into entirely new products.
Old tires, for instance are shredded and turned into rubberized road surfacing
Newspapers become cellulose insulation, kitchen wastes become a valuable soil
amendment and steel cans become new automobiles and construction materials.
Benefits of Recycling
Recycling is usually a better alternative to either dumping or burning
wastes. It saves money, energy, raw materials and land space while also
reducing pollution. Recycling also encourages individual awareness and
responsibility for the refuse produced.
Another benefit of recycling is that it could cut our waste volumes
drastically and reduce the pressure on disposal systems. In addition. recycling
lowers our demands for raw resources.
Recycling also reduces energy consumption and air pollution. Plastic
bottle recycling could save 50 to 60 percent of the energy needed to make new
ones. Making new steel from old scrap offers up to 75 percent energy savings.
Producing aluminum from scrap instead of bauxite ore cuts energy use by 95
percent.
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(C) Composting
Pressed for landfill space many cities have banned yard waste from
municipal garbage. Rather than bury this valuable organic material, they are
turning it into a useful product through composting i.e. biological degradation
or breakdown of organic matter under aerobic (oxygen-rich) conditions. The
organic compost resulting from this process makes a nutrient-rich soil
amendment that aids water retention slows soil erosion and improves crop
yields.
In contrast to a sanitary landfill, compositing of refuse is an aerobic
method of decomposing solid waste. Many types of microorganisms, already
present in the waste, stabilize the organic matter in the waste to produce a soil
conditioner. The organisms include bacteria, which predominate at all stages,
fungi, which often appear after the first week, and actinomycetes, which assist
during the final stages.
Modern methods of composting fall into two broad categories : manual
and mechanical. For towns with a rural bias, the manual window system is more
attractive. In India two methods of composting refuse/night-soil mixtures have
been developed. In the Indore process, layers of vegetable waste and night-soil
are alternated, each about three inches thick to a depth of upto 1.5 metres in a
trench or form a mound above ground called a windrow. The mixture is kept
aerobic by turning regularly for two or three months. The compost is then left
for another month or so without turning the whole process thus takes about four
months.
A modified process, known as the Bangalore process, is now widely
adopted by municipal authorities throughout the country. The material is placed
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in layers, as in the Indore process, in a trench about a metre deep. The material
is not turned but is digested under essentially anaerobic conditions whereby
decomposition is complete in four to five months. Though the process avoids
turnings altogether, it lays great emphasis on the initial C/N ratio of the
compost heap and initial mositure content. The compost is free from pathogenic
organisms and contains 1.5% N, 1.1%P (P2O5) and 1.5% K (K2O) on dry basis
and proves a valuable nutrient for the soil.
Fully mechanized plants involve shredding, grinding and machanical
separation of high-density solids. There are basically four processes of
mechanical compositing available in India. These are : (a) the Buhler process,
(b) the Dano process, (c) the Tollemache process, and (d) the Nusoil process.
In the Buhler process the material is ground in two stages in hammer
mills; the non-compostable inorganic materials are separated by strong sifting
action on circular swinging sieves. The material is then decomposed aerobically
in open windrows; stabilization may take about two to three months.
The Dano process uses a long rotating drum, called a bio-stabilizer unit,
for decomposing the refuse. The rotating drum is inclined so that the waste
flows from one end to the other. The refuse is partially decomposed in the drum
and the outcoming refuse is generally free from odour and pathogenic
organisms. It is then completely decomposed in windrows; the entire operation
may take about four weeks.
In the Tollemache process the refuse is pulverized in a vertical pulveriser
and then passed through a screening plant to screen out paper, plastics, etc. The
pulverized-sereened refuse is allowed to decompose in the windrows for three
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weeks, with three to four turnings. The compost is then cured for four to five
weeks; the complete stabilization thus takes about two months.
In the Nusoil process the noncompostable material is separated from the
refuse which is then pulverized in a hammer mill. The pulverized matter then
goes to a vertical digester where the decomposition takes place. The digester is
a circular unit having seven sections; the refuse moves downward through each
section of the digester. It is kept for about a day in each section, and air flow
rate and water addition are regulated so that decomposition takes place under
optimum conditions. The digestion process is completed in seven days and the
resultant compost is satisfactory for direct field application without the addition
of supplementary nutrients.
(d) Energy from Waste
Every year, we throw away the energy equivalent to 80 million barrels of
oil in organic waste. In developing countries up to 85 percent of the waste
steam is food. textiles, vegetable, matter and other biodegradable materials.
This valuable organic material can be burnt in an incinerator rather than
being buried in landfills but there are worries about air pollution from
incineration.
Anaerobic digestion also can be done on a small scale. Millions of
household methane generators provide fuel for cooking and lighting for homes
in China and India.
(e) Demanufacturing
Demanufacturing is the disassembly and recycling of obsolete consumer
products such as television sets personal computers, refrigerators, washing
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machines and air conditioners. Together with deconstruction of houses it is a
good way to recover valuable materials.
(f) Reuse
Even better than recycling or composting is cleaning and reusing
materials in their present form thus saving the cost and energy of remaking
them into something else. We do this already with some specialized items. Auto
parts are regularly sold from junkyards especially for older car models. In some
areas stained-glass windows brass fittings fine woodwork and bricks salvaged
from old houses bring high prices. Some communities sort and reuse a variety
of materials received in their dumps
(g) Excess packaging of food and consumer products is one of our greatest
sources of unnecessary waste. Paper, plastic, glass and metal packaging
material make up 50 percent of our domestic trash by volume. Much of that
packaging is primarily for marketing and has little to do with product
protection. Manufacturers and retailers might bye persuaded to reduce these
wasteful practices if consumers ask for products without excess packaging.
Thus there can be four categories.
(1) no packaging, (2) minimal packaging, (3) reusable packaging and (4)
recyclable packaging. This plan set a target of 50 percent reduction in excess
packaging.
Thus a proper waste disposal (Management) will involve-
1. Screening of the waste-material into different classes e.g.
(i) Unconmbustible material
(ii) Combustible material (wood, garbage)
(iii) Highly combustible material (paper, plastic, rubber etc.)
(iv) Reusable material
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2. Disposal of material according to their classification e.g. material suitable
for composting should be used for the purpose, while material useful for energy
production should be used for bio-gas preparation and combustible material
should be burnt in proper incinerators
Check Your Progress-2
Note : (1) Write your answers in the space given below.
(2) Compare your answers with those given at the end of the unit.
(i) The principal toxic metals are ..............., ................, .................,
............... and .................
(ii) Most of the synthetic polymers are .................... source of
pollution, as they are .................................
(iii) Sources of artificial (man made) modes of nuclear pollution are.
(a) ................................................
(b) .................................................
(c) .................................................
(d) .................................................
(e) .................................................
(iv) Modern methods of solid waste disposal are :
(a) ................................................
(b) ................................................
(c) ................................................
(d) .................................................
(e) .................................................
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7.14 LET US SUM UP
After going through this unit you must have achieved the objectives
stated at the start of the unit. Let us recall what we have discussed so far :
The indiscriminate and mushrooming growth of industries in all around
residential colonies complicated the scenario. The smoke from chimneys
and gases from burning of fossil fuel started polluting our environment,
resulting in menace like acid rains, green house effect, smog formation
and ozone-hole.
Cement is one of the most important building material at the present
time. The main pollutants released from cement industry are CO2 (due to
decomposition of lime stone) and the particulate matter.
Sugar industries release effluents in large quantity containing high degree
of organic pollution hence if effluent stagnates in an area for a few hours,
biological action starts and septic condition gives H2S gas imparting
black colour to the effluent and have high BOD value.
In India annual distillery discharge figures approximately between 100-
110 million litres and this can afford to produce 10-250 tonnes of
nitrogen, 1000-2500 tonnes of potash and 50-100 tonnes of phosphorous,
besides aminoacids, nitrates and microorganisms like phytoplankton and
zoo-plankton.
Drug industries are divided into three groups : (i) Antibiotics, (ii) Natural
drugs and (iii) Synthetic drugs. The main source of pollution from drug
industry include microorganisms and toxic organic chemicals.
Effluents from paper and pulp industry include wood-chips, bits of bark,
cellulose fibres and dissolved lignin, in addition to a mixture of
chemicals. All these produce a sluge which bankets fish spawning
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grounds and destroys certain types of aquatic life. The effluents contain
chlorine, SO2, methyl mercaptan etc, which are very poisonous to fish.
The coal consumption of thermal plants is several million tones. The
chief pollutants are fly ahs, SO2 and other gases and hydrocarbons. Most
of the thermal and electric power plants also discharge considerable
quantities of hot effluents/water into nearby streams or rivers.
Metal industries usually discharge effluents containing copper, lead,
chromium, cadmium, zinc etc, which are toxic to man as well as to
aquatic life.
Further, roasting, calcinations and smelting process also release toxic
gases such as CO2 and SO2. Similarly refining operations release toxic
cyanide, chemicals such as thiosulphate etc.
Synthetic polymers, particularly plastics such as PVC are highly toxic
substances, because they are non bio-degradable. They destroy the
fertility of animals and their respiratory system.
The noise pollution is an unwanted sound which gets dumped into
atmosphere without regard to the adverse effect it may have.
Mechanised industry is the most serious of all large scale noise
producers. In industrial areas noise usually emanates from a wide variety
of machines making it very complex in nature.
The major harmful effects of noise are : impairing hearing, cause
difficulty in falling asleep and to awaken people who are already asleep,
and many other physiological and psychological effects such as nervous
irritability and accidents and blood circulatory digestive and metabolic
difficulties.
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Radioactive elements such as uranium and radium possess highly
unstable atomic nuclei. Their disintegration results in radiation emission.
Similarly atomic power plants, radiations from medical and dental
exposures, telivision sets, atomic fall out and nuclear wastes are also
dangerous sources of radioactive pollution.
Solid waste, often called the third pollution after air and water pollution,
is that material which arises from various human activities and which is
normally discarded as useless or unwanted.
Major sources of solid wastes are : municipal, domestic, commercial,
industrial, mining and agriculture.
Solid waste disposal and its management starts with efficient collection
and transportation to a transfer station, and then disposing it using an
efficient disposal method.
The traditional methods of disposal involve open dumping, sanitary
landfilling and exporting wastes. While the modern methods are
incineration, recycling, composting, generating energy and reuse.
7.15 Check Your Progress : The key
1. (a) (i) hydrosphere
lithosphere
biotic
the climate
alnino effect
(ii) dust
bronchitis
emphysema
(iii) Organic
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biological action
septic
H2S
black
(iv) 100-110
nitrogen
potash
phosphorous
amino acids
nitrates
micro
(b) (i) micro organisms
toxic organic chemicals
(ii) wood Chips
bits of bark
cellulose fibre
lignin
mixture
chemicals
(iii) hot effluents
streams
rivers
2. (i) mercury
lead
arsenic
cadmium
chromium
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(ii) dangerous source
bio non-degradable
(iii) (a) radiations from medical and dental exposure
(b) radiations from TV
(c) nuclear power plants
(d) atomic fallout
(e) nuclear waste
(iv) (a) incineration
(b) recycling
(c) composting
(d) bio-energy
(e) reuse.
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UNIT-VIII ENVIRONMENTAL TOXICOLOGY
Structure
7.1 Introduction
7.2 Objectives
7.3 Chemical Solution to Environmental Problems
7.4 Biodegradability
7.5 Principles of Decomposition
7.6 Better Industrial-Processes
7.7 Chemical-Industrial-Hazards
7.7.1 Bhopal Gas Tragedy
7.7.2 Chernobyl Tragedy
7.7.3 Three Mile Island Tragedy
7.7.4 Minamata Tragedy
7.8 Let Us Sum Up
7.9 Check Your Progress : The Key
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8.1 INTRODUCTION
Health is a state of physical, mental and social well being, not mearly the
absence of disease or infermity. Nearly every human disease probably has some
connection to environmental factors. For most people in the world, the greatest
health threat in the environment is still, as it always has been, from pathogenic
organisms. Bacteria, viruses, protozoans, parasitic worms, and other infectious
agents probably kill more people each year than any other cause of death.
Highly lethal emergent disease, such as Ebola and AIDS, along with new drug-
resistant forms of old diseases are an increasing worry everywhere in the world.
Dangerous chemical agents are divided into two broad categories :
hazardous and toxic. Hazardous means dangerous. This category includes
flammables, explosives, irritants, sensitizers, acids, and caustics. Many
chemicals that are hazardous in high concentrations are relatively harmless
when diluted. Toxins are poisonous. This means they react with specific cellular
components to kill cells. Because of this specificity, toxins often are harmful
even in dilute concentrations. Toxins can be either general poisons that kill
many kinds of cells, or they can be extremely specific in their target and mode
of action.
Allergens are substances that activate the immune system. Some
allergens act directly as antigens; that is, they are recognized as foreign by
white blood cells and stimulate the production of specific antibodies. Other
allergens act indirectly by binding to other materials and changing their
structure or chemistry so they become antigenic and cause an immune response.
Formaldehyde is a good example of a widely used synthetic chemical
that is a powerful sensitizer. It is both directly and indirectly allergenic. Some
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people who are exposed to formaldehyde in plastics, wood products insulation,
glue, fabrics, and a variety of other products become hypersensitive not only to
formaldehyde itself but also to many other materials in their environment,
sometimes called the "sick building" syndrome.
Immune system depressants are pollutants that seem to suppress the
immune system, rather than activate it. Little is known about how this occurs or
which chemicals are responsible.
Neurotoxins are a special class of metabolic poisons that specifically
attack nerve cells (neurons). The nervous system is so important in regulating
body activities that disruption of its activities is especially fast-acting and
devastating. Different types of neurotoxins act in different ways. Heavy metals,
such as lead and mercury, kill nerve cells and cause permanent neurological
damage. Anesthetics (ether, chloroform, haloethane, etc.) and chlorinated
hydrocarbons (DDT, Dieldrin, Aldrin) disrpt nerve cell membranes necessary
for nerve action. Organophosphates (Malathion, Parathion) and carbamates
(carbaryl, zeneb, maneb) inhibit acetyl-cholinesterase, an enzyme that regulates
signal transmission between nerve cells and the tissues or organs they innervate
(for example, muscle). Most neurotoxins are both acute and extremely toxic.
More than 850 compounds are now recognized as neurotoxins.
Mutagens are agents, such as chemicals and radiation, that damage or
alter genetic material (DNA) in cells. This can lead to birth defects if the
damage occurs during embryonic or fetal growth. Later in life, genetic damage
may trigger neoplastic (tumor) growth. When damage occurs in reproductive
cells, the results can be passed on to future generations. Cells have repair
mechanisms to detect and restore damaged genetic material, but some changes
may be hidden, and the repair process itself can be flawed. It is generally
320
accepted that there is no "safe" threshold for exposure to mutagens. Any
exposure has some possibility of causing damage.
Teratogens are chemicals or other factors that specifically cause
abnormalities during embryonic growth and development. Some compounds
that are not otherwise harmful can cause tragic problems in these sensitive
stages of life. One of the most well known examples of teratogenesis is that of
the once widely-used sedative thalidomide. In the 1960s, thalidomide (marketed
under the trade name Cantergan) was the most popular sleeping pill in Europe.
It seemed to have no unwanted side effects and was sold without prescription.
When used by pregnant women, however, it caused abnormal fetal development
resulting in phocomelia (meaning seal-like limbs), in which there is a hand or
foot, but no arm or leg. Evidence indicates that taking even a single thalidomide
pill in the first weeks of pregnancy is sufficient to cause these tragic birth
defects. Altogether, at least 12,000 children were affected before this drug was
withdrawn from the market. Fortunately, thalidomide was not approved for sale
in the United States because the Food and Drug Administration was not
satisfied with the laboratory tests of its safety.
Perhaps the most prevalent teratogen in the world is alcohol. Drinking
during pregnancy can lead to fetal alcohol syndrome- a cluster of symptoms
including craniofacial abonormalities, developmental delays, behavioral
problems, and mental defects that last throughout a child's life.
Carcinogens are substances that cause cancer-invasive out-of-control
cell growth that results in malignant tumors. Cancer rates rose in most
industrialized countries during the twentieth century, and cancer is now the
second leading case of death, Some blame cancer increases due to toxic
synthetic chemicals in our environment and diet.
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There are many sources of toxic and hazardous chemicals in the
environment. Many factors related to each chemical itself, its route or method
of exposure, and its persistence in the environment, as well as the
characteristics of the target organism, determine the danger of the chemical. We
can think of an ecosystem as a set of interacting compartments among which a
chemical moves, based on its molecular size, solubility, stability, and reactivity.
The routes used by chemicals to enter our bodies also play important roles in
determining toxicity.
Solubility is one of the most important characteristics in determining
how, where, and when a toxic material will move through the environment or
through the body to its site of action. Chemicals can be divided into two major
groups : those that dissolve more readily in water and those that dissolve more
readily in oil. Water-soluble compounds move rapidly and widely through the
environment because water is ubiquitos. They also tend to have ready access to
most cells in the body because aqueous solutions bathe all our cells. Molecules
that are oil-or fat-soluble (usually organic molecules) generally need a carrier to
move through the environment and into or within the body. Once inside the
body, however, oil-soluble toxins penetrate readily into tissues and cells
because the membranes that enclose cells are themselves made of similar oil-
soluble chemicals. Once inside cells, oil-soluble materials are likely to
accmulate and to be stored in lipid deposits, where they may be protected from
metabolic breakdown and persist for many years.
A fundamental concept in toxicology is that every material can be
poisonous under some conditions, but most chemicals have some safe level or
threshold below which their effects are undetectable or insignificant. Each of us
consumes lethal doses of many chemicals over the course of a lifetime. One
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hundred cups of strong coffee, for instance, contain a lethal dose of caffeine.
Similarly, 100 aspirin tablets, or 10 kg (22 lbs) of spinach or rhubarb, or a liter
of alcohol would be deadly if consumed all at once. Taken in small doses,
however, most toxins can be broken down or excreted before they do much
harm. Furthermore, the damage they cause can be repaired. Sometimes,
however, mechanisms that protect us from one type of toxin or at one stage in
the life cycle become deleterious with another substance or in another stage of
development.
8.2 OBJECTIVES
The main aim of this unit is to discuss toxic effects of certain chemicals
and industrial hazards resulting from their toxic effects. After going through
this unit you will be able to :
discuss different types of toxic substances,
describe chemical solutions to environmental problems
understand biodegradibility and principles of decomposition and
discuss causes of some well known industrial hazards resulting from
toxic chemicals.
8.3 CHEMICAL SOLUTION TO ENVIRONMENTAL PROBLEMS
The most amazing features of our planet may be the self-sustaining
ecological system. However the greed and lust of selfish human has made
environmental pollution condition more complicated. Amongst the major
environmental problems, the problems related with atmosphere, water and solid
wastes are most important.
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Air :
Although there are thousands of pollutants present in the air in industrial
cities, out of these most important are oxids of carbon, nitrogen, sulphur,
hydrocarbons and particulate matter. Various chemical reactions may be used to
detect and determine these pollutant in air-Thus –
1. hydrocarbons from exhaust can be controlled by using chemical
techniques such as absorption, incineration, condensation, adsorption and
combustion.
The pollutants NOx and CO can also be converted into harmful products
by the above said techniques. By combustion techniques CO and
hydrocarbons can be converted into CO2 :
OHCOnHydrocarbo 2
Combustion
2
CombutionCOOCO
CO can be analysed by exhaust gas analyser :
2. Particulate emissions can be controlled by cyclone collector, cyclonic
separators, gravity setting chamber, filters, scrubbers and elecrostatic
precipitators.
While the metallic particles are determined and estimated using atomic
absorption spectroscopy.
3. Ozone may be measured qualitatively and quantitatively using benzidine
test paper or tetrabase paper.
(a) Benzidine paper is prepared by moistening filter paper with an alcoholic
saturated solution of di-p diamine diphenyl NH2C6H4. C6H4. NH2)
The paper will change colour to-
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(i) brown in presence of ozone,
(ii) blue, then brown in presence of chlorine,
(iii) blue in presence of bromine, nitrogen dioxide.
The paper is not affected by ammonia, hydrogen sulphide hydrogen
peroxide, ammonium sulphide and hydrogen cyanide.
(b) Tetra base, tetramethyl di-p-diamino di phenyl methane [(CH3)2 N. C6H4
CH2. C6H4 N. (CH3)2] paper is made by soaking filter paper in an
alcoholic solution of the reagent. It changes colour to pale-violet by
ozone and to blue by halogens.
4. Hydrogen sulphide (generally in sewage) is determined by methylene
blue which is decolourised in presence of H2S.
The sulphide is determined by optical density method.
5. Sulphur dioxide and sulphur Trioxide, generally fond mixed with
hydrogen sulphide and methyl carptan, hence these gases are first
separated by chromatography and then determined.
(i) A definite amount is passed through indicator which consists of solid
matter in a glass tube. The alumina a silica gel is used as Carrier.
The indicator for SO2 is phend red or brome methyl blue which changes
colour when gas passes through the tube.
For H2S, silver cyanide is used as indicator, which changes colour when
gas is passed through the tube.
(ii) SO2 is also determined by colorimetry in reaction with pyridine
nitroprussate.
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(iii) In West and Geake method, SO2 in air sample is absorbed in 0.1 molar
sodium tetra-chloro merculate. On addition of acid-bleached para
rosaniline and formaldehyde to the complex ion produces red purple para
rosaline methyl sulphonic acid, which is determined
spectrophotometrically.
6. Hydrogen Cyanide turns whatman-50 paper impregnated with FeSO4,
blue and the stain compared with standards.
7. Phosgene (COCl2) gives blue colour with N-ethyl N-2 hydroxy
ethylanaline, p-dimethyl amino-benzaldehyde and diethyl phthalate.
8. Nitrogen dioxide is determined either by Griess-Saltzman or by Jacob
and Hochheiser method.
(i) In Griess-Saltzman method NO2 in the sample is allowed to react with
sulphanilic acid to form diazonium salt. This couples with N (1-
naphthyl) – ethylenediamine dihydrochloride to form a red violet azodye.
The concentration of NO2 in the sample is measured
spectrophotometrically at 5500 Aº.
(ii) In Jacob- Hochheiser method, NO2 is collected by bubbling air through a
sodium hydroxide-sodium arsenite solution to form solution of sodium
nitrite. The nitrite solution is reacted with phosphoric acid, sulfinilamide
and N (1-naphthyl) ethylene diamine dihydrochloride to form an azo dye
and then determined colorimetrically.
9. Carbon monoxide is determined by non-dispersive infrared analysis or by
ultraviolet and catalytic techniques.
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Water :
The raw water available from various sources is contaminated or contains
impurities and hence it is made safe for the purposes for which it is to be used.
All the impurities can not be fully eliminated but they are reduced to such an
extent that water becomes suitable for intended use.
The following chemical methods are used :
1. Removal of salts by reverse osmosis – Various salts and toxic
substances have been successfully removed by using semi-permeable
membrane under a pressure higher than the osmotic pressure. Due to this
mechanism, the flow occurs in reverse direction with the result that salts or
toxic substances are separated from the water. The method is applied now-a-
days to purify the water from the sewage.
In America, scientists have used solar energy in killing the micro-
organisms by using suitable catalyst and also got success in the decomposition
of pesticides like DDT, PCBs etc. by using suitable catalysts. The polluted
waters have also been purified by this solar energy.
2. Use of Bioreactors – Factory waters and organic substances can be
removed by about 95% by using bio-reactors. Heavy metals, alkalies, acids and
toxic industrial wastes can also be removed to the tune of 90-95% by using Bio-
reactors in quicker time.
3. Use of water hyacinth – The Environmental Research Lab. of National
Space Technology, America has used water hyacinth as natural filters to adsorb
toxic substances from the industrial wastes. Using suitable temperature and
waste stabilisation ponds the adsorption power can be increased upto 95% i.e.
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95% of the toxic metals can be removed easily from the waste waters. This is an
economical technique which can be used for developing countries successfully.
4. Barks of Babul – Similarly chromium (VI), iron, nickel, cobalt,
copper,zinc and aluminium are successfully removed upto 90% by using barks
of Babul. Similarly Cr (VI) and Cadmium can be removed upto 95% by using
barks of babul at 35ºC.
5. Oxidation ditches and aerated lagoons can be used to remove
pollutants from the waste waters. (This technique has been recommended by
NEERI, Nagpur).
Similarly, Council of Scientific and Industrial research developed
techniques for removal of pollutants from water :-
(i) Phenolic Componds – Polymeric absorbents have been used to remove
phenolie substances from industrial wastes.
(ii) Mercury – Mercuury-selective ion exchange resin has been used to
remove mercury from chloro-alkali effluents.
(iii) Phosphorus Compounds – If industrial waste containing phosphorus
compounds is passed over bed of aluminium turnings than P-containing
compounds can removed from the waste water easily due to formation of
cage effect.
(iv) Ammonia – It can be removed from waste water by using ion exchange
technique.
(v) Sodium salts – They can be removed by reverse osmosis method.
6. Many dissolved gases can be removed by boiling, decompression or by
means of chemical treatment, except oxygen and nitrogen all other gases can be
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reduced by aeration. Aeration process removes carbon dioxid, hydrogen
sulphide, and odours very rapidly. Following are some of the methods of
aeration.
(i) By mechanically agitating water.
(ii) By diffusing compressed air inside the water
(iii) Mixing air in water under pressure.
(iv) By spraying water into the atmosphere through nozzles 1 to 2.3 metres.
(v) Flowing water through perforated trays and coke beds, so that the water
filters through them.
(vi) By flowing water over weire, steps etc. so that water is exposed to sun as
much as possible.
7. Manganese and iron are generally found together, in raw waters. Iron is
found in the form of ferrous sulphate and ferrous biarbonates.
Iron alone in the absence of organic matter can usually be removed by
aeration of any type followed by sedimentation and filteration. Combination of
iron and manganese or iron alone loosely bound to organic matter may require
aeration to organic matter may require aeration in multiple coke trays (Fg. 1)
containing coke, gravel or crshed pyroluste (pyrolusite is a negative manganese
dioxide.)
Iron alone in the absence of organic matter can usually be removed by
aeration of any type, followed by sedimentation of iron and manganese or iron
alone Loosely bound to organic matter may require aeration in multiple coke
trays containing coke, gravel or crushed pyroluste (pyrolusite is a negative
manganese dioxide).
It has been revealed that matahosphates may be used to prevent
precipitation of iron or manganese. Their use is generally applicable when the
iron concentration is less than 1 ppm.
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For the removal of manganese alone, Green sand and carbonaceous
cation exchangers may be used, with salt for regeneration.
During aeration soluble ferrous and manganese compounds get converted
into insoluble ferric and manganese compounds which are then removed in
settling tanks of filters. The Iron is mostly present in water in ferrous
bicarbonate form. During aeration the following reactions take place.
Fe(HCO4)2 + 2H2 FeO + 2CO2 + 3H2O
4FeO + O2 = 2Fe2O3
Fe2O3 + 3H2O = 2Fe(OH)3
Fe (OH)3 is insoluble in water.
Similar action takes place with manganese bicarbonate.
When iron and Mn occur in water in combination with organic matter, it
becomes difficult to break to bond between them. Once the bond is broken, the
treatment is done as mentioned above. The bond may be broken either by
adding lime and raising pH value of water to about 8.50 to 9.0 or by adding
chlorine or potassium permanganate.
8. Silica may be removed -
(i) By using magnesium hydroxide with carbon dioxide, calcium
bicarbonate or magnesium bicarbonate which produce magnesium
carbonate absorbing silica.
(ii) Apply ferric sulphate and lime to develop ferric hydroxide which absorbs
silica.
9. Removal of Dissolved Minerals –
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Kenzelite and Zepholite proprietary, base-exchange compounds, have
been used successfully in the removal of lead, zinc, dissolved solids from 1000
to 3000 ppm may be demineralized successfully be the application of a direct
electric current is specially designed cells with canvas or similar diaphragms.
10. The hard water has to be made soft by certain methods before it is
supplied to the consumers.
Types of hardness : Temporary hardness is caused due to the presence of
bicarbonates of calcium and magnesium.
The permanent hardness is caused by the presence of sulphates, chlorides
and nitrates of calcium and magnesium. This is also called non-carbonate
hardness.
Removal of temporary hardness : This hardness of water can be removed
by either boiling or by edding lime. Chemical reaction may be as follows :
Ca (HCO3)2 + Heating CaCO3 + H2O CO2
Ca (HCO3)2 + Ca (OH)2 2CaCO3 + 2H2O
Mg (HCO3)2 + Ca(OH)2 CaCO3 + MgCO3+2H2O
Removal of permanent hardness : The following three methods
may be adopted for this purpose.
(i) Zeolite process.
(ii) Demineralization process.
(iii) Lime soda process.
(i) Lime soda process : Hydrated lime removes permanent hardness due to
magnesium sulphate, magnesium chloride and calcium chloride while washing
soda eliminates permanent hardness due to calcium sulphate, calcium chloride
and magnesium chloride. Chemical reactions are given here.
331
CO2 + Ca(OH)2 CaCO3 + H2O
MgSO4 + Ca (OH)2 Mg (OH)2 + CaSO4
Ca SO4 + Na2CO3 CaCO3 + Na2SO4
MgCl2 + Ca(OH)2 Mg(OH)2+ CaCl2
CaCl2 + Na2 CO3 CaCO3 + 2NaCl
MgCl2 + Na2CO3 MgCO3 + 2NaCl
Mg (HCO3)2 + Ca(OH)2 CaCO3 + MgCO3+ H2O
(a) Excess lime treatment : In this method, raw water is overtreated
with lime in order to completely precipitate magnesium. Sod ash is added to
neutralize the excess lime, converting all alkalinity to sodium alkalinity. After
filteration if the pH is about 8.0, it will be good for water with hardness of
about 30 ppm.
(b) Recarbonation : In this process excess lime is added to raw water.
Excess lime is then neutralized by the action of CO2
11. The effluents of various industries require proper designing and treatment
for their safe disposal for example-
(i) Separation and drying of solids from electroplating industry is done by
treating the cyanide effluents by alkaline chlorination in one reactor, the
chromium by ferrous sulphate reduction in another reactor and the two treated
effluents, mixed together along with acid effluents containing other toxic metals
in a third reactor to precipitate the heavy metals at a pH of 8.5 and above. The
metals are treated with FeSO4 to reduce Cr (vi) ions and others are precipitated
by adjusting pH. The sludge. containing metal precipitates may be dried on sand
beds and disposed of on fallow land as a filling material of flow shell
combining all these operations is shown ahead.
332
Fig 7.1 Overall flow sheet for the treatment of various wastes from electroplating works
(ii) For treatment of effluents from sugar factory the following flow sheet is used :
FERRIC SULPHATE FERRIC CHLORIDE
CLARI-FLOCCULATOR
ALKALINE
CHLORINATION
REDUCTION TO
TRIVALENT
CHROMIUM
CYANIDE WASTES
CHROMIUM WASTES
REDUCTION TO
TRIVALENT
CHROMIUM
METAL
PRECIPITATOR
pH 8.5
SETTLING
TANK
TR
EA
TE
D
EF
FL
UE
NT
TO
DR
AIN
EL
EC
TR
OL
PL
AT
ING
WO
RK
S
ALKALI
SLUDGE
DRYING
BEDS
SLUDGE TO
LAND FILL
OTHER METAL
BEARING ACID WASTES
FILTRATE
GAS CLEANING PLANT
OF BLAST FURNACE
OXYGEN PLANT
STEEL MAKING
FURNACE
ROLLING MILLS
SLURRY CONTAINING
FLYASH
WASTES FROM RAW MATERIALS HANDLING, PIG
CASTING MACHINES SLAG
PLANT ETC.
COKE OVEN
PICKLING WASTES
PICKLING RINSE WATER
SETTLING TANK
SETTLING TANK
AMMONIA
RECOVERY SETTLING TANK
EXTENDED
AERATION
AMMONIA
RECOVERY
AMMONIA
RECOVERY
AMMONIA
RECOVERY
LIME SLUDGE
LIME
SETTLING TANK NEUTRALIZATION
WITH LIME
CLARIFIER
TREATED EFFLENTS
TO DISCHARGE
Fig. 8.2 Flow sheet for the treatment of steel plant effluents.
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(iii) The treatment of effluent from paper industry is done in two stages:
1. Primary treatment : Which is called chemical clarification, and
2. Secondary treatment : which is called activated sludge process.
In Primary treatment, chemical clarification is done in three stages – (i)
chemical coagulation with hydrated lime, (ii) chemical coagulation with (alum
+ lime) at pH 10.5 to 11.0 and (iii) pH adjustment to 6-7. The first and 2nd
stages are followed by flocculation and sedimentation. Thus with primary
treatment, we achieve removal of BOD and COD upto 90% respectively.
In Secondary treatment, the activated sludge process is capable of
converting most organic waste (soluble and insoluble) into more stable
inorganic forms or to cellular mass.
PRIMARY SECONDARY
TREATMENT TREATMENT
ALUM + LIME
LIME AT pH 116 ACID Mg. SALT SEEDLING TO SLUDGE
DRYING BED
EFFLUENT
FROM PLANT TO
PRIMARY COAGULATION pH-ADJUST- AERATION DRAIN
FLOCULATION MENT TANK SECONDARY
SEDIMENTATION
TO SLDGE DRYING BEDS
Fig. 8.3 Flow sheet for the treatment of paper waste
12. Sewage treatment involves the following chemical processes :
The composition and strength of sewage may vary from place to place
and country to country. The concentration of sewage depends upon the order of
turbidity of sewage.
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Solid Wastes
After toxic air and polluted water mountains of solid and hazardous
wastes are creating one of greatest problems, since disposal of millions of tons
of these dangerous material is a difficult task. Modern methods of their disposal
present many chemical processes, such as see nit – VI
1. Incineration or Energy Recovery
2. Recycling and
3. Composting
7.4 BIODEGRABILITY
In a body when any foreign substance enters two processes take place :
One the process of bioaccumulation and biomagnification and the other,
biodegradation.
Bioaccmulation and Biomagnification
Cells have mechanisms for bioaccumulation, the selective absorption and
storage of a great variety of molecules. This allows them to acquire nutrients
and essential minerals, but at the same time , can also result in the absorption
and buildup of harmful substances. Toxins that are rather dilute in the
environment can reach dangerous levels inside cells and tissues through this
process.
The effects of toxins also are magnified through food webs.
Biomagnification occurs when the toxic burden of a large number of organisms
at a lower trophic level is accumulated and concentrated by a predator in a
higher trophic level. Phytoplankton and bacteria in aquatic ecosystems, for
instance, take up heavy metals or toxic organic molecules from water or
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sediments. Their predators- zooplankton and small fish-collect and ratain the
toxins from many prey organisms, building up higher toxin concentrations. The
top carnivores in the food chain- game fish, fish-eating birds, and humans – can
accumulate such high toxin levels that they suffer adverse health effects. One of
the first known examples of bioaceumulation and biomagnification involved
DDT, which accumulated through food chains so that, by the 1960s, it was
shown to be interfering with reproduction of peregrine falcons, bald eagles,
brown pelicans, and other predatory birds at the top of their food chains.
Biodegradation
Most organisms have enzymes that process waste products and
environmental poisons to reduce their toxicity. In mammals, most of these
enzymes are located in the liver, the primary site of detoxification of both
natural wastes and introduced poisons. Sometimes, however, these reactions
work to our disadvantage. Compounds such as benzepyrene, for example, that
are not toxic in their original form are processed by these same liver enzymes
into cancer-causing carcinogens. Why would we have a system that makes a
chemical more dangerous? Evolution and natural selection are expressed
through reproductive success or failure. Defense mechanisms that protect us
from toxins and hazards early in life are "selected for" by evolution. Factors or
conditions that affect postreprodctive ages (like cancer or premature senility)
usually don't affect reproductive success or exert "selective pressure."
8.5 PRINCIPLES OF DECOMPOSITION
Some chemical compounds are very unstable and degrade or decompose
rapidly under most environmental conditions so that their concentrations
decline quickly after release. Most modern herbicides and pesticides, for
instance, quickly lose their toxicity. Other substances are more persistent and
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last for long times. Some of the most useful chemicals, such as
chlorofluorocarbons, PVC plastics, chlorinated hydrocarbon pesticides, and
asbestos, are valuable because they are resistant to degradation. This stability,
however, also cause problems because these materials persist in the
environment and have unexpected effects far from the sites of their original use.
In 2000, negotiators from 121 nations agreed to ban or phase out the 12
most notirious persistent organic pollutants, including aldrin, chlordane, DDT,
dieldrin, endrin, heptachlor, hexachloroben.
Some materials produce antagonistic reactions – that is, they interfere
with the effects or stimulate the breakdown of other chemicals. For instance,
vitamins E and A can reduce the response to some carcinogens. Other materials
are additive when they occur together in exposures. Rats exposed to both lead
and arsenic show twice the toxicity of only one of these elements. Perhaps the
greatest concern is synergistic effects. Synergism is an interaction in which one
substance multiplies the effects of another. For example, occupational asbestos
exposure increases lung cancer rates 20-fold. Smoking increases lung cancer
rates by the same amount. Asbestos workers who also smoke, however, have a
400-fold increase in cancer rates.
8.6 BETTER INDUSTRIAL PROCESSES
In the developing world of which we are a part, human kind is facing a
dilemma : demographic pressures on the one hand and dire need and poverty on
the other. The challenge lies in providing the basic necessities like food, shelter,
clothing, clean drinking water, energy, fodder for animals and medicare,
without jeopardising the resource base which is located in biosphere. What
follows is that on the one side we have ecodegradation and pollution due to dire
need, poverty and want, and on the other side of greed, prosperity and
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affluence; a question of survival on the one side and of surplus on the other; of
immediate need on one side, and of future and long range environmental
security on the other. Thus arises the need of sustainable development.
However with the increasing population and attempt to fulfil its need
industrialization is must. Although legislations are there to protect the
environment, air, water, forest and wild and land conservation and control of
pollution, but the need is for the sustainable industrial development i.e. such
industrial development which uses the resources and our environment in such a
way that they are conserved. For this we need better industrial processes which
are ecofriendly.
This involves need to develop and to use such technology in the
industries : Which liberates less or least pollution
(1) The design of the factories and the production methods should be
modified in such a manner that there is check on generation of pollutants.
(2) The technology should be such that the use of fossil fuels is decreased to
minimum and use of solar energy is encouraged
(3) Further, structures of internal combustion engines should be modified so
that there is complete combustion of fuel
(4) An deal industry will be one in which use of soot-free fuels are
encouraged
(5) The chimney of different industries and chemical factories should have
sufficient height and should be filted with suitable filters and electric
precipitants.
(6) Most of the industries are by the sides of rivers or big lakes; hence
mixing of untreated effluents in to water bodies should be strictly banned.
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(7) The garbage should not be burnt in the open, but can be used to produce
energy as well as filler for cement, bricks, asphalt, pavings.
(8) Some of these wastes, if they could be shifted and separated, can even be
recycled as raw material for the industry.
(9) Last but not the least, there should be strict monitoring of all anti-
pollution measurements.
Check Your Progress-1
Notes:(1) Write your answers in the space given below.
(2) Compare your answers with those given at the end of the unit.
(a) (i) The hazardous chemicals may be –
(a) ..........................................
(b) .........................................
(b) .........................................
(d) .........................................
(e) .........................................
(ii) A fundamental concept in toxicology is that every material can be
............................. under ................................, but most chemicals
have some ........................ or ......................... below which their
effects are .........................
(iii) Various .............................. may be used to ......................... and
...................................... the pollutants.
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(b) (i) Most organisms have ........................... that process ...................
and ............................. to reduce their toxicity.
(ii) Some chemical compounds are ............................. and
........................... rapidly under most environmental conditions so
that their-concentration .......................................... after release.
(iii) Better industrial processes are those which use such
............................ which liberate ................................ or
..........................
8.7. Chemical-Industrial-Hazards
Negligence on the part of maintenance of safety measures in a chemical
industry and their regular monitoring and/or human error has resulted in a
number of industrial hazards. Amongst these worst of worst are Bhopal Gas
Tragedy, Chernobyl tragedy, Three Mile Island tragedy and Minamata tragedy.
8.7.1 Bhopal Gas Tragedy
The 'Union Carbide' factory at Bhopal was manufactoring 'Sevin', a MIC
(Methyl isocyanate) based pesticide since 1971. On December 2/3, 1984
leakage of MIC gas from the factory, making the city as a gas chamber was the
worst industrial disaster in the world, in the history of chemical industrie. After
Hiroshima and Nagasaki, it is the third case in the history when 2500 people-
babies and children, fathers and mothers, siblings and grand parents died on the
spot and still uncounted death toll and leaving no fewer than 50,000 affected,
were quickly dwarfed by the tidal wave of human suffering that spread quickly
across the city like the poison cloud that caused it. As people fled their homes,
hospitals overflowed with tens of thousands unable to breathe, unable to see,
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unable to eat, as doctors battled to contain the unending flow of the sick.
According to a rough estimate more than one lac people who live in the vicinity
of the factory were exposed to MIC in varying degrees.
The Union Carbide Manual on 'Standard operating procedure' warns that
if water leaks into the system, it "results in the evolution of a lot of gas (thereby
increasing equipment pressure) and liberation of a lot of heat (thereby raising
temperature). This, is retrospect, in precisely what happened in Bhopal. The
sequence of events went as follows :
(1) At 11.00 p.m. the pressure in the tank 610 is noticed to have risen
from the normal 8 ponds per square inch to 10. As it happens, the
pressure in neighbouring tank 611 has been increased deliberately (by
injecting nitrogen into it) to move the MIC into the pesticide
manufacturing unit. Consequently, the new staff pays little heed to the
pressure rise in tank 610 possibly believing that this tank too has been
pressurised by the earlier shift to transfer MIC to the pesticide unit.
(2) 11.30 p.m., the operating staff in the ability area sense a little irritation
in the eyes because of small MIC leak and ignore it because tiny leaks
are not unusual. Around midnight, the operators around the MIC unit
also sense the leak, and they report in to Production Assistant Shakil
Ibrahim Qureshi. At the same time, the MIC control room operator
reported to Qureshi that the pressure in tank 610 is high.
(3) 12.00, A few minutes after midnight, a mechanic and an operator
check tank 610 and find that cupturedisc, a device that bursts when the
pressure reaches 40 pounds per square inch, has indeed burst and the
safety valve, which is the next check point, has popped.
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(4) 00.30 a.m., The water washing the tubes is hurriedly turned off, but it
was already too late to save the situation.
(5) 1.00 a.m., Untreated MIC vapour is seen escaping through the nozzle
of the 33-metre high atmosphere vent line out into Bhopal's cool night
air.
It must have been a chilling sight. Worse, it was confirmation that at least
five elaborate fail-safe systems designed precisely to prevent such an
occurrence had failed just when they were most needed. Not that this was
unknown to the management of Union Carbide some of the systems were under
repair and had been so for some time. According to experts, the management
had no business to be operating the MIC unit without at least two preventive
devices in perfect working order.
The systems that failed were : Vent gas scrubber, the flare, the water
curtain and the refrigeration system, all very necessary for the safety measures.
Had the systems been working, had the employees kept their wits about
them and reacted the way they have been taught in emergency drills, most of
the MIC escaping into the air could have been rendered harmless. Systems do
fail, and accidents do happen, but Union Carbide's past record, even by
admission of its US principles, is far from exemplary.
This desaster resulted in long-lasting effects not only on human and
animals but also on vegetation, soil and water :
(1) Effect on human health and animals: Methyl Isocyanate affects on
human health and causes in general stomach disorder, bronchitis, chest pain,
irritation in eyes and even blindness along with skin diseases.
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In lung, Methyl isocyanate (MIC) reacts with water to form carbon
dioxide and methyl amine. These compounds remove the oxygen from the place
and which causes death. The methyl isocyanate (MIC) also reacts with nucleic
acid, protein, enzyme, haemoglobin and harmone to produce changes in them.
With the result that man suffers from vomiting, headache, eye irritation,
burning in skin, pressure on lungs, etc. The MIC also affects heart and kidney.
Many people became blind and almost all remaining are suffering from various
ailments (Many died).
The earlier experiments have shown that when a mixture of 5 molecules
of MIC and 10 lakh molecules of air is given to rabbits then within 2
1 hour,
they became blind and deaf. The similar results have been noticed in the cases
of rats and cats in Bhopal when a mixture of 2.0 molecules of MIC+10 lakh
molecules of air were given to cows and dogs then they were found blind within
30 minutes. Now consider the fate of 46 ton MIC gas which was mixed with air
in Bhopal on 3rd
Dec. 1984. Many animals died on the road on 3rd
Dec. 1984 for
30 minutes. There was a problem to shift them to a safer place to avoid odour
pollution problem.
Effect on Vegetation : The analytical results of some plants of Bhopal have
shown that methyl isocyanate has produced structural changes in coriander
leves (Dhania), carrot (Gajar), Knolkhol (Ganth Gobhi), Brassica-Capestrice
(Patta Gobhi), Spinach (Palak), Cabbage (Band gobhi), Buck wheat (Methi),
etc. and even some type of grasses. The experiments are going on potato, onion,
and other vegetables to find out if any structural changes have occurred or not.
In fact it will take a long time to discover the total effects of gas on vegetation
but it is certain that it has affected almost all plants by producing changes in the
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growth and reproduction system. The gas had also affected on the quantity of
fruits in the fruit giving plants.
Effect on Soil and Water :
The gas has affected the soil and water in the nearly area of the factory.
The researches are going on to know the details of the effect of MIC on
environment and the life time effect it will have on the people.
8.7.2 Chernobyl Tragedy
The Chernobyl disaster was a nuclear accident that occurred on 26 April
1986, at the Chernobyl Nuclear Power Plant in Ukraine (then in the Ukrainian
Soviet Socialist Republic, part of the Soviet Union). It is considered the worst
nuclear power plant accident in history and is the only level 7 event on the
International Nuclear Event Scale.
The disaster occurred on 26 April 1986, at reactor number four at the
Chernobyl plant, near the town of Pripyat in the Ukrainian Soviet Socialist
Republic (USSR), during an unusual and (as carried out) unsafe systems test at
low power. A sudden rapid growth in power output took place, and when an
attempt was made for emergency shutdown, an unexpected and more extreme
spike in power output occurred which led to a reactor vessel rupture and a series
of explosions. This event exposed the graphite moderator components of the
reactor to air and they ignited; the resulting fire sent a plume of radioactive
fallout into the atmosphere and over an extensive geographical area, including
Pripyat. The plume drifted over large parts of the western Soviet Union, Eastern
Europe, Western Europe, and Northern Europe. Large areas in Ukraine,
Belarus, and Russia had to be evacuated, with over 336,000 people resettled.
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According to official post-Soviet data, about 60% of the fallout landed in
Belarus.
The sequence of events went as follows :
On 26 April 1986, at 01:23 a.m. (UTC+3), reactor 4 suffered a
catastrophic power increase, leading to explosions in the core. This dispersed
large quantities of radioactive fuel and core materials into the atmosphere and
ignited the combustible graphite moderator. The burning graphite moderator
increased the emission of radioactive particles, carried by the smoke, as the
reactor had not been contained by and kind of hard containment vessel (unlike
all Western plants). The accident occurred during an experiment scheduled to
test a potential safety emergency core cooling feature, which took place during
the normal shutdown procedure.
Nuclear power reactors require cooling, typically provided by coolant
flow, to remove decay heat, even when not actively generating power. As the
name suggests, Pressurised Water Reactors use water flow at high pressure to
remove waste heat. Once the reactor is scrammed, the core still generates a
significant amount of residual heat, which is initially about seven percent of the
total thermal output of the plant. If not removed by coolant systems, the heat
could lead to core damage.
Following an emergency shutdown (scram), reactor cooling is still
required to keep the temperature in the reactor core low enough to avoid fuel
damage. The reactor consisted of about 1,600 individual fuel channels, and each
operational channel required a flow of 28 metric tons (28,000 liters (7,400
USgal) of water per hour. There had been concerns that in the event of a power
grid failure, external power would not have been immediately available to run
the plant's cooling water pumps. Chernobyl's reactors had three backup diesel
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generators. Each generator required 15 seconds to start up, but took 60-75
seconds to attain full speed and reach the capacity of 5.5 MW required to run
one main cooling water pump.
This one-minute power gap was considered unacceptable, and it had been
suggested that the mechanical energy (rotational momentum) of the steam
turbine could be used to generate electricity to run the main cooling water
pumps while the turbine was still spinning down. In theory, analyses indicated
that this residual momentum had the potential to provide power for 45 seconds,
which would bridge the power gap between the onset of the external power
failure and the full availability of electric power from the emergency diesel
generators. This capability still needed to be confirmed experimentally.
The countries of Russia, Ukraine, and Belarus have been burdened with
the continuing and substantial decontamination and health care costs of the
Chernobyl accident. A 2006 report prepared by the Chernobyl Forum, led by
the World Health Organization (WHO) states, "Among the 134 emergency
workers involved in the immediate mitigation of the Chernobyl accident,
severely exposed workers and fireman during the first days, 28 persons died in
1986 due to ARS (Acute Radiation Syndrome), and 19 more persons died in
1987-2004 from different causes. Among the general population affected by
Chernobyl radioactive fallout, the much lower exposures meant that ARS cases
did not occur". It is estimated that there were 4,995 additional deaths, between
1991 – 1998, among the approximately 60,000 most highly exposed people.
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This disaster resulted in the following effects :
Spread of radioactivity
The initial evidence that a major release of radioactive material was
affecting other countries came not from Soviet sources, but from Sweden,
where on the morning of 28 April. workers at the Forsmark Nuclear Power
Plant (approximately 1,100 km (680 ml) from the Chernobyl site were found to
have radioactive particles on their clothes. It was Sweden's search for the source
of radioactivity, after they had determined there was no leak at the Swedish
plant, that at noon on April 28 led to the first hint of a serious nuclear problem
in the western Soviet Union. Hence the evacuation of Pripyat on April 27, 36
hours after the initial explosions, was silently completed before the disaster
became known outside the Soviet Union. The rise in radiation levels had at that
time already been measured in Finland, but a civil service strike delayed the
response and publication.
Contamination from the Chernobyl accident was scattered irregularly
depending on weather conditions. Reports from Soviet and Western scientists
Indicate that Belarus received about 60% of the contamination that fell on the
former Soviet Union. However, the 2006 TORCH report stated that half of the
volatile particles had landed outside Ukraine, Belarus, and Russia. A large area
in Russia south of Bryansk was also contaminated, as were parts of
northwestern Ukraine. Studies in surrounding countries indicate that over one
million people could have been affected by radiation.
Recently published data from a long-term monitoring program (The
Korma-Report) show a decrease in internal radiation exposure of the inhabitants
of a region in Belarus close to Gomel. Resettlement may even be possible in
prohibited areas provided that people comply with appropriate dietary rules.
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Radioactive Release
Two reports on the release of radioisotopes from the site were made
available, one by the OSTI and a more detailed report by the OECD, both in
1998. At different times after the accident, different isotopes were responsible
for the majority of the external dose. The dose that was calculated is that
received from external gamma irradiation for a person standing in the open. The
dose to a person in a shelter or the internal dose is harder to estimate.
Health of plant workers and local people
In the aftermath of the accident, 237 people suffered from acute radiation
sickness, of whom 31 died within the first three months. Most of these were fire
and rescue workers trying to bring the accident under control, who were not
fully aware of how dangerous exposure to the radiation in the smoke was.
Whereas, the World Health Organization's report 2006. Report of the Chernobyl
Forum Expert Group from the 237 emergency workers who were diagnosed
with ARS, ARS was identified as the cause of death for 28 of these people
within the first few months after the disaster. There were no further deaths
identified in the general population affected by the disaster as being caused by
ARS. Of the 72,000 Russian Emergency Workers being studied, 216 non cancer
deaths are attributed to the disaster, between 1991 and 1998. The latency period
for solid cancers caused by excess radiation exposure is 10 or more years, thus
at the time of the WHO report being undertaken the rates of solid cancer deaths
were no greater than the general population. Some 135,000 people were
evacuated from the area, including 50,000 from Pripyat.
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Residual radioactivity in the environment
(Rivers, lakes and reservoirs)
The Chernobyl nuclear power plant is located next to the Pripyat River, which
feeds into the Dnipro River reservoir system, one of the largest surface water
systems in Europe. The radioactive contamination of aquatic systems therefore
became a major issue in the immediate aftermath of the accident. In the most
affected areas of Ukraine, levels of radioactivity (particularly radioiodine : I-
131, radiocaesium : Cs-137 and radiostrontium : Sr-90) in drinking water
caused concern during the weeks and months after the accident. After this initial
period, however, radioactivity in rivers and reservoirs was generally below
guideline limits for safe drinking water. Bio-accumulation of radioactivity in
fish resulted in concentrations (both in western Europe and in the former Soviet
Union) that in many cases were significantly above guideline maximum levels
for consumption. Guideline maximum levels for radiocaesium in fish vary from
country to country but are approximately 1,000 Bq/kg in the European Union.
In the Kiev Reservoir in Ukraine, concentrations in fish were several thousand
Bq/kg during the years after the accident. In small "closed" lakes in Belarus and
the Bryansk region of Russia, concentrations in a number of fish species varied
from 0.1 to 60 kBq/kg during the period 1990-92. The contamination of fish
caused short-term concern in parts of the UK and Germany and in the long term
(years rather than months) in the affected areas of Ukraine, Belarus, and Russia
as well as in parts of Scandinavia.
Ground Water
Groundwater was not badly affected by the Chernobyl accident since
radionuclides with short half-lives decayed away long before they could affect
groundwater supplies, and longer-lived radionuclides such as radiocaesium and
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radiostrontium were adsorbed to surface soils before they could transfer to
groundwater. However, significant transfers of radionuclides to groundwater.
However, significant transfers of radionuclides to groundwater have occurred
from waste disposal sites in the 30 km (19 ml) exclusion zone around
Chernobyl.
Flora and fauna
After the disaster, four square kilometers of pine forest in the immediate
vicinity of the reactor turned reddish-brown and died, earning the name of the
"Red Forest". Some animals in the worst-hit areas also died or stopped
reproducing. Most domestic animals were evacuated from the exclusion zone,
but horses left on an island in the Pripyat River 6km (4ml) from the power plant
died when their thyroid glands were desroyed by radiation doses of 150-200 Sv.
Some cattle on the same island died and those that survived were stunted
because of thyroid damage. The next generation appeared to be normal.
8.7.3 Three Mile Island Tragedy
The Three Mile Island accident was a partial core meltdown in Unit 2 (a
pressurized water reactor manfactured by Babcock & Wilcox) of the Three Mile
Island Nuclear Generating Station in Dauphin County, Pennsylvania near
Harrisburg. The plant was owned and operated by General Public Utilities and
the Metropolitan Edison Co. It was the most significant accident in the history
of the American commercial nuclear power generating industry, resulting in the
release of up to 481 PBq (13 million curies) of radioactive gases, but less than
740 GBq (20 curies) of the particularly dangerous iodine-131.
America's worst accident at a civilian nuclear power plant occurred on
March 28, 1979. Unbeknown to anyone, half the fuel melted in one of two
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nuclear reactors on Three Mile Island near Harrisburg. Pa. Large quantities of
radioactivity leaked from the reactor, but most of it was contained. In all
probability, no one received a harmful amount of radiation. The enormous
damage to the reactor was revealed only years later when TV cameras and a
specially developed ultrasonic, sonar-like imaging system looked inside the
reactor vessel.
The sequence of events went as follows :
In the nighttime hours preceding the accident, the TMI-2 reactor was
running at 97 percent of full power, while the companion TMI-I reactor was
shut down for refueling. The chain of events leading to the partial core
meltdown began at 4 a.m. EST on March 28, 1979, in TMI-2's secondary loop,
one of the three main water/steam loops in a pressurized water reactor. As a
result of mechanical or electrical failure, the pumps in the condensate polishing
system stopped running, followed immediately by the main feedwater pumps.
This automatically triggered the turbine to shut down and the reactor to scram :
control rods were inserted into the core and fission ceased. But the reactor
continued to generate decay heat, and because water was no longer flowing
through the secondary loop, the steam generators no longer removed that heat
from the reactor.
Once the primary feed water pump system failed, three auxiliary pumps
activated automatically. However, because the valves had been closed for
routine maintenance, the system was unable to pump any water. The closure of
these valves was a violation of a key NRC rule, according to which the reactor
must be shut down if all auxiliary feed pumps are closed for maintenance. This
failure was later singled out by NRC officials as a key one, without which the
course of events would have been very different. The pumps were activated
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manually eight minutes later, and manually reactivated between 1 and 2 hours
later, as per procedure, due to excessive vibration in the pumps.
Due to the loss of heat removal from the primary loop and the failure of
the auxiliary system to activate, the primary side pressure began to increase,
triggering the pilot-operated relief valve (PORV) at the top of the pressurizer to
open resulting in the release of up to 481 PBq (13 million curies) of radioactive
gases, but less than 740 GBq (20 curies) of the particularly dangerous iodine-
131.
In the end, the reactor was brought under control, although full details of
the accident were not discovered until much later, following extensive
investigations by both a presidential commission and the NRC. The Kemeny
Commission Report concluded that "there will either be no case of cancer or the
number of cases will be so small that it will never be possible to detect them.
The same conclusion applies to the other possible health effects. "Several
epidemiological studies in the years since the accident have supported the
conclusion that radiation releases from the accident had no perceptible effect on
cancer incidence in residents near the plant, though these findings have been
contested by one team of researchers.
8.7.4 Minamata Tragedy
Minamata is a small factory town dominated by the Chisso Corporation.
The town faces the Shiranui Sea, and Minamata Bay is part of this sea. In
Japanese, "Chisso" means nitrogen. The Chisso Corporation was once a
fertilizer and carbide company, and gradually advanced to a petrochemical and
plastic-maker company. From 1932 to 1968, Chisso Corporation, a company
located in Kumamoto Japan, dumped an estimated 27 tons of mercury
compounds into Minamata Bay. Kmamoto is a small town about 570 miles
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southwest of Tokyo. The town consists of mostly farmers and fisherman. When
Chisso Corporation dumped this massive amount of mercury into the bay,
thousands of people whose normal diet included fish from the bay,
unexpectedly developed symptoms of methyl mercury poisoning. The illness
became known as the "Minamata Disease". The mercury poisoning resulted
from year of environmental destruction and neglect from Chisso Corporation.
By 1925, the Chisso Corporation was dumping waste into Minamata Bay
and destroying the fishing areas. The theory behind Noguchi's industry was to
pay off the Minamata fisherman in exchange for damaging their fishing
environment. According to Eugene Smith's interview of the people who lived in
Minamata, the company believed that it was much cheaper to pay off the few
people who were opposed to the dumping, rather than implement an
environmentally safe technique of waste removal. Therefore, since the villagers
accepted this practice through compensation of money, and the government was
behind the industry, the entire process appeared ethical.
Chisso Corporation started developing plastics, drugs, and pefumes
through the use of a chemical called acetaldehyde in 1932. Acetaldehyde is
produced using mercury as a compound, and was key component in the
production of their products.
Not until the mid-1950's did people begin to notice a "strange disease".
Victims were diagnosed as having a degeneration of their nervous systems.
Numbness occurred in their limbs and lips. Their speech became slurred, and
their vision constricted. Some people had serious brain damage, while others
lapsed into unconsciousness or suffered from involuntary movements.
Furthermore, some victims were thought to be crazy when they began to
uncontrollably shout. People thought the cats were going insane when they
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witnessed "suicides" by the cats. Finally, birds were strangely dropping from
the sky. Series of these unexplainable occurrences were bringing panic to
Minamata.
Dr. Hajime Hosokawa from the Chisso Corporation Hospital, reported on
May 1, 1956 that, "an unclarified disease of the central nervous system has
broken out". Dr. Hosokawa linked the fish diets to the disease, and soon
investigators were promulgating that the sea was being polluted by poisons
from the Chisso Corporation. The Chisso Corporation denied the accusations
and maintained their production. However, by 1958, Chisso Corporation
transferred their dumping from the Minamata Bay to the Minamata River
hoping to diminish accusations toward the company.
The Minamata River flows past the town Hachimon, and into the Shirani
Sea. The people of this area also began developing the "strange disease" after a
few months. The Kumamoto Prefecture government responded by imposing a
ban which allowed fisherman to "catch" fish, but not to "sell" fish from the bay.
Since this was their main food source, the people continued to eat fish at home,
but the ban released government officials from any responsibility for those who
developed the illness.
Finally, in July 1959, researchers from Kumamoto University concluded that
organic mercury was the cause of the "Minamata Disease". A number of
committees, of which Chisso Corporation employees were members, formed to
research the problem. The committees denied this information and refuted the
direct link of mercury to the strange disease. Finally, Dr. Hosokawa performed
concealed cat experiments in front of the Chisso Corporation management, and
illustrated the affects of mercury poisoning by feeding the cats acetaldehyde.
Dr. Hosokawa was the first person who made a valiant effort in proving to
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chisso Corporation that they were the ones accountable for the mercury
poisoning. After the meeting with Chisso officials, Dr. Hosokawa was restricted
from conducting any further research or experiments, and his findings were
concealed by the corporation.
Chisso corporation began to make deals with the victims of the
"Minamata Disease". People who were desperate and legally ignorant signed
contracts which stated that Chisso Corporation would pay them for their
misfortunes, but would accept no responsibility. In fact, there was even a clause
which read, "if Chisso Corporation were later proven guilty, the company
would not be liable for further compensation".
By 1974 only 798 victims had been officially recognized as having
"Minamata Disease". Approximately 3,000 more people were waiting
verification from the board of physicians in Kumamoto Prefecture. Thousands
of people continue to eat fish from the Shiranui Sea, but there are no reportings
of significant health hazards or mercury poisoning like those people who
suffered in Minamata. In 1993, almost forty years later, victims were still being
compensated for damages.
Check Your Progress – 2
Notes: (1) Write your answers in the space given below.
(2) Compare your answers with those given at the end of the
unit.
(a) (i) Bhopal gas tragedy is related with the release of ....................., a
lethal gas used in the manufacture ....................... in .................
Bhopal.
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(ii) Chernobyl disaster was a .......................................... that occurred
on 26 April ...........................
(iii) The Three Mile Island accident was a ......................................... in
unit-2 of the ........................................................ in Daphin country
................................ near Harrisburg.
(iv) Minamata Tragedy is related with the .......................................
resulting due to dumping of waste from ................................... in
............................. bay.
8.8 LET US SUM UP
By going through this unit you must have achieved the objectives stated
at the start of the unit. Let us recall what we have discussed so far :
Health is a state of physical, mental and social well being, not mearly the
absence of disease or infirmity.
Dangerous chemical agents are divided in to two broad categories :
hazardous and toxic.
Hazardous means dangerous. This category includes flammables,
explosive, irritants, sensitizers, acids, and caustics.
Toxins are poisonous. This means they react with specific cellular
components to kill cells.
Allergens are substances that activate immune system. While
Neurotoxins are special class of metabolic poisons that specifically attack
nerve cells. Similarly Mutagens are agents, such as chemicals and
radiation, that damage or alter genetic material (DNA) on cells.
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Carcinogens are substances that cause cancer-invasive, out of control cell
growth that results in malignant tumors.
The most amazing features of our planet may be the self sustaining
ecological system. However, the problems due to increasing pollution of
air, water and solid wastes may be solved using chemical processes.
In a body when any foreign substance enters, two processes take place:
one the process of bioaccumulation and biomagnification and the other
biodegradation.
Most organisms have enzymes that process waste products and
environmental poisons to reduce their toxicity. In mammals, most of
these enzymes are located in the liver, the primary site of detoxification
of both natural wastes and introduced poisons.
Some chemical compounds are very unstable and decompose rapidly
under most environmental conditions so that their concentrations decline
quickly after release.
Better industrial processes are those which use such technology which
liberate least pollution and have design of the production methods which
generate least pollutants.
Negligence on the part of maintenance of safety measures in a chemical
industry and their regular monitoring has resulted in a number of
industrial hazards.
Bhopal gas tragedy was related with the release of methyl isocyanate
(MIC), lethal gas used in the manufacture of Sevin pesticide. On
December 2/3, 1984 leakage from Union Carbide factory at Bhopal,
making the city as a gas chamber was the worst industrial disaster in the
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world in the history of chemical industries. This resulted in the death of
more than 2500 babies, children, men and women, old and young.
The Chernobyl disaster was a nuclear accident that occurred on 26 April
1986, at the chernobyl Nuclear Power Plant in Ukraine. In the aftermath
of the accident 237 people suffered from acute radiation sickness, of
whome 31 died within the first three months.
The Three Mile Island accident was a partial core meltdown in unit-2 of
the Three Mile Island Nuclear Generating station in Dauphin Country
Pennsylvania near Harrisburg. This resulted in the release of up to 481
PBq (13 million curies) of radioactive gases.
Minamata tragedy was related with water pollution through mercury. In
1950 near the Japanese cost in Minamata gulf, fisherman suffered from
blindness, weakness, mental illness, paralysis etc. It was found that
effluents discharged from a plastic factory contained mercury which
entered the fish and by eating those fish all the fisherman suffered from
effects of mercury poisoning.
7.9 CHECK YOUR PROGRESS : THE KEY
1 (a) (i) (a) Toxins
(b) Allergens
(c) Nerotoxins
(d) Teratogens
(e) Carcinogens
(ii) poisonous
some conditions
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safe levels
threshold
undetectable
(iii) chemical reactions
detect
determine
(b) (i) enzymes
waste products
environmental poison
(ii) very unstable
decompose
decline quickly
(iii) technology
less
least pollution
2. (i) methyl isocyanate (MIC)
Sevin
(ii) nuclear accident
1986
(iii) partial Core melt down
three Miles Island Nuclear Generating station Pennysy Ivania
(iv) mercury poisoning
Chisso Corporation Japan