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CHAPTER- I GENERAL INTRODUCTION

Groundwater Quality in India: Present Scenario

Water is essential for all living beings. It is an excellent solvent and is only second to air

and followed by soil in importance for the survival of life in the biosphere (Hasan, 2003).

The United Nations has proclaimed the years of 2005– 2015 as the international decade

for action on “Water for Life” (UN, 2004). Groundwater is a valuable resource that

India needs to exploit sustainably in order to meet the growing demands in its domestic,

agricultural, and industrial sectors (Gupta and Deshpande, 2004; Kumar et al., 2005).

Ground water has played a significant role in maintenance of India‟s economy and in

meeting its requirements for domestic consumption as well as agricultural and industrial

use. It is estimated that approximately one third of the world‟s population use

groundwater for drinking (Nickson et al., 2005).

In the middle of the 20th century India continually faced major challenges and threats on

the public health front from water-borne diseases such as cholera, dysentery, and

typhoid. Yet another contentious issue was in ensuring food security for its ever-growing

population. Before independence, the irrigation and drinking water needs of India were

largely met by rivers, ponds, lakes, dug wells, and rainwater sources. At the same time,

overall watershed management was also poor, placing farmers at the mercy of seasonal

rains that allowed only a single harvest per year. Such food supplies were also

susceptible to droughts and insufficient for the ever increasing population. The

Environmental Hygiene Committee (EHC) of India, constituted shortly after

independence for addressing drinking water challenge, estimated in a 1949 report that

cholera, dysentery, and diarrhoea were alone responsible for over 400,000 annual deaths

in India from 1940 to 1950 (Chakraborti et al., 2011). Then, in the light of these

problems, the World Health Organization (WHO) and UNICEF proposed the large-scale

installation and utilization of tube wells water for drinking and irrigation purposes,

beginning of the first half of 1960, anticipating that groundwater would be relatively free

from the contaminants plaguing surface water. Groundwater is considered to be less

vulnerable than surface sources to climate fluctuations and can therefore help to stabilize

agricultural populations and reduce the need for farmers to migrate when drought

threatens agricultural livelihoods (Shankar et al., 2011). In other words, groundwater

resources provide a reliable drought buffer in large regions of the world (Kumar and Raj,

2013).

The studies revealed the increasing dominance of groundwater as a source of irrigation in

the nation. Of the addition to net irrigated area of about 29.75 million hectares between

1970 and 2007, groundwater accounted for 24.02 million hectares (80%). On an average,

between 2000-01 and 2006-07, about 61% of the irrigation in the country was sourced

from groundwater. The share of surface water has declined from 60% in the 1950s to

30% in the first decade of the 21st century. The most dramatic change in the

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groundwater scenario in India is that the share of tube wells in irrigated areas rose from a

mere 1% in 1960-61 to 40% in 2006-07. By now, tube wells have become the largest

single source of irrigation water in India. Data from Minor Irrigation Census (2001)

showed that three states (Punjab, Uttar Pradesh and Haryana) accounted for 57% of the

tube wells in India (Shankar et al., 2011).

According to the latest available data from the National Sample Survey, 56% of the rural

households get drinking water from hand pumps or tube wells, 14% from open wells and

25% from piped water systems based on groundwater (NSSO, 2006). According to the

department of drinking water supply (DDWS), GOI, nearly 90% of the rural water

supply currently is sourced from groundwater (Shankar et al., 2011).

Ground water forms the major source of water supply for drinking purposes in most parts

of India. India is by far, the largest and fastest growing consumer of groundwater in the

world, with around 80% of the rural population and 50% of the urban population use

groundwater for domestic purposes. Over the last four decades, around 84% of the total

addition to the net irrigated area has come from groundwater sources. Groundwater also

plays a significant role in the ecological functions of various ecosystems. However, as a

consequence of population growth, urbanization, industrialization, irrigation, mining and

waste disposal practices, a large number of anthropogenic contaminants have emerged as

serious threat to groundwater resources. At the same time, geogenic contamination by

arsenic, fluoride and others in many parts of the world also poses an important threat to

groundwater quality with grave implications in human health (Biswas et al., 2001;

Hasan, 2003).

The major problem with groundwater is that once contaminated, it is difficult to restore

the quality. Rise in soil pollution due to dumping of municipal and industrial waste,

heavy use of chemical fertilizers in agricultural land and other human interferences are

altering the properties of underground water. Groundwater is being exploited beyond

sustainable levels and with an estimated 30 million groundwater structures in play, India

is hurtling towards a serious crisis of groundwater over-extraction and quality

deterioration and there is a dire need for a paradigm shift in water sector of our country

in the 12th

plan (Shah, 2013). Nearly 60% of all districts in India have problems related

to either the quantity or the quality of groundwater or both and more than 33% of the

country‟s groundwater resources are unfit for consumption. According to the Central

Ground Water Board‟s latest assessment, the stage of groundwater development is now

61 percent on an all India basis. At the state level, groundwater development has crossed

100 percent in Punjab, Haryana, Rajasthan and Delhi has, closely followed by Tamil

Nadu (80%) and UP (71%). The nature and concentration of various ions, particularly

the properties of the divalent and monovalent cations are important for assessing water

quality (CGWB, 2009).

Groundwater usually contains negligible amounts of suspended and organic impurities

but may contain appreciable amount of mineral impurities brought into solution due to

disintegration of mineral deposits and insoluble carbonate or aluminosilicate rocks by the

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combined action of high underground temperature, hydration, dissolved oxygen, carbon

dioxide and organic acids produced by aerobic and anaerobic decay of organic matter

with which water has been in contact (Vermani and Narula, 1989). Groundwater

composition in a region depends on natural processes such as wet and dry deposition of

atmospheric salts, evapotranspiration, and soil/rock-water interactions as well as

anthropogenic processes, which can alter or modify the natural hydrological cycle

(Subha and Reddy, 2006; Singh et al., 2006). Zuane (1990) has stated that the type and

extent of chemical contamination of groundwater is also dependent on the geochemistry

of the soil through which water flows prior to reaching the aquifers. The different regions

of India are now facing several problems in the quality of their groundwater. Arsenic

contamination is prevalent in the Ganga–Brahmaputra–Meghna Basin; high levels of

fluoride, salinity (electrical conductivity), nitrate, chloride, and iron are encountered in

several areas; and microbial contamination affects shallow aquifers throughout the

country (Majagi et al., 2008; Chakraborti et al., 2009; Pujari and Soni, 2009; CGWB,

2010). In our country, 70% of the water is seriously polluted and 75% of illness and 80%

of child mortality are attributed to water pollution (Raja and Venkatesan et al., 2010).

Therefore, water quality assessment and its sustainable management options need to be

given greater attention in India and other developing countries in order to meet the

growing demands in their domestic, agricultural, and industrial sectors (Gupta and

Deshpande, 2004; Kumar et al., 2005). The primary anthropogenic sources of

groundwater pollution in India are from sewage disposal, agriculture, and industry.

Bacterial Contamination

Indian cities are estimated to generate 20 million m3 of sewage per day, and only 10% of

this sewage is treated prior to reaching groundwater or surface water ecosystems

(Chaudhary et al., 2002). Furthermore, the majority of Indian domestic waste is

improperly disposed. Rapid urbanization throughout India will compound these

problems of inadequate waste treatment and management services. It was reported that

about 40% of shallow tube well water sampled from the Ganga Plain was contaminated

with bacteria and that contamination decreased with increasing tube well depth. Poor

sanitation practice and infrastructure are though to contribute towards this contamination

(Chakraborti et al., 2011).

Nitrate Contamination

One of the most common contaminant identified in groundwater is dissolved nitrogen in

the form of nitrate (NO3-). Groundwater nitrate (NO3

-) contamination is mainly from (a)

agricultural runoff from the over application of nitrogen fertilizers and (b) disposal of

poorly treated or untreated human and/or animal waste. Non-agricultural sources of

nitrogen, such as septic systems and leaking municipal sewers, are generally less

significant regionally but may affect groundwater in specific localities. High

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concentrations of nitrate have been reported in groundwater in different parts of India

and other regions of the world (Wakida and Lerner, 2005; Chakraborti et al., 2011).

Nitrate contamination exceeds the Indian permissible level (45 mg/L) in 11 of the 28

states of India (Mehta, 2006; Chakraborti et al., 2011). In Rajasthan, the groundwater in

22% of villages has excessive NO3– contamination. In Assam and Arunachal Pradesh,

nitrate content was marginally above the permissible limit in some areas, while it was

within the safe range in the rest of the six states of north-eastern region. Higher

concentration of NO3- can cause methaemoglobinaemia, or “blue baby” disorder, gastric

cancer, goiter, birth malformation and hypertension (Spalding and Exner, 1993;

Chakraborti et al., 2011).

Pesticides

The pesticides belong to a category of chemicals used worldwide as herbicides,

insecticides, fungicides, ro-denticides, molluscicides, nematicides, and plant growth

regulators in order to control weeds, pests and diseases in crops as well as for health care

of humans and animals. Even at low concentration, pesticides may exert several adverse

effects, which could be monitored at biochemical, molecular or behavioral levels. The

factors affecting water pollution with pesticides and their residues include drainage,

rainfall, microbial activity, soil temperature, treatment surface, application rate as well as

the solubility, mobility and half life of pesticides. In India organochlorine insecticides

such as DDT and HCH constitute more than 70% of the pesticides used at present.

Reports from Delhi, Bhopal and other cities and some rural areas have indicated

presence of significant level of pesticides in fresh water systems as well as bottled

drinking mineral water samples (Agrawal et al., 2010). Pesticide consumption increased

rapidly in India through the green revolution and into the mid 1990s, reaching 74.323

billion metric tons in the year 1995. Pesticide residues are often retained in soil for long

periods of time and leach steadily into groundwater thereby affecting its quality. In

Howrah district of West Bengal, for example, the groundwater of many areas is unfit for

drinking due to elevated pesticide levels (Chaudhary et al., 2002; Chakraborti et al.,

2011).

Industrial Discharge

Groundwater pollution due to industrial effluents is a common problem in major Indian

cities, including Delhi, Mumbai, Kolkata, Ludhiana, and Kanpur. In Kolkata, industrial

wastes discharged from Paris-Green (copper acetoarsenite) insecticide factory resulted in

As contamination of hand tube wells used for drinking. More than 7000 people were

affected and many of them developed dermatological symptoms of chronic As poisoning

(Chakraborti et al., 2011). In these and other cases of industrial pollution, shallow tube

wells are more susceptible to contamination than deep tube-wells. There are about 2.6

million small-scale industries (SSIs) in India, concentrated largely in urban

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agglomerations. Most of these SSIs do not treat their industrial discharge. The industrial

city of Ludhiana, Punjab depends entirely on groundwater that is contaminated in many

areas (Chaudhury et al., 2001; Chakraborti et al., 2011) with hexavalent chromium (Cr

[VI]) (9-27400 μg L-1

), a suspected carcinogen, and cyanide (3-10000 μg L-1

). Due to the

lack of surface water resources for waste disposal, some factories in this city have been

found directly discharging industrial effluents into groundwater through soak pits. In a

survey in Chennai, the capital of Tamil Nadu, almost 60% of groundwater was found to

be unfit for consumption. The unregulated activities of tanneries in the city have resulted

in serious groundwater chromium contamination in 4 districts. The routine dumping of

hazardous chemicals by a Union Carbide factory in Bhopal, Madhya Pradesh

contaminated local groundwater (Chaudhury et al., 2002; Chakraborti et al., 2011).

Despite the signing of the Basel Convention by 65 countries in 1989, several South

Asian countries, including India, have not imposed this Convention‟s restrictions on the

export of hazardous wastes. During the last 10 years alone, India imported millions of

metric tons of such hazardous wastes. For metal wastes, 10-15% is recovered while the

rest is discharged into the soil (Chaudhury et al., 2002; Chakraborti et al., 2011),

potentially reaching groundwater. The main geogenic groundwater quality problems in

India include salinity (predominantly chloride [Cl-] salts), fluoride ions (F

-), and iron

(Fe), with arsenic (As) posing the largest threat to public health.

Salinity

Groundwater salinity is primarily caused by (a) seawater ingress in coastal areas and (b)

inappropriate irrigation practices that result in groundwater level rise, water logging, and

subsequent heavy evaporation in non coastal and largely semiarid areas. Groundwater

salinity is a growing problem in several Indian states, particularly in coastal areas where

previously sweet (fresh) groundwater sources are becoming saline due to

overexploitation. In the states of Maharashtra, Punjab, Rajasthan, Haryana, Gujarat,

Karnataka, Uttar Pradesh, and Bihar, instances of inland salinity have been documented,

resulting mainly from excessive groundwater use for irrigation. In India, it has been

estimated that about 2 million hectares of land are now affected by saline water. In some

areas of Rajasthan and Gujarat, groundwater salinity is so high that it is utilized for salt

production. The groundwater of 21 of 26 districts of Gujarat and 27 of 33 districts of

Rajasthan is found to be too saline for consumption (Chakraborti et al., 2011).

The increasing dependence on ground water as a reliable source of water has resulted in

its large-scale and often indiscriminate development in various parts of the country,

without due regard to the recharging capacities of aquifers and other environmental

factors. The unplanned and non-scientific development of ground water resources,

mostly driven by individual initiatives has led to an increasing stress on the available

resources. The adverse impacts can be observed in the form of long-term decline of

ground water levels, de-saturation of aquifer zones, increased energy consumption for

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lifting water from progressively deeper levels and quality deterioration due to saline

water intrusion in coastal areas in different parts of the country. In rural India, where

roughly 70% of the population resides, many communities utilize very shallow tube

wells. Therefore, increasing salinity of shallow groundwater also puts them under

economic constraint since they have to explore deeper layers at higher cost (Chakraborti

et al., 2011).

Fluoride Contamination

Fluorosis is the most prevalent groundwater-related disease in India, which in turn is the

most severely affected country worldwide. Nearly 12 million of the 85 million tons of

fluoride deposits on the earth‟s crust are found in India. In Indian continent the higher

concentration of fluoride in groundwater is associated with igneous and metamorphic

rocks. It is estimated that around 200 million people, from among 25 nations the world

over, are under the dreadful fate of fluorosis. India and China, the two most populous

countries of the world, are the worst affected. Estimation finds that 65% of Indias

villages are exposed to fluoride risk. In India, an estimated 62 million people, including 6

million children suffer from fluorosis because of consuming Fluoride-contaminated

water (Raju et al., 2009; Suthar et al., 2008). In India alone, more than 66 million people

are estimated to be suffering from fluorosis, including 6 million children below 14 years

of age (Ayoob and Gupta, 2006). It was found that 20 of 28 Indian states have some

degree of groundwater fluoride contamination, impacting 85-97% of districts in some

states (Nayak et al., 2009). A number of cases of fluorosis have been reported mostly

from the granite and gneissic complex of different states such as Andhra Pradesh,

Assam, Bihar, Chhattisgarh, Delhi, Gujarat, Haryana, Jammu & Kashmir, Jharkhand,

Karnataka, Kerala, Maharashtra, Madhya Pradesh, Orissa, Punjab, Rajasthan, Tamil

Nadu, Uttar Pradesh, West Bengal (Sankararamakrishnan, et al., 2008; CGWB, 2010;

Chakraborti et al., 2011)

Iron Contamination

Iron is an essential element for both plant and animal metabolism. Iron is a common

constituent in soil and ground water. It is present in water either as soluble ferrous iron or

the insoluble ferric iron. Water containing ferrous iron is clear and colorless because the

iron is completely dissolved. When exposed to air, the water turns cloudy due to

oxidation of ferrous iron into reddish brown ferric oxide. The concentration of iron in

natural water is controlled by both physico-chemical and microbiological factors. It is

contributed to ground water mainly from weathering of ferruginous minerals of igneous

rocks such as hematite, magnetite and sulphide ores of sedimentary and metamorphic

rocks. Fe concentrations below 0.3 mg/L do not impart a noticeable taste to drinking

water. Concentrations of 1-3 mg/L may also be acceptable in case of scarcity, while >3

mg/L iron is likely to be unacceptable to most people. Concentrations of 1-3 mg L-1

may

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also be acceptable in case of scarcity, while >3 mg L-1

iron is likely to be unacceptable to

most people. People often refuse to drink water containing high Fe due to poor taste and

discoloration. Widespread and elevated groundwater Fe levels have been found in 12

states in India with Rajasthan, Orissa, and Tripura being particularly contaminated. In

Rajasthan, 20 out of the total 33 districts have groundwater contaminated with high Fe.

High concentrations of Iron in groundwater have been observed in more than 1.1 lakh

habitations in the country. High concentration of Iron (>1.0 mg L-1

) in ground water has

been found in the states of Andhra Pradesh, Assam, Bihar, Chhattisgarh, Goa, Gujarat,

Haryana, Jharkhand, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Manipur,

Meghalaya, Orissa, Punjab, Rajasthan, Tamil Nadu, Tripura, Uttar Pradesh, West Bengal

& Andaman & Nicobar (CGWB, 2010; Chakraborti et al., 2011). In North East India,

the amount of iron is relatively high and groundwater in almost all states contains iron

above the permissible limit. Higher concentrations of iron were observed in Assam,

Arunachal Pradesh, Meghalaya, Mizoram, and Tripura (Singh, 2006; CGWB, 2010).

Trace Elements in Groundwater

The presence of trace elements, particularly arsenic in groundwater is an important issue

in recent years because of their toxicity, persistence and bioaccumulave nature in

environment (Pekey et al., 2004). Trace elements are generally present in low

concentrations in natural water systems. Trace elements are contributed to groundwater

from a variety of natural (minerals containing trace elements in the soil zone or the

aquifer material) and anthropogenic (mining, fuels, smelting of ores and improper

disposal of industrial wastes) sources (Abollino et al., 2004; Leung and Jiao, 2006).

Trace metals, including chromium (Cr), nickel (Ni), cadmium (Cd), and mercury (Hg)

have also been found in the groundwater of 43 districts of 14 states in India (Mehta,

2006).

The toxicity of an element depends on the concentration of the chemical form, route of

exposure, bio-availability, and distribution in the body and storage and excretion

parameters. Some of the trace elements like iron (Fe), manganese (Mn), copper (Cu),

zinc (Zn), cobalt (Co), nickel (Ni) etc are essential in trace levels for the human body to

activate vital functions and biological processes. Their deficiency or excess in the human

system can lead to a number of disorders, while other trace metals like Pb, As, Hg etc are

not only biologically non essential and known to be persistent environmental

contaminants, they are also definitely toxic to most forms of life (Quyang et al., 2002;

Jinwal et al., 2009). Trace elements may be contributed by domestic and industrial

waste-water, use of chemical fertilizers and pesticides in agriculture and also through

water-rock interaction.

The presence of trace elements including arsenic in the ground water of north-eastern

states was also documented (Chakraborti et al., 2004; Singh, 2006; Bhuyan and Bhuyan,

2011). In Arunachal Pradesh and Meghalaya, cadmium was detected to be slightly above

the permissible level (>0.005 mg L-1

) in some groundwater sources. In few places in

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Nagaland, Tripura and Sikkim also, the concentrations of cadmium, nickel and lead were

detected to be slightly above the permissible level of BIS (Dhyani et al., 2008 and Raja

et al., 2013). Chakrabarty and Sarma (2011) have reported that a good number of

drinking water sources of Kamrup District of Assam, India, were contaminated with

cadmium, manganese, and lead. Borah et al. (2009) reported higher concentration of lead

and iron beyond the maximum contamination level in groundwater in the tea garden belt

of Darrang district, Assam. High contamination of groundwater in Tripura with respect

to iron (51.5 %), manganese (26.9 %) and arsenic (6.35 %) was reported (Banerjee et al.,

2011). The concentrations of copper, zinc, nickel, cadmium and lead in groundwater

exceeded the BIS permissible level (>0.05 mg L-1

) in Meghalaya. In Mizoram, the

concentration of lead (>0.005 mg L-1

) was observed to be slightly above the drinking

water standards (Singh, 2006). Besides trace elements, the physico-chemical parameters

in drinking water are also important and their high and low concentration can directly or

indirectly affect human health.

Physico-chemical parameters as well as hydrochemistry were studied by many

researchers to assess the characteristics of groundwater (Subba et al., 2002; Bhardwaj

and Singh, 2010). The pH is one of the important indicators of water quality and level of

pollution in aquatic ecosystem. The electrical conductivity (EC) qualitatively estimates

the status of inorganic dissolved solids and ionized species in water (Jonnalagadda and

Mhere, 2001). High nitrate (NO3) concentration is toxic especially for bottle fed babies

causing the „blue baby syndrome‟ (Leeuwen, 2000). The adult average daily intake of

potassium (K) through water ingestion is generally <0.1% (Lattorre and Toro, 1997). For

normal body functions, like other light elements, sufficient amount of K is very

significant. The low concentration of K can cause heart problems, hypertension, muscle

weakness, bladder weakness, kidney diseases, asthma, while its high concentration can

cause rapid heartbeat, cystitis, ovarian cysts, reduced renal function and abnormal

metabolism of protein (Marijic and Toro, 2000). Mineral deposits are the main sources of

sodium (Na) in water. Low concentrations of Na+ can cause numerous health problems

such as mental apathy, low blood pressure, fatigue, depression, and dehydration, while

its high concentration is responsible for edema, hypertension, stroke, headaches, kidney

damage, stomach problems and nausea (Robert and Mari, 2003). The deficiency of base

cations like calcium (Ca) and magnesium (Mg) in drinking water has been associated

with cardiovascular diseases (Yang et al., 2006).

Brief Account on Arsenic

History of Arsenic

Of the trace elements cited above, arsenic (As) and its contamination of drinking water is

among the most awesome environmental health challenges nowadays, threatening the

well-being and livelihood of more than a hundred million people worldwide

(Bhattacharya et al., 2007). Arsenic (As) is known to be used in Persia and other

countries since ancient times. The word arsenic is borrowed from a Persian word

Zarnikh, meaning yellow orpiment. The word zarnikh was borrowed by the Greek and

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called as arsenikon. Albert Magnus (Albert the Great, 1193–1280) is believed to have

been the first to isolate the element in 1250. In 1649 Johann Schroder published two

methods of preparing arsenic. As the symptoms of arsenic poisoning were somewhat ill-

defined (Dakeishi et al., 2006; Smith, 2007; Azizur Rehman et al., 2008), it was

frequently used for murder until the advent of the Marsh Test, a sensitive chemical test

for its presence. Due to its use by the ruling class to murder one another (Steck-Flynn,

2007) and its potency and discreetness, arsenic has been called the Poison of Kings and

the King of Poisons (Sprando et al., 2007). Arsenic is known as „Senko Bish‟ in Bengali

(Rahman, 1999), which truly means “King of Poisons”. The use of arsenic as a deadly

poison has been known and reported for many years. There is a well-known historical

fact about the poisonous character of arsenic. After winning the War of Waterloo, the

British force reportedly used arsenic to kill the French Emperor Napoleon Bonaparte.

After his death on May 5, 1821 (Hindmarsh and Corso, 1998), it was announced that

Napoleon died due to stomach cancer. But many years after his death, the hair of

Napoleon, reserved at a museum, was tested and it was proved that he was killed by

arsenic poisoning. Thus, in 1960, activation analyses at the Harwell Nuclear Research

Laboratory of the University of Glascow, London, of authenticated hairs of Napoleon

Bonaparte taken immediately after his death confirmed Napoleon‟s chronic arsenic

poisoning on the island of St. Helena (Weider and Fournier, 1999). The arsenic

concentration in Napoleon‟s hair was 13 times more than the normal level and it was

considered to be the reason of his death.

Arsenic Chemistry

Groundwater contamination by arsenic (As) has become a global concern in recent years.

Arsenic is a metalloid (atomic no. 33 and an atomic mass of 74.91) widely distributed in

the earth‟s crust. Elemental arsenic is member of Group V A of the periodic table, with

nitrogen, antimony and bismuth. It can exist in 4 valency states: -3, 0, +3, and + 5.

Under reducing conditions, arsenite [As (III)] is the dominant form; arsenate [As (V)] is

generally the stable form in oxygenated environments. Arsenic and its compounds occur

in crystalline, powder, and amorphous or vitreous forms. It usually occurs in trace

quantities in all rock, soil, water and air. Environmental characteristics strongly influence

arsenic movement in soil. Movement is a strong function of speciation and soil type. In a

non-absorbing sandy loam, arsenite is 5-8 times more mobile than arsenate The pH of

soil also influences arsenic mobility. At a pH of 5.8, arsenate is slightly more mobile

than arsenite, but when pH changes from acidic to neutral to basic, arsenite increasingly

tends to become the more mobile species, though mobility of both arsenite and arsenate

increases with increasing pH. In strongly absorbing soils, transport rate and speciation

are influenced by organic carbon content and microbial population. Both arsenite and

arsenate are transported at a slower rate in strongly absorbing soils than in sandy soil

(Ahamed, 2006). Structures of some naturally occurring inorganic and organic arsenic

species are shown in Figure 1.

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Figure 1 Structures of arsenic compounds

Sources of Arsenic

Sources of arsenic in the environment can be categorized as: i) geological (geogenic), ii)

anthropogenic (human activities), and iii) biological (biogenic). Arsenic is a natural

constituent of the earth‟s crust and is the 20th

most abundant element. Long before man‟s

activities had any effect on the balance of nature, arsenic was distributed ubiquitously

throughout earth‟s crust, soil, sediment, water, air and living organisms (Mandal and

Suzuki, 2002; WHO, 2011). The average concentration of arsenic in the continental crust

is 1-2 mg/kg. Arsenic is released in the environment through natural processes such as

weathering of rocks and minerals and volcanic eruptions, and may be transported over

long distances as suspended particulates and aerosols through water or wind or water

erosion. Volcanic action is the most important natural source of arsenic. Most

environmental As problems are the result of mobilisation under natural conditions.

Arsenic naturally occurs in over 200 different mineral forms, of which approximately

60% are arsenates, 20% sulfides and sulfosalts and the remaining 20% includes

arsenides, arsenites, oxides, silicates and elemental arsenic (Mandal and Suzuki, 2002).

High concentrations of inorganic arsenic occur in sulphide minerals and metal oxides,

especially iron oxides. Major natural arsenic bearing minerals are arsenopyrite (FeAsS),

realgar (AsS), and orpiment (As2S3). Arsenopyrite is the most common arsenic ore

mineral (Mandal and Suzuki, 2002). The levels of arsenic in the soils vary considerably

among geographic regions. Arsenic is present in soils in higher concentrations than those

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in rocks. Uncontaminated soils usually contain 1–40 mg kg−1

of arsenic, with lowest

concentrations in sandy soils and those derived from granites, whereas higher

concentrations are found in alluvial and organic soils (Mondal and Suzuki, 2002). The

natural level of arsenic in sediments is usually below 10 mg kg−1

, dry weight and varies

considerably all over the world. In air, arsenic exists predominantly absorbed on

particulate matters, and is usually present as a mixture of arsenite and arsenate, with the

organic species being of negligible importance except in areas of arsenic pesticide

application or biotic activity. The amount of arsenic inhaled per day is about 50 ng or

less (assuming that about 20 m3 of air is inhaled per day) in unpolluted areas. The

concentration of arsenic in unpolluted fresh waters typically ranges from 1– 10 µg L−1

,

rising to 100–5000 µg L−1

in areas of sulfide mineralization and mining (Smedley et al.,

1996). In groundwater arsenic is mostly found as trivalent arsenite [As (III)] or

pentavalent arsenate [As (V)]. Organic arsenic species are abundant in seafood, and

include such forms as monomethyl arsenic acid (MMAA), dimethyl arsenic acid

(DMAA), and arseno-sugars. They are very much less harmful to health, and are readily

eliminated by the body (ICAR, 2004). However, anthropogenic sources such as mining

activity, combustion of fossil fuels, use of arsenical pesticides, herbicides and crop

desiccants, and the use of As as an additive to livestock feed could comprise some

additional sources of arsenic. Approximately 97% of the arsenic produced enters end

product manufacture in the form of white arsenic and remaining 3% as metal for

metallurgic additives, especially lead and copper alloys (Mandal and Suzuki, 2002).

About 70% of the world production of arsenic is used in timber treatment, 22% in

agricultural chemicals, and the remainder in glass, pharmaceuticals and metallic alloys

(NIH and GGWB, 2010). Mining, metal smelting; burning of fossil fuels and coal-fired

power plants are the major industrial processes that contribute arsenic contamination to

air, water and soil. Earlier arsenic was widely used for preparation of arsenical

insecticide (Paris green/ copper acetoarsenite, lead arsenate, calcium arsenate),

herbicides (sodium arsenate), desiccants (arsenic acid), wood preservatives (chromate

copper asrsenate, and ammonical copper arsenate) feed additives (H3AsO4, 3-nitro-4-

hydroxy phenylarsonic acid, 4-nitrophenylarsonic acid), drugs (Donovan‟s solution,

tryparsamide and carbarsone), and poison as homicidal and suicidal agent (Mandal &

Suzuki, 2002). The biogenic sources are predominant in marine ecosystems.

Mechanisms of Arsenic Mobilization

Widely accepted mechanisms of arsenic mobilization in groundwater are yet to be

established. However, based on arsenic geochemistry, three hypotheses describing

probable mechanisms of arsenic (As) mobilization in groundwater, especially with

reference to Holocene aquifers such as those in West Bengal and Bangladesh, have been

suggested (Bose and Sharma, 2002). These are i) Pyrite Oxidation Hypothesis: Insoluble

As- bearing pyrite minerals, such as Arsenopyrite (FeAsS) are rapidly oxidized when

exposed to atmosphere, realizing soluble As (III), sulfate (SO42-

), and ferrous iron (Fe2+

).

The dissolution of these As-containing minerals is highly dependent on the availability

12

of oxygen and the rate of oxidation of sulphide. The released As (III) is partially oxidised

to As (V) by microbially mediated reactions. The chemical reaction (Ravenscroft et al.,

2001) is given as:

FeAsS + 13Fe3+

+ 8H2O → 14Fe2+

+ SO42-

+ 13H+ + H3AsO4 (aq)

ii) Oxyhydroxide Reduction Hypothesis: According to this hypothesis, arsenic is released

in groundwater by reductive dissolution of FeOOH under reducing condition, which is

driven by natural organic molecules (e.g., acetate) in peaty strata both within the aquifer

sands and in the overlying confining unit. Such reducing conditions are usually found in

recently deposited fine-grained deltaic and alluvial sediments. The chemical reaction

(Nickson et al., 2000; Bhattacharya et al., 2007) is given as:

8FeOOH - As(s) + CH3COOH + 14 H2CO3 → 8 Fe

2+ + As (d) +16 HCO3

- + 12 H20

Where As(s) is sorbed As, and As (d) is dissolved As.

This mechanism involving dissolution of FeOOH under reducing conditions is

considered to be the most probable reason for excessive accumulation of As in

groundwater (Harvey et al., 2002; Smedley and Kinniburgh, 2002).

iii) Competitive Exchange of Phosphate from Fertilizer: This hypothesis is based on the

greatly increased use of phosphate fertilizers over the past 15 years in Bangladesh. But

there is no causal link between arsenic and the application of fertilizer. Among other

objections to this hypothesis, experiments showed that 2 µgL-1

of arsenic would be

desorbed by 5 µgL-1

phosphorus concentration (upper limit in Bangladesh groundwater)

in groundwater (Ravenscroft et al., 2001).

Health Effects

Chronic exposure to As can cause harm to human cardiovascular, dermal,

gastrointestinal, hepatic, neurological, pulmonary, renal and respiratory systems

(ATSDR, 2000) and reproductive system as well (Mandal and Suzuki, 2002). Besides,

other impacts include impacts on agricultural food such as vegetables and rice, cow milk

and cow dung, impacts on social life, and impacts on climate change. A summary of

health effects is presented in table 1.

13

Table 1 Summary of effects of chronic arsenic exposure on human health (Mandal and

Suzuki, 2002)

System Health Effects

Cardiovascular Heart attack, cardiac arrhythmia, thickening of blood vessels, loss of

circulation leading to gangrene of extremities, hypertension

Dermal

Hyperpigmentation, abnormal skin thickening, narrowing of small

arteries leading to numbness (Raynaud‟s Disease), squamous and

basal-cell cancer

Gastrointestinal Heartburn, nausea, abdominal pain

Hematological Anemia, low white-blood-cell count (leucopenia)

Hepatic Cirrhosis, fatty degeneration, abnormal cell growth (neoplasia)

Neurological Brain malfunction, hallucinations, memory loss, seizures, coma,

peripheral neuropathy

Pulmonary Chronic cough, restrictive lung disease, cancer

Respiratory Laryngitis, tracheal bronchitis, rhinitis, pharyngitis, shortness of

breath, perforation of nasal septum

Renal Hematuria, proteinuria, shock, dehydration, cortical necrosis, cancer

of kidneys and bladder

Reproductive Spontaneous abortions, still-births, congenital malformations of

fetus, low birth weight

Guidelines and Standards

Because of the proven and widespread negative health effects on humans, WHO lowered

the health-based provisional guideline for a “safe” limit for arsenic concentration in

drinking water from 50 μgL-1

to 10 μgL-1

in 1993. The guideline value for arsenic is

provisional because there is clear evidence of hazard but uncertainty about the actual risk

from long-term exposure to very low arsenic concentrations (WHO, 2004). The value of

10 μgL-1

was set as realistic limit taking into account practical problems associated with

arsenic removal to concentrations lower than this. The WHO provisional guideline of 10

μgL-1

has been adopted as a national standard by many countries, including Japan,

Jordan, Laos, Mongolia, Namibia, Syria and the USA, and by the European Union (EU).

Implementation of the new WHO guideline value of 10 μgL-1

is not currently feasible for

a number of countries strongly affected by the arsenic problem, including Bangladesh

14

and India, which retain the 50 μgL-1

limit. Other countries that have not updated their

drinking water standards recently and retain the older WHO guideline of 50 μgL-1

include Bahrain, Bolivia, China, Egypt, Indonesia, Oman, Philippines, Saudi Arabia, Sri

Lanka, Vietnam and Zimbabwe. The most stringent standard currently set for acceptable

arsenic concentration in drinking water is by Australia, which has a national standard of

7 μgL-1

(UN, 2001).

Metabolism of Arsenic

Humans are exposed to many different forms of inorganic and organic arsenic species

(arsenicals) in food, water and other environmental media. Each of the forms of arsenic

has different physicochemical properties and bioavailability and Biotransformation is the

major metabolic pathway for inorganic arsenic (iAs) in humans and in most of the

animal species. Biomethylation of inorganic arsenic occurs in vivo/ human body through

intake of water, food and inhalation of respiratory dust and fumes. Methylation of

inorganic arsenic mainly occurs in liver but other organs also have the arsenic

methylation activity (Vahter, 2002). When ingested in dissolved form, inorganic arsenic

is readily absorbed in the gastrointestinal tract. Absorbed arsenic is transported in the

blood, bound to -SH groups in proteins and low molecular weight compounds such as

GSH or cysteine, to the organs in the body. Most of the arsenic in blood is cleared with a

half-time of about 1 hr. Tissue distribution depends on blood perfusion, tissue volumes,

diffusion coefficients, membrane characteristics, and tissue affinities. In this process

inorganic arsenic is enzymatically biotransformed to methylated arsenicals including

monomethyarsonic acid (MMA) and di-methyl arsinic acid (DMA); these metabolites

(less toxic) are excreted in urine and the biomarker of chronic arsenic exposure (Thomas

et al., 2001). iAs (V) → iAs (lll)→ MMA (V) → MMA (lll) → DMA (V)

This methylation process has traditionally been considered as the detoxification pathway

for iAs, because methylated compounds (MMA and DMA) are less acutely toxic, less

mutagenic, less reactive with tissue components and excreted faster in urine when

methylated compounds are compared with iAs, ( Hopenhayn, 2006). Methylation also

facilitates the excretion of iAs from the body. However, not all iAs is completely

methylated to DMA, as can be shown by the presence of iAs as well as MMA and DMA

in the urine; urination is the main route of elimination of ingested iAs in humans,

accounting for approximately 70% of the intake. The average proportions of arsenic

metabolites in urine are about 15–25% iAs, 10–15% MMA, and 70–80% DMA.

Methylation of iAs, as reflected by the relative concentrations of species (iAs, MMA,

and DMA) in urine, varies widely among individuals and, to a lesser extent, among

populations. It is also affected by factors such as gender (women are more efficient

methylators, i.e. they have a greater proportion of methylated species in urine), smoking

(which lowers methylation efficiency), and ethnicity (some groups, such as native

Andeans, appear to have increased capacity for methylation) (Hopenhayn, 2006). Other

factors that also seem to play a role in methylation are protein consumption and

15

availability of certain micronutrients, such as selenium and beta-carotene. A few studies

have reported direct links between methylation ability and health outcomes, suggesting

that individuals with lower methylation capacity are at increased risk of bladder cancer

(Chen et al., 2007) and skin cancer (Yu et al., 2000). Firstly, reduction of iAs (v) to iAs

(lll) is mediated by glutathion, which acts as reducing agent and then methyl group is

transferred to iAs (lll) from S-adenosyl methionine to form MMA (V). Then MMA (V)

is reduced to form an intermediate metabolite monomethylarsonous acid (MMAIII) and

during the second methylation, MMA (III) is oxidized to DMA (V) (Le et al., 2000).

Glutathion and S – adenosyl methionine acts as co-substrate. The activity of first and

second methylation steps is represented by the ratios of iAs / MMA and MMA / DMA,

respectively. Methylation is considered to be good if the ratio is low and methylation is

poor if the ratio is high (Le et al., 2000). Children are poor methylator and good excretor

in comparison to the adults. Thus children are less susceptible to arsenicism (Chowdhury

et al., 2003).

Toxicity

The bioavailability and toxicity of arsenic is dependent on its chemical form. In general,

the inorganic forms of arsenic are much more toxic than the organo-arsenic forms.

Organo-arsenic species such as tetraethyl-arsonium ion arsenobetaine and arsenocholine,

are common in marine organisms. However recently it has been discovered that some of

the organic arsenic species like MMA (III), DMA (III), which have been identified in

urine are very toxic (Ahamed, 2006). Arsenic toxicity could be acute toxicity and

chronic toxicity. Acute toxicity of arsenic is related to its chemical form and oxidation

state. The characteristic symptoms of acute arsenic toxicity in humans include

gastrointestinal discomfort, vomiting, diarrhea, bloody urine, anuria, shock, convulsions,

coma and death. The greater acute toxicity of the methylated trivalent intermediates of

arsenic suggests that the methylation of arsenic is not solely a detoxication mechanism.

Chronic exposure to inorganic arsenic affects many different systems within the body.

One of the hallmarks of chronic toxicity in human from oral exposure to arsenic is skin

lesions, which are characterized by hyperpigmentation, hyperkeratosis, and hypo

pigmentation (IARC, 2004).

Mechanism of Toxicity

Inactivation of enzyme systems which serve as biological catalyst leads to altered cell

activity. The As V is first reduced to As III (arsenate to arsenite) which exerts its effect.

Aposhian postulated that binding of trivalent arsenic (As III) to non essential sulfhydryl

groups in the cells may be an important route of arsenic detoxification. The trivalent

arsenic interferes with enzymes by binding to HS-1 groups especially where there are

two adjacent HS, HS-1 and HO-1 groups in the enzyme. Arsenic inhibits enzymes such

as pyruvic oxidase. S-amino acid oxidase, choline oxidase and transaminase. Arsenic (V)

16

as arsenate can be disruptive by competing with phosphate. Arsenate uncouples

oxidative phosphorylation. Oxidative phorphorylation is the process by which adenosine

-5-triphosphate (ATP) is produced while at the same time reduced nicotinamide adenine

dinucleotide phosphate (NADP) is oxidised.

3ADP +SH3PO4 3ATP +3H2O

NADP + H + 1/2O2 NAD + H2O

The arsenate disrupts this process by producing an arsenate ester of ADP, which is

unstable and undergoes, hydrolyses non enzymatically. This process was termed

arsenolysis. Glucose 4 arsenate is produced rather than Glucose-6- phosphate, hence the

energy metabolism is inhibited. Arsenic inhibits the action of selenium which causes the

apparent deficiency of glutathione peroxide system, a selenium dependent enzyme (Saha,

2002).

Global Arsenic Scenario

Over the past two or three decades the occurrences of high arsenic concentrations in

drinking water have been recognized as a major public health concern in several parts of

the world. Before 2000 there have been five major incidents of ground water arsenic

contamination in Asian countries: Bangladesh, West Bengal, India and some places in

China. Between 2000 and 2005 arsenic-related groundwater problems have also emerged

from other Asian countries including new sites in China, Mongolia, Lao people

Democratic Republic, Nepal, Cambodia, Myanmar, Afghanistan, DPR Korea and

Pakistan. The countries affected at present include: Afghanistan, Argentina, Australia,

Bangladesh, Brazil, Bulgaria, Canada, Cambodia, Chile, PR China, Czech Republic,

Egypt, Fairbanks Alaska, Finland, Germany, Ghana, Greece, Hungary, India, Iran, Japan,

Lao PDR, Mexico, Myanmar, Nepal, New Zealand, Pakistan, Philippines, Poland,

Romania, Sri Lanka, Spain, Sweden, Switzerland, Taiwan China, Thailand, United States

of America, United Kingdom, and Vietnam. Figure 2 shows the arsenic contamination

situation round the world. With the discovery of newer sites in recent past the arsenic

contamination scenario around the world especially in the Asian countries has changed

considerably. Figure 3 shows the current arsenic contamination scenarios in Asia

(Mukherjee et al., 2006; Rahman et al., 2009).

17

1. AFGANISTHAN 11. EGYPT 21. MEXICO 31. SRI LANKA

2. ARGENTINA 12. FINLAND 22. MONGOLIA 32. SWEDEN

3. AUSTRALIA 13. GERMANY 23. MYANMAR 33. SWITZERLAND

4. BANGLADESH 14. GHANA 24. NEPAL 34. TAIWAN

5. BRAZIL 15. GREECE 25. NEW ZEALAND 35. THAILAND

6. BULGARIA 16. HUNGARY 26. PAKISTAN 36. UNITED KINGDOM

7. CAMBODIA 17. INDIA 27. PHILIPPINES 37. USA

8. CANADA 18. IRAN 28. POLAND 38. VIETNAM

9. CHILE 19. JAPAN 29. ROMANIA

10. CHINA 20. LAO PDR 30. SPAIN

Figure 2 Current arsenic contamination scenarios around the world

Figure 3 Current arsenic contamination scenarios in Asia

Xinjiang China

Inner Mongolia,

China Jilin, China

Liaoning, China

Ningxia, China

Shanxi, China

Jhelum, Pakistan

Gujarat, Pakistan

Bangladesh

Nepal

Guizhou, China

Taiwan

Hanoi, Vietnam

Myanmar

Lao, PDR

West Bengal, India

Cambodia

Rhonphibun,

Thailand Sri Lanka

Kurdistan, Iran

Bihar, India

Uttar Pradesh, India

Jharkhand, India

Assam, India

Manipur, India

18

Arsenic Contamination in GMB Plain

Groundwater As contamination in South Asia and Ganga-Meghna-Brahmaputra (GMB)

Plain, India, is primarily observed in the floodplains of rivers originating in the

Himalayan Mountains (Chakraborti, 2009). The first groundwater arsenic incident and its

health effects in India were reported in 1976 in the Union Territory of Chandigarh

(Datta, 1976). Arsenic contamination in the groundwater of West Bengal was first

reported in the late 1980s (Chakraborti et al., 2004). The mechanism and cause of As

release and mobilization in groundwater has been explained by a series of plausible

hypothesis such as oxidation of pyrite (Roy Chowdhury et al., 1999; Chakraborti et al.,

2001), reduction of Fe-oxyhydroxides (Nickson et al., 2000), carbon reduction (Harvey

et al., 2002), and microbial reduction (Akai et al., 2004). Arsenic contamination in

groundwater was reported from the state of Bihar in 2002 (Chakraborti et al., 2003;

Mukherjee et al., 2006). Arsenic contamination of groundwater in Uttar Pradesh was first

discovered in late 2003 (Chakraborti et al., 2004; Ahamed et al., 2006). Arsenic

contamination of groundwater in Jharkhand state was reported in December 2003

(Bhattacharjee et al., 2005; Mukherjee et al., 2006). Arsenic contamination in

groundwater of Rajnandangaon district of Chhattisgarh was first identified in 1999

(Chakraborti et al., 1999). High concentrations of arsenic in northeast states (Assam,

Arunachal Pradesh, Nagaland and Manipur) were also reported (Mukherjee et al., 2006;

Chakraborti et al., 2008; Singh et al., 2013). Figure 4 highlights the arsenic contaminated

regions in GMB Plain, India.

Figure 4 Arsenic contaminated regions in GMB Plain, India.

19

Sources of Water and Use Pattern in Manipur

At the beginning of the twentieth century, there were approximately 500 lakes in

Manipur State (Manipur, 2007) with innumerable small ponds, swamps and marshes

along lakesides and inter-riverine tracts and many community and household ponds.

Many of these water bodies no longer exist due to encroachments for paddy cultivation

and human settlement. At present there are still a number of large and small lakes.

Loktak in Bishnupur district is the largest and most important freshwater lake (289 km2)

in the North Eastern Hill states and could be used as a potable water resource after

appropriate treatment. There are 155 water bodies covering an area of 530 km2 (World

Bank, 2005). Two main rivers drain Manipur: the Barak drains the west and the Manipur

drains the east, including the Manipur Valley. The Manipur catchment has an area of

6,332 km2

and an average annual yield is 51.9 x 108

m3. The Central Groundwater Board

(CGWB) estimated the groundwater resource potential of the Manipur Valley to be

around 44 x 106 m

3 per annum (Mastec, 2007). Manipur receives rainfall from the SW

and NE monsoons, with an average annual rainfall of about 2,000 mm.

Prior to 1980s, almost all water used for domestic purposes in Manipur was drawn from

sources like rivers, lakes, ponds (local name Pukhris) and in hilly areas dug-wells and

streams. Agriculture in Manipur is predominantly rain-fed. With the increase in

population from 1.0 million in 1971 to 2.29 million in 2001, use of land for human

settlement, increased agricultural activities along with extensive use of fertilizers,

pesticides, insecticides, herbicides, etc. has not only reduced water availability but also

led to deteriorating water quality and also increased exploitation of groundwater

(Chakraborti et al., 2008). In some cases, there are indications that sufficient surface

water is not available. For example, Kakching Municipality (Thoubal district) was

previously supplied from a natural reservoir which dried up, and so PHED installed 52

hand tube wells and local people installed 90 tube wells. Similarly, when PHED could

not get enough surface water to supply in Khundrakpam village (Imphal East) they

installed a tube well-based supply. Presently, there are 10 tube well-based schemes

covering 31 villages in Manipur Valley (PHED, 2006).

Groundwater Quality in Manipur

In the North Eastern region of India, natural springs and dug wells are the only cost

effective and viable means of fulfilling the needs of freshwater for present population. In

hilly areas, most of the drinking water is used to be harnessed from rivers, ponds and

natural springs. Many springs are reportedly becoming seasonal. In valleys, most of the

domestic water is harnessed from groundwater through shallow tube wells and dug wells.

Available literature shows the presence of excess fluoride, arsenic, iron, chloride, nitrate,

sodium along with other trace metals in groundwater sources of northeast States

particularly Assam and Manipur (Singh, 2004). Groundwater use in Manipur started with

the installation of Public Health Engineering Department (PHED) in 1982, and more

20

hand tube wells were installed in Manipur after 1991–1992. The status report on

groundwater quality in the four districts of Manipur Valley indicates that except iron, the

shallow and deeper groundwater aquifers of this region is characterized by low electrical

conductivity, chloride, nitrate, fluoride, arsenic and other elements (CGWB, 2010).

However, Singh (2004, 2006), Chakraborti et al. (2008) and Oinam et al. (2011) have

reported arsenic contamination in groundwater in Manipur. Besides Arsenic, Iron and

Phosphate concentrations are higher than the permissible limit at certain locations in this

region. Singh et al. (2013) also reported the elevated presence of arsenic, iron, chloride,

sodium, sulfate, total dissolved solids, conductivity and turbidity in the groundwater

sources of Imphal West district of Manipur.

Arsenic in N-E Region and Manipur: Plausible Sources

The actual source and mechanisms of groundwater arsenic contamination in the N-E

region of India, particularly Manipur, is yet to be firmly established. The sources of

arsenic may be natural or partly stem from anthropogenic activities like intense

exploitation of groundwater, application of fertilizers, burning of fossil fuels and

leaching of metals from coal-ash tailings. Pentavalent Arsenate and trivalent Arsenite

are commonly found in natural ground water which is mainly sourced from arsenic ores

like Realgar or Arsenic disulphide, Oripiment or Arsenic trisulphide and Arsenopyrite or

Ferrous arsenic sulphide. From the different available studies, it is now known that

arsenic originates in the Himalayan head waters of the Ganga and Brahmaputra rivers

and has lain undisturbed beneath the surface of the region‟s deltas for thousands of years

in thick layers of fine alluvial mud deposited by the rivers. So far, studies indicate that

arsenic contaminated ground water is found within the sediments between 20 – 100 m

bgl in Brahmputra alluvial plain. The arsenic free ground water occurs in phreatic aquifer

(within 20m from GL) and within semi-confined to confined aquifers between 150 to

400m bgl. In most of the areas it is found that a thick impervious clay bed occurs below

the arsenic contaminated aquifers. The thick clay bed acts as a barrier to prevent the

vertical percolation of arsenic contaminated ground water with the arsenic free ground

water below 150m depth. It also appears from analytical results for arsenic in Assam that

groundwater adjacent to foothills is highly arsenic contaminated. This area lies within an

alluvial basin bounded by Himalayan Mountains. The alluvial sediments are composed

of a mixed sequence of sands, silts and clay deposits eroded from the surrounding

mountains. The probable reason of arsenic contamination in those areas may be heavy

deposition of sediments due to surface erosion from surrounding hills and creating

aquifers. Several other studies have shown that the ground water in the region is

generally in a reducing state (presence of relatively high concentration of sedimentary

organic matter) and suggest that arsenic is being released when arsenic – iron bearing

minerals in the sediments are reduced by oxygen deficient ground water. Although,

arsenic contents beyond the guideline values of WHO (World Health Organisation) have

been found in a large number of samples, no report of Arsenocosis from the area has

been known till date (Singh, 2004; Baruah et al., 2003). Chakraborti et al., 2008 reported

21

that the potential sources of groundwater arsenic contamination in Manipur valley is the

Himalayas and surrounding mountains which are the hotspots of arsenic bearing

minerals. Again, Oinam et al. (2011) reported that the source of arsenic in Bishnupur

district, Manipur Valley is perhaps from the sediments deposited from the mountains

surrounding the Valley plain land. In addition to the geological origin, arsenic variability

may also be due to groundwater recharge influenced by agricultural activities such as

addition of fertilizers and insecticides (Singh, 2006). Chowdhury et al. (2000) also

observed arsenic enrichment from east to west within the north-eastern region of India

and increased mobility of arsenic in its carbonaceous matter.

So, in the light of above facts, it is quite obvious that the groundwater resources in

Manipur state have been severely contaminated with arsenic, iron, chloride, sodium,

alkalinity, total dissolved solids, electrical conductivity, and turbidity. Continuous

consumption of this groundwater by the local people will lead to serious health hazard.

No systematic study has so far been conducted on the groundwater quality of Manipur by

any research organization to explore the presence of trace elements, particularly arsenic

and other associated variables. Moreover, the available data is very limited to assess the

magnitude of groundwater contamination in the area. Testing of water quality on a

regular basis is, therefore, an important part of maintaining a safe and reliable source.

Considering the enormity and severity of the groundwater problems in Manipur, the

present study entitled “Trace Element Analysis of Underground Water in Manipur with

Special Reference to Arsenic Contamination” was undertaken.

22

Objectives

The main objectives of present investigation are:

i) to determine the general physico-chemical properties of groundwater in the

four districts of Manipur Valley, viz., Imphal West, Imphal East, Thoubal and

Bishnupur.

ii) to determine the concentrations of selected toxic heavy metals like As, Fe, Pb,

Cd, Ni, Cr, Mn, Cu, and Zn, and compare the analytical results with the

WHO (2004) Standards ;

iii) to examine the seasonal variation of the ground water quality parameters

under study;

iv) to evaluate the suitability of groundwater for domestic, agricultural,

especially in terms of the severity of arsenic contamination that poses a health

risk;

v) to explore and determine the usefulness of multivariate statistical techniques

in improving our understanding of groundwater properties and interactions;

and

vi) to recommend stringent remedial measures to effectively prevent the menace

of arsenic toxicity.