heavy metal pollution and remediation in urban and peri-urban agriculture soils

@2013, ICE, All rights reserved

Heavy Metal Pollution & Remediation In Urban and

Peri-Urban Agriculture

Larry Chikukura

CESCRA

NEW DELHI


Outline

• What is a heavy metal?

– What causes heavy metal pollution?

– International examples: Basel , Sandoz, Japan

– Regulatory limits for HM

• Remediation Techniques

– Traditional techniques

– Modern techniques

– Phytoremediation/Hyperaccumulation

– Nanoremediation

– Options for resource poor farmers

• Conclusion


Introduction

Throughout the world, there is a long tradition of farming

intensively within and at the edge of cities (Smit et al., 1996).

However, most of these peri-urban lands are contaminated with

pollutants including heavy metals i.e. Cu, Zn, Pb, Cd, Ni, and Hg

soil quality in these areas is closely associated with human health

and welfare

hence much focus on soil quality degradation from heavy metal

contamination and soil remediation (Wilcke et al., 1998; Li et al,

2001; Lu et al., 2003; Imperato et al., 2003; Hu et al., 2004; Zhang

and Ke, 2004).


What is a Heavy Metal (HM)??

Criteria used to define heavy metals have included density, atomic

weight, atomic number, or periodic table position

Density criteria range from above 3.5 g/cm3 to above 7 g/cm3

Atomic weight definitions start at greater than sodium (22.98) to

greater than 40

Atomic numbers of heavy metals are generally given as greater

than 20; - sometimes this is capped at 92 (uranium).

The term heavy metals has been called “meaningless and

misleading” due to the contradictory definitions and its lack of a

“coherent scientific basis (Duffus, 2002).


Introduction

Heavy metal is a member of an ill-defined subset of elements that exhibit metallic

properties, which would mainly include the transition metals, some, metalloids

lanthanides and actinides


Categorization of heavy metals

There are two categories of heavy metals:

i) Essential heavy metals

essential trace elements needed in very low quantities - vital to the

proper functioning of the various biological systems.

The essential heavy metals include iron, zinc, manganese, copper,

cobalt, selenium etc.

ii) Non-essential heavy metal

occur in traces in the human body but have been designated as

non-essential - harmless below their “threshold level”

These metals include chromium, silicon, nickel etc.


Metals have unique chemical properties

1. Do not decay like organics

2. Necessary and beneficial to plants

3. Always present at background levels from parent rock weathering

4. Often occur as cations, which are actively exchanged in plant cell processes


What causes heavy metal pollution?

Sediment from solid wasteIndustrial waste

Mining waste


Some heavy metals and their environmental and physiological

effects

Brady and Weil, 1999

*

*

*

*


REGULATORY LIMITS FOR HEAVY METALS


THE BIGGEST DISASTERS WITH „A SPECIAL

APPEARANCE” OF HEAVY METALS

1932-1952 Minamata

Sewage containing mercury was released by Chisso's chemicals works into Minimata Bay in Japan. The mercury accumulated in sea creatures, leading eventually to mercury poisoning in the population.

In 1952, the first incidents of mercury poisoning appear in the population of MinimataBay in Japan, caused by consumption of fish polluted with mercury, bringing nearly 1000 fatalities. Since then, Japan has had the strictest environmental laws in the industrialised world.




• Itai-itai disease was the documented case of mass cadmium

poisoning in Toyama Prefecture, Japan starting around 1912.

• The cadmium was released into rivers by mining companies in the

mountains. The cadmium poisoning caused softening of the bones

and kidney failure.

• The mining companies were successfully sued for the damage.

Itai-itai disease is known as one of the Four Big Pollution Disease

of Japan.




1986-11-01 Sandoz

Water used to extinguish a major fire carried 30 t fungicide containing

mercury into the Upper Rhine.

a fire at a chemical factory Sandoz near Basel, Switzerland, sending

tons of toxic chemicals into the nearby river Rhine and turning it

red

Fish are killed over a stretch of 100 km.




1998-04 Spanish nature reserve contaminated after

environmental disaster

Toxic chemicals in water from a burst dam belonging to a mine

contaminate the Coto de Donana nature reserve in southern Spain.

5 million m3_ of mud containing sulphur, lead, copper, zinc and

cadmium flow down the Rio Guadimar. Experts estimated that

Europe's largest bird sanctuary, as well as Spain's agriculture and

fisheries, will suffer permanent damage from the pollution.


TRADITIONAL TREATMENTS FOR SOIL CONTAMINATION

Traditional treatments (engineering-based remediation methods for

metal contamination in soils

Treatments can be done in situ (on-site), or ex situ (removed and

treated off-site).

Some treatments that are available include:

High temperature treatments (produce a vitrified, granular, non-

leachable material).

Solidifying agents (produce cement-like material).

Washing process (leaches out contaminants)

These are expensive and cost prohibitive when large areas of soil

are contaminated.

Glass, 1999


TRADITIONAL TREATMENTS FOR SOIL CONTAMINATION

Once metals are introduced and contaminate the environment,

they will remain.

The only exceptions are Hg & Se, which can be transformed and

volatilized by microorganisms.

However, in general it is very difficult to eliminate metals from the

environment.

@2013, ICE, All rights reservedReeves and Baker , 2000; Koyko et al., 2014

uptake and

transpiration of

contaminants,

primarily organic

compounds, by plant.

Roots stimulates soil

microbial communities in

plant root zones to

breakdown contaminants

Plant enzymatic

breakdown of organic

contaminants both

internally & thru

secreted enzymes

Adsorption of

contaminants &

stored above

ground shoots &

their harvestable

parts & roots

Roots & exudates

immobilize

contaminants thru

adsorption,

accumulation,

precipitation

within the root

zone

Phytoremediation => green technology that uses plants systems for remediation and restoration

@2013, ICE, All rights reservedReeves and Baker , 2000

Use of hyperaccumulator plants

Synthetic chelates stimulate the release of metals into soil solution and enhance the potential for

uptake into roots.

A variety of synthetic chelates have this potential to induce Pb desorption from the soil matrix eg.

EDTA > HEDTA >DTPA >EGTA >EDDHA.

Natural (A) & (B) Assisted phytoextraction.


Brassica juncea (Indian mustard)Thlaspi caerulescensAlyssum serpyllifolium

The ability to hyperaccumulate toxic metals compared to related species is

because of their ‘Detoxification or Tolerance Mechanism’ .


Case Studies

Aim => to efficiently utilise Brassica juncea L.to remove lead (Pb).

effect of different concentration of EDTA on lead accumulation

EDTA is the typical chelating agent

Different concentrations of EDTA (3mmol/kg, 4mmol/kg, and 5mmol/kg)

electrodic phytoremediation. The eletrodic phytoremediation system included

electrodes, a power supply, EDTA and plants. Copper wires were used for

electrodes.


Results

The addition of EDTA was shown to significantly increase the accumulation of lead in

Brassica juncea

However, the use of electric potential with EDTA caused increased phytoremediation

to manyfolds

However, at high EDTA concentration it proved to be necrotic for the plants resulting

in burning effect.


Nanoremediation

use of nanotech in the improvement of a contaminated site to prevent, minimize or

mitigate damage to human health or the environment.

potential not only to reduce the overall costs of cleaning ;

reduction in clean-up time,

eliminate the need for treatment and disposal of contaminated soil,

reduce the contaminant concentrations to near zero— all in situ

Nano alginite

nZVIbentonite

Nano carbon

Nano scale zero valentiron “nZVI”,

used as a potential sorbents to eliminate Cd and Pb from polluted soil

The “nZVI” is reported as an ideal candidate for in-situ remediation because of its

large active surface area and high heavy metal adsorption capacity [Yaacob et al.,

2012].


Adsorption & Desorption isotherms of

Cd & Pb

Marzoog et al., 2014

isotherms show that high

quantities of Cd (approximately 30-

40 g kg-1 ) - Cd was completely

removed from solutions

Generally the quantities of Pb

adsorbed on nano particles are

lower than their corresponding of

Cd

quantities of Pb & Cd desorbed

from the previously adsorbed ones

– tho ratios are low

Fate of the desorbed

contaminants???

@2013, ICE, All rights reservedCluin, 2014

Cost Implication of Nanoremediation

Remediation Technology Cost of Remediation ($)

Traditional remediation methods using

pump and treat (without nano-enhancement) 5,000, 000

Traditional remediation methods e.g.

permeable reactive barriers (PRBs) 3,400,000

Nano-enhanced remediation methods

using nano-zero valent iron (nZVI) 600,000

Traditional remediation methods or technologies are costly and may take as many as 40 years to clean up all sites across the United States

http://www.cluin/


Options for resource poor farmers

Soil and crop mgt practices will not remove the HM contaminants,

but will help to immobilize them in the soil

& reduce the potential for adverse effects from the metals

The soil becomes the sink, breaking the soil-plant animal or human

cycle through which the toxin exerts its toxic effects (Brady and

Weil, 1999)

Note that the kind of metal (cation or anion) must be considered:


Organic matter binds heavy metals (make

sure not contaminated) --the case of Cr

Brady & Weil, 1999

Active organic matter

is effective in

reducing the

availability of

chromium


Add lime (make sure source not contain heavy metals)

Brady & Weil, 1999

Increasing the soil pH

to 6.5 or higher -

Cationic metals are

more soluble at lower

pH levels,

less available to

plants & th4 less likely

to be incorporated in

their tissues and

ingested by humans

Raising pH has the

opposite effect on

anionic elements.


Management of Contaminated Soils

Draining wet soils- improves soil aeration and will allow metals to

oxidize, making them less soluble. Therefore when aerated, these

metals are less available (opposite for Cr)

Applying phosphate - reduce the availability of cationic metals, but

have the opposite effect on anionic compounds like arsenic.

Care - high levels of P in the soil can result in water pollution.

Carefully selecting plants for use on metal-contaminated soils


Which crops are safe & suitable in HM soils???

Aim =>to examine the crop species differences in HM accumulation &

distribution in various edible and non-edible plant parts

to suggest the cultivation of different vegetable crops in soil contaminated with

different HM based on their accumulation in edible plant part.

@2013, ICE, All rights reservedTable 1 & 2 (Combined)

remarkable difference in metal concentration of various plant parts

cauliflower and cabbage recorded highest uptake of Zn, Pb and Ni, while mustard showed higher

uptake of Zn and Cd.

radish, carrot, spinach, amaranthus, mustard, cauliflower and cabbage showed higher distribution

of metals to the edible parts


Leafy vegetables namely, spinach, amaranthus and mustard seemed to be unsafe

and not suitable for cultivation on heavy metal contaminated soil

Most of the fruit type vegetables could be suggested for cultivation on Cd contained

soil but not for Ni and Pb contained soil.


Conclusion

A number of options are there for remediation of soils

Cost and access determine which method will be used

Resource poor farmers can cultivate specific crops depending on the soil and HM

All methods are effective but some have be known to be more efficient , though no

study has been made to compare all

Phytoextraction - less expensive than any other clean up process and the possibility

of the recovery and re-use of valuable metals

Nanoremediation is is an emerging technology that can perhaps be used in the near

future to clean contaminated environments (cost is still prohibitive)

WHERE POSSIBLE - PREVENTION IS CHEAPER & SAFER THAN CLEANING

UP


THANK YOU FOR

LISTENING

heavy metal pollution and remediation in urban and peri-urban agriculture soils

Environment

categories of heavy

term heavy metals

heavy metal hm

heavy metal contamination

nonessential heavy metal

atomic numbers of heavy

transition metals

soil science