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 valent
iron “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???

Cluin, 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

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

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