Soil pollution

 Soil is the loose and unconsolidated outer layer of earth’s crust that is
powdery in nature and made up of small particles of different sizes. Soil
ecosystem includes inorganic and organic constituents, and the microbial
groups. Soil microorganisms are the active agents in the decomposition of
plant and animal solid wastes and said to be nature’s garbage disposal
system.

 The soil microbes keep our planet earth free of unwanted waste materials
and recycle the elements (C, N, and P) through mineralization. Soil microbes
decompose a variety of compounds, cellulose, lignin, hemi cellulose,
proteins, lipids, hydrocarbons etc. The soil microbial community has little or
no action on many man-made synthetic polymers. The persistent molecules
that fail to be metabolized or mineralized have been termed as recalcitrants.

 An undesirable change in the physical, chemical or biological

characterization of soil may harmfully affect the life or create a potential
health hazard of any living organisms.Soil pollution could result from a
whole range of situations, and can have lasting effects on all types of
ecosystems and human health. Soil may become contaminated through dry
deposition or by toxins becoming integrated into in the ground water.

Soil Pollutants

Soil Pollutants

1. Acid rain : Oxides of sulphur and nitrogen

2. Heavy metals: Lead, Cadmium, Chromium, Copper, Nickel, Arsenic,
Titanium, Mercury, Selenium etc.
3. Industrial wastes
 4. Sewage
5. Agricultural wastes: Fertilizers, Pesticides, Herbicides, Other Chemicals
6. Volcanoes
7. Oil, grease and other petroleum products
8. Asbestos
9. Other solid wastes
Paper and paper products, Polythene bags and covers, Oil cans , Cloth wastes, Tires,
Carcasses, Radioactive wastes, Municipal solid wastes, Hospital wastes, Animal
wastes, Plastics, glass and other bio non degradable wastes, Crop residues

Plastics

 Plastics form a major part of global domestic and industrial waste. Not being
biodegradable, waste plastic accumulates, adding to pollution. In USA
plastic are 7% in weight of all solid waste but 30% of the volume. Standard
plastic takes several hundreds of years to disintegrate, over 400 years for the
plastic bottles used for mineral water.Using photodegradable plastic or
biodegradable plastic can solve plastic pollution problem. Photodegradable
plastic contains an element sensitive to UV rays. Under the effect of solar
rays the element is activated and breaks the polymeric chain of the
photodegradable plastic. It results in small fragments that are easily digested
by microbes.
Biodegradable plastic

 Biodegradable plastic is made by adding at least 6% starch and an oxidizing agent

(vegetable oil) to the polymers during manufacture. In the biologically active soil
environment, the biodegradable plastic is decomposed easily. The metallic salts naturally
present in soil interact with the oxidizing agent to form ferro oxides, which attack the
polymer bonds and set the biodegradation of plastic in motion. Parallely, soil microbes
break up the starch grains (amyloids), which results in an increased attack surface and
accelerates the auto oxidation process.
 The presence of starch reduces the water resistance of plastic. Addition of a fine
protective layer to the starch based plastic; make it possible to obtain high degree of
water-resistance. In future, plastics with 50% starch will appear in the market.
Biodegradable plastics may offer many solutions to the pollution problems.
Heavy metals

Lead

 Contamination of soils by lead is a major concern in many countries at the moment

including the U.K. It is believed that the primary cause of the increased levels found in
many soils is car exhaust emissions. Although unleaded petrol has been available for
some time now the lead particles still remain from the time when lead was added to fuel
as a thinner. In America, lead poisoning has been termed 'the silent epidemic'. 900,000
children under the age of 6 have a blood lead concentration of at least 10 nano grams /
litre, this is the critical threshold, above this level lead is believed to have psychological
effects on factors such as intelligence.

 The high concentrations of lead were also seen in hair and blood samples of local
residents, although not to such an extent. This suggests that there is some kind of barrier
which reduces the bioavailability of lead, within the body. In Derbyshire this is the
process whereby the lead is slowly eroded into the secondary element of pyromorphite,
which has a very low bioavailability is not easily put into solution.

Chromium
 As a trace element, chromium is essential for many organisms (just like iron), however an
excess in chromium and many chromium compounds are poisonous. Chromium
compounds are found in pigments and wastewater from tanneries. These materials can be
cancerous, lead to eczema or impair the mucous membranes in the period 1985-1995.

Copper

 Copper is a toxic heavy metal. It ends up in the marine environment particularly through
rivers and polluted dredged materials. Since the ban on using paint containing tin, copper
is often used as an anti-foul material on ship hulls. In the vicinity of military training
grounds, the bottom is locally polluted with copper from munition remnants. The
Netherlands contributes around 25% to the total load of copper in the North Sea. With
algae, a concentration of 0.5 microgametes of copper per litre seawater will decrease
photosynthesis (and thereby growth decline). With higher concentrations (around 10
microgametes per litre), crustaceans will also be affected.

Nickel

 Nickel is found in nature. It is a heavy metal applied in producing steel and as a surface
layer for metal products. In addition, nickel is used in a large number of alloys, batteries,
the electrochemical industry and as catalyst, for example in congealing vegetable fats. It
is in all probability an essential trace element. Some nickel compounds are cancerous. A
concentration of 0.003 to 0.1 mg/l will lead to a decrease in bacteria growth

Arsenic

 Arsenic has been known to be poisonous for centuries. It is a heavy metal. The inorganic
arsenic compounds are reputed to be extremely toxic, and are used in cases such as rat
poison. Arsenic compounds are used in the production of copper, lead, zinc, steel and
iron, as well as in agriculture. Arsenic affects fish and amphibians by increasing the
 chance in changes in hereditary material, and could cause an unnaturally high death rate
among birds.

Cadmium

 Cadmium is a heavy metal. It is found throughout nature, especially as an impurity in

zinc minerals. It is a white metal, fairly soft, easily flexible and non-corrosive. Due to
dumping by human activities (especially the industry, and indirectly from dredging
activities), the concentration of cadmium measured in the coastal waters is approximately
5 times higher than the natural concentration. Cadmium is poisonous for almost all
organisms. That's why limiting the dumping of cadmium in the past decade has had a
high priority, and with great success: the discharges have decreased by 81%.

Mercury

 Mercury is a heavy metal, originating from industry, most often from burning fossil fuels
and from dumps. In addition, mercury is found in pesticides and fertilizers, is used in the
production of chlorine and the removal of sulphur from natural gas. Actually, mercury is
found naturally in low amounts in natural gas. Mercury poisoning damages the nerves,
which can lead to deafness, blindness and paralysis. Less acute poisoning could lead to
loss of concentration and memory and memorial disorders

Titanium

 In the 1980s, Greenpeace successfully conducted a campaign against the dumping of

titanium dioxide wastes; for example, they prevented dumping ships from entering the
harbours. In addition, Greenpeace gathered evidence concerning the effects dumping had
on sea life. Scientists also discovered the consequences for those fish which had come
into contact with the waste. With such evidence and facts on hand, pressure could be
applied on the policy makers and the titanium dioxide dumpers themselves. Titanium
dumping has deceased since 1989.
Agriculture

 Agriculture is an industry which works directly with the soil as a result it is bound to
have some effects on the makeup of the soil. The uses of pesticides and fertilizers have
come under scrutiny for many reasons. One of the most harmful ecotoxicological effects
is that of the eutrophication of water bodies. This occurs due to over use and poor
management of Phosphorous and Nitrogen fertilizers. It leads to over productivity in the
water body and eventually to deoxygenating of the water, meaning that more fragile
populations and communities cannot survive. This has many implications, not only for
the environment and wildlife involved but it may also affect human activity such as
drinking water, or leisure activities like swimming and fishing.

 Bioaccumulation and biomagnifications of these poisons as they move along the food
chain is also a major problem which has influence on the whole ecosystem. One of the
most famous incidents was that of the near extinction of the Peregrine Falcon in areas of
North America during the late 1960's which lead to the den of the pesticide DDT.

 Persistent Organic Pollutants (POPs) are chemical substances that persist in the
environment, bioaccumulate through the food web, and pose a risk of causing adverse
effects to human health and the environment. With the evidence of long-range transport
of these substances to regions where they have never been used or produced and the
consequent threats they pose to the environment of the whole globe, the international
community has now, at several occasions called for urgent global actions to reduce and
eliminate releases of these chemicals.

Industrial Effluents
 Contamination of drinking water supplies from industrial waste is a result of various
types of industrial processes and disposal practices. Industries that use large amounts of
water for processing have the potential to pollute waterways through the discharge of
their waste into streams and rivers, or by run-off and seepage of stored wastes into nearby
water sources. Other disposal practices which cause water contamination include deep
well injection and improper disposal of wastes in surface impoundments.

 Industrial waste consists of both organic and inorganic substances. Organic wastes
include pesticide residues, solvents and cleaning fluids, dissolved residue from fruit and
vegetables, and lignin from pulp and paper to name a few. Effluents can also contain
inorganic wastes such as brine salts and metals.

Effects of soil pollutants

Effects of soil pollutants

1. Affects soil health and productivity

2. Affects plant and animals
3. Affects soil microbes
4. Ground water contamination through seepage
5. Affects human health
6. Causes biomagnification etc.
7. Soil Remediation process

Phytoremediation

 The process of recovery of hazardous substances from soil or ground water

contaminated with municipal or industrial wastes etc. by using plants is
called phytoremediation. Among vascular plants, some aquatic weeds such
as species of Salvia, Lemna, Azolla, sedges and tree species are known to
tolerate and uptake heavy metals. Bamboo can accumulate Zn, Cd, Ni and
 Pb (lead). Flower crops could be an effective method of remediating soil
polluted due to disposal of tannery effluent.

Biological transformation of heavy metals

 Biological transformation of heavy metals is an important detoxification

mechanism that can occur in many habitats and can be carried out by a
variety of microorganisms especially bacteria and fungi. As a result of
biological action, metals undergo changes in valency and or conversion into
organometallic compounds.
10.Bioconversions involving changes in valency and resulting in
production of volatile or less toxic compounds have been shown in
several cases. e.g. oxidation of As (III) to As (V) and mercury ion to
metallic mercury.
11.Transformation of metals into organometallic compounds by
methylation, e.g. lead, mercury. Although the product of methylation
may be more toxic than free metal, they are often volatile and released
into atmosphere. Organometallic compounds can also undergo
degradation, which may result in the metal being liberated in a volatile
form. e.g. mercury.

Recovery of heavy metals

 Green plants such as specific strains of Indian mustard (Brassica juncea) can
accumulate heavy metals when grown in chromium-contaminated soils.
Modified strains of this plant have been shown to accumulate up to 40% of
their biomass as heavy metals, such as lead and chromium. While
microorganisms breakdown the organic bonds, the plants themselves take up
the metals through their root system and sequester the contaminants in their
cells. Useful plants can be found growing on ore outcroppings or
contaminated areas. For instance, a variety of tree, Seberia acuminata
 (Sapotaceae), a native of New Caledonia accumulates an astonishing 20 to
25% of its body dry weight of nickel. The plant bleeds bluish green latex
(sap).

 The lead accumulating plants, such as common ragweed (Ambrosia

artemisiifolia) and hemp dogbane (Apocynum cannabinum) exhibited shoot
concentrations of 400 and 250 mg Pb kg-1 respectively. Efforts are being
made to develop more efficient soil remediation methodologies by breeding
or bioengineering plants which have the ability to absorb, translocate, and
tolerate Pb while producing sufficient biomass.

 Bio stimulation: Stimulation of the native microbes for site remediation

 Bioventing: It is the In-situ method of bio remediation in which air is
supplied to an unstaturated soil zone through installation of wells connected
to associated pumps and blowers which draw a vacuum on the soil.
 Air spraying: It involves the injection of air into the saturated zone of a
contaminated soil