15.8 phosphorous, potassium, calcium, magnesium, sulphur are15.8 phosphorous, potassium, calcium, magnesium, sulphur are

15.8 Soil

 Soil is a thin layer of organic and inorganic material that covers
the earth’s rocky surface. Soil is the foundation of all ecology. It
constitutes the upper crust of the earth, which supports land, plants and
animals. Soil pollution is defined as

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 “The contamination
of the soil system by considerable quantities of chemical or other substances,
resulting in the reduction of its fertility or productivity with respect to the
quality and quantitative yield of the crops.”

          Soil pollution affects the structure
and fertility of soil, groundwater quality and food chain in biological

15.8.1 Sources of soil pollution

 The major sources of which
pollute the soil are discussed below

1) Artificial fertilizers:

 Soil nutrients are useful for
growth of plants. Plant obtains carbon, hydrogen and oxygen from air or water.
Whereas other essential nutrients like nitrogen, phosphorous, potassium,
calcium, magnesium, sulphur are being absorbed from soil. To remove the
deficiency of nutrients in soil, farmers add artificial fertilizers. Increased
use of phosphate fertilizers or excess use of artificial fertilizers like NPK
in soil, results in reduced yield in that soil. 

2) Pesticides:

 Insects, microbes and other
animals attack on plants for their nutrients. To protect the plant, farmers use
pesticides. Pesticides are being absorbed in soil and reduce its fertility.
These pesticides enter into plants from soil and respectively in human body and
other living beings from plants that are harmful to their health. Insecticide
like DDT (Dichloro diphenyltrichloroethane) is banned in India and in most of
the other countries. (Discussed in 15.8.2)

3) Dumping of Solid wastes in Soil:

  Waste from garbage, commercial, industrial and
agricultural sectors is in the form of solid wastes. They contain kitchen
wastes, paper, cardboards, plastics, glass, and construction material waste,
toxic substances. When non-biodegradable solid wastes are dumped, remain in
soil for a longer period affects the structure and fertility of soil.

4) Deforestation:

      Deforestation occurs due to rapid urbanisation,
industrialisation and population explosion. To cater their needs forests are
destroyed by humans. Deforestation results in erosion of fertile top soil. Such
soil cannot be utilised for agriculture.

Biomedical Waste

of biomedical waste from hospital, research laboratories and drug companies
like pathological and surgical wastes, drug and chemical residues and
containers, discarded linen, clothing and bandages, disposable needles,
syringes and surgical instruments creates soil pollution.

15.8.2 Pesticide Pollution:

include chemicals to protect crops from insects (insecticides) weeds (herbicides)
disease causing micro-organism (fungicides and bactericides) rodents
(rodenticides). Pesticides also include chemicals that control pests directly
hazardous to animals and humans particularly vectors like mosquitoes, flies, lice
that transmit diseases. Following are the common catagories  of pesticides

(i)  Organo
chlorine compounds (Chlorinated hydrocarbons)

            Example: Aldrin, dieldrin, DDT
and BHC,etc.

Organo phosphorus compounds

            Example: Parathion, ethion, malathion, etc.

(iii)  Organo Carbonates (Inorganic

            Example: Toxciphene, propoxar,  Carbo fural etc.

   Pesticides contaminate ground water
as the soil soaks in rain and irrigation water. The presence of pesticides in
ground water is a matter of great concern because pesticides cannot be filtered
out by making use of most of the filtration techniques.


DDT and other chlorinated pesticides are toxic, persistent
and bio accumulative.

While spraying some of the pesticides fall on the
ground soil. These pesticides are detoxified in the soil by absorption and
degradation. However, their presence in the soil for a long time could
adversely affect the fertility and pollute nearby water bodies.

Organochloride pesticides are the most dangerous
because they are non biodegradable and are soluble in fats and oils only. When
consumed by human body reduces the quantity of fats and gives rise to various
diseases of stomach, kidney, heart, etc.

Pesticides like BHC, causes tumors, leukemia, liver and
kidney damage and damage to the nervous system. BHC contaminators are found in
food grains, oil seeds, pulses vegetables, meat and poultry as well as in
breast milk.

Most herbicides are toxic to mammals but are not as
persistent as organo chlorides.  They
become concentrated in food web. Some herbicides may cause birth defects.

    The harmful effects of a pesticide depend on
its toxicological properties and the degree of exposure of human to the
pesticide residue. Many of these pesticides are harmful to living beings,
including man. Some can be accumulated by lower organism (aquatic microbes, plants)
and increase in concentration 
successively goes up in the food chain until toxic concentration is consumed
by the  higher  animals (birds, animals).This  increase 
in concentration ,up the  food
chain is called biological magnification
or biological amplification. Increasing concentration of DDT in organism of
aquatic food chain in higher tropic level is an example of biological











Fig. 15.4 DDT Concentration (ppm)

Now days the pesticides are turning out to be
global threat.