Soil Pollution

 

SOIL POLLUTION

 

“ It is the introduction of substances, biological organisms into the soil, resulting in a change of the soil quality, which is likely to affect the normal use of the soil”

The soil is a resources for which there is no substitute.  It is a thin covering over the land consisting of mixture of minerals of minerals, organic material, living organisms, air and water.  Several factors like mechanical weathering of rocks due to temperature changes, wind, moving water, glaciers and chemical weathering activities contribute to the soil formation.  Mature soils are arranged in a series of zones called ‘soil horizons’.  Soils vary in their content of clay, silt, sand and gravel.  Soil with equal mixtures of clay, sand, silt, and humus are called loams.

SOIL POLLUTANTS

Crop residues, ashes, garbage, paper, plastics, rubber, leather, cloth, bricks, sand, broken glasses, demolished buildings, dead animals, and discarded furniture, automobiles, insecticides, oil spillage and herbicides.

PESTICIDES:

They are chemical used to kill pests like insects, rats, fungi, herbs etc.  They are of the following types.

1)  Insecticides: chemicals used to kill insect pests

2)  Rodenticides: kill rats

3)  Fungicides:  kill fungi

4)  Herbicides:  kill weeds

5)  Helminthicides:  Kill helminth worms

 

CHEMISTRY OF PESTICIDES

Based on chemical composition, pesticides are divided into three main groups.  They are 1. chlorinated hydrocarbons.  2.  Organic phosphorus insecticides and 3.  Inorganic insecticides

1.  Chlorinated hydrocarbons:

DDT, aldrin, dieldrin, endrin form chlorinated hydrocarbon.  They are very poisonous, very persistent,hightly mobile and highly capable dissolving in fat.  They are non degradable pollutants

2.  Organic phosphorus insecticides:  These are alkyl or organic phosphates.  Parathion and malathion are well known organic phosphates.  They are biodegradable

3.  Inorganic insecticides:  These include arsenic and sulphur compounds.  They are much less in use.

ECOLOGICAL EFFECTS OF PESTICIDES

1. Mutation:  Insecticides induce gene mutation in human beings

2.  Cancer:  DDT produces cancer in human tissues

3.  Congenital birth defects:  Certain herbicides like dioxin increase birth defects in both human and cattle.

4.  Sex hormones:  DDT affects sex hormones in mammals and birds.

5.  Calcium metabolism:  DDT interferes with calcium metabolism resulting in delayed ovulation and inhibition of gonad development

6.  Biomagnification:  As the pesticides are non degradable the accumulate in the tissues of higher organisms through food chain and food web.  It is called biomagnifications or biological amplification.

 

CONTROL OF PESTICIDE POLLUTION

a)  Minimal use:  Pesticides should be used at minimum rates and that too when required

b)  Sterilization:  Juvenile hormones prevent metamorphosis maturation in insects.  They can be used to control insect pests.

c)  Biological control:  Pests should be killed either by rearing predator or parasites.  For e.g Mosquito larvae can be eradicated by culturing fishes as they feed these larvae as effective food materials

d)  Integrated pest management:  It promotes the use of biopesticides,  Biopesticides are derived from three sources

1)  Microbial pesticides are microorganisms such as bacteria, fungus, virus or protozoa.  They produce toxins specific to the pests and produce disease in them.  The most commonly used biopesticide is bacillus thuringiensis

2)  Biochemical pesticides:  Contain several chemicals that affect the reproductive and digestive mechanisms of the pests

3)  Botanical pesticides:  Plant products like azardiractin from nee, Azardiracta indica is used as an effective pesticide.