Soil pollution is an extremely complicated process. The problem of soil pollution differs from water and air pollution in the respect that the pollutants remain in direct with the soil for relatively longer period. The soil is getting polluted day-by-day by toxic materials and dangerous micro-organisms which enter air, water and food chain.
Sources :
Soil pollution may be result from the following sources:
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1. Industrial wastes
2. Urban wastes
3. Agricultural wastes
4. Radioactive wastes
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5. Biological agents.
1. Industrial Wastes :
Disposal of industrial wastes is the major problem of soil pollution. Industrial pollutants are discharged mainly from paper and pulp mills, chemical industries, oil refineries, sugar factories, distilleries, fertilisers, textiles, pesticide industries, mining and coal industries and cement factories etc.
Industrial sludges are even more dangerous than industrial solid wastes.
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2. Urban Wastes :
Urban wastes comprise both commercial and domestic waste consisting of dried sludge of sewage. All urban wastes are known as refuse urban and are more dangerous as they cannot be easily degraded. The leechates that comes out of the polluted soil contain poisonous gases along with the partly decomposed organic matter such as food, vegetables, toxic hydrocarbons and pathogenic microbes.
3. Agricultural Practices :
Modern agricultural practices pollute the soil a great extent, with the advancing agrotechnology, huge quantities of fertilizers, pesticides, herbicides, weedicides and soil conditioning agents are used to increase the crop yield. A part from these wastes, farm wastes, debris, soil erosion containing inorganic chemicals cause soil pollution.
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4. Radioactive Wastes :
Radioactive wastes contain several nuclides e.g. Sr90, I129, Cs137 and isotopes of iron. Nuclear reactor produces wastes containing Ru90, I131, Ba140, La140, Cs14. Rain water carry Sr90 and Cs137 to be deposited on the soil. Soil erosion and heavy rains carry away the deposited Cs137 and Sr90 with the silt and clay.
Soil get large quantities of human, animals and birds excrete which constitute major source of soil pollution by biological agents. The pathogenic organisms that pollute the soil are of three types:
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(i) Pathogenic organisms occurring naturally in contaminated soil.
(ii) Pathogenic organisms excreted by man, and
(iii) Pathogenic organisms excreted by animals. Soil Formation
Most soil begins as bedrock. Exposure of this rock to the elements gradually breaks in down into small bits and pieces that make up most of the soil’s parent inorganic material. These physical and chemical processes are called weathering. Other soils develop from the weathering of sediments that have been deposited on bedrock by wind, water (alluvial soils), volcanic eruptions, or melting glaciers.
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The slope of the land affects the type of soil and the rate at which the slope is steep; the actions of wind, flowing water, and gravity quickly erode the soil. That is why soils on steep slopes often are thin and infertile. By contrast, valley soils, which receive mineral particles nutrients, water, and organic matter from adjacent slopes, are fertile and highly productive if not too wet. Soil Texture and Porosity: Soils vary in their content of clay (very fine particles), silt (fine particles), sand (coarse particles), and gravel (large particles). The amounts of the different sizes and types of particles determine soil texture.