The Sources of Soil Pollution
In fact, soil pollution refers to lowering of its quality (disequilibrium stage) either due to heavy concentration of undesirable foreign elements through chemicalization or due to depletion of soil nutrients through accelerated rate of soil erosion.
“The main factors of soil pollution are accelerated rate of soil erosion consequent upon major land use changes (e.g., deforestation), excessive use of chemical fertilizers, pesticides, insecticides and herbicides, polluted waste water from industrial and urban areas, a few micro-organisms, forest fires, dumping of urban and industrial solid wastes, water logging and related capillary process, leaching processes, drought etc.
Agricultural expansion and development cause environmental degradation and pollution through land use changes (i.e., deforestation and cultivation) and introduction of modern I technologies. The soils are extensively polluted through large-scale chemicalization in the developed I countries while the land is being degraded due to ever increasing population in the developing I countries.
The increased rate of soil erosion caused by deforestation for increasing agricultural I land to increase the food supply in view of increasing population causes chain effects on environmental conditions in the affected areas as well as in the far off regions, e.g., deforestation causes soil erosion which causes loss of fertile top-soils and thus decreases productivity, soil erosion increases sediment load of the rivers which causes siltation and the rise of the river beds which results in the reduction of water accommodating capacity of the river valleys which thus increases the frequency, magnitude and dimension of floods which damage agricultural crops in the flood plain areas.
Anthropogenic factor has recently become most important factor of accelerated rate of soil erosion resulting in the depletion of soil nutrients and thus soil fertility.
The human activities responsible for soil erosion fall in three broad categories, e.g.: (i) land use changes (removal of forest and grassland covers for increase in agricultural area, space for industrial expansion and urbanization, for expansion of mining, for construction of rails, roads, reservoirs, dams etc.) (ii) Farm practice changes (greater use of machines for ploughing and harvesting, frequent changes
in the nature of farming and cropping patterns etc.) And (iii) management measures (crop am land-management).
The main biological agents polluting the soil are considered as follows. (a) Pathogenic organisms excreted by human beings and ultimately transmitted to him, (b) pathogenic organism of animals transmitted to man through soils, (c) eatables and, (d) enteric bacteria and protozoa contaminating the soil. It has been found that sometimes phosphorus fertilizers caused pollution problems as a result of chemical reactions with calcium compounds already present in soil.
In addition to this, the contamination of pollutants in soils is governed by soil composition and its structure, which also affect virus movement. For example, viruses are already absorbed in the clay under appropriate condition and higher the clay content of the soil, the greater is the expected removal in the same manner, sandy loams and soils having organic matter are also favourable for virus removal.
Soil containing sands, making sand and gravel mixture do not achieve good removal, while fissured limestone aquifers under shallow soil allow viruses to travel for greater distances and can present serious groundwater pollution as well as soil contamination.
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