anthropogenic (man-made).
Natural sources
Important natural sources are surface run-off, seepage from ground water and swamp drainage. In urban areas, rain water is reported to be acidic. This is due to reaction between water droplets and atmospheric oxides of sulphur and nitrogen. The atmospheric sulphur dioxide (S02) is always accompanied by a little amount of sulphur tri-oxide (S03) which, under humid condition, reacts with water vapour to form sulphuric acid thus causing acid rain. The chemical reaction involved in this process is represented as follows:
Leachates from animal excreta, decaying bodies of animals and plants, solid waste landfill sites and the decay of large quantities of organic matter in swamps or deep ponds also introduce appreciable amounts of soluble organics and microorganisms which in turn contaminate the adjacent ground water.
Anthropogenic sources
Anthropogenic sources are the result of industrial, domestic, agricultural and mining activities of man.
Industrial sources
Nowadays, industries are the major contributors of water pollution. Water is an essential raw material in almost all manufacturing plants. In India, industries such as tanneries, sugar mills, pulp and paper mills, distilleries, oil refineries, etc. generate a large quantity of wastewater which is discharged into natural waterways either without treatment or after partial treatment. The characteristics of industrial wastewater depend primarily on the type of industry and the chemicals used in various processes.
Domestic sources
In urban areas, municipal sewage is discharged into the nearby canal, thus polluting the canal and also deteriorating the ground water. Municipal sewage includes wastewater from houses, commercial buildings and institutions. The important pollutants present are biodegradable organic matter, coliforms and pathogens.
Agricultural sources
Pollutants discharged into water courses due to agricultural activities include:
1. Soil and silt removed by erosion
2. Agricultural run-off
3. Synthetic fertilizers, herbicides and insecticides
4. Plant residue.
Receiving water bodies get fertilised with nutrients, thus resulting in Eutrophication. Some common insecticides in use are chlorinated hydrocarbons such as DDT (dichloro diphenyl trichloroethane), aldrin, heptachlor, PCBs (polychlorinated biphenyl) etc. Most of the chlorinated hydrocarbons are persistent to degradation and hence remain in the environment for a very long time. Indiscriminate use of insecticides could make them an integral part of the biological, geological and chemical cycles of the earth. Measurable quantities of DDT residues may be found in air, soil and water several thousand kilometres away from the point where it originally entered the ecosystem.
Mining sources
Natural or man-made geochemical alterations are also sources of wastewater pollution. Fines from ore washings disposed off in water suspension may be transferred to the natural water bodies to pollute them in due course. Mining operation also produces soluble toxic materials depending on the geological formation. Acid drainage from coal mines and arsenic residue from gold mines are some of the burning problems of environmental concern.
You May Also Like:
Comments