Water is regarded as ‘polluted ‘when its quality or composition is changed directly or indirectly as a result of human activities, so that, it becomes less suitable for drinking domestic, agricultural, recreational, fisheries or other purposes.
In India, rapid industrialization and urbanization have taken place during the last four decades. With this the higher risk of deterioration of environmental quality through discharge of wastes by industries and sewage by growing population has challenged the productive capacity of aquatic ecosystems.
The latter comprise several interacting physico- chemical parameter with organic and inorganic compounds, in dissolved or suspended state, and a variety of flora and fauna.
Normally the chemical and biological factors of an ecosystem exist in the dynamic equilibrium in a fixed space and time. The water bodies because of harboring primary producers (aerobic autotrophy) have been endowed with a remarkable capacity to rejuvenate their vitality. But the disposal of sewage and /or industrial effluents into them affects their capacity of reunification and influences the biological system either directly or indirectly.
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Most of the industrial units discharge their effluents in nearby water bodies, which adversely affect their normal life. The effluents usually contain high amount of inorganic salts, acids or alkalis, organic matter, suspended solids, toxic chemicals and heated water.
The gravity of water pollution problem warrants a systematic research with a view to devise suitable methods for its detection, assessment and control. Since water pollution is biological approach and most of the microphysics grows in a wide variety of polluted and non-polluted habitats, one may hope that knowledge about their pollution biology would provide a useful solution to this problem.
The changes in water quality brought about by waste disposal in aquatic system can be assessed by observing changes in its physico- chemical characteristics and the latter’s effect on the distributional pattern and growth behavior of aquatic organisms. It has been established that the changes thus brought about exert a selective action on the flora and fauna and the effect produced in them can be profitably used to establish biological indices of water quality.
Studies on the deleterious effect of industrial wastes on physico-chemical properties of water and aquatic organism have incited considerable interest during the past two decades and researches in this discipline have considerably advanced.
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Besides land degradation another key environmental problem is the ground water and surface water pollution. In a number of sites the ground water is severely contaminated with toxic metal such as manganese and chromium. In the concentration far so exceeding the limits prescribes for safe portable water by WHO. About 70% of the available surface water resources are severely polluted.
Another consequence of such pollution spreading of water borne diseases which accounts for 2/3 of illness in India affecting productivity of the water. The per capita annual water availability was 5236 m3 in India which declined to 2464 m3 and this is expected to decline further in near future.
Water quality is closely linked to type of water use and level of economic development.
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Rapid industrialization in developing countries and intensive agriculture have added a further dimension to water pollution in the form of chemical contamination. Urban populations are now exposed to hazardous chemicals as well as infectious agents in surface and ground water. Aspects of water pollution which have a direct effect on human health are mentioned as follows:
(a) Sewage:
Untreated or inadequate treated municipal sewage to a major source of surface and ground water pollution. This is a cause for considerable concern since the biological degradation of organic material that is discharged with the municipal sewage into water courses use substantial amount of oxygen (so called BOD), upsetting the ecological balance of rivers and lakes. Sewage also carries microbial pathogen, faecal coliforms levels m?” be very high in sewage contaminated rivers.
(b) Nutrients:
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Domestic wastewater agricultural drainage water and much industrial effluents contain and they thus served as source of additional nutrients for aquatic organism and can cause severe eutrophication of lakes and rivers. Intensive fertilizers use in agriculture has also contaminated ground water sources with nitrates with the result nitrate levels in drinking water often for exceed the safe levels recommended by WHO (50 mg per litre of nitrate).
(c) Synthetic organisms:
Many of the 100000 synthetic compounds in use today find their way into the aquatic environment and accumulate in the food chain. Persistent organic pollutant (POP’s) represents the most harmful group for ecosystem and ecohealth. These chemicals can be bioaccumulated in the fresh and shell fish to levels that are hazardous to human health. If pesticides are used on a measure scale ground waters may become contaminated leading to chemical contamination of drinking water.