Water, the most abundant and wonderful natural resource is extremely essential for survival of all living organism. But today water has become a precious commodity and its quantity is threatened by numerous pollutants.
Few of them are sewage and domestic wastes, industrial effluents, soap and detergents, pesticides, fertilizers and heavy metals.
Sewage and Domestic wastes: About 75%of the water pollution is caused by sewage and domestic waste and food processing plants. It also includes human excreta, soap, detergent, metals, glass, plastic etc. Domestic sewage contains trace quantities of toxic metals such as Cu, Cr, Zn, Mn, Pb and Ni.
Industrial effluents: The industrial effluents discharged into water contain toxic chemicals, hazardous compounds, phenols, ketones, aldehydes, amines, oils, greases, dyes, suspended solids, non biodegradable matter radioactive wastes etc.
Soap and detergents are cleaning agents popularly used. While soap contain sodium or potassium salt of higher fatty acids and the detergents contain ingredients like surfactants, builders, additives and stabilizers. The surfactants in detergents are alkyl benzene Sulphonate (ABS) and builders are usually a sodium phosphate. Most of the ingredients by soap are biodegradable. But that of detergents are not biodegradable. Hence detergents cause more water pollution than soap.
Pesticides are the organic chemicals used to control unwanted and dangerous species of plants and animals. Pesticides include fungicides, bactericides, insecticides, nematicides, herbicides, rodenticides etc. Pesticides enter the aquatic system either directly or indirectly through the following sources: Rain water, Spray Drift, Run off from agricultural fields, industrial effluents and domestic sewage.
Fertilizers: Modern agricultural techniques have introduced NPK fertilizers into after system. The excess of fertilizers not consumed by crops are washed away from land by rain water and pollute water.
Heavy metals: toxic metals are added in aquatic system from industrial process, domestic sewage, street dust, fossil fuel burning. Traces of heavy metals as Hg, Cd, Pb, As, Co, Mn, Fe and Cr have been identified in aquatic ecosystem.