Metal and pesticide pollution scenario in Ganga River system

Abstract

The River Ganga passes through a large number of cities, towns, villages and agricultural fields. A sizable fraction of effluents and sewages generated from all these diverse sectors enters into the river. The incoming water is, therefore, carrying huge amounts of organic substances, residues of the used pesticides and metals along with other contaminants. Review of the pesticide residue studies indicate that hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT) and endosulfan were the major contaminants in water and biota while HCH, DDT, aldrin and dieldrin dominate the sediment phase. In water the residues are frequently crossing the permissible limits of US EPA standards for aquatic organisms and their consumers, indicating various levels of risk. In fishes, the permissible limits for HCH, endosulfan and DDT are exceed only in some occasions, signifying minor risks on human consumption. Regarding metal contaminations, the uppermost stretch, up to Haridwar, is relatively free from pollutions. The middle stretch, receiving diverse kinds of effluents, is markedly polluted. Although a significant stretch of the estuarine zone is densely industrialized and regularly receives effluents, the tidal action is maintaining the metals in lower level than the middle stretch. However, in majority of the cases the reported levels in water were much higher than the US EPA permissible limits for aquatic organisms. With respect to the metal contaminations in sediments, the river is found moderately polluted. In some fishes, contamination of Pb, Hg and Cr crosses the limits. However, the alkaline pH, high sediment transportation and rigorous flushing during monsoons are protecting the river from accumulation of these toxic contaminants. With respect to aquatic health, it is anticipated that the metal and pesticide contaminations might have adversely affected fish health. Systematic studies are, however, lacking on this aspect.