RESUMO
Hussainsagar Lake in the heart of Hyderabad City (India) receives toxic substances through five streams draining from a catchment area of 245 km(2). Of particular interest are heavy metals received from urban runoff as well as municipal sewage and industrial effluents. Heavy metals entering the lake get adsorbed onto the suspended sediments, which eventually settle down in the bottom of the lake. In this study, fractionation of metal ions has been studied on the bed sediments of Hussainsagar Lake in order to determine the ecotoxic potential of metal ions. Comparison of sediments with average shale values indicated anthropogenic enrichment with copper, nickel, lead, cadmium, and zinc. The risk assessment code as applied to the present study reveals that 10-17% of manganese, 10-18% of nickel, 14-24% of chromium, 10-19% of lead, 21-30% of cadmium, and 18-28% of zinc exist in exchangeable fraction and, therefore, comes under medium risk category and may enter into food chain. The association of these metals with the exchangeable fraction may cause deleterious effects to aquatic life. The present database will help in formulating guidelines for carrying out dredging operations under restoration programs in the Hussainsagar Lake.