Metal fractionation study on bed sediments of lake Nainital, Uttaranchal, India.

Lake Nainital in the heart of Nainital Town in the State of Uttaranchal (India) receives toxic substances through various open drains through the catchment of the lake. The toxic substances of particular interest are heavy metals derived from urban runoff as well as municipal sewage and industrial effluents. Heavy metals entering the lake get adsorbed onto the suspended sediments, which in turn settle down in the bottom of the lake. In this study fractionation of metal ions has been studied on the bed sediments of lake Nainital with the objective to determine the eco-toxic potential of metal ions. Comparison of sediments with average shae values indicated anthropogenic enrichment with nickel, lead, cadmium and zinc. The risk assessment code as applied to the present study reveals that 4-13% of manganese, 4-8% of copper, 17-24% of nickel, 3-5% of chromium, 13-26% of lead, 14-23% of cadmium and 2-3% of zinc exist in exchangeable fraction and therefore comes under low to medium risk category and may enter into food chain. The association of these metals with exchangeable fraction may cause deleterious effects to aquatic life. The present database will help in formulating guidelines for carrying out dredging operations and/or restoration programmes in the Nainital lake.