Risk assessment and mitigation measures on the heavy metal polluted water and sediment of the Kolleru Lake in Andhra Pradesh, India

The Kolleru Lake is a famous Ramsar wetland of international significance. In this study heavy metal contents in water and sediment samples are reported. It is found that certain potentially toxic metal ions like chromium (4.5-80 µg/L), copper (1-20 µg/L), manganese (1-313 µg/L) and zinc (1.2-57 µg/L) are present in variable quantities in the lake water. When normalized with respect to concentration of each element in clean surface waters, the normalized ratio is found to be highly heterogeneous (chromium=4.5-80, copper=0.3-3.3, manganese=0.07-20.8, zinc= negligible to 2.8). At several places, the normalized ratio is greater than 1, indicating anthropogenic input.  The concentration of iron (4-20 µg/L) in water, however, is less compared to the clean surface waters.  Chemical analyses and quality assessment of Kolleru Lake sediments have been carried out through estimation of four pollution indices, which include enrichment factor (EF), geoaccumulation index (Igeo), contamination factor (CF) and pollution load index (PLI). Evaluation of these contamination indices with respect to average sediment composition of Taylor & McLennan (2001) confirmed that the Kolleru Lake sediment is polluted with a number of heavy metals that include cobalt (EF=2, Igeo=0.64, CF=2.4) , chromium (EF=1.5, Igeo=0.18, CF=1.7), copper (EF=1.6, Igeo=0.29, CF=1.9), manganese (EF=1.3, Igeo=0, CF=1.4), vanadium (EF=1.5, Igeo=0.19, CF=1.7) and zinc (EF=1.5, Igeo=0, CF=1.5). The level of contamination, however, is minor to moderate and is in good agreement with the heavy metal chemistry of the lake water. Based on these results some measures for environmental rehabilitation of the lake and its surroundings have been proposed.