Anthropogenic Mercury Contamination of Vembanad Backwater, Wes Tern Coast, India - Evidence from Sediments

Abstract

Mercury concentration and its pollution profile in the sediments of polluted (\1ulavukadu) and less polluted (Kumarakom) regions ofVembanad Backwater, a Ramsar site were studied. Sediment core samples and surface sediment samples were .:ollected seasonally from these sites and analyzed for total mercury (THg), organic carbon and pH. Mean THg concentrations in the surface sediments ranged from 61.1 to 2054.3 ng/g. High THg content was observed in the sediments collected from the Mulavukadu region with an average value of 1238 ng/ g. The high concentration of THg was observed during pre-monsoon season. Kumarakom (less polluted) region showed comparatively lower values (20.9ng/g - 370 ng/ g). THg in surface sediments showed significant correlation with pH and organic carbon. The high concentration observed in the Mulavukadu region was a clear indicatH I of anthropogenic contamination. The core samples collected from Mulavuka u region exhibited higher values than the core taken from the Kurnarakom region. The core sediment samples showed that THg values were much higher in the subsurface sediment than that of surface sediments. These low concentrations in the upper few centimeters of the sediment suggest that recent mercury inputs were substantially low in these areas. High mercury content in the subsurface sedimentary region might be due to the historic discharges from a chloralkali plant which had stopped the use of mercury cell process few years ago.