Studies were carried out on the level of mercury and other water quality parameters in the effluent lagoon of Dharangadhara Chemical Works, Tuticorin and the adjacent open sea over a period of three years and the impact of effluent discharge in bulk quantity into the coastal marine environment, over a distance of 18 km.The present study indicated that the presence of mercury, acidity and low oxygen concentration are the major impacts of effluent discharge. The mean concentration of mercury in the open sea during 1999 – 2002, was 4.7 μg. l-1 which got reduced to 1.68 μg.l-1 after five years,indicating the improvement of effluent treatment measures. However the mercury levels are still higher compared to those reported elsewhere. Except for salinity and pH, no statistically significant difference was observed in the variation of other parameters between stations during 1999-2002, but highly significant differences were observed in the variation of dissolved oxygen, chlorophyll, pH and salinity between stations during 2007-2008.

Mercury, effluent discharge, acidity