Distribution of Metal Contamination and Risk Indices Assessment of Surface Sediments from Cooum River, Chennai, India

Abstract

Rivers are the mostly vulnerable water bodies due to carrying off and assimilating pollutants from both point sources and non-point sources. This study deals with the metal pollution in sediments of the Cooum River, Chennai, India. Eleven sampling stations were selected along the 18 km stretch of the Cooum River, which lies in the urban part of the Chennai City and the concentration of metals such as As, Zn, Mn, Ni, Co, Cr, Cu, Pb, Cd, and Hg in the sediments were determined. The study reveals a progressive increase in the concentration of metals in the downstream due to increase in domestic and industrial drainage (out falls) into the river. Spatial distribution of sediment particle size indicated the dominance of smaller particles ranging from 425 to 75 µm. The concentration of metals in the Cooum River sediments was in the following order: As > Zn > Cr > Cu > Pb > Cd > Hg. Significant positive correlations exist between Cd and Zn, Cu and Pb, Cd and Hg, and Cr and Hg. Ecological risk indices denote predominant levels (> 70%) of cadmium throughout the sampling points as indicated from contamination factor. Potential ecological risk assessment specified the alarming levels of cadmium and mercury above the standard limits in the sediments assessed. Based on the observations, it is evident that the Cooum River is highly polluted and it becomes essential that the urban effluents should not be overlooked before their discharge into the river.