The historical trend in trace metal enrichment in core sediments from Cochin Estuary, Southwest coast of India

Abstract The sedimentary record of trace metals in Cochin Estuary (Southwest coast of India) during the past few decades have evaluated by analyzing core sediment and examined their ecological risk. The collected cores were examined for the depositional trends, metal enrichment, and distribution of organic carbon. Sedimentation rate was determined using the 210 Po/ 210 Pb isotope method. Chronological study reveals that Core I has aged between 1940’s to the present and Core II has been formed since 1880’s. For Core I, the average sedimentation rate obtained is 1.27 ± 0.52 cm/year, and for the Core II, it is 1.19 ± 0.23 cm/year. Both the core samples have shown similar down core distribution pattern of metals and are in the order of Zn > Cu > Pb > Cd. Metal concentration of the core samples displays an increasing trend from the bottom layer to successive upper layers. A notable variation was observed on both the core sample from 30 cm depth to the surface. The results of this study assume that the metal contamination issue of the lake system has been mounting after the industrialization of 1940's. The increase in elemental concentration after 1990's demonstrates the progressive increment and recent addition of metallic contaminants. Present study suggests regional specific preindustrial background concentration of Zn, Pb, Cu, and Cd, which can be utilized for monitoring sediment quality of the estuarine systems in India.