Trends in heavy metal concentrations in sediment, finfishes and shellfishes in inshore waters of Cochin, southwest coast of India

Abstract

Profile of Cadmium, Zinc, Copper and Lead in sediment and tissues from four species of finfishes and shellfishes from estuarine and inshore regions of Cochin were analysed from the monthly data, collected for ten years since 1990. Annual mean levels of Zinc in Nemipterus japonicus registered a gradual decreasing trend towards 1998 with a peak (35 ppm) during 1992. Similar trend was also observed in Metapenaeus dobsoni and Suneffa scripfa. However, an increasing trend was noticed in Ofolithus ruber, registering a peak (9 ppm) during 1995. Lead concentrations were higher in M. dobsoni followed by N. japonicus with an increasing trend. On the other hand, Cadmium and Copper levels showed a decreasing trend with peak levels in Nemipterus (Cd 0.58 ppm, Cu 10.43 ppm) and M. dobsoni (Cd 1.16, Cu 8.87 ppm) than the molluscs and the croaker species. Levels of these four metals in sediment were higher in inshore regions than in the estuarine areas. Copper, Lead and Cadmium content in sediments of estuarine as well as the inshore regions showed an increasing trend over the ten years period. However, the levels of Zinc showed no significant variation in the inshore areas and a marked decreasing trend in the estuarine regions. The profile of metals in tissues and sediment samples were correlated in relation to the state of health of these resources and ecosystem in the light of increasing port and anthropogenic activities.