Trace metal levels in nearshore sediments close to industrial discharges off Cuddalore (Bay of Bengal)

Abstract

Trace metals in the sediment and in the overlying water column along with texture characteristics in the vicinity of industrial discharges at Cuddallore were analyzed, covering the seasonal changes to identify probable anthropogenic influence on this coast. During monsoon, cadmium and zinc had insignificant correlation with other trace metals. Other metals, except Mn, had a positive significant correlation. The spatial distribution of metals and the correlation were drastically changed during post-monsoon, loosing significant correlation for Pb, Ni, and Mn with other metals and the observed correlations being mostly negative. Cobalt and copper had strong positive correlation with all metals. Among the trace metals in water column Cu and Ni had strong positive correlation (0.88). Most of the correlation was positive except for Fe and Ni. During post-monsoon, levels of Cd, Co, Cu, Pb, Zn, and Mn had dropped down to 33-94%. The maximum amount of lowering was noticed for Pb and Cu. Ni (148%) and iron (110%) levels had an increasing trend. The trace metals in the water column had a similar decreasing trend (41-76%) for Cu, Ni, Fe and Zn. Cluster analysis had shown three distinct clusters of sampling points and was classified as least (4 stations), moderate (5 stations) and high (5 stations) and high (5 stations) trace metal contaminated regions. The least contaminated stations were all in the offshore area. Wilks lambda (0.027) denoted the good discriminatory power of the current model with the three groups. Partial lambdas indicated that Cr contributed the most, Cd, the second most, Ni the third most and Mn contributed the least for the overall discrimination. The other trace metals also contribute to this function, but with negative sign. The forcing mechanisms behind the rapid changes in trace metal levels; their spatial distribution patterns and correlation strengths were indicated