Geochemical speciation of selected metals to understand source, bioavailability and toxicity in mudflat core sediments of a tropical (Vaghotan) estuary, India

Abstract

The geochemical speciation of Fe, Ni, Co, Cu and Cr in mudflat core sediments representing sub (V-1) and main (V-2) channels of the Vaghotan estuary was investigated to understand the metal source and its bioavailability to sediment associated biota. The toxicity of metals to biota was assessed using the sediment quality values (SQV). In core V-2, the concentration of Co (36.69 percent) was significantly high in the bioavailable fraction which revealed the anthropogenic source of Co to the main channel of the Vaghotan Estuary. The labile fraction (exchangeable and carbonate) constitutes 10.23 percent of the Co and thus indicated its bioavailability with changing pH. Sediment quality values indicated toxicity of Co (sub and main channels) and to a certain extent of Cu (sub channel) to sediment associated biota. However, the metals viz. Fe, Ni, Cu and Cr (in cores V-1 and V-2), and Co (in core V-1) were present in more than 80 percent in the residual fraction. Their dominance in the environmentally immobile fraction suggested natural weathering of basalts and laterites from the catchment area as a major source of metals to the estuary.