A study of lead and cadmium speciation in some estuarine and coastal sediments

Chemical speciation of lead (Pb) and cadmium (Cd) in the coastal and estuarine sediments along the central east coast of India was studied by applying sequential and kinetic extraction methods. The results of this study suggest that concentrations of non-residual and dynamic complexes (which are good indicators of bioavailability) of these toxic metals gradually increase with increasing total metal loading in sediments. Increase in bioavailability of these toxic metals with increasing total metals concentrations in the sediments can be a potential threat to benthic organisms and aquatic biota in the system. This study shows that total organic carbon (TOC) is one of the key factors which play a crucial role in controlling speciation of these toxic metals in sediments. However, distribution and speciation of these metals are influenced by their total metal loading and trace metal competitions rather than only TOC content in sediments. An attempt was made to identify the key factors which control speciation of these toxic metals in natural system and provides a better understanding to predict and control pollution of Pb and Cd in coastal and estuarine sediments.