CHEMICAL SPECIATION AND BIOAVAILABILITY OF LEAD AND CADMIUM IN AN AQUATIC SYSTEM POLLUTED BY SEWAGE DISCHARGES

A physico-chemical scheme encompassing anodic stripping voltammetry (ASV) as an analytical tool, and ultraviolet irradiation techniques, has been applied to determine the species of lead and cadmium in sewage polluted and unpolluted fresh-waters of a major perennial river located downstream of a metropolitan city in India. The physico-chemical and bioavailable species that have been identified and quantified include ASV-labile (bioavailable), particulate bound, total dissolved, non-labile or bound and organically bound metal. For precise and rapid assessment of the toxic bioavailable fraction, the ASV technique has been proposed as an analytical tool. The river stretch, divided into reference, impact and recovery zones, has been monitored for any alteration in the distribution and partitioning of Pb and Cd amongst various physico-chemical forms. An attempt has been made to assess the impact of effluent discharge upon the receiving river by correlating concentrations of various metal-species with reference to the properties of the stream and drainage basin. Speciation analysis revealed complete association of Cd with particulates and a significant proportion of Pb in labile form, downstream of effluent outfall, thus an immediate toxic impact on the aquatic system may be posed.