Risk assessment of heavy metal contamination in sediments of a tropical lake.

The risk assessment of heavy metal contamination was carried out in sediments of an urban tropical lake system (Akkulam-Veli) under threat from rapid unplanned urbanization and poor sewage management. Heavy metals were selected due to their persistent and bioaccumulative nature. Sequential extraction of the metals was carried out to resolve the sediments to their component phases. Well-established models were employed for risk analysis. The two pathways of contamination-ingestion and dermal contact-were considered for assessing risk. Risk Assessment Code of each metal was determined based on the lability of it in the different component phases. Cd was found to be the most hazardous metal by virtue of its high concentration in exchangeable and carbonate phases. Hazard indices of the metals were determined based on their total concentration in Akkulam-Veli (AV) Lake sediments. All heavy metals studied fall well below the threshold limit. However, Cr, Pb, and As, on account of their known toxicity, need to be monitored. Ni content in the lake system could potentially cause cancer to 134 adults in a population of one million. Concentrations of other metals are at carcinogenically safe limits. The study stresses the looming hazard faced by the Akkulam-Veli Lake system by heavy metal contaminants and the urgency in formulating remedial management plans.