Assessing heavy metals toxicity in marine bed sediments of the Bay of Bengal: A novel baseline study on geochemical speciation, source, and risks

The crucial marine water body, i.e., the Bay of Bengal in Bangladesh, is threatened due to heavy metal contamination. Though the country's economy depends on the Bay of Bengal, heavy metals in the geochemical forms of bed sediments in this vast water body have not been studied yet. This study investigated heavy metals in geochemical forms of sediments for the first time and assessed ecological and health risks. The mean levels of Cr, Cu, As, Ni, Cd, Fe, Pb, Mn, and Zn in sediments were 47.1, 31.9, 7.20, 40.6, 1.66, 3.07(%), 21.6, 461, and 49.6 mg/kg. The chemical speciation result showed that As, Cd, Pb, and Ni were primarily distributed in the active sediment fractions (exchangeable and bound to carbonate), suggesting their increasing degree of mobility and toxicity, so that heavy metals can easily migrate and be taken up by the aquatic organisms and the human body. Results of ecological risk indexes suggested that the evaluated sediments were moderately contaminated by Cr, As, Pb, and Mn while severely contaminated by Cd. The multivariate statistical technique indicated that heavy metals were enriched in sediments from anthropogenic activities. The results also demonstrated that children were more susceptible to heavy metals in causing non-carcinogenic and carcinogenic risks than adults.