Abstract:
The Zuari Estuary is of ecological importance and has a long history of metal contamination, primarily driven by extensive iron ore mining in the catchment area. The estuary serves as a crucial habitat for diverse marine organisms and supports local fisheries, making it essential to assess contamination levels of metals and their impact on both estuarine ecosystem and human health. Therefore, ecological toxicity of Fe, Mn, Zn, Cu, Co, and Ni in the Zuari Estuary was investigated through the study of bioavailability in sediment and bioaccumulation in edible bivalves. Additionally, the potential of mangroves to remediate metal pollution was evaluated. The study aimed at understanding seasonal (pre-monsoon, monsoon, and post-monsoon) variability in metal bioavailability, bioaccumulation and toxicity. Sediments were polluted with metals during all seasons and was ascribed to ore mining, agriculture, ship maintenance, fishery, tourism, and domestic activities. Screening Quick Reference Table indicated toxicity of Mn, Co, Fe, Zn and Cu to biota. Toxicity of a metal varied at different sampling stations and seasons. It was attributed to discrepancies in metal sources, and factors influencing the bioavailability namely, changes in salinity, oxidation-reduction potential, pH and ionic composition. Saccostrea cucullata displayed a nearly similar pattern (Zn > Fe > Mn > Cu > Ni > Co) of metal accumulation at different stations and seasons, while it differed in accumulation pattern to that of Paphia malabarica (Fe > Zn > Mn > Cu > Ni > Co) during pre-monsoon season. It was ascribed to species-specific feeding habits. During all seasons, metals in bivalves surpassed the acceptable limit indicating potential toxicity to bivalves and humans. Avicennia officinalis displayed variability in metal translocation from pneumatophores to aerial parts between pre- and post-monsoon seasons. Also, Kandelia candel exhibited variations between pre-monsoon and monsoon seasons. Therefore, it underscored the role of intrinsic (metal sources and bioavailability) and extrinsic (plant age, size, etc.,) factors in the assimilation of metals by mangroves.
