Heavy metals toxicity in edible bivalves and risk exposure to humans through its consumption from Adyar Estuary, Tamilnadu, India – A baseline study

The Adyar estuary, situated at the heart of Chennai city, India, has been subjected to significant anthropogenic pollution over the past decade due to rapid urbanization and industrialization.

This study endeavored to explore the bioaccumulation patterns of heavy metals within bivalve species including Perna viridis, Mercenaria mercenaria, and Lamellidens marginalis. Additionally, it aimed to assess the concentrations of heavy metals present in water samples obtained from ten discrete stations within the Adyar estuary across different seasonal periods. To better understand the dynamics of contamination, metal pollutants including Cd, B, Cu, Fe, Mn, Pb, and Zn were analyzed in the soft tissues (Gill, Kidney, and Muscle) of the bivalves using Atomic Absorption Spectrophotometer (AAS) (ELICO's SL- 176). The study also investigated the seasonal changes in biochemical constituents affecting the nutritional quality of these edible bivalves following conventional methods, and estimated the risk (both carcinogenic and non-carcinogenic) to consumers. Results showed that the biochemical constituents of Perna viridis and Mercenaria mercenaria were comparatively lower than those of the freshwater bivalve Lamellidens Marginalis (p > 0.05). Heavy metal accumulation in the mussels followed the order Mn > Zn > Cu > Pb > Fe > Cd > B. The highest uptake of metals by the bivalves occurred during the post-monsoon season, while the least uptake was observed during the monsoon season. The overall metal burden for the studied species followed the descending order M. mercenaria > P. viridis > L. marginalis. The study indicated that both carcinogenic and non-carcinogenic risks to humans from consuming these mussels were higher due to the excessive accumulation of metals Zn and Mn in all three studied bivalves.