Heavy metals that enter the aquatic environment pose a serious threat to the biota due to their toxicity. This review reveals that various concentrations of copper and mercury at varying lengths of exposure alter the activity of protein, carbohydrate, lipid, phosphatase, and aminotransferase significantly in the different soft tissues and hemolymph of molluscs, and toxicity is metal, organ, or species specific. The alterations in the levels of biochemical constituents and enzymes suggest adaptations of molluscs to meet high metabolic needs under metal stress. The apparent sensitivity of these biochemical and enzymatic parameters’ activities suggests that they have the potential to be promising and reliable biomarkers of water pollution due to copper and mercury and can constitute an important diagnostic tool in toxicological studies. Additionally, the shells of molluscs should be considered contamination biomarkers as they sequester pollutants. A review of the literature also indicates that molluscs can be considered full-time biomonitors as they react to pollutants and can provide useful information on the water quality over time. The “Molluscs Watch” program should be included in environmental surveillance programs to keep watch on the health of the aquatic ecosystem and to protect aquatic biodiversity. This review provides an overview of the effects of heavy metals (copper and mercury) on biochemical constituents such as protein, carbohydrate, lipid, and the activity pattern of enzymes such as acid and alkaline phosphatases, aspartate, and alanine aminotransferases in molluscs.
Key words: Biochemical composition, Biomarker, Biomonitor, Enzymes, Heavy metal stress, Molluscs