Genotoxic and Biochemical Biomarker Responses in Meretrix Casta Exposed to Environmentally Relevant Concentrations of Cadmium

Cadmium (Cd) enters estuarine water by surface runoffs from mines, phosphate fertilizers from agricultural fields and other anthropogenic sources which may pose a threat to the fauna inhabiting these waters. Bivalve molluscs which are a source of seafood may accumulate Cd leading to deteriorated health of the organisms and may also cause various health consequences in man. The present study was carried out to assess the toxicity of Cd in the estuarine backwater clam, Meretrix casta. In the experimental setup, the bivalves were exposed to three environmentally relevant concentrations of CdCl 2 (0.75 μg/L, 1.5 μg/L, 3 μg/L) for a period of 15 days. Genotoxicity tests [Micronucleus Test (MN) and comet assay], oxidative stress parameters [Catalase Assay (CAT) and Lipid Peroxidation Assay (MDA)], neurotoxicity test [Acetylcholinesterase Assay (AChE)] and physical condition (condition index) were employed to evaluate the effects of Cd in M. casta. A dose-dependent increase of DNA damage was seen at all the concentrations of Cd. Catalase activity was not significantly changed at the lowest concentration compared to the control, but increased significantly at the higher concentrations. Lipid peroxidation was found to be significantly increased at all the concentrations of Cd. However, the levels of AChE were found to decrease in a dose-dependent manner. The condition index ratio was also found to be lowered with increasing dose. DNA damage was highly correlated with oxidative stress suggesting the mechanism of action of Cd on DNA. Oxidative stress was negatively correlated with AChE and may possibly be a contributing factor to neurotoxicity. M. casta can therefore be used as a potential sentinel species for monitoring the Cd in the estuarine environment using these biomarkers