Evaluation of enzymatic and non-enzymatic biomarkers of sublethal cadmium toxicity in the freshwater mussel (Unio tigridis)

Mussels are filter-feeding animals with a sedentary lifestyle and thus, they were accepted as good bioindicator animals to investigate environmental pollution. In this study, freshwater mussels (Unio tigridis) were exposed to cadmium (0, 30, 90, 270 µg Cd/L) for up to 21 days. Then, the responses of several biomarkers belonging to the antioxidant, osmoregulation and nervous systems, as well as the energy reserves of mussels were investigated. The animals were fed on laboratory-cultured algae (Chlorella vulgaris) during the experiments. Data showed that the exposure conditions did not cause mussel mortality within 21 days, though the levels of all biomarkers altered significantly (p < 0.05) compared to controls. Cadmium exposures significantly altered the activities of antioxidant enzymes in the digestive glands. Similarly, malondialdehyde (MDA) levels in the digestive glands significantly increased after cadmium exposures. Likewise, acetylcholinesterase (AChE) activity and Ca-ATPase activity in the muscle significantly decreased. There were decreases in Na-ATPase and increases in Mg-ATPase activities in the gill. The total energy reserves of mussels significantly decreased, especially at the higher cadmium concentrations. This study showed that environmentally relevant cadmium concentrations could alter the levels of biomarkers belonging to different metabolic systems, emphasizing their possible usage in evaluating metal contamination.