Multiple effects of copper on the freshwater mussel Anodonta anatina

Background and Objective Numerous metals are increasingly distributed in the environments due to a multitude of industrial activities. Therefore, many of them show the tendency to increase in their concentrations over natural levels and accumulate in environmental compartments, especially in river sediments. Metals with high toxicity such as copper (Cu) and cadmium (Cd) were shown to be involved in the wide-spread decline of freshwater mussels living at the interface of free-flowing water and the sediment phase. There, copper can exist in dissolved form and/or associated with suspended food particles; mussels can take up Cu from water, food or both. Although Cu is essential to mussels at about 20 mg kg-1 body weight, it is toxic above 80 mg kg-1 body weight. The aims of this research are to study Cu accumulation in Anodonta anatina and its effects on calcium homeostasis, metallothionein (MT), glutathione (GSH), malondialdehyde (MDA), and the activities of enzymes involved in detoxification of reactive oxygen species (ROS) such as catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPX), or superoxide dismutase (SOD). Material and Methods Mussels were exposed to 0 and 25 µg L-1 63Cu in water; and in food (1.5 mg L-1 63Cu-loaded algae) for 24 days, followed by depuration for 12 days. Three mussels were taken from each group every 6 days for sampling organs (kidney, gills, mantle, digestive gland), hemolymph (HML), and extrapallial fluid (EPF). Results Cu accumulation was highest in the digestive gland followed by the mantle and the gills. Uptake of Cu via water was higher than via food. Corresponding to the increase in Cu, Ca content increased in the digestive gland, the mantle, and in HML. Highest MT content was observed in the digestive gland followed by the kidney, the gills, and the mantle as well as an increase in activity of possibly CAT, GR and GPX. GSH decreased slightly until day 24, the lowest being observed in the mantle. Cu was eliminated during depuration accompanied by decreases in MT, MDA, and enzymatic activities, but increased GSH (correlation analysis showed positive correlation between Cu content and all observed parameters, except GSH (r > 0.6; P < 0.05)). Discussion Cu accumulation affects the physiological and metabolic functions of those organs which are in direct contact with water or food. Higher Cu accumulation via the water leads to stronger effects indicated by higher Ca, MT, and MDA contents as well as increased ROS-detoxifying enzyme activities. Cu interferes with Ca homeostasis, by inhibition of Ca-ATPase. Conclusion Exposure of mussels to Cu via the water results in higher Cu accumulation than exposure via the food. Increased copper uptake causes decreased GSH, increased MT and MDA, increased activities of the ROS-detoxifying enzymes, and interference with Ca homeostasis