Copper uptake, patterns of bioaccumulation, and effects in glochidia (larvae) of the freshwater mussel (Lampsilis cardium)

The early life stages of freshwater mussels are particularly sensitive to copper (Cu) contamination. We measured the acute toxicity, bioaccumulation, and sublethal effects of Cu in glochidia. In addition, we used radiolabeled Cu (⁶⁴ Cu) to examine the time-dependent kinetics of uptake over 24 h. Uptake of ⁶⁴ Cu by live and dead glochidia exposed to 0.11 μmol/L exhibited similar hyperbolic patterns over the first 40 min, indicating an adsorptive phase independent of larval metabolism. Thereafter, uptake was linear with time, with a 10-fold lower bioaccumulation rate in live than in dead animals, representing a close to steady state of Cu regulation. In contrast, dead glochidia exhibited a progressively increasing uptake, possibly attributable to the fact that metal-binding sites become more accessible. Mortality was strongly correlated with bioaccumulation (48 h); live glochidia exposed to Cu concentrations >0.27 μmol/L lost their regulatory ability and accumulated Cu to an even greater extent than dead animals. Exposure to Cu induced significant decreases in whole-body Na⁺ and Mg²⁺ concentrations; increases in reactive oxygen species concentration, lipid peroxidation, and protein carbonylation; and a decrease in antioxidant capacity against peroxyl radicals. Overall, these results clarify the patterns of Cu uptake and regulation, emphasize the importance of distinguishing between live and dead larvae, and indicate that toxicity is associated with Cu bioaccumulation, involving both ionoregulatory disturbance and oxidative stress. Environ Toxicol Chem 2018;37:1092-1103. © 2017 SETAC.