Inter-species difference of copper accumulation in three species of marine mussels: Implication for biomonitoring

Marine mussels have been used widely as biomonitors of coastal contamination in many countries. Due to the restrain of their geographical distributions, it is often necessary to employ more than one species of mussels within a large-scale biomonitoring program. In the present study, we compared the differences of copper (Cu) bioaccumulation in three species of marine mussels (green mussel Perna viridis, blue mussel Mytilus edulis, and hard-shelled mussel Mytilus coruscus) widely distributing along the Chinese coastal waters, under identical Cu exposure conditions. Over the 21-days exposure to dissolved Cu, the green mussels and blue mussels exhibited comparable newly accumulated Cu concentrations, possibly due to their comparable Cu uptake rate constant k_u (blue mussel, 0.573 L g^-1 d^-1; green mussel, 0.530 L g^-1 d^-1) and efflux rate constant k_e (blue mussel, 0.053 d^-1; green mussel, 0.065 d^-1). In contrast, there was no net Cu accumulation in the hard-shell mussels, which may be accounted by the lower k_u (0.394 L g^-1 d^-1) but higher k_e (0.081 d^-1) than the other two mussel species. Further subcellular distribution analyses showed that the cellular debris and metallothionein-like protein (MTLP) fraction were the key binding sites for Cu, and the MTLP fraction may act as a main contributor in Cu regulation and elimination in the blue mussels and hard-shell mussels. There was no strong evidence that the subcellular partitioning and dynamics of Cu in the mussels were responsible for the difference underlying the Cu accumulation in the three species of mussels. Our comparative study thereby suggested that it may be feasible to directly compare the Cu bioavailability in the green mussels and blue mussels based on their Cu biomonitoring data. Cu biomonitoring data from the hard-shell mussels may underestimate the actual Cu bioavailability of the sampling area given its much stronger regulation of Cu bioaccumulation as compared to the other two mussel species.