Biodynamics to explain the difference of copper body concentrations in five marine bivalve species

Copper is an essential metal for organisms but can be toxic when high intake occurs. The interspecific and intraspecific differences in concentrations of Cu in the tissues of different bivalve species have been recognized but the underlying mechanisms leading to these differences remain speculative. In this study, the biokinetics of Cu, using 67Cu as a radioactive tracer, was investigated in five species of marine bivalves, including scallops Chlamys nobilis, clams Ruditapes philippinarum, green mussels Perna viridis, black mussels Septifer virgatus, and oysters Saccostrea cucullata. All species have contrasting Cu concentrations in their bodies. Our results demonstrated the clear importance of biokinetics in controlling Cu concentrations in the bodies of bivalves. Assimilation efficiency (AE), feeding activity (filtration rate), and efflux rate all contributed to the observed interspecies differences. The AE and efflux rate were positively correlated with the respective Cu body burden, indicating their important roles in Cu concentrations in the body. The efflux rate also explained the intraspecies difference in Cu bioaccumulation. The subcellular distribution of Cu varied among different species of bivalves. There was a positive relationship between the newly accumulated Cu in the metallothionein-like protein (MTLP) fraction and the efflux rate, suggesting that MTLP may be responsible for Cu elimination and may control Cu regulation in bivalves. Calculations showed that the Cu partitioning coefficient and ingestion are important in determining the relative contribution of waterborne and dietborne exposure pathways to overall Cu accumulation. However, the dietary pathway was the most important source of Cu in bivalves under most circumstances.