Bioaccumulation of Cd, Se, and Zn in an estuarine oyster (Crassostrea rivularis) and a coastal oyster (Saccostrea glomerata).

We compared the bioaccumulation of Cd, Se, and Zn in an estuarine oyster (Crassostrea rivularis) and a coastal oyster (Saccostrea glomerata) from both the dissolved and particulate phases. A bioenergetic-based kinetic model was used to predict the exposure pathways of metals in the oysters. The assimilation efficiencies (AEs) of metals, determined for four species of phytoplankton and natural sediment, were in the range of 30-75% for Cd, 25-75% for Se, and 30-80% for Zn, respectively, in the two oysters. There was little difference in metal AE between the two oysters and among the three metals on the same particle type. Metal uptake rate constant, determined from the log-log relationship between metal influx rate and metal concentration in the dissolved phase, was higher for Cd and Zn in the estuarine oyster C. rivularis than in the coastal oyster S. glomerata. The uptake rate constants quantified for Cd, Se, and Zn were the highest among different bivalve species studied so far. The calculated metal absorption efficiency from the dissolved phase was similar to those found in other bivalve species. The measured efflux rate constant in the estuarine oyster C. rivularis was in the range of 0.01-0.03 day(-1) for Cd, Se, and Zn, and were comparable to those found in mussels and clams. In contrast, the efflux rate constant of Cd and Zn in the coastal oyster S. glomerata was 0.003-0.004 day(-1), which may be responsible for the high Cd and Zn concentrations in the oysters. The bioenergetic-based kinetic model predicts that under most circumstances likely experienced by oysters in nature, the majority of Se and Zn in the two oysters stem from uptake from the dietary phase. Dissolved uptake contributes significantly to metal accumulation only when the metal concentration factor (CF) in the particles is in the lower portion of the range typically found in nature. Sensitivity analysis indicates that the metal CF is a critical parameter in determining the exposure pathways of metals in the oysters. Our study demonstrated that estuarine and coastal oysters differed in their strategies in accumulating a high metal concentration in their tissues.