Allometry of cadmium and zinc concentrations and bioaccumulation in the scallop Chlamys nobilis

Scallops (Bivalvia: Pectinidae) contain very high concentrations of cadmium (Cd) and zinc (Zn) in their body tissues. We investigated the allometry of Cd and Zn concentrations in the scallop Chlamys nobilis and the underlying biokinetic mechanisms. The metal influx rate from the dissolved phase and the weight-specific clearance rate decreased with body size, whereas the dietary assimilation efficiency (AE) increased with increasing body size. The dietary AEs of metals in the scallops were comparable when measured by the mass balance and the dual radiotracer techniques. The efflux rate of Cd in the scallops was lower than those in other bivalves, whereas the efflux of Zn was comparable to those in other bivalves. Growth dilution appeared to be important in the overall metal accumulation in the scallops. The allometric dependencies of the biokinetic parameters were then combined with the measurements of metal concentrations in the water to predict the likely metal concentrations in scallops of different sizes using the biokinetic model. The modeling suggested that the very high AE and low efflux rate for Cd explained the high Cd concentrations in the scallops. Dietary uptake dominated the overall metal accumulation in the scallops. Both the predicted metal concentrations and the allometric coefficients of metals were comparable to the measured values. This study shows, for the first time, that the biokinetic model can be used to predict the effects of body size on the bioaccumulation of metals in marine invertebrates. The allometry of ingestion rate, compared to other biokinetic parameters, is mainly responsible for the allometry of metal bioaccumulation in the scallops. © Inter-Research 2008.