Contrasting patterns of cadmium bioaccumulation in freshwater cladocerans

We investigated the patterns of cadmium (Cd) bioaccumulation in three freshwater cladocerans with contrasting calcium (Ca) contents and Ca uptake and loss kinetics. Ca content and dissolved Cd uptake rate were significantly correlated. The large interspecies differences in sensitivity to aqueous Cd exposure were explained by the differences in the Cd uptake rate. The high‐Ca species, Daphnia galeata and Ceriodaphnia dubia , had higher dissolved Cd uptake rates and were more sensitive to aqueous Cd exposure than the low‐Ca species, Moina macrocopa . Food was the dominant Cd source for all of the cladocerans. Feeding on the same Cd‐containing food, M. macrocopa attained the highest Cd body concentration due to its higher assimilation efficiency and ingestion rate, which led to its susceptibility to dietary Cd despite its relatively high intrinsic tolerance. C. dubia suffered most from the dietary Cd exposure, probably due to its higher intrinsic sensitivity. The efflux of Cd from the cladocerans was well described by a two‐compartment model. Although the efflux rate constants from both compartments were comparable among the species, D. galeata had a much higher proportion of the internalized Cd distributed into the fast compartment, and thus eliminated Cd at a much faster rate. The diversity of Cd bioaccumulation patterns in cladocerans indicates that no simple generalization can be made from data on only a few species. Because cladocerans are often the major zooplankton in lakes, their contrasting Cd accumulation and loss suggest that the biogeochemistry of Cd would be different in waters dominated by different cladocerans.