Effects of chronic dietary and waterborne cadmium exposures on the contamination level and reproduction of Daphnia magna.
Regulatory assessments of metal toxicity on freshwater organisms assume that toxic effects are caused by dissolved metals. In aquatic systems, organisms are exposed to both dissolved and particulate-bound metals. In this study, the chronic toxicity of dietary cadmium (Cd) on the reproduction and Cd body burden of Daphnia magna was investigated. Daphnids (<24 h) were successively exposed to dissolved Cd (8 h) and then to uncontaminated or contaminated algae (16 h) for 21 d. The results show a higher Cd burden in daphnids because of the addition of contaminated food and reveal that Cd uptake by D. magna from water and food was additive for the lowest Cd concentrations tested. Similar Cd distributions (cytosolic and insoluble fractions) were observed in the two groups of organisms, showing similar potential toxicity of Cd accumulated from the two exposure routes. Dietary Cd induces deleterious effects on D. magna reproduction. On the basis of Cd body burden of daphnids, the results support the claim that waterborne and dietary Cd exposures were additive in causing toxicity for Cd concentrations lower than 25 microg/L. At the highest Cd concentrations, the importance of dietary Cd on the daphnid contamination level decreases and confounding factors such as feeding rate reduction seem to appear, which induce an effect on neonate reproduction. In this study, we illustrate the need to take the dietary pathway into account in regulatory assessments and to establish effective concentrations with particulate-bound metals.