Effects of chronic dietary and waterborne Cd 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 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 days. Results show a higher Cd burden of daphnia due to contaminated food addition and show that Cd uptakes by D. magna from water and food were 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. Based on Cd body burden of daphnids, results supports the claim that waterborne and dietary Cd exposures were additive in causing toxicity for Cd concentration lower than 25 µg.L-1. At the highest Cd concentrations, the importance of dietary Cd on daphnids contamination level decrease and confounding factors such as feeding rate reduction seem appear, allowing to induce an impact on neonate reproduction. This study illustrates the need to take the dietary pathway into account in regulatory assessments and to establish effective concentrations with particulate-bound metals.