TA3 Metals in the Environment: Aquatic Biological Perspectives
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() Cd dietary and waterborne exposure to Daphnia magna: implications for bioaccumulation and chronic toxicity.

Goulet, R.1, Doyle, P.1, Vigneault, B.2, McGeer, J.2, Hare, L.3, 1 Environment Canada, Assessment division, Gatineau, Quebec, Canada2 Natural Resources Canada, Environment Group, CANMET Mining and Mineral Science Laboratory, Ottawa, Ontario, Canada3 INRS-ETE, Universite du Quebec, Quebec, Quebec, Canada

ABSTRACT- Considerable uncertainty about the importance of the dietary route of exposure in contributing to the impact of metals to aquatic invertebrates. For example, studies have shown conflicting results ranging from the conclusion that dietary metals contribute to chronic toxicity to conclusions that dietary exposure protect against chronic toxicity. In the laboratory, we conducted 21 days Cd exposure experiments with Daphnia magna. In a first set of exposure experiments, we exposed Daphnids to 0.094, 0.32, 0.85, 4.8, and 9.3 nanomolar free ionic Cd in water only and measured reproduction and growth. In a second set of experiment, we first exposed the algae, Chlamydomonas reinhardtii to the same free ion Cd concentrations so as to get a gradient of Cd contaminated food. Daphnids were then exposed to different levels of contaminated algae (food only exposure). Results from our exposure experiments suggest that waterborne Cd exposure leads to toxicity at free ion Cd concentration much lower than when exposed to food only. When Daphnids were exposed to contaminated algae previously exposed to 9.3e-9M free Cd ion (Levels rarely encountered in natural waters), we did not observed any noticeable toxic effects. In fact, the number of neonates produced increased with increasing levels of Cd in food. We are presently investigating the extent to which Daphnia magna accumulated Cd in as a result of either waterborne or dietary exposures and whether bioaccumulation will explain our intriguing results. Additional considerations include quantifying the quality of the food given to the daphnids and the role this can have on uptake and toxicity. Our preliminary results suggest food does not contributed to Cd chronic toxicity to Daphnia magna and therefore models that consider only waterborne exposure (i.e. Biotic Ligand Model) are likely suitable to predict chronic toxicity of Cd to Daphnia magna.

Key words: Cadmium, Daphnia magna, bioaccumulation, chronic toxicity

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