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(70-45) Zinc and Daphnia magna: speciation, body burdens and chronic toxicity. Heijerick, Dagobert*,1, Janssen, Colin1, 1 Laboratory of Environmental Toxicology, J. Plateaustraat 22, Ghent, Belgium ABSTRACT- Acute and chronic toxicity of metals in the aquatic environment is affected by various abiotic factors (pH, hardness, dissolved organic carbon). Empirical and semi-mechanistic models (e.g. BLM-approach) have been developed for predicting zinc toxicity to the waterflea Daphnia magna as a function of these parameters. The relationship between the physico-chemical composition of the test medium, the internal concentration and the observed sub-lethal long-term effects has not been investigated yet. In this study, juvenile D. magna were exposed to sub-lethal zinc concentrations in 10 artificial media with different pH, hardness and DOC (Central Composite Model Design). Internal concentrations in the test organisms were measured after 5, 10 and 20 days of exposure. Statistical analysis revealed that zinc uptake was enhanced by both lower DOC-concentration and lower hardness of the test medium and the interaction of the two parameters. No significant pH-effect was observed which was probably due to 1) the narrow pH range which was used in the experimental setup (6.5 to 8.0) leading to limited shifts in Zn-speciation, and 2) possible interaction of different pH-related processes (Zn-speciation versus proton-competition for binding to DOC). The tested physico-chemical factors also affected the internal Zn-concentrations in a time-independent manner, i.e. similar trends were observed after 5, 10 or 20 days of exposure. Comparison between the results of chronic zinc toxicity tests in these media and the internal concentration indicates that the latter only partially determines the observed chronic effects. Key words: daphnia magna, zinc uptake, internal concentration, dissolved organic carbon |
