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(M/EH130) Influence of water quality characteristics and natural organic matter on chronic copper bioavailability and toxicity for Daphnia magna: implications for biotic ligand modeling. De Schamphelaere, Karel1, Vasconcelos, Flavio2, Janssen, Colin1, Allen, Herbert2, 1 2 ABSTRACT- The development and application of Biotic Ligand Models (BLM), aimed at predicting metal bioavailability in surface waters, is receiving increased attention from academic and regulatory communities. To date, BLMs for predicting acute copper toxicity have been developed for fish (Di Toro et al., in press Environ. Toxicol. Chem.) and daphnids (Santore et al., in press Environ. Toxicol. Chem.; De Schamphelaere and Janssen, submitted to Environ. Sci. Technol.). The present study is the first aimed at testing the applicability of the BLM assumptions to chronic copper toxicity data for Daphnia magna. We investigated the independent effects of Ca (0.8 to 5 mM), Mg (0.2 to 4 mM), Na (0.078 to 10 mM) and pH (6 to 8) on the 21-day chronic copper toxicity (net reproduction) for D. magna in a standard artificial medium (EEG) containing 5 mg DOC L-1 (Aldrich Humic Acid). No clear relationships were observed between Ca, Mg, Na concentration, pH and 21-day EC50s and NOECs. Moreover, in all tests NOECs only differed by less than a factor 3. To validate these findings a set of chronic toxicity tests in artificial media with varying pH, hardness (Ca:Mg = 4:1) and DOC-content was performed, according to a central composite statistical design (Lock et al.,Environ. Toxicol. Chem., 2000, 19, 2666-2671). ANOVA analysis revealed that DOC-content explained over 80% of the observed variance of 21-day EC50s and NOECs and thus is the key factor controlling copper bioavailability. Based on this knowledge, we performed additional chronic bioassays with natural organic matter, collected by reverse osmosis from four different surface waters in Europe. Only small differences were observed between the different types of DOC regarding to their chronic copper toxicity modifying effect for D. magna. Based on the results of this study the possibilities and limitations of BLMs for predicting chronic copper toxicity are discussed. Key words: bitoic ligand model (BLM), Daphnia magna, chronic copper toxicity, natural organic matter (NOM) |
