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(33-04) Modeling chronic copper toxicity to Daphnia magna and Raphidocelis subcapitata in natural waters: implications for risk assessment . De Schamphelaere, Karel*,1, Heijerick, Dagobert1, Janssen, Colin1, 1 Laboratory of Environmental Toxicology and Aquatic Ecology - Jozef Plateaustraat 22, Ghent, Belgium ABSTRACT- Biotic ligand models (BLM) have been developed to predict toxic effect concentrations of metals to freshwater organisms like fish and daphnids. These models, however, suffer from three major shortcomings: (1) they mostly predict acute metal toxicity but not chronic, long-term toxicity, (2) one key taxonomic group, the algae, has not yet been considered in these modeling efforts and (3) the variability (both geographical and seasonal) of chemical properties (i.e. metal complexing capacity) of natural dissolved organic matter (DOM) is not (yet) been incorporated in this type of models. Here, we will focus on the establishment of a (biotic ligand) model predicting chronic copper toxicity to Daphnia magna and the green alga Raphidocelis subcapitata. For D. magna, chronic copper toxicity could be modeled using the conventional BLM concept. For R. subcapitata, the conventional BLM approach did not correspond to the experimental data as both the number of copper binding sites and the copper stability constants on the algal surface seemed to be dependent on pH, resulting in an increase of copper toxicity with increasing pH. However, after the incorporation of these interactions into the BLM framework, relatively accurate predictions (mostly < factor 2) of copper toxicity to i>R. subcapitata were obtained, both with reconstituted waters with natural DOM additions and with field waters. Additional experiments showed that UV-VIS light absorption of organic matter could be related to the capacity of DOM to reduce copper toxicity to both daphnids and algae. These findings will be discussed in the light of the further improvement of ecologically relevant risk assessment procedures for metals. Key words: Daphnia magna, Raphidocelis subcapitata, Biotic Ligand Model, Copper toxicity |
