Daphnids, ecotoxicity estimation

ECOSAR is a freely available software system which matches the structure of a query molecule to one (or more) of its defined chemical class(es). For most classes, aquatic ecotoxicity values are then predicted using available hn-ear correlations between toxicity and hydrophobicity. Row is estimated for the query molecule using KOWWIN (discussed in the chapter by Howard). The most recent version of ECOSAR (used in this study) contains over 150 relationships for approximately 50 chemical classes. For the purposes of assessing ECOSAR for predicting, transformation product toxicity, the structures of each of the chemicals in the data set were entered into the software system and in instances where the query compound was matched to one or more chemical classes, the most potent ecotoxicity estimate for daphnids was selected for comparative purposes. 

Five techniques were used to estimate daphnid acute ecotoxicity, these included freely available and commercial QSAR models, expert systems and an approach derived using data on structurally similar molecules called the read-across approach . 

Table 5 Summary statistics for the ability of five approaches to accurately estimate transformation product acute ecotoxicity to daphnids... 

In order to determine the mixture risk quotients for each of the study sites on each sampUng occasion, data were obtained from the literature on the ecotoxicity of the parent compounds to fish and daphnids. Experimental ecotoxicity data were also obtained for the transformation products where available. In instances where experimental data were not available for the transformation products, estimates of ecotoxicity were obtained using the predictive approach of Escher which is described in the previous section. Experimental and predicted ecotoxicity data were then used alongside the monitoring data to calculate mixture risk quotients for each of the sampHng sites on each sampling occasion for fish and daphnids. The mixture risk quotients were calculated a) using only the parent compound occurrence data and b) the parent compound and transformation product data. 

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