Assessment of aquatic experimental versus predicted and extrapolated chronic toxicity data of four structural analogues.

The present study was developed to assess the chronic toxicity predictions and extrapolations for a set of chlorinated anilines (aniline (AN), 4-chloroaniline (CA), 3,5-dichloroaniline (DCA) and 2,3,4-trichloroaniline (TCA)). Daphnia magna 21 d chronic experimental data was compared to the chronic toxicity predictions made by the US EPA ECOSAR QSAR tools and to acute-to-chronic extrapolations. Additionally, Species Sensitivity Distributions (SSDs) were constructed to assess the chronic toxicity variability among different species and to investigate the acute versus chronic toxicity in a multi-species context. Since chlorinated anilines are structural analogues with a designated polar narcotic mode of action, similar toxicity responses were assumed. However, rather large interchemical and interspecies differences in toxicity were observed. Compared to the other three test compounds, TCA exposure had a significantly larger impact on growth and reproduction of D. magna. Furthermore, this study illustrated that QSARs or a fixed ACR are not able to account for these interchemical and interspecies differences. Consequently, ECOSAR was found to be inadequate to predict the chronic toxicity of the anilines and the use of a fixed ACR (of 10) led to under of certain species. The experimental ACRs determined in D. magna were substantially different among the four aromatic amines (ACR of 32 for AN, 16.9 for CA, 5.7 for DCA and 60.8 for TCA). Furthermore, the SSDs illustrated that Danio rerio was rather insensitive to AN in comparison to another fish species, Phimphales promelas. It was therefore suggested that available toxicity data should be used in an integrative multi-species way, rather than using individual-based toxicity extrapolations. In this way, a relevant overview of the differences in species sensitivity is given, which in turn can serve as the basis for acute to chronic extrapolations.