Analysis of the ECETOC aquatic toxicity (EAT) database II. Comparison of acute to chronic ratios for various aquatic organisms and chemical substances

Environmental risk assessment often requires prediction of potential chronic effects in aquatic species from acute toxicity data. The scientific rationale for using extrapolation factors for this continues to be debated. As a contribution to the debate this paper analyses the acute-chronic-ratios (ACRs) based on acute EC50s (or LC50s) and (sub)chronic NOEC values using information in the ECETOC Aquatic Toxicity (EAT) data base. The ACRs were calculated separately for all aquatic species available and the results presented according to specific substance classes. It was unusual to find more than three species giving ACRs for a single chemical but eight of the 28 species in the analysis gave ACRs for five or more chemicals. Based on the commonly used 90%-ile ACR (whose usefulness is underlined by the data presented here), 90%-ile ACRs were observed from 192 (for metals/organometals to 20 for ‘other inorganics’. For organic chemicals resembling those which may be submitted for registration under the European Community 7th Amendment Directive (92/32/EEC), the results were further analysed based on time-specific ACRs and gave the 90%-ile as 24.5: the maximum ACR observed for such organic substances was 28.3. ACRs for individual taxonomic groups (e.g. fish, daphnids) were also calculated. Except for three cases an ACR derived from studies on Pimephales promelas was within a factor of 2 of the ACRs of five other fish species. In contrast, the ACRs for Daphnia magna varied to a greater extent from the ACRs for other invertebrates. For a quarter of cases the ratios differed by 5.0 or more. The results are discussed with respect to current environmental risk assessment procedures.