Development of Acute-to-Chronic Ratios (ACRs) to Support Ecotoxicity Prediction for Surfactants

Surfactants are used extensively in both industrial and domestic products. Whilst they degrade rapidly, their high production volumes necessitate recurrent safety assessments to ensure robust environmental management. Although substantial historical ecotoxicological data exist, gaps remain for some surfactants particularly with respect to chronic toxicity endpoints. One approach to fill these gaps, especially in light of a growing transition towards non-animal approaches, is to use acute-to-chronic extrapolation by leveraging existing surfactants' ecotoxicity data. Therefore, we established a dataset of 49 unique surfactants identified by Chemical Abstracts Service (CAS) number, including both acute and chronic data, to derive the surfactant-class-specific acute-to-chronic ratios (ACRs) for three regulatory used taxonomic groups, i.e., algae, daphnids, and fish, to represent different trophic levels. The relationship between acute and chronic toxicity was well fitted by linear regression across aquatic species. Regardless of the surfactant class, the median ACR values for algae, daphnids, and fish were 3.8, 7.1, and 4.5, respectively, and the corresponding 90th percentile ACRs were 9.4, 19.4, and 26.4. Furthermore, by employing an external test set (i.e., consisting of data independent from that used for the purposes of training) in order evaluate the predictivity of these derived ACRs, we demonstrated that the derived 90th percentile ACRs performed well with regards to predicting in vivo chronic toxicity from the respective acute value across these three taxonomic groups, with the predicted chronic toxicity of all surfactants no more than one order of magnitude higher than the measured chronic values. These transparent and robust surfactant-tailored ACR values are thus recommended for further application in regulatory safety assessment, supporting a weight-of-evidence justification for waiving additional chronic testing of surfactants.