Ecotoxicity effects on functional diversity - A proof of concept using a sensitivity distribution approach

Current approaches for estimating the effects of chemical exposure commonly rely on species sensitivity distributions, which are well-established in ecotoxicological assessments for chemical registration and authorisation. However, this method does not consider the functional roles of species within ecosystems, an aspect captured by functional diversity. In this paper, we present a method to estimate the toxic effects of chemicals on functional diversity, with an emphasis on functional richness. Our approach integrates ecotoxicity data with abundance and trait data to determine the potentially affected fraction of functional diversity across chemical concentrations. For this purpose, we fitted a functional sensitivity distribution, similar to a species sensitivity distribution, and derived the concentration-response slope factor for a given species group and chemical. We demonstrate our method using the terrestrial plant order Poales (including grasses such as wheat) and the aquatic fish order Cypriniformes (ray-finned fish such as carp). Our results show increasing negative effects on both functional and species richness with increasing chemical concentrations. Notably, a toxic effect on species richness did not always lead to an effect on functional richness, highlighting the added value of considering functional traits. A key challenge of this method is the limited availability of trait and ecotoxicity data for many species and chemicals. Nevertheless, as data availability improves, integrating functional sensitivity distributions into chemical risk assessment offers a promising tool for evaluating chemical-induced ecological effects, supporting authorisation and registration decisions, and triggering risk management measures for chemicals already on the market.