Pollution‐induced community tolerance as a measure of species interaction in toxicity assessment

Abstract

1 The assessment of the environmental hazards posed by chemical pollutants typically results from single-species tests that are extrapolated to ecosystems. The aim of the present study was to compare this type of extrapolation for a herbicide with the chronic effects that may be observed at a community level and to evaluate currently applied risk assessment strategies for their ability to predict chemical effects on complex communities. 2 Freshwater periphyton communities, grown in indoor aquaria, were exposed to the pollutant diuron for 3 months. Acute toxic effects of diuron were detected as photosynthesis inhibition using quenching analysis of chla-fluorescence. Chronic effects of the herbicide were observed in terms of changes in biomass and algal class composition as well as pollution-induced community tolerance (PICT). The PICT concept is based on a chemical exerting selection pressure on a community and therefore eliminating sensitive species. As a result, the measured community tolerance increases. 3 Short-term effects of diuron arise from 4–9 µg L−1 as half-maximal effect concentration (EC50). It is further shown that diuron concentrations down to 0·08 µg L−1 caused chronic effects in two independent microcosm studies. The observed threshold concentration of 0·08 µg L−1 still caused changes in biomass and class composition as well as an increased community tolerance. The determined EC50 values increased by a factor of 2–3 in diuron-exposed periphyton communities. This threshold value could not be predicted by advanced extrapolation methods such as species sensitivity distribution or acute-to-chronic effect ratios. 4 Synthesis and applications. The chronic community-level effects of the pollutant diuron were not predictable from single-species tests. However, regulations such as the EC Water Framework Directive or the EC-REACH process (Registrations, Evaluation and Authorisation of Chemicals) rely on this type of information. The management of chemicals in the environment should be based upon higher-tier assessment tools. Species interaction, detectable and quantifiable by the PICT methodology, may serve as a prognostic tool in chemical hazard assessment when extrapolating effects from single-species tests to community level.