Combining Polar Organic Chemical Integrative Samplers(POCIS) with Toxicity Testing on Microalgae to Evaluatethe Impact of Herbicide Mixtures in Surface Waters

Pesticide risk assessment within the European Union Water Framework Directive is largely deficient in the as-sessment of the actual exposure and chemical mixture effects. Pesticide contamination, in particular herbicidal loading, hasbeen shown to exert pressure on surface waters. Such pollution can have direct impact on autotrophic species, as well asindirect impacts on freshwater communities through primary production degradation. The present study proposes ascreening method combining polar organic chemical integrative samplers (POCIS) with mode of action–specific toxicitytesting on microalgae exposed to POCIS extracts as a standard approach to effectively address the problem of herbicidemixture effects detection. This methodology has been tested using Luxembourgish rivers as a case study and has proven tobe a fast and reliable information source that is complementary to chemical analysis, allowing assessment of missing targetanalytes. Pesticide pressure in the 24 analyzed streams was mainly exerted byflufenacet, terbuthylazine, nicosulfuron, andforamsulfuron, with occasional impacts by the nonagricultural biocide diuron. Algae tests were more sensitive to endpointsaffecting photosystem II and reproduction than to growth and could be best predicted with the concentration additionmodel. In addition, analysis revealed that herbicide mixture toxicity is correlated with macrophyte disappearance in thefield,relating mainly to emissions from maize cultures. Combining passive sampler extracts with standard toxicity tests offerspromising perspectives for ecological risk assessment. The full implementation of the proposed approach, however, requiresadaptation of the legislation to scientific progress.Environ Toxicol Chem2022;00:1–12. © 2022 The Authors.EnvironmentalToxicology and Chemistrypublished by Wiley Periodicals LLC on behalf of SETAC.