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

Abstract

Pesticide risk assessment within the European Union Water Framework Directive is largely deficient in the assessment of the actual exposure and chemical mixture effects. Pesticide contamination, in particular herbicidal loading, has been shown to exert pressure on surface waters. Such pollution can have direct impact on autotrophic species, as well as indirect impacts on freshwater communities through primary production degradation. The present study proposes a screening method combining polar organic chemical integrative samplers (POCIS) with mode of action-specific toxicity testing on microalgae exposed to POCIS extracts as a standard approach to effectively address the problem of herbicide mixture effects detection. This methodology has been tested using Luxembourgish rivers as a case study and has proven to be a fast and reliable information source that is complementary to chemical analysis, allowing assessment of missing target analytes. Pesticide pressure in the 24 analyzed streams was mainly exerted by flufenacet, terbuthylazine, nicosulfuron, and foramsulfuron, with occasional impacts by the nonagricultural biocide diuron. Algae tests were more sensitive to endpoints affecting photosystem II and reproduction than to growth and could be best predicted with the concentration addition model. In addition, analysis revealed that herbicide mixture toxicity is correlated with macrophyte disappearance in the field, relating mainly to emissions from maize cultures. Combining passive sampler extracts with standard toxicity tests offers promising perspectives for ecological risk assessment. The full implementation of the proposed approach, however, requires adaptation of the legislation to scientific progress.

Investigative Approaches for Pollutants in Water: Aligning with Water Framework Directive Maximum Allowable Concentrations

“…Beyond the sampler type and exposure duration, the sampling Rs is affected by factors such as temperature, pH levels, ionic strength, water flow rate, solute concentration, and the type and conditions of the water systems [141,142,148,149]. So far, a large number of passive samplers have been developed depending on the priority of the analysis, of which POCIS (for hydrophilic) substances and SPMDs (mainly for hydrophobic compounds) are the two most common [148,[150][151][152][153]. Passive samplers are frequently employed alongside spot sampling to harmonize and contrast outcomes, facilitating the assessment of the combined contribution of both approaches.…”