Europe-wide spatial trends in copper and imidacloprid sensitivity of macroinvertebrate assemblages

Exposure to synthetic chemicals, such as pesticides and pharmaceuticals, affects freshwater communities at broad spatial scales. This risk is commonly managed in a prospective environmental risk assessment (ERA). Relying on generic methods, a few standard test organisms, and safety factors to account for uncertainty, ERA determines concentrations that are assumed to pose low risks to ecosystems. Currently, this procedure neglects potential variation in assemblage sensitivity among ecosystem types and recommends a single low-risk concentration for each compound. Whether systematic differences in assemblage sensitivity among ecosystem types exist or their size, are currently unknown. Elucidating spatial patterns in sensitivity to chemicals could therefore enhance ERA precision and narrow a fundamental knowledge gap in ecology, the Hutchinsonian shortfall. We analyzed whether taxonomic turnover between field-sampled macroinvertebrate assemblages of different broad river types across Europe results in systematic differences in assemblage sensitivity to copper and imidacloprid. We used an extensive database of macroinvertebrate assemblage compositions throughout Europe and employed a hierarchical species sensitivity distribution model to predict the concentration that would be harmful to 5% of taxa (HC₅) in each assemblage. Predicted \(H{C}_{5}\) $H{C}_5$ values varied over several orders of magnitude. However, variation within the 95% highest density intervals remained within one order of magnitude. Differences between the river types were minor for imidacloprid and only slightly higher for copper. The largest difference between river-type-specific median \(H{C}_{5}\) $H{C}_5$ values was a factor of 3.1. This level of variation is below the assessment factors recommended by the European Food Safety Authority and therefore would be captured in the current ERA for plant protection products. We conclude that the differences in taxonomic composition between broad river types translate into relatively small differences in macroinvertebrate assemblage sensitivity toward the evaluated chemicals at the European scale. However, systematic differences in bioavailability and multi-stressor context were not evaluated and might exacerbate the differences in the ecological effects of chemicals among broad river types in real-world ecosystems.