A demonstrable need to follow scientific evidence in the derivation of environmental quality standards: a case study of European surface waters.

The article focuses on the derivation and revision of environmental quality standards (EQS) for nickel in European freshwater under the European Water Framework Directive. It critiques the 2022 European Commission revision, which lowered the chronic (annual average, AA) and acute (maximum allowable concentration, MAC) nickel EQS by increasing assessment factors despite the availability of expanded ecotoxicity data and updated bioavailability models. This approach led to inconsistencies where sites comply with chronic standards but fail acute ones, undermining ecological relevance and regulatory applicability. The authors advocate for evidence-based derivations that incorporate all relevant scientific data, bioavailability considerations for both chronic and acute exposures, and practical ecological assessments, while emphasizing the need to separate scientific evaluation from political decision-making in setting legally binding standards.