Mixture risks threaten water quality: the European Collaborative Project SOLUTIONS recommends changes to the WFD and better coordination across all pieces of European chemicals legislation to improve protection from exposure of the aquatic environment to multiple pollutants

Abstract Evidence is mounting that chemicals can produce joint toxicity even when combined at levels that singly do not pose risks. Environmental Quality Standards (EQS) defined for single pollutants under the Water Framework Directive (WFD) do not protect from mixture risks, nor do they enable prioritization of management options. Despite some provisions for mixtures of specific groups of chemicals, the WFD is not fit for purpose for protecting against or managing the effects of coincidental mixtures of water-borne pollutants. The conceptual tools for conducting mixture risk assessment are available and ready for use in regulatory and risk assessment practice. Extension towards impact assessment using cumulative toxic unit and mixture toxic pressure analysis based on chemical monitoring data or modelling has been suggested by the SOLUTIONS project. Problems exist in the availability of the data necessary for mixture risk assessments. Mixture risk assessments cannot be conducted without essential input data about exposures to chemicals and their toxicity. If data are missing, mixture risk assessments will be biassed towards underestimating risks. The WFD itself is not intended to provide toxicity data. Data gaps can only be closed if proper feedback links between the WFD and other EU regulations for industrial chemicals (REACH), pesticides (PPPR), biocides (BPR) and pharmaceuticals are implemented. Changes of the WFD alone cannot meet these requirements. Effect-based monitoring programmes developed by SOLUTIONS should be implemented as they can capture the toxicity of complex mixtures and provide leads for new candidate chemicals that require attention in mixture risk assessment. Efforts of modelling pollutant levels and their anticipated mixture effects in surface water can also generate such leads. New pollutant prioritization schemes conceived by SOLUTIONS, applied in the context of site prioritization, will help to focus mixture risk assessments on those chemicals and sites that make substantial contributions to mixture risks.