Micropollutants in European rivers: A mode of action survey to support the development of effect‐based tools for water monitoring

Environmental quality monitoring of water resources is challenged with providing the basis for safeguarding the environment against adverse biological effects from exposure to anthropogenic chemicals originating from diffuse and point sources. Although current regulatory efforts focus on monitoring and assessing a few legacy chemicals, many more anthropogenic chemicals are and will become detected in aquatic resources as a result of progress in analytical techniques. Assessing this type of exposure information based on available standard approaches from prospective risk assessment for single chemicals inevitably leads to indication of risk in most surface water bodies. As an alternative to generic assessment approaches, effect‐based monitoring approaches are suggested. This offers the advantage of reducing uncertainties of effect extrapolation and additionally accounts for mixture effects. To become a credible complement to chemical monitoring information, however, a better understanding of the capabilities and gaps of available effect‐based tools is needed. The authors therefore undertook to 1) compile organic contaminants detected in freshwater monitoring studies, 2) provide a synopsis of the mode of action knowledge available for the detected compounds, 3) perform a hazard ranking to identify priority mixtures, and 4) reflect on the challenges to make bioassays fit for effect‐based monitoring. The present Focus article shows that chemical occurrence in European freshwaters seems to be highly variable in composition and relative abundancies. Further, although the present mode of action knowledge remains limited, the authors already see the need for batteries of effect‐based tools if a more comprehensive coverage of prevailing effect qualities for mixtures is to be targeted. Finally, they suggest a list of organic compounds that could serve as a reference list for effect‐based tool validation studies.