Author's personal copy A new risk assessment approach for the prioritization of 500 classical and emerging organic microcontaminants as potential river basin specific pollutants under the European Water Framework Directive Peter Carsten von der Ohe a, ⁎, Valeria Dulio b , Jaroslav Slobodnik c , Eric De Deckere d , Ralph Kühne e , Ralf-Uwe Ebert e , Antoni Ginebreda f , Ward De Cooman g , Gerrit Schüürmann e,h , Werner Brack a a UFZ, Department of Effect-Directed Analysis, Helmholtz-Centre for Environmental Research—UFZ, Leipzig, Germany b Direction Scientifique, INERIS, Verneuil-en-Halatte, France c Environmental Institute, Kos, Slovak Republic d Institute of Environment & Sustainable Development, University of Antwerp, Antwerp, Belgium e UFZ, Department of Ecological Chemistry, Helmholtz-Centre for Environmental Research—UFZ, Leipzig, Germany f Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research, Spanish Council for Scientific Research (IDAEA-CSIC), Barcelona, Spain g Flemish Environment Agency (VMM), Erembodegem, Aalst, Belgium h Institute for Organic Chemistry, Technical University Bergakademie Freiberg, Freiberg, Germany abstract article info Article history: Received 29 November 2010 Received in revised form 26 January 2011 Accepted 27 January 2011 Keywords: PNEC acute PNEC chronic P-PNEC Prioritization River basin specific pollutants Pesticides Given the huge number of chemicals released into the environment and existing time and budget constraints, there is a need to prioritize chemicals for risk assessment and monitoring in the context of the European Union Water Framework Directive (EU WFD). This study is the first to assess the risk of 500 organic substances based on observations in the four European river basins of the Elbe, Scheldt, Danube and Llobregat. A decision tree is introduced that first classifies chemicals into six categories depending on the information available, which allows water managers to focus on the next steps (e.g. derivation of Environmental Quality Standards (EQS), improvement of analytical methods, etc.). The priority within each category is then evaluated based on two indicators, the Frequency of Exceedance and the Extent of Exceedance of Predicted No- Effect Concentrations (PNECs). These two indictors are based on maximum environmental concentrations (MEC), rather than the commonly used statistically based averages (Predicted Effect Concentration, PEC), and compared to the lowest acute-based (PNEC acute ) or chronic-based thresholds (PNEC chronic ). For 56% of the compounds, PNECs were available from existing risk assessments, and the majority of these PNECs were derived from chronic toxicity data or simulated ecosystem studies (mesocosm) with rather low assessment factors. The limitations of this concept for risk assessment purposes are discussed. For the remainder, provisional PNECs (P-PNECs) were established from read-across models for acute toxicity to the standard test organisms Daphnia magna, Pimephales promelas and Selenastrum capricornutum. On the one hand, the prioritization revealed that about three-quarter of the 44 substances with MEC/PNEC ratios above ten were pesticides. On the other hand, based on the monitoring data used in this study, no risk with regard to the water phase could be found for eight of the 41 priority substances, indicating a first success of the implementation of the WFD in the investigated river basins. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The WFD aims to achieve good status of the European surface waters and groundwater by 2015 and to prevent their further deterioration, which might be caused by a variety of stressors, including toxic chemicals. The Chemical Status of surface water is therefore assessed according to Article 16 of the WFD on the basis of a limited set of 33 priority or priority hazardous substances (PS, daughter Directive 2008/ 105/EC (Commission, 2008)), including eight priority hazardous substances (PHS) coming from previous legislation, which are regulated and monitored at the European scale. If the remaining chemicals are discharged in significant quantities, they are considered under the Ecological Status assessment (Commission, 2000). To this purpose, Annex VIII of the WFD provides an “Indicative list of the main pollutants” that Member States should use as a basis for identification of the chemicals of potential concern for the Ecological Status assessment, referred to as “specific pollutants” (Commission, 2000; Wilkinson et al., 2007). It should be noted that these specific pollutants may also consist of pesticides, despite a rather strict pre-market pesticide approval process, which are regulated under Directive 91/414, to prevent Science of the Total Environment 409 (2011) 2064–2077 ⁎ Corresponding author. Tel.: +49 341 2351581. E-mail address: peter.vonderohe@ufz.de (P.C. von der Ohe). 0048-9697/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2011.01.054 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv