A novel risk assessment approach for the prioritisation of emerging substances and its application to 500 organic microcontaminants
Résumé
Given the huge number of chemicals in commerce, there is a need of prioritising chemicals for risk assessment and monitoring. 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. 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 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 QSAR models for acute toxicity to the standard test organisms Daphnia magna, Pimephales promelas and Selenastrum capricornutum. The prioritisation revealed that about three-quarter of the 44 substances with MEC / PNEC ratios above ten were pesticides.