Using Exposure Data to Identify Priority Substances Under the European Water Framework Directive: The Quest to Reflect Uncertainties.

The European Water Framework Directive (2000/60/EC) identifies "Priority Substances" (PS) as those posing a significant risk to or via the aquatic environment. Both reliable exposure data and a reliable Predicted No Effect Concentration (PNEC) are necessary for a robust risk assessment. Unfortunately, the exposure datasets used to evaluate candidate PS contain a large proportion of undetected or unquantified samples. This highlights the left-censored characteristics (i.e., having a high proportion of unquantified results) of many of these datasets. Without appropriate consideration of these non-detects, the risk assessment becomes meaningless, since it does not provide objective evidence that exposure occurs above the relevant PNEC over wide areas or at a significant number of sites. This article is protected by copyright. All rights reserved.