Evaluating the usefulness of existing environmental threshold concentrations (ETCs), with a focus on pharmaceuticals in surface water: a European perspective

Environmental Threshold Concentrations (ETCs), such as the Predicted No Effect Concentrations (PNECs) and European Environmental Quality Standards (EQSs), represent the concentration of a chemical in an environmental compartment at or below which no adverse effects are expected. While multiple ETCs may exist for a given substance across regulatory frameworks and scientific literature, selecting the most useful value can be challenging. Even when only one ETC exists, its usefulness must be evaluated. This paper addresses this challenge by providing a systematic and stepwise framework for selecting and interpreting ETCs, with a focus on human pharmaceuticals and European regulatory frameworks. However, the ideas behind this may be applied more broadly. The proposed approach begins by defining the context of the assessment and the associated protection goals. It then requires a systematic evaluation of all available ETCs, regarding their relevance and reliability. This includes the use of the most appropriate methodology and underlying data, as well as newly published information. It also considers overall uncertainties, the need to address chronic or short-term peak exposures, and whether the ETCs have been independently reviewed. We apply the framework to metoprolol to demonstrate its usefulness in ensuring that ETCs used in environmental assessments and management decisions are robust and fit for purpose.