December 8, 2021 by Dean Leverett

Dean, Graham and Iain have just published: Environmental quality standards for diclofenac derived under the European Water Framework Directive: 1. Aquatic organisms in Environmental Sciences Europe.

The paper focuses on the derivation of Water Framework Directive (WFD) Environmental Quality Standards (EQS) for the pharmaceutical diclofenac.

Diclofenac is a nonsteroidal anti-inflammatory human and veterinary medicine widely detected in European surface waters, especially downstream from Wastewater Treatment Plants (WWTPs). Proposed EQS, which include an assessment of toxicity to aquatic organisms, are under consideration by the European Commission (EC) to support the aims of the WFD.

The EC approach to EQS derivation for diclofenac favours the use of a deterministic (single test value and an assessment factor) approach to the derivation of a direct toxicity EQS for diclofenac, resulting in an EQS of 0.040 μg/L, based on a single mesocosm study. In the paper, we discuss potential issues with this approach with respect to the EC’s own guidance on EQS derivation, and derive an alternative EQS of 0.126 μg/L using a probabilistic (species sensitivity distribution) approach that accounts for all of the reliable and relevant data, and is in accordance with the guidance.

Europe-wide freshwater monitoring data for diclofenac are presented to provide an indicative compliance assessment using the EC and the alternative evidence-driven EQS.

The implications of not utilising all the available data to derive an EQS, and deviating from the accepted guidance on EQS derivation, are also discussed.