June 9, 2026 by Lucy Kennelly

Lucy is the lead author on a brief communication recently published in IEAM by wca discussing the need for a consistent approach to account for transformation products when deriving environmental quality standards (EQS).

This work has been driven by reviewing recent EQS for substances published under the European Water Framework Directive. While EQS for parent substances are typically derived using a well-established framework based on laboratory generated ecotoxicity data, a lack of guidance on how to account for transformation products has led to inconsistencies in the derivations for different chemicals.

For example, at least two of the recent EQS (for the pharmaceuticals carbamazepine and clarithromycin), have taken different approaches to derivation to account for transformation products. These approaches deviate from the existing guidance and each other by applying additional assessment factors or requiring monitoring of parent and transformation products in surface waters to assess compliance. In this publication we have put forward an evidence-driven scheme to address how transformation products could be incorporated into the EQS derivation process, ensuring a repeatable and transparent approach that uses all the relevant and reliable data for effects and exposures.

We are keen for researchers and practitioners in the field to review and further develop this approach, so that it could be incorporated into an upcoming revision to the EQS technical guidance. Consistency and transparency are needed in derivation processes if scientifically robust and ecologically relevant EQS for parent substances and their transformation products are to be derived and implemented.