Response to commentary article on environmental quality standards for diclofenac derived under the European water framework directive: 1. Aquatic organisms, by Maack et al. 2022

In this short article, we respond to a Commentary by Maack et al. (Environ Sci Eur 34:24, 2022) in which they challenge recommendations in Leverett et al. (Environ Sci Eur 33:133, 2021) for setting an aquatic Environmental Quality Standard (EQS) for the pharmaceutical diclofenac. Maack et al. recommend the use of results from a stream mesocosm study as the main point of departure for setting the EQS and dismiss the use of a Species Sensitivity Distribution (SSD) containing relevant and reliable single species data because of bimodality in this distribution. We present the key mesocosm data used by Maack et al. and note that these are highly variable, include control mortalities of up to 60%, and, as reported by the original authors, show a significant effect only at the highest test concentration and not at the estimated value proposed by Maack et al. We also show that there are neither regulatory nor technical grounds for dismissing the use of an SSD and respond to minor criticisms of our compliance assessment (comparison of different EQS values with reported concentrations in European surface waters). Finally, we provide comment on the EQS derivation process and subsequent opinion of the diclofenac EQS dossier by the European Commission's Scientific Committee on Health, Environmental and Emerging Risks (SCHEER).

Automated summary

This article responds to the challenges made by Maack et al. regarding the recommendations for setting an aquatic Environmental Quality Standard (EQS) for diclofenac. The authors present data and arguments to support the original recommendations and discuss the use of Species Sensitivity Distribution (SSD) and mesocosm study results in the EQS derivation process.