Environmental quality standards for diclofenac derived under the European Water Framework Directive: 3. Marine ecotoxicity

Background Diclofenac is a nonsteroidal anti-inflammatory human and veterinary medicine widely detected in European waters downstream of Wastewater Treatment Plants. Proposed Environmental Quality Standards (EQS) for diclofenac, which include an assessment of toxicity to aquatic organisms, have been proposed by the European Commission to support the objectives of the Water Framework Directive, including EQS aimed at protecting marine species. In this paper, we present previously unpublished studies assessing the effects of diclofenac on four marine species, three echinoderms and an annelid worm. The results of these new tests were incorporated into the long-term marine ecotoxicity dataset for diclofenac and an updated marine EQS derived. Finally, these updated prospective EQS were compared with measured diclofenac concentrations in European marine waters to assess potential risk. Results Limited effects on fertilisation were measured in echinoderms at diclofenac concentrations beyond environmental relevance. However, fertilisation in the annelid worm Arenicola marina was found to be sensitive to diclofenac exposure, with a No Observed Effect Concentration of 578 ng/L. Using the updated marine ecotoxicity dataset for diclofenac, prospective marine EQS of 58 and 37 ng/L were derived, respectively, using deterministic and probabilistic (species sensitivity distribution) derivation approaches. The indicative compliance of European marine waters with the prospective EQS is 79–97%. Conclusions Comprehensive investigations into the potential of diclofenac to inhibit fertilisation on echinoderms and annelid worms failed to reproduce the extremely sensitive results previously reported in published studies. The reduced sensitivity observed here were potentially a result of methodological differences between the studies, such as pre-exposure of gametes versus exposure only during fertilisation, the time allowed for the fertilisation process, as well as the possibility of differential uptake of diclofenac owing to use of a solvent or pH variation. Compliance with the prospective EQS depended on the method used to treat the censored measured concentration data but was generally high across all monitored European marine waters. This entirely marine-focused hazard and risk assessment suggests that a proposed EU EQS of 4 ng/L, derived entirely from a single freshwater mesocosm study, is likely to be over-precautionary for European marine waters.