Environmental quality standards for diclofenac derived under the European water framework directive: 2. Avian secondary poisoning

Diclofenac is a nonsteroidal anti-inflammatory human and veterinary medicine widely detected in European surface waters, especially downstream from Wastewater Treatment Plants. With some notable exceptions, veterinary uses of diclofenac in Europe are greatly restricted, so wastewater is the key Europe-wide exposure route for wildlife that may be exposed via the aquatic environment. Proposed Environmental Quality Standards (EQS) which include an assessment of avian exposure from secondary poisoning are under consideration by the European Commission (EC) to support the aims of the Water Framework Directive (WFD). In this paper we summarise information on avian toxicity plus laboratory and field evidence on diclofenac bioaccumulation and bioconcentration in avian food items. A safe diclofenac threshold value for birds of 3 μg kg⁻¹ wet weight in food was previously derived by the European Medicines Agency and should be adopted as an EQS under the WFD to maintain consistency across European regulations. This value is also consistent with values of 1.16–3.99 µg kg⁻¹_diet proposed by the EC under the WFD. Water-based EQS of 5.4 or 230 ng L⁻¹ in freshwater are derived from these dietary standards, respectively, by the EC and by us, with the large difference caused primarily by use of different values for bioaccumulation. A simple assessment of potential water-based EQS compliance is performed for both of these latter values against reported diclofenac concentrations in samples collected from European freshwaters. This shows that exceedances of the EC-derived EQS would be very widespread across Europe while exceedances of the EQS derived by us are confined to a relatively small number of sites in only some Member States. Since there is no evidence for any declines in European waterbird populations associated with diclofenac exposure we recommend use of conservative EQS of 3 µg kg⁻¹_diet or 230 ng L⁻¹ in water to protect birds from diclofenac secondary poisoning through the food chain.