How important is it to update the existing environmental quality standard for nickel? An example based on the UK†

In Europe the Environmental Quality Standard (EQS) for nickel in freshwaters was set in 2013 based on the best available evidence at the time. Since then, additional information about the toxicity of nickel to aquatic organisms and the effects of water chemistry conditions on nickel bioavailability have become available, and there is much more information available about the water chemistry conditions that affect nickel toxicity in freshwaters. This study has taken the updated information about nickel ecotoxicity and bioavailability and evaluates how this could potentially affect the EQS for nickel if it was to be updated. Although the sensitivity of freshwaters to nickel based on the update is very similar to the EQS on a site-specific basis, the thresholds derived are slightly lower. A broader range of water chemistry conditions can be covered by the update than are currently covered by the existing EQS. An updated standard of 2.9 μg L⁻¹ bioavailable nickel could be derived based on the UK dataset evaluated here, which is slightly lower than the existing EQS of 4 μg L⁻¹ bioavailable nickel. Consequently, a slightly higher number of potential compliance failures would be expected based on the update. A simple and practical approach toward the incorporation of local nickel background concentrations into the compliance assessment process for sites that fail the bioavailability based EQS is also proposed. Initial assessments suggest that compliance with the existing EQS could potentially result in more than 5% of species in freshwater aquatic ecosystems being affected, but that with the exception of a very small number of cases the proportion of potentially affected species would be less than 8% of species in the ecosystem. In regions where the existing EQS is not fully implemented, particularly through limited consideration of bioavailability, the adoption of the updated standard is likely to be less beneficial than focusing on better implementation of the existing EQS. However, in regions where the existing EQS has been implemented extensively for some time the updated standard offers a refinement in terms of the coverage of a higher proportion of surface waters and a slightly higher level of protection for sensitive species than the existing EQS.