March 23, 2023 by Adam Peters

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Adam and Iain have recently published a study evaluating the protectiveness of the bioavailability based Environmental Quality Standard for zinc that is used in the UK based on an assessment of field evidence along with colleagues from the International Zinc Association. The study was able to identify eight taxa that showed a response to increasing bioavailable zinc exposures exhibiting a range of sensitivities to the metal. However, the robustness of any thresholds that could be derived based on individual taxa were judged to be highly uncertain due to the fact that many taxa are absent from many sampling sites regardless of their zinc exposures. This is due to a large extent to the suitability of local habitats for different species, but also to the present of additional stressors such as food availability, predation, flow regimes, and other toxicants. Measures of ecological quality that are based on the total abundance of several zinc responsive taxa were used to derive thresholds for bioavailable zinc concentrations that would not result in a  significant reduction in the abundance of zinc sensitive species.

Overall the Environmental Quality Standard for zinc was concluded to be protective of these zinc sensitive taxa, despite the exposures at the sites that were included in the assessment potentially including a mixture of other contaminants at trace levels. These findings are relatively consistent with the findings of mesocosm studies that have found EQS values for zinc to be protective of aquatic communities.