Secondary poisoning risk assessment of terrestrial birds and mammals exposed to nickel

The European Union's Existing Substances regulation (EEC 793/93) was developed to assess the ecological risks posed by chemical substances such as Ni and includes the assessment of secondary poisoning risks. The basic structure of this secondary poisoning risk assessment followed the Technical Guidance Document on Risk Assessment and thus included development of predicted exposure concentrations (PECs) and predicted no-effect concentrations (PNECs). A PEC to PNEC ratio greater than 1.0 is indicative of potential risk. The Technical Guidance Document on Risk Assessment provides a generic framework for assessing secondary poisoning risks and prescribes the following terrestrial food chain: soil → earthworm → worm-eating bird or mammal. This secondary poisoning evaluation was conducted at the regional level, and it was found that the generic approach resulted in widespread estimates of potential risk, even at ambient Ni soil concentrations. Accordingly, a tiered approach was used with increasing levels of refinement, including consideration of bioavailability, consideration of a variable diet, and development of dose-based PNEC values. Based on the refined approach, all PEC to PNEC ratios were less than 1.0, except for a ratio of 1.4 in a scenario focused on a regional clay soil, which was of natural origin. This regional-level secondary poisoning evaluation highlighted key risk assessment components that should be considered in future localized secondary poisoning assessments of Ni and other metals, including ingestion rate to body weight ratios for the test organisms used to derive PNECs versus the representative wildlife species evaluated, the appropriateness of high assessment factors for deriving PNECs for naturally occurring essential elements, representative dietary compositions, relative metal bioavailability between the dietary toxicity study and natural diets, and ground-truthing of the risk predictions versus background concentrations.