Based on the outcome of the tiered secondary poisoning risk assessment for Ni, it is observed that none of the aquatic (marine or freshwater) food chains resulted in RCRs >1. For the terrestrial compartment, based on the refined approach of the upper tiers of the assessment, all RCRs were <1, except for one soil eco-region with an RCR of 1.4. This one soil with an RCR of 1.4 was a clay soil with naturally high Ni concentrations, indicating that the approach used to evaluate secondary Ni poisoning erred toward conservatism, even when considering the higher tiers of the assessment. The secondary poisoning evaluation described in this fact sheet focuses on the regional-level analyses, but application of the tiered approach succeeded in reducing the number of sites at risk for secondary poisoning under local scenarios that tended to have higher environmental Ni concentrations. This secondary poisoning evaluation highlighted key risk assessment components that should be considered in future localized, or site-specific, secondary poisoning assessments of Ni and other metals, including:

  • consideration of 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; 
  • the use of relevant dietary assumptions; 
  • an evaluation of relative metal bioavailability between the dietary toxicity study and natural diets; and 
  • verifying the risk predictions versus background concentrations.