Effects Assessment

The PNECs represent dietary Ni concentrations below which adverse effects are not expected for birds or mammals. PNECs were identified in two tiers. In Tier 1, derivation of PNECs followed the standard guidance in the TGD and did not account for any species-specific differences in food ingestion rates and body weight. In Tier 2, PNECs were derived on the basis of species-specific food ingestion rate-to-body weight ratios for the birds and mammals considered in this evaluation.

The PNECs were based on the most sensitive (i.e., lowest) dietary no-observed-effect concentrations (NOECs). For birds, six sub-chronic and chronic feeding studies in which bird diets were spiked with Ni were identified in the literature. The lowest NOECs, focusing on endpoints related to survival, growth, and the occurrence of tremors, were >150 mg Ni kg-1 based on a 42-day chicken study and 200 mg Ni kg-1 based on a 90-day study with mallard ducklings. For mammals, the lowest NOEC of 22 mg Ni kg-1 was derived from the no-observed-adverse-effect level (NOAEL) taken from the previously completed human health Ni risk assessment, which was identified as 1.1 mg Ni kg-1 bw d-1. Following the TGD, these NOECs were divided by an assessment factor (AF) of 30 to account for interspecies variation in sensitivity and laboratory-to-field extrapolation, thereby resulting in Tier 1 bird PNECs of 5.0-6.7 mg Ni kg-1 and a mammal PNEC of 0.73 mg Ni kg-1 (Table 3). For Tiers 2 and 3, the NOECs were adjusted based on the food ingestion rate-to-body weight ratios of the specific species being evaluated relative to the species used in the toxicity tests. These ingestion rate-adjusted NOECs were divided by an AF of 10 in order to derive Tiers 2 and 3 PNECs (Table 3).

Predator Class System Species NOEC
(mg Ni kg-1)
Ingested Rate-Adjusted NOEC
(mg Ni kg-1)
Assessment
Factor Applied
PNEC
(mg Ni kg-1)
Birds All Generic 150 --- 30 5.0
200 --- 30 6.7
Marine Oystercatcher 200 123 10 12.3
Freshwater Mollusk-eating bird 200 123 10 12.3
Terrestrial Worm-eating bird 200 85 10 8.5
Mammals All Generic 22 --- 30 0.73
Marine Harbor seal 22 46 10 4.6
Terrestrial Shrew 22 1.2 10 0.12
Freshwater Otter 22 23 10 2.3

Table 3:  Predicted no effect concentrations for nickel in wildlife diets