Nickel difluoride

Toxicity to birds

Description of key information

Several sub-chronic and chronic feeding studies in which the diet was spiked with a Ni salt were identified as key studies. From these studies, generic NOEC values of 150 and 200 mg Ni/kg were determined in a tier I approach. In a tier II approach, refined NOEC values of 12.3 mg Ni/kg and 8.5 mg Ni/kg were determined for the aquatic foodchain and earthworm-eating birds respectively.

Additional information

Several key studies covering the toxicity of Ni to birds were identified (Ling and Leach, 1979; Cain and Pafford, 1981; Eastin and O'Shea, 1981). The most sensitive LOEC from these studies, focusing on endpoints relative to survival, growth, and reproduction, was 300 mg/kg (as added Ni) based on a 21-day study with White Plymouth Rock day-old male chicks (Ling and Leach, 1979). This LOEC is based on a 14% reduction in body weight relative to the control chicks. A NOEC of 150 mg/kg was estimated by dividing the LOEC by 2 as per TGD guidance.

Cain and Pafford (1981) observed tremors in all ducklings fed a dietary Ni concentration of 800 mg/kg or greater. Although all but two ducklings in the 800 mg/kg dietary treatment survived throughout the 90-day exposure period, all ducklings that developed tremors also had pronounced edema in the toes and leg joints. At a dietary Ni concentration of 200 mg/kg, all ducklings survived and none developed tremors.

Overall, therefore, 200 mg/kg appears to be an appropriate NOEC for this secondary poisoning analysis. No effects on growth, survival, or reproduction in chickens or mallards have been observed at this measured dietary concentration or lower. Further, more confidence is placed in the NOEC of Cain and Pafford (1981) than that of Ling and Leach (1979) because the former was a measured NOEC from a longer study.

In a tier I approach, the NOEC values of 150 and 200 mg/kg ww are considered as key values used for deriving PNEC oral values for birds.

 

In a tier II approach, PNEC oral values for birds were further refined to differentiate aquatic birds and terrestrial birds.

For the aquatic foodchain, a NOEC values were calculated based on the sensitivity of mallards to Ni. Because mallards are presumed to have different food ingestion rate-to-body weight ratios than the oystercatcher or European starling, the mallard-based dietary NOEC can be used to estimate oystercatcher- and starling-based dietary NOECs using the ingestion rate-to-body weight ratios for the two species. As a first step, a dose-based no observed adverse effect level (NOAEL) for the mallard can be estimated using the mallard duckling body weights in Cain and Pafford (1981) and the allometric equation from Nagy (1987) for estimating the food ingestion rate. In Cain and Pafford (1981) tremors were observed in ducklings at about 28 days of age; therefore, the 28-day body weights were used to determine the relevant body weight (457 g wet wt. based on the mean of males and females). Using the allometric equation for birds from Nagy (1987) results in an estimated food ingestion rate of 34.9 g/d on a dry weight basis (175 g/d on a wet weight basis assuming a water content of 80%). Thus, the estimated body weight (bw)-to-daily food intake (dfi) for mallard ducklings is estimated to be 2.6 (457 g body weight divided by 175 g/d wet weight.). The resulting estimated NOAEL for mallard ducklings is 77 mg Ni per kg body weight per day (mg/kg/day). Based on a study by Goss-Custard (1977), the mean body weight and food ingestion rate for the oystercatcher were 0.555 and 0.338 kg/d wet wt., respectively, resulting in a bw/dfi of 1.6. Multiplying the duckling-based NOAEL of 77 mg/kg/day by the bw/dfi of 1.6 results in an estimated dietary NOEC for the oystercatcher of 123 mg/kg.

For the earthworm-eating bird, as discussed in the previous section, it is assumed to consume up to 90% of its body weight daily. Based on this food consumption rate, the bw/dfi conversion factor is 1.1 (1 kg wet body weight divided by 0.9 kg wet food per kg wet body weight per day). Applying the bw/dfi conversion factor of 1.1 to the duckling-based NOAEL of 77 mg/kg/day results in a dietary NOEC of 85 mg/kg for the earthworm-eating bird.