Comparative toxicity of nickel oxide, nickel sulfate hexahydrate, and nickel subsulfide after 12 days of inhalation exposure to F344/N rats and B6C3F 1 mice

Abstract

The relative toxicity of nickel oxide (NiO), nickel sulfate hexahydrate. (NiSO 4·6H 2O), and nickel subsulfide (Ni 3S 2) was studied in F344/N rats and B6C3F 1 mice after inhalation exposure for 6 h/day, 5 days/week for 12 exposure days. Exposure concentrations used (as mg Ni/m 3) were 0.9–23.6 for NiO; 0.8–13.3 for NiSO 4·6H 2O, and 0.4–7.3 for Ni 3S 2. For each compound there were 5 exposure groups plus a control group. NiSO 4·6H 2O was the most toxic compound with exposure related mortality seen at exposure concentrations of 13.3 mg/m 3 in rats and 1.6 mg/m 3 and above in mice. For Ni 3S 2, mortality was seen in mice (but not in rats) at the highest exposure concentration (7.3 mg/m 3). No mortality was seen after NiO exposure. Lesions of the lung and nasal cavity were seen in both rats and mice after exposure to NiSO 4·6H 2O and Ni 3S 2 at the 4 highest exposure concentrations. Lesions of the lung were seen primarily at the highest exposure concentrations after NiO exposure. The amount of nickel in the lungs at the end of exposure varied in relation to the water solubility of the compounds. Based on these 2-week studies, the toxicity ranking was NiSO 4·6H 2O > Ni 3S 2 ⪢ NiO. Additional studies are in progress to assess the relative toxicities of these three nickel compounds after 90-day exposures.