Pathogenicity of inhaled nickel compounds in hamsters

To investigate the pathogenicity of nickel oxide (NiO), hamsters received life-span exposures to that compound (approximately 55 mg/m3) seven hours per day, five days per week. Heavy pulmonary nickel oxide burdens resulted in pneumoconiosis but in no significant carcinogenicity, specific toxicity, or mortality. Two-month exposures of hamsters to nickel-enriched fly ash (NEFA) or fly ash (FA) aerosols (approximately 185 mg/m3) resulted in a deep lung burden of about 5.7 mg, dark discoloration of lungs, heavily dust-laden macrophages, and significantly higher lung weights than in controls, but only minimal inflammatory reaction and no deaths. The NEFA contained 9% nickel; FA contained 0.03% nickel. Exposure to aerosols of NEFA (70 or 15 mg/m3; 6% nickel) or FA (70 mg/m3; 0.3% nickel) for 20 months had no effect on body weight or life-span of the animals. Lung weights and volumes of the high-NEFA- and FA-exposed animals were higher than those of the low-NEFA group and controls. The incidence and severity of interstitial reaction and bronchiolization were significantly higher in the dust-exposed groups than in the controls. The severity of dust deposition, interstitial reaction, and bronchiolization was significantly lower in the low-NEFA group than in the high-NEFA and FA groups. Our findings revealed no significant nickel-specific toxicity/carcinogenicity in hamsters exposed to aerosols of nickel oxide or NEFA, but exposure to high concentrations of the oxide resulted in nonspecific dust pneumoconiosis.