Retention of nickel oxide (green) aerosol in rat lungs by long-term inhalation

Wistar male rats were exposed to green nickel oxide NiO(G)] aerosols (mass median aerodynamic diameter, 0.6 μm) for 7 h/d, 5 d/wk for up to 12 mo. The average exposure concentration was controlled at 0.3 mg/m³ and 1.2 mg/m³ during the exposure period. Some rats were sacrificed just after the 3- and 6-mo exposures, and others were sacrificed after the termination of the 12-mo exposure. There were no differences in body weight gain between NiO(G) exposure groups and controls. The lung weights in the exposed rats were heavier than those in the control ones. Nickel concentrations in lungs of exposure groups were much higher than those of controls. The nickel concentrations in liver, kidney, spleen, and blood slightly increased with the passing of the exposure time. The nickel content in rat lungs during the 12-mo exposure was estimated theoretically. The estimated values agreed with the experimental data. This result shows that the clearance rate increases with the decreasing of the particle diameter.