Pulmonary deposition and clearance of a nickel oxide aerosol by inhalation

Wistar male rats were exposed to nickel oxide (NiO) aerosols (mass median aerodynamic diameter, 1.2 μm). The average exposure concentration was controlled from low level (0.6 mg/m(3)) to high level (8.0 mg/m(3)) and total exposure time ranged from 140 to 216 h. Some rats were sacrificed just after the exposure, whereas others were exposed for 1 mo and kept for a 1-yr clearance period before sacrifice.There were no differences in body weight gain between NiO exposure groups and controls.Nickel concentrations in lungs of exposure groups were much higher than those of controls. No apparent deposition of nickel was observed in liver, kidney, spleen, heart, brain, and blood, but lung burdens of up to about 2.35 mg of NiO were found. The apparent deposition fractions were 19.8 and 14.5% after the exposure to average concentrations of 1.4 and 6.5-7.0 mg/m(3), respectively.The clearance rate of NiO deposited in lungs may be small.