Pulmonary deposition and clearance of a coal fly ash aerosol by inhalation

Wistar male rats were exposed to coal fly ash aerosols at average exposure concentration of 10.4 mg/m3 for 7 hr/day, 5 days/week for 1 month. Some rats were sacrificed just after the exposure, while others were kept for 6 or 10 months clearance time before sacrifice. There were no differences in body weight gain between fly ash exposure groups and controls. The burden of fly ash was estimated by the measurement of aluminum contents in rat organs. Aluminum concentrations in lungs of exposure groups were much higher than those of controls. No apparent deposition of fly ash was observed in the liver, kidneys, spleen, and blood, but lung burdens of up to about 0.7 mg of fly ash were found. The apparent deposition fraction was 5.1% after the 1-month exposure. The clearance rate of fly ash deposited in rat lungs may be very slow.