Clearance of inhaled ceramic fibers from rat lungs.

Deposition, clearance, retention, and durability of inhaled particles in lung are important factors for induction of pulmonary fibrosis or lung cancer. To study the deposition and clearance of aluminium silicate ceramic fibers from the lung, male Wistar rats were exposed to ceramic fibers, with a mass median aerodynamic diameter (MMAD) of 3.7 microns, for 6 hr/day, 5 days/week for 2 weeks. The average exposure concentration was 27.2 mg/m3 (SD 9.0). The rats were killed at 1 day, 1 month, 3 months, and 6 months after the end of exposure, and the fiber numbers and dimensions were measured with a scanning electron microscope. No significant difference in length of residual ceramic fibers in the lungs was found among the groups. The geometric mean diameter and number of ceramic fibers, however, decreased according to the clearance period. These findings suggest that the fibers were dissolved at their surface.