Pleural migration of chrysotile fibers after intratracheal injection in rats.

After intratracheal injection of 0.5 mg of UICC chrysotile, rats were sacrificed at various time intervals over a 1-month period, and their pleural cavity washed with saline. Samples were examined by means of transmission electron microscopy for identification, quantitation, and sizing of chrysotile fibers. No fibers were found in control rats injected with saline. The size and quantity of fibers that reached the pleural cavity of test rats was time-dependent, with two peaks on day 7 (mean number = 9.6 X 10(4); mean length = 1.3 micron) and on day 21 (mean number = 1.3 X 10(5); mean length = 0.3 micron). Such variations are compatible with a heterogeneous migration of chrysotile fibrils toward the pleura.