The pathological effects of asbestos clouds of different fibre dimensions on the lungs of rats.

The pathological influence exerted on the lungs by exposure to asbestos (1332214) clouds containing fibers of different dimensions was studied in rats. Rats were exposed to chrysotile (12001295), crocidolite (12001284), or amosite (12172735) dusts at concentrations of 10 milligrams per cubic meter (mg/m3); to chrysotile dust at a concentration of 2mg/m3; or to crocidolite dust at a concentration of 5mg/m3 for a period of 1 year. At both concentrations, chrysotile dust caused fibrosis to develop to a greater extent than any of the amphibole clouds. All of the malignant pulmonary neoplasms observed were detected in chrysotile treated animals. An examination of the fiber length distributions of these 3 types of asbestos under a scanning electron microscope revealed that 7 percent of the fibers contained in the chrysotile dust clouds were longer than 20 microns, while only about 0.5 percent of the crocidolite and amosite fibers achieved that length. During peak exposure studies, test animals were exposed to amosite and chrysotile dust clouds at respective concentrations of 50 and 10mg/m3 for comparison to the former 10 and 2mg/m3 exposures. The degree of dust deposition associated with these 2 exposure regimens was remarkably similar, with greater deposition and retention being indicated to a slight extent during peak dosing. Peak dosed test animals exhibited a greater degree of interstitial fibrosis in the later stages of exposure than evenly dusted animals, with two malignant lung tumors being detected in the amosite group. The authors conclude that peak dosing apparently does not produce large changes in the extent of resultant lung pathologies.