| Abstract: | Changes in the dimensions of inhaled asbestos fibers in the lung and translocation of intrapulmonary asbestos fibers into mesothelial tissues were investigated in 17 baboons (5 exposed to amosite, 4 to chrysotile, 5 to crocidolite, and 3 unexposed). The animals received different cumulative doses of asbestos by inhalation, followed by varying recovery periods (0–69 months). All asbestos types induced pulmonary asbestosis with severity directly related to the cumulative dose. There were a larger number of asbestos bodies in the lung of the amphibole-exposed animals than in those exposed to chrysotile. A tissue burden study, using transmission electron microscopy on 25-μm paraffin sections, ashed in a low-temperature asher, was performed. Intrapulmonary amosite fibers were shorter in geometric mean length compared with a standard amosite sample (UICC) (3.3 μm). In explanation, it was considered that long fibers might not be able to reach the lower respiratory tract and/or long fibers might be fragmented into shorter fibers. Further, in the amosite-exposed group, the mean length of intrapulmonary fibers increased with the extension of recovery period, suggesting that shorter fibers had been cleared from the lung. The chrysotile standard sample (UICC) had a shorter geometric mean length (1.1 μm) than amosite. The mean length of intrapulmonary chrysotile did not noticeably change with the extension of inhalation and recovery periods; however, the mean width decreased with the extension of these periods. This finding strongly suggested that separation of thick chrysotile fibers had occurred in the lung. The crocidolite standard sample (Transvaal) had a shorter geometric mean length (1.4 μm) than amosite. The mean length of intrapulmonary crocidolite fibers increased with the extension of inhalation and recovery periods, suggesting that shorter fibers had been cleared from the lung during both the inhalation and recovery periods. There was no specific tendency of size distribution among four distinct interstitial locations (peribronchiolar, alveolar septal, subpleural, and interlobular connective tissue) within the same lung exposed to either amosite, chrysotile or crocidolite. In four animals, malignant mesothelioma developed in the pleura (2 amosite and 1 UICC crocidolite) and the peritoneum (1 UICC crocidolite). Asbestos fibers were found in the mesotheliomas. Their size distribution in mesotheliomatous tissue and lung was not significantly different in two animals, but the fibers were shorter and thinner in another two. The presence of fibers in the neoplasms was confirmed, and translocation of fibers from the lung into the pleura or the peritoneum was strongly suggested. © 1993 Wiley-Liss, Inc. |
