The effects of inhaled crocidolites from Transvaal and North-west Cape mines on the lungs of rats and guinea-pigs.

A group of guinea-pigs and another of rats were successively placed for 400 hours in an atmosphere containing a high concentration of North-west Cape (NWC) crocidolite fibres. A further group of guinea-pigs inhaled Transvaal (TVL) crocidolite for an equal time. Guinea-pigs that inhaled NWC crocidolite were substantially outlived by animals of the other 2 groups, of which the longest survivors were 2 guinea-pigs. No mesotheliomata were found but in all the lungs cellular proliferation of the septa caused a reduction in alveolar space. Giant cells were common and asbestos bodies developed in guinea-pigs, but in rats only a very few, atypical asbestos bodies were seen, and giant cells were rare. All lungs contained uncoated fibres, long fibres (occasionally exceeding 50 μm) being seen in subpleural regions in older animals and in peribronchiolar accumulations. NWC fibres reached the muscular coats of larger bronchioles of guinea-pigs sooner than TVL crocidolite. Proliferation of bronchiolar epithelium was produced in guinea-pigs and 2 rats by NWC crocidolite, but not by TVL crocidolite. Guinea-pigs dying over 3 months and rats over 18 months after inhalation of NWC crocidolite had several small emphysematous regions at the lung periphery, but only one small area was seen in each of the last 2 guinea-pigs that inhaled TVL fibres. Thus, NWC crocidolite produced greater disruption of the respiratory surfaces. Severe lung fibrosis was not seen, although fine collagen strands were found in interalveolar septa of animals dying at over 5 months after dusting began. Dense subpleural areas of collagen produced by TVL crocidolite were, however, found in the 4 oldest guinea-pigs. Inhalation of these 2 crocidolites results in different pathological responses, although no difference in distribution in the lung were found to explain differences in survival time, bronchiolar epithelial proliferation or subpleural collagen formation.