Abstract
Five groups of rats were treated by inhalation for 12 months, with the U.I.C.C. preparations of the 3 main commercially used asbestos types, chrysotile, crocidolite and amosite. The experiment was designed so that the effects of both fibre mass and fibre number could be examined. The results indicated that chrysotile dust caused far more lung fibrosis than either amphibole type even when the fibre numbers in the dust clouds were similar. All malignant pulmonary neoplasms found during this study occurred in animals treated with chrysotile. The fibre-number calculations used for the generation of dust clouds were evaluated using the parameters recommended by the Health and Safety Executive in 1976, by which all fibres over 5 microgram long are counted using a phase-contrast light microscopy. When fibre-length distributions were calculated using a scanning electron microscope, however, it was found that the chrysotile clouds used in this study contained many more fibres over 20 microgram long than either of the amphibole clouds. The results, therefore, support previous suggestions that long asbestos fibres are more dangerous than short. They also indicate that neither a single mass standard, nor the present fibre-number standards are satisfactory.
Highlights
MATERIALS AND METHODSThe U.I.C.C. sample of amosite has the fewest fibres. and chrysotile the most, with crocidolite fibres being somewhere between the 2
Summary.-Five groups of rats were treated by inhalation for 12 months with the U.I.C.C. preparations of the 3 main commercially used asbestos types, chrysotile, crocidolite and amosite
Knowledge of the relative importance of the different asbestos tyes in the production of neoplasia is no more precise and, crocidolite has been specially linked with the production of mesotheliomas (Wagner, Sleggs and Marchand, 1960), subsequent epidemiological studies have indicated that at least some of the other asbestos types may cause this type of tumour (McDonald, 1973; Selikoff, Hammond and Seidman, 1973)
Summary
The U.I.C.C. sample of amosite has the fewest fibres. and chrysotile the most, with crocidolite fibres being somewhere between the 2. M.R.E. sampler (Casella Type 113A; Dun- lesions produced in the rat lungs by the more, Hamilton and Smith, 1964) was used to different asbestos clouds, the following method measure the concentrations in the crocidolite was adopted. Undersample, and a vertical elutriator system Of the animals that survived until the final (Beekett, 1975) wNas used to killing date at 860 days, 6 were examined monitor the chrysotile clouds The remaining were based on the number of squares that animials wNere left with the intention of contained the small areas of fibrous tissue and allowing them to survive their full life-span, the results from all 4 sections were again in ordei to study the frequency of lung- presented as a percentage. For histological examination the larynx was serially sectioned in the longitudinal plane and approximately 8 evenly spaced sections were mounted for examination from each specimen
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