EXPERIMENTAL STUDY ON LONG-TERM EFFECTS OF INHALED MMMF ON THE LUNGS OF RATS

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Abstract
Two glass and rock wools (Saint-Gobain) were compared with a glass microfibre (Johns Manville 100) and a chrysotile fibre in order to determine the retention of fibres in different parts of the lung and the risk of fibrous and tumorous lesions forming. The rats were exposed in dust chambers containing equal respirable mass concentrations (5 mg m −3 of these materials. After 12 and 24 months of exposure followed by various periods for lesion development, fibre retention was analysed and the tissues were examined. The numbers of fibres retained were 20–30 times greater for JM 100 and chrysotile than for SG glass wool and about 10 times higher for SG glass wool than for SG rock wool. Fibres which migrated into the lymph nodes were shorter than those in the lungs. During their period of residence in the lungs, the four types of fibre showed changes amounting to almost total disintegration in some cases. Under the conditions of the experiment, the noxious character of the SG glass and rock wools was very low. Only chrysotile produced a significant increase in pulmonary collagen. The tumour-inducing power of the glass and rock wools was practically non-existent.

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