In parallel inhalation and intraperitoneal injection (i.p.) experiments with rats, the glass fibre JM 104, Tempstran 475, exemplifying a very thin and durable man-made mineral fibre (MMMF). was compared with crocidolite (South Africa) and chrysotile (California, Calidria RG 144). Aerosol concentrations were 2.2-6mg m −3 Exposures lasted 1 yr. No significant tumour rate was found in the inhalation test nor from an exposure combination of 100 ppm SO 2 and glass fibres. In 74% of the animals exposed to crocidolite bronchiolo-alveolar hyperplasia was detected. Intraperitoneal injection of 0.5 mg of the three different fibre types showed a tumour rate of 17% for glass fibre JM 104, 55% for crocidolite and only 6% for Calidria chrysotile. Calidria chrysotile seems to be much less persistent than other chrysotile samples. The long persistence of JM 104/475 in the lung (half-time of lung clearance about 600 days) and the carcinogenic effects of these fibres after intraperitoneal injection indicate that after inhalation of thin (< 1 μm). long and durable MMMF the suspicion of a carcinogenic potency of these fibres is still well-founded.
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Muhle et al. (1987) studied this question.