Inhalation and injection experiments in rats to test the carcinogenicity of MMF

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 chrysosotile (California. Calidria RG 144). Aerosol concentrations were 2.2-6 mg m(-3). Exposures lasted 1 yr. No significant tumour rate was found in the inhalation test nor from an exposure combination of 100 ppm SO2 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 tate of 17% for glass fibre JM 104, 55% for crocidolite and only 6% for Calidria chrysotile. Calidria chrysotile seems to be much less persitent 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 i ndicate that after inhalation of thin (smaller than 1 mym), long and durable MMMF the suspicion of a carcinogenic potency of these fibres is still well-founded.