Persistence of man-made mineral fibres -MMMF- and asbestos in rat lungs

In a 2-yr study the persistence of some MMMF, crocidolite and chrysotile in the rat lung was examined after intratracheal instillation. Experiments were based on the assumption that thin, long and durable fibres are of special importance for the carcinogenic potency of these types of substance. Parameters measured included number of fibres, diameter and length distribution of fibres retained in lung ash and leaching of various elements from fibres. The results of the half-time of fibre clearance of the fibre fraction longer than 5 mym has been most important. For a special type of glass microfibre and for ceramic wool, which both had a low alkaline earth content, the half-times of lung clearance were at a level similar to that of crocidolite. For another type of glass microfibre with a high alkaline earth content and a median diameter of about 0.1 mym. a very low half-time was detected. The glass and rock wools studied, which were thicker than the other fibres, had a medium half-time. The acid pretreatment of fibrous material showed that chemical leaching of some alkaline earth and alkali cations increases the in vivo solubility