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

In a two years' 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 this type of substances. Parameters measured include number of fibres, diameter and length distribution of fibres retained in lung ash and leaching of various elements from fibres. The persistence of MMMF in lungs covers a wide range. For a special type of glass microfibre and for ceramic wool, which both had a low alcali earth content, half-times of lung clearance were in a similar level as that of crocidolite. For another type of glass microfibre with a high alcaline earth content (CaO + MgO = 22%) a very high in vivo solubility was detected. The studied glass wool and rock wool, showed a medium solubility in the rat lung. By the means of analytical transmission electron microscopy (ATEM) and proton-induced x-ray emission (PIXE) the leaching of alcaline and alcaline earth cations could be established for some types of fibres. The acid pretreatment of fibrous material showed, that by chemical leaching of some alcaline earth and alcaline cations the in vivo solubility increases.