Clearance of man made mineral fibres from the lungs of sheep.

OBJECTIVES To compare the clearance rate, the related pathology, and the chemical and morphological changes of three man made mineral fibres (MMMFs) in the sheep model of pneumoconiosis. METHODS Fibrous particles were extracted from lung parenchyma and analysed by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). RESULTS The concentration of MMMF11, MMMF21, refractory ceramic fibre (RCF-1), and crocidolite asbestos fibres decreased with time according to a slow and a fast kinetic component. There was a statistical difference in the four regression lines as a function of time and the type of fibres (p < 0.001). The diameter of MMMFs decreased during the course of the time, whereas the crocidolite fibres did not seem to show any change. There was a statistical difference in the four regression lines as a function of time (p = 0.037) and type of fibres (p < 0.001). Ferruginous bodies were counted in the 40 sheep for which the latency period was 2 years. No typical ferruginous bodies were found in the groups exposed to MMMFs. The geometric mean concentration of asbestos bodies in the group exposed to crocidolite was 2421 bodies/g lung tissue (95% CI 385 to 15260). CONCLUSIONS The number of initially retained fibres decreased with time according to a slow and a fast kinetic component. MMMF11 and MMMF21 have similar clearance, faster than RCF-1 and crocidolite. The geometric mean diameter and length of MMMF decreased with time, but crocidolite did not. After 2 years in the sheep tracheal lobe, ferruginous bodies were not found in all three MMMF groups but were substantial in the crocidolite group. Clearance is thought to proceed through dissolution and macrophage translocation.