Clearance of man made mineral fibres from the lungs of sheep

Objectives-To compare the clearance rate, the related pathology, and the ch emical and morphological changes of three man made mineral fibres (MMMFs) i n the sheep model of pneumoconiosis. Methods-Fibrous particles were extracted from lung parenchyma and analysed by transmission electron microscopy (TEM) and energy dispersive spectroscop y (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 fo ur 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 statistica l difference in the four regression lines as a function of time (p=0.037) a nd type of fibres (p<0.001). Ferruginous bodies were counted in the 40 shee p for which the latency period was 2 years. No typical ferruginous bodies w ere found in the groups exposed to MMMFs. The geometric mean concentration of asbestos bodies in the group exposed to crocidolite was 2421 bodies/g lu ng tissue (95% CI 385 to 15260). Conclusions-The number of initially retained fibres decreased with time acc ording to a slow and a fast kinetic component. MMMF11 and MMMF21 have simil ar clearance, faster than RCF-1 and crocidolite. The geometric mean diamete r 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.