Subchronic studies on man-made vitreous fibres. Kinetics of inhaled particles

After subchronic exposure of rats to different fibre types [calcium magnesium silicate fibre, calcium magnesium zirconia silicate fibre, refractory ceramic fibre (RCF), non-fibrous material of that RCF and long amosite] lung fibre burden accumulation was proportional to biopersistence. The lung burden of non-fibrous particulate was so pronounced (>2µl/lung) that macrophage clearance collapsed and considerable inflammation occured. The effects of the three vitreous fibres also correlated with effects on clearance. A fibre (RCF) with the same composition as the particles accumulated to a similar mass/volume level but had less effect. Amosite fibres accumulated more than the other test materials investigated, mostly in the interstitial tissue, but produced only a small effect on clearance of labelled particles, however, amosite had the highest effect on cell proliferation. The toxicity results of this study are presented in an accompanying paper.