Subchronic studies on man-made vitreous fibres. Toxicity results

Two 'alkaline earth silicate' wools - a calcium magnesium silicate and a calcium magnesium zirconium silicate - were examinated in a subchronic '90-day' rat inhalation assay. A preparation of a high-purity refractory ceramic fibre (RCF), a non-fibrous particulate (NFP) with the same, aluminosilicate chemical composition and a sample of long-fibred amosite were also examined. The assay was similar to that proposed by the European Union but was undertaken before that protocol was finalized. Exposure was to a single fibre concentration only (150 fibres >20µm long/ml); NFP was used at an equal mass aerosol concentration to that of the RCF. The rats were followed for 1 yr after exposure. Neither of the alkaline earth silicates accumulated in the lung to a sufficient level to cause any significant effect. The non-fibrous particulate produced more inflammation than any of the fibres. All inflammatory effects were proportional to the inhibition of macrophage-mediated particle clearance. As the amosite fibres are thin, this material accumulated to lower mass burden than the man-made fibres. Compared with the man-made fibres, amosite caused less inflammation but more cell proliferation