The Threshold Limit Value for Various Forms of Amorphous Silica.
NIOSH 1990 Nov:1134-1135
A brief review was presented of the chemical and physical structure of silica (7631869), crystalline silica, amorphous silica, fused silica, and elemental silicon (7440213). Precipitated silica and silica gel have been considered the prototypical nuisance dusts. Silica gel injected intratracheally in rats has not been demonstrated to cause fibrosis and neither have inhalation exposures. Macrophage accumulations and mild proliferation of reticulin fibers were observed. In a group of 165 workers exposed to precipitate silica estimated to be near or below 10mg/m3 for an average of 8.6 years, no serial changes in pulmonary function or chest radiographs were observed. Fumed silica and silica fume display entirely different toxicities. Fumed silica appeared to be only slightly more toxic than precipitated silica and silica gel. However, several studies have indicated that silica fume produced a unique complex of acute and chronic effects which were reversible after exposure ceased. Brief high exposures to silica fume produced symptoms of metal fume fever which have been observed to persist up to three months. Chronic exposure produced X-ray and pulmonary function evidence of silicosis. The threshold limit value (TLV) for fumed silica has been set at 10mg/m3. While no value has been established for silica fume, a TLV of 0.2mg/m3 was suggested. The author concludes that additional uses of fused quartz (14808607) in modern technology make it important to gather more solid toxicological data on this material as well.
Miners; Air-quality-monitoring; Airborne-dusts; Mineral-dusts; Dust-inhalation; Workplace-studies; Coal-dust; Silica-dusts;
7631-86-9; 7440-21-3; 14808-60-7;
Proceedings of the VIIth International Pneumoconioses Conference