Abstract
Examinations of workmen employed in Wyoming bentonite processing plants revealed a high incidence of what appeared to be silicosis. In one subject, silicosis was proved by mineral analysis and microscopic examination of lung tissue obtained by biopsy. Dust analyses made in bentonite milling plants revealed dangerous concentrations of silica that at various times between 1950 and the present ranged from two to ten times the safe maximal concentration according to the formula of the U.S. Bureau of Mines. Silicotuberculosis developed in 4 patients, and a totally disabling or fatal disease occurred in at least 4 workers after periods of exposure of from 6 to 14 years. Bentonite dust, once believed to be harmless, must now be added to the list of potentially hazardous dusts because of its content of free crystalline silica.
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