Radiologic abnormalities in South African mica millers: a survey of a mica milling plant in the Limpopo Province.

All 73 workers at a South African mica milling plant were surveyed for radiographic evidence of abnormalities related to dust exposures at work. Chest x-rays were taken and questionnaires administered to determine occupational and environmental exposure histories. Dust levels to which workers were exposed were measured. All but one of 12 airborne inhalable and respirable dust levels were below the occupational exposure limits (OEL-RLs) of 10 mg/m3 and 5 mg/m3 respectively. The mica concentrations were below the OEL-RL of 1 mg/m3 for respirable mica. Mean age and service duration of the workers were 45 and 14 years, respectively. 19 workers (27%) had changes referable to their exposures to asbestos, mica, silica, or combinations. Of these, four showed additional radiographic changes in keeping with tuberculous lung scarring. Six had evidence of lung changes consistent with past tuberculosis alone. Rates of radiologic abnormalities were higher in older workers and those with longer service. An association between mica and radiologic changes could not be convincingly shown because of the nature of the survey and the co-exposure to other mineral dusts. Nevertheless, six workers had radiologic changes consistent with pneumoconiosis attributable to mica or the combination of mica and silica.