Silicosis among gold miners: exposure - response analyses and risk assessment.
Am J Publ Health 1995 Oct; 85(10):1372-1377
A study of the risk of silicosis in gold miners exposed to silica (14808607) was conducted. The cohort consisted of 3,300 white males who worked for at least 1 year in a South Dakota gold mine between 1940 and 1965. The cohort was followed until 1990. Silicosis cases that developed were identified through reviews of death certificates or analysis of chest X-rays obtained during two cross sectional surveys conducted in 1960 and 1976. Data on respirable silica exposures was obtained from two surveys conducted in the mine in the 1970s. The data were used in conjunction with a job exposure matrix to estimate cumulative dust exposures of the workers. Associations between cumulative dust exposures and the risk of silicosis were assessed by case/control and survival analysis techniques. A total of 170 cases of silicosis occurred in the cohort. For the entire cohort, the median silica dust exposure was 0.15mg/m3 for workers hired before 1930, 0.07mg/m3 for those hired between 1930 and 1950, and 0.02mg/m3 for those hired after 1950. The number of silicosis cases generally increased with increasing cumulative silica dust exposure. Five cases occurred among those with the lowest cumulative exposure, 0 to 0.2mg/m3 years (mg/m3yr). Twenty cases occurred in those with the highest cumulative exposure of over 4.0mg/m3yr. By exposure category, the largest number of cases, 44, occurred in those with cumulative exposures of 2.0 to 3.0mg/m3yr. The rates of silicosis after adjusting for age and calendar time varied from 9.6x10(5) for those in the 0 to 0.2mg/m3yr exposure group to 2082.2x10(5) for those in the over 4.0mg/m3yr exposure group. The silicosis cases with the lowest cumulative exposures were exposed in the most recent years and, thus, had short durations of exposure. This suggested that some workers could get silicosis after only brief exposures to silica dust. The cumulative risk, adjusted for age and calendar time, varied from 0.002 to workers in 0 to 0.2mg/m3yr exposure group to 0.678 for those in the 4.0mg/m3yr group. The silicosis risk for lifetime exposure (45 years) to silica dust at the OSHA standard of 0.09mg/m3 was estimated to be 35 to 47%. The authors conclude that if their data and analyses are correct, the OSHA standard for silica dust is unacceptably high.
NIOSH-Author; Respiratory-system-disorders; Silica-dusts; Occupational-exposure; Underground-miners; Epidemiology; Risk-analysis; Industrial-hygiene; Dose-response; Case-studies; Job-analysis;
Kyle Steenland, PhD, National Institute for Occupational Safety and Health, 4676 Columbia Pkwy, MS R13, Cincinnati, OH 45226
American Journal of Public Health