Silicosis among gold miners: exposure--response analyses and risk assessment.
OBJECTIVE
This study sought to estimate the risk of silicosis by cumulative exposure-years in a cohort of miners exposed to silica, as well as the lifetime risk of silicosis under the current Occupational Safety and Health Administration (OSHA) standard (0.09 mg/m3).


METHODS
In a cohort study of 3330 gold miners who worked at least 1 year underground from 1940 to 1965 (average 9 years) and were exposed to a median silica level of 0.05 mg/m3 (0.15 mg/m3 for those hired before 1930), 170 cases of silicosis were determined from either death certificates or two cross-sectional radiographic surveys.


RESULTS
The risk of silicosis was less than 1% with a cumulative exposure under 0.5 mg/m3-years, increasing to 68% to 84% for the highest cumulative exposure category of more than 4 mg/m3-years. Cumulative exposure was the best predictor of disease, followed by duration of exposure and average exposure. After adjustment for competing risks of death, a 45-year exposure under the current OSHA standard would lead to a lifetime risk of silicosis of 35% to 47%.


CONCLUSIONS
Almost 2 million US workers are currently exposed to silica. Our results add to a small but increasing body of literature that suggests that the current OSHA silica exposure level is unacceptably high.
Steenland
K
K
National Institute for Occupational Safety and Health, Cincinnati, OH 45226, USA.
Brown
D
D
D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D006046:Gold; D006801:Humans; D008297:Male; D008452:Maximum Allowable Concentration; D008875:Middle Aged; D008906:Mining; D016273:Occupational Exposure; D011159:Population Surveillance; D011859:Radiography; D018570:Risk Assessment; D012307:Risk Factors; D012829:Silicosis / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D013023:South Dakota / Q000453:epidemiology; D014481:United States; D014489:United States Occupational Safety and Health Administration
D006046:Gold