Mortality study of gold miners exposed to silica and nonasbestiform amphibole minerals: an update with 14 more years of follow-up.

We have updated a study of 3,328 gold miners who worked underground for at least 1 year between 1940-1965 in South Dakota, extending the follow-up from 1977 to 1990. The exposures of concern were silica and nonasbestiform amphibole minerals. The lung cancer standardized mortality ratio (SMR) was 1.13 (95% confidence interval [CI] 0.94-1.36, 115 observed) when the U.S. population was used as the referent group, increasing to 1.25 (95% CI 1.03-1.51) when the county was used as the referent, and to 1.27 (1.02-1.55) for person-time with more than 30 years potential latency. However, lung cancer mortality did not show a positive exposure-response trend with estimated cumulative dust exposure. Data on smoking habits suggested that the miners smoked slightly more than the U.S. population in a 1960 cross-sectional survey. In contrast to lung cancer, other diseases known to be associated with silica exposure (tuberculosis and silicosis) were significantly increased (SMR = 3.44 and 2.61) and exhibited clear exposure-response trends. Nonmalignant renal disease, also associated with silica exposure, was elevated for those hired in early years and showed a significant positive exposure-response trend. Multiple-cause analysis revealed significant excesses of arthritis, musculoskeletal diseases (including systemic lupus and sclerosis), and skin conditions (including scleroderma and lupus), diseases of autoimmune origin which have been associated with silica exposure in other studies. Multiple cause analysis also showed a significant excess of diseases of the blood and blood-forming organs.