A study of mortality of vermiculite (1318009) miners and millers exposed to tremolite (14567738)/actinolite (1332214) was conducted. The study group consisted of 575 males hired before 1970 and employed for at least 1 year at a vermiculite mine (SIC-1499) near Libby, Montana. Vital status of 569 subjects as of December 31, 1981, was determined. Death certificates for all deceased workers were reviewed. Individual cumulative fiber exposure estimates in fiber per years (f/yr) were calculated from job exposure estimates and work histories. Standard mortality ratios (SMRs) were computed. The data were analyzed according to various statistical models. SMRS for lung cancer and nonmalignant respiratory disease, 223 and 243, respectively, were increased significantly over expected values. The average latency was 21.8 years for lung cancer and 23.1 years for nonmalignant respiratory disease. In terms of exposure, the SMRs for all causes, all malignant neoplasms, lung cancer, and nonmalignant respiratory disease were 157, 268, 576, and 401, respectively, for workers with 399f/yr exposure. In the 50 to 99 and 100 to 399f/yr groups, mortality was not significantly increased for any selected cause of death, but tended to be elevated for lung cancer, digestive cancer, and nonmalignant respiratory disease. In the less than 50f/yr group, mortality was significantly increased for nonmalignant respiratory disease, nonsignificantly increased for lung cancer, and decreased for digestive cancer, ischemic heart disease, and diseases of the circulatory system. The authors conclude that based on a linear model, the estimated percentage increase in lung cancer mortality risk is 0.6 percent for each f/yr of exposure for a 20 year exposure. For 5f/yr exposure, it is 2.9 percent for a nonthreshold linear model and 0.6 percent for a survival model.
H.E. Amandus, PhD, Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, 944 Chestnutt Ridge Road, Morgantown, WV 26505