A retrospective cohort mortality study of males mining and milling attapulgite clay

To evaluate the possible health effects of occupational exposure to a nonasbestos mineral fiber, a cohort of 2,302 males employed for at least 1 month between 1940 and 1975 at an attapulgite (clay fiber) mining and milling facility was followed through 1975. A significant deficit of mortality (SMR = 43, 90% CI 23–76) from nonmalignant respiratory disease (NMRD) was observed for the cohort based on age‐, calendar year‐, and race‐specific rates for U.S. males. A marked deficit of NMRD was seen regardless of presumed dust exposure level, induction‐latency period, or duration employed. A statistically significant excess of mortality from lung cancer was observed among whites (SMR = 193, 90% CI 121–293), but a deficit occurred among nonwhites (SMR = 53, 90% CI 21–112). Lung cancer risk in either race was not altered substantially with presumed dust exposure level, induction‐latency period, or duration employed with one exception—those employed for at least 5 years in high‐exposure‐level jobs.