Dose-response associations of silica with nonmalignant respiratory disease and lung cancer mortality in the diatomaceous earth industry.
Checkoway-H; Heyer-NJ; Seixas-NS; Welp-EA; Demers-PA; Hughes-JM; Weill-H
Am J Epidemiol 1997 Apr; 145(8):680-688
A study of mortality of workers in the diatomaceous-earth (DE) industry was conducted to examine possible associations between crystalline silica (14808607) exposure and lung cancer and nonmalignant respiratory disease (NMRD) risk among DE industry workers. The cohort consisted of 2,342 males employed for at least 1 year at a DE mining and processing facility at Lompoc, California between January 1, 1942 and December 31, 1987. They were exposed to silica, primarily cristobalite (14464461). The subjects were followed to the end of 1994 at which time their vital status was determined. Standardized mortality ratios (SMRs) were computed for the decedents using mortality rates for US white males as the reference population. Associations between NMRD and lung cancer mortality and cumulative silica dust exposures estimated from industrial hygiene monitoring data and detailed job histories of the decedents were examined. Possible confounding by asbestos (1332214) exposure and smoking was evaluated by utilizing historical exposure monitoring data for jobs in which asbestos was handled directly and by company data on employee smoking habits. A total of 749 deaths occurred in the cohort during the study period. Deaths from all causes were close to the number expected, SMR 1.02. Mortality from lung cancer and NMRD was significantly increased, SMRs 1.29 and 2.01, respectively. NMRD mortality increased sharply with increasing silica dust exposure. The most pronounced trend was seen when the highest exposure level, 50mg/m3-years (mg-yr/m3), lagged for 15yr was compared with the lowest exposure level, 0.5mg-yr/m3, risk ratio (RR) 5.35. The same comparison showed a significant, but weaker trend for lung cancer, RR 2.15. Adjusting for cumulative asbestos exposure did not alter the dose response relationship for NMRD. Adjusting for smoking reduced the maximum RRs for NMRD and lung cancer to 4.15 and 1.67, respectively. The authors conclude that a strong dose response relationship with silica dust has been found for NMRD in this population of DE industry workers. A weaker dose response trend for lung cancer has been detected. These associations are unlikely to reflect the effects of asbestos exposure or smoking and add further support to the view that silica dust is involved in the etiology of lung cancer.
Pulmonary-system-disorders; Silica-dusts; Occupational-exposure; Lung-cancer; Epidemiology; Mortality-data; Dose-response; Organic-dusts; Cigarette-smoking;
Author Keywords: lung neoplasms; occupational exposure; respiratory tract diseases; silicon dioxide
Dr. Harvey Checkoway, Department of Environmental Health, University of Washington, Box 357234, Seattle, WA 98195-7234
14808-60-7; 14464-46-1; 1332-21-4
American Journal of Epidemiology
University of Washington, Seattle, Washington