DOSE-RESPONSE ASSOCIATIONS OF SILICA WITH NONMALIGNANT RESPIRATORY-DISEASE AND LUNG-CANCER MORTALITY IN THE DIATOMACEOUS-EARTH INDUSTRY

The potential carcinogenicity of crystalline silica to humans remains a controversial issue, The authors conducted an historical cohort mort ality study of 2,342 male workers exposed to crystalline silica, predo minantly cristobalite, in a diatomaceous earth mining and processing f acility in California. During the years 1942-1994, mortality excesses were detected for nonmalignant respiratory diseases (NMRD) (standardiz ed mortality ratio = 2.01, 95% confidence interval (Cl) 1.56-2.55) and lung cancer (standardized mortality ratio = 1.29, 95% Cl 1.01-1.61), NMRD mortality rose sharply with cumulative exposure to respirable cry stalline silica; allowing for a 15-year latency, the rate ratio for th e highest exposure stratum (greater than or equal to 5.0 mg/m(3)-years ) was 5.35 (95% Cl 2.23-12.8), The rate ratio for lung cancer reached 2.15 (95% Cl 1.08-4.28) in the highest exposure category. These associ ations were unlikely to have been confounded by smoking or asbestos ex posure. ?he findings indicate a strong dose-response relation for crys talline silica and NMRD mortality. The lung cancer results, although l ess convincing, add further support to an etiologic role for crystalli ne silica.