title: Extended follow-up of lung cancer and non-malignant respiratory disease mortality among California diatomaceous earth workers.
abstract: OBJECTIVE
  Millions of workers worldwide are employed in occupations involving potentiality hazardous exposure to crystalline silica. The diatomaceous earth industry can have particularly high exposures, but there is a lower likelihood of simultaneously occurring confounding exposures. We extended follow-up for diatomaceous earth industry workers previously studied for mortality.
  
  
  METHODS
  The cohort included 2342 white men who were employed for at least 1 year at a diatomaceous earth plant in Lompoc, California beginning in 1942. Workers' vital status was updated using the National Death Index through 2011, an extension of 19 years from earlier studies. Detailed work history and quantitative air monitoring measurements estimated exposure intensity. Cox proportional hazards modelling estimated HRs and 95% CIs. SMRs were calculated.
  
  
  RESULTS
  Elevated mortality was observed by quartile of cumulative crystalline silica exposure for lung cancer (HR=2.03, 95% CI 1.07 to 3.85, highest quartile, unlagged) and non-malignant respiratory disease (NMRD) (HR=3.59, 95% CI 1.94 to 6.67, highest quartile, unlagged), although trends were not statistically significant. Associations were attenuated when adjusted for smoking and asbestos exposure. Mortality from NMRD was significantly increased over the entire follow-up compared to the general population (SMR=1.37, 95% CI 1.17 to 1.60). An increase for lung cancer was confined to the earlier follow-up (SMR=1.29, 95% CI 1.01 to 1.61).
  
  
  CONCLUSIONS
  The risk of lung cancer and NMRD mortality remained elevated, although generally non-significant, and exposure-response trends with cumulative crystalline silica persisted on extended follow-up of this cohort. The findings support a generally consistently observed aetiological relation between crystalline silica and lung cancer.
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington, USA.
authors.forename: Lisa G
authors.initials: LG
authors.lastname: Gallagher
authors.affiliation: US Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Cincinnati, Ohio, USA.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Park
authors.affiliation: Department of Family & Preventive Medicine, University of California San Diego, San Diego, California, USA.
authors.forename: Harvey
authors.initials: H
authors.lastname: Checkoway
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002140:California / Q000453:epidemiology; D002423:Cause of Death; D007692:Diatomaceous Earth / Q000009:adverse effects*; D005500:Follow-Up Studies; D006801:Humans; D007221:Industry; D008175:Lung Neoplasms / Q000209:etiology* / Q000401:mortality; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000209:etiology* / Q000401:mortality; D016273:Occupational Exposure / Q000009:adverse effects*; D016016:Proportional Hazards Models; D012120:Respiration Disorders / Q000209:etiology* / Q000401:mortality; D012140:Respiratory Tract Diseases / Q000209:etiology / Q000401:mortality; D018570:Risk Assessment; D014937:Work; D055815:Young Adult
chemical_list: D007692:Diatomaceous Earth
keywords: cohort; lung cancer; mortality; silica