Cohort mortality study of North American industrial sand workers. II. Case-referent analysis of lung cancer and silicosis deaths

Background: A cohort mortality study of 2670 men in nine North American ind ustrial sand plants resulted in 83 deaths from lung cancer 20 or more years after hire (standardized mortality ratio 139) and 37 deaths from silicosis (including seven from silico-tuberculosis). The lung cancer excess was unr elated to duration of employment and not found in all plants. Objectives: The primary aim was to determine whether lung cancer risk among these employees was related to quantitative estimates of crystalline silic a exposure, after allowance for cigarette smoking. A secondary aim was to d o the same for silicosis mortality, partly as a means of validating the est imated levels of exposure. Methods: A nested case-referent study was undertaken with cases matched wit h up to two controls on plant, age and date of first employment from men wh o survived the case. Exposures were estimated by linking work histories to a job-exposure matrix, undertaken separately. Cigarette smoking information was obtained from medical records and other sources, blind as to case-cont rol status. Matched statistical analyses were conducted using conditional l ogistic regression. Findings: Odds ratios for silicosis mortality were significantly related to cumulative silica exposures and tended to a relationship with category of average crystalline silica concentration, but inconsistently with length of employment. After accounting for a strong effect of cigarette smoking, odd s ratios for lung cancer were related to cumulative crystalline silica expo sure and to average silica concentration, but not to length of employment. Conclusion: These findings support a causal relationship between lung cance r and quartz exposure after allowance for cigarette smoking, in the absence of cristobalite or other known occupational carcinogens. (C) 2001 British Occupational Hygiene Society. Published by Elsevier Science Ltd. All rights reserved.