Exposure to benzene and risk of leukemia among shoe factory workers

The study attempted to add years of follow-up to an earlier study describing excess leukemia among workers exposed to benzene-based glues in a shoe-factory and to conduct a quantitative exposure assessment of the exposure to benzene and the risk of leukemia.

The cohort comprised 1687 persons with complete work histories, at work on 1 January 1950, and followed through 31 December 1999. For each subject, time-specific cumulative exposure (ppm-years) was calculated as the sum of the products of job-specific concentrations of benzene (ppm) and the duration (years) for each job. Standardized mortality ratios (SMR) were estimated using national and regional rates specific for gender, age, and period.

The cumulative exposure ranged from 0 to >500 ppm-years. The SMR values for all hematolymphopoietic malignancies and leukemia for the men and women combined were elevated in all but the lowest exposure category. Leukemia risk was significantly elevated in the highest exposure category and the most evident among the men. The SMR values for the men were 1.4 [95% confidence interval (95% CI) 0.2-5.0], 3.7 (95% CI 0.1-20.6), 3.0 (95% CI 0.4-10.9), and 7.0 (95% CI 1.9-18.0) for benzene, the cumulative exposure equaling <40, 40-99, 100-199, and >200 ppm-years, respectively.

The results indicate that leukemia mortality is associated with exposure to benzene in this factory and that the risk increases with increasing cumulative exposure. The relevance of these findings for estimating risk at much lower levels is limited because of the small study size.