Risk of low red or white blood cell count related to estimated benzene exposure in a rubberworker cohort (1940-1975)

This study evaluated the relationship between benzene exposure and low white blood cell (WBC) and red blood cell (RBC) counts. Hematologic screening data collected over a 35 year period at a rubber hydrochloride manufacturing plant were analyzed; an increased risk of leukemia had been demonstrated previously among workers at the plant [Infante et al. (1977).' Lancet 2:76-78; Rinsky et al. (1981): Am J Ind Med 2:217-45 (1987): NEJM 316:1044-1050/. Hematologic screening data were available for 657 of 1,037 (63.3%) individuals employed at the plant from 1939 through 1976. There was a total of 21. 710 blood test records (range per individual 1-354). The study utilized a case-control design and estimated benzene exposures using the job exposure matrix developed by Rinsky et al. (1987): NEJM 316:1044-1050]. The effects of benzene exposure in the 30, 90, and 180 days before the blood test date, as well as cumulative exposure up until the blood test date, were examined using conditional logistic regression. For WBCs there was a strong exposure response and all of the exposure metrics selected showed a significant relationship with low blood count. For RBCs there was a weak positive exposure-response, which was significant (p = 0.03) for one of the dose metrics. The finding of an exposure-response relationship in the range of exposures represented in this study, where the maximum daily benzene exposure estimate was 34 ppm, is consistent with findings of several animal studies demonstrating a decrease in peripheral lymphocyte counts at benzene exposures as low as 10 ppm, and a stronger effect of benzene exposure on lymphocytes (as reflected in total WBC count) than on red cells. There was no evidence for a threshold for the hematologic effects of benzene exposure, suggesting that even exposure to relatively low levels of benzene (e.g., <5 ppm) may result in hematologic suppression.