The relationship between exposure to benzene (71432) and low red and white blood cell counts was studied over a 35 year period in workers at a rubber film (rubber-hydrochloride) factory. Hematologic data for 657 of the 1,037 people employed at the factory during the period studied were available in the form of 21,710 records of blood tests, ranging from one to 354 per individual. Nineteen of the 657 workers were female. A case/control design was used and benzene exposure was estimated by a previously developed job exposure matrix. The first occurrences of low red or white cell counts were defined as incident cases and controls were selected from individuals tested within 6 months, before or after, the case's blood test. Conditional logistic regression was used to evaluate the effects of exposure to benzene 30, 90 and 180 days prior to the blood tests and of cumulative exposure up to the test date. Estimation of exposure in the 180 day interval was considered crucial because the lifespan of red blood cells and most white cells is less than 180 days. Benzene exposure was significantly correlated with low white cell counts according to all the measures employed. Red cell counts were weakly responsive to benzene exposure and the relationship was significant for one dose metric. The estimated maximum daily exposure to benzene was 34 parts per million (ppm). The study produced no evidence of a threshold for the hematologic response to benzene. The authors suggest that exposure to benzene, even at levels below 5ppm, might cause hematologic suppression. The relationship between exposure to benzene and the risk of low cell counts is stronger for white blood cells than for red blood cells.
Elizabeth M. Ward, National Institute for Occupational Safety and Health, Division of Surveillance, Hazard Evaluations and Field Studies, lndustrywide Studies Branch, 4676 Columbia Parkway, R-16, Cincinnati, OH 45226
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