Benzene exposure and risk of benzene poisoning in Chinese workers

Benzene is a known hematoxin and leukemogen that can cause benzene poisoning (BP), that is, a persistent reduction in white cell counts that is strongly associated with increased risk of lymphohematopoietic malignancies. Data are needed on the exposure–response, particularly at low doses and susceptible populations for clinical and regulatory purposes. In a case-cohort study among 110,631 Chinese workers first employed 1949–1987 and followed up during 1972–1999, BP risk was evaluated according to benzene exposure level and risk modification was examined by subject (sex, attained age) and exposure-related factors (latency, exposure windows, age at first benzene exposure, coexposure to toluene) using excess relative risk and excess absolute risk models. There were 538 BP cases and 909 benzene-exposed referents. The exposure metric with best model fit was cumulative benzene exposure during a five-year risk window, followed by a nine-month lag period before BP diagnosis. Estimated excess absolute risk of BP at age 60 increased from 0.5% for subjects in the lowest benzene exposure category (>0 to 10 ppm-years) to 5% for those in the highest category (>100 ppm-years) compared with unexposed subjects. Increased risks were observed at low cumulative exposure levels and for workers who were first exposed at <30 years of age. These results showed a clear association between benzene exposure and BP, beginning at low cumulative benzene exposure levels with no threshold, and with higher risks for workers exposed at younger ages. These findings are important since BP has been linked to a strongly increased development of lymphohematopoietic malignancies.