Assessment of butadiene exposure in synthetic rubber manufacturing workersin Texas using frequencies of hprt mutant lymphocytes as a biomarker

1,3-Butadiene (BD), which is used to manufacture synthetic rubber, is a mut agen and carcinogen. Because past occupational exposures have been associat ed with an increased risk of leukemia, there has been a dramatic reduction in workplace exposure standards. The health benefits of these reduced level s of occupational exposure to BD will be difficult to evaluate using relati vely insensitive traditional epidemiological studies; however, biomarkers c an be used to determine whether there are genotoxic effects associated with recent exposures to BD. In past studies of BD-exposed workers in Southeast Texas, we observed an increase in the frequency of lymphocytes with mutati ons in a reporter gene, hprt. Frequencies of hprt mutant cells correlated w ith air levels of BD and with the concentration of a BD metabolite in urine . Average exposures to 1-3 parts per million (p.p.m.) of BD were associated with a threefold increase in hprt variant (mutant) frequencies (Vfs). We n ow report results from a follow-up study of workers in a synthetic rubber p lant in Southeast Texas. Thirty-seven workers were evaluated on three occas ions over a 2-week period for exposure to BD by the use of personal organic vapor monitors and by determining the concentration of a BD metabolite in urine. The frequency of hprt mutants was determined, by autoradiography, wi th lymphocyte samples collected 2 weeks after the final exposure measuremen t. Based on their work locations, the study participants were assigned to h igh-exposure (N = 22) or low-exposure (N = 15) groups. The BD exposure, +/- standard error. of the workers in the high-exposure group (1.65 +/- 0.52 p .p.m.) was significantly greater than the low-exposure group (0.07 +/- 0.03 p.p.m., P < 0.01). The frequency of hprt mutant lymphocytes was also signi ficantly different in the two groups (high. 10.67 +/- 1.5 x 10(-6); low, 3. 54 +/- 0.6 x 10(-6); P < 0.001). The concentration of the urine metabolite was greater in the high-exposure group, but the difference was not signific ant. The correlation coefficient between hprt Vf and BD exposure levels was r = 0.44 (CI95, 0.11-0.69; P = 0.011). This study reproduced the findings from a previous study at this plant. Although studies of butadiene-exposed workers in other countries have not detected an effect of exposure on frequ encies of hprt mutant lymphocytes, we have repeatedly observed this result in our studies in Texas. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.