A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering. Inter-University Program on Environmental Toxicology, Technology and Management, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 2001

Occupational exposure to benzene was interested for the study, because benzene has been classified as a human carcinogen. The objectives of this study were, 1) To determine the benzene level at the working area, 2) To measure the level of benzene exposure in workers (both environmental and biological monitoring), compared to controls, 3) To study the relationship between environmental benzene concentration and biomarkers of exposure to benzene in workers, and 4) To evaluate the effect of smoking on the risk of benzene exposure. Level of benzene in workplaces and individuals, and biomarkers determined as blood benzene concentration and urinary trans, trans-Muconic acid were carried out. The study was carried out in thirteen gasoline service stations, 45 gasoline service attendants and one aromatic chemical factory, 45 workers. Study in gasoline service stations, benzene levels in working area was the highest in the urban area gasoline service station (238.76 ppb) and lowest at the station located in outer area of Bangkok (1.74 ppb). The location and time of sampling, related to traffic volume, were the major effects on benzene concentration in the working area. All of gasoline service attendants in the study exposed to benzene higher than controls, which below the threshold limit value (TL V-8hTW A). Blood benzene concentrations in nonsmoking and smoking workers (median = 507.36 ppt and 968.49 ppt, respectively) was significantly higher (P<0.001) than those of corresponding controls. Smoking significantly (P<0.01) contributed to the blood benzene concentration. The level of ttMA, only nonsmoking workers that showed significantly (P<0.01) higher than in corresponding controls in the post shift and during work shift (8hours) samples (median = 125.15 ng/mL in post shift, and 103 .46 ng/mL in during work shift samples). In aromatic chemical factory, benzene levels in production process area was quite low (maximum 21.4 7 ppb) compared with gasoline service station. The level of individual exposure in plant workers was not much difference with controls. But, blood benzene concentration (421.77 ppt in nonsmokers, and 427.88 ppt in smokers) was significantly (P <0.001 in nonsmokers, and P<0.05 in smokers) higher than controls (213.00 ppt in nonsmokers, and 200.46 ppt in smokers). It indicated that the bioaccumulation might occur in plant workers. Smoking significantly (P<O.O 1) contributed to the level of ttMA (post shift, mg/g creatinine) in the plant workers. All plant workers excreted ttMA in the post shift samples below BEi. Study in laboratory units of aromatic chemical factory, benzene levels was higher than that of gasoline service station (maximum 276.96 ppb). All of laboratory workers were nonsmokers, exposed to benzene higher than controls. Only two workers exposed to benzene above TLV. Blood benzene concentrations in workers (median = 1599.48 ppt) was significantly higher (P<0.001) than the corresponding controls. The level of ttMA showed significantly (P<0.05) higher than in corresponding controls in the post shift and during work shift (8hours) samples (median= 108.92 ng/mL, 0.2 mg/g creatinine in post shift, and 0.127 mg/g creatinine in during shift samples). Two laboratory workers excreted ttMA above BEi. It can be observed that this occupation cause higher risk to exposure to benzene than general people. Smoking also affected on benzene exposure. For selected biomarkers of benzene exposure, blood benzene concentration was showed the higher correlation (r=0.600, P<0.01) with the level of individual benzene exposure than the levels of urinary trans, trans-Muconic acid.