A thesis proposal submitted in partial fulfillment of the requirements for the degree of Doctor of Technical science in Environmental Toxicology, Technology and Management Inter-University Program

Thesis (Ph.D.) - Asian Institute of Technology - Chulabhorn Research Institute - Mahidol University, 2010

The present study aimed to evaluate the effects of styrene exposure at levels below the recommended standards of the Threshold Limit Value (TLV-TWA8) of 20 ppm (ACGIH, 2004) in reinforced fiberglass plastics workers. Study subjects comprised 50 exposed workers and 40 control subjects. The exposed workers were stratified by styrene exposure levels, i.e. group I (<10 ppm), group II (10- 20 ppm), and group III (> 20 ppm). The mean styrene exposure levels of exposed workers were significantly higher than those of the control workers. Respiratory particles increased significantly in factory workers (1.05±0.17 mg/m3; p< 0.01) compared to control (0.36±0.93 mg/m3). Factory workers stratified by job activity showed that there was a significant difference of exposure levels among study groups (p<0.01). Respiratory particle level in trimming workers (1.79±0.31mg/m3) was significantly higher than resin laminator workers (0.54±0.05 mg/m3). Biomarkers of exposure to styrene, including blood styrene and the urinary metabolites, mandelic acid (MA) and phenylglyoxylic acid (PGA), were significantly increased with increasing levels of styrene exposure, but were not detected in the control group. DNA damage, such as DNA strand breaks, 8-hydroxydeoxyguanosine (8-OHdG), and DNA repair capacity, were used as biomarkers of early biological effects. DNA strand breaks and 8-OHdG/105 dG levels in peripheral leukocytes of exposed groups were significantly higher compared to the control group (P<0.05). In addition, DNA repair capacity, determined by the cytogenetic challenge assay, was lower in all exposed groups when compared to the control group (P<0.05). The expression of CYP2E1, which is involved in styrene metabolism, in all styrene exposed groups, was higher than that of the control group at a statistically significant level (P<0.05). Levels of expression of the DNA repair genes hOGG1 and XRCC1 were significantly higher in all exposed groups than in the control group (P <0.05). In addition to styrene contamination in ambient air, a trace amount of benzene was also found, but the correlation between benzene exposure and DNA damage or DNA repair capacity was not statistically significant. The results obtained from this study indicate an increase in genotoxic effects and thus health risk from occupational styrene exposure, even at levels below the recommended TLV-TWA8 of 20 ppm.