Health risk assessment of BTEX exposure at roadside and on-road traveling route in Bangkok Metropolitan Region

Exposure to high levels of benzene, toluene, ethylbenzene, and xylenes (BTEX) poses health risks in high-traffic urban areas. BTEX exposure at two microenvironments, the roadside and along the traveling routes, within urban and suburban areas of the Bangkok Metropolitan Region was examined to assess cancer and noncancer risks. The lifetime cancer risk (LCR) for benzene and noncancer hazard index (HI) for all BTEX compounds were evaluated for adult male and female groups (drivers, passengers, and street vendors) in two scenarios: average case and worst case. With the assumption of negligible exposure outside the two considered microenvironments, the pickup drivers had the highest LCR and HI. Higher exposure risks were found in urban areas than in the suburbs and among men than females. Higher toluene levels were found at all monitoring sites in two microenvironments, but benzene was the most important in causing noncancer risk. The HI for all target groups ranged from 8.5E-03 to 4.0E-01, indicating a low noncancer risk from BTEX exposure (HI < 1). The LCR caused by benzene exposure ranged from 1.7E-06 to 7.2E-05, which is higher than the United States EPA most health-protective limit (1E-06). Further research should include other microenvironments by assessing the 24-hour exposure of all considered groups.