Automobile emissions benzene exposure

Hexane may be expected to comprise around 2% of the VOCs in urban air polluted with hydrocarbons from automobile emissions or other combustion byproducts (Barrefors and Petersson 1993). The -hexane concentrations in urban air will typically be approximately 60% of the concentrations of benzene (Daisey et al. 1994). Close proximity to the exhaust systems of cars or other gasoline-powered vehicles can lead to exposures to increased concentrations of -hexane. Under rush-hour conditions, the concentrations in the interior air of buses will tend to be lower (55 g/m3 or 19.8 ppbv) than the interior levels in cars (69 g/m3 or 24.9 ppbv) or the air around persons riding motorcycles (106 g/m3 or... 

Workplace exposure limits for benzene have been regulated to levels as low as 0.5 ppm (43). Industrial emissions affecting the pubHc ate now low enough that the EPA considers that a greater hazard exists from mosdy indoor sources such as smoking, automobile exhausts, and consumer products (44). 

Although several figures in Table IV are significant, the estimates are probably accurate to the first digit at best. However, they do suggest that widespread but low-level exposures from automobiles and service stations provide the majority of benzene molecules that enter human bodies. Whether these are the most biologically significant emissions depends on the behavior of dose-response relationships at low dose levels. 

All outdoor sources, including automobile exhaust and stationary source emissions, account for only about 20% of the total population exposure to benzene (Wallace 1989b). The main outdoor source is likely to be automobile exhaust (Wallace 1995). Average air intake of benzene for urban/suburban residents (assuming atypical concentration range of 2.8-20 ppb and an intake of 20 m3 air/day) is 180-1,300 pg/day. 

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