The commuters’ exposure to volatile chemicals and carcinogenic risk in Mexico City

The commuters’ exposure levels to volatile organic compounds were investigated in the following public transport modes: private car, microbus, bus, and metro along three commuting routes in the Metropolitan Area of Mexico City. The target chemicals were benzene, toluene, ethylbenzene, m/p-xylene, and formaldehyde. Integrated samples were taken while traveling during the morning rush hour (weekdays 7:00–9:00 a.m.) for six consecutive weeks in June and July, 2002. Scheffe test showed that the average concentrations of all chemicals inside cars and microbuses were statistically higher than in metro trains (P<0.05). For non-formaldehyde chemicals, the average levels inside automobiles were significantly higher than in metro trains and buses (P<0.05). The exposure level of formaldehyde in the microbus was much higher than those in the car, bus, and metro (P<0.05). On the other hand, there were no differences in the exposure levels among transport routes. These findings suggest that for commuting trips of comparable durations, car and microbus passengers are exposed to higher levels of volatile organic compounds than bus and metro commuters. These findings are consistent with previous studies looking at exposure of commuters to carbon monoxide. The lifetime carcinogenic risk from commuting by car was 2.0×10−5–3.1×10−5, that by microbus was 3.1×10−5–4.0×10−5, that by bus was 2.0×10−5–2.7×10−5, and that by metro was 1.3×10−5–1.7×10−5 in Mexico City.