Commuting in Los Angeles: lung cancer health risks of roadway, light-rail and subway transit routes

Abstract

Los Angeles workers are exposed to significant amounts of airborne particulate matter (PM) during their daily commutes, which often exceed 30-60 minutes each way. Carcinogenic components of PM associated with transit along these commuter routes, including Benzo[a]pyrene (BaP) and hexavalent chromium (Cr6+), substantially increase respiratory health risks, including the risk of developing lung cancer. PM samples were collected and quantitatively speciated along five of LA9s major commuter routes, including the METRO red line (underground subway) and gold line (above-ground light rail), the I-110 and I-710 freeways, and high-density surface streets (Sunset and Wilshire Boulevards). Using measured concentrations of transition metals and Polycyclic Aromatic Hydrocarbons (PAHs), along with cancer potency (CP) and Reference Dosage (RfD) factors published by the United States EPA and California9s Office of Environmental Health Hazard Assessment (OEHHA), cancer and non-cancer health risks were calculated. In contrast to previous research indicating that PAHs found in Los Angeles roadway PM (e.g. along the I-710 freeway) led to the greatest cancer risk, the current analysis reveals that exposure to carcinogenic transition metals, particularly hexavalent chromium, which are especially prevalent along the METRO red subway line, results in the greatest lung cancer and non-cancer respiratory health risks. We conclude that the best option for commuters is to use above-ground light-rail transportation, i.e. the METRO gold line in Los Angeles, as its greater ventilation allows for reduced exposure to traffic-generated PAHs as well as carcinogenic transition metals associated with railway exposures.