Now travelling by Metro, which was once considered the safest to travel, is no longer to be so considered, says a study. According to a study in the US, travelling in underground metro trains may expose commuters to higher concentration of cancer-causing agents. Polluted air was responsible for about 6.5 million deaths worldwide in 2015. Particulate matter is considered to be one of the most toxic forms of air pollution, researchers said. Two major compounds found in airborne particulate are polycyclic aromatic hydrocarbons (PAHs) and hexavalent chromium. Both types of compounds include carcinogens as well as chronic non-cancer health risks, such as cardiovascular and respiratory distress. The researchers from the University of Southern California (USC) in the US found that the maximum Excess Lifetime Cancer Risk for the Red Line was 10 times higher than the acceptable threshold of one-in-a-million, set by government and health organisations like the World Health Organisation (WHO) and the US Environmental Protection Agency (EPA).
This was the result of high levels of airborne hexavalent chromium measured within the train cars, likely due to a buildup of dust resulting from friction on the steel tracks, as well as the lack of ventilation on the underground line.
The study was published in the journal Aerosol and Air Quality Research, the reasearchers collected air samples using battery-operated devices with particle sensors. On raods, measurements were taken inside a zero-emissions test vehicle, whereas for railways, measurements were taken both on train platforms and inside cars, with the assumption that commuters spend about 25 percent of their time on the plaform and 75 percent on the train.
Samples were collected on either Teflon or quartz microfiber filters and analysed to determine concentrations of polycyclic aromatic hydrocarbons and transition metals.By using cancer potency factors obtained from the EPA and California’s Office of Environmental Health Hazard Assessment (OEHHA), cancer and non-cancerous health risks were calculated on the basis of the lifetime exposure commuting one hour a day, five days a week, for 50 weeks a year, and assuming 30 years of employement.