Columbia University researchers have found that the New York City subway produces a large amount of steel dust, composed of iron, manganese and chromium, all of which is breathed in by subway riders in amounts 100 times greater than the levels in other nearby indoor and outdoor settings.
Geochemist Steven Chillrud says, "This study in no way suggests that people should avoid riding the subway. There are no known health effects at the levels that we observed in the NYC subway system. Furthermore, reducing subway ridership would just increase surface traffic emissions.
"?Interestingly, the particle counting data showed that particle numbers were 5 to 10 times lower in air conditioned subway cars as compared to underground subway stations. This suggests that the filtration systems of the car air conditioners are very effective at removing the steel dust from the passenger cars and that much of the increased exposure is probably occurring on the station platforms."
Researcher Patrick Kinney says, "It is important to stress that there are no known health effects at these levels. Even though the levels?observed in the subway system were more than 100 times greater than those observed in ambient and home indoor settings, the subway levels are more than 1000 times lower than the United States Occupational Safety and Health Administration's Permissible Exposure Limit guidelines for workers."
Researcher Sonja Sax says, "One way of putting into perspective the potential health risks of these levels of exposure is to consider published cancer risk guideline concentrations, which suggest that the cancer risks associated with exposure due to commuting by the subway would be much smaller than those that people get from exposure to a variety of volatile organic compounds in the home."
But Chillrud says, "With the large number of people who ride in underground subways, we do think subway exposures are worth investigating further." Are subways in other cities a problem as well? Dust produced by different subway systems may have different levels and mixtures of elements, depending on the type of steel used to build the tracks. Also, subway cars with rubber wheels produce less dust.
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