Subway air quality comes under study

Columbia University, harvard study reveals high level of airborne metals

By Phillip L. Polakoff, M.D.

Columbia University researchers have found that steel dust generated in New York City's subway system significantly increases the total amount of airborne iron (Fe), manganese (Mn) and chromium (Cr) that people breathe.

The airborne levels of these metals associated with fine particulate matter in the subway environment were observed to be more than 100 times greater than the levels in home indoor or outdoor settings in New York City.

The research findings were scheduled to appear in the Jan. 15, 2004, issue of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.

The results are part of the TEACH (Toxic Exposure Assessment, a Columbia and Harvard) study to understand pathways and levels of personal exposures to potentially toxic air pollutants in inner city areas of New York City and Los Angeles.

This study raises interesting questions. What about pollutants in other inner city underground public transit and workplaces? What are people in Chicago, Boston, London and Paris - to name a few - breathing as they work and ride to and from work, school, shopping, medical and other office appointments?

A disclaimer was included in the report that should be noted here: There are no known health effects at the pollutant levels observed in the New York subway system. Nor was there any suggestion that people avoid riding the subway. Reducing subway ridership would just increase surface traffic emissions.

Dr. Sonja Sax, a co-author of the report from the Harvard School of Public Health, makes this comment:

"One way of putting into perspective the potential health risks of these levels of exposure is to consider published cancer risk guideline concentrations, which roughly estimate the risk of obtaining cancer from chronic exposure to single chemicals such as Cr (chromium).

"These estimates together with the data from the TEACH study suggest that the cancer risks associated with exposure to Cr 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 there is another side to this issue that also must be take into account. What about the health effects of long-term exposure to low levels of pollutants such as chromium and manganese, as well as from inhaling airborne transition metals?

There is increasing interest in finding answers to this and similar questions.

With large numbers of people who work and ride underground public transit, the researchers think subway exposures are worth further investigation.

Along these lines, the Columbia researchers are beginning a study to look at whether the elements in airborne steel dust are absorbed into the bodies of transit workers in New York City.

The TEACH study suggests that subway systems would be conducive to health studies as well as comparison studies with different subway systems in order to better understand how design characteristics can effect air pollutant exposure levels.

Dust produced in different subway systems could potentially have different levels and mixtures of elements. The steel used in New York, for example, was relatively devoid of nickel (Ni). But many types of steel contain nickel, as well as higher levels of chromium and manganese. Furthermore, some subway systems use rubber wheels.

These studies are a good start on investigating a potential public health risk that has gone on too long without expert attention.

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© 2004 Brotherhood of Locomotive Engineers and Trainmen