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Steel Dust Kicks Up Metal Levels in Subway

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WASHINGTON, Jan 07, 2004 (United Press International via COMTEX) -- New research suggests steel dust kicked up by the New York City subway appears to increase significantly the amount of iron, manganese and chromium riders inhale.

A team from Columbia University in New York City and Harvard University in Cambridge, Mass., found elevated levels of these elements among a group of study participants who commuted to school by subway. Study results showed these fine particulate metals were 100 times greater in the subway stations than on the streets of Manhattan or in the study participants' homes.

"The importance of our work is to show exposures in the subway that also include these elements that the research community has become interested in understanding," Steven Chillrud, lead study author and a geochemist with the Lamont-Doherty Observatory, a division of Columbia's Earth Institute, told United Press International.

The study involved 41 teens attending a public high school in Harlem. During the winter and summer of 1999, they wore battery-operated pumps on their backpacks that collected air samples as they rode the subway to and from school. Battery-operated pumps also were installed at each participant's home.

Air samples from all the various pumps were collected and compared. Researchers looked at the ratios of these elements in the samples and suspected the elevated levels of iron, manganese and chromium came from ground steel dust. This led scientists to suspect the subway.

During the winter, for example, when students had to commute to school by subway, these element levels were significantly higher than they were when students were on summer vacation. The subway hypothesis later was confirmed by measuring air samples from two subways stations over an eight-hour period.

Researchers found, however, that these element levels dropped inside an air-conditioned subway car. The particle count data showed these metals were 5 to 10 times lower in air-conditioned subway cars when compared to the particle counts taken from the subway station. Chillrud said this indicates the air conditioner filtering systems are very effective in removing steel dust particles from the passenger cars, therefore reducing exposure.

Although the levels of chromium, iron and manganese were 100 times greater than those observed in the students' indoor or outdoor settings, these subway levels still were more than 1,000 times lower than the United States Occupational Safety and Health Administration exposure limits, researchers said.

"I think more work needs to be done to see whether there's any health impact or not," Chillrud said.

Excessive levels of manganese, such as those seen in industrial settings, have been linked to neurological problems, he explained, and high chromium levels have been connected to cancer.

"No one knows if there are any impacts from the levels seen in the subway," Chillrud added. "I think it's very important to start off with, to say that just because someone breathes something in doesn't mean it's bad for them. There's no evidence at the moment that there's any health concern. I don't think there's any reason to stop riding the subway. If you're not riding the subway, you're going to be taking a taxi or a bus and there are known health impacts from breathing tailpipe emissions."

These findings are to be published in the Jan. 15 issue of Environmental Science and Technology, a journal of the American Chemical Society.

Dr. Gilbert Ross, medical director of the American Council of Science and Health in New York, said the findings were "much ado about nothing."

"I'm not sure what is the public health threat from iron, manganese or chromium," Ross told UPI. "I don't know of any slightly elevated body burden levels of these elements that are associated with any public health risk."

Ross pointed out millions of people in New York have been riding steel subway cars for decades and no known health risk has been detected.

"One would think it's going to take an awful lot of exposure to get subway workers' levels up to an exposure that exceeds federal level guidelines," Ross said. "Even the federal guidelines are overly cautious."

Chillrud said scientists plan to look at blood and urine samples from New York subway transit works next.

Ross also questioned other parts of the study.

"This was done in 1999," Ross said. "Why did it take three or four years to get this into print? Seems like an extremely simple study."

Michael Dixon, spokesman for the U.S. Steel Corp. based in Pittsburgh, told UPI, "I don't see how there would be an economic impact on U.S. Steel and if it's (subway levels) 1,000 times below government safety recommendations ... that's an extremely, extremely minimal risk, if any."


Katrina Woznicki covers health research for UPI Science News. E-mail

Copyright 2004 by United Press International.

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