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Researching Airborne Metals in Transit Workers’ Bodies
A pilot study gathers baseline information on subway workers’ exposure

transit worker
Steel dust exposure in the NYC subway system has been of concern to subway workers and transit police for decades. A study by Lamont-Doherty Earth Observatory researchers will examine the level of airborne metal in subway workers. Photo credit: Mark Inglis

by Jennifer Freeman

Working in the subway several hours each day, subway workers and transit police breathe more subway air than the typical commuter. Subway air has been shown to contain more steel dust than outdoor or other indoor air in New York City. But do transit workers’ bodies harbor elevated levels of these metals? And does this translate into a health concern for the workers?

In a new paper called Steel Dust in the New York City Subway System as a Source of Manganese, Chromium, and Iron Exposures for Transit Workers, Steven Chillrud, a research scientist at the Lamont-Doherty Earth Observatory, and colleagues discuss an ongoing pilot study that takes a closer look at these questions. The paper will be published in the March issue of the Journal of Urban Health, a special issue focusing on subway health research.

The pilot study is expected to show whether 40 transit workers’ blood and urine contains elevated levels of the metals that have been shown to exist in air collected in subway stations. “This is the type of information you need before deciding whether it is worthwhile to investigate any potential health impacts,” Chillrud explains. “Airborne metals levels that have been studied in the past were much higher than those in subway air, but subway levels are higher than outdoor air. So it’s an interesting in-between area.”

As Chillrud and colleagues write in the new paper, “Steel dust exposure in the NYC subway system has been of concern to subway workers and transit police for decades. As one of the largest subway systems in the world, the NYC subway environment could provide important information relevant to evaluating the potential for health effects from exposures to airborne metals.” The authors are researchers from the Lamont-Doherty Earth Observatory at Columbia, the Mailman School of Public Health, and Harvard’s School of Public Health.

Emphasizing that no adverse health effects have been linked to the levels of steel dust present in the subways, Chillrud says no one should stop riding the subway based on his research “We do know that increases in surface traffic emissions have adverse health effects,” he says.

A study published last year, in which high school students who commuted by subway collected air samples during their commutes, suggested that steel dust generated in the New York City subway did significantly increase the total amount of iron, manganese, and chromium that the students breathed. Furthermore, the levels of these airborne metals in the subway air were more than 100 times higher than outdoor or other indoor air in New York, but still 1000 times lower than the Occupational Safety and Health Administration’s Permissible Exposure Limit guidelines for workers. The current study extends the previous research to 40 transit workers, who could be expected to have higher exposure levels than commuters. (For more information on the earlier study, see

Also in the March issue, Dr. Robyn Gershon of the Mailman School of Public Health publishes a paper called Health and Safety Hazards Associated with Subways: A Review, which provides a comprehensive look at health and safety hazards that might affect both riders and subway workers, and indicates that while subways in general, and the New York City subway system in particular, are relatively safe, subway systems are vulnerable to a range of health and safety hazards. These include the threat of terrorist attacks, transmission of infectious diseases, subway noise, and a special concern with respect to crime, despite the fact that crime rates generally have been dropping.

Chillrud is one of many Earth Institute scientists whose research focuses on New York City’s environmental problems. Though Earth Institute research extends around the globe, its New York City Initiative encourages and coordinates New York-focused research projects, on topics ranging from garbage to climate to Hudson River ecology. A catalog of New York research by Earth Institute scientists can be found on the Web at

In the past five years, Steven Chillrud’s New York area research has included studying toxins in truck drivers who carted debris from the World Trade Center site, analyzing highway runoff, analyzing groundwaters and Hudson River sediments for studies of contaminant transport, and looking at relations between diesel emissions and asthma.

The Lamont-Doherty Earth Observatory, a member of The Earth Institute at Columbia University, is one of the world's leading research centers examining the planet from its core to its atmosphere, across every continent and every ocean. From global climate change to earthquakes, volcanoes, environmental hazards and beyond, Observatory scientists provide the basic knowledge of Earth systems needed to inform the future health and habitability of our planet.

The Earth Institute at Columbia University is among the world's leading academic centers for the integrated study of Earth, its environment, and society. The Earth Institute builds upon excellence in the core disciplines — earth sciences, biological sciences, engineering sciences, social sciences and health sciences — and stresses cross-disciplinary approaches to complex problems. Through its research training and global partnerships, it mobilizes science and technology to advance sustainable development, while placing special emphasis on the needs of the world's poor.

For more information, visit