Study sees little dust risk for subway workers

New York subway commuters may worry more about rats and rising fares than dust floating through the system, but for the workers who spend their whole shift below ground, air quality has long been a concern. Results from a new pilot study using miniaturized air samplers to look at steel dust exposure may help them breathe easier.

Steel dust, produced as thousands of train wheels roll through the tunnels each day, is a major source of pollution in one of the world’s most extensive commuter rail systems. In the study, published this month in the journal Environmental Research, scientists tracked exposure in 39 subway workers and measured biological responses to three metals found in steel dust: iron, chromium and manganese. The study found no strong or consistent evidence of a biological response that might indicate elevated risk of dust-related disease. It also showed that workers were exposed to levels well below standards set by the U.S. Occupational Safety & Health Administration (OSHA).

“The results are good news, even though this was a small pilot study and not a comprehensive evaluation of potential subway-worker health risks from steel dust,” said coauthor Steven Chillrud, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory.

Chillrud got interested in subway air when he coauthored a 2004 study aimed at understanding how and where teenagers were exposed to a variety of air pollutants. He and colleagues recruited high school students in Harlem to wear air-sampling backpacks to measure personal exposure. At the same time, fixed-site monitors ran inside and outside their homes and school. When the results came in, many students’ backpacks showed much higher airborne levels of iron, manganese and chromium than the fixed-site samplers. These students shared one thing in common: they rode the subway.

To confirm that subways were the source of the metals, Chillrud had a Columbia student collect duplicate air samples while riding trains and sitting in stations. Signature ratios of metals were the same as those seen in the samples collected by the high-school students. Furthermore, the air-borne metal concentrations observed in stations and trains were more than a hundred times higher than above ground. It was lowest in cars, where dust gets trapped by air-conditioning filters, and highest in stations, where trains brake as they reach the platform.