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There is increasing interest in potential health effects of airborne exposures to hazardous air pollutants at relatively low levels. This study focuses on sources, levels, and exposure pathways of manganese, chromium, and iron among inner-city high school students in New York City (NYC) and the contribution of subways. Samples of fine particulate matter (PM[sub2.5]) were collected during winter and summer over 48 h periods in a variety of settings including inside homes, outdoors, and personal samples (i.e., sampling packs carried by subjects). PM[sub2.5] samples were also collected in the NYC subway system. For NYC, personal samples had significantly higher concentrations of iron, manganese, and chromium than did home indoor and ambient samples. The ratios and strong correlations between pairs of elements suggested steel dust as the source of these metals for a large subset of the personal samples. Time--activity data suggested NYC subways as a likely source of these elevated personal metals. In duplicate PM[sub2.5] samples that integrated 8 h of underground subway exposure, iron, manganese, and chromium levels (>2 orders of magnitude above ambient levels) and their ratios were consistent with the elevated personal exposures. Steel dust in the NYC subway system was the dominant source of airborne exposures to iron, manganese, and chromium for many young people enrolled in this study, with the same results expected for other NYC subway riders who do not have occupational exposures to these metals. However, there are currently no known health effects at the exposure levels observed in this study. [ABSTRACT FROM AUTHOR]

The article cites the Columbia/Harvard study that highlights that the New York City subway riders have an increased exposure to fine particles of some metals. The study establishes that steel dust from subway rails contributes to relatively high levels of airborne iron, chromium and manganese near New York City's subway platform. However, whether the measured exposures are more than 3 orders of magnitude below standards set by the U.S. Occupation Safety and Health Administration effects at those levels have not been established.