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John K. McGee,¹ Lung Chi Chen,² Mitchell D. Cohen,² Glen R. Chee,² Colette M. Prophete,² Najwa Haykal-Coates,¹ Shirley J. Wasson,³ Teri L. Conner,⁴ Daniel L. Costa,¹ and Stephen H. Gavett¹

¹National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; ²Nelson Institute of Environmental Medicine, New York University School of Medicine, Tuxedo, New York, USA; ³National Risk Management Research Laboratory, and ⁴National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA

Abstract

The catastrophic destruction of the World Trade Center (WTC) on 11 September 2001 caused the release of high levels of airborne pollutants into the local environment. To assess the toxicity of fine particulate matter [particulate matter with a mass median aerodynamic diameter < 2.5 µm (PM_2.5) ], which may adversely affect the health of workers and residents in the area, we collected fallen dust samples on 12 and 13 September 2001 from sites within a half-mile of Ground Zero. Samples of WTC dust were sieved, aerosolized, and size-separated, and the PM_2.5 fraction was isolated on filters. Here we report the chemical and physical properties of PM_2.5 derived from these samples and compare them with PM_2.5 fractions of three reference materials that range in toxicity from relatively inert to acutely toxic (Mt. St. Helens PM ; Washington, DC, ambient air PM ; and residual oil fly ash) . X-ray diffraction of very coarse sieved WTC PM (< 53 µm) identified calcium sulfate (gypsum) and calcium carbonate (calcite) as major components. Scanning electron microscopy confirmed that calcium-sulfur and calcium-carbon particles were also present in the WTC PM_2.5 fraction. Analysis of WTC PM_2.5 using X-ray fluorescence, neutron activation analysis, and inductively coupled plasma spectrometry showed high levels of calcium (range, 22-33%) and sulfur (37-43% as sulfate) and much lower levels of transition metals and other elements. Aqueous extracts of WTC PM_2.5 were basic (pH range, 8.9-10.0) and had no evidence of significant bacterial contamination. Levels of carbon were relatively low, suggesting that combustion-derived particles did not form a significant fraction of these samples recovered in the immediate aftermath of the destruction of the towers. Because gypsum and calcite are known to cause irritation of the mucus membranes of the eyes and respiratory tract, inhalation of high doses of WTC PM_2.5 could potentially cause toxic respiratory effects. Key words: carbon analysis, ICP-AES, ICP-MS, inhalation toxicology, neutron activation analysis, scanning electron microscopy, X-ray diffraction, X-ray fluorescence. Environ Health Perspect 111:972-980 (2003) .