Environ. Sci. Technol. 2009, 43, 1449–1454
Method Development for Analysis of Urban Dust Using Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry to Detect the Possible Presence of World Trade Center Dust Constituents A M Y M . B E R N , * ,† H E A T H E R A . L O W E R S , ‡ GREGORY P. MEEKER,‡ AND JACKY A. ROSATI§ U.S. Environmental Protection Agency, National Enforcement Investigations Center, Building 25, Denver Federal Center, P.O. Box 25227, Denver, Colorado 80225, U.S. Geological Survey Central Region, Denver Federal Center, MS 973, Denver, Colorado 80225, and.S. Environmental Protection Agency, Office of Research and Development, National Homeland Security Research Center, E343-06, 109 T.W. Alexander Drive, Research Triangle Park, North Carolina 27711B
Received March 27, 2008. Revised manuscript received August 22, 2008. Accepted December 16, 2008.
The collapse of the World Trade Center Towers on September 11, 2001, sent dust and debris across much of Manhattan and in the surrounding areas. Indoor and outdoor dust samples were collected and characterized by U.S. Geological Survey (USGS)scientistsusingscanningelectronmicroscopywithenergydispersive spectrometry (SEM/EDS). From this characterization, the U.S. Environmental Protection Agency and USGS developed a particulate screening method to determine the presence of residual World Trade Center dust in the indoor environment using slag wool as a primary “signature”. The method describes a procedure that includes splitting, ashing, and sieving of collected dust. From one split, a 10 mg/mL dust/ isopropanol suspension was prepared and 10-30 µL aliquots of the suspension placed on an SEM substrate. Analyses were performed using SEM/EDS manual point counting for slag wool fibers. Poisson regression was used to identify some of the sources of uncertainty, which are directly related to the small number of fibers present on each sample stub. Preliminary results indicate that the procedure is promising for screening urban background dust for the presence of WTC dust. Consistent sample preparation of reference materials and samples must be performed by each laboratory wishing to use this method to obtain meaningful and accurate results.
Introduction The collapse of the World Trade Center (WTC) Towers in New York City on September 11, 2001, sent a cloud of dust across much of Manhattan and in the surrounding areas. * Corresponding author phone: 303-462-9128; fax: 303-462-9141; e-mail:
[email protected]. † National Enforcement Investigations Center. ‡ U.S. Geological Survey Central Region. § U.S. Environmental Protection Agency, Office of Research and Development. 10.1021/es800865n
Not subject to U.S. Copyright. Publ. 2009 Am. Chem. Soc.
Published on Web 02/02/2009
The U.S. Environmental Protection Agency (U.S. EPA) sought to develop a method to identify residential or business environments in the greater NY region that may be affected by, and thereby require cleanup of, WTC dust. The desired method would be able to rapidly screen a large number of indoor dust samples (1) for WTC dust residue. The analysis method also needed to be able to distinguish WTC dust levels from background urban dusts in indoor samples without requiring measurement of the area of the sampled surface, as used in microvacuum techniques (2) because of the need to sample irregular surfaces that could be difficult to reach. Since the analysis would be performed by several commercial laboratories, the method needed to provide consistent measurements. Finally, the method needed to be able to be performed quickly with readily available analytical software. This paper describes the development of a scanning electron microscopy with energy dispersive spectrometry (SEM/EDS) sample preparation and analysis method to analyze indoor dusts for the presence of WTC dust. The screening method uses slag wool as an indicator of impact from WTC-derived dust. A more thorough presentation of the screening method was presented to the World Trade Center Expert Technical Review Panel and included polarized light microscopy (PLM) and transmission electron microscopy (TEM) analyses in addition to SEM/EDS (1). Also included was an EDS X-ray mapping procedure to determine relative ratios of the concentrations of Ca-rich components. Three government laboratories collaborated for the SEM/ EDS method development described in this paper. This manuscript describes the development process and government agency testing of the SEM/EDS fiber counting method.
Background Immediately following the WTC collapse, scientists from the U.S. Geological Survey (USGS) collected dust samples from indoor and outdoor locations throughout the affected lower Manhattan area (3-5). The USGS Denver Microbeam Laboratory identified particle types within the WTC dust by SEM/EDS and then quantified the components by calculating the percent area of each component as calculated from SEM images (6). Dusts not impacted by the WTC collapse (background dusts) were subsequently analyzed for fiber compositions (7). The most common man-made vitreous fibers (MMVF) found in background dusts were a combination of Ca-Al-Si glass and a fiberglass insulation consistent with the composition of soda-lime glass (8). Soda-lime fibers were present in WTC dust as well as background dusts, although at low concentrations (
