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The collapse of the World Trade Center (WTC) towers on September 11, 2001, caused lower Manhattan and adjacent areas to be covered in millimeters to centimeters of dust. WTC dust penetrated into indoor spaces, and public health concerns remain regarding exposure to possible residual dust in the affected areas. The goal of the studies outlined in this review was to determine which, if any, components of the bulk WTC dust are sufficiently above typical background dust levels in New York City to develop an analytical method to screen for the component(s). Components of the <150-microm-size fraction of the dust are gypsum, phases compatible with crushed concrete, man-made vitreous fibers (MMVFs), silica, lead, chrysotile asbestos, and other materials. Slag wool was the most common WTC MMVF, whereas soda-lime glass and rock wool were minor to trace constituents. Most background samples also contained gypsum, phases compatible with concrete, and MMVF. However, the proportions of the various MMVF in background samples are typically unlike those characteristic of bulk WTC dust. Results indicate that slag wool can be used as a signature marker to identify areas that contain potential residual WTC dust contamination at concentrations that are less than average background levels for the material.

A personal exposure study was conducted in New York City as part of the Urban Dispersion Program (UDP). It examined the contact of individuals with four harmless perflourocarbon tracers (PFT) released in Midtown Manhattan with approval by city agencies at separate locations, during two types of experiments, completed during each release period. Two continuous 1 h release periods separated by a 1.5 h ventilation time were completed on 3 October 2005. Stationary site and personal exposure measurements were taken during each period, and the first half hour after the release ended. Two types of scripted exposure activities are reported: Outdoor Source Scale, and Outdoor Neighborhood Scale; requiring 1- and 10-min duration samples, respectively. The results showed that exposures were influenced by the surface winds, the urban terrain, and the movements of people and vehicles typical in urban centers. The source scale exposure data indicated that local conditions significantly affected the distribution of each tracer, and consequently the exposures. The highest PFT exposures resulted from interaction of the scripted activities with local surface conditions. The range measured for 1- min exposures were large with measured values exceeding 5000 ppqv (parts per quadrillion by volume). The neighborhood scale measurements quantified exposures at distances up to seven blocks away from the release points. Generally, but not always, the PFT levels returned quickly to zero indicating that after cessation of the emissions the concentrations decrease rapidly, and reduce the intensity of local exposures. The near source and neighborhood personal exposure route results provided information to establish a baseline for determining how a release could affect both the general public and emergency responders, and evaluate the adequacy of re-entry or exit strategies from a local area. Finally, the data also show that local characteristics can produce "hot spots".

The attack on the World Trade Center (WTC) resulted in a new era of awareness on terrorism in the United States and the issues surrounding the potential for acute and/or long-term health outcomes caused by personal exposures to toxicants released during a terrorist event or an accident. The aftermath of the collapse yielded a situation usually not encountered in environmental health science: a large population's exposure to a previously uncharacterized complex mixture of airborne gases and particles, and re-suspendable particles (>2.5 microm in diameter). This led to a series of rapidly changing potential and actual exposure categories, both in space and time that were associated with the complex mixture of heterogeneous composition and character; e.g., very large particles mixed with much smaller amounts of fine particles, and gases released by uncontrolled combustion. The four categories of outdoor exposure that were encountered will be discussed over the period from September 11 until the fires ended on December 20, 2001. Further, the complex issue of indoor exposure to deposited dust will be highlighted from the beginning through the residual exposure issues being examined today (Category 5 period). The strength of the information on the initial WTC dust and smoke, and the smoke plumes from the fires and the continuing (permanent) gaps in our knowledge within the exposure sciences will be discussed, as well as our attempt to reconstruct exposure for various segments of the population in southern Manhattan and the surrounding areas. This all will be tied to lessons that must be considered in response to future events, natural or otherwise.

New York City Firefighters (FDNY-FFs) were exposed to particulate matter and combustion/pyrolysis products during and after the World Trade Center (WTC) collapse. Ten months after the collapse, induced sputum (IS) samples were obtained from 39 highly exposed FDNY-FFs (caught in the dust cloud during the collapse on 11 September 2001) and compared to controls to determine whether a unique pattern of inflammation and particulate matter deposition, compatible with WTC dust, was present. Control subjects were 12 Tel-Aviv, Israel, firefighters (TA-FFs) and 8 Israeli healthcare workers who were not exposed to WTC dust. All controls volunteered for this study, had never smoked, and did not have respiratory illness. IS was processed by conventional methods. Retrieved cells were differentially counted, and metalloproteinase-9 (MMP-9), particle size distribution (PSD), and mineral composition were measured. Differential cell counts of FDNY-FF IS differed from those of health care worker controls (p < 0.05) but not from those of TA-FFs. Percentages of neutrophils and eosinophils increased with greater intensity of WTC exposure (< 10 workdays or greater than or equal to 10 workdays; neutrophils p = 0.046; eosinophils p = 0.038). MMP-9 levels positively correlated to neutrophil counts (p = 0.002; r = 0.449). Particles were larger and more irregularly shaped in FDNY-FFs (1-50 microm; zinc, mercury, gold, tin, silver) than in TA-FFs (1-10 microm; silica, clays). PSD was similar to that of WTC dust samples. In conclusion, IS from highly exposed FDNY-FFs demonstrated inflammation, PSD, and particle composition that was different from nonexposed controls and consistent with WTC dust exposure.

The collapse of the World Trade Center (WTC) on September 11, 2001, generated large amounts of dust and smoke that settled in the surrounding indoor and outdoor environments in southern Manhattan. Sixteen dust samples were collected from undisturbed locations inside two uncleaned buildings that were adjacent to Ground Zero. These samples were analyzed for morphology, metals, and organic compounds, and the results were compared with the previously reported outdoor WTC dust/smoke results. We also analyzed seven additional dust samples provided by residents in the local neighborhoods. The morphologic analyses showed that the indoor WTC dust/smoke samples were similar to the outdoor WTC dust/smoke samples in composition and characteristics but with more than 50% mass in the <53-microm size fraction. This was in contrast to the outdoor samples that contained >50% of mass above >53 microm. Elemental analyses also showed the similarities, but at lower concentrations. Organic compounds present in the outdoor samples were also detected in the indoor samples. Conversely, the resident-provided convenience dust samples were different from either the WTC indoor or outdoor samples in composition and pH, indicating that they were not WTC-affected locations. In summary, the indoor dust/smoke was similar in concentration to the outdoor dust/smoke but had a greater percentage of mass <53 microm in diameter.

The explosion and collapse of the World Trade Center (WTC) was a catastrophic event that produced an aerosol plume impacting many workers, residents, and commuters during the first few days after 11 September 2001. Three bulk samples of the total settled dust and smoke were collected at weather-protected locations east of the WTC on 16 and 17 September 2001; these samples are representative of the generated material that settled immediately after the explosion and fire and the concurrent collapse of the two structures. We analyzed each sample, not differentiated by particle size, for inorganic and organic composition. In the inorganic analyses, we identified metals, radionuclides, ionic species, asbestos, and inorganic species. In the organic analyses, we identified polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, polychlorinated dibenzodioxins, polychlorinated dibenzofurans, pesticides, phthalate esters, brominated diphenyl ethers, and other hydrocarbons. Each sample had a basic pH. Asbestos levels ranged from 0.8% to 3.0% of the mass, the PAHs were > 0.1% of the mass, and lead ranged from 101 to 625 microg/g. The content and distribution of material was indicative of a complex mixture of building debris and combustion products in the resulting plume. These three samples were composed primarily of construction materials, soot, paint (leaded and unleaded), and glass fibers (mineral wool and fiberglass). Levels of hydrocarbons indicated unburned or partially burned jet fuel, plastic, cellulose, and other materials that were ignited by the fire. In morphologic analyses we found that a majority of the mass was fibrous and composed of many types of fibers (e.g., mineral wool, fiberglass, asbestos, wood, paper, and cotton). The particles were separated into size classifications by gravimetric and aerodynamic methods. Material < 2.5 microm in aerodynamic diameter was 0.88-1.98% of the total mass. The largest mass concentrations were > 53 microm in diameter. The results obtained from these samples can be used to understand the contact and types of exposures to this unprecedented complex mixture experienced by the surviving residents, commuters, and rescue workers directly affected by the plume from 11 to 12 September and the evaluations of any acute or long-term health effects from resuspendable dust and smoke to the residents, commuters, and local workers, as well as from the materials released after 11 September until the fires were extinguished. Further, these results support the need to have the interior of residences, buildings, and their respective HVAC systems professionally cleaned to reduce long-term residential risks before rehabitation.