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Potential Exposures to Airborne and Settled Surface Dust in Residential Areas of Lower Manhattan Following the Collapse of the World Trade Center --- New York City, November 4--December 11, 2001

Following the terrorist attacks of September 11, 2001, which destroyed the World Trade Center (WTC) in lower Manhattan, the New York City (NYC) Department of Health and Mental Hygiene (DOHMH) and the Agency for Toxic Substances and Disease Registry (ATSDR), with assistance from the U.S. Public Health Service (PHS) Commissioned Corps Readiness Force* and the WTC Environmental Assessment Working Group, assessed the composition of outdoor and indoor settled surface and airborne dust in residential areas around the WTC and in comparison areas. This report summarizes the results of the investigation, which found 1) similar levels of airborne total fibers in lower and in upper Manhattan, 2) greater percentage levels of synthetic vitreous fibers (SVF) and mineral components of concrete and building wallboard in settled dust of residential areas in lower Manhattan than in upper Manhattan, and 3) low levels of asbestos in some settled surface dust in lower Manhattan residential areas (1). Based in part on the results of this investigation, the U.S. Environmental Protection Agency (EPA) is cleaning and sampling residential areas as requested by lower Manhattan residents. In addition, to assess any short- or long-term health effects of smoke, dust, and airborne substances around the WTC site, DOHMH and ATSDR are developing a registry that will track the health of persons who were most highly exposed to these materials.

During November 4--December 11, 2001, air and settled surface dust samples were collected in and around 30 residential buildings within three concentric circles surrounding the WTC site in lower Manhattan, including 59 residential units (2). In addition, five residential units in four buildings located north of 59th Street (approximately 5 miles northeast of the WTC site) were sampled for purposes of comparison. Attention was focused on building material constituents 1) that have irritant properties (e.g., SVF, including fiberglass and gypsum) or might have negative long-term health effects (e.g., crystalline silica and asbestos) and 2) that were reasonably presumed to be either in the initial WTC collapse dust cloud or in dust generated by subsequent rescue and recovery activities at the WTC site. All samples collected during the investigation were analyzed for the presence of asbestos, SVF, crystalline mineral components of concrete (e.g., silica, calcite, and portlandite), and crystalline mineral components of building wallboard (e.g., gypsum, mica, and halite).

At each sampling location, time-weighted air sampling was conducted for three or four particulate matter (PM) fractions (i.e., PM 100 microns, 10 microns, 4 microns, and 2.5 microns) (3--5). Each PM fraction was analyzed for crystalline minerals by using X-ray diffraction (XRD) analysis (6). The XRD analysis for crystalline minerals was semiquantitative (i.e., estimated). Air samples for fibers were analyzed first by phase contrast microscopy (PCM) (5). If the concentration of total fibers was higher than the maximum concentration of fibers found in the comparison homes (0.003 fibers per cubic centimeter of air [f/cc]), the sample was re-analyzed for asbestos fibers by using transmission electron microscopy (TEM) (5). In addition, scanning electron microscopy (SEM) to look for SVF was used for PCM fiber counts >0.003 f/cc if the settled surface dust sample from that area contained SVF.

Settled surface dust samples also were taken at each sampling location and analyzed for crystalline minerals and fibers (Figure). Fiber analysis of settled dust samples for asbestos and SVF was conducted by using polarized light microscopy (PLM) (7). If asbestos levels were below the detection limit (i.e., <1%), samples were re-analyzed by using TEM (7). The dust samples also were analyzed for crystalline mineral content by using XRD.

Air Sampling Results

For 111 (94.9%) of the 117 air samples, the concentrations of fibers found in lower Manhattan residential areas were similar to the concentration of fibers found in comparison areas (<0.003 f/cc). The six lower Manhattan areas that had elevated total fiber counts were re-examined by TEM and SEM to determine the types of fibers; the results indicated that neither asbestos nor SVF (e.g., fiberglass) contributed to the elevated total fiber counts.

Air sampling results for minerals detected quartz and other building material constituents in lower Manhattan. No other forms of crystalline silica were detected in any air samples except for a one-time detection of cristobalite (15 micrograms per cubic meter [µg/m3]§). The estimated concentrations of these minerals in air were low. In some locations, mineral components of concrete (quartz [not detected (ND)--19 µg/m], calcite [ND--14 µg/m], and portlandite [ND--95 µg/m]) and mineral components of building wallboard (gypsum [ND--15 µg/m], mica [ND--43 µg/m], and halite [ND--19 µg/m]) were detected at higher estimated levels in air samples in lower Manhattan than in samples collected in comparison areas. Gypsum was the only mineral detected in the comparison building air samples (ND--5 µg/m). No other minerals tested (i.e., quartz, calcite, portlandite, mica, and halite) were detected in comparison building air samples.

Settled Surface Dust Results

In lower Manhattan, asbestos and SVF were found in some indoor settled dust samples from residential units and common areas (Table 1). No asbestos or SVF was detected in the comparison area dust samples. Quartz, calcite, portlandite, and gypsum comprised a higher percentage of the dust in 29 samples from buildings in lower Manhattan compared with eight samples from comparison area buildings (Table 2). Only two (2.1%) of the 97 dust samples collected provided enough bulk material for pH analysis. The samples, which were collected from two outdoor locations in lower Manhattan, had pH values of 8.6 and 9.8, respectively.

Reported by: NL Jeffery, MPH, C D'Andrea, MS, J Leighton, PhD, New York City Dept of Health and Mental Hygiene, New York. SE Rodenbeck, ScD, L Wilder, CIH, D DeVoney, PhD, S Neurath, PhD, CV Lee, MD, RC Williams, MS, Div of Health Assessment and Consultation, Agency for Toxic Substances and Diseases Registry.

Editorial Note:

Exposure to substantial amounts of SVF, mineral components of concrete, and mineral components of building wallboard might cause skin rashes, eye irritation, and upper respiratory irritation, all of which were reported more frequently than expected seasonal rates by community members and first responders after the collapse of the WTC towers (8--10). If the reported irritant effects were associated with WTC-related materials, these effects would subside once exposure to SVF, mineral components of concrete, and mineral components of building wallboard ceased. Persons with pre-existing heart or lung diseases (e.g., asthma) or a previous history of occupational exposure to these materials might be more sensitive to their irritant effects.

Settled surface dust might become airborne if disturbed, potentially causing exposures to occur through inhalation. Several worst-case assumptions were made to assess the potential long-term public health risks for inhaling airborne asbestos and quartz. These assumptions included 1) that no cleaning of indoor spaces had occurred or would occur, 2) that all airborne fibers were asbestos, and 3) that the highest levels detected during sampling represented long-term air levels. Under these worst-case conditions, prolonged exposure (i.e., decades) to airborne asbestos and quartz might increase the long-term risk for persons developing lung cancer and other adverse lung health effects (approximately one additional case per 10,000 persons exposed). However, persons who clean their residences frequently as recommended (1) or who participate in the EPA cleaning and sampling program are unlikely to be exposed to worst-case conditions.

The findings of this investigation are subject to at least two limitations. First, the results do not necessarily reflect conditions found in other buildings, the time period immediately after the collapse, or the time period after December 12, when the sampling was completed. Second, a limited number of samples were obtained from comparison areas to determine NYC background levels of asbestos, SVF, mineral components of concrete, and mineral components of building wallboard. The comparison area results might not reflect NYC background levels.

Following the investigation, DOHMH and ATSDR made three recommendations (1). First, because more asbestos, SVF, mineral components of concrete and building wallboard were found in settled surface dust in lower Manhattan residential areas than in comparison residential areas, residents of lower Manhattan were advised to continue cleaning frequently with high-efficiency particulate air (HEPA) filter vacuums and damp cloths/mops to reduce the potential for exposure. Second, to ensure the effectiveness of the recommended cleaning, DOHMH and ATSDR recommended additional monitoring of residential areas in lower Manhattan and an investigation to define background levels specific to NYC for asbestos, SVF, mineral components of concrete, and mineral components of building wallboard. EPA is implementing this recommendation and conducting this investigation. Finally, lower Manhattan residents concerned about possible WTC-related dust in their residential areas were advised to request cleaning and testing from EPA no later than December 31, 2002. EPA is conducting the requested cleaning and testing of lower Manhattan residential areas.

DOHMH and ATSDR are developing a registry of those persons who were most highly exposed, including persons living, working, or attending school in lower Manhattan; persons who responded to the emergency; persons working at the WTC site or the Staten Island landfill following the attacks; and persons working in buildings that were damaged or destroyed in the attacks. The registry will track the health of participants to determine whether their exposures to smoke, dust, and airborne substances around the WTC site might have any short- or long-term impacts on their physical health. Additionally, the registry is intended to track the mental health of the approximately 100,000--200,000 persons who might enroll.


  1. New York City Department of Health and Mental Hygiene and Agency for Toxic Substances and Disease Registry. Final report of the public health investigation to assess potential exposures to airborne and settled surface dust in residential areas of lower Manhattan. Atlanta, Georgia: U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 2002.
  2. New York City Department of Health and Mental Hygiene and Agency for Toxic Substances and Disease Registry. Ambient and indoor sampling for public health evaluations of residential areas near World Trade Center, New York, New York: sampling protocol. New York, New York: New York City Department of Health and Mental Hygiene, 2001.
  3. American Conference of Governmental Industrial Hygienists. Documentation of TLVs and BEIs, 7th edition. Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists, 2001.
  4. U.S. Environmental Protection Agency. National ambient air quality standards for particulate matter; final rule. Federal Register, Part II, 40 CFR Part 50, July 18, 1997.
  5. CDC. Manual of analytical methods, 4th edition. Atlanta, Georgia: U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, CDC, August 1994.
  6. EMSL Analytical, Inc. EMSL Laboratory's MSD 0700: operating procedures for the analysis of silica by X-ray diffraction (XRD). Westmont, New Jersey: EMSL Analytical, Inc., January 2000.
  7. New York State Department of Health. Environmental Laboratory Approval Program (ELAP) certification manual. Albany, New York: New York State Department of Health, March 1997.
  8. CDC. Self-reported increase in asthma severity after the September 11 attacks on the World Trade Center---Manhattan, New York, 2001. MMWR 2002;51:781--4.
  9. CDC. Injuries and illnesses among New York City Fire Department rescue workers after responding to the World Trade Center attacks. MMWR 2002;51(Special Issue):1--5.
  10. CDC. Community needs assessment of lower Manhattan residents following the World Trade Center attacks --- Manhattan, New York City, 2001. MMWR 2002:51(Special Issue):10--3.

* A cadre of PHS Commissioned Corps officers who can be mobilized during disaster, strife, or other public health emergencies and in response to domestic or international requests.
A group formed on September 15, 2001, that comprises representatives of the U.S. Department of Health and Human Services, Environmental Protection Agency (EPA), Department of Labor, and New York State and NYC government and private organizations to coordinate  public health and occupational sampling and data review among the three federal agencies in support of state and city health departments.
§ Estimated.

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Table 2

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Figure 3
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