The destruction of the World Trade Center

(WTC) on 11 September 2001 caused the

largest acute environmental disaster that ever

has befallen New York City (Claudio 2001;

Landrigan 2001). The combustion of more

than 90,000 L of jet fuel at temperatures

above 1,000°C released a dense and intensely

toxic atmospheric plume containing soot,

metals, volatile organic compounds (VOCs),

and hydrochloric acid. The collapse of the

towers pulverized cement, glass, and building

contents and generated thousands of tons of

particulate matter (PM) composed of cement

dust, glass fibers, asbestos, lead, polycyclic

aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides, and polychlorinated furans and

dioxins (Clark et al. 2003; Lioy et al. 2002;

McGee et al. 2003). These materials dispersed over lower Manhattan, Brooklyn, and

for miles beyond. They entered nearby office,

school, and residential buildings. Much

remained at the site to form Ground Zero, a

six-story pile of smoking rubble that burned

intermittently for more than 3 months.

Populations at greatest risk of exposure

included firefighters, police, paramedics,

other first responders [Prezant et al. 2002;

Centers for Disease Control and Prevention

(CDC) 2002], and construction workers and

volunteers who worked initially in rescue and

recovery and then for many months cleared

rubble at Ground Zero. Others at potentially

elevated risk included workers who cleaned

WTC dust from nearby buildings, women

who were pregnant on 11 September and succeeding weeks in lower Manhattan and adjacent areas of Brooklyn, and community

residents, especially the 3,000 children who

resided within 1 km of the towers and the

5,500 who attended school there.

Previous studies have documented the

acute traumatic consequences of the attacks on

the WTC, most notably the occurrence of

Environmental Health Perspectives • VOLUME 112 | NUMBER 6 | May 2004 731

Address correspondence to P.J. Landrigan, Mount Sinai School of Medicine, One Gustave L. Levy Place, Box 1057, New York, NY 10029 USA. Telephone: (212) 241-4804.

Fax: (212) 996-0407. E-mail: phil.landrigan@mssm.edu

*The NIEHS World Trade Center Working Group includes Mark Becker, Patrick N. Breysse, Beverly Cohen, Max Costa, Christos Efstathiou, Steven Eisenreich, Gary

Foley, Robert Frank, John K. McGee, John D. Groopman, Robin Herbert, Julie Herbstman, Eric Jayjock, Michaela Kendall, Sally A. Lederman, H.J. Lim, Morton

Lippmann, Polina Maciejczyk, J. Millette, Ady Miretzky, Sheung P. Ng, John H. Offenberg, Haluk A. Özkaynak, Joachim D. Pleil, Francesca Pozzi, Chunli Quan, Joan

Reibman, J. Ross, Jonathan M. Samet, Regina M. Santella, Margo Schwab, Pamela Shade, Mary Sobo, G. Stenchikov, Qing Sun, J. Morel Symons, Barbara Turpin, Vikram

Vyas, Sheng Wei Wang, Clifford P. Weisel, D’Ann L. Williams, Mary S. Wolff, Lih Ming Yiin, Mianhua Zhong, and Michael A. Gallo.

We thank S. Perry and R. Thompson of the U.S. Environmental Protection Agency (EPA) for their guidance on atmospheric modeling.

This research was supported by grants from the National Institute of Environmental Health Sciences (NIEHS) through the Superfund Basic Research Program (P42

ES07384 to Mount Sinai School of Medicine and P42 ES05948 to UNC-Chapel Hill); through grants from the Centers for Environmental Health Science (P30

ES09089-04S at Columbia University; P30 ES00260 at New York University (NYU); P30 ES03819 at Johns Hopkins University; P30 ES05022 at The University of

Medicine and Dentistry of New Jersey (UMDNJ); by the U.S. EPA through the Particulate Matter Health Research Center Program (R827351 at NYU) and a university

partnership between the National Exposure Research Laboratory and the Environmental and Occupational Health Sciences Institute (CR-827033 at UMDNJ); and by

grants from the September 11th Fund created by the New York Community Trust and United Way of New York City (NYTF CU517002 and SEPELES CU 517438 to

Columbia University and MSSM 0266-0507 to Mount Sinai School of Medicine.

This manuscript was reviewed and approved for release by the National Health and Environmental Effects Research Laboratory, U.S. EPA. Approval does not signify that the

contents necessarily reflect the views and policies of the U.S. EPA, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

The authors declare they have no competing financial interests.

Received 27 August 2003; accepted 18 February 2004.

Health and Environmental Consequences of the World Trade Center Disaster

Philip J. Landrigan,1 Paul J. Lioy,2 George Thurston,3 Gertrud Berkowitz,1 L.C. Chen,3 Steven N. Chillrud,4

Stephen H. Gavett,5 Panos G. Georgopoulos,2 Alison S. Geyh,6 Stephen Levin,1 Frederica Perera,7

Stephen M. Rappaport,8 Christopher Small,4 and the NIEHS World Trade Center Working Group*

1Mount Sinai School of Medicine, New York, New York, USA; 2Environmental and Occupational Health Sciences Institute of New Jersey,

New Brunswick, New Jersey, USA; 3New York University School of Medicine, Nelson Institute of Environmental Medicine, Tuxedo, 

New York, USA; 4Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, USA; 5U.S. Environmental Protection

Agency, Office of Research and Development, Research Triangle Park, North Carolina, USA; 6Johns Hopkins University Bloomberg

School of Public Health, Baltimore, Maryland, USA; 7Mailman School of Public Health of Columbia University, New York, New York,

USA; 8School of Public Health, University of North Carolina, Chapel Hill, North Carolina, USA

The attack on the World Trade Center (WTC) created an acute environmental disaster of enormous

magnitude. This study characterizes the environmental exposures resulting from destruction of the

WTC and assesses their effects on health. Methods include ambient air sampling; analyses of outdoor and indoor settled dust; high-altitude imaging and modeling of the atmospheric plume; inhalation studies of WTC dust in mice; and clinical examinations, community surveys, and prospective

epidemiologic studies of exposed populations. WTC dust was found to consist predominantly (95%)

of coarse particles and contained pulverized cement, glass fibers, asbestos, lead, polycyclic aromatic

hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and polychlorinated furans and dioxins.

Airborne particulate levels were highest immediately after the attack and declined thereafter.

Particulate levels decreased sharply with distance from the WTC. Dust pH was highly alkaline

(pH 9.0–11.0). Mice exposed to WTC dust showed only moderate pulmonary inflammation but

marked bronchial hyperreactivity. Evaluation of 10,116 firefighters showed exposure-related

increases in cough and bronchial hyperreactivity. Evaluation of 183 cleanup workers showed newonset cough (33%), wheeze (18%), and phlegm production (24%). Increased frequency of newonset cough, wheeze, and shortness of breath were also observed in community residents.

Follow-up of 182 pregnant women who were either inside or near the WTC on 11 September

showed a 2-fold increase in small-for-gestational-age (SGA) infants. In summary, environmental

exposures after the WTC disaster were associated with significant adverse effects on health. The

high alkalinity of WTC dust produced bronchial hyperreactivity, persistent cough, and increased

risk of asthma. Plausible causes of the observed increase in SGA infants include maternal exposures

to PAH and particulates. Future risk of mesothelioma may be increased, particularly among workers and volunteers exposed occupationally to asbestos. Continuing follow-up of all exposed populations is required to document the long-term consequences of the disaster. Key words: air pollution,

airway hyperresponsiveness, asbestos, occupational lung disease, PM2.5, PM10, small for gestational

age (SGA). Environ Health Perspect 112:731–739 (2004). doi:10.1289/ehp.6702 available via

http://dx.doi.org/ [Online 18 February 2004]

Research Workgroup Report
2,726 deaths, including 343 deaths among firefighters and 60 among police officers (CDC

2002). Early clinical and epidemiologic assessments documented a high prevalence of respiratory symptoms, particularly, persistent cough in

firefighters and rescue workers exposed to

WTC dust (CDC 2002; Prezant et al. 2002).

The prevalence of those symptoms was related

to intensity and duration of smoke and dust

exposure. Studies of the mental health consequences of the disaster have documented a high

prevalence of posttraumatic stress disorder

(PTSD) (Galea et al. 2002b; Fairbrother et al.

2003) and other psychological sequelae, including increased rates of drug and alcohol abuse

(Boscarino et al. 2002; Galea et al. 2002a;

Stuber et al. 2002; Vlahov et al. 2002a, 2002b).

In this report we summarize a comprehensive assessment of the impacts on human

health and the environment of the chemical

contaminants generated by destruction of the

WTC. The work was undertaken by a consortium of six research centers supported by the

National Institute of Environmental Health

Sciences (NIEHS) in collaboration with the

New York City Department of Health, the

U.S. Environmental Protection Agency

(EPA), and the CDC.

Environmental Exposure

Assessment

Four distinct phases can be distinguished in

the sources and patterns of environmental

contamination that followed the attack on the

WTC. We have been able to construct a

chronology of this contamination from the

environmental sampling data (Table 1).

Settled dust. To evaluate the composition

of material deposited in lower Manhattan

immediately after destruction of the WTC,

samples of settled dust were collected at sites

in lower Manhattan (Lioy et al. 2002; McGee

et al. 2003). In the inorganic fraction of these

samples, metals, radionuclides, ionic species,

and asbestos were identified. In the organic

fraction, PAHs, PCBs, polychlorinated

dibenzodioxins and dibenzofurans, pesticides,

phthalate esters, brominated diphenyl ethers,

and other hydrocarbons were found (Lioy

et al. 2002; Offenberg et al. 2003).

Each sample of settled dust had a highly

alkaline pH (9.0–11.0). Asbestos levels ranged

from 0.8% to 3.0% of mass; PAHs comprised

> 0.1% of total mass; and lead content ranged

from 101 to 625 ppm. Morphologically, most

of the dust was fibrous and contained mineral

wool, glass fibers, asbestos, wood, paper, and

cotton fibers (Figure 1). Coarse cement particles were also a major component (Figure 2).

To assess the composition of settled dust

by size, samples were mechanically sieved and

then separated aerodynamically into three fractions (Lioy et al. 2002; McGee et al. 2003).

More than 95% of the mass consisted of PM

> 10 μm in diameter. The largest mass concentration consisted of PM > 53 μm in diameter,

and there were proportionately more particles

in this large size range in outdoor than in

indoor samples. PM ≤ 2.5 μm in aerodynamic

diameter (PM2.5) comprised 0.88–1.98% of

total mass. Alkalinity decreased with decreasing particle size, and PM2.5 had a more nearly

neutral pH (Lioy et al. 2002; McGee et al.

2003). This finding is consistent with the

dominant presence of highly alkaline, coarse

cement particles in the large size fraction.

There was no geographical variation in particle

size distribution in the settled dust samples,

nor was a relationship found in indoor samples between particle size distribution and

height above the ground.

To measure the elemental concentration

of dust particles, X-ray fluorescence and

inductively coupled plasma–mass spectrometry (ICP-MS) analyses were employed.

Additionally, selected samples of PM > 2.5 μm

were sent to the National Institute of Standards

and Technology (NIST; Gaithersburg, MD)

for neutron activation analysis. Results showed

that chlorine was detectable only in the PM2.5

fraction, whereas antimony, aluminum, titanium, and magnesium were present principally in the PM10–53 fraction, and iron, zinc,

and calcium were most highly abundant in the

PM2.5–10 and PM10–53 fractions. A possible

explanation for this distribution is that Cl in

particulates was generated by high-temperature combustion of plastics and thus was concentrated in the smaller size fractions, whereas

elements associated with the larger particles

generated by collapse of the buildings, such as

Fe, Zn, and Ca, predominated in the larger

fractions.

Organic pollutants were analyzed in

14 samples of settled dust separated according

to particle size, including one indoor sample

(Lioy et al. 2002; Offenberg et al. 2003).

PCBs comprised less than 0.001% of total

mass. Organochlorine pesticides, including

chlordanes, hexachlorobenzene, heptachlor,

4,4 ́-dichlorodiphenyldichloroethylene

(DDE), 2,4 ́-dichlorodiphenyltrichloroethane

(DDT), and mirex, were found at low concentrations. PAHs were found in greatest concentrations in the relatively larger particles

(PM10–53), although concentrations greater

than those typically found in urban air were

found also in PM2.5. An estimated 100–1,000

tons of PAHs were spread over a localized area

of lower Manhattan within 0.5 km of Ground

Zero (Lioy et al. 2002; Offenberg et al. 2003).

Airborne PM. Collection of airborne

PM2.5 samples was initiated at a site in lower

Manhattan on 14 September 2001. Levels of

daily PM2.5 and of hourly airborne carbon

Workgroup Report | Landrigan et al.

732 VOLUME 112 | NUMBER 6 | May 2004 • Environmental Health Perspectives

Table 1. Sequence of environmental exposures after the attack on the WTC, September through December 2001. 

Time period Predominant sources of pollution Airborne pollutants

First 12 hr after collapse Burning jet fuel Combustion products: gaseous and particulate

(11 September 2001) Fires Evaporating gases from the collapse of towers

Collapse of the Twin Towers Coarse particles

Days 1 and 2 Burning jet fuel Combustion products: gaseous and particulate

Resuspension of settled dust/smoke Gases evaporating from piles

Resuspended coarse particles

Days 3–13 Smoldering fires Combustion products: gaseous and particulate

Resuspension of settled dust/smoke Coarse particle resuspension

Diesel exhaust

Day 14 through 20 December 2001 Smoldering fires with occasional flareups Combustion products: gases and particulates

Removal of debris by trucks and other heavy equipment Diesel exhaust

Data from Lioy et al. (2002).

Figure 1. A glass fiber in a dust sample collected

near the WTC, New York City, 12 September 2001.

The figure is reproduced from Lioy et al. (2002) with

permission from Environmental Health Perspectives. 
soot levels were measured at the New York

University (NYU) Downtown Hospital

(located 0.3 km east of Ground Zero) and at

a site adjacent to the NYU Medical Center at

First Avenue and 26th Street (0.7 km from

Ground Zero). Collection of air samples at

these locations continued until the last fire

was extinguished on 20 December (Thurston

and Chen 2002; Thurston et al. 2003; U.S.

EPA 2004).

Levels of PM2.5 very highly elevated above

normal urban background were detected in

the first days after 11 September (Figure 3).

The sampling sites were not located directly

in the path of the WTC plume, and thus

actual levels may have been still higher.

PM2.5 levels peaked in the night hours

when winds were calm and thermal inversions

allowed pollution to accumulate to higher levels

than during the day (Figure 4). Levels decreased

on rainy days when fires and wind-blown dust

were diminished. Levels declined as the fires

were extinguished, and they came to approach

background ambient levels by mid-October.

Demolition and removal of debris began

at Ground Zero in mid-October after the

fires had decreased in intensity. Coarse dust

generated by demolition was detectable in

ambient air until December, when pollution

from the site diminished greatly.

Trace elements. Concentrations of lead

and Cl in PM2.5 were intermittently elevated

above background at sites near the WTC

until mid-October, with occasional small

peaks through October and into November.

Ca levels, by contrast, were highest in

October and November, possibly reflecting

release of Ca-containing dust during demolition work at the site.

Dioxin and other chlorinated compounds.

The extensive use of polyvinyl chloride (PVC)

plastics within the WTC made possible the

generation of dioxins during the fires. U.S. EPA

monitoring data indicate that dioxin toxic

equivalent (TEQ) levels in air samples near

Ground Zero were several orders of magnitude above those typical of urban areas in the

United States (U.S. EPA 2002). From

23 September through late November, dioxin

levels in lower Manhattan ranged from 10 to

> 150 pg TEQ/m3. Dioxin concentrations several blocks from Ground Zero ranged from 1 to

10 pg, levels above typical urban background

but considerably lower than those measured

closer to Ground Zero. Dioxin levels declined

rapidly during the autumn, and the U.S. EPA

data suggest that by December 2001 they had

decreased to typical urban background.

Asbestos. Asbestos, primarily chrysotile,

was used for fire insulation in the construction

of the North Tower of WTC up to the 40th

floor (Nicholson et al. 1971; Reitze et al.

1972). Because of its known carcinogenic

potential (Nicholson and Landrigan 1996),

asbestos became a major health concern after

11 September. More than 10,000 ambient air

samples from lower Manhattan were tested for

asbestos by the U.S. EPA using phase-contrast

light microscopy (PCM) to identify fibers

>5μm in length; more than 8,000 of these

samples were also examined by transmission

electronic microscopy (TEM) to identify fibers

of ≥ 0.5 μm in length (Columbia University

2003; U.S. EPA 2004).

Twenty-two of the air samples analyzed by

the U.S. EPA were found to contain asbestos

Workgroup Report | Consequences of the WTC disaster

Environmental Health Perspectives • VOLUME 112 | NUMBER 6 | May 2004 733

Figure 2. Photomicrograph of settled dust from the WTC containing cement particles and glass fibers,

collected 12 September 2001.

Figure 3. Airborne PM2.5 mass concentrations at NYU Downtown Hospital (five blocks east of Ground Zero)

and other sites in Manhattan, September through mid-October 2001. PS, public school. Data from Thurston

et al. (2003).

80

70

60

50

40

30

20

10

0

Date

PM2.5 concentration (μg/m3)

Hunter

College

NYU Hospital

Pace University

PS 64

8 Sep 11 Sep 14 Sep 17 Sep 20 Sep 23 Sep 26 Sep 29 Sep 2 Oct 5 Oct 8 Oct 11 Oct 14 Oct

Figure 4. Mean airborne concentration of seven

PAHs at Ground Zero and at 290 E. Broadway,

Manhattan, September 2001 through April 2002.

3

2

1

0

Date

PAHs (ng/m3)

●

▲

●

●

● ● ●

▲ ● ▲ ▲

16 Sep

2001

5 Nov

2001

25 Dec

2001

13 Feb

2002

4 Apr

2002

Ground Zero

290 E. Broadway

●

▲
at levels above the clearance standard of 70

fibers/mm2 established under the Asbestos

Hazard Emergency Response Act (U.S. EPA

1986). This standard uses the TEM measurement technique. Most of the elevated asbestos

levels in air were observed in the earliest days

after 11 September.

There were no 8-hr time-weighted average

asbestos exposures to workers above the

Occupational Safety and Health Administration

standard (U.S. Department of Labor 2003),

which uses the PCM measurement technique

of 0.1 fiber/cm3, although workers undoubtedly had short-term peak exposures when they

disturbed asbestos-containing rubble at

Ground Zero.

Asbestos was detected in settled dust samples within apartments and other buildings

(Lioy et al. 2002). Because some residents had

prolonged exposures to uncleaned apartments, these indoor exposures may have

added significantly to ambient exposures.

Airborne PAHs. To characterize PAHs in

PM2.5 from the WTC, the National Exposure

Research Laboratory (NERL) of the U.S. EPA

collected air samples with 47-mm Teflon filters at and near Ground Zero from late

September 2001 through May 2002. Samples

were collected from three Ground Zero fenceline locations and at 290 E. Broadway (about

0.7 km from Ground Zero). Researchers at

the University of North Carolina at Chapel

Hill and the NERL used an assay developed to

measure the larger (five- and six-ring) PAH

molecules to determine the content of PAHs

in these samples.

The PAHs in those samples consisted of a

complex mixture including benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene,

benzo(e)pyrene, ideno(1,2,3-c,d)pyrene,

dibenzo(a,h)anthracene, and benzo(g,h,i)perylene. All except benzo(e)pyrene are known or

suspected carcinogens and typically are produced by incomplete combustion of organic

material. Levels at Ground Zero were highest

immediately after the attack and declined

over subsequent weeks (Figure 4). The consistently greater abundance of PAHs at Ground

Zero than farther away indicates that burning

debris at the site was a major source of airborne PAH pollution in lower Manhattan

(Lioy et al. 2002; Offenberg et al. 2003). The

unique pattern of PAHs found in these samples further confirmed that the WTC was the

source.

Source identification. Multi-element

analyses by ICP-MS of airborne samples collected at Ground Zero were used to generate

chemical profiles that could identify specific

sources of emission (Chillrud et al., unpublished data; McGee et al. 2003). These studies

relied on factor analyses. 

The principal emission sources identified

included a) torch-cutting and heating of steel

products (e.g., structural beams); b) combustion of building materials and contents;

c) resuspension of earth crustal materials; and

d) combustion of fossil fuels in engines with

catalytic converters. A quantitative source

apportionment analysis of ambient PM2.5

samples collected in lower Manhattan five

blocks from Ground Zero indicated that airborne emissions from several of these same

sources had spread to the surrounding community. Levels of WTC pollutants in the

nearby community declined rapidly after

September, and emissions from other conventional sources (e.g., oil heating combustion)

came to predominate as the fires subsided.

Mapping the WTC plume. To better

characterize the spatial distribution of the

material released to the atmosphere by the

destruction of the WTC, researchers at the

Lamont-Doherty Earth Observatory, the U.S.

Geological Survey (USGS), NASA (National

Aeronautics and Space Administration), the

U.S. EPA, and Analytical Imaging and

Geophysics, LLC (Boulder, CO, USA) used

images of lower Manhattan acquired on 16, 18,

and 23 September 2001 by NASA’s Airborne

Visible/Infrared Imaging Spectrometer

(AVIRIS). The resulting data had sufficiently

clear resolution (1.7 m) to quantify the structure of the plume within street canyons in

lower Manhattan (Chillrud et al., unpublished

data; Clark et al. 2003).

The AVIRIS images indicate that the

plume moved southeast from Ground Zero

on the afternoon of 11 September across

lower Manhattan and over areas of Brooklyn.

The optical opacity of the plume appeared to

diminish significantly from the fifth to the

seventh days and to the twelfth day postcollapse, probably reflecting overall weakening

of the fires during that time. On 16 and

18 September, the plume moved southward.

By 23 September the plume had become significantly weaker (McCurdy et al. 2000).

Pollution modeling and individualized

exposure assessment. Preliminary estimates of

the plume location and relative dilution models have been used to develop 8-hr average

characterizations of plume spread over

Manhattan and Brooklyn for the first 2 weeks

after 11 September. For the days immediately

after 11 September, this information

includes SPOT (Satellite Pour l’Observation

de la Terre) and LANDSAT satellite images,

NASA space station photographs, and

MODIS (Moderate Resolution Imaging

Spectroradiometer) images (Figure 5).

To go beyond the AVIRIS data and comprehensively model individual exposures from

the WTC plume, the high-altitude imagery is

being integrated with information on the geographic location of individuals within the epidemiologic study populations and with health

outcomes data. A nested/multiscale WTC

plume location and relative dilution model

being developed by the Environmental and

Occupational Health Sciences Institute

(EOHSI) will be used in this program to

reconstruct individual exposure profiles for

incorporation in the epidemiologic studies

within the NIEHS program.

Health Risk Assessment

Overview. Health risk assessments by the

NIEHS Centers began by identifying populations at high risk of exposure to WTC contaminants and then undertaking clinical and

epidemiologic studies within these groups

(Landrigan 2001). Future analyses will seek to

relate health outcomes data to geocoded

information on contaminant levels (McCurdy

et al. 2000).

Firefighters. Firefighters were among the

most heavily exposed populations. They also

suffered the greatest loss of life of all occupational groups. In the first 24 hr after the

attack on the WTC, 240 New York City firefighters sought emergency medical treatment;

of these, 50 (20.8%) received treatment of

acute respiratory symptoms caused by inhalation of airborne smoke and dust (Prezant

et al. 2002; Spadafora 2002). Firefighters

described walking through dense clouds of

dust and smoke in the hours immediately

after the attack, in which “the air was thick as

soup” (CDC 2002).

Follow-up medical evaluation of 10,116

firefighters was conducted over the 6 months

after the attack (Prezant et al. 2002). Persistent

cough accompanied by other respiratory

symptoms so severe as to require at least

4 weeks’ leave of absence, termed “World

Trade Center cough,” was diagnosed in

332 firefighters (Chen and Thurston 2002;

Scanlon 2002). Prevalence of WTC cough

was related to intensity of smoke exposure,

and occurred in 128 (8%) of 1,636 firefighters with a high level of exposure, in 187 (3%)

of 6,958 with moderate exposure, and in 17

(1%) of 1,320 with low-level exposure

(Figure 6). Among firefighters without WTC

cough, bronchial hyperreactivity was present

in 77 (23%) of those with a high level of

exposure, and in 26 (8%) of those with moderate exposure (Prezant et al. 2002). One case

of eosinophilic pneumonia was diagnosed in a

firefighter (Beckett 2002; Rom et al. 2002).

Induced sputum analysis of New York City

firefighters showed increases in sputum PM

levels as well as in neutrophil and eosinophil

counts. Those abnormalities were positively

correlated with levels of exposure to WTC

dust and combustion products, as well as with

levels of PAHs in the bodies of firefighters

(Edelman et al. 2003).

Cleanup and recovery workers. Many hundreds of workers were involved in clearing

rubble and transporting it off-site. To assess

Workgroup Report | Landrigan et al.

734 VOLUME 112 | NUMBER 6 | May 2004 • Environmental Health Perspectives
the occupational exposures and health status

of these workers, many of whom were truck

drivers, a team from the Bloomberg School of

Public Health at Johns Hopkins University

and the Mailman School of Public Health at

Columbia University undertook area air monitoring, personal exposure assessment, and

health studies.

Air monitoring was conducted in October

2001 and April 2002. It focused on PM,

asbestos, and VOCs. Monitoring was conducted across both day and night shifts,

7 days/week. Personal monitoring was conducted for 69 truck drivers. A total of 458 personal and area air samples were collected.

In October 2001, the highest concentrations of total dust were found at the debris

pile (median, 1,603 μg/m3). Total dust levels

on the pile in October were approximately

five times higher than at the perimeter. By

April 2002, total dust concentrations of the

site had become significantly lower and were

more uniformly distributed. In October

2001, median personal particulate exposure

was 323.7 μg/m3. By April 2002, median

exposure had fallen to 137.7 μg/m3. Airborne

asbestos concentrations were found to be generally low. The fibers detected were mostly

very short. Concentrations of VOCs were

generally low.

To assess prevalence of respiratory symptoms and lung dysfunction, a cross-sectional

clinical and epidemiologic study was initiated

in December 2001. A convenience sampling

strategy was used to recruit workers on-site.

Inclusion criteria required that participants be

at least 18 years of age, employed at the site,

and willing to answer a respiratory health questionnaire. Informed consent was obtained from

all participants. Chronic respiratory symptoms

were assessed using an interviewer-administered questionnaire adapted from the American

Thoracic Society questionnaire. Spirometric

measurements were performed using American

Thoracic Society guidelines (American

Thoracic Society 1994) to characterize lung

function and to identify individuals with lung

function below the normal range. Two trained

pulmonary function technicians certified by

the National Institute for Occupational Safety

and Health (NIOSH) conducted all spirometric assessments. Questionnaires and spirometry

were administered to 183 rubble removal

workers.

Among the 183 workers surveyed, a high

proportion (32.8%) reported experiencing

cough that began after the start of employment at the WTC site; 24.0% reported new

onset of phlegm production; and 17.5%

reported new onset of wheeze. Approximately

half of all workers reported that they had experienced at least one new symptom since they

had begun working at the WTC site. The

average percentage of predicted values for

forced expiratory volume in 1 sec (FEV1) and

forced vital capacity (FVC) were 96.3% and

98.8%, respectively, and the mean FEV1:FVC

ratio was 80.5%.

Community residents. To assess prevalence of new-onset respiratory symptoms after

11 September 2001 among previously healthy

persons in lower Manhattan as well as in residents with preexisting asthma, a team from

NYU Medical Center in collaboration with

the New York State Department of Health

and the New York Academy of Medicine

conducted a clinical and epidemiologic survey

(Reibman et al. 2003). Symptoms were

assessed by questionnaire, and pulmonary

Workgroup Report | Consequences of the WTC disaster

Environmental Health Perspectives • VOLUME 112 | NUMBER 6 | May 2004 735

Figure 5. AVIRIS imagery of lower Manhattan acquired on 16 September 2001. (A) Visible color composite of the plume (RGB = 0.66/0.55/0.44 μm). (B) The shortwavelength visible blue band (0.44 μm) shows the extent of aerosol scattering as brighter areas. (C) The near-infrared band ratio (0.94 μm/0.86 μm) indicates the

spatial extent of the plume.

A B C

Figure 6. Prevalence of persistent cough in New

York City firefighters exposed to smoke and dust

from the WTC, September 2001 through March 2002.

Data from Prezant et al. (2002).

Low

Moderate

High

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

Prevalence (%)

Exposure category

n = 1,320

n = 6,958

n = 1,636
function was evaluated in a subset of the

study population by standard screening

spirometry.

A total of 2,166 residents of lower

Manhattan living within a 1.6-km radius of

the WTC were enrolled in this survey and

compared with 200 persons living 1.6–8.0 km

distant. Spirometry was performed in 52 residents. Preliminary data indicate that previously healthy persons living near Ground Zero

had a greater increase in prevalence of respiratory symptoms after 11 September than did

more distant residents. These symptoms were

predominantly cough, wheeze, and shortness

of breath. Symptoms were not associated with

abnormal screening spirometry.

Preexisting asthmatic residents in the

exposed area also reported a higher prevalence

of respiratory symptoms after 11 September.

They also reported an increased use of asthma

medication relative to controls.

Toxicologic studies. To complement the

clinical and epidemiologic studies of workers,

toxicologic examinations of WTC dust were

performed (Gavett et al. 2003).

Methodology. Samples of PM2.5 were

obtained by size fractionation of bulk settled

WTC dust. These samples were chemically

characterized (McGee et al. 2003). Consistent

with findings in the total bulk dust samples,

these samples were found to contain Ca, sulfur,

and Ca–carbon particles. Levels of Ca ranged

from 22 to 33%, and sulfur (as sulfate) ranged

from 37 to 43%. Only very low levels of transition and metallic elements were present.

These samples were administered to mice by

aspiration in doses of 10, 31.6, or 100 μg. The

samples administered included WTC PM2.5

from seven individual collection sites, a sample

pooled from these seven locations (WTCX),

and a sieved sample from an eighth location

(WTC3). Comparison PM2.5 samples were

derived from Mount Saint Helen’s dust, residual oil fly ash (ROFA), and NIST Standard

Reference Material 1649a (urban PM from

Washington, DC). 

Results. Aspirated samples of WTCX

PM2.5 were found to induce a mild to moderate

degree of pulmonary inflammation in rodents

at a relatively high dose (100 μg) (Figure 7).

This inflammatory response was not as great

as that caused by ROFA or NIST 1649a

(Gavett et al. 2003).

A 100-μg dose of WTC PM2.5 was found

to cause a striking degree of airway hyperresponsiveness to methacholine aerosol. This

hyperresponsiveness was comparable with that

produced by NIST 1649a and greater than

that produced by ROFA (Figure 8). Although

the pulmonary neutrophilic inflammation

observed in exposed mice diminished 1–3

days after exposure, the hyperresponsiveness to

methacholine did not diminish significantly in

that time period.

Mice exposed to lower doses of pooled

WTC PM2.5 (10 μg and 31.6 μg) and mice

exposed by nose-only inhalation manifested

neither neutrophilic inflammation nor methacholine responsiveness. No variation in

response was noted in relation to the geographical locations at which the dust samples

had been collected.

Pregnant women and their offspring.

Many pregnant women were either working in

the WTC or working or residing in the communities of lower Manhattan on 11 September

2001. To assess pregnancy outcomes in these

women and impacts on their infants, teams

from the Mount Sinai School of Medicine and

the Mailman School of Public Health of

Columbia University established complementary prospective epidemiologic cohort studies.

Populations. The Mount Sinai population

consisted of 187 pregnant women who were

either in or near the WTC on 11 September

(Berkowitz et al. 2003). Twelve were actually

inside the towers, and an additional 122

(65%) were within 10 blocks. A comparison

group (n = 2,367) consisted of all private

patients not known to have been near the

WTC who delivered at Mount Sinai Hospital

during the same time period.

The racial/ethnic composition of the

exposed group in the Mount Sinai study was

72.5% white, 11.0% African American, 6.6%

Hispanic, 3.9% Asian, and 6.0% of mixed or

other race/ethnicity. Participants were relatively old: 15.4% were younger than 30 years

of age, 40.1% were 30–34 years of age, 33.0%

were 35–39 years of age, and 11.5% were ≥ 40

years of age. The women in the Mount Sinai

study were evenly distributed by trimester of

pregnancy on 11 September. Of the 187

women originally recruited into the study,

3 miscarried and 2 were lost to follow-up, leaving 182 participants with live births. The last

delivery occurred in June 2002. Deliveries took

place at 47 hospitals in the New York City

area. The Mount Sinai School of Medicine

team is collaborating with EOHSI exposure

modelers who are developing individualized

exposure profiles for each woman based on

their location (e.g., in an affected structure, in

a downwind location) and the time spent in

each location (indoors and outdoors) in the

days and weeks after 11 September. 

Workgroup Report | Landrigan et al.

736 VOLUME 112 | NUMBER 6 | May 2004 • Environmental Health Perspectives

Figure 7. Number of cells recovered by bronchoalveolar lavage from mice 1 day after aspiration of PM samples in saline or saline vehicle alone. (A) Macrophages. (B) Neutrophils. MSH, Mount Saint Helen’s dust.

*Significantly greater number of neutrophils than for saline control groups.

50

40

30

20

10

0

25

20

15

10

5

0

Saline 0

MSH

100

ROFA

10

ROFA

100

WTCX

10

WTCX

31.6

WTCX

100

Cells (× 104)

Cells (× 104)

*

* *

Dose (μg)

A B

Saline

0

MSH

100

ROFA

10

ROFA

100

WTCX

10

WTCX

31.6

WTCX

100

Dose (μg)

Figure 8. Airway responsiveness to methacholine aerosol in mice exposed to PM sample or saline vehicle and

tested 1 day later. Penh (enhanced pause) is an indicator of airway resistance; changes in Penh have been

demonstrated to correlate with changes in airway resistance during methacholine challenge.

*Significantly more responsive than all other groups. **Significantly more responsive than all except the WTCX 100-μg

group.

Dose (μg)

Sensitivity to methacholine

(Penh area under curve: Penh-sec)

4,800

4,000

3,200

2,400

1,600

800

0 Saline

0

MSH

100

ROFA

10

ROFA

100

WTCX

10

WTCX

31.6

WTCX

100

Methacholine (mg/mL)

0

4

8

16

32

64 **

*
The population in the Columbia study

consisted of 329 women who were recruited

when they arrived in labor at one of three hospitals in lower Manhattan (Beth Israel Medical

Center, NYU Downtown Hospital, as well as

its affiliated St. Vincent’s Hospital and Medical

Center, and its affiliated Elizabeth Seton

Childbearing Center). Women were eligible to

participate if they were between 18 and

39 years of age, were not having a multiple

birth, had not smoked during pregnancy, did

not report having had any of a list of specified

health conditions, and provided a maternal

(n = 211) and/or cord (n = 290) blood sample.

Women’s eligibility for participation in the

exposed (n = 160) or control (n = 169) groups

was based on the distance of their residence

and work sites from the WTC and the number

of hours they had spent at these locations during the 2 weeks after 11 September 2001. All

women were enrolled between 13 December

2001 and 27 June 2002.

The 329 women in the final Columbia

sample were 40% white, 34% Asian, 15%

African American, and 10% “other” or not

reported. Twenty-one percent also identified

themselves as Hispanic. The languages of

interviews were English, 76%; Mandarin,

21%, Spanish, 1.5%, and Cantonese, 1.2%.

Over 80% of the women were married or

cohabiting > 7 years. Average educational

attainment was 13.9 years; 18.5% of the subjects did not have a high school diploma, and

42% had at least a college degree. Household

incomes of ≤ $50,000 were reported by

55.7% of the women who reported incomes.

Continuing follow-up. The Mount Sinai

team is currently following the infants. In addition to obtaining indices of growth, two assessments of early cognitive development have

been performed: the Fagan Infantest and the

Visual Expectation Paradigm (Canfield et al.

1997; Canfield and Kirkham 2001; Jacobson

et al. 1992; Shepherd and Fagan 1987). To

date, cognitive assessments at 9 months of age

have been completed on 159 infants. Further

follow-up assessments are planned to at least

3 years of age.

In the Columbia study, participants were

reinterviewed by phone when infants reached

6 months of age. Information was sought

regarding the diet of each child as well as

breast-feeding patterns. All hospitalizations

and their causes were recorded. Two hundred

ninety-four women completed this interview.

To assess cognitive and motor function, the

Bayley Scales of Infant Development (Bayley

and Gyurke 1993) is being administered at

the 1-year follow-up visit. Each child’s

weight, height, and head circumference were

measured. The mother was reinterviewed at

this meeting to determine any changes in key

variables, to obtain details about the mother’s

and infant’s health and postnatal exposures,

and to complete the list of the infant’s hospitalizations through the first year of life.

Pregnancy outcomes. In the Mount Sinai

cohort, no significant differences were found

between the groups in mean gestational age or

mean birth weight. There were no significant

differences in frequency of preterm births

(< 37 weeks of gestation) or in incidence of low

birth weight (Table 2) (Berkowitz et al. 2003).

However, the Mount Sinai WTC cohort

had a 2-fold increased risk of small-forgestational-age (SGA) infants, defined as

infants with a birth weight below the 10th percentile for gestational age in the nomogram of

Brenner et al. (1976) (Table 2). This statistically significant difference was still evident after

controlling for relevant covariates and potential

confounders, including maternal age, parity,

race/ethnicity, sex of the infant, and maternal

smoking history. No significant difference in

the frequency of SGA infants was observed

according to the trimester of pregnancy on

11 September. No associations were evident

between symptoms of posttraumatic stress,

based on the PTSD Checklist (Schlenger et al.

2002), and frequency of preterm birth, low

birth weight, or SGA infants.

In the Columbia study, there was no difference between the exposed and control

groups in newborn birth weight (3,377 vs.

3,459 g), length, head circumference, or

Apgar scores, but gestation duration was significantly shorter in the exposed group (274.3

vs. 275.9 days; p = 0.045). The study groups

did not differ significantly in maternal age,

height, prepregnancy weight, parity, or marital

status, but the exposed group had 1 more year

of education (14.4 vs. 13.4 years; p < 0.05).

Discussion

This report presents the most comprehensive summary to date of the environmental

exposures resulting from the attack on the

WTC and of their effects on human health.

Our main focus was on chemical exposures.

Our findings complement earlier reports

describing the acute physical consequences of

the disaster (CDC 2002; Prezant et al. 2002)

and its psychological impacts (Boscarino et al.

2002; Fairbrother et al. 2003; Galea et al.

2002a, 2002b; Stuber et al. 2002; Vlahov

et al. 2002a, 2002b).

Our assessments show that exposures to

chemical contaminants were not uniform in

New York after 11 September (Clark et al.

2003; Lioy et al. 2002; McGee et al. 2003;

Offenberg et al. 2003). Instead, there were

sharp gradients by time after the attack and by

distance from Ground Zero (Table 1). In the

first few hours, extremely heavy exposures to

high levels of dust and smoke as well as to

gaseous products of combustion predominated. This pattern continued for the next

2 days, when there occurred rapid decline of

smoke and dust levels and continuing decline

in levels of combustion products as jet fuel and

flammable building contents were consumed.

A large fraction of the outdoor dust was eliminated over the first weekend after the disaster

by rain that fell on Friday, 14 September, and

by the U.S. EPA’s cleanup of the Wall Street

area. Over the next several weeks, airborne particulate levels in lower Manhattan continued to

decline but rose intermittently at night and

when the air was still. Transient increases were

noted also when the pile was disturbed and

fires flared. Diesel exhaust became an important contaminant with the arrival on site of

scores of cranes, heavy trucks, and other construction equipment. For weeks, an acrid cloud

hung over lower Manhattan and areas of

Brooklyn until the fires were finally extinguished on 20 December.

Asbestos was of great concern to the public

in New York City and to government agencies

after 11 September. Asbestos, principally

chrysotile, was used in the early 1970s in construction of the WTC as fireproofing up to the

40th floor of the North Tower (Nicholson

et al. 1971; Reitze et al. 1972). Asbestos was

not used beyond that point because of the

recognition of its hazard and its replacement in

the remainder of the construction with nonasbestiform fireproofing materials. Although

some of this asbestos had been removed over

the preceding 30 years, hundreds of tons

remained on 11 September 2001 and were

blasted free. Ambient air samples showed that

asbestos exposures were initially elevated but

fell to within U.S. EPA standards after the first

few days (U.S. EPA 2004). Asbestos was found

in settled dust at Ground Zero in concentrations ranging from 0.8 to 3.0% (Lioy et al.

2002). Asbestos was found in dust in nearby

apartments, sometimes at higher levels than in

the outside environment (Lioy et al. 2002).

Airborne lead levels were elevated in the

first days after 11 September, but never highly.

Workgroup Report | Consequences of the WTC disaster

Environmental Health Perspectives • VOLUME 112 | NUMBER 6 | May 2004 737

Table 2. Pregnancy outcomes in relation to the attack on the WTC, September 2001 through June 2002.

WTC group Control group p-Value

No. 187 2,367 —

Mean gestational age (weeks) 39.1 39.0 0.55

Mean birth weight (g) 3,203 3,267 0.14

Frequency of preterm birth (%) 9.9 9.2 0.76

Frequency of low birth weight (%) 8.2 6.8 0.47

Frequency of SGA infants (%) 8.2 3.8 < 0.01

Data from Berkowitz et al. (2003).
There is little indication that ambient air lead

exposures posed substantial health risks to the

population of lower Manhattan (U.S. EPA

2004).

Airborne dioxin levels were elevated substantially above normal urban background

levels in the initial days after 11 September.

The U.S. EPA’s initial risk analysis suggests

that these elevations did not result in a significant elevation in cancer or noncancer risk

(U.S. EPA 2003). Further follow-up of

exposed populations will be required to evaluate the accuracy of that assessment.

Risks to health were determined by the

timing, duration, and chemical composition of

exposures as well as by proximity to Ground

Zero. Firefighters, police, and other first

responders sustained heaviest initial exposures.

Studies of firefighters confirmed the presence

of a positive relationship between intensity and

duration of exposure and severity of pulmonary effects (Figure 6) (Prezant et al. 2002)

as well as of PM levels in sputum. Prolonged

exposures occurred among firefighters and

other public safety personnel who remained at

Ground Zero as well as among construction

workers, volunteers, and workers removing

rubble (Levin et al. 2002; Lippy 2002).

Workers cleaning nearby buildings may also

have sustained potentially serious exposures

(Malievskaya et al. 2002).

Health data from the study of rubble

removal workers confirm that these workers,

many of whom worked at Ground Zero for

many months, had sustained clinically significant exposures to airborne irritants, resulting

in symptoms consistent with upper and lower

airway inflammation (Levin et al. 2002). To

extend these initial studies, the team at

Mount Sinai has initiated the World Trade

Center Worker and Volunteer Medical

Screening Program. This program, supported

by NIOSH, has already examined more than

10,000 workers. These workers will be followed prospectively to assess long-term and

delayed effects.

Toxicologic studies have elucidated the

pathophysiologic mechanisms underlying the

clinical findings seen in worker populations

(Gavett et al. 2003). High-dose exposures to

fine airborne particulates (PM2.5) from the

WTC, such as occurred in the immediate

aftermath of the collapse, were shown in mice

to produce mild to moderate degrees of respiratory inflammation and a very striking degree

of hyperresponsiveness of airways. A property

of the dust that appears to have contributed to

its intense respiratory irritability was its high

alkalinity (Lioy et al. 2002; McGee et al.

2003). Larger particles composed principally

of cement dust were especially alkaline

(pH 9.0–11.0). These particles were of a size

likely to be caught in the upper airways. Along

with inhaled glass fibers, they were probably

responsible for the intense irritation of the

nasal passages as well as for the chronic debilitating cough observed in heavily exposed

populations (Chen and Thurston 2002;

Scanlon 2002; Thurston and Chen 2002).

Further experiments will be necessary to

determine whether the pulmonary hyperresponsiveness observed in mice is persistent.

Such research may provide insights also into

the anticipated duration of the pulmonary

effects in workers. Factors that may influence

persistence in workers include level of exposure, use of respiratory protection, individual

differences in sensitivity, and interspecies 

differences.

Airborne exposures in the residential and

business communities of lower Manhattan

beyond Ground Zero were much lower than

those sustained by workers (U.S. EPA 2004).

Daily average levels of fine particulate pollution in these communities were generally

within U.S. EPA limits when averaged over a

24-hr period. Higher short-term peaks were,

however, observed especially at night and

could have contributed to reported health

effects, especially in susceptible populations

such as children, the elderly, and persons with

respiratory or cardiac disease. Indoor exposures to resuspended dust may have added to

total exposures (Lioy et al. 2002). Residents in

these communities reported an increased frequency of new-onset pulmonary symptoms

(Reibman et al. 2003) but had no abnormalities

on pulmonary function testing. These findings

are consistent with the observed gradient of

exposures.

An increase in incidence of SGA was the

major adverse health effect seen in infants

born to women who were inside the towers or

within approximately 10 blocks of the WTC

on 11 September (Berkowitz et al. 2003).

Incidence of SGA infants was 2-fold greater

among the WTC mothers than in a demographically similar comparison population

not known to have been in lower Manhattan

on 11 September 2001 (p < 0.01).

SGA is an index of intrauterine growth

restriction (IUGR). Biologically plausible

causes of IUGR in these babies include exposures to fine PM and PAHs. Previous studies

have found associations between particulate

air pollution and IUGR (Bobak et al. 2001;

Dejmek et al. 1999); other investigations have

linked air pollution to preterm births (Ritz

et al. 2000). High levels of PAH–DNA

adducts in umbilical cord leukocytes have

been associated with reduced birth size

(Perera et al. 1998). Prenatal exposure to cigarette smoke, which contains PAHs among

other toxins, is a well-established risk factor

for IUGR. Maternal stress is another possible

cause of the observed increase in SGA, but we

were unable to detect any correlation between

reported levels of stress and SGA incidence.

Important questions about possible future

risks to health of persons exposed to contaminants from the WTC remain unanswered:

• Will pulmonary disease persist in workers

exposed to dust, especially in those who sustained very heavy exposures in the first days

after 11 September and those with prolonged

exposures?

• Will an increased incidence of mesothelioma

result from exposures to asbestos? All types of

asbestos fibers have been shown in laboratory

as well as clinical studies to be capable of causing mesothelioma (Nicholson and Landrigan

1996). Pathologic studies have found short

chrysotile fibers, the predominant type of

fiber in WTC dust, to be the predominant

fiber in mesothelioma tissue (Dodson et al.

1991; LeBouffant et al. 1973; Suzuki and

Yuen 2002). Mesothelioma has been reported

in persons with relatively low-dose, nonoccupational exposure to asbestos (Anderson

1982; Camus et al. 1998; Magnani et al.

2001). The greatest future risk of mesothelioma would appear to exist among first

responders who were enveloped in the cloud

of dust, other workers employed directly at

Ground Zero, and workers employed in

cleaning asbestos-laden dust from contaminated buildings. The risk of mesothelioma to

residents of lower Manhattan must be considered to be extremely low but may still be elevated above background.

• Will exposure to airborne dioxin in lower

Manhattan in the days and weeks after

11 September increase risk of cancer, diabetes,

or other chronic disease (Kogevinas 2001)?

• Will the increased frequency of SGA

observed in babies born to women who were

within or near the WTC on 11 September

result in long-term adverse effects on growth

or development (Berkowitz et al. 2003)?

Full elucidation of these and other questions concerning the long-term and delayed

health effects of exposures resulting from the

attack on the WTC will require continuing,

prospective, multiyear clinical and epidemiologic follow-up and further refinement of

exposure assessments. That work is under way.

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