972 VOLUME 111 | NUMBER 7 | June 2003 • Environmental Health Perspectives

World Trade Center | Mini-Monograph

The attack on the World Trade Center (WTC)

in New York City on 11 September 2001, in

addition to causing the immediate and tragic

loss of thousands of lives, resulted in the release

of significant quantities of pollutants into the

environment of the surrounding neighborhoods, including particulate matter (PM),

asbestos, metals, and organic compounds [U.S.

Environmental Protection Agency (U.S. EPA)

2002b]. Dust infiltrated indoors into homes

and apartments, in many cases up to several

inches in depth. Fires at the WTC site continued for several months before finally being

extinguished, and recovery and reconstruction

efforts contributed to emissions of fine [particulate matter with a mass median aerodynamic

diameter (MMAD) < 2.5 μm; PM2.5], coarse

(> 2.5 and < 10 μm; PM2.5–10), and larger

(> 10 μm) PM fractions. As people have

returned to their residences and businesses,

potential exposure issues are associated with

redispersal of residual dust.

Recent studies have assessed the chemical

and physical properties of bulk samples of

WTC PM. The dust particles from the WTC

site appear to be quite alkaline in nature,

probably because of partial dissolution of concrete, gypsum, and glass fiber particles [U.S.

Geological Survey (USGS) 2002]. Lioy and coworkers (2002) found that bulk settled–dust

samples of WTC PM were composed of particles of cement, carbon, cellulose, and several

fiber types including mineral wool, fiberglass,

cellulose, and asbestos. These authors also

found significant concentrations of phthalate

esters, polycyclic aromatic hydrocarbons

(PAHs), and other hydrocarbons (Offenberg

et al. 2003). However, a detailed analysis of

the PM2.5 fraction of WTC dust has not been

previously reported.

Exposure to ambient air PM has been

associated with both acute and chronic

adverse health effects, especially in sensitive

populations (Dockery et al. 1993). Both fineand coarse particles are readily inhaled into

the human respiratory tract. Reviews of current literature suggest that fine particles are

more strongly implicated in cardiovascular

effects than coarse particles, while both impact

respiratory end points (U.S. EPA 2002c). Fine

particles are typically formed from gases or

from combustion processes, whereas coarse

particles are produced by mechanical breakdown of crustal material. However, the PM2.5

size range may also include a significant fraction of coarse particles that are broken down

into smaller particles by strong mechanical

forces (U.S. EPA 2002d). The unique situation of the WTC disaster may have generated

a significant amount of crustal (building)

material–derived particles in the PM2.5 size

range. Although PM2.5–10 may have adverse

health effects, quantities of WTC PM samples

in this size range were limited (see “Size

fractionation of bulk samples” in “Materials

and Methods”). In addition, PM2.5 is very relevant toxicologically, as it is associated with

epidemiologic findings of adverse health

effects in humans (Dockery et al. 1993).

Consequently, our objective in this article was

to describe the collection, size fractionation,

and chemical analysis of samples of WTC

PM2.5 for use in toxicologic studies. To determine whether respirable WTC PM2.5 is more

or less toxic than typical ambient air PM2.5,

we compared the toxicity of WTC PM2.5 with

well-characterized reference PM2.5 samples in

a companion article (Gavett et al. 2003).

In this study we collected samples of

settled dust from several sites in the immediate vicinity (< 0.5 miles) of Ground Zero on

12 and 13 September 2001. Samples were

separated into fine, coarse, and larger fractions that could be studied for toxicologic

effects. We thoroughly characterized the

WTC PM2.5 samples using a number of

chemical and physical techniques to compare

Chemical Analysis of World Trade Center Fine Particulate Matter for Use 

in Toxicologic Assessment

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

This article is part of the mini-monograph “World

Trade Center Fine Particulate Matter—Chemistry

and Toxic Respiratory Effects.”

Address correspondence to S.H. Gavett, Pulmonary

Toxicology Branch (Mail Code B143-02), U.S. EPA,

Research Triangle Park, NC 27711 USA. Telephone:

(919) 541-2555. Fax: (919) 541-0026. E-mail:

gavett.stephen@epa.gov

Acknowledgments of personnel and financial support have been placed at the end of this article.

This paper has been reviewed and approved for

release by NHEERL, 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 conflict of interest.

Received 12 August 2002; accepted 18 November

2002.

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 (PM2.5)],

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 PM2.5 fraction was isolated on filters. Here we report the chemical and physical properties of PM2.5 derived from these samples and

compare them with PM2.5 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 PM2.5 fraction. Analysis

of WTC PM2.5 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 PM2.5

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 PM2.5 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). doi:10.1289/ehp.5930 available via http://dx.doi.org/ [Online

20 November 2002]
the composition of these samples with other

well-studied PM2.5 reference samples. Solid

samples of WTC and reference PM2.5 were

analyzed by scanning electron microscopy

(SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), carbon fraction analysis, and

neutron activation analysis (NAA). Analyses

were also carried out on water-extracted or

1 M hydrochloric acid–extracted suspensions

of WTC and reference PM2.5, including

pH, endotoxin, and inductively coupled

plasma–mass spectrometry (ICP-MS) and

inductively coupled plasma–atomic emission

spectrometry (ICP-AES). The analytical

results will contribute to the understanding of

the composition and possible mechanisms of

toxicity of PM2.5 derived from the destruction

of the WTC.

Detailed experimental findings of these

studies are available in a U.S. EPA report

(2002a).

Materials and Methods

Collection of World Trade Center PM samples.

Using a paper scoop, we sampled several outdoor locations as well as one indoor location,

all of which appeared undisturbed since the

collapse of the towers, as judged by the presence of a smooth uniform layer of dust and

the absence of indicators of recent human

activity. All samples were collected within a

half-mile of Ground Zero and labeled with

numbers (1–13) on 12 September 2001, and

letters (A–F) on 13 September 2001. After

examination of the available inventory of

samples, we selected seven locations (8, 11,

13, B, C, E, and F) to assess toxicity of samples from different geographical locations as

well as overall toxicity of a pooled sample

from these locations (Figure 1). The locations

were selected to represent a distribution surrounding Ground Zero, with more collection

sites in the east reflecting the direction of the

predominant winds during the collapse of the

WTC towers and surrounding buildings.

Size fractionation of bulk samples. Bulk

samples of the seven dust samples described

above were sieved with a 53-μm diameter mesh

screen (USA Standard Testing Sieves; Fisher

Scientific, Pittsburgh, PA) on a shaker

(Portable Sieve Shaker; Tyler Industrial

Products, Mentor, OH). We processed the

sieved material (PM53) in an apparatus

designed to isolate different PM fractions

(Figure 2). The PM53 fraction was aerosolized

through a 10-μm aerodynamic diameter cut

Wedding inlet (Anderson Instrument Co.,

Fultonville, NY) to remove particles in the

10–53 μm range and isolate the PM10 fraction.

The PM10 fraction was then passed through a

2.5-μm cut cyclone (BGI, Inc., Waltham, MA)

to remove the coarse fraction. The PM2.5 fraction was collected on Teflon filters (Zefluor

Supported PTFE, 2-μm pore size, 47-mm

diameter; Pall Gelman Sciences, Port

Washington, NY). Ten to 40 filters were

used in the size fractionation of each WTC

sample. Roughly half the sample was in the

PM53-sieved fraction. About 80–89% of the

PM53 fraction was in the 10- to 53-μm size

range, which is too large to use in respiratory

toxicology studies, as deposition of particles

>5μm is minimal in small laboratory animals

(Raabe et al. 1988). The amount of the 2.5- to

10-μm fraction was very small (0.04–1.14% of

the PM53 fraction, except 3.23% in sample 13)

and was therefore not feasible to study. The

PM2.5 fraction, however, was present in sufficient amounts (2.29–4.06% of PM53 fraction)

to study for potential respiratory health effects.

The sum of the size fraction percentages does

not total 100% of the original PM53 fraction

because of sample loss during fractionation.

After overnight desiccation, filter weights were

determined using an electrobalance (Model

C-30; Thermo Cahn, Madison, WI). A total

quantity of about 50 mg from each site, collected on 1–3 filters per site, was used in the

study (Table 1). Mechanical scraping did not

efficiently remove the PM2.5 from the filters, so

it was necessary to isolate the PM2.5 using an

aqueous extraction procedure.

Extraction of PM2.5 from Teflon filters.

Filters containing the PM2.5 fraction were

extracted using a modification of a method by

Biran and co-workers (1996). Filters from

each of the seven individual collection sites

were extracted into distilled water (Gibco

Invitrogen, Carlsbad, CA) in the ratio of

0.5 mL/mg sample (24.96–27.14 mL water).

Mini-Monograph | Chemical analysis of WTC PM2.5

Environmental Health Perspectives • VOLUME 111 | NUMBER 7 | June 2003 973

Figure 2. Apparatus used to separate bulk samples

of WTC PM into different size fractions. Sieved

WTC dust (PM53) was aerosolized in the resuspension chamber (A), then passed through a 10-μm cut

inlet (B) and a 2.5-μm cut cyclone (C). PM2.5 were

collected on Teflon filters (D) and pulled through by

a pump (E).

Figure 1. WTC dust samples were collected by New York University scientists from 13 sites on

12 September 2001 (numbers) and from 6 sites on 13 September 2001 (letters). Collection sites are shown

only for samples reported in this article. Map reference: U.S. Census Bureau (2002).
This volume of water was pipetted into a

100-mL sterile plastic cup containing a

3 mm–thick Teflon ring on the bottom

designed to support the filter. Each filter was

wetted with 200 μL 70% ethanol on the particle side, placed on top of the ring with the

particle side down, and a 6 mm–thick Teflon

ring was placed on top of the filter. The cup

with the filter was placed on ice and secured to

an orbital shaker (Titer Plate Shaker; Lab-Line

Instruments, Melrose Park, IL). Samples were

shaken at a low speed and sonicated for

30 min at a power setting of 30 (Sonic 300

Dismembrator; Artek Systems Corp.,

Farmingdale, NY). Ten milliliters was pipetted from each of the seven samples into a single sterilized 150-mL Erlenmeyer flask on ice

to make a pooled sample (WTCX). The pH

of the pooled and individual site samples was

determined immediately after extraction

(Model 440; Corning Incorporated, Corning,

NY). Sonicated filters were desiccated before

reweighing to determine quantity extracted

(i.e., removed) from the filters (Table 1).

Pooled and individual site samples were frozen

at –80°C and lyophilized for 2 days at –55°C

and 140 mtorr (Virtis Company, Gardiner,

NY). Lyophilized samples were stored at 4°C

and subsequently brought to room temperature

for chemical or physical analysis, or for use in

toxicologic studies in mice (Gavett et al. 2002).

Sample used for inhalation exposure toxicity testing. Because we needed to conduct a

nose-only inhalation exposure study to assess

upper airway responses of test animals (Gavett

et al. 2003), a sufficient quantity of sample

was necessary for the exposure system (> 2 g).

As there was not enough PM2.5 or PM2.5–10

sample available to conduct this study, we

decided to use a PM53 sample (sieved but not

further fractionated) that was available in sufficient quantity to run through the inhalation

exposure system. The inhalation exposure system uses a 2.5-μm cut cyclone to remove

larger particles (Ledbetter et al. 1998), and

therefore measurement of the PM concentration in the exposure zone of the chamber represents exposure to PM2.5. A sample of PM53

from location no. 3 (Figure 1; WTC3 in

Table 1), 0.3 miles east of Ground Zero (in

the predominant wind direction), was available in sufficient quantities for the nose-only

inhalation exposure study.

Control PM samples. To assess the relative

toxicity of WTC PM2.5, pooled and individual

site samples were compared with three other

well-characterized control PM2.5 samples. We

chose samples representing an urban ambient

PM with moderate toxicity, a crustal PM with

low toxicity, and an emission source PM with

high toxicity (Table 1). National Institute of

Standards and Technology (NIST) Standard

Reference Material (SRM) 1649a is an urban

ambient PM collected in the Washington, DC,

area in 1976–1977 over a 12-month period

and represents a time-integrated sample (NIST

2001). This material was selected for comparison of toxicity of WTC PM2.5 with other typical urban air PM2.5 (albeit from an earlier era

when leaded gasoline was still in use). This

material was collected as a total suspended particulate (TSP) sample with a large amount of

coarse PM and larger nonrespirable PM.

Consequently, SRM 1649a was size-fractionated and extracted using the procedures

described above for comparison with the WTC

PM2.5 samples.

WTC PM2.5 was also compared with a previously size-separated PM2.5 fraction of ash

from Mt. St. Helens (MSH) in Washington

State (Graham et al. 1985). About half of MSH

is crystalline in nature, primarily plagioclase, a

series of compounds beginning with sodium

aluminum silicate (NaAlSi3O8) and ending

with calcium aluminum silicate (CaAl2Si2O8)

that show continuous solid solution from albite

to anorthite, with CaAl replacing NaSi as the

series progresses. The remaining portion is

amorphous (glass) and contains minor amounts

of cristobalite (3%) and quartz (< 1%). The

PM2.5 fraction of MSH has low toxicity in rats

and mice (Hatch et al. 1984).

Residual oil fly ash (ROFA) is a PM sample with a high content of bioavailable transition metals including vanadium (V), nickel

(Ni), and iron (Fe). Numerous studies have

demonstrated that these metals are associated

with lung injury in both healthy animals and

animal models of cardiopulmonary injury

(Dreher et al. 1997; Gavett et al. 1999;

Kodavanti et al. 1998). For this study, we

chose a sample of ROFA (no. 3; Kodavanti

et al. 1998) from a boiler system that is toxic,

yet not as soluble in water as previous samples

of ROFA, and is therefore more comparable to

WTC PM samples, which are not extremely

water soluble. ROFA sample no. 3 has an

MMAD of 2.665 μm, slightly larger than

other PM2.5 samples used in this study but still

acceptable for toxicity testing.

Overview of analytical methods. Analytical

chemistry of WTC, SRM 1649a, MSH, and

ROFA PM2.5 samples entailed measurements

of both solid samples and their liquid extracts.

Solid (including lyophilized) samples were

characterized by SEM/energy dispersive X-ray

analysis (SEM/EDX), XRD, NAA, XRF, and

carbon fraction analysis of the organic, elemental, and carbonate fractions (OC/EC/CC).

Deionized water extracts were characterized by

pH, endotoxin, and ion chromatography (IC)

analysis. Elemental and sulfate (SO4) content

Table 1. Description of samples used in study.

Extracted

Sample Collection Size Total weight weight (mg)

code date Location, description fraction on filters % Extracted

WTC site samples

WTC8 12 Sept. 2001 Beekman St.: filters #9, #14 PM2.5 53.316 mg 46.70

0.4 miles E of Ground Zero 87.6

WTC11 12 Sept. 2001 55 Church St.: filters #13, #14, #15 PM2.5 50.097 mg 29.79

In front of Millennium Hilton Hotel 59.5

0.1 miles E of Ground Zero

WTC13 12 Sept. 2001 Church and Liberty Sts.: filters #4, #5 PM2.5 51.006 mg 46.29

0.1 miles SE of Ground Zero 90.8

WTCB 13 Sept. 2001 Trinity Pl. and Rector St.: filter #4 PM2.5 52.969 mg 42.31

From a car hood and windshield 79.9

0.25 miles S of Ground Zero

WTCC 13 Sept. 2001 Winter Garden Park: filters #4, #7 PM2.5 54.285 mg 47.67

From a park bench facing the Hudson River 87.8

0.2 miles WNW of Ground Zero

WTCE 13 Sept. 2001 Murray and Greenwich Sts.: filters #5, #6 PM2.5 49.919 mg 45.13

From a window ledge 90.4

0.25 miles NNE of Ground Zero

WTCF 13 Sept. 2001 Inside 120 Broadway: filters #2, #12 PM2.5 53.600 mg 38.73

From a marble staircase with no footprints 72.3

0.25 miles SE of Ground Zero

WTC3 12 Sept. 2001 23 Park Row: ground sample in front of PM< 53 21.521 g Not extracted;

J&R Electronics (across City Hall Park) sieved size-separated

0.3 miles E of Ground Zero material during exposure

Control PM samples

SRM 1976–1977 SRM 1649a PM2.5 47.984 mga 39.33 

1649a (urban dust collected in Washington, DC) 82.0

MSH 1980 Mt. St. Helens ash, Washington State, from PM2.5 > 10 ga Previously sizeGraham et al. (1985) separated

ROFA 1994 Residual oil fly ash, ROFA sample 3 from MMAD: > 2 ga Milled; not

Kodavanti et al. (1998) 2.665 μm extracted

Abbreviations: E, east; NNE, north-northeast; S, south; SE, southeast; WNW, west-northwest. 

aWeight available.

Mini-Monograph | McGee et al. 

974 VOLUME 111 | NUMBER 7 | June 2003 • Environmental Health Perspectives
of deionized water and 1 M HCl extracts

were measured using ICP-MS and ICP-AES.

The two extraction liquids are used to estimate easily bioavailable and total bioavailable

metal content, respectively. Although this

speciation scheme is a rough approximation

of bioavailability for PM2.5 samples of complex multielemental composition, it has

proven useful in characterizing inhalation toxicology end points for various source and

ambient particulates (Costa and Dreher 1997;

Kodavanti et al. 1998).

Sufficient quantities of MSH, ROFA, and

pooled WTCX samples were available to perform all analyses. Quantities of the individual

site WTC samples and SRM 1649a were very

limited (Table 1), and analyses were prioritized

to yield the greatest information possible.

SEM/EDX testing required < 1 mg and was

selected for all samples. NAA was chosen as the

next most applicable analysis to provide total

elemental composition data to support

SEM/EDX. We performed OC/EC/CC, ICPMS, ICP-AES, and IC analyses on remaining

samples where possible. XRD and XRF analyses

were performed only on the WTC3 sample.

SEM/EDX analysis. SEM/EDX provided

physical and chemical characterization of particles and fibers found in the control samples

and lyophilized WTC PM2.5 samples, and on

PM2.5 on polycarbonate filters taken during

the inhalation exposure study using the WTC3

sample. SEM/EDX was carried out using a

Personal SEM (PSEM) (formerly R.J. Lee

Instruments, Ltd., now Aspex Instruments,

Trafford, PA) as previously described (U.S.

EPA 2002e). For lyophilized WTC or control

samples, a small amount was applied to an

adhesive carbon tab affixed to an aluminum

SEM stub. For filter samples, small pieces (< 1

cm2) were affixed to aluminum SEM stubs

using a carbonaceous suspension. Because only

15–30 images were examined from each sample, the results should not be interpreted as

quantitative or comprehensive (Mamane et al.

2001). Rather, these qualitative results were

used primarily to determine consistency with

other analytical techniques described below.

X-Ray diffraction analysis. XRD was used

to qualitatively determine the presence of any

crystalline compounds in the WTC3 sample

used in the inhalation exposure study. The

PM53 sample was side-drifted into an aluminum holder and mounted into the Siemens

D-500 diffractometer (Bruker Analytical XRay Systems, Madison, WI). The generator,

set at 45 kilovolts and 40 milliamperes (mA),

generated X-rays from a copper-target X-ray

tube. The filament current was 3.46 mA.

Intensities were collected by a lithium-drifted

silicon detector fitted with a monochromator

riding on a goniometer in the coupled

θ/2θ mode, where θ = diffraction angle. Peaks

were collected in the range 2θ = 5 to 85

degrees. Collection software used was Datascan

(version 3.2; Materials Data, Inc., Livermore,

CA). Evaluation software was MDI Jade 5

using the pattern library Powder Diffraction

File (PDF), release 2000 (International Centre

for Diffraction Data, Newtown Square, PA).

Neutron activation analysis. NAA was

used to determine the total elemental content

of lyophilized WTC and control PM2.5 samples (NCSU 2002). Samples of these materials

(3–7 mg) were packaged in precleaned polyethylene vials in a clean hood, and irradiated as

follows. For aluminum (Al), chlorine (Cl),

copper (Cu), magnesium (Mg), manganese

(Mn), sodium (Na), titanium (Ti), and V content, samples were irradiated for 30 sec at

≤ 900 kWth, decayed for 10–30 min, and

counted for 5 min. For all other elements,

samples were irradiated for 6 hr at ≤ 900 kWth.

For arsenic (As), potassium (K), molybdenum

(Mo), and antimony (Sb) content, samples

were decayed for 1 week and counted for

15 min each. For Fe, Ni, barium (Ba), calcium

(Ca), chromium (Cr), strontium (Sr), and zinc

(Zn) content, samples were decayed for 2 weeks

and counted for 30 min each. γ-Ray spectra

were counted and compared against calibration

and quality control standards, and quantitative

analyses were performed.

X-Ray fluorescence analysis. Five polycarbonate filters (Isopore 0.8 μm, 47-mm

diameter, Millipore Corporation, Bedford,

MA) loaded with the WTC3 PM2.5 sample,

with five lot-matched blank filters, were

mounted in liquid-type polyethylene sample

cups, placed in a stainless steel sample holder,

and analyzed. X-ray intensities were collected

with the Philips PW2404 XRF (Philips

Analytical, Natick, MA) using the Philips

proprietary software SuperQ. Net intensities

(peak–background) were analyzed using the

standardless software UniQuant 4 (Omega

Data Systems, Veldhoven, the Netherlands)

after subtraction of the intensities due to the

blank filter system. The constituents of the

dust were evaluated as oxides.

Carbon fraction analysis. Carbon speciation into OC/EC/CC fractions was performed

on control and lyophilized WTC PM2.5 samples and on quartz filters taken during the

inhalation exposure to WTC3 PM2.5. The

thermo-optical method, based upon sequential

pyrolytic vaporization and detection of the

three carbon fractions, was performed (Sunset

Laboratory, Forest Grove, OR) as previously

described (Birch and Cary 1996; Sunset 2002).

Endotoxin analysis. One-milliliter aliquots

of filter extracts from each individual site sample were analyzed for endotoxin content using

the limulus amebocyte lysate gel-clot method

(Associates of Cape Cod, Inc., Falmouth,

MA). Samples were titered using a 2-fold dilution scheme against control standard endotoxin [CSE; lot no. 85, Escherichia coli O113,

5 endotoxin units (EU)/ng]. Preliminary inhibition tests (positive product controls) were

performed on the undiluted samples spiked

with CSE equivalent to twice the sensitivity

(λ; 0.03 EU/mL). The error of the gel-clot

method is ± one 2-fold dilution.

ICP-MS and ICP-AES. Control PM2.5

samples, lyophilized WTC PM2.5 samples,

and polycarbonate filters taken during the

inhalation exposure to WTC3 PM2.5 were

extracted with deionized water or 1 M HCl

and analyzed for their elemental content.

Samples (4–6 mg) were extracted with 1.6 mL

of either liquid. Polycarbonate filters containing 2–3 mg WTC3 PM2.5 were extracted with

13 mL of either liquid. High-speed centrifugation was used to separate the liquid and solids

(17,000 × g for 1.6-mL samples; 51,000 × g for

13-mL samples). After dilution, extraction solutions were analyzed quantitatively using ICPMS (ELAN 6000; PerkinElmer Instruments,

Shelton, CT) and ICP-AES (Model P40;

PerkinElmer Instruments) as previously

described (U.S. EPA 2002f, 2002g, respectively). Filter blanks levels for all elements

were negligible compared with the levels in the

PM samples.

Ion chromatography of deionized water

extracts. Deionized water extracts from the

ICP sample prep as described above were analyzed quantitatively for anion and cation content using IC (ManTech Environmental,

Research Triangle Park, NC). A DX-500 ion

chromatograph (Dionex, Sunnyvale, CA) was

used with an AS14 column (Dionex) for

anion analysis in Suppressor-ASRS UltraAutoSuppressor Recycle mode, with 3.5 mM

Na2CO3/1.0 mM NaHCO3 eluent. A CS12

column (Dionex) was used for cation analysis

in Suppressor-CSRS II Ultra-AutoSuppressor

Recycle mode, with 20 mM methanesulfonic

acid eluent.

Results

Analytical chemistry of solid samples.

SEM/EDX analysis. Water-extracted and

lyophilized WTC PM2.5 samples were dominated by large snowflakelike crystals composed of Ca, sulfur (S), and oxygen (O)

(Figure 3A). Aggregates of fine particles composed of various combinations of Ca, Mg, Al,

S, O, and silicon (Si) were also prominent

(Figure 3B). Fibers approximately 1 μm in

diameter were found in most of the samples

and had a composition similar to the fine

particle aggregates (Figure 3C). Metallic particles [mostly Ti and Fe, although Zn, lead

(Pb), Ba, and Cu were also found] were

found typically as inclusions in the large

aggregates of fine particles (Figure 3D).

SEM/EDX analysis of the aerosolized

PM2.5 fraction of WTC3 (not water extracted)

showed the same overall chemistry as the

extracted and lyophilized WTC PM samples;

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Environmental Health Perspectives • VOLUME 111 | NUMBER 7 | June 2003 975
the majority of particles were composed of Ca,

carbon, and O with S (Figure 4A) [or without

significant levels of S (Figure 4B)] and some

also contained Si. In contrast to the crystals

and aggregates of the lyophilized samples

described above and shown in Figure 3, the

WTC3 particles were small, typically about 1

μm, with rough, irregular features. The different physical form of the Ca-based particles in

WTC3 reflects the dry size segregation of the

inhalation exposure system. These results suggest that the large crystals and aggregates

observed in the lyophilized samples were not

originally present in the PM2.5 Teflon filters

but were formed during the aqueous extraction

and lyophilization process.

Particles with other compositions were

found with far less frequency. These included

particles composed of Fe, carbon, and Sb–Zn

(one example found). One or more possible

asbestos fibers (Mg–Si composition) were also

found; however, polarized light microscopy

rather than SEM/EDX is the preferred method

for identifying asbestos in bulk materials.

SEM/EDX analysis performed on MSH,

SRM 1649a PM2.5, and ROFA showed results

typically found in previous analyses of these

materials (data not shown). 

X-Ray diffraction analysis. XRD analysis of

WTC3 PM53 (before size segregation by the

inhalation exposure system) showed a complex

pattern containing 25 peaks, indicating the

presence of several crystalline materials. The

peak area above the background curve was

50.6%. The 49.4% below the curve indicated

that WTC3 PM53 consisted of about half

amorphous materials. Four patterns were identified as being consistent with peaks identified

in the dust. Figure 5 shows the XRD spectra of

WTC3 PM53 and those of the matched compounds. Two compounds were identified as

major constituents [calcium sulfate dihydrate

(gypsum) and calcium carbonate (calcite)], and

two were identified as minor constituents [bassanite (calcium sulfate hemihydrate) and quartz

(silicon dioxide); Table 2]. The predominance

of Ca-based compounds by XRD supports the

major findings of the SEM/EDX analysis of

WTC PM2.5—the WTC PM materials are

composed predominantly of Ca compounds,

some of which are water soluble. The sample of

MSH was also analyzed by XRD, and the

results were consistent with those previously

reported (Graham et al. 1985; data not shown).

Total elemental analysis by neutron activation analysis and X-ray fluorescence analysis.

Both NAA and XRF analyses showed that

there were large amounts (range 22–33%) of

Ca in the WTC PM2.5 samples (Table 3). XRF

analysis showed 37.5% S as SO4 in the WTC3

PM2.5 sample. Together, Ca and SO4 account

for 64% of the WTC3 PM2.5 sample, in good

agreement with the SEM/EDX and XRD

analyses. For all other elements, NAA and XRF

Figure 3. SEM/EDX results from water-extracted lyophilized WTCX PM sample. The upper-left quadrant of

each photomicrograph shows a field of view with the particle of interest within the smaller square in that

field. The upper-right quadrant shows a zoomed-in view of the feature (the area from within the square in

the upper-left quadrant), and the lower half shows the elemental spectrum acquired with the electron

beam centered on the small (barely visible) square in the zoomed-in view. (A) Example of crystal with

Ca, S, and O, which dominated the samples. (B) Example of fine particle aggregate that was prominent in

the samples. (C) Example of fiber found in the samples. (D) Example of metallic particle (Ti) within fine

particle aggregate.

Figure 4. SEM/EDX results showing predominant particle types found in aerodynamically size-separated

WTC3 PM2.5 sample used in nose-only inhalation exposure study (Gavett et al. 2003). (A) Example of

particle containing Ca, S, O, and carbon. (B) Example of particle containing Ca, O, and carbon without

significant levels of S.

Mini-Monograph | McGee et al. 

976 VOLUME 111 | NUMBER 7 | June 2003 • Environmental Health Perspectives
results for the various WTC PM2.5 samples

show good agreement. This consistency in

composition is remarkable, considering the

wide area over which the original WTC dust

samples were collected (Figure 1). Besides Ca

and SO4, only Si, Al, Mg, and Fe are present

in levels approaching or greater than 1% of

total mass. The relative weight–percent ratios

of Al, Mg, and Fe are in the range of those

found in portland cement, a major component

of concrete (McKetta 1978). Of the transition

and heavy metals and other toxic elements

such as Sb and As, only Zn and Ti are present

in levels approaching 0.5% of total mass,

whereas all others are present at maximum levels of hundreds of micrograms per gram (parts

per million). Within the group of seven WTC

PM2.5 samples analyzed using NAA, WTCE

has the highest content of total metals and

toxic elements (e.g., Sb and As); combined levels of these elements were about twice those of

the other WTC samples. Comparison of the

total metal and toxic elemental content of the

WTC PM2.5 samples with the control dusts

shows the overall metal levels as MSH < WTC

< SRM 1649a < ROFA.

Carbon fraction analysis. The WTC PM2.5

samples had low total carbon content, in the

range of 1.5–8.5% (Table 4), in contrast with

control samples such as SRM 1649a (26%) and

ROFA (16%). MSH had almost no carbon, as

expected from this crustal PM sample. The

WTC3 PM2.5 sample used in the inhalation

study had about 4 times as much carbon as the

other two WTC PM2.5 samples. This result

may be due to differences in the method by

which the samples were isolated (physical separation vs. aqueous extraction and lyophilization) or may simply be due to variability in

carbon content of samples from different locations. Despite the variation in total carbon content of WTC PM samples, the ratios of the

carbon fractions were similar. Carbonate carbon is most likely associated with Ca (as calcite,

Table 2) and other alkaline earth metals (e.g.,

Mg). The level of carbonate carbon is relatively

small compared with the overall alkaline earth

content, yet levels are high enough to make Ca

and/or other alkali earth carbonates the likely

source(s) of the high pH values measured (see

below). Elemental carbon levels (an indicator of

carbon black produced by incomplete combustion during the fires prior to collapse) were low,

indicating that the fine fraction of WTC PM2.5

was dominated by the presence of pulverized

building materials rather than the products of

incomplete combustion. Organic carbon levels

are relatively high and can be attributed to

many sources in the WTC building and to jet

fuel (Lioy et al. 2002).

Analytical chemistry of aqueous extracts of

samples. pH and endotoxin levels. pH levels

of water-extracted WTC PM2.5 and control

samples are shown in Table 5. The pH of

water-extracted WTC PM2.5 samples before

lyophilization ranged from 8.88 in WTCE to

10.00 in WTC8. The alkaline pH results from

the building materials comprising much of the

dust, most likely the alkaline earth (Ca, Mg)

compounds. Calcium carbonate, identified by

XRD, is a major component of cement

(McKetta 1978) and other building materials.

It is almost insoluble in water (14 μg/mL), yet

a saturated solution produces a pH of 9.4

(Weast 1985). For a 2 mg PM/mL ratio, this

requires < 7 μg soluble calcium carbonate/mg

PM. Such a level is easily attainable in the

WTC samples, given the percent ranges of Ca

and carbonate carbon measured by elemental

and OC/EC/CC analysis. The pH of lyophilized WTC PM2.5 reconstituted in

unbuffered saline was very close to neutral

(pH 7.36), whereas MSH was only slightly

acidic (pH 6.61) and ROFA was moderately

acidic (pH 3.74). It is not known why the pH

of WTC PM2.5 should be close to neutral after

reconstitution in saline.

Endotoxin levels in WTC PM2.5 samples

were minimal compared with other urban

PM samples such as SRM 1649a, which was

also low (Table 5). Several thousand times

this level of endotoxin caused an acute neutrophilic response in the lungs of CD-1 mice

(Dhingra et al. 2001). The level of endotoxin

in the samples used in this study would not

be anticipated to contribute directly to any

inflammatory response in the lungs.

Extractable elemental/ion analysis by

ICP-MS, ICP-AES, and IC. Elemental and

ion compositions were consistent within each

sample group tested (Table 6). The ICP-AES

data for S were treated as SO4, as both XRD

and XRF showed S was present in this oxidized form. The SO4 content of the WTC

PM2.5 samples ranged from 38 to 44% of total

weight, and the WTC3 ICP-AES and XRF

results (Table 3) were nearly identical. The

ICP-AES data showed that water-soluble Ca

accounted for 18–19% of WTC PM2.5 samples, which was about 8–15% lower than

results from XRF and NAA analyses (Table 3).

This may reflect an incomplete extraction in

the 1-hr time frame, the relatively mild solutions and conditions used in the extraction

method, or the presence of other insoluble

Figure 5. X-Ray diffraction analysis of sieved WTC3 sample (PM53 before aerodynamic size separation).

Peaks were collected in the range of 2θ = 5–85°. Collection software used was Datascan (version 3.2;

Materials Data, Inc.). Intensity (counts)

1,000

750

500

250

0

[020118A.MDI] WTC dust, as received

33-0311> Gypsum - CaSO4 · 2 H2O

41-0224> Bassanite - CaSO4 · 0.5 H2O

05-0586> Calcite - CaCO3

46-1045> Quartz - SiO2

2-Theta (°) 10 20 30 40 50 60 70 80

Table 2. XRD analysis of compounds present in

WTC3 sample.a

Relative

ICDD no. Formula Mineral amount

05-0586 CaCO3 Calcite Major

33-0311 CaSO4·2H2O Gypsum Major

41-0224 CaSO4·0.5H2O Bassanite Minor

46-1045 SiO2 Quartz Minor

ICDD, International Centre for Diffraction Data.

aSample was sieved (PM53) but not further size-separated.

Analysis showed about half crystalline materials (50.6%

above background), and the remainder was amorphous.

After smoothing and subtracting background, evaluation

software (Jade 5; Materials Data, Inc.) was used to match

patterns with library available from the Data Diffraction

File (release 2000; International Centre for Diffraction

Data). Relative amounts: major is > 20 weight %; minor is

> weight % but < 20 weight %.

Mini-Monograph | Chemical analysis of WTC PM2.5

Environmental Health Perspectives • VOLUME 111 | NUMBER 7 | June 2003 977
forms of Ca in the WTC PM2.5 samples. ICP

data for the 1 M HCl-soluble extracts of

WTC PM2.5 showed an additional 1–2 weight

percent Ca content relative to the water-soluble extracts. The increase may be attributed to

calcite or other water-insoluble Ca salts that

are soluble in 1 M HCl.

The same ordering of water-soluble element < 1 M HCl-soluble element < total element content held for all other analytes. Total

content measured by NAA/XRF and acidsoluble content measured by ICP agreed

within 25% for elements such as Mg and Zn,

which exist in compounds more amenable to

acid dissolution (Budavari 1996; Weast

1985). Elements such as Al, Fe, and Ti,

which are in the form of complex oxides usually in combination with Si, are much less soluble under the acid extraction conditions

used in this study and do not agree as well

(Budavari 1996; Weast 1985). Water-extractive contents were < 10% of the total content

values for nearly all transition and heavy metals. Acid-extractive contents were almost all

< 50% of the total content values. 

Comparison of the water-soluble transition and heavy metal levels of the WTC samples with the control dusts used in this study

shows the overall metal content trend as

MSH < WTC < SRM 1649a < ROFA. ROFA

has high levels of water-soluble transition

metals, including V, Ni, and Fe, which are

important in its toxicity (Kodavanti et al.

1998). The 1 M HCl-soluble metal content

trend is MSH < WTC < ROFA (not enough

SRM 1649a PM2.5 sample was available to

run this test). Extractable elemental content

of the WTC samples more closely resembled

the crustal MSH sample than the urban

ambient SRM 1649a PM2.5 sample. 

Discussion

We collected samples of fallen dust at various

locations in the immediate vicinity of the

WTC site 1 and 2 days after the WTC disaster

and analyzed the PM2.5 fraction, using several

physical and chemical techniques. The XRD

analysis showed that the sieved WTC PM53

sample consists primarily of Ca-based compounds, specifically calcium sulfate (gypsum)

and calcium carbonate (calcite; the main component of limestone). The NAA, XRF, and

ICP analyses strongly suggest that these compounds are present in the PM2.5 fraction as

well. Ca and SO4 compose about two-thirds of

WTC PM2.5 on a weight percent basis. Taken

together, the total elemental analysis data

account for 79% of the weight of the WTC3

PM2.5 sample and indicate that the main components are construction materials such as

cement, concrete aggregate, ceiling tiles, and

wallboard. The remaining mass fraction is

most likely due to moisture content and to O,

hydrogen, and nitrogen associated with both

the organic and inorganic constituents.

The content of transition and heavy metals and other toxic trace elements in WTC

PM2.5 samples is low compared with that of

combustion-derived ROFA, as expected from

crustal-derived building materials. Levels of

elements that could be attributed to metal

wiring (Cu), plumbing (Fe, Cu, Pb), structural steel (Fe, Mn), and communication and

computer equipment (Cu, Fe, Zn, others) are

also low. This may be attributed to the relatively small proportion of metal-containing

building contents compared with the building

itself, or perhaps these materials resisted

crumbling and pulverization into the PM2.5

fraction. Elemental analysis of water and acid

extracts of WTC PM2.5 provides speciation

information on chemical constituents that are

potentially bioavailable after inhalation, or

which can be easily released into the environment from rain and washing of streets and

buildings. The extractable amounts of metals

and toxic elements are low compared with

Table 3. Analysis of WTC and control PM2.5 samples by XRF or NAA (micrograms analyte per gram solid sample).a

Sample: WTC8 WTC11 WTCB WTCC WTCE WTCF WTCXb WTC3c SRM 1649a MSH ROFA

Method: NAA NAA NAA NAA NAA NAA NAA XRF NAA NAA NAA 

Analyte

SO4

–2 375,300

Ca 242,000 226,000 333,000 257,000 205,000 243,000 287,000 265,600 29,800

Si 30,000

Al 15,400 13,500 7,560 10,600 23,900 16,000 5,810 9,930 37,600 97,200 27,700

Mg 7,040 5,340 2,870 4,540 9,070 5,150 2,900 6,550 6,900

Fe 8,360 7,360 3,630 4,480 15,100 6,930 2,730 6,290 30,500 29,200 30,900

Cl 1,940 3,580 1,460 1,570 1,710 2,100 3,310 3,330 2,790 1,680 1,030

K 4,660 2,890 2,690 15,300 8,880

Zn 2,310 1,960 1,380 1,280 5,860 2,020 813 1,760 1,330 56 9,760

Ti 2,630 5,730 1,230 1,820 4,920 2,640 1,130 1,450 3,550 3,060

PO4

–3 779

Na 2,030 1,700 760 1,250 1,520 2,070 1,250 725 4,420 38,500 32,400

Mn 358 295 136 257 302 340 107 268 770 1,000

Cu 428 560 484 306

Ba 84.7 344.0 97.0 958 371.0 762

Sb 102 63.0 64.2 59.3 308 81.8 49.3 73.1 681

Mo 48.7 35.7 29.3 19.9 125 36.5 23.8 355

Ni 252 20,500

Cr 178 196 62.3 78.9 225 131 56.4 302 17.9 582

As 3.5 3.6 2.2 2.9 6.1 4.0 2.2 102 82.7

V 65.7 280 29.5 72.0 158 103 38.3 583 75.3 45,400

Sr 826 1,100 506 557 422 646

Total μg/g 282,466 267,297 352,213 283,030 274,609 281,940 308,764 704,404 98,756 217,157 171,153

% Total mass 28.3 26.7 35.2 28.3 27.5 28.2 30.9 70.4 9.9 21.7 17.1

aWTC PM2.5 samples were extracted and lyophilized. Analytes are arranged in order of decreasing content in WTC3 sample (including liquid extract samples; Table 6) by whatever

analysis provided highest content. S and P measured by XRF were oxidized and assumed to be SO4

–2 and PO4–3, respectively. Sample WTC13 was not analyzed because of insufficient

sample quantity. Missing values were either not determined or below detection limit. bWTCX = pooled sample of WTC8, WTC11, WTC13, WTCB, WTCC, WTCE, and WTCF. cWTC3 was

size-separated to PM2.5 using nose-only inhalation exposure system; average values are shown (n = 5).

Table 4. Carbon fraction analysis of PM2.5 samples.a

Sample

Carbon fraction WTC3 WTCX (pooled) WTCB MSH ROFA SRM 1649a

OC 6.88 0.93 2.11 0.06 1.31 10.82

EC 0.31 0.00 0.01 0.07 13.63 15.10

CC 1.39 0.60 0.35 0.00 1.32 0.00

Total 8.58 1.53 2.47 0.13 16.26 25.92

aCarbon fractions were analyzed as described in text. Results are expressed as percent of total mass of sample.

Mini-Monograph | McGee et al. 

978 VOLUME 111 | NUMBER 7 | June 2003 • Environmental Health Perspectives
those of the ROFA and ambient air SRM

1649a samples, partly because of the small

total amounts present in the original material,

and partly because of the limited solubility of

most of these elements at the alkaline pH

levels (8.9–10.0) of the water extracts

(Hoffland 2002; Neubauer et al. 2000).

The results of this study differ in some

respects from those of the USGS (2002) and

Lioy and co-workers (2002), who performed

chemical and physical analyses of whole (not

size-separated) WTC PM samples collected

within a 3-km radius of the WTC site. The

USGS (2002) collected several dust samples on

17 and 18 September that had only limited

protection from the rain that fell on 14

September and possibly changed sample composition. The USGS study found Ca in the

whole dust approximately in the same proportion (average 18%) that we found in the PM2.5

fraction, but S averaged 3% (or 9% as SO4), a

level about 4-fold lower than reported here,

suggesting that SO4 may have been washed

away by rain more easily than other species.

The USGS also found a notably higher level

of Si (average 15% vs. 3% here), probably

reflective of a large amount of glass fiber present in very coarse fractions (Lioy et al. 2002;

USGS 2002), which do not fragment into

PM2.5 as easily as gypsum and other building

materials. Lioy and co-workers (2002) collected three samples on 16 and 17 September

from sheltered locations and found that Ca

and SO4 in the settled dust were present in the

same ratio as in our study. However, the combined levels comprised about 6% of the whole

dust, a level about 10-fold lower than that

found in the PM2.5 fraction in our study.

We conclude that water-soluble Cacontaining compounds were enriched in the

WTC PM2.5 fraction compared with those in

the whole settled dust. Additionally, the WTC

PM2.5 samples were remarkably homogeneous

in their overall elemental content, considering

the wide geographic range of sample collection. These results were unexpected, given the

complexity of the building material composition and scale of the disaster. However, they

are reasonable, considering the prevalent use

of gypsum in building materials such as ceiling

tiles, wallboard, and cement, and the ease with

which these materials can be crumbled into a

fine powder, mix, and homogenize.

The likely major acute inhalation hazards of

WTC PM2.5 based on the results from this

study are due to the presence of gypsum,

calcite, and cement or concrete dust components. Both gypsum and calcite irritate the

mucus membranes of the eyes, nose, throat,

Table 6. Elemental and ion analysis of extracts of WTC and control PM2.5 samples.a

Sample: WTCB WTCX (pooled) WTC3 SRMb MSH ROFA 

Diluent: DI H2O DI H2O 1 M HCl DI H2O 1 M HCl DI H2O DI H2O 1 M HCl DI H2O 1 M HCl

No. analyses: 1 2 1 4 4 1 2 1 2 1 

Analyte

SO4

–2 432,600 439,100 379,400 376,500 344,400 86,720 955 973 275,000 242,300

Ca 183,800 187,500 196,700 184,900 218,000 12,650 352 1,971 18,590 19,660

Mg 354 651 2,258 1,113 5,414 1,141 37.3 1,250 24,900 24,660

Al 537* 555* 1,477 1,346 4,072 1,049 48.4* 1,260 6,740 8,604

Cl– 2,699 2,851 1,164 1,103 302

Fe 6.0* 6.7* 1,098 150* 2,450 407 0.1* 1,833 763 19,510

Zn 4.1 13.4 410 22.7 1,413 504 0.0* 3.7 6,556 5,932

Na+ 1,139 1,290 2,153 721 44,179

NO3

– 6,496 938 7,390 0.0 0.0

F– 799 406 466 0.0 352

Ti 4.0 5.2 41.6 12.1 181 1.8 1.3 17.6 2.6 138

Pb 0.4 0.7 33.4 2.2 141 1,379 0.0* 0.5 17.9 790

Mn 0.7 1.8 24.0 4.5 108 77.2 3.8 38.4 365 459

Cu 4.7 6.4 21.8 5.5 76.0 83.6 0.6 6.8 573 628

Ba 7.2 8.7 31.0 25.6 75.6 11.2 0.1* 5.0 3.0 57.5

Sb 7.0 9.4 17.4 17.7 43.8 3.5 0.0* 0.0* 1.5 146

NO2

– 0.0 38.0 0.0 0.0 0.0

Mo 4.9 1.8 3.2 1.0 33.7 1.8 0.1 0.1 0.0* 339

Ni 1.8 4.1 3.1 2.6 19.7 32.2 0.0 0.9 17,030 16,990

Sn 0.1* 1.3 3.1 0.8 12.1 0.1* 0.0* 0.0* 0.0* 51.0

Cr 1.2* 1.4* 10.0 6.1 0.1* 6.1

Cd 0.3 0.7 1.9 0.3 7.2 19.9 0.0 0.0 8.9 11.9

Be –0.1* 0.3* 0.2* 0.0* 2.7* 0.1* 0.0* 0.0* 1.4* 1.7*

Co 0.1* 0.8 0.9 0.2* 1.6 2.1 0.0* 0.4* 495 510

NH4

+ 0.0 0.0 25,355 0.0 0.0

PO4

–3 0.0 0.0 3,317 0.0 0.0

As 0.3 1.1 –0.4* 1.3 –10.4* 13.5 0.1 0.2 1.7 106

Tl 0.1* 0.5 –1.2* 0.1* –25.5* 0.3 0.0* –0.1* 0.0* –0.2*

V 1,749 35,690

Total μg/g 617,300 639,000 581,600 569,600 576,500 143,900 3,223 7,362 397,600 376,700

% Total mass 61.7 63.9 58.2 57.0 57.6 14.4 0.3 0.7 39.8 37.7

Abbreviations: Be, beryllium; Cd, cadmium; Co, cobalt; F, flouride; NH+

4, ammonium; NO–2, nitrite; NO–3, nitrate; Sn, tin; Tl, thallium. aResults shown are average values for number of analyses

indicated, expressed as micrograms soluble analyte per gram solid sample extracted, for deionized (DI) water and 1 M HCl extractions. Analytes are arranged in order of decreasing content in WTC3 sample by whatever analysis provided highest content. Analyte concentrations were determined by ICP-MS, except values shaded in light blue, which were determined by

ICP-AES, and values shaded in dark blue, which were determined by IC. bSRM 1649a size-classified to PM2.5 (see “Materials and Methods”). *Indicates value below detection limit. 

Table 5. pH and endotoxin levels of PM2.5 samples.

Sample pH in Endotoxinb pH in

code watera EU/mL Inhibition salinec

Extraction water 5.28

WTC8 10.00 0.50 None

WTC11 9.16 0.25 None

WTC13 9.47 0.50 None

WTCB 9.54 0.25 None

WTCC 9.32 0.50 None

WTCE 8.88 0.25 None

WTCF 9.55 0.50 None

SRM 1649a 4.20 25 None

Sterile saline 6.67

WTCX 9.35 7.36

MSH 6.61

ROFA 3.74

apH and endotoxin levels of SRM 1649a and all WTC samples after water extraction from filters in the ratio of 0.5

mL/mg PM2.5. bEndotoxin levels measured as EU/mL water

extract. Samples were tested for inhibition of the endotoxin assay (none was detected). cpH of samples after

resuspension in sterile saline (2 mg/mL; pooled WTCX

extract was lyophilized and resuspended); average of

three to four measurements.

Mini-Monograph | Chemical analysis of WTC PM2.5

Environmental Health Perspectives • VOLUME 111 | NUMBER 7 | June 2003 979
and upper airways (Stellman 1998). Calcium

carbonate dust causes coughing, sneezing, and

nasal irritation (NLM 2002). These symptoms

of inhalation exposure are similar to those

reported by rescue and cleanup workers in the

immediate aftermath of the WTC attack

(Kelley 2001). The high content of gypsum

and calcite in the WTC PM2.5 fraction suggests

that potentially toxic effects may also extend

into the smaller airways and lung parenchyma.

The physical and chemical characterization

of the samples described here contributes to

the understanding of biologic responses in the

companion article (Gavett et al. 2003), which

describes short-term acute respiratory tract toxicology of the WTC PM2.5 and control PM2.5

samples. Further detailed analyses and toxicity

testing of the WTC PM2.5 fraction may be

necessary to evaluate other components found

in the bulk WTC fallout dust, which may be

enriched in the smaller inhalable particle sizes,

and which have known long-term health consequences. Identified WTC bulk PM components that are known inhalation hazards are

asbestos, crystalline silica, and toxic organics

such as PAHs, polychlorinated biphenyls, and

dioxins (Lioy et al. 2002; Offenberg et al.

2003; USGS 2002). Calcite and gypsum are

often contaminated with small amounts of silica, which is the main concern for long-term

occupational health hazards (Stellman 1998).

Minor amounts of silica were detected in the

WTC PM samples (Table 2). The results of

this study are also of special interest because of

resuspension of the dust during cleanup operations of both the Ground Zero site and building interior surfaces throughout lower

Manhattan (Johnson 2002). WTC PM that

infiltrated into buildings is most likely of

smaller particle sizes and more of an inhalation

hazard than that found outdoors.

Acknowledgments: The authors thank M. Zhong,

M. Blaustein, S-I. Hsu, J. Duffy, K. Schermerhorn, M.

Lippmann, J. Zelikoff, and M. Costa (New York

University School of Medicine); J. Vandenberg, T.

Hughes, B. Culpepper, I. Gilmour, J. Lehmann, and

H. Hilliard (NHEERL, ORD, U.S. EPA); G. Ross

(National Caucus for Black and Aging/Senior

Environmental Employees Program, Research Triangle

Park, NC); D. Williams and W. Ellenson (ManTech

Environmental Technology, Inc., Research Triangle

Park, NC); R. Cary and D. Smith (Sunset Laboratory,

Forest Grove, OR); and S. Lassell (Department of

Nuclear Engineering, North Carolina State University,

Raleigh, NC) for their excellent assistance.

LCC and MDC were supported by National Institute

of Environmental Health Sciences center grant

ES00260 and U.S. EPA PM center grant R827351.

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980 VOLUME 111 | NUMBER 7 | June 2003 • Environmental Health Perspectives