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Open-File Report 01-0429

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

Environmental Studies of the 

World Trade Center area after 

the September 11, 2001 attack. 

Version 1.1 

Published November 27, 2001

Roger N. Clark1, Robert O. Green2, Gregg A. 

Swayze1, Greg Meeker1, Steve Sutley1, Todd M. 

Hoefen1, K. Eric Livo1, Geoff Plumlee1, Betina 

Pavri2, Chuck Sarture2, Steve Wilson1, Phil 

Hageman1, Paul Lamothe1, J. Sam Vance3, Joe 

Boardman4 Isabelle Brownfield1, Carol Gent1, Laurie 

C. Morath1, Joseph Taggart1, Peter M. 

Theodorakos1, and Monique Adams1

___________

1U. S. Geological Survey, Denver, Colorado

2Jet Propulsion Lab Pasadena, California

3U.S. Environmental Protection Agency, Region 8 Denver, Colorado

4Analytical Imaging and Geophysics, LLC Boulder, Colorado 

Table of Contents 

Navigating through this report: At the end of each section will be a link to the next 

section in the sequence below, or click on the links to go directly to a section or subsection. 

● Executive Summary

● Introduction 

Asbestos Definitions.

● Imaging Spectroscopy Mapping Results 
Field spectral measurements and calibration site.

Thermal Hot Spot Maps: Sept 16 and 23, 2001 

Asbestiform Minerals Map 

Dust and Debris Plume Map 

Ferrous and Ferric-Bearing Materials Map 

Clays and other Materials Map 

Organic Compounds Map 

Water Sediment Map 

● Sample Collection in the WTC Area 

● Laboratory Studies of Samples 

Overview 

X-Ray Diffraction (XRD) Analysis 

Laboratory Reflectance Spectroscopy (RS) Studies 

Reflectance Spectroscopy 

Laboratory Spectra of WTC Samples 

Description of Spectroscopy Methods and Results 

Possible Sources of Abestos in the WTC Dust 

Spectral Detectability of Chrysotile 

Spectral Interference 

Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray 

Analysis (EDS) 

Chemical Compositions 

Sampling and analytical methods 

Chemistry Table 1,

Results 
Interpretation 

Leachate Studies 

Leaching of World Trade Center dusts using a 

simulated precipitation leaching procedure 

Results 

Leach Table 1

Interpretation 

Summary and potential environmental implications 

● Integration of Results and Conclusions

● References 

Executive Summary 

This web site describes the results of an interdisciplinary environmental characterization 

of the World Trade Center (WTC) area after September 11, 2001.

Information presented in this site was first made available to the World Trade Center 

emergency response teams on September 18, 2001 (Thermal hot spot information), 

and September 27, 2001 (maps and compositional results).

The Airborne Visible / Infrared Imaging Spectrometer (AVIRIS), a hyperspectral remote 

sensing instrument, was flown by JPL/NASA over the World Trade Center (WTC) area on 

September 16, 18, 22, and 23, 2001 ( Link to the AVIRIS JPL data facility). A 2-person 

USGS crew collected samples of dusts and airfall debris from more than 35 localities 

within a 1-km radius of the World trade Center site on the evenings of September 17 

and 18, 2001. Two samples were collected of indoor locations that were presumably not 

affected by rainfall (there was a rainstorm on September 14). Two samples of material 

coating a steel beam in the WTC debris were also collected. The USGS ground crew also 

carried out on-the-ground reflectance spectroscopy measurements during daylight 

hours to field calibrate AVIRIS remote sensing data. Radiance calibration and 

rectification of the AVIRIS data were done at JPL/NASA. Surface reflectance calibration, 

spectral mapping, and interpretation were done at the USGS Imaging Spectroscopy Lab 

in Denver. The dust/debris and beam-insulation samples were analyzed for a variety of 

mineralogical and chemical parameters using Reflectance Spectroscopy (RS), Scanning 

Electron Microscopy (SEM), X-Ray Diffraction (XRD), chemical analysis, and chemical 

leach test techniques in U.S. Geological Survey laboratories in Denver, Colorado.
Results of these studies to date lead to several important conclusions:

● The dusts released from the WTC building collapse are largely composed of 

particles of glass fibers, gypsum, concrete, paper, and other miscellaneous 

materials commonly used in building construction.

● Laboratory analyses (RS, SEM, XRD) have detected chrysotile asbestos only in 

trace levels (less than 1 weight percent) in over two thirds of the dust and 

airfall debris samples. To date, no amphibole asbestos minerals have been 

detected in any of the dust samples. For definitions of asbestos, CLICK HERE 

(use the back button on your browser to return here). 

● Laboratory analyses of the material coating a steel beam in the WTC debris 

have detected the presence of chrysotile asbestos (a serpentine mineral) at 

levels as high as 20% (by volume) of the coating material. No amphibole 

asbestos has been detected in this beam coating material.

● AVIRIS mineral maps do not show widespread distribution of chrysotile or 

amphibole asbestos at the few-percent detection limit of the instrument at the 

ground surface. AVIRIS mapping keyed to the detection of minerals that may 

occur in asbestiform habits has identified isolated pixels or pixel clusters (each 

pixel is approximately 2m x 2m) in the area around the WTC. In these areas, 

potentially asbestiform minerals might be present in concentrations of a few 

percent to tens of percent. Some spectral absorption strengths in the AVIRIS 

data are similar to those observed in spectra of the chrysotile asbestosbearing beam coating. The absorption features mapped by AVIRIS only 

indicate the presence of serpentine mineralogy and not if the serpentine has 

asbestos form. Non-asbestiform serpentine minerals can occur naturally in 

rocks and such rocks may have been used in building materials. The AVIRIS 

maps could indicate areas of higher concentrations of asbestos or simply 

areas of non-asbestiform mineralogy and would need field sampling and 

laboratory analysis to confirm the presence of any asbestos. The AVIRIS maps 

show the surface materials only and not any buried materials.

● AVIRIS mineral maps show a few isolated pixels of amphibole minerals, but 

these pixels are isolated with no clusters like those seen in the chrysotile 

pixels. The few mapped amphibole pixels are at a statistical noise level in the 

WTC area similar to the pixel noise level mapped throughout the city. The 

absorptions mapped by AVIRIS only indicate the presence of amphibole 

mineralogy, which can occur naturally (non-asbestiform) in rocks that are 

used in building materials, and field sampling of those pixels would be 

necessary to confirm the presence of asbestos. The AVIRIS maps of 

serpentine chrysotile and amphibole mineralogy are consistent with laboratory 

analyses of the field samples.

● Laboratory analyses and the AVIRIS mapping results indicate the dusts are 

variable in composition, both on a fine scale within individual samples and on 

a coarser spatial scale based on direction and distance from the WTC. 

Replicate mineralogical and chemical analyses of material from the same 
sample reveal variability that presumably is due to the heterogeneous mixture 

of different materials comprising the dusts. The spatial variability is observed 

at large scales of tens of meters to centimeter and smaller scales. AVIRIS 

mapping suggests that materials with higher iron content settled to the southsoutheast of the building 2 collapse center. Chrysotile may occur primarily 

(but not exclusively) in a discontinous pattern radially in west, north, and 

easterly directions perhaps at distances greater than 3/4 kilometer from 

ground zero.

● Although only trace levels of chrysotile asbestos have been detected in the 

dust and airfall samples studied to date, the presence of up to 20 volume % 

chrysotile in material coating steel beams in the WTC debris, and the potential 

areas indicated in the AVIRIS mineral maps indicates that asbestos can be 

found in localized concentrations.

● Chemical leach tests of the dusts and airfall debris samples indicate that the 

dusts can be quite alkaline. When reacted with rain water or wash water from 

cleanup efforts, the dusts can produce slightly alkaline to very alkaline 

solutions, due to partial dissolution of concrete, gypsum, and glass fiber 

particles. Indoor dust samples generated the highest pH levels (11.8) in the 

leach tests, indicating that dusts that have not been exposed to rainfall since 

September 11th are substantially more alkaline than those that have been 

leached by rainfall.

● At least some heavy metals and metalloids (such as aluminum, chromium, 

antimony, molybdenum, and barium) are readily leached from the dusts into 

rain or wash water. Indoor dust samples showed greater proportions of 

leachable metals than outdoor dust samples. These metals may also be 

potentially bioavailable if the dusts are accidentally inhaled or ingested. 

Chemical leach tests of the material coating steel girders in the WTC debris 

indicate that the coatings can contain soluble chromium.

● AVIRIS data collected on September 16, 2001, revealed a number of thermal 

hot spots in the region where the WTC buildings collapsed. Analysis of the 

data indicated temperatures greater than 800oF in these hot spots (some over 

1300oF) . Over 3 dozen hot spots of varying size and temperature were 

present in the core zone of the WTC. By September 23, most of these fires 

that were observable from an aircraft had been eliminated or reduced in 

intensity.

● Our finding that trace levels of asbestos are present in the dust samples is 

consistent with results of other studies carried out by the U.S.Environmental 

Protection Agency (www.epa.gov). Our results provide further clarification by 

showing that 1) elevated concentrations of asbestos may be present in beam 

coatings and possible localized area as indicated by the AVIRIS maps, and 2) 

asbestos in the dusts and beam coating materials is composed only of 

chrysotile asbestos and does not contain amphibole asbestos. A significant 

body of research conducted over the last twenty years by toxicologists, 

epidemiologists and mineralogists has indicated that chrysotile asbestos is less 
carcinogenic than the amphibole asbestos minerals (Ross, 1999; Skinner et 

al., 1988; Van Oss et al., 1999; McDonald, 2001). This conclusion, however, 

has not been universally accepted by the scientific community. A recent and 

thorough discussion of these ongoing issues can be found in Nolan, et al. 

(2001).

● Results of our mineralogical characterization studies, chemical leach tests, and 

AVIRIS mapping provide further support for the EPA and New York 

Department of Public Health recommendations that cleanup of dusts and the 

WTC debris should be done with appropriate respiratory protection and dust 

control measures. These results include: the presence of up to 20 volume % 

chrysotile in material coating steel beams in the WTC debris (which could be 

unintentionally released into the air as dust during cleanup); the small areas 

in the AVIRIS mineral maps indicating that asbestos might be found in 

localized concentrations in the dusts; the highly alkaline nature of the dusts; 

and, the presence of potentially bioavailable metals in the dusts.

● For information on the health aspects of the dusts, readers are referred to 

web sites of the EPA: (http://www.epa.gov) and New York department of 

Public Health: ( http://www.nyc.gov/html/em/health.html, and http://www.

nyc.gov/html/doh/html/alerts/911.html)

Next section: continue to the Introduction, below.

Back to Table of Contents 

Introduction 

The information in this report describes the results of an interdisciplinary environmental 

characterization of the World Trade Center (WTC) area following requests from other 

Federal agencies after the attack on September 11, 2001. The scientific investigation 

included two main aspects: 1) imaging spectroscopy mapping of materials to cover a 

large area around the WTC and 2) laboratory analysis of samples collected in the WTC 

area.

Spectroscopy is a tool that detects chemical bonds in molecules (solid, liquid or gas) 

through absorption (or emission) features in the spectrum of the material. Imaging 

spectroscopy obtains a spectrum for every spatial pixel in an image format. Data from 

the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) were collected over the 

WTC area by NASA/JPL for this study. The results of the imaging spectroscopy mapping 

are shown below.

The analytical techniques applied to this study include X-Ray Diffraction (XRD), 

Scanning Electron Microscopy (SEM) with elemental analysis by Energy Dispersive 

Spectroscopy (EDS), laboratory Reflectance Spectroscopy (RS), leachable metals, and X-
Ray Fluorescence Spectroscopy (XRF).

For definitions of asbestos, CLICK HERE (use the back button on your browser to return 

here).

Next section: click on the link to Results of Imaging Spectroscopy Mapping, below

Back to Table of Contents 

 

Results of 

Imaging 

Spectroscopy 

Mapping

Click on the link 

above to see:

● Thermal Hot 

Spot Maps: 

Sept 16 and 

23, 2001 

● Asbestiform 

Minerals Map 

● Dust and 

Debris Plume 

Map 

● Ferrous and 

Ferric-Bearing 

Materials Map 

● Clays and 

other 

Materials Map 

● Organic 

Compounds 

Map 
● Water 

Sediment Map 

 

Back to Table of Contents 

 

 

Sample Collection in the WTC Area

Ground 

sampling 

consisted 

of 

collecting 

debris 

from 35 

locations 

in the 

WTC 

area, 

including 

33 dust, 

2 

concrete, 

and 2 

steel 

beam insulation samples.

Optical photographs of a typical dust sample on the left (sample WTC01-27) and what 

appeared to be an insulation coating from a steel beam on the right (WTC01-8). The 

coating contains as much as 20% chrysotile asbestos. Scale bar is 10 millimeters. 

Back to Table of Contents 

Laboratory Studies of Samples
Overview 

The objective of the laboratory analysis was to characterize the samples for potential 

environmental impacts and to provide feedback to imaging spectral analysis and field 

confirmation of the imaging spectroscopy results. In certain cases the laboratory studies 

provide better detection levels than airborne imaging spectroscopy, thus providing 

complimentary information that allowing a more robust characterization of the entire 

site.

● X-Ray Diffraction (XRD) Analysis 

● Laboratory Reflectance Spectroscopy (RS) Studies 

Reflectance Spectroscopy 

Laboratory Spectra of WTC Samples 

Description of Spectroscopy Methods and Results 

Possible Sources of Abestos in the WTC Dust 

Spectral Detectability of Chrysotile 

Spectral Interference 

● Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis 

(EDS) 

● Chemical Compositions 

Sampling and analytical methods 

Chemistry Table 1,

Results 

Interpretation 

● Leachate Studies 

Leaching of World Trade Center dusts using a simulated 

precipitation leaching procedure 

Results 

Leach Table 1

Interpretation 
Summary and potential environmental implications 

Back to Table of Contents 

Integration of Results and Conclusions 

References 

Acknowledgements 

Back to Table of Contents 

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OFR 01-0429: World Trade Center Asbestos Primer

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Asbestos 

Asbestos is a commercial term that represents several different silicate minerals which separate into long thin 

fibers, are heat resistant, and are chemically inert. Over the years, asbestos has been used in numerous 

commercial applications including fire proofing materials, ceiling tiles, floor tiles, insulation, brake linings, and 

many more. Since the nineteen seventies, the use of asbestos in commercial products has greatly diminished due 

to health concerns and demonstrated links to diseases such as asbestosis, mesothelioma and lung cancer. 

Asbestos can be divided into two major classes of minerals, serpentines and amphiboles.

Chrysotile (includes the minerals clinochrysotile and orthochrysotile) is the only asbestos mineral of the 

serpentine group and has been the most widely used commercially. Chrysotile is a sheet silicate comprised of 

bundles of extremely small, tightly rolled sheets that form tubes or rods. Chrysotile has been more widely used 

than amphibole asbestos because it is usually more flexible, forms longer thinner fibers, and can easily be woven 

into cloth. Chrysotile is not as chemically inert as the asbestiform amphibole minerals.

All other asbestos belongs to the amphibole family of minerals. Amphiboles are chain silicates that include over 

fifty different minerals, most of which do not crystallize in asbestiform varieties. Of the few amphiboles recognized 

to crystallize in asbestiform varieties, those that have been used commercially are grouped into five materials 

that are referred to both in commercial and regulatory nomenclature as; amosite (includes the asbestiform 

varieties of the amphibole minerals cummingtonite and grunerite), crocidolite (asbestiform variety of the mineral 

riebeckite), tremolite (asbestiform variety of the mineral tremolite), actinolite (asbestiform variety of the 

mineral actinolite), and asbestiform anthophyllite. Other amphiboles can occur in asbestiform varieties, but 

these minerals have generally not been used in commercial products and are often not cited in the regulatory 

literature.

Listed below are the nominal (pure) chemical formulas for the most common asbestos minerals. It is rare, 

however, to find pure compounds in natural materials. Considerable chemical substitution often occurs in in these 

minerals, particularly the amphiboles. As examples, some amount of sodium (Na) and potassium (K) often 

substitutes for calcium (Ca), and aluminum (Al) and titanium (Ti) can substitute for silicon (Si).
 

A significant body of research conducted over the last twenty years by toxicologists, epidemiologists and 

mineralogists suggests that the amphibole asbestos minerals are more toxic than chrysotile (Ross, 1999; Skinner 

et al., 1988; Van Oss et al., 1999; McDonald, 2001). This conclusion, however, has not been universally accepted 

by the scientific community. A recent and thorough discussion of this ongoing debate can be found in Nolan, et al. 

(2001).

Definitions:

Asbestiform: The physical form or appearance of minerals that consists of long, thin and 

sometimes flexible fibers or needle-like structures.

Chain Silicate: A class of silicate minerals that form in structural chains. In some of these 

minerals the chains can separate easily along parallel crystallographic planes and can form 

fibrous or needle-like structures. Amphiboles and pyroxenes are members of the chain 

silicate family.

Mineral: A naturally occurring material with a specific chemical composition or range of 

compositions, and a specific crystalline structure.
Sheet Silicate: A class of silicate minerals that form in structural sheets and often break 

easily along one crystallographic plane so as to form extremely thin flat plates. Members of 

this mineral group include micas, clays, and serpentines.

* The above definitions are descriptive and are not intended to be used in the technical evaluation of materials 

containing asbestos.

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OFR 01-0429: World Trade Center USGS Imaging Spectroscopy

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Contents

● Imaging Spectroscopy Mapping Results for the World Trade Center 

Area 

Thermal Hot Spot Maps: Sept 16 and 23, 2001 

Asbestiform Minerals Map 

Dust and Debris Plume Map 

Ferrous and Ferric-Bearing Materials Map 

Clays and other Materials Map 

Organic Compounds Map 

Water Sediment Map 

Imaging Spectroscopy Mapping Results for the World Trade 

Center Area 

The AVIRIS instrument measures upwelling spectral radiance in the visible through 

short-wavelength infrared. The instrument has 224 spectral channels (bands) with 

wavelengths from 0.37 to 2.5 microns (micrometers) with sufficient spectral resolution 

to characterize diagnostic spectral features in materials. AVIRIS was flown at 2 

altitudes in the WTC area for this study to give pixel sizes of approximately 2 and 4 

meters.

The AVIRIS instrument was flown by NASA/JPL over the World Trade Center (WTC) 

area on Sept 16, 18, 22, and 23, 2001, after the attack on the WTC. This page shows 

results of analysis of the Sept 16 data. Collection of data on Sept 18 and 22 was 

hampered by clouds. Analysis of the Sept. 23 data includes an assessment of the 

change in thermal hot spots.

The 13 Gigabytes of September 16th data were sent to the USGS in Denver on 

September 17-18th. Atmospheric absorptions, instrument response and the solar 
spectrum were removed using ground calibration that employs spectra of large, 

uniform areas in new Jersey outside the WTC debris zone. The areas were spectrally 

calibrated with real-time feedback from a field crew (Gregg Swayze and Todd Hoefen) 

on site with portable field spectrometers (Sept. 17-19).

The calibration measurements, field site, and AVIRIS coverage of the New York area 

are detailed within the next link. This is a data page and includes registered images 

with map coordinates for context. This page does not need to be read to follow the 

analysis and conclusions of this report, but is included for others trying to work with 

the AVIRIS data. Click here for the field spectral measurements, registered 

images, and calibration site information.

Once calibrated, the data were analyzed for the presence of specific spectral features 

to identify materials expressed in the spectrum at each pixel in the image. The 

methods employed, from calibration, to imaging spectroscopy analysis (the Tetracorder 

analysis system), to verification of results follows the procedures and methods 

established in Clark and Roush (1984), Clark et al., (1990b, 1991, 1995, 2001), Clark 

1999, King et al., (2000), and Swayze et al., (2000). Reference spectra for the 

mapping are from Clark et al., (1993), Clark (1999), measurements made for the 

above studies, and this study.

Because AVIRIS measures reflected sunlight it cannot detect materials deeper than can 

be seen with the human eye. For most solid materials this optical penetration is 

measured in millimeters.

The materials maps below from AVIRIS and the USGS Tetracorder analysis (Clark et 

al., 2001) describe results from the imaging spectroscopy analysis. Click on the 

thumbnails or text below for full resolution image maps and explanatory text.

Click here to go to the AVIRIS mapping. At the end of each page will be a link to the 

next mapping page. You can jump to specific mapping pages by clicking on the links 

below, or from the index. 

Thermal hot-spot maps. Images of the World Trade Center site show significant 

thermal hot spots on Sept. 16, 2001. By Sept. 23, 2001, most of the hot spots had 

cooled or the fires had been put out. The thermal images show the relative ground 

temperature at the World Trade Center for Sunday Sept 16, 2001 using infrared 

wavelengths sensitive to high temperatures. Red, orange, and yellow spots are regions 

of high thermal emission (high temperatures) with the yellow areas being the hottest 

and red the coolest.
A key concern has been whether asbestos minerals, such as chrysotile, which may 

have been used in the WTC construction, were released into the environment as dusts 

by the WTC collapse. AVIRIS remote sensing images do not show widespread 

distribution of chrysotile or amphibole asbestos at the detection limit of the instrument. 

However, there is an indication of an east-west spread of possible chrysotile 

mineralogy. 

 

Serpentine and Amphibole minerals map.

 

Serpentine and Amphibole minerals map, 

same as at right, but zoomed in to lower 

Manhattan.

Maps of the dust and debris materials are shown. This map shows the asymmetric 

distribution of materials after the building collapsed. 
 

Dust/Debris plume map.

 

Dust/Debris plume map, same as at right, but zoomed in 

to lower Manhattan.

Iron-bearing Material Map: ferric- and ferrous-bearing materials are shown. This map 

shows the asymmetric distribution of materials after the building collapsed. 

 

Ferrous, ferric iron absorption features 

map.

 

Ferrous, ferric iron absorption features 

map, same as at right, but zoomed in to 

lower Manhattan.

The material map of clays and other materials with hydroxyl vibrational absorption 

features shows the asymmetric distribution of materials after the building collapsed, in 

agreement with the ferric and ferrous absorption map above. 
 

Vibrational absorption features map.

 

Vibrational absorption absorption features 

map, same as at right, but zoomed in to lower 

Manhattan.

The organic material map can includes paint, plastics, many types of solvents, 

gasoline, and other materials containing C-H bonds. 

 

Organic materials absorption map.

 

Organic materials absorption map, same as at 

right, but zoomed in to lower Manhattan.

Sediment Map: Sediment in the water in the New York area is common. The maps 

show possible sources (yellow and orange) where material from the World Trade 

Center may be entering the river.
Back to document Table of Contents 

For further information, contact:

Dr. Roger N. Clark

rclark@usgs.gov 

Link to the AVIRIS JPL data facility) 

For information about AVIRIS, contact: 

Robert O. Green

AVIRIS Experiment Scientist 

rog@spectra.jpl.nasa.gov

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Open-File Report 01-0429: AVIRIS Calibration Sites and Spectra

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Here are the calibration site image and corresponding spectral data files as measured 

on the ground using an Analytical Spectral Devices ASD-FR field-spectrometer. (Use of 

trade names is for descriptive purposes only and does not constitute endorsement but 

the USGS.) Several dozen field spectra were collected, averaged, and the results 

smoothed in areas where atmospheric absorption and instrument artifacts occurred. 

Figure 1. Parking Garage Roof (West Bank of the Hudson River, NJ). 
Figure 2. Spectrum Plot of Parking Garage Roof, NJ. 

 

Click here for the ASD spectrometer ASC-II data of the Parking Garage Roof, NJ, 

717 channels (field spectra averaged). Note: wavelengths are in Column 1, 

reflectance data are in Column 2. 

 

Click here for the ASD spectrometer ASC-II data of the Parking Garage Roof, NJ, 

224 channels (field spectra averaged and convolved to 2001 AVIRIS wavelengths). 

Note: wavelengths are in Column 1, reflectance data are in Column 2. 

Here is the full Run 2 image (channel 150) showing the field calibration 

site within the red box at the lower right.
 

Larger 1747 KB image 

Figure 3. Calibration site: AVIRIS Run 2, Sept. 16, 2001. 

Here is the full flight coverage mosaic of AVIRIS (12,500 feet) for Sept. 

16, 2001 (except for Run 8, where the WTC material is being disposed).
 

Larger 6010 KB image 

Figure 4. AVIRIS run02-run07 (W to E) Mosaic

3.3 meter pixels, 0 degrees rotation

WGS-84/NAD83 datum

Joe Boardman, AIG

Back to Imaging Spectroscopy Mapping Results 
Back to document Table of Contents 

For more information contact: 

K. Eric Livo

elivo@usgs.gov 

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OFR 01-0429: World Trade Center USGS Thermal

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Images of the World Trade Center Site Show Thermal Hot Spots on 

September 16 and 23, 2001. 

Results of Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) remote sensing data and 

interpretations show the distribution and intensity of thermal hot spots in the area in and around the 

World Trade Center on September 16 and 23, 2001. Data collected on the 16th were processed, 

interpreted and released to emergency response teams on the 18th of September, 2001. The 

September 23 data were processed, interpreted and the results released on October 12, 2001. The 

images of the World Trade Center site show significant thermal hot spots on Sept. 16, 2001. By Sept. 

23, 2001, most of the hot spots had cooled or the fires had been put out.

The AVIRIS instrument is a National Aeronautics and Space Administration (NASA) remote sensing 

instrument that measures upwelling spectral radiance in the visible through short-wavelength infrared. 

The instrument has 224 spectral channels (bands) with wavelengths from 0.37 to 2.5 microns 

(micrometers). 

In response to requests from the EPA through the USGS, NASA flew AVIRIS on a De Havilland Twin 

Otter over lower Manhattan at mid-day on September 16 and 23, 2001. For these deployments, the 

Twin Otter was flown at altitudes of 6,500 and 12,500 feet. The spectral data for the maps shown here 

were measured at 6,500 feet and have a spatial resolution (pixel spacing) of approximately 6 feet (2 

meters).

AVIRIS records the near-infrared signature of heat remotely. The accompanying maps are false color 

images that show the core affected area around the World Trade Center. Initial analysis of these data 

revealed a number of thermal hot spots on September 16 in the region where the buildings collapsed 5 

days earlier. Analysis of the data indicates temperatures greater than 800oF. Over 3 dozen hot spots 

appear in the core zone. By September 23, only 4, or possibly 5, hot spots are apparent, with 

temperatures cooler than those on September 16 (Thermal Figure 1).
 

Thermal Figure 1. Hot spots show as orange and yellow areas. Dozens of hot spots are seen on 

September 16, but most had cooled or the fires had been put out by September 23. 

The images (larger area shown below) also show vegetated areas as green. Water appears blue, and 

the smoke from the fires appears as a light blue haze. White and lighter blue areas are rooftops, roads, 

and concrete as well as dust and debris from the collapsed buildings. Dust, probably more than a 

millimeter thick, appears in shades of brown around the core WTC area on the 16th.

On the September 16th, 2001 image (Thermal Figure 2), large areas around the World Trade Centers 

show brownish colors, indicating the debris. On September 20, 2001 there was a significant rain storm 

that washed away some of the dusty debris. Reduction of the distribution of dust/debris is apparent in 

the September 23 image (Thermal Figure 3), and can be attributed to the cleanup effort along with the 

rain.

There are other red/orange spots that show in the images in the area south of the World Trade Center 

zone. These are hot spots from chimneys or heating exhaust vents and are normal and not other 

uncontrolled fires.

The AVIRIS data were processed at the Jet Propulsion Laboratory (JPL) in Pasadena California where 

the data are calibrated to radiance and corrected for aircraft yaw, pitch, and roll. Acquisition and 

calibration of AVIRIS data at JPL are under the direction of Robert O. Green. The data were then 

transmitted to the U.S. Geological Survey (USGS), Imaging Spectroscopy Group in Denver, Colorado, 

under the direction of Dr. Roger N. Clark. Atmospheric and ground calibrations were applied to derive 

apparent surface reflectance and maps were then made of surface materials. The USGS imaging 

spectroscopy group includes Dr. Gregg Swayze, Eric Livo, and Todd Hoefen.
 
Thermal Figure 2. AVIRIS image from September 16, 2001. Hot spots show as orange and yellow 

areas. Yellow is hotter than red (because of color mixing in the way the 3-color image was produced). 
 
Thermal Figure 3. AVIRIS image from September 23, 2001. Only a couple of hot spots remain in view. 

 

Larger 254 KB image 

Thermal Figure 4. Index for the locations of some of the hot spots observed on September 16, 2001.
Temperature of the Hot Spots 

Remote measurement of the temperature is difficult because the source of the thermal emission can be 

less than the field of view of the measuring instrument. In that case a thermal sensor has an 

ambiguous solution: a hotter temperature of a smaller area or lower temperature of a larger area can 

result in the same total received thermal radiation.

A spectrometer, however, overcomes the ambiguity problem above, because the shape of the thermal 

spectrum can be used to derive a unique temperature, and the intensity gives the area of the emitting 

source. If a large enough spectral range is covered, a range of temperatures and the area of each can 

be derived. In the near infrared spectral range of AVIRIS, reflected solar radiation also contributes to 

the signal. The solution to the generalized problem involving all these effects is given in Clark (1979).

We derived temperatures using two methods: calibrated radiance, and derived reflectance following 

Clark's (1979) methods. In derived reflectance, thermal radiation is the Planck response divided by the 

solar spectrum. This has several effects: 1) the data are corrected for atmospheric absorption and 

scattering, 2) the reflected solar component can be readily assessed and compensated for, and 3) the 

ratio of the Black-Body response by the solar spectrum produces a very steep curve that is readily 

distinguishable from reflected sunlight and reflectance of surface materials.

Simple temperature derivation from derived reflectance is illustrated in Thermal Figure 5a and b. Here 

the hot spot is assumed to fill the pixel. The thermal response of hot spot A (from Thermal Figure 4) 

shows the AVIRIS response higher than the 800 kelvin curve. The 800 Kelvin temperature is a lower 

limit to the temperature. While the upper limit might be the 900 Kelvin curve, we see the slopes do not 

match. As temperatures increase, the peak in Black Body emission moves to shorter wavelengths and 

the slope of the curve decreases at positions on the short wavelength side of the peak (the case here).

Hot spot C (Thermal Figure 5b) shows similar effects. For hot spots covering the full area of the pixel, 

the temperature must be greater than 700 Kelvin. At about 1.3 microns, the model at 800 Kelvin 

matches the AVIRIS data, but the 800 Kelvin curve has a higher slope. This indicates the hot spot is 

smaller than the size of the pixel, but hotter than 800 Kelvin.

Solutions that include reflected solar radiation, hot spot temperature and hot spot area are shown in 

Thermal Figures 6a and b. Hot spot A, which from Thermal Figure 5 has a temperature greater than 

800 Kelvin, is found to have a 1000 Kelvin temperature in a spot covering ~15% of a pixel, or 0.56 

square meter. Similarly, hot spot C is found to have a 900 kelvin temperature over 20% of a pixel, or 

0.8 square meter.

The sensitivity of the solution of area and temperature is illustrated in Thermal Figure 7. An excellent 

fit is obtained for hot spot C with a 900 Kelvin spot filling 20% of the pixel. At 1000 Kelvin, only 8% is 

required but the fit is noticeably worse. For temperatures in the 800-1000 Kelvin range, temperature 

accuracy is estimated to be ± 30 Kelvin and the area ± 5%. For smaller spots, like spot G in Table 1, 

the temperature accuracy is similar, but the accuracy on such small areas is approximately +5%, -

0.5%. For example, decreasing the temperature to 1000 Kelvin (from 1020 Kelvin) on spot G increases 

the fractional area to about 5%.

Positions, temperatures and equivalent areas for hot spots A-H are given in Table 1 and the 

geometrically rectified location map is shown in Thermal Figure 8.
 

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Thermal Figure 5a.
 

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Thermal Figure 5b
 

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Thermal Figure 6a
 

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Thermal Figure 6b
 

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Thermal Figure 7.

Table 1 Thermal Hot Spot Data

Location Temperature Area 

Hot Spot N Latitude W Longitude (Kelvin) % 

FOV sq meter

A 40o 42' 47.18" 74o 00' 41.43" 1000 15 0.56 

B 40o 42' 47.14" 74o 00' 43.53" 830 2 0.08 

C 40o 42' 42.89" 74o 00' 48.88" 900 20 0.8 

D 40o 42' 41.99" 74o 00' 46.94" 790 20 0.8 

E 40o 42' 40.58" 74o 00' 50.15" 710 10 0.4 

F 40o 42' 38.74" 74o 00' 46.70" 700 10 0.4 

G 40o 42' 39.94" 74o 00' 45.37" 1020 1 0.04
H 40o 42' 38.60" 74o 00' 43.51" 820 2 0.08

Positions are in degrees-minutes-decimal seconds, datum WGS84. 

Position accuracy is estimated to be approximately +/- 6 meters (18 feet). 
Click here for 180 KB geo-tif image 

Thermal Figure 8. Geometrically rectified image of the WTC core region showing hot spot locations.

Additional temperature analysis: ftp://popo.jpl.nasa.gov/pub/outgoing/WTC_AVIRIS_HOT.htm 

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OFR 01-0429: World Trade Center Asbestiform Minerals Map

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Images of the World Trade Center site show weak patterns of 

materials with spectral absorptions indicating the possible 

presence of asbestiform minerals.

Spectral reflectance mapping keyed to minerals that can have asbestiform varieties shows only scattered 

possible occurrences at the surface around the World Trace Center area. Spectroscopy identifies 

mineralogy by detecting absorptions, due to molecular bonds, at a characteristic wavelength and with a 

diagnostic band shape. The grain size of a mineral affects the intensity and, to some extent, the shape of 

its spectral absorptions, but spectroscopy may not be sensitive to whether a mineral has an asbestiform 

shape (long needle-like shapes with diameters less than a micrometer). Research is underway to see if 

spectroscopy can, at some level, be used to differentiate asbestiform from nonasbestiform mineral shapes.

To read about asbestos mineralogy and definitions, click here. Use the back key on your browser to return 

here.

To the extent that the top few millimeters contain mineralogy that is representative of the underlying 

material, spectral mineral maps can be used to assess potential asbestos distribution in the WTC debris. It 

is also possible that asbestos-bearing debris is buried beneath the surface and that AVIRIS was not be 

able to detect it.

Building materials can contain trace serpentine and amphibole minerals that are naturally occurring but 

not asbestiform. During the era when the WTC was built, industrial asbestos was reportedly used. 

Therefore, detection of asbestiform mineralogy warrants further investigation.

The map, A-Figure 1a, b, shows possible weak absorption features indicative of minerals that may occur 

with asbestiform morphology. The map shows relatively isolated pixels indicating areas that may warrant 

further investigation (colored pixels). The detection limits are still under study, but are probably in the few 

percent range for these data. Note that in shadows, there is not enought light for spectroscopic 

determination of surface mineralogy, so it is unknown if these locations have asbestos-bearing debris.

Laboratory Spectroscopy of the WTC samples (discussed in detail in the laboratory spectroscopy section, 

and in the integration of results section) show, in all but one case (sample WTC01-08), only very weak, if 

any, spectral features from chrysotile because the occurrence of chrysotile asbestos is present in trace 

abundances less than about 1 %. Such abundances are not detectable by AVIRIS. Thus, is is not 

surprising that the AVIRIS map shows little asbestiform mineralogy. The lack of large contiguous clusters 

of colored pixels at the WTC site, indicates that spectral mineral mapping has NOT detected widespread 

concentrations of asbestos in the debris above a few percent, mostly leaving just the black and white base 

image (see Iron-bearing Material Map or Dust Plume for examples of contiguous clusters of colored pixels).

The AVIRIS map (A-Figure 1a, b) does show pockets (or small clusters of pixels) of serpentine (closest 

spectral match is chrysotile, A-Figures 2, 3). The strengths of the spectral signatures indicate levels of a 

few percent, up to the 10 and 20% levels (A-Figures 2, 3) observed in sample WTC01-08. Again, some or 

all of these pixels may be non-asbestiform serpentines in building materials. 

Mineralogic characterization of field samples (discussed in the laboratory sections) suggests that only 

trace levels of chrysotile asbestos were present in some of the samples from the WTC area, with one 

exception. The exception is a coating from a steel beam (sample WTC01-08) which showed chrysotile 

levels that could be as high as 20%. It should be noted that the field sampling sites do not coincide with 

AVIRIS pixel locations that indicate possible chrysotile or amphibole presence (A-Figure 4). But many field 

sample locations whose samples contain trace asbestos occur near locations in the AVIRIS map that 

indicate higher levels of serpentine minerals.

The correlation of mineralogically characterized field samples and AVIRIS mapped serpentine and 

amphibole mineralogy is shown in A-Figure 4. There appears to be a bias in chrysotile detection into a 
broad east-west trend, in both the AVIRIS and the laboratory results. This asymmetry in the dust/debris 

composition is supported by other compositional analyses, both AVIRIS and laboratory (see lab 

spectroscopy and integrations of results sections of this report).

The lower limit of detection of the AVIRIS instrument for asbestos minerals and, consequently, the WTC 

AVIRIS data set is probably in the few percent range as noted above. Asbestos levels below this detection 

limit and the implications of low levels of asbestos on human health are beyond the scope of this report.

The fact that field sampling shows high levels of chrysotile asbestos in some of the steel beam coatings 

(up to 20%) indicates the need for dust control during beam removal. Workers who are removing the 

beams should wear proper respiratory protection. However, video from news reports of the cleanup 

activity show that many of the steel beams no longer have the insulation coating. Where did the coatings 

go? It is probably now in the dust and debris. Thus the possibility exists that there may be other pockets 

of high levels of chrysotile, leading to the conclusion that workers should employ protective measures 

when cleaning up any dust or debris.

 

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A-Figure 1a. Serpentine and 

Amphibole minerals map.

 

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A-Figure 1b. Serpentine and Amphibole minerals map, same as 

at right, but zoomed in to lower Manhattan.
 

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A-Figure 2. Spectra of some of the mapped chrysotile is a close match to the spectra of coating WTC01-

08 which contains up to about 20% chrysotile.
 

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A-Figure 3. Example areas in the image with serpentine-like hydroxyl absorption feature.
 

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A-Figure 4. WTC Sample analyses are shown plotted on the serpentine/amphibole AVIRIS map. There is 

a loose correlation of chrysotile locations spread in an east-west direction in both the laboratory analyses 

and the AVIRIS data.

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OFR 01-0429: World Trade Center USGS Dust/Debris Plume Map

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Maps of dust and debris show asymmetric distribution of 

materials. 

The map images on this page (Dust Figures 1a, 1b, 2a, 2b) show locations of materials with spectral 

shapes similar to the spectra of field samples of dust and debris collected around the lower Manhattan 

area. These materials/minerals include common building materials; therefore, the maps may include 

materials in buildings not associated with the World Trade Center (WTC) collapse. While the minerals 

mapped in any one location may or may not be associated with the WTC event, a pattern is seen that 

appears to show the distribution of materials related to the WTC collapse. Further, the debris map 

qualitatively agrees with on scene observations 2 days after the imaging spectroscopy data were 

acquired. Production of a dust/debris map was challenging because building materials are similar all over 

the city (e.g. concrete occurs in many locations). However, the pulverized dust/debris does have some 

general spectral characteristics that can be used.

Spectra of the field samples shows a general range of spectral characteristics (Dust Figure 3). Samples 

WTC01-37B and WTC01-37Am are concrete that display ferrous iron absorptions (most likely due to the 

aggregate). The spectrum of concrete minus the aggregate is shown in sample WTC01-37A: the cement 

shows less ferrous absorption. Pervasive in the spectra of the debris is gypsum, and with the variations in 

abundance of other components, spectra of the dust and debris show the spectral variations seen in Dust 

Figure 3. We mapped for these general spectral shapes over the spectral range 0.5 to 2.4 microns. The 

ultraviolet was not included because scattering from smoke affects shorter wavelengths to much. The 

strategy proved effective. The maps should not be interpreted as indicating that these specific materials 

were mapped, only that the spectral shape is similar. However, red and yellow colors indicate areas 

showing more ferrous-like absorptions, and this is apparent in the WTC core zone where many steel 

girders dominate. Green copper roofs have a similar absorption to ferrous minerals, so they would map as 

red or yellow.

Two versions of the dust/debris map are shown (Dust Figure 1a, 1b, 2a and 2b). Dust Figure 2a, b is the 

same as Dust Figure 1a, b but without the grey-scale image background. Dust Figure 2a, b allows one to 

see the mapped materials without the apparent clutter of the grey-scale image.

The plume map in Dust Figures 1 and 2 indicate an asymmetry in the dust/debris distribution, with more 

iron bearing materials to the south by southeast. It is difficult to locate the outer boundary of the dust/

debris because of the problem of matching common materials throughout the city.

The reference spectra used for matching the dust/debris was: 

wtc01-37B (Note the strong Fe2+ absorption near 1-um.)

wtc01-37Am 

wtc01-37A 

wtc01-15 

wtc01-28 

wtc01-36 
 

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Dust Figure 1a. Dust/Debris 

plume map.

 

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Dust Figure 1b. Dust/Debris plume map, same as at right, but 

zoomed in to lower Manhattan.
 

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Dust Figure 2a. Dust/Debris 

plume map without the image 

background so the mapped 

materials are easier to see.

 

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Dust Figure 2b. Dust/Debris plume map, same as at right, but 

zoomed in to lower Manhattan.
 

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Dust Figure 3. Reference spectral shapes used for making the dust/debris map. The colors match the 

colors on the maps in Dust Figures 2, 3.

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OFR 01-0429: World Trade Center USGS Ferric-Ferrous Map

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Images of the World Trade Center site show significant patterns 

of materials with spectral absorptions near 1-micron.

The images on this page (Iron Figure 1, 2) show locations of materials with ferric and ferrous absorption 

features. These materials/minerals may include common building materials; therefore, the map may 

include materials in buildings not associated with the World Trade Center (WTC) collapse. While the 

minerals mapped in any one location may or may not be associated with the WTC event, a pattern is seen 

that shows the distribution of materials related to the WTC collapse. This is because the debris from the 

collapse tends to appear contiguous near the WTC or in patches unrelated to the layout of roads and 

buildings. Building materials that map with sharp boundaries as roads and building shapes may not be 

WTC debris.

Fe-bearing materials occur in the WTC area and appear to be distributed in and around the collapse zone. 

Materials that were mapped show absorption features indicative of both ferric (Fe3+) and ferrous iron (Fe2

+). Many minerals have similar ferrous absorptions, so maps show only the presence of Fe-bearing 

minerals and not specific mineralogy. In the maps below, the ferric and ferrous materials are identified 

only by numbered color. Pixels mapped as each numbered color indicate similar absorption position and 

shape and are likely similar in composition, but that composition is not generally a unique identifier of 

mineralogy.

The ferric absorptions are interpreted to be due to hematite (Fe2O3 - iron rust), or goethite (FeOOH). The 

red coatings on iron beams seen in news reports and by are field team are consistent with hematite or 

goethite.

Fe-bearing minerals are common in the aggregate in concrete. The Fe-absorptions appear in spectra of 

the debris samples and are prominent in spectra of the concrete debris. To see laboratory spectra of the 

dust and debris samples, CLICK HERE. 

The map shows an asymmetric distribution of debris that extends to the SSE of the site. Similar 

distribution patterns are seen on the debris map (see previous section Dust and Debris Plume Map.) and 

the vibrational absorption map (next section), indicating a consistent finding of asymmetric distribution. 

Iron Figure 2 is the same as Iron Figure 1 but without the grey-scale image background. The debris 

pattern is more obvious without the background.

The asymmetry in the iron-bearing materials map may be related to the asymmetry in the asbestiform 

minerals map. The AVIRIS data and the laboratory analyses of the field samples indicate a lower 

abundance of chrysotile in the the southern direction from the WTC, the same direction of the increase in 

iron-bearing materials. The implications of this distribution will be explored in the Integration of results 

and conclusions section, below.
 

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Iron Figure 1a. Ferrous, ferric 

iron absorption features map.

 

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Iron Figure 1b. Ferrous, ferric iron absorption features map, 

same as at right, but zoomed in to lower Manhattan.
 

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Iron Figure 2a. Ferrous, ferric 

iron absorption features map, 

without the image background so 

the mapped materials are easier 

to see.

 

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Iron Figure 2b. Ferrous, ferric iron absorption features map, 

same as at right, but zoomed in to lower Manhattan.

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OFR 01-0429: World Trade Center USGS Vibrational Processes Map

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Images of the World Trade Center site show patterns of 

materials with spectral absorptions due to vibrational processes

The map on this page (Vibrational Figure 1) shows locations of materials with vibrational absorption 

features commonly found in clays and other phyllosilicates (like muscovite), carbonates, and waterbearing sulfates. Such minerals are commonly found in building materials. For example, walls are often 

constructed with a board containing gypsum, a sulfate. Gypsum has been identified in samples from the 

WTC area (see sample analysis section). Muscovite, carbonates, and other hydroxyl-bearing minerals 

have also been identified in the WTC samples (see the Integration of Results section).

The debris contains common building materials, therefore, the map also shows these materials in other 

buildings not associated with the World Trade Center (WTC) collapse. While the minerals mapped in any 

one location may or may not be associated with the WTC event, a pattern is seen that shows the 

distribution of materials related to the WTC collapse. This pattern matches the pattern from the ferric and 

ferrous absorption features map.

The spectral absorptions due to vibrational processes are normally diagnostic of mineralogy or material 

type. The spectral signatures in the WTC debris are, however, quite weak (see laboratory spectroscopy of 

field samples, below). Because of their weak strength, and influences of the spectral signatures of other 

materials, including organics, definitive identifications could not be made in this case. Definitive 

identifications might be made on such samples if the sensor had a higher signal to noise.

Both the iron maps, dust/debris maps, asbestiform mineralogy maps, and vibration absorption maps show 

a pattern of materials suggesting asymmetric distributions to the composition of the debris/dust. 

Again, at any one location in the image, the mapped materials may be unrelated to the WTC debris 

because they may be common building materials used in the area. However, if a certain type of debris 

must be cleaned up, this and the other maps indicate the locations to investigate on the ground where 

similar compositions occur.
 

Larger 1477 KB image 

Vibrational Figure 1a. 

Vibrational absorption features 

map.

 

Larger 526 KB image 

Vibrational Figure 1b. Vibrational absorption absorption 

features map, same as at right, but zoomed in to lower 

Manhattan.

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OFR 01-0429: World Trade Center USGS Organic Components Map

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Images of the World Trade Center site show patterns of 

materials with spectral absorptions indicating the presence of CH (organic) compounds. 

The map of materials containing organic compounds (Figure 1a, 1b) shows no pattern that is indicative of 

the distribution of debris from the WTC collapse at the detection limit of AVIRIS. Organic compounds 

include any material containing C-H chemical bonds (e.g. plastics, paints, gasoline, and many types of 

solvents).

Because there are literally thousands of organic compounds and our reference materials spectral library 

only contains a few samples, we do not have the capability to uniquely identify the various types of 

organic materials. Because the reference spectra covering the AVIRIS spectral range is sparse, it is also 

unknown if AVIRIS has the spectral resolution to uniquely separate some types of organic compounds. 

Thus the organics map here does not indicate unique compounds. But the different colors indicate 

different spectral classes of organics and indicate broadly similar compositions.

The majority of the organics mapped in this area are probably related to plastics and paints. Paper, wood, 

and vegetation are also organic, but the spectral signatures of these materials occur with other known 

absorptions (e.g. from lignin, cellulose, and nitrogen) and are excluded from this map. Some aged wood, 

however, does have spectral features that can be confused with the other organics here (e.g. due to 

decreased signatures of lignin, cellulose, and nitrogen), and might be included in this map.

Imaging spectroscopy has not detected more than a few percent organic material in the WTC debris. It 

may be possible that more organic material exists but was not spectrally observable at the surface with 

AVIRIS. 

Absorptions due to CH occur near 2.3 microns: the same location as (OH) absorptions in serpentines and 

amphiboles (asbestiform minerals). This coincidence results in a higher threshold detection limit for 

asbestiform minerals when CH-absorptions are present in the spectrum. Fortunately, CH-compounds also 

have additional absorption features (e.g. those near 1.65 to 1.75 microns, Figures 2a, b, c) that make 

detecting such compounds possible and reducing false positive identifications of asbestiform minerals. 

Thus, locations on this map where CH-compounds are present also indicate locations where asbestiform 

minerals are indeterminate.
 

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CH Figure 1a. Organic materials 

absorption map.

 

Larger 519 KB image 

CH Figure 1b. Organic materials absorption map, same as at 

right, but zoomed in to lower Manhattan. 
 

Larger 18 KB image 

CH Figure 2a. Example spectra of CH compounds used to map the organics in CH Figure 1. The colors of 

the spectra match the colors of the materials on the map.
 

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CH Figure 2b. More spectra of CH compounds used to map the organics in CH Figure 1. The colors of the 

spectra match the colors of the materials on the map.
 

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CH Figure 2c. More spectra of CH compounds used to map the organics in CH Figure 1. The colors of the 

spectra match the colors of the materials on the map.

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OFR 01-0429: World Trade Center USGS Water Sediment Map

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Images of the World Trade Center area show sediment in the water. 

The maps in Water Figures 1, 2, produced by analysis of spectral data from the NASA/JPL Airborne Visible/Infrared Imaging 

Spectrometer (AVIRIS) instrument, shows sediment in the water next to the World Trade Center. Relative abundances of 

solids determined for this AVIRIS data set are qualitative because the absorption strengths have not been calibrated to 

abundance and are shown along with presence of chlorophyll. Water absorption feature shape changes with relative 

abundance of sediment load. Here, the load has been differentiated as high (orange) and low (yellow) on the map. In 

regions of lower sediment load, chlorophyll (blue) can be detected. Water mapped as black is either clear water with low 

chlorophyll or areas where a surface film inhibits seeing into the water.

Waterborne sediment is shown on the map along the eastern shore of the Hudson River and in the East River. Along the 

Hudson River, sediment is most apparent west of the World Trade Center and alongside piers and docks. Areas with high 

sediment load are candidates for sampling to determine if such sediments originated from the region of the World Trade 

Center.

The apparent source region of the sediment occurs where debris from the WTC is being loaded onto barges. Thus, the 

sediments at this location may be from the WTC.

The black area on the map at the south end of Manhattan Island in the 15:15 GMT data (Water Figure 1) shows high 

infrared reflectance indicating the presence of a surface film. In the data from 16:21 (Water Figure 2), the surface film is 

mostly dissipated.

 
Water Figure 1. 4-meter pixel data shows sediment in the water. 
 

Water Figure 2. 2-meter pixel data shows sediment in the water. 

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OFR 01-0429: World Trade Center USGS Thermal

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Sample collection in the World Trade Center area, 

Sept 17-18, 2001 

A 2-person USGS crew collected grab samples from 35 localities within a 0.5 - 1 km 

radius circle centered on the World trade Center site on the evenings of September 17 

and 18, 2001 (see sample collection map, below). This same crew also carried out onthe-ground reflectance spectroscopy measurements during daylight hours to calibrate 

Airborne Visible /Infrared Imaging Spectrometer (AVIRIS) remote sensing data.

Many of the streets bordering the collection locations were cleaned or were in the 

process of being cleaned at the time of sample collection. Given this limitation, 

collection of dust samples was restricted to undisturbed window ledges, car 

windshields, flower pots, protected areas in door entry ways, and steps. Occasionally, 

samples were collected from the sidewalk adjacent to walls that were afforded some 

degree of protection from the elements and cleanup process. In many cases the 

samples formed compact masses suggestive of having been dampened by rain and 

having dried in the intervening 3 - 4 days. Two samples of an insulation coating 

(WTC01-8 and WTC01-9) were collected from steel girders recently removed from the 

debris pile of the WTC. Samples were gathered by nitrile-gloved hand and put into 

doubled plastic sample bags (sample bag in another sample bag). Initially, Global 

Position Satellite (GPS) locations were collected for the sample collection locations, but 

this approach was abandoned because of difficulty in acquiring a satellite signal 

between tall buildings. Instead, sample locations were identified using road 

intersections where road signs remained intact. All but two of the samples were 

collected outdoors and had been subjected to wind and water during a rain storm the 

night of September 14. One sample (WTC01-20) was collected indoors near the 

gymnasium in the World Financial Center directly across West Street from the World 

Trade Center. Samples of concrete (WTC01-37A and WTC01-37B) were collected from 

the WTC debris at the same location as WTC01-9. A sample of dust (WTC01-36) blown 

by the collapse into an open window of an apartment located 30 floors up and 0.4 km 

from the center of the WTC site was also acquired a few days later.

For further information, contact: 

Dr. Gregg A. Swayze

gswayze@usgs.gov

or

Todd Hoefen
thoefen@usgs.gov 

 

Larger 92 KB image 

SL Figure 1. Sample location map.
SL Figure 2. Optical image of dust and debris collected 0.3 km from ground zero 

(sample WTC01-27).
SL Figure 3. High magnification optical image of dust and debris collected 0.3 km 

from ground zero (sample WTC01-27). Most of the fibers seen in the image are 

probably glass fibers (e.g. from rock wool or fiberglass insulation) with a probable 

trace of chrysotile asbestos as detected by X-ray diffraction in this sample.
SL Figure 4. Optical image of an insulation coating collected from a steel beam 

removed from the WTC debris pile (sample WTC01-8). 

This insulation contains up to 20 volume % chrysotile asbestos.
SL Figure 5. High magnification optical image of an insulation coating from a steel 

beam removed from the WTC debris pile (sample WTC01-8). 

This insulation contains up to 20 volume % chrysotile asbestos.

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OFR 01-0429: X-Ray Diffraction (XRD) Analysis

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X-Ray Diffraction (XRD) analyses of WTC samples (Table 1, on the Integration of Results page) indicate that 

most samples contain varying amounts of crystalline quartz, gypsum, calcite, anhydrite and amorphous 

material (e.g. XRD Figure 1). Other phases identified in small amounts include: muscovite, feldspar, 

magnesiohornblende, lizardite (non-asbestiform serpentine), dolomite, bassanite, illite, portlandite, larnite, 

polymorphs of calcium silicates, possible asbestiform chrysotile, and others. The results are reported as major 

(>20% by weight), minor (>5% but <20% by weight), and trace (<5% by weight). These ranges were 

determined by operator experience for the purpose of informing analysts and other interested parties of the 

relative concentrations of the phases present in samples. 

All of the above mentioned phases can be components of the building dry wall material, concrete foundation, 

and/or insulation. Determining the presence of chrysotile at very low concentration levels by XRD is difficult due 

to the amount of other crystalline substances and the increased background due to large amounts or X-ray 

amorphous "slag wool," contained in all dust samples. It is possible that small amounts of chrysotile (probably 

<1.0%, XRD Figure 2) may be present in a few samples (see Table 1 on the Integration of Results page). The 

presence of chrysotile can sometimes be verified by other analytical methods; due to the heterogeneity of the 

samples, the splits that were made may not be representative, so results may vary. More work may be 

necessary to try to separate the chrysotile from the other material to determine if chrysotile is indeed present in 

any of the samples, especially if it's presence can be verified by only one method. 

XRD Figure 1. X-ray diffractogram of World Trade Center dust sample WTC01-6. Note domination of peaks 

from calcite, quartz, gypsum, and anhydrite, the main minerals in most of the 33 samples collected. Also note 

the increased background, which indicates a major concentration of X-ray diffraction amorphous (noncrystalline) material. This sample contains no detectable chrysotile asbestos and was therefore used in 

preparing synthetic mixtures of dust + chrysotile. 
XRD Figure 2. Details of a diagnostic X-ray diffraction peak attributed to chrysotile (NIOSH standard CH-19) in 

synthetic mixtures of chrysotile in sample WTC01-6 in weight percent. This set of diffractograms was used as a 

guide for determining relative chrysotile concentrations in the 33 dust samples collected from around the WTC 

site. Sample splits were not homogenous so results can vary. 

NEXT Section of Report: Laboratory Reflectance Spectroscopy (RS) Studies 

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For further information concerning XRD analyses, contact: 

Stephen J. Sutley

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OFR 01-0429: Laboratory Reflectance Spectroscopy (RS) Studies of WTC 

Samples 

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

Reflectance Spectroscopy

Spectroscopy is a tool that detects chemical bonds in molecules (solid, liquid or gas) 

through absorption (or emission) features in the spectrum of the material. While 

crystallinity affects the shape of spectral features, non-crystalline materials (such as 

glass or plastic) still display absorption features in their spectra. Results of the spectral 

analysis of the WTC samples is given in Results Table 1 (in the Integration of Results 

section, below). In general, ultraviolet to near-infrared reflectance spectroscopy used 

for this analysis (0.35 to 2.5 microns) has different sensitivities to materials than XRD. 

Reflectance spectroscopy in this spectral range is particularly sensitive to hydroxyl and 

water-bearing materials (OH and H2O), organic compounds (materials containing C-H), 

carbonates (e.g. found in marble), water-bearing sulfates (like gypsum used in 

wallboard), and iron-containing compounds (like hematite: iron rust used to color 

bricks red).

Laboratory spectroscopy differs from airborne imaging spectroscopy in 3 respects: 1) 

Single spots are analyzed, not images, 2) There is little interfering atmosphere to block 

portions of the spectrum, and 3) Signal to noise in the laboratory is much higher. 

Consequently, laboratory analyses have much higher sensitivity to the individual 

materials in a sample.

To see plots of spectra for each sample, and to get the digital spectral data for each 

sample (ascii list), CLICK HERE. 

Description of Spectroscopy Methods and Results 

Reflectance spectra of 33 dust samples collected on Sept. 17, 18, and 19th from areas 

within a 1 km radius circle of the WTC collapse site (RS Fig. 1) were measured in a 

laboratory High Efficiency Particulate Air Filter (HEPA) fumehood with an Analytical 

Spectral Devices Full Range Spectrometer over the range from 0.35 - 2.5 microns 

using a halogen lamp for illumination and spectralon panel for reference. (Use of trade 

names is for descriptive purposes only and does not constitute endorsement but the 

USGS.) The entire unsplit sample was first poured from the plastic sample bag onto a 

clean sheet of paper, then the sample was mixed with a spatula leaving a relatively flat 

broad pile up to a few centimeters thick for spectral measurement. Mixing allowed us 

to avoid possible inadvertent effects of particle sorting that may have occurred during 

transport. Given that reflectance spectroscopy does not detect materials any deeper 
than can be seen with the eye, we tried to compensate by first measuring ten spectra 

of the pile and then remixing the pile before collecting an additional ten spectra. Our 

intent was to expose previously unmeasured material at the surface for the last set of 

measurements. The spectrometer optical fiber was held a few centimeters above the 

pile and moved constantly in an elliptical manner to spatially average the surface of all 

but the edges of the pile. This method allowed us to spectrally characterize about two 

thirds of the entire sample. Samples were then split by quartering and portions sent 

out for various other analyses. We used one quarter of the sample as a research split 

supplementing evenly from the other three quarters as needed to build the bulk of the 

split. After separating the research split any remaining sample was then recombined 

and set aside as a chain of custody archive sample.

 

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RS Figure 1. Surface sample collection locations in lower Manhattan Sept 17 - 

19th, 2001. 

Spectra of each dust sample were averaged and corrected to absolute reflectance 

using a National Institute for Standards and Technology traceable spectral correction. 

Overall spectra of the dust samples look nearly identical with reflectance levels that 

vary between 20 - 45 % with a strong absorption edge between 0.35 - 0.8 microns 

(sharp downturn in RS Fig. 2). There are only weak spectral absorptions, apart from 

the absorption edge, in the electronic region of the spectra (0.35 - 1.35 microns) 

indicating that the dust contains only low abundances of materials with Fe absorptions 

or absorptions from other transition elements. However, there are numerous spectral 

absorptions in the vibrational spectral region from 1.35 - 2.5 microns principally at 

1.45, 1.75, 1.94, 1.97,and from 2.2 - 2.4 microns. The strongest spectral feature is at 

1.94 microns and is due to structural and adsorbed water, with the next weaker 

feature at 1.45 microns (due to water and/or OH) which varies in depth from 2 - 6 % 

and up to 13 % in WTC01-17. Spectral features at 1.75 microns are next weakest with 

depths of only a few %. Spectral features in the 2 micron region are weakest varying 

from a fraction of a percent up to 1 % depth.
 

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RS Figure 2a. Reflectance spectrum of a sample of World Trade Center dust 

collected indoors near the "gym" immediately adjacent to the WTC site. The 

0.35 - 2.5 micron spectral region is dominated by vibrational absorptions caused 

by gypsum from pulverized wallboard. 

 

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RS Figure 2b 
 

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RS Figure 2c 

Absorption features can be diagnostic of the materials contained in the dust. Gypsum, 

probably from crushed wallboard, has the strongest spectral features accounting for 

most of the bands observed in the vibrational portion of the spectra. This mineral has 

three diagnostic bands that form a stair-step like triplet between 1.42 - 1.54 microns 

recognizable in nearly all dust samples. It also has bands at 1.75, 1.95, 1.975, 2.17, 

2.217, and 2.268 microns closely matching the positions and geometry of the bands 

observed in the dust. In addition to those absorptions attributable to gypsum, an 

absorption at 1.413 microns may be due to portlandite or muscovite, both mineral 

components of the WTC concrete (see XRD results in Table 1 for samples WTC01- 

37A&B). Spectral evidence for muscovite is seen in the 2 micron region where the 

overall shape of the absorptions match gypsum but the expected band position of 

gypsum at 2.217 microns is shifted to 2.209 microns as would be expected in a sample 

containing both gypsum and muscovite. Additional absorptions located at 2.307 and 

2.343 microns are due to C-H stretches from organic materials.

SEM energy dispersive analysis indicates fibrous glass with elemental composition 

closely matched by slag wool in all dust samples analyzed by this method. Slag wool 

has only weak spectral absorptions and is virtually spectrally transparent over the 

0.35- 2.5 micron spectral range. However, other materials associated with slag wool 

may contribute to some of the spectral features observed in the dust. An asbestos-free 

coating (WTC01-9) taken from a steel girder from the debris pile west of WTC tower 1 

has relatively strong 2.307 and 2.343 micron absorptions that match the positions of 

similar but weaker bands in all of the dust samples. Although the positions of these 

bands are compatible with C-H absorptions in most organic materials (e.g. plastics, 

paper, fabric) washing of sample WTC01-9 with methanol was sufficient to significantly 

reduce the strength of these absorptions indicating they are caused by a soluble 

organic material, possibly an oil used as a dust suppressant in insulation containing 

slag wool. Spectra of both girder coating samples (WTC01-8 and WTC01-9) have an 

absorption at 1.725 microns, perhaps too weak to be seen in the dust samples, that 

closely matches the position of a C-H absorption found in oil. Use of slag wool, a type 

of mineral wool insulation, was widespread in the WTC towers (Hyman Brown, personal 

communication) as part of fireproof coatings on steel girders and the undersides of 
floors, thermal insulation around glass windows, and possibly in ceiling tiles. The 

apparent widespread use of slag wool and its brittle nature may explain its presence in 

all of the dust samples as a volumetrically significant component.

Notably absent from the reflectance spectra of the dust samples is evidence for paper 

in the form of a cellulose absorption expected at 2.1 micron. Visual examination of the 

dust samples reveals numerous strips of paper. A possible explanation is that 

microscopic gypsum particles form an optically opaque coating on the paper and other 

coarser fragments thereby concealing them from spectral detection. When pieces of 

dust coated paper are cleaned and then re-measured their spectra have distinct 2.1 

micron absorptions. Gypsum from pulverized wallboard, in the dust samples, has a 

strong wide absorption at 1.95 microns that may obscure the 2.1 micron cellulose 

absorption from paper.

Possible Sources of Abestos in the WTC Dust 

There are several possible sources of asbestos in the collapsed buildings at the WTC. 

One source is the fireproof coatings sprayed onto steel girders and the undersides of 

floors. Asbestos was reportedly used in a fireproof coating in Tower 1 up to the 20th 

floor (Hyman Brown, personal communication). Sample WTC01-8 was taken from a 

coating on a steel girder removed from the debris pile west of WTC tower 1. Most 

notable in its spectrum are absorptions at 1.385 and 2.323 microns which match in 

position and overall shape those of chrysotile (RS Figure 3). Chrysotile is one of three 

serpentine minerals and the only one to form with an asbestiform crystal habit. XRD 

analysis and the depth of these spectral absorptions is consistent with chrysotile 

forming up to 20 wt% of this coating material. The position of the 2.323 micron 

absorption in WTC01-8 is consistent with that of chrysotile but the band width is 

somewhat wider possibly indicating the presence of overlapping 2.307 and 2.343 

micron absorptions from dust suppressant oil.

 

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RS Figure 3. Reflectance spectrum of chrysotile asbestos. The 0.35 - 2.5 micron 

region is dominated by strong 1.385 and 2.323 micron vibrational absorptions.
Other potential asbestos sources are ceiling tiles and to a more limited extent, vinyl 

flooring (Hyman Brown, personal communication). Apparently the cement used to 

construct the WTC towers probably did not contain asbestos (Leslie Robertson, written 

communication). Spectroscopy and XRD analysis of our two concrete samples did not 

reveal any chrysotile asbestos. Vermiculite has the potential to contain amphibole 

asbestos, but its possible use in fireproof coatings at the WTC is unclear at this time. 

Vermiculite was not present in the one sample of an asbestos-free coating (WTC01-9) 

we collected at the site. Vermiculite was not detected in the dust samples during SEM, 

XRD, and spectral analysis. No amphibole asbestos was identified by these analytical 

methods either. However, a few flakes of a vermiculite-like mica were noted during 

visual examinations of the dust.

Constructed Mixtures 

To better constrain the abundance of chrysotile asbestos in the dust, we constructed 

mixtures of dust and chrysotile. We chose WTC01-6 as representative of an asbestosfree dust sample based on XRD and spectral evaluations. We added known amounts of 

a well characterized, very finely ground, National Institute of Occupational Safety and 

Health (NIOSH) Chrysotile standard (CH-29) to splits of WTC01-6 dust to create 

mixtures with 0.25, 0.5, 1.0, 2.5 and 5.0 weight % chrysotile. These samples were 

then measured spectrally and characterized by XRD, to provide a set of spectra and 

diffractograms that could be directly compared to those of the dust samples. Chrysotile 

(RS Fig. 3) has, as mentioned earlier, two strong absorptions at 1.385 and 2.323 

microns due to the 1st OH stretch overtone and an Mg-OH combination band 

respectively. Even though the 2.323 micron chrysotile absorption is the stronger of the 

two bands, its wavelength position is wedged between stronger C-H absorptions at 

2.307 and 2.343 microns, and overlaps with a 2.317 micron absorption from concrete 

(e.g. muscovite?), all of which tend to mask the presence of chrysotile in the dust 

samples at levels below 1 wt% in laboratory spectra. The weaker 1.385 micron 

chrysotile absorption occurs in a relatively less cluttered spectral region on the short 

wavelength side of the 1st OH stretch overtone gypsum absorption at 1.446 microns, 

thus providing a means of estimating chrysotile contents at even lower concentrations.

Spectral Detectability of Chrysotile 

RS Figure 4A shows spectra of dust + chrysotile mixtures with contina removed from 

the 1.4 micron region (Clark and Roush, 1984). The presence of chrysotile is indicated 

by a distinct absorption in the 5, 2.5, and 1 wt% mixtures and as an inflection in the 

0.5, and 0.25 wt% mixtures. RS Figure 4B shows these same samples with a curved 

continuum removed from the region centered on the 1.385-micron chrysotile 

absorption. Non-chrysotile bearing dust samples have convex upward curves in the 

1.385 micron region. Band depths of the 1.385 absorption do not increase linearly with 

increasing chrysotile abundance due to the effects of multiple scattering (e.g. Clark 

and Roush, 1984). Sensitivity to changes in concentration is lowest for mixtures with 

trace amounts of chrysotile, however, the lack of convexity at the wavelength 
corresponding to the 1.385 micron chrysotile band, is a reliable indicator of the 

presence of chrysotile for the WTC dust samples. Because the chrysotile absorptions 

are relatively weak, even for the 5 wt% mixture (about 0.25 % depth), diagnostic 

spectral measurements must be done with high signal-to-noise ratio.

 

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RS Figure 4A. Details of the 1.3 - 1.5 micron spectral region of dust + chrysotile 

synthetic mixtures constructed from an asbestos-free World Trade Center dust 

sample and a NIOSH chrysotile asbestos standard. Note the progressive growth 

of a chrysotile absorption from a mere inflection (0.25 wt%) to full fledged 

band (5 wt%) with increasing chrysotile content. Chrysotile-free dust samples 

have convex upward spectral curves in the 1.385 micron region. 

 

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RS Figure 4B. Same mixture spectra as in RS Figure 4A with the spectral region 

centered on the chrysotile 1.385 micron absorption divided by the asbestos-free 

WTC01-6 spectrum. Removal of this curved continuum from the mixture spectra 

produces distinct absorption bands even in at the 0.25 and 0.5 wt% mixtures.
RS Figure 5A shows examples of the detection of chrysotile in three of the WTC dust 

samples at the 0.25, 0.5, and 0.75 wt% level. Arrows mark the inflection points (or 

shoulders) of the 1.385 micron chrysotile absorption. Note how the inflection points 

move outward as chrysotile content increases. Sequentially overlaying all of the dust 

spectra on top of the asbestos-free WTC01-6 spectrum provided a means of detecting 

these inflection points and thereby estimating the amount of chrysotile present in each 

sample. Figure 5B shows the same spectra as in RS Figure 5A with a convex continuum 

(provided by WTC01-6) removed from the 1.385 micron region. This process reveals 

absorptions due to chrysotile even in the 0.25 and 0.5 wt% samples.

 

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RS Figure 5A. Actual examples of World Trade Center dust with variable 

chrysotile asbestos contents. Arrows mark outer edges of an absorption band 

caused by trace levels of chrysotile. These inflection points move progressively 

outward as the chrysotile content increases.

 

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RS Figure 5B. Same spectra as in RS Figure 5A with the spectral region centered 

on the chrysotile 1.385 micron absorption divided by the asbestos-free WTC01-6 
spectrum. This continuum removal process reveals distinct absorptions due to 

chrysotile.

The lower limit of detection for chrysotile in the WTC dusts depends to a degree on the 

grain size and albedo (brightness) of the dust. RS Figure 6 shows a series of dust + 

chrysotile mixtures constructed using dust sample WTC01-15, a coarser gained sample 

than WTC01-6. The dotted curves are spectra of the mixtures after hand grinding to 

fine powders. Because diffuse reflectance is a non-linear process, decreasing the grain 

size of the dust results in more scattering causing a decrease in the strength of all the 

absorptions including those of chrysotile. The size of individual grains in the 33 WTC 

dust samples is quite variable ranging from centimeter-sized fragments to submicron 

diameter fibers. It is likely that the grain size of the hand ground mixtures is smaller 

than the average grain size of even the finest of the dust samples, therefore the hand 

ground samples may represent the worst case detection scenarios. Even though 

grinding does significantly decrease the depths of the chrysotile absorption, the lack of 

convexity over the 1.385 micron chrysotile band is still evident in spectra of the hand 

ground mixtures down to the 0.5 wt% level. As an empirical rule of thumb, a given 

estimate of chrysotile content decreases by about half the wt% value over this 

extreme grain size range.

 

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RS Figure 6. Unground versus finely ground synthetic mixtures of World Trade 

Center dust WTC01-15 + NIOSH chrysotile. Note decrease in strength of 

spectral absorptions in the hand ground samples. Spectral sensitivity to the 

presence of chrysotile decreases as grain size of the dust decreases. 

Lowering the albedo of a mixture results in less scattering thereby decreasing the 

likelihood that a given photon will encounter a chrysotile fiber and be scattered to the 

sensor, resulting in a lower sensitivity to chrysotile content. The albedo of the dust 

samples varies from 0.2 to 0.4 in the 1.4 micron spectral region, with about 80 % of 

the samples varying between 0.29 and 0.35. The dust samples used for the mixtures 

have albedos around 0.32 in the 1.4 micron region. The effects of albedo on spectrally 
measuring chrysotile contents have not been quantitatively evaluated. However, 

because most of the dust samples have an albedo similar to that of the samples used 

to create the mixtures, errors in estimating chrysotile content will probably be smaller 

than those due to grain size variations. In samples brighter than the mixture samples, 

chrysotile contents may be systematically overestimated. The reverse is true for 

samples darker than the mixture samples.

Spectral Interference 

Spectroscopy could not be used to estimate chrysotile content of the dust below the 

1wt% level for 9 out of 33 samples because of interference from nearby spectral 

absorptions. RS Figure 7 shows a 1wt% chrysotile + dust mixture compared with dust 

sample WTC01-2 which contains a relatively high concentration of portlandite and/or 

muscovite. These minerals have strong OH overtone absorptions located at 1.41 - 1.42 

microns, with shoulders that overlap and conceal the nearby chrysotile 1.385 micron 

band. None of the 9 samples contained more than 1wt% chrysotile as determined by 

spectroscopy. XRD did detect trace levels of chrysotile in 7 of these samples. The other 

known constituent of the dust samples that has a weak spectral absorption near the 

1.385 micron chrysotile absorption is that of bassanite (CaSO4*1/2H20) at 1.391 

microns. Potential interference from this bassanite absorption is negligible because in 

at least one of those samples where it was detected with XRD (WTC01-19), the 

spectral curve was convex upward in the 1.385 micron region showing neither the 

presence of chrysotile or bassanite.

 

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RS Figure 7. Spectra of dust samples that contain significant concentrations of 

portlandite and muscovite (probably from pulverized concrete) have wide 1.42 

micron absorptions that overlap and conceal chrysotile absorptions that may be 

present at 1.385 microns. 
Chrysotile Asbestos Contents of WTC Dust Samples 

Spectral and XRD estimates of chrysotile content were made for all 33 dust samples 

(RS Fig. 8). Circles represent dust samples from the surface that contain trace levels of 

chrysotile asbestos. Solid circles represent detection of chrysotile by both spectroscopy 

and XRD analysis. Circles with their upper halves filled represent detection of chrysotile 

by spectroscopy; circles with their lower halves filled represent detection of chrysotile 

by XRD analysis. The size of the circle represents the amount of chrysotile detected by 

spectroscopy. Circles with their right halves filled represent samples where spectral 

interference prevented an estimate of chrysotile below 1% but where XRD analysis did 

detect chrysotile. Triangles represent samples where spectral interference prevented 

an estimate of chrysotile content but where XRD analysis revealed no chrysotile at or 

above the 1 wt% level. Squares represent samples where neither spectroscopy or XRD 

analysis were able to detect chrysotile at or above the 0.25 wt% (spectroscopy) and 

1.0 wt% (XRD) levels. Samples 20 and 36 were collected indoors and where not 

subjected to rain and wind during the September 14th thunderstorm. The large filled 

"I" represents the location of the chrysotile bearing coating collected from the steel 

girder; the smaller "I" represents the the asbestos-free coating collected from a 

different steel girder. If plotted in its true proportion, the "I" representing the 

chrysotile bearing coating (WTC01-8) would be so large that it would conceal 

information from the other samples on this diagram, therefore its size is not 

proportional to its estimated 10 - 20 wt% chrysotile content.

Chrysotile was detected in a little over two thirds of the dust samples. Neither 

spectroscopy or XRD analysis revealed a chrysotile concentration higher than about 

0.75 wt% in any of the 33 dust samples. Chrysotile was detected in 24 of the dust 

samples (exclusive of the girder coatings and concrete samples) with spectroscopy 

detecting it in 15 of the samples and XRD analysis detecting it in 16 of the samples. 

Chrysotile was detected by both methods in 7 dust samples. One explanation for the 

apparent disagreement between methods is the heterogeneous nature of the dust 

samples. While XRD measurements were made on 1.5 gram splits of each dust sample, 

spectroscopic measurements were made on approximately two thirds of the entire 

sample (or between 50 - 300 grams of material). Initial XRD measurements on 

samples WTC01-14 and 28 showed no trace of chrysotile, while replicate XRD 

measurements on different splits of these samples revealed chrysotile in 28. The 

problems of detecting unevenly distributed chrysotile in the dust are likely to plague 

any analytical method.

From RS Figure 8 it is apparent that trace levels of chrysotile were distributed with the 

dust radially in west, north, and easterly directions perhaps at distances greater than 

3/4 kilometer from ground zero. The lack of chrysotile at levels above the detection 

limits of both spectroscopy and XRD analysis in samples collected south of ground zero 

(except in WTC01-33) may indicate that chrysotile was not distributed uniformly during 

the collapse.
 

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RS Figure 8. Chrysotile concentrations in surface dust samples in Lower 

Manhattan. Two thirds of the dust samples have chrysotile asbestos 

concentrations above 0.25 wt%. See text for a more detailed explanation of the 

map symbols. 

NEXT Section of Report: Scanning Electron Microscopy (SEM) and Energy Dispersive XRay Analysis (EDS) 

Back to document Table of Contents 

For more information, contact: 

Dr. Gregg A. Swayze

gswayze@usgs.gov 

or 

Dr. Roger N. Clark

rclark@usgs.gov

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OFR 01-0429: Laboratory Spectra of WTC Samples

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

All spectral plots on one page (78 plots, approx 450 kbytes download) 

Spectra and ascii data for each sample: 

wtc01-

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wtc01-33 

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wtc01-35 

wtc01-36 

wtc01-37Aa 

wtc01-37Ac 

wtc01-

37Am 

wtc01-37B 

 

Larger 81 KB image 

Sample Location Map

Back to NEXT Section of: 
Laboratory Reflectance Spectroscopy (RS) Studies 

Description of Spectroscopy Methods and Results 

Back to document Table of Contents 

For more information, contact: 

Dr. Gregg A. Swayze

U.S. Geological Survey 

303-236-0925 

gswayze@usgs.gov 

or 

Todd Hoefen

U.S. Geological Survey 

303-236-2456 

thoefen@usgs.gov 

or 

Dr. Roger N. Clark

U.S. Geological Survey 

303-236-1332 

rclark@usgs.gov

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Open-File Report 01-0429: World Trade Center USGS SEM Studies

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

Electron Microscopy and Energy Dispersive X-Ray Analysis 

Selected WTC dust samples were analyzed by scanning electron microscopy (SEM) and energy dispersive xray microanalysis (EDS) at the USGS Denver Microbeam Laboratory (exit to the Denver Microbeam 

Laboratory web site by clicking here). The primary purpose of the SEM/EDS analysis was to determine if the 

WTC dust contained asbestos. Electron microscopy was used because extremely low levels of asbestos 

fibers can be detected and chemically analyzed. Representative portions of samples wtc01-3, wtc01-8, 

wtc01-14, wtc01-15, wtc01-16, wtc01-20, wtc01-22, wtc01-25, wtc01-27, wtc01-28 and wtc01-36 were 

selected for this analysis (See sample location map for exact collection sites).

Amphibole asbestos was not detected in the dust samples by SEM/EDS analysis. However, trace amounts of 

chrysotile asbestos have been identified in several of the samples. There are also abundant glass fibers in 

all samples analyzed so far. Other phases found in these samples include gypsum and/or anhydrite (calcium 

sulfate minerals), calcium-rich phases compatible with concrete materials, and rock and mineral fragments 

such as quartz and feldspar. A large variety of other materials are present at trace levels including 

unidentified organic materials compatible with wood, paper, etc., and particles enriched in Fe, Pb, Zn, Sr, 

Bi, Cu and other metals. 

Preliminary SEM and EDS analysis of material coating a steel beam (sample 8) from the WTC debris 

indicates that chrysotile asbestos is present at a level possibly as high as 20% by volume. So far, no 

amphibole asbestos has been detected in this material. This material also contains abundant glass fibers. 

Energy dispersive x-ray microanalysis (EDS) was performed to determine the chemical composition of 

selected materials in the dust. Representative compositions of the glass fibers are given in Table SEM-1. 

The chemical composition of the majority of glass fibers (and glass spheres) in all samples is consistent 

with slag wool, a synthetic fiber commonly used in building materials like ceiling tiles (Nomenclature 

Committee of TIMA Inc., 1991). Glass fibers of other compositions were also found in some of the dust 

samples (see Table SEM-1, analysis wtc 22 sp2), and may indicate a different source material. Sample 8, 

collected from a coating on a steel beam, contains glass fibers, chrysotile and gypsum and/or anhydrite. 

The chrysotile in sample 8 is similar in composition and appearance to that found as a trace phase in the 

dust samples.

SEM Figure 1 is a scanning electron microscope (SEM) image of a representative portion of sample 22, 

collected from an area near the World Trade Center. SEM Figure 2 is an image of a representative portion of 

sample 3 collected near Battery Park. Both images show abundant glass fibers along with particulate debris. 

SEM Figure 3 is an image of a bundle of chrysotile asbestos from sample 8. The chrysotile was found as a 

trace constituent in two of the samples analyzed so far by SEM/EDS and in several others analyzed by XRD. 

SEM Figure 4 is a SEM image of gypsum and/or anhydrite particles consistent with dry wall material. 

Representative analyses of some of these phases are given in Table SEM-1. Images from other samples can 

be seen in the Integration of Results section.

Sample 36 was recovered from an indoor location near the Trade Center complex and had not been affected 

by rain as were the outdoor samples. This sample was thoroughly analyzed for metal-rich particles to better 

understand the types of materials from which metals might be leached (see leachate studies section). 

Images of several metal-rich particles can bee seen by clicking here.

Table SEM-1. EDS analyses of representative phases given in oxide weight percent. 

Analysis 

I.D. Na2O MgO Al2O3 SiO2 SO3 K2O CaO TiO2 MnO FeO Material 
wtc 22 

sp 5 2 11 12 44 trace 1 24 1 BDL 4

glass 

fiber

wtc 22 

sp 1 trace 11 9 47 trace 1 32 trace BDL BDL

glass 

fiber

wtc 22 

sp 2 12 2 3 71 trace trace 11 trace BDL trace

glass 

fiber

wtc 3 

sp 3 trace 11 11 43 trace trace 32 1 BDL BDL

glass 

fiber

wtc 3 

sp 6 trace 11 10 44 trace trace 32 trace BDL 1

glass 

fiber

wtc 8 

sp 1 BDL 8 9 43 trace trace 36 1 BDL 1

glass 

fiber

wtc 15 

sp 1 BDL 10 10 42 trace trace 36 trace trace BDL

glass 

sphere

wtc 22 

sp 4 BDL 12 8 47 trace trace 31 BDL BDL BDL

glass 

sphere

wtc 8 

sp 8 BDL 47 BDL 50 trace BDL trace BDL trace 2 chrysotile

wtc 14 

sp 5 BDL BDL 1 2 53 BDL 43 BDL BDL BDL

Gypsum/

anhydrite

Data normalized to 100%. BDL=below detection limit. Analytical error is approximately +/- 5% relative 

concentration 
SEM Figure 1. Secondary electron SEM image of a representative portion of sample 22. The image 

shows abundant glass fibers (red arrows) and other materials as described above. The round 

object at the right side of the image is a glass sphere with a composition similar to the fibers (see 

Table SEM-1). Spheres like these are typical components of slag wool.
SEM Figure 2. Secondary electron SEM image of a representative portion of sample 3 collected from 

Battery Park. The image shows abundant glass fibers and other materials as described above. 
SEM Figure 3. SEM image of a chrysotile bundle (center) and glass fibers from sample 8. Similar 

bundles have been identified at trace levels in several of the dust samples. 
SEM Figure 4. Secondary electron SEM image of gypsum and/or anhydrite crystals from sample 20. 

NEXT Section of Report: Chemical Compositions 

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Open-File Report 01-0429: World Trade Center USGS Bulk Chemistry Results

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

Chemical compositions of the WTC dusts and girder coating materia 

Representative splits of samples of dusts from the WTC area and of steel girder coatings from the WTC debris 

were analyzed for total major element composition by Wavelength-Dispersive X-Ray Fluorescence (WD-XRF), 

for total major and trace element composition by Inductively Coupled-Plasma Mass Spectrometry (ICP-MS), 

for total carbon and sulfur by combustion, and for carbonate carbon by coulometric titration.

Sampling and analytical methods

Representative sub-samples of the dust and beam-coating samples were obtained using a standard cone and 

quartering approach. The sub-samples were then ground and homogenized prior to chemical analysis. 

X-ray fluorescence analytical methods, which are summarized in Arbogast (1996), involve heating the sample 

at 925°C for 40 minutes to determine the weight of volatiles lost from the sample. The sample is then mixed 

with lithium tetraborate and fused for 56 minutes at 1120°C. The molten sample is poured into a mold and 

cooled, producing a homogeneous glass disc of the sample material. This disc is then analyzed in a WD-XRF 

spectrometer, and results are given in total weight percent. The amounts of volatile components in a sample, 

such as organic material (wood, paper, plastic, other organic compounds), water, sulfur, inorganic carbon, and 

nitrogen compounds, can be determined by the weight lost by the sample during its initial heating. 

ICP-MS analysis was carried out on splits of the samples that were first dissolved using a multi-acid digestion 

combining hydrochloric, hydrofluoric, nitric, and perchloric acids (Crock et al.,1999, and references therein). 

ICP-MS methods are given in Briggs and Meier (1999), and Crock et al. (1999). 

Total carbon and total sulfur were analyzed by combustion (Crock et al., 1999). Carbonate carbon was 

determined by coulometric titration, and organic carbon determined by the the difference between total 

carbon and carbonate carbon (Crock et al., 1999). 

Analytical results are tabulated in Chemistry Table 1, and summarized graphically in Chemistry Figures 1-4. 

The elements measured by the chemical analyses are those routinely measured by the USGS for studies of 

rocks, sediments, soils, and environmental samples. Total mercury concentrations have not been measured in 

the WTC solid samples, but have been measured in leach solutions derived from the samples (see the next 

section of this report). Quality-assurance, quality control data and information for the analyses are available 

upon request. 

These analytical methods determine the total concentration (in weight percent or parts per million) of each 

element in any given sample. The samples are likely to contain a mixture of different components, such as 

particles of gypsum, concrete, steel, etc., that together make up the total concentration of elements. 
Larger 141 KB image 

Chemistry Figure 1.

Plot showing the concentration ranges (colored boxes) and means (horizontal white bars) for major and trace 

elements in samples of WTC dusts and girder coatings. Several samples had arsenic concentrations below the 

analytical detection limits, indicated on the graph by the arrow extending downward from the detection limit 

concentration. Concentrations of some elements (such as tin) were not determined n these samples. For 

comparison, 1 percent equals 10,000 parts per million. 
 Larger 

215 KB image 

Chemistry Figure 2. 

Map of lower Manhattan showing (as stacked bar charts) variations in concentration (in percent) of major 

elemental components of WTC dust and girder coating samples. Dust samples collected indoors are indicated 

by the single hatch pattern and girder coating samples by the cross-hatch pattern; all others are dust samples 

collected outdoors. For comparison with Chemistry Figure 4, 1 percent equals 10,000 parts per million. 
 Larger 

207 KB image 

Chemistry Figure 3. 

Map of lower Manhattan showing (as stacked bar charts) variations in concentration (in percent) of inorganic 

carbon, carbonate carbon, and total sulfur of WTC dust and girder coating samples. Dust samples collected 

indoors are indicated by the single hatch pattern and girder coating samples by the cross-hatch pattern; all 

others are dust samples collected outdoors. For comparison with Chemistry Figure 4, 1 percent equals 10,000 

parts per million. 
 Larger 220 

KB image 

Chemistry Figure 4. 

Map of lower Manhattan showing (as stacked bar charts) variations in concentration (in parts per million) of 

some predominant trace elements of WTC dust and girder coating samples. Dust samples collected indoors are 

indicated by the single hatch pattern and girder coating samples by the cross-hatch pattern; all others are 

dust samples collected outdoors. For comparison with Chemistry Figures 2 and 3, 1 percent equals 10,000 

parts per million. 
Results 

WD-XRF results show that silicon, calcium, sulfur, magnesium, aluminum, iron, and carbon are the 

predominant elemental components of the dusts. The contents of volatile compounds in the dusts approach 

nearly 20% by weight. The identities and amounts of volatile components (such as water bonded in minerals 

and adsorbed onto materials; organic materials such as papers, plastics, etc.) in the samples have not been 

determined. The WD-XRF analyst noted a smell of burning wood or paper in all of the dust samples during 

sample combustion, another indication that organic material is present in the dusts. 

There are no systematic differences in total element composition between the dust samples collected indoors 

and outdoors, nor are there systematic spatial variations in dust composition between sample sites. 

The two samples of girder coating material have generally similar major-element concentrations to those in 

the dust samples. One notable exception is magnesium, which is somewhat elevated in the girder coating 

sample (WTC01-08) that has higher chrysotile asbestos content (as determined by SEM analysis). 

The dust and girder coating samples are substantially more variable in their trace element compositions than 

in their major element compositions. In most dust samples, zinc is the predominant trace metal, with 

concentrations as high as 3000 parts per million. With the exception of one sample that is high in barium 

(WTC01-16), the trace metals barium, lead, copper, and chromium are present in concentrations of hundreds 

of parts per million. Concentrations of other trace metals and metalloids such as molybdenum, antimony, and 

titanium, are tens of parts per million or less. As with the major elements, there are no discernible differences 

in trace metal content between the dust samples collected outdoors and those collected indoors. There are 

also no apparent spatial variations in trace-element composition between sample sites. 

The girder coating materials (samples WTC01-08, and -09) contain quite low concentrations of trace metals 

relative to the dust samples. 

Interpretation

The total element compositions of the dust samples reflect the chemical makeup of materials such as: glass 

fibers (containing silicon, aluminum, calcium, magnesium, sodium, and other elements); gypsum (containing 

calcium and sulfate); concrete and aggregate (containing calcium and aluminum hydroxides, and a variety of 

silicate minerals containing silicon, calcium, potassium, sodium, and magnesium); particles rich in iron, 

aluminum, titanium, and other metals that might be used in building construction; and particles of other 

components, such as computers, etc. Organic carbon in the dusts is most likely from paper, wallboard binder, 

and other organic materials. 

The trace metal compositions of the dust and girder coatings likely reflect contributions of material from a 

wide variety of sources. Possibilities include metals that might be found as pigments in paints (such as 

titanium, molybdenum, lead, and iron), or metals that occur as traces in, or as major components of, 

wallboard, concrete, aggregate, copper piping, electrical wiring, and computer equipment. Further detailed 

SEM studies of dust and beam coating samples are needed to develop a better understanding of the 

residences of metals in the samples. A detailed review of the materials used in construction, and the elemental 

composition of materials commonly found in office buildings would also be useful to understand more 

completely the potential sources and compositions of the materials in the dusts. 

It is important to note that the total chemical analyses presented in this section do not provide an indication of 

the metals in the dusts and girder coating materials that may potentially be bioavailable (readily assimilated 

by organisms). For example, heavy metals, such as lead, may occur in forms that range from highly soluble to 

highly insoluble in water or body fluids. Consequently, high concentrations of total lead in dust samples may 

or may not translate into elevated concentrations of readily bioavailable lead. Chemical leach tests such as 

those presented in the next section of this study aid in understanding potential release and bioavailability of 

heavy metals and other constituents from the girder coatings and dust samples. 

NEXT Section of Report: Leachate Studies 

Back to document Table of Contents 

Contacts 

For further information on sub-sampling and sample preparation methods, contact: 
Steve Wilson, 

swilson@usgs.gov 

For further information on XRF methods, contact: 

Joe Taggart, 

jtaggart@usgs.gov 

For further information on ICP-MS analytical methods, contact: 

Paul Lamothe, 

plamothe@usgs.gov 

For further information on results and interpretation, contact: 

Geoff Plumlee, 

gplumlee@usgs.gov 

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Chemistry Table 1. This Table summarizes data for major elements and all trace elements analyzed in 

the WTC dust and beam coating samples. Some elements (such as mercury and tin) were not analyzed in 

these samples. Major elements are listed in percent concentration and trace elements are listed in parts 

per million concentration. One percent equals 10,000 parts per million. 

Chemistry Table 1

Outdoor dust samples

WTC 01-02 WTC 01-03 WTC01-05 WTC01-06 WTC 01-14

Silicon % 21.2 26.3 11.4 11.4 15.3

Calcium % 15.01 9.58 20.94 20.58 17.65

Magnesium % 3.11 2.23 2.73 2.73 2.83

Sulfur % 1.33 0.87 nm nm 4.32

Iron % 4.13 2.16 1.41 1.42 1.87

Aluminum % 4.13 2.75 2.75 2.73 2.86

Carbon, organic % 0.98 3.55 nm nm 3.08

Carbon, Carbonate 

% 1.24 1.63 nm nm 1.46

Sodium % 0.82 0.76 0.50 0.50 0.59

Potassium % 0.63 0.69 0.46 0.47 0.56

Titanium % 0.39 0.25 0.24 0.24 0.31

Manganese % 0.15 0.08 0.10 0.10 0.12

Phosphorous % 0.03 0.05 0.03 0.03 0.02

Loss on Ignition % 7.96 13.6 19.6 19.6 18.1

Barium ppm 765 376 nm nm 461

Strontium ppm 1000 409 nm nm 643

Zinc ppm 2990 1200 nm nm 1570

Lead ppm 710 176 nm nm 276

Copper ppm 438 142 nm nm 242
Cerium ppm 108 50.9 nm nm 68.8

Yttrium ppm 58.9 30.2 nm nm 46.5

Chromium ppm 224 98 nm nm 116

Nickel ppm 88.4 30.8 nm nm 28.6

Lanthanum ppm 51 25.8 nm nm 34.8

Antimony ppm 52.1 26.3 nm nm 40.2

Vanadium ppm 38.8 42.5 nm nm 30.6

Molybdenum ppm 25.4 14.5 nm nm 19.1

Lithium ppm 27.4 17.4 nm nm 23.2

Thorium ppm 11.2 5.56 nm nm 7.92

Rubidium ppm 21.2 23.7 nm nm 25.2

Cobalt ppm 13.9 8.4 nm nm 7.1

Niobium ppm 11 7.8 nm nm 9.1

Scandium ppm 8.8 6.6 nm nm 6.1

Uranium ppm 3.92 1.96 nm nm 2.89

Cadmium ppm 7.3 3.2 nm nm 3.4

Arsenic ppm 6.8 3.7 nm nm 5.1

Gallium ppm 6 5.4 nm nm 4.1

Beryllium ppm 3.7 2.2 nm nm 2.9

Silver ppm 1.2 3.8 nm nm 1.2

Cesium ppm 0.73 0.76 nm nm 0.88

Bismuth ppm 0.5 0.68 nm nm 0.56

Thallium ppm 0.1 0.13 nm nm 0.11

nm - not measured; ppm - parts per million

Chemistry Table 1, continued

Outdoor dust samples, continued

WTC 01-15 WTC 01-16 WTC01-17 WTC 01-21 WTC 01-22

Silicon % 13.6 17.0 16.0 12.8 17.0

Calcium % 18.58 13.36 17.01 18.94 16.80

Magnesium % 2.64 1.79 2.06 2.68 2.77

Sulfur % 5.40 3.68 nm 5.10 3.70
Iron % 1.87 1.92 1.71 1.49 2.78

Aluminum % 2.59 2.27 2.30 2.73 2.78

Carbon, organic % 2.30 2.51 nm 4.02 2.55

Carbon, Carbonate % 1.48 1.47 nm 1.44 1.31

Sodium % 0.66 0.87 0.93 0.50 0.83

Potassium % 0.49 0.69 0.54 0.50 0.52

Titanium % 0.25 0.26 0.25 0.24 0.29

Manganese % 0.10 0.07 0.07 0.12 0.12

Phosphorous % 0.03 0.02 0.02 0.03 0.03

Loss on Ignition % 17.3 22.8 15.9 21.2 15.3

Barium ppm 405 3670 nm 460 452

Strontium ppm 736 3130 nm 787 710

Zinc ppm 1110 1410 nm 1500 1380

Lead ppm 152 208 nm 278 452

Copper ppm 367 307 nm 153 130

Cerium ppm 64.9 132 nm 77 72

Yttrium ppm 46.1 31.4 nm 54.5 47.6

Chromium ppm 129 95.2 nm 104 111

Nickel ppm 32.9 31.4 nm 31.2 30.6

Lanthanum ppm 32.7 69.9 nm 38.6 35.4

Antimony ppm 30.2 148 nm 33.1 27.5

Vanadium ppm 27.1 24.9 nm 27.9 29.7

Molybdenum ppm 12.1 10 nm9 6.9

Lithium ppm 22.1 18 nm 23.3 23

Thorium ppm 7.3 5.36 nm 8.48 8.5

Rubidium ppm 21.6 21.6 nm 21 21.1

Cobalt ppm 6.5 6.5 nm 5.3 6.3

Niobium ppm 7.6 6.6 nm9 9.2

Scandium ppm 5.9 4.4 nm 6.2 6.2

Uranium ppm 2.71 2.3 nm 3.16 3.09

Cadmium ppm43 nm 4.6 3.8
Arsenic ppm 4 4.3 nm 3.6 6.6

Gallium ppm 3.9 4.3 nm 3.9 4

Beryllium ppm 2.4 1.8 nm 2.9 2.9

Silver ppm 1.4 1.5 nm 2.4 1.4

Cesium ppm 0.78 0.87 nm 0.76 0.76

Bismuth ppm 0.25 0.28 nm 0.5 0.43

Thallium ppm 0.11 0.12 nm 0.1 0.1

nm - not measured; ppm - parts per million

Chemistry Table 1, continued

Outdoor dust samples, continued

WTC 01-25 WTC 01-27 WTC 01-28 WTC01-30 WTC01-34

Silicon % 13.2 15.2 13.8 15.1 12.2

Calcium % 20.37 19.51 19.65 19.73 20.51

Magnesium % 3.29 3.04 2.83 3.49 3.01

Sulfur % 4.03 4.29 4.56 nm nm

Iron % 1.33 1.72 1.80 1.85 1.45

Aluminum % 3.28 3.05 2.95 3.59 2.98

Carbon, organic % 2.94 1.95 2.42 nm nm

Carbon, Carbonate 

% 1.87 1.82 1.68 nm nm

Sodium % 0.62 0.62 0.76 0.71 0.50

Potassium % 0.56 0.50 0.54 0.56 0.51

Titanium % 0.29 0.29 0.26 0.29 0.25

Manganese % 0.15 0.12 0.12 0.14 0.12

Phosphorous % 0.03 0.03 0.02 0.04 0.03

Loss on Ignition % 17.5 14.4 16.7 17.5 18.5

Barium ppm 624 470 491 nm nm

Strontium ppm 695 701 711 nm nm

Zinc ppm 1910 1650 1720 nm nm

Lead ppm 756 204 234 nm nm

Copper ppm 251 188 218 nm nm
Cerium ppm 85 77.7 75 nm nm

Yttrium ppm 61.6 54.9 53.8 nm nm

Chromium ppm 134 126 106 nm nm

Nickel ppm 39.2 39.4 26.1 nm nm

Lanthanum ppm 43.5 39.5 38.4 nm nm

Antimony ppm 65.8 50.4 51.8 nm nm

Vanadium ppm 30.5 30 28.9 nm nm

Molybdenum ppm 30.9 27.1 42 nm nm

Lithium ppm 28.5 25.2 24.8 nm nm

Thorium ppm 9.94 9.14 8.48 nm nm

Rubidium ppm 24 21.7 22.5 nm nm

Cobalt ppm 7.4 6.2 5.9 nm nm

Niobium ppm 11 11 10 nm nm

Scandium ppm 7.1 6.6 6.2 nm nm

Uranium ppm 3.78 3.36 3.27 nm nm

Cadmium ppm 7.5 5 5.2 nm nm

Arsenic ppm 4.2 5 4.8 nm nm

Gallium ppm 4.3 4.3 4.1 nm nm

Beryllium ppm 3.6 3.2 3.1 nm nm

Silver ppm 1.4 1.4 1.7 nm nm

Cesium ppm 0.83 0.77 0.76 nm nm

Bismuth ppm 0.67 0.4 0.48 nm nm

Thallium ppm 0.1 0.09 0.11 nm nm

nm - not measured; ppm - parts per million

Chemistry Table 1, continued

Indoor dust samples Girder coatings

WTC 01-20 WTC 01-36 WTC 01-08 WTC 01-09

Silicon % 14.2 11.7 15.0 15.5

Calcium % 19.44 21.30 20.73 26.01

Magnesium % 2.59 2.88 6.94 3.23

Sulfur % 5.51 5.77 1.39 1.23
Iron % 1.25 1.38 1.25 0.55

Aluminum % 2.55 2.86 2.92 3.56

Carbon, organic % 2.68 2.32 2.48 2.45

Carbon, Carbonate % 1.27 1.50 1.89 1.86

Sodium % 1.16 0.58 0.12 0.16

Potassium % 0.46 0.46 0.28 0.32

Titanium % 0.25 0.23 0.21 0.28

Manganese % 0.10 0.11 0.14 0.19

Phosphorous % 0.02 0.02 0.01 0.01

Loss on Ignition % 15.7 16.9 15.8 13

Barium ppm 390 438 317 472

Strontium ppm 706 823 444 378

Zinc ppm 1330 1400 57.4 101

Lead ppm 153 159 9.13 11.7

Copper ppm 176 95 10.3 12.8

Cerium ppm 61.6 70.2 202 356

Yttrium ppm 44.1 52.6 134 243

Chromium ppm 94 107 153 86.5

Nickel ppm 29.8 28.5 202 22.6

Lanthanum ppm 31.3 35.6 102 175

Antimony ppm 38.9 33.9 0.56 1.2

Vanadium ppm 25 28.6 30.5 40.1

Molybdenum ppm 19 16.1 0.85 1.2

Lithium ppm 21.9 24.9 25.2 36.4

Thorium ppm 7.25 8.64 17.9 30.7

Rubidium ppm 18.9 21.18 8.2

Cobalt ppm5 5.3 12.3 1.7

Niobium ppm89 4.4 6.3

Scandium ppm 5.4 6.4 9.2 9.8

Uranium ppm 2.7 3.23 4.72 7.57

Cadmium ppm 4.2 5.8 0.11 0.21
Arsenic ppm 3.5 3.8 < 2 < 2

Gallium ppm 3.6 4 2.8 4.2

Beryllium ppm 2.5 3.1 4 4.2

Silver ppm 3.5 1.6 1.8 0.96

Cesium ppm 0.72 0.78 0.18 0.22

Bismuth ppm 0.64 0.82 0.008 0.01

Thallium ppm 0.09 0.09 0.02 0.02

nm - not measured; ppm - parts per million

Chemistry Table 1, continued

minimum maximum mean*

Silicon % 11.4 26.3 14.8

Calcium % 9.58 26.01 18.36

Magnesium % 1.79 6.94 2.88

Sulfur % 0.87 5.77 3.11

Iron % 0.55 4.13 1.63

Aluminum % 2.27 4.13 2.90

Carbon, organic % 0.98 4.02 2.48

Carbon, Carbonate 

% 1.24 1.89 1.55

Sodium % 0.12 1.16 0.57

Potassium % 0.28 0.69 0.50

Titanium % 0.21 0.39 0.26

Manganese % 0.07 0.19 0.11

Phosphorous % 0.01 0.05 0.02

Loss on Ignition % 7.96 22.8 16.35

Barium ppm 317 3670 533.38

Strontium ppm 378 3130 726.61

Zinc ppm 57.4 2990 1004.70

Lead ppm 9.13 756 166.75

Copper ppm 10.3 438 136.31

Cerium ppm 50.9 356 91.23
Yttrium ppm 30.2 243 57.45

Chromium ppm 86.5 224 116.61

Nickel ppm 22.6 202 37.77

Lanthanum ppm 25.8 175 45.96

Antimony ppm 0.56 148 24.84

Vanadium ppm 24.9 42.5 30.67

Molybdenum ppm 0.85 42 11.34

Lithium ppm 17.4 36.4 24.00

Thorium ppm 5.36 30.7 9.31

Rubidium ppm 8 25.2 19.01

Cobalt ppm 1.7 13.9 6.36

Niobium ppm 4.4 11 8.34

Scandium ppm 4.4 9.8 6.63

Uranium ppm 1.96 7.57 3.29

Cadmium ppm 0.11 7.5 2.80

Arsenic ppm 3.5 6.8 ***

Gallium ppm 2.8 6 4.15

Beryllium ppm 1.8 4.2 2.96

Silver ppm 0.96 3.8 1.66

Cesium ppm 0.18 0.88 0.64

Bismuth ppm 0.008 0.82 0.28

Thallium ppm 0.02 0.13 0.08

*Geometric mean for all parameters except pH; ***Geometric mean not calculated due to one 

or more samples having concentrations below detection limit; ppm - parts per million

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Open-File Report 01-0429: World Trade Center USGS Leachate

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

Evaluation of World Trade Center dusts and girder coatings 

using a simulated precipitation leaching procedure 

A subset of the loose dust samples and samples of material coating girders collected from around the 

World Trade Center was subjected to chemical leach tests to examine potential release of metals from the 

dusts and beam coatings. The USGS leach test is a modification of a test described in detail in Hageman 

and Briggs (2000). This leach test and the one developed by Hageman and Briggs (2000) are 

modifications of the US EPA 1312 (Synthetic Precipitation Leaching Procedure, or SPLP) method. The 

USGS tests were originally designed as a screening method to quickly assess potential metal release from 

mine wastes.

As applied to the materials from the World Trade Center, these leach tests can be used to infer the 

potential for release of various metals, anions, and cations from the dusts as a result of rainfall or 

interactions with water used in fire fighting or street washing. The test also provides an indication of 

metals that might be bioavailable should the dusts be inhaled, ingested, or discharged into ecosystems. 

For this leach test, deionized (DI) water (pH ~5.5) is used as the extractant. Dust samples were leached 

at a 1:20 ratio (2.5 grams dust / 50 milliliters DI water). A representative subsample of each dust sample 

was weighed on a balance. Each dust sample was then placed in a 125 milliliter (ml) high-density 

polyethylene (HDPE) bottle to which 50.0 ml DI water was added. Each sample was then shaken for 5 

minutes. Following shaking, the solution was allowed to settle for 5 minutes. Leachate solutions were then 

filtered using plastic syringes and 0.45 micrometer pore size nitrocellulose membrane filters. Sub-samples 

of the leachate were collected and preserved for further analysis.

The procedure uses deionized water as the extractant solution rather than the synthetic acid rain used in 

the EPA 1312 method. It also uses a 5 minute agitation rather than an 18-hour agitation. Hence, it is 

possible that the concentrations of soluble metals measured with this test would be less than those 

measured using EPA 1312 method. However, it is likely that the leach procedure used in this study 

successfully reveals the metals likely to be mobilized from the dusts and girder coatings. A comparative 

study between the EPA Method 1312 (SPLP) procedure and this simplified leach can be found in Hageman 

and Briggs (2000).

The leachate samples were analyzed for major cations and trace metals by Inductively-Coupled PlasmaMass Spectrometry (ICP-MS) following the protocols outlined by Lamothe et al. (1999) and for anions by 

ion chromatography. The elements measured by the chemical analyses are those routinely measured by 

the USGS for studies of rocks, sediments, soils, and environmental samples.

Leachate solutions for a subset of the dust samples were also analyzed for dissolved mercury 

concentrations. For these samples, an aliquot was filtered using a syringe and disposable 0.45 micrometer 

pore size nitrocellulose filter, and then acidified and preserved by the addition of a 1 percent sodium 

dichromate/concentrated nitric acid solution in a ratio of 1:19 (one part sodium dichromate/nitric acid 

solution to 19 parts water sample). Leachate samples were stored in nitric acid-washed, flint glass bottles 

with Teflon lined lids. Samples were then analyzed for mercury using a Lachat QuikChem Mercury 

Analyzer with fluorescence detector. This method has a lower reporting limit of 5 part per trillion (ng/L).

Quality assurance-quality control information for the process and the chemical analyses are available 

upon request.
 Larger 249 

KB image 

Leach Figure 1. Plots showing the ranges (blue boxes) and means (horizontal white bars) in pH and 

specific conductance (upper plot), major cations and anions (middle plot), and trace elements (lower plot) 
in leachate solutions from WTC dusts and girder coatings. Elements for which one or more samples were 

below the analytical detection limits are indicated by arrows extending downward from the detection limit 

concentration. Abbreviations: mg/L = milligrams per liter (approximately the same as parts per million); 

μg/L = micrograms per liter (approximately the same as parts per billion); mS/cm = milliSiemens per 

centimeter. For comparison, 1 milligram per liter equals 1000 micrograms per liter, and 1 part per million 

equals 1000 parts per billion. Also, one mS/cm in specific conductance is approximately equal to 1000 

milligrams per liter dissolved solids. 
Larger 207 KB image 

Leach Figure 2. Map of lower Manhattan showing variations in pH (blue columns) and specific 

conductance (yellow columns) of leachate solutions from the various dusts and girder coating samples. 

Dust samples collected indoors are indicated by the single hatch pattern and girder coating samples by 

the cross-hatch pattern; all others are dust samples collected outdoors. 

Larger 210 KB image 
Leach Figure 3. Map of lower Manhattan showing variations (as stacked bar charts) in major cation and 

anion concentrations of leachate solutions derived from the various dusts and girder coating samples. 

Dust samples collected indoors are indicated by the single hatch pattern and girder coating samples by 

the cross-hatch pattern; all others are dust samples collected outdoors. 

Larger 202 KB image 

Leach Figure 4. Map of lower Manhattan showing variations (as stacked bar charts) of metals and anions 
present in intermediate concentrations in leachate solutions derived from the various dusts and girder 

coating samples. Dust samples collected indoors are indicated by the single hatch pattern and girder 

coating samples by the cross-hatch pattern; all others are dust samples collected outdoors. Note changes 

in scale of the concentration axis of the plots between this figure and leach figures 2-6. 

Larger 206 KB image 

Leach Figure 5. Map of lower Manhattan showing variations (as stacked bar charts) in concentrations of 
predominant trace metals and metalloids for leachate solutions derived from the various dusts and girder 

coating samples. Dust samples collected indoors are indicated by the single hatch pattern and girder 

coating samples by the cross-hatch pattern; all others are dust samples collected outdoors. Note changes 

in scale of the concentration axis of the plots between this figure and leach figures 2-6. 

Larger 214 KB image 

Leach Figure 6. Map of downtown Manhattan showing variations (as stacked bar charts) in 
concentrations of less abundant trace metals and metalloids for leachate solutions derived from the 

various dusts and girder coating samples. Dust samples collected indoors are indicated by the single hatch 

pattern and girder coating samples by the cross-hatch pattern; all others are dust samples collected 

outdoors. Note changes in scale of the concentration axis of the plots between this figure and leach 

figures 2-5. 

Results 

Results of the leach tests are summarized in Leach Table 1, and in Leach Figures 1-6. The metal 

concentrations summarized in Leach Table 1 may not represent truly dissolved material, because the 

nitrocellulose filter (0.45 micrometer pore size) used to filter the leachate fluids prior to analysis will not 

filter out metals present in very small particles or colloids.

Interpretation

In general, the leachate solutions developed moderately alkaline to alkaline pH values (8.2 - 11.8), and 

high specific conductances (1.31 - 3.41 milliSiemens/cm, indicating high dissolved solids). Alkalinities of 

the leachate solutions were not measured due to insufficient sample volume, but are by inference from 

the pH and specific conductances, likely to be quite high. The leachate solutions are composed primarily of 

sulfate, bicarbonate, carbonate, and calcium, with lesser concentrations of the major cations sodium, 

potassium, and magnesium. 

The alkaline pH of the leach solutions, coupled with the high concentrations of calcium, carbonate, and 

sulfate, are consistent with an origin resulting primarily from the dissolution of concrete, glass fibers, 

gypsum, and other material in the dusts. The leach fluids with the highest pH and highest specific 

conductance are from dust samples collected indoors (including WTC01-20, collected indoors from the 

gymnasium across West Street from the World Trade Center, and WTC01-36, which was collected in a 

30th-floor apartment in a building southwest of the WTC). The higher specific conductances and pH values 

of indoor dust samples indicate that the outdoor samples have already experienced some leaching by 

rainfall and water used for fighting fires and street cleaning between September 11 and the time that the 

samples were collected. Leach solutions from the indoor dust samples also contain slightly less sulfate, 

but greater calcium, than leach solutions from several outdoor dust samples (Leach Figure 2). This 

suggests that dissolution of concrete or glass fibers is greater in the indoor dusts than in the outdoor 

dusts, and is another indication that the outdoor dusts have already undergone some leaching by rainfall 

or wash waters. 

Heavy metals and metalloids are present in low to quite high concentrations in many of the leach 

solutions Leach Table 1, Leach Figure 1). Mercury is present in generally low concentrations in the 

leachate solutions from outdoor dust samples (near 10 nanograms per liter, or parts per trillion). Mercury 

concentrations in leachate solutions from indoor dust samples (as high as 130 nanograms per liter), 

although low compared to concentrations of other metals in the leachate solutions, are relatively high 

compared to mercury concentrations measured in many types of environmental water samples. Arsenic, 

cobalt, cadmium, thorium, and uranium are present in relatively low concentrations in the leachate 

solutions (maximum concentrations of 3.3, 3.2, 1.6, 0.5, and 0.5 micrograms per liter, μg/L, 

respectively). Lead, selenium, and vanadium are present in moderate concentrations (maximum 

concentrations of 11.5, 10.5, and 16.1 μg/L, respectively). Metals or metalloids present in relatively high 

concentrations in the leachate solutions include (maximum concentrations listed in parentheses): 

aluminum (702 μg/L), chromium (403 μg/L), antimony (74 μg/L), molybdenum (140 μg/L), barium (62 

μg/L), manganese (35 μg/L), copper (39 μg/L), and zinc (62 μg/L). 

Of the various major and trace elements, aluminum is leached in greatest amounts from the indoor dust 

samples relative to outdoor dust samples. This indicates that the indoor dusts, in addition to having a 

greater proportion of reactive concrete, also contain some sort of reactive aluminum-bearing material. 

This material has presumably been partly to largely leached from the outdoor dusts by rain water and 

wash water. 

Leachate solution from one of the beam coating samples (WTC01-09) contain unusually high amounts of 

chromium (408 μg/L). As noted in the SEM section, the mineralogy of this sample is generally similar to 

those of the dust samples in overall mineralogy. However, the source of the leachable chromium in the 
material is currently unknown. 

The source of the metals and metalloids in the leach solutions is unclear, but many components of the 

dust and debris are possible sources, including particles from concrete, aggregate, gypsum wallboard, 

glass fibers, construction steel, wiring, computer equipment, etc. 

The results of the leach tests also show that metals are not leached from the dusts and beam coating 

samples in proportion to their total concentrations in the samples (compare concentrations in Leach Table 

1 with those in Chemistry Table 1 from the previous section). For example, chromium, molybdenum, and 

antimony are leached in relatively high amounts from the samples, but occur in relatively low total 

concentrations in the samples. In part, these trace elements are likely being leached in greater 

proportions from the samples due to their enhanced solubilities in alkaline solutions. It is also possible 

that they are being leached more aggressively because they may occur in materials that are more readily 

dissolved in alkaline solutions. In contrast, iron, zinc and lead, which are relatively more abundant in the 

samples (Chemistry Table 1), are leached in proportionally quite low amounts from the samples (Leach 

Table 1). These metals are generally less mobile in alkaline solutions, and may also occur in materials 

that are not readily soluble in alkaline solutions. 

Summary and potential environmental implications 

Results of the leach tests indicate that the dusts released from the WTC collapse, when exposed rainwater 

or wash water, likely produce slightly alkaline to quite alkaline, calcium-sodium-potassium-sulfatebicarbonate-carbonate solutions. At least some heavy metals and metalloids may be readily leached from 

the dusts: aluminum, chromium, antimony, molybdenum, and barium are generally leached in the 

greatest amounts, but other metals such as zinc, copper, manganese, titanium, vanadium, lead and 

mercury are also leached in measurable quantities. It is unclear if these heavy metals and metalloids may 

be leached in sufficient quantities to be of environmental or health concern. These results indicate that 

continued EPA monitoring of runoff water quality is warranted. Continued rainfall will likely continue to 

decrease the amounts of metals and alkalinity that can be released from the outdoor dusts. 

The results of the leach tests also indicate that cleanup of dusts should be done with appropriate 

respiratory protection to prevent possible inhalation of alkaline material with potentially bioavailable 

heavy metals and metalloids. This is especially true for cleanup of dusts from indoor localities that have 

not been exposed to rainfall. 

NEXT Section of Report: Integration of Results and Conclusions 

Back to document Table of Contents 

Contacts 

For further information on the leach test procedures, contact: 

Philip L. Hageman 

phageman@usgs.gov 

For further information on interpretation of the leach test results, contact: 

Geoffrey S. Plumlee 

gplumlee@usgs.gov 

For further information on analytical chemistry procedures, contact: 

Paul Lamothe 

plamothe@usgs.gov 

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Leach Table 1. Table summarizing analytical results for solutions leached from WTC dust and beam 

coating samples. Details of the leach test methods are summarized in the text. 

Leach Table 1

Outdoor dust samples

WTC-01-2 WTC-01-3 WTC-01-05 

WTC-01-

06 

WTC-01-

14

pH 10.1 9.51 9.9 9.65 9.68

Specific 

Conductance mS/cm 1.58 1.31 1.9 2.01 2.03

Chloride mg/L 7.8 3.7 nm nm 5.1

Fluoride mg/L <.8 <.8 nm nm <1.6

Nitrate mg/L 1.5 0.5 nm nm 1.4

Calcium mg/L 388 314 577 523 544

Magnesium mg/L 1.75 2.83 3.2 3.65 3.52

Potassium mg/L 6 3.8 7.71 6.33 6.9

Silicon mg/L 5.8 4.5 8.1 5.9 6.4

Phosphorous mg/L 0.05 0.1 0.04 0.03 0.05

Sodium mg/L 6.1 2.84 7.69 5.76 3.05

Sulfate mg/L 834 694 1210 1040 1250

Aluminum μg/L 111 44.6 24.3 26 30.3

Antimony μg/L 33.1 22.9 46.3 42 35.9

Arsenic μg/L 1 1 < 3 < 3 1

Barium μg/L 36.5 28.4 38.3 36 45.1

Beryllium μg/L < 0.05 < 0.05 < 0.05 < 0.05 < 0.05

Bismuth μg/L < 0.005 0.01 < 0.005 < 0.005 0.01

Cadmium μg/L 0.44 0.26 1.08 0.82 0.37
Cerium μg/L < 0.01 0.03 0.02 0.02 0.01

Cesium μg/L 0.08 0.05 0.04 0.04 0.06

Chromium μg/L 25.9 9 25.1 18.2 31.4

Cobalt μg/L 1.23 0.72 1.04 1.02 1.15

Copper μg/L 19.2 19.8 22.4 13.5 11.4

Gallium μg/L 0.23 0.1 0.1 0.1 0.1

Germanium μg/L 0.07 0.09 0.1 0.08 0.07

Iron μg/L < 50 < 50 < 50 < 50 < 50

Lanthanum μg/L < 0.01 0.01 < 0.01 0.01 < 0.01

Lead μg/L 0.64 0.5 0.5 0.51 0.97

Lithium μg/L 11.2 4.1 11.2 9.4 9.8

Manganese μg/L 1 3.2 2 3.8 2.3

Mercury ng/L nm nm 18 7 nm

Molybdenum μg/L 56.8 14 45.7 42.2 30.8

Nickel μg/L 18.1 14.4 21.4 19.4 25.2

Niobium μg/L < 0.02 0.03 0.1 0.1 0.02

Rubidium μg/L 12.6 8.08 12.4 12.9 14.1

Scandium μg/L 1.8 1.3 2.2 1.9 1.9

Selenium μg/L 2.5 1 < 5 < 5 1.9

Silver μg/L < 3 < 3 nm nm < 3

Strontium μg/L 834 561 1150 1100 1230

Thallium μg/L < 0.05 < 0.05 0.2 0.06 < 0.05

Thorium μg/L 0.04 0.09 0.8 0.37 0.06

Titanium μg/L 17.9 13.4 18.9 18.7 25.7

Uranium μg/L 0.03 0.15 0.08 0.09 0.06

Vanadium μg/L 6.2 6 11.8 8.8 9.7

Yttrium μg/L < 0.01 < 0.01 0.08 0.08 0.11

Zinc μg/L 10.7 7.7 15.6 20.9 11.6

Zirconium μg/L 0.07 0.1 0.5 0.3 0.08

nm - not measured; ppm - parts per million; mg/L - milligrams per liter; μg/L - micrograms per 

liter; ng/L - nanograms per liter; mS/cm - milliSiemens per centimeter
Leach Table 1, continued

Outdoor dust samples, continued

WTC-01-15 WTC-01-16 WTC-01-17 

WTC-01-

21

WTC-01-

22

pH 10 8.22 9.47 9.98 10.4

Specific 

Conductance mS/cm 2.01 2.08 1.96 2.02 2.02

Chloride mg/L 3.4 8.5 nm 7.8 8.1

Fluoride mg/L <1.6 <1.6 nm <1.6 <1.6

Nitrate mg/L 1.5 <1.6 nm 2.4 1.5

Calcium mg/L 528 526 517 549 529

Magnesium mg/L 1.71 20.2 2.54 2.61 2.12

Potassium mg/L 5.9 9.2 4.83 7.7 5.2

Silicon mg/L 4.9 4.3 2 5.8 5.4

Phosphorous mg/L 0.02 0.03 < 0.01 0.04 0.05

Sodium mg/L 2.65 5.09 4.81 4.11 5.69

Sulfate mg/L 1230 1350 1110 1270 1170

Aluminum μg/L 53.9 6.33 50.6 53.6 153

Antimony μg/L 15.3 28.6 11.2 21.2 17

Arsenic μg/L < 1 2 < 3 1 < 1

Barium μg/L 28.9 23.2 17.5 33.9 32.2

Beryllium μg/L < 0.05 < 0.05 < 0.05 < 0.05 < 0.05

Bismuth μg/L 0.01 0.01 < 0.005 0.006 0.01

Cadmium μg/L 0.55 0.39 0.47 0.25 0.16

Cerium μg/L 0.01 0.02 0.02 0.01 0.02

Cesium μg/L 0.05 0.05 0.03 0.06 0.05

Chromium μg/L 42 20.8 17.4 19.3 27.7

Cobalt μg/L 1.02 1.29 1.04 1.16 0.98

Copper μg/L 10.2 15.6 14.4 6.2 9.6

Gallium μg/L 0.1 0.05 0.08 0.2 0.27

Germanium μg/L 0.06 0.1 0.05 0.05 0.04

Iron μg/L < 50 < 50 < 50 < 50 < 50
Lanthanum μg/L < 0.01 0.01 < 0.01 < 0.01 < 0.01

Lead μg/L 1.5 0.4 0.3 1.1 0.68

Lithium μg/L 6.4 11.2 6.9 7.4 7.8

Manganese μg/L 1.2 35.1 1.7 1.4 1

Mercury ng/L nm nm 8 nm nm

Molybdenum μg/L 10.6 46.3 35.5 10.7 7.42

Nickel μg/L 22.2 25 21.9 24.6 24.8

Niobium μg/L 0.02 0.02 0.07 0.04 0.04

Rubidium μg/L 12.4 14.1 8.91 14.1 10

Scandium μg/L 1.5 1.2 0.8 1.7 1.5

Selenium μg/L < 1 3 < 5 2.2 1.6

Silver μg/L < 3 < 3 nm < 3 < 3

Strontium μg/L 1060 999 1000 1020 943

Thallium μg/L < 0.05 < 0.05 < 0.05 < 0.05 < 0.05

Thorium μg/L 0.06 0.24 0.2 0.1 0.17

Titanium μg/L 24.8 25.1 19.4 25.9 24

Uranium μg/L 0.03 0.52 0.01 0.02 0.02

Vanadium μg/L 6.6 6.5 2.7 8 5.5

Yttrium μg/L 0.1 0.1 0.05 0.1 0.07

Zinc μg/L 10.6 24.1 12.7 9.6 6.5

Zirconium μg/L 0.2 0.2 0.09 0.2 0.2

nm - not measured; ppm - parts per million; mg/L - milligrams per liter; μg/L - micrograms per 

liter; ng/L - nanograms per liter; mS/cm - milliSiemens per centimeter

Leach Table 1, continued

Outdoor dust samples, continued

WTC-01-25 WTC-01-27 WTC-01-28

WTC-01-

30 

WTC-01-

34 

pH 9.37 10 9.93 9.63 9.8

Specific 

Conductance mS/cm 2.16 2.31 2.02 1.9 2.02

Chloride mg/L 37 52 12 nm nm
Fluoride mg/L <1.6 <1.6 <1.6 nm nm

Nitrate mg/L 113 3.2 nm nm

Calcium mg/L 558 568 553 461 524

Magnesium mg/L 6.15 2.01 2.85 5.27 3.2

Potassium mg/L 11.7 9.7 11.3 3.22 5.06

Silicon mg/L 8.1 7.2 8.65 4.2

Phosphorous mg/L 0.06 0.04 0.04 0.02 0.02

Sodium mg/L 12.9 12.7 5.57 4.28 2.76

Sulfate mg/L 1240 1240 1250 986 1180

Aluminum μg/L 23.8 33.4 45 22.6 27.8

Antimony μg/L 73.6 25.5 43.6 35.5 33.5

Arsenic μg/L 3.232 < 3 < 3

Barium μg/L 58.4 38.6 43.5 53.9 32.4

Beryllium μg/L < 0.05 < 0.05 < 0.05 < 0.05 < 0.05

Bismuth μg/L 0.01 0.01 0.007 < 0.005 < 0.005

Cadmium μg/L 1.56 0.38 0.54 1.06 1.04

Cerium μg/L 0.02 0.02 0.02 0.02 0.02

Cesium μg/L 0.08 0.05 0.1 0.04 0.03

Chromium μg/L 24.4 15.7 34.5 26.1 16.2

Cobalt μg/L 3.18 1.17 1.25 0.72 0.87

Copper μg/L 39 21.59 14 10.6

Gallium μg/L 0.1 0.2 0.2 0.1 0.1

Germanium μg/L 0.2 0.05 0.08 0.09 0.08

Iron μg/L < 50 < 50 < 50 < 50 < 50

Lanthanum μg/L 0.01 < 0.01 0.02 0.01 < 0.01

Lead μg/L 11.5 0.4 0.83 0.2 0.5

Lithium μg/L 29.7 24.3 11.2 9.6 7.9

Manganese μg/L 4.912 3.3 1.8

Mercury ng/L nm nm nm 12 10

Molybdenum μg/L 140 126 50.4 30.6 27.9

Nickel μg/L 32.1 27 25.9 18.1 20.7

Niobium μg/L 0.03 0.06 0.03 0.07 0.06
Rubidium μg/L 19.3 14.9 25 9.26 10.8

Scandium μg/L 2.2 2.1 2.5 1.6 1.4

Selenium μg/L 7.4 8.8 3.5 < 5 < 5

Silver μg/L < 3 < 3 < 3 nm nm

Strontium μg/L 1240 1440 1160 1540 1070

Thallium μg/L < 0.05 < 0.05 < 0.05 < 0.05 < 0.05

Thorium μg/L 0.13 0.16 0.08 0.12 0.1

Titanium μg/L 25.5 25 26.3 16.5 18.9

Uranium μg/L 0.13 0.008 0.04 0.09 0.03

Vanadium μg/L 13.2 16.1 12.2 7.2 7

Yttrium μg/L 0.11 0.09 0.12 0.08 0.07

Zinc μg/L 11 8.4 12.1 5.3 12.2

Zirconium μg/L 0.2 0.2 0.2 0.2 0.1

nm - not measured; ppm - parts per million; mg/L - milligrams per liter; μg/L - micrograms per 

liter; ng/L - nanograms per liter; mS/cm - milliSiemens per centimeter

Leach Table 1, continued

Indoor dust samples Girder coatings

WTC-01-20 WTC-01-36 WTC-01-8 

WTC-01-

9 

pH 11.8 11.8 INS 10.8

Specific 

Conductance mS/cm 3.41 3.4 INS 1.43

Chloride mg/L 45 40 16 3

Fluoride mg/L <1.6 <1.6 <.8 <.8

Nitrate mg/L 9.1 17 62 4.1

Calcium mg/L 718 888 528 336

Magnesium mg/L 0.11 0.08 10.3 1.1

Potassium mg/L 10.9 12.3 3 1

Silicon mg/L 3.4 3.2 6.7 11.3

Phosphorous mg/L 0.09 0.09 < 0.01 < 0.01

Sodium mg/L 15.3 18.3 2.1 1.54
Sulfate mg/L 1320 1640 1090 674

Aluminum μg/L 611 702 10.8 121

Antimony μg/L 20.8 17.1 8.72 7.97

Arsenic μg/L 3.3 3.3 < 3 < 3

Barium μg/L 61.7 57.2 22.8 10.4

Beryllium μg/L < 0.05 < 0.05 < 0.05 < 0.05

Bismuth μg/L 0.02 < 0.005 < 0.005 < 0.005

Cadmium μg/L 0.18 0.18 0.02 0.02

Cerium μg/L < 0.01 0.01 0.26 0.4

Cesium μg/L 0.09 0.08 0.02 < 0.01

Chromium μg/L 69.4 109 18 408

Cobalt μg/L 1.84 2.21 1.27 0.75

Copper μg/L 15.1 33.6 5.6 3.5

Gallium μg/L 0.59 0.97 0.08 0.38

Germanium μg/L 0.05 0.07 0.1 < 0.02

Iron μg/L < 50 < 50 < 50 < 50

Lanthanum μg/L 0.01 0.01 0.05 0.18

Lead μg/L 5.8 10.9 0.4 0.3

Lithium μg/L 18.5 19.5 1.3 0.3

Manganese μg/L 1.3 1.7 5.5 2.1

Mercury ng/L 130 125

Molybdenum μg/L 73.8 72.9 1.74 1.18

Nickel μg/L 36.2 42.6 24.9 16.6

Niobium μg/L 0.08 0.05 0.08 < 0.02

Rubidium μg/L 17.7 20.8 3.54 1.35

Scandium μg/L 1.2 2.1 3.6 5.5

Selenium μg/L 10.5 10.3 < 5 < 5

Silver μg/L < 3 < 3 < 3 < 3

Strontium μg/L 1420 1690 990 758

Thallium μg/L 0.08 < 0.05 < 0.05 < 0.05

Thorium μg/L 0.51 0.38 0.52 0.18

Titanium μg/L 25.5 28.4 24.9 15.3
Uranium μg/L 0.01 < 0.005 0.02 0.006

Vanadium μg/L 6.5 7.8 13.8 14.4

Yttrium μg/L 0.13 0.16 0.31 0.27

Zinc μg/L 28.4 61.8 20.1 15.8

Zirconium μg/L 0.4 0.4 3.7 0.2

nm - not measured; ppm - parts per million; mg/L - milligrams per liter; μg/L - micrograms per 

liter; ng/L - nanograms per liter; mS/cm - milliSiemens per centimeter

Leach Table 1, continued

minimum maximum mean*

pH 8.22 11.8 10.00

Specific 

Conductance mS/cm 1.31 3.41 2.03

Chloride mg/L 3 52 11.27

Fluoride mg/L <1.6 <1.6 ***

Nitrate mg/L 0.5 62 3.69

Calcium mg/L 314 888 519.83

Magnesium mg/L 0.08 20.2 2.27

Potassium mg/L 1 12.3 6.03

Silicon mg/L 2 11.3 5.43

Phosphorous mg/L 0.02 0.1 0.04

Sodium mg/L 1.54 18.3 5.16

Sulfate mg/L 674 1640 1121.72

Aluminum μg/L 6.33 702 49.68

Antimony μg/L 7.97 73.6 24.37

Arsenic μg/L 1 3.3 1.83

Barium μg/L 10.4 61.7 33.90

Beryllium μg/L < 0.05 < 0.05 ***

Bismuth μg/L 0.006 0.02 0.01

Cadmium μg/L 0.02 1.56 0.33

Cerium μg/L 0.01 0.4 0.02

Cesium μg/L 0.02 0.1 0.05
Chromium μg/L 9 408 29.50

Cobalt μg/L 0.72 3.18 1.17

Copper μg/L 3.5 39 13.21

Gallium μg/L 0.05 0.97 0.15

Germanium μg/L 0.04 0.2 0.07

Iron μg/L <50 <50 ***

Lanthanum μg/L 0.01 0.18 0.02

Lead μg/L 0.2 11.5 0.83

Lithium μg/L 0.3 29.7 7.91

Manganese μg/L 1 35.1 2.31

Mercury ng/L 7 130 21.26

Molybdenum μg/L 1.18 140 25.54

Nickel μg/L 14.4 42.6 23.46

Niobium μg/L 0.02 0.1 0.05

Rubidium μg/L 1.35 25 11.02

Scandium μg/L 0.8 5.5 1.82

Selenium μg/L 1 10.5 3.58

Silver μg/L < 3 < 3 ***

Strontium μg/L 561 1690 1083.10

Thallium μg/L 0.06 0.2 0.10

Thorium μg/L 0.04 0.8 0.16

Titanium μg/L 13.4 28.4 21.65

Uranium μg/L 0.006 0.52 0.04

Vanadium μg/L 2.7 16.1 8.24

Yttrium μg/L 0.05 0.31 0.11

Zinc μg/L 5.3 61.8 13.38

Zirconium μg/L 0.07 3.7 0.22

*Geometric mean for all parameters except pH; ***Geometric mean not calculated due to one 

or more samples having concentrations below detection limit; nm - not measured; ppm - parts 

per million; mg/L - milligrams per liter; μg/L - micrograms per liter; 

ng/L - nanograms per liter; mS/cm - milliSiemens per centimeter
ins - insufficient leachate solution volume to measure pH and conductivity 

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OFR 01-0429: World Trade Center USGS Integration of Results and 

Conclusions

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The results of analyses completed so far show a consistent picture: the samples are largely 

composed of gypsum, cellulose, and miscellaneous materials common in a building, with 

minor asbestiform minerals. However, one sample analyzed, the coating on a steel beam, 

indicates the presence of a significant abundance of chrysotile asbestos (as much as 20% 

by volume). The confirmed abundant chrysotile sample and the potential pockets of 

chrysotile indicated in the AVIRIS mineral maps indicates that asbestos can be found in 

localized concentrations. Thus, appropriate precautions should be taken when handling 

debris, especially coatings on metal beams.

Sample results are summarized in Table 1, below. To see the full resolution SEM image and 

description, click on the image in the table. In the spectroscopy column in the table below, 

CH indicates organic compounds, including paints and plastics. Fe2+ indicates minerals or 

materials containing ferrous iron. Amounts are qualitative and indicate (from low to high) 

trace as (tr), weak as (wk), and strong as (str). No indication indicates between weak and 

strong.

The composition of samples collected in the WTC area, as indicated by spectroscopy, XRD, 

SEM, and from the visual examination during splitting of the samples, show similarities, yet 

each sample shows differences. Thus, while the samples appear to be a "grey dust", the 

data indicate the dust was not well mixed. The sample analyses and the AVIRIS mapping 

results agree in this regard. 

Table 1 

; 

Sample 

Number Spectroscopy XRD SEM Leach pH Location

WTC01-01 

(calibration)

asphalt 

from NJ

WTC01-02

gypsum, 

muscovite 

(tr), 

CH, 

Fe2+

Quartz - Minor 

Calcite - Minor 

Gypsum - Minor 

Dolomite - Trace 

Anhydrite - Trace 

Orthoclase - Trace 

*Major amorphous 

material

10.1

Water & 

Vietnam 

Vet. Plaza 

4506052N 

583559E
WTC01-03

gypsum, 

muscovite 

(tr), 

CH, 

Fe2+ (wk)

Quartz - Major 

Gypsum - Minor 

Calcite - Minor 

Anhydrite - Trace 

*Major amorphous 

material

9.51

Battery 

Park, 

east 

central 

4506123N 

583217E 

drainage 

disc

WTC01-04

gypsum, 

muscovite 

and/or 

portlandite 

(tr), 

CH, 

Fe2+ (wk)

Calcite - Major 

Gypsum - Minor 

Anhydrite - Minor 

Quartz - Trace 

Muscovite - Trace 

Microcline - Trace 

*Major amorphous 

material

Battery 

Park, 

NE end 

4506284N 

583233E

WTC01-05

gypsum, 

muscovite 

and/or 

portlandite 

(tr), 

CH, 

Fe2+(wk)

Calcite - Major 

Quartz - Minor 

Gypsum - Minor 

Anhydrite - Minor 

Calcium Sulfate 

Hydrate - Trace 

*Major amorphous 

material

9.9

Broadway 

& 

Wall St. 

from Bank 

of NY

WTC01-06

gypsum, 

muscovite 

and/or 

portlandite 

(tr), 

CH, 

Fe2+

Calcite - Minor 

Quartz - Minor 

Gypsum - Minor 

Anhydrite - Minor 

Muscovite - Trace 

Calcium Sulfate 

Hydrate - Trace 

*Major amorphous 

material

9.65

Greenwich 

& 

Morris

WTC01-07

gypsum, 

muscovite 

and/or 

portlandite 

(tr), 

CH, 

Fe2+

Gypsum - Minor 

Calcite - Minor 

Quartz - Minor 

Anhydrite - Minor 

Muscovite - Trace 

Microcline - Trace 

*Major amorphous 

material

Rector & 

Greenwich 

from 

sidewalk
WTC01-08

chrysotile 

gypsum 

CH, 

Fe2+ (str) 

Calcite - Minor 

Chrysotile - Minor 

Gypsum - Minor 

Talc - Trace 

Anhydrite - Trace 

Microcline - Trace 

Rozenite - Trace 

*Possible trace 

rozenite 

*Major amorphous 

material

West End 

& 

Vesey, 

steel girder

WTC01-09

gypsum, 

muscovite, 

CH, 

Fe2+ (str)

Calcite - Minor 

Gypsum - Minor 

Thaumasite - Minor 

Quartz - Trace 

Calcium Silicate - 

Trace 

Larnite - Trace 

*Major amorphous 

material

10.8

West End 

& 

Vesey, 

steel girder

WTC01-10

gypsum, 

muscovite 

(tr), 

CH, 

chrysotile 

(tr) 

Fe2+

Gypsum - Minor 

Calcite - Minor 

Quartz - Minor 

Anhydrite - Trace 

Muscovite - Trace 

*Major amorphous 

material

West End 

& 

Vesey

WTC01-11

gypsum, 

muscovite 

(tr), 

CH, 

Fe2+

Quartz - Minor 

Gypsum - Minor 

Calcite - Minor 

Anhydrite - Minor 

Microcline Trace 

Muscovite - Trace 

Chrysotile - Trace 

Calcium Sulfate - 

Trace 

*Major amorphous 

material

West End 

& 

Barclay

WTC01-12

gypsum, 

muscovite 

(tr), 

CH, 

Fe2+

Quartz - Minor 

Calcite - Minor 

Gypsum - Minor 

Anhydrite - Minor 

Muscovite - Trace 

Chrysotile - Trace 

*Major amorphous 

material

West End 

& 

Warren
WTC01-13

gypsum, 

muscovite 

(tr), 

CH, 

Fe2+ (wk) 

possible 

trace 

chrysotile

Quartz - Minor 

Calcite - Minor 

Gypsum - Minor 

Anhydrite - Minor 

Muscovite - Trace 

*Major amorphous 

material

Broadway 

& 

Barclay

WTC01-14

gypsum, 

muscovite, 

CH, 

Fe2+ (wk), 

chrysotile 

(wk)

Gypsum - Minor 

Calcite - Minor 

Quartz - Minor 

Anhydrite - Trace 

Muscovite - Trace 

*Major amorphous 

material

9.68

Church & 

Barclay 

from a 

windowsill

WTC01-15

gypsum, 

muscovite, 

CH, 

Fe2+ (wk) 

possible 

trace 

chrysotile

Gypsum - Major 

Anhydrite - Minor 

Quartz - Minor 

Calcite - Minor 

Muscovite - Trace 

*Major amorphous 

material

10

Maiden Ln. 

& 

Church

WTC01-16

gypsum, 

muscovite 

and/or 

portlandite 

(tr), 

CH, 

Fe2+ (wk)

Quartz - major 

Gypsum - Major 

Calcite - Minor 

Anhydrite - Trace 

Albite - Trace 

Orthoclase - Trace 

*Major amorphous 

material

8.22

Broadway 

& 

Dey

WTC01-17

gypsum, 

muscovite 

and/or 

portlandite 

(tr), 

CH, 

Fe2+

Quartz - Minor 

Gypsum - Minor 

Calcite - Minor 

Anhydrite - Minor 

Calcium Sulfate 

Hydrate - Trace 

Muscovite - Trace 

*Major amorphous 

material

9.47

Greenwich 

& 

Albany
WTC01-18

gypsum, 

portlandite 

(tr), 

CH, 

Fe2+ (wk)

Gypsum - Minor 

Calcite - Minor 

Quartz - Minor 

Muscovite - Minor 

Anhydrite - Minor 

Portlandite - Trace 

Bassanite - Trace 

Chrysotile - Trace 

*Possible trace 

chrysotile 

*Major amorphous 

material

Washington 

& 

Albany

WTC01-19

gypsum, 

muscovite 

(tr), 

CH, 

Fe2+ (wk)

Gypsum - Minor 

Calcite - Minor 

Quartz - Minor 

Muscovite - Trace 

Anhydrite - Trace 

Bassanite - Trace 

*Major amorphous 

material

South End 

& 

Ceder

WTC01-20

gypsum, 

muscovite 

and/or 

portlandite 

(tr), 

CH, 

chrysotile 

(tr), 

Fe2+ (wk)

Quartz - Minor 

Calcite - Minor 

Gypsum - Minor 

Anhydrite - Minor 

Portlandite - Trace 

Bassanite - Trace 

Muscovite - Trace 

Clinochrysotile - 

Trace 

*Very slight 

possibility of a trace 

of chrysotile 

*Portlandite and 

bassanite are trace 

to minor 

*Major amorphous 

material

11.8

Liberty & 

South End 

2 World 

Financial 

Center: 

indoor 

sample
WTC01-21

gypsum, 

muscovite, 

CH, 

chrysotile 

(tr) 

Fe2+ (wk)

Gypsum - Minor 

Quartz - Minor 

Calcite - Minor 

Anhydrite - Minor 

Microcline - Trace 

Clinochrysotile - 

Trace 

Muscovite 

*possible trace 

Chrysotile 

*Major amorphous 

material

9.98

Directly 

West of 

WTC at 

ferry dock 

and ped. 

mall

WTC01-22

gypsum, 

muscovite, 

CH, 

Fe2+ (wk)

Gypsum - Major 

Anhydrite - Minor 

Quartz - Minor 

Calcite - Minor 

Muscovite - Trace 

Paragonite - Trace 

Lizardite - Trace 

Magnesionhornblende 

- Trace 

Clinochrysotile - 

Trace 

*possible trace 

(<.5%) chrysotile 

and/or Lizardite 

*trace amphibole 

(<.5%) 

*Major amorphous 

material

10.4

1/2 way 

between 

WTC and 

Ferry Dock 

along ped. 

mall 

from a 

windowsill

WTC01-23

gypsum, 

muscovite 

(tr), 

CH, 

chrysotile 

(tr) 

Fe2+ (wk)

Gypsum - Minor 

Muscovite - Minor 

Calcite - Minor 

Quartz - Minor 

Anhydrite - Trace 

Bassanite - Trace 

*Major amorphous 

material

Broadway 

& 

Murray
WTC01-24

gypsum, 

muscovite 

(tr), 

CH, 

chrysotile 

(tr) 

Fe2+ (wk)

Gypsum - Minor 

Calcite - Minor 

Anhydrite - Minor 

Dolomite - Minor 

Muscovite - Minor 

Quartz - Trace 

Microcline - Trace 

Calcium Sulfate - 

Trace 

*Major amorphous 

material

Broadway 

& 

Chambers

WTC01-25

gypsum, 

muscovite/

illite, 

CH, 

chrysotile 

(tr) 

Fe2+ (wk)

Calcite - Minor 

Quartz - Minor 

Gypsum - Minor 

Anhydrite - Minor 

Dolomite - Trace 

Illite - Trace 

*Major amorphous 

material

9.37 Church & 

Warren

WTC01-26

gypsum, 

muscovite 

(tr), 

CH, 

Fe2+ (wk)

Calcite - Minor 

Gypsum - Minor 

Anhydrite - Minor 

Muscovite - Minor 

Quartz - Trace 

Dolomite - Trace 

Microcline - Trace 

Calcium Sulfate - 

Trace 

Chrysotile - Trace 

*Major amorphous 

material

1/2 way 

between 

Broadway 

and 

Church on 

Park

WTC01-27

gypsum, 

muscovite, 

CH 

Anhydrite - Minor 

Calcite - Minor 

Quartz - Minor 

Gypsum - Minor 

Orthoclase - Trace 

Albite - Trace 

Muscovite - Trace 

Clinochrysotile - 

Trace 

*Major amorphous 

material

10

Broadway 

& 

Vesey
WTC01-28

gypsum, 

muscovite, 

CH, 

chrysotile 

(wk), 

Fe2+ (wk)

Calcite - Minor 

Gypsum - Minor 

Quartz - Minor 

Anhydrite - Minor 

Chrysotile - Trace 

*Major amorphous 

material

9.93 Ann & 

Nassau

WTC01-29

gypsum, 

muscovite 

(tr), 

CH, 

chrysotile 

(tr), 

Fe2+ (wk)

Calcite - Minor 

Gypsum - Minor 

Quartz - Minor 

Anhydrite - Minor 

Muscovite - Trace 

Chrysotile - Trace 

*Major amorphous 

material

William & 

Fulton

WTC01-30

gypsum, 

muscovite, 

CH, 

Fe2+

Calcite - Minor 

Quartz - Minor 

Dolomite - Minor 

Anhydrite - Minor 

Gypsum - Minor 

Chrysotile - Trace 

*Possible trace 

chrysotile 

*Major amorphous 

material

Fulton & 

Cliff St. 

from on 

top of a car

WTC01-31

gypsum, 

muscovite, 

CH, 

Fe2+ (wk)

Calcite - Minor 

Gypsum - Minor 

Quartz - Minor 

Anhydrite - Minor 

Muscovite - Trace 

Chrysotile - Trace 

*Major amorphous 

material

William & 

Platt

WTC01-32

gypsum, 

muscovite, 

CH, 

Fe2+

Calcite - Minor 

Gypsum - Minor 

Quartz - Minor 

Anhydrite - Minor 

Muscovite - Trace 

Chrysotile - Trace 

*Possible trace 

chrysotile 

*Major amorphous 

material

William & 

Pine
WTC01-33

gypsum, 

muscovite 

(tr), 

CH, 

Fe2+ (wk)

Gypsum - Minor 

Calcite - Minor 

Quartz - Minor 

Muscovite - Minor 

Anhydrite - Trace 

Magnesiohornblende 

- Trace 

Chrysotile - Trace 

*Major amorphous 

material

Battery 

Park, 

middle

WTC01-34

gypsum, 

muscovite, 

CH, 

chrysotile 

(tr) Fe2+

(wk)

Quartz - Major 

Calcite - Minor 

Gypsum - Minor 

Anhydrite - Trace 

*Major amorphous 

material

9.8

South End 

& 

Thames

WTC01-35

gypsum, 

CH, 

muscovite, 

chrysotile 

(tr) 

Fe2+

Gypsum - Minor 

Calcite - Minor 

Quartz - Minor 

Anhydrite - Trace 

Muscovite - Trace 

Chrysotile - Trace 

*Major amorphous 

material

Albany & 

Hudson 

River

WTC01-36

gypsum, 

muscovite 

and/or 

portlandite 

(tr), 

CH, 

Fe2+, 

possible 

trace 

chrysotile

Gypsum - Minor 

Calcite - Minor 

Quartz - Minor 

Anhydrite - Minor 

Bassanite - Minor 

Portlandite - Minor 

Dolomite - Trace 

Illite - Trace 

Chrysotile - Trace 

*possible trace 

chrysotile 

*Major amorphous 

material

11.8

South End 

& 

Albany 

(30th 

floor): 

Indoor 

sample

WTC01-37A

gypsum, 

muscovite, 

portlandite, 

Fe2+

Quartz - Major 

Albite - Major 

Portlandite - Minor 

Magnesiohornblende 

- Minor 

Orthoclase - Trace 

Muscovite - Trace

concrete 

from WTC 

area
WTC01-37B portlandite, 

Fe2+

Quartz - Major 

Orthoclase - Minor 

Portlandite - Minor 

Albite - Trace 

Calcite - Trace 

Magnesiohornblende 

- Trace 

Muscovite

concrete 

from WTC 

area

* Amorphous material is not identifiable by XRD, but its presence is detectable.

* "Possible trace chrysotile" means at or near the detection limit with XRD.

The question of asbestos distribution was investigated and the results show an asymmetric 

distribution pattern (Results Figure 1). More chrysotile was detected in an east-west 

direction than south. This pattern occurs in both the AVIRIS maps and from field samples 

(Results Figure 2). While there is a general trend, it is not exclusive, meaning that 

chrysotile was detected in all directions. It also should be noted that samples obtained next 

to each other (on the map this means a city block apart) can show different results: one 

has asbestos, another has no chrysotile above the detection limit.

Composition of samples on a centimeter scale was examined with a spectrometer. Small 

variations in chrysotile content throughout a sample were observed. Thus from scales of cm 

to tens of meters, chrysotile content varies. Such variability makes sampling and overall 

assessment of a site difficult.

The fact that some materials in the WTC debris were observed to contain higher levels of 

chrysotile (sample WTC01-08) on a steel beam, and that the coatings on the beams have 

largely been stripped, leads to the question of where did the coatings go and how well 

distributed/dispersed is the chrysotile? Because a patch of coating showed up to 20% 

chrysotile, and the field samples and the AVIRIS maps show varying levels of serpentine 

(chrysotile) leads to the possibility that other patches of chrysotile may exist in the debris.

The asymmetry in the AVIRIS iron-bearing materials map may be related to the asymmetry 

in the asbestiform minerals map. The AVIRIS data and the laboratory analyses of the field 

samples indicate a lower abundance of chrysotile in the the southern direction from the 

WTC, the same direction of the increase in iron-bearing materials. The one field sample, 

WTC01-08, from an iron beam, which had up to 20% chrysotile also contains a strong Fe2+

absorption. Thus one might expect a higher chrysotile content in iron-bearing materials. 

However, this is clearly not the case, at least in general. This may indicate other sources of 

the chrysotile besides the beam coatings.

AVIRIS imaging spectroscopy mapping provides a synoptic view that samples more area 

than possible with other methods. The AVIRIS maps shown here represent only a portion of 

the data collected, and effectively provide data for about 4.7 million sample locations, all 

obtained within a couple of hours. The sampling includes land, air and water.

The fact that the field sampling missed the highest concentrations of serpentines in the 

AVIRIS maps shows the limitations of limited sampling methodologies. Ideally, the field 

sampling team would have the AVIRIS materials maps to guide the field sampling. 

Unfortunately, this was not possible in this rapid response case (but we routinely employ 

such methods in geologic studies where the region does not change rapidly). Even so, the 

materials maps for this study were produced faster than any other imaging spectroscopy 

effort to our knowledge. The AVIRIS data were received within 24 hours of acquisition, and 

the data were initially calibrated to help the field team obtain the final calibration data with 

real time feedback via cell phone. In this case, scientists in Denver communicated 
composition of field calibration sites using initially calibrated AVIRIS data (of the parking lot 

structure) while the field team was investigating where the best portion of the parking lot 

was located. The real-time feedback resulted in avoidance of portions of the parking lot 

with strong absorption features, not visible to the human eye, that could have compromised 

the quality of the final calibration.

With further development of on-board solar calibration targets on the aircraft with the 

AVIRIS sensor, the refinement of analysis software, the development of more reference 

spectral libraries, and the use of faster computers, an even faster response is possible in 

the future. The challenge is formidable. To analyze the data for this study, we used 

approximately 300 gigabytes of disk space and performed over 50 trillion calculations. The 

results of the AVIRIS mapping are limited by knowledge of the spectral properties of 

materials and the detection levels are limited by the sensor signal-to-noise. The detection 

limits could be substantially improved with existing technology in a new sensor design.

The combination of field sampling with laboratory analysis and imaging spectroscopy 

remote sensing provide a powerful assessment combination. We estimate the analysis 

effort of this highly experienced team to be 1.8 person years to complete this study plus 

another 0.6 person-year for the AVIRIS data collection effort. This study includes analysis 

of 20% of the AVIRIS data from Sept 16, and 7% of the data from Sept 23 (thermal hot 

spot analysis only).

The scientific data from this study is presented with no assessment of health effects. It is 

beyond the scope of this study to assess health effects of a fraction of a percent chrysotile 

asbestos, for example.

Other Conclusions have already been presented in the Executive Summary. 
 
Larger 92 KB image 

Results Figure 1. Sample location map coded by asbestos detection. 

 

Larger 633 KB image 

Results Figure 2.WTC Sample analyses from Results Figure 1 are shown plotted on the 

serpentine/amphibole AVIRIS map. There is a loose correlation of chrysotile locations 

spread in an east-west direction in both the laboratory analyses and the AVIRIS data.

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OFR 01-0429: References

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

● Arbogast, B.F. (ed.), 1996, Analytical methods manual for the Branch 

of Geochemistry, U.S. Geological Survey: U.S. Geological Survey OpenFile Report 96525, 248 pp. 

● Briggs, P.H., and Meier, A.L., 1999, The determination of forty two 

elements in geological materials by Inductively Coupled Plasma - Mass 

Spectrometry, U.S. Geological Survey Open File Report 99-166, 15 p. 

● Clark, R.N., 1979, Planetary Reflectance Measurements in the Region of 

Planetary Thermal Emission, Icarus, 40, 94-103. 

● Clark, R.N. and T.L. Roush, 1984, Reflectance Spectroscopy: 

Quantitative Analysis Techniques for Remote Sensing Applications, J. 

Geophys. Res., 89, 6329-6340. 

● Clark, R.N., A.J. Gallagher, and G.A. Swayze, 1990a, Material 

Absorption Band Depth Mapping of Imaging Spectrometer Data Using a 

Complete Band Shape Least-Squares Fit with Library Reference 

Spectra, Proceedings of the Second Airborne Visible/Infrared Imaging 

Spectrometer (AVIRIS) Workshop. JPL Publication 90-54, 176-186, 

1990a. 

● Clark, R.N., T.V.V. King, M. Klejwa, G. Swayze, and N. Vergo, High 

Spectral Resolution Reflectance Spectroscopy of Minerals: J. Geophys 

Res. 95, 12653-12680. 

● Clark, R.N., G.A. Swayze, A. Gallagher, N. Gorelick, and F. Kruse, 1991, 

Mapping with Imaging Spectrometer Data Using the Complete Band 

Shape Least-Squares Algorithm Simultaneously Fit to Multiple Spectral 

Features from Multiple Materials, Proceedings of the Third Airborne 

Visible/Infrared Imaging Spectrometer (AVIRIS) Workshop, JPL 

Publication 91-28, 2-3. 

● Clark, R.N., G.A. Swayze, A. Gallagher, T.V.V. King, and W.M. Calvin, 

1993, The U. S. Geological Survey, Digital Spectral Library: Version 1: 

0.2 to 3.0 m, U.S. Geological Survey, Open File Report 93-592, 1340 

pages. Online at: http://speclab.cr.usgs.gov. 

● Clark, R.N. and Swayze, G.A., 1995, Mapping Minerals, Amorphous 

Materials, EnvironmentalMaterials, Vegetation, Water, Ice and Snow, 

and Other Materials: The USGS Tricorder Algorithm. Summaries of the 

Fifth Annual JPL Airborne Earth Science Workshop, January23- 26, R.O. 

Green, Ed., JPL Publication 95-1, p. 39-40. 

● Clark, R.N. 1999, Chapter 1: Spectroscopy of Rocks and Minerals and 

Principles of Spectroscopy, Manual of Remote Sensing (Invited), (A.N. 
Rencz, ed.) John Wiley and Sons, New York, p 3- 58. 

● Clark, R.N., G. A. Swayze, K. E. Livo, J. B. Dalton, R. F. Kokaly, R.R. 

McDougal, S. J.Sutley, and C. A. Gent., 2001, Imaging Spectroscopy: 

Earth and Planetary Remote Sensing with the USGS Tetracorder and 

Expert Systems, J. Geophys Res, in review. 

● Crock, J.G., Arbogast, B.F., and Lamothe, P.J., 1999, Laboratory 

methods for the analysis of environmental samples, in Plumlee, G.S., 

and Logsdon, M.J., eds., The Environmental Geochemistry of Mineral 

Deposits, Part A: Processes, techniques, and health issues: Reviews in 

Economic Geology, Volume 6A, Society of Economic Geologists, 

Littleton, Colorado, p. 265-288. 

● Hageman, Philip L, and Briggs, Paul H., 2000, A simple field leach test 

for rapid screening and qualitative characterization of mine-waste dump 

material on abandoned mine lands, in ICARD 2000: Proceedings from 

the Fifth International Conference on Acid Rock Drainage, Denver, 

Colorado, May 21-24, 2000: Society for Mining, Metallurgy, and 

Exploration Inc., p. 1463-1475. 

● King, T.V.V. and R.N. Clark, 1989, Spectral Characteristics of 

Serpentines and Chlorites Using High Resolution Reflectance 

Spectroscopy: J. Geophys. Res. 94, 13997-14008. 

● King, T.V.V., R.N. Clark, and Gregg A. Swayze, 2000, Applications of 

ImagingSpectroscopy Data: A Case Study at Summitville Colorado, in 

Remote Sensing for Site Characterization (F. Kuehn, T. King, B. Hoerig, 

D. Pieters, eds.), Springer, Berlin, p 164- 185. 

● Lamothe, P.J., Meier, A.L., Wilson, S.. 1999. The determination of forty 

four elements in aqueous samples by Inductively Coupled Plasma - 

Mass Spectrometry. U.S. Geological Survey, Open-File Report 99-151, 

Denver, CO, 14 p. 

● Nolan, R.P., A.M. Langer, M. Ross, F.J. Wicks, and R.F. Martin, 2001, 

The Health Effects of Chrysotile Asbestos, Contribution of Science to 

Risk-Management Decisions, The Canadian Mineralogist Special 

Publication 5, Mineralogical Association of Canada, Ottawa, 304 pp. 

● Nomenclature Committee of TIMA Inc., 1991, Nomenclature of ManMade Vitreous Fibers., TIMA Inc.

● McDonald, C., 2001, Carcinogenicity of fibrous tremolite in workplace 

and general environments: 2001 Asbestos Health Effects Conference, 

EPA-NIOSH, Oakland, California, May 24-25, 2001, 4 p. 

● Ross, M., 1999, The health effects of mineral dusts, in The 

Environmental Geochemistry of Mineral Deposits, Part A: Processes, 

Techniques, and Health Issues: Society of Economic Geologists Reviews 

in Economic Geology, 6A, p. 339-356. 

● Skinner, H.C.W., Ross, M., and Frondel, C., 1988, Asbestos and other 

fibrous minerals: Oxford Univ. Press, New York, 204 p. 

● Swayze, G.A., K.S. Smith, R.N. Clark, S.J. Sutley, R.N. Pearson, G.S. 

Rust, J.S. Vance,P.L. Hageman, P.H. Briggs, A.L. Meier, M.J. Singleton, 

and S. Roth, 2000, Using imaging spectroscopy to map acidic mine 

waste, Environmental Science and Technology, 34, 47-54. 
● Van Oss, C.J., J.O. Naim, P.M. Costanzo, R.F. Giese, Jr., W. Wu, and A.

F. Sorling, 1999, Impact of different asbestos species and other mineral 

particles on pulmonary pathogenesis: Clays and Clay Minerals, v. 47, 

no. 6, p. 697-707. 

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OFR 01-0429: Acknowledgements

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

The authors would like to extend their great thanks to a number of people who 

provided extremely helpful technical or policy reviews of all or portions of this report, 

including: Phil Bethke, Jim Crowley, Marty Goldhaber, Dan Knepper, Kathy Smith, Rich 

Wanty, Jim Devine, Ed du Bray, Jim Crock, and Warren Day.

Back to main page of report. 

AccessibilityFOIAPrivacyPolicies and Notices

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URL: <http://pubs.usgs.gov/of/2001/ofr-01-0429/

acknowledgements.html> 

Questions or Assistance: Contact USGS

Page Last Modified: Mon Aug 22 17:57 EDT 2005 

 


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OFR 01-0429: World Trade Center USGS Lab Spectroscopy Studies

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

Laboratory Spectra of WTC Sample WTC01-02

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Dust sample from: Water & Vietnam Vet. Plaza 4506052N 583559E

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Laboratory Spectra of WTC Sample WTC01-03 
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Location: Battery Park, east central 4506123N 583217E drainage disc

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Laboratory Spectra of WTC Sample WTC01-4 

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Dust sample from: Battery Park, northeast end 
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Laboratory Spectra of WTC Sample WTC01-5 

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Dust sample from: Broadway and Wall St. 

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Laboratory Spectra of WTC Sample WTC01-6 

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Laboratory Spectra of WTC Sample WTC01-7 

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Dust sample from: Rector and Greenwich 
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Laboratory Spectra of WTC Sample WTC01-08 

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Location: West End & Vesey, Coating on steel girder.

The 1.4 and 2.32-absorptions are mainly due to chrysotile. 

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Laboratory Spectra of WTC Sample WTC01-09 

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Dust sample from: West and Vesey, steel girder 

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Laboratory Spectra of WTC Sample WTC01-10 

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Dust sample from: West and Vesey 

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Laboratory Spectra of WTC Sample WTC01-11 

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Dust sample from: West and Barclay

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Laboratory Spectra of WTC Sample WTC01-12

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Dust sample from: West and Warren

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Laboratory Spectra of WTC Sample WTC01-13

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Dust sample from: Broadway and Barclay

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Laboratory Spectra of WTC Sample WTC01-14

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Dust sample from: Church and Barclay

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Laboratory Spectra of WTC Sample WTC01-15

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Dust sample from: Maiden Ln. and Church

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Click here to get ascii data. 

Laboratory Spectra of WTC Sample WTC01-16

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Dust sample from: Broadway and Dey

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Click here to get ascii data. 

Laboratory Spectra of WTC Sample WTC01-17

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Dust sample from: Greenwich and Albany

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Laboratory Spectra of WTC Sample WTC01-18

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Dust sample from: Washington and Albany

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Laboratory Spectra of WTC Sample WTC01-19

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Dust sample from: South End and Cedar

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Click here to get ascii data. 

Laboratory Spectra of WTC Sample WTC01-20

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Dust sample from: Liberty and South End

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Click here to get ascii data. 
Laboratory Spectra of WTC Sample WTC01-21

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Dust sample from: Directly west of the WTC at ferry dock on pedestrian mall

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Click here to get ascii data. 

Laboratory Spectra of WTC Sample WTC01-22

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Dust sample from: half way between WTC and ferry dock along pedestrian mall

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Click here to get ascii data. 

Laboratory Spectra of WTC Sample WTC01-23

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Dust sample from: Broadway and Murray

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Laboratory Spectra of WTC Sample WTC01-24

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Dust sample from: Broadway and Chambers

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Laboratory Spectra of WTC Sample WTC01-25

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Dust sample from: Church and Warren

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Laboratory Spectra of WTC Sample WTC01-26

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Dust sample from: one half way between Broadway and Church on Park

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Laboratory Spectra of WTC Sample WTC01-27

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Dust sample from: Broadway and Vessey

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Laboratory Spectra of WTC Sample WTC01-28

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Dust sample from: Ann and Nassau

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Laboratory Spectra of WTC Sample WTC01-29

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Dust sample from: William and Fulton

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Laboratory Spectra of WTC Sample WTC01-30

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Dust sample from: Fulton and Cliff St.

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Laboratory Spectra of WTC Sample WTC01-31

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Dust sample from: William and Platt

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Laboratory Spectra of WTC Sample WTC01-32

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Dust sample from: William and Pine

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Laboratory Spectra of WTC Sample WTC01-33

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Dust sample from: middle of Battery Park

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Laboratory Spectra of WTC Sample WTC01-34

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Dust sample from: South End and Thames

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Laboratory Spectra of WTC Sample WTC01-35

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Dust sample from: Albany and Hudson River

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Laboratory Spectra of WTC Sample WTC01-36

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Dust sample from: South End and Albany (inside apartment)

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Laboratory Spectra of WTC Sample WTC01-37Aa

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Dust sample from:
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Laboratory Spectra of WTC Sample WTC01-37Ac

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Dust sample from:

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Laboratory Spectra of WTC Sample WTC01-37Am
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Dust sample from:

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Laboratory Spectra of WTC Sample WTC01-37B

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Dust sample from:
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Back to Laboratory Spectra of WTC Samples page

Back to: Laboratory Reflectance Spectroscopy (RS) Studies 

Back to document Table of Contents 

For more information, contact: 

Dr. Gregg A. Swayze

U.S. Geological Survey 

303-236-0925 

gswayze@usgs.gov 

or 

Todd Hoefen

U.S. Geological Survey 

303-236-2456 

thoefen@usgs.gov 

or 

Dr. Roger N. Clark

U.S. Geological Survey 

303-236-1332 

rclark@usgs.gov

AccessibilityFOIAPrivacyPolicies and Notices

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URL: <http://pubs.usgs.gov/of/2001/ofr-01-0429/spectra.

samples/wtc01.all.html> 

Questions or Assistance: Contact USGS

Page Last Modified: Mon Aug 22 19:42 EDT 2005 

 















































































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OFR 01-0429: Laboratory Spectra of WTC Sample WTC01-02 

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

 

Larger 10 KB image 

Dust sample from: Water & Vietnam Vet. Plaza 4506052N 583559E 

 

Larger 12 KB image 

Click here to get ascii data. 

For more information, contact: 

Dr. Gregg A. Swayze

U.S. Geological Survey 

303-236-0925 

gswayze@usgs.gov 

or 

Todd Hoefen

U.S. Geological Survey 
303-236-2456 

thoefen@usgs.gov 

or 

Dr. Roger N. Clark

U.S. Geological Survey 

303-236-1332 

rclark@usgs.gov

AccessibilityFOIAPrivacyPolicies and Notices

U.S. Department of the Interior | U.S. Geological Survey

URL: <http://pubs.usgs.gov/of/2001/ofr-01-0429/spectra.

samples/wtc01.02.html> 

Questions or Assistance: Contact USGS

Page Last Modified: Mon Aug 22 19:27 EDT 2005 

 
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OFR 01-0429: Laboratory Spectra of WTC Sample WTC01-03 

 About USGS / Science Topics / Maps, Products & Publications / Education / FAQ 

 

Larger 10 KB image 

Location: Battery Park, east central 4506123N 583217E drainage disc 

 

Larger 12 KB image 

Click here to get ascii data. 

For more information, contact: 

Dr. Gregg A. Swayze

U.S. Geological Survey 

303-236-0925 

gswayze@usgs.gov 

or 

Todd Hoefen

U.S. Geological Survey 
303-236-2456 

thoefen@usgs.gov 

or 

Dr. Roger N. Clark

U.S. Geological Survey 

303-236-1332 

rclark@usgs.gov

AccessibilityFOIAPrivacyPolicies and Notices

U.S. Department of the Interior | U.S. Geological Survey

URL: <http://pubs.usgs.gov/of/2001/ofr-01-0429/spectra.

samples/wtc01.03.html> 

Questions or Assistance: Contact USGS

Page Last Modified: Mon Aug 22 19:27 EDT 2005