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CATEGORIES: ENVIRONMENTAL HEALTH , MINERALS POSTED ON SEPTEMBER 10, 2011 AT 3:53 PM LAST UPDATE 4:04 PM BY TANIA LARSON

Smoke streaming from Ground Zero illuminates the night skyline of lower Manhattan in a view looking east from New Jersey. The photo was taken on September 16, 2001, by USGS field crew members Todd Hoefen and Gregg Swayze. On September 11, 2001, as the twin towers of the World Trade Center exploded and collapsed, clouds of dust billowed into the sky and across the city. Photographs from the outskirts show the thick clouds swallowing much of lower Manhattan. Satellite images reveal that the clouds were large enough to be seen from space. Survivors overtaken by the clouds emerged covered in a thick layer of dirt and debris. They reported that the clouds were so dense that they blacked out the sun. As the dust settled, it coated outdoor surfaces in a layer of fine powdered material up to 3 inches thick. It snuck in through doors, windows, and ventilation systems, contaminating apartments, offices, and public buildings. The dust from these clouds was inhaled and i ngested by thousands of people, not only on September 11, but for days afterward. Many were concerned about the health and environme ntal implications of the dust and debris. What were the clouds formed out of? How harmful wa s it to breathe the pulverized particulates? How would the dust respond to environmental processes? The U.S. Environmental Protection Agency and the U.S. Publ ic Health Service asked the USGS to examine the dust, to categorize i ts components, and to identify those substances that might affect the health of emergency responders, resi dents, visitors, and survivors of the terro rist attacks. 

### Data from Above

Of particular concern was whether the dust contained a significantamount of asbestos. To find o ut, USGS remote sensing expert Roger Clark worked with NASA to arrange an airplane to fly over lower Manhattan carrying a special instrument that the USGS had been using in other asb estos studies. This remote sensing platform, called the Airborne Visible and Infr a-Red Imaging Spectrometer (AVIRIS), measures light (in the v isible through nearinfrared spectrum) reflected from the ground surface. Becaus e individual minerals reflect li ght in characteristic ways, scienti sts would be able to use the light reflection measurements gathered by AVIRIS to id entify and map the materials in the settled dust. (Read How Spectrometry Works ) 

### Locating Fires The measurements from AVIRIS came back to the USGS electronica lly, and Clark and his remote sens ing colleagues immediately bega n processing the data. 

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8 / 17 /201 5 http://www.usgs.gov/blogs/features/usgs_top_story/september-11-2001-studying -th e -dust-...Through a creative use of the data, they were able to make and se nd emergency responders a thermal image — one that showed fire fighters where fires were still burning deep in the debris. In some areas, temperatures were over 1300°F. The USGS team provided this information to emergency response agencies on September 18, 2001. Another flyover on September 23 revealed that by that date most of the hot spots had been eliminated or reduced in intensity. (See Thermal Hot Spot Maps ) 

### Collecting and Analyzing Samples Two USGS scientists, Gregg Swayze and Todd Hoefen, flew from D enver to New York City on one of the first available commercial f lights after the terrorist attacks. During the day, they collected ground data needed to calibrate the remotely sensed data from AVIRIS. At night, they wa lked around lower Manhattan collecting both indoor and outdoor samples of the dust and debris around the fallen towers. The sample suite they col lected for analysis ended up being the most comprehensive of all studies done on the dusts , both in terms of the number of samples collected and the spat ial extent over which the samples were collected.

When Swayze and Hoefen returned, they and an entire team of USGS researchers, including Geoff Plumlee, Greg Meeker, Phil Hagema n, Heather Lowers, Paul Lamothe, Eric Livo, and many others, brought their expertise together to analyze the samples and provide answers a bout the components of the dust. They analyzed the samples for a variety of mineralogical and ch emical parameters. They used reflectance spectros copy, scanning electron microscopy with x-ray micro-analysis, x-ray diffraction, chemical analysis, chemical leach testi ng, and other more specialized analyses. The team worked with a somber drive. “Our team of analysts got busy, throwing all of our analytical capabi lities at the dusts, driven by the hope that we would be a ble to help deal with the disaster that had shaken the nation,” wrote Plumlee in a 2009 article for Earth Magazine

. 

### Dust Components The dust samples were largely made up of a mix of materials comm only used in building constructi on or found in office buildings : particles of glass fibers, gypsum wallboard, concrete, paper, window glass, etc. The dust contained higher amounts of lead, zi nc, antimony, copper, and other elements of building materials than found in natural soils. The level of lead in some samples was high enough to be a potential concern. The team also found the less dangerous variety of asbestos, chrysoti le asbestos, in most samples at higher levels than what is found in urban particulate matter. However, the team was grateful not to find amphi bole asbestos — the kind generally viewed as the more dangerous, more carcinoge nic form of asbestos — in any of the samples. Even though this more dangerous form of asbestos was absent from the dust samples, the materials that were found indicated a po tential health threat, and USGS scientists reported that cleanup of dusts and debris should be done with appropriate resp iratory protection and dust c ontrol measures. By combining the remotely sensed data with the lab results, the team produced a series of maps that showed the distribution of asbestos, concrete, and other materials in the dust around lower Manhattan. As one migh t expect, heavier materials tended to settle closer to Ground Ze ro, while lighter materials traveled further away. 

### Mixing with Water Some metals found in the dust (such as aluminum, chromium, and antimony) are soluble, and another issue of both health and envi ronmental concern was whether water that interacted with the dust would be harmful. To find out, the USGS team performed chemic al leach tests on the dust samples. Water they passed through the samples that had b een collected indoors came away highly alkaline and caustic, but the water passed through the samples collected outside had much lower pH values. The difference was that the outdoor samples had been exposed to rain before the samples had been collected. The higher pH value s from the indoor samples were produced by dissolution of calcium hydroxide from th e concrete particles. The outdoor dust samples, however, had a lready been at least partly neutralized by reactions with carbonic acid in the rainwater. These results indicated that the dust could be c hemically reactive when it came in contact with rain or wash water — or moistur e in the eyes, mouth, or respiratory system. Fortunately, continued reactions of water and atmospheric carbon dioxide with the dust helped to neutralize their caustic alkalinity. Dust indoors, on the other hand, was potentially more harmful than the dust that had been exposed to rain and other elements. (Read the Chemical Leaching Study .) 

### Identifying World Trade Center Dust in the Long Term Like many natural and human-caused disasters, the potential dange rs posed by the collapse of the twin towers didn’t end with th e event itself. With wildfires, there is the risk of landslides. With earthquakes, there is the risk of aftershocks and compromised buildings. With erupting volcanoes, there is the risk of damage from the ash clouds to airplanes. And after the collapse of the twin towers, there remained the risks of dust co ntamination. 

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### Related: Firefighter surrounded by dust and debris from the twin towers. Photo credit Jim Watson, U.S. Navy Years after the event, questions remained about the possible presenc e of dust from the World Trade Center in both indoor and ou tdoor environments. To address these questions, officials needed a way to positively identify dust that originated from the World Trade Center. And with so many agencies and organizations involved in different studies and efforts, they needed some standardization of meth ods for determining if dust ca me from the September 11 events. But how do you tell one urban dust sample from any other? They needed a diagnostic signature that could be used as a sort of fingerprint for identifying dust from the World Trade Center

. USGS scientists Gregory Meeker, Amy Bern, Heather Lowers, and Is abelle Brownfield set to work to develop analytical methods and standards that would help others to detect and measure trace levels of World Trade Center dust. By examining the dust samples, they were able to determine common abundance ratios of major and minor components of the dust. T hey found that five components — slag wool, rock wool, soda-lime glass, concrete pa rticles, and gypsum — could be used to as primary signature comp onents for identifying dust from the World Trade Center. They also identified possibl e secondary signature components: FeOx, ZnOx, silica, and chrysot ile. (Read the Determination of a Diagnostic Signature for World Trade Center Dust , Analysis of Background Residential Dust for World Trade Center Signature Components , Particle Atlas of World Trade Center Dust .) 

### Trying to Identify Dust in the Lungs More recently, scientists have been trying to determine whether thi s dust signature can help link exposure to World Trade Cente r dust to respiratory problems experienced by some of the Septem ber 11 survivors and emergency responders. In 2009, Dr. David Prezant, the chief medical officerat the Office of Medical Affairs for the New York City Fire Department, as ked Meeker to examine the lung tissue of a firefighter who had developed pulmonary fibrosis . Prezant wanted to know whether particles the firefighter had inhaled as a first responder may have contributed to the disease. Due to his disease, the firefighter had had a lung transplant, and with both a sample of lung tissue and the means to potential ly identify World Trade Center dust, USGS scientists examined the tissue to see if they could demonstrate a link. What they found was inconclusive. They found an abundance of parti cles in the lung tissue, but no definitive proof that any of it was dust from the World Trade Center. This lack of proof was not surprising as most glas s fibers dissolve in the lungs over time, and it would be unlik ely that the particles found in the lung tissue years after the event would be in the same ratios and form as the samples collected. But this was just one sample, and as more lung tissue becomes av ailable for testing more data may help experts to find better a nswers about the possible link between exposure to the dust and long-term health problems. 

### Applying What we have Learned to Other Disasters Over the past 10 years, the USGS has responded to a number of events, both natural and human-caused, in which emergency responders, public health officials, cleanup organizers, and citizens need information to understand the material fallout of a disaster, how these materials could interact with the environment, and how these materials might impact the environment and human health. Events such as Hurricanes Katrina and Rita in 2005 (PDF) , the eruption of Mount St. Helens in 2004 and the eruption of Alaskan volcanoes in 2008 and 2009, the Gulf oil spill in 2010, the wildfires in Southern California in 2007 and 2009 and those in Texas occurring now remind us that there will always be new challenges to face. (Video: Spectrometer use in 2007 Wildfires Ash Study ) With each event, we have learned valuable lessons, and we continue to improve our capabilities for analyzing materials and contam ination, for understanding and predicting their behavior in the environment, for examining how best to protect our communities from their potentially harmful impacts, and for communicating results in ways that are useable and understandable. It is impossible to remember the events of September 11, 2001, without a sense of honor for those who lost and gave their lives. As individuals, our hearts remain with those who lost their lives or those of loved ones. As a Nation, we are grateful for those who put their lives on the line for the sake of others. And as an agency, we stand at the ready to provide la wmakers, community planners, emergency responders, public health officials, and every American with the mapping and natural science information they need to understand, prepare for, and respond to such events.

For More Information

• Various USGS studies of the World Trade Center area Links Top Stories Science Picks 

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U.S. Department of the Interior | U.S. Geological Survey URL: www.usgs.gov/blogs/features/usgs_top_story/september- 11-2001-studying-the-dust-from-the-world-trade-center-collapse/ Page Contact Information: Ask USGS Page Last Modified: November 7, 2013

• Overview Fact Sheet (PDF) Note: While USGS scientists provide information about the mater ial and chemical makeup of the dust deposits left by the

collapse of the World Trade Center, the USGS has no medical expertise. For health-related information on the World Trade Center collapse, please visit agencies such as the U.S. Environmental Protection Agency

• New York Department of Public Health

• Environmental and Occupational Health Sciences Institute

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