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Trade Center Debris Pile Was a Chemical Factory, Says New Study

September 10, 2003

Photo: Thomas Cahill talking to TV reporters at World Trade Center

At Ground Zero in New York City, UC Davis Professor Emeritus Thomas Cahill describes his air-quality findings to reporters on Feb. 23, 2002, just before testifying at an EPA investigative hearing in Manhattan. (Sylvia Wright/UC Davis News Service file photo)

The fuming World Trade Center debris pile was a chemical factory that exhaled pollutants in particularly dangerous forms that could penetrate deep into the lungs of workers at Ground Zero, says a new study by UC Davis air-quality experts.

The new work helps explain the very fine particles and extraordinarily high concentrations found by an earlier UC Davis study, the first to identify very fine metallic aerosols in unprecedented amounts from Ground Zero. It will be essential to understanding the growing record of health problems.

The conditions would have been "brutal" for people working at Ground Zero without respirators and slightly less so for those working or living in immediately adjacent buildings, said the study's lead author, Thomas Cahill, a UC Davis professor emeritus of physics and atmospheric science and research professor in engineering.

"Now that we have a model of how the debris pile worked, it gives us a much better idea of what the people working on and near the pile were actually breathing," Cahill said. "Our first report was based on particles that we collected one mile away. This report gives a reasonable estimate of what type of pollutants were actually present at Ground Zero.

"The debris pile acted like a chemical factory. It cooked together the components of the buildings and their contents, including enormous numbers of computers, and gave off gases of toxic metals, acids and organics for at least six weeks."

Cahill, an international authority on the constituents and transport of airborne particles, will summarize the new study today (Sept. 10) at the national meeting of the American Chemical Society, being held this year in New York City.

Cahill heads the UC Davis DELTA Group (for Detection and Evaluation of Long-range Transport of Aerosols), a collaborative association of scientists at several universities and national laboratories. The DELTA Group has made detailed studies of small airborne particles, called aerosols, from the trade-center collapse, 1991 Gulf War oil fires, volcanic eruptions and global dust storms, and has most recently finished a massive 21-site study of Asian aerosols for the National Science Foundation.

The new study reinforces and extends conclusions that DELTA Group reached in February 2002 in what is still the most extensive analysis of the dust and smoke from the hot collapse piles after the trade center collapse.

In the 2002 report, DELTA researchers described their analysis of over 8,000 air samples collected Oct. 2-30, 2001, on a rooftop at 201 Varick St., one mile north-northeast of the trade center complex.

They detailed very high levels of very fine airborne particles -- particles that pre-Sept. 11 EPA summaries had showed could raise a person's risk of lung damage and heart attacks. That analysis has been accepted for publication in the peer-reviewed journal Aerosol Science and Technology.

Now the researchers have added analyses of samples collected through May 2002, and constructed a timeline with physical and chemical explanations for the results.

The new study also confirms, Cahill said, that the very fine particles observed were almost totally from the trade center debris pile and not from other upwind sources, such as power plants and the diesel trucks used to haul away the debris.

When the trade center towers burned and collapsed, tons of concrete, glass, furniture, carpets, insulation, computers and paper were reduced to enormous, oxygen-poor debris piles that slowly burned until Dec. 19, 2001.

In that hot pile, some of the debris' constituent elements combined with organic matter and abundant chlorine from papers and plastics, and then escaped to the surface as metal-rich gases. These then either burned or chemically decomposed into very fine particles capable of penetrating deeply into human lungs.

In the trade-center air samples, Cahill identified four classes of particles that have been named by the EPA as likely to harm human health:

  • Fine and very fine transition metals, which interfere with lung chemistry.
  • Acids, in this case sulfuric acid, which attack cilia and lung cells directly.
  • Very fine, un-dissolvable (insoluble) particles, in this case glass, which travel through the lungs to the bloodstream and heart.
  • High-temperature organic matter, many components of which are known to be carcinogens.

"For each of these four classes of pollutant, we recorded the highest levels we have ever seen in over 7,000 measurements we have made of very fine air pollution throughout the world, including Kuwait and China," Cahill said.

After the debris fire was out, pollution levels dropped, Cahill said. DELTA Group measurements at the trade-center site made in May 2002, with the American Lung Association of New York, showed that levels of almost all of the very fine components had declined more than 90 percent,

Cahill will report the new findings to the chemical society members today in a special symposium on the trade center. The presentation is titled "Very fine particles from the WTC collapse piles: anaerobic incineration?" It is scheduled for 9:35 a.m. in Javits Convention Center, Room 1A22.

A news conference will follow the symposium at noon.

The American Chemical Society is the world's largest scientific society. Nine thousand people are expected to attend the Sept. 7-11 conference.

Cahill's co-authors on the new study are: assistant research engineer Steve Cliff, professor Jim Shackelford and researchers Mike Dunlap and Mike Meier, all of UC Davis; Kevin Perry, assistant professor of meteorology at the University of Utah, Salt Lake City; and Robert Leifer, DOE Environmental Measurement Laboratory, New York.

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