Air Today . . . Gone Tomorrow Article|
Trade Center debris pile
was a chemical factory, says new study
By Sylvia Wright, University of
California - Davis, September 10, 2003
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
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
"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 this Wednesday (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 on Sept. 10 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;
Graham Bench, project investigator at the Center for Accelerator Mass Spectroscopy, U.S.
Department of Energy's Lawrence Livermore National Laboratory; and Robert Leifer, DOE
Environmental Measurement Laboratory, New York.
-- World Trade Center Health Registry: http://www.wtcregistry.org
-- American Chemical Society: http://www.chemistry.org
-- Aerosol Science & Technology, the journal of the American Association of Aerosol
-- February 2002 news release, "Trade Center Air Held Unprecedented Amounts of Very
Fine Particles, Silicon, Sulfates, Metals, Say UC Davis Scientists":
-- September 2002 news release, "New Study of Ground Zero Air Shows Indoor Spaces Can
Be Cleaned": http://www-news.ucdavis.edu/search/news_detail.lasso?id=6172
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