UC Toxics News: Winter/Spring
2002
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An Ill
Wind:
|
In
the most thorough analysis yet of the dust and smoke blown through lower Manhattan
after the collapse of the World Trade Center, researchers at UC Davis found
unprecedented amounts of very fine particles of such worrisome substances
as sulfates, silicon and metals.
“No one has ever reported a situation like the one we see in the World
Trade Center samples,” said Thomas Cahill, an international authority
on airborne particles. “The air from Ground Zero was laden with extremely
high amounts of very small particles, probably associated with high temperatures
in the underground debris pile. Normally, in New York City and in most of
the world, situations like this just don’t exist.”
 During a February press conference, Thomas Cahill shows the media the monitor, top, and collector strip, middle, his team used to evaluate air samples in Manhattan after the collapse of the World Trade Center towers. Photo: Debbie Aldridge/UC Davis Mediaworks |
Cahill heads the UC
Davis DELTA Group (for Detection and Evaluation of Long-range Transport of
Aerosols), a collaborative association of aerosol scientists at several universities
and national laboratories. The DELTA Group has made detailed studies of aerosols
from the 1991 Gulf War oil fires, volcanic eruptions, global dust storms and
most recently Asia.
The Manhattan air samples were collected at the request of a U.S. Department
of Energy scientist from Oct. 2 through mid-December, by a DELTA Group air
monitor placed on a rooftop one mile north-northeast of the trade center complex.
The DELTA team analyzed the samples to determine not only their chemical makeup
but also the size of the particles. The group found that very fine particles,
.24 micrometers to .09 micrometers in diameter, were a large fraction of the
total mass in the samples. Very fine particles can travel deep into human
lungs. They may have no immediate apparent health effects in moderate concentrations,
but they typically are removed from the lungs through the bloodstream and
heart, increasing the possibility of health impacts.
The very fine particles contained high levels of sulfur and sulfur-based compounds,
which in early analyses appear to have been dominated by sulfuric acid. The
very fine particles also contained high levels of very fine silicon, potentially
from the thousands of tons of glass in the debris.
Many different metals were also found in the samples of very fine particles—some
at the highest levels ever recorded in air in the United States. Present in
relatively high concentrations were iron, titanium (associated with powdered
concrete), vanadium and nickel (often associated with fuel-oil combustion),
copper and zinc. Mercury and lead were seen occasionally in fine particles
but at low concentrations.
Virtually all the air samples from the trade center site also carried high
concentrations of coarse particles—those about 12 micrometers to 5 micrometers
in diameter. Coarse particles are typically filtered by the nose or coughed
out of the throat and upper lungs. They can irritate the mucous membranes,
causing coughs and nosebleeds. In some individuals, they can cause allergic
reactions or breathing problems.
“These particles simply should not be there,” Cahill said. “It
had rained, sometimes heavily. That rain should have settled these coarse
particles.” The finding suggests that coarse particles were being continually
generated from the hot debris pile.
In February, when the results were announced, the team was continuing to analyze
the metal content of the coarse particles.
For more information, visit the DELTA Web site at http://delta.ucdavis.edu/.
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