NEWS & UPDATE
|OTHER ARTICLES IN THE WTC
Why Did the World Trade Center Collapse? Science, Engineering, and Speculation by Thomas Eagar and Christopher Musso
Better Materials Can Reduce the Threat from Terrorism by Toni G. Maréchaux
An Initial Microstructural Analysis of A36 Steel from WTC Building 7 by J.R. Barnett, R.R. Biederman, and R.D. Sisson, Jr.
Figure 3. A month after the World Trade Center was leveled, crews continued digging in the smoldering debris. (Photo by Michael Rieger, FEMA)
As smoke wafted from the World Trade Center site weeks after the buildings
crumbled, questions arose about how much of the debris was airborne, and the
potential danger to workers responsible for the clean-up (Figure
3). Immediately after the towers fell, the U.S. Environmental Protection
Agency (EPA) began taking samples to detect contaminants in the air, water,
river sediment, drinking water, and dust. To examine the types of particulates
in the air, a team of specialists from the University of California at Davis
was called to the scene.
The Detection and Evaluation of Long-range Transport of Aerosols (DELTA) Group from U.C. Davis was called upon for its extensive experience in analyzing the composition and movement of airborne particles. Since October 1, the group had a rotating monitoring unit on the roof of a Manhattan building, downwind from ground zero, continuously collecting air samples. The Davis Rotating Unit for Monitoring collects samples in eight size ranges, from ten micrometers to 0.09 micrometers in diameter, according to Tom Cahill, a U.C. Davis professor of applied science at atmospheric sciences.
Then, we apply a number of techniques, including a synchrotron x-ray microprobe, to scan elements from sodium to uranium, Cahill said. With these data, we can characterize the particles that go deep into the lung and lodge there.
The first batch of samples were sent to U.C. Davis in early November, for analysis at the Lawrence Berkeley National Laboratorys Advanced Light-Source Lab. There, scientists examined the samples for health threats such as inhalable particles, toxic metals, asbestos, and byproducts of burning plastic.
The DELTA Groups assistance was requested by the U.S. Department of Energy shortly after excavation began at the site. With the information gleaned from the sampling, environmental experts will be able to determine whether safety gear has been adequate and if workers need to take additional steps to protect local residents. The first samples were to have been returned by mid November, with data collection continuing until authorities decide it is no longer necessary, Cahill said.
Although the EPA monitoring has revealed high levels of pollutants such as asbestos and dioxin in some areas tested, those levels only exceeded the agencys guidelines for 30 years of exposure. These levels do not pose a short-term health effect but should be monitored if they persist for a longer period of time, according to information on the EPA web site. Summaries of the collected data, which are updated regularly, are available on that web site, at www.epa.gov/epahome/wtc/data_summary.htm.
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