The Legacy of World Trade Center DustJonathan M. Samet, M.D., Alison S. Geyh, Ph.D., and Mark J. Utell, M.D. More than 5 years after the World Trade Center disaster on September 11, 2001, uncertainty and controversy remain about the health risks posed by inhaling the dust from the collapse of the twin towers, the subsequent fires, and the cleanup effort. In addition to the matter of the immediate and persistent respiratory effects on "first responders," occupants of the towers, cleanup workers, and neighborhood residents, concern has arisen about longer-term risks, including the risk of cancer. The level of concern with regard to the respiratory effects of the disaster may well be compounded by the psychological consequences. Already, some responders have received compensation, and litigation is in progress for thousands of people with alleged illnesses caused by inhaling the dust.
With the collapse of the towers, the air at ground zero became heavily contaminated. Subsequently, the smoke and dust from fires and resuspended debris and the engine exhaust from cleanup equipment and vehicles were major sources of airborne contaminants.1 Because air was not sampled immediately after the disaster, data are lacking on the identity of the contaminants and their concentrations in the plume at that time. Photographs showing a dense cloud at street level imply that the concentrations of particles in the air must have been on the order of milligrams per cubic meter — orders of magnitude greater than typical ambient levels. Analyses of settled dust samples revealed the presence of combustion-related carcinogens, building materials, and some asbestos. The samples were dominated by larger particles, which settle more quickly than smaller ones. The smaller particles, which can penetrate into the deep lung and would have been generated by burning materials, were probably not captured in these samples.
Soon after the disaster, agencies and academic institutions implemented monitoring for particles, volatile organic compounds, polychlorinated biphenyls, and dioxins and metals associated with particles. The composition of the mixture changed as debris removal progressed and as fires were extinguished. Analyses of archived filters for carcinogenic polycyclic aromatic hydrocarbons (PAHs) indicated very high concentrations from fires in the early days and lower levels later, probably from diesel engines. In October 2001, samples collected from streets bordering the disaster site showed high concentrations of particulate matter less than 2.5 µm in aerodynamic diameter; by April 2002, the median concentrations had decreased substantially.2 Even at far lower levels, exposure to airborne particles in U.S. cities has been linked to premature death and disease. The characteristics of the particles present at the time of the disaster were undoubtedly quite different from those in typical urban air pollution, but without specific estimates of exposure for workers and the population, the risks from these materials cannot be quantified.1
The risks posed by exposure to airborne particles depend on the doses delivered to the respiratory tract. Particle size is also key: particles larger than 5 µm are effectively filtered out by impaction in the upper airways, unless concentrations are high. Smaller particles penetrate the lungs, and nanosized particles generated by combustion can be deposited throughout the respiratory tract. It is likely that particles of all sizes were initially present in the dust at very high concentrations that decreased over time.1 A biomonitoring study of firefighters suggests that they may have received substantial doses of larger particles.3 Analysis of induced sputum collected from involved firefighters 10 months after the disaster showed a significantly higher percentage of large mineral particles than that found in a comparison group of firefighters from Tel Aviv. Irregularly shaped particles were seen in epithelial cells and alveolar macrophages, and their mineral content, unlike that in the comparison group, included such elements as gold, tin, and titanium. A correlation was reported between the estimated level of exposure to this dust and markers of inflammation in the firefighters.
http://content.nejm.org/cgi/content/full/356/22/2233?query=TOCSource InformationDr. Samet is a professor and chair of the Department of Epidemiology, and Dr. Geyh is an assistant professor of environmental health sciences, at the Johns Hopkins Bloomberg School of Public Health, Baltimore. Dr. Utell is a professor of medicine and environmental medicine at the University of Rochester School of Medicine and Dentistry, Rochester, NY.
An interview with Dr. Robin Herbert, codirector of the World Trade Center Medical Monitoring Program at Mount Sinai Hospital, New York, can be heard at www.nejm.org.
The New England Journal of Medicine is owned, published, and copyrighted © 2007 Massachusetts Medical Society. All rights reserved.
Printer-friendly format
Email this thread to a friend
Bookmark this thread
(1000+ posts)
Send PM |
Profile |
Ignore
