"Except for inhalation exposures that may have occurred on 9/11, and a few days afterward, the ambient (air concentration) data suggest that persons in the general population were unlikely to suffer short-term or long-term adverse health effects caused by inhalation exposures," scientists at the U.S. Environmental Protection Agency (EPA) will report in the journal Risk Analysis.

"Assessment of Inhalation Exposures and Potential Health Risks to the General Population that Resulted from the Collapse of the World Trade Center Towers" appears in the latest issue of the peer-reviewed journal (Vol. 27, No. 5, 2007). The journal is published by the McLean-based Society for Risk Analysis .

Matthew Lorber of the EPA's National Center for Environmental Assessment (NCEA), Office of Research and Development (ORD), Washington; four EPA colleagues, and a scientist with the consulting firm Sciences International, Alexandria, Va., write: "While these (air concentrations) were substantially elevated above typical background for the early days, they only occasionally exceeded health benchmarks after the first few weeks, and they had returned to typical background levels by November and December 2001."

In the days following the collapse of the World Trade Center (WTC) towers, the EPA initiated numerous air-monitoring activities to better understand the ongoing impact of emissions from that disaster, the authors report. Contaminants evaluated included particulate matter (PM), metals, polychlorinated biphenyls (PCBs), dioxins, asbestos, volatile organic compounds, particle-bound polycyclic aromatic hydrocarbons (PAHs), silica and synthetic vitreous fibers (SVFs).

EPA began taking limited site-related measurements the afternoon of September 11. By September 14, fixed air-monitoring sites had been established for asbestos and other contaminants, and by September 16 the first samples of dioxin, PAHs and PCBs were taken from these fixed sites.

Using these data, the scientists conducted an inhalation exposure and human health risk assessment to the general population. The report does not address exposures and potential impacts that could have occurred to rescue workers, firefighters and other site workers, nor does it address exposures that could have occurred in the indoor environment.

The authors also found that:

- "Persons exposed to extremely high levels of ambient PM and its components, SVF, and other contaminants during the collapse of the WTC towers and for several hours afterward were likely to be at risk of acute and potentially chronic respiratory effects," and

- "Following the extremely high levels of contaminants associated with the collapse of the WTC towers, available data suggest that concentrations within and near (Ground Zero) remained significantly elevated above background levels for a few days."

The authors acknowledged limitations to their study, including uncertainty about air quality during the first few hours and days after 9/11, and the fact that difficulties associated with site access and security, power supply sources, equipment availability and analytical capacity hindered efforts to begin regular monitoring for several days.

The authors also noted that while this analysis by EPA evaluated the potential for health impacts based on measured air concentrations, epidemiological studies conducted by organizations other than EPA have identified respiratory effects in worker and general populations, and developmental effects in newborns whose mothers were near Ground Zero on 9/11 or shortly thereafter.

These researchers have concluded that exposure to WTC contaminants (and/or maternal stress, in the case of developmental effects) resulted in these effects, and have identified the time period including 9/11 itself and the days and few weeks afterwards as a period of most concern based on high concentrations of key pollutants in the air and dust.

In addition to Lorber, the authors are Lester Grant, Joseph Pinto and David Cleverly, also of the EPA's NCEA ORD, Washington; Joachim Pleil of the EPA's National Exposure Research Laboratory, ORD, Research Triangle Park, N.C., and Sciences International's Herman Gibb.

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