New UNC, EPA 9/11 study suggests that pollutants posed small cancer risks

July 26, 2004

On Sept. 11, 2001, when hijacked jetliners smashed into the World Trade Center, stunning the world, collapse of the twin towers and the fires that followed lofted an estimated million tons of dust and smoke into the air of New York City. After the first 100 days when officials declared the fires extinguished, trucks and other heavy equipment involved in the cleanup continued to spew pollutants in the form of soot into the atmosphere.

To help assess the health threat of a group of cancer-causing chemicals known as polycyclic aromatic hydrocarbons (PAHs) in the smoke and soot, scientists from the University of North Carolina at Chapel Hill and the U.S. Environmental Protection Agency monitored PAHs from Sept. 23, 2001 to March 27, 2002. The fires and diesel equipment used in the cleanup produced the PAHs, as did cars and buses in New York City.

"We found that the levels of PAHs were very high soon after 9/11 -- about 65 times the normal values -- but that they diminished rapidly over the next month or so as fires were extinguished," said Dr. Stephen M. Rappaport, professor of environmental health at the UNC School of Public Health. "Because the PAH levels were only high for a short time, we concluded that there was little increase in lifetime cancer risk from these compounds among people living in the vicinity of the World Trade Center. That was assuming that people lived in that vicinity for 70 years.

"At the same time, we are concerned that there might be harmful effects among the offspring of women living nearby who were or became pregnant at the time these exposures occurred," Rappaport said. "A particular effect that has been associated with PAH exposure is a condition known as intrauterine growth restriction (IUGR), which results in babies being born smaller than they otherwise would be. Another group of scientists reported last year that IUGR was more common among women living close to Ground Zero on 9/11 than those living in other parts of New York City. Our results suggest that PAHs might indeed have played a role in causing IUGR in these women."

Findings from the team's work appear online this week in the newest issue of the Proceedings of the National Academy of Sciences. Besides Rappaport, authors of the report are Joachim D. Pleil and Alan F. Vette of the EPA's National Exposure Research Laboratory, and Brent Johnson of the School of Public Health's biostatistics department.

In their study, the researchers used a new, simpler technique they developed last year for measuring PAHs in samples of particulate air pollution. They analyzed 243 samples of fine particles collected by the EPA at three sites near the World Trade Center, as well as from a fourth site a mile away at 290 Broadway. In each sample, they measured 9 PAHs, including some of the most carcinogenic compounds known.

Air concentrations of the PAHs on Sept. 14, 2001 ranged from 1.3 to 15 nanograms per cubic meter and were among the highest values ever reported from outside sources, Rappaport said. "These high initial air concentrations resulted from fires that diminished over the first 100 days," he said. "Diesel sources predominated over the next 100 days, during which time PAHs declined slowly to normal levels."

An estimated 11,000 tons of fine particles with diameters less than 2.5 microns were released, the scientist said. Such microscopic sooty fragments are of concern to the public health community because they penetrate deep into lungs and contain the toxic PAHs. Being products of incomplete combustion, the PAHs resulted mainly from fires fueled by 91,000 liters of jet fuel, 100,000 tons of organic debris, 490,000 liters of transformer oil, 380,000 liters of heating oil and fuel from thousands of cars parked under the World Trade Center.

"We believe that this study is important because it shows the time trend in air levels of PAHs after 9/11," Rappaport said. "This class of carcinogens was often mentioned as being potentially important in and around Ground Zero, but virtually no air measurements had been reported."

The team did not measure other cancer-causing compounds released into the atmosphere, he said. Neither could they gauge levels of PAHs and other pollutants to which emergency personnel and cleanup crews were exposed.
The National Institutes of Environmental Health Sciences sponsored the study.

University of North Carolina at Chapel Hill

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