WASHINGTON (AP) – A group of hazardous chemicals released into the air following the collapse of the World Trade Center doesn’t appear to be much of a cancer risk to local residents.

Previous studies have indicated the chemicals may have some endangered unborn babies of women in the area. But a new report says the chemicals dissipated rapidly and any increase in the danger of cancer is very small.

A team led by Stephen M. Rappaport of the University of North Carolina studied 243 samples collected near Ground Zero, analyzing the amounts of nine chemicals known as polycyclic aromatic hydrocarbons, which are known to cause cancer.

“The public was exposed to some toxic PAHs at levels that were quite high soon after the collapse. However, due to the rapid decline in PAH levels, with the dissipation of the fires, the long-term risks of cancer were minuscule,” Rappaport said.

“Nonetheless, ” he added, “sensitive populations, such as the offspring of women who were pregnant at the time, were at particular risk and may well have suffered as a result of their exposure to PAH during that critical time period.”

Rappaport said the risk of cancer related to PAHs would be 0.157 cases per million people over 70 years near Ground Zero, and this would increase only to 0.167 cases per million as a result of the chemicals released in the building collapse and resulting cleanup.

The report, appearing in this week’s issue of Proceedings of the National Academy of Sciences, concluded that more than 90 percent of the airborne particles released in the building collapse were larger than 10 microns across, a size that tends to settle quickly out of the air. Ten-microns is about one-seventh the width of the average human hair.

A fraction of the particles were 2.5 microns or less, a size that can easily remain in the air and penetrate into the lung, the report noted. These particles were released in the fires accompanying the collapse and from diesel engines used in the cleanup, the report said.

The researchers added that while the cancer risk for area residents was small, workers taking part in the cleanup could have been exposed to much higher levels of PAHs than indicated in their samples. They also said that if chemicals were concentrated inside apartments and offices, there may have been higher exposures, and there may have been other cancer-causing chemicals released in addition to PAHs.

A study published last year in the Journal of the American Medical Association noted an increase in smaller babies among women who were near the collapsing towers. Those women faced double the normal risk of delivering babies that were up to half-a-pound smaller than babies born to non-exposed women, that report said.

Rappaport’s new analysis was done in collaboration with the Environmental Protection Agency and was funded by the National Instate of Environmental Health Sciences.

On the Net:

PNAS: http://www.pnas.org

AP-ES-07-26-04 1427EDT

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