Pollutant levels in lower Manhattan after Sept. 11 may have been higher than those reported by previous researchers, according to a study by Canadian scientists.
Six weeks after the 2001 World Trade Center attacks, film found on windows within one kilometer (.62 miles) of Ground Zero revealed high levels of PCBs, flame retardants and other organic pollutants. Concentrations of the chemicals were up to 10 times greater than New York City's normal background levels and possibly 100 times higher than surrounding rural areas.
The report is scheduled to appear in the July 1 print edition of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.
"We were very concerned just after 9/11, as were most people in North America," says Miriam Diamond, a professor in the Department of Geography at the University of Toronto and lead author of the paper. "We were sitting around the lab shortly after the attack and said, 'Why don't we go down and use our simple method to see what the contaminant levels are like?'"
Diamond's method involved "washing a bunch of windows" in lower Manhattan and then analyzing the resulting samples for four potentially toxic organic pollutants: polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs).
"All the samples within one kilometer of the World Trade Center were high," Diamond says. "For the PAHs, PCNs and PCBs, they were about a factor of 10 relative to Brooklyn." A site in Brooklyn was used as a baseline for the New York City area because of its location 3.5 kilometers upwind of the towers.
Diamond's earlier research in Toronto showed a similar factor of 10 difference between window films in urban and rural locations, so the concentrations near Ground Zero could have been as much as 100 times greater than surrounding rural areas, she deduces.
In the aftermath of Sept. 11, many scientists converged on Manhattan to study the fallout from the attacks, including a team that suggested the potential risk of exposure from inhaling toxic organic compounds was lower than expected. The researchers reported no evidence of PCBs and, while they did find some PAHs, they said the particles were too big to pose a threat to human health.
This earlier team may have detected lower levels because their samples were diluted by the large amounts of building material emitted in the initial explosion, according to Diamond. "By the time we got there six weeks later, we were picking up the signal of the slow burn, not the catastrophic expulsion of debris," she says.
Diamond is hesitant to speculate about potential health effects for a number of reasons, including the limited number of samples: the findings were based on window films from only nine buildings in lower Manhattan. [MD1]
She was surprised that concentrations dropped to background levels beyond one kilometer from Ground Zero. "To me that's good news; I thought it would be further," Diamond says. "The flip side is that it's bad news that New York City and other urban areas have such high background concentrations of these compounds."
New York City, with a population of about 8 million, had twice the background levels of PBDEs typically found in Toronto, a city of about 4.5 million people. Beyond population differences, the higher concentrations in New York could be due to the incredible density of the "technosphere" - the large mass of manmade material, Diamond suggests.
"This should be seen in the context of a continuum," Diamond continues. "The urban areas contain the largest mass of these chemicals. They're storehouses, in effect, and we're fools to think that they're permanent storehouses." Whereas these attacks were a catastrophic event, building fires are extremely common in cities, releasing chemicals to the urban atmosphere on a daily basis. More research needs to be done to examine how these fires affect exposure to hazardous pollutants, according to Diamond.
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