Chemical Studies of 9/11 Disaster Tell Complex Tale of 'Bad Stuff'

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Science  19 Sep 2003:
Vol. 301, Issue 5640, pp. 1649
DOI: 10.1126/science.301.5640.1649

NEW YORK CITY—The destruction of the World Trade Center (WTC) towers 2 years ago spewed toxic gases into the air like a “chemical factory,” says a new analysis of the environmental effects of the 11 September terrorist attacks. But the good news is that Manhattanites largely escaped serious exposure to most of the toxic substances, as heat from the fires quickly carried most of the material far above the city. The data, presented here last week at a meeting of the American Chemical Society (ACS),* buttress a new internal report that criticizes the Environmental Protection Agency (EPA) for being too reassuring to the public in the days after the towers collapsed.

The data represent the most comprehensive accounting of environmental conditions at and around Ground Zero in the aftermath of the attacks. More than a dozen research teams used a wide range of instruments to identify and quantify the amount of particulate matter, trace metals, and combustion byproducts that wafted over lower Manhattan. “It was bad stuff, and lots of it,” says Thomas Cahill, a professor emeritus of physics and engineering at the University of California, Davis, who led a group studying ultrafine particles in smoke.

In the hours after the disaster, thousands of office workers, police, and firefighters were exposed to very high levels of pollutants from pulverized concrete, wallboard, ceiling tiles, computers, electrical equipment, and office furniture. Because no air-quality monitors were set up then, researchers have little precise knowledge of the contents of the initial cloud. Instead, many early studies have analyzed the dust that blanketed lower Manhattan immediately after the collapse and the smoke that continued to rise from the buildings' remains.


Airborne spectrometers mapped the spread of debris and chemicals from the collapsed WTC towers.


Those reports tell a mixed story. Last year, for example, a team led by New York University environmental scientist George Thurston found that the WTC dust contained only a small fraction of hazardous metals, asbestos, and organic compounds. Moreover, most of the dust particles—a combination of concrete, gypsum from wallboard, and glass fibers—were too large to be inhaled deep into the lungs. Later work fingered the highly alkaline dust as the chief culprit behind the “WTC cough” that plagued many Ground Zero workers and lower Manhattan residents, and other studies last year flagged more serious health concerns. One, for example, revealed that 75% of the first wave of Ground Zero workers studied in a federal screening program suffered from ear, nose, or throat problems 10 months after the attack, and 50% still suffered lung problems.

At the ACS meeting, most of the concern focused on the noxious fumes spewed by debris fires that burned until 20 December 2001. Paul Lioy, an environmental scientist at Rutgers University in Piscataway, New Jersey, says that his team recorded over 400 different compounds in the WTC smoke, many of which they had never seen before. Cahill says he believes that anoxic conditions underneath the debris pile allowed chlorine to oxidize a wide variety of metals and organic compounds, creating a chemical stew normally seen only coming from municipal incinerators.

A series of studies found that the plume contained high levels of polycyclic aromatic hydrocarbons (PAHs), many of which are considered toxic. Cahill found that levels of these compounds 1.8 kilometers northeast of Ground Zero spiked several times in September and October and peaked on 3 October, a day when a regional inversion plunged much of the smoke down to ground level. Although he has sampled sites around the globe, including the persistent haze in Beijing, China, and the Kuwaiti oil fires that raged during the 1991 Persian Gulf War, “October 3rd was the worst,” Cahill says.

From the ashes.

Rising smoke carried deadly substances away from Manhattan but exposed workers at Ground Zero.


Fortunately for residents, Cahill and others agree that the heat from the flames carried most of the smoke aloft. “The concerns have become more and more focused on Ground Zero,” Cahill says. No pollution-tracking equipment was set up at the recovery site. But nearby readings suggest that workers without respirators were likely exposed to high levels of toxic substances. A team led by EPA analytical chemist Erick Swartz noted PAH levels six times as high as those found during dangerous Los Angeles smogs. Those smog events usually last 2 to 3 days, Swartz says, “but the exposures at Ground Zero lasted for months.” “The measurements we have seen are certainly worthy of the most serious kind of concern,” Cahill says.

The good news was that beyond Ground Zero, few people likely received dangerous long-term exposures to this witch's brew. “There was a very quick decrease in concentration [of hazardous compounds] from inside Ground Zero to outside,” says Lioy. Levels dropped off quickly over time, too. Measurements taken five blocks from Ground Zero by Thurston's team showed that trace elements such as lead, vanadium, and chlorine spiked in September and early October 2001, but nearly all returned to background levels by late October.

Still, lower Manhattan residents aren't in the clear yet. The collapse of the towers filled nearby buildings with a fine coating of dust. At least three of those buildings remain too contaminated to reopen. And one of EPA's own scientists has cautioned that the agency's efforts to oversee cleanup of dust in one building have left behind possibly dangerous levels of asbestos, lead, and other potentially toxic substances. How those chemicals will affect New Yorkers likely won't be apparent for many years.

  • *226th ACS National Meeting, 7–11 September 2003, New York City.

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