Scientists say the thick layer of irritating dust that blanketed Lower Manhattan after the September 11 terrorist attacks probably will not cause alarming increases in cancer, emphysema and other serious long-term health problems.
An analysis found that most of the potentially toxic dust particles collected in the week after the attacks were too large to lodge deep into people’s lungs. Only 1 percent of the dust samples were composed of finer particles, researchers said.
In addition, the chemical composition of the dust appears less toxic than originally feared.
Many Lower Manhattan residents and rescue workers at ground zero have reported continuing respiratory problems. The dust from the collapsed World Trade Center towers was largely a combination of pulverized glass and concrete, among other materials, that can be extremely alkaline and irritating.
Scientists said the dust particles were large enough that people probably coughed them out of their upper airways, but the study did not directly test whether inhalation of any of the dust was deep.
“In terms of potential lifetime exposures, we’re probably going to be very lucky in that these may not be exposures of significant health risk,” said Paul Lioy, one of the authors of the report. Mr. Lioy is associate director of the Environmental and Occupational Health Sciences Institute, jointly run by Rutgers University and the University of Medicine & Dentistry of New Jersey.
Scientists examined the dust for persistent organic pollutants (POPs), stable compounds that endure in the environment and can be toxic to humans and wildlife.
They said they found no evidence of high levels of two particular POPs: pesticides and polychlorinated biphenyls, which were used in hundreds of industrial and commercial applications until their production was banned in 1977.
However, the team estimated that the dust contained 100 to 1,000 tons of polycyclic aromatic hydrocarbons, a group of compounds including some that are classified by the Environmental Protection Agency as probable human carcinogens.
The report will be published in the February issue of Environmental Science & Technology. A summary of the article appears on the Web site of the American Chemical Society, which publishes the journal.
The report is unlikely to resolve all the air quality issues still swirling more than 15 months after the attacks.
In some apartments and offices, the dust was 3 inches thick. The EPA has pledged to clean up residences throughout Lower Manhattan.
Previous studies showed the collapsed towers did not spread high levels of asbestos throughout the area.
Mr. Lioy’s team took dust samples from 13 locations around the site from Sept. 12 to 17 last year. They did not collect any samples in Brooklyn and other areas farther from ground zero where the dust plume spread.
The smaller particles have been the focus of air quality regulations nationwide. Even in normal city air, high levels of the particles can accumulate from vehicle exhaust, pulverized sand and dust from tires and brakes.
The director of the Environmental Research Foundation, a New Jersey-based public-interest group, said enough toxic particles existed to cause concern.