6 Years Later, 9/11 Health Questions Linger

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Another expert pointed to the discord that exists between EPA air samples and those garnered by private testing firms. Those firms were hired by banks and other corporations to test whether it was safe for workers to return to their lower Manhattan offices in the weeks after 9/11.

Those private environmental testing services "found a list that was longer in terms of contaminants, and in higher concentrations, for weeks afterwards and possibly even for longer," compared to EPA readings, said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City. "There's a conflict of the information that we got at the time and what private companies were getting."

Stellman refuted that argument, however, saying that Horovitz was comparing "apples and oranges." She said that while the EPA was taking samples of outdoor air quality, most of the sampling done by the private firms was done inside buildings.

"It's very hard to make these comparisons because the EPA, I don't believe, had a lot of indoor air quality data," Stellman said.

But criticism of the Mount Sinai research program continues. In a Sept. 7, 2007, article in The New York Times, a number of critics charged that the findings from the Selikoff center -- founded in the 1980s with political backing from labor unions -- are biased in favor of boosting the number of workers thought to be affected by contaminants.

The center's supporters -- including Stellman -- shot back that the Mount Sinai team's efforts were stymied early on by a lack of federal funding and the government's emphasis that worker health screening, not research, be the focus of their efforts at the site.

So, questions on the long-term health effects of those weeks of grueling work at Ground Zero remain unresolved and may never be resolved due to a paucity of data, the experts said.

"What we don't know certainly weighs much more heavily than what we do know," according to Horovitz.

One thing scientists do understand, he said, is that particles under 2.5 micrometers can lodge in the lungs' tiniest channels for years, potentially causing lung disease, atherosclerosis ("hardening of the arteries"), and even cancers.