While the attacks on the World Trade Center have had incalculable effects on Americans, a recently released and widely publicized study gives hope that at least one of the effects of the disaster the release into the air of a substance known, at high doses, to be a carcinogen is not a long-term health concern even for those who spent a lot of time near the site.1
The study examined the air concentration of nine types of polycyclic aromatic hydrocarbons (PAHs) in places near Ground Zero for six months after the attack. Dozens of studies of workers who have inhaled elevated levels of PAHs over long durations of time have demonstrated that the compounds can increase the risk of lung cancer.2 A few days after the attacks, the concentrations of PAHs in areas near Ground Zero had increased to approximately sixty-five times the usual background level, placing them among the highest outdoor PAH concentrations ever reported. However, the concentrations of PAHs subsided over the months following the attacks as the flames the source of PAHs were extinguished, and as the substances dissipated.
Researcher Thomas Cahill, who led a group that studied the fine particle content of the smoke of the ruins, initially said that the elevated PAH levels near the site were "certainly worthy of the most serious kind of concern."3 While the increase in these potentially cancer-causing substances may at first seem frightening, the authors of the recent study indicate that it was not enough in amount and duration to have much of an effect on the public's health. The authors estimate that the elevation in lifetime cancer risk for those in the immediate area will be extremely minimal an increase equivalent to causing only one additional case of cancer over seventy years per 100 million people. Therefore, the additional expected cases of cancer in the area's population is extremely close to zero.
The study did not examine the levels of any other potentially harmful substances that may also have been released into the air and did not discuss the risk posed to workers at the site who have had greater exposure to PAHs. Therefore, it does not show that the debris overall will necessarily be harmless in terms of its long-term effects on cancer risk. However, while scientists and the public ponder the potential long-term health consequences of the disaster, as well as the effects of the presence of carcinogens in general in the environment, it is important to keep in mind the point the study underscores: even seemingly alarming increases in substances capable of harmfully affecting humans must be put in the proper context. Both the level and duration of exposure are crucial in assessing the health effects of exposure. In other words, the study illustrates the general rule that even when it comes to known human carcinogens, it is the dose that makes the poison.
Rivka Weiser is a research intern at the American Council on Science and Health.
(1) Pleil JD, Vette AF, Johnson BA, Rappaport SM. Air levels of carcinogenic polycyclic aromatic hydrocarbons after the World Trade Center disaster. Proceedings of the National Academy of Sciences published online on July 27, 2004, http://www.pnas.org/cgi/content/abstract/0404499101v1
(2) Armstrong B, Hutchinson E, Unwin J, Fletcher T. Lung cancer risk after exposure to polycyclic aromatic hydrocarbons: a review and meta-analysis. Environmental Health Perspectives. 2004 :112(9): 970-8.
(3) Service, RF. Chemical Studies of 9/11 Disaster Tell Complex Tale of 'Bad Stuff.' Science. 2003; 301: 1649.