Tiny Particles, Big Dilemma
It's a monumental regulatory brouhaha. On July 16, the Environmental Protection Agency announced new air pollution standards that not only tightened existing ozone standards but also set limits on a new and previously unregulated pollutant--microscopic particles floating in the air that come from combustion of fuels. According to EPA Administrator Carol M. Browner, a wealth of scientific studies show that the new rules on the tiny particles will prevent 15,000 premature deaths a year once they go into effect in about 2007.
Or will they? Predictably, affected industry groups, along with scores of congressional backers, argue that the research behind the regs is profoundly flawed. But they aren't the only skeptics. Epidemiologist Joseph L. Lyon of the University of Utah likens some of the evidence to "witchcraft." And a recent editorial in the journal Science asks how the EPA can protect people from fine particles "if it does not know what they are or which, if any, have deleterious physiological effects?"
"GUINEA PIGS." Supporters of the rules concede they don't understand all the details. But they insist there is more than enough evidence to take action. "If we wait until science gives us all the answers, we are essentially using people as guinea pigs," says University of North Carolina epidemiologist Carl M. Shy.
The fine-particles debate illustrates the core conundrum of regulation--how to make sound public policy amid uncertainty. Still, most scientists agree that regulating the tiny particles is the right decision. Go back to episodes such as one in London in 1952, experts say. That year, an unusual December weather pattern swathed the city in a shroud of coal smoke and other pollution. In one week, 2,484 people died, up from 945 the prior week. Deaths from bronchitis and emphysema rose almost tenfold, and hospital admissions for all diseases doubled. The lesson: Bad air kills.
That and similar episodes raised two key questions. What was the chief culprit in the witch's brew of air pollution? And was it still a threat at the lower levels typically experienced? In 1974, when the Arab oil embargo threatened to increase coal use, researchers at Harvard University began a study to find out. They picked six cities, ranging from Steubenville, Ohio, in an industrial region, to the cleaner city of Portage, Wis., and followed thousands of people for more than a decade. The leading hypothesis--that acidic pollution would cause discernible health effects--was proven resoundingly wrong. But the study also looked at particles smaller than 2.5 microns in diameter, dubbed PM2.5, which come from power plants, autos, wood fires, and other combustion sources. The researchers found the death rate to be 26% higher in particulate-packed Steubenville than in Portage. "We could hardly believe the effects were as large as they appeared to be," says Brigham Young University epidemiologist C. Arden Pope III.
It was so unexpected that "we said we have to verify this," says Harvard epidemiologist Douglas W. Dockery.
So the researchers arranged to tap into data the American Cancer Society was collecting on 300,000 people in 151 cities as part of a cancer study. When the Harvard team added in their air pollution data, they found a similar link between particulates and death and disease. By 1993, they were confident enough to publish their findings.
Those results were backed up by a host of epidemiological studies that used a different approach. Researchers gathered day-to-day records on deaths and hospital admissions and compared them to air pollution levels. In city after city, they found an association between particulates and health problems. In Toronto, for instance, "we have evidence for adverse effects of air pollution at levels well below the proposed EPA standards," says Richard Burnett, senior research scientist for Canada's health agency. Add it all up, and there's a "huge body of evidence that particles are related to mortality," says Burnett. That's why public-health officials in Canada, Britain, and the World Health Organization have recommended far tighter limits on particulates than the new EPA rules.
But in the U.S., where industry leaders claim the standards would cost hundreds of billions of dollars, the particulate crackdown is far more controversial. Every time a key study is published, the critics are out in force within weeks, attempting to poke holes in the analyses. Most experts agree that at least some of the attacks are fallacious. For instance, among the many criticisms in a new book, Polluted Science, from the conservative American Enterprise Institute, is the claim that epidemiology
isn't capable of spotting links as weak as those alleged between particulates and health risks. It is true that for cancer, epidemiologists have a hard time spotting links between environmental exposure and certain relatively rare medical conditions unless the incidence of disease is more than 100% higher. But for more common illnesses, such as heart disease, the task is easier. The risk of disease and death from air particulates is similar to the increased risk of heart disease with elevated blood pressure or cholesterol, says Dockery, "and we don't question those."
Even prominent skeptics agree that the associations are statistically significant. But the critics still question whether the tiny particles are responsible for the statistical jump. Maybe something else that isn't being accounted for in the studies is the real cause. "People who are anxious to show that the sky is falling would be delighted to blame air pollution," says Fred Lipfert, an epidemiologist who recently retired from Brookhaven National Laboratory. "The rest of us would prefer to hang it on other factors, like exercise."
Lipfert suggests that people in Ohio may tend to be more sedentary than those in Wisconsin, which could explain the higher death rate in Steubenville. But the Harvard scientists retort that Lipfert has no proof that the people followed in the Six Cities study show this pattern--and the researchers did take into account data on body mass index, a rough measure of exercise.
Similarly, skeptics suggest that factors such as humidity or age account for the results. So Pope, Dockery, and others have reexamined their analyses for other causes. Their conclusion: While it's possible to find another explanation for the health effects observed in any one city or study, the alternatives can't explain the overall results.
CHIEF CULPRIT. The question gets thornier, however, when it comes to figuring out why tiny particles are the chief culprit. "It is a very difficult problem understanding how [relatively low levels] can cause the type of morbidity and mortality that the epidemiology seems to find," says lung specialist Mark J. Utell of the University of Rochester medical school. One theory espoused by Harvard epidemiologist Joel Schwartz is that mammalian lungs have evolved defenses against large air particles. But they haven't had time to fashion a defense against smaller particles from burning fuels, which can lodge deep in the lungs and may affect both the immune and central nervous systems. Indeed, there's tantalizing evidence from Harvard's John Godleski, a toxicologist, that already sick animals may die if they breathe fine particles. But most toxicologists say it will take several years to prove if this is true or not.
So it's back to the central public policy dilemma: What to do in the face of scientific uncertainty? For particulates, there's a general consensus among scientists that some regulation is necessary, even if the case hasn't been proved. For one, cutting fine particles will also result in reductions in most of the other pollutant suspects in many parts of the U.S., Burnett says. And one reason the EPA's scientific advisory committee backed a PM2.5 standard was to put in place a network of monitors to help resolve many of the uncertainties.
Thus, in five years, when states are scheduled to begin developing plans to meet the EPA's new particulate rules, scientists expect to have a much clearer understanding of the threat particulates pose. While a strong case could be made that we should wait until then to set levels, at that point, this fight may seem like so much wasted breath.