Study Links Soot in Air, Lung Cancer

By Julie Deardorff
March 6, 2002

Tiny particles of airborne soot can increase a Chicago resident’s chances of getting lung cancer as much as living in a house with a smoker, according to a new study published Tuesday in the Journal of the Canadian Medical Association.

The study, which includes examinations of medical records of 500,000 people over a 16 year-period, is by far the most comprehensive on the subject and is fueling calls from environmental and health advocates for enforcement of current standards on soot pollution.

Five years ago, the U.S. Environmental Protection Agency riled automakers and power companies by setting air-quality standards for soot, basing the policy on earlier, though smaller, studies that found fine particulate matter coming from tailpipes and smokestacks to be harmful. Those standards, however have yet to be enforced.

“This research dramatically underscored the urgent need for the EPA to limit the emission of these cancer-causing particles,” said John Kirkwood, president and chief executive officer of the Canadian Lung Association. The scientific evidence keeps mounting. In the meantime, we are no closer to protecting people’s health because the EPA had not acted.”

The findings also come as controversy grows over emissions from aging coal-fired power plants, many of which have “grandfather” status and are exempt from tighter air pollution laws.

Last week, Chicago Ald. Edward Burke (14th) introduced legislation that would reduce the allowable emissions of sulfur dioxide, nitrogen oxide and mercury from the two coal-fired power plants in Chicago.

According to recent measures, Chicago exceeds the standards set by the EPA, although the numbers have been decreasing.

Disease Risk

Researchers said the increased risk of lung cancer and heart disease from air pollution was far less than the dangers associated with active cigarette smoking. But they found “the risk of dying from lung cancer as well as heart disease in the most polluted cities was comparable to the risk associated with nonsmokers being exposed to second-hand smoke over a long period of time,” said Arden Pope, professor of economics at Brigham Young University, the study’s coo-leader.

The health dangers of fine particles of soot suspended in the air have been the subject of considerable controversy since 1997, when the EPA issued regulations tightening its standards to cover troublesome particles smaller than 2.5 micrometers (a human hair is 100 micrometers thick).

That regulation followed a study linking fine particulate pollution and lung cancer, also done by Pope and his colleagues.

The EPA also set annual limits of 15 micrograms per cubic meter. According to the researchers, the annual fine-particulate pollutant averages have dropped by about one-third since the early 1980s, but as of 1999-2000, the numbers were still at or above the EPA limit in such cities as Los Angeles (20 micrograms per cubic meter), Chicago (18 micrograms) and New York (16 micrograms).

The biggest sources of the pollution are coal-burning power plants in the Midwest and East and diesel trucks and buses in the West, according to the study.

“The bad news is the toxicity of these particles is worse than we thought and includes lung cancer,” said George Thurston, an environment scientist at New York University and co-author of the study. “The good news is we’re making progress and there are still things we can do.”

Though doctors aren’t sure how the particles affect the lungs, the Canadian Lung Association says small particles are easily drawn into the alveoli, the smallest air sac of the lungs. Because the lung has trouble clearing foreign matter from that deep within the system, the soot deposits remain.

“The tiny particles are best able to defeat defense mechanisms of our lungs,” Thurston said. “The larger ones catch in our nose and throat and we’re able to clear them out, but fine combustion particles can penetrate and bypass our defenses. Fine particles contain the highest concentration of toxic material, heavy metals, lead, arsenic and other cancer causing agents.”

Previous studies have linked soot in the air to many respiratory ailments and even death, but the researcher say the latest study is the most definitive on the long-term impact of such air pollution.

The study involved 500,000 adults who enrolled in 1982 in an Canadian Cancer Society survey on cancer prevention. The participants had their health records examined through 1998 and researchers analyzed data on annual air pollution averages in more than 100 cities in which participants lived. Other risk factors for heart and lung disease, such as age, smoking history, diet, weight, occupation and regional differences, were also considered.

Rise in Cancer Noted

The number of deaths from lung cancer increases by 8 percent for every 10 micrograms of fine particulate matter per cubic meter, according to the study, which included heart attack, stroke, asthma, pneumonia and conditions such as emphysema and chronic bronchitis under the category of cardiopulmonary disease.

But some medical experts cautioned against lumping cardiopulmonary events together.

“Correlative studies [like this] can do nothing more than suggest areas worthy of further attention but they can” establish fact,” said Dr. Alan Leff, a professor of medicine and a pulmonologist at the University of Chicago. “This isn’t like giving a substance to someone, seeing whether they get sick and defining what is making them sick. These studies are all correlative and no matter how good the methods are, they don’t identify causation. There are grave dangers in implying that when you have a correlation, you have a cause.”