Cancer Linked to Particulate Air Pollution

New study addresses previous criticisms.

Published: 20-Mar-2002

PROVO, Utah -- Tiny particles of pollutants emitted by automobiles, power plants and factories significantly increase the risk of dying from lung cancer in the United States, according to a study led by Brigham Young University epidemiologist Arden Pope.

The research, which was published in the March 6 issue of the "Journal of the American Medical Association," also substantiates Pope’s controversial previous work that demonstrated an association between increased levels of air pollution and an increase in total and cardiorespiratory deaths.

"The findings of this study provide the strongest evidence to date that long-term exposure to air pollution common to many metropolitan areas in the United States is an important risk factor for cardiopulmonary and lung cancer mortality, " said Pope, professor of economics at BYU.

Pope and coauthors from the University of Ottawa, the American Cancer Society and the New York University School of Medicine linked health statistics and levels of air pollution in scores of cities across the United States. The researchers tracked 500,000 individuals over 16 years, noting their body mass, smoking status, occupational exposure, cause and date of death and even dietary habits - information that was used to explore other potential causes of lung cancer and cardiopulmonary illness. Then the scientists fed the mountains of data into complex statistical models that isolated the health effects of the type of air pollution under scrutiny.

"In order to understand how air pollution might increase the risk for lung cancer, we first had to account for the effects of smoking on lung cancer risk," Pope said. "The dominant risk factor observed in our study was active cigarette smoking. Elevated risks due to air pollution were more comparable to long-term exposure to passive cigarette smoke."

George Thurston, associate professor of environmental medicine at the NYU School of Medicine and a coauthor, said, "The lung cancer risk that we found associated with living in a polluted city in the U.S. is comparable to the risk reported by the Environmental Protection Agency and National Research Council for a nonsmoker living with a smoker."

The pollutants to blame are particles of soot smaller than 2.5 microns, also called fine particulate matter or PM2.5. They are generated by combustion, most commonly by automobiles, manufacturing and coal-fired power plants. The researchers found that larger particles and gaseous pollutants other than sulfur dioxide did not increase mortality risk.

The EPA has declared that the annual average level of PM2.5 particles in the air should not exceed 15 micrograms per cubic meter. Pope’s study showed that each 10 micrograms-per-cubic-meter increase in fine particulate air pollution is accompanied by an 8 percent increase in the number of lung cancer deaths. At the study’s inception in the early 1980s, the most polluted cities in the United States had fine particulate pollution levels about 20 micrograms per cubic meter higher than the least polluted. As a result, the citizens in the most polluted cities have an approximately 16 percent excess risk of dying from lung cancer due to fine particulate air pollution.

Pope teamed with Harvard researchers to report similar risks associated with cardiopulmonary mortality and fine particulate matter in two studies published in the mid-1990s. Automobile and manufacturing industry groups attacked the research as faulty science, and their scorn grew when the EPA used the studies as the basis for tightening particulate pollution standards in 1997. The U.S. Supreme Court ruled in favor of the EPA in February 2001 after an industry lawsuit challenged the new regulations.

In addition to the new insights into lung cancer risk, Pope believes the new study’s main contribution is putting to rest many of the detractors’ claims.

The study provides the following responses to previous common criticisms:

Pope emphasized that the study’s findings are "good news." Since the early 1980s, the annual U.S. average of PM2.5 has dropped from 21 to 14 micrograms per cubic meter.

"The risk factor we have identified - fine particulate air pollution - is controllable," he said. "If we can further reduce our exposure to this risk factor we can reduce the number of deaths attributed to heart disease, lung cancer and respiratory illnesses."

The study’s other coauthors are: Richard Burnett and Daniel Krewski of the University of Ottawa, Ottawa, Canada; Michael Thun and Eugenia Calle of the American Cancer Society, Atlanta; and Kazuhiko Ito of the NYU School of Medicine.

The research was supported by a grant from the National Institute of Environmental Health Sciences and in part by government grants to the NYU School of Medicine.

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