CHICAGO – A study published Wednesday presents the strongest evidence yet linking air pollution in many U.S. cities with fatal lung cancer, scientists say.
The risks are comparable to those faced by nonsmokers who live with smokers and are exposed to secondhand cigarette smoke, said George Thurston, who co-authored the study.
Such risks have been estimated at 16 percent to 24 percent higher than those faced by people living with nonsmokers, said Thurston, a New York University scientist.
The study involved 500,000 adults who enrolled in an American Cancer Society survey on cancer prevention in 1982. The researchers examined participants' health records through 1998 and analyzed data on annual air pollution averages in the more than 100 cities in which participants lived.
Results appear in Wednesday's Journal of the American Medical Association.
Allen Dearry, a scientist at the National Institute of Environmental Health Sciences, which funded the study, called it "the best epidemiologic evidence that we have so far that that type of exposure is associated with lung cancer death."
The JAMA study did not list data from individual cities in which the participants lived. Researchers said the study was designed to examine the overall health risk posed by fine particulate matter in the United States — not compare pollution levels in various cities.
The risk is from what scientists call combustion-related fine particulate matter — soot emitted by cars and trucks, coal-fired power plants and factories.
The researchers took into account other risk factors for heart and lung disease such as cigarettes, diet, weight and occupation.
Lung cancer death rates were compared with average pollution levels, as measured in micrograms per cubic meter of air. The researchers found that the number of lung cancer deaths increased 8 percent for every increase of 10 micrograms. Other heart- and lung-related causes of death increased 6 percent for every 10-microgram increase.
In the early 1980s, when the study began, some major cities had air pollution levels of 25 to 30 micrograms per cubic meter, which would confer a more than 20 percent increased risk of lung cancer mortality, said co-leader C. Arden Pope III, an environmental epidemiologist at Brigham Young University.
The Environmental Protection Agency set average annual limits at 15 micrograms per cubic meter in 1997, when it tightened its standards to include fine particulate matter — pollutants measuring less than 2.5 micrometers. That is about 1/28th the width of a human hair.
That regulation followed a previous study by Pope linking fine particulate pollution and lung cancer, done on many of the same participants as the JAMA study.
Pope said the new study doubles the follow-up time and does a better job of considering other risk factors, to address criticism from industry groups who challenged the earlier study and sued the EPA over the 1997 regulations. The Supreme Court last year upheld the way the EPA set those standards.
Industry challenges to the standards themselves are ongoing in lower courts, said Jayne Brady, spokeswoman for the Edison Electric Institute, which represents most of the nation's major electric utilities, including operators of many coal-powered plants.
Despite those challenges, Brady said, "We are trying to do everything we can to reduce emissions."
Thurston said annual fine-particulate pollutant averages have fallen significantly since the early 1980s but as of 1999-2000 were still at or above the EPA limit in such metropolitan areas as New York, Washington, Chicago and Los Angeles.
He said the biggest sources of such pollution are coal-burning power plants in the Midwest and East, and diesel trucks and buses in the West.
Thurston said the study gives new impetus to efforts in Washington, D.C., to clean up aging coal-fired power plants.
The EPA said the agency will consider the research as part of its continuing review of air quality standards for particulate matter.