CHICAGO (AP) _ Long-term exposure to the air pollution in some of America's biggest metropolitan areas significantly raises the risk of dying from lung cancer and is about as dangerous as living with a smoker, a study of a half-million people found.
The study echoes previous research and provides the strongest evidence yet of the health dangers of the pollution levels found in many big cities and even some smaller ones, according to the researchers from Brigham Young University and New York University.
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 study appears in Wednesday's Journal of the American Medical Association.
It involved 500,000 adults who enrolled in 1982 in an American Cancer Society survey on cancer prevention. 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.
The researchers first 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.
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.''
``This study is compelling because it involved hundreds of thousands of people in many cities across the United States who were followed for almost two decades,'' said co-author George Thurston, an NYU environmental scientist.
Thurston said the lung cancer risks were virtually identical to those faced by nonsmokers who live with smokers and are exposed long-term to secondhand cigarette smoke.
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 study linking fine particulate pollution and lung cancer. That research was done on many of the same participants by C. Arden Pope III, an environmental epidemiologist at Brigham Young University and a co-leader of the JAMA study.
Pope said the new study doubles the follow-up time and does a better job of taking other risk factors into account, to address criticism from industry groups who challenged the earlier study and sued the EPA over the 1997 regulations. The Supreme Court upheld the tightened standards last year.
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 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.