Long-term exposure to air pollution that contains high concentrations of tiny particles of soot and dust significantly increases the risk of dying from lung cancer and heart disease, according to a new nationwide study. Over many years, the danger of breathing soot-filled air in polluted cities is comparable to the health risks associated with long-term exposure to second-hand smoke, according to the authors of the study, which evaluated the effects of air pollution on human health over a 16-year period.
Previous studies have linked soot in the air to many respiratory ailments and even death, but the new study is the most definitive yet on the long-term impact of such air pollution, according to NYU School of Medicine and Brigham Young University researchers who led the study. Investigators from University of Ottawa and the American Cancer Society also collaborated on the study, which is published in this week's issue of the Journal of the American Medical Association.
"This study is compelling because it involved hundreds of thousands of people in many cities across the U.S. who were followed for almost two decades," says George Thurston, Sc.D., Associate Professor of Environmental Medicine, at NYU School of Medicine, the study's co-leader.
The study assesses the impact of particles smaller than 2.5 micrometers (called fine particulate matter) in cities across the United States. It analyzed data from some 500,000 adults who were followed from 1982 to 1998 as part of an ongoing cancer study. The data, which included cause of death, were linked to air pollution levels for cities nationwide using advanced statistical modeling to control for individual risk factors, such as age, smoking status, body mass, and diet, as well as for regional differences among the study populations.
The researchers calculated that the number of deaths from lung cancer increases by 8% for every 10 micrograms of fine particulate matter per cubic meter, according to the study. Larger particles and gaseous pollutants were generally not as associated with higher number of deaths.
"The increased risk of lung cancer and heart disease from air pollution was clearly far less than the risks associated with active cigarette smoking," says Arden Pope, Professor of Economics at Brigham Young University in Provo, Utah, the study's co-leader. "However, we found that 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," says Dr. Pope.
The health dangers of tiny particles of soot in the air have been the focus of considerable controversy since 1997, when the Environmental Protection Agency issued new regulations tightening its standards to cover particles smaller than 2.5 micrometers (a human hair is 100 micrometers thick). Industry fought the regulations, but the EPA prevailed and the agency is now considering new rules for limiting the emission of the particles.
The EPA set annual average limits on fine particular matter to 15 micrograms per cubic meter in 1997. However, many cities presently exceed that standard. According to the study, from 1979 to 1983, the annual average was 24 ug/m3 in New York City, 27 ug/m3 in Los Angeles, 23 ug/m3 in Chicago and 26 ug/m3 in Washington D.C. The levels have come down over the years, and in 1999 and 2000 the annual average was 16 ug/m3 in New York, 20 ug/m3 in Los Angeles, 18 ug/m3 in Chicago and 15 ug/m3 in Washington, D.C. Despite this improvement in levels, the study shows that the prevailing levels of fine particulate matter air pollution in the U.S. are still associated with significant risk of cancer and cardio-pulmonary deaths.
The new study extends previous studies that linked chronic exposure to the small particles to deaths from lung cancer and other causes, and addresses many of the criticisms of the earlier studies. It substantially extends the follow-up analysis of an earlier study by Dr. Pope and colleagues of this same cohort, for example. It greatly expands exposure data to include gaseous co-pollutant data on gaseous pollutants and the newest data on fine particulate matter collected nationwide in 1999 and 2000. It also incorporates extensive individual-level information on other cancer risk factors such as occupation and diet, including total fat consumption and consumption of fruit and vegetables.
The study's co-authors are: Richard Burnett, Ph.D., and Daniel Krewski, Ph.D., of University of Ottawa, Ottawa, Canada; Michael Thun, M.D. and Eugenia Calle, Ph.D., of American Cancer Society, Atlanta; and Kazuhiko Ito, Ph.D., of New York University School of Medicine.
The study was supported by a grant from the National Institutes of Health and in part by government grants to the NYU School of Medicine's National Institute of Environmental Health Sciences Center for Environmental Health and to its EPA Particulate Matter Health Research Center.