Tiny Pollution Particles Linked To Lung Cancer
By Cat Lazaroff
WASHINGTON, DC, March 6, 2002 (ENS) - Long term exposure to soot filled air carries nearly the same risk of lung cancer as breathing second hand smoke. A new study by researchers in the United States and Canada finds that breathing air containing high concentrations of tiny soot and dust particles increases the risk of dying from lung cancer and heart disease.
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 New York University (NYU) School of Medicine and Brigham Young University researchers who led the 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.
The researchers calculated that the number of deaths from lung cancer increases by eight percent for every additional 10 micrograms of fine particulate matter found in a cubic meter of air.
"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," said George Thurston, associate professor of environmental medicine at NYU School of Medicine, the study's co-leader.
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."
The study assesses the impact of particles smaller than 2.5 micrometers, called fine particulate matter, in cities across the United States. It analyzes 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. The researchers controlled for individual risk factors such as age, smoking status, body mass and diet, as well as for regional differences among the study populations.
The number of deaths from lung cancer increases by eight percent for every 10 micrograms of fine particulate matter per cubic meter, the researchers found. 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," said 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."
The health dangers of tiny particles of soot in the air have been the focus of considerable controversy since 1997, when the U.S. Environmental Protection Agency (EPA) issued new regulations tightening its standards to cover particles smaller than 2.5 micrometers. For comparison, a human hair is 100 micrometers thick.
Particles this small are easily drawn into the aveoli, the smallest air sacs of the lungs. Because the lung is slow to clear foreign bodies from that deep within its system, the soot deposits can cause damage over long periods of time.
Sources of small particulate matter pollutants include diesel bus and truck emissions as well as ordinary auto exhausts, industrial and utility smokestacks, mining and construction.
These industries fought the EPA's 1997 regulations, taking their case as far as the U.S. Supreme Court. The EPA prevailed in February 2001 when the nation's highest court ruled unanimously that the federal government need not consider the financial costs of meeting clean air standards when creating new regulations.
But because of the industry challenges, the EPA has yet to issue rules describing the measures states must use to meet the fine particle regulations.
John Kirkwood, president and CEO of the American Lung Association, said the study adds urgency to the need for the EPA to immediately implement strong new rules to curb fine particle emissions.
"This research dramatically underscores the urgent need for EPA to limit the emission of these cancer causing particles," said Kirkwood. "It's been almost five years and EPA has yet to issue the rules needed to implement its own health standards. The scientific evidence keeps mounting."
In 1997, the EPA set annual average limits for fine particular matter in cities to 15 micrograms per cubic meter. Many cities presently exceed that standard, though particulate air pollution levels have fallen considerably since 1979, the earliest year covered by the current study.
For example, from 1979 to 1983, the annual average was 24 micrograms per cubic meter in New York City, and 27 micrograms per cubic meter in Los Angeles. In 1999 and 2000, the annual average was 16 micrograms per cubic meter in New York and 20 micrograms per cubic meter in Los Angeles.
Despite this improvement, the study shows that current U.S. levels of fine particulate matter air pollution are still high enough to be associated with a significantly increased 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. For example, it extends the follow up analysis of an earlier study by Dr. Pope and colleagues of this same group of patients.
The current study also expands exposure data to include data on gaseous pollutants and the newest data on fine particulate matter collected nationwide in 1999 and 2000. It incorporates individual level information on other cancer risk factors such as occupation and diet, including total fat consumption and consumption of fruit and vegetables.
The EPA is now considering new rules for limiting the emission of the particles that would apply to the major sources of smog and soot: power plants, incinerators, industrial smokestacks, and motor vehicles.
However, the agency is also considering an overhaul of the new source review section of the Clean Air Act. The provision requires large air pollution sources that are too old to be covered by the Act to install new emissions control equipment if they undergo significant upgrades or increase their capacity.
"The EPA is considering weakening the Clean Air Act as it applies to many of the largest sources of particle pollution - coal fired power plants, refineries, pulp and paper mills, and other large industrial facilities," said the American Lung Association's Kirkwood. "In the meantime, we are no closer to protecting people's health because EPA has not acted."
The cancer 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.
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