What is air pollution? Does it cause cancer?
Related cancers: Lung cancer, pleural and peritoneal mesotheliomas, gastrointestinal cancers, laryngeal cancer, cancers of the lymphatic and blood-forming systems (1,3-butadiene).
Definition: Air pollution is the presence of contaminants, many of which are carcinogens, in the air. Outdoors, pollution is largely a consequence of the combustion of fossil fuels for transport, power generation, and other human activities. Indoors, pollution is generated by burning solid fuels, and the air may also contain asbestos, radon gas, environmental tobacco smoke, formaldehyde, and volatile organic compounds.
Exposure routes: Inhalation
Where found: Indoor and outdoor air. Outdoor pollutants can be carried far from their original source by air currents.
At risk: Populations exposed to smog and particulate matter in air pollution, including inner-city residents; people living near electric-power-generating plants, factories, and refining plants; occupationally exposed railroad workers and synthetic rubber industry workers; people cooking indoors with solid fuels
Etiology and symptoms of associated cancers: According to the World Health Organization, the air contains a complex mixture of pollutants, including primary emissions such as diesel soot particles and oxides of nitrogen produced during combustion processes, the products of atmospheric transformation such as ozone, and the sulfate particles formed by burning sulfur-containing fuels.
Although air pollution is a minor contributor to lung cancer compared with tobacco smoke, it can affect entire populations, and components of the pollutant mix might interact with other carcinogens, possibly increasing their effects.
In 1995 researchers Aaron Cohen and C. Arden Pope III analyzed epidemiological studies and found that they consistently suggested that ambient air pollution, chiefly as a result of the incomplete combustion of fossil fuels, is responsible for increased rates of lung cancer.
A study published in 1998 of nonsmoking adults over a fifteen-year period by David Abbey and his coworkers showed a strong association between ozone levels and lung cancer. The ozone at ground level (which people inhale) is not emitted directly into the air. It is created by chemical reactions between oxides of nitrogen, emitted in motor vehicle exhaust and by industrial facilities, and volatile organic compounds from many sources, including gasoline vapors and chemical solvents. The relation between ozone levels and lung cancer has been reported in many additional scientific studies.
The major outdoor air pollutants linked to lung cancer are particulate matter, sulfur oxides, ozone, oxides of nitrogen, and volatile organic compounds. Particulate matter is the term for a mixture of solid particles and liquid droplets found in the air that come from soot, smoke, and diesel exhaust. The particles of most concern are those smaller than 10 micrometers in diameter. Once inhaled, the smaller particles can travel to the deepest regions of the lungs, where chemicals (such as those adsorbed to diesel exhaust particulate) can be released. Some of these chemicals cause deoxyribonucleic acid (DNA) mutations, which can lead to cancer.
Many studies have demonstrated that exposure to indoor air pollutants has adverse effects on health. More than three billion people worldwide depend on solid fuels, including biomass fuels and coal, for their cooking and energy needs. Combustion of these materials indoors produces high levels of smoke that contains many pollutants, and there is consistent evidence of lung cancer in adults exposed to coal-generated pollutants, according to the World Health Organization. Inhaling asbestos fibers released from damaged or crumbled insulating materials or other products containing this material can lead to mesothelioma and several other cancers. Other common indoor air pollutants include formaldehyde, environmental tobacco smoke, radon gas, and polycyclic aromatic hydrocarbons (a class of volatile organic compounds).
History: Many of the components of air pollution are recognized as known or reasonably anticipated carginogens, such as asbestos, benzene, 1,3-butadiene, radon, tobacco smoke, diesel exhaust particulate, formaldehyde, and polycyclic aromatic hydrocarbons. Other components have scientific research supporting their link to human cancer.
The Clean Air Act as amended in 1990 requires the U.S. Environmental Protection Agency to set national ambient air quality standards for ozone, oxides of nitrogen, particulate matter, and sulfur oxides. The agency is mandated to work with state and local governments to reduce the release of other air pollutants classified as toxic air pollutants.
Beeson, W. L., D. E. Abbey, and S. F. Knutsen. “Long-Term Concentrations of Ambient Air Pollutants and Incident Lung Cancer in California Adults.” Environmental Health Perspectives 106 (1998): 813-822.
Cohen, A. J., and C. Arden Pope III. “Lung Cancer and Air Pollution.” Environmental Health Perspectives 103, suppl. 8 (1995): 219-224.
Jacobson, M. Z. Atmospheric Pollution. New York: Cambridge University Press, 2002.
Krzyzanowski, M., B. Kunnadibbert, and J. Schneider, eds. Health Effects of Transport-Related Air Pollution. Geneva, Switzerland: World Health Organization, 2005.
McGranahan, G., and F. Murray. Air Pollution and Health in Developing Countries. London: Earthscan, 2003.
Pluschke, P., ed. Indoor Air Pollution. New York: Springer, 2004.
Pope, C. Arden, III, et al. “Lung Cancer, Cardiopulmonary Mortality, and Long-Term Exposure to Fine Particulate Air Pollution.” Journal of the American Medical Association 287 (2002): 1132-1141.
Ramachandran, G. Occupational Exposure Assessment for Air Contaminants. New York: CRC Press, 2005.
U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program. Eleventh Report on Carcinogens. Research Triangle Park, N.C.: Author, 2005.