Air pollution and cancer
Air pollution refers to the presence of harmful contaminants in the air, many of which are known or suspected carcinogens. Major sources of outdoor air pollution include the combustion of fossil fuels for vehicles and power generation, while indoor pollution often arises from burning solid fuels and the presence of substances like asbestos and radon. Research has linked various air pollutants, such as diesel exhaust particulate, benzene, and formaldehyde, to an increased risk of several cancers, particularly lung cancer and mesothelioma. While tobacco smoke remains the leading cause of lung cancer, studies indicate that air pollution may contribute to higher rates of this disease across populations, especially in urban areas or near industrial sites. Furthermore, recent studies suggest a potential association between air pollution and other cancers, including breast cancer. The Clean Air Act mandates the U.S. Environmental Protection Agency to regulate air quality standards to mitigate the health impacts of these pollutants. Understanding the links between air pollution and cancer is crucial for public health and environmental policies aimed at reducing exposure to carcinogenic substances in both indoor and outdoor settings.
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Air pollution and cancer
ROC STATUS: Asbestos, known human carcinogen since 1980; diesel exhaust particulate, reasonably anticipated human carcinogen since 2000. Other air pollutants that are known human carcinogens include benzene, 1,3-butadiene, radon, and tobacco smoke; those that are reasonably anticipated human carcinogens include formaldehyde and polycyclic aromatic hydrocarbons. Air pollutants such as ozone, oxides of nitrogen, and sulfur oxides are not listed in the Report on Carcinogens (RoC); however, epidemiologic studies (studies on populations) provide some evidence of their association with lung cancer. Of the many components of particulate matter (PM), only diesel exhaust particulate has been the subject of studies that led to its current classification.
ALSO KNOWN AS: Criteria air pollutants, toxic air pollutants
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 transportation, 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, such as mold.
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 relationship 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).
Though air pollution is typically associated with lung cancer, a study released by the Journal of the National Cancer Institute in 2023 demonstrated an eight percent increase in breast cancer incidence in locations with high particulate air pollution. The study, which began in 1995, was conducted in the United States and monitored a group of men and women over twenty years. It adds to a growing body of research that suggests air pollution is linked to breast cancer.
History: Many of the components of air pollution are recognized as known or reasonably anticipated carcinogens, 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.
Bibliography
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.
White, Alexandra J., et al. “Ambient Fine Particulate Matter and Breast Cancer Incidence in a Large Prospective US Cohort.” JNCI: Journal of the National Cancer Institute 116.1 (2024): 53-60. Oxford Academic, https://academic.oup.com/jnci/article/116/1/53/7260521. Accessed 14 June 2024