Carcinogens (Encyclopedia of Environmental Issues, Revised Edition)
Cancer is a leading cause of death throughout the world. Environmentalists and others have raised concerns regarding the cancer-causing (carcinogenic) potential of exposure to a constantly growing number of both newly developed and long-existing chemicals in the environment. In addition, humans seem to be increasingly exposed to various sources of electromagnetic waves, such as microwaves, and some groups and individuals are concerned about the possible carcinogenicity of these physical phenomena.
Carcinogens can be categorized based on their origin as chemicals (naturally occurring or synthetic), physical agents, or infectious agents. Chemical carcinogens can be classed as compounds that occur naturally, such as aflatoxins, chromium 6 compounds, and arsenic compounds; and others that are largely synthetic in origin, such as benzene, formaldehyde, vinyl chloride, and dioxins. In addition there are carcinogenic minerals, such as asbestos. Other carcinogenic chemicals are elements or substances such as radon (a radioactive gas), beryllium, and cadmium. Some carcinogens—such as tobacco smoke and alcoholic beverages—are mixtures of compounds. Physical agents that are carcinogens include solar radiation (primarily ultraviolet radiation), gamma rays, and X rays.
Infectious disease agents that have been implicated as carcinogens include human papilloma virus (HPV), which can cause cervical cancer; Helicobacter pylori (H....
(The entire section is 521 words.)
Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Hill, Marquita K. “Chemical Exposures and Risk Assessment.” In Understanding Environmental Pollution. 3d ed. New York: Cambridge University Press, 2010.
McKinnell, Robert. G., et al. The Biological Basis of Cancer. 2d ed. New York: Cambridge University Press, 2006.
Ward, Elizabeth M. “Cancer.” In Occupational and Environmental Health: Recognizing and Preventing Disease and Injury, edited by Barry S. Levy et al. 5th ed. Philadelphia: Lippincott Williams & Wilkins, 2006.
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Types and Effects (Magill’s Medical Guide, Sixth Edition)
Carcinogens include chemicals, radiation, or viruses that can alter the deoxyribonucleic acid (DNA) in a normal human cell and eventually transform it into a cancer cell. Some carcinogens change DNA structure directly, while others make DNA more susceptible to damage from other sources or increase the possibility of DNA changes by causing cells to divide faster than normal.
Susceptibility to different carcinogens varies widely from person to person and is highly dependent upon genetic makeup, physiology, exposure time, dose of the carcinogen, and nutrition.
The Report on Carcinogens (RoC) released by the U.S. government in January, 2005, lists 246 cancer-causing agents. Of these carcinogens, 58 are known to produce cancer in humans, while 188 may very likely produce human cancer. For the first time, the list includes viral carcinogens, including hepatitis B virus (HBV), hepatitis C virus (HVC), and human papillomaviruses (HPVs). A list of carcinogens is also published by the International Agency for Research on Cancer (IARC).
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Classification and Reducing Risk (Magill’s Medical Guide, Sixth Edition)
Identification and classification of carcinogens is made from human observation and from laboratory studies that include animal experimentation and cell cultures. The RoC data include information about the ability of each substance to cause cancer, its ability to damage genes, and the biological changes that it can produce in the body. It also reports the potential for human exposure to the listed substances and the federal regulations that are imposed to limit exposure.
A number of important measures can lower the risk of exposure to carcinogens. Avoiding cigarette smoking, excessive alcohol consumption, and abnormal exposure to ultraviolet (UV) radiation from sunlight reduces the risk of many cancers. Being informed about carcinogens that may be present in the workplace or in the home and exercising necessary precautions with them provides protection. It is very important to follow the directions on any chemical containers.
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
The identification of carcinogens dates back to the 1930’s when dozens of substances, including industrial and tobacco smoke, were classified as carcinogens. U.S. federal law requires that the secretary of Health and Human Services publish the RoC through the National Toxicology Program (NTP) every two years. In addition to listing carcinogens, the IARC report also lists substances that have been studied and determined not to be carcinogens.
Recent RoC and IARC reports indicate that acrylamide, a chemical in french fries and potato chips, is a possible carcinogen, as well as the charred residue on barbecued meats. The Food and Drug Administration (FDA) reported that in a test of 124 cosmetics, over half of them contained the carcinogens triethanolamine (TEA) and diethanolamine (DEA). Not all carcinogens can be absolutely avoided. For example, tamoxifen, used effectively in the treatment of breast cancer, increases the risk of some types of uterine cancer.
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Benigni, Romualdo, ed. Quantitative Structure-Activity Relationship (QSAR) Models of Mutagens and Carcinogens. Boca Raton, Fla.: CRC Press, 2003.
McKinnell, Robert Gilmore, ed. The Biological Basis of Cancer. 2d ed. New York: Cambridge University Press, 2006.
Milman, Harry A., and Elizabeth K. Weisburger, eds. Handbook of Carcinogen Testing. 2d ed. Park Ridge, N.J.: Noyes, 2001.
Pohanish, Richard P., ed. Sittig’s Handbook of Toxic and Hazardous Chemicals and Carcinogens. Vols. 1 and 2. 5th ed. Norwich, N.Y.: William Andrew, 2008.
Weinberg, Robert. The Biology of Cancer. New York: Garland Science, 2007.
(The entire section is 85 words.)