Radon (Salem Health: Cancer)
Exposure routes: Inhalation, ingestion
Where found: Uranium mines and mills, hard-rock mines, phosphate mines, granite formations, groundwater, soil, air, building materials
At risk: Workers in uranium mining and milling, workers in iron-ore and fluorite mining, general population exposed to indoor radon levels of 4 picoCurie per liter (pCi/L) or higher
Etiology and symptoms of associated cancers: Radon is the second leading cause of lung cancer after cigarette smoking and accounts for 15 percent of lung cancers worldwide. Most of the risk to humans is from inhaled radon daughters that can lodge in the lungs and emit energetic particles. Damage to epithelial cells in lung tissue can eventually lead to cancer. For smokers, the risk of lung cancer is even greater because of the synergistic effects of radon and smoking.
The deadliest of all cancers, lung cancer has an overall five-year survival rate of less than 15 percent. Radon-related lung cancers include squamous cell carcinoma, adenocarcinoma, and large-cell carcinoma. In its early stages, lung cancer may be asymptomatic or have nonspecific symptoms (weight loss, fatigue, and fever). By the time symptoms develop that are suggestive of the disease(chronic coughing, shortness of breath, hoarseness, bloody sputum, difficulty swallowing, wheezing, and chest pain), the cancer has usually spread to other...
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Radon (Encyclopedia of Environmental Issues, Revised Edition)
Unsafe levels of radon have been detected in structures built over soils and rock formations containing uranium. One of the radioactive products of uranium is radium, which decays directly to radon. Every 3 square kilometers (1.2 square miles) of soil to a depth of 15 centimeters (6 inches) contains about 1 gram (0.035 ounces) of radon-emitting radium. Certain regions across the United States and around the world contain comparatively high concentrations of radium in their rocks and soils. One such area is the Reading Prong, which stretches from southeastern Pennsylvania to northern New Jersey and portions of New York.
Three forms of radon are generated in the decay of uranium in rocks and soils. The potential health risks are posed by the radon isotope with an atomic mass of 222 (radon 222), which has a 3.8-day half-life. Radon 220 and radon 219 also form in rocks and soils, but these isotopes have half-lives of 56 seconds and 4 seconds, respectively. The shorter half-lives of these isotopes compared to radon 222 give them a much greater chance to decay within rocks and soils before they can become airborne; thus they are of lesser radiological significance.
Radon is chemically inert, and within its 3.8-day half-life, the gas can become airborne and enter buildings through small fissures in the foundations. Indoor radon levels are typically four or five times more concentrated than outdoor levels, because air dilution occurs in...
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Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Hill, Marquita K. “Pollution at Home.” In Understanding Environmental Pollution. 3d ed. New York: Cambridge University Press, 2010.
McKinney, Michael L., Robert M. Schoch, and Logan Yonavjak. “Air Pollution: Local and Regional.” In Environmental Science: Systems and Solutions. 4th ed. Sudbury, Mass.: Jones and Bartlett, 2007.
Pipkin, Bernard W., et al. Geology and the Environment. 5th ed. Belmont, Calif.: Thomson Brooks/Cole, 2008.
(The entire section is 60 words.)
Radon (Chemical Elements)
Radon is the last member of the noble gas family. The noble gases are the elements that make up Group 18 (VIIIA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to one another. The noble gases get their name because they are inactive chemically. They combine with other substances under only extreme conditions. Their tendency to avoid contact with other elements was seen by early chemists as "royal" or "noble" behavior. The noble gases are also called the inert gases.
Radon is a radioactive element. A radioactive element is one that gives off radiation and breaks down to form a different element. Radon is formed when heavier radioactive elements, like uranium and thorium, break down. In turn, radon breaks down to form lighter elements, such as lead and bismuth.
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Radon (Encyclopedia of Public Health)
Radon-222 and radon-220 (thoron) are invisible, inert, and odorless radioactive gases formed in the decay of uranium-238 and thorium-232, respectively. Uranium-238 and thorium-232 are radionuclides that are widely distributed in the earth's crust. The half-life of radon-222 is long enough (3.82 days) to enable appreciable quantities of this element to accumulate in the environment, whereas the half-life of radon-220 is so short (55 seconds) that it does not attain environmental concentrations that produce demonstrable biological effects. Radon-222, seeping out of the soil, is ubiquitous in outdoor air, where its concentration averages about 15 becquerels per cubic meter (5 Bqm-3 or 0.4 pCi/L). (The becquerel [Bq] and the curie [Ci] are units of radioactivity; 1 Bq = 1 disintegration per second, and 1 Ci = 3.7 1010disintegrations per second. Radon is measured in picocuries per liter of air [pCi/L] or becquerels per cubic meter [Bqm-3].) In indoor air, the concentration of radon tends to be much higher than in outdoor air, especially in poorly ventilated basements and underground mines, where it may exceed 1,000 Bqm-3 (20 pCi/L). Indoor levels may be increased substantially by the use of groundwater or well water containing elevated concentrations of radon.
The alpha particles emitted by radon outside the body do not penetrate the skin, and radon itself, like other inert gases, is breathed in and out of the lungs without interacting significantly with the surrounding tissues. Hence the biological effects of radon result from inhalation of its solid, short-lived, alpha-emitting decay products (principally polonium-218 and polonium-214), which deposit on the lining of the bronchial airway. The dose to internal organs from radon that is ingested in drinking water, even at high concentrations, is extremely low.
In humans and laboratory animals, the risk of lung cancer increases with increasing exposure to inhaled radon and its short-lived decay products. In underground miners the risk appears to increase in proportion to the total cumulative dose to cells lining the airway, and to be about two times higher in smokers than in nonsmokers. The risk from exposure to residential indoor radon at a given concentration, although yet to be defined precisely, is generally estimated to be comparable to the corresponding risk in miners. As a result, radon is thought to be the single most important cause of lung cancer in nonsmokers and to cause 10 to 15 percent of all lung cancers, or 15,000 to 20,000 lung cancer deaths each year in the United States. Hence, the U.S. Environmental Protection Agency has recommended that indoor radon concentrations not be allowed to exceed 4 pCi/L, a concentration that might be expected to double the risk of lung cancer if inhaled throughout an average lifespan.
Methods for reducing the concentration of radon and its decay products in indoor air include ventilation; air filtration; sealing of cracks in basement floors and walls; installation of a subslab exhaust system beneath the basement floor; and remediation of heavily contaminated groundwater or well water that is used for drinking, bathing, or showering. Radon can be measured in the home with a number of relatively inexpensive devices, which are available from some state and local governments as well as private firms. Pertinent information can generally be obtained from the local state radiation or the Environmental Protection Agency office.
ARTHUR C. UPTON
Eisenbud, M., and Gesell, T. (1997). Environmental Radioactivity: From Natural, Industrial, and Military Sources, 4th edition. San Diego, CA: Academic Press.
Harley, N. (2000). "Radon and Daughters." In Environmental Toxicants, 2nd edition, ed. M. Lippmann. New York: John Wiley and Sons.
National Academy of Sciences/National Research Council (1998). Health Effects of Exposure to Radon. Washington, DC: National Academy Press.
U.S. Geological Survey. The Geology of Radon. Available at .