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Radon and Lung Cancer
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13166 |
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Section : |
NATURAL SCIENCE
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| Issue
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11 / 1987 |
1,906 Words |
| Author
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Richard E. Toohey
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"Radon gas cited as cancer source."
"Your house may be a death trap."
Such alarming headlines have become commonplace over the past two years as public concern increases over the possible health hazards of radon in the home and workplace.
Radon is a radioactive gas naturally produced in minute quantities in soil and groundwater. Outdoors, it is too diluted to be harmful. When it seeps into modern, airtight buildings, however, it can become trapped and accumulate in potentially dangerous proportions. Radon is the single largest source of radiation exposure for the average person. It may rank second only to cigarette smoking as a cause of lung cancer in the United States.
Radon-222--a colorless, odorless, tasteless inert gas--is a naturally occurring radioactive element. It is continually produced from its parent, radium-226, which is present in trace amounts in all rocks and soil. Radium, in turn, is continually produced from uranium. Consequently, geological formations rich in uranium produce high levels of radon.
Radon is not chemically reactive, since it is in the same family as helium, neon, and argon, and it has a fairly long radioactive half-life (the time required for it to lose half its radioactivity) of 3.8 days. Thus, radon can move long distances through the soil in which it is produced and still remain radioactive. It may enter a house through cracks, drains, unpaved crawl spaces, and pipe openings, or it may be dissolved in groundwater. Unless the house is very well ventilated, the radon concentration can build to potentially hazardous levels.
Radon is measured in picocuries per liter of air. One picocurie (pCi) is equivalent to 2.22 radioactive atoms disintegrating (i.e., emitting radiation) every minute. The typical outdoor concentration of radon-222 is about 0.1 pCi per liter of air, and average indoor concentrations are thought to be 10 or 20 times high at 1 to 2 pCi/1.
Radon is a proven human carcinogen. In fact, a lung disease known as Joachimstaler Bergkrankheit was identified in miners in the Joachimstal region of Czechoslovakia in the 16th century by the physician Gerogius Agricola. The symptoms described are those of lung cancer, and it is now thought that the high radon levels in the mines were responsible. Modern data gathered in studies of uranium and other hard-rock miners worldwide clearly establish radon as carcinogenic, with lung cancer incidence at high exposure rates up to ten times normal levels.
Exposure Levels
Based on studies of cancer incidence in uranium miners, the Environmental Protection Agency established an upper limit of 4 pCi/1 as a guideline for indoor exposure to radon. Exposure to this amount of radon over a 50-year period may increase the risk of lung cancer to 2 percent. Indoor radon levels exceeding 10 to 20 pCi/1 are considered quite dangerous. The highest level observed to date occurred in a house in eastern Pennsylvania, which had a concentration of 2,700 pCi/1 in the basement.
The EPA estimates that 12 percent of
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