Radon - Frequently Asked Questions

  • Definitions of Radon

Radon is a gaseous radioactive element having the symbol Rn, the atomic number 86, an atomic weight of 222, a melting point of -71°C, a boiling point of -62°C, and (depending on the source, there are between 20 and 25 isotopes of radon - 20 cited in the chemical summary, 25 listed in the table of isotopes); it is an extremely toxic, colorless gas; it can be condensed to a transparent liquid and to an opaque, glowing solid; it is derived from the radioactive decay of radium and is used in cancer treatment, as a tracer in leak detection, and in radiography. (From the word radium, the substance from which it is derived.)  Sources: Condensed Chemical Dictionary, and Handbook of Chemistry and Physics, 69th ed., CRC Press, Boca Raton, FL, 1988. EPA's Integrated Risk Information System profile on Radon 222 [CASRN 14859-67-7] is located at: www.epa.gov/iris/subst/0275.htm

  • Sources of Radon

Earth and rock beneath home; well water; building materials.

  • What are the Health Effects From Exposure to Radon

No immediate symptoms. Based on an updated Assessment of Risk for Radon in Homes (see Figure 187) radon in indoor air is estimated to cause about 21,000 lung cancer deaths each year in the United States. Smokers are at higher risk of developing Radon-induced lung cancer. Lung cancer is the only health effect which has been definitively linked with radon exposure. Lung cancer would usually occur years (5-25) after exposure. There is no evidence that other respiratory diseases, such as asthma, are caused by radon exposure and there is no evidence that children are at any greater risk of radon induced lung cancer than adults.

  • What is  the Average Level of Radon Found in a Home?

Based on a national residential radon survey completed in 1991, the average indoor radon level is 1.3 picoCuries per liter (pCi/L) in the United States. The average outdoor level is about 0.4 pCi/L.

  • What's the Debate on Radon?

There is no debate about radon being a lung carcinogen in humans. All major national and international organizations that have examined the health risks of radon agree that it is a lung carcinogen. The scientific community continues to conduct research to refine our understanding of the precise number of deaths attributable to radon. The National Academy of Sciences BEIR VI Report has estimated that radon causes about 15,000 to 22,000 lung cancer deaths annually based on their two-preferred models.

A few scientists have questioned whether low radon levels, such as those found in residences, increase the risk of lung cancer because some small studies of radon and lung cancer in residences have produced varied results. Some have shown a relationship between radon and lung cancer, some have not. However, the national and international scientific communities are in agreement that all of these residential studies have been too small to provide conclusive information about radon health risks. Major scientific organizations continue to believe that approximately 12% of lung cancers annually in the United States are attributable to radon.

  • How do we know radon is a carcinogen?

The World Health Organization (WHO), the National Academy of Sciences, the US Department of Health and Human Services, as well as EPA, have classified radon as a known human carcinogen, because of the wealth of biological and epidemiological evidence and data showing the connection between exposure to radon and lung cancer in humans.

There have been many studies conducted by many different organizations in many nations around the world to examine the relationship of radon exposure and human lung cancer. The largest and most recent of these was an international study, led by the National Cancer Institute (NCI), which examined the data on 68,000 underground miners who were exposed to a wide range of radon levels. The studies of miners are very useful because the subjects are humans, not rats, as in many cancer research studies. These miners are dying of lung cancer at 5 times the rate expected for the general population. Over many years scientists around the world have conducted exhaustive research to verify the cause-effect relationship between radon exposure and the observed increased lung cancer deaths in these miners and to eliminate other possible causes.

In addition, there is an overlap between radon exposures received by miners who got lung cancer and the exposures people would receive over their lifetime in a home at EPA's action level of 4 pCi/L, i.e., there are no large extrapolations involved in estimating radon risks in homes.

  • Does the Auvinen Finnish Study Prove that Residential Radon Does Not Cause Lung Cancer?

No, the Finnish study by itself is too small with only 1055 subjects to provide any definitive proof. Scientists from the U.S. Public Health Service Agencies recently reviewed the radon risk assessment and the proliferation of small residential epidemiological studies like the Finnish study. They concluded that residential epidemiology studies would need a minimum of 10,000 to 30,000 lung cancer cases plus twice a many controls to adequately address this issue.

Clarification: The residential epidemiology study recently reported out of Finland, examined homes with low radon levels; the median indoor radon level was 1.8 picoCuries per liter (pCi/L) of air.

Dr. Jonathan Samet, chairman of the National Academy of Sciences BEIR VI Committee, responded to the Finnish study stating, "...by itself, the study is too small in size and consequently without sufficient statistical power to characterize precisely the risk of lung cancer associated with indoor radon. Consequently, the conclusions of the article are overstated and the authors judgment as to the implications of their findings, "Indoor radon exposure does not appear to be an important cause of lung cancer,"" is not supported by the evidence presented."

  • Why does it take so many cases to make residential radon epidemiology studies meaningful?

To have a reasonable certainty in the conclusions, many thousands of cases are required to detect the increased risk of lung cancer due to radon. This is because the more things that cause a disease the harder it is to separate one cause from another, thus it takes many cases to pinpoint the risk from each separate cause. The U.S. Public Health Service radon experts estimate that 10,000 to 30,000 cases, and twice as many controls would be needed to conduct a definitive epidemiologic study of residential radon lung cancer risk. The residential studies conducted to date have all included between 50 and 1500 cases and thus have been too small to provide conclusive information.

Some years ago this same process was used to detect an increased risk of lung cancer due to cigarette smoking. It took many years of study to make the positive link between the cause and effect of smoking and lung cancer. Most of the increased lung cancer risk is attributable to smoking through mathematical modeling. The research process for smoking was very laborious. However, radon's process is even more challenging because radon's contribution to increased lung cancer risk (12%) is difficult to see against the large background of lung cancer due to other causes, which include smoking, asbestos, some heavy metals and other types of radiation; i.e., detecting radon-related lung cancer is like trying to detect a 12% increase of sand on a beach already full of sand.

Finally, it is difficult to accurately determine radon exposures in residential settings since we are estimating past exposures from current measurements. The number of required study participants increases with the difficulty in determining the exposure.

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