This fact sheet answers the most frequently asked health questions about radon. For more information, you may call the ATSDR Information Center at 1-888-422-8737. This fact sheet is one in a series of summaries about hazardous substances and their health effects. This information is important because this substance may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present.

Radon is a naturally occurring radioactive gas that is odorless and tasteless. It is formed from the radioactive decay of uranium. Uranium is found in small amounts in most rocks and soil. It slowly breaks down to other products such as radium, which breaks down to radon.

Radon also undergoes radioactive decay. It divides into two parts-one part is called radiation, and the other part is called a daughter. The daughter, like radon, is not stable, and it also divides into radiation and another daughter. The dividing of daughters continues until a stable, nonradioactive daughter is formed. During the decay process, alpha, beta, and gamma radiation are released. Alpha particles can travel only a short distance and cannot travel through your skin. Beta particles can penetrate through your skin, but they cannot go all the way through your body. Gamma radiation can go all the way through your body.

Radon is no longer used in the treatment of various diseases including cancer, arthritis, diabetes, and ulcers. Radon is used to predict earthquakes, in the study of atmospheric transport, and in exploration for petroleum and uranium.

• Radon enters the environment from the soil, from uranium and phosphate mines, and from coal combustion.
• Radon has a radioactive half-life of about 4 days; this means that one-half of a given amount of radon will decay to other products every 4 days.
• Some of the radon produced in the soil will move to the surface and enter the air.
• Radon daughters attach to dust and other particles in the air.
• Most of the radon will remain in the soil.
• Radon also moves from the soil and enters the groundwater.

• Radon is found at very low levels in outdoor air.
• It is found at higher levels in indoor air in homes, schools, and office buildings.
• Cracks in the basement or foundation of a home may allow higher levels of radon inside the home.
• Indoor radon levels are affected by the radium and uranium levels in soil, the porosity of the soil, the composition and condition of the foundation materials, and the ventilation rate of the room.
• Miners, particularly those who mine uranium and hard rock, are exposed to higher levels of radon.
• Radon is found in drinking water and may be higher in well water.

Exposure to high levels of radon may result in an increased incidence of lung diseases, such as emphysema and pulmonary fibrosis. These diseases have been seen at a higher rate than normal among underground miners who were also exposed to arsenic, silica dust, diesel fumes, and cigarette smoke. Lung disease has been reported to increase with increasing exposure to radon and cigarette smoking.

Effects on the lung have also been seen in animals exposed to radon.

People exposed to high levels of radon have an increased incidence of lung cancer.

Radon in human tissues is not detectable by routine medical testing. However, several of its decay products can be detected in urine and in lung and bone tissue. These tests cannot tell how much radon you were exposed to, nor can they be used to predict whether you will develop harmful health effects.

The EPA has set a guideline for radon in air inside homes of 4 picocuries per liter (4 pCi/L) of air.

The EPA has also set a standard of 20 picocuries per square meter per second (20 pCi/m²/sec) for emissions of radon-222 (a radon daughter) to the air from uranium mill tailings in non-operational piles.

The federal recommendations have been updated as of July 1999.

CAS: Chemical Abstracts Service.

Emphysema: A lung disease.

Millirem (mrem): A unit used to measure radiation dose.

National Priorities List: A list of the nation's worst hazardous waste sites.

Picocurie (pCi): A unit used to measure the quantity of radioactive material.

Pulmonary fibrosis: Formation of fibrous tissue in the lung.

Agency for Toxic Substances and Disease Registry (ATSDR). 1990. Toxicological Profile for radon. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.

ATSDR can tell you where to find occupational and environmental health clinics. Their specialists can recognize, evaluate, and treat illnesses resulting from exposure to hazardous substances. You can also contact your community or state health or environmental quality department if you have any more questions or concerns.

For more information, contact:

Agency for Toxic Substances and Disease Registry
Division of Toxicology
1600 Clifton Road NE, Mailstop F-32
Atlanta, GA 30333
Phone: 1-888-42-ATSDR (1-888-422-8737)
FAX:   (770)-488-4178
Email: ATSDRIC@cdc.gov