Radon is a naturally occurring colorless, odorless, tasteless radioactive gas that is formed from the normal radioactive decay of uranium. Uranium is present in small amounts in most rocks and soil. It slowly breaks down to other products such as radium, which breaks down to radon. Some of the radon moves to the soil surface and enters the air, while some remains below the soil surface arid and enters the groundwater (water that flows and collects underground). Uranium has been around since the earth was formed and has a very long half-life (4.5 billion years), which is the amount of time required for one-half of uranium to break down. Uranium, radium, and thus radon, will continue to exist indefinitely at about the same levels as they do now.
Radon also undergoes radioactive decay and has a radioactive half-life of about 4 days. This means that one-half of a given amount of radon will be changed or decayed to other products every 4 days. When radon decays, it divides into two parts. One part is called radiation, and the second part is called a daughter. The daughter, like radon, is not stable; and it also divides into radiation and another daughter. Unlike radon, the daughters are metal and easily attach to dust and other particles in the air. The dividing of daughters continues until a stable, nonradioactive daughter is formed. During the decay process, alpha, beta, and gamma radiations are released. Alpha particles can travel only a short distance and cannot go through your skin. Beta particles can penetrate your skin, but they cannot go all the way through your body. Gamma radiation, however, can go all the way through your body. Thus there are several types of decay products that result from radon decay.
Since radon is a gas and radon daughters are often attached to dust, you are exposed to them primarily by breathing them in. They are present in nearly all air. However, background levels of radon in outdoor air are generally quite low, about 0.003 to 2.6 picocuries of radon per liter of air. A picocurie is a very small amount of radioactivity equal to one quintillionth (1/1018) of an ounce of radon. In indoor locations, such as homes, schools, or office buildings, levels of radon and daughters are generally higher than outdoor levels. Indoor radon levels are generally about 1.5 picocuries radon per liter of air. Cracks in the foundation or basement of your home may allow increased amounts of radon to move into your home. You may also be exposed to radon and daughters by drinking water obtained from wells that contain radon. Average levels of radon in groundwater are about 350 picocuries of radon per liter of water. However, most radon in water is rapidly released into the air and can be breathed in. In some areas of the country the amount of uranium and radium in some rock types, such as phosphate or granite, is high. In these areas radon levels in outdoor air or in groundwater will generally be higher.
Pathways in the body
Radon and its radioactive daughters can enter your body when you breathe them in or swallow them. By far, the greater amounts are breathed in. Most of the radon is breathed out again. However, some radon and most of the daughters remain in your lungs and undergo radioactive decay. The radiation released during this process passes into lung tissue and is the cause of lung damage. Some of the radon that you swallow with drinking water passes through the walls of your stomach and intestine. After radon enters your blood stream most (greater than 90%) of the radon goes to the lungs where you breathe most of it out. This occurs very shortly after it is taken in. Any remaining radon undergoes decay.
Radon that does not go to the lungs goes to other organs and fat where it may remain and undergo decay. There is very limited information on whether radon gas can penetrate the skin, but some radon may be able to pass through the skin when you bathe in water containing radon.
Long-term exposure to radon and radon daughters in air increases your chances of getting lung cancer. When exposures are high, noncancer diseases of the lungs may occur, such as thickening of certain lung tissues. While noncancer health effects may occur within days or weeks after exposure to radon, it will be several years before cancer effects become apparent. This is known from studies of workers exposed to radon in mines, primarily uranium miners, and from tests on laboratory animals. Although radon is radioactive, it gives off little gamma radiation. Therefore, harmful health effects from external exposure (when the chemical does not come into direct contact with your body) are not likely to occur. In addition, it is not known if radon causes health effects other than to the lung. Also, the effects of drinking water or eating food containing radon are not known.
In studies of uranium miners, workers exposed to radon levels of 50 to 150 picocuries of radon per liter of air for about 10 years have shown an increased frequency of lung cancer. Although there is some uncertainty as to how much exposure to radon increases your chances of getting lung cancer, the greater your exposure to radon, the greater your chance of developing lung cancer. Even small exposures may increase your risk of developing lung cancer, especially if you smoke cigarettes. There is no information on the effects of radon if you drink water or eat food containing radon.
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, however, are not generally available to the public and are of limited value since they cannot be used to accurately determine how much radon you were exposed to, nor can they be used to predict whether you will develop harmful health effects.
Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Agency for Toxic Substances and Disease Registry. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Agency for Toxic Substances and Disease Registry should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.