Environmental Contamination: Radon

Radon is a colorless, odorless, and tasteless radioactive gas produced from the decay of the element radium, itself a decay product of uranium. Because trace amounts of radium are present in most rocks and soils, radon exists nearly everywhere in the world as a soil gas and groundwater contaminant. Because [Page 175]it is a gas, radon can travel easily in the earth, between soil and rock particles. It enters houses through cracks and openings in foundations walls and floors when those buildings come under negative pressure, a situation caused when air leaves a building and must be replaced.

Air leaves a building in several ways. The most common is the stack effect. As warm air rises in a structure, it escapes through cracks and other openings around windows, doors, and spaces between dissimilar building materials. As that air leaves, it creates suction pressure on the structure's lower levels, including those in contact with the ground. This same pressure occurs when interior air is used as combustion air for furnaces, boilers, and other space conditioning equipment. That air eventually leaves a building through a chimney or other vent. Exhaust fans create the same effect. Radon can also enter a house through the water supply, from which it can be released into house air through aeration at faucets, shower heads, and water-using appliances.

Radon is a health concern because it continues to decay into solid radioactive elements, referred to as radon decay products or progeny, which can become attached to dust and other particles in the air and then be inhaled. Radiation released by radon decay products that become lodged in lung tissue is considered to be the cause of over 20,000 deaths annually in the United States. Risks of developing lung cancer from radon exposure are much higher for smokers than for nonsmokers.

Radon concentrations are usually expressed in radiation units known as picocuries per liter of air (pCi/L). The U.S. Environmental Protection Agency (EPA) considers concentrations above 4 pCi/L as hazardous.

The presence of radon can be detected under different testing conditions and with a number of special devices. Activated charcoal canisters are typically used for short-term tests. Long-term tests can be conducted using alpha track detectors. Electronic devices are used for continuous radon measurements. Radon levels vary over time, and for this reason, long-term tests provide more reliable estimates of average concentrations in a building. Because radon levels vary within communities and even neighborhoods, testing is the only way to determine a particular home's radon level.

Steps taken to reduce indoor radon levels are referred to as mitigation measures, which in some cases consist of procedures as simple as sealing cracks in floors and walls. In other cases, special ventilation systems that draw soil gas from beneath concrete slabs and then expel the gas to the outdoors are used. This approach is referred to as sub-slab depressurization and consists of plastic pipe and exhaust fans. Costs for these systems can be minimal if they are installed at the time houses are constructed.

No reliable method exists for testing a site for radon gas and using the test results to predict radon levels in a structure to be built there. Although the site could be characterized with tests, modifications made to the site during construction are likely to change its characteristics. In addition, the depth at which tests are conducted may prevent the identification of problem spots. However, widespread awareness of radon gas has caused both builders and buyers alike to seek assurances that new homes will be free of this environmental hazard. To address this concern, radon-resistant construction features can be included in the design and construction of new homes. If implemented during construction, these measures add little to building costs. Some states and localities have mandated the use of radon-resistant construction features through provisions in building codes.

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