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Air Quality - Radon Fact Sheet Environmental Health 303-271-5700
Radon is a cancer-causing, radioactive gas. It is colorless, odorless, and tasteless. When a person breathes radon, they increase their chances of getting lung cancer. In fact, the U.S. Surgeon General has warned that radon is the second leading cause of lung cancer in the U.S. today. Radon comes from rocks, soil, and well water that contain uranium and radium. Radon is found throughout the United States, and is particularly prevalent in Colorado. The U.S. EPA has ranked Colorado as a Zone 1 area, which means that the average house will probably exceed the EPA's action level for indoor radon. Testing for radon is easy and inexpensive. Having a radon mitigation system installed by a National Environmental Health Association (NEHA) or National Radon Safety Board (NRSB) listed contractor usually costs between $700 and $1,200. Radon is produced as a decay product from uranium and radium. This naturally occurring radioactive gas is found in most soil and rock, and in most ground water. All buildings contain some radon as does outdoor air, although at very low levels. Since radon is a gas and is an inert element, it can easily travel through cracks and pores, without being chemically bound or attached to other elements. Voids and porous materials are found under every building, allowing easy entry for radon. The radioactive decay process begins with uranium. Uranium decays through several intermediate elements to produce radium and radon. The following diagram illustrates this process: U238 Ra226 Rn222 Po218 Pb214 Bi214 Po214 Pb210 The decay products from radon are called radon decay products (RDPs) or progeny. These progeny are solids; only radon is a gas. Radon has a half-life of 3.8 days, which means half of the element will decay into RDPs in that time. The RDPs are different from radon in that they are short-lived (less than 30 minutes), they have a static charge, they are chemically reactive, and are solid particles, which act as aerosols in the air. Radiation from radon and its RDPs is measured in picocuries per liter (pCi/L). For measurement, most experts assume a .5 ER which means that ½ the RDPs plate out (attach) to solid objects such as walls, and ½ of the RDPs are in aerosol form, available for inhalation. Radon is a known human carcinogen. As early as the 1400s, lung disease was associated with metal mining in Eastern Europe. In the 1800s, lung cancer was being reported in miners in this same region. A study of uranium miners on the west slope of Colorado in the 1950s and 1960s, determined RDPs caused lung cancer. Radon was found in homes built with radium containing materials and built on uranium mill tailings in the 1960s,. In the 1980s, many homes were found to contain naturally occurring radon. Radon and the RDPs are inhaled and the RDPs attach to the lung lining. Here they decay emitting high-energy alpha particles. The main culprits in the RDPs are Polonium?218 and Polonium-214, both of which emit alpha particles. The alpha particles can damage the cells DNA, which can lead to lung cancer. This is why exposure to radon and its progeny doesn't mean you will contract cancer, it means that you have an increased risk of getting cancer. In 1986, the United States Environmental Protection Agency recommended that all homes be tested for radon. In 1987, the National Institute for Occupational Safety and Health recommended that exposure for underground miners be reduced from 4 WLM to 1 WLM per year. In 1988, the United States Congress enacted the Indoor Radon Abatement Act, which set a national goal the reduction of radon in buildings to the ambient level of outdoor air. As a result, EPA set an action level of 4 pCi/L for indoor radon. EPA recommends that if radon is found above 4 pCi/L, you should fix your home. There is still some risk at level below 4, and EPA suggests that people may want to mitigate their homes to get them as close to ambient outside air as possible (outside air has approximately 0.4 pCi/L). Comparison of International Radon Action Levels
Radium containing soil, rock, well water and building materials produce radon. Elevated levels of radon in structures depends upon:
In most buildings 95% of the radon entering the structure comes from the rock and soil under it. The radon is pulled into the building by air pressure differentials. These differentials are created by natural and mechanical ventilation. Natural ventilation occurs because of stack effect (hot air rising in the home), wind, and temperature differences between inside and outside air. Rain and low barometric pressure can also increase radon entry. Exhaust fans in the home, as well as negative pressure relative to the outdoors caused by heating systems also increase radon entry. Because of these factors, radon varies constantly, both daily and seasonally. The highest levels are expected in the winter, while in the summer, with windows and doors open, we would expect lower concentrations. Well water and building materials may cause radon in homes, but usually account for less than 5% of the radon that enters. Even though the biological effect of radon is caused by RDPs, radon gas is usually measured, rather than RDPs. This is because there are fewer variables in radon measurements, since gas concentration is not affected by circulation or plate out, it is easier to make time-weighted measurements of radon gas, and radon gas measurements are a good indicator of RDPs. There are three basic methods of sampling for radon:
The most common measurement method is time-integrated sampling, where a device is exposed to the radon gas for a measured amount of time. Charcoal canisters and alpha-track devices are typical of passive devices used in most homes. Charcoal devices are usually left out for 2 to 7 days, then sealed up and sent to a laboratory where they are analyzed. Alpha-track devices are usually left for longer periods, typically three months to one year. Both types are simple and inexpensive to use. Continuous monitors and grab sampling usually require expensive, complex electronic equipment. These require constant calibration to maintain accuracy. Professionals and scientists doing research use this type of equipment. For short-term devices, the following protocols should be followed:
Results of the test, if above 4 pCi/L, should be verified by either deploying a second device in the same location, or deploy a long-term device. The National Environmental Health Association (NEHA.org) and the National Radon Safety Board (NRSB.org) lists people who have taken a course and passed an exam based on measurement protocols and theory. These lists are available from their respective web sites or from the Colorado Department of Public Health and Environment. Radon mitigation can be accomplished by mitigating one or more of the following factors:
Of these, controlling radon transport by pressure driven entry is the most common mitigation technique used in Colorado. This is called Active Soil Depressurization (ASD). This technique creates a suction or area of low pressure beneath the structure that is stronger than the partial vacuum applied to the soil by the building. ASD systems are comprised of pipes connected to a fan, which draws gasses from under the building. Radon is captured and vented to the outside before it has a chance to enter the home. Several types of ASD systems exist:
All of these ASD systems require expert installation, additional sealing of openings into the home, and of course, testing to verify that radon levels have been reduced to below 4 pCi/L. Details of design, location, installation, and safety precautions are available in the manual "Protecting Your Home From Radon," D.L. Kladder and Associates., Colorado Vintage Companies, Colorado Springs, CO. This manual is available in all Colorado public libraries, and is also available at the Jefferson County Department of Health and Environment. Professional radon mitigators, like those doing measurements, are also listed by NEHA and NRSB. Soil gas is the largest natural source of radon in homes, however well water can be a significant factor if dissolved radon at high concentrations is found. It takes high levels of radon in water to result in significant elevation of radon in air. The EPA uses a "rule of thumb" of 1:10,000. That is, if you have 10,000 pCi/L of radon in water, you might increase indoor radon concentrations by 1 pCi/L. Recent studies have indicated that elevated levels of radon in water are not only an inhalation threat, but may be an ingestion hazard as well, increasing the risk of stomach cancer. In 1992, EPA proposed a maximum contaminant level (MCL) of 300 pCi/L for public water supplies. At this time, this MCL has not been promulgated. There is also an alternate MCL being proposed, of 4,000 pCi/L, but what the water supplier has to do to be eligible to qualify for this has not been established. As a result of these proposed MCLs, radon may become the most common treated-for contaminant in well water. Radon in well water in Colorado averages well above the proposed MCL. Treatment for Radon in Water There are three recognized treatment methods to remove radon from water:
Water storage until the radon decays is somewhat impractical, since it takes 27 days for radon to decay (99%). For a typical family of four using 300 gallons of water per day, they would need 8,100 gallons of storage. A tank this large is impractical and expensive. Aeration is a preferred method of treatment for radon in water. As the water is aerated, radon is released and piped outside. This method requires another pump to pressurize the pressure tank, a radon fan, and biological treatment of the aerated water, as it may be contaminated by the air used for aeration. Granular activated carbon (GAC) removes radon in water by adsorbing the radon onto the carbon. However, gamma radiation results from the RDPs that accumulate in the filter. The filter needs to be shielded or remotely located to prevent radiation hazards to the occupants.
Last Modified: Jun 8, 2009 01:29 PM |
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