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Infrequently Asked Questions

Radon and Indoor Air Program

Why is 4 pCi/L the recommended action level for Radon?

The U.S. Environmental Protection Agency (EPA) recommended this action level in 1986 for several reasons. First, at lower levels (< 2 pCi/L) measurement devices’ false negative errors increased threefold, and false positive errors increased twofold. Secondly, mitigation research indicates that elevated levels can be reduced to less than 4 pCi/L 95% of the time. Research shows that 2 pCi/L can be achieved 70% of the time. Further, today’s mitigation technology can reduce radon levels to between 2 and 4 pCi/L most of the time. Finally, cost benefit analysis performed in 1986 indicate that an action level of 4 pCi/L results in a cost of about $700,000 per lung cancer death saved. If the action level was set at 3 pCi/L, the cost would be $1.7 million, and if set at 2 pCi/L, the cost would be $2.4 million per lung cancer death saved. EPA states that 4 pCi/L is a recommended action level, yet homeowners can further reduce their potential lung cancer risk by mitigating homes that are below 4 pCi/L.

Does Radon break down and disappear from a building?

Radon does decay (break down); however, the ability for any given patch of land to produce a radon problem in a building placed on it is effectively constant during your life time.
Radon-222 is a radioactive element in the Uranium-238 decay chain. The 'parent' element to radon is Radium-226. While radon has a half-life of 3.8 days and thus decays out rather quickly, Radium-226 has a half-life of 1620 years. Any radon in the ground is continually being replenished by the decay of the radium in the soil. With a half-life of 1620 years, the amount of radium and the rate of radon production during an individual's life, or the design life expectancy of your average building, is effectively constant. Radon is constantly generated and available to enter and accumulate in buildings at high concentrations.

Is there any evidence on the health effects associated with radon?

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. The science on radon has been formidable over the years, but never before have we had such overwhelming scientific consensus that exposure to elevated levels of radon causes lung cancer in humans. In February of 1998, the National Academy of Sciences (NAS) presented the findings of their Biological Effects of Ionizing Radiation (BEIR) VI Report: "The Health Effects of Exposure to Indoor Radon." This new report by the NAS is the most definitive accumulation of scientific data on indoor radon. The report confirms that radon is the second leading cause of lung cancer in the U.S. and that it is a serious public health problem. The study fully supports U.S. EPA estimates that radon causes about 21,000 lung cancer deaths per year.

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., the lung cancer risk in miners has been documented at exposure levels comparable to those which occur in homes/residences. The scientific experts agree that the occupational miner data is a very solid base from which to estimate risk of lung cancer deaths annually. While residential radon epidemiology studies will improve what we know about radon, they will not supersede the occupational data.

Are there any residential epidemiology studies finding increased risk of lung cancer due to radon?

Yes, several residential epidemiology studies have found an increased risk of lung cancer due to residential exposures (i.e. Sweden, New Jersey, Iowa) These studies are also just pieces of a much bigger puzzle that is being put together. The National Academy of Sciences' Biological Effects of Ionizing Radiation (BEIR VI) Report examines in detail the available studies of radon and lung cancer in homes, as well as the studies of underground miners.

Why are residential epidemiology studies of radon so complicated?

There are many factors that must be considered when designing a residential radon epidemiology study. It is very expensive and often impossible to design a study that takes all the pertinent factors into consideration. These factors include:

■Mobility: people move a lot over their lifetime; it is virtually impossible to go back and test every home where an individual has lived;
■Housing Stock Changes: over time, older homes are often destroyed or remodeled, thus radon measurements will be non-existent or highly varied; a home's radon level may change, over time if new ventilation systems are installed, the occupancy patterns are substantially different, or the home's foundation shifts or cracks appear.
■Inaccurate Histories: often a majority of the lung cancer cases (individuals) being studied are deceased or too sick to be interviewed by researchers. This requires reliance on second-hand information which may not be as accurate. These inaccuracies primarily affect:
■Residence History: a child or other relative may not be aware of all residences occupied by the patient - particularly if the occupancy is distant in time or of relatively short duration. Even if the surrogate respondent is aware of a residence they may not have enough additional information to allow researchers to locate the home.
■Smoking History: smoking history historically has reliability problems. Individuals may under-estimate the amount they smoke. Conversely, relatives or friends may over-estimate smoking history.
■Other: complicating factors other than variations in smoking habits include an individual's: genetics, lifestyle, exposure to other carcinogens, and home heating, venting and air conditioning preferences.

Do I still need to test my home if I don't live in an area designated as a high radon zone?

Yes. The only way to know for sure if you have a radon problem, and to protect your family from radon, is to test your home. Various federal and state agencies have conducted radon surveys through the United States. In addition, the EPA has broken the state down into three zones according to their potential for high indoor radon levels, with Zone 1 having the highest radon potential. Homes in Zones 1 and 2 have a statistically higher chance of having elevated levels of radon. However, elevated levels of radon have been found in homes in many counties designated as low radon potentials (zone 3).