Answer to Question #12071 Submitted to "Ask the Experts"

I don't think that our radon mitigation system was working very well for maybe around six years, and it may not have been working at all for some time. If you are exposed for five years or so to higher-than-optimal levels of radon (but not off-the-chart numbers), but then you fix the situation and are exposed to levels that are low enough not to be considered a big risk for most of the rest of your life, can your lungs repair themselves the way that lungs can repair themselves from the effects of smoking many years after you quit? Or do the radon particles lodge themselves in your lungs and just stay there for the rest of your life? Also, does that same exposure over six years result in a higher level of radiation (and therefore higher risk of lung cancer) for children?

I know that one of the things that radon decays to is lead. Could a serum lead test help to indicate if a child or adult was recently exposed to radon, especially if you know that there weren't other sources of exposure (like lead in paint or water)? I know that some of this is probably dependent upon the level and time of radon exposure.

Briefly, your cumulative exposure to radon determines your potential risk of lung cancer. For this reason, I applaud your decision to install and maintain a radon mitigation system. I gather from your question that you have taken a measurement recently that has caused you to be concerned that your system is not working properly.

As I noted, the risk of lung cancer from exposure to radon (actually the radioactive decay products of radon, commonly called radon daughters or radon progeny) depends on the cumulative exposure over a lifetime. The risk factors have been estimated based on epidemiologic studies of underground miners and residential indoor exposures. With regard to your question about repair over time, there is some indication from uranium miner studies that the lung cancer risk decreases somewhat with the time since exposure, indicating the possibility of repair (Tomasek 2002; NCRP 1984). The National Academy of Sciences/National Research Council (NAS/NRC) was tasked with reviewing the epidemiologic studies. The risk models in their report, Health Effects of Exposure to Radon (the BEIR VI Report) (NAS/NRC 1999), included factors to account for a decrease in risk with time since exposure. The model was based on underground miner exposures. However, residential radon epidemiological studies, with lower cumulative exposures, have not reported a decrease in risk with time since exposure.

With regard to the risk from exposure during childhood, the BEIR VI Report states that there is "no clear indication of the effect of age at exposure" (NAS/NRC 1999). Therefore, in calculating risks from lifetime exposure, the risk models did not adjust specifically for exposure at earlier ages. The report does include a small adjustment for exposure to infants. Since most of the studies of the risk from radon involved underground miners, nearly all of whom were adults exposed at high levels relative to residential exposures, it would have been difficult to identify a specific risk for exposure in childhood. No such effect has been reported in the studies of lung cancer risk from residential radon exposure.

The decay products of radon (radon progeny) that are deposited in the lung have relatively short half-lives ranging from less than a millisecond (0.000164 seconds) to about 27 minutes; therefore, they emit radiation for only a short period of time, about three to four hours. However, the damage done to the cells persists and may result in an increased risk of lung cancer. As you noted, radon decays through a series of radioactive progeny to stable lead (lead-206 or ²⁰⁶Pb). The number of atoms of ²⁰⁶Pb resulting from the radioactive decay of radon or radon progeny in the body is so small that no increase in lead concentration would be detectable.

The bottom line is that cumulative radon exposure determines the potential risk of lung cancer. It should be noted, however, that since radon risk is multiplicative with the risk from smoking, tobacco use is, by far, the primary factor in lung cancer risk from radon. That is, smoking multiplies the risk from radon; therefore, if the risk of lung cancer from smoking is reduced, the risk from radon is also reduced.

Janet A. Johnson, PhD, CHP, CIH

References
National Academy of Sciences/National Research Council (NAS/NRC). Health effects of exposure to radon. Washington, DC: National Academy Press. BEIR VI Report; 1999.

National Council on Radiation Protection and Measurements (NCRP). Evaluation of occupational and environmental exposures to radon and radon daughters in the United States. Bethesda, MD: NCRP; NCRP Report No. 78; 1984.

Tomasek L. Czech miner studies of lung cancer risk from radon. J Radiol Prot 22:A107–A112; 2002.