Answer to Question #12725 Submitted to "Ask the Experts"

I live in a two-story home with a sealed basement crawl space. The radon measurement on the first floor (above the basement) is generally about 70 becquerels per cubic meter (Bq m^-3) with mitigation and about 300 Bq m^-3 without. I do not know what the basement measurement is. For several years now, I have stored objects, including baby clothing, in the basement. My wife and I are expecting twins, and I recently brought up the clothes and other items to the first floor. Is the clothing safe to use? I know that radon decays quickly into non-noble products that can attach themselves to solid objects and that these decay products are not healthy. But I'm confused as to what happens to these decay products. Are they likely to stay on clothing? Should I discard the objects from the basement? Is lead-210 (²¹⁰Pb) harmful like "regular" lead is considered harmful? Thank you.

Your concern is understood and very much appreciated, given that the levels of radon in your basement are unknown, and therefore the amount of radon decay products that may have attached to clothing or other objects stored in the basement is of concern. However, you do not need to be overly concerned about the health risk from radon decay products that may have attached themselves to clothing or other objects you have or in the future may wish to bring upstairs into the living areas of your home. The levels of radon that have been measured upstairs, (including prior to mitigation) are not very high relatively, and along with what might be measured in the basement, these levels may be indicative of the positive influence of the sealed crawl space. Radon concentrations at these levels should not unto themselves be a cause for concern relative to production of the decay products. Here is why.

The Science of Radon Decay Products

Radon-222 (²²²Rn), as we most commonly experience in our homes, as you are apparently aware, is an inert gas. This means it does not react very well with anything. When we breathe it in, most of it gets breathed out without interacting with our lung tissues. However, several of the decay products of radon (we refer to them as radon progeny), are particulates (like very small dust particles) that can attach themselves to lung surfaces, delivering a radiation dose from the alpha particles that the radon progeny emit. Accordingly, for naturally occurring radon gas in our homes, the radiation dose (and therefore the health risk) isn't really from the gas itself but from these progeny that the radon atoms turn into. These are particles of other types of atoms that the radon atoms become when they decay because of their physical (atomic) properties.

The Importance of the Science to Your Situation

Although this might sound concerning, in your situation it would not be for several reasons:

1. The amount of radioactivity associated with the progeny particles can never be more than the amount of radioactivity associated with the radon gas parent. This is a basic condition (or rule) of physics that we call secular equilibrium that is applicable to the relationship between radon and its progeny. Accordingly, the radon in air measurements you have made in your house, assuming the levels in the basement are not many times higher, suggests that the amount of particulate progeny that are available to attach to clothing is also quite small.
2. The particulate radon progeny that emit alpha particles and are therefore of greatest concern to producing a radiation dose to the lungs have very short half-lives. The half-life of a radioactive atom is the time it takes 50% of the atoms to decay into another atom (the next progeny in the chain). Virtually 100% of the alpha-emitting radon progeny, once removed from the radon source (removed from the basement), would be essentially all decayed away (gone) within a day or two. As you are aware, these short-lived, alpha-emitting progeny initially decay into a radioactive form of lead (²¹⁰Pb) with a half-life of 22 y, which poses a very low radiation risk but ultimately decays into a stable form of common lead, (²⁰⁶Pb). But the amounts of lead we are talking about are tiny: 1 Bq of radioactivity = a single atom decaying every second.
3. The radon concentrations you have measured in your home are, in relative terms and even before mitigation, not very high. According to the National Council of Radiation Protection and Measurements (NCRP 2009), the average indoor radon concentration in US homes is about 46.3 Bq m^-3. As a point of comparison, it is not uncommon in the United States for natural radon levels in our homes to be near or in excess of the US Environmental Protection Agency's (EPA) recommended 4 picocurie per liter (pCi L^-1) standard (or 150 Bq m^-3; EPA 2013.¹ Note that your current radon measurement of about 70 Bq m^-3 is well below the EPA recommendation. About 6% of homes in the United States exceed the EPA-recommended concentration (Marcinowski et al. 1996), and the Colorado Department of Public Health and Environment estimates that over 50% of the homes in Colorado exceed EPA's 4 pCi L^-1 recommendation.
4. In the US EPA's guidance for radon in homes (EPA 2013), it is recognized that most of the radiation dose comes from the radon progeny (particles), not from the radon gas itself, and it is assumed that in a typical home with average ventilation, the concentration of the progeny particles would be about 50% of the radon gas. So in your case, if we assume the 300 Bq m^-3 measurement prior to mitigation was also typical in the basement with a sealed crawl space, this would result in an estimate of 150 Bq m^-3 (50%) of each of the two alpha-emitting progeny, polonium-218 (²¹⁸Po) and polonium-214 (²¹⁴Po). Is this a lot? No it isn't—as a frame of reference, there are about 0.04–0.08 Bq per gram (Bq g^-1) each of naturally occurring radioactive uranium, thorium, radium, and radon progeny in typical soil (NCRP 2009), so there are several becquerels of naturally occurring radioactivity in just a handful of soil from almost anywhere in the United States.

Conclusions

The radon levels as measured in your first floor, although originally somewhat higher than EPA's recommendation prior to mitigation, are common in many locations in the United States and do not pose an undue risk from the amount of progeny particulates that could be associated with this radon concentration (about 50% of the radon radioactivity according to EPA). Additionally, the radon particulate progeny that pose the greatest risk because they emit alpha particles have very short half-lives and will decay (be gone by changing into another type of atom) after a day or two of having been removed from the basement. So even if the radon gas concentrations in the basement are many times higher than you originally measured in the living areas, still no worries. If you have any concern, wait a day or two before using the clothing after removing it from the basement. And with regard to your concern about the health hazard from lead, remember how small these units of radioactivity are: 1 Bq of radioactivity = 1 atom decaying each second, so the amount of lead resulting from this decay is miniscule.

Steven H. Brown, CHP

References

Colorado Department of Public Health and Environment. Understanding radon [online]. Available at https://www.colorado.gov/pacific/cdphe/understanding-radon. Accessed 27 November 2018.

Marcinowski F, Lucas RM, Yeager WM. National and regional distributions of airborne radon concentrations in US homes. Health Phys. 66(6):699–706; 1994.

National Council of Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States. Bethesda, MD: NCRP; NCRP Report 160; 2009.

US Environmental Protection Agency. Home buyer's and seller's guide to radon. Washington, DC: EPA; EPA 402/K-13/002; 2013. Available at https://www.epa.gov/radon/home-buyers-and-sellers-guide-radon. Accessed 27 November 2018.