Chemical Education Today
Report
Radon in Homes: Recent Developments by Charles H. Atwood
In the late 1980s and early 1990s, radon in homes was a national concern receiving attention in the national press as well as the scientific literature. A possible linkage of radon in mines with excess lung cancer occurrence in miners was proposed and investigated in several studies. A proposal that radon accumulation in home air could cause lung cancer was also examined (1–6). These studies were described in detail in this Journal (7). Over the intervening 14 years public awareness of radon hazards has been replaced with concerns about the health effects of smoking, breast cancer, and diet, but radon is still being generated in our homes. In fact, several recent developments in large scale case-control studies in North America and Europe have shown that a linkage between radon exposure and an increased incidence of lung cancer exists (8–10). In this paper, we shall examine how radon is formed and enters homes, why it is a radiological concern, see what light the recent case studies can shed upon the radon risk in our homes, and list some methods for detection and remediation in homes. Radon Gas: Formation, Accumulation, and Radiological Effects There are 28 known isotopes of radon all of which are radioactive. The most common radon isotopes occur as the decay products of the three natural radioactive families that begin with 232Th, 235U, or 238U. In these decay families, only gaseous radon is not a solid, which allows it to be introduced into the air. Any uranium-bearing soil such as granite, shale, phosphate, or pitchblende minerals will introduce radon into the surrounding air. Each of the decay series generates one radon isotope on the way to a stable lead isotope. However, only the 238U to 206Pb family generates a radon isotope with a half-life greater than one minute, 222Rn (t1/2 = 3.8 days). Shorter lived isotopes cannot migrate from the soil to air in appreciable amounts prior to their disintegration into solid decay products. It is safe to assume that essentially all indoor radon contamination comes from 222Rn (7). All houses have devices that exhaust interior air to the exterior: bathroom vents, exhaust fans, clothes dryers, and dishwashers as well as home heating, which creates the stack effect of “hot air rising”. These create a lower pressure in the interior of the house, drawing the radon from the air adjacent to the soil into the living space. Air beneath the house (in a crawlspace or beneath a concrete slab) enters the living space by passing through cracks in floors, air vents, etc. Our better insulated homes, designed to conserve energy, also restrict airflow with the exterior. Consequently, radon is trapped inside. This increases the probability that humans will ingest it in normal breathing. If the radioactive decay of 222Rn occurs while inside the lungs, solid aggregates of 218Po and subsequent members of this radioactive family are captured inside the lungs. The next four decays in the series occur quickly (longest t1/2 is 19.8 min) until 210Pb is reached. Alpha decay 1436
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… the larger the radon exposure, the greater the risk of lung cancer; no minimum exposure level exists that is free of risk.
of 210Pb to 210Bi has a t1/2 of 22 years. From a radiological viewpoint, alpha particle emitting nuclei trapped inside the bronchial walls or lung tissue is a source of considerable damage to cells and presumably a viable condition for the generation of lung cancers (7). Results of Recent Case Studies Research conducted on cell damage due to alpha-particle collisions has shown that a single alpha-particle collision inflicts permanent cell damage (11). Furthermore, the damaged cell can induce comparable damage to nearby cells in a bystander mutagenic effect (12). Consequently, the overall effect is greater than that expected from a single collision. Accordingly, it appears that radon exposure damage is amplified by this bystander effect (8). Determining a definite link of radon inhalation with enhanced risk of lung cancer is only possible in large-scale case studies involving accurate and reliable radon measurements for large numbers of lung cancer patients and control groups. In both North America and Europe, smaller studies were conducted and then the data were pooled to provide samples large enough for statistical analysis (10, 13). Both studies conclude that the dose–response relationship is linear and does not have a threshold (8). In other words, the larger the radon exposure, the greater the risk of lung cancer; no minimum exposure level exists that is free of risk. The European study concluded that lung cancer risk increased by 8.4% per 100 Bq/m3 (2.7 pCi/L) of increased radon concentration while the North American study concluded the risk increased by 11% per 100 Bq/m3 (8, 10, 13).1 According to the U.S. Environmental Protection Agency (EPA), the average home radon concentration in the United States is 48 Bq/m3 (1.3 pCi/L) (14). Thus the inhabitants of a home with a radon concentration of 148 Bq/m3 have approximately a ten percent increased chance of contracting lung cancer than the average. Radon exposure is second only to smoking as a cause of lung cancer in the United States. The EPA estimates that about 160,000 U.S. citizens die annually from smoking compared to about 21,000 from radon exposure. Of those 21,000 some 2,900 will have never smoked. The EPA recommends that any home with radon concentrations greater than 148 Bq/m3 (4.0 pCi/L) be remediated to reduce the radon concentration (14).
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Chemical Education Today
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Figure 2. Charcoal canister detectors. Photo courtesy of WPB Enterprises, Inc., Riegelsville, PA; used with permission.
Figure 1. Median living-area radon levels for counties in the contiguous United States. Map courtesy of the Radon Project, administered by Columbia University’s Statistics Department and Lawrence Berkeley National Laboratory; used with permission (16).
Determining and Remediating Your Home’s Radon Risk There are several simple steps that any individual can take to determine a home’s radon risk level. Several large research projects to determine the risk for a given geological area have been conducted. Their conclusions are accessible via the Internet. The U.S. Geological Survey has a geologic radon potential map available (15). Another excellent source is the Radon Project, developed by Lawrence Berkeley National Laboratory and Columbia University; their Web site generates a risk estimate based upon the county of residence as shown in Figure 1 (16). These sites can help you determine whether your state or county are in radon-rich areas of the U.S. Measuring radon levels in a home is both simple and relatively inexpensive. A short-term measurement of two to 90 days can be done using charcoal canisters that absorb the radon (Figure 2). After exposure, the canister is sealed and mailed to a lab where the associated alpha particles are measured. Other possibilities include alpha track detectors (pieces of plastic that have visible tracks left in them upon exposure to alpha particles) and electret ion detectors that measure the residual charge left by the passage of an alpha particle (Figure 3). Average cost of these measurements is typically less than $100. It is a good idea to perform these measurements during spring or summer as home heating during the winter raises the typical radon levels. If the short term measurements indicate radon levels greater than 148 Bq/m3 (4.0 pCi/L), a long-term test of greater than 90 days may be necessary. More information on home testing is available online from the EPA (17). In the unfortunate event that your home has excessive radon levels, remediation may be necessary to reduce the concentration to acceptable levels. Generally, this consists of sealing cracks in floors or slabs, sealing the entry points for pipes into the living area, and exhausting to the outside the air from crawl spaces or basements. This can be as simple as placing 1438
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Figure 3. Electret ion detector used by professional radon mitigation companies to measure long-term radon exposure. Photo courtesy of WPB Enterprises, Inc., Riegelsville, PA; used with permission.
Figure 4. Exterior view of a professionally installed radon mitigation system. Photo courtesy of WPB Enterprises, Inc., Riegelsville, PA; used with permission.
an exhaust fan in an exterior wall of the home’s crawl space (Figure 4). While costs vary considerably from region to region, the repair costs are typical for normal home maintenance except for homes with inordinately high radon levels. Conclusion Recent case studies conducted in North America and Europe have shown a definite link between home radon exposure and increased lung cancer. Increases in the radon concentration of 100 Bq/m3 is associated with approximately a 10% increased chance of contracting lung cancer. The risk increase is linear with radon concentration and does not have a threshold below which the risk becomes “safe”. Fortunately, there are readily available resources to help assess the associated radon risk in any region of the United States.
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Note 1. The Becquerel (Bq) and Curie (Ci) are units of radioactive decay. A Bq is defined as 1 disintegration per second and the Ci is 3.7 ⫻ 1010 disintegrations per second. One pCi/L equals 37 Bq/m3.
Literature Cited 1. Cross, F. T. Radon and Its Decay Products in Indoor Air, W. W. Nazaroff, W. W.; Nero, A. V., Eds.; Wiley: New York, 1988. 2. Clarke, R. M.; Southwood, T. R. E. Nature 1989, 338, 197– 198. 3. Nero, A. V. Phys. Today 1989, 42, 32–39. 4. Nero, A. V.; Schwehr, M. B.; Nazaroff, W. W.; Revzan, K. L. Science 1986, 234, 992–997. 5. Committee on the Biological Effects of Ionizing Radiations, National Research Council. Health Risks of Radon and Other Internally Deposited Alpha-Emitters, (BEIR IV); National Academies Press: Washington, DC, 1988. 6. Cohen, B. L. Health Physics 1986, 51, 175–183. 7. Atwood, C. H. J. Chem. Educ. 1992, 69, 351–355. 8. Samet, J. M. J. Toxicol. Environ. Health A 2006, 69, 527–531. 9. Field, R. W.; Krewski, D.; Lubin, J. H.; Zielinski, J. M.; Alavanja, M.; Catalan, V. S.; Klotz, J. B.; Letourneau, E. G.; Lynch, C. F.; Lyon, J. L.; Sander, D. P.; Schoenberg, J. B.; Steck, D. J.; Stolwick, J. A.; Weinberg, C.; Wilcox, H. B. J. Toxicol. Environ. Health A 2006, 69, 599–631. 10. Krewski, D.; Lubin, J. H.; Zielinski, J. M.; Alavanja, M.; Catalan, V. S.; Field, R. W.; Klotz, J. B.; Letourneau, E. G.; Lynch, C. F.; Lyon, J. L; Sander, D. P.; Schoenberg, J. B.; Steck, D. J.; Stolwick, J. A.; Weinberg, C.; Wilcox, H. B. J. Toxicol. Environ. Health A 2006, 69, 533–597. 11. Committee on the Biological Effects of Ionizing Radiation, National Research Council. Health Effects of Exposure to Radon, BEIR VI; National Academies Press: Washington, DC, 1999. 12. Hall, E. J.; Hei, T. K. Genomic Instability and Bystander Effects Induced by High-LET Radiation. Oncogene 2003, 22, 7034–7042. 13. Darby, S.; Hill, D.; Auvinen, A.; Barros-Dios, J. M.; Baysson, H.; Biochicchio, F.; Deo, H.; Falk, R.; Forastiere, F.; Hakama, M.; Heid, I.; Kreinenbock, L.; Kreuzer, M.; LaGarde, F.; Makelainen, I.; Muirhead, C.; Oberaigner, W.; Pershagen, G.; Ruano-Ravina, A.; Ruosteenjoa, E.; Rosario, A. S.; Timarche, M.; Tomasek, L.; Whitley, E.; Wichmann, H. E.; Doll, R. Br. Med. J. 2005, 330, 223–228. 14. The Web site of the U.S. Environmental Protection Agency has many useful publications on radon: http://www.epa.gov/iaq/ radon (accessed Aug 2006). 15. The radon potential map is at http://energy.cr.usgs.gov/radon/ usrnpot.gif (accessed Aug 2006). 16. The map showing risk or radon in the continental U.S. is available at http://www.stat.columbia.edu/~radon/ (accessed Aug 2006). 17. The EPA has information about home testing for radon: http:// www.epa.gov/radon/pubs/citguide.html (accessed Aug 2006).
Charles H. Atwood is in the Chemistry Department, University of Georgia, Athens, GA 30602;
[email protected] www.JCE.DivCHED.org
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