Radon Hazards in Nevada

Summer 1989

Radon is a colorless, odorless, tasteless radioactive gas that has been in the news a lot lately--it is the gas that has been shown to cause lung cancer in humans and has been found in high concentrations in the air in some homes in the United States. The most abundant isotope of radon, radon-222, forms by the decay of uranium isotope-238, which is found in some rocks of the Earth's crust and in soils derived from these rocks. If your home happens to be situated over or near any uranium-containing rocks or soils, radon can seep into your home through cracks and other openings in the foundation and accumulate inside the house, especially in the lower levels. If the radon concentrations in your home are high enough, and if you live in that house for a number of years, you run a higher risk of contracting lung cancer sometime during your lifetime than you would otherwise. (Actually, by itself, radon poses little danger to one's health, because, being a gas, once inhaled, it is usually immediately exhaled. Rather, it is two decay products of radon-222, polonium-218 and polonium-214, that are of the greatest health concern. Being solids, they can become lodged on tissue in one's airway, causing damage to nearby cells through their radioactivity.)

Even though much has been written about radon in the last few months, almost all published information is based on studies outside of Nevada, mostly in highly populated eastern states, where the health hazard of radon in indoor air was first recognized. Within Nevada, there has been some testing for radon by individuals and the American Lung Association of Nevada is collecting some indoor radon testing data (unpublished) in parts of the state. However, no uniform statewide survey of radon had been made until the Nevada Bureau of Mines and Geology undertook a study of its own this past winter.

This study, which is nearing completion, has two objectives. The first and primary objective is to determine whether radon poses a health hazard to the citizens of Nevada by accumulating in homes anywhere in the state at levels exceeding the Environmental Protection Agency's (EPA) recommended guideline for remedial action (action level) of 4 picocuries of radon per liter of air (4 pCi/L). Secondly, if radon is accumulating at levels in excess of 4 pCi/L, then we want to determine if any correlations exist between local radon production and the state's varied geology. To accomplish these goals, we purchased 400 charcoal canister radon gas detectors from the Radon Project of the University of Pittsburgh. These detectors were mailed to approximately 350 volunteers across the state. Several duplicates were sent as quality-control checks. Many of these volunteers were geologists or other geoscientists; the remainder were primarily public health and secondary school personnel. Although not all cities or sections of the state were sampled, the volunteers were relatively evenly distributed.

The radon detectors were placed in the homes or offices of the volunteers for approximately 7 days beginning in mid-February. Actual locations of the detectors within the homes were left up to the homeowners; detectors were placed in basements, crawl spaces, ground floors, and higher floors of homes. Although some detectors still have not been returned to the University of Pittsburgh for analysis, 238 have been returned and analyzed. As can be seen in the figure, about 20% of the sampled homes had levels above 4 pCi/L, with 57.2 pCi/L being the highest value sampled to date (although this may represent an inaccurate analysis--this individual's house is currently being retested). The data from Nevada match the data from the rest of the country quite closely, which, as mentioned, has come mostly from some of the eastern states. The arithmetic and geometric means for our Nevada survey are 3.0 and 1.6 pCi/L, respectively, while the national arithmetic and geometric means of some 34,000 homes surveyed in other states are 3.6 and 1.7 pCi/L, respectively.

At this time, it is difficult to draw any firm conclusions regarding these results. More of the unanalyzed detectors will have to be analyzed for radon content, and more time will have to be spent determining the local geology and soil conditions around homes with measured radon levels above 4 pCi/L. It is apparent, however, that homes in some areas of the state may be accumulating excessive amounts of radon (see table). Although radon may pose a health problem for some Nevada communities, it does not seem to pose a problem for most Nevadans; however, not enough data have been gathered thus far to draw any conclusions. The state hopes to conduct a pilot study next winter, with the help of the EPA, that will analyze radon gas in approximately 2,000 homes.

As for our original objectives, evidence based upon our preliminary study indicates that radon may present a potential health risk to individuals living in certain Nevada communities; however, there does not seem to be any evidence to date that would indicate that radon poses a widespread problem in our state. Investigations into the geologic source (our second objective) of the radon in the areas with a high proportion of the tested homes showing radon levels above EPA action levels will continue.

Individuals wishing to determine radon concentrations in their homes or offices can conduct their own radon testing using relatively inexpensive (about $12-30) radon detectors which are available from several mail-order companies. There are two basic types of detectors available, charcoal-adsorbent and alpha-track. The charcoal- adsorbent, or charcoal canister, type is designed for short-term radon sampling only, generally being exposed to the air in your home for 3 to 7 days. The more expensive alpha-track, or track-etch, type is designed for longer-term measurement, generally 3 months to 1 year. Both types are equally accurate, but since the amount of radon escaping from the Earth varies from day to day and season to season due to atmospheric and soil conditions, the longer-term alpha-track detector will give a more representative assessment of actual radon content in the home. The only drawback of this type of detector is that you have to wait at least 3 months to find out if radon is a problem in your home.

When you receive your detector in the mail, follow the instructions that come with it for its use and placement in your house. Based upon EPA guidelines, the directions will probably recommend that you sample the lowest liveable level of your house because if this level is low in radon, it is sure to be low in other areas of the house. This is because radon tends to accumulate in the lower levels of structures. If your detector's analysis comes back above 4 pCi/L, you should consider retesting the area (preferably with an alpha-track detector) to confirm the earlier results. If the retest also indicates a high radon content, then you need to consider various remedial actions to reduce your risk of lung cancer. For guidance in taking remedial actions, or for additional information on radon, contact your regional office of the EPA; for Nevada and California, this is EPA Region 9 at 215 Fremont Street, San Francisco, CA 94105.

For a list of companies selling radon detectors, contact the Radiological Health Section of the Nevada Division of Health (505 East King Street, Carson City, Nevada 89710, phone 702-885-5394). Detectors are also available from the American Lung Association of Nevada (P.O. Box 7056, Reno, Nevada 89510, phone 702-825-5864), and from some hardware stores.

---Jim Rigby, Engineering Geologist