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Though you can’t see, smell, hear, or feel it, radon nonetheless poses a significant risk to human health. This naturally occurring radioactive gas comes from uranium, found in nearly all soils, and infiltrates our homes through cracks in foundations. Radon can become trapped in our houses and build to unhealthy levels if not remediated.

Radon exposure will not cause acute or specific symptoms, but over the long term, it’s estimated to cause about 21,000 preventable lung cancer deaths per year, second only to smoking. Smokers exposed to elevated radon levels have a greatly increased risk of lung cancer; nonsmokers have a somewhat increased risk.

As public understanding of radon has risen, it has become increasingly standard practice for home buyers to expect that radon has been tested for and remediated if found at elevated levels, and some states require disclosure of radon test results in home sales. If you’re looking to buy a home, ask whether the home has been tested for radon, and if it hasn’t you can ask to have it tested.

What are Sources of Radon Exposure?

1) Radon gas in soils beneath buildings. The primary way we are exposed to radon is in our homes, where radon accumulates at the lowest level and becomes dispersed throughout the house. All types of buildings — newer, older, leaky, tight — can have radon problems. Especially in the heating season, the “stack effect” of a building (meaning heat moves upward, drawing in cooler replacement air from below) draws in radon-containing air from the soil beneath the house. The EPA estimates that 1 in 15 homes have elevated levels of radon. Other buildings in which we spend significant amounts of time will likewise contribute to our exposure. You can ask whether your workplace or your child’s school or daycare has been tested for radon, and urge administrators to pursue testing if they haven’t already.

The EPA notes that every state in the U.S. has areas suspected to be high in radon. Though the EPA has produced a map showing areas where higher readings are expected, living in a lower-radon zone is no guarantee that your home’s air falls within what are considered safe limits, and they recommend testing regardless. Because radon levels are affected by soil geology as well as the way buildings are constructed, homes in the same neighborhood can have very different levels of radon.

2) Water. We can also be exposed to radon in the water piped into our homes. Some private wells and public water supplies that draw from groundwater (as opposed to surface water) may have radon contamination, though some public water services treat for radon before delivering it to consumers. Contact your water supplier or have your well tested if you’re concerned.

Certain water filters can remove radon from water. They may be installed at point of entry, filtering all the water used in your house, or at point of use, which typically only addresses drinking water, but not the radon released from other uses, such as showers. Note that filters can accumulate radiation and may require special disposal. Though you may ingest or inhale radon from water, research suggests that radon in water has a far smaller impact on cancer rates than radon in air. (The National Research Council’s “Risk Assessment of Radon in Drinking Water” estimates that inhalation of radon from water accounts for 160 lung cancer deaths and ingestion of radon in water accounts for 20 stomach cancer deaths versus 21,000 lung cancer deaths from radon in air.)

3) Building materials. In a small number of cases, building materials such as concrete may expose us to radon, though they’re rarely the sole cause of a radon problem. You might remember some media coverage of radon-emitting granite countertops several years ago. Some granite can contain small amounts of uranium, which gives off radon gas as it decays. Though only a small fraction of granite contains uranium, some counters have been found to emit radon at levels that far exceed the EPA’s action level, so while you’re testing your house for radon, you might want to include your counters or other granite surfaces in your testing areas.

Should I Test for Radon?

The EPA recommends that everyone test the lowest level of their home with a do-it-yourself kit (available in hardware stores and for free through some counties — google “free radon test kit” + your state and/or county to find out if there’s a program in your area). If the test reading comes in at 4 pCi/L (picocuries per liter of air) or above, then you should follow up with additional tests.

According to the EPA, “The higher your initial short-term test result, the more certain you can be that you should take a short-term rather than a long-term follow up test. If your first short-term test result is more than twice EPA’s 4 pCi/L action level, you should take a second short-term test immediately.” Note that though 4 pCi/L is considered an “action level” it doesn’t mean that anything below that level is safe. There is no known safe level of radon. (For comparison, the “background level” of radon in most outside air is 0.4 pCi/L. The EPA estimates the average indoor air level is about 1.3 pCi/L.

A short-term test kit will let you know your radon levels over the 2 – 90 days you leave it in the test area, but it won’t tell you about the fluctuations that occur throughout the year. You could test at a time that levels are lower and not realize that other times of year (particularly the heating season), readings approach levels of concern. You should plan to test at different times of year to get more complete information.

Long-term test kits stay in place for more than 90 days and give a better picture of the radon you’re exposed to year-round. The EPA sponsors a radon-education program at Kansas State, and discounted tests are sold through their website ($15 for short term and $25 for long-term test).

What to Do If You Find Elevated Levels of Radon

If your tests come back with elevated radon levels, it’s time to bring in the pros. Radon mitigation can be handled in different ways, and a licensed professional should evaluate the specifics of your situation. The most common way to address elevated radon levels is installing a venting system below the building’s slab or in a crawl space, so radon doesn’t have a chance to enter the your house.

Called active subslab suction (or subslab depressurization), this method involves installing a tube below the slab with a fan running constantly to vent the air outside the house. These systems usually cost in the neighborhood of $1200. Additionally, the fan requires electricity to run, and the venting will likely also draw conditioned air from your house, so you will likely see an increase in your utility bill. (However, Green Building Advisor’s Martin Holladay reports that these systems may reduce basement moisture, so you won’t need to run a dehumidifier as much, which could offset some of the additional electrical draw of your radon-reduction system.) The fan will also need regular maintenance, and will likely need to be replaced every five years or so, for a cost of $200-$350.

If you have a crawl space, mitigating radon can be as simple as sealing off the exposed earth with plastic sheeting, but again you should consult a licensed professional. Often a pipe will vent air from beneath the sheeting, either with or without a fan. For more detailed explanations of the methods available and their effectiveness, check out this guide from Iowa State University.

However you choose to proceed, be sure the professional you hire is certified by either the National Radon Proficiency Program or the National Radon Safety Board. Many states also certify radon contractors. Contact your state radon office for further information.

HUD and the EPA administer some grants to help with the cost of radon mitigation:
For further information, check out the EPA’s radon map and click on your state to connect to the state radon site.

If You’re Building a New Home

Though many building codes don’t yet require it, new home construction can build in radon-reduction elements, using simple methods such as crushed stone and plastic sheeting below basement slabs and installing venting pipes that passively keep radon from infiltrating the house without more costly and energy-consuming measures.

As we gain greater understanding of radon and other unseen health hazards, we can adopt the precautionary principle and safeguard against them. Ready to check your home for radon?