image: National Academy of Sciences

Home sweet home may not be the safe haven you thought it was. A large-scale study released today by University of Iowa researchers has found that radon in homes may increase the lifetime risk of getting lung cancer by 50 percent.

Although studies involving uranium miners exposed to high levels of radon had previously shown its link to cancer, this is the first study to examine the health effects of residential radon so closely.

Looking at long-term radon exposure

Radon is a colorless, odorless gas that comes from the natural breakdown of uranium found in soil, rocks, and water. "It’s probably the leading environmental carcinogen, at least for lung cancer," says epidemiologist Bill Field, one of the lead researchers of the study.

The Iowa Radon Lung Cancer Study, which appears in the June 1 issue of the American Journal of Epidemiology, found that as radon concentrations increased, lung cancer rates also increased. "Even at the EPA [Environmental Protection Agency] action level of 4 picocuries per liter (pCi/l) there was about a 50 percent increased risk in developing lung cancer that would be attributable to radon exposure," says Field.

A. Cracks in concrete slabs B. Spaces behind brick veneer walls that rest on uncapped hollow-brick foundation C. Pores and cracks in concrete blocks D. Floor-wall joints E. Exposed soil, as in a sump F. Weeping (drain) tile, if drained to open sump G. Mortar joints H. Loose fitting pipe penetrations I. Open tops of block walls J. Building materials such as some rocks K. Water (from some wells) image: EPA

From 1993 to 1997, scientists studied more than 1,000 Iowa women between the ages of 40 and 84 who had been living in their homes for at least the past 20 years. (Researchers included only women because they tend to spend more time at home and are therefore more exposed to residential radon.) Unlike previous studies using only one or two detectors, they placed at least four radon detection devices in different areas of the study homes for one year. To get a more precise idea of home owners’ exposure to radon, the researchers linked radon detector readings to where the study participants spent the majority of their time (the bedroom, living room, outdoors, etc.).

"The Iowa study is exceptionally well designed and well executed," says Kristy Miller of the EPA’s radon division. "It adds to the body of knowledge which designates radon as the second leading cause of lung cancer."

Where does radon come from?

All rocks contain some uranium. As it breaks down, radon is released. Because it’s a gas, it can move up through the ground to the air above, or into groundwater. It seeps into homes by way of cracks in walls and foundations. Radon itself isn’t harmful, but its by-products are. As it decays, it emits tiny radioactive particles that when inhaled, can damage the cells lining the lungs. These damaged cells can become cancerous.

"I think it is misunderstood and sometimes underappreciated, the risk that radon does pose," says Field. "It is naturally occurring, it’s invisible, and it doesn’t really have any sensory stimuli that would cause you to think about it."

Iowa was a particularly suitable location to conduct the lung cancer study because it has the highest average radon concentrations in the U.S. The radon there comes from soil deposited by glaciers more than 10,000 years ago.

But radon is found all over the country. The Environmental Protection Agency (EPA) estimates that one out of every 15 U.S. homes has elevated radon levels. Each year about 15,000 to 22,000 lung cancer deaths are attributable to radon exposure, according to the EPA. Smokers have a higher risk of developing radon-induced lung cancer than

What can I do?

A radon testing device. image: National Academy of Sciences

The first step in reducing radon exposure is to have your home tested. You can buy radon devices in retail stores or hire a state-certified tester. The EPA recommends fixing the problem if the radon level is 4 pCi/l or higher, but even lower levels can pose a risk and can often be treated.

There are several approaches to reducing radon levels. The first is to seal cracks and other openings in the foundation to prevent additional radon from creeping in. But most homeowners also install what’s called a sub-slab depressurization system that ventilates the air under basement slabs or crawl spaces. Radon mitigation contractors can recommend other systems based on the design of your home. According to the EPA, fixing the problem can range in cost anywhere form $500 to $2,500.

Where to Call If you have questions, call The National Radon Information Line at (800) SOS-RADON If you have already tested your home, call the Radon FIX-IT Program at (800) 644-6999

Elsewhere on the web:

Lawrence Berkeley Lab Radon Page - This page will estimate the radon level in your house.

State Radon and Indoor Air Quality Contacts

The EPA’s Home Buyer’s and Seller’s Guide to Radon

U.S. Geological Survey Map of Radon Potential in the U.S.

National Radon Safety Board

The Geology of Radon

The National Environmental Health Association’s National Radon Proficiency Program