One in four homes in the greater Portland, Ore., area contain radon levels well above the safety limits set by the U.S. Environmental Protection Agency (EPA), according to a recent study by Portland State University.

Radon is a naturally occurring, colorless, odorless gas that enters homes through cracks, gaps and other seams in the foundation or through water systems. Radon, which is generated by the breakdown of naturally occurring uranium, can build up in a home or building over time and produce serious health risks. It is the second most common cause of lung cancer in the U.S. behind smoking. According to the EPA, an estimated 20,000 lung cancer deaths in the U.S. each year are linked to radon exposure, the majority of which are directly linked to patients who are also smokers.

According to a report from The Oregonian, Portland is of particularly high risk for radon because of its granite-infused sediment, which contains a high level of natural uranium that settled in the area during the last ice age.

The new study, the first since 2003, tested 33,000 homes in Portland, Beaverton, Oregon City, Hillsboro and the surrounding cities and broke the results down by ZIP code (pdf). Nineteen ZIP codes were judged to have a high radon potential, and 79 percent of all ZIP codes were found to have a high or moderate risk.

Oregon health officials are recommending that all homeowners have their houses checked. Commercial test kits are available for as little as $35, and The Oregonian says any problems can often by fixed by contractors for between $1,000 and $2,100. "It's a geological hazard that can be dealt with cheaply," said PSU geology professor Scott Burns, who conducted the tests with his students. "We need to reduce the amount of radiation in our lives, and this is one way of doing that."

Related air-quality posts on MNN:

Portland radon levels reveal potential health risks
1 in 4 homes in the area have potentially unsafe levels of radon, a new PSU survey reveals.