Beware summer radon-test results

Measuring radon with testing kits that sit in a house for just a few days can yield misleadingly low values in summer, a new study finds.

Alabama maintains a statewide database of 36,000 domestic measurements of radon, a radioactive gas emitted by rocks in soil. Although these data revealed some geographical hot spots, radon readings in such areas were often unexpectedly low if testing had occurred in summer.

To investigate a possible seasonal bias, James L. McNees of the Alabama Department of Public Health in Montgomery and Susan H. Roberts of the Alabama Radon Education Program at Auburn University offered free radon-test kits to state residents whose homes had recently undergone summer testing.

Of the 186 homes resampled in winter, 63 percent exhibited higher radon values than they had in summer. Indeed, 27 percent of these homes revealed air concentrations more than five times the 4-picocuries-per-liter federal guideline for taking remedial action. The researchers report their findings in the July Health Physics.

The Environmental Protection Agency recommends measuring radon over an entire year. However, because many people test for radon only when they put their homes on the market, several-day testing has become common.

McNees and Roberts suspect that the summer-radon effect traces to fairly constant temperatures in air-conditioned homes. Normally, they say, temperature differentials would prompt warmer air to rise into the attic, drawing radon-laden air into the home from the soil below it.

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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