By John DeFore

“Critical mass” may not be the most comforting metaphor to use about coverage of radiation in kitchen countertops, but it’s hard to resist. After stories by such high-profile outlets as The New York Times and Associated Press, long-simmering concerns about granite counters have become sufficiently mainstream that Stephen Colbert can joke that, on the upside, the counter in a new McMansion might do double duty as a microwave.

Much of the attention centers on work done by Rice University professor W.J. Llope, who as the Houston Chronicle recently reported has made unsettling findings in his study of granite available from Houston-area dealers. In a sample of 55 stones, Llope tells the paper, he found some that “could expose homeowners to 100 millirems of radiation — the annual exposure limit set by the Department of Energy for visitors to nuclear labs — in just a few months.”

That’s because the stone can contain uranium, which produces gamma radiation and radon gas. As the Times summarized the situation, “The E.P.A. recommends taking action if radon gas levels in the home exceeds 4 picocuries per liter of air (a measure of radioactive emission); about the same risk for cancer as smoking a half a pack of cigarettes per day.” Their story featured a homeowner’s kitchen where “readings were 100 picocuries per liter.”

None of the reports assert that this is something, as Llope put it, for homeowners to “lay awake worrying themselves to death about.” And naturally, stone dealers are quick to downplay any risk: The Marble Institute of America has posted a response online including such headings as “Radioactivity in Granite: It’s Natural” and asserting that the bad publicity is being generated by companies hoping to sell synthetic alternatives to granite. The MIA response notes that soil and concrete, and even well water and outdoor air, emit the vast majority of radon found in and around homes.

If that’s all there is to the issue, of course, granite purveyors should welcome the researchers’ call for more testing of household stone, if only to clear the air of doubt.

• Should sampling show that your home’s radon exceeds the EPA’s safe threshold of 4 pCi/L, the government agency recommends further testing. To find qualified radon testers in your area see the EPA’s radon info. Or visit the National Environmental Health Association website, which also hosts a list of radon professionals.

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