HOUSTON -- A physics professor at Rice University is warning of a radioactive threat found in some kitchen countertops.

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W.J. Llope says some granite countertops contain levels of uranium high enough to be dangerous to humans.

Using a spectrometer, Llope tested 25 varieties of granite bought from Houston-area dealers. He says in some cases he found countertops that could expose homeowners to 100 millirems of radiation in just a few months. That’s the annual exposure limit set by the Department of Energy for visitors to nuclear labs.

Llope’s findings remain unpublished, although he said he plans to seek publication in a peer-reviewed journal.

A spokesman for the Marble Institute of America, a trade group that represents the granite industry, warned of “junk science.” Jim Martinez also cited a University of Akron study that found granite varieties used in 85 percent of countertops were safe.

Still, Martinez says the trade group is assembling scientists to develop a protocol for testing granite for radioactivity.

As many as 1,600 varieties of granite from 64 countries are sold for household use in the United States. None of them is routinely tested for radioactivity.