A scientist in the U.S. has issued a warning concerning the use of granite bench tops.
Physics Professor W.J. Llope has suggested that some granite counter tops have high amounts of uranium that could create a health risk for humans.
The Rice University professor says gamma radiation and radon gas produced by uranium-rich stones used to make the bench tops could cause cancer in humans.
Professor Llope reportedly tested 55 stones of 25 varieties of granite stones purchased from local dealers and found some homeowners would be exposed to 100 millirems of radiation in just a few months - this exceeds the annual exposure limit set by the Department of Energy for visitors to nuclear laboratories.
Some stones he tested were apparently imported from Brazil and Namibia and contained hazardous levels of radiation.
According to Professor Llope most granite in terms of radioactivity are safe but some he tested were extremely 'hot'.
The Marble Institute of America (MIA) has dismissed the claims as 'junk science' and say the U.S. Environmental Protection Agency (EPA) says radon gas and radiation released from granite countertops do not pose a risk.
On his website, Llope says there is no safe threshold for radiation and the general guideline is that each rem of radiation would cause cancer in 4 people in a population of 10,000 - some granite countertops he tested reportedly released 1 rem of radiation in just 250 hours or 10 days.
The MIA says scientific standards and protocol need to be established which allow consistent testing in a logical fashion and that repeated studies have found that granite is safe.
The EPA however does acknowledge that "it is possible for any granite sample to contain varying concentrations of uranium that can produce radon gas and some bench tops may contribute variably to indoor radon levels but also says there is a dearth of reliable data on the issue".