A new study of the most popular granites used for kitchen countertops in the U.S. concludes that granite is safe to use in kitchens.

The study, designed to determine whether radon gas sometimes released by natural stone poses any health risk, was released by the Marble Institute of America (MIA) and conducted by an independent geochemistry researcher. Included in this study were 13 of the most popular types of granites used in countertop applications, representing up to 85% of the granite countertops sold in the U.S.

"This is the first time anyone has taken a comprehensive, scientific look at the array of granite actually being used in kitchens across the U.S.," said L. L. Chyi, a Ph.D. and professor of Geology and Civil Engineering at The University of Akron in Ohio. "Based on the testing results and EPA standards, we can conclude that the most popular granites used as countertop surfaces pose no health threat to homeowners."

The issue of granite containing radon has surfaced repeatedly over the years, often fueled by manufacturers of radon detection devices and producers of synthetic stone countertops. Each time, the MIA and several natural stone producing companies have responded by engaging independent researchers to determine if any potential health hazard exists. Studies have consistently verified that granite countertops are safe.

The 13 granites used in the study were selected because they are among the most popular countertop surfaces in the U.S. They include:

New Venetian Gold, which is imported from Brazil. It is a medium-grained, yellow-beige gneiss with many dark red garnets.

Ubatuba, also imported from Brazil. It is a medium- to coarse-grained, olive-green granite.

Santa Cecilia, from Brazil. It is a coarse-grained, yellow-grey gneiss with up to pie-sized, red garnets.

Tropic Brown, from Saudi Arabia. It is a medium-grained, brown granite.

Absolute Black, from India. It is black basalt.

Tan Brown, from India. It is a black-brown igneous rock with big, shapeless, brown-red feldspar crystals.

Giallo Ornamental, from Brazil. It is a coarse-grained, brown-yellow granulite with some brown-red garnets.

Crema Bordeaux, from Brazil. It is also known as Juparana Crema Bordeaux (Brunello), an exceptionally coarse exotic material that is commercially sold as granite, even though it is not geologically a granite.

Baltic Brown, from Finland. It is a brown-black granite.

Giallo Veneziano, from Brazil. It is a medium- to coarse-grained, ochre-yellow to golden-brown, also light pink, gneiss.

Dakota Mahogany, from the U.S. It is a medium- to coarse-grained, brown-red granite.

China Black, from China. It is a fine-grained basalt.

Yellow Star, from China. It is a medium-grained yellow to pink granite.

The results found that Crema Bordeaux, which emitted the greatest amount of radon, contributes less than 7% of the EPA's standard for action. The stone emitted 0.27 pCi/L, or less than 7% of the EPA's level of 4.0 pCi/L, well below any cause for health concerns. Tropic Brown and Baltic Brown, second and third in radon emanation based on Dr. Chyi's testing, amounted to only 1% of the standard for action. The other granites added almost immeasurable amounts of radon to the house.

Tests were designed to measure the amount of radon each granite type added to the interior of a 2,000-square-foot home with 8-foot ceilings. However, the study did not reflect the ventilation normally found in a typical home, through windows, vents, heating and air conditioning. A typical heating, ventilation, air-conditioning system can exchange a home's air up to six times per hour. This natural ventilation would dissipate radon gas levels significantly.

"Because the study does not reflect the natural ventilation typically found in homes, real-world radon concentrations are likely to be even lower than those measured in this study," said Dr. Chyi.

The test results are available on MIA's Web site, www.marble-institute.com.