POSITION STATEMENT:
Science and Technical Committee of the American Association of Radon Scientists and Technologists (AARST), August 4, 2008:
At this time, the EPA does not believe sufficient data exists to conclude that the types of granite commonly used in counter-tops are significantly increasing indoor radon levels. Soil, sand, and rock underneath the home are the primary sources of indoor radon gas. The soil under a house always contains traces of uranium that eventually decays into radium that then decays directly into radon. This soil constitutes an enormous surface area for release of radon gas into the air and into buildings. Materials inside a building such as concrete, granite, slate, marble, sand, shale and other stones can also contain traces of radium that release radon with varying intensities. While natural rocks such as granite may emit some radon gas, the subsequent levels of radon in the building that are attributable to such sources are not typically high. The contribution from building materials to the indoor radon concentration is very dependent upon the building ventilation rate.
Read more: http://www.aarst.org/images/AARST_Granite_Position_Statement_8-04-2008.pdf