Answer to Question #9809 Submitted to "Ask the Experts"
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As you noted, there has been a great deal of research on and discussion of the radioactivity of granite countertops. The prevailing scientific opinion is that most granite countertops are unlikely to present a significant health hazard (see the Health Physics Society's discussion of radiation from granite countertops and other information on this topic at http://hps.org/publicinformation/ate/cat10.html#128).
Quartz countertops have received less attention. Quartz is an engineered stone; it is not a slab stone like granite or marble, but is a composite of quartz crystals (making up typically 93 percent of the material) bound together by a polymer additive. Quartz is also a component of granite, along with other minerals such as feldspar and mica. Quartz and granite contain varying amounts of uranium, thorium, and potassium, which are naturally radioactive. Uranium and thorium decay to a radioactive gas, radon, which in turn decays to other radionuclides.
With both granite and quartz countertops, we are concerned about two primary ways in which consumers can be exposed to radiation: by inhaling radon gas released when uranium and thorium decay and by exposure to gamma radiation emitted by natural radionuclides. Let's consider the hazards of radon inhalation first.
In a study sponsored by Cosentino, a company that distributes quartz, granite, and marble surfaces, researchers found that the engineered stones they tested released little or no radon. In comparison, they were able to measure radon released from natural stones and from a granite countertop (Kitto ME et al. "Emission of Radon from Decorative Stone," Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium, Las Vegas, NV; see http://www.aarst.org/radon_research_papers.shtml). This is not too surprising because, although both quartz and granite surfaces contain uranium and thorium (which decay to radon gas), quartz composites are much less porous than granite surfaces (recall that a polymer binds the quartz crystals) so radon gas may not be readily released from quartz countertops. A single study is not definitive, of course, but it does suggest that radon from quartz countertops is an insignificant hazard.
Turning to the hazard of being exposed to gamma radiation, we know that uranium, thorium, and potassium in natural rocks emit gamma radiation. Again, this is true of both quartz and granite materials, and while there are a lot of data about gamma dose rates from granite, there has been little research done on gamma dose rates from quartz countertops.
The manufacturer of one quartz composite material, Caesarstone, has published data on the radionuclide content of its product (see the Caesarstone Technical Data Manual at http://www.caesarstoneus.com/products/tech-info). This manufacturer notes that its product meets European standards for radioactivity of building materials cited in the European Commission's Radiation Protection Report 112 (see http://ec.europa.eu/energy/nuclear/radiation_protection/publications_en.htm). The European standards limit gamma radiation dose from building materials to less than 0.3 millisieverts (mSv) per year, a limit that is equivalent to the gamma radiation dose you would receive if you lived in an apartment made of concrete with the same concentrations of radium (a decay product of uranium), thorium, and potassium that is in the earth's crust. Since the manufacturer's published radionuclide concentrations in its products are about one-tenth the radionuclide concentrations in the earth's crust (as cited by the European standard) and since a countertop surface is much smaller than all the wall surfaces of an apartment, it seems unlikely that gamma radiation from quartz countertops will prove to be a significant hazard.
Linnea Wahl, CHP