NATURAL STONE COUNTERTOPS AND RADON
Numerous scientific studies conclude that there are two ways in which countertops, tiles and other finishes made of granite might emit any level of radiation.
The first is by the release of tiny amounts of the radioactive gas, radon. The second is by direct radiation from the surface itself to the homeowner.
In both cases, the radiation emitted is from the same process – natural radioactive decay of one element into another. Compared to other radiation sources in the home and outside, the risk to the homeowner from radioactivity or radon gas emitted from a granite countertop or tiles is practically non-existent.
The U.S. EPA ( reports: “Based on existing studies, most types of granite used in countertops and other aspects of home construction are not typically known to be major contributors of radiation and radon in the average home.”
The Florida Department of Health (DOH) goes a bit further with a recent statement: “Staff from the Florida Department of Health’s Bureau of Radiation Control and from DOH’s Radon Program have had the opportunity over the years to survey various granite samples for gamma emissions, including a few granite counter tops, and have yet to find granite thought to be a significant gamma radiation hazard.
The term ‘significant’ is used because there was measurable gamma radiation from the granite as there is Always around us, just not at level of concern.
Radon gas occurs naturally in the environment and is present in outdoor and indoor air throughout the world. Radium, which is the source of radon gas, is a natural and minor constituent of many common building materials such as concrete, brick, gypsum, and natural stone. Granite and other stones that are a popular choice for countertops and other decorative features in homes have been evaluated extensively. Over 500 measurements of radon emissions from granite have been published in the peer reviewed scientific literature. This information provides a reasonable basis for preliminary estimates of typical and upper bound levels of radon in indoor air of homes associated with emissions from natural stone countertops.
The average and maximum radon concentrations estimated from these data to result from emissions by natural stone are low in comparison to relevant benchmarks of radon exposure. The radon concentration estimated as a result of average radon emissions from natural stone reported in the scientific literature is approximately:
Radon Emissions from Stone Countertops
The amount of radon relased from a Natural Stone Countertops in a home depends on the surface area of counterop in the home and the amount of radon released per unit area of stone. Sufficient information is available to derive reasonable estimates for both of those parameters.
An average kitchen with stone counteertops has a working surface area of approximately 50 sq ft according to a large sample of sales data provided to Environmental Health & Engineering, Inc. By the Marble Institute of America, while a typical bathroom installation is approximately 18 ft2 of stone.
Accounting for both the kitchen and bath, the underside face of the countert, and the thickness of the stone a typical installation of stone countertop includes a total suface area of approximately 140 sq ft. To produce the most health protective estimates, we assume that the entire surface area is open to the room and contributing radon to the indoor air.
Over 500 measurements of radon released from granite and marble have been reported in peer reviewed articles published in the leading scientific journals that focus on radiation and health. 1-17 stones included in those studies were mined from quarries throughout the world and reflect the diversity of stones in the US market. Radon emissions, sometimes called the exhalation rate, are expressed as the amount of radioactivity released per sq ft of stone per hour ( pCi ft-2 h-1 ) .