Tuesday, January 19, 2010

Radiation From Granite

Any naturally formed rock material has the potential of containing varying amounts of naturally occurring radiation. Natural radioactive elements like uranium, radium, and thorium can be present in a wide number of minerals that appear as crystals in granite from around the world. So, it is not unusual for materials such as granite to have some amount of radioactivity (emissions of alpha or beta particles or gamma rays). Depending on the composition of the molten rock from which they formed, some pieces of granite can exhibit more radioactivity than others.

EPA has not conducted studies on radioactivity in granite countertops. However, based on the limited information available, EPA believes that most types of granite used in countertops and other aspects of home construction are probably not major contributors of radiation and radon in the home. EPA will continue to monitor and analyze the evolving research on this issue and will update its recommendations if appropriate.

When present, certain radioactive elements in granite will decay into radon, a colorless, odorless, radioactive gas which may be released from the granite over time. You can see in the diagram below how the decay of Uranium-238 (a radioactive element) produces Radon-222 gas:

However, since granite is generally not very porous, less radon is likely to escape from it than from a more porous stone such as sandstone. It’s important to know that radon originating in the soil beneath homes is a more common problem and a far larger public health risk than radon from a granite countertop or other building materials. Also, any radon from granite in kitchens or bathrooms is likely to be somewhat diluted in the typical home since those rooms are among the most ventilated. To reduce your risk of lung cancer from exposure to radon you should test the air in your home.

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