To reduce the radon risk you should first test the air in your home to determine the radon level.
Marble have radon.
It is relieving to hear that the radioactive levels in granite and marble are too small to be of any concern but all construction materials in general emit a small amount of radon gas which is radioactive and can easily accumulate in poorly ventilated buildings.
When materials such as granite are mined from the earth they naturally contain these radioactive elements and may occasionally emit radon gas.
For some objective information on the subject check the latest recommendations from the u s.
Marble is dominantly calcium carbonate and is very depleted in uranium.
Some granite samples and countertops have been tested and some have shown elevated levels of radon emissions.
There are many do it yourself radon test kits available through retail outlets and on line starting at about 25.
Granites from india and egypt have very low emanation rates and are by far the best in the world in this regard.
However tests on other types of granite have been negative for radon.
However some articles have circulated that claim granite is a source of harmful radiation specifically radon.
Radon can be found in soil rock air and even water.
Environmental protection agency epa and the american association of radon scientists and technologists aarst.
If you have granite countertops and want to test them for radon place a short term home radon test kit near the granite and another kit in the basement or lowest usable level of the home.
Over years of exposure radon can cause cancer the primary health concern with this gas.
November 2013 thanks to quick and forceful action by the marble institute of america and its legal team the doctor s show has retracted a show segment in which it reported that living in a home with granite countertops could be as bad as smoking a half package of cigarettes a day.
This has put some people off granite countertops.
Seven days after the report the doctors show.
If the levels of radon in the area containing the granite are higher than your indoor levels in another area of your home and the surface top test devices also return high results then it is possible that the granite is contributing to or is the source of your indoor radon levels.
Radiation and radon are generally lower in marbles but both marble and granite has been studied for many years on these issues.
The doctors show admits it erred in granite radon segment.
Here is the truth about granite countertops and radiation.
Here is a link for several studies from all over the world.
You would not expect to have radon produced from exposure of marble to air.