Granite Countertops & Radon: What the Granite Industry Doesn’t Want You to Know

Some granite emits enough radon to increase the radon concentration in a kitchen.  The radon in Cathy Woods’ kitchen was three times as high as the radon in her bedroom.  That lung cancer risk at that level was nearly as high as smoking 10 cigarettes a day.

Not long after Green Options posted my article Granite Counters: Uranium Ore In Disguise?, the Managing Editor received a communication from the publicity firm representing the Marble Institute of America (MIA).  That letter stated:

In order to demonstrate why these articles/posts are not only inaccurate but also misleading, I wanted to supply some additional information including results from the most comprehensive scientific study of granite to-date that found not a single stone slab that poses a health risk to consumers.

Let’s look at data from the study funded by MIA.  The MIA White Paper on Natural Stone Countertops and Radon reported average radon emitted from granite was 1.9 picoCuries/square foot in each hour (pCi/ft2-hr).  The maximum radon emitted in the MIA-funded study was 34 pCi/ft2-hr.

Now let’s look at a study that was not funded by MIA.  Dr. Michael Kitto found radon emission up to 770 pCi/ft2-hr, more than 20 times the highest level reported by MIA.  In Dr. Kitto’s study, 1/3 of granite emitted more than 50 pCi/ft2-hr, and 2/3 emitted less.  My own client, Cathy Woods, had 350 pCi/ft2-hr emitted from her Jupurana Bordeaux.

Let’s also examine the calculations done in the White Paper by the MIA.  They assume that all the radon emitted by the granite is instantaneously well-mixed with all of the air throughout the home.  That assumption is not valid.

Dr. Mark Nicas at U.C. Berkeley specializes in mathematical modeling of airborne contaminant concentrations.  A simple model assumes ¾ of a contaminant remains in the “near field”, the kitchen in this case.  The remaining ¼ of the contaminant is distributed throughout the “far field”, the remainder of the home.

That model predictions are close to the actual radon distribution we measured in Cathy’s well-ventilated home.  Measured radon was slightly higher than the model predicted, indicating Cathy has a low level of background radon present in her home.

Cathy Woods Home Predicted Radon from Granite Measured Radon in Home
Bedroom (Doorway open) 0.3 pCi/L 1.2 pCi/L
Kitchen (Doorway open) 2.3 pCi/L 2.4 pCi/L
Kitchen (Doorway closed) 3.1 pCi/L 3.8 pCi/L

(Calculations used the equation given by MIA and their assumption of 50 square feet of granite, emitting radon from both surfaces.)

Now let’s estimate radon from granite in older, well-ventilated homes compared to newer, well-insulated homes.  These calculations do not include background radon, just the radon from 50 square feet of granite mixed throughout a 100 square foot kitchen.

100 Square Foot Kitchen Well-ventilated (AER = 0.5) Well-insulted (AER = 0.2)
Typical Granite (50 pCi/ft2-hr) 0.4 pCi/L 1.1 pCi/L
Cathy’s Granite (350 pCi/ft2-hr) 3.1 pCi/L 7.8 pCi/L
Dr. Kitto’s Granite (770 pCi/ft2-hr) 6.8 pCi/L 17.2 pCi/L

(Calculations used the equation given by MIA and their assumption of 50 square feet of granite, emitting radon from both surfaces.)

At 4 pCi/L of radon, EPA estimates about 7 out of 1,000 people will get lung cancer, the same risk as smoking 10 cigarettes a day.  At 10 pCi/L of radon, about 18 people out of 1,000 will get lung cancer.  The risk is considerably higher for smokers.

We don’t spend 24 hours a day in our kitchens, exposing ourselves to elevated levels of radon.  However, some families occupy their kitchens and family rooms for several hours each day.  Young children are especially likely to be in the area.

Testing a home for radon only takes a few days, and test kits are inexpensive.  The state of California provides radon test kits to residents for $5.  Radon test kits are available from certified laboratories for around $25.

Photo by Linda Kincaid.

Related articles:

Granite Counters: Uranium Ore In Disguise?

Worries About Granite Lead to California Homes with Radon

Lung Cancer Victims Blame Radon: Call Government Policy a “Deadly and Impotent Failure”