Question

Are engineered stone (quartz) countertops really green?

Asked by susan
Fort Lauderdale, FL

I am considering Caesarstone countertops, and I got these results of a test done on the stone of interest: 226 Ra = 6.7 Bq/Kg, 232 Th = 3.7 Bq/Kg, 40 K = 4.6 +/- 2.7 Bq/Kg. I'm not sure when these tests were conducted, and whether the component of every slab is the same. In other words, whether the quartz in my slab is the same as the quartz in the tested slab. Unfortunately, 99.999% of the manufacturers are unwilling to give these details. Are these figures anything that should concern me? I have small children who are home all the time, and we spend most of our time in the kitchen.

Answer

David Edwards PhD

Answered by David Edwards PhD

Santa Clara, CA

EarthBound Homes

June 5, 2010

Since you have actual radiation emanation data, I will answer this question directly, but for background information on the link between radiation from granites and quartz and cancer, please see the question titled "Should I be concerned about the radiation that quartz countertops emit?" which I answered previously.

To help you understand what these numbers mean, let's give you some definitions: 226 Ra = 6.7 Bq/Kg, 232 Th = 3.7 Bq/Kg, 40K = 4.6 +/- 2.7 Bq/Kg are three different measures and, for clarity, should be arranged like this:

226 Ra = 6.7 Bq/Kg
232 Th = 3.7 Bq/Kg
40 K = 4.6 +/- 2.7 Bq/Kg

The first number/letter combination refers to the radioactive element (the number) and the molecular weight of that element. So 226 Ra is radium, with a molecular weight of 226 grams/mol (6.02 x 1023 atoms of this element). 232 thorium and 40 potassium are also radioactive elements.

Now the information you have here is actually really great, because the manufacturer is giving you not only the radium number (radium is a radioactive breakdown product of uranium and a precursor to radioactive decay into radon), but also that of thorium and potassium, two other radioactive elements that are not commonly identified as radioactive concerns in granites and other stone countertop materials.

Here is the upshot: without getting into long calculations that involve the size of your countertop, the size of your house, how well your house is ventilated, whether you lay on your countertop or just work around it, etc., you can be sure that the amount of all of the radioactivity emitted by all the elements referenced here would not be a significant threat to your family's health.

Here are some relative numbers to help ease your mind:

  1. You would have to eat your entire 400-lb. countertop to equal 75% of the radiation your body gets from radioactive elements that are already inside your body. This does not include the radiation that you get from the sun and other exterior sources.
  2. If all of the radiation were suddenly to turn into radon-based radiation exposure (i.e., airborne), it would equal 6.5% of your daily exposure level if your house were airtight. Fortunately, much of this radioactivity is blocked by the cabinets and the granite or quartz material itself, and only 40% of it is radium/radon based radiation, which mixes with the air and gets diluted out anyway.

With that said, I again refer you to the question titled “Should I be concerned about the radiation that quartz countertops emit?" so that you can make your own informed decision about what you define as an acceptable risk level for radiation exposure.

Best of luck.

Tagged In: home air quality, stone

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