Houston KHOU Channel 11 aired a news story during the 10 p.m. broadcast
on May 7, 2008 that investigated the possible dangers from natural
stone
countertops in homes in the Houston area. I contributed some on-air
comments,
as well as a short write-up.
I have a dedicated gamma-ray detection system and will be
using it to gather detailed radionuclide identification information
from as many countertop stone samples that I can find.
This page is the web home for my work on this
subject.
So check
back periodically!
(& refresh this page in your browser if you've been here before!)
Links:
Newscast May 7 (HTML KHOU) (PDF
this site) (KHOU Video)
"Radiation and Radon from Natural Stone" (PDF)
Rice News article (HTML)
NaI(Tl) Calibration Note (PDF)
Please feel free to contact me via e-mail at
SaxumSubluceo@gmail.com
if you have any questions or comments.
I will periodically share (below) the best comments
and questions and my responses on this web page.
(no personal information will be made
available here!)
E-mail'ed
Q's & A's
Q: Is there a site
available to research what types of granite are relatively safe or what
mining locations are safe or unsafe?
A: Not that I know of,
unfortunately. One really needs to measure what's going on
stone by stone. As we saw in the story, there can be wide variations of
the radiation rate on a single countertop. It is thus not unreasonable
to assume countertops made from different blocks of the same type of
stone from the same quarry would vary widely in their radioactivity.
Q:
Can you use the coloration of the granite as a guide? Are darker or
lighter granites more likely to be more radioactive?
A: I'm not really aware of
hard and fast relationships between the color of the stone and the
radiation emitted by it. There might well be general rules of thumb
regarding the color of the stone and its porosity that could certainly
affect how much radon can escape the stone and how much is trapped
inside. But the basic answer is "no" as far as I know.
Q:
If you used a radon test kit on your granite, how would you know if you
were in the "right" spot? Your geiger counter changed its
readings within a foot.
A: The radon detector is
sampling the air, so the detector need not be sitting directly over the
hottest spots to see radon if it's there. If I were doing the test, I
would use several test kits in parallel over different sections of
stones with different colors.
Q:
One site mentioned sealing the granite, like you did in your
article. However, I don't understand this point. If
I seal the top of the granite, as ours is, have I stopped the
release of radon? What about the underside of the
granite? Does radon only emit upwards? Would
sealing have any effect on the radiation emitted?
A:
Generally, I'd think the
sealant on the top surface would have little effect on the
radon or the radiation that escapes the block of stone. The point
there (which - you are right - I should have made clearer in the
article) is that if the sealant is
defeated and you prepare food directly on the countertop, then there is
some chance you will be ingesting stone dust. And if there are
radioactive materials in the stone, then you are at some level
ingesting radioactive materials. These can be toxic, and the radiation
they emit can certainly do more damage to you from the inside
of you compared to the case when they are radiating you from the
outside from some distance away.
Q: Would you expect the
workers in the Houston area who cut, grind, and polish granite during
the installation process to have a greater incidence of cancer than
other groups?
A:
If the stone being processed in a fabrication shop is hot, then it is
certainly reasonable to be concerned if the workers that cut and polish
this stone are breathing the airborne dust that must be released in
great quantities during the cutting and polishing processes. This is a
danger to the lungs of these workers that is distinct from
the radon concern to homeowners with finished
countertops. Only the personnel at these shops would be expected
to breathe this raw stone dust, but the danger goes beyond radon itself
in this case. This dust in principal contains the same
admixtures of Potassium-40, Uranium-238, and Thorium-232 (and their
daughters) that the stone itself contains. The federal Occupational
Safety & Health Administration (OSHA) recognizes respiratory dangers in the workplace and, according to this link, takes the enforcement of these respiratory regulations at stone fabrication shops seriously.
Q:
What was the name and country of origin of the granite you investigated
in the story and in your write-up?
A:
I know it, but I am not
going to say it. According to the question and answer above, there can
be wide variations in the radioactivity from a single countertop, so I
am not going to condemn all stones of this variety on the basis of the
one sample that I've studied. I am in the process of collecting more
samples, which I will test for the radiation rate and the gamma spectra to
directly identify the radionuclides (if present). The results of these
further studies will show up on this web page over the next week or
two.
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