How dangerous might my countertops be?

[Syanna]

Recently in the news, there have been stories about the potential dangers of radon and radiation emissions from granite countertops. I have linked an article from Rice University. One of their Physics Professors is trying to publish his findings in a peer review journal.

Can anyone shed some light on how real of a concern this might be? I have Uba Tuba granite in my house and was curious about how realistic of a threat these emissions may pose.

http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=11004"

Syanna

 

[mgb_phys]

If they emitted enough to be hazardous to you - they would be fatal to thin celled bacteria living directly on them, which would reduce your chance of food poisoning!

It's just another case of media 'n' word scares.

 

[uart]

Many rocks contain small amounts of radioctivity contributing to natural background radiation. It's something that humans have been exposed to throughout our entire evolution and in most cases should not be of any health risk.

I'd say that if you're concerned then first off make sure you have reasonal ventilation in the kitchen. Most kitchens need ventilation anyway to vent off steam and smoke from cooking (oh yes smoke, that's me cooking). Radon accumulation is typically only an issue when houses are built in areas of high natural radiation AND they have poor ventilation, epsecially say a poorly ventilated basement for example.

Apart from that you could consider buying a cheap geiger counter type device to set you mind at ease. There are low cost detectors available for about $20 upward on ebay.

 

[gmax137]

see the "Radiation Fear Gets Silly" entry from July 21 on depletedcranium dot com blog for some interesting (?) comments on these "news" stories.

 

[Vanadium 50]

I would encourage everyone to read what's on Bill Llope's website at Rice. In his measurements he finds a wide range of variation in radiation from countertops, and the most radioactive ones are surprisingly hot. I believe 4 mR/hour was the hottest. At 5 mR/hour, the proper signage for one's kitchen would be "Caution: Radiation Area".

If I brought such a counter top into work, I would have to label it as "Caution: Radioactive Material Class 2" and it would require permission of the radiation safety officer to move it anywhere on site.

Again, this is the hottest, not a typical counter top.

 

[mgb_phys]

4 mR - that's about a chest x-ray, pretty hot.
Is this from Radon? That should disperse, the rate of production for a thin slab of granite can't be that high.

It's still probably good for you given the incidence of food posioning compared to the radiation risk!

 

[Vanadium 50]

There is radon, but the 4mR/hr is largely from Bi-214, another radium daughter.

One other point is that I am not so sure I would want an alpha source in my kitchen, where the possibility of internal uptake is much higher than it would be in, say, my basement.

 

[mgb_phys]

If the source is well encapsulated in the granite though you aren't likely to absorb much of the Bi, alpha gets a high REM number because of the damage internal alpha does so it's probably an overestimate for a sealed source.

Interestingly I hadn't realized that Q was so much lower for virus/bacteria than humans so would you need seriously hot granite do any good, I had assumed that their thin skin meant they got hit a lot harder by alpha.

 

[Vanadium 50]

Bi-214 is a gamma emitter. I assume the 4mR/hr is beta/gamma as the alphas are almost certainly undetected. One concern about alphas stems from the fact that dough is often kneaded directly on the counter top, so it's entirely possible that one picks up small quantities of alpha emitters (Rn, Po) and ingests them. The other is that one spends more time in the kitchen than the basement.

Llope has measured Rn at a few pCi/l, so the radon contribution is not negligible, at least for some of the counter tops.

 

[gmax137]

vanadium50 said "One concern about alphas stems from the fact that dough is often kneaded directly on the counter top, so it's entirely possible that one picks up small quantities of alpha emitters (Rn, Po) and ingests them."

So, all those centuries of eating (granite) stone-ground flour must have been really deadly to the human race - I mean, compared to the dough kneaded on these polished slabs... and who does the polishing? Are they all dead now too? Vermont, can you hear me? Vermont!? my god, we've lost vermont...

 

[russ_watters]

Yeah, this one lights up my B.S.-O-Meter like a Christmas Tree.

 

[Vanadium 50]

So, all those centuries of eating (granite) stone-ground flour must have been really deadly to the human race - I mean, compared to the dough kneaded on these polished slabs... and who does the polishing? Are they all dead now too? Vermont, can you hear me? Vermont!? my god, we've lost vermont...

Of course not. Like I said, this comes from the highest measurement Llope has observed. Typical pieces of granite are much lower. Looking at a radon map of Vermont indicates their granite appears to be relatively low in radium concentration.

Are people overreacting? Of course they are. But that doesn't mean that there is no risk. From Llope's numbers, it appears that the worst of the countertops would exceed workplace standards. Workplace standards are set to be well below where there has been demonstrated harm.

I think it's entirely reasonable to take a survey meter to a piece of granite I would plan to install in my house and prepare food on, and if it indicated it was a Class 2 radioactive material, to buy another piece instead.

 

[Syanna]

Thank you everyone for the feedback.

Would the general consensus be that I should test my countertops to err on the side of caution or would that be overkill?

If so, I've come across links for people that will come out for about $300 to run these tests. Does anyone know if that sounds like an appropriate cost?


Syanna

 

[gmax137]

Please do look at the link I posted earlier ("Radiation Fear Gets Silly" entry from July 21 on depletedcranium dot com blog). They link to a video of this guy frisking countertops. He has the probe resting right on the slab (not "1 cm above") - so I believe his readings are not comparable to the standards vanadium50 cites. There are problems with his radon measurement technique as well. This is an egregious example of fear mongering -

If you have a slab you are afraid of, please send it to me.

 

[Vanadium 50]

I wouldn't draw the conclusion gmax137 did from a few minute TV spot - in particular, the writeup on Llope's website discusses using a different detector entirely. What one is seeing is a portable counter and a random slab, so he may well need to get very close to move the needle at all. Remember - his conclusions are that most countertops are not substantially radioactive.

I also wouldn't spend $300 on a test. The $15-20 radon tests should work just fine, provided you have three days when you won't be boiling water in your kitchen. (High humidity can screw up the test) If it's positive, I'd do an alpha track test. ($30 and 90 days)

 

[CynthiaMcG]

Hopefully, I can get this conversation re-started!

I am about to start on home renovations, and I have always wanted granite countertops. I've done a little research and am now a bit nervous about the radioactivity/radon gas issues.

I realize that there isn't an accepted test one can use at the granite dealer's shop to select a safer slab before installation. I sent some questions to the EPA, citing an article by L.L. Chyi of the University of Akron (posted by the Marble Institute at: http://www.marble-institute.com/industryresources/radontesting_u-akron2008.pdf ) In addition to asking for their opinion on his report, I asked about whether some geographic sources or color varieties tended to be more/less risky. They didn't have an answer to the second question since samples can vary greatly even within one quarry. Here's their response to the research:

"There are numerous minerals which may be present in granites that contain the radionuclides of uranium, radium, and thorium. Apatite and biotite are just two, and the percentage of zircon and titanium minerals (rutile, leucoxene, ilmenite), for example, were not determined in the study due to the examination method used."

So here's my more-specific thought: Does gabbro tend to contain less of these troublesome minerals than granite as a rule? Is Uba Tuba actually a gabbro rather than a granite?

Thank you!