solidsurfacealliance.org Blog

There has been some concern on the Garden Web forum about Bordeaux granites, which ones tend to be high level and which ones tend to be low level. I thought I would share what I have found so far in both informal testing and what little professional testing done so far.

To put things in perspective 10 uR/hr reading at some state recycling centers will be reported to the state radiation control office. Other states like Kansas, allow 25 uR/hr over background radiation (typically 6 to 8 in our area), so a 31 to 33 uR/hr scrap metal will cause alarm. Uranium processing plants being decommissioned must clean the soil till it reaches 5 uR/hr, average radiation level for soil.

Personally, from the last few years research, I set a level of 25 uR/hr over background for the slabs I am willing to let my workers fabricate.

Juparana Bordeaux, shortened to Bordeaux, is one of the ones that MUST be tested prior to purchase. Rarely do you see a Bordeaux below 50 uR/hr Gamma. Much is at 75 to 100 uR/hr. That doesn’t mean you won’t find a low level slab if you go through enough of them.

Crema Bordeaux is one of the lower level Bordeaux. We have tested 5 slabs so far, using the LENi Geiger counter. From 240 to 1500 uR/hr counting Alpha, Beta, Gamma. The fact that there are 240 uR/hr slabs out there shows that one can find lower level slabs. Counting Gamma only, Crema Bordeauxs can run as low as 25 uR/hr, right at our cut off level for safe slabs. Crema Bordeaux did test rather high in the MIA sponsored tests, 292 times more than some of the others, so a Radon detector is a good idea. States sometimes offer them at great deals.

We found one Bordeaux, Golden Bordeaux, that was quite low, 13 uR/hr. Only one slab available for testing, so it doesn’t represent a range, but it is worth looking into if you have your heart set on a Bordeaux.

To put things in perspective on Bordeaux, though, consider the test results on the Houston slab, done by American Radiation Services International . Here is a list of the elements causing it’s radiation.

Potassium 40, 53.9 .
Scandium 46 , 31.65
Colbalt 60 , .13
Caesium137 , .189
Thallium 208, 37.8
Lead 210 , 415.5
Bismuth 212 , 85.46
Bismuth 214 , 410.77
Lead 214, 484.99
Radium 226 , 986.95
Radium 228 , 128.34
Thorium 228 , 144.76
Uranium 235 , 37.83

Total 2,670.196 pCi/g or if you want to compare it in uR/hr, multiply by .95, or 2,337.088 uR/hr.

That slab, in addition to its radiation, one should consider its heavy metal content and the health risks if any.

Potassium is quite harmless, both chemically and it’s decay chain products. It does react with water though, so keeping a granite top dry is always a good idea. The number one reported repair to granite is waterdamage around sinks, according to two companies that repair all types of tops.

Scandium doesn’t seem to have any health effects.

Cobalt 60, yes that Cobalt 60, is another story. Luckily, in this case, the amount in the granite was pretty low. It does produce a dust that is a problem for radiation control. Cobalt 60 has an afinity for Arsenic, another commonly found element in granite, so don’t use granite as a cutting board, don’t roll dough on it.

Caesium is used in atomic clocks, mildly toxic for our discussion because it replaces potassium used in bodily functions.

Thallium is highly toxic, once used in rat poison and insecticides, but banned in the US in 1975. Thallium is also highly water soluable and readily absorbed through the skin. Again it is very close to potassium and can be taken up in the body’s potassium uptake pathways. Thallium has been used as a poisioning agent in murders, although an antidote, Prussian Blue, is available.

Lead needs little explanation, it is a neurotoxin that accumulates in soft tissue and bones.

Radium is taken up by the body as calcium, depositing in the bones and destroying bone marrow. It is a major source of the Gamma radiation in granite.

Thorium produces Thoron gas, which like Radon can decay inside the lungs. Ingestion is the biggest hazard, so again don’t use granite countertops as cutting boards or dough rolling surfaces.

Uranium is both water soluble and acidic liquid soluble, so acidic foods and liquids need to be cleaned up carefully off granite. Uranium is a toxic metal, has been linked to birth defects. Once in the body, it tends to bioaccumulate. Breathing the dust another hazard, of course the Radon that decays out of it is a hazard as well.

The complete lab report on the Juparana Bordeaux granite countertop can be found at the SolidSurfacealliance.org website