solidsurfacealliance.org Blog


Time is Running Out to Participate in the Houston Home Testing Program

Posted in Recent Info on the testing effort by Administrator on the June 29th, 2008

June 2008

Dear Houston Homeowner,

Time is running out to get your countertops tested for potential radon and radiation emission! The test is FREE and will give you peace of mind knowing your family is not being exposed to potentially unsafe levels of radon and radiation in your home. http://www.epa.gov/radiation/tenorm/consumer.html

BuildCleanTM, a Houston-based, not-for-profit organization, is conducting the tests to determine which granite colors, when used in indoor applications such as countertops and floors, may emit radon gas and/or radiation at levels above U.S. EPA recommended action levels. Exposure to indoor radon, which is the second leading cause of lung cancer in the United States, is a significant health risk. Studies conducted around the world over the last decade have concluded that certain types of granite—some of which are sold commercially in the U.S. far exceed the EPA’s action limit of 4 picocuries per liter. The issue is what type of granite do you have in your home and do you have adequate ventilation to mitigate any potential radon or radiation exposure. .

Why should you participate?

The only way to know if your home is safe is to test!

Your participation will contribute to a growing body of knowledge that will help determine future guidelines.

Participation is not limited to homes with granite; BuildClean™ is testing any “stone-like” product. If you have marble, Corian®, concrete, ceramic tile or quartz-based surfaces, you can still sign up.

Participation is quick and easy. BuildClean™’s certified radiation technician will install and pick up the tests at your convenience. The test units are safe, small and unobtrusive.

The test is absolutely free and both time and remaining test appointments are limited. Visit www.buildclean.org and sign up today!

BuildClean™ is dedicated to educating consumers and the building industry about safe, healthy and environmentally friendly building materials. By funding both laboratory testing and conducting the Houston in-home radiation and radon study, BuildClean™ hopes to determine which granites are a safe choice for use indoors.

To learn more or sign up to participate in this free study, please call 713-533-4509 or visit www.buildclean.org.

Sincerely,

Sara Speer Selber Ashli Ayer

President

What Information is Available on the Toxic Elements in Granite Countertops?

Posted in Granite Toxic Heavy Metal Issues by Administrator on the June 29th, 2008

For more info, go to forum.solidsurfacealliance.org

In addition to the radioactive elements in granite countertops, many of the elements are toxic as well. A wealth of information is available on ATSDR. This link is to the Radium toxicological profile. Click on the individual PDF for more information. There are also short version writen for laypersons that explains the risks in non technical terms.

They had this to say about Radium:

“There is no clear evidence that long-term exposure to radium at the levels that are normally present in the environment (for example, 1 pCi of radium per gram of soil) is likely to result in harmful health effects. However, exposure to higher levels of radium over a long period of time may result in harmful effects including anemia, cataracts, fractured teeth, cancer (especially bone cancer), and death. Some of these effects may take years to develop and are mostly due to gamma radiation. Radium gives off gamma radiation, which can travel fairly long distances through air. Therefore, just being near radium at the high levels that may be found at some hazardous waste sites may be dangerous to your health.”

To put this in perspective, the Houston TV report showed 1,115 pCi/Gram of Radium (adding RA 226 to RA 228) or 1,115 times higher than what is normally present in soil. This report on three hazardous waste sites show comprable levels of Uranuim, Thoruim, Radium and Lead.

At the SLAPS, a site used to store radioactive waste, the gamma exposure rate has been measured at 9 to 261uR/hr, with an average of 84 uR/hr. Some granite countertops are less than 9 uR/hr and the ones that concern us are from 25 uR/hr and up. So basically, this SLAPS hazardous waste site, protected by fencing and warning signs, is about the same gamma exposure that you would get from a higher level granite countertop! These hazardous waste sites have cost millions of dollars to clean up, control ground water and dust from escaping, and will cost millions of dollars to maintain. Yet we allow granite countertops with the same levels of contamination into our homes?

Here is a table showing the amount of contamination in pCi/Grams so you can compare it to the Houston Juparana Bordeaux.

What the Experts say about Radiation in Granite Countertops

Posted in Recent Info on the testing effort by Administrator on the June 29th, 2008

We ran across Dr. Chiodo last week on a Green Building site. He had this to say on that site:

“Radon infiltration, despite over three decades of educational exposure, is still is very much an issue. It is so much more latent. You see it in a lot of granite, igneous type of rock. Those often contain a lot of Radium, the radioactive parent of radon gas. You don’t just see it in basements. A lot of people have granite countertops and that can contain radium,” warns Chiodo.”

Of course I was intrigued, so I contacted Dr. Chiodo via email and got a phone call from him the next day. He was very concerned about the high radiation levels we are finding in granite countertop slabs, enough so that Dr. Chiodo warned us to contact a local environmental lawyer to write a disclosure/release form for customers to sign prior to purchase.

Dr. Chiodo also warned that any family members or children of the customers would not bound by the disclosure/release form. Since people usually stand in close contact to the granite edge while using a granite countertop, Dr. Chiodo warned of the potential for sterility lawsuits, even potential birth defect lawsuits.

Dr. Chiodo is uniquely qualified to offer an opinion on granite countertop radiation. He is a physician, attorney, industrial hygienist, and biomedical engineer with board certification in internal medicine, occupational and environmental medicine, public health and general preventive medicine, and industrial hygiene.

He received his Master of Public Health from Harvard University. He is the former Medical Director of the Detroit Health Department. He is an assistant professor of internal medicine at Wayne State University. He is currently the President-Elect of the Michigan Industrial Hygiene Society and Vice-Chairman of the Environmental Litigation and Administrative Practice Committee of the State Bar of Michigan. He has clinical privileges at the Henry Ford Health System and serves as the attorney for the Medical Staff of Henry Ford Macomb Hospitals-Warren Campus. He is licensed to practice medicine and law in Michigan and Illinois.

Dr. Chiodo also authored two books on Toxic Tort law.

Dr. Chiodo said that a storm of claims is potentially possible. I understand that in some sections of the country, claims don’t have to be proven beyond doubt. It will be up to granite fabricators to prove that their product didn’t cause the birth defect or sterility.

Florida Tests Granite Countertop

Posted in Granite Radiation, Recent Info on the testing effort by Administrator on the June 29th, 2008

Florida state has recently evaluated several residential units in high-rise buildings in south Florida to find the source of the Radon in the structures. Since soil based Radon usually is cut in half for each story upward, finding Radon in twenty story condos was a surprise.

As part of their search, they recorded the gamma spectra of the radiation emanating from various building materials including granite counter tops. That data is still under evaluation and they are still developing the techniques to interpret it. The evaluation should be complete by the end of August.

Other buildings have been studied and the concrete found to be the culprit. In one unit, it was a concrete ceiling that contributed the lions share of the Radon.

Once the information has been released, we will share the results.

A Report on the Juparana Bordeaux granite countertop in the Houston TV Report

Posted in Granite Radiation by Administrator on the June 16th, 2008

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

Dr. Harley on Long Term and Low Level Ionizing Radiation

Posted in Does Low Level Radiation Really Cause Harm? by Administrator on the June 13th, 2008

Some in the epidemiology field doubt that long term, low level ionizing radiation are harmful to humans. Some believe in “Hormesis”, a theory that radaition is good for you. In the following white paper, Professers Rudi H. Nussbaum and Wolfgang Köhnlein address the inconsistincies and open questions in the Hormesis theory.

It is a very readable paper, for its length.

Open questions and inconsistencies on health effects of low dose radiation

Another view on this subject is Dr. Walden’s article on Long term and low level effects of ionizing radiation.

Very readable and covers just about everything you would want to know about low level radiation.

Radon and Granite Countertops

Posted in Granite and Radon by Administrator on the June 13th, 2008

A few weeks ago, the MIA, Marble Institute of America, broke a 14 year old position that said granite countertops contained no Radon or radioactivity. An unpublished study was used, claiming that of 13 stones tested, only one had very high levels 292 pCi/L. Their calculation was predictably low, as the MIA set the protocol for the test. 26 square feet of Crema Bordeaux, the 292 pCi/L level granite in the test, was shown to add .27 pCi/L to a 2,000 square foot home.

Three main organizations have set dose/risk factors for Radon, the ICRP, the EPA, and BEIR IV. The factors range between .2 and 1.2 extra cancers from a lifetime exposure to 1 pCi/L.

If the MIA study is taken at face value, that would mean between .05% risk and .32% risk of developing cancer from 26 square feet of Crema Bordeaux. But there is a problem with the MIA study, the amount of granite was too low for a home of that size.

The average countertop sold in the US is between 65 and 75 square feet, versus 26 square feet from the MIA study. So a more realistic square footage would be from 2.5 to 2.9 times more granite. One should take the .27 pCi/L found in Crema Bordeaux and call it between .675 and .78 pCi/L which would cause between 1.35% and 3.48% increased risk of cancer.

That is a significant difference.

Another problem with their study was the highest level granite is actually a pretty low emitter. Crema Bordeaux usually measures around .24 mR/hr (Alpha, Beta, and Gamma) for a area like that used in the MIA study, they show a picture of the Crema Bordeaux section tested in the study.

So, .24 mR/hr put out .27 pCi/L of Radon in a home? But some Crema Bordeax will run as high as 1.45 mR/hr, or 1.63 pCi/L using their ratio of radon to radiation. But use a reasonable amount of granite in that home, say 65 square feet, and now the Radon level is That level of Radon will cause from 4 pCi/L to 4.7 pCi/L in that example. Radon at that level has dose/risks factors between .9% and 5 %.

Here is an excellent white paper on Radon risks, recently updated. Note that over 20 Radon studies are currently in progress, they take time to track the people exposed and wait for them to develop health problems.

Harley report on Radon

Another paper by one of the same authors above mentions that sealing aluminum foil or a dense coat of enamel paint helps the Radon gas decay in place, which has the effect of increasing Gamma radiation in the home.

Letting Radon out of your granite countertop lowers Gamma levels if a home is well ventilated

Here is the EPA FAQ site where they say to test all homes with granite countertops for Radon.

More Than 6,000 children From Benin Forced to Work in Granite Quarries

Posted in Granite social and envirnomental issues by Administrator on the June 12th, 2008

Police in Nigeria rescued 74 boys as young as 4 years old from granite quarries were they were forced to work. Sold into bondage by their parents in many cases, these boys carried stone for 35 cents a day.

The entire story can be read here
http://www.stoneworld.com/Articles/Industry_News/b8eb9f4b606f7010VgnVCM100000f932a8c0____?from=email

The Search for a Safe Radiation Level for a Granite Countertop

Posted in Granite Radiation by Administrator on the June 12th, 2008

What level of radiation is safe for a granite countertop? Using existing laws in the US, we were able to come up with some levels that might apply.

First off is a paper outlining what various states use for NORM, Normally Occurring Radioactive Material, found in the oil and gas industry. The industry seems to have an exemption allowing higher levels of radiation. From 5 pCi/g to 30 pCi/g is the range, with almost all states using the lower figure of 5 pCi/gram.

Oil and Gas equipment is allowed to be used if under 50 to 25 uR/hr above background. Gamma measurements are used because they are simple to take and inexpensive. Dose limits are taken from the IRCP and the NCRP recommended levels of 1 milliseivert per year (100 millirem per year), but both organizations recommend that the upper level should never be met, expected doses should be much less than the limit.

On yearly limits, NCRP says that anything over 5 times the yearly normal background radiation (100 millirems) needs to be mitigated, but they warn that ALARA principles should always be followed, that the goal should be significantly lower radiation than the allowed levels.
The paper concludes by recommending that levels be set at the ICRP levels of 50 pCi/g (47.5 uR/hr) for contaminated pipe and equipment, and waste and 15 pCi/g (14.25 uR/hr) for sludge and waste particles such as stone cuttings from the drilling of wells.

For remediation work such as salvaging or cleaning equipment to lower the radiation levels, the committee set a level of 30 pCi/g (28.5 uR/hr) exposure at which permission from the authorities must be obtained. They insist that some public good must come by the exposure, such as cleaning up a contaminated site, to justify the risk to the workers during cleanup.

You can view the original document here

http://www.osti.gov/bridge/servlets/purl/750593-B3YgBx/webviewable/750593.pdf

——————————————————————————————-

Another source is the EPA Project Summary that was written for the state of Florida on allowed levels of radiation in concrete for use in homes.
This study recommended the concrete was lower than 5 pCi/g (4.75 uR/hr) and that no material over 10 pCi/g (9.5 uR/hr) is used as a material.
This level may well be unobtainable by many of the granite types available. The lowest radiation level granite we have found is Absolute Black, with around 5 uR/hr after background levels are removed.
You can view the original document here
http://www.p2pays.org/ref%5C07/06324.pdf
—————————————————————————

This document details a survey of an area contaminated by Gamma radiation. Measured at a level of three feet off the ground, averaged levels of 13.8 uR/hr, with hot spots up to 27.5 uR/hr.

The study said this,

“radioactive contamination is defined as exceding the normal ambient gamma radioactivity level at one meter height by more than 5uR/hr — the criteria limit for this project.”

The original document is here

http://www.etec.energy.gov/library/D&D_page/N704SRR990034_FSDF_Baseline_Survey.pdf

Recent Info on the Granite Radiation Testing Effort

Posted in Granite Radiation, Recent Info on the testing effort by Administrator on the June 11th, 2008

June 10th, 2008
Major break through today on setting safe levels for granite countertops. A few weeks ago, Christina, my better half, contacted the EPA asking about granite slabs with specific levels of radiation.

They responded by asking for more time, then about a week ago, they responded by changing their online position on Radon and granite countertops, recommending that granite countertop owners have their homes tested for Radon.

Today, we received further information, including some info on what is considered a safe level of radiation in granite.

Below are some exerts from the letter, with the entire letter posted at the end of the article.

“The available data on the contribution of radon emissions from granite countertops to the indoor air level in homes is too inadequate to allow us to comment about it at this time.
While most granites used for building stone may not be considered harmful from a radiological viewpoint, some granitic deposits in the U.S., Canada, and elsewhere in the world, as you pointed out, host economically recoverable concentrations of uranium ore.”

So there it is, official proof that high radiation level granite countertop slabs can be qualified as containing Uranium ore.

Due to the economics of extraction, miners searching for uranium in granitic rock tend to look for concentrations primarily in intrusive veins or pegmatites. These ore bodies tend to be distinctive looking and separate from other parts of the surrounding “country rock” granite–this is the case for Namibian deposits for example. It is possible that enrichment could be found in adjacent host rocks, as either outliers of the commercial ore zones or an increase in naturally occurring radioactive minerals in the “country rock” used by quarries. However, most prudent mine claims, leases, or license boundaries are located if possible outside the mine able zones to ensure that current and potentially future economic resources are captured by the operation.

Dr. Hans Hensel stated on Garden Web a few days ago, that granite with veining pegatites were in high demand as countertop slabs, and that they were distinctive and unusual looking. The rest of the paragraph talks about the normal process of drilling core holes and mapping the Uranium deposits so that maximum use of the mining claim is taken. Outliers are dykes or veins that continue outside the main areas of ore.

“See Table 1.3 of our uranium report, volume 1, http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-voli/402-r-08-005-v1.pdf which illustrates the average naturally occurring radionuclide concentration values for igneous and sedimentary rocks, but this does not include the variations in range for each. The numbers below would not cause concern in a well-ventilated kitchen. “

The link seems to be broken for now, but here is the granite portion of that table.

All data in pCi/g
EPA average content for granite in table 1.3 in your Uranium Report.
EPA figures RA 226 1.3 U 238 1.3 TH 1.3 K 40 22
————————————————————————————-
Sample M RA 226 986.95 U 235 37.83 TH 144.76 K 40 53.96

Sample N RA 226 312.82 U 235 13.145 TH 36.92 K 40 30.139
Sample O RA 226 156.6 U 235 5.143 TH 22.458 K 40 37.912

Samples M through O are content levels in samples tested from a Bordeaux countertop that was removed earlier this year due to Radon hazards.

As you can see, all three samples from that Bordeaux countertop were much, much, higher than what the EPA said is average. Hundreds of times higher in some cases. You can also see that despite MIA expert Dr. Hans Hensel claims that most of the radiation in granite countertops comes from Potassium 40 ( K 40), in fact most of the radiation comes from Radon and Thorium.

“Assuming that the readings were accurate, a measurement of 7 micro Roentgens (microR) per hour would be considered a background reading from average soil and rock samples as naturally occurring radionuclides are found in most everything. The much higher readings you cite from the Brazilian sample and Tacoma slab, if accurate, could, under certain circumstances, pose a problem however for some people. The exposures would have to be continuous (e.g., hours per day) and prolonged (e.g., years) in order for there to be a significant increase in risk. The higher the exposure, the less time would be needed to create a higher risk. “

The readings are accurate, we had three of the same meter measuring the Niagara Gold slab, and all read the same. A check source came with our Leni Geiger counter, and the meter was calibrated before shipping by an expert in the field. In addition, a radiation enthusiast used his other methods of measurement to confirm that our meters were accurate and calibrated correctly. We find the questioning of the levels understandable, in this case, this expert had no idea that such radioactive granite countertop slabs were being imported. Note that the EPA expert said that “could, under certain circumstances, pose a problem however for some people.

“Data at this time is inadequate to characterize the radiation risk posed to individuals who spend extended periods of time in close proximity to countertops with the elevated levels of radiation as you describe. “

So there it is, even the EPA says that the radiation risks are unknown…… This is not good.

“Federal and state agencies generally provide controls for exposures of members of the public to radioactive substances. Without going into a lot of detail on this topic, EPA and some State agencies have used an exposure of 20 microR/hour as a remediation action level for entire rooms, homes or buildings. Any review of the contribution of countertops to overall dose from radiation and radon in a home would examine, among other factors, time spent in a kitchen versus other living and sleeping areas, which minimizes the exposure from a single source such as a countertop. “

Early on, after getting our meters, I chose 20 uR/hr as an arbitrary level of radiation that a hunch told me was the dividing line between good granite and dangerous granite. Turns out that I was pretty close. Much of the “hunch” came from reading for months on this subject, some of it must have soaked in.

Twenty microRems per hour is written as 20uR/hr. In the coming days, as our radioactive granite data gets posted, you can use this figure to put readings in perspective. One thing, though, they using this figure not on contact as we are, they are holding the meter about 3 feet off the ground. So to get exact figures, we will need to start measuring 3 feet away from the slab. And some granites will exceed this, as much as 150 uR/hr at three feet in the case of Four Seasons.

The rest of the letter is about fabrication shops like ours, the dangers from working a high level granite and the steps we should take to prevent problems. After reading that section, one wonders why the granite industry generally wants to derail the testing effort. It seems they and their employees have more to be afraid of than homeowners in most cases.
We will be replying tomorrow, outlining our check sources and quality control methods used in testing, as well as asking if the Juparana Bordeaux countertop was a risk to the homeowners before it was removed.

Here is the emai from the EPA, I removed the authors contact info so he doesn’t get a bunch of hate mail.

Dear Ms. Weigel,
Thanks for sending all this research information. I will try and address your concerns.

Uranium, radium, and thorium are natural constituents of the wide number of mineral species occurring as crystals which can be found in granites from around the world. Some granites are more radioactive than others, depending on the geothermal fluids present in the matrix which then cooled to form the mineral grains.
The presence of radium and thorium in the mineral matrices can decay into radon which may be released over time through radioactive decay. The presence of these minerals in an igneous rock matrix (which includes granites) rather than sediment acts to decrease the radon flux rate however. The available data on the contribution of radon emissions from granite countertops to the indoor air level in homes is too inadequate to allow us to comment about it at this time.

While most granites used for building stone may not be considered harmful from a radiological viewpoint, some granitic deposits in the U.S., Canada, and elsewhere in the world, as you pointed out, host economically recoverable concentrations of uranium ore.

Due to the economics of extraction, miners searching for uranium in granitic rock tend to look for concentrations primarily in intrusive veins or pegmatites. These ore bodies tend to be distinctive looking and separate from other parts of the surrounding “country rock” granite–this is the case for Namibian deposits for example. It is possible that enrichment could be found in adjacent host rocks, as either outliers of the commercial ore zones or an increase in naturally occurring radioactive minerals in the “country rock” used by quarries. However, most prudent mine claims, leases, or license boundaries are located if possible outside the mineable zones to ensure that current and potentially future economic resources are captured by the operation.

See Table 1.3 of our uranium report, volume 1, http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-voli/402-r-08-005-v1.pdf which illustrates the average naturally occurring radionuclide concentration values for igneous and sedimentary rocks, but this does not include the variations in range for each. The numbers below would not cause concern in a well-ventilated kitchen.

Radiological testing of imported, or domestic, granite is not a common practice. There have been numerous studies on the contribution of building stones to background radiation, and some limited studies on comparisons of radiological levels between different granites.

One problem in conducting the research you cited is that radiation detectors must be checked against a source of a known radiation level (check source) to verify that its readings are accurate. The divergence in numbers you cited for the Brazilian sample using different machines suggests checking their accuracy might be useful. Assistance from geologists, health physicists, or other licensed radiation professionals would be helpful in this instance–you might want to inquire at Oklahoma State University, or the Oklahoma Department of Environmental Quality’s Radiation Management Section, both in Oklahoma City, for example.

Assuming that the readings were accurate, a measurement of 7 microRoentgens (microR) per hour would be considered a background reading from average soil and rock samples as naturally occurring radionuclides are found in most everything. The much higher readings you cite from the Brazilian sample and Tacoma slab, if accurate, could, under certain circumstances, pose a problem however for some people. The exposures would have to be continuous (e.g., hours per day) and prolonged (e.g., years) in order for there to be a significant increase in risk. The higher the exposure, the less time would be needed to create a higher risk.

The dose of radiation an individual receives is based on the amount and types of radiation (gamma, alpha, beta for example), distance to the radiation source, shielding (useful primarily for alpha or beta radiation, not so much for gamma), and time of exposure. When measuring the dose rate with a meter, health physicists will examine the radiation level both at the source, and at a distance (in a room’s center for example, with the measurement at waist level) to more objectively portray the likely exposure of an individual. Data at this time is inadequate to characterize the radiation risk posed to individuals who spend extended periods of time in close proximity to countertops with the elevated levels of radiation as you describe.

Federal and state agencies generally provide controls for exposures of members of the public to radioactive substances. Without going into a lot of detail on this topic, EPA and some State agencies have used an exposure of 20 microR/hour as a remediation action level for entire rooms, homes or buildings. Any review of the contribution of countertops to overall dose from radiation and radon in a home would examine, among other factors, time spent in a kitchen versus other living and sleeping areas, which minimizes the exposure from a single source such as a countertop.

Occupational exposures to stone cutters, cabinet or carpentry employees is another concern. In such instances, the potential for increased direct radiation, inhalation, and ingestion of particles as well as radon gas might be increased in shops where large amounts of stone with elevated levels of radiation are stored and worked. There are a few immediate courses of action you may be able to take. The first would be to take radon measurements in the workplace with charcoal canisters (generally available at larger hardware stores or online) or other radon detectors. If so, place them in accordance with the manufacturer’s/laboratory instructions in locations likely to be accessed by workers (though probably not on top of one of the suspect granite slabs). Also, carefully follow the instructions on handling, packaging and returning the devices for analysis. Although EPA does recommend an action level of 4 picocuries/liter of air for homes, schools, and a few industries (drinking water treatment and sewage treatment plants), you may wish to consider the advisability of increasing indoor ventilation should your own readings equal or exceed that level. Secondly, consider having a licensed health physicist conduct a radiation survey of your shop and make recommendations on health and safety practices to minimize worker exposures to radiation. Again, the Oklahoma Department of Environmental Quality’s Radiation Management Section may be able to provide you with some additional guidance or list of qualified radiation specialists.

I hope this information is helpful. Please contact me if you have any further questions.

(Mr.) L S

Geologist
U.S. Environmental Protection Agency

1200 Pennsylvania Ave., NW
Washington, DC 20460

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