What is the most radioactive substance found in nature?
December 12th, 2010
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What is the most radioactive substance found in nature?
That sounds like a very simple question, but in fact it’s a much more complex one than it seems at first glance. It is, however, an important one, because when it comes to nuclear waste disposal, it’s fair to ask how the material compares to what is already found in the environment.
To answer this question, it is necessary to qualify what “most radioactive substance found in nature” really means:
- It must be found on earth and at this time, thus disqualifying substances that may have once existed on earth but have decayed away.
- The “substance” must exist on its own, in concentrations found in nature. This disqualifies substances that are highly radioactive but only found in minuscule concentrations, mixed with other material. Thus, lead-210 would not qualify, because it is always found mixed with its parent radionuclides, but bulk uranium ore would qualify, because it found in natural concentrations and non-microscopic quantities.
- It must exist in a concentration and activity as the result entirely of non-human activities. Thus fallout from Chernobyl that has accumulated would not qualify, nor would radium-226 paint, even though radium-226 is a natural isotope.
A major issue inherent to this question is the issue of radioactivity. The shorter the half-life of a radioisotope, the more radioactive it is and the longer that half-life, the less radioactive it is. However, shorter half-lives also mean that the substance decays away faster, before it can accumulate in any significant quantity in a natural setting.
Any radioisotope found in nature can be categorized into one of three basic groups:
- It is extremely long lived, with a half-life of billions of years, thus allowing it to continue to exist in significant quantities from primordial times. These radionuclides were part of the material that initially formed the earth and have been concentrated into minerals by geological forces, just as other elements have. Examples of this include thorium and uranium.
- They are continuously produced by a natural force, such as cosmic rays in the upper atmosphere. An example of this would be carbon-14.
- They are the decay product of a long-lived or continuously produced isotope.
.PNG)
The fact that only natural forces can concentrate these substances is problematic. For one thing, isotopic separation is a complex and energy-intensive process that does not occur to any major extent in nature. Therefore, an isotope like carbon-14 will always be found mixed with other non-radioactive carbon and potassium-40 will be found with non-radioactive potassium, this reducing the total bulk activity of the sample. Thus, for concentration to occur at all, it must be an isotope of an element that does not have abundant non-radioactive isotopes.
The other problem is that natural forces are generally too slow to concentrate the most radioactive radionuclides. The formation of minerals normally takes thousands to millions of years. Therefore, a substance like polonium will not be concentrated by these processes. Polonium is found in uranium ores, but the amount is always tiny and the time it would take to leach out of the ore and form into its own mineral is far too long given the fact that the half-life of Po-210 is 138 days and the half-life of polonium-218 is three minutes.
Finally, the answer to the question:
Having done some research on this topic, I’ve come up with a couple of good candidates.
Radon-222 – Radon is a daughter product in the uranium decay chain, resulting from the alpha decay of radium-226. Most daughter products will remain suspended in the material they originated from, but radon-222 is unique because it is an inert gas. Radon may remain immobile if it arises deep in solid rock and has no place to escape to, but in circumstances where a void exists or the material is porous, the radon can concentrate in pockets.
The concentration which radon can accumulate to is also limited by its short half-life of 3.8235 days. If the area is open to the atmosphere, the radon will be diluted by air, but it may still exist in very high concentrations. However, the short half-life also means that it is an extremely radioactive substance. Hazardous levels of radon have been found in uranium mines and are blamed for chronic health problems in uranium miners who worked in the industry before good ventilation practices were implemented.
Radian barite / Radiobarite- Radian Barite (AKA Radiobarite) probably fits the bill best for “most radioactive substance found in nature.” This mineral is composed of radium-226 and barium sulfate. It may be found in the form of radium-rich barite compounds, often in ground water, in areas where uranium and barium are both present in the local enviornment. On occasion, pure, highly concentrated radium-rich barite may be found on its own, though this is rare.
The most concentrated grades of radian barite contain a whopping .85 grams of radium per kilogram. That’s a huge amount – more than enough to make the material dangerous to handle. The most concentrated forms of radiobarite can produce lethal irradiation in a short period of time. Much of the radioactivity comes not from the radium itself, but from its own daughter products. Radian barite will generate huge amounts of radon gas and daughter products like bismuth-214, polonium-210 and lead-210.
Radium-226 is a daughter product of uranium decay. As mentioned above, most daughter products are too short lived to ever be found anywhere other than with the material that produces them. Radium-226, however, is an exception. With a half-life of 1600 years, Radium-226 lasts just long enough to allow it to accumulate outside its parent ore. Radium is also chemically reactive and soluble.
In areas where the proper geochemistry and hydrology exists, radium found in uranium ore deposits forms water soluble salts, such as radium sulfate. These radium compounds leach out into ground water. Chemically, radium is very similar to barium and thus will often crystallize with barium to form radian barite.
This natural process is very similar to the first steps of process of separating radium from uranium ore, as was pioneered by Marie Curie. Curie used a series of steps to dissolve and separate uranium ore components down to a highly concentrated solution of radium and barium compounds, which were then further separated to concentrate the radium from the barium.
How potent the radiobarite is depends on a number of things, including the concentration of radium and how much of it has decayed away. However, even after two to three half-lives, the mineral is still very radioactive.
Highly concentrated soluble radium has also been known to be found in the drilling sludge brought to the surface by natural gas exploration.
More information on highly concentrated radium minerals can be found on this thread.
Natural nuclear reactor material (honorable mention) – This material is not currently very radioactive, because it has been decaying for more than one billion years, but at one time, naturally occurring nuclear reactors produced highly concentrated material similar to modern spent fuel. These reactors were able to reach criticality at a time when uranium ores contained more U-235 than they presently do because less time had passed for it to decay.
The best known example of a natural nuclear reactor is found in Gabon, Africa. The reactor achieved a self-sustaining fission reaction about two billion years ago. The material has remained largely in place and has not resulted in the sky falling or any other global disaster.
This entry was posted on Sunday, December 12th, 2010 at 6:40 pm and is filed under Enviornment, Good Science, History, Misc, Nuclear. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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December 12th, 2010 at 7:33 pm
Ramsar, Iran is a city located along the Caspian Sea north of the mountain range of Elburz. There are many hot-springs in the city which have high radium concentrations. This makes the area one with the highest background radiation in the world. The background radiation there has been measured at 22μGy/h at 1 m high and 73μGy/h on the surface. Yet demographic data shows no significant increase in the frequency of death, abortion or cancer among inhabitants of this area.
Not really on topic I guess…
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December 12th, 2010 at 7:36 pm
DV82XL said:
No, I’d say that’s on topic
Those numbers would be considered absolutely unacceptable for any kind of waste storage facility or processing facility or anything like that.
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December 12th, 2010 at 11:00 pm
I think you hit it with Radiobarite. Radium-226 is known to mobilize from uranium deposits when the uranium is porous and it can be carried by groundwater. It has a reasonably long halflife, but with radium it’s not actually the decay of the radium itself that is necessarily the big concern. Radium is a high energy alpha emitter but most of the gammas come from its decay products. If I recall correctly bismuth-214 is the major gamma emitter. When you have ra-226 that has been sitting for any period of time you actually have a complete series of decay products in equilibrium, about ten of them total, so the mixture is roughly ten times the activity that the halflife of radium-226 alone would indicate. VERY HOT STUFF.
High concentrations of radium sulfates and other compounds are known to come from some groundwater. “Radium springs” were once considered therapeutic, and yes they do have high radium concentrations, although they vary by a lot. It’s like a natural radium-extraction operation. All in all, most of the springs that have radium are not high enough to be acutely dangerous from limited exposure, but if it crystallizes and you end up with radium-barium concentrates, then that would be very hot.
I think you could make the argument that some of these minerals are far worse than spent fuel. Spent fuel and most other forms of high level waste are chemically inert and not mobile. Radium compounds can be very reactive, soluble and have high biological uptake.
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December 12th, 2010 at 11:32 pm
Interesting. I think you are meaning that the shorter the half life the higher the ‘specific activity’ rather than simply ‘radioactivity’ although I would concede in general terms one might consider them to mean the same. Clearly the mass of say 1g, of pure Co-60 is going to be more ‘active’ (radioactive) than say 1g of pure U-238 (which of course has a much longer half life). But looking at it another way, I would rather stand next to 1g of H-3 in a glass vial (12.3 year half life, low energy beta emitter), rather than 1g of Ra-226 (much longer half life but alpha, beta and medium energy gamma emitter)!
Anyway, some of the ‘hottest’ places I have stood whilst doing my job is in a Uranium and Thorium mineral store – would make the toes curl of many a ‘nuclear worker’.
Mark
p.s. “nucleotides” or “radionuclides”
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December 13th, 2010 at 9:06 am
Great post. Though I would note that if you are concerned with radioactive material in terms of health effects, then activity is only part of the equation. Decay mode (alpha, beta, gamma, etc.) and energy need to be considered to actually determine absorbed dose rates. Also, different types of radioactive decay will result in different exposure pathways (e.g. gamma rays are whole body irradiators, while alpha particles have a very short range and are only a hazard when internalized). If you really want to get technical, you should also consider the biochemistry of each nuclide. For example, ingested lead and uranium find their way into bones and can irradiate tissue over a very long time period, while something like tritiated water will be excreted in a shorter period of time and through different biological pathways.
Also, I can’t help but nitpick:
Nucleotide – class of organic molecules forming the structural basis of DNA and RNA
Nuclide – a species of atom as described by the content, and energy state, of its nucleus (i.e. Z,N,m)
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December 13th, 2010 at 9:13 am
DV82XL said:
This is similar to a case in Taiwan where several apartment buildings were constructed using rebar that contained high concentrations of Co-60. The buildings had already been inhabited for some time when this was finally discovered. Apparently cancer rates among inhabitants have been found to be lower than for the general population. I used to have an article on this, but I can’t seem to find it. You can probably Google it…
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December 13th, 2010 at 9:39 am
MedPhys said:
The article is available on PubMed. PMCID: PMC2477708
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December 13th, 2010 at 12:23 pm
MedPhys said:
Think I have highlighted this article before, Chen et al study on “Effects of Cobalt-60 Exposure on Health of Taiwan Residents Suggest New Approach Needed in Radiation Protection”, is an interesting article which I thought of as well when I saw the post about Ramsar.
What I would like to know is how they managed to get hold of Co-60 contaminated rebar in the first place, Co-60 is from neutron activated Co-59 and has no natural sources on this scale…
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December 13th, 2010 at 12:33 pm
Matte said:
It isn’t the first time this has happened, and always it traces back to some radiotherapy machine that has been improperly scrapped by some treatment facility. The lackadaisical attitude with which medical sources are handled in many countries is appalling, and while there have been few deaths, it is just not acceptable. The nuclear power industry would have been pilloried for any one of these accidents, someone would have gone to jail, and we would have never been allowed to forget it. Medical facilities are hardly given a slap on the wrist.
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December 13th, 2010 at 12:38 pm
“Hazardous levels of radon have been found in uranium mines and are blamed for chronic health problems in uranium miners who worked in the industry before good ventilation practices were implemented.”
Ironically, there are “health spas” that take clients deep into abandoned and unventilated uranium and gold mines (uranium is often found in proximity to gold) and claim that radon exposure can provide relief from chronic pain. Those people are nuts. Or at least I haven’t seen a reputable study that accounts for the placebo effect that backs up their claim.
Regarding Ramsar, my understanding is that there have been no rigorous statistical evaluations of life expectancy or health effects, but anectdotally we know the people there are not dropping like flies or walking around with two heads despite living in an area with background radiation levels several times higher than the average. There is speculation that the people there may have developed an adaptive response in the form of a gene variant that affords radiation exposure tolerance just as Tibetan Sherpas are known to carry a gene variant that allows them to better tolerate low oxygen concentrations at higher elevations. Evolution at work.
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December 13th, 2010 at 12:56 pm
Blubba said:
There is some truth to that observation. In industrial hygiene this is called the ‘healthy worker effect’ where due to the fact that those adversely effected by conditions leave, of die, the group left shows less of a health impact than is expected.
However there are places, like Colorado in the US, where background radiation from NORM is about three times higher than the national average that does have good data over a long time frame where there is compelling evidence for the positive effect of low dose radiation on longevity.
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December 13th, 2010 at 1:26 pm
Mark said:
Yeah, sorry. My spell check does not reconize “nucleoide” and auto corrected a couple of them to “nucleotide” which it does recognize.
I corrected it.
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December 13th, 2010 at 1:41 pm
Matte said:
Cobalt, of course, is ferrous. When scrap metal is recycled, it is common for cobalt to be mixed with iron and steel of various grades, which are sent back to be resmelted. This has resulted in cobalt-60 sources from medical and industrial sources ending up in the mix when steel products are fabricated from recycled scrap.
It has happened a number of times actually. Of course, how severe it is depends on how much cobalt-60 went into a given quantity of iron scrap.
Blubba said:
Despite the fact that I generally support homeostasis over LNT, I find this kind of thing absolutely insane. There’s no evidence that it actually helps with an acute condition like pain relief, and when it comes to the possible beneficial effects of low levels of radiation exposure, this still strikes me as a very bad idea. Radon is just not a good pathway to do it. It would not give you consistent whole body exposure. Some parts of the body get negligible exposure and the lungs get much higher exposure relative to the general full body dose.
You could end up with decay products causing high exposure to the lungs for extended periods of time while the exposure to most organs is negligible.
On top of that, there’s no reliable metering or dosimetry in these spas, and I consider that highly irresponsible.
MedPhys said:
Of course this is all true, and I think someone noted that radium compounds found in nature are much worse for biological uptake than the ceramic oxide-based spent fuel rods or the vitrified waste from reprocessing.
Yeah, this can get much more complicated. Alpha and low energy beta are not harmful outside the body, but in terms of radiotoxicity they’re worse than gamma emitters (all things being equal) but gamma emitters are harmful by proximity exposure.
Then there are issues of biological halflife and whether it bioacumulates and environmental mobility… etc etc etc.
And of course, it will vary depending on the background and nutrition of the individual. A person with low calcium uptake is more likely to uptake certain elements into their bones etc etc.
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December 13th, 2010 at 2:00 pm
DV82XL said:
My understanding is the healthy worker effect is due to the simple fact that healthy people are more likely to be in the workforce to begin with, have better access to health care than nonworkers, have access to higher quality food, etc. The unhealthy are not necessarily genetically defective or unadapted. They may, for example, be permanently disabled due to a car or household accident or may have caught a chronic illness due to factors unrelated to a work environment that make employment difficult. It does not necessarily have anything to do with a physiological response or genetic adaptation to specific environmental stresses.
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December 13th, 2010 at 2:02 pm
Speaking of Polonium…
Next time you’re bored and want something amusing, look up the people who blame polonium in cigarettes for making them extra double deadly dangerous.
(The mechanism is supposedly that some form of fertilizer or other ends up concentrating it… which is plausible, but what little I recall from researching it the last time a nutter said it at me suggested that the amounts are still so low as to be irrelevant compared to the carcinogenic effects of the smoke itself.
Needless to say there’s overlap between this theory and pushing “organic” tobacco products…)
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December 13th, 2010 at 2:18 pm
Blubba said:
HWE is not a single cause issue but a spectrum of explanations that show up as confounding variables in industrial heath studies. The main ones are:
The Healthy Hire Effect. Employers have the right to reject certain persons for employment because of physical disabilities, or poor general health. An employer will exclude those obviously at high risk.
The Healthy Worker Survivor Effect. This is the one I was referring to, where, for example iron foundry workers seem to have a higher tolerance for heat. This is because those that can’t take it leave. But it can also show up for other insults, where some workers just have a higher threshold of exposure than others.
The Time-since-hire Effect. The length of time the workforce has been followed. HWE is a characteristic of actively employed workers. Incomplete follow-up of the out-migrating section of the cohort could result in failure to track every individual to determine his vital status.
The Beneficial Effect of Work. This is the one you are commenting on. Improved access to healthcare, routine disease screening and physical exercise is the beneficial effect of work. While there is a wide agreement on the first three factors, there is debate on the extent of the beneficial effect of this one, however there is some logic in it I think.
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December 13th, 2010 at 2:25 pm
drbuzz0 said:
Compared to the exposure uranium miners back in the Cold War heyday recieved from daily constant exposure, and relative to the exposures patients routinely recieve from when injected with Tc-99, I-131 and other medical isotopes, the spas strike me as a simple scam rather than a potential health hazard.
I used to be a proponent of radiohormesis, but over the years it seems that any effect, if it exists at all is too small to matter. By the same token, even if you believe in LNT, the public health risks associated with the tritium leaks from leaking nuclear plants is likely negligible…but does make for a sensational story for those who don’t know better.
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December 13th, 2010 at 3:18 pm
MikeC said:
Oh FFS….don’t mention this to the chemtrail crowd – you just know what’ll happen if they find out that Barium of any variety is involved in anything that is also radioactive……;)
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December 13th, 2010 at 3:21 pm
Blubba said:
The evidence for radiation hormesis is a bit better than what you are suggesting. While I agree its not as overwhelming as some proponents claim it is, what is there is solid, and has withstood the test of time. That is to say that the data gathered over the last forty years has demonstrated that a radiation hormesis effect is more plausible than LNT effect for low dose chronic exposure.
I agree any health effect claimed from the spas are nonsense, (except for those that work there maybe) but I did get a bit of a rush (purely physiological of course) when I climbed into the one at Radium Springs B.C. several decades ago with my wife. It was almost worth putting up with the reaction of my mother-in-law who went on about the potential damage we had done to her yet to be conceived grandchildren for years afterward.
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December 13th, 2010 at 5:38 pm
Sigivald said:
I certainly will not disagree that tobacco smoking has a very strong link to increased risk of cancer (and a number of other things) It may be the single most direct and preventable environmental factor in cancer.
I have always disagreed about the polonium exposure, however. While it may well contain some naturally occurring polonium-210, I doubt that causes the damage. I’d be more worried about the numerous chemical carcinogens known to exist in abundance in tobacco smoke.
It’s not unlike the uranium in coal smoke thing. I’ve been accused of being pro-coal because I am not concerned about the uranium emitted by coal plants. In fact, while I’m not concerned about the uranium, I am very concerned about the enormous amounts of mercury, cadmium, arsenic, nitrous oxides, sulfur dioxide, soot, fly ash and other nasty things.
All I can think of with the Po-210 tobacco thing is some people might stupidly be more afraid to smoke once they hear the word “radioactive” versus telling them all day about all the toxic chemicals they’re inhaling.
Anyway, unless the contention is that tobacco also contains lead-210 (and thus would continuously regenerate the Po-210) then there’s a simple solution to getting rid of the Po-210 from your smokes: keep your cigarettes in storage for a few years before smoking.
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December 13th, 2010 at 10:13 pm
Serendipitously I found this on Wiki while reading about Niue: (http://en.wikipedia.org/wiki/Niue)
I have no idea where these fit in the scheme of radioactive things tho……
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December 14th, 2010 at 12:09 am
Someone used this on a forum as an example of why nuclear power is good. I call bull****.
Radioactive stuff should be left in the ground but anything made in nuclear waste is bound to be 100x dangerous. Does it matter though? What we should make more of this crap? Leave it before it kills some more babies, I think.
Solar and wind is the way to go and pretty much everyone agrees with that anyway because no waste.
This is so crappy. I bet you would not want that stuff in your house. So why in your childrens?
How about depleted uranium. There’s nothing depleted about it.
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December 14th, 2010 at 1:01 am
Spiz said:
We stagger back against such crisp logic combined with such a scintillating delivery, no doubt though (just for form’s sake, of course) that you can supply some proof for your brilliant arguments, so that we all can learn the source of such deep wisdom.
You @sshole
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December 14th, 2010 at 2:12 am
Spiz said:
Not enough room inside (I have an apartment), but I’d totally get one of those Hyperion generators if I could afford the price tag (assuming they spec out as predicted) and had a decent-sized backyard.
No more power outages, and imagine the grill you could run off of one of those as a heat source (BBQ a whole cow in a couple min)…
Bugger – just made myself hungry.
Hey DrBuzz0 – Speaking of natural radiation sources, I’ve heard some conjencture that the natural Gabon reactor might have caused a slightly higher mutation rate in its region, resulting in, well, us. Any idea whether there’s any research on that?
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December 14th, 2010 at 1:40 pm
drbuzz0 said:
How many people would actually do that?
But anyway, if there’s lead in the cancer sticks it’d probably be worse than any Polonium (especially since to get Pb210 you’d probably need quite a bit of stable lead as well).
Is it just me or do the trolls (such as Spiz) all sound alike, as if it might just be a handful of people using multiple names?
Spiz said:
This line in particular looks very familiar, I’m sure it’s come up by quite a few different people around here.
Matthew said:
I doubt it’d be all the significant and it was a couple of billion years ago, long before even the Cambrian explosion.
Though the ever reliable Wikipedia claims that a Science Fiction novel had the Oklo reactors actually being alien and used to create mutations to lead to humans.
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December 14th, 2010 at 1:52 pm
Anon said:
Hmm… could be a fun read. What was the author/title?
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December 14th, 2010 at 4:29 pm
Matthew said:
I would very very much doubt it. First, even when the reactor was critical, it would really be a drop in the bucket of background radiation, except when right on top of it.
Also, homo sapians are far too new a species to really have anything to do with the potentially higher radiation. Even mammals are too new.
these reactions happened close to two billion years ago. By the time the first dinosaurs were roaming the earth they had already been decaying and buried under layers of sediment for over one and a half billion years, and most of he radioactivity was gone.
Any of our ancestors around at the time of the reaction or shortly thereafter would have to be very very distant.
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December 14th, 2010 at 9:05 pm
Matthew said:
There might be a reference somewhere at http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor#In_fiction
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December 15th, 2010 at 12:40 am
Anon said:
oohh… Zelazny…
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December 15th, 2010 at 4:50 pm
I think I have discovered the source of much of your frustration – http://www.alternet.org/story/149193/study_confirms_that_fox_news_makes_you_stupid
Having read the URL title you pretty much knows what it is going to say!
The little bit that it doesn’t cover is that the effect is cumulative – the more you watch Fox, the more stupid you become!
Of course that does make the corolory true – not watching Fox does not make you intelligent – we dont’ have Fox here (AFAIK), and there’s plenty of stupid around – http://chemtrailsnorthnz.wordpress.com/
And presumably not EVERYONE who watches Fox is stupid – I am sure there is some immunity breeding into the population….humanity is resilient like that…perhaps some natural radiation if creating a Fox-resistant gene in an otherwise susceptible stand of DNA as I type…
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December 15th, 2010 at 5:49 pm
MikeC said:
Oh, I think that a better title for that article would be “Website Confirms that Its Authors Don’t Understand the Difference Between Correlation and Causation.”
So people with certain opinions about some rather divisive issues tend to vote a certain way or watch a certain TV channel. Why is this news? Why is anyone surprised by this?
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December 15th, 2010 at 6:08 pm
BMS said:
How about: “Website confirms that Its Authors Are Human – Think Anyone Who Disagrees With Them is an Idiot”
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December 15th, 2010 at 6:30 pm
Or even “Blog commentators lack sense of humour”? :p
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December 17th, 2010 at 7:53 pm
MikeC said:
All that website does is demonstrate that Mr. Howard is either stupid or so wrapped up in himself that he has no grasp whatsoever of reality. The funny thing is that with the possible exception on O’s birth certificate, which the jury is still out on, everything he claimed was a Fox lie, happened to be true.
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December 26th, 2010 at 9:40 pm
hottest mineral I’ve ever personally seen: http://webmineral.com/data/Betafite.shtml
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December 29th, 2010 at 10:59 pm
~4 uSv/h g is pretty hot for a natural mineral, nice find!
Spiz said:
Do you even know what depleted uranium is? Any knowledge in basic chemistry? No?!
Solar and wind does produce a lot of waste, the lubrication oils for a wind turbine does have a significant local impact close to the turbine. Solar panels contain heavy metals (especially thin film type) such as cadmium, arsenic, molybdenum and others. Not to mention all the energy required to make the concrete and steel structures…
Also wind power requires neodymnium (spelling?) for the magnets in the generator, a finite and expensive resource. Guess which country in Europe emits the most amount of CO2 per generated kWh electricity (only counting power generating industry). Yepp, it is Denmark (most amount of wind power per capita in Europe) , proving that wind power has a long way to go.
I have references for my rant, but am currently not at home so can’t post them at present time, can do if anybody is interested.
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January 10th, 2011 at 8:50 pm
I got this from a mailing list I belong to:
Dear colleagues:
Attached is a new OnlineFirst Cancer Epidemiology, Biomarkers & Prevention Journal publication by Michelle Turner et al. (2011) titled “Radon and Lung Cancer in the American Cancer Society Cohort.” (link to descriptive article) The paper (provided by Jerry Cuttler) is another example of misinformation being spread claiming harm from low-level radon in the home. Please note that multiple levels of adjustments were made to the data in order to come to the conclusions presented.
In a previous publication, I have pointed out several tricks that are used by some researchers in such studies to allow for concluding an LNT-type, dose-response for low-dose, radiation-induced cancer. One of the tricks is ignoring evidence for threshold and hormetic-type dose-responses and forcing an LNT function through the low-dose data after including high-dose data where cancer risk is clearly elevated.
As can be seen in the attached paper, the data presented in column 5 of Table 3 for what is called the minimally-adjusted hazard ratio (HR [estimates relative risk]) implicated a hormetic dose-response for lung cancer mortality as has been demonstrated by Richard Thompson and colleagues and by Bernie Cohen. For the minimal-adjustment results, data were stratified according to age, race, and gender and the HR was less than 1 for radon levels < 150 Bq/cubic meter.
Apparently, to get rid of the hormetic response, multiple additional adjustments were made to the data.
Adjustments were made for education, marital status, body mass index, body mass index squared, cigarette smoking status, cigarettes per day, cigarettes per day squared, duration of smoking, duration of smoking squared, age started smoking, passive smoking, vegetable/fruit/fiber consumption, fat consumption, industrial exposures, and the occupation dirtiness index. Please note that some of these factors are strongly correlated (i.e., are not independent, e.g. cigarettes per day and cigarettes per day squared).
The adjustments did the job of getting rid of the hormetic response but did not eliminate the threshold as can be seen from the data in column 6 of Table 3 for the fully-adjusted HR which shows no significant increase in the HR for radon levels < 150 Bq per cubic meter. An additional adjustment was also then made by stratifying on the state of residence. This too did not eliminate the indicated threshold (no significant increase in the HR for < 150 Bq/cubic meter).
Thus, the authors relied on a trend test with the high dose data included and LNT model being applied to allow for the following conclusion and impact statements: "Conclusion: This large prospective study showed a positive association between an ecological indicator of residential radon and lung cancer. Impact: These results further support efforts to reduce radon concentrations in homes to the lowest possible level." Further, based on imposing the LNT model, they state the following: "A 15% … increase in the risk of lung cancer mortality was observed per each 100 Bq/m3 increase in radon."
Any comments you may have on the paper and are willing to share with those on this e-mail list would be very much appreciated.
Best wishes,
B. R. Scott
Senior Scientist
Lovelace Respiratory Research Institute
2425 Ridgecrest Drive SE
Albuquerque, NM 87108 USA
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January 11th, 2011 at 4:31 pm
I think I told the story about when I was a kid and my parents were selling the house. One of the home inspectors said we needed to have it checked for radon. A company charged a lot to put an air sampler in the basement for a few days.
After that, they said we had too much radon, our levels were above the standards. Not much above, mind you, but slightly above. So we had a choice: have it tested again or have them do something to reduce the radon levels. The test levels can vary a lot depending on weather, barometric pressure and such.
Anyway, not wanting to spend the money for another test only to fail, my parents asked what to do. The company recommended a radon removal system – a couple thousand dollars. Given that my parents did not want to spend this much, they asked for another option. The company said that they could remove our sump pump and put in a sealed sump system. This was not parenteral to reduce radon enough, but they said there was a good chance it would.
So, a few hundred dollars for the new sump pump system and a couple hundred on more radon testing and… It was lower, but still above what we were told were the standards.
So now they told us we had to go for the big system anyway – the one that the new sump pump was supposed to avoid.
I was just a young lad at the time, but I was skeptical about it and thought we were being taken for a ride.
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January 11th, 2011 at 6:15 pm
What I liked about this item was that it showed clearly how observations are forced into the LNT model by statistical jiggery-pokery, while suppressing evidence of a hormetic response.
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