Thanks Mark/BRAWM! Where the rubber meets the road: Banana Equivalent Dose (Posted by Bill)
First and foremost, thank you for identifying for me and several of us the crux of the issue over equivalent doses and exposure and assessments of risk.
It gave me the opportunity to do a little research and get a better picture of your position and it REALLY clarified for me WHY you folks are so chill over the radiocesium levels. Now we know that iodine 131 acts differently CHEMICALLY in the body because it concentrates in ther thyroid (unless one has ingested sufficient iodine to prevent uptake).
I did some research and found that, intetrestingly, cesium 137 acts something like Potassium and thus research has shown that ingesting additional potassium will speed up elimination from the body of radiocesium (I don't have a link for it but it was an authoritative source).
On further research I came across this GREAT piece on the "Banana Equivalent Dose" which explains WHY using comparison of ingesting radioactive potassium (found in bananas, brazil nuts and other foods) to other radiosotopes is a false comparison for a variety of reasons but primarily because the STABLE potassium in homestasis in the body causes the rapid elimination of potassium K40 (it doesn't stick around) which MAY be, I would surmise, an evolutionary adaptive mechanism in our biology which to some degree neutralizes the harm or risk from potassium K-40.
So this gets again to the crux of my concern, that radioCesium 137 REMAINS and disperses throughout the body and is not "neutralized" by a stable cesium adaptation of human beings (and other living things) and is not eliminated quickly and thus has a very different impact on the body than K-40.
Take a look at this rather amusing but also informative link and PLEASE Mark can you comment on whether you agree with the scientific analysis and/or critique?
Thanks Bill -- you have
Fixing the Banana
So Mark,
Would you consider that removal of K-40 from the human metabolism would be a good thing?
Mechanical separation of the radioisotope K-40, from the begnign and stable K-39 and K-41 would be relatively simple, by industrial processes.
Most of our potassium uptake is dietary rather than inhalation.
Whilest plants and chemical do not have the capacity to distinguish among isotopes, human ingenuity does.
The relative weights of the most common K-39 and the radioactive K-40 are much greater than the differences involved in U-235 separation. Plus the chemistry is much less toxic. The objective could probably be substantially achieved by wicking of aqueous potassium chloride.
Please read response here
Please read response here
Is this study Peer reviewed?
http://www.nukeworker.com/study/hp/rct/pdf/core_1-06.pdf
Good study with a section on natural radiation vs artificial radiation yes it's artificial!
K-40 Activity ~ 7,600 Bq.
K-40 Activity ~ 7,600 Bq.
Does somebody want to check the math? Hashing over this with a friend, this is the result.
http://energyfromthorium.com/tech/physics/activity1/
The activity of a pure sample is simply the decay constant of that material multiplied by the number of radionuclei present.
The mass of 40K in the body is (250)*(0.00012) = 0.03g. From the table, the specific activity of potassium-40 is 254,000 Bq/gm. Therefore, the activity of potassium-40 in the body is (254000 Bq/gm)*(0.03gm) = 7600 Bq.
I started to talk about this
I started to talk about this on your previous comment, but this brings up some more discussion...
Although I agree wholeheartedly that we should not be talking about a "banana equivalent dose", that does not mean that our comparisons to natural potassium are wrong. We are not claiming that eating bananas (or brazil nuts, or whatever) will give you extra dose, but that the the very potassium that is already in equilibrium in your body is giving you a lot of background dose.
There is plenty of K-40 in your body; it is constantly being recycled, but never "neutralized". When you eat some food, it adds a little K-40; when you go to the bathroom, you lose a little K-40. But the overall concentration of K-40 stays the same. It is incorrect to say that "the STABLE potassium in homestasis in the body causes the rapid elimination of potassium K40." The body has no mechanism of separating out stable isotopes from radioactive ones. All it can do is make sure there is not too much potassium accumulates in the body -- but it doesn't control which isotope accumulates.
Or think of it this way -- if you could somehow find pure stable potassium (only K-39 and K-41, no K-40), then yes, you could eat it and it would flush out the K-40 (but please don't try this, or you'll overdose on potassium...). There is, however, no food that contains only stable potassium. They all contain the same percentage of K-40.
That's a funny thing to say!
That's a funny thing to say! If we were able to remove K-40 from potassium supplements or nutrients in soil in which we grow food, why would we suddenly overdose on potassium? Do you believe that the body uses the radioactivity of K-40 to recognize and excrete excess potassium? If so, what leads you to believe that? It certainly doesn't seem intuitive.
Fair enough! I stand corrected on that one point. However:
The action of cesium in the body is DIFFERENT from Potassium and the action of radiocesium is DIFFERENT from K40 Potassium.
I did read the article to indicate that stable potassium would prevent the absorption (and hurry the elimination) of K40 -- and the piece I site is slightly ambiguous on this point (or not entirely clear a hazard with wiki - oh well)
But STILL as radiostrontium and radioiodine act differently in the body and influence different organs and structures etc (thyroid and bone) isn't the impact of cesium 137 potentially more hazardous that K40 because of cesium's toxicity and interference with cells and bodily functions etc.???
Is it not possible that we have adapted and evolved to handle K40 metabolically and NOT evolved to handle cesium 137 or strontium 90 or radioidine and other man made mutagens and cell killers?
Chemically different, radioactively similar
Bill, you are absolutely right that Potassium and Cesium and Strontium all act differently in the body. They are different chemicals, and so they undergo different chemical reactions with your body. I think one of the issues you are coming across is toxicity -- this is a chemical phenomenon and not a radiological phenomenon, so our expertise definitely doesn't lie there.
Regarding the question of whether we have evolved to handle K-40, I made some comments here:
http://www.nuc.berkeley.edu/node/4226#comment-8591
Basically, what matters most is the type of radiation and the energy of the radiation. Of course, if a particular isotope concentrates in certain areas of the body (due to chemistry), one also has to account for that increased susceptibility of the tissue. This is done when performing effective dose calculations. For example, we use dose conversions for I-131 that take the thyroid dose into account. A large amount of the field of health physics over the years has been devoted to determining exactly those effects for each and every possible radioactive isotope.
Does this clear some things up?
Mark [BRAWM Team Member]
You know, You have made an impact on my perspective
One thing that is troublesome is the fact that there is still not a lot known about cesium 137 on its own. I am much more familiar with strontium 90 due to the research by the radiation and public health project (see www.radiation.org)
But again I am STILL concerned about whether strontium 90 is accompanying the cesium in the food chain etc.
However I entirely GET the idea that we have naturally occurring potassium (K40) which is consistently affecting us internally and I also appreciate your explanation of the effective dose calculations.
My own perspective is that industry and academia have really failed to accurately assess the risk factors due to a wide variety of influences, but one of them is, to some degree, complacency and acceptance of unstudied representations from seven decades of nuclear industry and government manipulation of public and academic perceptions and some outright propaganda.
In any case I appreciate your patience and willingness to engage as the questions I ask are the ones many who have more than minimal knowledge are likely to ask or address.
Radiocesium may bioaccumulate in ways UNLIKE K40 and in muscle and other tissues in ways that may be more harmful at long term persistent rates AND the body MAY well have an unknown or undiscovered means of coping with K40.
I do not pretend to really understand how something which has such a long half life as K40 has such a higher rad rate than something with a faster decay rate as cesium 137. Perhaps too there may be synergistic biological mechanisms which make the radiocesium more deadly (for example, the K40 functioning in cells may well cause immediate repair of dmamaged cells whereas the toxic effect of cesium may prevent such repair. These are the issues which make such comparisons, as you pretty much acknowledge, not too reliable. Too much is unknown.
I would add, for you BRAWM folks, a link to an article which refers to another well known UCBerkeley Physicist who is one of my heroes in all of this craziness: Read the article, "an Open Letter to Physicists" and maybe you will understand better how I (and many of us) perceive some of these issues and why I am always asking more questions.
http://www.ccnr.org/open_letter.html#eff
i HOPE you are right and the cesium will cause little or no likely damage. But I cannot rely on that because there is just too much still unknown about all this.
Again - YOUR data will help make the risks and the pathways etc clearer for all future researchers and so it is all invaluable and much appreciated. More samples are always warranted for food chain whether or not YOU think we need not worry: only history and future researchers will really be the judge of whether or not our concern was valid.
Thanks, Bill. I appreciate
Here is the excerpt on problems with Potassium 40 comparison
from the wikipedia entries I linked in the previous post (for those who's prefer the crux of the issue here)
I would add that I do NOT have any agenda other than to really understand these issues and to get it clear for all of us AND if the critique re: naturally occurring potassium K40 is NOT comparable to cesium 137 in the body IS valid I am hoping to see whether this changes the BRAWM perception. Seems to me that IF we have evolved a biological adaptation to cope with retention and the elimination of K-40 in the body but have NOT adapted to man made radiocesium 137, then my concerns are MORE valid than BRAWM seems to think they are. If you ADD a load of radiocesium 137 to the entire body where it is absorbed in bones and organs and soft tissue and REMAINS and accumulates for 70 days from initial ingestion, THEN we may have a VERY different issue than the normal natural body response we have to Potassium K40.
Here is the excerpt:
Radiation From Potassium 40The major natural source of radioactivity in biomass is potassium. In the natural mix of potassium found in food, the human body and throughout nature, 0.0117% is an unstable isotope, potassium-40 (abbreviated 40K). This isotope decays extremely slowly, it has a half-life of about a billion years (4×1016 s). Therefore, out of a gram of potassium about 30 atoms disintegrate per second, or in other words the activity of potassium is 31 Bq g-1.[5] An average banana contains about half a gram of potassium.[6] Therefore it will have an activity of 15 Bq. Hoewever, the human body contains 160 grams of potassium in homeostasis, which means the net effect of eating a banana is zero increase in radiation.
From the activity in Bq, equivalent dose is calculated by converting into sieverts. The EPA [7] lists a conversion factor of 5.02 nanoSieverts/Bq for committed effective dose equivalent of ingested pure potassium-40 (not of natural potassium). This results in a calculated dose of 75 nanosieverts per banana, which is roughly (since the calculation is only accurate to one significant figure) the 0.1 ?Sv quoted as the BED in most sources.[3]
[edit] CriticismThe calculation of the effective radiation dose ingested from a banana was subsequently recognized as misleading,[1] since it neglects the actual cycle of ingested potassium in the body. The actual amount of radioactive potassium retained is not the same as the amount that would be retained if an equivalent amount of pure potassium 40 were ingested; it ignores the effect of the stable isotope of potassium (39K) also present in a banana.[7] The stable isotope displaces potassium atoms already present long-term in the body, and excess potassium (including the radioisotope) is quickly eliminated, resulting in homeostasis.
The additional radioactivity of the banana is only experienced for a short period after ingestion. The human body maintains potassium under homeostasis, at a fairly constant level.[8] Therefore, eating an extra banana will not cause more potassium to be assimilated into the body than would otherwise have occurred. Instead it will cause the body to excrete potassium more quickly until the level is returned to what it was beforehand.
The value of the BED mentioned above was calculated by taking the amount of 40K in an average banana, then multiplying the activity of this amount by the dose conversion factor for ingestion of pure radioactive 40K, e.g. not in a mixture with other potassium isotopes. This is incorrect and gives a value which is too high, because pure 40K displaces some of the stable isotope of potassium, 39K, from the body: although the total amount of potassium in the body does not change, the fraction of the radioactive isotope increases. This effect is not present for potassium with natural isotopic composition. The amount of 40K ingested with bananas is quickly balanced by an equal amount of 40K being excreted in urine, so the amount of 40K in the body does not change.
Geoff Meggitt (former UK Atomic Energy Authority) was paraphrased, [2]
Bananas are radioactive—But they aren't a good way to explain radiation exposure. When you eat a banana, your body's level of Potassium-40 doesn't increase. You just get rid of some excess Potassium-40. The net dose of a banana is zero.
I would caution anyone from
I would caution anyone from relying on Wikipedia for information. It is unreliable, and increasingly (and strategically) manipulated by industry with outright lies. Links to peer-reviewed scientific articles are one thing, but anything summarized or paraphrased on Wikipedia I would take with more than a grain of salt (in fact, I wouldn't give it any credence).
I primarily cited wikipedia to address the critique
re: potassium 40 which is directly addressed in the article (and subject to discussion).
I want to also just add here that I appreciate the negagement with BRAWM on these issues and intend to respond at more length later re Petkau and Gofman.
In the meantime, wikipedia is not something to be relied on but is a useful quick nutshell read withy sources to follow up on for almost any given subject and usually collects the most salient info in a neat packet.
I thought the banana dose equivalent was both funny and informative and subject to critique and I stand by that. The links there, btw, are also very useful. I found it googling to get a better understanding of the issue and it has proven to be a pretty useful means of promoting dialogue even if not a reliable scientific or academic source all on its own - but wiki citations (the links on any given page) are often the best primary sources for such info.
I look forward to your reply
I look forward to your reply about the relation between the Petkau effect and Gofman's linear no-threshold model.
If you are going to include some references to Potassium-40, please don't forget this quote from the wikipedia article you posted: "The amount of 40K ingested with bananas is quickly balanced by an equal amount of 40K being excreted in urine, so the amount of 40K in the body does not change."