Could (natural, normal) radioactive Potassium-40 (K-40) be the main cause of elevated radiation levels in food?

This blogpost was written before I had radioisotope analysis lab results of store-bought Japanese seaweed samples (Autumn 2013 samples); The results of these lab tests were later published in full on this blog and are summarized @  which lead me to various discoveries, put together on my key blogpost (incl. K-40 vs. Cs-137) to help you see through nuclear deceptions: Pointers To See Through Nuclear Deceptions

———original blogpost left as-was:—–

I want to know this.

DISCLAIMER & Share Policy — No matter how badly some food appears contaminated, some people (usually pro-nuclear) tend to blame “normal higher natural background radiation, like in bananas”.  I don’t like dismissing allegations ad hominem.  It’s not because someone is associated with a hazardous waste-producing industry, or a non-transparent money-corrupted government with fascist tendencies, or because they hold other opinions I disagree with, that they can’t have valid points.

[!!!–> Added April 5, 2015:  This blogpost was written before I had the lab results of various food items bought in Japan.  The lab data were published shortly after, see the Full Disclosure HERE and its summary HERE.  After that, several blogposts were written that add more to this one, and which I highly recommend for better understanding some of the intricacies and nuances:

Original blog posting continues:  ]

In this blogpost I delve into Potassium-40 and particularly the possibly high levels in Kelp.

I’ll begin with why I didn’t think it was the cause of elevated radiation levels I detected in food (in Japan, but also reported by many in the US), and why I now think it is entirely possible that this (K-40) is the main cause after all.  To really find out requires lab tests. (patience, patience, I’m waiting on those…)

SO, first I looked at what I already have:  the data I gathered last spring (April 2013):  The first time I sent samples to a lab (2 soil samples, 1 sample of seaweeds and 1 of wild-harvested mushrooms, all from Northern California in April 2013), I blogged about it then:  I made all my lab results public in the June 5, 2013 blogpost, ‘Radioisotope Analysis Results for sampled Seaweed, Soil & Mushrooms – (Northern Humboldt County, California)‘, and have put them in two easy tables (w/ SI units in Bq/kg), see below.

I was focussed on finding evidence of Fukushima fallout locally.  I did find some in soil samples, but not significantly or provable in mushrooms (although there’s 23 Bq/kg Cs-137, the absence of Cs-134 from Fukushima makes it more likely that the Cs-137 is mainly leftover from Chernobyl and nuclear bomb testing in the 20th century).  Seaweeds  harvested on a Pacific shore (at Trinidad, just north of Arcata, California) measured nothing man-made at all.

Now, revisiting these data, I’m having a look at the Potassium-40 contents (Kalium-40 in Latin, hence the K).  I didn’t pay much attention to it, as it’s a given fact that Potassium comes with radioactive Potassium and that it’s reportedly not dangerous.

It shows that K-40 was the main radioactive element in both soil samples, and made up almost all radioactivity of mushrooms and 100% of the radioactivity in that seaweed sample.  I’ve reprocessed the data, showing this in easily readable tables for the soil samples and the food samples, seperately:

  • Notice the naturally occurring radioisotopes in these soil samples:
    Click Image for details, including undetected radioisotopes. Data © Michaël Van Broekhoven - DO NOT COPY.  See Disclaimer
Click Image for details, including undetected radioisotopes.
Data © Michaël Van Broekhoven – DO NOT COPY.  See Disclaimer for share policy.
  • Notice K-40 is the only natural radioisotope content for these food items:Click Image for details, including undetected radioisotopes. Data © Michaël Van Broekhoven - DO NOT COPY.  See Disclaimer for share policy.
Click Image for details, including undetected radioisotopes.  No radioactive Iodine (131, 132, 129) was detected in either mushrooms, soil samples, nor seaweed sample (in April 2013 in those Northern California samples)
Data © Michaël Van Broekhoven – DO NOT COPY.   See Disclaimer for share policy.

I have been saying from the beginning that Geiger Counter results are not enough to draw conclusions from:  It takes lab tests.   But I admit:  I did assume that the elevated levels in seaweeds I found in Japan was due to nuclear contamination.   Lab results could very well prove that assumption wrong.  We’ll see.

Nowhere did I read that when a basic Geiger Counter responds very significantly to elevated radiation levels in food, that any increase is most likely due to its high Potassium content, except for the much advertised “radioactive bananas” and brazil nuts.  In fact, I found various expert statements about Geiger counters simply not being sensitive enough to pick up radiation in food.  I listed some of these experts’ statements at the beginning of my blogpost, ‘My Travel Collection of Japanese Seaweeds – An Overview with 10 minute CPM averages‘.

{Added 1/19/2014:  My own Lab data are in, see the Summary @  }

I added nuance to some of these past blogposts, and that brings me to one of the reasons why I really don’t like it when people copy-paste stuff, without asking me permission, nor letting me know that they shared something I put on my blog.  Side-rant:

When I discover something that debunks a previous belief, and I know someone shared the old belief, I can let them know the same info.  It’s mostly the more alarmist anti-nuclear sites (on which really good info is mixed with questionable interpretations to sound really bad) that cherry pick something that fits their narrative.  These  tend to be less interested in getting to the scientific bottom of the matter, and more interested in fanning the flames of fear, at least so it seems sometimes.  It’s also why I updated my DISCLAIMER and Share Policy: You don’t have permission to share my data or photos unless I give you permission.

And moreover, sometimes people take screenshots, and don’t date ‘m.  I make changes to blogposts when I find errors; more often I add nuance, or tone down (or up if that were appropriate) the alarming tone of a blog post I wrote.  And thus I get a little annoyed when something I once wrote still floats around, although I long made edits or at least added a nuance disclaimer.

For example, the fine folks at, after confusing the activity of a 33,000 square meters of kelp forest canopy off the coast of California with a kilogram of kelp, and other glaring distoritions, they also mentioned my seaweed discovery in Iwaki, Fukushima. (AGRB never contacted me, but at least linked to my blogpost).  From a Green Road Blog (as it still appeared on Jan. 8, 2014):

 “[…]  More recently, a tourist went to Japan and measured some seaweed for sale in a grocery store, with a standard Geiger Counter, which normally is not sensitive enough to pick up radiation in food. In this case, the one brand of seaweed turned out to be very ‘hot’.  Measured on 8/11/2013 in Iwaki, Japan. 

Source: […]

A nuance-disclaimer has since been added to that and other blogposts.

My initial assumption that this elevated level was almost certainly the result of manmade radioactive contamination was influenced by a great number of online claims and allegations.  Before I’ll look at Potassium contents of food and share some more experimental tests, I’ll share these two key claims, as they are influencing many others as well:

1) “Above 3 times background radiation = a hazmat situation”

Here is the grounds for that claim:  It’s implied by the text describing an incident in a 2011 Nuclear Regulatory Commission (NRC) report (See NRC Event # 47518, from Dec. 16, 2011), California Highway Patrol (CHP) guidelines regard 3 times background as a potential hazardous materials (hazmat) incident.  Screenshot:

Source: United States Nuclear Regulatory Commission, Dec 16, 2011 Annotated screenshot showing part of report.  CLICK IMAGE to see full report.

Source: United States Nuclear Regulatory Commission, Dec 16, 2011
Annotated screenshot showing part of report. CLICK IMAGE to see full report.

As your can see clearly mentioned in this report: “The CHP said that their protocols dictate that anything above three times background is treated as a hazmat incident […].”  Thát is where that ground for concern comes from when people measure 3 or more times background (BG) radiation levels.  It seems rather unusual for some kind of radioactivity ‘hazmat’ situation to radiate off health foods.  So when it appears to do just that, it pretty logical to assume the worst.

The problem with this report is that it’s almost anecdotal: it wasn’t a test set up, it was a CHP discovery doubled-checked:  As such it doesn’t give much specifics on the distance, nor the shielding, between the emitting source and the measuring device that first found over 3x BG.  The initial high radiation measured was likely not with the Geiger Counter laying on the medical-isotopes-contaminated hospital sheets, but from at least several feet away just outside the linen truck.  Except for that oddly radioactive beach near San Francisco (see Half Moon Bay Review, Jan 7, 2014), where elevated radiation was obvious many feet above the sand, in most cases, at least when toying around with Geiger Counters, food is tested within millimeters from a test sample, usually with just air, plastic foil or thin mica in between.

California is a major food production area.  If trucks transporting all kinds of high-potassium foods would set off radiation alerts from a few feet away, wouldn’t CHP protocols be different?  They would be quite busy checking on potassium levels all over the state, I’d think (see more at ‘Bananas’).

If ‘detection’ happens on contact with the food, that’s normal.  How ‘detectable’ is not clarified, though, leaving much room to interpret 3X BG as beyond a mere ‘detection’.  To non-experts like myself, many times background appears rather significant.

2) BANANAS are reported as perhaps the most significantly naturally radioactive food.  

And yet the few times I tested bananas, they simply did not cause much of a measured radiation increase upon contact, certainly not compared to kelp seaweeds, hence my assumption that the kelp seaweeds were radioactive due to  unnatural radioactive particles.  

Geiger Counter manufacturers do mention their products’ sensitivity to K-40, but not that this fact (presence of lots of K-40) might actually make it essentially impossible to determine if there’s also fallout present or not:

On my Geiger Counter’s FAQ site,, Medcom clarifies the following [my emphasis]:

CLICK IMAGE FOR INFO SOURCE. [my emphasis added]

CLICK IMAGE FOR INFO SOURCE. [my emphasis added]

This “higher sensitivity” of MedCom Inspector Alert doesn’t just make it more sensitive to Cesium-137 and Strontium-90, but also to Potassium-40…  The bananas I tested before going to Japan in autumn 2013, as well as there, and since, were not dried banana chips (and I did not test salt substitutes, either).  But I did test (fresh) unpealed and pealed bananas and was not impressed.   The increase was minimal compared to kelp (or white beans, see further below!).

Here are some reports and statements that had given me the (wrong) impression that bananas in particular were at the top of the highest K-40 content list:

You may have read about everyday objects setting off radiation alarms at border crossings between the US and Canada and Mexico.  […] It’s pretty easy to understand why tile, granite, and kitty litter are radioactive. They contain low levels of minerals that naturally decay.  Bananas are radioactive for a similar reason.  The fruit contains high levels of potassium.   Radioactive K-40 has an isotopic abundance of 0.01% and a half-life of 1.25 billion years. The average banana contains around 450 mg of potassium and will experience about 14 decays each second.  […]  If you have a banana in your car for your lunch you aren’t going to set off a Geiger counter.  If you carry a produce truck full of them, you might encounter some problems.  Ditto for a truck of potatoes or potassium fertilizer.”

FORBES: ‘Fukushima Radiation In Pacific Tuna Is Equal To One Twentieth Of A Banana‘, by Tim Worstall, November 6, 2013; excerpt [my emphasis]:

“[…] They went off and tested a whole bunch of pacific blue fin tuna for the signature isotopes known to have been released in the Fukushima disaster. The result was that a standard sized serving of fish would expose you to about the same radiation as one twentieth of a banana. Or about the same amount as one of those dried banana chips they used to sell at Trader Joe’s. Not something to get particularly worked up about in fact.  The paper is here […]”

Boing Boing:  Bananas are radioactive—But they aren’t a good way to explain radiation exposure’ by Maggie Koerth-Baker, Aug 27, 2010; excerpt [my emphasis]:

Just look at that radioactive banana. There’s nothing special about it or where it was grown. All bananas are radioactive, because all bananas contain the radioactive isotope Potassium-40. In fact, a lot of things you might not suspect of being radioactive are, including Brazil nuts, and your own body. And this fact is sometimes used to downplay the impact of exposure to radiation via medical treatments or accidental intake. […]”

Going around in US grocery stores, I did not easily detect significantly elevated levels in foods.  In rocks, granite counter tops, elevated levels near rain pipes, on soils, sure, but not through the peel of fresh bananas.  Seaweed is rarely ever mentioned in these lists.  I will look at some of the nutrition data for kelp, after the white beans test.

So first thing I need to admit:  It wasn’t clear to me that the Inspector Alert™ is at least as good detecting K-40 as Cs-137 and other artificial radioisotopes, and that measured significantly elevated levels in food could thus just as well be from high K-40 levels rather than from Sr-90, Cs-137 and/or Pu-239 (etc.) levels which may have to be quite high to over-shadow K-40.

Unfortunately, only lab tests can bring clarity when there’s such uncertainty.  It’s almost bizarre that many people who make claims about Fukushima fallout, based on Geiger Counter measurements aren’t at least sending one sample to a lab.  Just one, the worst, to find out if their suspicions are correct, or not.  One sample can be analyzed for less than $150, sometimes much less depending on the lab and precision.

  • What about Iodine?

 [Added Jan 10-12, 2014, in response to two comments]:

Seaweeds are known to be excellent sources of stable natural iodine (I-127 or 127I).  Their inclusion in the Japanese diet, especially in a macrobiotic diet, contributed to the healing of many Japanese affected by the atomic bombings of Hiroshima and Nagasaki (A strict diet of “brown rice, miso and tamari soy soup, seaweed, and sea salt; and completely abstaining from sugar and sweets” is said to have been very helpful. See also Dietary Practice of Hiroshima/Nagasaki Atomic Bomb Survivors , by Hiroko Furo, Ph.D.).

The main radioactive isotopes of Iodine released in a nuclear accident are short-lived: I-131 and I-132.  Over 99% of these is completely gone, decayed into stable isotopes, in less than 4 months.  Another key fission-created Iodine is long-lived I-129, normally only found in trace amounts.    A little elaboration on why I would be sadly surprised if there was Iodine-131/132 in any of my samples:

Iodine-132: is a decay daughter of Tellurium-132, both are important in the first few days after a criticality.  They were reportedly responsible for a large fraction of the dose inflicted on workers at Chernobyl in the first week.  The isobar forming 132Te/132I is: Tin-132 (half-life 40 seconds) decaying to antimony-132 (half-life 2.8 minutes) decaying to tellurium-132 (half-life 3.2 days) decaying to iodine-132 (half-life 2.3 hours) which decays to stable xenon-132.  In other words, if any I-132 were absorbed into the seaweed sample, it would not be detectable, since well over a month passed since I bought the sample in November 2013.  What it decayed into, all decayed to stable Xe-132.  There really would be nothing detectable left.

The more common Iodine-131, with a half-life of 8 days, is, a major hazard from nuclear fallout, comprising nearly 3% of the total products of fission (by weight).    Iodine (both stable and radioactive) concentrates in the thyroid gland, which is why a diet rich in Iodine (such as the Japanese diet, in part thanks to (uncontaminated) seaweed) reduced the chances of thyroid cancer.  [Disclaimer: I’m not an expert nor health care professional]  I-131 was spewed in massive quantities by Fukushima nuclear disaster in March 2011.  (See also my May 23, 2011 blogpost, Iodine-131: two months later, the monkey comes out of the sleeve…, with the below I-131 deposition map for Japan back then; and my May 26, 2011 blogpost, IODINE-131 a basic map comparison: Fukushima versus Chernobyl).  Iodine-131 decays into stable Xe-131, and thus within less than 4 months more than 99% of its initial radioactivity is completely gone.

Annotated Iodine-131 deposition map from spring 2011.  All this I-131 has by now decayed to practically undetectable levels.  I-129 deposition levels, however, for which no fallout maps were made public, would be statistically unchanged.

Annotated Iodine-131 deposition map from spring 2011. All this I-131 has by now decayed to practically undetectable levels. I-129 deposition levels, however, for which no fallout maps were made public, would be statistically unchanged.

It was extremely suspicious that I-131 was detected by South Korea in summer 2013 in seaweed: Up to 5.25 Bq/kg of iodine was detected in six samples of tangleweed.  5.25 Bq is so little, that just two weeks later it would already be reduced to 1.7 Bq/kg.  Three months later it would be undetectable, as you can check for yourself with this handy Decay Calculator (just added to my Radiation Units page):

If Iodine-131 is detected in my Japanese seaweeds, it would imply fissioning occurred after August 2013, and tat either ocean currents or aerial deposits sent it over 500 kilometers north.  CLICK to access the Decay Calculator

If Iodine-131 is detected in my Japanese seaweeds, it would imply fissioning occurred after August 2013, and that either ocean currents or aerial deposits sent it over 500 kilometers north. CLICK to access the Decay Calculator  (Now also added to my ‘Radiation Units’ page under the tab ‘Nuclear’ in the top bar of this blog.

This was why I wrote the blogpost (August 3, 2013) Radioactive Iodine in Seaweed and Sludge, Summer 2013? (Hints of Recent Criticality Events…) + Data suggests radioactive fallout still blowing around the world….

So, I am going by the assumption that no fissioning happened after that report in  August 2013.  Also, IF such a fissioning event had happened this recently, it is unlikely that the (likely relatively small) amount of such fallout made its way to far-Northern Japan in significant enough amounts to still be detectable one to two months after I bought my seaweeds.  I would be very surprised if I-131 were detected.  (But given TEPCO’s track record of lying and convenient omissions, one never knows.)

Rarely mentioned Iodine-129 (129I) is the longest-living of the 36 radio-isotopes  of iodine (+ stable I-127), a product of manmade nuclear fission as well.  129I decays with a half-life of 15.7 million years, with low-energy beta and gamma emissions, to stable xenon-129.   A scientific study, ‘Iodine Isotopes in Precipitation: Temporal Responses to 129I Emissions from the Fukushima Nuclear Accident‘ (Environ. Sci. Technol., 2013, 47 (19), pp 10851–10859 DOI: 10.1021/es401527q Publication Date (Web): September 3, 2013), mentioned that, after the Fukushima Dai-ichi Nuclear Distaster, at Fukushima, “[…] 29I concentrations of 1.2 × 108 atom/L [were observed] in 2010 before the accident [and these] dramatically increased by 4 orders of magnitude to 7.6 × 1011atom/L in March 2011 immediately after the accident, with a 129I/127I ratio up to 6.9 × 10–5.  Afterward, the 129I concentrations in precipitation decreased exponentially […]. “

More Iodine factsheet by the Health Physics Society, “Human Health Fact Sheet ANL, October 2001” (excerpt):

In a thermal neutron fission reaction of U-235, the amount of newly created radioisotopes varies from isotope to isotope. (See Wikipedia: Fission Product Yield). I-129 comprises about 1/3rd of I-131.

  • I-131: 2.8336% (with a half-life of 8.02 days)
  • I-129: 0.6576%  (with half-life of 15.7 million years, yet just tiny fraction of specific activity)
  • Cs-137:  6.0899% (with a half-life of 30.17 years)
  • Sr-90:  5.7518% (with half-life of 28.9 years)

More importantly for my research, the activity per gram of I-129 is less than 1/millionth of I-131’s, and while I-131 comprises 3% of spent fuel (fission waste or fallout by weight), I-129’s is 1/3rd of that.  In other words, Long-lived I-129 could be great as a fallout tracer and may be useful to calculate the likely deposition of I-131, but in itself it will barely (if at all) contribute to heightened radiation levels in food.

More over, the I-129’s gamma ray energy is around 25 keV, below what many gamma spectroscopes can detect (above 59 keV), so even if it is present it won’t be detected.  If I understand the Sensitivity of the Medcom Inspector Alert Geiger Counter correctly, its response efficiency would certainly be no more than 5.3% (which is the value given for C-14, with an energy of 49 keV avg.,  156 keV max.).   So it is not the reason for high measurements with “household Geiger Counters.”

My conclusion on Iodine remains:  Even if less than 1 Bq/kg of I-131 were detected, that would be major news, as it would mean that either such a sample contained over 100,000 Bq/kg on August 1, 2013 (or even more recently before – See Decay Calculator); or even more recent recriticality events released unreported fresh amounts of these ‘recent fissioning fingerprints’, which would be disturbing: nothing of such nature has been admitted to by Japan, Tepco or the IAEA since 2011, as far as I know.   I-132 and the many other short-lived iodine isotopes would also have decayed away with the 1-2 months after harvesting.  And the amount of I-129 would be far below detectable levels (both due to equipment insensitivity as by the fact of its fraction of activity per weight, and that only a third of I-131 would have been released), even in the unlikely event I-131 were detected.

[Thanks for the comments.  I learned a few new things.]

To continue probing the possibility of K-40 being the most important factor in elevated radioation measurements of food:

The old White Beans CPM test:  (K40 –> Ar40)

I searched and found this list of the ‘Top 10 Foods Highest in Potassium‘, which puts White Beans and Azuki Beans at the top.   Other lists have some differences.  Here, White Beans are listed as containing about 5.6 g Potassium per kilogram beans (561 mg per 100 g), while bananas only contain some 3.6 g Potassium per kilogram bananas (358 mg per 100 g).

  • Some K-40 contents per gram examples (Source:  this list does not include seaweeds
    • Dried Apricots (10.2 pCi/g or 377.4 Bq/kg)
    • Potato (4.3 pCi/g or 159.1 Bq/kg)
    • Cod (4.3 pCi/g or 159.1 Bq/kg)
    • Dried Bananas (2.5 pCi/g or 92.5 Bq/kg)

I tested dried apricots in a nearby grocery the way I tested seaweeds (if no noticeable elevated level becomes apparent through the packaging within 10 seconds, I move on to the next item to sample), and like everything else (including locally sold seaweeds), I found nothing that peaked my interest/concern.  All seemed unable to get my Geiger Counter to leave the natural background fluctuation quickly.  Maybe it would show up in a 10 minute CPM test, but for seaweeds that was not required to find the ones with higher radiation levels.  Just going by my experience.

A friend had these old white beans, and they did, very obviously as soon as I put my Medcom Inspector Alert to the package, show significantly elevated radiation levels, which I now assume must be due to K-40.  

So I conducted another little background and sample test:

  • Background at 4300 ft (6108 counts over 98 minutes =  62.3 CPM)

Note: I’ve taken so many background tests at the same spot, it has always between 58 and 69 CPM, which is why I feel okay taking background levels over less than 12 hours: if after a few hours it’s still within that range then go with the latest BG).

  • White Beans (over 5 yrs. old; USA, pre-Fukushima):  4695 counts over 22 minutes = 213 CPM
    • Added radiation from White Beans: + 151 CPM (whoa!)
    • When pressing the Geiger Counter into the bag of white beans, I observed the dose rate measuring as high as +1.1 µSv/hr (!), adding over +0.8 µSv/hr to background, significantly higher even than what I observed with the highest-measuring seaweeds in Japan (!).  [I wish I had taken a photo of that.] (See also: My Travel Collection of Japanese Seaweeds – An Overview with 10 minute CPM averages).
  • Amazed by the possibility of K-40 doing this, I did another test over-nite and measured 100,500 counts in 1,186 minutes = 84.6 CPM,  strangely much lower…
    • Background (892 counts over 13 minutes =  68.61)
    • Added radiation from White Beans: + 16 to 22 CPM (on the low end compared to some seaweeds)
    • Upon taking a new dose reading, it did not surpass 0.3 µSv/hr, either, only adding +1.5 (ish) µSv/hr max.

Why this huge difference between the two tests?  

The expiration date on the package is August 2008, and I’m told it had just been laying there for “at least 5 years”.  I’m wondering if simply handling a package (moving the beans around) may have released some of the radioactive particles from the not-air-tight package.  (There are many tiny holes in the old package).  Potassium-40, in part decays in to radioactive Argon-40, a noble gas.  My guess is that Ar-40 had built up inside the bag, which was measured in the first test, but no longer present in the same high concentration in the second test.

Annotatated screeshot 22 minutes in of Geiger Counter test of old white beans.  White beans are reportedly among the highest in Potassium.

Annotatated screeshot 22 minutes in of Geiger Counter test of old white beans. White beans are reportedly among the highest in Potassium.  The high test result may also be due to Ar-40, which may have dissipated through handling the bag, resulting in a significantly lower radioactivity measured during a second test.  Photo by © Michaël Van Broekhoven – DO NOT SHARE my photos or data – See DISCLAIMER for Share Policy.

In any case, the levels first measured in old white beans were at least on par with the levels measured in the highest measuring Hokkaido kelp seaweeds.  The possibility is thus very real that the high measurements seen with kelps may be caused by unusually high concentrations of potassium, rather than industrial  radioactive contamination from the ongoing leaking from Fukushima-Daiichi nuclear disaster site.  (A more definitive answer will be revealed as soon as I get quality lab results!)

Kelp Nutritional Data

Data on kelp varies widely…

  • One  website does put ‘seaweed’ in the second highest Potassium content category, after salt substitute, and well before bananas:  It lists it as containing “>25 meq/3.5 ounces”, which I don’t know how to convert to something more universally used.  So, not really helpful for calculations…
  • This list of “24 Potassium Rich Foods That Are Not Bananas” puts ‘dried seaweed’ at #11 and lists its concentration as “Serving Size (1 tablespoon), 95 milligrams of potassium”, which makes converting it to grams complicated, as tablespoon is volume, not weight… Not helpful…
  • A question at SFGate, “How Much Potassium Does Kelp Have?” provided this answer: “A 3.5-ounce serving of raw kelp contains 233 milligrams of potassium.”  3.5 ounces is 99.2233 grams, so 1kg kelp would thus contain… (233mg / 99.2233 x 1000 =)  2348.24 mg K per 1000 g kelp, or 2.35 grams K per kilo kelp
  • SELFnutritionData lists these nutrition facts on kelp, ascribing a mere 0.89 grams K per kilo kelp:

Kelp, nor any other seaweed, is even in this website’s top 100 for high Potassium levels (Search on for highest Potassium content)

Moving on to K-40 content:

  • An analysis by the University of Maine of a set of seaweeds tested in Summer 2012 found zero evidence of Fukushima radionuclides, and remarked:

“The activities of the samples ranged from 740 Bq/kg to 930 Bq/kg, and this is well within the range expected for seaweed.   For comparison, bananas contain about 150 Bq/kg, spinach is about 250 Bq/kg and again this is almost entirely due to high potassium content and does not represent any risk or potential hazard.” (See UM June 20, 2012, tests done for

So:  Completely natural radiation, caused mainly by K-40 can be as high as some 1000 Bq/kg  for Seaweeds,  for Spinach about 250 Bq/kg, and for them famously radioactive Bananas, only about 150 Bq/kg…  almost all due to Potassium-40 presence.  Okay…

In this Idaho State University (Physics Dept.) overview page, ‘Natural radioactivity‘, the ocean contains on average 11 Bq/L K40.  In a small table with some high-natural-radioactivity foods (listing bananas, but not seaweeds), the highest in both Potassium-40 and Radon-226 are brazil nuts, listed as containing an average 207.2 Bq/kg of K40 and up to 259 of Ra226.

But does that explain the way my Geiger Counter responds to some foods, like it did to various seaweeds I found for sale in Japan? (Again: see My Travel Collection of Japanese Seaweeds – An Overview with 10 minute CPM averages).  I really want to know.

If it’s just from K-40, then there’s no point in keeping this an issue of concern.  And it would likely debunk a large number of YouTube videos, too.  But check it out… It may not be as likely either, after all:

  • Another Kelp test:

I cut open one of the 2 packages of Hokkaido kelp shown in ‘Test 10” in my Nov 29, 2013 blogpost, “My Travel Collection of Japanese Seaweeds – An Overview with 10 minute CPM averages“.  It measured 124% above BG, or better put: added an average of 47.9 CPM to background.

the size of the piece of kelp, likely less than 3 grams, that adds 20 CPM to background radiation... as shown on the back of the MedCom Inspector Alert
Photo:  the size of the piece of kelp, certainly less than 3 grams, that adds 20 CPM to background radiation… as shown laying on the back (bottom) of the MedCom Inspector Alert

I cut out a little square of kelp, maybe just a tiny bit over a square inch,  let’s say 7 cm^2.   I don’t have a scale right now, but given the size in comparison with the whole package of 100 g, I estimate it weighs no more than 1 gram.  In any case, it can’t weigh more than 3g.  3 grams is what one entire sheet of the thinner nori seaweed tends to weigh.

Now, when I put my MedCom Geiger Counter on it, the radiation fluctuation range shifts up to about +0.06 µSv/hr. (Due to rounding up and overestimating the weight, results of this calculation are thus very conservative and the final result could be as much as four times as high.).  Pretending it’s 3 g:

CPM test for “3 grams” of Hokkaido Kelp:

  • Background in 10 minutes preceding it averaged:  61.5 CPM
  • 10 minute CPM with 7 cm^2 of kelp averaged:      87.5 CPM
  • Background in 10 minutes preceding it averaged  65.1 CPM
  • –> <3g of Kelp added CPM:  at least 22 CPM
  • Visually observing the fluctuation range, it increases by some 0.06 µSv/hr on average: the upper limit of fluctuation would go from 0.240 µSv/hr to over 0.3 µSv/hr).

For calculation purposes:  I’ll just pretend that all of this little piece of kelp’s activity was concentrated at 0.25 cm (2.5 mm) from the sensor, how much Bq/kg would that kelp have to contain for 3g to cause a dose increase of 0.06 µSv/hr.  (for more on radiation units and conversions, see also my Radiation Units page)

I used the handy Rad Pro Calulator to fill in the activity level until it corresponds with the measured dose rate increase:

Annotated Screenshot Click Image for calculator:

Annotated Screenshot
Click Image for calculator:

So 20.5 Bq in 3 g.  If that’s all from K-40, then (divide by 3, multiply by 1000)–>

6,833 Bq per kilogram of kelp.  (compare to the average of 314 Bq/kg, or the 930 Bq/kg found in Maine kelps).  More than 700% more Potassium in my Hokkaido kelp than the most Potassium-rich Maine kelp in the test results shown above…  Really?  Well, perhaps…   [This was an attempt to guess, see the actual lab results HERE]

Given how some kelp measured higher than the one used in this example, and the fact that the actual K-40 content could be three-four (let’s say 3.5) times as high (if sticking with assuming that it’s all from K-40, and none from a nuclear accident’s pollution).

Could kelp naturally contain… 6833 x 3.5 = 23915.5  …
Could kelp naturally contain 24,000 Bq of K-40 per kilo kelp?

It’s already clear that K-40 is capable of causing very significantly raised radiation measurements.  Based on all of the above, I cannot rule out that these seaweeds are just incredibly nutritious.

All assumptions aside, just sticking to my calculated 6833 Bq/kg (K40), and now calculating the Potassium content of this kelp based on its possible activity:

  • 1 gram of K-40 generates an activity of  261,700 Bq (See Nucleonica)
  • 40K (aka K-40) makes up 0.012% of K

6833 Bq of K40 = 0.02611 g K40 (in 1 kg kelp)
0.02611 g K40 = 0.00012 x K => K = 0.02611 / 0.00012 = 217.58 g of Potassium per kilo Kelp… Really?   Doesn’t that seem rather unlikely?  Instead of the 2.35 grams K per kilo kelp (mentioned in How Much Potassium Does Kelp Have?), this Japanese kelp would somehow contain over 200g Potassium per kilo kelp, literally as if Kelp is 1/5th Potassium?  That’s ridiculous.  I must have made some wrong assumptions or a calculation error.

Or… This type of Geiger Counter is much more sensitive to K-40 than many people using them realized (I suspect this may be the case).

Or… there is something else in this kelp, perhaps nuclear contamination from Fukushima that traveled over 500 kilometers with ocean currents… (This too cannot be ruled out until lab results are in).

  • Conclusion:  

If Pre-Fukushima White Beans, known to be among the highest in Potassium, and thus Potassium-40 and its decay daughters, such as Argon-40 gas, can add 150 CPM to the background radiation level, then it seems quite possible that these naturally occurring radioisotopes are also what’s causing the elevated levels in most other foods testing similarly high, including the highest-radiation-level kelp seaweeds I found in Japan.

Lab tests would also reveal how sensitive the MedCom Inspector Alert really is to Potassium-40 (and as a result how useful or utterly useless Geiger Counters may be to find trace amounts of fallout from nuclear accidents far away).

My believe that the elevated levels found in some Japanese food items were unnatural, and likely caused by the Fukushima-Daiichi nuclear disaster, could be entirely wrong.  This remains a possibility.   (Somewhat embarrassing for me, particularly regarding my comparing the foods (which are just as likely extremely high in K-40) to “low level nuclear waste”, but potentially actually REALLY GOOD NEWS for seafood lovers.  This possibility was certainly not what I expected, but – best case scenario: my investigation might put a lot of similar Geiger Counter studies’ conclusions to shame as well.  (Or official statements.)   No way to tell until lab results shed more light on this matter…

Let me repeat that phrase again:  No certainty until lab results are in, but I have hope that my lab results (such as for Hokkaido seaweed samples with significantly elevated radiation levels) will actually ease a lot of people’s concerns.  I like the new thought that I may have bought a bunch of high-quality seaweeds in Japan that just happen to be incredibly nutrient-rich.

More soon, later this month.

[Added 1/19/2014:  My own Lab data are in, see the Summary @  ]

[Last edited: April 5, 2014: Due to uptick in blog traffic,
I added some relevant links that followed later, see the green text
Start into with later important links added: Sept 6, 2014.]
This entry was posted in Politics and tagged , , , , , , , , , . Bookmark the permalink.

2 Responses to Could (natural, normal) radioactive Potassium-40 (K-40) be the main cause of elevated radiation levels in food?

  1. A túladagolt kálium növénymérgező, aszálykárfokozó és vérmérgező hatásait bizonyító hatás- vizsgáló méréseket lásd a honlapomon. Köszönöm a tájékoztatást. Üdv, Tejfalussy András

  2. Google Translate detects Hungarian and makes this of it: Evidentiary testing plant is poisonous, and blood aszálykárfokozó toxic effects of an overdose of potassium impact measurements see my website. Thanks for the information. Hi Andrew Milk Falussy

    With “aszálykárfokozó perhaps being two words: aszálykár fokozó -> increased drought -> Which would make the text: Examining evidence of an overdose of potassium toxic plant, drought and increased blood toxic effects of impact measurements see my website. Thanks for the information. Hi Andrew Milk Falussy

    Checked your site, but Hungarian apparently does not translate so well yet on Google… ;-/

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