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"One Particle Of Inhaled Plutonium Causes Cancer"

I wish I had a nickel for every time I've seen or heard that written or said.

Radiation increases the risk of cancer, it doesn't "cause" it in a deterministic sense.  If I hit a window with a hammer the glass will shatter.  That is a deterministic cause and effect relationship.

Instead, cancer becomes more probable with greater radiation doses, it is a stochastic cause and effect relationship.  Every additional bit of radiation increases the risk that someone will get cancer in the future.

Okay, maybe you think I'm parsing particle of plutonium "contributes" to cancer, is still very onerous, right?


From Argonne National Labs comes:

"As a note, for inhalation (the exposure of highest risk), breathing in 5,000 respirable plutonium particles of about 3 microns each is estimated to increase an individual’s risk of incurring a fatal cancer about 1% above the U.S. average."

So, the increased cancer risk is very small from a single particle of plutonium.


Another often heard myth is that one pound of Pu distributed over the face of the Earth will kill everyone.  Here is an old link that explains why that's not true (some of the numbers are old, but the logic is sound).


  1. Hi. I'm planning to travel to Japan in March. I had a few questions for you.

    1. Can you comment on why the Japanese government is monitoring for cesium and not strontium in food.
    2. I hear plutonium and strontium were found near Fukushima. Any chance these reached Tokyo?
    3. Fukushima Diary (FD)states it found Americium 241 in Tokyo. Is FD and its author, Iori Mochizuki, credible? Is this experiment credible? Is Americium dangerous if inhaled or ingested in small amounts? Was americium released at Fukushima?Here are the links:

  2. Hi Anon:

    1. Strontium is a beta emitter which decays to Y-90 which is also a beta emitter. Cs-137 is a beta emitter which decays to Ba-137m. The Ba-137m emits gamma radiation. It is very easy to detect gamma radiation as compared to beta radiation. To accurately detect the beta radiation associated with strontium one would have to do a lot of chemical separation of the strontium. It is not necessary to do so with cesium (because of the gamma radiation of the barium).

    2. Unless something is prohibited by the laws of physics, there is always a chance.

    3. Americium is radiotoxic if inhaled or ingested in large quantities. Your first link shows Am-241 is "<3.7 Bq". That means it is less than the detection limit and may not be present at all. Your second link shows FD detecting Am-241 via gamma emission. A better way is to detect it through the alpha particles it emits. This is because other isotopes may emit gamma rays of similar energies and the detector (assuming it's properly calibrated to begin with) may mis-identify.

  3. Thanks Bob. Based on what you know about Fukushima, do you think its safe to travel to Tokyo for 2 weeks and is the air, water and food safe? What is the likelihood that a 2 week exposure to radionuclides in Tokyo at the current levels contribute to long term health effects? What is the likelihood of exposure to cesium, strontium, americium, and plutonium?

  4. Yes it is safe, using the relative meaning of the word (ie, compared to other activities people don't concern themselves about). I don't know where you're traveling from, but you may receive more cosmic radiation from your flight than from any terrestial radionuclides:

    You are likely exposed to cesium, strontium, americium, and plutonium wherever you are due to fallout. The likelihood is high, but the quantity to which you are exposed is minute. Same with Tokyo, though the likelihood and quantities may be higher, they are still trivially low. You may be exposed to relatively higher levels of other carcinogens like radon, diesel exhaust or second hand tobacco smoke.

    If I were making the trip, I'd be more concerned about the flight especially if you plan on using Japan Airlines:

  5. I should add, I wouldn't be overly concerned about the flight either. The risk of anything going wrong is less than the risk of dying in a car accident in any year. But none of these risks are zero, that's why they're risks.

  6. Thanks for your responses Bob

    I’m no radiation expert, just an average Joe, so I’m a bit confused by your response on Point 1 in my original post. I’m a bit concerned by a slide I read regarding the monitoring of radionuclides from Japan’s Ministry of Health, Labor, and Agriculture. Here is quote from the slide (Link to slides and page # at end of quote for your reference)

    “The new standard limits for radioactive cesium are established for effective dose of
    radionuclides (including Sr-90, Ru-106, Pu) not to exceed 1mSV/year.
    Because radionuclides other than Cs-134 and Cs-137 require a longer time for measurement,
    following procedure is taken to establish new standard limits.
    ■Analyze the migration ratio of each radionuclide according to migration pathway, derive the
    contribution of radioactive cesium according to product and age categories , and establish
    standard limits for radioactive cesium so that the sum of effective dose not exceed
    e.g.)The contribution of radionuclides other than radioactive cesium is about 12% (in case of people aged 19 and older)”

    (Reference: Slide 6) Link:

    From reading this, my impression is that the government is only checking for cesium and not strontium, or other radionuclides like plutonium, and americium. From what I understand, The government has set limits for cesium that are a lot stricter than other countries that this takes into account the possible presence of other radionuclides such as strontium and plutonium, but is not necessarily checking for them because they are hard to detect. Is my interpretation correct?

    What’s more concerning is what I heard that although they are monitoring food in Japan, not everything is monitored, its only spot checked. From reading the MLHW site in Japanese and translating through Google Translate I found the following quote (Note: obviously the translation is off, but you might be able to get the jist of what is being explained) :

    Can not you inspect all food Q5?
    Since it is not possible to inspect all food inspection is performed to expand the system as much as possible, we have stopped shipping for each region.

     Hacking the food, to the test, I will not be long, if you do not measure further inspection equipment. In addition, a large-scale equipment, a limited number.
     Therefore, when the inspection focused, more food and more food and more likely, while expanding the inspection system as much as possible, the radioactive substance is detected, the amount eaten, exceeds the reference value, production For each region where you are, I have to stop the shipment.
     In addition, as a result of the inspection was carried out by local governments in this way, I have put together and publish daily.

    (Note: you will need to translate this from Japanese to English using google translate or google chrome)
    I hear strontium can cause lukemia and don’t even know about ameiciums effects

    I hear plutonium is not a concern if ingested, only if inhaled, and cesium has a short half life in the body, so these 2 don’t seem to be too concerning.

    However strontium according to the EPA stays in the body for a while and can cause bone cancer or lukemia, and americium I haven’t heard much about if ingested.

    So over a two week period, whats the likelihood of taking in strontium and americium considering that the government only checks cesium in food/air/ water, and spot checks food or have I misinterpreted these slides?

    As you can tell I’m kinda worried!

    BTW - Where are you a health physicist at?

  7. Yes, your interpretation is correct and that was related to my answer to your original question 1. The reason it is easier to monitor for Cs-137 compared with Sr-90 is because it's easier to detect gamma radiation (Cs) compared with beta radiation (Sr).

    The biological effect of concern for all radionuclides is cancer (leukemia is a form of cancer). A typical American has a 42% chance of getting cancer over one's lifetime. If one receives an excess dose of 1 mSv (what the Japanese food radioactivity limits are based on), the cancer risk increases to 42.01%, which is a trivial increase.

    But the underlying assumption of the food radioactivity limit is that someone will be eating contaminated food (at the limit) all year long. Since you will only be there 2 weeks, you could eat food at 26 times the limit (52 weeks/year / 2 weeks) to incur the same risk increase. And to the extent any food you actually eat has no excess radioactivity, means you could make further upwards adjustment on the radioactivity levels of the food that is contaminated. Obviously you can't do this in practice, I'm speaking conceptually.

    And if you realize that there really isn't much practical difference between a 42% & a 43% cancer risk...the food you eat could be many hundreds of times the limit (highly unlikely), and still pose little need to worry.

    I'm retired...when I checked out a few websites to keep up on things I found they were either pro-nuclear (downplayed the risks of radiation) or anti-nuclear (exaggerated the risks). So I decided to start blogging as a way to force myself to stay current with health physics and be a resource for those looking for facts, not propaganda.

  8. Are cesium and strontium/plutonium always found together? From watching a video of a Q and A session regarding Food Safety in Japan put together by Safecast, the nuclear engineer mentioned that cesium acts like a marker. .if you find cesium, then radionuclides are present...if there is no cesium, there are no radionuclides..can you confirm this? If this is the case then i can understand the japanese thinking. . . at the very least, regardless of the radionuclide you ingest, the total amount you consume does not exceed 1msv a year. However if strontium can exist independent of cesium and plutonium, i see a potential for gaps in the monitoring.

  9. Well, it's a matter of scale. If your scale is the island of Japan, than cesium is found together with the others. If your scale is a cubic centimeter of soil on the island of Japan, you might find only cesium and nothing else and in another cubic centimeter you might find strontium and cesium and no plutonium, and on and on.

    The isotopes have different masses (137 for Cs, 90 for Sr, etc.) and different chemical properties (they are different chemical elements) and so these realities work against uniformity of deposition and transport in the environment.

  10. ok, so then i guess strontium and plutonium can be independent of cesium, in which case there could be gaps since the Japanese government is only monitoring for strontium???:)

  11. oops i meant "monitoring for cesium???:)"

  12. It works both ways.

    There could be instances in food where there is strontium &/or plutonium but no cesium. This would lead to a detection gap. The risk of the strontium &/or plutonium would not be known.

    But there could also be instances in food where there is cesium only, yet the food limit assumes it is accompanied with strontium & plutonium, which actually aren't there. This would lead to an overestimate of the risk of that food, and the overestimate would not be known.

  13. Yikes! There's nothing wrong with being oversafe in the second instance, but the first instance of not detecting the strontium or plutonium doesn't sound good! I read that plutonium doesnt digest very well and gets excreted. But what about the strontium?

  14. Strontium is chemically similar to calcium, so it's absorbed and used where one finds calcium in the body, like the bones.

    Hypothetically, you could take a calcium supplement in the morning and eat foods which tend to block calcium (and strontium) absorption in the day. This should tend to minimize any strontium uptake, though I do NOT know of any studies which have tested this hypothesis.

  15. so are you saying that strontium is not as dangerous as it sounds? The way it is described on Wiki and on the EPA websites makes it sound like its going to cause lukemia once its in the body since it stays in the body.

  16. Here is a fact sheet, similar to the one I originally posted on Pu, way up above:

    See if that helps.

  17. Bob,

    Thanks for providing this fact sheet.

    Again I’m no expert at radiation, and I was terrible at math in school so I was wondering if you can help interpret this table for me.

    I understand pci stands for pico curie, which can be converted to BQ.

    The way I interpret this table is that for 1 pico curie inahaled(does the –1 after pci mean anything), the risk of cancer from strontium is .0000000001%. Is that correct?

  18. The "-1" after pCi mean "per pCi". The risk is .0000000001 per pCi, there is no "%". This is equivalent to .000000003 per Bq. Note this is the risk of mortality (dying). The risk of getting the cancer will be higher (but since some people who get cancer survive, the risk of dying is lower than the risk of getting the disease).

  19. that's confusing. i usually think of probability in percentages. so what does .0000000001 mean if it is not a percentage. .maybe i missed this one in statistics.

    And if the risk of getting cancer is higher, what is it?

  20. "%"'s are normalized in terms of 100%. As an example, suppose a group of 25 is exposed to something that results in the death of 5. 5/25 =0.2. So, the risk of death is 0.2.

    One can normalize this in terms of 100% by multiplying by 100 and adding the "%" symbol. The 0.2 is equivalent to 20%. It's the same risk stated in two equivalent ways.

    So you can take the risks in my previous post, multiply by 100 (take away two of the zeros), and tack on the "%" symbol, but it still means the same thing as not multiplying by 100 and not tacking on the "%" symbol.

  21. Ok so 1 bq = 27 pci

    If the risk of dying from cancer is .0000000001/pci
    And the percentage is .00000001%


    The risk of dying from inhaling 1 bq of SR 90 = .0000000027 or .00000027%

    Is that correct?

    130BQ/KG was found in Tokyo. So this would mean inhaling a kg of this would give someone ..lemme do the math

    130BQ = 2702 pci

    If the risk of dying from cancer is .0000000001/pci
    And the percentage is .00000001%


    The risk of dying from inhaling 130 bq of SR 90 = .0000000027 or .00000027%

    Is that correct?

    1. The first half of your calculation are correct, that's why if you look above I already did that (I rounded 2.7 to 3). But 130 Bq x (27pCi/Bq)= 3,510 pCi, not 2,702 pCi.

      The risk of dying is correct, as I mentioned in an earlier post.

  22. ok. whats your take on this article? is this legit or is this making mountains out of molehills..

  23. I guess my rational mind tells me to listen to the Japanese Government and their assumption that strontium levels are low, because low amounts have been found near the reactors which are 120 miles away from Tokyo.

    But my worrying mind wonders, if any of it has traveled to Tokyo and if it is in Tokyo’s air. I see the cesium levels in Tokyo air are low. But how do they know that strontium levels are low, if they haven’t even checked. The only proof I’ve seen the Japanese government are spot tests in areas between Fukushima and Tokyo. The closest area to Tokyo found 19 BQ

    If cesium is gamma and strontium is beta, and gamma is easier to detect, doesn’t this mean that the beta radiation could be invisible, undetectable and potentially exist in high quantities in the air? I mean the nice thing about cesium is that it leaves the body, but strontium does not. I think it would bring more comfort to people if they actually test instead of making assumptions. Given that its been 2 years since the accident, I'm surprised the Japanese government hasn't done strontium testing in Tokyo where a large population lives and post the results. That would certainly put the nail on the coffin to sites like FD.

  24. Sorry, but I like reality. Beta radiation isn't invisible (you can't see it with your eyes, nor can you see gamma radiation with your eyes, but that doesn't mean they're "invisible". They can be detected) nor undetectable.

    Cesium is cleared from the body more rapidly than strontium, but strontium is cleared eventually. Only about 8% of that ingested remains after 1 month, and this decreases to 4% after 1 year! To say strontium does not leave the body is incorrect.

    You seem to want to worry....if you stop wanting to, you won't.

  25. Yes. I would like to stop worrying about this! When I told a coworker of mine that I was thinking of coming to Japan, he said he was afraid of the radiation. Since them I’ve been trying to get clarity on the situation there. To add to the situation, a safecast member told me that although food monitoring is effective, yet imperfect, a contact from a food page called Japan Food Safety quoted that only 1% of food is being checked, but that japan has a pretty effective sampling procedure in place, whereby if they find contaminated food on one farm, they will end up searching the entire farm.

    So I confirmed that MEXT actually did take strontium readings for each month after 3/11 . And I can see that as of Dec 2011 SR is undetectable in Tokyo. This data also confirms the higher cesium to strontium ratios that the Japanese have been basing their assumption on holds true for areas outside of Fukushima

    This also confirms what Mochizuki was saying about strontium 90 in Tokyo, but he obviously sensationalized it as the readings had already dropped by the time of his posting, and I guess his concern was why this didn’t come out till 7 – 8 months after the incident. Not to mention I see his refernce to the Japanese being communists and the Chris busby reference who I understand is an anti nuke that was once tied to the green party.


    Anyways, I feel a little more comfortable about Tokyo after reading this. Now I’m just concerned about the 1% food being checked.

  26. Why don't you take your food if you're that concerned? It's only two should be able to pack that into a suitcase (canned meat/fish, dried fruits, noodle bowls, etc.)?

  27. Bob - What does .89 MBQ/KM2 per Month of SR 90 equal if converted to BQ/KG?. I believe M stands for MegaBequerel. This is the amount of SR in Tokyo right as reported by MEXT after the Fukushima Incident.

    What does .14 MBQ/KM2 per Month of SR 90 equal if converted to BQ/KG?. This is the amount of SR in Chiba(next to Tokyo) 9 months after the incident in December 2011. Tokyo itself reported 0 MBQ/KM2 Month.

  28. For reference, these amounts came from the following document:

  29. You can't directly convert MBq/km2 to Bq/Kg. Yes, M stands for Mega (or 1 million). But the per km2 is based on area (squared kilometers) and the Kg is based on the mass of food. The "per month" really makes no sense at all.

  30. If you look at the upper right hand corner of page 4 it specifies that the unit is "MBq/Km2 - Month". Any inkling on what they mean?

  31. Nope. A sample is usually taken at a given point in time, so MBq/km2 would make sense...the amount of radioactivity per area. The activity per area per month, could make some sense if one is analyzing sample after sample, month after month in the same area.

    But that is very abnormal, except in very dynamic situations. Fukushima isn't that dynamic.

  32. Bob - when background radiation is reported on websites such as on the website for the Japanese National Tourist Organization, does the background reading include beta, gamma, and alpha radiation combined? I'm just wondering if this includes strontium?

  33. It depends on the context in which the data is presented. It usually does NOT include all the radiations combined.