Miniscule Levels Of Radioisotopes Found in Japanese Food

March 20th, 2011
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As the situation at the Fukushima nuclear plants has begun to stabilize, a new threat to the economic recovery of Japan and the livelihood of Japanese farmers and exporters has begun to rear its ugly head. Reports are now surfacing of food testing positive for radioisotopes traced to the core venting at Fukushima.

Via CNN International:

Japan’s radioactive food found in major local producer
The disclosure Saturday by Japanese authorities that milk and spinach have shown higher-than-normal levels of radiation contamination has raised concerns about food safety and supplies in one of Japan’s most heavily populated regions.

Tainted milk was found 30 kilometers (18 1/2 miles) from the Fukushima Daiichi nuclear plant and spinach was collected as far as 100 kilometers (65 miles) to the south, almost halfway to Tokyo. The plant was badly damaged after a 9.0 earthquake and subsequent tsunami hit the coast on March 11.

But Chief Cabinet Secretary Yukio Edano stressed to reporters Saturday afternoon that the levels were not extremely high: A person who consumed these products continuously for a year, he said, would take in the same amount of radiation as that of a single CT scan.

The U.S. Food and Drug Administration said that equates to 7 millisieverts, more than double the 3 millisieverts that a person in an industrialized country is typically exposed to in a year.

Health effects would become more evident, he said, if such products were taken in daily for a lifetime. Edano said high radiation levels were not systemic for all spinach and milk tested, and that more data would be collected and analyzed under the Japanese health ministry’s watch to help determine what steps to take next.

The Fukushima prefecture, or province, is just to the northeast of Tokyo. According to the prefecture’s website, Fukushima plays an important role in supplying food, not only to Tokyo, but also to the nation. The prefecture is Japan’s fourth-largest farmland area and ranks among the top producer of fruits, vegetables, rice, tobacco and raw silk. The favorable climate lends itself to an active agricultural industry that includes livestock farming.

The website also states that the prefecture’s 159 kilometer-long coastline is home to a thriving fishing and seafood processing industry, and the area’s haul of fish is among Japan’s largest.

Neighboring Ibaraki prefecture supplies Tokyo with a significant amount of fruits and vegetables. Ibaraki is the largest producer of Andes melons in Japan, according to the prefecture’s website, as well as the country’s third-largest producer of pork.

Most information available is fairly vague about both the type of radioisotope found in foods and the total amount. That said, current measurements may not be entirely reliable, since levels tend to vary quite widely and a small number of samples may not provide a reliable reflection of the actual levels in the overall food supply.

Based on official statements that eating such foods for a year would result in the same level of radiation exposure as a single CT scan, it appears that the levels of radioactivity are extremely low. While this would indeed result in a greater dose than most people get in a year, this is only if you ate exclusively the spinach and milk every day for breakfast, lunch and dinner for 365 days. Of course this would never happen in the real world, where a person might drink a glass or two of milk a day (not all of which generally comes from one source) and, at most, may have a couple of servings of spinach per week. In that circumstance, the worst reasonable dose anyone could be expected to receive is extremely low.

Further press reports have indicated that the radioisotope which has been detected in many of the foods is iodine-131. This isotope is considered dangerous because of the potential to cause thyroid cancer, although it seems levels detected thus far are very low and thus such concerns are not warranted.

Via UPI

Cabinet secretary Yukio Edano said spinach and milk were the only products from nearby farms found with abnormally high radiation levels. But many farms have not yet been tested amid the overwhelming crisis.

Inspectors said milk had five times the safe level of iodine-131 and spinach was more than seven times higher.

This is in fact very good news when it comes to the long term safety of Japanese food supplies. It is known that low levels of iodine-131 were present in the steam vented from the Fukushima nuclear plant. Iodine can exist as a gas and tends to be fairly mobile in the enviornment. The fact that this is the only isotope mentioned means that the incident at Fukushima does not appear to have released significant quantities of less volatile but more persistent isotopes.

Because iodine-131 has a very short half-life, it is not normally found in the enviornment in any measurable concentration. The iodine-131 produced by nuclear tests in the 1950′s has long decayed away. Therefore, even the tiniest concentration of iodine-131 will stand out when tested for, and modern testing methods, such as liquid scintillation spectroscopy are extremely sensitive to even the tiniest traces of such isotopes.

Although the current concentrations may, in some cases, exceed the extremely conservative standards for iodine-131 in foods, this does not mean that the foods are dangerous at all. However, even if the levels are high enough to preclude their sale, they also do not need to be thrown away. Since iodine-131 has a half-life of about eight days, foods found to be containing it can simply be diverted to use in processed food products, such as canned spinach, ice cream, evaporated milk, frozen dinners and so on. Such products typically are kept in storage for some time before making it to consumers anyway, and canned foods may be stored for months. This provides ample time for all the iodine-131 to decay away. Furthermore, the short half-life of iodine-131 means that the levels present in Japanese foods will be down to approximately zero within a few weeks.

The greater concern is not the health effects but the panic and bad press that this has generated. Some countries are already stating that they will be inspecting Japanese food imports for radioactivity. Considering the toll that the earthquake and tsunami has taken on the Japanese economy, the country can’t afford to see another crisis develop over irrational fears. The livelihood of Japanese farmers and exporters may depend on a rational response to this non-issue.


This entry was posted on Sunday, March 20th, 2011 at 10:09 am and is filed under Agriculture, Bad Science, Enviornment, media, Nuclear, Politics. 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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23 Responses to “Miniscule Levels Of Radioisotopes Found in Japanese Food”

  1. 1
    DV82XL Says:

    I have my doubts that this newfound ‘radiation’ is even from this event. In particular the milk findings are very questionable given the timeline. As well, there is no mention of where the contamination has been found on the surface of the tested greens, or in the flesh, as a good washing would remove the former, and again the time factor would make any contribution from the current incident unlikely for the latter.

    In other words there is something fishy about these findings, this close to the start of the event.


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  2. 2
    Chem Geek Gregor Says:

    I am continually irritated by reports like this that give none of the raw data and only the most vague of information on the actual concentration and exposure.

    How much was found? How many becquerels per kilogram?

    How many samples were taken and what was the deviation on them? Is this the reading of just one sample or is it the average or what?

    What technique was used to measure the levels and what is the error for the reading?

    Without this basic information it’s all but impossible to tell what this actually means. However, the media is going nuts on it anyway.


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  3. 3
    Alan(UK) Says:

    I am still very confused about radiation doses. A raw count in Bq I can understand. A dose in Gy seems much more difficult to measure. If the 1kg referred to is human tissue, how do you allow for the gamma radiation that passes straight through without absorption? Measuring Sv seems to be even more problematic; no doubt it can be carefully evaluated in a clinical situation where the exact type and energy of the source is known but how can a meaningful measurement be taken by just waving an instrument around in the general vicinity of a nuclear reactor?

    Even more difficult to understand is that a reading obtained corresponding to a nuclear worker in a proper protection suit could just ignore alpha and beta radiation but the measurement corresponding to an unprotected member of the public would have to take them into account.

    Also, does ‘dose’ refer to exposure to an external source alone or can it also include radiation from radionuclides already ingested?

    When we measure in Sv are we measuring absorbed dose or just some radiation ‘in the air’ as it were. The formal definition implies the former but the way one actually hears it being used, ‘the radiation at the plant gates’ implies the latter.

    Finally, here is a quotation from the Guardian:

    Huw Alun Evans’s farm, Hengwrt Uchaf in north Wales, is one of the 369 inside one restricted area. Thousands of his sheep have been scanned for more than two decades. Evans’s animals have failed radiation tests if they have been on higher ground, but the danger levels drop after they have been brought down to graze on lower pastures.

    The implication from the whole article is that the offending radionuclide is caesium-137. Would this make sense? Could it be that the sheep is getting radiation on its wool from the Sellafield reprocessing plant and it simply gets washed off? Is there some natural cause for the radiation detected?


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  4. 4
    ddp Says:

    Since I doubt samples were taken before the earthquake, I wonder if these are really increases or just natural readings.

    It might be interesting if someone found some old milk and spinach from the week before the earthquake and did the same analysis.


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  5. 5
    drbuzz0 Says:

            Alan(UK) said:

    I am still very confused about radiation doses. A raw count in Bq I can understand. A dose in Gy seems much more difficult to measure. If the 1kg referred to is human tissue, how do you allow for the gamma radiation that passes straight through without absorption? Measuring Sv seems to be even more problematic; no doubt it can be carefully evaluated in a clinical situation where the exact type and energy of the source is known but how can a meaningful measurement be taken by just waving an instrument around in the general vicinity of a nuclear reactor?

    Even more difficult to understand is that a reading obtained corresponding to a nuclear worker in a proper protection suit could just ignore alpha and beta radiation but the measurement corresponding to an unprotected member of the public would have to take them into account.

    Also, does ‘dose’ refer to exposure to an external source alone or can it also include radiation from radionuclides already ingested?

    There are different units of measurement for radiation. The sievert (Sv) is an attempt to create a unit of human dose equivalent. It’s a standard scale of what the equivalent biological effect is.

    If you are exposed to radioactivity indirectly versus if you ingest something, the total effect is going to be different. It will also be different depending on the energy level and the type of radiation.

    Thus the sievert is supposed to compensate for all this. A number of formulas are used based on the route of exposure and such things. In theory, if you ingest a substance and it’s calculated that this causes 1 Sv of exposure then the biological effects should be the same as 1 Sv of exposure by proximity to a source.

    So it can be in the air or by some other path of exposure.

    One thing to remember is that it’s only an approximation.


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  6. 6
    DV82XL Says:

            Alan(UK) said:

    I am still very confused about radiation doses. A raw count in Bq I can understand. A dose in Gy seems much more difficult to measure. If the 1kg referred to is human tissue, how do you allow for the gamma radiation that passes straight through without absorption? Measuring Sv seems to be even more problematic; no doubt it can be carefully evaluated in a clinical situation where the exact type and energy of the source is known but how can a meaningful measurement be taken by just waving an instrument around in the general vicinity of a nuclear reactor?

    You are right, Sieverts have been flung about in the media and on web sites by people that do not understand this measurement, to people that do not understand it. In fact there is some confusion between micro and milli in many reports adding to confusion and underlining the lack knowledge out there.


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  7. 7
    Happy Stupid Says:

    Does this mean we can shave a minute or two off of the time in the microwave?


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  8. 8
    DV82XL Says:

    One of the biggest issues that I see in the larger discussion on radiation as it pertains to this event is that there is almost total confusion among non-experts as to the difference between prompt radiation and radioactive contamination. There is also much confusion about the phenomena of induced radioactivity in otherwise non-radioactive material.

    What is worse is that this lack of understanding doesn’t seem to be apparent to many of those that are knowledgeable leading to the belief in those that aren’t that they are being lied to.

    While this is not happening on this blog, it is sure prevalent elsewhere. We have got a lot of work ahead of us in the coming months, and we have to be very sure that we are not talking past our audience, because our opponents will exploit this sort of confusion, to the max, as they have in the past.


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  9. 9
    dmfdmf Says:

    Here is a chart that puts things in relative context;
    http://www.xkcd.com/radiation/


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  10. 10
    Mark Says:

    You have every right to be confused – but particularly, unlike a lot of the media, you are actually enquiring rather than just accepting.

    The (Bq) is the unit of activity (radioactivity). Getting from (Bq) to ‘dose’ (or dose rate) is not as easy as you might think. Here is an example:

    Take Cs-137 (a beta / gamma emitter – the gamma coming from Ba-137m daughter). For a point source of Cs-137 the dose rate, measured in micro Sv/h, for an activity of 1MBq, is at 10cm about 8. I just know this, or you can calculate. The ‘8’ comes from knowing the types of emissions (e.g. gamma), the energy of emissions (662 KeV in this case), the number of emissions (related to activity), the distance from the source, the air attenuation etc etc. There are complicating factors when you consider shielding, dispersed sources (i.e. not a point source), scatter (sky-shine) from large activity inventories and so on.

    To use the proper term, the ‘dose’ that the media have been using – the mSv = (1/1000 of a Sv) is actually ‘whole body effective dose’. This really is not a dose at all, but an expression of ‘risk’. The value of ‘mSv’ can be derived from internal hazards (that is radioactive material that is inside the body), and external hazards (that is radioactive material that is either on the outside of the body, or some distance from it).

    To complicate matters, and this might appear to be conflicting with what I have said above, I actually think for external radiation, the unit of ‘ambient dose equivalent’ has been reported – this is typically what a gamma monitor will report in. However, for practical purposes, if you receive a whole body dose (i.e. whole body within radiation field) then if the monitor says 1mSv/h then this can be treated as 1mSv effective dose (if you stay there the whole hour). This has a lot to do with ‘tissue equivalent filtration’.

    You mentioned the Gy – this is the absorbed dose and is a fundamental dose quantity (in the US 1 Gy = 100 RAD). The Gray has nothing to do with Stochastic radiation risk (i.e. risks that present themselves as cancer at some point later on in life). When we are talking about cancer risk (typically at lower doses) we talk in Sv, when we are considering ‘deterministic radiation effects’ we should be talking in Gy (for at this point the radiation and tissue weighting factors that are applied in the derivation of the Sv are of little concern). The media probably did not use Gy because (1: they do not understand it, 2: they did not need to use it – which is good !). Some charts (there are some good ones too), that report that 7Sv is enough to kill you (that is true) should really report in Gy (but that would complicate things !!).

    I agree that the original measurements being reported at certain points (e.g. 8mSvh etc etc) probably did not take into account internal radiation risks – although I believe from reading other reports that these were not significant. If you are exposed to an external field of 5mSv/h (gamma) there is not a lot you can do about that (unless you can find a shielded area, increase distance, lower exposure time). If you are wearing full protective clothing (and adequate respirator) then you are completely protective from the internal radiation risk (but not that whilst, for example, there is Cs-137 dust on your protective suit, you are potentially being irradiated externally).

    Some more info, comment and videos about some of the matters you raise can be found here:

    http://www.ionactive.co.uk/blog.html

    A specific blog entry dealing with the points you raise, with some video resource, can be found here:

    Ionactive Blog: Nuclear events in Japan – Radiation Dose ‘high enough to effect human health’:

    http://t.co/i8gzStT


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  11. 11
    Jason Ribeiro Says:

    I just looked this up. It should be noted that Iodine 131 decays to stable Xenon, a noble gas. Nowhere in the popular media have I heard this mentioned.


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  12. 12
    EL Says:

    The Japanese government is providing these numbers on a regular basis, but they are buried in Japanese language sites to access them. Results from environmental sampling of radiation twice daily from 28 sites outside evacuation zone can be found here.

    Food sampling results are a little more difficult to find. Here are the numbers for the first reported findings on spinach and milk. Nominal levels have been reported for Cs-137.  Iodine-131 has been showing up at levels 3-5 times the safe levels for ingestion established by the Japanese government (at a distance of 90 km from the power plants), 11-15 times the amount for milk used to manufacture powdered baby formula.  

    New reports today indicate “abnormal levels” for spinach in neighboring Tochigi and Gunma prefectures, canola in Gunma Prefecture, and chrysanthemum greens in Chiba Prefecture (but I haven’t searched for numbers yet).  Also, water concerns have showed up in Iitate village (30 km from power plants), and Health Ministry has ordered that residents not drink the tap water.


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  13. 13
    Mark Says:

    Thanks EL (14)..

    Remember, the use of phrases like ‘safe level’ etc is perhaps easy for the public to understand, but meaningless in terms of what the measurements are about. They are looking at the ingestion of radioactive material, which will then be turned into a committed whole body effective (in nSv or micro Sv I guess). These are then really expressions of ‘risk’ – therefore what we are really saying is what is the ‘acceptable’ risk rather than is it ‘safe’ or ‘not safe’. The public find it difficult to deal with that concept…

    In those terms, the acceptable risk ‘increase’ (i.e. more risk) is negligible (IMHO).

    (Note added: it is possible to have deterministic effects from intakes of radioactive materials, but that is just not going to happen with the levels found on food stuff).


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  14. 14
    BMS Says:

    Exactly, Mark.

    If the Chernobyl accident taught us anything, it is that the phrase “safe level” depends on whom you ask. Throughout Europe and the rest of the world what was defined as “safe” varied quite substantially (often by an order of magnitude or more) from country to country. The regulations depended much more on the amount of irrational panic on the part of the bureaucrats than anything else. Certainly, very little credible science was involved in these decisions.


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  15. 15
    Critical Information and Methods for Bulimia Therapy | Solar Kits Says:

    [...] Miniscule Levels Of Radioisotopes Found in Japanese Food … [...]


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  16. 16
    drbuzz0 Says:

            EL said:

    The Japanese government is providing these numbers on a regular basis, but they are buried in Japanese language sites to access them. Results from environmental sampling of radiation twice daily from 28 sites outside evacuation zone can be found here.

    Food sampling results are a little more difficult to find. Here are the numbers for the first reported findings on spinach and milk. Nominal levels have been reported for Cs-137.  Iodine-131 has been showing up at levels 3-5 times the safe levels for ingestion established by the Japanese government (at a distance of 90 km from the power plants), 11-15 times the amount for milk used to manufacture powdered baby formula.

    Thanks for the info, although this still does not really shed much light on the issue of whether it’s a single sample or the average of many, although it would seem to imply that it is only a single sample.

    I’m becoming less concerned about this as I have found more data. Any kind of processed foodstuff like baby formula is going to get milk from many sources, so a few higher levels will ultimately average out and be diluted down when it all goes into the mix.

    Also, something like powdered baby formula is not perishable. It is not generally sold quickly after it is manufactured. From the time the milk is drawn to the time the final product hits the store shelves could be weeks. Plenty of time for the iodine-131 to decay away.

     

            EL said:

    New reports today indicate “abnormal levels” for spinach in neighboring Tochigi and Gunma prefectures, canola in Gunma Prefecture, and chrysanthemum greens in Chiba Prefecture

    “abnormal levels” would be anything above zero or at least very close to zero. The only natural source of iodine-131 is spontaneous fission.


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  17. 17
    Emily Says:

    They say less than two weeks now until the radiation gets to the British Coast. How great do you think the danger is and if there is some time what can be done to prepare? I live north of London. Some of my family lives near Scotland. Do you think the danger is less or more in one place or the other?


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  18. 18
    Anon Says:

    The danger does not exist outside of Japan and even in Japan it is very localised.

    Stop worrying (and giving in media beatups) and just live your life.


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  19. 19
    Mark Says:

    At (17) – the danger is ‘negligible’. If there is one thing I do before I give up work, is to try and get the general acceptance of the phrase ‘negligible’ with respect to radiation exposure.


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  20. 20
    Matte Says:

            Emily said:

    They say less than two weeks now until the radiation gets to the British Coast.
    How great do you think the danger is and if there is some time what can be done to prepare?
    I live north of London.
    Some of my family lives near Scotland.
    Do you think the danger is less or more in one place or the other?

    Well, I think you should stay away from Scotland. The risk of catching a headcold is quite high up there…but then getting mugged in Peterborough can be a life ending experience too or being run down by a London cab. Umm…anyway I would be more worried about those sorts of things if I where you.

    I recently got a report of radio Iodine being detected in Stockholm at 1/100000-part from the Radon threshold, 0.3 mBq/m^3. Assuming the concentration in England is roughly the same, you need to suck up all the radioiodine in 3 333 m^3 of air to atain 1 Bq of Iodine 131, which will give you a internal thyroid dose of 0.3 micro Sv. Assuming your lungcapacity is 5 litres (and you hyperventilate) it would take you ~58 days to inhale all that air…at which point most of it will have decayed away anyway, so the dose would be even smaller. At least I gave you a worst case. The increased risk of thyroid cancer is so low it is not quantifiable.

    If you are still worried you could always poison yourself with some potassium iodide tablets, but I would not recomend it.


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  21. 21
    Mark Says:

    What Matte said !!


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  22. 22
    drbuzz0 Says:

            Matte said:

    Well, I think you should stay away from Scotland. The risk of catching a headcold is quite high up there…but then getting mugged in Peterborough can be a life ending experience too or being run down by a London cab. Umm…anyway I would be more worried about those sorts of things if I where you.

    Definitely stay away from Scotland. One can’t underestimate the risk of being eaten by Nessie, which is likely much higher than being poisoned by radiation from Japan if you live in Northern Europe.


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  23. 23
    Changed DNA: Radiation risk higher for children | Radiation Report Blog Says:

    [...] only lead to a minimal increase in their risk of getting cancer. View the original article hereUpdated higher radiation levels are now being admitted at Fukushima. As usual we need to consid…ed to the level of Chernobyl, people have started to panic about the health threat from the [...]


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