Fukushima Prefecture and Fukushima Medical University Fail to Report a Thyroid Cancer Case

On March 30, 2017,  it was broadcast on both Fukushima and nationwide NHK channels that Fukushima Prefecture has not reported thyroid cancer diagnosed in a boy who was age 4 at the time of the 2011 Fukushima Daiichi nuclear power plant accident. The case came to light when the 311 Fund for Children with Thyroid Cancer revealed he was one of six applicants that received aid in February 2017. (Video of the statement in Japanese on this website. See the section "Thyroid cancer cases outside Fukushima Prefecture" on this post for more information on the 311 Fund for Children with Thyroid Cancer).

The TUE, commissioned by Fukushima Prefecture to Fukushima Medical University, is conducted through the fund provided by the central government. The primary examination is screening by ultrasound. Those meeting certain criteria go on to the confirmatory examination where the majority end up being placed back on the regular screening schedule every 2-5 years. However, some are shifted to regular medical care covered by the national health insurance, either for follow-up with more frequent ultrasound or for further testing and/or treatments such as cytology and surgery. This shift apparently puts these cases beyond the scope of screening as per Fukushima Medical University, which has consistently refused to provide detailed information on such cases, citing privacy concerns. 

The child was diagnosed with thyroid cancer while under follow-up after going through the confirmatory examination during the second round of the Thyroid Ultrasound Examination (TUE) conducted in FY2014-2015. After the fine-needle aspiration cytology in 2015 showed suspected cancer, he underwent thyroidectomy in the first half of 2016. The fact his case—the youngest reported so far at age 4—never appeared in the officially reported results suggests cancer cases diagnosed during follow-up are not reported, which was admitted by Fukushima Medical University. There are over 2500 individuals followed up from the first to third rounds so far (see table in this Japanese article). 

Below is an unofficial translation of the NHK nationwide coverage posted here and archived here.


Thyroid Examination After the Nuclear Power Plant Accident: Cancer Diagnosed in a Four-Year-Old Boy Goes Unreported

March 30, 8:24pm

Since the Fukushima Daichi nuclear power plant (FDNPP) accident, Fukushima Prefecture has been conducting the Thyroid Ultrasound Examination in children who were ages 18 or younger at the time of the accident, reporting the results to an expert committee evaluating health effects of the accident, the Oversight Committee for the Fukushima Health Management Survey. However, NHK’s investigation revealed thyroid cancer diagnosed in a child who was 4 years old at the time of the accident time has not been reported to the Committee.

After the FDNPP accident, Fukushima Prefecture commissioned Fukushima Medical University to conduct the Thyroid Ultrasound Examination to detect lumps in the thyroid gland of about 380,000 children who were age 18 or younger at the accident time. This age group is known to be sensitive to the effect of radioactive iodine.

Fukushima Prefecture reports the results to the Oversight Committee evaluating health effects of the accident. By the end of the last year, it was reported that 185 individuals in the age range 5-18 at the time of the accident had been diagnosed with cancer or suspected cancer.

However, NHK’s investigation revealed that Fukushima Medical University was aware of but failed to report to the Oversight Committee about the youngest patient to date—a child aged 4 at the time of the accident—who was diagnosed with thyroid cancer after the Thyroid Ultrasound Examination and had the thyroid gland removed.

The Thyroid Ultrasound Examination consists of two steps: the primary and the confirmatory examinations. Fukushima Prefecture and Fukushima Medical University explain, “We report cases in patients who were diagnosed with cancer or suspected cancer during the confirmatory examination. We do not report thyroid cancer cases diagnosed either in patients assigned to “follow-up” as a result of the confirmatory examination or in patients diagnosed after transferring to other medical facilities, due to difficulties in comprehensive recording of such cases.”

When an Oversight Committee member questioned two years ago about a potential issue in reporting cancer cases diagnosed during follow-up, Fukushima Medical University explained that patients diagnosed with thyroid cancer after the confirmatory examination would be “reported separately.” However, no such reporting has occurred.

An Oversight Committee member and former vice president of Fukushima University, Special Professor Shuji Shimizu points out, “The mission here is to release and analyze accurate information. So that no doubt arises that anything might be hidden, thyroid cancer cases should be disclosed as facts no matter what the circumstances of diagnosis may be.”

What is thyroid cancer?

Thyroid gland is a small, butterfly-shaped organ, located below the Adam’s apple and weighing about 10 to 20 grams. Its function is to secrete hormones involved with growth promotion.

After the FDNPP accident, “thyroid cancer” became a concern as it can be caused by the thyroid gland absorbing “radioactive iodine” which is one of the radioactive materials released due to the accident.

In particular, children in a growth process are considered to be sensitive to the effect of radioactive iodine, because the repair of chromosomal damages cannot keep up with active and repeated cell divisions occurring in the body.

After the Chernobyl nuclear power plant accident in former Soviet Union, residents in surrounding areas took in “radioactive iodine” mostly through consumption of milk and dairy products. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reported that about 6000 residents developed thyroid cancer and 15 died by 2006.

All children who were 18 or younger targeted by the Thyroid Ultrasound Examination

After the FDNPP accident, Fukushima Prefecture commissioned Fukushima Medical University to conduct the Thyroid Ultrasound Examination in all 380,000 children who were age 18 or younger and lived in the prefecture at the time of the accident.

Using the 78 billion yen ($700 million) fund contributed by the central government, the Thyroid Ultrasound Examination is conducted once every two years up to age 20 and every five years after age 20.
The Thyroid Ultrasound Examination consists of two steps. The primary examination, often conducted in school settings, involves placing the ultrasound probe on the neck to detect any lumps in the thyroid gland. The results are given as four-level assessments.

Those who are assessed to have lumps above a certain size undergo the confirmatory examination for more detailed testing. 
The confirmatory examination consists of more detailed ultrasound examination, blood tests, and fine-needle aspiration cytology (FNAC) as needed. In FNAC, a needle is inserted into the lump in order to distinguish between benign and malignant tumors.

The first round of the examination commenced in October 2011, and the second round in 2014. Currently the third round is underway.

The latest data reported last month shows a total of 185 individuals—116 in the first round and 69 in the second round—were diagnosed with “cancer” or “suspected cancer” as of December 31, 2016.

Age at accident ranges from 5 to 18, with the youngest being a 5-year-old boy reported in June 2016.

An Oversight Committee member says “The level of confidence for the Thyroid Ultrasound Examination might fall”

Regarding the revelation of thyroid cancer patients not reported to the Oversight Committee, an expert points out that the level of confidence for the Thyroid Ultrasound Examination might suffer. 

The Thyroid Ultrasound Examination results are regularly reported to the Oversight Committee consisting of 15 experts including cancer specialists and university professors. The Committee conducts scientific evaluation regarding the relationship between thyroid cancer and the nuclear accident. 

In 2015 and 2016, the Oversight Committee released mid-term reports on thyroid cancer diagnosed in Fukushima Prefecture after the FDNPP accident, stating, “Overall, they are unlikely to be due to the effects of radiation.” 

Reasons mentioned in the report include the following: radiation doses were much lower compared to those after the Chernobyl accident; thyroid cancer cases were not seen in ages 5 or younger as commonly seen in Chernobyl; and Fukushima cases were detected in a short time span of 1-4 years after the Fukushima accident, while the Chernobyl cases were discovered beginning 5 years after the Chernobyl accident.

Later, it was reported to the Oversight Committee meeting in June 2016 that thyroid cancer had been diagnosed in a 5-year-old boy for the first time. Nevertheless, the Committee’s stance, “unlikely due to the effect of radiation,” has not changed.

An Oversight Committee member and former vice president of Fukushima University, Special Professor Shuji Shimizu emphasized that the news of thyroid cancer in the youngest patient to date—a child who was four at the time of the accident—should be calmly received. He stated, “This case is neither surprising nor strange because the risk for cancer increases with age.” He further commented about the unreported cancer cases, “The mission here is to release and analyze accurate information. Any thyroid cancer cases should be disclosed as facts no matter what the circumstances of diagnosis may be, with special precaution to ensure protection of personal information. Otherwise doubts will arise that something might be hidden, reducing the level of confidence for the Thyroid Ultrasound Examination as a whole.”

Fukushima Prefecture “will consider the release of information based on discussion at the Oversight Committee”

Regarding unpublicized thyroid cancer patients, Fukushima Medical University states the department in charge of the Thyroid Ultrasound Examination does not have information on thyroid cancer cases diagnosed during follow-up or as a result of medical care and testing at other medical facilities unrelated to Fukushima’s Thyroid Ultrasound Examination.
Fukushima Medical University further explains that the “regional cancer registry” system mandating submission of cancer patient data by medical facilities is collecting and releasing more precise information.

A physician who was in charge of the Thyroid Ultrasound Examination at Fukushima Medical University stated during NHK’s interview that “Most of the patients diagnosed with thyroid cancer during follow-up after the confirmatory examination are receiving medical treatments at Fukushima Medical University, but we do not have exhaustive information covering all cases. Release of such information should be conducted carefully in order to avoid arbitrariness. We are doing the best for the sake of the patients without a doubt.” Regarding the reporting system that excludes patients diagnosed with cancer during follow-up after the Thyroid Ultrasound Examination, he further stated, “How to deal with that is a real problem which has remained an issue since I was in charge of the Thyroid Ultrasound Examination.”  

Fukushima prefectural government's Division of the Fukushima Health Management Survey that commissions the Thyroid Ultrasound Examination to Fukushima Medical University states, “We are aware that thyroid cancer cases diagnosed during follow-up after the Thyroid Ultrasound Examination are not included in the reported results. We understand such cases potentially exist, but we are unaware of individual cases. We will consider releasing such information in the future based on discussion at the Oversight Committee.”

Radiation Testing of Canned Salmon Caught in the North Pacific Ocean Before and After the 2011 Fukushima Nuclear Accident

Below are the results of radiation testing on canned salmon produced by an American seafood company, Vital Choice Wild Seafood and Organics. (Here is the Japanese article).

Becquerel (Bq) is a unit of radioactivity: 1 Bq means "one disintegration event per second."
Picocurie (pCi) is a unit of radioactivity: 1 pCi = 0.037 Bq

  • In this citizen-driven project, Pacific salmon cans from a U.S. seafood company, Vital Choice Wild Seafood and Organics, underwent radiation testing by citizen labs in Japan. Salmon cans before and after the 2011 Fukushima nuclear accident (2009, 2011, 2012, 2014) were analyzed for 4 radionuclides: Cesium-134, Cesium-137, Strontium-90 and Tritium.
  • A very small amount of Cesium-137 was detected in all 4 samples, mostly due to background Cesium-137 ("legacy Cesium-137) from nuclear weapons testing.
  • The 2011 sample canned in August 2011 had a slightly higher level of Cesium-137 than the other 3 samples, and the difference of about 0.02 Bq/kg might be due to the Fukushima accident if Cesium-134 coexists.
  • However, no Cesium-134 was detected. Based on the Fukushima-specific Cesium-137 to Cesium-134 activity ratio of 1:1 and the 2-year half life of Cesium-134, any Cesium-134 potentially present in the 2011 sample falls below the minimum detection limit. 
  • The higher Cesium-137 level in the 2011 sample is likely to be related to the Fukushima accident, but data is inconclusive.
  • No Strontium-90 or tritium (both free-water and organically-bound) was detected above the detection limit.


This voluntary "project" came together spontaneously in the summer of 2015 when concerned citizens wanted to verify the alarmingly high strontium level detected in sockeye salmon in Vital Choice's 2015 radiation testing. 

Since the March 2011 Fukushima nuclear accident, Vital Choice has taken an initiative to conduct--once or twice year--radiation testing of seafood used in their products. For the 2015 test for Strontium 90, the sockeye salmon sample consisting of six 6-oz frozen, boneless fillets with skin on was received by the lab, SGS, on December 11, 2014. A separate batch was sent to another lab, Eurofins, for radioactive cesium testing. 

According the the SGS report obtained from Vital Choice, an unexpectedly high level of Strontium-90 was detected in sockeye salmon at 1.76 ± 0.863 pCi/g (65.12 ± 31.93 Bq/kg) with the minimum detection limit of 1.45 pCi/g (53.65 Bq/kg). 

This Strontium-90 test result of 65.12 Bq/kg seemed extraordinarily high for several reasons:
  1. The highest Strontium-90 level detected in seafood testing conducted by the Japanese government was 1.2 Bq/kg with the detection limit of around 0.03 Bq/kg in rockfish harvested off the coast of Fukushima Prefecture on December 21, 2011 (refer to row #10 in this PDF found on this page of the Japanese Fisheries Agency website. The location where the sample was taken is also plotted as "10" in the first map of this PDF).
  2. In the 2015 study of fish caught within the harbor adjoining the Fukushima Daiichi nuclear power plant in 2012 and 2013, the highest level of Strontium-90 detected in whole fish without internal organs was 170 ± 1.2 Bq/kg (wet). This study also showed that the Cesium-134/137 levels were 200-330 times the Strontium-90 levels.
  3. As just mentioned, strontium has been found at a much lower level than cesium in general, consistent with the amounts released from the accident. For instance, the Japanese government sample of rockfish with 1.2 Bq/kg of Strontium-90 mentioned above also contained 970 Bq/kg of cesium—390 Bq/kg of Cesium-134 and 580 Bq/kg of Cesium-137. Although the Vital Choice samples tested for cesium and strontium consisted of two different sets of six 6-oz boneless fillets with skin, the sockeye salmon sample from Vital Choice's 2015 test showed non-detectable levels of both Cesium-134 and Cesium-137 with the detection limit of 1.0 Bq/kg each. Thus it is highly unlikely that the Vital Choice sockeye salmon would contain any detectable amount of Strontium-90.
  4. In addition, whereas other tests mentioned here used muscle for the cesium testing and whole fish without organs for the strontium testing, the Vital Choice sockeye salmon sample was just muscle and skin without any bones, consisting of six 6-oz boneless fillets with skin, which makes the reported Strontium-90 level of 65.12 Bq/kg highly questionable.  (The 2015 study mainly analyzed otoliths—calcium carbonate structures in the inner ear—but also mentioned the strontium level in whole fish without internal organs).
  5. Also, the reported result, 65.12 ± 31.93 Bq/kg, has a high error margin of 31.93 Bq/kg. With the minimum detection limit of 53.65 Bq/kg, much higher than the detection limit around 0.03 Bq/kg employed in the Japanese government's test, the quality of testing is doubtful.
(Note: Vital Choice attributes the high level of Strontium-90 to lab errors, as explained at the end of their 2015 report).

With the Internet abuzz with the news of the high strontium level detected during Vital Choice's 2015 test, an idea arose to have confirmatory tests conducted by citizen labs in Japan which have—in response to people's demand—acquired sophisticated equipment and skills to detect very small amounts of radionuclides. Granted, it would not be possible to test the exact same fish, but at least fish caught in the same year, 2014, could be tested. 

Then it occurred to me that I myself owned (and still own) quite a few of Vital Choice's canned salmon with bone and skin produced in 2009 and purchased immediately after the 2011 Fukushima accident. A local friend also had Vital Choice's canned salmon with bone and skin produced in the summer of 2011 after the Fukushima accident. Furthermore, rather than having boneless frozen fillets tested, it made sense to have canned salmon with bone and skin tested for Strontium-90, because strontium accumulated in bone due to its chemical resemblance to calcium. (Shipping frozen fillets would also be cost prohibitive). In addition, testing the same sample for cesium would also yield pre-Fukushima baseline levels of Cesium-137 in salmon. 

Vital Choice generously agreed to provide canned salmon from 2014. As a "bonus" the warehouse accidentally sent me canned salmon from 2012, so now we had pre-Fukushima (2009) and post-Fukushima (2011, 2012 and 2014) sets of canned salmon, all with bone and skin. Although it was not possible to know exactly when and where in the Pacific Ocean the fish was caught, can codes showed when the can was processed. (Salmon is caught and canned in the same year). All the can codes and their explanations are provided here.

Cans were sent to Japan in multiple U.S. Postal Services flat-rate boxes. Some individuals helped with transporting them to a citizen lab in Tokyo for the cesium testing and then to another citizen lab in Fukushima for testing for strontium and tritium. (After the cesium testing was completed in Tokyo, the remaining samples were frozen and transported to the Fukushima lab by a citizen volunteer at a later time. Fee for testing was either donated by the lab or privately covered.


Actual reports (in Japanese) can be accessed here.
Results are tabulated here and detailed information on tested samples can be found here.


The strontium testing was conducted by the only citizen-run lab in Japan capable of beta radiation analysis, Mother's Radiation Lab Fukushima. The analytical method used is a liquid scintillation counter (shown in this Japanese PDF). The use of liquid scintillation counter is explained in detail here. Strontium-90 was not detectable in any of the samples with much lower detection limits than the lab originally used by Vital Choice (0.15-0.17 Bq/kg vs. 53.65 Bq/kg).

The actual report obtained from Vital Choice indicated "ASTM D5811-95" as the analytical method, which is the "Standard Test Method for Strontium-90 in Water" as described hereIt was developed to measures Strontium-90 in environmental water samples in the range of 0.037 Bq/L (1.0 pCi/L) or greater, using Beta Gas Proportional Counter (β-GPC) as described here. β-GPC is an analytical method for testing for strontium in drinking water, as shown in Table 7-2 of this PDF, a chapter of Toxicological Profile for Strontium on the website of the Agency for Toxic Substances and Disease Registry (ATSDR). 

Vital Choice also conducted Strontium-90 testing in November 2013. This testing, performed by Pace Analytical Services, Inc. and reviewed by SGS, also showed "ASTM D5811-95" as the analytical method used. All three types of fish tested at the time—sockeye salmon, king salmon, and albacore tuna—had no strontium detected above the minimum detection limits of 0.0513 pCi/g, 0.0635 pCi/g and 0.0456 pCi/g, respectively. 

Although these detection limits were two-fold higher than what the analytical method would be capable of (1.0 pCi/L or 0.037 Bq/L), the minimum detection limit of 1.45 pCi/g (53.65 Bq/kg) in 2015 was even two-fold higher than 0.0513 pCi/g (1.90 Bq/kg) in 2013. This large discrepancy suggests some sort of errors, such as in converting units.


The tritium testing was also conducted by Mother's Radiation Lab Fukushima. None of the samples showed either free-water or organically-bound Tritium.


Cesium testing was conducted at Shinjuku Yoyogi Citizens' Radiation LabResults are not decay corrected. Actual reports can be seen here: 200920112012, and 2014.

The 2009 result of 0.084 Bq/kg shows the pre-Fukushima, background level of legacy cesium—Cesium-137 derived from nuclear testing. The 2011 result is about 25% higher at 0.108 Bq/kg, then it goes down to 0.088 Bq/kg in 2012 and 0.080 Bq/kg in 2014, about the same levels as the pre-Fukushima level. The 2011 result of 0.108 Bq/kg is 0.024 Bq/kg more than the 2009 result, and this 0.024 Bq/kg might be from the Fukushima accident. Results are not decay corrected. Actual reports can be seen here: 2009, 2011, 2012, and 2014.

Cesium-134 was not detected in any of the four samples. Due to its half-life of 2 years, Cesium-134 derived from the nuclear testing is not expected in the 2009 sample. Any potential amount in the 2011 sample and later, by the time of testing in September 2015, would fall below the detection limit.


Neither Strontium-90 nor tritium (free-water and organically-bound) was detected above the detection limit in any of the samples. 

Can codes indicate that the 2011 sample was canned on August 9, 2011 (see this). Can codes for the 2011 sample also include a symbol that refers to "Skeena River," meaning this particular salmon originated from the Skeena River system. (Other samples do not have a similar designation of a specific river system, and it is uncertain why the 2011 sample does). Vital Choice says, 
"Nearly all salmon—if conditions are favorable—return to the same river system from which they came, and all salmon could be distinguished according to a specific river system from which they came. It is unclear why this got specifically ‘called out’ as Skeena (and others not). Salmon are harvested in the wider areas of ocean/bay feeding into the river systems by various fishing methods."
However, no information available in regards to whether this salmon was caught in Skeena River or caught in the Pacific ocean near Skeena River. Just how the 2011 salmon might have been exposed to Fukushima-derived cesium depends on whether the salmon was returning to or just came down the river, and there is no way of knowing this. According to a paper that reviewed the oceanic release and transport of Fukushima-derived radionuclides in the first 5 years after the accident, the 2011 salmon was most likely exposed to the atmospheric fallout in the ocean or river.

Interestingly, salmon fillets caught in an Alaskan river in 2011, 2012 and 2013 were tested by the Department of Nuclear Engineering at University of California at Berkeley. It was found that the 2011 salmon had traces of Fukushima-derived Cesium-134 and Cesium-137 (see their report here). Considering the fact and timing the salmon was caught in a river, it was suggested that:
[...] salmon's exposure may not have been from its life in the Pacific Ocean, but rather from the airborne fallout collecting/concentrating (still at small levels) in river water.
For the cesium testing conducted in the Japanese citizen lab, the samples were tested in a "wet" condition, and the results reported are in "wet" weight. The UC Berkeley lab report states, "The mass used in the analysis was the wet or frozen weight of the fish — not the dry ’baked’ weight, which was considerably less." Apparently the sample weight reported in their results is the wet weight, but the sample was baked. If the reported cesium levels are indeed per wet weight, the background Cesium-137 level of 0.14 Bq/kg detected from both 2012 and 2013 samples is higher than 0.080-0.088 Bq/kg detected in the canned salmon. (An inquiry was made through the online contact form if the reported results have been converted from the dry weight to the wet weight, but there has been no reply).

FDA's radiation testing in Alaskan seafood yields results in wet weight (see this PDF for the 2016 report), but the detection limit over 1 Bq/kg does not allow comparisons with the canned salmon results.

Although a different species, the 2012 Pacific bluefin tuna study shows post-Fukushima cesium levels, except they are in dry weight and not directly comparable to the canned salmon resultsHowever, other data available corroborate the background level of Cesium-137 seen in the canned salmon: 
1)   The Japanese government data of radiation testing on salmon since 2000, collected from the environmental radiation database and compiled here 
2)    In a joint research project between the University of Tokyo and a citizen lab (Akita Radiation Measuring Station "Beguredenega"), the University of Tokyo conducts a high sensitivity analysis on the sample dried and concentrated by the citizen lab as described in this study. I2014salmon caught in Hokkaido, Japan, showed the presence of Cesium-134, while salmon caught in Hokkaido, Japan, in 2015 didn't. The results shown on the citizen lab website (20142015) are converted to the wet weight. The 2015 salmon contained 0.0727 Bq/kg wet weight of Cesium-137.

This project revealed mostly background levels of Cesium-137 in canned salmon, which were only detected due to much lower detection limits than widely employed. No Strontium-90 or tritium was detected above the detection limit. The 2011 sample showed a small increase in Cesium-137 that might be due to the Fukushima nuclear accident.

Putting it in context

This post is not intended to give dietary advices, but it might be helpful to learn a few facts in putting the measured radiation levels in perspective and making informed, personal decisions on what to eat or not.  

1. It should be noted that the very small levels of Cesium-137 detected in canned salmon were only detected because: 
a) The testing was actually conducted.b) The testing was sensitive enough to detect a very small level of Cesium-137.
2. Many foods contain background radionuclides—natural and manmade. 

FDA's Total Diet Study which includes analysis of radionuclides shows Cesium-137 and Strontium-90 present in foodstuffs. When the most recent report from 2006-2014 (here) show all but 3 food items (TDS Food No. 74, 320 and 376) with the value "0," one might erroneously conclude there isn't any Cesium-137 in most of the food. The trick is that a specific food item is reported as "0" as long as all the multiple samples (10-12 for most foods) for the item show Cesium-137 levels below the reporting limit of 5 Bq/kg. When one or more of the multiple samples for a specific food item shows Cesium-137 over 5 Bq/kg, mean, standard deviation, and maximum levels are provided. (By the way, maximum levels shown for the three food items are: 10.8 Bq/kg for item #74, raisin bran; 93.3 Bq/kg for item #320, baby food squash; and 40.5 Bq/kg for item #376, salad dressing).

For accuracy, all the "0" values should really be denoted as "<5 Bq/kg." An even better and more accurate option is to indicate the minimum detectible level (probably 1.0 Bq/kg for Cesium-137) and denote "ND (not detected)" rather than using "0" values. 

For Strontium-90, the reporting limit is 0.1 Bq/kg. Quite a few food items contain very small amounts of Strontium-90 (see pages 22-29 of this PDF). 

3. Radiation testing of fish only shows what is contained in the particular fish tested. Other fish in the vicinity might show a similar trend, but it all depends on where the fish has been and what it has eaten. 

4. Another important fact to learn is how radiation levels are described and compared. 

Radiation levels detected in air, water and food are often misleadingly compared to "the number of CT scans or X-rays" or "hours flown on airplanes." CT scans, X-rays and airplane flights represent external exposure that lasts for a limited length of time. On the other hand, intake of radioactive material through inhaling, drinking, and eating constitutes internal exposure that lasts as long as the radionuclides remain in the body. Moreover, radionuclides incorporated into the body accumulates in and affect specific organs, and thus it is inappropriate to compare external exposure and internal exposure just by the exposure dose.

Also the radiation levels are frequently compared to the limits permitted in food established by FDA called "Derived Interventional Levels (DILs)"—guidance levels for radionuclide activity concentration in imported and domestic food—as described hereDIL is 1200 Bq/kg for the total cesium (Cesium-134 and Cesium-137) and 160 Bq/kg for Strontium-90. (See this for details on how DILs were derived). A domestic coalition is calling for lowering of DIL from 1200 Bq/kg to 5 Bq/kg for total cesium, while two international organizations jointly recommend lowering the EU limit of 370 Bq/kg for baby food and 600 Bq/kg for all other foods to 8 and 16 Bq/kg, respectively (more on this later).

DILs are based on Protective Action Guides (PAGs). As described on the FDA website, "PAGs are radiation dose levels to an individual at which protective action should be considered to limit the radiation dose to that individual." In 1998, an annual committed effective dose of 5 mSv was adopted as the PAG, which essentially accepts increased cancer deaths of 2 in 10,000 from radiation exposure. (The FDA document on this subject is quite complicated: the April 14, 2011 article in Forbes explains it in an easier term). 

In 1998, the current DIL of 1200 Bq/kg for Cesium-134/137 replaced the Levels of Concern (LOCs) established in 1986, which was 370 Bq/kg. The increase is due to the fact that LOCs assumed 100% of of food was contaminated, whereas DILs assumed 30%, but essentially the levels mean the same: It's just that you can eat more of less contaminated food before reaching the PAG of 5 mSv.

For record, DIL of 1200 Bq/kg for cesium is twice the EU limit of 600 Bq/kg for import foods. It is ten times the Japanese limit of 100 Bq/kg with the maximum permissible dose of 1 mSv per year. It's more than twice the previous, emergency limit of 500 Bq/kg with the maximum permissible dose of 5 mSv per year imposed by the Japanese government immediately after the Fukushima accident. (See this document for details on Japan's old and new permissible levels of radioactivity in food. Japan's most current limit, 100 Bq/kg, assumes 50% of marketed foods are contaminated). 

As mentioned earlier, two different groups—Beyond Nuclear and coalition in the United States and foodwatch and German IPPNW internationally—have come up with recommendations to lower the permissible level of radioactive cesium in food as follows: 
a) From 1200 Bq/kg to 5 Bq/kg for DIL (Beyond Nuclear and coalition)
b) From 370 Bq/kg to 8 Bq/kg for baby food and milk, and from 600 Bq/kg to 16 Bq/kg for all other foodstuffs for the EU limit for the import (foodwatch/German IPPNW)
Beyond Nuclear and coalition of other groups have based their recommendation--5 Bq/kg both cesium-134 and cesium-137 combined--on the work of Yuri Bandazhevsky, a Belarusian pathologist who have done research on health effects of Cesium-137. 

Recommendation by foodwatch and German IPPNW--based on a study by German Society for Radiation Protection--is derived from the maximum annual exposure limit of 0.3 mSv for an individual from “discharge of radioactive substances through air or water” in
normally operating nuclear facilities. An excerpt from their report has some important points:
"Setting official maximum levels of radionuclides to be tolerated in food is supposed to protect the population from danger. But, in contrast to chemical toxins, there is no threshold below which radioactivity is harmless. Thus there is also no dose of radiation, no matter how small, that is harmless, benign or unobjectionable. The authority (government or international organization) that recommends or sets standards, or maximum permissible value limits, basically decides on how many fatalities or cases of illness will be acceptable in a given situation.(...)  
A significant reduction in current limits is needed to reduce the risk of health problems. To derive limits that can be used as a standard to achieve this reduction, our calculations are based on a person being exposed to a maximum annual effective radiation dose of 0.3 millisieverts (mSv). This is the maximum exposure limit set out in Germany’s radiation protection legislation for normal operations in nuclear power plants; the figure applies to the exposure pathways of air and water. 
This means that current EU value limits must be reduced to 8 becquerels per kilogram of total cesium for baby food and 16 becquerels per kilogram of total cesium for all other foods."

Appreciation is extended to Vital Choice and BR for providing the canned salmon samples, Shinjuku Yoyogi Citizens' Radiation Lab and Mothers' Radiation Lab Fukushima for offering their analytical services, and NK and AT for transporting the canned salmon after arrival in Japan.

Fukushima Thyroid Examination February 2020: 186 Surgically Confirmed as Thyroid Cancer Among 237 Cytology Suspected Cases

Highlights   The third round: 1 case newly diagnosed as suspicious or malignant, and 5 new cases surgically confirmed.  The fourth ...