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Thursday, March 9, 2017

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.

Friday, February 24, 2017

Fukushima Thyroid Examination February 2017: 184 Thyroid Cancer Suspected/Confirmed (1 Additional Case)

  • One more case of suspected thyroid cancer was diagnosed by cytology since the last report.
  • No additional surgeries since the last report: the number of confirmed cancer cases remains at 145 (101 in the first round and 44 in the second round)
  • Total number of confirmed/suspected thyroid cancer diagnosed (excluding a single case of benign tumor) is 184 (115 in the first round and 69 in the second round)
  • The second round screening data is still not final (confirmatory examination still ongoing).
  • Thyroid Examination Evaluation Subcommittee will be convened in May or June 2017 to evaluate the results of the second round screening.
On February 20, 2017, less than two months since the last report, the 26th Oversight Committee for Fukushima Health Management Survey convened in Fukushima City, Fukushima Prefecture. Among other information, the Oversight Committee released the latest results (as of December 31, 2016) of the second and third rounds of the Thyroid Ultrasound Examination (TUE). Official English translation of the results is posted here. The narrative below presents basic facts of TUE and its current results in perspective, including information covered during the committee meeting and the subsequent press conference.

As of December 31, 2016, there is only 1 more case with cancer or suspicion of cancer from the second round, making a grand total of 184 (185 including the single case of post-surgically confirmed benign nodule) for the first and second round screening results combined. The number of surgically confirmed cancer cases, excluding the aforementioned case of benign nodule, did not change from the previous report (101 from the first round and 44 from the second round), and the remaining 38 (14 from the first round and 24 from the second round) continue to be under observation. 

The second round screening (the first Full-Scale screening) was originally scheduled to be conducted from April 2014 through March 2016, and the primary examination (with the participation rate of 70.9% and the progress rate of 100.0%), is essentially complete. But the confirmatory examination (with the participation rate of 79.5% and the progress rate of 95.0%) is still ongoing. 

The third round screening (the second Full-Scale Screening) began on May 1, 2016 and is scheduled to run through March 2018--the end of Fiscal Year 2018. As of December 31, 2016, 87,217 out of the survey population of 336,623 residents have participated in the ongoing primary examination at the participation rate of 25.9%. The confirmatory examination began on October 1, 2016, with the participation rate of 29.6% so far. 

Full-Scale Screening (first and second)
To be conducted every 2 years until age 20 and every 5 years after age 20, the Full-Scale screening began with the second round screening (the first Full-Scale Screening) in April 2014, including those who were born in the first year after the accident. There are 381,282 eligible individuals born between April 2, 1992 and April 1, 2012. As of December 31, 2016, 270,489 actually participated in the primary examination. 

The participation rate remained the same as 3 months earlier at 70.9% but lower than 81.7% from the first round screening. Results of the primary examination have been finalized in 270,468 participants, and 2,226 (increased by 4 since the last Oversight Committee meeting) turned out to require the confirmatory examination. 

The confirmatory examination is still ongoing for the second round. Of 2,226 requiring the confirmatory examination, 1,770 have participated at the participation rate of 79.5% (increased from the previous 75.8% but still lower than 92.8% from the first round screening). So far 1,681 have received final results including 95 that underwent fine needle aspiration cytology (FNAC) which revealed 69 cases suspicious for cancer. 

Confirmation of thyroid cancer requires pathological examination of the resected thyroid tissue obtained during surgery. There has been no additional surgical case since the last reporting. As of December 31, 2016, 44 underwent surgery and 43 were confirmed to have papillary thyroid cancer. One remaining case was confirmed to have "other thyroid cancer" according to the classification in the seventh revision of Japan's unique thyroid cancer diagnostic guidelines. A specific diagnosis was not revealed, but it has been reported as a differentiated thyroid cancer that is not known to be related to radiation exposure and it is allegedly neither poorly differentiated thyroid cancer nor medullary cancer. 

The third round screening or the second Full-Scale Screening has covered 87,217 or 25.9% of the survey population of 336,623. The primary examination results have been finalized in 71,083 or 81.5% of the participants, revealing 483 to require the confirmatory examination. Results of the confirmatory examination have been finalized in 64 of 143 (29.6%) that have been examined. FNAC was conducted in one person with a negative result: No cancer case has been diagnosed from the third round as of now. 

Confusing issues
Conducted every 2 years up to age 20, the TUE transitions at age 25 to milestone screenings to be conducted every 5 years. Some residents are beginning to participate in the age 25 milestone screening, and if they have never participated in the TUE, their milestone screening results will be added to the second round screening results. Thus the number of the second round screening participants is expected to increase even though the screening period technically ended in March 2016. 

However, the third round screening survey population excludes the age 25 milestone screening participants: their results will be tallied up separately.

Also in some cases, confirmatory examinations from the second and third rounds might be simultaneously ongoing, or there could be significant delays in conducting confirmatory examinations due to logistical issues such as the lack of manpower. A two-year screening period originally designed for subsequent rounds of the Full-Scale Screening is essentially spread over a longer time period, overlapping with the next round of screening. A precise interpretation of results from each round of screening might be nearly impossible.

A newly diagnosed case in the second round
In the second round, only 1 case was newly diagnosed by FNAC with suspicion of cancer. It is a female from Koriyama-City who was 17 years old at the time of the March 2011 disaster. Her first round screening result was A1.

Prior diagnostic status of the cases newly diagnosed with cancer in the second round
Of 69 total cases suspected or confirmed with cancer in the second round, 32 were A1, 31 were A2, and 5 were B in the first round. One remaining case never underwent the first round screening (no information such as age, sex or place or residence, is available regarding this case).

Thirty-two cases that were A1 in the first round, by definition, had no ultrasound findings of cysts or nodules, whereas 7 of 31 cases that were previously diagnosed as A2 had nodules with the remaining 24 being cysts. All 5 cases that were previously diagnosed as B were nodules, and at least 2 of them had undergone the confirmatory examination in the first round. 

This means 56 (32 "A1" and 24 "A2 cysts")of 69 cases had no nodules detected by ultrasound in the first round which could have developed into cancer. This is 81% of the second round cases suspected or confirmed with cancer. It has been speculated by some that these 56 cases were new onset since the first round, suggesting the cancer began to form in 2 to 3 years after the first round screening, conflicting with the common notion that thyroid cancer in general is slow growing. 

Akira Ohtsuru, the head of the TUE, explained that even though some of the small nodules are very easy to detect by ultrasound, exceptions arise when 1) the border of the lesion is ambiguous, 2) the density of the lesion is so low that it blends into the normal tissue, or 3) the lesion resembles the normal tissue. Thus, it is not because the nodules newly formed since the first round screening, but because the nodules were simply not detected even though they were there, that cases which previously had no nodules are now being diagnosed with cancer. Ohtsuru said that when such previously undetected nodules become relatively large enough to become detectable by ultrasound, they might look as if they suddenly appeared. Ohtsuru added that nodules that have already been detected by ultrasound do not to appear to grow very rapidly in general.

This is a better, more legitimate explanation than the previous ones he offered that stated the nodules were present in the first round albeit invisible. However, 56 out of 69 cases seem like a lot to be explained by this.

An issue of the female to male ratio
The female to male ratio of cancer cases warrants a special attention. For thyroid cancer, the female to male ratio is nearly 1:1 in the very young, but it is known to increase with age and decrease with radiation exposure. (See below Slide 2 in this post for more information). In the second round, the female to male ratio has been ranging from 1.19:1 to 1.44:1 overall, but the FY2015 municipalities have consistently shown a higher number of males than females with the most recent female to male ratio of 0.7:1.

What Ohtsuru said about the the female to male ratio boils down to the following: 
The female to male ratio for thyroid cancer is influenced by the reason for diagnosis and the age. When the confirmatory examination of the second round screening is completed, the data will be analyzed by adjusting for age and participation rates by sex. The female to male ratio in Japan's cancer registry data, including all ages, is around 3:1, but it used to be bigger at 4:1 or 6:1 in the 1980's and earlier. In Fukushima, the TUE was conducted in asymptomatic youth around puberty--a different condition than the cancer registry. Yet even in the cancer registry, the female to male ratio tends to be close to 1:1 up to the puberty. Autopsy data of occult thyroid cancer in individuals who died of causes other than thyroid cancer show the female to male ratio of 1:1 or smaller (more males) in adults. This fact indicates that thyroid cancer screening would yield the female to male ratio close to 1:1 even in adults. Thus, it is scientifically expected that thyroid cancer screening in general leads to a smaller female to male ratio.
He is claiming that thyroid cancer diagnosed by cancer screening before becoming symptomatic--as opposed to symptomatic thyroid cancer diagnosed clinically--is expected to show the female to male ratio near 1:1 or smaller, i.e., as many males are diagnosed as females, or more males are diagnosed than females. 

To say the least, calling extrapolation from autopsy data to screening "scientific" seems a bit of a stretch. Furthermore, Ohtsuru's claim does not add up scientifically. South Korea, where active screening increased the incidence of thyroid cancer, did not observe a smaller female to male ratio as shown in the table of thyroid cancer incidence by sex and age group compiled from Ahn et al. (2016). It is obvious the female incidence is much higher than the male incidence without actually calculating the ratio.

Thyroid cancer incidence by sex and age group per 100,000 
in the 16 administrative regions in Korea
 Compiled from Supplementary Tables 2 & 3 in Ahn et al. (2016) Thyroid Cancer Screening in South Korea Increases Detection of Papillary Cancers with No Impact on Other Subtypes or Thyroid Cancer Mortality (link)

Furthermore, Ohtsuru's claim that the female to male ratio tends to be close to 1:1 up to the puberty in the cancer registry is not corroborated by the actual data. The table below was compiled from the National estimates of cancer incidence based on cancer registries. The number of thyroid cancer cases for each sex was listed side-by-side for each year and age group. Then a total from 2000 to 2012 was tallied for each sex and age group to obtain the female to male ratio, because the number of cases varies from year to year. Even without knowing exactly which age range Ohtsuru meant by "up to the puberty," it is clear that the female to male ratio is not at all close to 1:1.

The number of thyroid cancer cases by sex and age group from 2000 to 2012
Compiled from the National estimates of cancer incidence based on cancer registries in Japan (link)

According to this study, the female to male ratio peaks at puberty and declines with age, as excerpted below:
The increased F:M ratio in thyroid cancer incidence does not remain static with age. Female predominance peaks at puberty. [...] This pattern occurs as the thyroid cancer incidence begins to increase at an earlier age in females than in males, leading to a rise in the F:M ratio. The ratio starts to decline as the male incidence rate begins to increase and, concurrently, the rate of increase in female incidence rate slows down. The steady decrease in F:M ratio with age continues, and the peak male rate does not occur until between 65 and 69 years of age, compared with the earlier peak female rate between 45 and 49 years of age, just before the mean age of menopause at 50 years.

An issue of the participation rate
The primary examination participation rate of 70.9% in the second round screening is lower than 81.7% in the first round. Most notable is the participation rate of the oldest age group: 52.7% for ages 16-18 (age at exposure) in the first round plummeted to 25.7% for ages 18-22 (age at examination) in the second round. It is 6.6% for ages 18-24 (age at examination) for the ongoing third round so far.

Younger age groups in school have maintained pretty high participation rates thanks to the school-based screening. The older age group often leave the prefecture for college or jobs, and it becomes increasingly difficult to get them to participate, especially with their interests fading in their busy lives.

The status of the new third-party committee
The "international, third-party, neutral, scientific, up-to-date and evidence-based" expert committee proposed by Chairman Hokuto Hoshi at the last committee meeting is being discussed at the prefectural level in consultation with the central government. The prefectural official admitted that the plan was to establish an independent entity that will offer, from a neutral standpoint, latest knowledge of thyroid cancer needed by the Oversight Committee.

A committee member Tamami Umeda from the Ministry of Health, Labour and Welfare elaborated on her vision of the third-party committee as an entity to review and organize the latest clinical and epidemiological knowledge and studies. It would be separate from the Thyroid Examination Evaluation Subcommittee that is intended to evaluate and analyze the status of the TUE, including the evaluation of radiation effects. (Note: In reality, the Thyroid Examination Evaluation Subcommittee has been far from being effective in analyzing the TUE data due to lack of information released by Fukushima Medical University on the premise of protecting personal clinical data).

Explaining that international organizations frequently separate a scientific review process from discussions relating to policy making in order to maintain neutrality, Umeda said she thought a similar process might be useful for the Fukushima Health Management Survey. This comment drew questions from committee members as well as the press about the status of the Oversight Committee itself: Is it a policy-making body? Is it not scientific enough?

It would make more sense to invite experts to join the Thyroid Examination Evaluation Subcommittee to incorporate knowledge gained from the latest research on thyroid cancer. Why it has to be an "international" committee is unclear other than to say that it was recommended by the Organizing Committee of 5th International Expert Symposium in Fukushima on Radiation and Health, including Shunichi Yamashita. A former chair to the Oversight Committee, Yamashita resigned from the position in March 2013 amid controversies surrounding "secret meetings." Although no longer involved with the Oversight Committee, he has maintained ties with the Survey as Founding Senior Director of the Radiation Medical Science Center for the Fukushima Health Management Survey, the Office of International Cooperation for the Survey.


Below is the summary of the basic information from each round of screening.

First Round Screening (October 2011 - April 2015)
(This is the final results as of March 31, 2016. It is unchanged from the September 2016 report).

Total number targeted: 367,672
Number of participants in primary examination: 300,476
Number with confirmed results: 300,476
  • A1   154,607 (51.5%) (no nodules or cysts found)
  • A2   143,575 (47.8%) (nodules ≦ 5.0 mm or cysts ≦ 20.0 mm)
  • B        2,293   (0.8%) (nodules ≧ 5.1 mm or cysts ≧ 20.1 mm)
  • C               1   (0.0%) (requiring immediate secondary examination)
(Note: Cysts with solid components are treated as nodules).

Number eligible for confirmatory (secondary) examination: 2,294
Number of participants in confirmatory (secondary) examination: 2,128
Number with confirmed results : 2,086
Number of fine-needle aspiration cytology (FNAC): 545
Number suspicious or confirmed of malignancy: 116 (including one case of benign nodules)

Number with confirmed tissue diagnosis after surgery: 102
  • 1 benign nodule
  • 100 papillary thyroid cancer
  • 1 poorly differentiated cancer
Second Round Screening (April 2014 - March 2016) (see report here)

Total number targeted: 381,282
Number of participants in primary examination: 270,489
Number with confirmed results: 270,468
  • A1   108,688 (40.2%) (no nodules or cysts found)
  • A2   159,554 (59.0%) (nodules ≦ 5.0 mm or cysts ≦ 20.0 mm)
  • B        2,226   (0.8%) (nodules ≧ 5.1 mm or cysts ≧ 20.1 mm)
  • C              0   (0.0%) (requiring immediate secondary examination)
(Note: Cysts with solid components are treated as nodules).

Number of residents requiring confirmatory (secondary) examination: 2,226
Number of participants in confirmatory examination: 1,770
Number with confirmed results: 1,681
Number of FNAB: 195
Number of cases with malignancy or suspicion of malignancy: 69
Number with confirmed tissue diagnosis after surgery: 44
  • 43 papillary thyroid cancer
  • 1 "other thyroid cancer"
Third Round Screening (May 2016 - March 2018) (see report here)

Total number targeted: 336,623
Number of participants in primary examination: 87,217
Number with confirmed results: 71,983
  • A1   25,182 (35.4%) (no nodules or cysts found)
  • A2   45,418 (63.9%) (nodules ≦ 5.0 mm or cysts ≦ 20.0 mm)
  • B          483  (0.7%) (nodules ≧ 5.1 mm or cysts ≧ 20.1 mm)
  • C             0   (0.0%) (requiring immediate secondary examination)
(Note: Cysts with solid components are treated as nodules).

Number of residents requiring confirmatory (secondary) examination: 483
Number of participants in confirmatory examination: 143
Number with confirmed results: 64
Number of FNAB: 1
Number of cases with malignancy or suspicion of malignancy: 0
Number with confirmed tissue diagnosis after surgery: 0

Second Round Screening

Table 6. Cytology results (including information from Appendix 6: Number of surgeries among cases with malignancy or suspicion of malignancy) as of December 31, 2016

Table 6. Cytology results for FY 2014-2015 
(including information from Appendix 6: Surgical cases of suspicious or malignant cases) 
(Data as of December 31, 2016)

Age distribution of 69 cases confirmed or suspected of thyroid cancer in the second round screening (as of December 31, 2016)
Age at the time of the March 11, 2011 nuclear accident