“UN Scientific Committee on the Effects of Atomic Radiation” (UNSCEAR) published a report on the impact of the 11 March 2011 accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) of the Tokyo Electric Power Company (TEPCO) in Japan (2020/2021 Report) on March 9, 2021.
UNSCEAR’s mandate is to comprehensively assess important matters regarding the effects of radiation on humans and the environment and report to the United Nations. Its focus is on preparing reports based on science, not on making recommendations to other international organizations or countries. (It is the role of other international organizations such as IAEA, WHO, and ICRP, to prepare recommendations and formulate guidelines in their respective fields, in response to UNSCEAR’s report. Based on those recommendations, each country prepares policies. See the figure below.)
UNSCEAR released a report on the FDNPS accident in 2013(referred to as the “2013 Report” hereafter). In the following years, it also released three white papers reflecting newly published papers and survey results in 2015, 2016, and 2017.
Following are the two takeaways from the 2020/2021 report.
1. No discernible health effects of radiation exposure have been observed on the residents of Fukushima after the nuclear accident. It is not expected in the future either.
The 2020/2021 report is based on more measured data, more realistic scenarios, and more accurate estimates than the 2013 report. And it concludes that the radiation exposure of Fukushima residents after the FDNPS accident will not affect the health of the inhabitants.
On the other hand, it reports an increase in cases such as diabetes and obesity among evacuees. They are associated with lifestyle changes and psychosocial stress, not with radiation exposure.
2. Many cases of cancer were found in the thyroid among young people (thyroid cancer screening test was administered for children and young people under the age of 18 at the time of the nuclear accident). However, they can be considered to be the result of the application of highly sensitive ultrasound screening procedures that have revealed the prevalence of thyroid abnormalities in the population not previously recognized, and is not a result of radiation exposure.
The consequential overdiagnosis (detection of thyroid cancer that would not have been detected without the screening and would not have caused symptoms or death during a person’s lifespan) of these thyroid cancers, many of which may never result in clinical symptoms, has the potential to cause considerable anxiety among some of those screened and to lead to unnecessary treatment, the detrimental effects of which may outweigh those of the radiation exposure itself, especially if the thyroid doses are relatively low.
The examination has been conducted in Fukushima prefecture since October 2011, after the nuclear accident occurred, as part of the Fukushima Health
Management Survey (FHMS). So far, 274 people have been diagnosed with thyroid cancer and 227 have had part or all of the thyroid gland removed by operation (as of May 2022).
The 2020/2021 report states that thyroid cancer found was “not due to radiation,” but “due to screening with a highly sensitive ultrasound device.”
In addition, as stated above, the report points out that overdiagnosis of thyroid cancer has the potential of causing unnecessary anxiety and treatment for children and adolescents who would otherwise be living as healthy individuals.
UNSCEAR’s mandate is to conduct “independent and objective evaluations based on science,” and “does not develop policy or provide advice to governments or regional or international bodies.”
To ensure the report’s impartiality, Japanese researchers didn’t join the main authors (Expert Group) but served ancillary roles as Working Group. Having Expert Group composed of researchers from countries other than Japan, UNSCEAR keeps neutrality of the report on Fukushima. All the participating researchers are checked with no conflict of interest.
We interviewed Mr. Makoto Akashi of Tokyo Health Care University. He was involved in the preparation of the report as UNSCEAR’s former representative from Japan and is currently senior technical advisor.
“All the scientific information available”
— The 2020/2021 report is a summary of “all the scientific information available relating to the levels and effects of radiation exposure due to the FDNPS accident.” What exactly does “scientific information” mean here?
“Scientific information” refers to peer-reviewed papers (evaluated and verified by different researchers in the same field) and data, such as measurements taken by local governments. The 2020/2021 report goes through all peer-reviewed papers published up to the end of 2019 and analyzes such data.
— Even though papers are all peer-reviewed, their conclusions may vary pretty much depending on conditions such as research method, don’t they?
I suppose you are asking about which paper to refer to. To make this report, about 2000 papers had been reviewed. Of those about 500 were chosen as reference. The procedure was as follows:
First, the main authors in each field decide which paper to refer to based on objective figures. There is no Japanese among them. In addition, a peer-review group is set up to check the author’s reference criteria. They are translated as “critical reviewers” In Japanese and also check the content of the report. No Japanese is a member of this review group either.
Through this multilayered check system, fairness is achieved.
— What is an “objective figure”?
It is the number actually measured by the measuring instruments.
Compared to the 2013 report, the number of actually measured data has significantly increased for the 2020/2021 report. Thanks to the availability of more figures, the accuracy of the estimation model has improved dramatically. This means the outcome of the model has also become more scientifically reliable.
Using both the newly reported measured data and more reliable estimates, we can better understand how much radioactive material was released, in which direction and when. Based on those figures, more papers are read and evaluated. These figures are also used to conduct a verification of analysis by UNSCEAR itself.
— How about “all scientific information”? Does it mean that all peer-reviewed papers are put under consideration, even if their conclusions may disagree with UNSCEAR’s view?
You’re right. That’s what it means to “read everything.”
Estimates become more realistic
— How does the 2020/2021 report differ from previous ones?
The biggest point is “the uncertainty of estimation has been reduced by more measured data.”
Suppose there are five points, B, C, D, and E in a region. Of these, you can’t measure point B and need to estimate the value. If measured data from other 4 points are available, you can better estimate than using only, say, values of A and E.
In other words, the more points with accurate measurements are available, the better estimates you can get.
Let’s compare it to the reading of a dosimeter. The error margin of the reading was very large at the time of the 2013 report. It improved greatly in the 2020/2021 report because the range has shrunk considerably smaller. It means the estimates are closer to the actual values.
— There was criticism that the 2013 report adopted the highest value in the error range (the radiation dose was estimated to be much higher than it actually was). What do you have to say about it?
“Assuming the worst number” is called “taking it on the safer side” or “looking conservatively” in radiation protection. As is the case with medical care, when something happens and numbers range, the worst number is assumed.
For example, if you are to tell a patient whose estimated life expectancy is between 3 to 6 months, you would say “Your life expectancy is 3 months,” not 6 months. In doing so, you can prevent the patient from arranging the rest of his life on the premise that he would live 6 full months but die before that.
At the time of the 2013 report, there weren’t sufficient data and the range of estimation was wide. So the report used the worst values, assuming that the radiation dose was the highest possible.
— Radiation doses to the thyroid gland are also shown as estimates in this report. Is it appropriate to think that the actual values exist somewhere within the range of this estimated value?
Yes. It’s more likely so in the 2020/2021 report than in the 2013 report.
A more realistic model
— What are other differences between the 2020/2021 report and the 2013 report?
I’d like to repeat that the availability of more actual measured data contributed a lot this time. Specifically, the actual external radiation dose of each inhabitant using a personal dosimeter and the measurements of the radiation in the environment.
In addition, more information was gathered on how and where residents moved at the time of the nuclear accident, as well as the lifestyle patterns of Japanese people. Combining the information and the measured data enabled the 2020/2021 report to better estimate the radiation dose, using more realistic models than the 2013 report.
— Please elaborate on the “realistic model”
In the 2013 report, residents’ radiation doses were based on rather unrealistic conditions, such as keeping on living where they had been without evacuation or assuming they stay outdoors all day and night, in an unshielded environment 24 hours a day. Such conditions are not realistic, deployed for the sake of calculation.
On the other hand, in the 2020/2021 report, more reliable, closer-to-the-reality data became available thanks to activity surveys or sample checkups of the children from the evacuation zone. For example, the paper by Gen Suzuki et al., referred to in the report examines 37 evacuation patterns, whereas the 2013 report employed only three scenarios. In total, 40 scenarios were deliberated in the 2020/2021 report.
— What other figures are estimated based on more realistic models?
Internal radiation exposure from food is a good example. The 2013 report estimated that food was the biggest source of radioactive substances for the residents’ exposure. However, it was found that the exposure through ingestion was even lower than inhalation, which had been known to be very low based on the measurements of the atmosphere. This is another result of estimation using a more realistic model.
— What is the “more realistic model” in the case of internal exposure from food?
Data regarding intake from food was scarce when the 2013 report was prepared, hence the uncertainty was big. Therefore, they chose the “worst” end of the range, or the highest figure, to make further estimations.
On the contrary, many measured data for radioactive substances in food have been collected for the 2020/2021 report. This made it possible to reduce uncertainty and attain a more validated estimates of levels of exposure, which turned out to be very low. I consider this one of the most important outcomes of this report.
— Why was the amount of radiation exposure from food was kept such low after the accident?
One big factor would be a restriction on shipping food was implemented fairly early. But I attribute it to the Japanese lifestyle, people buy and eat a diverse range of food from different places including overseas. Most of us go to supermarkets and do not solely depend on vegetables and berries from backyard gardens or nearby mountains.
— On March 15th and 16th, 2011, the plants exploded and a huge amount of radioactive substances was scattered. But restrictions on shipping and ingestion of foods were not yet applied (the provisional regulation was issued on March 17 by the Ministry of Health, Labor, and Welfare). Is there a possibility that people have taken in radioactive iodine through eating contaminated foods during those couple of days?
The half-life of radioactive iodine-131 is 8 days. And if you were to eat food containing much amount of radioactive iodine within several days after the accident, it might be from mountains and fields close to the nuclear power plant. I wonder how many people would have harvested such food during that period of time and ingested so much that it may affect their health.
The possibility may not be zero, but it’s not a realistic assumption that the majority of people were doing so. Particularly for children, it was a time many parents were very cautious and warily selecting their food fearing exposure to radioactive iodine. Considering also the lifestyle of Japanese people to eat diverse kinds of food from different places, it is hard to imagine there were many who chose and consumed a large amount of food harvested in the back mountains immediately after the accident.
— In addition to the evacuation scenario, I understand that more estimates were calculated with data that are more accurate and are closer to the reality in various areas.
For food, there are many actual values as well as estimates. Some measurements are still implemented such as the school lunch inspection or market-basket type inspection by the Ministry of Health, Labor and Welfare. Using both the measured data and the realistic scenario from the behavioral survey, you can understand the radiation dose was very low for the residents in Fukushima after the accident.
UNSCEAR warns overdiagnosis of thyroid exams
— The 2020/2021 report points out that overdiagnosis may have been caused by thyroid examinations administered in Fukushima after the nuclear accident.
It deviates slightly from UNSCEAR’s original aim to report on the effects of radiation, but it cannot be looked over considering the sheer impact it has on society. The warning also plays a role to prevent the spread of misunderstanding that the thyroid cancer found in Fukushima might be the effect of radioactive substances from the nuclear accident.
— In the past 10 years, a considerable amount of papers that focus on mental health problems and social psychological issues caused by overdiagnosis have been published. Still, only a few were referenced in the report.
The most important thing is that exposure to the thyroid gland was very little for residents in Fukushima. Of course, thyroid cancer has been found in the thyroid examination of the FHMS, and more might be found in the future. Still, that is unlikely to be the effect of radiation.
— A group of people diagnosed with thyroid cancer after the nuclear accident has filed a lawsuit. They claim that they developed thyroid cancer due to radiation exposure from the nuclear accident. Here I see a difference in perspective. In the current report, UNSCEAR states that “no exposure effects will be seen (discernible) in the future,” based on more realistic and validated estimates levels of exposure in the population groups than before. On the other hand, the court may focus on the risk associated with the level of exposure in a particular individual. How do you explain the difference?
First of all, please know that no judgment is made solely by scientific facts.
For example, let’s consider a case of leukemia occupational accident certification. If the radiation dose is less than 100 mSv, scientifically it’s hard to consider the dose to be the cause of leukemia. However, occupational accident certification takes more than science into consideration. From the viewpoint of worker compensation, if over a year has passed since the exposure, and the amount of exposure exceeds 5 mSv per year multiplied by the number of years of labor, and if other factors such as infectious diseases are not found, it can be certified as a work-related accident. In some cases, leukemia has actually been certified as an industrial accident.
— Some reports state that the risk of thyroid cancer increases even if the radiation dose to the thyroid gland is less than 100 mSv. Even about 50 mSv.
It is known that the average dose to the thyroid gland for each municipality in Fukushima Prefecture does not exceed 30 milliGy (≒ mSv). Therefore, it is unlikely that an increase in thyroid cancer cases in municipalities in Fukushima will be observed compared to others outside.
One caveat is that this is the average value when viewed as a group. There is no way to know how much radiation each individual person was exposed to right after the nuclear accident.
In the case of the lawsuit, it would be best if the plaintiff’s thyroid radiation dose was actually measured right after the nuclear accident. That was impossible. But even though actual figures are unknowable, now you may be able to estimate each individual’s radiation dose by referencing detailed data on the map one by one.
And say it turned out that the plaintiffs’ radiation dose was, for example, 50 mSv. Can you say the radiation caused the cancer? The story is not that simple. For example, it takes a long time for thyroid cancer to develop enough to be detected. In the case of the Chornobyl nuclear accident, thyroid cancer was found after four years of the accident. There are many factors to consider and it’s difficult to give a clear-cut scientific conclusion. Still in trials, judgment takes in various conditions such as social factors.
–No matter what the outcome of the trial, it will not directly affect the conclusion of the 2020/2021 report, that says “There may be no discernible increase in all cancers in the future.” Am I right?
We believe so.
Final Report on the Fukushima Daiichi Nuclear Power Plant Accident
— What’s the conclusion of the 2020/2021 report?
As for the health effects of radiation caused by the nuclear accident, there were no deterministic effects (tissue reactions such as burns that appear when an excessive dose is delivered over a short period of time). And all cancers, including thyroid cancer, have not increased and will not be expected to show a discernible increase in all age groups, from children to the elderly. And hereditary effects, including effects on the next generation, have not occurred and will not be likely to occur in the future. The core conclusions haven’t changed much from the 2013 report.
— What is the significance of the 2020/2021 report then, if its conclusions are not so much different from those of the 2013 report?
The 2013 report was issued while there were few data such as measured data. The significance of the 2020/2021 report is that it was prepared using more realistic reports analyzing much more collected data.
This time, we were able to get a considerable amount of data including municipality-average doses. Some data were requested by the UNSCEAR Secretary-General who visited the office in person. The local residents also cooperated. You need solid data to make a realistic report. It means you have to get the real, measured data. Some authors asserted that no actual measurements, no estimation.
— Why is it so important to collect a vast amount of measured data?
Because the more data you get, the more clearly you can see what was not possible before with little data.
At the time of the 2013 report, even in the scarcity of data, scientifically we had to consider the possibility of much higher radiation dose of the residents.
This time, much more data were available and we were able to analyze with more ease, still keeping the possibility in mind. After all, it was found that the radiation dose to the Fukushima residents were much lower than that reported in 2013.
— So, the 2020/2021 report can be considered as the “final edition” on the effects of radiation after the Fukushima Daiichi nuclear accident?
Yes, I think it is.
United Nations Scientific Committee on the Effects of Atomic Radiation UNSCEAR 2020/2021 Report
UNSCEAR 2013 Report on the Effects of Atomic Radiation
“About UNSCEAR 2020 Fukushima Report” (44th “Prefectural Health Survey” Review Committee Material / Makoto Akashi’s presentation material)
Takashi Ohba, Tetsuo Ishikawa, Haruyasu Nagai, Shinji Tokonami, Arifumi Hasegawa & Gen Suzuki
Reconstruction of residents’ thyroid equivalent doses from internal radionuclides after the Fukushima Daiichi nuclear power station accident, Scientific Reports volume 10, Article number: 3639 (2020), https://doi.org/10.1038/s41598-020-60453-0
Jay H Lubin 1, M Jacob Adams 2, Roy Shore 3, Erik Holmberg 4, Arthur B Schneider 5, Michael M Hawkins 6, Leslie L Robison 7, Peter D Inskip 1, Marie Lundell 8, Robert Johansson 9, Ruth A Kleinerman 1, Florent de Vathaire 10, Lena Damber 9, Siegal Sadetzki 11, Margaret Tucker 1, Ritsu Sakata 3, Lene HS Veiga
Thyroid Cancer Following Childhood Low-Dose Radiation Expose: A Pooled Analysis of Nine Cohorts, The Journal of Clinical Endocrinology & Metabolism, Volume 102, Issue 7, 1 July 2017, Pages 2575–2583, https://doi.org/10.1210/jc .2016-3529