The United Nations Scientific Committee on the Effects of Atomic Radiation reported in 2020 on the sources, effects, and risks of ionizing radiation. Specifically on the levels and effects of radiation exposure due to the accident at the Fukushima Daiichi Nuclear Power Station and on the implications of information published since the UNSCEAR 2013 Report.
[Although there are 20 conclusions in the new report, of particular note are the following items:]
(c) Releases of radionuclides into the Pacific Ocean occurred directly and indirectly and still continue, albeit at decreasing rates. They comprise:
(i) direct releases in the first three months (in leakage and deliberate release of water containing radionuclides), amounting to about 10 to 20 PBq of 131I and about 3 to 6 PBq of 137Cs;
(ii) deposition of radionuclides on to the ocean surface following their release to, and dispersion in, the atmosphere, amounting to about 60 to 100 PBq of 131I and 5 to 8 PBq of 137Cs;
(iii) direct release of about 60 TBq of 137Cs in groundwater draining from the site up to October 2015, when measures were taken to reduce these releases, and about 0.5 TBq per year thereafter; and
(iv) continuing indirect releases of about 5 to 10 TBq of 137Cs per year via rivers draining catchment areas on to which radioactive material released to the atmosphere was deposited;
[and:]
(d) The material released to the Pacific Ocean was rapidly dispersed and diluted in seawater: by 2012, the concentrations of 137Cs, even in the coastal waters off the FDNPS site, were little above the levels prevailing before the accident. Concentrations of 137Cs in marine foods have declined rapidly: 41% of samples caught off the coast of Fukushima Prefecture in 2011 exceeded the long-term limit established by the Japanese Government, decreasing to 17% in 2012, and, from the beginning of 2015, to just four samples out of 9,000;
[and:]
(q) No adverse health effects among Fukushima residents have been documented that are directly attributable to radiation exposure from the FDNPS accident. The Committee’s revised estimates of dose are such that future radiation-associated health effects are unlikely to be discernible. The Committee believes that, on the balance of available evidence, the large increase, relative to that expected, in the number of thyroid cancers detected among exposed children is not the result of radiation exposure. Rather, they are the result of ultrasensitive screening procedures that have revealed the prevalence of thyroid abnormalities in the population not previously recognized. An increase in the incidence of cancers is unlikely to be discernible in workers for leukemia, total solid cancers or thyroid cancer. The Committee has insufficient information to reach an informed judgement on the risk of cataracts;
[and:]
(r) Care is needed over the widespread use and interpretation of sensitive ultrasound thyroid screening following radiation exposure as a result of events such as the FDNPS accident. There is compelling evidence that sensitive ultrasound screening detects many more cases of abnormalities and cancer in the thyroid than would be detected following the presentation of clinical symptoms. The consequential over-diagnosis of 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. If such screening is to be carried out, perhaps including even further advances in thyroid assessment equipment and techniques, as well as determining evidence of a dose-response, an unexposed control group needs to be studied at the same time and using an equivalent protocol and technical equipment. These safeguards will reduce the risk that cancers diagnosed following any future accident are attributed wrongly to exposure to radiation;
[and:]
(s) The Committee continues to consider that regional impacts on wildlife populations with a clear causal link to radiation exposure resulting from the FDNPS accident would have been unlikely, although detrimental effects on individual organisms might have been possible, and some effects have been observed in plants and animals in the absence of any wide-scale group impacts. A few studies have indicated substantial population impacts on selected wildlife groups, but these findings remain subject to some doubt. It is possible, however, that current assessment methodologies are not adequate and further analysis of impacts under field conditions could be valuable. Further research could also be useful on the impacts of radiation exposure on non-human biota under field conditions that are able to take account of higher levels of biological organization, within natural environments, and elements of ecosystem function and structure.
[Note: Read full report for context involved in the the conclusions of the comprehensive report]
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