On March 9, the United Nations Scientific Committee on Atomic Radiation (UNSCEAR) published an advance copy of its latest (third) report on the health effects from the Fukushima Daichi nuclear accident which commenced on March 11, 2011. UNSCEAR 2020 Report – Annex B – Advance Copy
The report shows signs of having been rushed out as it is an advance copy and is unfinished. It states 23 electronic attachments with supplementary information on detailed analyses of doses to the public and their outcomes are currently in production and will be available soon on the UNSCEAR website.
I shall look at the Report in more detail when the additional information is published. However at the 10th anniversary of the nuclear catastrophe at Fukushima in 2011, it’s necessary to have an initial look at the Report’s comments on contentious issues arising from the accident – (a) the number of expected fatal cancers and (b) the continuing controversy over the cause(s) of the large observed increases in thyroid cancers (TCs) in Japan since 2011.
On (a), the 2020 Report concludes that there are no observed ill health effects from the accident but this conclusion is inconsistent with UNSCEAR’s own estimates of high collective doses from the accident. Table 13 (page 72) of UNSCEAR’s 2020 report shows that, in the first 10 years after the accident, the whole body collective dose from the accident was 32,000 man Gy. When we apply the widely-accepted fatal cancer risk estimate of 10% per Gy to this figure, we see that about 3,000 fatal cancers will have occurred due to the accident, correct to one significant figure. The report’s strange, unscientific conclusion to the contrary is inconsistent with these estimates. The only assumption used here is that radiation’s dose-response relationship follows the linear-no-threshold model, as recognised and used by all the world’s radiation protection authorities.
On (b), the 2020 Report (page 107, para q) concludes that the sharp increase in observed thyroid cancers post-Fukushima was not due to thyroid intakes of iodine isotopes from the accident but due to increased surveillance.
However large collective doses to the thyroid are also published in UNSCEAR’s new 2020 report. In the first 10 years after the accident, the 2020 report states the collective thyroid dose to the Japanese population from the accident was 44,000 man Gy. Again, this is a high number, but the absence of an authoritative risk factor for thyroid cancer – especially among young children aged 0 to 4 who were exposed to both internal intakes of radioactive iodine plus external exposures to ground-deposited Cs-134 and C-137 means that reliable estimates of the actual numbers of thyroid cancer cases due to the accident are unfortunately not possible. The supplementary information yet to be released may enable such calculations to be made. However the large collective dose to the thyroid from Fukushima casts doubt on UNSCEAR’s conclusion that the observed increases are not due to the accident.
I would not be surprised to learn that the negative conclusions in the UNSCEAR 2020 Report might be a reason why an advance copy was rushed out in unfinished form before the anniversary of the Fukushima accident.
I add the caveat that the above analysis is a (second) draft and has not yet been fully peer-reviewed. However many requests have been made for views on the UNSCEAR’s 2020 report, so I’m publishing this quickly. Any errors which are pointed out will be corrected in a later post.