Year : 2020 | Volume
: 5 | Issue : 1 | Page : 16--22
Some aspects of the Fukushima Daiichi nuclear accident
Sergei V Jargin
Department of Pathology, Peoples' Friendship University of Russia, Moscow, Russia
Sergei V Jargin
Department of Pathology, Peoples' Friendship University of Russia, Miklukho-Maklaya 6, 117198, Moscow
Average whole-body doses after the Fukushima accident remained within the limits of natural radiation background. Thyroid doses were much lower than after the Chernobyl accident. Associations between detection rate of thyroid cancer (TC) and radiation doses after the Fukushima accident were reported, although there have been contradicting data. There are various factors and bias that can contribute to the associations: screening effect, recall bias, dose-dependent quality of diagnostics, selection, and self-selection. There have been methodological differences of the screening in different areas. In the screened young-age group, TCs were found predominantly in adolescents, but not in vulnerable children ≤5 years at exposure, suggesting that tumors are not radiogenic. A possibility of overdiagnosis was pointed out, i.e., detection of thyroid tumors that would not, if left untreated, result in symptoms. Furthermore, exaggeration of perinatal complications may cause anxiety and lead to interruption of wanted pregnancies, as it happened after the Chernobyl accident. In conclusion, no discernible increase of radiation-related health effects is expected after the Fukushima accident. There are no reasons to disagree with the judgment by the UNSCEAR that an increased risk of thyroid tumors among most exposed children could be theoretically inferred, although occurrence of large numbers of radiation-induced cases can be discounted. The monitoring of populations exposed to low-dose radiation is important, but will hardly add much reliable information. It can be expected that the screening and increased attention of exposed people to their health would result in more reports on elevated risks that would prove no causality.
|How to cite this article:|
Jargin SV. Some aspects of the Fukushima Daiichi nuclear accident.Environ Dis 2020;5:16-22
|How to cite this URL:|
Jargin SV. Some aspects of the Fukushima Daiichi nuclear accident. Environ Dis [serial online] 2020 [cited 2023 Mar 29 ];5:16-22
Available from: http://www.environmentmed.org/text.asp?2020/5/1/16/283009
A tendency to overestimate health risks from low-dose, low-rate ionizing radiation has been discussed previously., Apparently, certain scientists exaggerating medical and ecological consequences of the anthropogenic increase in the radiation background contribute to a strangulation of the atomic energy, which would agree with the interests of fossil fuel producers. Nuclear power has returned to the agenda because of the concerns about increasing global energy demand and climate changes. Health burdens are greatest for power stations based on lignite, coal, and oil. The health burdens are smaller for natural gas and still lower for nuclear power. The same ranking applies also to greenhouse gas emissions and thus probably to climate changes.
The estimated average effective whole-body doses to adults, 10-year-old children, and 1-year-old infants over the 1st year after the Fukushima Daiichi nuclear accident (2011) in the Fukushima prefecture were correspondingly 1.0–4.3, 1.2–5.9, and 2.0–7.5 mSv. According to later data, higher doses were received by senior people compared to other adults and especially to children/adolescents (0–19 years old). This is in contrast with the 2013 report where doses to infants and children were assessed to be higher than doses to adults. In Minamisoma city, ~25 km from the Fukushima Nuclear Power Plant (FNPP), 881 schoolchildren participated in a screening program evaluating individual doses received during 2012–2013. The total annual effective doses ranged from 0.025 to 3.5 mSv with a median of 0.7 mSv. In the whole Fukushima prefecture including the evacuation zone, the doses were ≤3 mSv in 99.4% of residents surveyed. For comparison, the worldwide annual exposures to natural radiation sources are generally expected to be in the range of 1–10 mSv. Some national averages exceed 10 mSv. In the United States (US), the average annual individual exposure from the natural radiation background (NRB) is 3.10 and in Japan, it is 1.5 mSv/year; medical exposures add in the USA at 3.0 and in Japan, at 2.3 mSv/year. Additional doses to the residents of the Fukushima prefecture have thus remained within the limits of the NRB. According to the concept discussed previously,, with the dose rates tending to the background level, radiation-related risks would tend to zero, and can even fall below zero in accordance with hormesis. Thyroid doses are discussed below.
Thyroid cancer (TC) is a special topic because thyroid doses after the Chernobyl and Fukushima accidents were higher than whole-body doses. In evacuees, the median thyroid doses were estimated to be 4.2 mSv and 3.5 mSv for children and adults, respectively, and the maximum thyroid doses were, respectively, 23 mSv and 33 mSv, i.e., much lower than that in Chernobyl evacuees. The districts with the highest average estimated doses were within the 20-km evacuation zone and deliberate evacuation area. It was reported that thyroid doses, determined in March 2011 in children of the above-named territories, were ≤10 mSv in 95.7% of the children with a maximum ~43 mSv. For 1-year-old infants, the effective dose to the thyroid was estimated to be up to ~80 mGy. Some infants may have received thyroid doses of 100 mGy or more. Later estimates produced lower values, with the average thyroid doses to 1-year-old infants in different municipalities of the Fukushima prefecture being estimated from <10 to 30 mSv. All the doses have apparently remained below the intervention value for iodine prophylaxis equal to 100 mGy according to the Basic Safety Standards. For comparison, thyroid doses in Chernobyl children ranged up to several thousand mGy.
An association between the detection rate of TC and external radiation dose rate after the Fukushima accident has been reported, although there have been contradicting reports.,, In a recent study, no dose-dependent pattern emerged from the geographical distribution of doses and TC detection rate in participants within 4–6 years after the accident, i.e., the TC risk showed no association with the doses. There are various factors and bias unrelated to ionizing radiation that can contribute to the associations.,, Dose–effect correlations can be caused or overestimated due to the screening effect, improved diagnostics after an accident, recall bias, dose-dependent quality of diagnostics, selection, and self-selection. There have been methodological differences of the screening in different areas. Both the participants and medical personnel were informed about the contamination level in a given area so that their action might have been consciously or subconsciously influenced by doses. Expectedly, the ultrasound-based screening detected a large number of thyroid nodules, including TC “that would not normally have been detected without such intensive screening.” In the screened young-age group, TC was found predominantly in adolescents, but not in the most vulnerable children ≤5 years at the time of the accident, suggesting that the thyroid tumors may not be radiogenic., The International Atomic Energy Agency (IAEA) concluded that the thyroid abnormalities were unlikely to be associated with radiation exposure from the accident and most probably denote the natural occurrence of thyroid abnormalities in children of this age.
In contaminated areas after the Chernobyl accident, where thyroid doses were much higher than after Fukushima, the numbers of supposedly radiogenic TC have been overestimated.,, Prior to the Chernobyl accident, the registered incidence of pediatric TC was lower in the former Soviet Union (SU) than that in other developed countries. The screening detected not only small nodules but also late-stage TC misinterpreted as rapidly growing radiogenic cancers., In addition, some cases from noncontaminated areas were registered as Chernobyl victims. Unlike Chernobyl, most TC cases after the Fukushima accident were of the classical papillary TC (PTC) type (not the less differentiated solid variant of PTC),, which indicates that there were virtually no neglected TC cases in the Japanese population. This certifies the high baseline diagnostic level in Japan. The statement “if there were really no biological effects from the elevated ionizing radiation, only few, if any, TCs should have been detected after the nuclear accidents in the Fukushima prefecture” disagrees with the known fact that the screening can significantly elevate a TC detection rate due to a “reservoir of clinically silent cancers.” The following statement is potentially misleading: “It is true that the higher the participation rate, the more cancer cases can be detected, which increases the numerator, but at the same time more participants increase the person-years in the denominator.” It can be reasonably assumed that the probability of participation would be higher in those persons who have reasons to suppose a higher received dose and/or having relevant symptoms (self-selection). Apart from the detection of clinically silent and neglected cases, the classification of microcarcinomas, tumors with uncertain malignant potential and other borderline lesions as cancers, false-positivity, and registration of nonexposed patients as radiation exposed, have contributed to the TC incidence increase after the Chernobyl accident.,,,, The radiophobia and high cancer expectancy in the exposed populations as well as in some medical personnel also played a role. Admittedly, we do not know, whether and to what extent the above-mentioned mechanisms were active after the Fukushima accident. A possibility of overdiagnosis after Fukushima was pointed out., Apart from the false positivity that occurred after Chernobyl,,, the overdiagnosis includes detection of thyroid tumors that would not, if left untreated, result in symptoms or death. The overdiagnosis and/or suppositions about enhanced aggressiveness of radiogenic cancers and precancerous lesions after the Chernobyl accident resulted in the overtreatment in some cases, not only of the thyroid.,
Consequences of the Fukushima accident have been discussed,,, with reference to the article, describing the increase in the perinatal mortality in contaminated areas as a possible consequence of the radiation exposure. A series of reports by the same and other researchers, arguing for a cause–effect relationship between radioactive contamination after the Chernobyl accident, nuclear testing, etc., and the shift of the gender ratio at birth toward males, was commented previously; the conclusion was that the cause–effect relationships have not been proven. In reply, it was argued: “The doubling of the background radiation level, say, from 1 to 2 mSv/year, represents a doubling of an important physical environmental parameter relevant for the development of life on earth, and cannot as such be considered a 'low dose' and of no effect.” Note that after a local increase from 1 to 2 mSv/year, the doses would remain under the global average, which is 2.4 mSv/year. Given the evolutionary prerequisite of the best fitness, living organisms have probably been adapted by natural selection to the background level of ionizing radiation existing today or to some average from the past when the background was higher.
It is not surprising that disasters with evacuation of people, causing stress and disturbances of the health care, of diets and lifestyles, are accompanied by an increase in the morbidity and mortality. This is in agreement with the data on the enhanced mortality among residents of evacuated nursing homes and enhanced frequency of diabetes mellitus and hyperlipidemia after the Fukushima accident., Exposures to stress reinforced by anxiety due to supposed radiation-related risks may have detrimental effects on pregnancy., Expectant mothers with anxiety and posttraumatic stress disorders were reported to be at an increased risk of preterm birth; more details and references are available in literature.,,, The induced abortion rate per 100 pregnancies in the Fukushima prefecture increased after the accident from 17.61 to ≥18.5, i.e., by ~5.1%, which was deemed insignificant. The elevation of the perinatal mortality in the eastern part of Germany after 1986, discussed in literature,,, as a supposed consequence of the radiation exposure after the Chernobyl accident (GDR plus West Berlin: 1986 - 9.02; 1987 - 9.24 per 1000 total births, thus increased by ~4.9%), was of a similar scale. This slight elevation might have been caused by social factors and/or emigration of some medical personnel from the former GDR to the West. In general, oscillations of the perinatal mortality in the former Eastern Bloc after the Chernobyl accident, could have been caused by sociopolitical perturbations of that time. According to our observations, the quality and availability of some medicaments, foodstuff, and infant food decreased in the former SU at that time.
Reiterations of the perinatal mortality “jump”,, after the Fukushima accident without consideration of doses from the NRB, diagnostic radiography, and other factors potentially influencing the perinatal mortality, can contribute to anxiety in pregnant women and to an increase in the abortion rate. According to this mechanism, wanted pregnancies were interrupted after the Chernobyl accident. Moreover, it cannot be excluded that radiophobia contributed also to illegal abortions in the last trimester of pregnancy, possibly influencing the perinatal mortality statistics. Considering that a certain percentage of abortions induced after a prenatal ultrasonic gender testing might have been gender-selective due to son preference, the enhanced abortion rate may also contribute to an increase in the male-to-female ratio at birth. Of note, the UNSCEAR does not expect any increase in spontaneous abortions, miscarriages, perinatal mortality, and congenital defects, resulting from exposures during pregnancy due to the Fukushima accident. The general health survey in Fukushima prefecture revealed that the incidence of congenital malformations was 2.73% in 2011 and 2.32% in 2012. These values are deemed normal as the average rate in Japan is 3%–4%. Similar data have been published for the period 2011–2014.
The papers,,,,,,,,,, do not prove any dose–effect relationships. According to the UNSCEAR, no discernible incidence increase of radiation-related health effects is expected among exposed members of the public or their descendants after the Fukushima accident. It is known that radiation exposure of the developing embryo or fetus can cause damage. Based on animal studies and observations following high-dose exposures of pregnant women, the UNSCEAR and IAEA considered that there is a threshold for these effects at about 100 mGy,, which is much higher than the doses discussed above. As for TC, there are no reasons to disagree with the judgment by the UNSCEAR that an increased TC risk “among those children most exposed to radiation could be theoretically inferred, although the occurrence of a large number of radiation-induced TC in Fukushima prefecture – such as occurred after the Chernobyl accident – could be discounted because absorbed doses to the thyroid after the accident at Fukushima were substantially lower.”
The monitoring of populations exposed to low-dose low-rate radiation is important, but will hardly add much reliable information on the health risks. It can be reasonably assumed that the screening effect and increased attention of exposed people to their own health will result in new reports on the elevated cancer and other health risks from the areas with enhanced natural and anthropogenic radiation background. Dose–response relationships at low radiation doses can be further studied in large-scale animal experiments with different species. The life duration is known to be a sensitive endpoint attributable to radiation exposures. To enable extrapolations to humans, the doses and dose rates in experiments must be comparable to those in corresponding human populations, taking into account the radiosensitivity and life duration of the animals.
The author is grateful to Yamamoto et al. for their reply to the letter. The following citations from the reply should be further commented. The author feels that these quotes are essential for the argument.
Yamamoto et al.: Increased TC risks were found after exposure to doses above 50 mGy.
Author: In the cited review it is written: “The risk is significantly increased for radiation doses to the thyroid of 50–100 mGy…” with reference to, where it is stipulated: “For persons exposed to radiation before age 15 years, linearity best described the dose response, even down to 0.10 Gy.” The low figures had primarily come from a study of Israeli children who received radiotherapy to the scalp for ringworm, whereas an estimated thyroid dose 90 mGy was linked to a fourfold increase of TC and a twofold increase of benign tumors. Considering pathogenetic differences between TC and benign tumors, the causality was questioned, the data deemed outstanding and needing experimental verification., In the author's opinion, this latter result was probably caused by observation bias and/or screening effect with increased detection of thyroid nodules.
Yamamoto et al.: According to the UNSCEAR report 2013 (Appendix C-16), the thyroid dose to a 10-year-old child increases linearly with the Cs-137 deposition by 49.2 mGy per every MBq/m2 Cs-137.
Author: All average absorbed doses to the thyroid of 10-year-old children during the 1st year after the accident for Fukushima prefecture (excluding evacuated areas), presented in the table C-16.2, are <49.2 mGy, while all deposition density values of Cs-137 on soil in the same table are <1 MBq/m2. If even there are correlations between deposition values and individual doses given in table C-16.2, they do not prove cause–effect relationships and do not justify extrapolations, the more so as thyroid doses are caused mainly by I-131. According to the IAEA, the deposition levels at the most affected areas were of the order of 10 MBq/m2, while many areas had levels ~1 MBq/m2. The distribution of deposits in the Fukushima prefecture was inhomogeneous, with the levels immediately outside the most affected areas being ~10 KBq/m2.
Yamamoto et al.: The same report in its Appendix C-9 documents an estimated total Cs deposition in 1 km2 grid cells from March 12, to April 01, 2011, of up to 9.8 MBq/m2… the realistic maximum thyroid doses certainly exceeded 500 mGy.
Author: According to the UNSCEAR, deposition densities of I-131 and Cs-137 were estimated from samples of soil collected at distances 32–58 km from the FNPP between 18 and 26 March 2011. The average values of deposition density for I-131 ranged from 0.2 to 25 MBq/m2 and for Cs-137 from 0.02 to 3.7 MBq/m2. On April 22, “deliberate evacuation areas” were established for specific areas beyond the 20-km zone where the effective dose might exceed 20 mSv within a year. Most residents of these areas were then evacuated between April and June. The highest measured value for Cs-137 was 15 MBq/m2 in Okuma town, where the corresponding ambient dose rate at the time of measurement was 55 μSv/h. Obviously, the peak values are unsuitable for direct calculation of accumulated, for example, annual doses.
Yamamoto et al.: SV Jargin questioned the increase in TC after the Chernobyl accident….
Author: The undeniable increase in the TC incidence after the Chernobyl accident has never been questioned. Neither it was denied that TC could have resulted from radiation exposures; however, the quantity of radiogenic cases after Chernobyl has been overestimated.,,,,
Yamamoto et al.: However, the frequent occurrence of TC in contaminated regions after Chernobyl was evident and subsequent screenings of children born in the same regions after the decay of I-131 demonstrated the absence of frequent TC.
It is written in the cited source: “Nowadays, 20 years after the Chernobyl tragedy, incidence of thyroid cancer in children in the affected countries decreased to the levels just somewhat elevated compared to the pre-accident rate,” which is not exactly the same as the above citation from; but even that is only seemingly the case. Before the Chernobyl accident, the registered incidence of pediatric TC had been considerably lower in the former SU than in other developed countries., Accordingly, there must have been neglected TC in the population.,, For the period 1981–1985, the TC incidence among children ≤15 years old in the northern regions of Ukraine (overlapping with the areas contaminated by the Chernobyl fallout) was reportedly 0.1 and in Belarus –0.3/million/year. The TC incidence in Belarus in people ≤18 years old has remained on an enhanced level (15.7/million/year reported in 2012) or at least thrice the level of other countries,, although the radiation factor has no longer been active (t1/2 of I-131 ≈ 8 days). This indicates that other mechanisms such as enhanced vigilance and improved diagnostics have contributed to the high detection rate.
Yamamoto et al.: …the association between the TC increase and radiation has been clearly demonstrated.
Author: The correlations per se do not prove causality being at least in part caused by nonradiation-related factors; commented in,, also with references to.
Yamamoto et al.: SV Jargin states “The screening detected not only small nodules, but also late-stage TC interpreted as rapidly growing radiogenic cancers. Unlike Chernobyl, most cases after the Fukushima accident were of the classical papillary TC (PTC) type.” This perception is incorrect… In Fukushima, the percentage of PTC was 100/101 (99.0%) in the first screening and 49/50 (98%) in the second round, totaling 149/151 (98.7%), which is not much different from PTC after Chernobyl.
Author: If not the whole sentence is cited, a dot of the ellipsis (…) is needed. The complete sentence in the letter is as follows: “Unlike Chernobyl, most cases after the Fukushima accident were of the classical PTC type (not the less differentiated solid variant) which indicates that there were virtually no neglected advanced TC in the Japanese population.” From the incomplete citation resulted a misunderstanding. The “less differentiated solid variant” of PTC and its high prevalence among first wave post-Chernobyl (diagnosed during ~10 years after the accident) TC is well known. The first wave PTC after Chernobyl was averagely of larger size and higher grade than those detected later, presumably, due to old neglected cases gradually sorted out by the screening.,,,
In conclusion, inexact citations specified in this appendix potentially interfere with objective discussion. More argumentation is in the body of the present article and in some other articles.,,,
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Conflicts of interest
There are no conflicts of interest.
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