Reconstruction of residents' thyroid equivalent doses from internal radionuclides after the Fukushima Daiichi nuclear power station accident

Lignin-based materials for iodine capture and storage: A review

The safety of nuclear energy, as a low-carbon energy source, has received widespread attention. One of the concerns is the appropriate handling of volatile radioactive elements (e.g., 129I and 131I) generated during the operation of nuclear reactors. These radioactive iodine isotopes are potentially hazardous to the environment and human health, so their effective removal is essential. Adsorption has become a popular method for capturing radioiodine due to its simplicity and low cost, which eliminates the need for highly corrosive solutions. Porous solid adsorbents have been widely studied and applied in practice for the efficient removal of radioactive iodine elements. However, most of these adsorbents are expensive, have limited capture capacity, and can burden the environment. Currently, researchers have now begun to experiment with the use of lignin as a substrate to develop new green and inexpensive adsorbents to enhance the capture efficiency of radioactive iodine. This review article begins by discussing the design of lignin-based iodine capture materials, detailing their application in iodine capture, and analyzing their performance, mechanisms, and practical application cases. Considering the challenges and opportunities in the field of radioactive iodine capture, it is hoped that this work can provide a reference point for future research.

Radiation-Related Thyroid Cancer

Radiation is an environmental factor that elevates the risk of developing thyroid cancer. Actual and possible scenarios of exposures to external and internal radiation are multiple and diverse. This article reviews radiation doses to the thyroid and corresponding cancer risks due to planned, existing, and emergency exposure situations, and medical, public, and occupational categories of exposures. Any exposure scenario may deliver a range of doses to the thyroid, and the risk for cancer is addressed along with modifying factors. The consequences of the Chornobyl and Fukushima nuclear power plant accidents are described, summarizing the information on thyroid cancer epidemiology, treatment, and prognosis, clinicopathological characteristics, and genetic alterations. The Chornobyl thyroid cancers have evolved in time: becoming less aggressive and driver shifting from fusions to point mutations. A comparison of thyroid cancers from the 2 areas reveals numerous differences that cumulatively suggest the low probability of the radiogenic nature of thyroid cancers in Fukushima. In view of continuing usage of different sources of radiation in various settings, the possible ways of reducing thyroid cancer risk from exposures are considered. For external exposures, reasonable measures are generally in line with the As Low As Reasonably Achievable principle, while for internal irradiation from radioactive iodine, thyroid blocking with stable iodine may be recommended in addition to other measures in case of anticipated exposures from a nuclear reactor accident. Finally, the perspectives of studies of radiation effects on the thyroid are discussed from the epidemiological, basic science, and clinical points of view.

Confounding factors and biases involved in regional differences in the detection rate of thyroid cancer in the second-round Thyroid Ultrasound Examination: the Fukushima Health Management Survey

In response to concerns about health due to radiation exposure, the Fukushima Prefecture launched the Thyroid Ultrasound Examination program for residents aged 0-18 years at the time of the earthquake. Herein, we considered the confounding factors involved in the regional differences in the development of thyroid cancer. In this study, the 242 065 individuals who participated in both first- and second-round surveys were classified into four groups by address according to their air radiation dose. The number of participants diagnosed as malignant or suspicious for malignancy by cytological examination were 17, 38, 10 and 4 with detection rates of 53.8, 27.8, 21.7 and 14.5 per 100 000 participants in Regions 1, 2, 3 and 4, respectively. Sex (P = 0.0400), age at the time of the primary examination (P < 0.0001) and interval between the first- and second-round surveys (P < 0.0001) were significantly different among the four regions, and these were suspected to be confounding factors affecting regional differences in malignant nodule detection rates. In addition, significant regional differences were observed in the participation rate in the confirmatory examination (P = 0.0037) and the fine needle aspiration cytology implementation rate (P = 0.0037), which could be potential biases. No significant regional differences in the detection of malignant nodules were found in the multivariate logistic regression analysis after adjusting for the survey interval alone or for sex, age and survey interval. The confounding factors and biases identified in this study that may have important impacts on thyroid cancer detection rate should be fully considered in future studies.

Comparison between external and internal doses to the thyroid after the Fukushima Daiichi Nuclear Power Plant accident

To analyze the association between radiation dose and thyroid cancer after the 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, external doses have often been used because of the difficulty to estimate internal thyroid doses individually due to the lack of human data. However, no evaluation has been made as to whether external dose is a good surrogate marker for internal thyroid dose individually. This study aimed at analyzing the relationship between external doses and internal thyroid doses estimated by recently developed methodology. For four municipalities affected by the accident, 200 individuals aged under 20 at the time of the accident per municipality were randomly selected, and their external and internal thyroid doses and their ratios were estimated individually. In a separate analysis, median and arithmetic mean values for external thyroid doses estimated for persons of 16 municipalities that included the above four were compared with those for previously estimated internal thyroid doses. The ratios of the median of internal thyroid dose to that of external thyroid dose in these 16 municipalities ranged from 0.56 to 13.8 for 15-year-old children and 0.91 to 21.1 for 1-year-old children. No consistent relationship between external and internal thyroid doses was found in all 16 municipalities. Thus, thyroid doses from both external and internal exposures should be used to analyze the association between radiation dose and thyroid cancer detection rates for persons who lived in Fukushima Prefecture at the time of the FDNPP accident. (240).

Estimation of children's thyroid equivalent doses in 16 municipalities after the Fukushima Daiichi Nuclear Power Station accident

To elucidate the association between radiation dose and thyroid cancer after the 2011 Fukushima Daiichi Nuclear Power Station (FDNPS) accident, it is essential to estimate individual thyroid equivalent doses (TEDs) to children. In a previous study, we reported a methodology for reconstructing TEDs from inhalation. That methodology was based on individual behavioral survey sheets of the Fukushima Health Management Survey (FHMS) combined with a spatiotemporal radionuclides database constructed by an atmospheric transport, diffusion, and deposition model (ATDM)-the Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI) in seven municipalities. In the present study, we further refined our methodology and estimated the combined TEDs from inhalation and ingestion among children in 16 municipalities around the nuclear power station utilizing 3256 individual whereabouts questionnaire survey sheets. Distributions of estimated TEDs were similar to estimates based on direct thyroid measurements in 1080 children in Iwaki City, Kawamata Town, Iitate Village, and Minamisoma City. Mean TEDs in 1-year-old children ranged from 1.3 mSv in Date City to 14.9 mSv in Odaka Ward in Minamisoma City, and the 95th percentiles varied from 2.3 mSv in Date City to 28.8 mSv in Namie Town. In the future, this methodology can be useful for the epidemiological studies of thyroid cancer after the FDNPS accident.

Estimation of the Thyroid Equivalent Doses to Residents in Areas Affected by the 2011 Fukushima Nuclear Disaster Due to Inhalation of 131I Based on Their Behavioral Data and the Latest Atmospheric Transport and Dispersion Model Simulation

ABSTRACT

It has been challenging to obtain reliable estimates of thyroid equivalent doses (TEDs) to residents involved in the 11 March 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident because of the shortage of direct human measurements associated with 131I, the largest contributor to the dose of concern. The present study attempted to perform the estimation of the TEDs by inhalation of 131I to residents from Namie-town, one of the most radiologically-affected municipalities, by means of the latest atmospheric transport and dispersion model (ATDM) simulations with the Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI) ver. 2, coupled with personal behavioral data containing the history of the whereabouts of individuals shortly after the accident. We analyzed 1,637 residents who underwent direct measurements with whole-body counters several months after the accident and provided their personal behavioral data. We divided the subjects into two groups based on whether the distances between their locations and the FDNPP were >20 km as of 15:00 on 12 March in relation to the timepoint of the hydrogen explosion at the Unit 1 Reactor building. As a result, the 90th percentile TEDs of the 1,249 prompt evacuees and 388 late evacuees were 3.9 mSv (adult)-6.8 mSv (10-y-old) and 24.1 mSv (adult)-35.6 mSv (5-y-old), respectively, excluding 16 persons whose TEDs exceeded 50 mSv. The 90th percentile (median) TEDs to 1-y-old children (not included in the subjects) for the prompt and late evacuation groups were 8.1 (1.0) mSv and 36.3 (19.7) mSv, respectively. Additionally, this study provided the evidence to support the view that the explosive event at the Unit 1 Reactor building on the afternoon of 12 March 2011 could have caused the critical group among Namie-town's residents, whereas the largest release event on 15 March gave relatively small doses to the residents because their exposure took place mostly at sites that were distant from the FDNPP. However, the present dose estimation has potentially large uncertainty at the individual level; further validations are thus necessary.

Achievements and Current Status of the Fukushima Health Management Survey

The Fukushima Health Management Survey (FHMS) was established in response to the Fukushima Daiichi Nuclear Power Plant accident on March 11, 2011. The primary objectives of the study are to monitor residents' long-term health and promote their future well-being, and to determine the health effects of long-term low-dose radiation exposure. This special issue summarizes the results and current status of the FHMS and discusses the challenges and future directions of the FHMS. The FHMS, a cohort study of all people who were residents in Fukushima Prefecture at the time of the accident, consists of a Basic Survey, Thyroid Ultrasound Examination, Comprehensive Health Check, Mental Health and Lifestyle Survey, and Pregnancy and Birth Survey. The radiation exposure was estimated based on the behavioral records examined using the Basic Survey. Although the response rate was low in the Basic Survey, the representativeness of the radiation exposure data was confirmed using additional surveys. There appears to be no relationship between the radiation exposure and risk of thyroid cancer, although more thyroid cancer cases were detected than initially expected. The ongoing Comprehensive Health Check and Mental Health and Lifestyle Survey have provided evidence of worsening physical and mental health status. The Pregnancy and Birth Survey showed rates of preterm delivery, low birth weight, and congenital abnormalities similar to the national average. Considering the above evidence, the Fukushima Prefectural Government decided to end the Pregnancy and Birth Survey at the end of March 2021, as recommended by the Prefectural Oversight Committee. The framework of the FHMS has not changed, but the FHMS needs to adapt according to the survey results and the changing needs of the eligible residents and municipalities.

Effects of External Radiation Exposure Resulting From the Fukushima Daiichi Nuclear Power Plant Accident on the Health of Residents in the Evacuation Zones: the Fukushima Health Management Survey

BACKGROUND

Associations have been reported between lifestyle-related diseases and evacuation after the Great East Japan Earthquake (GEJE). However, the relationship between lifestyle-related diseases and the effective radiation dose due to external exposure (EDEE) after the GEJE remains unclear.

METHODS

From among 72,869 residents of Fukushima Prefecture (31,982 men; 40,887 women) who underwent a comprehensive health check in fiscal year (FY) 2011, the data of 54,087 residents (22,599 men; 31,488 women) aged 16 to 84 years were analyzed. The EDEE data of 25,685 residents with incomplete results from the basic survey, performed to estimate the external radiation exposure dose, were supplemented using multiple imputation. The data were classified into three groups based on EDEE (0 to <1, 1 to <2, and ≥2 mSv groups and associations between the incidence of diseases and EDEE from FY2011 to FY2017 were examined using a Cox proportional hazards model, with FY2011 as the baseline.

RESULTS

A higher EDEE was associated with a greater incidence of hypertension, diabetes mellitus, dyslipidemia, hyperuricemia, liver dysfunction, and polycythemia from FY2011 to FY2017 in the age- and sex-adjusted model. However, after further adjustment for evacuation status and lifestyle-related factors, the significant associations disappeared. No association was found between EDEE and other lifestyle-related diseases.

CONCLUSION

EDEE was not directly associated with the incidence of lifestyle-related diseases after the GEJE. However, residents with higher external radiation doses in Fukushima Prefecture might suffer from lifestyle-related diseases related to evacuation and the resultant lifestyle changes.

Interaction process between gaseous CH3I and NaCl particles: implication for iodine dispersion in the atmosphere

Gaseous iodomethane (CH₃I) is naturally emitted into the atmosphere by biological activity in oceans and during severe accidents (SAs) in nuclear power plants. In this latter case, a part of radioactive iodine such as ¹³¹I may be released. Improving the knowledge of CH₃I transport and reactivity in the atmosphere is important since they are strongly linked to first the cycle of ozone and second to the dispersion of radioactive CH₃I with potential radiological consequences on both the environment and human health. Here, the interaction process of CH₃I with NaCl as a surrogate of atmospheric aerosols was investigated under ambient air conditions by using Diffuse Reflectance Fourier Transform Spectroscopy (DRIFTS). The DRIFTS spectra of NaCl clearly evidenced CH₃I adsorption on the NaCl particle surface. A part of CH₃I ((1.68 ± 0.85) × 10¹⁴ molecule per mg_NaCl) was found to be strongly bonded to NaCl since no desorption was observed. The CH₃I adsorption on the NaCl surface presented a 1^st order kinetics relative to its gas phase concentration. The uptake coefficient was determined to be in the order of 10^-11. These results show a low probability of CH₃I to be taken up by halide-containing aerosols. These data are crucial for completing the iodine atmospheric chemical scheme.

Estimation of the Early Cs-137 Intake of Evacuees from Areas Affected by the 2011 Fukushima Daiichi Nuclear Power Plant Accident Based on Personal Behavioral Data and the Latest Atmospheric Transport and Dispersion Model Simulation

ABSTRACT

More than 9 y have passed since the 2011 nuclear disaster in Fukushima Prefecture, Japan. During this period, much effort has been spent on the dose reconstruction for Fukushima residents; however, the estimation of the internal dose due to the potential intake of the short-lived radionuclides (mainly iodine-131) has been challenging because of the lack of direct human measurements at the early phase of the accident. Our previous study revealed that the residual cesium body contents observed in delayed whole-body counter (WBC) measurements of residents from Namie-town, one of the most affected municipalities, varied greatly with the timepoint of their evacuations on 12 March 2011 when the first explosive event occurred at the accident site; i.e., the late evacuees had much higher residual cesium body contents compared to the prompt evacuees. The present study thus aimed to clarify this finding by reproducing the exposure situation based on the evacuees' personal behavioral data in combination with the latest atmospheric transport and dispersion model (ATDM) simulation for 356 selected subjects in adult and 15-y (13-17 y) age groups. The results demonstrated that the ATDM simulation-based method could reasonably reproduce the subjects' exposure situation, supporting the previous finding. However, the residual cesium-137 body contents calculated by this method were only 10%-20% of those in the subjects' WBC measurements. This large discrepancy was considered to be caused by both the present method's underestimation and the overestimation of the subjects' early intake in the WBC measurements due to a conservative intake scenario not assuming potential additional intake. Additional studies are needed to further clarify the reasons for the discrepancy and to evaluate the magnitude of the inhalation dose in the accident.

Comparative risk assessment of non-communicable diseases by evacuation scenario- a retrospective study in the 7 years following the Fukushima Daiichi nuclear power plant accident

Background: As a result of the Fukushima Daiichi nuclear power plant accident, many residents evacuated and were exposed to changes in their living environment and socioeconomic status, and to persistent stressors. Past studies have suggested the potential for these circumstances to contribute to long-term changes to population health.Objective: The objective of this study was to gain a better understanding of long-term health effects of evacuation, by evaluating the risk of non-communicable diseases among evacuees from Minamisoma City (one of the closest municipalities to the power plant) until 2017.Methods: The study evaluated data from annual health check-ups for residents aged 40-74 years covered by National Health Insurance (who are largely self-employed) from 2010 to 2017 administered by Minamisoma City. Diabetes, hyperlipidemia, and hypertension were defined from the results of blood sampling. Annual changes in age-adjusted prevalence were estimated by evacuation scenario. We also performed an inverse-probability weighting (IPW) analysis to adjust for baseline covariates in 2010 and estimated the differences in the risk of diabetes, hyperlipidemia, and hypertension by evacuation scenario as of the 2017 health check-up in reference to the no-evacuation group.Results: A total of 1,837 individuals were considered in this study. Regardless of evacuation scenario, there was statistical evidence suggesting an upward and a downward trend in diabetes and hypertension from 2010 to 2017, respectively, while hyperlipidemia showed no remarkable change. IPW analyses demonstrated that disease risks in 2017 did not differ significantly among people with different evacuation scenarios.Conclusions: Region-specific factors played an important role in the health effects of the evacuation. Our findings have important implications for the need of an assessment of the health effects of evacuations in more localized manner. Further research in this area will strengthen the communities' preparedness for future disasters that require mass evacuation.

Communicating with residents about 10 years of scientific progress in understanding thyroid cancer risk in children after the Fukushima Dai-ichi Nuclear Power Station accident

After the Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident in 2011, radiation-related risk of childhood thyroid cancer remains a matter of concern among residents living in areas affected by radioactive plumes. As a countermeasure to that, the Fukushima Prefectural Government-in conjunction with Fukushima Medical University-began the Fukushima Thyroid Examination (FTE) campaign in 2011. As 116 definite or suspected thyroid cancer cases were found after the first round of FTE and the total number of cases was >240 as of June 2020, residents' concerns have deepened. Some researchers claim that these cases are radiation-induced, while others claim a screening effect (because FTE uses high-resolution ultrasound equipment) and express concern about over-diagnosis. Researchers therefore must address two conflicting issues: one is to elucidate radiation effects on thyroid cancer, which requires continuation of FTE; the other is to solve ethical problems associated with FTE. As to over-diagnosis, surgeons claim that early diagnosis benefits children by reducing the side-effects of treatment and prolonging disease-free survival, while cancer epidemiologists claim that early diagnosis will result in overtreatment without reducing the death rate. 'To receive FTE or not' and 'to stop FTE or not' are ongoing dilemmas for children (and their parents) and other stakeholders, respectively. To facilitate building a consensus among stakeholders, I overview recent findings about dose reconstruction, the dose-response relationship of thyroid cancer, over-diagnosis, and the natural history of thyroid cancer, all of which contribute to judging the risk-benefit balance of thyroid screening.

Lessons learned from conducting disease monitoring in low-dose exposure conditions as a counter-measure after a nuclear disaster

The complex disaster of the Great East Japan Earthquake and the Fukushima nuclear accident caused concern about their various health impacts. Many types of intervention are desired as a countermeasure, depending on the phase of the disaster cycle. The importance of developing and applying codes of conduct has recently been emphasized for post-disaster investigations. Thyroid examination as a type of cancer screening survey was launched from October 2011 after the Fukushima nuclear accident as part of the Fukushima Health Management Survey. In this article, we reviewed the results of three rounds of thyroid examination from 2011 to 2018, and summarized the points to consider in the health survey conducted after the Fukushima nuclear accident. Large-scale mass screening by ultrasound thyroid examination resulted in many cancer diagnoses, >200 cases from a large reservoir of thyroid cancer that goes mainly unnoticed without screening. To prevent the harms of such over-diagnosis, we should be aware of the disadvantage of mass-screening based on the expected natural history of thyroid cancer. A change in strategy from mass-screening to individual monitoring is urgently needed according to international recommendations that are opposed to thyroid ultrasound cancer screening even after a nuclear disaster. To guarantee autonomy and informed choice on post-disaster disease monitoring for residents in a disaster-zone, it is important to set protocol participation and on a voluntary code of conduct basis.