Daiichi Nuclear Power Plant Accident Research Articles

Report of the CCRI(II) supplementary international comparison of measurement of activity per unit mass of Cs-134 and Cs-137 in wheat flour (CCRI(II)-S13)

Main textA supplementary international comparison of measurement of activity per unit mass of Cs-134 and Cs-137 in wheat flour (CCRI(II)-S13) was carried out by CCRI in 2018. The matrix of the sample was wheat harvested in 2011 after the Fukushima Daiichi Nuclear Power Plant accident. No spiking was applied to the sample. Twelve institutes reported their results. Averages of the reported results and the associated uncertainties were obtained using the power-moderated mean. This report describes the supplementary comparison reference value, the degrees of equivalence of the results, the procedures of this comparison, and the sample preparation and measurements by the participants. Successful participation in this comparison by a laboratory may provide evidential support for Calibration and Measurement Capability (CMC) claims for Cs-134 and Cs-137 measured using the laboratory's method(s) used in the comparison or methods calibrated by those used for the comparison.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Association Between the Deaths Indirectly Caused by the Fukushima Daiichi Nuclear Power Plant Accident (Disaster-Related Deaths) and Pre-Disaster Long-Term Care Certificated Level; A Retrospective Observational Analysis

Association Between the Deaths Indirectly Caused by the Fukushima Daiichi Nuclear Power Plant Accident (Disaster-Related Deaths) and Pre-Disaster Long-Term Care Certificated Level; A Retrospective Observational Analysis

Regional Case Studies: Environmental Radioactivity Levels and Estimated Radiation Exposure Doses of Residents and Workers in Areas Affected by the Fukushima Daiichi Nuclear Power Plant Accident

Regional Case Studies: Environmental Radioactivity Levels and Estimated Radiation Exposure Doses of Residents and Workers in Areas Affected by the Fukushima Daiichi Nuclear Power Plant Accident

Circulation of Radioactive Cesium in Deciduous Broad-leaved Forests due to the Fukushima Daiichi Nuclear Power Plant Accident

Circulation of Radioactive Cesium in Deciduous Broad-leaved Forests due to the Fukushima Daiichi Nuclear Power Plant Accident

Latest Topics of Interest on Radiation Risk Communication: A Decade After Japan's Fukushima Daiichi Nuclear Power Plant Accident.

Latest Topics of Interest on Radiation Risk Communication: A Decade After Japan's Fukushima Daiichi Nuclear Power Plant Accident.

Temporal evolution of plutonium concentrations and isotopic ratios in the Ukedo - Takase Rivers draining the Difficult-To-Return zone in Fukushima, Japan (2013–2020)

In 2011, the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) accident released significant quantities of radionuclides into the environment. Japanese authorities decided to progressively reopen the Difficult-To-Return Zone after the decontamination of priority reconstruction zones. These areas include parts of the initially highly contaminated municipalities located to the north of the FDNPP, including Namie Town, an area drained by the Ukedo and Takase Rivers. Eleven years after the accident, research focused on the spatial distribution of plutonium (Pu) and radiocesium (Cs) isotopes at contrasted individual locations. To complement previous results, the current research was conducted on flood sediment deposits collected at the same locations after major flooding events during eleven fieldwork campaigns organised between 2013 and 2020 at the outlet of the Ukedo and Takase Rivers (n = 22).The results highlighted a global decrease of the Pu and 137Cs contents in sediment with time during the abandonment phase in the region, from 2013 (238.20 fg g−1) to 2020 (4.28 fg g−1). Furthermore, based on the analysis of the 240Pu/239Pu isotopic ratios, the plutonium transiting these rivers (range: 0.166 – 0.220) essentially originated from the global fallout (0.180 ± 0.014 (Kelley et al., 1999)). Sediment showed contrasted properties in the two investigated rivers, which is likely mainly the result of the occurrence of Ogaki Dam on upper sections of the Ukedo River as it strongly impacts the material supply from this river to the Pacific Ocean. A statistical analysis highlighted the strong correlation between Pu activity concentrations and 137Cs activities in both rivers, confirming that both radionuclides are transported with a similar pathway. Despite it was detected early after the accident (2011–2013), the current research demonstrates that plutonium originating from FDNPP is no longer detected in these rivers draining the Difficult-To-Return Zone at the onset of the reopening of the area to its former inhabitants.

Awareness of Medical Radiologic Technologists of Ionizing Radiation and Radiation Protection.

Japanese people experienced the Hiroshima and Nagasaki atomic bombings, the Japan Nuclear Fuel Conversion Co. criticality accident, it was found that many human resources are needed to respond to residents' concerns about disaster exposure in the event of a radiation disaster. Medical radiologic technologists learn about radiation from the time of their training, and are engaged in routine radiographic work, examination explanations, medical exposure counseling, and radiation protection of staff. By learning about nuclear disasters and counseling, we believe they can address residents' concerns. In order to identify items needed for training, we examined the perceptions of medical radiologic technologists in the case of different specialties, modalities and radiation doses. In 2016, 5 years after the Fukushima Daiichi nuclear power plant accident, we conducted a survey of 57 medical radiologic technologists at two medical facilities with different specialties and work contents to investigate their attitudes toward radiation. 42 participants answered questions regarding sex, age group, presence of children, health effects of radiation exposure, radiation control, generation of X rays by diagnostic X ray equipment, and radiation related units. In a comparison of 38 items other than demographic data, 14 showed no significant differences and 24 showed significant differences. This study found that perceptions of radiation were different among radiology technologists at facilities with different specialties. The survey suggested the possibility of identifying needed training items and providing effective training.

Mortality risk associated with nuclear disasters depends on the time during and following evacuation of hospitals near nuclear power plants: An observational and qualitative study

This study aimed to examine the factors correlated with emergency evacuations on patients’ prognosis in hospitals severely affected by the Fukushima Daiichi nuclear power plant (FDNPP) accident in March 2011, and to recommend measures mitigating potential health risks among them in future disasters. Seven hospitals within a 20-km radius of the FDNPP were designated as the evacuation zone, of which three hospitals located within a 5-km radius were examined. Information regarding hospital emergency evacuation among the three hospitals from previous literature and official reports were integrated and interview outcomes of staff at each hospital were qualitatively analyzed using thematic analysis. Our thematic analysis identified four themes: insufficient preparedness for disaster, difficulty of patient evacuation, insufficient materials, and insufficient information. Comparison of the three hospitals located within a 5-km radius of the FDNPP revealed that hospitals with several patients or those with a high proportion of bedridden or critically ill patients faced more difficulty in emergency evacuation and experienced higher fatalities. In addition to individual evacuation plans, for future preparedness, external and public organizations should prepare disaster responses such as procedures to integrate information on the status of each medical facility and measures to support them individually.

The effect of exposure on cattle thyroid after the Fukushima Daiichi nuclear power plant accident

Nuclear plant accidents can be a risk for thyroid cancer due to iodine radioisotopes. Near the Fukushima Daiichi nuclear power plant, cattle were exposed to radiation after the accident occurred in May 2011. Here we estimated the total radiation exposure to cattle thyroid and its effects on thyroid function. Until October 2016, the estimated external exposure dose in Farm A was 1416 mGy, while internal exposure dose of 131I, 134Cs, and 137Cs were 85, 8.8, and 9.7 mGy in Farm A and 34, 0.2, and 0.3 mGy in Farm B, respectively. The exposed cattle had thyroid with relatively lower weight and lower level of stable iodine, which did not exhibit any pathological findings. Compared with the control, the plasma level of thyroid-stimulating hormone (TSH) was higher in Farm A cattle born before the accident, while the plasma thyroxine (T4) was higher in Farm A cattle born after the accident, suggesting that exposed cattle showed slight hyperactivation of the thyroid gland. In addition, Farm A cattle have higher level of cortisol, one of the anterior pituitary gland-derived hormones. However, we did not observe a causal relationship between the radiation exposure and cattle thyroid.

Associations Between External Radiation Doses and the Risk of Psychological Distress or Post-traumatic Stress After the Fukushima Daiichi Nuclear Power Plant Accident: the Fukushima Health Management Survey.

The relationship between radiation levels and mental health status after a nuclear disaster is unknown. We examined the association between individual external radiation doses and psychological distress or post-traumatic stress after the Fukushima Daiichi nuclear power plant accident in March 2011 in Japan. The Mental Health and Lifestyle Survey was conducted from January 2012. Based on the estimated external radiation doses for the first 4 months, a total of 64,184 subjects were classified into <1 mSv, 1 to <2 mSv, and ≥2 mSv groups. Odds ratios (ORs) and 95% confidence intervals (CIs) of psychological distress and post-traumatic stress, with the <1 mSv group as the reference, were calculated using logistic regression analysis adjusted for age, sex, evacuation, perception of radiation risk, and subjective health status. The prevalence of psychological distress/post-traumatic stress in the <1 mSv, 1 to <2 mSv, and ≥2 mSv groups was 15.1%/22.1%, 14.0%/20.1%, and 15.0%/21.7%, respectively. In women, although the ≥2 mSv group tended to have a higher risk of psychological distress with the age-adjusted OR of 1.13 (95% CI, 0.99-1.30), the adjusted OR decreased to 1.00 (95% CI, 0.86-1.16) after controlling for all variables. On the other hand, there were no dose-dependent associations between radiation dose and post-traumatic stress. Although external radiation doses were not associated with psychological distress, evacuation and perception of radiation risk may increase the risk of psychological distress in women in the higher dose group.

Effects of External Radiation Exposure on Perinatal Outcomes in Pregnant Women After the Fukushima Daiichi Nuclear Power Plant Accident: the Fukushima Health Management Survey.

This study aimed to investigate the effects of maternal exposure to external radiation on perinatal outcomes among women who experienced the Fukushima Daiichi Nuclear Disaster (FDND) using the Fukushima Health Management Survey (FHMS). Data from the Pregnancy and Birth Survey and Basic Survey in the FHMS were combined to analyze external maternal radiation exposure following the FDND, and the relationship between radiation dose and perinatal outcomes was analyzed using binomial logistic regression analysis. Missing dose data were supplemented using multiple imputation. A total of 6,875 individuals responded to the survey. Congenital anomalies occurred in 2.9% of patients, low birth weight (LBW) in 7.6%, small for gestation age (SGA; <10th percentile) in 8.9%, and preterm birth in 4.1%. The median maternal external radiation dose was 0.5 mSv (maximum, 5.2 mSv). Doses were classified as follows: <1 mSv (reference), 1 to <2 mSv, and ≥2 mSv. For congenital anomalies, the crude odds ratio for 1 to <2 mSv was 0.81 (95% confidence interval [CI], 0.56-1.17) (no participants with congenital anomaly were exposed to ≥2 mSv). At 1 to <2 mSv and ≥2 mSv, the respective adjusted odds ratios were 0.91 (95% CI, 0.71-1.18) and 1.21 (95% CI, 0.53-2.79) for LBW, 1.14 (95% CI, 0.92-1.42) and 0.84 (95% CI, 0.30-2.37) for SGA, and 0.91 (95% CI, 0.65-1.29) and 1.05 (95% CI, 0.22-4.87) for preterm birth. External radiation dose due to the FDND was not associated with congenital anomalies, LBW, SGA, or preterm birth.

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.

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. 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. 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. 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.

The Effects of the Great East Japan Earthquake on Perinatal Outcomes: Results of the Pregnancy and Birth Survey in the Fukushima Health Management Survey.

There are limited studies on the long-term effects of natural/environmental disasters, especially nuclear disasters, on obstetric outcomes. This study aimed to review the results of perinatal outcomes immediately after the Great East Japan Earthquake (GEJE) and the Fukushima Daiichi Nuclear Power Plant accident, as well as their long-term trends over 8 years, in the Fukushima Health Management Survey. The annual population-based Pregnancy and Birth Survey is conducted as part of the Fukushima Health Management Survey. The Fukushima Prefecture government launched it to assess the health conditions of pregnant women and their neonates after the GEJE. The self-reported questionnaire was sent to 115,976 pregnant women by mail from January 2012, with 58,344 women responding to the questionnaire (50.3% response rate). Pregnancy complications, such as gestational hypertension, respiratory diseases, and mental disorders, increased in some women who were pregnant at the time of the earthquake and immediately after the earthquake. However, the direct effects on newborns, such as preterm birth, low birth weight, and congenital anomalies, were not immediately clear after the earthquake. Although there were significant differences in the occurrence of preterm birth and low birth weight among the districts, there was no change in the occurrences of preterm birth, low birth weight, or anomalies in newborns in Fukushima Prefecture from the fiscal year 2011 to the fiscal year 2018. Therefore, the long-term effects of the post-disaster radiation accident on perinatal outcomes are considered to be very small.

Trends in Lifestyle-related Diseases and Their Risk Factors After the Fukushima Daiichi Nuclear Power Plant Accident: Results of the Comprehensive Health Check in the Fukushima Health Management Survey.

Residents were forced to evacuate owing to the radiation released after the Fukushima Nuclear Power Plant (NPP) accident following the Great East Japan Earthquake on 11/03/2021; thus, their lifestyles drastically changed. The Comprehensive Health Check (CHC) of the Fukushima Health Management Survey (FHMS) was performed to evaluate health statuses and prevent lifestyle-related diseases in evacuation area residents. The first part of the CHC survey is a retrospective analysis of pre- and post-disaster data on health check-ups of evacuation area residents. The second part is a cross-sectional, prospective analysis of post-disaster (fiscal year (FY) 2011-2017) data on health check-ups. Subjects were men and women living in 13 municipalities in areas surrounding the NPP in Fukushima Prefecture. Post-disaster (FY 2011-2012) overweight, hypertension, dyslipidemia, diabetes mellitus, metabolic syndrome, liver dysfunction, hyperuricemia, polycythemia and atrial fibrillation cases increased from the pre-disaster (FY 2008-2010) levels. This tendency was strongest among residents who were forced to evacuate. Proportion of overweight people remained unchanged, the prevalence of liver dysfunction decreased and the proportion of people with treated hypertension and dyslipidemia increased during FY 2011-2017. Meanwhile, the prevalence of diabetes mellitus and mean levels of HbA1c increased. Furthermore, Evacuees showed higher risks of diabetes mellitus, dyslipidemia, chronic kidney diseases and liver dysfunction than non-evacuees. Therefore, residents in the evacuation area, especially evacuees, are at high risk of developing lifestyle-related diseases, especially cardiovascular diseases; therefore, it is necessary to observe health statuses and implement measures to prevent lifestyle-related diseases.

Post-evacuation return of psychiatric hospital inpatients evacuated to hospitals outside the Fukushima prefecture after the nuclear accident: A Retrospective Cohort Study.

Post-evacuation return after mandatory hospital evacuation due to complicated disasters is often overlooked and not well-discussed. In this study, we explored the factors which are related to the ease or difficulty of the post-evacuation return to Fukushima prefecture of psychiatric inpatients who had been evacuated to hospitals outside the prefecture because of the Great East Japan Earthquake (GEJE) and subsequent Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. This retrospective cohort study included evacuated psychiatric hospital inpatients who were registered in the Matching Project for Community Transition (MPCT) and had been traced until July 31, 2019. A total of 531 patients were included for the analyses. Univariable and multivariable analysis were conducted to detect the patients' traits including their psychiatric/physical backgrounds which were associated with their outcome - the time from GEJE to the date of return to Fukushima. Over half of the patients returned to Fukushima. In the multivariable analysis, the patients' gender (male), age (older), and psychiatric diagnoses of schizophrenia, schizotypal and delusional disorders (ICD-10, F20-29) showed lower hazard ratio (HR) and statistically significant association with the difficulties of post-evacuation return. Meanwhile, disorders of psychological development (F80-89), diseases of the nervous (G00-99, except G40-41) and genitourinary (N00-99) systems showed higher HR and statistically significant association with the ease of return. The specific characteristics of the psychiatric inpatients including their psychiatric and physical status are associated with their post-evacuation return to their hometown. These results indicated that the evacuated hospitals' practitioners and staffs from the MPCT understood the necessity of the earlier return of inpatients to their hometown. Moreover, clinicians should pay more attention to some symptoms unique to psychiatric patients which contributed to their difficulties in returning safely or expressing their hope to return.

Dietary Patterns and New-Onset Type 2 Diabetes Mellitus in Evacuees after the Great East Japan Earthquake: A 7-Year Longitudinal Analysis in the Fukushima Health Management Survey.

Background: Dietary patterns may be linked to the incidence of type 2 diabetes mellitus (T2DM) after disasters. We investigated the association between dietary patterns and new-onset T2DM in evacuees of the Great East Japan Earthquake and the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Methods: Among the 22,740 non-diabetic participants aged 20-89 years who completed the dietary assessment in the Fukushima Health Management Survey between July 2011 and November 2012, the incidence of T2DM was evaluated until 2018. Principal component analysis with varimax rotation was applied to derive dietary patterns based on a validated, short-form food frequency questionnaire. The identified dietary patterns were categorized as typical Japanese, juice, and meat. Results: The cumulative incidence of T2DM was 18.0 and 9.8 per 1000 person-years in men and women, respectively, during the follow-up period. The multiple-adjusted hazard ratio (95% confidence interval) of the highest vs. lowest quartile of the typical Japanese pattern scores for T2DM was 0.80 (0.68, 0.94; P for trend = 0.015) in total, 0.85 (0.68, 1.06; P for trend = 0.181) in men, and 0.76 (0.60, 0.95; P for trend = 0.04) in women. Conclusions: A typical Japanese dietary pattern may be associated with a reduced new-onset T2DM risk in evacuees, especially women, after the Great East Japan Earthquake and the FDNPP accident.

Loss of participation among evacuees aged 20–37 years in the disaster cohort study after the Great East Japan Earthquake

The present study aimed to clarify the characteristics of young evacuees who had missed the Comprehensive Health Check of the Fukushima Health Management Survey (FHMS) after the Great East Japan Earthquake in 2011. The FHMS has been conducted as a prospective cohort study to evaluate the health status of evacuees annually after the great earthquake in 2011. This study focused on the annual participation rate in the Comprehensive Health Check of evacuees aged between 20 and 37 years in 2011 who evacuated due to the Fukushima Daiichi Nuclear Power Plant accident. The characteristics of subjects who did not participate after the second survey year were identified with a multivariate logistic regression model. The participation rate was estimated at 26.6% (9720 among 36,502 residents) and 15.6% (5691 residents) in 2011 and 2012, respectively. The logistic regression model revealed the following characteristics at baseline as independent predictors of non-participation after the second year of the survey: age ≤ 24 years (adjusted odds ratio 2.11, 95% CI 1.84–2.42), 25–29 years of age (1.28, 1.13–1.45), men (1.52, 1.38–1.69), evacuation outside the municipality but within Fukushima prefecture (1.54, 1.40–1.70), evacuation outside the Fukushima prefecture (1.40, 1.21–1.63), anemia (1.23, 1.06–1.43), smoking habit (1.34, 1.21–1.48), and drinking habit (1.20, 1.09–1.32). A medical history of heart disease showed opposite odds ratios, which indicate the association with continuous participation (0.43, 0.26–0.72, respectively). We observed deteriorated participation in the prospective study of the Comprehensive Health Check of the FHMS among evacuees of a younger age group, men, those evacuated outside their municipalities, and those with history of anemia, smoking and drinking habits. Hence, the cohort study may have missed certain population groups with worse health behaviors. Thus, it is necessary to consider various measures to increase the participation rate in the disaster cohort study to understand the long-term health effects of disasters on younger residents in evacuation zones.

Spatial distributions of and species differences in 90Sr accumulation in marine fishes from the Fukushima coastal region

Large amounts of radionuclides were released into the ocean during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. One of the released radionuclides, 90Sr, tends to accumulate in bone, and could conceivably have long-term negative impacts on fishes. Here, we investigated 90Sr radioactivity concentrations in the vertebrae of demersal fishes collected off the coast of Fukushima Prefecture in January and July 2014. High 90Sr radioactivity concentrations were detected in fish collected from central Fukushima (offshore of the FDNPP) and southern Fukushima (offshore of Iwaki City), but were almost hardly detected in northern Fukushima (offshore of Soma City). Additionally, 90Sr radioactivity concentrations were higher among rays (Okamejei kenojei and Hemitrygon akajei: from 1.1 ± 0.5 to 103.3 ± 15.1 mBq/g Ca) and soles (Cynoglossus joyneri and Paraplagusia japonica: from 18.5 ± 2.8 to 52.8 ± 11.3 mBq/g Ca) than among other species. Vertebral stable Sr/Ca ratios also differed by fish species. Ca concentrations were relatively constant among species, but Sr concentrations were higher among elasmobranchs and soles, indicating that differences in Sr/Ca might be related to differences in 90Sr accumulation in fish vertebrae.

Radiation dose and gene expression analysis of wild boar 10 years after the Fukushima Daiichi Nuclear Plant accident

The Fukushima Daiichi Nuclear Power Plant accident led to contamination with radioactive cesium in an extensive environment in Japan in 2011. We evaluated the concentration of radioactive cesium in the skeletal muscles of 22 wild boars and the expression of IFN-γ, TLR3, and CyclinG1 in the small intestine and compared them with those of wild boar samples collected from Hyogo prefecture. The average 137Cs radioactivity concentration in wild boars in the ex-evacuation zone was 470 Bq/kg. Most of samples still showed radioactivity concentration that exceeded the regulatory limit for foods, but the dose remarkably decreased compared with samples just after the accident. IFN-γ expression was significantly higher in wild boars in the ex-evacuation zone than in samples from Hyogo prefecture. TLR3 expression was also upregulated. CyclinG1 expression also tended to be high. Hence, wild boars might have received some effects of low-dose radiation, and immune cells were activated to some extent. However, pathological examination revealed no inflammatory cell infiltration or pathological damage in the small intestine of wild boars in the ex-evacuation area. Long-term monitoring would be necessary, but we consider that the living body responds appropriately to a stimulus from a contaminated environment.