Abstract
Following the accident at Fukushima Daiichi nuclear power plant, Fukushima Prefecture is conducting the Fukushima Health Management Survey, which has been contracted out to Fukushima Medical University. The purpose of this survey is to investigate the exposure doses and health conditions of the residents of Fukushima Prefecture in order to prevent, diagnose, and treat diseases at an early stage, and to maintain and improve the health of residents in the future.
This survey consists of a basic survey to estimate external exposure doses and detailed surveys to investigate health conditions. The detailed surveys comprise: (i) thyroid ultrasound examination; (ii) comprehensive health check; (iii) mental health and lifestyle survey; and (iv) pregnancy and birth survey.
In the basic survey, the external exposure dose was estimated for >466,000 people during the first 4 months after the accident; it was estimated to be <5 mSv for 99.8% of residents.
The thyroid ultrasound examination included four rounds of echo examinations covering approximately 380,000 children aged <18 years at the time of the accident in each round. The first, second, third, and fourth examinations identified 116, 71, 31, and 21 children with thyroid cancer/suspected cancer, respectively. The Fukushima Prefectural Oversight Committee analysed the results from the first and second examinations, and evaluated that ‘the detected increased rate is unlikely to be the impact of radiation’. However, the Oversight Committee is deliberating the future direction of thyroid examination, taking into consideration the advantages and disadvantages of the examination as well as ethical viewpoints.
In the comprehensive health check, approximately 210,000 people in the evacuation area were examined, and increased rates of lifestyle-related diseases [e.g. obesity, hypertension, diabetes, and dyslipidaemia (low high-density-lipoprotein cholesterol)] were confirmed. In the mental health and lifestyle survey, approximately 210,000 people, including residents in the evacuation area, were examined. A deterioration in general mental health was found for the period immediately after the accident across a wide range of age groups, and although recovery was seen over the years, the rate of mental health issues remains above the national average. The pregnancy and birth survey revealed that the pre-term birth rate, low-birthweight rate, and rate of congenital anomalies did not differ from the national average.
The purpose of Fukushima Health Management Survey is not only to collect data on the health of the residents of Fukushima Prefecture, but to provide direct support to residents regarding the health issues clarified by the survey. Moreover, various initiatives are being implemented in cooperation with various local government authorities with the aim of maintaining and promoting the health of the residents.
Keywords
1. INTRODUCTION
The accident at Fukushima Daiichi nuclear power plant, triggered by the Great East Japan Earthquake, occurred on 11 March 2011. Large amounts of radioactive substances were released into the environment, and there is concern about the impact on the health of the residents. High dose rates have been recorded in air in Soso District, Iwaki City, Fukushima City, Iitate Village, and other areas in Fukushima Prefecture. The evacuation alert area has expanded over time from the initial 3-km area to a 20-km area. In addition, certain regions outside the 20-km area were designated by the Japanese Government as deliberate evacuation areas (where there is a risk of annual exposure ≥20 mSv) and evacuation-prepared areas (to be evacuated in case of emergency). As a result, >113,000 residents were forced to evacuate. Fukushima Prefecture started the Fukushima Health Management Survey in 2011 with the aim of monitoring the health of residents for a long period of time, and maintaining and improving their health in the future. This survey is being conducted by Fukushima Medical University Radiation Medical Science Centre for the Fukushima Health Management Survey.
2. OVERVIEW OF FUKUSHIMA HEALTH MANAGEMENT SURVEY
The Fukushima Health Management Survey includes a basic survey which aims to estimate the external exposure dose of residents, and detailed surveys to address different health conditions (Yasumura et al., 2012; Kamiya, 2018; Fukushima, 2020a). There are four detailed surveys and tests comprising: (i) thyroid ultrasound examination; (ii) comprehensive health check; (iii) mental health and lifestyle survey; and (iv) pregnancy and birth survey.
2.1. Basic survey
In a radiation accident, it is extremely important to estimate the individual exposure dose of the inhabitants in order to evaluate the health effects of radiation exposure and to manage health. Therefore, in the basic survey, the effective dose of external exposure for the 4 months immediately after the accident was estimated for the entire prefectural population of approximately 2,050,000 people (Fukushima, 2020a,c). The external exposure dose estimation system, developed by the National Institutes for Quantum and Radiological Science and Technology, was used to estimate the external exposure dose of each individual. This method uses a combination of information on the behaviour of residents for 4 months immediately after the nuclear accident and a dose rate map created from temporal radiation monitoring information of the area, etc. (Nagataki et al., 2013; Ishikawa and Tanaka, 2015; Kamiya et al., 2016).
The basic survey clarified the estimated values for effective external exposure dose for >466,000 people over the 4 months immediately after the accident. The external exposure dose to the inhabitants was <5 mSv for 99.8% of the residents and <2 mSv for 93.8% of the residents. The maximum value was 25 mSv, the mean value was 0.8 mSv, and the median value was 0.6 mSv (Fukushima, 2020c). The Fukushima Health Management Survey Oversight Committee evaluated that it was unlikely that exposure in this dose range would have a significant detectable impact on health (Fukushima, 2020c).
2.2. Detailed survey: thyroid ultrasound examination
2.2.1. Methods of thyroid ultrasound examination, results, and analysis
In the thyroid ultrasound examination, approximately 370,000–380,000 prefectural residents aged <18 years at the time of the accident were examined, mainly by ultrasonography (Suzuki et al., 2016a).
In total, 116, 71, 31, and 21 children with thyroid cancer or suspected cancer were identified in the first, second, third, and fourth rounds of the thyroid ultrasound examination, respectively (Suzuki, 2016; Suzuki et al., 2016b; Fukushima, 2020d). It follows from these results that the prevalence of thyroid cancer calculated from the first examination was approximately 30 times higher compared with prevalence rates that had been reported previously (Katanoda et al., 2016).
On the other hand, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reported the exposure dose of the thyroid gland as follows. The average thyroid doses following the accident in Chernobyl were 1100, 440, and 330 mGy in Belarus, Russia, and Ukraine, respectively (UNSCEAR, 2011). The highest thyroid dose following the accident in Fukushima was found in 1-year-old children, and was 47–83 mGy (UNSCEAR, 2014, 2015). Therefore, the thyroid dose from the accident in Fukushima was lower than that from the accident in Chernobyl. Ohira et al. analysed the dose–response relationship between the thyroid dose estimated by UNSCEAR and the corrected odds ratio for the detection of thyroid cancer in each region, and found no increase with dose (Fukushima, 2020d; Ohira, 2020).
The age distribution of the detected childhood thyroid cancers differed between Fukushima and Chernobyl. In Chernobyl, thyroid cancer was frequently observed in children aged 0–4 years 5–8 years after the accident (1990–1993); in Fukushima, thyroid cancer has not been detected in this age group 7 years after the accident (Tronko et al., 2014; Fukushima, 2020a,d).
2.2.2. Evaluation of the thyroid ultrasound examination results and the future
Fukushima is not the only place where thyroid ultrasound examinations have led to the discovery of many cases of thyroid cancer. In South Korea, a 15-fold increase in the incidence of thyroid cancer was observed in 2011 compared with 1993, which was before ultrasound examination for thyroid cancer commenced (Ahn et al., 2014). This increase in incidence is presumed to be due to the sensitivity of ultrasound examinations. A similar trend has also been observed in the USA, Europe, and other parts of the world where ultrasound examinations are performed.
Based on the evidence mentioned above, the Fukushima Oversight Committee evaluated that the rate of thyroid cancer found in the first and second examinations was unlikely to be an effect of radiation exposure from the accident in Fukushima (Fukushima, 2016, 2020a,d). However, this is not the final conclusion, and there is a need to continue with careful and unprejudiced analysis of the examination results.
It is important that thyroid ultrasound examinations are only performed in individuals who have given their consent after understanding the advantages and disadvantages of the procedure. For this reason, on-site briefings for parents and lessons for students are held as part of the thyroid ultrasound examination, where the characteristics of thyroid cancer and the advantages and disadvantages of the thyroid ultrasound examination are explained in an easy-to-understand manner. At the same time, information is transmitted via the web and explanation leaflets for the thyroid examination. The future direction of the thyroid ultrasound examination is being discussed by the Oversight Committee and countermeasures will be taken according to the results of the review.
2.3. Detailed surveys: comprehensive health check, mental health and lifestyle survey, and pregnancy and birth survey
2.3.1. Comprehensive health check
The comprehensive health check targeted approximately 210,000 residents of the evacuation area (Fukushima, 2020a). This examination revealed an increase in obesity, hypertension, diabetes, dyslipidaemia (low high-density lipoprotein cholesterol), chronic kidney disease, liver dysfunction, and polycythaemia, indicating that evacuation-related lifestyle changes following the Great East Japan Earthquake can be considered as risk factors for these diseases (Sakai et al., 2014; Satoh et al., 2015, 2016a,b; Ohira et al., 2016a,b; Takahashi et al., 2017). The results made it apparent that changes in living environment, lifestyle, and eating habits, as well as changes in the local community due to long-term evacuation had a strong impact on the health status of residents. It is possible that the risk of lifestyle-related diseases will continue to increase among evacuees as their evacuation lifestyle becomes long term, and thus health management is becoming an important topic (Hashimoto et al., 2017).
2.3.2. Mental health and lifestyle survey
Approximately 210,000 residents in the evaluation area are in the scope of this survey (Fukushima, 2020a). As part of this survey, residents who are considered to be in need are provided with care and support via telephone or printed documents (Oe et al., 2016a,b; Maeda and Oe, 2017; Fukushima, 2020c).
A Kessler 6 scale (K-6) evaluation was conducted on overall mental health, including anxiety, among evacuees aged ≥16 years. Those with a score ≥13 points in the K-6 evaluation were considered to be in need of support. According to the K-6 score, the proportion of Japan’s general population in need of mental health support is 3.0%. The current survey showed a value of 14.6% among evacuees in 2011, but a decrease over time was observed, and a value of 5.7% was reported in 2018 (Fukushima, 2020c). However, even in 2018, approximately 7 years after the accident, the value remains approximately double that of the general population of Japan, indicating that the general mental health condition of evacuees had not fully recovered at this time. On the other hand, traumatic reactions in those aged ≥16 years were evaluated by the PTSD checklist (PCL) survey, and emotions and problematic behaviour in children were evaluated by the Strength and Difficulties Questionnaire (SDQ) survey. The percentage of residents who were evaluated as needing assistance in both surveys was high in the year immediately after the accident at Fukushima, but decreased over time. The proportion of children in need of assistance according to the SDQ survey is now almost the same as the national average.
With respect to attitudes towards radiation risk, in 2011, immediately after the accident, approximately 60% of the residents stated a belief that radiation exposure from the accident in Fukushima may have some impact on the next generation. Although this has decreased since then, in 2018, approximately one-third of residents still believed that there may be some impact on the next generation (Fukushima, 2020c). Major challenges remain in risk communication and radiation literacy.
2.3.3. Pregnancy and birth survey
Between 145,000 and 160,000 pregnant women in Fukushima Prefecture are surveyed each year. Most of these women have been issued a mother and child health handbook. The survey investigates the physical and mental health of women, takes measures to reduce anxiety, and provides necessary care (Fukushima, 2020a). The survey clarifies that the pre-term birth rate, low-birthweight rate, and congenital anomaly rate did not differ in the period from 2011 to 2018 between women in Fukushima Prefecture and the national average (Fujimori et al., 2014; Fukushima, 2020b). However, it was revealed that the rate of postpartum depression among new mothers was high in Fukushima. This survey provides scientific evidence on pregnancy- and childbirth-related health issues in Fukushima, and is also a source of information against reputational damage.
3. CONCLUSION
Radiation disasters have a strong and shocking impact on multiple aspects of public life, such as health, society, and the environment. The effects on health are not only linked directly with the exposure dose, but are also strongly affected by sudden changes in the living environment. This is particularly valid in the case of evacuation. Therefore, when considering the health effects of nuclear accidents, it is necessary to deliberate not only the exposure dose but also various other factors that affect health. In such a situation, the Fukushima Health Management Survey plays an important role in monitoring, maintaining, and improving the health status of residents.