Evaluation of environmental contamination and estimated exposure doses after residents return home in Kawauchi Village, Fukushima Prefecture

Risk Perception of Health Risks Associated with Radiation Exposure among Residents of Okuma, Fukushima Prefecture

Ten years have passed since the Great East Japan Earthquake and the subsequent Fukushima Daiichi nuclear power plant accident on 11 March 2011. Okuma is a town hosting the Fukushima Daiichi nuclear power plant. The evacuation order for Okuma was partially lifted in April 2019. To clarify factors associated with risk perceptions of radiation among the residents of Okuma, we conducted a questionnaire survey in January 2021. Our results revealed that resident anxieties regarding the health effects of radiation exposure from living in Okuma were independently associated with positive PCL-Specific score, recognition of the consultation services with radiation experts in the municipal government of Okuma, and planned request for consultation service regarding radiation exposure by radiation experts, along with being female and living with a child. It is important for radiation experts to promote periodic communication of risks with individuals on a small scale to provide accurate information about the health effects of radiation and to provide maternal and child healthcare services and support regarding child-rearing and radiation exposure, to reduce concerns about radiation exposure and facilitate healthy living and wellbeing in Okuma.

LOCAL LEVELS OF RADIATION EXPOSURE DOSES DUE TO RADIOCESIUM FOR RETURNED RESIDENTS IN TOMIOKA TOWN, FUKUSHIMA PREFECTURE

Tomioka Town is located within a 20-km radius of the Fukushima Daiichi Nuclear Power Station. Radiation dose rates due to radiocesium in residents' living spaces were evaluated from the measurements of ambient dose rates and environmental samples after returning home. The mean ambient dose rates were 0.15-0.18-μSv/h indoors and 0.23-0.26-μSv/h outdoors during 2018 and 2019, and the additional radiation dose rates were calculated to be 1.4 mSv/y in 2018 and 1.1 mSv/y in 2019. Ambient dose equivalent from surface soils within housing sites were estimated to be 0.66 mSv/y in 2018 and 0.54 mSv/y in 2019. Moreover, committed effective doses from local foods were calculated in 19-74 μSv/y for children and 39-100 μSv/y for adults during 2018 and 2019. These findings suggest that current radiation exposure doses have been controlled at the levels close to the public dose limit (1 mSv/y) in residents' living spaces.

Experiences of crisis communication during radiation emergency and risk communication for recovery of the community in Fukushima

Since 2011, Nagasaki University (Nagasaki, Japan) has been assisting the reconstruction efforts of Kawauchi Village (Fukushima Prefecture), which was the first village to decide to return to their home town after the evacuation due to the accident at the Fukushima Daiichi Nuclear Power Station. In April 2013, Nagasaki University and the Kawauchi Government Office concluded an agreement concerning comprehensive cooperation toward the reconstruction of the village. Furthermore, we began comprehensive support for the residents of Tomioka who returned to their hometown in 2017, and of Ohkuma town in 2020. On the basis of the experiences in Kawauchi, Tomioka and Ohkuma, it is clear that the cooperation of residents, local authorities and specialists is essential for the recovery of areas affected by the accident at the Fukushima Daiichi Nuclear Power Station. Accumulated experiences and practices should be carefully evaluated and recorded to prepare for unexpected nuclear disasters in the future.

Assessment of potentially reusable edible wild plant and mushroom gathering sites in eastern Fukushima based on external radiation dose

Edible wild plant/mushroom gathering, an essential food acquisition and outdoor recreation activity in rural areas, has declined in the area near the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in eastern Japan. The present study first evaluated the spatial distribution of potential gathering sites of various edible wild plant/mushroom species before the accident by administering a face-to-face questionnaire survey to local gatherers as well as utilizing the group analytical hierarchy process (AHP) and geographic information systems (GIS). Then, the damage to and future reusability of previous gathering sites were estimated from the perspective of the external radiation dose by overlaying maps of potential gathering sites and the time-series air dose rate (ADR) up to 2050 incorporating different gathering frequency scenarios. The study area is located in Kawauchi village in the eastern Fukushima prefecture, at 12-30 km southwest of FDNPP. The spatial distributions of gathering sites before the accident differed widely among species at the local scale because of their different environmental preferences. In contrast, the temporal variation in the reusability of the gathering sites was notably small among different species. The external radiation dose in the potential gathering sites declined sharply in the early post-accident years and gradually in the later years through the physical decay of radiocesium, i.e., ¹³⁴Cs and ¹³⁷Cs, with different half-lives. Moreover, the gathering frequency and heterogeneous distribution of radiocesium substantially affected the temporal variation in reusability for the gathering sites. These results indicate that an early resumption of gathering would be possible by reducing the gathering frequency and avoiding higher ADR areas, whereas it will take a much longer period to resume gathering in areas with higher ADR. Further research is required that considers both internal and external radiation doses in the geospatial context for the restoration and safer use of edible wild plants/mushrooms.

Radiocesium levels in contaminated forests has remained stable, even after heavy rains due to typhoons and localized downpours

In recent years, Japan has suffered serious damage due to natural disasters such as earthquakes, heavy rains due to tropical storms (typhoons) and localized downpours. To assess the chronological changes in the attenuation of external exposure doses and environmental radiation contamination due to the rainfall associated with typhoons and heavy rains during October to December 2019 in Fukushima, we measured environmental radiation levels in forest areas along the Mt Okura hiking trail in Tomioka Town, Fukushima Prefecture, near the Fukushima Daiichi Nuclear Power Station. We confirmed that (1) current ambient dose rates of 0.38-0.95 μSv/h in most forest areas were 79.9-84.7% higher than in residential areas; (2) the number of sites along the hiking trail where 137Cs was detected was limited (1.1-4.7%); and (3) individual dose rates of 0.21-0.34 μSv/h were lower than ambient dose rates. These findings suggest that radiocesium has remained stable in natural forests that have not been decontaminated even though current levels are low, despite the occurrence of heavy rainfall associated with Super Typhoon Hagibis in 2019 and localized downpours. Hiking while managing exposure to environmental contamination using a personal dosimeter may be the safest model for spending time of leisure activities.

Road Dust as a Significant Radiocesium Transporter from Land to River

This study made it clear that road dust plays an important role for Cs-137 dynamics emitted by the Fukushima Daiichi nuclear power plant accident. It was proved from the Cs-137 and heavy metals determination in road dust, drainage gutter sediment beside pavement, and riverbed sediment around the inflow point of the gutter. Road dust and drainage gutter sediment contained significantly higher concentrations of Cs-137 and Cr, Ni, Cu, Zn, Mo, Cd, Sn, Sb, and Pb than riverbed sediment. These heavy metals are typically enriched in road dust in general and originate in anthropogenic sources. Concentrations of Cs-137 and the heavy metals were higher in riverbed sediments at the inflow point of drainage than in non-inflow points. Drainage gutter sediments exhibited Cs-137 and heavy metal accumulation at the downmost of the gutter, which is the inflow point into the river. Accordingly, distribution of Cs-137 and the heavy metals concentrations were consistent with each other. Moreover, the concentrations of Cs-137 and heavy metals were correlated positively and significantly, with different proportions between sampling sites but similar between sample type and survey date. This indicates that the discharge of Cs-137 and heavy metals is characteristic of the features of the locations, such as Cs-137 and heavy metals concentrations, (micro-) topography, structure of the road and gutter, pavement area, traffic density, and so on. We conclude that road dust is a major medium of Cs-137 transport from land into aquatic ecosystems.

Pistachio shells as remediating agents for uranium in contaminated industrial seawater

Waterways have histories of being contaminated by heavy and/or radioactive metals produced by industrial processes. Natural radioisotopes of uranium (²³⁸U, ²³⁵U and ²³⁴U), long-lived radiometals, are widespread in the environment as a result of both naturally occurring processes and anthropogenic processes. Uranium is considered a major threat to humans. Previous research has focused on using inorganic materials (e.g. ion-exchangers, extractants, nanoporous sorbents) to remove such metal. However, there has been a rise in using biodegradable, recyclable, and organic biological wastes to remove heavy toxic metals from aqueous solutions. The purpose of this study is to identify pistachio shells as good candidates for the removal of uranyl from aqueous solutions. The influences of pH, contact time, temperature, and initial uranyl concentration on uranyl uptake were investigated. The influence of pH was observed to be variable, with relatively high uptake occurring at pH 4 and at slightly alkaline pH values. Uptake increased as a function of contact time, temperature, and initial uranyl concentration. The mechanism followed pseudo-second-order and intraparticle kinetics models, and the shell was demonstrated to be a Freundlich isotherm. The shells were successfully demonstrated to be viable adsorbents for uranium in seawater samples, with obtained trends similar to those achieved in the batch studies.

Evaluation of Environmental Contamination and Estimated Radiation Exposure Dose Rates among Residents Immediately after Returning Home to Tomioka Town, Fukushima Prefecture

On 1 April 2017, six years have passed since the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, and the Japanese government declared that some residents who lived in Tomioka Town, Fukushima Prefecture could return to their homes. We evaluated environmental contamination and radiation exposure dose rates due to artificial radionuclides in the livelihood zone of residents (living space such as housing sites), including a restricted area located within a 10-km radius from the FDNPS, immediately after residents had returned home in Tomioka town. In areas where the evacuation orders had been lifted, the median air dose rates were 0.20 μSv/h indoors and 0.26 μSv/h outdoors, and the radiation exposure dose rate was 1.6 mSv/y. By contrast, in the “difficult-to-return zone,” the median air dose rate was 2.3 μSv/h (20 mSv/y) outdoors. Moreover, the dose-forming artificial radionuclides (radiocesium) in the surface soil were 0.018 μSv/h (0.17 mSv/y) in the evacuation order-lifted areas and 0.73 μSv/h (6.4 mSv/y) in the difficult-to-return zone. These findings indicate that current concentrations of artificial radionuclides in soil samples have been decreasing in the evacuation order-lifted areas of Tomioka town; however, a significant external exposure risk still exists in the difficult-to-return zone. The case of Tomioka town is expected to be the first reconstruction model including the difficult-to-return zone.

Monitoring 137Cs concentrations in bird species occupying different ecological niches; game birds and raptors in Fukushima Prefecture

This study was conducted to assess radiocesium accumulation in birds after the accident at Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station in 2011, with a particular focus on ¹³⁷Cs, which has a long physical half-life. Results of ¹³⁷Cs monitoring in four game bird species including two pheasant species and two duck species (copper pheasant, green pheasant, spot-billed duck and mallard) were assessed in Fukushima Prefecture. We also obtained samples from rescued raptors that died during treatment or rehabilitation at the Wildlife Symbiosis Centre in Fukushima Prefecture because of severe injury. We measured the muscle concentrations of ¹³⁷Cs in four of these raptor species (black kite, northern goshawk, peregrine falcon and ural owl). Comparison of the two pheasant species showed that the copper pheasants inhabiting forested areas had higher ¹³⁷Cs concentrations in muscle (Bq/kg, fresh mass) than the green pheasants inhabiting mountainous areas near human habitation (i.e., Satoyama). No clear tendencies were observed in ¹³⁷Cs concentration in muscle of copper pheasants over time, but a tendency to decrease was observed in green pheasants over time. The difference in tendencies between species may be attributable to differences in their food habits and its ¹³⁷Cs concentration, and also differences in the situation of ¹³⁷Cs accumulation in their habitat. No significant differences were observed in ¹³⁷Cs concentration in muscle between the resident spot-billed duck and migratory mallard because of the comparatively short biological of effective half-life of radiocesium. Analysis of ¹³⁷Cs concentration in muscle of raptor revealed that the concentration was similar to, or lower than, those of pheasants and ducks.

RECOVERY FROM NUCLEAR DISASTER IN FUKUSHIMA: COLLABORATION MODEL

Since 2011, Nagasaki University has been assisting the reconstruction efforts of Kawauchi Village in the Fukushima Prefecture, which was the first village to declare it safe for residents to return to their homes. In April 2013, Nagasaki University and the Kawauchi government office concluded an agreement concerning comprehensive cooperation toward reconstruction of the village. The present study evaluates the internal and external exposure doses of residents and conducted a risk communication based on each resident's radiation dose. Furthermore, researchers began a comprehensive support of Tomioka residents who have returned to their hometown in 2017. Based on the experiences in Kawauchi village, it is clear that the cooperation of residents, local authorities and specialists is essential for the recovery of areas affected by the nuclear disaster. Accumulated experiences and practices should be carefully evaluated and recorded to prepare for future unexpected nuclear disasters.

Effect of Radiological Countermeasures on Subjective Well-Being and Radiation Anxiety after the 2011 Disaster: The Fukushima Health Management Survey

After the Fukushima Daiichi Nuclear Power Station accident in 2011, concerns about radiation exposure and decline in subjective well-being have been reported. To tackle these problems, various countermeasures in relation to radiation have been implemented. In this study, we comprehensively evaluated the effects of radiological countermeasures on subjective well-being (e.g., satisfaction with life (SWL) and emotional well-being) and radiation anxiety, through a questionnaire survey targeting Fukushima residents (N = 1023). Propensity scores matching was applied to evaluate significant effects of radiological countermeasures on subjective well-being and radiation anxiety. Among the radiological countermeasures, thyroid examination, whole body counter, and air dose monitoring showed the highest proportions of participation, utilization, and useful evaluation, suggesting a high degree of public attention focused on these countermeasures. The basic survey was associated with significant increases in SWL and self-rated health (SH). Thyroid examination was significantly associated with not only a reduction in radiation anxiety but also an increase of emotional stress, suggesting the importance of careful design of system and detailed communication. Food inspection was associated with deterioration in SH. Those who utilized explanatory meetings showed increases in sadness, worry, and radiation anxiety, indicating that additional attention is required of the experts and authorities involved in explanatory meetings.

Radiocesium contamination and estimated internal exposure doses in edible wild plants in Kawauchi Village following the Fukushima nuclear disaster

Kawauchi Village, in Fukushima Prefecture, is located within a 30-km radius of the nuclear disaster site of the Fukushima Daiichi Nuclear Power Plant (FDNPP). "Sansai" (edible wild plants) in this village have been evaluated by gamma spectrometry after the residents had returned to their homes, to determine the residents' risk of internal exposure to artificial radionuclides due to consumption of these plants. The concentrations of radiocesium (cesium-134 and cesium-137) were measured in all 364 samples collected in spring 2015. Overall, 34 (9.3%) samples exceeded the regulatory limit of 100 Bq/kg established by Japanese guidelines, 80 (22.0%) samples registered between 100 Bq/kg and 20 Bq/kg, and 250 (68.7%) registered below 20 Bq/kg (the detection limit). The internal effective doses from edible wild plants were sufficiently low (less than 1 mSv/y), at 3.5±1.2 μSv/y for males and 3.2±0.9 μSv/y for females (2.7±1.5 μSv/y for children and 3.7±0.7 μSv/y for adults in 2015). Thus, the potential internal exposure doses due to consumption of these edible wild plants were below the applicable radiological standard limits for foods. However, high radiocesium levels were confirmed in specific species, such as Eleutherococcus sciadophylloides ("Koshiabura") and Osmunda japonica (Asian royal fern, "Zenmai"). Consequently, a need still might exist for long-term follow-up such as environmental monitoring, physical and mental support to avoid unnecessary radiation exposure and to remove anxiety about adverse health effects due to radiation. The customs of residents, especially the "satoyama" (countryside) culture of ingesting "sansai," also require consideration in the further reconstruction of areas such as Kawauchi Village that were affected by the nuclear disaster.

Radiocesium concentrations in wild mushrooms after the accident at the Fukushima Daiichi Nuclear Power Station: Follow-up study in Kawauchi village

Since the accident at the Chernobyl Nuclear Power Plant, it has become well known that radiocesium tends to concentrate in wild mushrooms. During the recovery process after the accident at the Fukushima Daiichi Nuclear Power Station (FDNPS), it is important to perform follow-up measurements of the activity concentrations of radiocesium in mushrooms. We evaluated the activity concentrations of the detected artificial radionuclides (radiocesium) in wild mushrooms collected from Kawauchi village, which is within 30 km of the FDNPS, in 2015, four years after the accident. We found that the radiocesium was determined in 147 of 159 mushroom samples (92.4%). Based on the average mushroom consumption of Japanese citizens (6.28 kg per year), we calculated committed effective doses ranging from <0.001 to 0.6 mSv. Although committed effective doses are relatively limited, even if residents have consumed mushrooms several times, continuous monitoring of the radiocesium in mushrooms in Fukushima is needed for sustained recovery from the nuclear disaster.

A Comparison of Remediation After The Chernobyl and Fukushima Daiichi Accidents

Extensive remediation was conducted on contaminated landscapes after the Chernobyl accident in 1986 and the Fukushima Daiichi accident in 2011. A comparison is made of a range of different features relevant to each accident including the characteristics of the contamination and the landscapes affected, the radiological criteria, the designation of areas to be remediated and the remediation measures adopted.

The Time-Dependent Transfer Factor of Radiocesium from Soil to Game Animals in Japan after the Fukushima Dai-ichi Nuclear Accident

Since the Fukushima Dai-ichi accident, monitoring of tissues from hunted game animals ensures compliance with the standard food limits for radionuclides in Japan. We quantified the transfer of (137)Cs from contaminated land to game animals using the Aggregated transfer factor (Tag = activity concentration in meat [Bq kg(-1) fw]/amount in soil [Bq m(-2)]) of (137)Cs for Asian black bear, wild boar, sika deer, green pheasant, copper pheasant and wild duck, collected between 2011 and 2015. Open data sources were used from Fukushima, Miyagi, Ibaraki, Tochigi, and Gunma prefectures. Our initially compiled data showed that the maximum reported (137)Cs activity concentration in wild boar after the Fukushima Dai-ichi accident were lower than those reported after the Chernobyl accident. The geometric mean Tag values (m(2)kg(-1) fw) of (137)Cs in 2015 for Asian black bear, wild boar, sika deer and copper pheasant were similar (1.9-5.1) × 10(-3) while those for green pheasant and wild duck were about 1 order of magnitude lower at (1.0-2.2) × 10(-4). Effective half-lives were 1.2-6.9 y except for sika deer and copper pheasant where no decreases were found. In contrast to the Chernobyl accident, no seasonal change occurred in the meat (137)Cs activity concentrations of the wild animals during the study period.

Communicating Radiation Risk to the Population of Fukushima

Radiological specialists from Nagasaki University have served on the medical relief team organized at Fukushima Medical University Hospital (Fukushima City) ever since the accident at the Fukushima Dai-ichi nuclear power plant. Furthermore, we have conducted the radiation crisis communication efforts by spreading correct information on the health effects of radiation as 'advisors on radiation health risk control'. Nagasaki University has been assisting the reconstruction efforts of Kawauchi Village in Fukushima Prefecture, which was the first village to declare that residents could safely return to their homes because radiation doses were found to be at comparatively low levels. In April 2013, Nagasaki University and the Kawauchi government office concluded an agreement concerning comprehensive cooperation toward reconstruction of the village. As a result, we established a satellite facility of the university in the village. In conclusion, training of specialists who can take responsibility for long-term risk communication regarding the health effects of radiation as well as crisis communication in the initial phase of the accident is an essential component of all such recovery efforts. Establishment of a training system for such specialists will be very important both for Japan and other countries worldwide.

Lifestyle-related diseases following the evacuation after the Fukushima Daiichi nuclear power plant accident: a retrospective study of Kawauchi Village with long-term follow-up

OBJECTIVES

Kawauchi Village lies 20 km west of the Fukushima Daiichi nuclear power plant. On 16 March 2011, evacuation was ordered due to the threat of radiological exposure, and was lifted in April 2012. In this study, we aimed to evaluate the predisaster and postdisaster health status of the Kawauchi Villagers, measured by routine yearly physical examinations.

METHODS

We analysed the annual health examination data of residents of Kawauchi Village from 2008 to 2013, as available from the Japanese National Health Insurance system. Data from 2011 were not available due to the disaster. Since the health data included the same participants repeatedly from year to year, the sample was non-independent and generalised estimated equation modelling was used. A predisaster time period (2008-2010) was categorised for comparison with postdisaster 2012 and 2013. The outcome examined was the prevalence of metabolic disease, and was adjusted for confounding factors.

RESULTS

Data for 20.6%-25.9% of the total residents were available in this period. In 2013, the prevalence of metabolic syndrome (from 17.0% to 25.2%, p<0.001), diabetes (from 11.3% to 17.0%, p<0.001), dyslipidaemia (from 43.2% to 56.7%, p<0.0001), hyperuricaemia (from 5.2% to 8.4%, p=0.006) and chronic kidney disease (from 16.1% to 26.7%, p<0.001) was found to be elevated significantly compared to predisaster years, while that of obesity or hypertension did not change.

CONCLUSIONS

The present follow-up study for Kawauchi Village revealed an increase in lifestyle-related disease following the March 2011 disaster and subsequent evacuation, and this trend still continues 2 years later.

Concentrations of Radiocesium in Local Foods Collected in Kawauchi Village after the Accident at the Fukushima Dai-ichi Nuclear Power Station

We evaluated the current concentrations of radiocesium in local foods collected in Kawauchi Village, which is located less than 30 km from Fukushima Daiichi Nuclear Power Station, to minimize public anxiety regarding internal radiation exposure through the consumption of locally produced foods after the 2011 Fukushima accident. The number of samples exceeding the regulatory radiocesium limit (100 Bq/kg for general foods) was five out of 4,080 vegetables (0.1%), 652 of 1,986 (32.8%) among edible wild plants and fungi, and eight of 647 (1.2%) in fruits. Our study confirmed that the internal radiation doses of ingesting these foods are acceptably low compared to the public dose limit, ranging from 24.4 to 42.7 μSv for males and from 21.7 to 43.4 μSv for females, although the potential for radiation exposure still exists. Long-term comprehensive follow-up should take place to clarify trends in radiocesium concentrations in local foods and the committed effective doses found in Fukushima-area residents. By constructing a system that allows residents to access information on radiocesium concentration in foods, a risk communication model between specialists and residents could be developed in the recovery phase after the Fukushima accident.

Current Measures on Radioactive Contamination in Japan: A Policy Situation Analysis

BACKGROUND

The Great East Japan Earthquake on 11th March 2011 and the subsequent Fukushima Dai-ichi nuclear power plant disaster caused radioactive contamination in the surrounding environment. In the immediate aftermath of the accident the Government of Japan placed strict measures on radio-contamination of food, and enhanced radio-contamination monitoring activities. Japan is a pilot country in the WHO Foodborne Disease Burden Epidemiology Reference Group (FERG), and through this initiative has an opportunity to report on policy affecting chemicals and toxins in the food distribution network. Nuclear accidents are extremely rare, and a policy situation analysis of the Japanese government's response to the Fukushima Dai-ichi nuclear accident is a responsibility of Japanese scientists. This study aims to assess Japan government policies to reduce radio-contamination risk and to identify strategies to strengthen food policies to ensure the best possible response to possible future radiation accidents.

METHODS AND FINDINGS

We conducted a hand search of all publicly available policy documents issued by the Cabinet Office, the Food Safety Commission, the Ministry of Health, Labor and Welfare (MHLW), the Ministry of Agriculture, Forestry and Fishery (MAFF) and prefectural governments concerning food safety standards and changes to radiation and contamination standards since March 11th, 2011. We extracted information on food shipment and sales restrictions, allowable radio-contamination limits, monitoring activities and monitoring results. The standard for allowable radioactive cesium (Cs-134 and Cs-137) of 100 Bq/Kg in general food, 50 Bq/Kg in infant formula and all milk products, and 10 Bq/Kg in drinking water was enforced from April 2012 under the Food Sanitation Law, although a provisional standard on radio-contamination had been applied since the nuclear accident. Restrictions on the commercial sale and distribution of specific meat, vegetable and fish products were released for areas at risk of radioactive contamination. Monitoring of radioactive materials in food products in the prefectures has been mainly conducted before shipment to restrict the distribution of radio-contaminated foods. Between March 2011 and March 2012, 133,832 tests of non-commercial and commercial products were conducted, and 1,204 tests (0.9%) were found to violate the provisional standards. Since April 2012, 278,275 tests were conducted, and 2,372 tests (0.9%) were found to violate the revised standards. MHLW assessment of representative market baskets of foodstuffs at 15 locations throughout Japan between February and March 2014 found very low estimated dietary intake of radioactive cesium (0.0007-0.019 mSv/year), as did assessments of the contents of an average day's food. Monitoring of fisheries products in coastal areas affected by the nuclear accident found very limited and declining radio-contamination of live fish outside of Fukushima prefecture. Fisheries monitoring is of limited geographical scope and covers only certain fishes.

CONCLUSIONS

Area-specific bans on production and distribution have been effective in preventing radioactive contamination in the Japanese food market. Currently there is no major concern about radioactive cesium concentrations in retail foodstuffs in Japan, and very low levels of contamination at the production and wholesale stage. However, because the residue limits and food safety policies were revised on an ad hoc, emergency basis after the nuclear accident, the monitoring procedure needs to be reviewed based on objective and scientifically rational criteria. A transparent and objective scientific framework is needed for prioritizing foodstuffs for inspection and revising Prefecture-specific restrictions. Monitoring of fishes and other seafood products in the wild should be regularized and the information made more publicly accessible, and monitoring activities expanded to identify foodstuffs that are no longer a food safety risk. Consultation with producers and consumers should be more formalized to ensure their concerns are incorporated into regular policy reviews in an appropriate and transparent manner. However, despite the limited available knowledge on best practice in food control and enforcement of provisional radio-contamination limits after the accident, current Japanese policy is sufficient to protect the Japanese public from major risk of radio-contamination from the commercial food market.

Radiocesium concentrations in wild mushrooms collected in Kawauchi Village after the accident at the Fukushima Daiichi Nuclear Power Plant

It is well known from the experience after the 1986 accident at the Chernobyl Nuclear Power Plant that radiocesium tends to concentrate in wild mushrooms. In this study, we collected wild mushrooms from the Kawauchi Village of Fukushima Prefecture, located within 30 km of the Fukushima Daiichi Nuclear Power Plant, and evaluated their radiocesium concentrations to estimate the risk of internal radiation exposure in local residents. We found that radioactive cesium exceeding 100 Bq/kg was detected in 125 of 154 mushrooms (81.2%). We calculated committed effective doses based on 6,278 g per year (age > 20 years, 17.2 g/day), the average intake of Japanese citizens, ranging from doses of 0.11-1.60 mSv, respectively. Although committed effective doses are limited even if residents eat contaminated foods several times, we believe that comprehensive risk-communication based on the results of the radiocesium measurements of food, water, and soil is necessary for the recovery of Fukushima after this nuclear disaster.

Bipolarization of Risk Perception about the Health Effects of Radiation in Residents after the Accident at Fukushima Nuclear Power Plant

The late health effects of low-dose rate radiation exposure are still a serious public concern in the Fukushima area even four years after the accident at Fukushima Daiichi Nuclear Power Plant (FNPP). To clarify the factors associated with residents' risk perception of radiation exposure and consequent health effects, we conducted a survey among residents of Kawauchi village in May and June 2014, which is located within 30 km of FNPP. 85 of 285 residents (29.8%) answered that acute radiation syndrome might develop in residents after the accident, 154 (54.0%) residents responded that they had anxieties about the health effects of radiation on children, and 140 (49.1%) residents indicated that they had anxieties about the health effects of radiation on offspring. Furthermore, 107 (37.5%) residents answered that they had concerns about health effects that would appear in the general population simply by living in an environment with a 0.23 μSv per hour ambient dose for one year, 149 (52.2%) residents reported that they were reluctant to eat locally produced foods, and 164 (57.5%) residents believed that adverse health effects would occur in the general population by eating 100 Bq per kg of mushrooms every day for one year. The present study shows that a marked bipolarization of the risk perception about the health effects of radiation among residents could have a major impact on social well-being after the accident at FNPP.

Measurement of individual doses of radiation by personal dosimeter is important for the return of residents from evacuation order areas after nuclear disaster

To confirm the availability of individual dose evaluation for the return of residents after the accident at the Fukushima Dai-ichi Nuclear Power Plant (FNPP), we evaluated individual doses of radiation as measured by personal dosimeters in residents who temporarily stayed in Evacuation Order Areas in Kawauchi village, which is partially located within a 20 km radius of the FNPP. We also compared individual doses with the external radiation doses estimated from the ambient dose rates and with doses estimated from the concentrations of radionuclides in the soil around each individual’s house. Individual doses were significantly correlated with the ambient doses in front of the entrances to the houses (r = 0.90, p<0.01), in the backyards (r = 0.41, p<0.01) and in the nearby fields (r = 0.80, p<0.01). The maximum cumulative ambient doses in the backyards and fields around the houses were 6.38 and 9.27 mSv/y, respectively. The maximum cumulative individual dose was 3.28 mSv/y, and the median and minimum doses were 1.35 and 0.71 mSv/y. The estimated external effective doses from concentrations of artificial radionuclides in soil samples ranged from 0.03 to 23.42 mSv/y. The individual doses were moderately correlated with external effective doses in the backyards (r = 0.38, p<0.01) and in the fields (r = 0.36, p<0.01); however, the individual doses were not significantly correlated with the external effective doses in front of the entrances (r = 0.01, p = 0.92). Our study confirmed that individual doses are low levels even in the evacuation order area in Kawauchi village, and external effective dose levels are certainly decreasing due to the decay of artificial radionuclides and the decontamination of contaminated soil. Long-term follow-up of individual doses as well as internal-exposure doses, environmental monitoring and reconstruction of infrastructure are needed so that residents may return to their hometowns after a nuclear disaster.

Internal radiation exposure dose in Iwaki city, Fukushima prefecture after the accident at Fukushima Dai-ichi Nuclear Power Plant

As a result of the accident at the Fukushima Daiichi Nuclear Power Plant (FNPP) on 11 March 2011, a huge amount of radionuclides, including radiocesium, was released and spread over a wide area of eastern Japan. Although three years have passed since the accident, residents around the FNPP are anxious about internal radiation exposure due to radiocesium. In this study, we screened internal radiation exposure doses in Iwaki city of Fukushima prefecture, using a whole-body counter. The first screening was conducted from October 2012 to February 2013, and the second screening was conducted from May to November 2013. Study participants were employees of ALPINE and their families who underwent examination. A total of 2,839 participants (1,366 men and 1,473 women, 1–86 years old) underwent the first screening, and 2,092 (1,022 men and 1,070 women, 1–86 years old) underwent the second screening. The results showed that 99% of subjects registered below 300 Bq per body in the first screening, and all subjects registered below 300 Bq per body in the second screening. The committed effective dose ranged from 0.01–0.06 mSv in the first screening and 0.01–0.02 mSv in the second screening. Long-term follow-up studies are needed to avoid unnecessary chronic internal exposure and to reduce anxiety among the residents by communicating radiation health risks.