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

The external and internal exposure doses due to artificial radionuclides after the return of residents to their homes in Kawauchi Village, Fukushima Prefecture, including the restricted area within a 20-km radius from the Fukushima Dai-ichi Nuclear Power Plant (FNPP), were evaluated by gamma spectrometry of the soils and local agricultural products. The prevalent dose-forming artificial radionuclides from all samples were determined to be (134)Cs and (137)Cs (radiocesium). The estimated external effective doses from soils sampled on December 24 and 25, 2012 were 0.0017-9.2 mSv/y in the areas within a 20- to 30-km radius from the FNPP and 0.39-1.3 mSv/y in the areas within a 20-km radius from the FNPP. These levels appeared to be decreasing, despite the distance from the FNPP (median: 0.21 (0.012-0.56) mSv/y), compared to the levels just before the return of the residents to their homes on December 19 and 20, 2011 (median: 0.85 (0.40-1.4) mSv/y). The committed effective doses from the local agricultural samples in Kawauchi Village from May 1, 2012 to March 31, 2013 were sufficiently low, in the range of 18-44 µSv/y for males and 20-48 µSv/y for females (the range was 18-48 µSv/y for children and 25-43 µSv/y for adults), compared to the public dose limit (1 mSv/y, ICRP, 1991), although the potential for radiation exposure still exists. Residents who have not yet returned may be able to return to their homes with a long-term follow-up of environmental monitoring and countermeasures to reduce unnecessary radiation exposure.

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.

Determinants of the return to hometowns after the accident at Fukushima Dai-ichi nuclear power plant: a case study for the village of Kawauchi.

The Great East Japan Earthquake in March 2011 destroyed the Fukushima Dai-ichi Nuclear Power Plant (FNPP) and almost all residents in a 20 km radius from the plant eventually evacuated. FNPP reactors were stabilised in December 2011; some evacuees decided to return to their hometowns, and the other evacuees remained. Efforts were made to identify the determinants that affect the decision to return home in order to promote recovery of the surrounding area of FNPP. Seventy-one residents who had not returned to hometown and 56 residents who had returned were selected. Logistic regression analysis adjusted for confounding factors showed that being female [odds ratio (OR): 2.43, p = 0.03], living in areas with relatively higher ambient doses (OR: 3.60, p=0.01) and expressing anxiety over radiation exposure (OR: 8.91, p < 0.01) were independently associated with decisions not to return. Results of this study suggest the importance of active participation by scientists and local authorities in communicating the risk to the general population involved in returning home.

Evaluation of environmental contamination and estimated radiation doses for the return to residents' homes in Kawauchi Village, Fukushima prefecture.

To evaluate the environmental contamination and radiation exposure dose rates due to artificial radionuclides in Kawauchi Village, Fukushima Prefecture, the restricted area within a 30-km radius from the Fukushima Dai-ichi Nuclear Power Plant (FNPP), the concentrations of artificial radionuclides in soil samples, tree needles, and mushrooms were analyzed by gamma spectrometry. Nine months have passed since samples were collected on December 19 and 20, 2011, 9 months after the FNPP accident, and the prevalent dose-forming artificial radionuclides from all samples were (134)Cs and (137)Cs. The estimated external effective doses from soil samples were 0.42-7.2 µSv/h (3.7-63.0 mSv/y) within the 20-km radius from FNPP and 0.0011-0.38 µSv/h (0.010-3.3 mSv/y) within the 20-30 km radius from FNPP. The present study revealed that current levels are sufficiently decreasing in Kawauchi Village, especially in areas within the 20- to 30-km radius from FNPP. Thus, residents may return their homes with long-term follow-up of the environmental monitoring and countermeasures such as decontamination and restrictions of the intake of foods for reducing unnecessary exposure. The case of Kawauchi Village will be the first model for the return to residents' homes after the FNPP accident.