Evaluation of Environmental Contamination and Estimated

Article

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Evaluation of Environmental Contamination and Estimated Exposure Doses after Residents Return Home in Kawauchi Village, Fukushima Prefecture † ∥ † † § ∥ ⊥ ⊥ Yasuyuki Taira, , Naomi Hayashida, Makiko Orita, Hitoshi Yamaguchi, , Juichi Ide, Yuukou Endo, ‡ † Shunichi Yamashita, and Noboru Takamura*, † Department of Global Health, Medicine and Welfare, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan ‡ Department of Radiation Medical Science, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan § Department of Ecomaterials Science, Nagasaki University Graduate School of Engineering, Nagasaki, Japan ∥ Nagasaki Prefectural Institute for Environmental Research and Public Health, Omura, Japan ⊥ Kawauchi Village Oﬃce, Kawauchi Municipal Government, Fukushima, Japan

ABSTRACT: Theexternalandinternalexposuredosesduetoartificial 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 134Cs and 137Cs (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.

■ INTRODUCTION contaminated soil. Six months after the FNPP accident, the designated emergency evacuation preparation zones within a On March 11, 2011, a 9.0-magnitude earthquake (The Great 4 East Japan Earthquake) and tsunami caused extensive damage 20- to 30-km radius from the FNPP were canceled. to the Fukushima Dai-ichi Nuclear Power Plant (FNPP), and a On January 31, 2012, the head of Kawauchi Village, located radioactive plume derived from Units 1, 2, 3, and 4 of the within the restricted area at a distance of less than 30 km from FNPP was dispersed into the atmosphere. The total amount of the FNPP, declared that residents could safely return to their radioactive materials released into the atmosphere from the homes because the radiation doses were found to be at FNPP corresponded to Level 7 on the International Nuclear comparatively low levels. Even though a year has passed since “ ” and Radiological Event Scale (INES) used by the International the declaration of the return and two years have passed since Atomic Energy Agency (IAEA). The effects of this accident are the FNPP accident, the return is still not progressing smoothly still being felt and will continue to affect Japan, as around the FNPP itself, including in Kawauchi Village. This is approximately 900 PBq (131I equivalent by INES) of radioactive because public anxiety persists with regard to the radiation substances were emitted, which is a sixth of the amount of the exposure derived from the FNPP accident. − emissions from the Chernobyl accident.1 3 Vast stretches of Some reports have shown the environmental contamination land, totaling 1800 km2, of Fukushima Prefecture now have and estimated exposure doses during the initial phase of the levels equaling a cumulative external dose of 5 mSv/y or more.2 However, levels of environmental radioactivity are decreasing Received: October 22, 2013 due to the decay of short-lived radionuclides such as 131I (half- Revised: March 8, 2014 life: 8.0 d), 129mTe (34 d), 95Nb (35 d), and 136Cs (13 d), and Accepted: March 18, 2014 through recovery efforts such as the remediation of

Figure 1. Location of sampling points, Kawauchi Village, Fukushima Prefecture. Open circles (○) are sampling points of soils used in the present study (December 24 and 25, 2012). Closed circles (●) are sampling points of soils used in the previous study (December 19 and 20, 2011). Dashed lines indicate sampling areas of foods used in the present study (from May 1, 2012 to March 31, 2013). Dark gray shading indicates areas where evacuation orders are ready to be lifted (Apr 1, 2012). Light gray shading indicates areas where residents are not yet permitted to live (Apr 1, 2012 to March 31, 2013) (available: http://www.meti.go.jp/english/earthquake/nuclear/roadmap/; accessed January 24, 2014).

− FNPP accident.5 9 Although our previous report also showed major roads, and (as in previous studies) before the residents the environmental contamination and estimated exposure doses returned to their homes. Sampling areas ranged from N37° 16′ just prior to the return to Kawauchi Village, the radiation to N37° 22′ and E140° 45′ to E140° 53′, and the distances exposure risk after the return to an area such as Kawauchi from the FNPP were between 15.0 and 26.2 km (Figure 1). 10 Village has not been absolutely reported. The risks of external The ambient dose rates at all sampling places were ’ and internal exposure during residents daily activities are monitored in the air 1 m above the ground using a portable becoming a matter of public attention, with a need to reassure 11,12 detector for the management of radiation exposure (PDR-201, public safety. Therefore, we evaluated the current environ- Hitachi-Aloka Medical, Ltd., Tokyo, Japan) (Table 1). mental contamination derived from the FNPP accident by The radioactive contaminant survey for the foods produced using gamma spectrometry to analyze the concentrations of fi and/or collected at Kawauchi Village has been carried out by arti cial radionuclides in the soil and local food samples ffi collected in residential areas and the forests of Kawauchi personnel at the Kawauchi Village O ce since May 1, 2012. Village. External and internal effective doses were also For this survey, 2654 food samples were widely collected from calculated from these samples for an estimation of radiation each district (Districts 1 through 8) in Kawauchi Village; and exposure status after the return of the residents to their homes 2351 vegetables, edible wild plants and mushrooms, and fruit in Kawauchi Village. samples (three food items) produced and/or collected at Kawauchi Village were selected, because these three items form ■ MATERIALS AND METHODS the major dietary components consumed by the residents of Sampling Places. The Fukushima Dai-ichi Nuclear Power Kawauchi Village and therefore might be expected to contribute Plant is located on the east coast of Honshu Island, substantially to internal doses (Figure 1, Table 2). On the other approximately 200 km northeast of Tokyo, Japan. Samples hand, animal products such as wild boar, pheasant, and river fi around the FNPP were collected at Kawauchi Village (the sh (tracers of the biological concentration) were collected at public office, N37° 20′, E140° 48′) and 22.0 km southwest of Kawauchi Village only to investigate radioactivity levels as these the FNPP (N37° 25′, E141° 02′). were not actually consumed. Therefore, in the present study, In Kawauchi Village, 22 soil samples were collected at public local meats and fish were not expected to contribute to the facilities including schools, assembly halls and forests along internal doses.

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e Table 1. Distribution of Detected Artiﬁcial Radionuclides in Soils

radionuclide concentration in Bq/kg-drya distance from FNPP radionuclide ratio in external eﬀective dose in ambient dose rate in points (km) 134Cs (2.1 y)b 137Cs (30 y) 134Cs/137Cs mSv/y μSv/h 1 25.3 414 ± 2.3 (2.4) 720 ± 3.0 (1.6) 0.58 0.14 0.17 2−1c 22.6 3.2 ± 0.3 (0.8) 5.1 ± 0.3 (0.8) 0.63 0.0017 0.12 2−2 22.6 246 ± 1.9 (2.0) 420 ± 2.4 (1.7) 0.59 0.12 3−1 22.0 510 ± 2.4 (2.3) 884 ± 3.1 (1.8) 0.58 0.21 0.14 3−2 22.0 19.4 ± 0.5 (0.9) 34.5 ± 0.6 (0.9) 0.56 0.14 3−3 22.0 8.9 ± 0.4 (0.9) 15.5 ± 0.5 (0.8) 0.57 0.14 4 24.7 1031 ± 3.1 (3.0) 1807 ± 4.1 (2.3) 0.57 0.51 0.17 5 21.7 10.8 ± 0.4 (0.8) 20.5 ± 0.5 (0.8) 0.53 0.0061 0.12 6 22.0 11.3 ± 0.4 (0.8) 19.3 ± 0.5 (0.8) 0.59 0.0063 0.12 7 21.5 38.5 ± 0.7 (1.2) 69.9 ± 0.9 (1.0) 0.55 0.014 0.22 8 21.3 5.5 ± 0.4 (0.9) 9.3 ± 0.4 (0.9) 0.59 0.0025 0.15 9 20.6 49.0 ± 0.8 (1.2) 86.8 ± 1.0 (1.0) 0.56 0.020 0.19 10 21.1 153 ± 1.2 (1.4) 268 ± 1.6 (1.2) 0.57 0.080 0.16 11 20.8 8141 ± 9.8 (8.9) 14135 ± 13 (6.1) 0.58 2.8 0.25 12 22.6 39.7 ± 0.9 (1.4) 71.5 ± 1.0 (1.1) 0.56 0.010 0.31 13 22.6 1835 ± 6.4 (6.0) 3093 ± 7.9 (4.6) 0.59 0.27 0.45 14 25.8 86019 ± 52 (43) 146728 ± 66 (32) 0.59 9.2 2.9 15 26.2 1603 ± 4.6 (4.3) 2767 ± 5.9 (3.3) 0.58 0.57 2.2 21 15.0 1356 ± 4.5 (4.2) 2348 ± 5.9 (3.3) 0.58 0.39 0.41 22 15.2 3775 ± 7.2 (9.3) 6378 ± 8.7 (4.9) 0.59 1.3 0.52 23 15.3 3052 ± 6.7 (5.5) 5243 ± 8.7 (4.6) 0.58 0.86 0.72 24 17.5 2363 ± 6.2 (5.7) 4093 ± 7.9 (4.1) 0.58 0.56 1.5 median 330 (24.2−1777)d 570 (43.4−3011) 0.21 (0.012−0.56) 0.28 (0.16−0.57) aError shows one sigma standard deviation from counting statistics (detection limit). bHalf-life. cBranch numbers show core samples (2−1: 0−5 cm, 2−2: 5−10 cm, 3−1: 0−5 cm, 3−2: 5−10 cm, and 3−3: 10−30 cm). d25−75th percentile. eRadiocesium, radionuclide ratios (134Cs/137Cs), external eﬀective doses from surface soils (0−5 cm) due to radiocesium and ambient dose rates by a gamma-ray survey meter in Kawauchi Village, Fukushima Prefecture.

h Table 2. Summary of the Radioactive Contaminants Survey for Foods

district vegetables edible wild plants and mushrooms fruits ﬁsha meatsb crops others n 1 346c (1)d 179 (63) 41 (2) 3 (3) 17 (12) 12 (0) 23 (7) 621 (88) 2 222 (0) 41 (9) 31 (0) 0 (0) 6 (2) 5 (0) 14 (1) 319 (12) 3 150 (0) 67 (31) 32 (0) 0 (0) 15 (11) 5 (0) 12 (3) 281 (45) 4 174 (2) 100 (26) 40 (1) 1 (1) 4 (3) 8 (0) 15 (3) 342 (36) 5 138 (0) 148 (85) 31 (0) 0 (0) 30 (12) 3 (0) 15 (2) 365 (99) 6 215 (1) 95 (36) 53 (1) 2 (2) 28 (25) 14 (0) 18 (6) 425 (71) 7 111 (1) 98 (53) 26 (0) 4 (2) 12 (7) 7 (0) 24 (6) 282 (69) 8 2 (0) 9 (4) 2 (0) - - - 6 (1) 19 (5) n 1358 (5) 737 (307) 256 (4) 10 (8) 112 (72) 54 (0) 127 (29) 2654 (425) >100 Bq/kg (%) 5d (0.4)e 307 (41.7) 4 (1.6) 8 (80.0) 72 (64.3) 0 (0) 29 (22.8) 425 (16.0) 20−100 Bq/kg (%) 28 (2.1) 147 (19.9) 46 (18.0) 2 (20.0) 23 (20.5) 2 (3.7) 15 (11.8) 263 (9.9) Maximum in Bq/kg 299f (7)g 9305 (7) 163 (6) 1440 (7) 5457 (5) 30 (1) 2048 (6) aRiver ﬁsh. bMainly wild boar and pheasant. cNumber of the analysis. dNumber in excess of the standard limit for radiocesium (100 Bq/kg for general foods). eExcess rate of the standard limit for radiocesium (100 Bq/kg for general foods). fMaximum value of radiocesium concentrations. gDistrict number. hThe radioactive contaminants survey for foods produced and collected at Kawauchi Village, Fukushima Prefecture.

Measurement of Radionuclides. The activity concen- and organic material, > 2 mm); then ﬁne particles (<2 mm) trations of radionuclides were analyzed in 17 samples of surface were prepared before measuring radionuclide activity. soil (0−5 cm) and 5 core samples of soil (0−5, 5−10, and 10− After preparation, the soil samples were put into plastic 30 cm) collected at Kawauchi Village on December 24 and 25, containers made of polypropylene and analyzed with a high 2012. Soil sampling was carried out using a core sampling purity germanium detector (ORTEC, GEM35, Ortec Interna- technique at all sampling sites. The size of the soil samples was tional Inc., Oak Ridge, TN) coupled to a multichannel analyzer 18.2 cm2 (a diameter of 4.8 cm) and the density of the surface (MCA7600, Seiko EG&G Co., Ltd., Chiba, Japan) for 80 000 s. soil layer ranged from 0.6 to 1.5 g/cm3-dry (the mass ranged The measuring time was set to detect the objective radio- from 28 to 166 g). nuclide, and the gamma-ray peaks used for the measurements After collection, all samples were dried in a ﬁxed temperature were 604.66 keV for 134Cs (2.1 y) and 661.64 keV for 137Cs (30 dryer (105 °C, 24 h) and sieved for rock fragments (pebbles y). Decay corrections were made based on the sampling data,

C dx.doi.org/10.1021/es404534y | Environ. Sci. Technol. XXXX, XXX, XXX−XXX Environmental Science & Technology Article and detector efficiency calibration for different measurement geometries was performed using mixed activity standard volume sources (Japan Radioisotope Association, Tokyo, Japan). The relative detection efficiency of this instrument was 37.7%, with 1332.47 keV for 60Co (5.3 y). Sample collection, processing, and analysis were executed in accordance with the standard methods of radioactivity measurement authorized by the Ministry of Education, Culture, Sports, Science, and Technology in Japan (MEXT).13 All measurements were performed at the Nagasaki Prefectural Institute for Environmental Research and Public Health in Nagasaki, Japan. Secondarily, the activity concentrations of artificial radionuclides (mainly 134Cs and 137Cs) were analyzed in 2654 samples of foods produced and/or collected at Kawauchi Village from May 1, 2012 through March 31, 2013 (Table 2). After preparation, local food samples (approximately 2000 g- Figure 2. Relationship between distances from the FNPP and external fresh) were put into plastic containers made of acrylic acid resin dose rates at the sampling points. Open circles (○) are sampling and analyzed using (mainly) the NaI (thallium doped sodium ϕ × points used in the present study (December 24 and 25, 2012). Closed iodide, 2 2 in.) detector (Canberra, CAN-OSP-NAI, circles (●) are sampling points used in the previous study (December AREVA NC Inc., Meriden, CT) coupled to a multichannel 19 and 20, 2011). analyzer (Genie 2000, Canberra Japan KK., Tokyo, Japan) for 1800 s. The resolution of this instrument was <7.5% on 661.64 × 10−5 mSv/Bq for 137Cs) and for adult intake (age: > 20, 1.9 × keV for 137Cs. The food sampling and measurements were 10−5 mSv/Bq for 134Cs and 1.4 × 10−5 mSv/Bq for 137Cs, the performed by the Kawauchi Village Office. International Commission on Radiological Protection (ICRP) Effective Dose. After the measurements, the external 199217), and e is quoted from the average daily intake data (g/ effective doses from the soil samples were estimated from the day) for age, gender, and season in areas around the FNPP radioactive fission product concentrations using the following issued by the Environmental Radioactivity Monitoring Center formula: of Fukushima, Fukushima Prefecture, Japan in 2009−2010.18 To calculate the committed effective doses, the undetected data H =·CD ·· fs (1) ext ext of the radiocesium was assumed to have activity concentrations where C is the activity concentration of the detected artificial corresponding to one-fourth of the detection limit for vegetable radionuclides (radiocesium) [kBq/m2; estimated from the samples, the detection limit itself for edible wild plant samples radiocesium concentration in Bq/kg-dry including soil particles (including mushrooms) and for fruit samples in District 8, and 2 (<2 mm) and collected areas of surface soil (0.00182 m )]; Dext one-half of the detection limit for fruit samples in Districts 1 is the dose conversion coefficient reported as the kerma-rate in through 7, based on the Global Environment Monitoring air 1 m above the ground per unit activity per unit area [(μGy/ System-Food Contamination Monitoring and Assessment h)/(kBq/m2)], with the assumption that the kerma-rate in the Programme (GEMS/Food) by the World Health Organization air and the absorbed dose rate in the air are the same value for (WHO) (available at http://www.who.int/foodsafety/chem/ radiocesium, with the relaxation mass per unit area (β: g/cm2) gems/en/; accessed January 24, 2014) and the new standard set to 3.0 due to the passage of less than 2 years after the limits for radionuclides in food by the Ministry of Health, accident at the FNPP [3.3 × 10−3 (μGy/h)/(kBq/m2) for 134Cs Labour, and Welfare in Japan (MHLW) (available at http:// and 1.3 × 10−3 (μGy/h)/(kBq/m2) for 137Cs, ICRU 1994];14 f www.mhlw.go.jp/english/topics/2011eq/dl/new_standard.pdf; is the unit conversion coefficient (0.7 Sv/Gy for the effective accessed January 24, 2014) (Table 3).19,20 The rates of dose rate in the body per unit of the absorbed dose rate in undetected data were over 80% for vegetable samples, in a air),15 and s is the occupancy-shielding factor (0.36 for the range of 60−80% for fruit samples (Districts 1 through 7) and public; 0.2 fractional time outdoors +0.8 fractional time indoors under 60% for edible wild plant samples including mushrooms, ×0.2 building shielding) (Table 1)15 or the decrease in the and fruit samples (District 8) (Table 3).20 In the present study, coefficient by a shielding factor against exposure to γ rays from vegetables, edible wild plants and mushrooms, and fruit samples a deposit 1 m above the ground (0.7 under the condition of (three food items) have been selected for calculating the typical land)16 (Figure 2). The annual external effective doses committed effective doses because these samples are taken due to radioactive cesium (134Cs and 137Cs) were calculated generally and are assumed to contribute to the potential for × × using eq 1 (Hext 24 h/day 365 days) (Table 1). internal exposure. Actually, these three food items were The internal effective doses (committed effective doses) frequently investigated for confirming the current radioactivity from the vegetables, edible wild plants and mushrooms, and in food samples (Table 2). Therefore, the committed effective fruit samples among all of the food samples were estimated doses were estimated assuming that the residents usually from the radioactive fission product concentrations with the ingested foods including vegetables, edible wild plants and following formula: mushrooms, and fruit (three food items) during the year after they return to their homes in Kawauchi Village. Hint=·CD int ·e (2) where C is the activity concentration (median) of detected ■ RESULTS artificial radionuclides (radiocesium) (Bq/kg-fresh) (Table 3), The distribution of detected artificial radionuclides (radio- ffi − 134 137 ff Dint is the dose conversion coe cient for child intake (age: 0 cesium), radionuclide ratios ( Cs/ Cs), external e ective 19, 1.3 × 10−5-3.0 × 10−5 mSv/Bq for 134Cs and 9.6 × 10−6-2.2 doses from surface soils (0−5 cm) due to radiocesium, and

D dx.doi.org/10.1021/es404534y | Environ. Sci. Technol. XXXX, XXX, XXX−XXX Environmental Science & Technology Article

e Table 3. Distribution of Radiocesium in Three Food Items

range (Bq/kg-fresh)b mean (Bq/kg-fresh) median (Bq/kg-fresh) seasona 134Cs 137Cs 134Cs 137Cs 134Cs 137Cs vegetables spring nd nd summer <21−122 <21−177 5.5 ± 5.3c 6.1 ± 8.3 5.0 (5.0)d 5.0 (5.0) autumn <25−27 <22−52 5.1 ± 1.3 5.5 ± 3.7 5.0 (5.0) 5.0 (5.0) winter <21−50 <26−95 6.5 ± 7.2 9.0 ± 16 5.0 (5.0) 5.0 (5.0)

edible wild plants and mushrooms spring <24−113 <21−155 27 ± 20 32 ± 30 20 (49) 20 (65) summer <20−230 <20−317 32 ± 31 42 ± 49 20 (54) 20 (80) autumn <20−3472 <23−5833 210 ± 438 369 ± 724 73 (447) 149 (765) winter <37−137 <23−571 33 ± 29 67 ± 118 20 (72) 20 (133)

fruits spring nd nd summer <21−45 <20−78 16 ± 8.8 25 ± 16 10 (27) 23 (43) autumn <24−81 <22−82 13 ± 11 19 ± 15 10 (20) 10 (34) winter <21−26 <21−48 12 ± 4.7 16 ± 11 10 (17) 10 (24) aFrom May 1, 2012 to March 31, 2013. Spring (from March to May), summer (from June to August), autumn (from September to November) and winter (from December to January). bnd: Not detected. cData are presented as mean ± SD. d90th percentile. eDistribution of radiocesium in vegetables, edible wild plants and mushrooms, and fruits in Kawauchi Village, Fukushima Prefecture. ambient dose rates using a gamma-ray survey meter in showed a slightly positive relationship as indicated by the linear Kawauchi Village are shown in Table 1. The prevalent dose- dependence between these doses (r = 0.73, y = 1.1976x 134 forming artificial radionuclides from all samples were Cs and +0.3307). 137 Cs, and the concentrations of radiocesium exceeded 8,000 The summary of the radioactive contaminants survey for Bq/kg-dry (which is the standard value for storing decontami- foods produced and collected at Kawauchi Village is shown in nation waste by Japanese guidelines) in some areas (Nos. fi 12 Table 2. This survey was carried out to con rm the levels of the Eleven and 14) within a 20- to 30-km radius from the FNPP. main radionuclides (134Cs and 137Cs) from May 1, 2012 The concentrations were also in excess of 8,000 Bq/kg in areas through March 31, 2013. The prevalent dose-forming artificial within a 20-km radius from the FNPP (No. 22 and 23). 134 137 134 137 radionuclides from the food samples were Cs and Cs (the Radiocesium ratios ( Cs/ Cs) in the soil samples ranged 131 from 0.53 to 0.63 at the time of sampling. short-lived radionuclides such as I causing thyroid doses by The 134Cs deposition in the soil samples within a 20- to 30- the ingestion of foods were not detected in any sample). The km radius from the FNPP ranged from 0.1 ± 0.01 to 769.3 ± number of samples exceeding the radiocesium regulatory limit 0.5 kBq/m2, whereas the 134Cs deposition in the samples within (100 Bq/kg for general foods) are five (0.4%) from the a 20-km radius from the FNPP ranged from 32.6 ± 0.1 to 109.7 vegetable samples, 307 (41.7%) from the edible wild plant ± 0.2 kBq/m2. The 137Cs deposition in the soil samples within samples (mainly mushrooms), and four (1.6%) from the fruit a 20- to 30-km radius from the FNPP ranged from 0.2 ± 0.01 samples.11 The distribution of radiocesium in the vegetables, ± 2 137 to 1312.2 0.6 kBq/m , whereas the Cs deposition in the edible wild plants and mushrooms, and fruits in Kawauchi samples within a 20-km radius from the FNPP ranged from Village is shown in Table 3. The radiocesium concentrations for ± ± 2 56.4 0.1 to 185.3 0.3 kBq/m (data not shown). all of the samples reflected an extremely wide range for every The estimated external effective doses (s = 0.36, the season, especially the radiocesium concentrations of edible occupancy-shielding factor for the public) were 0.0017−9.2 − μ (mainly mushrooms) wild plants, which ranged widely from mSv/y (0.00020 1.1 Sv/h) in areas within a 20- to 30-km 134 137 radius from the FNPP; the highest value was at No. 14, which <20 to 3472 for Cs and <23 to 5833 for Cs in autumn. ff was 25.8 km from the FNPP and the ambient dose rates were The committed e ective doses from agricultural produce 0.12−2.9 μSv/h when the soil samples were collected, whereas (three food items) due to radiocesium in the Kawauchi Village the estimated external effective doses were 0.39−1.3 mSv/y are summarized in Table 4, and ranged from 6.8 to 17 μSv/y (0.045−0.15 μSv/h) in the areas within a 20-km radius from for males and from 6.4 to 18 μSv/y for females (and ranged the FNPP; the highest value was at No. 22, which was 15.2 km from 6.4 to 17 μSv/y for children and from 12 to 18 μSv/y for from the FNPP and ambient dose rates were 0.41−1.5 μSv/h adults) due to the ingestion of vegetables; from 2.3 to 9.8 μSv/ when the soil samples were collected (Table 1). The median of y for males and from 2.9 to 12 μSv/y for females (from 2.3 to the external effective doses and the ambient dose rates were μ μ − − μ 12 Sv/y for children and from 2.9 to 12 Sv/y for adults) due 0.21 (0.012 0.56) mSv/y and 0.28 (0.16 0.57 Sv/h) in to the ingestion of edible wild plants and mushrooms; and from Kawauchi Village, respectively (Table 1). As shown in Figure 2, 8.6 to 22 μSv/y for males and from 8.5 to 21 μSv/y for females the external effective doses (s = 0.7, the decrease in the ffi γ (from 8.5 to 22 μSv/y for children and from 8.6 to 16 μSv/y for coe cient by a shielding factor against exposure to rays from ff a deposit 1 m above the condition of typical land) were adults) due to the ingestion of fruits. The committed e ective μ 0.00039−2.0 μSv/h within a 20- to 30-km radius from the doses ranged from 18 to 44 Sv/y for males and from 20 to 48 FNPP, whereas they were 0.087−0.29 μSv/h within a 20-km μSv/y for females (from 18 to 48 μSv/y for children and from radius from the FNPP. The external effective doses from the 25 to 43 μSv/y for adults) due to ingestion of the three food soil samples and ambient dose rates in Kawauchi Village items.

E dx.doi.org/10.1021/es404534y | Environ. Sci. Technol. XXXX, XXX, XXX−XXX Environmental Science & Technology Article

c Table 4. Committed Eﬀective Doses from Three Food Items

ageb item gender seasona estimated dose average 0−19 20−29 30−39 40−49 50−59 60−69 >70 vegetables male spring μSv/2 month female male summer μSv/3 month 5.4 2.7−6.6 4.2 5.0 4.8 5.8 7.1 7.1 female 5.5 2.4−5.9 4.6 5.0 5.9 5.7 7.7 6.1 male autumn μSv/3 month 3.8 1.8−4.5 4.0 2.7 3.5 4.2 5.4 4.2 female 3.8 1.9−4.7 3.5 3.5 3.5 4.2 5.7 3.9 male winter μSv/3 month 4.2 2.2−5.5 5.0 3.8 3.2 5.6 4.8 4.2 female 3.9 2.0−4.9 4.3 3.0 3.1 4.9 4.6 3.7 male total μSv/y 13 6.8−17 13 12 12 16 17 15 female 13 6.4−16 13 12 13 15 18 14

edible wild plants and mushrooms male μSv/2 month 0.34 0.18−0.44 0.19 0.29 0.19 0.56 0.42 0.49 female 0.40 0.34−0.83 0.21 0.29 0.15 0.46 0.50 0.49 male summer μSv/3 month 0.27 0.053−0.13 0.16 0.17 0.48 0.51 0.21 0.42 female 0.46 0.35−0.85 0.43 0.17 0.31 0.49 0.37 0.72 male autumn μSv/3 month 5.0 1.6−4.0 2.2 3.1 6.5 6.4 7.5 5.9 female 6.2 3.2−8.0 11 2.0 7.4 7.3 4.8 6.3 male winter μSv/3 month 1.2 0.44−1.1 0.73 0.79 1.2 2.4 1.3 1.4 female 0.69 0.72−1.7 0.66 0.40 0.84 1.4 2.0 1.1 male total μSv/y 6.8 2.3−5.7 3.3 4.3 8.4 9.8 9.5 8.2 female 7.7 4.6−12 12 2.9 8.7 9.6 7.6 8.6

fruits male spring μSv/2 month female male summer μSv/3 month 5.4 4.3−11 4.2 5.0 5.2 5.8 5.8 7.3 female 6.0 3.9−9.7 4.3 5.0 4.6 6.8 8.1 6.1 male autumn μSv/3 month 3.6 2.3−5.7 3.0 1.3 4.2 3.4 5.2 3.9 female 3.5 2.5−6.1 2.7 2.5 3.1 4.0 3.6 3.8 male winter μSv/3 month 3.4 2.3−5.5 1.5 3.2 2.2 3.9 5.0 3.9 female 3.8 2.1−5.2 2.0 3.7 3.7 3.9 4.6 5.3 male total μSv/y 13 8.9−22 8.6 9.6 12 13 16 15 female 13 8.5−21 9.0 11 11 15 16 15

three food items male μSv/y 33 18−44 25 25 31 39 43 39 female 34 20−48 33 26 33 39 42 37 aFrom May 1, 2012 to March 31, 2013 (approximately one year). Spring (from March to May), summer (from June to August), autumn (from September to November) and winter (from December to January). bDose conversion coefficients are from Internal Dose Easy Calculation Code by ICRP Publ.71. cCommitted effective doses from vegetables, edible wild plants and mushrooms, and fruits due to radiocesium in Kawauchi Village, Fukushima Prefecture. ■ DISCUSSION from Kawauchi Village by gamma spectrometry were 134Cs and 137 134 137 After one year had passed since the FNPP accident, Kawauchi Cs, and the Cs/ Cs values of these samples were around Village was designated as one of the “areas where residents are 0.58, which was a consequence of the relatively early decay of 134 − 134 not permitted to live” and “areas where evacuation orders are Cs (median: 330 (24.2 1777) Bq/kg-dry for Cs and 570 ready to be lifted” within a 20-km radius from the FNPP (Apr (43.4−3011) Bq/kg-dry for 137Cs, Table 1). Thus, the detected 1, 2012).4,21 Short-lived radionuclides are negligible and the radiocesium from these samples was obviously derived from the environmental radioactivity level is generally decreasing in the FNPP accident by the 134Cs/137Cs values, in addition to the Fukushima Prefecture.22 However, almost a year has passed detection of 134Cs itself. since the “declaration of the return of residents to their homes” Our previous report showed that the estimated external in Kawauchi Village and 1,163 residents have returned effective doses from artificial radionuclides (radiocesium) (approximately 40%, as of October, 2012) (available in detected in the soil samples from Kawauchi Village were Japanese http://shinsai.kawauchimura.jp/admin/wp-content/ 0.010−3.3 mSv/y (0.0011−0.38 μSv/h) within a 20- to 30- km uploads/2012/11/a362ba70b7945fe740982884561706f8.pdf; radius from the FNPP and 3.7−63.0 mSv/y (0.42−7.2 μSv/h) accessed January 24, 2014). within a 20-km radius from the FNPP on December 19 and 20, In our previous study conducted in December of 2011, the 2011, prior to the return of residents (median: 0.85 (0.40−1.4) 134Cs/137Cs values of the soil samples from Kawauchi Village mSv/y).7,10 Especially, the estimated external effective doses were around 0.80 (median: 2730 (1188−6948) Bq/kg-dry for were extremely low in areas within a 20- to 30-km radius from 134Cs and 3444 (1523−7696) Bq/kg-dry for 137Cs).10 In the the FNPP.10 Current external doses (median: 0.21 (0.012− present study, the artificial radionuclides detected in all samples 0.56) mSv/y) in Kawauchi Village are decreasing when

F dx.doi.org/10.1021/es404534y | Environ. Sci. Technol. XXXX, XXX, XXX−XXX Environmental Science & Technology Article compared to levels just before the residents returned to their the fine size fractions (<2 mm) consisting of clay-sized, silt- homes, although the estimated external effective doses of three sized, and sand-sized soil particles.8,28 Further investigation points (Nos. 11, 14, and 22) were over 1 mSv/y, which is the with detailed conditions is needed. public dose limit (ICRP, 1991) (Table 1).23 The remediation In conclusion, we evaluated current environmental contam- of soil contaminated by artificial radionuclides in Kawauchi ination and external and internal exposure doses derived from Village (such as by removing surface soil) may be extremely the FNPP accident in Kawauchi Village, Fukushima Prefecture. effective, coupled with the decay of artificial radionuclides.24 The present study confirmed that the current external doses are According to the Nuclear Regulation Authority in Japan decreasing despite the distance from the FNPP, compared to (NRA), the environmental radioactivity of areas around the our previous study, and that current internal doses are FNPP is decreasing, compared to levels immediately after the sufficiently low, compared to the public dose limit (1 mSv/y, Accident.25 ICRP, 1991), although radiation exposure potency still exists Following evaluation of the external effective doses from the after the residents returned to their homes. Moreover, the soil samples in Kawauchi Village, in the present study, monitoring system for local foods may work effectively as a risk committed effective doses were estimated from food samples communication tool in Kawauchi Village. Thus, residents who in Kawauchi Village. The internal exposure risk by intake of have not yet returned to their homes might now return. agricultural produce such as vegetables, edible wild plants and However, care should be also taken when consuming foods mushrooms is a subject of concern for residents because harvested from forests in order to avoid unnecessary chronic agriculture is a major industry and approximately 90% of the internal exposure due to artificial radionuclides, such as area of Kawauchi Village is covered in forests. Furthermore, radiocesium, because a certain amount of radiocesium derived edible wild plants including mushrooms are usually ingested by from the FNPP accident is still detected in some soil samples in habit. In the present study, the local accumulation of this area. Moreover, it is necessary that long-term follow-up radiocesium was not confirmed in Kawauchi Village and takes place, including environmental monitoring and counter- radiocesium was not detected in many samples, although measures such as further decontamination and restrictions of comparatively high contamination due to radiocesium (>100 the ingestion of foods for reducing unnecessary radiation Bq/kg) largely existed in the edible wild plants and mushrooms exposure. The case of Kawauchi Village will be the initiative (Table 2). Mushrooms are especially well-known as accumu- model for the return of residents to their homes after the FNPP lators of radiocesium.26 accident. The daily consumption (g/day) of vegetables and fruits contributedtotheresidents’ committed effective doses, ■ AUTHOR INFORMATION although concomitant levels of radiocesium were extremely Corresponding Author 18 low (Table 2, Table 3, and Table 4). In contrast, the *Phone: +81-95-819-7170; fax: +81-95-819-7172; e-mail: radiocesium concentration of edible wild plants and mush- [email protected]. ff rooms, contributed to the committed e ective doses because Notes the excess rate (>100 Bq/kg (%) for radiocesium) against the The authors declare no competing financial interest. standard limit for general foods in edible wild plants and mushrooms and these radiocesium concentrations were higher ■ ACKNOWLEDGMENTS than those of the vegetables and fruits (Table 2 and Table 3). Moreover, the present study suggests that dietary habits This work was supported by the JSPS KAKENHI Grant-in-Aid fi between generations (age) contributed to the committed for Scienti c Research on Innovative Areas Grant Number effective doses, and that the gender gap or the seasonal 25110509. We would also like to thank Mr. Yasuhiro Otsuka, differences did not always contribute (Table 4).18 The Mr. Masashi Shibata, and Mr. Kei Arakawa for their assistance ingestion of the three food items for forty years old and with sample collection. older was higher than average; however, the ingestion for those less than thirty was less.18 Additionally, the ingestion of edible ■ REFERENCES wild plants, mushrooms and fruits with the 20−30 year age (1) The United Nations Scientific Committee on the Effects of group was extremely low (Table 4).18 The present study Atomic Radiation. Annex D. Health effects due to radiation from the Chernobyl accident. Sources and Effects of Ionizing Radiation, suggests that the internal exposure risk of ingesting agricultural ff produce including radiocesium may be extremely low because UNSCEAR 2008 Report Vol. II: E ects, Reports to the General Assembly with Scientific Annexes C, D and E. 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