1
|
Zhang F, Zhong Q, Huang J, Huang D, Du J, Yu T. Continuous southwestward spread of Fukushima-derived 137Cs in the subtropical western North Pacific and its intrusion flux into the South China Sea. J Hazard Mater 2024; 467:133708. [PMID: 38341888 DOI: 10.1016/j.jhazmat.2024.133708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 01/31/2024] [Accepted: 02/01/2024] [Indexed: 02/13/2024]
Abstract
We provide transect profiles of 137Cs and 90Sr along 146.5°E, 136°E and 21°N in the subtropical western North Pacific (WNP) during May 2018. Exploiting the constant global fallout 137Cs/90Sr ratio, we separated Fukushima-derived 137Cs (137CsF) from background 137Cs. At most stations, 137CsF exhibited only one subsurface peak at 300 m depth, corresponding to subtropical mode water (STMW); however, at 25-28°N along 146.5°E and 25-26°N along 136°E, 137CsF exhibited two subsurface peaks, with another peak occurring at 500 m depth, corresponding to lighter central mode water (L-CMW). Temporal changes in 137CsF vertical profiles showed that 137CsF entrained by STMW has recirculated within the western subtropical gyre, while 137CsF entrained by L-CMW has turned southwestward and arrived the western basin in 2018. In the Luzon Strait, the entrance to the South China Sea (SCS), subsurface 137Cs increased since 2013 and peaked in approximately 2018. The estimated amount of 137CsF entering the SCS during 2013-2019 was 0.33 ± 0.10 PBq, equivalent to 1.7-2.2% of total leakage of 137CsF into the ocean. These results enhance our understanding of the protracted spread and fate of 137CsF in the subtropical WNP.
Collapse
Affiliation(s)
- Fule Zhang
- Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China
| | - Qiangqiang Zhong
- Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China
| | - Jiang Huang
- Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China
| | - Dekun Huang
- Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China.
| | - Jinzhou Du
- State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China
| | - Tao Yu
- Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China.
| |
Collapse
|
2
|
Manaka T, Komatsu M, Sakashita W, Imamura N, Hashimoto S, Hirai K, Miura S, Kaneko S, Sakata T, Shinomiya Y. Ten-year trends in vertical distribution of radiocesium in Fukushima forest soils, Japan. J Environ Radioact 2022; 251-252:106967. [PMID: 35930867 DOI: 10.1016/j.jenvrad.2022.106967] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 07/08/2022] [Accepted: 07/12/2022] [Indexed: 06/15/2023]
Abstract
To elucidate interannual changes in the vertical distribution of 137Cs in forest ecosystems contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident, we investigated 137Cs inventories in forest soils (both organic and mineral soil horizons) at 10 sampling plots with different 137Cs deposition levels and dominant species for up to 10 years after the accident. We examined the temporal variation of the 137Cs inventories by depth with exponential regression models (assuming that the transition and partitioning of 137Cs are still active) and exponential offset regression models (assuming a shift to a stable 137Cs distribution, defined as the "quasi-equilibrium steady-state" in the Chernobyl accident). In the organic horizon, the 137Cs inventories were exponentially decreasing, and it might take more time to converge in the quasi-equilibrium steady-state at most plots. In the mineral soil horizon, most of 137Cs was found in the surface layer of the mineral soil horizon (0-5 cm). In this layer, the inventories first increased and then become relatively constant, and the exponential offset model was selected at most plots, suggesting entry into the quasi-equilibrium steady-state over the observation period. Although we also observed exponentially increasing trends in a lower layer (5-10 cm) of the mineral soil horizon, there was no clear increasing or decreasing trend of 137Cs inventory in the deeper mineral soil layers (10-15 and 15-20 cm). Our calculation of the relaxation depth and migration center revealed that downward migration of 137Cs is not significant in terms of the overall 137Cs distribution in the mineral soil horizon over 10 years.
Collapse
Affiliation(s)
- Takuya Manaka
- Department of Forest Soils, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki, 305-8687, Japan.
| | - Masabumi Komatsu
- Department of Mushroom Science and Forest Microbiology, FFPRI, Tsukuba, Ibaraki, 305-8687, Japan; Center for Forest Restoration and Radioecology, FFPRI, Tsukuba, Ibaraki, 305-8687, Japan
| | - Wataru Sakashita
- Department of Forest Soils, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki, 305-8687, Japan; Center for Forest Restoration and Radioecology, FFPRI, Tsukuba, Ibaraki, 305-8687, Japan
| | - Naohiro Imamura
- Department of Forest Soils, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki, 305-8687, Japan
| | - Shoji Hashimoto
- Department of Forest Soils, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki, 305-8687, Japan
| | - Keizo Hirai
- Department of Forest Soils, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki, 305-8687, Japan
| | - Satoru Miura
- Center for Forest Restoration and Radioecology, FFPRI, Tsukuba, Ibaraki, 305-8687, Japan
| | - Shinji Kaneko
- Kansai Research Center, FFPRI, Kyoto, Kyoto, 612-0855, Japan
| | - Tadashi Sakata
- Department of Forest Soils, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki, 305-8687, Japan; Center for Forest Restoration and Radioecology, FFPRI, Tsukuba, Ibaraki, 305-8687, Japan
| | - Yoshiki Shinomiya
- Center for Forest Restoration and Radioecology, FFPRI, Tsukuba, Ibaraki, 305-8687, Japan
| |
Collapse
|
3
|
Kumamoto Y, Aoyama M, Hamajima Y, Inoue M, Nishino S, Kikuchi T, Murata A, Sato K. Fukushima-derived radiocesium in the western subarctic area of the North Pacific Ocean, Bering Sea, and Arctic Ocean in 2019 and 2020. J Environ Radioact 2022; 251-252:106949. [PMID: 35749953 DOI: 10.1016/j.jenvrad.2022.106949] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 06/04/2022] [Accepted: 06/14/2022] [Indexed: 06/15/2023]
Abstract
We measured dissolved radiocesium (134Cs and 137Cs) in surface seawater collected in the western subarctic area of the North Pacific Ocean, Bering Sea, and Arctic Ocean in 2019 and 2020. The radiocesium released from the accident of the Fukushima Dai-ichi nuclear power plant (FNPP1) in 2011 was still observed in these areas (∼2 Bq m-3 decay-corrected to the date of the accident). In 2019/2020, the FNPP1-derived radiocesium concentrations in the Bering Sea and the Chukchi Sea, which is a marginal sea of the Arctic Ocean connecting the Bering Sea to the Arctic Ocean, were within the range of those observed in 2017/2018. On the other hand, the FNPP1-derived radiocesium was detected in the Arctic Ocean farther north of the Chukchi Sea in 2019/2020 for the first time. This was probably derived from the long-range transport of the FNPP1-derived radiocesium from the North Pacific coastal area of Japan to the Arctic Ocean through the Bering Sea during the past decade. The transport of the FNPP1-derived radiocesium from the Bering Sea to the western subarctic area in 2019/2020 is not clear, which implies the retainment of the FNPP1-derived radiocesium within the Bering Sea.
Collapse
Affiliation(s)
- Yuichiro Kumamoto
- Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa, 2370061, Japan.
| | - Michio Aoyama
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, 3058577, Japan; Institute of Environmental Radioactivity, Fukushima University, Fukushima, 9601296, Japan.
| | - Yasunori Hamajima
- Low Level Radioactivity Laboratory, Kanazawa University, Wake, Nomi, Ishikawa, 9231224, Japan.
| | - Mutsuo Inoue
- Low Level Radioactivity Laboratory, Kanazawa University, Wake, Nomi, Ishikawa, 9231224, Japan.
| | - Shigeto Nishino
- Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa, 2370061, Japan.
| | - Takashi Kikuchi
- Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa, 2370061, Japan.
| | - Akihiko Murata
- Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa, 2370061, Japan.
| | - Kazutoshi Sato
- Faculty of Engineering, Kitami Institute of Technology, Kitami, 0908507, Japan.
| |
Collapse
|
4
|
Misonou T, Nakanishi T, Tsuruta T, Shiribiki T, Sanada Y. Migration processes of radioactive cesium in the Fukushima nearshore area: Impacts of riverine input and resuspension. Mar Pollut Bull 2022; 178:113597. [PMID: 35366555 DOI: 10.1016/j.marpolbul.2022.113597] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Revised: 03/16/2022] [Accepted: 03/20/2022] [Indexed: 06/14/2023]
Abstract
It is essential to evaluate secondary migration caused by riverine input and resuspension from seabed sediments to estimate the future distribution of radioactive cesium (137Cs) in the coastal area off Fukushima Prefecture. In particular, the inflow from rivers cannot be ignored because most of the 137Cs inflow from rivers is deposited on the coast without elute into seawater. Two mooring systems were installed near the Ukedo River's mouth (Fukushima Prefecture) from February 2017 to February 2018. The first contained a sediment trap system, collecting sinking particles during the period. The second comprised a turbidity sensor and a current sensor. The contribution of resuspension and inflow from the river to the mass flux was quantitatively evaluated using multiple regression equations. The results showed that resuspension caused 79%-83% of secondary 137Cs migration in nearshore areas, whereas the influence of riverine 137Cs input on the sediment was only 7% per year.
Collapse
Affiliation(s)
- Toshiharu Misonou
- Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 45-169, Kaihama-sukakeba, Minamisoma, Fukushima 975-0036, Japan.
| | - Takahiro Nakanishi
- Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 45-169, Kaihama-sukakeba, Minamisoma, Fukushima 975-0036, Japan
| | - Tadahiko Tsuruta
- Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 45-169, Kaihama-sukakeba, Minamisoma, Fukushima 975-0036, Japan
| | - Takehiko Shiribiki
- Sanyo Techno Marine, 1-3-17, Horidomecho, Nihonbashi, Chuouku, Tokyo 103-0012, Japan
| | - Yukihisa Sanada
- Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 45-169, Kaihama-sukakeba, Minamisoma, Fukushima 975-0036, Japan
| |
Collapse
|
5
|
Wang F, Men W, Huang J, Yu T, He J, Yu W, Li Y. Fukushima-derived radiocesium in the waters of the Northwest Pacific Ocean in the winter of 2011. Mar Pollut Bull 2022; 176:113465. [PMID: 35245875 DOI: 10.1016/j.marpolbul.2022.113465] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 02/10/2022] [Accepted: 02/11/2022] [Indexed: 06/14/2023]
Abstract
To understand the transport of Fukushima Dai-ichi Nuclear Power Plant Accident (FDNPPA)-derived nuclear contaminated water, which will be discharged into the Pacific Ocean in the future, the distributions of 134Cs and 137Cs in seawater in the public areas east of Japan in winter 2011 were reported in this study. The ranges of 134Cs and 137Cs activities were <MDA (Minimum Detectable Activity) -68.9 Bq/m3 and 1.3-85.9 Bq/m3, respectively. The average decay corrected FDNPPA-derived 134Cs/137Cs activity ratio was 0.97. The FDNPPA-derived radiocesium existed in the seawater at a relatively high level at most stations. The 134Cs and 137Cs activities were comparable throughout the upper 50 m at each station. The FDNPPA-derived radiocesium was mainly distributed north of 36.5°N due to the boundary formed by the Kuroshio Extension. The temporal variations of FDNPPA-derived 134Cs and 137Cs suggested that their environmental half-lives in the study area were 61 d and 63 d in the period of June 2011 to June 2012, respectively.
Collapse
Affiliation(s)
- Fenfen Wang
- The Laboratory of Marine Ecological and Environmental Early Warning and Monitoring, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen 361005, China
| | - Wu Men
- The Laboratory of Marine Ecological and Environmental Early Warning and Monitoring, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen 361005, China.
| | - Jiang Huang
- The Laboratory of Marine Ecological and Environmental Early Warning and Monitoring, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen 361005, China
| | - Tao Yu
- The Laboratory of Marine Ecological and Environmental Early Warning and Monitoring, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen 361005, China
| | - Jianhua He
- The Laboratory of Marine Ecological and Environmental Early Warning and Monitoring, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen 361005, China
| | - Wen Yu
- The Laboratory of Marine Ecological and Environmental Early Warning and Monitoring, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen 361005, China
| | - Yiliang Li
- The Laboratory of Marine Ecological and Environmental Early Warning and Monitoring, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen 361005, China
| |
Collapse
|
6
|
Chaif H, Coppin F, Bahi A, Garcia-Sanchez L. Influence of non-equilibrium sorption on the vertical migration of 137Cs in forest mineral soils of Fukushima Prefecture. J Environ Radioact 2021; 232:106567. [PMID: 33689934 DOI: 10.1016/j.jenvrad.2021.106567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 02/12/2021] [Accepted: 02/21/2021] [Indexed: 06/12/2023]
Abstract
Sorption hypotheses and models are required for the prediction of 137Cs migration in soils contaminated after nuclear reactor accidents and nuclear weapons tests. In assessment models, the Kd (distribution coefficient) hypothesis for sorption, which assumes that sorption is instantaneous, linear and reversible, has often been coupled with the convection-diffusion equation (CDE) to model 137Cs migration. However, it fails to describe 137Cs migration velocities which often decrease with time. Alternative equilibrium-kinetic (EK) hypotheses of 137Cs sorption/desorption have been suggested by laboratory experiments but have not been fully validated in field conditions. This work addressed the influence and magnitude of non-equilibrium 137Cs sorption in field conditions by reinterpreting, with an inverse approach, series of 137Cs profiles measured in mineral soils of forest plots located in Fukushima Prefecture (2013-2018). Our results show that the inclusion of non-equilibrium sorption significantly improves, compared to the equilibrium hypothesis, the realism of simulated 137Cs profiles. Fitted sorption parameters suggest a fast sorption kinetic (half-time of 1-7 h) and a pseudo-irreversible desorption rate (half-time of 3.2 × 100-3.4 × 106 years), whereas equilibrium sorption (4.0 × 10-3 L kg-1 on average) only affects a negligible portion of 137Cs inventory. By June 2011, such EK parameters fitted on our plots realistically reproduced profiles measured in the same forest study site (Takahashi et al., 2015). Predictive modeling of 137Cs profiles in soil suggests a strong persistence of the surface 137Cs contamination by 2030, with exponential profiles consistent with those reported after the Chernobyl accident. This study demonstrates that hypotheses and parameters of 137Cs sorption can be partially inferred from in situ measurements. However, further experiments in controlled conditions are required to better estimate the sorption parameters and to identify the processes behind non-equilibrium sorption.
Collapse
Affiliation(s)
- Hamza Chaif
- Institute of Radiological Protection and Nuclear Safety (IRSN), PSE-ENV, SRTE, LR2T, CE Cadarache, 13115, Saint Paul les Durance Cedex, France.
| | - Frédéric Coppin
- Institute of Radiological Protection and Nuclear Safety (IRSN), PSE-ENV, SRTE, LR2T, CE Cadarache, 13115, Saint Paul les Durance Cedex, France.
| | - Aya Bahi
- Institute of Radiological Protection and Nuclear Safety (IRSN), PSE-ENV, SRTE, LR2T, CE Cadarache, 13115, Saint Paul les Durance Cedex, France.
| | - Laurent Garcia-Sanchez
- Institute of Radiological Protection and Nuclear Safety (IRSN), PSE-ENV, SRTE, LR2T, CE Cadarache, 13115, Saint Paul les Durance Cedex, France.
| |
Collapse
|
7
|
Matsuura T. Assessment of potentially reusable edible wild plant and mushroom gathering sites in eastern Fukushima based on external radiation dose. J Environ Radioact 2021; 227:106465. [PMID: 33271395 DOI: 10.1016/j.jenvrad.2020.106465] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 10/31/2020] [Accepted: 11/15/2020] [Indexed: 06/12/2023]
Abstract
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.
Collapse
Affiliation(s)
- Toshiya Matsuura
- Tohoku Research Center, Forestry and Forest Products Research Institute, 92-25 Nabeyashiki, Shimokuriyagawa, Morioka, Iwate, 020-0123, Japan.
| |
Collapse
|
8
|
Ikenoue T, Kusakabe M, Yamada M, Oikawa S, Misonoo J. Temporal variation of iodine-129 concentrations in kelps (Saccharina) from coastal waters off northern Japan. Mar Pollut Bull 2020; 161:111775. [PMID: 33122149 DOI: 10.1016/j.marpolbul.2020.111775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 10/15/2020] [Accepted: 10/15/2020] [Indexed: 06/11/2023]
Abstract
Concentrations of 129I and 127I in kelps (Saccharina) collected from coastal waters off northern Japan were monitored from 2007 to 2019. During the 2007-2008 test operation of the Rokkasho nuclear fuel reprocessing plant, 129I discharge from the plant increased, and the 129I concentration and 129I/127I atom ratio in the kelps reached maxima of 42 μBq/g-dry and 264 × 10-11, respectively. By 2009, both had decreased by one order of magnitude. After the Fukushima Dai-ichi Nuclear Power Plant accident in 2011, the 129I concentration and 129I/127I atom ratio in the kelps increased to 2.24 μBq/g-dry and 11.6 × 10-11, respectively. After 2012, the ratio in kelps decreased to (2.1-8.9) × 10-11, which is almost the same as the seawater value off Aomori Prefecture before the test operation. The 129I/127I atom ratio in kelps thus represents the ambient seawater ratio during the growth period of the kelps.
Collapse
Affiliation(s)
- Takahito Ikenoue
- Central Laboratory, Marine Ecology Research Institute, 300 Iwawada, Onjuku-machi, Isumi-gun, Chiba 299-5105, Japan.
| | - Masashi Kusakabe
- Central Laboratory, Marine Ecology Research Institute, 300 Iwawada, Onjuku-machi, Isumi-gun, Chiba 299-5105, Japan
| | - Masatoshi Yamada
- Central Laboratory, Marine Ecology Research Institute, 300 Iwawada, Onjuku-machi, Isumi-gun, Chiba 299-5105, Japan
| | - Shinji Oikawa
- Central Laboratory, Marine Ecology Research Institute, 300 Iwawada, Onjuku-machi, Isumi-gun, Chiba 299-5105, Japan
| | - Jun Misonoo
- Head Office, Marine Ecology Research Institute, 7F Towa-Edogawabashi Building, 347 Yamabuki-cho, Shinjuku, Tokyo 162-0801, Japan
| |
Collapse
|
9
|
Men W, Wang F, Yu W, He J, Lin F, Deng F. Impact of the Fukushima Dai-ichi Nuclear Power Plant Accident on the neon flying squids in the Northwest Pacific from 2011 to 2018. Environ Pollut 2020; 264:114647. [PMID: 32380393 DOI: 10.1016/j.envpol.2020.114647] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Revised: 04/18/2020] [Accepted: 04/20/2020] [Indexed: 06/11/2023]
Abstract
Following nine years since the Fukushima Dai-ichi Nuclear Power Plant Acciden (FDNPPA), it might be the time to draw a much clearer conclusion for the impact of FDNPPA on marine biota. In this work, the evolution of the FDNPPA derived 134Cs, 137Cs and 110mAg in the neon flying squids in the Northwest Pacific from 2011 to 2018 were studied. The background level of 137Cs in neon flying squids (<0.10 Bq/kgfresh weight with the average of 0.017 Bq/kgfresh weight) before FDNPPA were estimated. The radioactive levels of 134Cs, 137Cs and 110mAg in neon flying squids decreased with time. 134Cs and 110mAg decreased at the half-lives of 7.6 months and 5.7 months at the population level, respectively. After May 2014, 134Cs and 110mAg cannot be detected and 137Cs activities returned to the background level before FDNPPA. BCFs of cesium isotopes (3.7-17.7 with the average of 10.8) and 110mAg (∼7 × 104) for neon flying squids were estimated. The amount of 110mAg released into the Northwest Pacific (∼20-∼26 TBq) were firstly calculated using a 134Cs/110mAgactivity ratio method. Radiation dose assessment demonstrated that it was far from causing radiation harm to neon flying squids in the open ocean of Northwest Pacific and humans who ingested these neon flying squids.
Collapse
Affiliation(s)
- Wu Men
- Laboratory of Marine Isotopic Technology and Environmental Risk Assessment, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen, 361005, China.
| | - Fenfen Wang
- Laboratory of Marine Isotopic Technology and Environmental Risk Assessment, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen, 361005, China
| | - Wen Yu
- Laboratory of Marine Isotopic Technology and Environmental Risk Assessment, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen, 361005, China
| | - Jianhua He
- Laboratory of Marine Isotopic Technology and Environmental Risk Assessment, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen, 361005, China
| | - Feng Lin
- Laboratory of Marine Isotopic Technology and Environmental Risk Assessment, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen, 361005, China
| | - Fangfang Deng
- Laboratory of Marine Isotopic Technology and Environmental Risk Assessment, Third Institute of Oceanography, Ministry of Natural Resources, 184 Daxue Road, Xiamen, 361005, China
| |
Collapse
|
10
|
Tsumune D, Tsubono T, Misumi K, Tateda Y, Toyoda Y, Onda Y, Aoyama M. Impacts of direct release and river discharge on oceanic 137Cs derived from the Fukushima Dai-ichi Nuclear Power Plant accident. J Environ Radioact 2020; 214-215:106173. [PMID: 32063291 DOI: 10.1016/j.jenvrad.2020.106173] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 01/16/2020] [Accepted: 01/16/2020] [Indexed: 06/10/2023]
Abstract
A series of accidents at the Fukushima Dai-ichi Nuclear Power Plant (1F NPP) following the Great East Japan Earthquake and tsunami of 11 March 2011 resulted in the release of radioactive materials to the ocean. We used the Regional Ocean Model System (ROMS) to simulate the 137Cs activity in the oceanic area off Fukushima, with the sources of radioactivity being direct release, atmospheric deposition, river discharge, and inflow across the domain boundary. The direct release rate of 137Cs after the accident until the end of 2016 was estimated by comparing simulated results with measured 137Cs activities adjacent to the 1F NPP. River discharge rates of 137Cs were estimated by multiplying simulated river flow rates by the dissolved 137Cs activities, which were estimated by an empirical function. Inflow of 137Cs across the domain boundary was set according to the results of a North Pacific Ocean model. Because the spatiotemporal variability of 137Cs activity was large, the simulated results were compared with the annual averaged observed 137Cs activity distribution. Normalized annual averaged 137Cs activity distributions in the regional ocean were similar for each year from 2013 to 2016. This result suggests that the annual averaged distribution is predictable. Simulated 137Cs activity attributable to direct release was in good agreement with measurement data from the coastal zone adjacent to the 1F NPP. Comparison of the simulated results with measured activity in the offshore area indicated that the simulation slightly underestimated the activity attributable to inflow across the domain boundary. This result suggests that recirculation of subducted 137Cs to the surface layer was underestimated by the North Pacific model. During the study period, the effect of river discharge on oceanic 137Cs activity was small compared to the effect of directly released 137Cs.
Collapse
Affiliation(s)
- Daisuke Tsumune
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646, Abiko, 270-1194, Japan.
| | - Takaki Tsubono
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646, Abiko, 270-1194, Japan
| | - Kazuhiro Misumi
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646, Abiko, 270-1194, Japan
| | - Yutaka Tateda
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646, Abiko, 270-1194, Japan
| | - Yasushi Toyoda
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, 1646, Abiko, 270-1194, Japan
| | - Yuichi Onda
- Faculty of Life and Environmental Sciences, Univ. of Tsukuba, 305-8577, Japan
| | - Michio Aoyama
- Faculty of Life and Environmental Sciences, Univ. of Tsukuba, 305-8577, Japan
| |
Collapse
|
11
|
Andoh M, Mikami S, Tsuda S, Yoshida T, Matsuda N, Saito K. Decreasing trend of ambient dose equivalent rates over a wide area in eastern Japan until 2016 evaluated by car-borne surveys using KURAMA systems. J Environ Radioact 2019; 210:105813. [PMID: 30348530 DOI: 10.1016/j.jenvrad.2018.09.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 05/29/2018] [Accepted: 07/11/2018] [Indexed: 06/08/2023]
Abstract
As part of the investigation of the distribution of ambient dose equivalent rates around the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), car-borne surveys using Kyoto University RAdiation MApping (KURAMA) systems have been conducted over a wide area in eastern Japan since 2011. The enormous volume of measurement data collected until 2016, including those until 2012 which were reported in the previous paper, was analyzed, and dependencies of the decreasing trend of the dose rates in regions within 80 km of the FDNPP on land-use categories, evacuation order areas and magnitude of the dose rates were examined. The air dose rates within 80 km of the FDNPP tended to decrease considerably with respect to the physical decay of radiocaesium. The decrease of the dose rate in the "forest" was slower than its decrease in other regions, while that in "urban area" was the fastest. The decrease in the air dose rate from 2011 was the fastest outside the evacuation order area until 2015, and it was the slowest in the "difficult-to-return zone". However, the decreasing trend starting from 2013 showed that the decrease in the "zone in preparation for the lifting of the evacuation order" and in the "residence restriction area" was the fastest. It was found that the air dose rates decreased depending on the magnitude of the dose rates and elapsed time from the FDNPP accident, i.e. the decrease in air dose rates in areas with relatively low dose ranges (such as 0.2-0.5 μSv/h) was the largest during a period relatively early after the accident, and the decreasing rate in the dose rate ranges of 1.9-3.8 and 3.8-9.5 μSv/h were the fastest after 2013. The averaged ratios were analyzed to obtain the ecological half-lives of the fast and slow decay components, and those in whole area within 80 km of FDNPP were estimated to be 0.44 ± 0.05 y and 6.7 ± 1 y, respectively. The ecological half-lives with respect to the land use categories, evacuation order areas and magnitude of the dose rates were also evaluated. The decrease in the dose rates obtained by the car-borne survey was larger than that obtained on flat ground with few disturbances using the NaI(Tl) survey meter during approximately 1.5 y after the FDNPP accident. Thereafter, the difference of decreasing tendencies in the air dose rates between both the measurements was negligibly small, with the ratio of dose rates by the car-borne survey to those by the fixed-point measurement of 0.72-0.77.
Collapse
Affiliation(s)
- Masaki Andoh
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan.
| | - Satoshi Mikami
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| | - Shuichi Tsuda
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| | - Tadayoshi Yoshida
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| | - Norihiro Matsuda
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| | - Kimiaki Saito
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| |
Collapse
|
12
|
Kato H, Onda Y, Gao X, Sanada Y, Saito K. Reconstruction of a Fukushima accident-derived radiocesium fallout map for environmental transfer studies. J Environ Radioact 2019; 210:105996. [PMID: 31262609 DOI: 10.1016/j.jenvrad.2019.105996] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Revised: 06/05/2019] [Accepted: 06/14/2019] [Indexed: 06/09/2023]
Abstract
Ascertaining the initial amount of accidently released radiocesium is fundamental for determining the extent of radioactive contamination following nuclear accidents, and is of key importance to environmental transfer models. A series of the airborne monitoring surveys of radioactivity have conducted by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), and provide basic information on radioactive contamination following the accident. However, there are no clear guidelines regarding the selection of airborne monitoring survey results for estimating the initial fallout input in studies of the environmental transfer of radiocesium. This study reconstructed a fallout map of Fukushima accident-derived radiocesium based on a comparison of the radiocesium deposition densities (Dl) derived from the third and fifth airborne monitoring surveys. The Dl derived from the fifth airborne monitoring survey were adjusted for variation in the measured radioactivity associated with the influence of radioactive decay, natural weathering processes, variation in the calibration procedure, and other, undefined mechanisms. The calibrated deposition density of the fifth airborne monitoring survey for each land use type (A'5th*l) were used to establish the initial fallout map in the East Japan area. Furthermore, the airborne monitoring surveys which were independently conducted in each prefecture area were used to complement the lack of data in the South Kanto region and the mountainous area in the North Kanto region due to snow cover during the measurement period of the fifth airborne monitoring survey. The reconstructed initial fallout map of the Fukushima accident derived 137Cs was opened to the public via the database of the Center for Research in Isotopes of Environmental Dynamics, University of Tsukuba, Japan (www.ied.tsukuba.ac.jp/∼fukushimafallout/). Finally, the total atmospheric deposition of Fukushima Dai-ichi Nuclear Power Plant accident-derived radiocesium onto each prefecture and land uses was estimated based on the reconstructed map in this study.
Collapse
Affiliation(s)
- Hiroaki Kato
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, 305-0006, Japan.
| | - Yuichi Onda
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, 305-0006, Japan
| | - Xiang Gao
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, 305-0006, Japan
| | - Yukihisa Sanada
- Fukushima Remote Monitoring Group, Fukushima Environmental Safety Center, Japan Atomic Energy Agency, Minami-soma, Fukushima, 975-0036, Japan
| | - Kimiaki Saito
- Fukushima Environmental Safety Center, Japan Atomic Energy Agency, Chiyoda-ku, Tokyo, 100-8577, Japan
| |
Collapse
|
13
|
Kato H, Onda Y, Yamaguchi T. Temporal changes of the ambient dose rate in the forest environments of Fukushima Prefecture following the Fukushima reactor accident. J Environ Radioact 2019; 210:106058. [PMID: 31630855 DOI: 10.1016/j.jenvrad.2019.106058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Approximately 70% of the total land area affected by the fallout from the Fukushima accident is forested, and therefore monitoring of the ambient dose rate in forest environments is essential to ensure that the population and natural habitats of these areas are protected from radiological hazards. However, there are little available data on the ambient dose rate for forest environments. This study investigated temporal changes in the ambient dose rate in different forest environments of Fukushima Prefecture. We conducted repeated measurements of the ambient dose rate in 2014 and 2016 at the same measurement points as those used by the Ministry of Agriculture, Fishery and Forestry of Japan (MAFF) in 2011. The measurements revealed that the decreasing trend in the ambient dose rate varied among the different forest types and time periods. The ambient dose rate in EGC decreased slower than that induced by the physical decay of radiocesium for the period of 2011-2014. However, such slow declining trend of ambient dose rate was likely followed by quick reduction during the following years (2014-2016 and 2011-2016). On the other hand, in MBL and DBF forests, the ambient dose rate decreased 10-20% faster than that induced solely by physical decay of radiocesium for the observation period 2011-2016.
Collapse
Affiliation(s)
- Hiroaki Kato
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan.
| | - Yuichi Onda
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| | - Toshiro Yamaguchi
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| |
Collapse
|
14
|
Yoshida-Ohuchi H, Matsuda N, Saito K. Review of reduction factors by buildings for gamma radiation from radiocaesium deposited on the ground due to fallout. J Environ Radioact 2019; 210:105810. [PMID: 30340872 DOI: 10.1016/j.jenvrad.2018.09.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 02/02/2018] [Accepted: 02/11/2018] [Indexed: 06/08/2023]
Abstract
In order to estimate residents' external dose due to radionuclide exposure resulting from fallout deposit on the ground, the shielding and dose reduction effects provided by structures such as houses and workplaces are taken into account as most individuals spend a large portion of their time indoors. Many works on both calculation and measurement for European and American settlements have been reported and factors such as, shielding factors, protection factors, reduction factors, and location factors have been determined. However, measurement data for Japanese settlements are lacking. Thus, the Japanese government used reduction factors given in the International Atomic Energy Agency documents from American and European settlements when Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident occurred. The United Nations Scientific Committee on the Effects of Atomic Radiation used location factors from European settlements for the same reason. Soon after the FDNPP accident, several measurements and calculations were performed to obtain specific reduction factors for Japanese settlements due to this lack of data. This research reviews previous studies that determined factors such as, shielding factors, protection factors, reduction factors, and location factors and summarizes specific results for Japan. We discuss the issues in determining these factors and in applying them to estimate indoor dose. The contribution of surface contamination to the indoor ambient dose equivalent rate is also discussed.
Collapse
Affiliation(s)
- Hiroko Yoshida-Ohuchi
- Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-ku, Sendai, Miyagi, 980-8578, Japan.
| | - Norihiro Matsuda
- Fukushima Environmental Safety Center, Japan Atomic Energy Agency, 2-2-2 Uchisaiwai-cho, Chiyoda, Tokyo, 100-8577, Japan.
| | - Kimiaki Saito
- Fukushima Environmental Safety Center, Japan Atomic Energy Agency, 2-2-2 Uchisaiwai-cho, Chiyoda, Tokyo, 100-8577, Japan.
| |
Collapse
|
15
|
Kato H, Onda Y, Saidin ZH, Sakashita W, Hisadome K, Loffredo N. Six-year monitoring study of radiocesium transfer in forest environments following the Fukushima nuclear power plant accident. J Environ Radioact 2019; 210:105817. [PMID: 30236975 DOI: 10.1016/j.jenvrad.2018.09.015] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 07/25/2018] [Accepted: 09/09/2018] [Indexed: 06/08/2023]
Abstract
The study investigated temporal changes in the 137Cs concentrations in vegetal and hydrological samples collected from various forests in Yamakiya District, Kawamata Town of Fukushima prefecture over six years following the Fukushima Dai-ichi nuclear power plant accident. Cesium-137 was detected in all forest environmental samples. However, the concentration in most samples decreased exponentially with time. The 137Cs concentrations in throughfall samples exhibited a double-exponential decreasing trend with time. Temporal changes in the 137Cs concentration in vegetal samples and stemflow were approximated by using a single-exponential equation. A comparison of the decline coefficient for the latter observation period (>2 y since the accident) revealed that the declining trend of 137Cs concentrations varied between foliage and the outer barks of the Japanese cedar and Japanese konara oak trees. The 137Cs concentration in cedar needles decreased exponentially while that in konara oak leaves was constant over the last six years. Conversely, the declining trend of 137Cs concentration in the outer bark of konara oak exceeded that of cedar. The results suggested that self-decontamination processes and internal recycling of 137Cs varied among tree species and different tree parts. The results indicated that the leaching of 137Cs in the throughfall in Japanese cedar was dependent on the 137Cs concentration in needles. However, a comparison of 137Cs concentrations in vegetal and hydrological samples from each sampling year showed that the leaching rate decreased with time. Conversely, the 137Cs concentrations in the stemflow were independent of the concentrations in the outer bark. The declining trend of 137Cs concentrations in litterfall (λ: 0.31-0.33 y-1) was similar to that of the mean of new/old needles (λ: 0.26-0.33 y-1) for cedar stands. With respect to the hydrological components, the 137Cs concentration in the stemflow (λ: 0.32-0.33 y-1) decreased at a slightly slower rate than that in the throughfall (λ: 0.36-0.54 y-1) for the cedar forest. The decline coefficients of 137Cs concentration in the aforementioned types of hydrological components slightly exceeded that for the vegetal samples. The results suggest that monitoring of 137Cs concentrations in hydrological components and vegetal samples can aid in further understanding the leaching mechanisms of 137Cs from trees to rainwater.
Collapse
Affiliation(s)
- Hiroaki Kato
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan.
| | - Yuichi Onda
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| | - Zul Hilmi Saidin
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| | - Wataru Sakashita
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| | | | - Nicolas Loffredo
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| |
Collapse
|
16
|
Nakanishi T, Sakuma K. Trend of 137Cs concentration in river water in the medium term and future following the Fukushima nuclear accident. Chemosphere 2019; 215:272-279. [PMID: 30317098 DOI: 10.1016/j.chemosphere.2018.10.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Revised: 10/02/2018] [Accepted: 10/04/2018] [Indexed: 06/08/2023]
Abstract
It is a critical to examine the migration behavior of radiocesium derived from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in river systems to predict the future contamination status and propose effective countermeasures to reduce exposure. We conducted a three-year-long observation (April 2015-March 2018) of the 137Cs concentration in two rivers which located surrounding the FDNPP. The result revealed a declining trend for the dissolved and particulate 137Cs concentration in river water from four to seven years after the FDNPP accident. The dissolved and particulate 137Cs concentrations for both rivers had similar temporal patterns and showed declining trends with time. However, the dissolved 137Cs concentration had longer half-life than the particulate 137Cs concentration and large seasonal variations related to water temperature. The environmental half-life for the dissolved 137Cs concentration was longer than previous reported values within three years after the accident, suggesting that the declining trend for the dissolved 137Cs concentration is gradually decreasing with time. The temperature dependency of the dissolved 137Cs concentration became weaker year by year. From the D10 equation we proposed, the dissolved 137Cs concentration will likely remain at the same level for several decades. The results of the present study promote our understanding of both the medium- and long-term impacts of the FDNPP accident on river systems.
Collapse
Affiliation(s)
- Takahiro Nakanishi
- Fukushima Environmental Safety Center, Japan Atomic Energy Agency, Fukushima, 975-0036, Japan.
| | - Kazuyuki Sakuma
- Fukushima Environmental Safety Center, Japan Atomic Energy Agency, Fukushima, 975-0036, Japan
| |
Collapse
|
17
|
Inoue M, Morokado T, Fujimoto K, Miki S, Kofuji H, Isoda Y, Nagao S. Vertical profiles of Fukushima Dai-ichi NPP-derived radiocesium concentrations in the waters of the southwestern Okhotsk Sea (2011-2017). J Environ Radioact 2018; 192:580-586. [PMID: 29724459 DOI: 10.1016/j.jenvrad.2018.04.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 04/05/2018] [Accepted: 04/22/2018] [Indexed: 06/08/2023]
Abstract
We examined the vertical 134Cs and 137Cs concentration profiles in the southwestern Okhotsk Sea in 2011, 2013, and 2017. In June 2011, atmospheric deposition-derived 134Cs from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) was detected at depths of 0-200 m (0.06-0.6 mBq/L). In July 2013, 134Cs detected at depths of 100-200 m (∼0.05 mBq/L) was ascribed to the transport of low-level 134Cs-contaminated water and/or the convection of radioactive depositions (<0.03 mBq/L at depths of 0-50 m). In July 2017, 134Cs was detected in water samples at depths above 300 m (0.03-0.05 mBq/L), and the inventory, decay-corrected to the FDNPP accident date, exhibited its maximum value (85 Bq/m2) during this period. Combining temperature-salinity data with the concentrations of global fallout-derived 137Cs led to a plausible explanation for this observation, which is a consequence of re-entry of FDNPP-derived radiocesium through the Kuril Strait from the northwestern North Pacific Ocean to the Okhotsk Sea and subsequent mixing with the south Okhotsk subsurface layer until 2017.
Collapse
Affiliation(s)
- Mutsuo Inoue
- Low Level Radioactivity Laboratory, Kanazawa University, Wake O-24, Nomi, Ishikawa, 923-1224, Japan.
| | - Toshiki Morokado
- Low Level Radioactivity Laboratory, Kanazawa University, Wake O-24, Nomi, Ishikawa, 923-1224, Japan
| | - Ken Fujimoto
- National Research Institute of Fisheries Science, Japan Fisheries Research and Education Agency, 2-12-4, Fukuura, Kanazawa, Yokohama, 236-8648, Japan
| | - Shizuho Miki
- National Research Institute of Fisheries Science, Japan Fisheries Research and Education Agency, 2-12-4, Fukuura, Kanazawa, Yokohama, 236-8648, Japan
| | - Hisaki Kofuji
- Low Level Radioactivity Laboratory, Kanazawa University, Wake O-24, Nomi, Ishikawa, 923-1224, Japan
| | - Yutaka Isoda
- Graduate School of Fisheries Sciences, Hokkaido University, Minato-cho, Hakodate, 041-8611, Japan
| | - Seiya Nagao
- Low Level Radioactivity Laboratory, Kanazawa University, Wake O-24, Nomi, Ishikawa, 923-1224, Japan
| |
Collapse
|
18
|
Andoh M, Mikami S, Tsuda S, Yoshida T, Matsuda N, Saito K. Decreasing trend of ambient dose equivalent rates over a wide area in eastern Japan until 2016 evaluated by car-borne surveys using KURAMA systems. J Environ Radioact 2018; 192:385-398. [PMID: 30048901 DOI: 10.1016/j.jenvrad.2018.07.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 05/29/2018] [Accepted: 07/11/2018] [Indexed: 06/08/2023]
Abstract
As part of the investigation of the distribution of ambient dose equivalent rates around the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), car-borne surveys using Kyoto University RAdiation MApping (KURAMA) systems have been conducted over a wide area in eastern Japan since 2011. The enormous volume of measurement data collected until 2016, including those until 2012 which were reported in the previous paper, was analyzed, and dependencies of the decreasing trend of the dose rates in regions within 80 km of the FDNPP on land-use categories, evacuation order areas and magnitude of the dose rates were examined. The air dose rates within 80 km of the FDNPP tended to decrease considerably with respect to the physical decay of radiocaesium. The decrease of the dose rate in the "forest" was slower than its decrease in other regions, while that in "urban area" was the fastest. The decrease in the air dose rate from 2011 was the fastest outside the evacuation order area until 2015, and it was the slowest in the "difficult-to-return zone". However, the decreasing trend starting from 2013 showed that the decrease in the "zone in preparation for the lifting of the evacuation order" and in the "residence restriction area" was the fastest. It was found that the air dose rates decreased depending on the magnitude of the dose rates and elapsed time from the FDNPP accident, i.e. the decrease in air dose rates in areas with relatively low dose ranges (such as 0.2-0.5 μSv/h) was the largest during a period relatively early after the accident, and the decreasing rate in the dose rate ranges of 1.9-3.8 and 3.8-9.5 μSv/h were the fastest after 2013. The averaged ratios were analyzed to obtain the ecological half-lives of the fast and slow decay components, and those in whole area within 80 km of FDNPP were estimated to be 0.44 ± 0.05 y and 6.7 ± 1 y, respectively. The ecological half-lives with respect to the land use categories, evacuation order areas and magnitude of the dose rates were also evaluated. The decrease in the dose rates obtained by the car-borne survey was larger than that obtained on flat ground with few disturbances using the NaI(Tl) survey meter during approximately 1.5 y after the FDNPP accident. Thereafter, the difference of decreasing tendencies in the air dose rates between both the measurements was negligibly small, with the ratio of dose rates by the car-borne survey to those by the fixed-point measurement of 0.72-0.77.
Collapse
Affiliation(s)
- Masaki Andoh
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan.
| | - Satoshi Mikami
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| | - Shuichi Tsuda
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| | - Tadayoshi Yoshida
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| | - Norihiro Matsuda
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| | - Kimiaki Saito
- Japan Atomic Energy Agency, 11601-13 Nishi-jusanbugyo, Hitachinaka-city, Ibaraki 319-1206, Japan
| |
Collapse
|
19
|
Kato H, Onda Y, Yamaguchi T. Temporal changes of the ambient dose rate in the forest environments of Fukushima Prefecture following the Fukushima reactor accident. J Environ Radioact 2018; 193-194:20-26. [PMID: 30179758 DOI: 10.1016/j.jenvrad.2018.08.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Revised: 05/30/2018] [Accepted: 08/13/2018] [Indexed: 06/08/2023]
Abstract
Approximately 70% of the total land area affected by the fallout from the Fukushima accident is forested, and therefore monitoring of the ambient dose rate in forest environments is essential to ensure that the population and natural habitats of these areas are protected from radiological hazards. However, there are little available data on the ambient dose rate for forest environments. This study investigated temporal changes in the ambient dose rate in different forest environments of Fukushima Prefecture. We conducted repeated measurements of the ambient dose rate in 2014 and 2016 at the same measurement points as those used by the Ministry of Agriculture, Fishery and Forestry of Japan (MAFF) in 2011. The measurements revealed that the decreasing trend in the ambient dose rate varied among the different forest types and time periods. The ambient dose rate in EGC decreased slower than that induced by the physical decay of radiocesium for the period of 2011-2014. However, such slow declining trend of ambient dose rate was likely followed by quick reduction during the following years (2014-2016 and 2011-2016). On the other hand, in MBL and DBF forests, the ambient dose rate decreased 10-20% faster than that induced solely by physical decay of radiocesium for the observation period 2011-2016.
Collapse
Affiliation(s)
- Hiroaki Kato
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan.
| | - Yuichi Onda
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| | - Toshiro Yamaguchi
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| |
Collapse
|
20
|
Yoshida-Ohuchi H, Matsuda N, Saito K. Review of reduction factors by buildings for gamma radiation from radiocaesium deposited on the ground due to fallout. J Environ Radioact 2018; 187:32-39. [PMID: 29494937 DOI: 10.1016/j.jenvrad.2018.02.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 02/02/2018] [Accepted: 02/11/2018] [Indexed: 06/08/2023]
Abstract
In order to estimate residents' external dose due to radionuclide exposure resulting from fallout deposit on the ground, the shielding and dose reduction effects provided by structures such as houses and workplaces are taken into account as most individuals spend a large portion of their time indoors. Many works on both calculation and measurement for European and American settlements have been reported and factors such as, shielding factors, protection factors, reduction factors, and location factors have been determined. However, measurement data for Japanese settlements are lacking. Thus, the Japanese government used reduction factors given in the International Atomic Energy Agency documents from American and European settlements when Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident occurred. The United Nations Scientific Committee on the Effects of Atomic Radiation used location factors from European settlements for the same reason. Soon after the FDNPP accident, several measurements and calculations were performed to obtain specific reduction factors for Japanese settlements due to this lack of data. This research reviews previous studies that determined factors such as, shielding factors, protection factors, reduction factors, and location factors and summarizes specific results for Japan. We discuss the issues in determining these factors and in applying them to estimate indoor dose. The contribution of surface contamination to the indoor ambient dose equivalent rate is also discussed.
Collapse
Affiliation(s)
- Hiroko Yoshida-Ohuchi
- Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-ku, Sendai, Miyagi, 980-8578, Japan.
| | - Norihiro Matsuda
- Fukushima Environmental Safety Center, Japan Atomic Energy Agency, 2-2-2 Uchisaiwai-cho, Chiyoda, Tokyo, 100-8577, Japan.
| | - Kimiaki Saito
- Fukushima Environmental Safety Center, Japan Atomic Energy Agency, 2-2-2 Uchisaiwai-cho, Chiyoda, Tokyo, 100-8577, Japan.
| |
Collapse
|
21
|
Kumamoto Y, Aoyama M, Hamajima Y, Nagai H, Yamagata T, Kawai Y, Oka E, Yamaguchi A, Imai K, Murata A. Fukushima-derived radiocesium in the western North Pacific in 2014. J Radioanal Nucl Chem 2017; 311:1209-1217. [PMID: 28250546 PMCID: PMC5306276 DOI: 10.1007/s10967-016-5055-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Indexed: 11/29/2022]
Abstract
In 2014, we measured activity concentration of radiocesium in the western North Pacific Ocean. In the north of Kuroshio Front high activity concentration of Fukushima-derived radiocesium in surface mixed layer in 2012 had been transported eastward by 2014. In the south of the front we found a radiocesium subsurface maximum in 200-600 m depth, which was similar to that observed in 2012. The subsurface maximum spread southward from 18°N to 15°N between 2012 and 2014, which suggests spreading of Fukushima-derived radiocesium into the whole western subtropical area by 2014 due to formation and subduction of the subtropical mode water.
Collapse
Affiliation(s)
- Yuichiro Kumamoto
- Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa 237-0061 Japan
| | - Michio Aoyama
- Institute of Environmental Radioactivity, Fukushima University, 1-1 Kanayagawa, Fukushima, Fukushima 960-1296 Japan
| | - Yasunori Hamajima
- Low Level Radioactivity Laboratory, Kanazawa University, Wake, Nomi, Ishikawa 923-1224 Japan
| | - Hisao Nagai
- Department of Chemistry, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajousui, Setagaya Ward, Tokyo, 156-8550 Japan
| | - Takeyasu Yamagata
- Department of Chemistry, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajousui, Setagaya Ward, Tokyo, 156-8550 Japan
| | - Yoshimi Kawai
- Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa 237-0061 Japan
| | - Eitarou Oka
- Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564 Japan
| | - Atsushi Yamaguchi
- Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido 041-8611 Japan
| | - Keiri Imai
- School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido 041-8611 Japan
| | - Akihiko Murata
- Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa 237-0061 Japan
| |
Collapse
|
22
|
Sugiura Y, Kanasashi T, Ogata Y, Ozawa H, Takenaka C. Radiocesium accumulation properties of Chengiopanax sciadophylloides. J Environ Radioact 2016; 151 Pt 1:250-257. [PMID: 26536624 DOI: 10.1016/j.jenvrad.2015.10.021] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 10/20/2015] [Accepted: 10/22/2015] [Indexed: 06/05/2023]
Abstract
Through the assessments of radioactive contamination after the Fukushima Dai-ichi Nuclear Power Plant (F1NPP) accident, it has been reported that some sprouts of Chengiopanax sciadophylloides (Franch. et Sav.) at the site contained radiocesium (((134),)(137)Cs) at higher concentrations than the other plants. To assess the phytoremediation properties of C. sciadophylloides for (137)Cs decontamination, we aimed to quantify the (137)Cs accumulation in C. sciadophylloides. We measured the (137)Cs concentrations in various organs of C. sciadophylloides collected from the forest in the town of Kawamata, Fukushima prefecture, together with the concentrations of other elements [potassium (K), rubidium, (133)Cs, calcium, strontium, and manganese] present. In addition, we compared the foliar concentrations of these elements in C. sciadophylloides with those in four different deciduous tree species. The mean of foliar (137)Cs concentration in C. sciadophylloides was 28.1 kBq kg(-1) DW, one order of magnitude higher than that found in the other species. The (137)Cs concentrations were in the order of leaves > bark > wood. The wood of the treetop, leaf scars, and roots contained higher amounts of (137)Cs than that of the trunk. From the distribution of (137)Cs in C. sciadophylloides, we confirmed that (137)Cs tends to accumulate in the young growing parts. The difference in the distribution of (137)Cs and (133)Cs indicated that surface uptake of (137)Cs occurs. A significant correlation between K and (137)Cs concentrations in each organ was found, which suggested that (137)Cs in the plant body is transferred through the same pathway as K. On the other hand, there was no correlation between foliar K and (137)Cs concentrations, implying that the uptake ratio of K to (137)Cs was different for each individual. To determine the factors driving specific (137)Cs accumulation and/or the variability of the ratio between K and (137)Cs, the distribution of (137)Cs and the root in soil, the difference of the expression of transporter, and the existence of mycorrhizal fungi should be considered. However, further research is required.
Collapse
Affiliation(s)
- Yuki Sugiura
- Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan.
| | - Tsutomu Kanasashi
- Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan.
| | - Yoshimune Ogata
- Graduate School of Medicine, Nagoya University, Nagoya, Aichi 461-8673, Japan.
| | - Hajime Ozawa
- Fukushima Prefectural Forestry Research Centre, Koriyama, Fukushima 963-0112, Japan.
| | - Chisato Takenaka
- Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan.
| |
Collapse
|
23
|
Yu W, He J, Lin W, Li Y, Men W, Wang F, Huang J. Distribution and risk assessment of radionuclides released by Fukushima nuclear accident at the northwest Pacific. J Environ Radioact 2015; 142:54-61. [PMID: 25644751 DOI: 10.1016/j.jenvrad.2015.01.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Revised: 01/05/2015] [Accepted: 01/06/2015] [Indexed: 06/04/2023]
Abstract
In order to understand the impact of Fukushima Nuclear Accident (FNA) on the marine environment, seawater and a composite squid (Ommastrephe bartrami) sample were collected on the monitoring cruise XT01 during June 16-July 4, 2011. The concentration levels of Cesium-134, Cesium-137, Strontium-90, Silver-110 m, Cobalt-58 and Cobalt-60 were measured both for the seawater and squid samples. The elevated activity levels of Cesium-134 and Cesium-137 were found in the sampling area. Cesium-134 and Silver-110 m, which were usually undetectable before FNA, were also found in the squid sample, with the activity levels of 1.65 ± 0.13 Bq/kg-wet and 0.07 ± 0.01 Bq/kg-wet, respectively. The radiological assessment result showed that the radioactive release from the FNA would not have a significant adverse effect on marine biota at the population level.
Collapse
Affiliation(s)
- Wen Yu
- Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China.
| | - Jianhua He
- Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| | - Wuhui Lin
- Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| | - Yiliang Li
- Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| | - Wu Men
- Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| | - Fenfen Wang
- Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| | - Jiang Huang
- Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| |
Collapse
|
24
|
Kumamoto Y, Aoyama M, Hamajima Y, Murata A, Kawano T. Impact of Fukushima-derived radiocesium in the western North Pacific Ocean about ten months after the Fukushima Dai-ichi nuclear power plant accident. J Environ Radioact 2015; 140:114-122. [PMID: 25461523 DOI: 10.1016/j.jenvrad.2014.11.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 11/07/2014] [Accepted: 11/14/2014] [Indexed: 06/04/2023]
Abstract
We measured vertical distributions of radiocesium ((134)Cs and (137)Cs) at stations along the 149°E meridian in the western North Pacific during winter 2012, about ten months after the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident. The Fukushima-derived (134)Cs activity concentration and water-column inventory were largest in the transition region between 35 and 40°N approximately due to the directed discharge of the contaminated water from the FNPP1. The bomb-derived (137)Cs activity concentration just before the FNPP1 accident was derived from the excess (137)Cs activity concentration relative to the (134)Cs activity concentration. The water-column inventory of the bomb-derived (137)Cs was largest in the subtropical region south of 35°N, which implies that the Fukushima-derived (134)Cs will also be transported from the transition region to the subtropical region in the coming decades. Mean values of the water-column inventories decay-corrected for the Fukushima-derived (134)Cs and the bomb-derived (137)Cs were estimated to be 1020 ± 80 and 820 ± 120 Bq m(-2), respectively, suggesting that in winter 2012 the impact of the FNPP1 accident in the western North Pacific Ocean was nearly the same as that of nuclear weapons testing. Relationship between the water-column inventory and the activity concentration in surface water for the radiocesium is essential information for future evaluation of the total amount of Fukushima-derived radiocesium released into the North Pacific Ocean.
Collapse
Affiliation(s)
- Yuichiro Kumamoto
- Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa 237-0061, Japan.
| | - Michio Aoyama
- Institute of Environmental Radioactivity, Fukushima University, 1-1 Kanayagawa, Fukushima 960-1296, Japan
| | - Yasunori Hamajima
- Low Level Radioactivity Laboratory, Kanazawa University, Wake, Nomi, Ishikawa 923-1224, Japan
| | - Akihiko Murata
- Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa 237-0061, Japan
| | - Takeshi Kawano
- Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natushima-cho, Yokosuka, Kanagawa 237-0061, Japan
| |
Collapse
|
25
|
Inoue M, Kofuji H, Fujimoto K, Furusawa Y, Yoshida K, Nagao S, Yamamoto M, Hamajima Y, Minakawa M. Delivery mechanism of (134)Cs and (137)Cs in seawater off the Sanriku Coast, Japan, following the Fukushima Dai-ichi NPP accident. J Environ Radioact 2014; 137:113-118. [PMID: 25036919 DOI: 10.1016/j.jenvrad.2014.07.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 06/26/2014] [Accepted: 07/02/2014] [Indexed: 06/03/2023]
Abstract
To assess the delivery mechanism of radiocesium emitted from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), we examined vertical profiles of (134)Cs, (137)Cs, and (228)Ra concentrations and the (228)Ra/(226)Ra ratio in the water columns off the Sanriku Coast in the northwestern Pacific Ocean, in July 2012, along with their surface lateral variations in July 2009. Radiocesium concentrations exhibited maximum peaks (3-5 mBq/L for (134)Cs) at depths of 100-200 m, accompanied by high (228)Ra concentrations (0.6-0.8 mBq/L) in comparison with shallower depths (∼0.4 mBq/L). Taking the circulation patterns of currents in the area into account, it was inferred that radioactive depositions were supplied to the (228)Ra-rich Tsugaru Warm Current Water (TWCW) in the offshore area of the Sanriku Coast following the FDNPP accident, and that after the spring of 2011, this water (∼26.5σθ) was covered by lower density surface water, which helped intrude its way to depths of 100-200 m.
Collapse
Affiliation(s)
- M Inoue
- Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan.
| | - H Kofuji
- Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan; Japan Marine Science Foundation, Minato, Mutsu, Aomori 035-0064, Japan
| | - K Fujimoto
- Fisheries Research Agency, National Research Institute of Fisheries Science, Fukuura, Kanazawa, Yokohama 236-8648, Japan
| | - Y Furusawa
- Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan
| | - K Yoshida
- Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan
| | - S Nagao
- Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan
| | - M Yamamoto
- Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan
| | - Y Hamajima
- Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan
| | - M Minakawa
- Fisheries Research Agency, National Research Institute of Fisheries Science, Fukuura, Kanazawa, Yokohama 236-8648, Japan
| |
Collapse
|