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Cs released by the Fukushima Daiichi Nuclear Power Plant to the coastal areaSato, Shun; Wakiyama, Yoshifumi*; Takahashi, Fumiaki; Takata, Hyoe*
Science of the Total Environment, 1000, p.180380_1 - 180380_14, 2025/10
We compared the ongoing direct release of Cs from the Fukushima Daiichi Nuclear Power Plant (FDNPP) and riverine inputs of Cs that have contributed to the persistent elevated Cs in coastal waters around the plant since 2012. The direct release of Cs clearly decreased from 17.5 TBq during 2012
2014 to 0.6 TBq during 20192021 because of measures implemented by the FDNPP. The riverine input decreased slightly from 2.2 TBq during 20122014 to 2.0 TBq during 20192021. The ratio of direct release to the total Cs flux into the coastal water around the FDNPP decreased from 89% during 20122014 to 23% during 20192021. This change resulted in part from a lowering of the limit of detection of Cs activities to avoid overestimation of Cs fluxes from the facility, but also from installation of an impermeable seaside wall. The trend of decreasing riverine Cs input might have been due entirely to environmental remediation. Our results indicate that the contribution of riverine input to the coastal waters will continue for a long time. Precise prediction of the long-term distribution of Cs in the marine environment will require consideration of a variety of environmental factors and anthropogenic effects.
Cs in a river-sea system boundary area after the Fukushima Dai-ichi Nuclear Power Plant accidentTakata, Hyoe*; Wakiyama, Yoshifumi*; Wada, Toshihiro*; Hirao, Shigekazu*; Aono, Tatsuo*; Nakanishi, Takahiro; Misono, Toshiharu; Shiribiki, Takehiko; Aoyama, Michio*
Marine Chemistry, 262, p.104384_1 - 104384_6, 2024/05
Times Cited Count：2 Percentile：33.34(Chemistry, Multidisciplinary)Cs concentrations in coastal sediments off FukushimaSuzuki, Shotaro*; Amano, Yosuke*; Enomoto, Masahiro*; Matsumoto, Akira*; Morioka, Yoshiaki*; Sakuma, Kazuyuki; Tsuruta, Tadahiko; Kaeriyama, Hideki*; Miura, Hikaru*; Tsumune, Daisuke*; et al.
Science of the Total Environment, 831, p.154670_1 - 154670_15, 2022/07
Times Cited Count：3 Percentile：8.46(Environmental Sciences)Takata, Hyoe*; Kuma, Kenshi*; Isoda, Yutaka*; Otosaka, Shigeyoshi; Senju, Tomoharu*; Minakawa, Masayuki*
Geophysical Research Letters, 35(2), p.L02606_1 - L02606_5, 2008/01
Times Cited Count：19 Percentile：41.42(Geosciences, Multidisciplinary)Concentrations of iron in seawater (dissolved and labile dissolved phases) in the two basins (Yamato Basin and Japan Basin) of the Japan Sea are measured and the origin and behavior of iron were discussed. Extremely high vertically integrated total dissolvable Fe inventories (300-350 
mol m
) were observed at the surface water in both basins (0-200 m depth), and was probably resulting from high atmospheric Fe input to the surface water. Labile dissolved Fe in both basins was characterized by mid-depth (1-2 km depth) maxima, which were regulated by the competition between dissolved Fe input from the microbial decomposition of sinking biogenic organic matter and Fe removal by particulate scavenging. The distributions of Fe in the Japan Sea would play an important role in understanding the biogeochemical cycle of iron in the ocean.
Chaboche, P.-A.*; Wakiyama, Yoshifumi*; Takata, Hyoe*; Wada, Toshihiro*; Evrard, O.*; Misono, Toshiharu; Shiribiki, Takehiko; Funaki, Hironori
no journal, ,
Chaboche, P.-A.*; Wakiyama, Yoshifumi*; Takata, Hyoe*; Wada, Toshihiro*; Misono, Toshiharu; Shiribiki, Takehiko; Funaki, Hironori
no journal, ,
The Fukushima Daiichi Nuclear Power Plant (FDNPP) incident, triggered by the Great East Japan Earthquake and subsequent tsunami in March 2011, resulted in the release of significant quantities of radionuclides into the terrestrial and marine environments of Fukushima Prefecture. While the activity of radiocesium (i.e., 
Cs and Cs) in these environments has decreased since the accident, continuous inputs through rivers draining and eroding the main terrestrial radioactive plume have been measured, maintaining elevated levels of Cs in riverine and coastal sediment deposited off the Prefecture's coast. Consequently, identifying the sources of sediment is required to elucidate the links between terrestrial and marine radiocesium dynamics and to anticipate the fate of persistent radionuclides in the environment.
Cs concentrations in coastal seawater after intensive river water flows in Fukushima, JapanWakiyama, Yoshifumi*; Takata, Hyoe*; Sato, Shun; Kurosawa, Honoka; Suzuki, Nobuhiro*; Taniguchi, Keisuke*
no journal, ,
The Fukushima Daiichi Nuclear Power Plant accident contaminated terrestrial environment in Fukushima with 3-6 TBq of Cs. Terrestrial Cs is washed off from catchments due to intensive rainfall and transported through river systems to the ocean, possibly resulting in increase of Cs concentrations in coastal seawaters. Although numerical simulations reproducing relevant processes were proposed, there are only a few data sets could be used for validating such simulations. This study presents observations in intensive river flow events on catchments of the Ukedo and the Abukuma river systems and their coastal seawaters. On the Ukedo river catchment (420 km
, 1200 kBq/m), water samples were collected at two downstream points and at seashore around its river mouth during 4-19 September 2023. On the Abukuma river catchment (5400 km, 86 kBq/m), water samples were collected at a downstream point and at seashore around its river mouth during 11-23 August 2024. All water samples were filtered and measured with Ge detectors for Cs concentration in suspended solids (SS), Cs
(kBq/kg) and dissolved Cs concentration, Cs
(mBq/L). Based on Cs concentrations in river water and hydrological datasets, particulate and dissolved Cs flux (Bq) were calculated. From the Ukedo river catchment, 190 GBq of Cs were discharged after intensive rainfall on 8 September. Responding to the discharge, respective Cs and Cs in coastal seawater reached 94 kBq/kg and 410 mBq/L, higher than 22 kBq/kg and 71 mBq/L of corresponding mean values (n = 8). These high Cs concentrations were attributed to selective suspension of fine particles and active desorption of Cs from SS in the coastal seawater. On the other hand, no significant increase of Cs concentrations in coastal seawaters was found at the Abukuma river's mouth after 82 GBq of Cs discharged on 17 August 2023. The Cs and Cs in coastal seawater after the peak from the Abukuma river were 0.29 kBq/kg and 3.1 mBq/L, respectively, lower than 0.38 kBq/kg and 4.3 mBq/L of corresponding mean values (n = 5). These results suggest that increase of Cs concentrations in coastal seawater is not necessarily proportional to terrestrial Cs input although further analyses on river catchment characteristics and seawater current conditions are required.
Cs from rivers to Cs concentrations in coastal sediment off FukushimaSuzuki, Shotaro*; Sakuma, Kazuyuki; Tsuruta, Tadahiko; Matsumoto, Akira*; Amano, Yosuke*; Enomoto, Masahiro*; Morioka, Yoshiaki*; Kamiyama, Kyoichi*; Takata, Hyoe*
no journal, ,
Aono, Tatsuo*; Nishikawa, Jun*; Otosaka, Shigeyoshi*; Takata, Hyoe*; Misono, Toshiharu; Nakanishi, Takahiro; Miura, Hikaru*; Fukuda, Miho*; Kambayashi, Shota*; Sakurada, Masanobu*; et al.
no journal, ,
From 2016 to 2020, four research voyages were conducted to investigate the dynamics of radioactive materials in the waters around Fukushima. Seawater and sediment samples were collected in the waters off the Fukushima Daiichi Nuclear Power Plant (FDNPS). The concentration of radioactive cesium (Cs) in seawater and sediment off the coast of Fukushima was surveyed to understand the status of the marine environment. As a result, no significant changes were observed in both seawater and sediment from 2016 to 2020.
Takata, Hyoe*; Otsuki, Azusa*; Sato, Shun*; Otosaka, Shigeyoshi*; Toda, Ryoji*; Nishikawa, Jun*; Kenmochi, Hideyuki*; Ishikura, Mei*; Yamada, Momoka*; Shinkai, Yusuke*; et al.
no journal, ,
Research cruises were conducted by the Shinsei Maru from October 7 to October 17, 2021, and from October 2 to 13, 2022, in the coastal waters off Fukushima Prefecture. Those cruises aimed to monitor radionuclide distribution and to clarify the dynamics of radionuclides in the coastal water and the environmental response of ecosystems after the Fukushima Daiichi Nuclear Power Plant accident in March 2011.
Aono, Tatsuo*; Fukuda, Miho*; Sakurada, Masanobu*; Takahashi, Hiroyuki*; Yamazaki, Shinnosuke*; Kambayashi, Shota*; Misono, Toshiharu; Nakanishi, Takahiro; Miura, Hikaru*; Nishikawa, Jun*; et al.
no journal, ,
From 2016 to 2020, R/V Shinsei-maru of JAMSTEC conducted four research cruises on the dynamics and bioavailability of radionuclides around off Fukushima. Seawater, sediments and organisms were collected mainly around off the Fukushima Daiichi Nuclear Power Plant (FDNPS). The purpose of those cruises is to observe the flux of radionuclides released into the ocean by the FDNPS accident and to understand the bioavailability of radionuclides. In order to understand the contaminated levels of the marine environment, the concentration of radiocaesium (Cs) in seawater and sediments around off Fukushima was investigated.
Aono, Tatsuo*; Nishikawa, Jun*; Otosaka, Shigeyoshi*; Takata, Hyoe*; Misono, Toshiharu; Nakanishi, Takahiro; Miura, Hikaru*; Kambayashi, Shota*; Fukuda, Miho*; Sakurada, Masanobu*; et al.
no journal, ,
From 2016 to 2020, the Tohoku Marine Ecosystem Research Vessel Shinsei-maru conducted four research cruises on the dynamics and bioavailability of radionuclides around off Fukushima. Seawater, sediments and organisms were collected mainly around off the Fukushima Daiichi Nuclear Power Plant (FDNPS). The purpose of those cruises is to observe the flux of radionuclides released into the ocean by the FDNPS accident and to understand the bioavailability of radionuclides. In order to understand the contaminated levels of the marine environment, the concentration of radioactive cesium (Cs) in seawater and sediments around off Fukushima was investigated. As a result, the concentration range of dissolved Cs-137 in the surface seawater near the FDNPS from 2016 to 2018 was 10-23 mBq/L, but decreased to 7 mBq/L in 2020. In terms of points, the concentrations of dissolved Cs-137 tended to decrease with time. On the other hand, in sediments, the Cs-137 concentrations were higher in the surface layer (0-2 cm) than the deep layer from 2016 to 2017 and tended to decrease with depth, but after 2018, subsurface vertical maximum of Cs-137 concentrations was observed at some stations. Although these concentrations tended to increase in the subsurface layer, the concentrations in the sediment also tended to decrease with time. In this presentation, we report on the concentration variation of Cs-137 and their characteristics in seawater and sediments around off Fukushima.
Cs in a river-sea system boundaryTakata, Hyoe*; Wakiyama, Yoshifumi*; Wada, Toshihiro*; Hirao, Shigekazu*; Aono, Tatsuo*; Nakanishi, Takahiro; Misono, Toshiharu; Shiribiki, Takehiko*; Aoyama, Michio*
no journal, ,
Chaboche, P.-A.*; Wakiyama, Yoshifumi*; Takata, Hyoe*; Wada, Toshihiro*; Evrard, O.*; Misono, Toshiharu; Shiribiki, Takehiko; Funaki, Hironori
no journal, ,
Cs in a river-sea system boundary areaTakata, Hyoe*; Wada, Toshihiro*; Wakiyama, Yoshifumi*; Hirao, Shigekazu*; Sato, Shun*; Aono, Tatsuo*; Nakanishi, Takahiro; Misono, Toshiharu; Shiribiki, Takehiko
no journal, ,
Takata, Hyoe*; Kuma, Kenshi*; Isoda, Yutaka*; Nishioka, Jun*; Otosaka, Shigeyoshi; Chikira, Mitsuru*; Takagi, Shogo*; Kamei, Yoshihiko*; Sakaoka, Keiichiro*
no journal, ,
The authors discussed on the difference of behavior of iron between two basins (the Yamato Basin and Japan Basin) in the Japan Sea by measurements of iron (dissolved and labile dissolved phases) and nutrients in seawater. Concentration of labile dissolved iron in the surface water was about 1.0 nM and did not show difference between the basins. On the other hand, concentration of labile dissolved iron in the Japan Basin increased to 4.5 nM at 1-2 km depth and decreased to 4 nM in the bottom layer. In the Yamato Basin, concentration of labile dissolved iron in deep water increased uniformly and was about 6 nM at the bottom layer. The difference in distribution of iron in seawater indicates that the transport processes of biogenic elements in the deep layers are different between the basins of the Japan Sea.
