Ten-year temporal changes in the supply source of Cs released by the Fukushima Daiichi Nuclear Power Plant to the coastal area

Sato, Shun; Wakiyama, Yoshifumi*; Takahashi, Fumiaki; Takata, Hyoe*

Science of the Total Environment, 1000, p.180380_1 - 180380_14, 2025/10

https://doi.org/10.1016/j.scitotenv.2025.180380

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 20122014 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.

Impacts of freeze-thaw processes and subsequent runoff on Cs washoff from bare land in Fukushima

Igarashi, Yasunori*; Onda, Yuichi*; Wakiyama, Yoshifumi*; Yoshimura, Kazuya; Kato, Hiroaki*; Kozuka, Shohei*; Manome, Ryo*

Science of the Total Environment, 769, p.144706_1 - 144706_9, 2021/05

https://doi.org/10.1016/j.scitotenv.2020.144706

Radionuclides from the Fukushima Daiichi Nuclear Power Plant in terrestrial systems

Onda, Yuichi*; Taniguchi, Keisuke*; Yoshimura, Kazuya; Kato, Hiroaki*; Takahashi, Junko*; Wakiyama, Yoshifumi*; Coppin, F.*; Smith, H.*

Nature Reviews Earth & Environment (Internet), 1(12), p.644 - 660, 2020/12

https://doi.org/10.1038/s43017-020-0099-x

Land use types control solid wash-off rate and entrainment coefficient of Fukushima-derived Cs, and their time dependence

Wakiyama, Yoshifumi*; Onda, Yuichi*; Yoshimura, Kazuya; Igarashi, Yasunori*; Kato, Hiroaki*

Journal of Environmental Radioactivity, 210, p.105990_1 - 105990_12, 2019/12

https://doi.org/10.1016/j.jenvrad.2019.105990

Temporal changes of radiocesium in irrigated paddy fields and its accumulation in rice plants in Fukushima

Yang, B.*; Onda, Yuichi*; Wakiyama, Yoshifumi*; Yoshimura, Kazuya; Sekimoto, Hitoshi*; Ha, Y.*

Environmental Pollution, 208(Part B), p.562 - 570, 2016/01

https://doi.org/10.1016/j.envpol.2015.10.030

Slope-scale Cs-137 wash-off processes estimated with erosion plot observations and laser-scanning

Wakiyama, Yoshifumi*; Manome, Ryo*; Onda, Yuichi*; Yoshimura, Kazuya

no journal, , 

no abstracts in English

Radiocesium wash-off associated with soil erosion from various land uses after the Fukushima Dai-ichi NPP accident

Wakiyama, Yoshifumi*; Onda, Yuichi*; Yoshimura, Kazuya; Kato, Hiroaki*

no journal, , 

Impacts of freeze-thaw processes and subsequent runoff on Cs wash-off from bareland in Fukushima

Igarashi, Yasunori*; Onda, Yuichi*; Wakiyama, Yoshifumi*; Yoshimura, Kazuya; Kato, Hiroaki*; Kozuka, Shohei*; Manome, Ryo*

no journal, , 

The Impact and fate of fallout radionuclides by Fukushima Daiichi Nuclear Power Plant Accident in hydrological systems and post-accident environmental recovery

Onda, Yuichi*; Taniguchi, Keisuke*; Yoshimura, Kazuya; Wakiyama, Yoshifumi*

no journal, , 

Variations in Cs concentrations in coastal seawater after intensive river water flows in Fukushima, Japan

Wakiyama, 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.