Radionuclide contamination in flood sediment deposits in the coastal rivers draining the main radioactive pollution plume of Fukushima Prefecture, Japan (2011–2020)

Olivier Evrard,Philippe Bonté,Caroline Chartin,Irène Lefèvre,Atsushi Nakao,Rosalie Vandromme,J Patrick Laceby,Hugo Lepage,Olivier Cerdan,Yuichi Onda,Yoshifumi Wakiyama,Hugo Jaegler

doi:10.5194/essd-13-2555-2021

Abstract

Abstract. Artificial radionuclides including radiocesium (134Cs and 137Cs) and radiosilver (110mAg) were released into the environment following the Fukushima Dai-ichi nuclear power plant accident in March 2011. These particle-bound substances deposited on soils of north-eastern Japan, located predominantly within a ∼3000 km2 radioactive fallout plume and drained by several coastal rivers to the Pacific Ocean. The current dataset (Evrard et al., 2021), which can be accessed at https://doi.org/10.1594/PANGAEA.928594, compiles gamma-emitting artificial radionuclide activities measured in 782 sediment samples collected from 27 to 71 locations across catchments draining ∼6450 km2 during 16 fieldwork campaigns. These campaigns were conducted in Japan between November 2011 and November 2020 in river catchments draining the main radioactive plume. This database may be useful to evaluate and anticipate the post-accidental redistribution of radionuclides in the environment and for the spatial validation of models simulating the transfer of radiocesium across continental landscapes.

Highlights

The accident that occurred in March 2011 at the Fukushima Dai-ichi nuclear power plant (FDNPP) released large quantities of radionuclides into the environment (Leelossy et al, 2011)
Typhoon Hagibis and the subsequent Tropical Storm Bualoi on 24–25 October 2019) did not lead to such a large decline in 137Cs activities in sediment as Typhoon Etau, these radionuclide levels decreased from a mean of 4808 Bq kg−1 in October 2018 to a mean of 2167 Bq kg−1 in October 2019. This is likely explained by the fact that sediment transported during the flooding events in 2019 mainly originated from decontaminated soils prepared for recultivation, which were already depleted in radiocesium (Evrard et al, 2020)
This database compiles radiocesium activities analysed in recent sediment deposits collected following a homogeneous protocol in the coastal catchments draining the main radioactive pollution plume in the Fukushima Prefecture, Japan

Summary

Introduction

The accident that occurred in March 2011 at the Fukushima Dai-ichi nuclear power plant (FDNPP) released large quantities of radionuclides into the environment (Leelossy et al, 2011). Among the radioactive substances emitted, two radiocesium isotopes (134Cs and 137Cs) are the most problematic over the medium to long term as they were released in abundant quantities (Shozugawa et al, 2012) They are characterized by relatively long half-lives (2 years for 134Cs and 30 years for 137Cs), which may cause their persistence in the environment (Evrard et al, 2015). Both radiocesium isotopes were released in equivalent proportions during the accident, with initial 134Cs : 137Cs activity ratios close to 1 (Kobayashi et al, 2017). As the soils located in the main radioactive pollution plume are drained by several coastal river systems to the Pacific Ocean, the redistribution of the initial contamination through water erosion and riverine sediment transfer processes was anticipated (Evrard et al, 2015; Onda et al, 2020)

Methods

Results

Conclusion