Radiocesium discharge from paddy fields with different initial scrapings for decontamination after the Fukushima Dai-ichi Nuclear Power Plant accident

Journal of Environmental Radioactivity

Onda

et al. 2015

Large quantities of radiocesium were deposited across a 3000 km(2) area northwest of the Fukushima Dai-ichi nuclear power plant after the March 2011 accident. Although many studies have investigated the fate of (137)Cs in soil in the months following the accident, the depth distribution of this radioactive contaminant in rice paddy fields requires further examination after the typhoons that occurred in this region. Such investigations will help minimize potential human exposure in rice paddy fields. Radionuclide activity concentrations, organic content and particle size were analysed in 10 soil cores sampled from paddy fields in November 2013, 20 km north of the Fukushima power plant. Our results demonstrate limited depth migration of (137)Cs with the majority concentrated in the uppermost layers of soils (<5 cm). More than 30 months after the accident, between 46.8 and 98.7% of the total (137)Cs inventories was found within the top 5 cm of the soil surface, despite cumulative rainfall totalling 3300 mm. Furthermore, there were no significant correlations between (137)Cs depth distribution and the other parameters. We attributed the maximum depth penetration of (137)Cs to grass cutting (73.6-98.5% of (137)Cs in the upper 5 cm) and farming operations (tillage - 46.8-51.6% of (137)Cs in the upper 5 cm). As this area is exposed to erosive events, ongoing decontamination works may increase soil erodibility. We therefore recommend the rapid removal of the uppermost - contaminated - layer of the soil after removing the vegetation to avoid erosion of contaminated material during the subsequent rainfall events. Further analysis is required to thoroughly understand the impacts of erosion on the redistribution of radiocesium throughout the Fukushima Prefecture.

Section: Implications For Contamination Redistribution Across the Catmentioning

confidence: 96%

Depth distribution of cesium-137 in paddy fields across the Fukushima pollution plume in 2013

Lepage

Journal of Environmental Radioactivity

Onda

et al. 2015

“…When paddies are puddled for the rice growing season, they are flooded with water potentially containing suspended sediment and adsorbed radiocesium (Endo et al, 2013;Wakahara et al, 2014;Yoshikawa et al, 2014). Further, when the paddies are drained, they are directly connected to the stream network and may become a significant source of sediment and radiocesium, as water and sediments discharged from paddy fields are often transferred directly to stream systems .…”

Section: Radiocesium Hillslope Transfersmentioning

confidence: 98%

“…Quantifying hillslope erosion is difficult for Japanese paddy fields as they may be both sources and sinks of sediment and sediment-bound radiocesium (Tanaka et al, 2013b;Wakahara et al, 2014). When paddies are puddled for the rice growing season, they are flooded with water potentially containing suspended sediment and adsorbed radiocesium (Endo et al, 2013;Wakahara et al, 2014;Yoshikawa et al, 2014).…”

Section: Radiocesium Hillslope Transfersmentioning

confidence: 99%

“…The authors concluded that the additional 137 Cs load from irrigation is negligible in comparison to the existing soil 137 Cs inventory. Wakahara et al (2014) examined the discharge of radiocesium from rice paddy fields reporting that a normally cultivated paddy field exported 1240 Bq m À2 of 137 Cs after puddling and 102 Bq m À2 after irrigation. Comparatively, a decontaminated paddy exported 48 Bq m À2 of 137 Cs after puddling and 317 Bq m À2 after irrigation.…”

Section: Radiocesium Hillslope Transfersmentioning

confidence: 99%

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Radiocesium transfer from hillslopes to the Pacific Ocean after the Fukushima Nuclear Power Plant accident: A review

Journal of Environmental Radioactivity

Laceby

Lepage

et al. 2015

159

The devastating tsunami triggered by the Great East Japan Earthquake on March 11, 2011 inundated the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) resulting in a loss of cooling and a series of explosions releasing the largest quantity of radioactive material into the atmosphere since the Chernobyl nuclear accident. Although 80% of the radionuclides from this accidental release were transported over the Pacific Ocean, 20% were deposited over Japanese coastal catchments that are subject to frequent typhoons. Among the radioisotopes released during the FDNPP accident, radiocesium ((134)Cs and (137)Cs) is considered the most serious current and future health risk for the local population. The goal of this review is to synthesize research relevant to the transfer of FDNPP derived radiocesium from hillslopes to the Pacific Ocean. After radiocesium fallout deposition on vegetation and soils, the contamination may remain stored in forest canopies, in vegetative litter on the ground, or in the soil. Once radiocesium contacts soil, it is quickly and almost irreversibly bound to fine soil particles. The kinetic energy of raindrops instigates the displacement of soil particles, and their bound radiocesium, which may be mobilized and transported with overland flow. Soil erosion is one of the main processes transferring particle-bound radiocesium from hillslopes through rivers and streams, and ultimately to the Pacific Ocean. Accordingly this review will summarize results regarding the fundamental processes and dynamics that govern radiocesium transfer from hillslopes to the Pacific Ocean published in the literature within the first four years after the FDNPP accident. The majority of radiocesium is reported to be transported in the particulate fraction, attached to fine particles. The contribution of the dissolved fraction to radiocesium migration is only relevant in base flows and is hypothesized to decline over time. Owing to the hydro-meteorological context of the Fukushima region, the most significant transfer of particulate-bound radiocesium occurs during major rainfall and runoff events (e.g. typhoons and spring snowmelt). There may be radiocesium storage within catchments in forests, floodplains and even within hillslopes that may be remobilized and contaminate downstream areas, even areas that did not receive fallout or may have been decontaminated. Overall this review demonstrates that characterizing the different mechanisms and factors driving radiocesium transfer is important. In particular, the review determined that quantifying the remaining catchment radiocesium inventory allows for a relative comparison of radiocesium transfer research from hillslope to catchment scales. Further, owing to the variety of mechanisms and factors, a transdisciplinary approach is required involving geomorphologists, hydrologists, soil and forestry scientists, and mathematical modellers to comprehensively quantify radiocesium transfers and dynamics. Characterizing radiocesium transfers from hillslopes to the Pacific Ocean is necess...

“…Although previous dosimetric studies demonstrated that currently the internal exposure of both the local population and the decontamination workers remains minimal, both internal and external exposures of these groups should be studied over longer temporal periods to help understand the longterm impacts of this accident on exposed population groups. More research is also required to understand the fate and dynamics of other longer-lived radionuclides in the Fukushima www.soil-journal.net/5/333/2019/ SOIL, 5, 333-350, 2019 region including radiocarbon (Paterne et al, 2018;Povinec et al, 2016;Xu et al, 2016), plutonium and uranium isotopes (Jaegler et al, 2018;Zheng et al, 2013;Steinhauser, 2014) as they may be persistent in the environment even though many were emitted only at the trace and ultra-trace levels.…”

Section: Perspectives For Future Researchmentioning

confidence: 99%

Effectiveness of landscape decontamination following the Fukushima nuclear accident: a review

Laceby

Nakao

2019

SOIL

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011 resulted in the contamination of Japanese landscapes with radioactive fallout. Accordingly, the Japanese authorities decided to conduct extensive remediation activities in the impacted region to allow for the relatively rapid return of the local population. The objective of this review is to provide an overview of the decontamination strategies and their potential effectiveness in Japan, focussing on particle-bound radiocesium. In the Fukushima Prefecture, the decision was taken to decontaminate the fallout-impacted landscapes in November 2011 for the 11 municipalities evacuated after the accident (Special Decontamination Zone -SDZ -1117 km 2 ) and for the 40 non-evacuated municipalities affected by lower, although still significant, levels of radioactivity (Intensive Contamination Survey Areas, 7836 km 2 ). Decontamination activities predominantly targeted agricultural landscapes and residential areas. No decontamination activities are currently planned for the majority of forested areas, which cover ∼ 75 % of the main fallout-impacted region. Research investigating the effectiveness of decontamination activities underlined the need to undertake concerted actions at the catchment scale to avoid renewed contamination from the catchment headwaters after the completion of remediation activities. Although the impact of decontamination on the radioactive dose rates for the local population remains a subject of debate in the literature and in the local communities, outdoor workers in the SDZ represent a group of the local population that may exceed the long-term dosimetric target of 1 mSv yr −1 . Decontamination activities generated ∼ 20 million m 3 of soil waste by early 2019. The volume of waste generated by decontamination may be decreased through incineration of combustible material and recycling of the less contaminated soil for civil engineering structures. However, most of this material will have to be stored for ∼ 30 years at interim facilities opened in 2017 in the vicinity of the FDNPP before being potentially transported to final disposal sites outside of the Fukushima Prefecture. Further research is required to investigate the perennial contribution of radiocesium from forest sources. In addition, the re-cultivation of farmland after decontamination raises additional questions associated with the fertility of remediated soils and the potential transfer of residual radiocesium to the plants. Overall, we believe it is important to synthesise the remediation lessons learnt following the FDNPP nuclear accident, which could be fundamental if a similar catastrophe occurs somewhere on Earth in the future.