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Accelerated radiocesium leaching from forest floor litter by heavy rainfall

Radioactive materials including 137Cs (cesium-137, half-life: 30.1 years) were released into the environment following the accident at Fukushima Daiichi Nuclear Power Plant. It has been about 10 years since the accident, but 137Cs remains in the environment, especially in forests. Many researchers have been studying the dynamics and transport processes of radioactive materials in the environment. It has been found that radioactive materials are carried along with the transfer of water and sediment. With the focus on the forested headwaters where radioactive materials remain in large quantities, it has been reported that the concentration of dissolved radiocesium in stream water increases during heavy rainfall.

Since rainwater does not contain radioactive cesium, the research group led by Assistant Professor Koichi Sakakibara of Shinshu University’s Faculty of Science was curious why the concentration of radioactive cesium in stream water increased during heavy rainfall without becoming diluted. The research team thought that radioactive cesium might have leached out from the forest litter and conducted leaching tests. They found that a large amount of radioactive cesium leached from such forest litter.

The next step was to ask the question, “Why does more radioactive cesium leach out of forest litter during heavy rainfall, when forest litter is still on the forest floor when it is not raining? (Background information: Most of the rainwater that falls on forests infiltrates into the subsurface area. The main reason for the increase in stream water volume during rainfall in forests is the discharge of groundwater. The groundwater contains almost no radioactive cesium.) So the research group set out to solve the mystery, “How is litter-derived radiocesium added to stream water during rainstorm?”

In contrast to the rainfall-runoff process, which is often focused only on rainfall and runoff, this study focused on the conversion process from rainfall to runoff, such as the variation of groundwater table level, the generation of saturated surface area at the bottom of the valley, and the variation of water quality and water age during rainfall. As a result, the answer to the problem to be solved in this study is that the main factor is the expansion of the contact area between water and litter due to the expansion of the saturated surface area caused by the rise of the groundwater table level in the forested headwater. Although previous research tended to focus only on the cause (rainfall) and the effect (runoff), Assistant Professor Sakakibara states, “we showed that the breakthrough to solve the unexplained reason lies in why the cause (rainfall) is converted into the effect (runoff).”

Uncertainty of results is inevitable when researching in the natural environment. How do results differ when the study is conducted at different times and places? How much error is there in the results due to the heterogeneity of the acquired samples from the environment? These are some of the questions that need to be answered. In the present study, the following questions were asked in-depth: 1) whether the same conclusions can be drawn for forests other than the target forest, 2) whether the samples collected for the study are representative of the Fukushima region, and 3) whether the results are affected by differences in the timing of litter falling from the trees and the degree of decomposition. Sakakibara says, “the most difficult part was to come up with a clear answer or idea to these uncertainties.”

Assistant Professor Sakakibara says, “the state and transport of radioactive materials in the environment are complex and need to be studied long-term. The half-life of 137Cs is 30 years. The results of this study only partly clarified this issue. Rivers that discharge from the forest area flow downstream to the ocean. We would like to clarify the whole picture of the pathway and process of radioactive materials originating from forests in the hydrological process from the headwater to the ocean. We believe that these findings are essential for creating a safe and secure environment and sustainable future and livelihood.”

The research was published in Science of The Total Environment.

Explore further

Dynamics of radiocesium in forests after the Fukushima disaster: Concerns and some hope

More information: Koichi Sakakibara et al, Radiocesium leaching from litter during rainstorms in the Fukushima broadleaf forest, Science of The Total Environment (2021). DOI: 10.1016/j.scitotenv.2021.148929

August 8, 2021 Posted by | Fukushima 2021 | , , | Leave a comment

Spatial pattern of plutonium and radiocaesium contamination released during the Fukushima Daiichi nuclear power plant disaster

November 14, 2018

Plutonium and radiocaesium are hazardous contaminants released by the Fukushima Daiichi nuclear power plant (FDNPP) disaster and their distribution in the environment requires careful characterisation using isotopic information. Comprehensive spatial survey of 134Cs and 137Cs has been conducted on a regular basis since the accident, but the dataset for 135Cs/137Cs atom ratios and trace isotopic analysis of Pu remains limited because of analytical challenges. We have developed a combined chemical procedure to separate Pu and Cs for isotopic analysis of environmental samples from contaminated catchments. Ultra-trace analyses reveal a FDNPP Pu signature in environmental samples, some from further afield than previously reported. For two samples, we attribute the dominant source of Pu to Reactor Unit 3. We review the mechanisms responsible for an emergent spatial pattern in 134,135Cs/137Cs in areas northwest (high 134Cs/137Cs, low 135Cs/137Cs) and southwest (low 134Cs/137Cs, high 135Cs/137Cs) of FDNPP. Several samples exhibit consistent 134,135Cs/137Cs values that are significantly different from those deposited on plant specimens collected in previous works. A complex spatial pattern of Pu and Cs isotopic signature is apparent. To confidently attribute the sources of mixed fallout material, future studies must focus on analysis of individual FDNPP-derived particles.



3.jpgIsoscapes of 134, 135, 137Cs and 239, 240Pu for part of the Fukushima prefecture surrounding FDNPP. The green marker is used to highlight an anomalous 240Pu/239Pu atom ratio of 0.64. R1, R2 and R3 correspond to ORIGEN estimated isotope ratio values for Reactor Units 1, 2 and 3, respectively27. SW indicates the mean value for the Cs isotope ratios measured to the southwest of FDNPP by Snow et al.19. 240Pu/239Pu atom ratio for Northern Hemisphere integrated global fallout is denoted by NHF28.

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November 30, 2018 Posted by | Fukushima 2018 | , , , , | Leave a comment

Loss of radioactivity in radiocesium-bearing microparticles emitted from the Fukushima Dai-ichi nuclear power plant by heating

In this article, we learn that microscopic glass beads containing Cesium 137 “lose” their radioactivity when, mixed with other radioactive debris, they are burned up in incinerators.
The researchers are pleased to see that the ashes from these incinerators will be free of Caesium 137.
It should be pointed out that radioactivity never disappears like that instantaneously. In the best of cases this Cesium will be, one can dream, filtered in the chimneys of incinerators. Otherwise the incineration will have simply served to disperse the radioactive cesium from the microscopic beads in the form of aerosols.
It is unfortunate that scientists are not working in a free vacuum, but need for their career and for their researches the approval and the financing of governmental and corporate institutions. In this case, those 4 Japanese scientists, Taiga Okumura, Noriko Yamaguchi, Terumi Dohi, Kazuki Iijima & Toshihiro Kogure, just spinned this paper into a ‘scientific’ propaganda to justify the Japanese government backed-up incineration.…
Radiocesium-bearing microparticles (CsPs) substantially made of silicate glass are a novel form of radiocesium emitted from the broken containment vessel of Fukushima Dai-ichi nuclear power plant. CsPs have a potential risk of internal radiation exposure caused by inhalation. Radiation-contaminated waste including CsPs is being burned in incinerators; therefore, this study has investigated the responses of CsPs to heating in air. The radioactivity of CsPs gradually decreased from 600 °C and was almost lost when the temperature reached 1000 °C. The size and spherical morphology of CsPs were almost unchanged after heating, but cesium including radiocesium, potassium and chlorine were lost, probably diffused away from the CsPs. Iron, zinc and tin originally dissolved in the glass matrix were crystallized to oxide nanoparticles inside the CsPs. When the CsPs were heated together with weathered granitic soil that is common in Fukushima, the radiocesium released from CsPs was sorbed by the surrounding soil. From these results, it is expected that the radioactivity of CsPs will be lost when radiation-contaminated waste including CsPs is burned in incinerators.

July 19, 2018 Posted by | Fukushima 2018 | , , , , | Leave a comment

Evaluating Different Radiocesium Decontamination Practices In A Forest Plantation Near The Fukushima Nuclear Power Plant

June 25, 2018
Owing to an earthquake and the resulting tsunami that occurred on March 2011 in central-eastern Japan, the Fukushima Dai-ichi Nuclear Power Plant was damaged by several hydrogen explosions.
This accident released a vast amount of radionuclides, including caesium 134 and 137 (ca. ratio 1:1). Initial fallout contaminated cultivated soils (mainly paddy fields), forests, water bodies, residential areas, asphalt and concrete surfaces. Since then, a variety of decontamination practices have been completed, reducing the ambient dose rates.
In a recent study, published in Environmental Pollution (available online since April 19, 2018) and conducted by Prof. Yuichi Onda (University of Tsukuba, Japan), Dr. Manuel López-Vicente (EEAD-CSIC, Soil Management and Global Change Group), and staff of Onda’s Laboratory and Asia Air Survey Co., eight decontamination practices were evaluated in a forest plantation located 16 km southwest of the power plant and within the exclusion area. The stand is composed of a forest plantation of Japanese cedar (Cryptomeria japonica) and natural understory vegetation. This plantation has an age of 58 years (in 2017) and is located on a steep hillslope (average slope gradient of 25⁰) near Kawauchi village, in the Fukushima Prefecture. Ten runoff plots were installed and managed by the Fukushima Prefectural Forestry Research Centre.
Radiocesium (Cs-137) concentrations and activities were calculated in soil and litter samples over 27 months (May 2013 – July 2015) and after decontamination practices. One plot was devoted to litter removal; two plots to tree thinning without litter removal (Th_1 with logged area, and Th_2 under remnant trees); two plots to tree thinning with litter removal (Th + LR_1 with logged area, and Th + LR_2 under remnant trees); and three plots to clearcutting with litter removal (CC + LR_1 without matting, CC + LR_2 matting with seeds, and CC + LR_3 matting without seeds). Finally, two plots (Co_1 and Co_2) remained as control plots without application of any decontamination practice.
Differences were statistically significant, and researchers distinguished four homogeneous groups. Tree thinning and litter removal greatly reduced the radioactivity. Tree thinning, clearcutting with litter removal, and litter removal also had higher discharge rates than those rates in the control plots. We only observed low rates in the two plots with matting (soil conservation practice). The temporal variability was explained by (i) the different rainfall depths registered during the measurement intervals (with heavy rainfall events and typhoons: accumulated precipitation from 14 to 361 mm during the measurement intervals); and (ii) the fluctuations of the total ground coverage (canopy and surface).
The vegetation recovery after the countermeasures triggered a reduction of hydrological connectivity in all compartments of the forest plantation. This fact explained the decreasing trend in radiocesium concentration that was very high in 2013, high in the first half of 2014, moderate in the second half of 2014, and low in 2015. This tendency will reduce the possibility of secondary pollution of the neighboring residential and/or agricultural areas. The average proportions of the contribution of Cs-137 discharge by soil and leaf fraction were 96.6% and 3.4%.
These findings are described in the article entitled Radiocesium concentrations in soil and leaf after decontamination practices in a forest plantation highly polluted by the Fukushima accident, recently published in the journal Environmental Pollution. This work was conducted by Manuel López-Vicente, Yuichi Onda, Junko Takahashi, and Hiroaki Kato from the University of Tsukuba, and Shinya Chayama and Keigo Hisadome from Asia Air Survey Co.
This research was funded by the project “Development of techniques for migration control against radioactive substances in forests (2012-2016)” of the Japanese Forestry Agency; and was carried out by Dr. Manuel López-Vicente during his postdoctoral stays at the University of Tsukuba (Prof. Onda Laboratory) in 2015 (Research Fellowships Program of the Canon Foundation in Europe, call 2014) and 2016.

June 26, 2018 Posted by | Fukushima 2018 | , , , | Leave a comment

Radioactive cesium detected in the urine of 100 children after the catastrophic accident of TEPCO Fukushima Daiichi nuclear power plant

 Cesium concentration found in more than 70% of the urine sample tested in Fukushima Prefecture



Scientific paper from Sachiko Saitou, Tomoya Yamauchi, Kobe University, submitted 16. January 2017.

Amounts of radioactive cesium, Cs-137 and Cs-134, in 24 h urine of 37 children have been determined using a HP-Ge detector, in Fukushima Prefecture between February 2014 and March 2016.

As comparisons, those of 25 children have been also measured who live in Western Japan from September 2016 to March 2017, and that of one child in Ibaraki Prefecture from April 2014 to January 2017.

We have found the cesium concentrations in the more than 70 % of urine samples from Fukushima Prefecture are in the ranges from 0.06 to 0.30 Bq/L.

No radioactive cesium is observed in the samples from Western Japan, under the detection limit of 0.1 Bq/L.

In the case of Ibaraki, the radioactivity keeps its value around 0.20 Bq/L during the inspection period, indicating the chronic ingestion of the radioactive cesium in his daily life.


July 21, 2017 Posted by | Fukushima 2017 | , , | Leave a comment