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Yoschenko V, Nanba K, Wada T, Johnson TE, Zhang J, Workman D, Nagata H. Late phase radiocesium dynamics in Fukushima forests post deposition. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2022; 251-252:106947. [PMID: 35732077 DOI: 10.1016/j.jenvrad.2022.106947] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2022] [Revised: 06/14/2022] [Accepted: 06/14/2022] [Indexed: 06/15/2023]
Abstract
The long term dynamics of radiocesium in typical forest ecosystems was studied in the radioactive contaminated areas in Fukushima Prefecture. Six observations sites located in Yamakiya Village (Kawamata Town; since 2014), Tsushima Village (Namie Town, since 2015), and Tomioka Town (since 2017) were monitored. The forests consisted of artificial plantations of Japanese cedar (Cryptomeria japonica) at Yamakiya Village, Tsushima Village, and Tomioka Town. Tsushima Village also had a natural mixed forest dominated by Japanese red pine (Pinus densiflora), and Tomioka Town had a young and a mature artificial plantation of Japanese cypress (Chamaecyparis obtuse). Concentrations of 137Cs were monitored in the samples collected from the main aboveground biomass compartments, fresh litterfall, forest litter, and soil. Concentrations of exchangeable forms of 137Cs and stable K were measured in soil samples. During the observation period, the litter radiocesium inventories at all sites decreased significantly to approximately 1% or less of the total ground deposition. Approximately 80% of the total radiocesium inventory is localized in the upper 5-cm layer of soil and there is little downward migration of radiocesium. At the sites with the longest monitoring series (Yamakiya and Tsushima), the radiocesium expectation depths and expectation mass depths were relatively constant at 2-3 cm and 5-6 kg m-2, respectively. Aboveground biomass compartments showed similar decreasing trends in radiocesium aggregated transfer factors, Tag, in the compartments that were exposed to atmospheric fallout in March 2011 (old foliage, small branches, and outer bark). The mean Tag in cedar stand compartments currently are in the range of 10-3-10-2 m2 kg-1 dw. However, the mean Tag and their dynamic trend significantly differed in the wood compartments of the cedar stands, which may indicate root uptake differences of orders of magnitude between observation sites. The difference in radiocesium concentration in wood between the sites becomes less pronounced when normalized by the ratio of exchangeable 137Cs/K in the soils.
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Affiliation(s)
- Vasyl Yoschenko
- Institute of Environmental Radioactivity at Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan.
| | - Kenji Nanba
- Institute of Environmental Radioactivity at Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
| | - Toshihiro Wada
- Institute of Environmental Radioactivity at Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
| | - Thomas E Johnson
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, 80523, United States
| | - Jian Zhang
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, 80523, United States
| | - Daniel Workman
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, 80523, United States
| | - Hiroko Nagata
- Institute of Environmental Radioactivity at Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
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Saidin ZH, Levia DF, Kato H, Kurihara M, Hudson JE, Nanko K, Onda Y. Vertical distribution and transport of radiocesium via branchflow and stemflow through the canopy of cedar and oak stands in the aftermath of the Fukushima Dai-ichi Nuclear Power Plant accident. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 818:151698. [PMID: 34798091 DOI: 10.1016/j.scitotenv.2021.151698] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2021] [Revised: 11/11/2021] [Accepted: 11/11/2021] [Indexed: 06/13/2023]
Abstract
Aiming to fill a need for data regarding radiocesium transport via both branchflow and stemflow through forests impacted by radioactive fallout, this study examined the vertical variation of radiocesium flux from branchflow and stemflow through the canopies of young Japanese cedar (Cryptomeria japonica (L. f.) D. Don) and Japanese oak (Quercus serrata Murray) trees in the aftermath of the Fukushima Dai-ichi Nuclear Power Plant accident. In forested areas approximately 40 km northwest of the location of the Fukushima Dai-ichi accident, the 137Cs concentration varied significantly among sampling periods and between the two forests, with the oak stand exhibiting higher 137Cs concentrations and depositional fluxes than the cedar stand. Expressed per unit trunk basal area, the depositional flux of 137Cs generated from the cedar and oak stands was 375 and 2810 Bq m-2 year-1, respectively. Of this total, 71% and 48% originated from the cedar and oak canopy, respectively, while the remainder originated from the trunk. Accordingly, the origin of radiocesium was more balanced for the oak stand with almost half of the flux coming from the canopy (48%) and the other half from the trunk (52%). Only about a quarter (29%) of the radiocesium flux originated from the trunk in Japanese cedar. Results from this work provide needed data that can enable a more thorough conceptualization of radiocesium cycling in forests. Coupling these empirical results with a physically-based model would likely lead to better forest management and proactive strategies for rehabilitating radioactively-contaminated forests and reducing the exposure risk of radiation dose rate for those that utilize forest products.
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Affiliation(s)
- Zul Hilmi Saidin
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Delphis F Levia
- Department of Geography and Spatial Sciences, University of Delaware, Newark, DE, USA; Department of Plant and Soil Sciences, University of Delaware, Newark, DE, USA
| | - Hiroaki Kato
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Momo Kurihara
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Janice E Hudson
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Kazuki Nanko
- Department of Disaster Prevention, Meteorology and Hydrology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan
| | - Yuichi Onda
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki, Japan.
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Gonze MA, Calmon P, Hurtevent P, Coppin F. Meta-analysis of radiocesium contamination data in Japanese cedar and cypress forests over the period 2011-2017. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 750:142311. [PMID: 33182179 DOI: 10.1016/j.scitotenv.2020.142311] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 09/07/2020] [Accepted: 09/07/2020] [Indexed: 06/11/2023]
Abstract
Since Fukushima accident, dozens of field studies have been conducted in order to quantify and understand the behaviour of atmospheric radiocesium (137Cs) fallouts in contaminated forests of Fukushima and neighbouring prefectures. In this paper, we carry out a detailed review of data acquired over 2011-2017 in Japanese cedar and cypress plantations, focusing on aerial tree organs, soil layers and tree-to-soil depuration fluxes. To enable comparison and reinforce the consistency between sites, radiological measurements were normalized by the deposit and interpolated onto the same spatio-temporal frame. Despite some (poorly explained) residual variability, we derived a "mean" pattern by log-averaging data among sites. These "mean" results were analysed with the help of a simple mass-balance approach and discussed in the light of post-Fukushima literature. We demonstrated that the activity levels and dynamics in all compartments were consistent and generally well reproduced by the mass balance approach, for values of the interception fraction between 0.7 and 0.85. The analysis indicated that about 5% of the initial deposit remained in the aerial vegetation after 6 years, more than two thirds of intercepted 137Cs being transferred to the soil due to throughfall. The simulations indicated that foliar uptake might have contributed between 40% and 100% to the activity transferred to stem wood. The activity concentration in canopy organs rapidly decreased in the first few months then more slowly, according to an effective half-life of about 1.6 years. The activity level in the organic layer peaked in summer 2011 then decreased according to an effective half-life of 2.2 years. After a rapid increase in 2011, the contamination of mineral horizons continued to increase more slowly, 85% of 137Cs incoming through the organic layer being retained in the 0-5 cm layer according to a mean residence time longer than in the upper layer (7 against 1.5 years).
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Affiliation(s)
- M-A Gonze
- Institute of Radiation Protection and Nuclear Safety, CE Cadarache-Bat 153, BP3, 13115 St-Paul-lez-Durance cedex, France.
| | - P Calmon
- Institute of Radiation Protection and Nuclear Safety, CE Cadarache-Bat 153, BP3, 13115 St-Paul-lez-Durance cedex, France
| | - P Hurtevent
- Institute of Radiation Protection and Nuclear Safety, CE Cadarache-Bat 153, BP3, 13115 St-Paul-lez-Durance cedex, France
| | - F Coppin
- Institute of Radiation Protection and Nuclear Safety, CE Cadarache-Bat 153, BP3, 13115 St-Paul-lez-Durance cedex, France
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Kenzo T, Saito S, Araki MG, Kajimoto T. Vertical distribution of radiocesium concentrations among crown positions and year-to-year variation in four major tree species after the Fukushima Daiichi Nuclear Power Plant accident. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2020; 225:106447. [PMID: 33091659 DOI: 10.1016/j.jenvrad.2020.106447] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Revised: 10/09/2020] [Accepted: 10/10/2020] [Indexed: 06/11/2023]
Abstract
To evaluate the distribution of radiocesium (137Cs) among crown positions in trees after the Fukushima Daiichi Nuclear Power Plant accident, we collected foliage and branch samples from different crown positions of four major tree species (Chamaecyparis obtusa, Cryptomeria japonica, Pinus densiflora, and Quercus serrata) from 2011 to 2019 in northeast Japan. We divided the samples into current-year and more than 1-year-old groups (called old foliage and old branches), which sometimes included directly contaminated parts. The 137Cs activity concentration in dry foliage and branches was measured using a germanium semiconductor detector. There were complex differences in the relative 137Cs activity concentration among species and organ types (i.e., foliage and branches) among crown positions. The relative 137Cs activity concentration in current-year foliage was higher in the upper crowns of C. obtusa, but higher in lower crown positions in C. japonica. No differences among crown positions were observed in P. densiflora and Q. serrata. In current-year branches, the relative 137Cs concentration in Q. serrata was similar among crown positions but higher in the upper crown in P. densiflora. The concentrations in old foliage and old branches in all species tended to be higher in the lower crown. The factors causing these interspecific and organ type differences among crown positions may be related to the organ turnover rate, dilution effect due to different growth rates, and potassium distribution within the crown. No year-to-year variation was observed in most foliage and branches in all species, except for current-year branches of Q. serrata, old foliage in C. japonica and P. densiflora, and old branches in P. densiflora. Our long-term data on the interspecific and inter-organ patterns of contamination, focusing on variation among crown positions and year-to-year trends, might help to improve the estimation of 137Cs deposition and dynamics in polluted forest ecosystems.
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Affiliation(s)
- Tanaka Kenzo
- Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, 305-8687, Japan.
| | - Satoshi Saito
- Kansai Research Center, Forestry and Forest Products Research Institute, Kyoto, 612-0855, Japan
| | - Masatake G Araki
- Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, 305-8687, Japan
| | - Takuya Kajimoto
- Tohoku Research Center, Forestry and Forest Products Research Institute, Morioka, 020-0123, Japan
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Kenzo T, Saito S, Miura S, Kajimoto T, Kobayashi NI, Tanoi K. Seasonal changes in radiocesium and potassium concentrations in current-year shoots of saplings of three tree species in Fukushima, Japan. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2020; 223-224:106409. [PMID: 32920309 DOI: 10.1016/j.jenvrad.2020.106409] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 08/28/2020] [Accepted: 08/29/2020] [Indexed: 06/11/2023]
Abstract
We studied seasonal changes in radiocesium (137Cs) activity and potassium concentrations in current-year leaves and branches of Pinus densiflora (naturally regenerated saplings), Cryptomeria japonica (planted saplings) and Quercus serrata (planted saplings and coppice shoots) in Fukushima, Japan. We collected current-year shoots from 10 individuals of each species over two growing seasons at intervals of 1-4 months, between June 2016 and December 2017. For the deciduous species Q. serrata, we also collected dead leaves that remained attached to branches in December to investigate reabsorption of 137Cs. All collected shoots were divided into leaves and branches, oven-dried, and ground; dry weights of each sample were recorded. 137Cs activity concentrations were measured using a germanium semiconductor detector. Potassium concentrations were quantified using inductively coupled plasma optical emission spectrometry (ICP-OES). Increases in dry weight were observed in both leaves and branches between May/June and August; growth then slowed considerably and virtually ceased after October. Clear seasonal changes in 137Cs activity concentrations were observed in both 2016 and 2017, regardless of tree species. Concentrations were higher in young leaves and branches during May and June, then decreased and changed relatively little from August to winter. Reduced 137Cs activity concentrations in dead leaves of Q. serrata were observed only in December 2017 (approximately 15% lower than in October). This reduction may indicate reabsorption of 137Cs in leaves prior to shedding. The changes in potassium concentrations were similar to those in 137Cs in both years. Potassium concentrations were higher in young leaves than in mature leaf and branch samples collected later in the year. A reduction of about 50% in the potassium concentrations in dead leaves of Q. serrata was also observed in December. A positive relationship between 137Cs and potassium concentrations in leaves and branches was observed in all species, except for planted Q. serrata. This relationship may indicate that 137Cs moves in tree shoots with potassium. Leaf and branch weight correlated negatively with 137Cs and potassium concentrations. Reduced concentrations may indicate dilution of these elements as a result of biomass increases over the growing season. Our results imply that irrespective of species, 137Cs exhibits seasonal variations resulting from dilution; these variations correspond with trends in potassium, with higher levels in young organs and decreased levels in older organs.
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Affiliation(s)
- Tanaka Kenzo
- Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, 305-8687, Japan.
| | - Satoshi Saito
- Kansai Research Center, Forestry and Forest Products Research Institute, Kyoto, 612-0855, Japan
| | - Satoru Miura
- Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, 305-8687, Japan
| | - Takuya Kajimoto
- Tohoku Research Center, Forestry and Forest Products Research Institute, Morioka, 020-0123, Japan
| | - Natsuko I Kobayashi
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, 113-0032, Japan
| | - Keitaro Tanoi
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, 113-0032, Japan
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Spatial variation and radiocesium flux of litterfall in hardwood-pine mixed forest and cedar plantations based on long-term monitoring data. J Radioanal Nucl Chem 2020. [DOI: 10.1007/s10967-020-07433-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Sakashita W, Miura S, Akama A, Ohashi S, Ikeda S, Saitoh T, Komatsu M, Shinomiya Y, Kaneko S. Assessment of vertical radiocesium transfer in soil via roots. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2020; 222:106369. [PMID: 32801027 DOI: 10.1016/j.jenvrad.2020.106369] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 07/22/2020] [Accepted: 07/22/2020] [Indexed: 06/11/2023]
Abstract
Several years after the Fukushima Daiichi Nuclear Power Plant accident, the surface mineral soil layer is believed to be the main reservoir of radiocesium (137Cs) in forest ecosystems in Japan. Dissolved 137Cs combines with clay minerals in the soil, and hence, it is not expected to easily infiltrate over time. However, previous studies have indicated that 137Cs derived from the older global fallout migrated deeper than that of the Chernobyl accident, and this cannot be explained by only the dissolved 137Cs vertical migration in the soil. Considering the carbon and nutrient dynamics in the forest floor, the 137Cs transfer process in soil via roots may alter its vertical distribution on a decadal scale. Therefore, in this study, we investigated the 137Cs activity concentrations in both roots and soil matrix, by considering four (0-20 cm) or six (0-30 cm) mineral soil layers taken at every 5 cm at seven study sites dominated by one of the six plant species (three coniferous forests, one deciduous forest, two deciduous forests covered by Sasa, and one bamboo forest) in eastern Japan in 2013. Comparing the results of 137Cs activity concentrations between roots and soil matrix taken at the same soil layer, roots at the surface (0-5 cm) layer often showed lower values than the soil matrix. However, roots deeper than 5 cm had higher activity concentrations than the soil matrix, conversely. The 137Cs inventories ratio of roots to soil matrix are about 1% at the 0-5 and 5-10 cm soil layer, and about 2% at the soil layers deeper than 10 cm. These results suggest that decomposition of root litter little affect the short-term vertical migration of 137Cs in the forest soil. However, it indicates that continuous production and mortality of roots with relatively high 137Cs activity concentrations have an important role for changing the vertical distribution of 137Cs on time scale of decades, particularly at deeper soil layers.
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Affiliation(s)
- Wataru Sakashita
- Center for Forest Restoration and Radioecology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan; Department of Forest Soils, FFPRI, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan.
| | - Satoru Miura
- Center for Forest Restoration and Radioecology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan
| | - Akio Akama
- Center for Forest Restoration and Radioecology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan
| | - Shinta Ohashi
- Center for Forest Restoration and Radioecology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan; Department of Wood Properties and Processing, FFPRI, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan
| | - Shigeto Ikeda
- Center for Forest Restoration and Radioecology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan; Department of Forest Soils, FFPRI, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan
| | - Tomoyuki Saitoh
- Tohoku Research Center, FFPRI, 92-25 Nabeyashiki, Shimokuriyagawa, Morioka, Iwate, 020-0123, Japan
| | - Masabumi Komatsu
- Center for Forest Restoration and Radioecology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan; Department of Mushroom Science and Forest Microbiology, FFPRI, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan
| | - Yoshiki Shinomiya
- Center for Forest Restoration and Radioecology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan; Department of Forest Soils, FFPRI, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan
| | - Shinji Kaneko
- Kansai Research Center, FFPRI, 68 Nagaikyutaroh, Momoyama, Fushimi, Kyoto, 612-0855, Japan
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Hara T, Takenaka C, Tomioka R. Change in the chemical form of 137Cs with age in needles of Japanese cedar. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2020; 213:106137. [PMID: 31983446 DOI: 10.1016/j.jenvrad.2019.106137] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Revised: 11/21/2019] [Accepted: 12/10/2019] [Indexed: 06/10/2023]
Abstract
Radiocesium (137Cs) derived from the accident of Fukushima Dai-ichi Nuclear Power Plant remains in forests. Although a large proportion of the 137Cs in forests has been transferred to soils, the rates of transfer to soils depend on the chemical form of 137Cs, which determines the mobility of 137Cs in plant tissues and subsequently during decomposition of leaf litter. In order to understand the dynamics of 137Cs in Sugi (Japanese cedar, Cryptomeria japonica) forests, we identified the chemical forms, such as water soluble, ion-exchangeable, and residual of 137Cs, 133Cs, K, and Rb in needle-bearing Sugi branches of different ages across several years. Compared with the results for K and Rb, Cs (133Cs + 137Cs) tended to change from a water-soluble form to an immobilized form with aging of needle-bearing branch segments. In addition, it was observed that a larger proportion of the immobilized Cs were accumulated in the green outer portions of the stems through aging.
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Affiliation(s)
- Tatsuya Hara
- Graduate School of Bioagricultural Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
| | - Chisato Takenaka
- Graduate School of Bioagricultural Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan.
| | - Rie Tomioka
- Graduate School of Bioagricultural Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
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Kato H, Onda Y, Saidin ZH, Sakashita W, Hisadome K, Loffredo N. Six-year monitoring study of radiocesium transfer in forest environments following the Fukushima nuclear power plant accident. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2019; 210:105817. [PMID: 30236975 DOI: 10.1016/j.jenvrad.2018.09.015] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 07/25/2018] [Accepted: 09/09/2018] [Indexed: 06/08/2023]
Abstract
The study investigated temporal changes in the 137Cs concentrations in vegetal and hydrological samples collected from various forests in Yamakiya District, Kawamata Town of Fukushima prefecture over six years following the Fukushima Dai-ichi nuclear power plant accident. Cesium-137 was detected in all forest environmental samples. However, the concentration in most samples decreased exponentially with time. The 137Cs concentrations in throughfall samples exhibited a double-exponential decreasing trend with time. Temporal changes in the 137Cs concentration in vegetal samples and stemflow were approximated by using a single-exponential equation. A comparison of the decline coefficient for the latter observation period (>2 y since the accident) revealed that the declining trend of 137Cs concentrations varied between foliage and the outer barks of the Japanese cedar and Japanese konara oak trees. The 137Cs concentration in cedar needles decreased exponentially while that in konara oak leaves was constant over the last six years. Conversely, the declining trend of 137Cs concentration in the outer bark of konara oak exceeded that of cedar. The results suggested that self-decontamination processes and internal recycling of 137Cs varied among tree species and different tree parts. The results indicated that the leaching of 137Cs in the throughfall in Japanese cedar was dependent on the 137Cs concentration in needles. However, a comparison of 137Cs concentrations in vegetal and hydrological samples from each sampling year showed that the leaching rate decreased with time. Conversely, the 137Cs concentrations in the stemflow were independent of the concentrations in the outer bark. The declining trend of 137Cs concentrations in litterfall (λ: 0.31-0.33 y-1) was similar to that of the mean of new/old needles (λ: 0.26-0.33 y-1) for cedar stands. With respect to the hydrological components, the 137Cs concentration in the stemflow (λ: 0.32-0.33 y-1) decreased at a slightly slower rate than that in the throughfall (λ: 0.36-0.54 y-1) for the cedar forest. The decline coefficients of 137Cs concentration in the aforementioned types of hydrological components slightly exceeded that for the vegetal samples. The results suggest that monitoring of 137Cs concentrations in hydrological components and vegetal samples can aid in further understanding the leaching mechanisms of 137Cs from trees to rainwater.
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Affiliation(s)
- Hiroaki Kato
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan.
| | - Yuichi Onda
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| | - Zul Hilmi Saidin
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| | - Wataru Sakashita
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
| | | | - Nicolas Loffredo
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Japan
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Yoshihara T, Kurita K, Matsumura H, Yoschenko V, Kawachi N, Hashida SN, Konoplev A, Yoshida H. Assessment of gamma radiation from a limited area of forest floor using a cumulative personal dosimeter. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2019; 204:95-103. [PMID: 30991205 DOI: 10.1016/j.jenvrad.2019.03.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Revised: 03/22/2019] [Accepted: 03/22/2019] [Indexed: 06/09/2023]
Abstract
To elucidate long term changes in gamma radiation from a limited region of interest of the forest floor, a simple monitoring procedure using a cumulative personal dosimeter (D-shuttle) was examined from 2016 to 2017. The test site was in a small forest in Abiko, Japan, where the initial radiocesium contamination from the Fukushima Dai-ichi Nuclear Power Plant was 60-100 kBq m-2. Three experimental plots basically containing a set of two 5 × 5 m2 observation areas were arranged at the site. The litterfall and decomposing organic layer of one area (D: decontaminated) were fully eliminated before the monitoring, whereas the other area (N: natural) was left unchanged. Five D-shuttle sets (i.e., D-shuttle, lead shield, and holder) per area were set up. One D-shuttle set could monitor the specific gamma radiation from radiocesium distributed within a limited area of ground (0.5 m radius of circle = ca. 0.8 m2 area of flat ground). The results indicated significant differences in the accumulated doses among each of the plots and areas, reflecting their soil radiocesium inventories. Interestingly, every index decreased with time, but the decreases were slower than the theoretical decay of radiocesium (134Cs and 137Cs). In addition, the accumulated dose decreased during heavy rainfall events. One possible explanation for these changes of the accumulated dose is a combination of meteorological and tree phenological phenomena, such as radiocesium from the forest canopy being newly added to the floor primarily by litterfall and soil moisture content disturbing radiation emitted from soils. This simple procedure enables long-term observation of gamma radiation from a limited area of forest floor non-invasively and semi-quantitatively.
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Affiliation(s)
- Toshihiro Yoshihara
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), 1646 Abiko, Abiko, Chiba, 270-1194, Japan.
| | - Keisuke Kurita
- Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma, 370-1292, Japan
| | - Hideyuki Matsumura
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), 1646 Abiko, Abiko, Chiba, 270-1194, Japan
| | - Vasyl Yoschenko
- Institute of Environmental Radioactivity of Fukushima University (IER), 1 Kanayagawa, Fukushima, Fukushima, 960-1296, Japan
| | - Naoki Kawachi
- Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma, 370-1292, Japan
| | - Shin-Nosuke Hashida
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), 1646 Abiko, Abiko, Chiba, 270-1194, Japan
| | - Alexei Konoplev
- Institute of Environmental Radioactivity of Fukushima University (IER), 1 Kanayagawa, Fukushima, Fukushima, 960-1296, Japan
| | - Hirohisa Yoshida
- Urban Environmental Sciences, Tokyo Metropolitan University (TMU), 1-1 Minami-Osawa, Hachioji, Tokyo, 192-0397, Japan
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Yoshihara T, Yoschenko V, Watanabe K, Keitoku K. A through year behavior of 137Cs in a Japanese flowering cherry tree in relation to that of potassium. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2019; 202:32-40. [PMID: 30776701 DOI: 10.1016/j.jenvrad.2019.01.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 01/09/2019] [Accepted: 01/24/2019] [Indexed: 06/09/2023]
Abstract
To understand the transfer of radiocesium (137Cs) in inside of deciduous trees, changes in 137Cs activity concentrations, primarily derived from the Fukushima accident in March 2011, were observed in the upper parts of a Japanese flowering cherry tree (Prunus x yedoensis cv. Somei-Yoshino) between 2015 and 2018. The sampling of the foliar parts occurred over the entire leaf life span from winter bud to litterfall and those of the branches were distinguished based on emergence years (2017, 2016, 2015, 2014-2011, and 2010/before). First, every tissue demonstrated a clear seasonal variation in 137Cs activity concentration. Second, a synchrony of seasonal variations in 137Cs activity concentration with those in the biological analogue of K concentration was observed in foliar parts during their growth season, but not in branches nor during the other seasons. With respect to the timing of changes in each tissue with tree phenology, it is possible that K and 137Cs alternate between leaves and branches via the same translocation mechanisms. The resorption efficiencies (i.e., 1 - [the concentrations in the last litterfall]/[the maximum concentrations in green leaves]) of K and 137Cs were 76% and 46% in average, respectively. In addition, both leaf buds and branches played an important role as reservoirs during dormancy. The buds storage ratio before and after bud burst (i.e., [the inventories in buds at the end of defoliation]/[those before and after bud burst]) for K were 0.57 and 0.10 in median, respectively, and those for and 137Cs were 1.14 and 0.14 in median, respectively. Consequently, the transfer of 137Cs in inside of trees was still visible seven years after deposition, even though the annual reduction in 137Cs activity concentration was apparent in each tissue.
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Affiliation(s)
- Toshihiro Yoshihara
- Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), 1646 Abiko, Chiba, 270-1194, Japan.
| | - Vasyl Yoschenko
- Institute of Environmental Radioactivity of Fukushima University (IER), 1 Kanayagawa, Fukushima, Fukushima, 960-1296, Japan
| | - Kenji Watanabe
- Institute of Environmental Radioactivity of Fukushima University (IER), 1 Kanayagawa, Fukushima, Fukushima, 960-1296, Japan
| | - Koji Keitoku
- Institute of Environmental Radioactivity of Fukushima University (IER), 1 Kanayagawa, Fukushima, Fukushima, 960-1296, Japan; Minamisoma City Hall, Odaka Ward Community Promotion Division, 2-28 Moto-machi Odaka, Minami Soma, Fukushima, 979-2195, Japan
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Yoschenko V, Takase T, Hinton TG, Nanba K, Onda Y, Konoplev A, Goto A, Yokoyama A, Keitoku K. Radioactive and stable cesium isotope distributions and dynamics in Japanese cedar forests. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2018; 186:34-44. [PMID: 29029765 DOI: 10.1016/j.jenvrad.2017.09.026] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2017] [Revised: 09/26/2017] [Accepted: 09/26/2017] [Indexed: 06/07/2023]
Abstract
Dynamics of the Fukushima-derived radiocesium and distribution of the natural stable isotope 133Cs in Japanese cedar (Cryptomeria japonica D. Don) forest ecosystems were studied during 2014-2016. For the experimental site in Yamakiya, Fukushima Prefecture, we present the redistribution of radiocesium among ecosystem compartments during the entire observation period, while the results obtained at another two experimental site were used to demonstrate similarity of the main trends in the Japanese forest ecosystems. Our observations at the Yamakiya site revealed significant redistribution of radiocesium between the ecosystem compartments during 2014-2016. During this same period radionuclide inventories in the aboveground tree biomass were relatively stable, however, radiocesium in forest litter decreased from 20 ± 11% of the total deposition in 2014 to 4.6 ± 2.7% in 2016. Radiocesium in the soil profile accumulated in the 5-cm topsoil layers. In 2016, more than 80% of the total radionuclide deposition in the ecosystem resided in the 5-cm topsoil layer. The radiocesium distribution between the aboveground biomass compartments at Yamakiya during 2014-2016 was gradually approaching a quasi-equilibrium distribution with stable cesium. Strong correlations of radioactive and stable cesium isotope concentrations in all compartments of the ecosystem have not been reached yet. However, in some compartments the correlation is already strong. An increase of radiocesium concentrations in young foliage in 2016, compared to 2015, and an increase in 2015-2016 of the 137Cs/133Cs concentration ratio in the biomass compartments with strong correlations indicate an increase in root uptake of radiocesium from the soil profile. Mass balance of the radionuclide inventories, and accounting for radiocesium fluxes in litterfall, throughfall and stemflow, enabled a rough estimate of the annual radiocesium root uptake flux as 2 ± 1% of the total inventory in the ecosystem.
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Affiliation(s)
- Vasyl Yoschenko
- Institute of Environmental Radioactivity of Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan.
| | - Tsugiko Takase
- Institute of Environmental Radioactivity of Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
| | - Thomas G Hinton
- Institute of Environmental Radioactivity of Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
| | - Kenji Nanba
- Institute of Environmental Radioactivity of Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
| | - Yuichi Onda
- Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Ibaraki Prefecture, 305-8572, Japan
| | - Alexei Konoplev
- Institute of Environmental Radioactivity of Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
| | - Azusa Goto
- Institute of Environmental Radioactivity of Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
| | - Aya Yokoyama
- Institute of Environmental Radioactivity of Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
| | - Koji Keitoku
- Institute of Environmental Radioactivity of Fukushima University, 1 Kanayagawa, Fukushima, Fukushima Prefecture, 960-1296, Japan
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Gonze MA, Calmon P. Meta-analysis of radiocesium contamination data in Japanese forest trees over the period 2011-2013. THE SCIENCE OF THE TOTAL ENVIRONMENT 2017; 601-602:301-316. [PMID: 28570967 DOI: 10.1016/j.scitotenv.2017.05.175] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 05/15/2017] [Accepted: 05/20/2017] [Indexed: 06/07/2023]
Abstract
The fate and dispersion of radiocesium in forests affected by the Fukushima atmospheric fallouts have been efficiently characterized by Japanese scientists thanks to monitoring surveys of radioactive contents in contaminated soil, water, and vegetation samples at numerous sites. In this paper, we carry out a meta-analysis of the field surveys conducted over the period 2011-2013 in evergreen coniferous and deciduous broadleaf forests of Fukushima or neighboring prefectures. The review focuses on contamination data acquired in tree vegetation - about 1500 spatio-temporal measurements of concentrations, inventories and depuration fluxes - with a particular interest for organs that were directly exposed to the atmospheric fallouts and subjected to depuration mechanisms (foliage, branches and outer bark). To reduce the spatial variability between the sites, radioactive data were normalized by the total deposit estimated at each site. Our analysis highlights the overall consistency of field observations despite the variety of experimental protocols, disparate sampling periods, differences in the forest stand characteristics and variability of the atmospheric deposition conditions. Assuming that the sites conformed to the same dynamics (within the range of residual variability), we then derive, discuss, and compare the mean representative evolutions of radiocesium contamination in the two categories of forest. Thanks to a simple mass balance approach, we finally demonstrate that: (i) about 90% of the radiocesium deposit was intercepted by evergreen coniferous vegetation, (ii) 80% of the deposit was gradually transferred to the forest floor in 3years, according to a well characterized depuration kinetics, and (iii) about 4% was readily absorbed by the foliage and translocated to internal organs (inner bark, stem wood and roots) at a rate of about 10-4d-1.
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Affiliation(s)
- M-A Gonze
- Institute of Radiation Protection and Nuclear Safety, CE Cadarache-Bat 153, BP3 - 13115 St-Paul-lez-Durance Cedex, France.
| | - P Calmon
- Institute of Radiation Protection and Nuclear Safety, CE Cadarache-Bat 153, BP3 - 13115 St-Paul-lez-Durance Cedex, France
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