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Yamaguchi, Akiko; Okumura, Masahiko; Kawamura, Naomi*; Takahashi, Yoshio*
Science of the Total Environment, 964, p.178585_1 - 178585_13, 2025/02
There are many unresolved issues in the adsorption reactions of clay minerals. One of the reasons is the existence of multiple adsorption sites. It is known that the contribution of each adsorption site depends on the concentration of adsorbed ions, and there is a challenge in comprehensively correlate the results of atomic-level simulations that employ limited number of atoms and inevitably deal high-concentration samples with actual environmental samples where concentrations are orders of magnitude lower. In this study, we combined experiments using synchrotron radiation and first-principles calculations to comprehensively elucidate the systematic changes in the local structure of adsorption sites and adsorbed ions based on the adsorption concentration at the atomic level, and demonstrated that the interaction between adsorbed ions and clay minerals involves ionic bonding.
Metcalfe, R.*; Benbow, S. J.*; Kawama, Daisuke*; Tachi, Yukio
Science of the Total Environment, 958, p.177690_1 - 177690_17, 2025/01
Uplifting fractured granitic rocks occur in substantial areas of countries such as Japan. A repository site would be selected in such an area only if it is possible to make a safety case, accounting for the changing conditions during uplift. The safety case must include robust arguments that chemical processes in the rocks around the repository will contribute sufficiently to minimise radiological doses to biosphere receptors. To provide confidence in the safety arguments, numerical models need to be sufficiently realistic, but also parameterised conservatively (pessimistically). However, model development is challenging because uplift involves many complex couplings between groundwater flow, chemical reactions between water and rock, and changing rock properties. The couplings would affect radionuclide mobilisation and retardation, by influencing diffusive radionuclide fluxes between groundwater flowing in fractures and effectively immobile porewater in the rock matrix and radionuclide partitioning between water and solid phases, via: (i) mineral precipitation/dissolution; (ii) mineral alteration; and (iii) sorption/desorption. It is difficult to represent all this complexity in numerical models while showing that they are parameterised conservatively. Here we present a modelling approach, illustrated by simulation cases for some exemplar radioelements, to identify realistically conservative process conceptualisations and model parameterisations.
Metcalfe, R.*; Tachi, Yukio; Sasao, Eiji; Kawama, Daisuke*
Science of the Total Environment, 957, p.177375_1 - 177375_17, 2024/12
A safety case for an underground radioactive waste repository must show that groundwater will not in future transport radionuclides from the repository to the near-surface environment (the biosphere) in harmful quantities. Safety cases are developed step-wise throughout a programme to site and develop a repository. At early stages, before a site is selected, safety cases are generic and based on simplified safety assessment models of the disposal system that have conservative parameter values. Later, when site-specific conditions are known, more realistic models are needed for the long-term geo-environmental evolution and their impacts on radionuclide migration/retention. Uplift is one such environmental change, which may be particularly important in countries near active tectonic plate boundaries, such as Japan. Here we review the state of knowledge about how the properties of fractured granitic rocks evolve during uplift, based on studies in Japan. Hence, we present conceptual models and a generic scenario for mass transport and retardation processes in uplifting granitic rocks as a basis for realistic numerical models to underpin safety assessment.
Uno, Koichiro*; Okumura, Masahiko; Nakao, Atsushi*; Yamaguchi, Akiko; Yanai, Junta*
Science of the Total Environment, 949, p.175012_1 - 175012_8, 2024/11
Times Cited Count:0 Percentile:0.00(Environmental Sciences)Frayed edge sites (FES), formed by the partial weathering of mica minerals, selectively adsorb Cs ions. However, the detailed mechanism of this adsorption has not been fully clarified. In this study, cation extraction and Cs adsorption experiments were conducted on mica. It was found that potassium-adsorbed mica adsorbed more Cs than rubidium-adsorbed mica. To elucidate the cause of this, the stability of Cs, rubidium, and potassium adsorbed on FES was evaluated using first-principles calculations. It was determined that the presence of potassium as the cation species prior to Cs adsorption is important for the stability of Cs on the FES.
Taniguchi, Takeshi*; Isobe, Kazuo*; Imada, Shogo*; Eltayeb, M. M.*; Akaji, Yasuaki*; Nakayama, Masataka; Allen, M. F.*; Aronson, E. L.*
Science of the Total Environment, 899, p.165524_1 - 165524_13, 2023/11
Times Cited Count:11 Percentile:81.35(Environmental Sciences)Dryland ecosystems experience seasonal cycles of severe drought and moderate precipitation. Desert plants typically have patchy distributions, and many may develop symbiotic relationships with root endophytic microbes to survive under the repeated wet and extremely dry conditions. Although community coalescence has been found in many systems, the colonization by functional microbes and its relationship to seasonal transitions in arid regions are not well understood. Here we examined root endophytic microbial taxa, and their traits in relation to their root colonization, during the dry and wet seasons in a hot desert of the southwestern United States. We used high-throughput DNA sequencing of 16S rRNA and ITS gene profiling of five desert shrubs, and analyzed the seasonal change in endophytic microbial lineages. In summer, Actinobacteria increased, although this was not genus-specific. For fungi, Glomeraceae selectively increased in summer. In winter, Gram-negative bacterial genera, including those capable of nitrogen fixation and plant growth promotion, increased. Neutral model analysis revealed a strong stochastic influence on endophytic bacteria but a weak effect for fungi, especially in summer. The taxa with higher frequency than that predicted by the neutral model shared environmental adaptability and symbiotic traits, whereas the frequency of pathogenic fungi was at or under the predicted value. These results suggest that community assembly of bacteria and fungi is regulated differently. The bacterial community was affected by stochastic and deterministic processes via the bacterial response to drought (response trait) and beneficial effect on plants (effect trait). For fungi, mycorrhizal fungi were selected by plants in summer. The regulation of beneficial microbes by plants in both dry and wet seasons suggests the presence of plant-soil positive feedback in this natural desert ecosystem.
Ikenoue, Tsubasa; Shimadera, Hikari*; Nakanishi, Takahiro; Kondo, Akira*
Science of the Total Environment, 876, p.162846_1 - 162846_12, 2023/06
Times Cited Count:5 Percentile:44.52(Environmental Sciences)We conducted 30 years simulation of environmental fate of Cs in the Abukuma River basin considering the characteristics of the
Cs behavior in land uses. Overall, in the Abukuma River basin, the
Cs transported into the ocean for 30 years was estimated to correspond to 4.6% of the initial deposition in the basin, and the effective half-life of
Cs deposited in the basin was estimated to be 3.7 years shorter (by 11.6%) than its physical half-life. These results suggested that
Cs deposited from the accident could still remain for decades. Based on the analysis of the
Cs behavior in land use, in 2011, the contribution of
Cs export to the ocean from urban lands was estimated to correspond to 70% of the total
Cs export. Meanwhile, from 2012 to 2040, the contribution of
Cs export from agricultural lands was estimated to correspond to 75% of the total
Cs export. The reduction ratios excluding radioactive decay of
Cs remained in areas with and without human activities for 30 years after the accident, defined as the ratios of the total outflow to the initial deposition, were estimated to be 11.5%-17.7% and 0.4%-1.4%, respectively. These results suggested that human activities enhance the reduction of
Cs remaining in land in the past and future.
Battulga, B.; Atarashi-Andoh, Mariko; Nakanishi, Takahiro; Koarashi, Jun
Science of the Total Environment, 849, p.157758_1 - 157758_11, 2022/11
Times Cited Count:7 Percentile:47.21(Environmental Sciences)Characterizing plastic-associated biofilms is key to the better understanding of organic material and mineral cycling in the "Plastisphere"-the thin layer of microbial life on plastics. In this study, we propose a new method to extract biofilms from environmental plastics, in order to evaluate the properties of biofilm-derived organic matter through stable carbon (C) and nitrogen (
N) isotope signatures and their interactions with radionuclides especially radiocesium (
Cs). After ultrasound-assisted separation from the plastics, biofilm samples were successfully collected via a sequence of syringe treatments. Biofilm-derived organic matter samples (14.5-65.4 mg) from four river mouths in Japan showed
Cs activity concentrations of
75 to 820 Bq kg
biofilm (dw), providing evidence that environmental plastics, mediated by developed biofilms, serve as a carrier for
Cs in the coastal environment. Significant differences in the (
C and
N signatures were also obtained for the biofilms, indicating the different sources, pathways, and development processes of biofilms on plastics.
Johansen, M. P.*; Child, D. P.*; Collins, R.*; Cook, M.*; Davis, J.*; Hotchkis, M. A. C.*; Howard, D. L.*; Howell, N.*; Ikeda, Atsushi; Young, E.*
Science of the Total Environment, 842, p.156755_1 - 156755_11, 2022/10
Times Cited Count:6 Percentile:41.40(Environmental Sciences)Suzuki, Shotaro*; Amano, Yosuke*; Enomoto, Masahiro*; Matsumoto, Akira*; Morioka, Yoshiaki*; Sakuma, Kazuyuki; Tsuruta, Tadahiko; Kaeriyama, Hideki*; Miura, Hikaru*; Tsumune, Daisuke*; et al.
Science of the Total Environment, 831, p.154670_1 - 154670_15, 2022/07
Times Cited Count:2 Percentile:12.53(Environmental Sciences)Wu, C.*; Tanaka, Kazuya; Tani, Yukinori*; Bi, X.*; Liu, J.*; Yu, Q.*
Science of the Total Environment, 821, p.153265_1 - 153265_9, 2022/05
Times Cited Count:48 Percentile:96.66(Environmental Sciences)Microplastics (MPs) with different particle sizes were co-cultured with a model freshwater fungus, strain KR21-2, to form biofilms on their surface. We also determined the changes in surface physicochemical properties of the biofilm-covered MPs (BMPs) and the heavy metal adsorption capacity of the original MPs and BMPs. The results revealed that the biofilms improve the adsorption of heavy metals on MPs, and the particle size of MPs plays a crucial role in biofilm colonization and adsorption of heavy metals by BMPs.
Ota, Masakazu; Koarashi, Jun
Science of the Total Environment, 816, p.151587_1 - 151587_21, 2022/04
Times Cited Count:8 Percentile:52.34(Environmental Sciences)In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with Cs. However,
Cs transfer processes determining tree contamination (particularly for stem wood, which is a prominent commercial resource in Fukushima) remain insufficiently understood. This study proposes a model for simulating the dynamic behavior of
Cs in a forest tree-litter-soil system and applied it to two contaminated forests (cedar plantation and natural oak stand) in Fukushima. The model-calculated results and inter-comparison of the results with measurements elucidated the relative impact of distinct
Cs transfer processes determining tree contamination. The transfer of
Cs to trees occurred mostly (
99%) through surface uptake of
Cs directly trapped by leaves or needles and bark during the fallout. By contrast, root uptake of
Cs from the soil was unsubstantial and several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, the internal contamination of the trees proceeded through an enduring recycling (translocation) of
Cs absorbed on the tree surface at the time of the accident. A significant surface uptake of
Cs at the bark was identified, contributing 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining surface uptake occurred at the needles) of the total
Cs uptake by trees. It was suggested that the trees growing at the study sites are currently (as of 2021) in a decontamination phase; the activity concentration of
Cs in the stem wood decreases by 3% per year, mainly through radioactive decay of
Cs and partly through a dilution effect from tree growth.
Uchiyama, Yusuke*; Tokunaga, Natsuki*; Azuma, Kohei*; Kamidaira, Yuki; Tsumune, Daisuke*; Iwasaki, Toshiki*; Yamada, Masatoshi*; Tateda, Yutaka*; Ishimaru, Takashi*; Ito, Yukari*; et al.
Science of the Total Environment, 816, p.151573_1 - 151573_13, 2022/04
Times Cited Count:10 Percentile:61.04(Environmental Sciences)no abstracts in English
Funaki, Hironori; Tsuji, Hideki*; Nakanishi, Takahiro; Yoshimura, Kazuya; Sakuma, Kazuyuki; Hayashi, Seiji*
Science of the Total Environment, 812, p.152534_1 - 152534_10, 2022/03
Times Cited Count:21 Percentile:71.64(Environmental Sciences)Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediment to water columns, which may contribute to a long-term contamination in aquatic products. This study systematically investigated the Cs activities between sediment and pore water, which is a direct evidence of the remobilisation of bioavailable
Cs from sediments, in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant accident. Our results strongly indicate a competitive ion exchange process between
Cs and NH
via a highly selective interaction with the frayed edges sites of phyllosilicate minerals to be the major reason for the variability of the Kd values between sediment and pore water, even in the Fukushima case.
Sakuma, Kazuyuki; Machida, Masahiko; Kurikami, Hiroshi; Iwata, Ayako; Yamada, Susumu; Iijima, Kazuki
Science of the Total Environment, 806, Part 3, p.151344_1 - 151344_8, 2022/02
Times Cited Count:7 Percentile:31.98(Environmental Sciences)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
Times Cited Count:4 Percentile:17.32(Environmental Sciences)Tanaka, Kazuya; Kanasashi, Tsutomu*; Takenaka, Chisato*; Takahashi, Yoshio*
Science of the Total Environment, 755, Part 2, p.142598_1 - 142598_8, 2021/02
Times Cited Count:5 Percentile:22.31(Environmental Sciences)In this study, we investigated coordination structures of Cs in Cs-doped bark, sapwood, heartwood, needle, and branch samples of trees collected in Fukushima by extended X-ray absorption fine structure (EXAFS) spectroscopy. We examined four representative tree species in Fukushima,
,
,
, and
. EXAFS spectra suggested that Cs was adsorbed as an outer-sphere complex on all parts of the four species, with electrostatic binding to negatively charged functional groups in components of tree tissues. These results were supported by extraction experiments where most of the sorbed Cs was desorbed from all parts of each tree species using 1 M CH
COONH
.
Kinoshita, Norikazu*; Nagaoka, Mika; Nakanishi, Takashi*
Science of the Total Environment, 753, p.142087_1 - 142087_10, 2021/01
Times Cited Count:5 Percentile:22.31(Environmental Sciences)The distribution of the anthropogenic radionuclide americium-241 (Am), a decay product of
Pu discharged from atmospheric tests of nuclear weapons, was investigated to resolve its horizontal and vertical migration in the Tropical East Pacific. We analyzed
Am concentrations in seawater samples collected in 2003. On comparing the
Am concentrations with the previously determined concentrations of
Pu in the same samples, the vertical profiles of
Am were found to be similar to those of
Pu. At some stations, the maximum concentration of
Am occurred 100-200 m deeper than that of
Pu. The
Am/
Pu ratios in the North Pacific and South Pacific were comparable to one another, and were typical of the ratio for the Pacific. The
Am distribution was influenced by the water mass at depths below 400 m. The
Am data support the view there is a current flowing at depths of 400-3000 m from the North Pacific through the equator to the South Pacific. In addition, the
Am vertical profile was explained by using a box model that considers the decay of
Pu and adsorption and scavenging by suspended particles. The different depths for the maximum concentrations of
Am and
Pu observed at some stations were well explained by the model and by the distribution of CaCO
particles. The residence time of
Am in the Pacific was also estimated by using the model.
Hosoda, Masahiro*; Nugraha, E. D.*; Akata, Naofumi*; Yamada, Ryohei; Tamakuma, Yuki*; Sasaki, Michiya*; Kelleher, K.*; Yoshinaga, Shinji*; Suzuki, Takahito*; Rattanapongs, C. P.*; et al.
Science of the Total Environment, 750, p.142346_1 - 142346_11, 2021/01
Times Cited Count:35 Percentile:85.36(Environmental Sciences)The biological effects of low dose-rate radiation exposures on humans remains unknown. In fact, the Japanese nation still struggles with this issue after the Fukushima Dai-ichi Nuclear Power Plant accident. Recently, we have found a unique area in Indonesia where naturally high radiation levels are present, resulting in chronic low dose-rate radiation exposures. We aimed to estimate the comprehensive dose due to internal and external exposures at the particularly high natural radiation area, and to discuss the enhancement mechanism of radon. A car-borne survey was conducted to estimate the external doses from terrestrial radiation. Indoor radon measurements were made in 47 dwellings over three to five months, covering the two typical seasons, to estimate the internal doses. Atmospheric radon gases were simultaneously collected at several heights to evaluate the vertical distribution. The absorbed dose rates in air in the study area vary widely between 50 nGy h and 1109 nGy h
. Indoor radon concentrations ranged from 124 Bq m
to 1015 Bq m
. That is, the indoor radon concentrations measured exceed the reference levels of 100 Bq m
recommended by the World Health Organization. Furthermore, the outdoor radon concentrations measured were comparable to the high indoor radon concentrations. The annual effective dose due to external and internal exposures in the study area was estimated to be 27 mSv using the median values. It was found that many residents are receiving radiation exposure from natural radionuclides over the dose limit for occupational exposure to radiation workers. This enhanced outdoor radon concentration might be as a result of the stable atmospheric conditions generated at an exceptionally low altitude. Our findings suggest that this area provides a unique opportunity to conduct an epidemiological study related to health effects due to chronic low dose-rate radiation exposure.
Funaki, Hironori; Sakuma, Kazuyuki; Nakanishi, Takahiro; Yoshimura, Kazuya; Katengeza, E. W.*
Science of the Total Environment, 743, p.140668_1 - 140668_9, 2020/11
Times Cited Count:26 Percentile:68.54(Environmental Sciences)Tachi, Yukio; Sato, Tomofumi*; Akagi, Yosuke*; Kawamura, Makoto*; Nakane, Hideji*; Terashima, Motoki; Fujiwara, Kenso; Iijima, Kazuki
Science of the Total Environment, 724, p.138098_1 - 138098_11, 2020/07
Times Cited Count:18 Percentile:57.82(Environmental Sciences)To understand and predict radiocesium transport behaviors in the environment, highly contaminated sediments from Ukedo and Odaka rivers around the Fukushima Daiichi Nuclear Power Plant were investigated systematically focusing on key factors controlling radiocesium sorption and fixation, including particle size, clay mineralogy and organic matter.