研究者データベース

渡邊 直子(ワタナベ ナオコ)
工学研究院 応用量子科学部門 量子エネルギー工学
准教授

基本情報

所属

  • 工学研究院 応用量子科学部門 量子エネルギー工学

職名

  • 准教授

学位

  • Ph D(University of California, Davis)

ホームページURL

J-Global ID

研究キーワード

  • 放射性セシウム   MD計算   有機物   土壌   収脱着   物質移行   腐食   放射性廃棄物   ベントナイト   オーバーパック   放射性廃棄物処分   

研究分野

  • エネルギー / 原子力工学

職歴

  • 2013年 北海道大学 工学(系)研究科(研究院) 准教授

研究活動情報

論文

  • Jaka Rachmadetin, Masaya Mizuto, Shingo Tanaka, Tamotsu Kozaki, Naoko Watanabe
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 56 11 959 - 970 2019年11月 [査読有り][通常論文]
     
    In the safety assessment of radioactive waste disposal, it is critical to understand the porewater chemistry in compacted bentonite in order to predict long-term migration behavior of radionuclides in the engineered barrier. This study estimates the activity coefficients of dissolved ions in the porewater of compacted bentonite from the concentrations of ions at which CaCO3 precipitation occurred. Solutions containing CaCl2 and NaHCO3 were introduced under electrical potential gradient from the opposite sides of the compacted Na-bentonite packed at the dry density of 1.0kg/dm(3). After the electromigration, the spatial distribution of ions along the compacted bentonite sample was determined. Sequential extraction method was developed to distinctly determine the concentrations of free ions in the porewater and in solid phase in bentonite. The results show that the exchangeable Na+ ions were progressively replaced by the incoming Ca2+ ions, and the compacted bentonite sample can be divided into three zones: Ca-, Ca-/Na-, and Na-bentonite zones. Precipitates of CaCO3 were observed both in Ca- and Ca/Na-bentonite zones. The experimentally determined activity coefficients were at least smaller by a factor of 3 compared to the theoretical approximation calculated using PHREEQC code assuming dilute-solution conditions with no electrostatic interactions between ions and bentonite surface.
  • Toshihiko Ohnuki, Fuminori Sakamoto, Naofumi Kozai, Kenji Nanba, Hitoshi Neda, Yoshito Sasaki, Tadafumi Niizato, Naoko Watanabe, Tamotsu Kozaki
    ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS 21 7 1164 - 1173 2019年07月 [査読有り][通常論文]
     
    The fate of radioactive Cs deposited after the Fukushima nuclear power plant accident and its associated radiological impacts are largely dependent on its mobility from surface soils to forest ecosystems. We measured the accumulation of radioactive Cs in the fruit bodies of wild fungi in a forest at Iitate, Fukushima, Japan. The transfer factors (TFs) of radioactive Cs from soil to the fruit bodies of wild fungi were between 10(-2) and 10(2), a range similar to that reported for the fruit bodies collected in Europe after the Chernobyl accident and in parts of Japan contaminated by the nuclear bomb test fallout. Comparison of the TFs of wild mushroom and those of fungal hyphae of 704 stock strains grown on agar medium containing nutrients and Cs-137 showed that the TFs of wild mushroom were lower. The TF was less than 0.1 after the addition of the minerals zeolite, vermiculite, phlogopite, smectite, or illite of 1.0% weight to the agar medium. These results indicate that the presence of minerals decreases Cs uptake by fungi grown on the agar medium, and filamentous fungi still accumulate radioactive Cs even when minerals are present in the medium.
  • Sarah C. Hafner, Naoko Watanabe, Thomas Harter, Brian A. Bergamaschi, Sanjai J. Parikh
    JOURNAL OF ENVIRONMENTAL MANAGEMENT 190 28 - 34 2017年04月 [査読有り][通常論文]
     
    Environmental release of veterinary pharmaceuticals has been of regulatory concern for more than a decade. Monensin is a feed additive antibiotic that is prevalent throughout the dairy industry and is excreted in dairy waste. This study investigates the potential of dairy waste management practices to alter the amount of monensin available for release into the environment. Analysis of wastewater and groundwater from two dairy farms in California consistently concluded that monensin is most present in lagoon water and groundwater downgradient of lagoons. Since the lagoons represent a direct source of monensin to groundwater, the effect of waste management, by mechanical screen separation and lagoon aeration, on aqueous monensin concentration was investigated through construction of lagoon microcosms. The results indicate that monensin attenuation is not improved by increased solid-liquid separation prior to storage in lagoons, as monensin is rapidly desorbed after dilution with water. Monensin is also shown to be easily degraded in lagoon microcosms receiving aeration, but is relatively stable and available for leaching under typical anaerobic lagoon conditions. (C) 2016 Elsevier Ltd. All rights reserved.
  • Keiko Yamaji, Satoshi Nagata, Toshikatsu Haruma, Toshihiko Ohnuki, Tamotsu Kozaki, Naoko Watanabe, Kenji Nanba
    JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 153 112 - 119 2016年03月 [査読有り][通常論文]
     
    We found that root endophytes of Cs-137 accumulator plant produce siderophores, resulting in the desorption of Cs-137 from the contaminated soil collected at Fukushima, Japan. We selected an endemic Japanese deciduous tree, Eleutherococcus sciadophylloides (Franch. et Say), that accumulates high concentrations of Cs-137 and Mn. Root endophytic bacteria were isolated from E. sciadophylloides and microbial siderophore production was evaluated via chrome azurol S (CAS) Fe and CAS Al assays. Of the 463 strains that we isolated, 107 (23.1%) produced the siderophores. Using eight strains that showed high siderophore production in our assays, we examined desorption of Cs-137, Mn, Fe and Al by the bacterial culture filtrates from Cs-137-contaminated soil after decomposing the soil organic matter using hydrogen peroxide. We found Cs-137 and Mn desorption concomitant with Al and Fe desorption, as well as a decrease of pH. We also detected succinic acid, a well-known siderophore, in the bacterial culture filtrates of our two root endophytic bacteria. Our results strongly suggest that the root endophytic bacteria of E. sciadophylloides produce the siderophores that enhance Cs-137 and Mn desorption in the rhizosphere, making the resulting Cs-137 and Mn ions easier for E. sciadophylloides to absorb from the rhizosphere. (C) 2015 Elsevier Ltd. All rights reserved.
  • Xunde Li, Edward R. Atwill, Elizabeth Antaki, Olin Applegate, Brian Bergamaschi, Ronald F. Bond, Jennifer Chase, Katherine M. Ransom, William Samuels, Naoko Watanabe, Thomas Harter
    JOURNAL OF ENVIRONMENTAL QUALITY 44 5 1435 - 1447 2015年09月 [査読有り][通常論文]
     
    Surveys of microbiological groundwater quality were conducted in a region with intensive animal agriculture in California, USA. The survey included monitoring and domestic wells in eight concentrated animal feeding operations (CAFOs) and 200 small (domestic and community supply district) supply wells across the region. Campylobacter was not detected in groundwater, whereas Escherichia coli O157:H7 and Salmonella were each detected in 2 of 190 CAFO monitoring well samples. Nonpathogenic generic E. coli and Enterococcus spp. were detected in 24.2% (46/190) and 97.4% (185/190) groundwater samples from CAFO monitoring wells and in 4.2% (1/24) and 87.5% (21/24) of CAFO domestic wells, respectively. Concentrations of both generic E. coli and Enterococcus spp. were significantly associated with well depth, season, and the type of adjacent land use in the CAFO. No pathogenic bacteria were detected in groundwater from 200 small supply wells in the extended survey. However, 4.5 to 10.3% groundwater samples were positive for generic E. coli and Enterococcus. Concentrations of generic E. coli were not significantly associated with any factors, but concentrations of Enterococcus were significantly associated with proximity to CAFOs, seasons, and concentrations of potassium in water. Among a subset of E. coli and Enterococcus isolates from both surveys, the majority of E. coli (63.6%) and Enterococcus (86.1%) isolates exhibited resistance to multiple (>= 3) antibiotics. Findings confirm significant microbial and antibiotic resistance loading to CAFO groundwater. Results also demonstrate significant attenuative capacity of the unconfined alluvial aquifer system with respect to microbial transport.
  • Toshihiko Ohnuki, Fuminori Sakamoto, Shinya Yamasaki, Naofumi Kozai, Hiroyuki Shiotsu, Satoshi Utsunomiya, Naoko Watanabe, Tamotsu Kozaki
    JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 144 127 - 133 2015年06月 [査読有り][通常論文]
     
    The accumulation of Cs by unicellular fungus of Saccharomyces cerevisiae in the presence of minerals has been studied to elucidate the role of microorganisms in the migration of radioactive Cs in the environment. Two different types of experiments were employed: experiments using stable Cs to examine the effect of a carbon source on the accumulation of Cs, and accumulation experiments of radioactive Cs from agar medium containing Cs-137 and zeolite, vermiculite, phlogopite, smectite, mica, or illite as mineral supplements. In the former type of experiments, the Cs-accumulated cells were analyzed by scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDS). In the latter type, the radioactivity in the yeast cells was measured by an autoradiography technique.When a carbon source was present, higher amounts of Cs accumulated in the cells than in the resting condition without a carbon source. Analyses with SEM-EDS showed that no mineral formed on the cell surface. These results indicate that the yeast cells accumulate Cs by adsorption on the cell surface and intracellular accumulation. In the presence of minerals in the agar medium, the radioactivity in the yeast cells was in the order of mica > smectite, illite >> vermiculite, phlogopite, zeolite. This order is inversely correlated to the ratio of the concentration of radioactive Cs between the minerals and the medium solution. These results strongly suggest that the yeast accumulates radioactive Cs competitively with minerals. (C) 2015 Elsevier Ltd. All rights reserved.
  • Hiroaki Takiya, Naoko Watanabe, Tamotsu Kozaki, Seichi Sato
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 52 5 728 - 738 2015年05月 [査読有り][通常論文]
     
    Apparent diffusion coefficients (D-a) of water and activation energies (E-a) of diffusion in hardened cement pastes (HCPs) were determined as a function of water-to-cement (w/c) ratio (0.36-0.60) and temperature (293-323K) using HTO and (H2O)-O-18 as tracers. The values of D-a and E-a ranged from 1.1x10(-11) to 1.7x10(-10) m(2) s(-1) and from 21.5 to 31.3 kJ mol(-1), respectively. No significant difference between the D-a values of HTO and (H2O)-O-18 suggests that water predominantly diffuses as H2O molecule and dissociation of water is not significant even at high pH range in HCP. The values of E-a at low w/c ratio were higher than in bulk liquid water, suggesting a contribution of a different water regime, such as supercooled bulk water. Two simple models consisting of capillary and gel pores were considered to estimate the volume ratio of gel pores to total pores by optimizing the model to fit with the experimental data. The result suggests that HCP has a pore network mostly consisting of capillary pores with some very narrow pores plugged with hydrates, where HTO must diffuse through gel pores. This view of the HCP pore network was made available through analysis of E-a values.
  • Thomas Harter, Naoko Watanabe, Xunde Li, Edward R. Atwill, William Samuels
    GROUNDWATER 52 126 - 136 2014年09月 [査読有り][通常論文]
     
    Inherently, confined animal farming operations (CAFOs) and other intense fecal-rich environments are potential sources of groundwater contamination by enteric pathogens. The ubiquity of microbial matter poses unique technical challenges in addition to economic constraints when sampling wells in such environments. In this paper, we evaluate a groundwater sampling protocol that relies on extended purging with a portable submersible stainless steel pump and Teflon (R) tubing as an alternative to equipment sterilization. The protocol allows for collecting a large number of samples quickly, relatively inexpensively, and under field conditions with limited access to capacity for sterilizing equipment. The protocol is tested on CAFO monitoring wells and considers three cross-contamination sources: equipment, wellbore, and ambient air. For the assessment, we use Enterococcus, a ubiquitous fecal indicator bacterium (FIB), in laboratory and field tests with spiked and blank samples, and in an extensive, multi-year field sampling campaign on 17 wells within 2 CAFOs. The assessment shows that extended purging can successfully control for equipment cross-contamination, but also controls for significant contamination of the well-head, within the well casing and within the immediate aquifer vicinity of the well-screen. Importantly, our tests further indicate that Enterococcus is frequently entrained in water samples when exposed to ambient air at a CAFO during sample collection. Wellbore and air contamination pose separate challenges in the design of groundwater monitoring strategies on CAFOs that are not addressed by equipment sterilization, but require adequate QA/QC procedures and can be addressed by the proposed sampling strategy.
  • Xunde Li, Naoko Watanabe, Chengling Xiao, Thomas Harter, Brenda McCowan, Yingjia Liu, Edward R. Atwill
    ENVIRONMENTAL MONITORING AND ASSESSMENT 186 2 1253 - 1260 2014年02月 [査読有り][通常論文]
     
    Generic Escherichia coli was isolated from surface water and groundwater samples from two dairies in Northern California and tested for susceptibility to antibiotics. Surface samples were collected from flush water, lagoon water, and manure solids, and groundwater samples were collected from monitoring wells. Although E. coli was ubiquitous in surface samples with concentrations ranging from several hundred thousand to over a million colony-forming units per 100 mL of surface water or per gram of surface solids, groundwater under the influence of these high surface microbial loadings had substantially fewer bacteria (3- to 7-log(10) reduction). Among 80 isolates of E. coli tested, 34 (42.5 %) were resistant to one or more antibiotics and 22 (27.5 %) were multi-antibiotic resistant (resistant to a parts per thousand yen3 antibiotics), with resistance to tetracycline, cefoxitin, amoxicillin/clavulanic acid, and ampicillin being the most common. E. coli isolates from the calf hutch area exhibited the highest levels of multi-antibiotic resistance, much higher than isolates in surface soil solids from heifer and cow pens, flush alleys, manure storage lagoons, and irrigated fields. Among E. coli isolates from four groundwater samples, only one sample exhibited resistance to ceftriaxone, chloramphenicol, and tetracycline, indicating the potential of groundwater contamination with antibiotic-resistant bacteria from dairy operations.
  • J. Lohwacharin, Y. Yang, N. Watanabe, A. Phetrak, S. Takizawa
    WATER SCIENCE AND TECHNOLOGY-WATER SUPPLY 14 1 165 - 172 2014年 [査読有り][通常論文]
     
    Water utilities in Japan want to reduce residual chlorine levels so as to reduce disinfection byproducts and the chlorine smell, but bacterial regrowth is a concern. In advanced water treatment plants using ozonation and biological activated carbon (BAC), BAC plays the most important role in reducing assimilable organic carbon (AOC). Therefore, we analyzed the removal of dissolved organic matter (DOM) and AOC by full-scale BAC filters with different operational periods. Seasonal variation in AOC in raw water was wide, with a maximum of 306 mu g acetate-C/L in November, and ozonation increased AOC. Nonetheless, BAC filters that had operated for 6 years produced water with lower AOC than ones with shorter operational periods, although they released a small amount of aromatic DOM. A diagram was constructed to derive the required levels of residual chlorine for no bacterial regrowth at various AOC levels of BAC effluents, which were linked with the operational periods of BAC filters and AOC in the ozonation effluents. Although BAC filters operated for longer than 100 weeks can effectively reduce AOC, lowering AOC levels in the ozonation effluent was indispensable for preventing bacterial regrowth in the water supply network at lower levels of residual chlorine than at present.
  • Takuya Ishida, Satoshi Takizawa, Naoko Watanabe, Michio Murakami, Hiroshi Sakai, Kumiko Oguma
    DESALINATION AND WATER TREATMENT 51 1-3 19 - 25 2013年01月 [査読有り][通常論文]
     
    Okinawa Island is located in the southern region of Japan and has a population of 1.22 million. Okinawa Prefectural Enterprise Bureau (OPEB) supplies 410,000 m(3)/d of water to 24 municipalities. Although OPEB uses multiple water resources including dam reservoirs and groundwater, increased water demand resulted in occasional water shortages until a seawater desalination plant (40,000 m(3)/d) started operations in 1997. In this study, a model was developed to simulate the water supply system of Okinawa Island using precipitation and OPEB operational data from 2009 to evaluate the role of the desalination plant in reducing risks associated with drought and power consumption of the plant. The simulation results indicate that without the desalination plant, the dam reservoir storage falls below 50% for 70 days, whereas with the desalination plant, storage remains above 50%. If the plant was operated at full capacity, the dam reservoir storage increased by 17.2% after 1 year of simulation time. However, the desalination plant consumes 4.5-14.7 times more electricity per unit volume of water than other water resources. Although the desalination plant plays an important role in avoiding water shortage in Okinawa Island, operational protocols to minimize power consumption need to be developed further using simulation models such as the one developed in this study.
  • A. Phetrak, J. Lohwacharin, N. Watanabe, M. Murakami, H. Sakai, K. Oguma, S. Takizawa
    WATER SCIENCE AND TECHNOLOGY-WATER SUPPLY 12 5 630 - 636 2012年 [査読有り][通常論文]
     
    Four strong-base anion exchange resins (AERs) with different properties were selected to investigate dissolved organic matter (DOM) removal from river water containing inorganic anions. Rapid sand-filtered water was obtained from a water treatment plant in Tokyo, Japan, and then concentrated by an ultrafiltration membrane for use in ion exchange experiments to simulate high dissolved organic carbon (DOC) and sulfate conditions. AERs removed 23-50% of DOC and 70-80% of UV254 within 30 min despite high sulfate concentration (121 mg/L). Although the materials and structure of the AERs did not affect the reduction of UV254, DOC removal was affected. The highest DOC reduction was achieved by a macroporous polyacrylic AER (Purolite), while the macroporous polystyrene IRA 910 had the lowest DOC removal. A pseudo-second-order kinetic model showed that the rate constants and the initial sorption rates of polyacrylic resins were higher than those by polystyrene resins, suggesting that more hydrophilic structure of AERs exhibited faster DOC removal. Aromatic DOM with a molecular weight (MW) of 800-3,000 Da was almost completely removed by AERs, whereas only half of aromatic DOMs smaller than 800 Da were removed by AERs. Adsorbed DOC comprised less than 6% of all exchanged anions, whereas the adsorbed sulfate was about 90% due to comparatively high concentration of sulfate in the water sample.
  • Y. Yang, S. Takizawa, H. Sakai, M. Murakami, N. Watanabe
    WATER SCIENCE AND TECHNOLOGY 66 6 1348 - 1353 2012年 [査読有り][通常論文]
     
    Dissolved organic matter (DOM) and phosphate in reclaimed water promote microbial growth in distribution systems and deteriorate water quality. In this study, we tested ferrihydrite (Fh) for its potential to remove both DOM and phosphate in order to control bacterial regrowth. Adsorption kinetics on Fh revealed that phosphate has a higher affinity with Fh than has DOM. The removal efficiency of DOM increased at lower pH. Fourier transform infrared spectroscopy (FT-IR) spectra of freeze-dried Fh showed that adsorbed DOM was rich in carboxyl/hydroxyl functional groups, indicating anion exchange at Fh surfaces to be a major mechanism, especially at low pH. Fh preferentially removed DOM greater than 1,000 Da. Specific ultraviolet absorption (SUVA) at 254 nm and DOC results suggest Fh adsorption removes more hydrophilic DOM than the coagulation-sand filtration process. Reduction of bacterial regrowth potential (BRP) by Fh was comparable to that of the coagulation-sand filtration process, which indicated that phosphorus was not the rate-limiting factor of microbial growth.
  • Naoko Watanabe, Brian A. Bergamaschi, Keith A. Loftin, Michael T. Meyer, Thomas Harter
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 44 17 6591 - 6600 2010年09月 [査読有り][通常論文]
     
    Environmental releases of antibiotics from concentrated animal feeding operations (CAFOs) are of increasing regulatory concern. This study investigates the use and occurrence of antibiotics in dairy CAFOs and their potential transport into first-encountered groundwater. On two dairies we conducted four seasonal sampling campaigns, each across 13 animal production and waste management systems and associated environmental pathways: application to animals, excretion to surfaces, manure collection systems, soils, and shallow groundwater. Concentrations of antibiotics were determined using on line solid phase extraction (OLSPE) and liquid chromatography-tandem mass spectrometry (LC/MS/MS) with electrospray ionization (ESI) for water samples, and accelerated solvent extraction (ASE) LC/MS/MS with ESI for solid samples. A variety of antibiotics were applied at both farms leading to antibiotics excretion of several hundred grams per farm per day. Sulfonamides, tetracyclines, and their epimers/isomers, and lincomycin were most frequently detected. Yet, despite decades of use, antibiotic occurrence appeared constrained to within farm boundaries. The most frequent antibiotic detections were associated with lagoons, hospital pens, and calf hutches. When detected below ground, tetracyclines were mainly found in soils, whereas sulfonamides were found in shallow groundwater reflecting key differences in their physicochemical properties. In manure lagoons, 10 compounds were detected including tetracyclines and trimethoprim. Of these 10, sulfadimethoxine, sulfamethazine, and lincomycin were found in shallow groundwater directly downgradient from the lagoons. Antibiotics were sporadically detected in field surface samples on fields with manure applications, but not in underlying sandy soils. Sulfadimethoxine and sulfamethazine were detected in shallow groundwater near field flood irrigation gates, but at highly attenuated levels.
  • Iris R. Gutierrez, Naoko Watanabe, Thomas Harter, Bruno Glaser, Michael Radke
    JOURNAL OF SOILS AND SEDIMENTS 10 3 537 - 544 2010年04月 [査読有り][通常論文]
     
    Up to 90% of antibiotics that are fed to livestock are excreted unaltered or as metabolites and thus are present in manure. By application of manure as fertilizer, veterinary antibiotics can reach soil and groundwater. The aim of this study is to determine the effect of three commonly used (and simultaneously applied) sulfonamide antibiotics on both function and structural diversity of soil microorganisms. To this end, the activity of the enzymes urease and dehydrogenase was determined, and the composition of phospholipid fatty acids (PLFA) was analyzed.Soil and manure were sampled at a dairy farm located in the Northern San Joaquin Valley, California, USA. Soil (700 g) was amended with either mineral water only (W-treatments), liquid manure (M-treatments), or with glucose solution (G-treatments). Each of these soil treatments was mixed with a cocktail of three sulfonamides: sulfadimethoxine (SDT), sulfamethoxazole (SMX), and sulfamethazine (SMZ) at five total concentration levels ranging from 0 (control) to 900 A mu g g (dm) (-1) . After 24, 48, 96, 168, 264, 384, and 504 h, UA and DHA were determined; PLFA composition in selected samples was analyzed at t = 168 h and 504 h of incubation.In the G-treatments, urease activity decreased with higher sulfonamide concentrations; no effect was observed when no glucose was added (W-treatments). While a dose-response relationship was observed for urease activity after 168 h, a similar inhibition was measured after 380 h at all sulfonamide concentrations. Sulfonamides also reduced dehydrogenase activity in the G-treatments, but results are less conclusive than for urease. With increasing sulfonamide concentration, microbial and bacterial biomass decreased in the G-treatments compared to the control at 168 h. Sulfonamides caused a relative community shift towards gram-negative bacteria and towards an increased proportion of fungal biomass. Strong inhibition of urease by manure (M-treatments) was observed even without the addition of sulfonamides.Sulfonamides clearly affected both the function and structural diversity of the soil microbial community over at least 16 days. The soil microbial community was affected by sulfonamides even at a relatively low concentration, although this soil receives regular input of manure that contains several antibiotics. Further research is needed addressing both long-term effects and lower sulfonamide concentrations under dynamic boundary conditions.
  • Naoko Watanabe, Thomas H. Harter, Brian A. Bergamaschi
    JOURNAL OF ENVIRONMENTAL QUALITY 37 5 S78 - S85 2008年09月 [査読有り][通常論文]
     
    Pharmaceuticals used in animal feeding operations have been detected in various environmental settings. There is a growing concern about the impact on terrestrial and aquatic organisms and the development of antibiotic-resistant strains of microorganisms. Pharmaceutical use in milking cows is relatively limited compared with other livestock operations, except for the ionophore monensin, which is given to lactating cows as a feed. By weight, monensin can be the most significant antibiotic used in a dairy farm. This study investigates the potential of monensin to move from dairy operations into the surrounding ground water. Using two dairy farms in California as study sites, we twice collected samples along the environmental pathway-from flush lanes, lagoon waters, and shallow ground water beneath the dairies and beneath its associated manured fields. Monensin concentrations were determined using solid-phase extraction and liquid chromatography-tandem mass spectrometry with positive electrospray ionization. Monensin was detected in all of the flush lane and lagoon water samples. Theoretical maximum concentration estimated from the actual dosing race and the theoretical excretion rate assuming no attenuation was one order of magnitude greater than observed concentrations, suggesting significant attenuation in the manure collection and storage system. Monensin was also detected, at levels ranging from 0.04 to 0.39 mu g L-1, in some of the ground water samples underneath the production area of the dairy but not from the adjacent manured fields. Concentrations in ground water immediately downgradient of the lagoons were one to two orders of magnitude lower than the concentrations detected in lagoons, suggesting attenuation in the subsurface. The data suggest the possibility of monensin transport into shallow (2-5 m) alluvial ground water from dairy management units, including manure storage lagoons and freestalls occupied by heifers, lactating cows, and dry cows.
  • N Watanabe, E Schwartz, KM Scow, TM Young
    ENVIRONMENTAL SCIENCE & TECHNOLOGY 39 16 6170 - 6181 2005年08月 [査読有り][通常論文]
     
    A set of four soils was extensively studied for composition, sorption/desorption, and biodegradation to investigate linkages among these three inter-related factors. Composition of soil organic matter (SOM) was quantitatively characterized using pyrolysis GC-MS; although CO2 dominated the total ion chromatogram for all soils, each soil produced a distinctively different pyrogram and 1.4-4.8% of the soil carbon was quantified as one of 205 pyrolysis marker compounds using external standards. Amorphous and free iron and aluminum contents were determined as potential indicators of the reactivity of the mineral phase, which may influence the configuration and accessibility of SOM domains within soil. We observed a statistically significant positive correlation between two-site model fast fraction f values derived from mineralization and desorption rate studies, which suggests that desorption limits biodegradation. However, no statistically significant correlation was observed between two-site model fast and slow rate constants (k(f), k(s)) for the two processes. No evidently strong correlations were found between functional parameters (organic carbon normalized distribution coefficient K-OC, hyeteresis index HI, and two-site model parameters f, k(f), and k(S) for both desorption and biodegradation and maximum rate and extent of biodegradation) and SOM structural descriptors (pyrolysis results). Lack of strong correlations may suggest (i) that multiple SOM structures are collectively responsible for desorption resistance or (ii) that the pyrolysis GC-MS method used in this study was unable to identify relevant structures. In contrast, amorphous and free iron and aluminum contents showed statistically significant correlations with K-OC and HI values, indicating the potential importance of underlying mineral phases in determining desorption and biodegradation rates.

その他活動・業績

共同研究・競争的資金等の研究課題

  • 多機能化金ナノ粒子を用いた地層処分バリア材性能評価手法の創成
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 小崎 完, 渡辺 直子
     
    高レベル放射性廃棄物の地層処分において、圧縮ベントナイトや母岩は、処分場から生物圏への放射性核種の移行を遅延させるバリア機能を有することが期待されている。従って、それら材料のバリア性能を評価することが重要な研究課題の一つである。本研究では、このバリア性能を、金ナノ粒子を用いて評価する新たな手法の確立を目標として、3年の研究期間に、課題(1) 天然・人工バリア中の多機能化金ナノ粒子の移行挙動研究、課題(2) 多機能化金ナノ粒子を用いたバリア材中の化学的雰囲気の原位置測定に関する実験及び考察、を行う計画である。研究初年度の平成30年度は、比表面積の大きな金微粒子の表面を特定の配位子で覆い、任意の粒子サイズで可溶化、安定化を図った多機能化金ナノ粒子を用い、多機能化金ナノ粒子の安定性および天然バリア模擬材料であるケイ砂を充填したカラム中の移行挙動試験を実施した。選定した多機能化金ナノ粒子は金ナノ粒子をポリエチレングリコールで修飾したものである。紫外可視分光法により、これは実験室環境下では安定であることを確認するとともに、ケイ砂を充填したカラム中を透過させると、放射性トレーサであるHTOの移行挙動と比較すると、粒子サイズの大きなものほど移行が遅延すること、またカラム透過後の金ナノ粒子の粒径分布に粒子サイズが大きなものほど顕著な変化が生じていることを確認した。この現象の理解を深めるため、ナノ粒子およびカラムに充填したケイ砂試料表面の電子顕微鏡観察に着手した。
  • 合理的廃止措置のためのコンクリート構造物解体に係る新たなシナリオ評価ツールの構築
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 渡辺 直子, 小崎 完, 田中 真悟
     
    原子力発電所の廃止措置において、大量のセメント材料が放射性廃棄物として生じることから、これらを安全かつ合理的に処理・処分することが重要となる。本研究では、原子力発電所の廃止措置により発生するコンクリート廃棄物を対象とし、廃止措置・廃棄物処分・クリアランス対象物の再利用に係るシナリオを評価するためのツールを開発することを目的とする。 平成30年度には、Particle and Heavy Ion Transport Code System (PHITS)とDCHAIN-SPのコードを用いて計算した熱遮蔽壁、生態遮蔽等のコンクリート構造物の放射化放射能濃度に基づき、放射能濃度ごとの廃棄物量の経時変化を解析した。また、硬化セメントペースト試料の空隙構造の変化が放射性核種の拡散係数、拡散の活性化エネルギーに与える影響について検討した。それらに基づき、安全貯蔵期間、廃棄物運搬費用、廃棄物受入単価等をパラメータとして廃止措置費用を算出するツールを構築し、ケーススタディを行った。 その結果、廃止措置費用には、廃棄物処分費用が大きな割合を占め、特に放射能レベルの比較的低い廃棄物及び放射能レベルの極めて低い廃棄物の処分費用が大部分であること、そのため極低レベル放射性廃棄物の輸送費用、処分単価を削減することの効果が大きいこと、クリアランス係るコストが大きいため、廃棄物を再利用に回すことの経済的なメリットがあまり大きくないことがわかった。また、放射性廃棄物処分施設が整備されない場合に関し、様々な選択肢の廃止措置費用の比較を行った結果、安全貯蔵期間を延長して対応するよりも、即時解体をし、廃棄物を保管する方が経済的なメリットがある場合があり得ることが示唆された。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2012年04月 -2015年03月 
    代表者 : 渡辺 直子, 小崎 完
     
    放射性Csを含む土壌廃棄物の中間貯蔵・最終処分の長期的な安定性に関する基礎的な知見を得るため、粘土鉱物とCsの相互作用に与える土壌有機物の影響を与えるメカニズムを検討した。粘土鉱物表面に外表面、層間、端面等、性質の異なるCs収着サイトを想定してモデル化して収着実験結果と比較すると、モンモリロナイト層間サイトでの収着容量はフミン酸存在下で減少、非常に選択性の高いイライトのFESではフルボ酸存在下で選択性が増加する等、サイトごとにまた、有機物の種類により影響は異なることがわかった。また、MD計算により、K型マイカ端面で非常に強い内圏錯体が形成される場合の構造を明らかにした。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2011年04月 -2014年03月 
    代表者 : 小崎 完, 渡辺 直子, 富岡 智, 香西 直文, 富岡 智, 香西 直文
     
    高レベル放射性廃棄物の地層処分の安全評価のため、人工バリアである粘土緩衝材中の鉄材料の腐食挙動およびそれに影響を及ぼす粘土緩衝材の諸性能を明らかにする必要がある。ここでは、電位勾配下の鉄材料の粘土緩衝材中の腐食挙動およびイオンの移行挙動を調べた。また、堆積岩の透水性に及ぼす高アルカリ水の影響を透水試験およびX線マイクロCT観察から検討した。さらに、ベントナイト緩衝材の変質がバリア性能に及ぼす影響を検討するため、Fe(II)型ベントナイトに対する透水試験を実施した。

教育活動情報

主要な担当授業

  • エネルギー工学概論
    開講年度 : 2018年
    課程区分 : 学士課程
    開講学部 : 工学部
  • Nuclear and Various Energy Systems(原子力・エネルギーシステムE)
    開講年度 : 2018年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 原子力、原子力安全、核燃料サイクル、核不拡散、核融合、再生可能エネルギー、次世代自動車
  • 原子力・エネルギーシステム特論
    開講年度 : 2018年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 原子力、原子力安全、核燃料サイクル、核不拡散、核融合、再生可能エネルギー、次世代自動車
  • Advanced Nuclear Waste Management(放射性廃棄物処分工学E)
    開講年度 : 2018年
    課程区分 : 修士課程
    開講学部 : 工学院
  • 放射性廃棄物処分工学特論
    開講年度 : 2018年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 放射性廃棄物の発生、使用済核燃料、再処理、処理技術、クリアランス、放射性廃棄物処分、安全評価
  • 大学院共通授業科目(一般科目):自然科学・応用科学
    開講年度 : 2018年
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
  • Nuclear and Various Energy Systems(原子力・エネルギーシステムE)
    開講年度 : 2018年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : 原子力、原子力安全、核燃料サイクル、核不拡散、核融合、再生可能エネルギー、次世代自動車
  • 原子力・エネルギーシステム特論
    開講年度 : 2018年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : 原子力、原子力安全、核燃料サイクル、核不拡散、核融合、再生可能エネルギー、次世代自動車
  • Advanced Nuclear Waste Management(放射性廃棄物処分工学E)
    開講年度 : 2018年
    課程区分 : 博士後期課程
    開講学部 : 工学院
  • 放射性廃棄物処分工学特論
    開講年度 : 2018年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : 放射性廃棄物の発生、使用済核燃料、再処理、処理技術、クリアランス、放射性廃棄物処分、安全評価
  • 工業英語演習
    開講年度 : 2018年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 工業英語、英文読解、英作文、英会話、プレゼンテーション、討論
  • 一般教育演習(フレッシュマンセミナー)
    開講年度 : 2018年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 放射線、放射能、放射線被ばく、放射線医療、原子炉、環境放射能、放射性廃棄物処理・処分、廃炉工学、オープン教材
  • エネルギー工学概論
    開講年度 : 2018年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 地球環境、火力発電、原子力発電、再生可能エネルギー、省エネルギー
  • 科学・技術の世界
    開講年度 : 2018年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 原子力技術、原子力発電、放射線、医療応用、宇宙探査、材料開発


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