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Journal Articles

Dynamics of radiocesium in coastal areas following river flood

Misono, Toshiharu; Nakanishi, Takahiro; Shiribiki, Takehiko; Nagao, Seiya*; Ochiai, Shinya*; Sanada, Yukihisa; Tsuruta, Tadahiko

Gekkan Kaiyo, 54(11), p.558 - 561, 2022/11

Sediment traps were set up around estuaries and in coastal areas to collect sinking particles at the time of river discharge. Around the estuary, changes in radiocesium concentration and mass flux of sinking particles linked to the discharge of radiocesium from the river were observed.

Journal Articles

Dynamics of radioactive cesium in coastal area linked with river discharge

Misono, Toshiharu; Tsuruta, Tadahiko; Shiribiki, Takehiko; Nakanishi, Takahiro; Nagao, Seiya*; Ochiai, Shinya*; Sanada, Yukihisa

Journal of Coastal Research, 114(SI), p.315 - 319, 2021/10

 Times Cited Count:1 Percentile:14.76(Environmental Sciences)

For understanding future radioactive Cs dynamics and its distribution in the coastal area of Fukushima Prefecture, it is important to evaluate the supply of radioactive Cs from river discharge. Especially particulate radioactive Cs supplied in floods might have a significant impact on the coastal area. However, there are few studies on the dynamics of particulate radioactive Cs at the coastal area linked with rivers at the flood event. As a result of measuring the $$^{137}$$Cs concentration of the sinking particles collected by the sediment trap, at the observation point installed in front of the river, the $$^{137}$$Cs concentration collected immediately after the typhoon Bualoi (October 25th) was about higher than before the typhoon. However, the $$^{137}$$Cs concentration of the sinking particles collected two days after the typhoon was almost the same as before the typhoon. The impact of rivers on coastal areas during torrential rain stuck is extremely limited.

Journal Articles

Radiocesium distribution in aggregate-size fractions of cropland and forest soils affected by the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Sato, Tsutomu*; Nagao, Seiya*

Chemosphere, 205, p.147 - 155, 2018/08

 Times Cited Count:15 Percentile:53.93(Environmental Sciences)

There is little understanding of how soil aggregation can affect the mobility and bioavailability of $$^{137}$$Cs in soils. To explore this, soil samples were collected at seven sites under different land-use conditions in Fukushima and were separated into four aggregate-size fractions. The fractions were then analyzed for $$^{137}$$Cs content and extractability and mineral composition. In forest soils, aggregate formation was significant, and $$^{137}$$Cs was largely associated with large-sized aggregates. In contrast, there was less aggregation in agricultural field soils, and most of $$^{137}$$Cs was in the clay- and silt-sized fractions. Across all sites, the $$^{137}$$Cs extractability was higher in the large-sized aggregate fractions than in the clay-sized fractions. The results demonstrate that large-sized aggregates are a significant reservoir of potentially mobile and bioavailable $$^{137}$$Cs in organic-rich (forest and orchard) soils.

Journal Articles

Characterization and thermodynamic study of humic acid in deep groundwater at Horonobe, Hokkaido, Japan

Kimuro, Shingo*; Kirishima, Akira*; Nagao, Seiya*; Saito, Takumi*; Amano, Yuki; Miyakawa, Kazuya; Akiyama, Daisuke*; Sato, Nobuaki*

Journal of Nuclear Science and Technology, 55(5), p.503 - 515, 2018/05

 Times Cited Count:4 Percentile:42.98(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Preface "Radionuclides in coastal sediments after the accident of Fukushima Daiichi Nuclear Power Plant; Distribution, dynamics and fate"

Nagao, Seiya*; Otosaka, Shigeyoshi; Kaeriyama, Hideki*

Journal of Oceanography, 73(5), P. 527, 2017/10

 Times Cited Count:1 Percentile:47.19(Oceanography)

More than five years have passed since the accident at the Fukushima Daiichi Nuclear Power Plant, and many investigations have been carried out in the marine environment. Regarding the radiocesium concentration in seabed sediment, from May 2011, monitoring survey is continuing mainly in the coastal areas of Miyagi, Fukushima, Ibaraki and Chiba prefectures. However, due to its heterogeneity, the difficulty of observation, etc., the assessment of the influence of the accident-derived radionuclides on seabed sediments and the benthic ecosystem is delayed compared to other environmental investigations. As the Guest Editors, the authors set up a special section in "Journal of Oceanography", including four papers arguing about factors affecting the temporal change of the radiocesium concentrations in estuarine, coastal and offshore sediments. This preface shows the planning intention of the special issue, and also outlines the contents.

Journal Articles

Summary of study on environmental radioactivity effected from the accident at the TEPCO Fukushima Daiichi Nuclear Power Plant in 5 years after the accident

Iimoto, Takeshi*; Kinoshita, Norikazu*; Sakaguchi, Aya*; Sugihara, Shinji*; Takamiya, Koichi*; Tagami, Keiko*; Nagao, Seiya*; Bessho, Kotaro*; Matsumura, Hiroshi*; Miura, Taichi*; et al.

KEK Report 2016-3, 134 Pages, 2017/03

This report is summary of study on environmental radioactivity effected from the accident at the TEPCO Fukushima Daiichi Nuclear Power Plant in 5 years after the accident. It was compiled efforts related to the accident reported from the 13th to the 17th "Workshop on Environmental Radioactivity" which was held at the High Energy Accelerator Research and Development Organization.

Journal Articles

Year-round variations in the fluvial transport load of particulate $$^{137}$$Cs in a forested catchment affected by the Fukushima Daiichi Nuclear Power Plant accident

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 310(2), p.679 - 693, 2016/11


 Times Cited Count:6 Percentile:52.61(Chemistry, Analytical)

Particulate $$^{137}$$Cs in stream water was collected continuously for two years in order to assess the long-term trend of the $$^{137}$$Cs discharge from the forest environment. Sampling was conducted from December 2011 to December 2013 in a mountainous stream, which received the $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Plant accident. A seasonal increase in fluvial transport load of particulate $$^{137}$$Cs associated with suspended solids (SS) was observed in August and September when rainfall was abundant. The particulate $$^{137}$$Cs concentration decreased at a faster rate than the rate due to radioactive decay. This decrease might be resulted from redistribution of the easily eroded and polluted soil surface due to heavy rain events such as typhoons. These findings indicate that the particulate $$^{137}$$Cs load was subject to the inter-annual variations in rainfalls, and decreased gradually over a long period of time due to a decrease in $$^{137}$$Cs concentration in SS.

Journal Articles

Physicochemical and ion-binding properties of highly aliphatic humic substances extracted from deep sedimentary groundwater

Saito, Takumi; Terashima, Motoki; Aoyagi, Noboru; Nagao, Seiya*; Fujitake, Nobuhide*; Onuki, Toshihiko

Environmental Science; Processes & Impacts, 17(8), p.1386 - 1395, 2015/08

 Times Cited Count:7 Percentile:27.16(Chemistry, Analytical)

The deep groundwater HSs were different from surface HSs, having high aliphaticities, sulfur contents, and small molecular sizes. The amounts of their acidic functional groups were comparable to or slightly larger than those of surface HSs; however, the magnitude of Cu$$^{2+}$$ binding to the deep groundwater HSs was smaller. The NICA-Donnan model attributed this to the binding of Cu$$^{2+}$$ to chemically homogeneous carboxylic-type sites via mono-dentate coordination at relatively low pH. The binding mode tended to shift to multi-dentate coordination with carboxylic-type and probably more heterogeneous alcoholic hydroxide-type groups at higher pH. This study shows the particularity of the deep groundwater HSs in terms of their physicochemical and ion-binding properties, compared with surface HSs.

Journal Articles

A Passive collection system for whole size fractions in river suspended solids

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; Nagao, Seiya*

Journal of Radioanalytical and Nuclear Chemistry, 303(2), p.1291 - 1295, 2015/02

 Times Cited Count:3 Percentile:27.63(Chemistry, Analytical)

An innovative, yet simple method for the passive collection of radioactive materials in river water has been developed and validated. The method employes large filter vessels, containing multiple cartridge filters. River water is led to the system naturally using a drop of the riverbed by hose from upstream. This method makes long-term, unmanned monitoring possible. In addition to regular radioactivity analyses, this method provides an opportunity for the characterization of suspended materials based on its ample collection quantities (more than several tens of grams). This method may also be applicable to sediment-bound chemicals.

Journal Articles

Biogeochemical signals from deep microbial life in terrestrial crust

Suzuki, Yohei*; Konno, Yuta*; Fukuda, Akari*; Komatsu, Daisuke*; Hirota, Akinari*; Watanabe, Katsuaki*; Togo, Yoko*; Morikawa, Noritoshi*; Hagiwara, Hiroki; Aosai, Daisuke*; et al.

PLOS ONE (Internet), 9(12), p.e113063_1 - e113063_20, 2014/12

 Times Cited Count:11 Percentile:36.41(Multidisciplinary Sciences)

We present multi-isotopic evidence of microbially mediated sulfate reduction in a granitic aquifer, a representative of the terrestrial crust habitat. Deep groundwater of meteoric origin was collected from underground boreholes drilled into the Cretaceous Toki granite, central Japan. A large sulfur isotopic fractionation of 20-60 permil diagnostic to microbial sulfate reduction is associated with the investigated groundwater containing sulfate below 0.2 mM. In contrast, a small carbon isotopic fractionation ($$<$$ 30 permil) is not indicative of methanogenesis. Our results demonstrate that the deep biosphere in the terrestrial crust is metabolically active and playing a crucial role in the formation of reducing groundwater even under low energy fluxes.

Journal Articles

The Present situation and future prospects of groundwater colloids studies on the performance assessment of geological disposal of radioactive wastes in Japan

Nagao, Seiya*; Niibori, Yuichi*; Tanaka, Tadao; Sasaki, Takayuki*; Saito, Takumi*; Kirishima, Akira*; Yoshikawa, Hideki; Iijima, Kazuki; Hama, Katsuhiro; Iwatsuki, Teruki; et al.

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 20(1), p.3 - 14, 2013/06

This paper shows a current status of groundwater colloids studies on the performance assessment of geological disposal of radioactive wastes in Japan, and summaries realistic approach of the colloids studies at a substantial research network for Japanese universities and institutes.

Journal Articles

Comparison of the vertical distributions of Fukushima nuclear accident radiocesium in soil before and after the first rainy season, with physicochemical and mineralogical interpretations

Matsunaga, Takeshi; Koarashi, Jun; Atarashi-Andoh, Mariko; Nagao, Seiya*; Sato, Tsutomu*; Nagai, Haruyasu

Science of the Total Environment, 447, p.301 - 314, 2013/03

 Times Cited Count:117 Percentile:95.18(Environmental Sciences)

The effect of intensive rainfall in the on distribution of Fukushima accident-derived $$^{137}$$Cs in soil was examined in Fukushima-city in post-rainy season and were compared with those in pre-rainy season. It is concluded that rainfall during the rainy season had a limited effect on $$^{137}$$Cs distribution in soil, indicating its overall immobility. Chemical extraction of $$^{137}$$Cs from selected soil samples indicated that $$^{137}$$Cs in soil was hardly water-soluble and extractable with 1M ammonium acetate. This supports the overall immobility of $$^{137}$$Cs in our soils. No direct relationship was obtained between the mineral composition and the $$^{137}$$Cs retention in upper soil layer. In contrast, positive correlations were found between the $$^{137}$$Cs extractability and soil properties such as pH, organic matter content, and finer-sized particle contents in the soils. These results suggest that the mineralogical effect may be masked by non-specific adsorption offered by physicochemical properties of the soils.

Journal Articles

Europium-binding abilities of dissolved humic substances isolated from deep groundwater in Horonobe area, Hokkaido, Japan

Terashima, Motoki; Nagao, Seiya*; Iwatsuki, Teruki; Fujitake, Nobuhide*; Seida, Yoshimi*; Iijima, Kazuki; Yoshikawa, Hideki

Journal of Nuclear Science and Technology, 49(8), p.804 - 815, 2012/08

 Times Cited Count:11 Percentile:65.34(Nuclear Science & Technology)

Journal Articles

Factors affecting vertical distribution of Fukushima accident-derived radiocesium in soil under different land-use conditions

Koarashi, Jun; Atarashi-Andoh, Mariko; Matsunaga, Takeshi; Sato, Tsutomu*; Nagao, Seiya*; Nagai, Haruyasu

Science of the Total Environment, 431, p.392 - 401, 2012/08

 Times Cited Count:144 Percentile:96.03(Environmental Sciences)

no abstracts in English

Journal Articles

Spatial distribution of $$Delta$$$$^{14}$$C values of organic matter in surface sediments off Saru River in northern Japan, one year after a flood event in 2006

Nagao, Seiya*; Irino, Tomohisa*; Aramaki, Takafumi*; Ikehara, Ken*; Katayama, Hajime*; Otosaka, Shigeyoshi; Uchida, Masao*; Shibata, Yasuyuki*

Radiocarbon, 52(3), p.1068 - 1077, 2010/08

 Times Cited Count:0 Percentile:0.01(Geochemistry & Geophysics)

This study discusses the effects of flooding on the spatial distribution of organic matter on the shelf region of off the Saru River, southern part of Hokkaido, Japan, on the basis of the $$Delta$$$$^{14}$$C and $$delta$$$$^{13}$$C values. Surface sediments on the shelf were collected in August 2007, one year after the severe flood in 2006. Suspended particles and sediment of the Saru River were also collected in August 2007 and 2008. The $$Delta$$$$^{14}$$C values of organic matter in the shelf sediments ranged from -665 to -77 per mil. The silt and clay sediments had $$Delta$$$$^{14}$$C values of -240 to -77 per mil, but the sandy sediments ranged from -665 to -388 per mil. The $$Delta$$ values of particulate organic carbon in the Saru River are -292 to -247 per mil at normal flow conditions. These results indicate that surface soil with relatively older organic matter is deposited on the shelf region by the flooding event, and freshly-produced organic matter in sea surface is deposited after the flooding.

Journal Articles

Complexation of Am with size-fractionated soil humic acids

Nagao, Seiya*; Aoyama, Masakazu*; Watanabe, Akira*; Tanaka, Tadao

Colloids and Surfaces A; Physicochemical and Engineering Aspects, 347(1-3), p.239 - 244, 2009/09

 Times Cited Count:5 Percentile:11.96(Chemistry, Physical)

Humic substances play important role in geochemical behavior of trace elements such as actinides in aquatic environments. The association properties of Am with humic substances were studied on the basis of structural feature of humic substances. Humic acids prepared from three types of soils, and separated two humic acids with different structural features: fluorescence-poor and higher molecular size fraction, HA and fluorescence-rich and lower molecular size fraction, FL. The association experiments were carried out in a medium of 0.01M NaClO$$_{4}$$ solution at a humus concentration of 10 mg/l and pH 6-8. The dominant size fractions of Am in the presence of the HA were 450nm - 100k Daltons and 100k - 30k Daltons. On the other hand, Am was presented in the size of 30k - 10k Daltons in the FL. These results indicate that characteristics of size-fractionated humic acids are related association properties with Am.

Journal Articles

Environmental behavior of plutonium isotopes studied in the area affected by the Chernobyl accident

Matsunaga, Takeshi; Nagao, Seiya*

Humic Substances Research, 5/6(1), p.19 - 33, 2009/00

The environmental behavior of Chernobyl-derived plutonium has been reviewed in the soil and the aquatic environment in Ukrainian affected areas. Dissolution of released fuel particles was an initiation for migration in the environment for the Chernobyl-derived plutonium. Once dissolved, the plutonium distributed persistently over surface soil layer with a limited infiltration ability. This relative immobility of plutonium in the soil environment can be attributed to its affinity for soil organics, based on chemical partitioning investigations. The relative immobility of plutonium was also seen in its fluvial transport along the Dnieper River. Dissolved organic matter, most probably humic substances, helped stabilize dissolved plutonium in the lake waters.

Journal Articles

Effects of groundwater humic substances on sorption of Np(V) on sandy materials

Nagao, Seiya*; Sakamoto, Yoshiaki; Rao, R. R.*; Fujitake, Nobuhide*

Humic Substances Research, 5-6(1), p.9 - 17, 2009/00

Sorption behavior of Np(V) onto sandy materials (sand, tuffaceous sand and sandy rock) was studied in the absence and presence of humic substances (HS) using a batch method at pH 5-6 and ionic strength of 0.01M. The effects of shallow land groundwater HS on the Np(V) sorption depend on the mineralogical components of sandy materials. The distribution coefficient (Kd) of Np(V) increased in the presence of HS. The Kd values were in the order of sand$$<$$tuffaceous sand$$<$$sandy rock samples. The Np(V) sorption in the presence of HS with different origin for the sandy rock sample was divided into two groups. The Kd values were positively correlated with aliphatic carbon contents of the lake and the shallow groundwater HS, except for the deep saline groundwater HS. These results indicates that the characteristics of the sandy materials and groundwater HS are important factors determining the Np(V) sorption because of the presence of Np(V)-bound HS.

Journal Articles

Origin and chemical speciation of anthropogenic Iodine-129

Shima, Shigeki*; Gasa, Shinichi*; Amano, Hikaru; Nagao, Seiya*; Yamamoto, Masayoshi*; Momoshima, Noriyuki*; Furukawa, Masahide*; Kimura, Hideki*; Kawamura, Hisao*

JAEA-Conf 2008-003, p.28 - 31, 2008/04

Concentrations of $$^{129}$$I in surface seawater around Japan were approximately 2$$times$$10$$^{7}$$atoms/L in literatures. However, the atomic ratio of iodine to cesium was ten times as high as that of the global fallout. The origin of $$^{129}$$I in the water columns seems to be difficult to be explained by only the global fallout. Discharge from European plants was one of the possible origins of iodine from the standpoint of air mass trajectory analysis. Concentration of $$^{129}$$I in rain water was 10 times higher than that in surface seawater. Anthropogenic inorganic iodine in surface seawater predominantly dissolves as an iodide ion (I$$^{-}$$).

Journal Articles

Molecular size distribution of Pu in the presence of humic substances in river and groundwaters

Nagao, Seiya*; Sakamoto, Yoshiaki; Tanaka, Tadao; Rao, R. R.*

Journal of Radioanalytical and Nuclear Chemistry, 273(1), p.135 - 139, 2007/07

 Times Cited Count:3 Percentile:25.99(Chemistry, Analytical)

no abstracts in English

93 (Records 1-20 displayed on this page)