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
no abstracts in English
Miura, Hikaru*; Ishimaru, Takashi*; Ito, Yukari*; Kuribara, Yuichi; Otosaka, Shigeyoshi*; Sakaguchi, Aya*; Misumi, Kazuhiro*; Tsumune, Daisuke*; Kubo, Atsushi*; Higaki, Shogo*; et al.
Scientific Reports (Internet), 11, p.5664_1 - 5664_11, 2021/03
For the first time, we isolated and investigated seven CsMPs (radioactive caesium-bearing microparticles) from marine particulate matter and sediment. From the elemental composition, the Cs/Cs activity ratio, and the Cs activity per unit volume results, we inferred that the five CsMPs collected from particulate matter were emitted from Unit 2 of the FDNPP, whereas the two CsMPs collected from marine sediment were possibly emitted from Unit 3. The presence of CsMPs can cause overestimation of the solid-water distribution coefficient of Cs in marine sediments and particulate matter and a high apparent radiocaesium concentration factor for marine biota. CsMPs emitted from Unit 2, which were collected from the estuary of a river that flowed through a highly contaminated area, may have been deposited on land and then transported by the river. By contrast, CsMPs emitted from Unit 3 were possibly transported eastward by the wind and deposited directly onto the ocean surface.
Fukuda, Miho*; Aono, Tatsuo*; Yamazaki, Shinnosuke*; Ishimaru, Takashi*; Kanda, Jota*; Nishikawa, Jun*; Otosaka, Shigeyoshi
Geochemical Journal, 52(2), p.201 - 209, 2018/00
To elucidate recent activity levels and the behavior of radiocesium in the coast off Fukushima Prefecture, lateral and vertical distributions of Cs in sediment were observed in 2013-2015 at 12 monitoring stations. At stations around the water depth of 100 m, relatively higher Cs activities were observed from surface sedimentary layer (0-3 cm). In these stations, sediments had high content of silt to clay particles and organic matter. The high Cs activities in the surface sediments were attributed to accumulation of highly mobile sediment particles. In October 2014, at some coastal stations, sharp peaks of Cs activities were observed in the subsurface (5-16 cm) sediments, whereas such broad peaks were not found in October 2015. These results suggest that the Cs activities in sediment had largely changed by lateral transport and re-sedimentation on the surface, as well as sediment mixing in the middle-layers.
Fukuda, Miho*; Aono, Tatsuo*; Yamazaki, Shinnosuke*; Nishikawa, Jun*; Otosaka, Shigeyoshi; Ishimaru, Takashi*; Kanda, Jota*
Journal of Radioanalytical and Nuclear Chemistry, 311(2), p.1479 - 1484, 2017/02
In order to investigate processes affecting distribution of radiocaesium in seawater in the adjacent region of Fukushima Daiichi Nuclear Power Plant (FDNPP), relationships between Cs activity in seawater and physical properties of seawater (salinity, temperature, and potential density) were observed in seven stations within 10 km radius from the FDNPP. As a whole, Cs concentrations in seawater were higher in the vicinity of the FDNPP, and were negatively correlated with potential density. From these results, it can be considered that river water discharge or export of seawater from the FDNPP's harbor has affected the higher activity levels of Cs in seawater. It was also observed that the Cs-elevated seawater can be advected to the 2050 m depths.
Ishimaru, Yasuhiro*; Kim, S.*; Tsukamoto, Takashi*; Oki, Hiroyuki*; Kobayashi, Takanori*; Watanabe, Satoshi; Matsuhashi, Shimpei; Takahashi, Michiko*; Nakanishi, Hiromi*; Mori, Satoshi*; et al.
Proceedings of the National Academy of Sciences of the United States of America, 104(18), p.7373 - 7378, 2007/05
Ishimaru, Yasuhiro*; Suzuki, Motofumi*; Tsukamoto, Takashi*; Suzuki, Kazumasa*; Nakazono, Mikio*; Kobayashi, Takanori*; Wada, Yasuaki*; Watanabe, Satoshi; Matsuhashi, Shimpei; Takahashi, Michiko*; et al.
Plant Journal, 45(3), p.335 - 346, 2006/02
Otosaka, Shigeyoshi*; Suzuki, Takashi; Tsuruta, Tadahiko; Misono, Toshiharu; Dohi, Terumi; Mino, Yoshihisa*; Sukigara, Chiho*; Ito, Yukari*; Kanda, Jota*; Ishimaru, Takashi*
no journal, ,
A time-series sediment trap was deployed from October 2017 to June 2018 at a station located in southeast of the Fukushima Daiichi Nuclear Power Plant to clarify the transport process of suspended radiocesium from the coast to the offshore area. Sinking particles of 39 periods were collected by this experiment. Radiocesium was detected from sinking particles throughout the observation period, and the concentration showed clear seasonal variation. The observed flux of radiocesium showed maxima in winter (December-January) and spring (March-April). From detailed analysis of physical and chemical characteristics of sinking particles, it was found that sinking particles were composed of biological particles with relatively low degradation in winter and fine-grained terrestrial particles in spring. Especially in spring, high radiocesium flux was observed, and it was presumed due to lateral transport of radiocesium-bound lithogenic particles from the coastal area to the offshore. However, the effect of redistribution of radiocesium in seabed sediments by this process is considered to be limited.