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Suzuki S, Amano Y, Enomoto M, Matsumoto A, Morioka Y, Sakuma K, Tsuruta T, Kaeriyama H, Miura H, Tsumune D, Kamiyama K, Wada T, Takata H. Temporal variability of 137Cs concentrations in coastal sediments off Fukushima. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 831:154670. [PMID: 35314234 DOI: 10.1016/j.scitotenv.2022.154670] [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: 01/08/2022] [Revised: 03/14/2022] [Accepted: 03/15/2022] [Indexed: 06/14/2023]
Abstract
Large amounts of radiocesium were released into marine environments following the Fukushima Daiichi Nuclear Power Plant accident in March 2011. Released radiocesium influenced not only marine environment but also marine biota in Fukushima. Since marine biota as fisheries products is important for Japanese market, it is important to assess the distribution of radiocesium in coastal environment off Fukushima for safety concerns of radioactive contamination. Radiocesium concentrations in sediments are important for understanding fishing ground conditions and for proving the safety of fisheries products in Fukushima. In this study, monthly monitoring data collected from May 2011 to March 2020 were analyzed to describe the temporal variability of 137Cs concentrations in coastal sediments off Fukushima (total of 3647 samples from eight lines at depths of 7-125 m off Fukushima, and three sites in Matsukawa-ura Lagoon). The 137Cs concentration in sediment showed a decreasing trend, but our nonlinear model fitting suggested that this rate of decrease had slowed down. Additionally, 137Cs concentrations were up to 4.08 times greater in shallow sampling sites (7, 10, 20 m depth) following heavy rainfall events (before five months vs. after five months), such as typhoons. These observations were consistent with increasing input from particulate 137Cs fluxes from rivers and increasing dissolved 137Cs concentrations in seawater. Finally, our numerical modeling suggested that riverine 137Cs input could maintain 137Cs concentrations in coastal sediment. These results indicate that riverine 137Cs input following heavy rainfall events is the main factor for maintaining 137Cs concentrations in coastal sediments near the Fukushima Daiichi Nuclear Power Plant.
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Affiliation(s)
- Shotaro Suzuki
- Fukushima Prefectural Fisheries and Marine Science Research Centre, Fukushima, Japan; Fukushima Prefectural Research Institute of Fisheries Resources, Fukushima, Japan.
| | - Yosuke Amano
- Fukushima Prefectural Fisheries and Marine Science Research Centre, Fukushima, Japan
| | - Masahiro Enomoto
- Fukushima Prefectural Fisheries and Marine Science Research Centre, Fukushima, Japan
| | - Akira Matsumoto
- Fukushima Prefectural Research Institute of Fisheries Resources, Fukushima, Japan; Fukushima Prefectural Fishery Office, Fukushima, Japan
| | - Yoshiaki Morioka
- Fukushima Prefectural Research Institute of Fisheries Resources, Fukushima, Japan
| | - Kazuyuki Sakuma
- Sector of Fukushima Research and Development, Japan Atomic Energy Agency, Fukushima, Japan
| | - Tadahiko Tsuruta
- Sector of Fukushima Research and Development, Japan Atomic Energy Agency, Fukushima, Japan
| | - Hideki Kaeriyama
- Fisheries Resources Institute, Japan Fisheries Research and Education Agency, Kanagawa, Japan
| | - Hikaru Miura
- Sustainable System Research Laboratory, Central Research Institute of Electric Power Industry, Chiba, Japan
| | - Daisuke Tsumune
- Sustainable System Research Laboratory, Central Research Institute of Electric Power Industry, Chiba, Japan
| | - Kyoichi Kamiyama
- Fukushima Prefectural Fisheries and Marine Science Research Centre, Fukushima, Japan; Fukushima Prefectural Inland Water Fisheries Experiment Station, Fukushima, Japan
| | - Toshihiro Wada
- Institute of Environmental Radioactivity, Fukushima University, Fukushima, Japan
| | - Hyoe Takata
- Institute of Environmental Radioactivity, Fukushima University, Fukushima, Japan
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Kambayashi S, Zhang J, Narita H. Significance of Fukushima-derived radiocaesium flux via river-estuary-ocean system. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 793:148456. [PMID: 34328972 DOI: 10.1016/j.scitotenv.2021.148456] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 06/08/2021] [Accepted: 06/10/2021] [Indexed: 06/13/2023]
Abstract
The environmental dynamics of Fukushima-derived radiocaesium from land to ocean and the impact of its flux on the marine environment are matters of concern because radiocaesium will be continually transported to the open ocean for the next several decades, or possibly more than one hundred years. In order to assess the distribution and flux of radiocaesium in a river-estuary-ocean system, we investigated the activity concentration of radiocaesium in Matsukawa-ura Lagoon, the largest lagoon in Fukushima, where it is very easy to carry out observations with a wide salinity gradient. Activity concentrations of dissolved 137Cs are elevated in seawater of low to intermediate salinity. It can thus be inferred that radiocaesium desorbs from suspended particles in an estuarine area. The porewater activity concentration of 137Cs in lagoon sediment was about 10 times higher than that in the overlying lagoon water. This direct measurement indicates that a significant amount of radiocaesium in sediment desorbs into porewater. From the results of a mass balance model, dissolved 137Cs flux from the lagoon's bottom is 15.3 ± 3.7 times greater than the riverine input, including desorption from particles. In the case of the whole Pacific coast of northeastern Japan (Miyagi, Fukushima, and Ibaraki Prefectures), dissolved 137Cs flux into the open ocean, including diffusion of porewater, is estimated to be up to 1.5 times greater than the sum of riverine input and the ongoing release from the Fukushima Dai-ichi Nuclear Power Station's harbor. Consequently, our results suggest that radiocaesium is transported to the open ocean under the control of various processes, not only by desorption from particles but also, for example, by the diffusion of porewater.
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Affiliation(s)
- Shota Kambayashi
- Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
| | - Jing Zhang
- Faculty of Science, Academic Assembly, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
| | - Hisashi Narita
- School of Marine Science and Technology, Tokai University, 3-20-1 Orido, Shimizu-ku, Shizuoka 424-8610, Japan
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Higuchi K, Arakawa H, Matsumoto A, Narita K, Morioka Y. Radiocesium concentrations in shallow water sediments (Matsukawa-ura Lagoon, Fukushima, Japan) from a compact NaI(Tl) scintillation spectrometer. Appl Radiat Isot 2021; 175:109797. [PMID: 34146769 DOI: 10.1016/j.apradiso.2021.109797] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 04/30/2021] [Accepted: 05/29/2021] [Indexed: 11/30/2022]
Abstract
We collected continuous sedimentary 137Cs concentration data from a shallow fishery ground (Matsukawa-ura Lagoon, Fukushima, Japan) in 2016 using a new compact underwater NaI(Tl) scintillation spectrometer and a quantitative technique. 137Cs concentrations in sediments were low (approx. 40 Bq/kg DW) at the lagoon mouth and high (641.2 Bq/kg DW) at the head of the lagoon. Some areas of locally elevated 137Cs concentrations (>500 Bq/kg DW) were also found.
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Affiliation(s)
- Ken Higuchi
- Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo, 108-8477, Japan.
| | - Hisayuki Arakawa
- Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo, 108-8477, Japan
| | - Akira Matsumoto
- Soma Branch, Fishery Office of the Fukushima Prefectural Government, 18-2 Oikawa, Obama, Soma, Fukushima, 976-0022, Japan
| | - Kaoru Narita
- Fishery Division of the Fukushima Prefectural Government, 2-16 Sugitsuma-cho, Fukushima, 960-8670, Japan
| | - Yoshiaki Morioka
- Fukushima Prefectural Research Institute of Fisheries Resources, 1-1-14 Koyo, Soma, Fukushima, 976-0005, Japan
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