Sedimentation and remobilization of radiocesium in the coastal area of Ibaraki, 70 km south of the Fukushima Dai-ichi Nuclear Power Plant
Sedimentation and remobilization processes of radiocesium were investigated from time-series observations at nine stations in the coastal area of Ibaraki, 70–110 km south of the Fukushima Dai-ichi Nuclear Power Plant (1FNPP). Sediment samples were collected four times between June 2011 and January 2012, and concentrations of radiocesium as well as sediment properties such as grain size and elemental compositions were analyzed. Cumulative inventory of 137Cs in sediment (0–10 cm) ranged between 4 × 103 and 3 × 104 Bq/m2 as of January 2012. This amount was generally higher at stations nearer 1FNPP and has remained at the same level since August 2011. From these results, it can be inferred that dissolved radiocesium advected southward from the region adjacent to the 1FNPP and was deposited to the sediment of the study area in the early stage after the accident. The incorporation of radiocesium into sediments was almost irreversible, and higher concentrations of 137Cs were obtained from the finer-grained fraction of sediments. In the northern offshore stations, resuspension of the fine-grained sediments formed a high-turbidity layer 10–20 m above the seabed. These results indicate that radiocesium-enriched fine particles were transported from the coast to offshore regions through the bottom high-turbidity layer.
KeywordsRadiocesium Fukushima Dai-ichi nuclear power plant Seabed sediment Coastal area Redistribution
- Aoyagi, K., & Igarashi, C. (1999). On the size distribution of sediments in the coastal sea of Fukushima Prefecture. Bulletin of the Fukushima Prefectural Fisheries Experimental Station, 8, 69–81 (in Japanese).Google Scholar
- Aoyama, M., Tsumune, D., & Hamajima, Y. (2012). Distribution of 137Cs and 134Cs in the North Pacific Ocean: impacts of the TEPCO Fukushima-Daiichi NPP accident. Journal of Radioanalitical Nuclear Chemistry. doi:10.1007/s10967-012-2033-2.
- Bustamante, P., Teyssie, J. L., Fowler, S. W., & Warnau, M. (2006). Assessment of the exposure pathway in the uptake and distribution of americium and cesium in cuttlefish (Sepia officinalis) at different stages of its life cycle. Journal of Experimental Marine Biology and Ecology, 331, 198–207.CrossRefGoogle Scholar
- JFA (Japan Fisheries Agency) (2011). http://www.jfa.maff.go.jp/e/inspection/pdf/201103-09_kekka_en.pdf. Accessed on May 16, 2012.
- Hjulstrøm, F. (1935). Studies of the morphological activity of rivers as illustrated by the River Fyris. Bulletin of the Geological Institution of the University of Upsala, 25, 221–527.Google Scholar
- Kawamura, H., Kobayashi, T., Furuno, A., In, T., Ishikawa, Y., Nakayama, T., et al. (2011). Preliminary numerical experiments on oceanic dispersion of 131I and 137Cs discharged into the ocean because of the Fukushima Daiichi Nuclear Power Plant disaster. Journal of Nuclear Science and Technology, 48, 1349–1356.CrossRefGoogle Scholar
- Kubo, H. (1988). Research on the oceanographic conditions of Kashima-Nada, off the east coast of Honshu. Bulletin of the Ibaraki Prefectural Fisheries Experimental Station, 26, 1–98 (in Japanese with English summary and captions).Google Scholar
- Lujanienė, G., Vilimaitė-Šilobritienė, B., & Jokšas, K. (2005). Accumulation of 137Cs in bottom sediments of the Curonian Lagoon. Nucleonika, 50, 23–29.Google Scholar
- MEXT (2011a). http://radioactivity.mext.go.jp/en/contents/4000/3325/24/1305745_0527.pdf. Accessed on July 2, 2012.
- MEXT (2011b). http://radioactivity.mext.go.jp/en/contents/4000/3324/24/1305745_0612.pdf. Accessed on July 2, 2012.
- MEXT (2011c). http://radioactivity.mext.go.jp/en/contents/4000/3331/24/1350_1108.pdf. Accessed on July 2, 2012.
- MEXT (2011d). http://radioactivity.mext.go.jp/en/contents/4000/3312/24/1304193_0331.pdf. Accessed on July 2, 2012.
- MEXT (2012a). Database of environmental radioactivity. http://search.kankyo-hoshano.go.jp. Accessed on July 2, 2012 (in Japanese).
- MEXT (2012b). http://radioactivity.mext.go.jp/en/contents/4000/3334/24/1350_012514.pdf. Accessed on July 2, 2012.
- MEXT (2012c). http://radioactivity.mext.go.jp/en/contents/4000/3285/24/1330_030114.pdf. Accessed on July 2, 2012.
- MEXT (Ministry of Education, Culture, Sports, Science and Technology) (2004). Gamma-ray spectrometry using a germanium detector. Radioactivity Measurement Series No. 7. Tokyo: Ministry of Education, Culture, Sports, Science and Technology (In Japanese).Google Scholar
- MLIT (Ministry of Land, Infrastructure and Transport, Japan). (2012). River discharges year book of Japan, year 2007. Tokyo: Japan River Association.Google Scholar
- MOE (Ministry of Environment, Japan) (2011). http://www.env.go.jp/jishin/monitoring/result_pw111202.pdf. Accessed on July 2, 2012.
- Nasu, N. (1964). The provenance of the coarse sediments on the continental shelves and the trench slopes off the Japanese Pacific coast. In R. L. Miller (Ed.), Papers in marine geology (pp. 65–101). New York: Macmillan Co.Google Scholar
- USEPA (United States Environmental Protection Agency). (1999). Understanding variation in partition coefficient, Kd, values Vol. II: review of geochemistry and available Kd values for cadmium, cesium, chromium, lead, plutonium, radon, strontium, thorium, tritium (3H), and uranium. EPA 402-R-99-004B. Washington: Office of Air and Radiation, US Environmental Protection Agency.Google Scholar