title: Radioactive Cs in the estuary sediments near Fukushima Daiichi Nuclear Power Plant.
abstract: The migration and dispersion of radioactive Cs (mainly (134)Cs and (137)Cs) are of critical concern in the area surrounding the Fukushima Daiichi Nuclear Power Plant (FDNPP). Considerable uncertainty remains in understanding the properties and dynamics of radioactive Cs transport by surface water, particularly during rainfall-induced flood events to the ocean. Physical and chemical properties of unique estuary sediments, collected from the Kuma River, 4.0km south of the FDNPP, were quantified in this study. These were deposited after storm events and now occur as dried platy sediments on beach sand. The platy sediments exhibit median particle sizes ranging from 28 to 32μm. There is increasing radioactivity towards the bottom of the layers deposited; approximately 28 and 38Bqg(-1) in the upper and lower layers, respectively. The difference in the radioactivity is attributed to a larger number of particles associated with radioactive Cs in the lower part of the section, suggesting that radioactive Cs in the suspended soils transported by surface water has decreased over time. Sequential chemical extractions showed that ~90% of (137)Cs was strongly bound to the residual fraction in the estuary samples, whereas 60~80% of (137)Cs was bound to clays in the six paddy soils. This high concentration in the residual fraction facilitates ease of transport of clay and silt size particles through the river system. Estuary sediments consist of particles <100μm. Radioactive Cs desorption experiments using the estuary samples in artificial seawater revealed that 3.4±0.6% of (137)Cs was desorbed within 8h. More than 96% of (137)Cs remained strongly bound to clays. Hence, particle size is a key factor that determines the travel time and distance during the dispersion of (137)Cs in the ocean.
authors.affiliation: Faculty of Pure and Applied Sciences and Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan. Electronic address: s-yamasaki@ied.tsukuba.ac.jp.
authors.forename: Shinya
authors.initials: S
authors.lastname: Yamasaki
authors.affiliation: Department of Chemistry, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Junpei
authors.initials: J
authors.lastname: Imoto
authors.affiliation: Department of Chemistry, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Genki
authors.initials: G
authors.lastname: Furuki
authors.affiliation: Department of Chemistry, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Asumi
authors.initials: A
authors.lastname: Ochiai
authors.affiliation: Advanced Science Research Center, Japan Atomic Energy Agency, Shirakata Shirane 2-4, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Ohnuki
authors.affiliation: Faculty of Pure and Applied Sciences and Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sueki
authors.affiliation: Department of Environmental Management, Faculty of Symbiotic System Science, Fukushima University, Kanayagawa 1, Fukushima, 960-1296, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Nanba
authors.affiliation: Department of Geological Sciences and Center for International Security and Cooperation, Stanford University, Stanford, CA 94305-2115, USA.
authors.forename: Rodney C
authors.initials: RC
authors.lastname: Ewing
authors.affiliation: Department of Chemistry, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Utsunomiya
mesh_terms: D002588:Cesium Radioisotopes / Q000032:analysis*; D063366:Estuaries; D062406:Fukushima Nuclear Accident; D019015:Geologic Sediments / Q000737:chemistry*; D055848:Nuclear Power Plants; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D014875:Water Pollutants, Radioactive
keywords: Autoradiography; Desorption experiment; Gamma spectrometry; Sequential extraction; Suspended soils