title: Temporal changes of radiocesium in irrigated paddy fields and its accumulation in rice plants in Fukushima.
abstract: About half of the total paddy field area, which is the dominant agricultural land in Fukushima Prefecture, was contaminated by radiocesium released by the Fukushima Daiichi Nuclear Power Plant accident. In this study, we investigated the temporal changes of radiocesium in soil, irrigation water, and rice plant in two adjacent rice paddies, with and without surface-soil-removal, in Fukushima Prefecture for over three years (2012-2014) after the nuclear accident. Our results showed that radiocesium migrated into 24-28 cm soil layers and that the activity concentration of radiocesium in paddy soils showed a significant reduction in 2014. The newly added radiocesium to paddies through irrigation water contributed only a maximum value of 0.15% and 0.75% of the total amount present in control and decontaminated paddies, respectively, throughout the study period. The radiocesium activity concentration in suspended sediment in irrigation water exponentially decreased, and the effective half-lives (Teff) for (137)Cs and (134)Cs were 1.3 and 0.9 years, respectively. Additionally, the average suspended sediment concentration in irrigation water increased between 2012 and 2014, suggesting that enhanced soil erosion had occurred in the surrounding environment. Radiocesium accumulation in rice plant also decreased with time in both paddies. However, the concentration ratio of radiocesium for rice plant in the decontaminated paddy increased compared with control paddy, despite approximately 96% of fallout radiocesium removed in paddy soil. Further analysis is required to clarify the reasons of high concentration ratio of radiocesium for rice plant in the decontaminated paddy.
authors.affiliation: Institute of Agro-products Processing Science and Technology, Chinese Academy of Agricultural Sciences, Beijing, 100193, China; Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, 305-8572, Japan. Electronic address: yangbl2011@hotmail.com.
authors.forename: Baolu
authors.initials: B
authors.lastname: Yang
authors.affiliation: Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, 305-8572, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Onda
authors.affiliation: Institute of Environmental Radioactivity, Fukushima University, Kanayagawa 1, Fukushima, 960-1296, Japan.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Wakiyama
authors.affiliation: Sector of Fukushima Research and Development, Japan Atomic Energy Agency, Tokyo, 100-8577, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Yoshimura
authors.affiliation: Faculty of Agriculture, Utsunomiya University, Utsunomiya, 321-8505, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sekimoto
authors.affiliation: Institute of Agro-products Processing Science and Technology, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
authors.forename: Yiming
authors.initials: Y
authors.lastname: Ha
mesh_terms: D000383:Agriculture; D002588:Cesium Radioisotopes / Q000032:analysis*; D003666:Decontamination; D062406:Fukushima Nuclear Accident; D012275:Oryza / Q000737:chemistry*; D012987:Soil; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D012987:Soil; D012990:Soil Pollutants, Radioactive; D014875:Water Pollutants, Radioactive
keywords: Concentration ratio; Irrigation water; Radiocesium; Rice; Soil