Physicochemical And Time Factors Affecting(137)Cs Transfer Through A Paddy Soil-Rice System

To clarify the factors affecting(137)Cs transfer from soil to brown rice in comparison with(133)Cs transfer and also to determine the key parameters of the solid-liquid partition coefficient (K-d), concentration factor from soil solution to brown rice (CF), and transfer factor from soil to brown rice (TF), we analyzed the results of our previous paper in which a rice pot-culture experiment under different fertilization treatments using three paddy soils in Fukushima 3 years after the Fukushima Daiichi Nuclear Power Station accident was conducted. The TF values for(137)Cs were the same as or smaller than the literature values obtained within 2 years of the accident, 2-17 times higher than those for global fallout(137)Cs from atmospheric nuclear tests, and 2-20 times higher than those for natural(133)Cs. The CF values for(137)Cs were negatively correlated with the soil solution K(+)concentration. A theoretical approach, under the assumption that(137)Cs in soil is mainly adsorbed at the frayed edge site (FES) and ion exchange of(137)Cs with K(+)and NH(4)(+)ions is in equilibrium, partly explained the variability in the soil solution(137)Cs concentrations under different soil and fertilization conditions and suggested that the major portion of(137)Cs in soil would be adsorbed in FES under lower K(+)and NH(4)(+)concentrations but fixed in the collapsed interlayer sites under higher K(+)and NH(4)(+)concentrations, the ranges of which are typically observed in agricultural soils. Our results indicate that the major factors affecting(137)Cs transfer from soil to brown rice would be the(137)Cs, K+, and NH(4)(+)concentrations in the soil solution and the time elapsed from the deposition of(137)Cs, and emphasize the necessity of including the dynamic(137)Cs adsorption and fixation process in soil into the TF prediction models applicable to agricultural soils received with periodical fertilizations.