Physicochemical and time factors affecting 137Cs transfer through a paddy soil–rice system

Abstract

ABSTRACT To clarify the factors affecting 137Cs transfer from soil to brown rice in comparison with 133Cs 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 137Cs 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 137Cs from atmospheric nuclear tests, and 2–20 times higher than those for natural 133Cs. The CF values for 137Cs were negatively correlated with the soil solution K+ concentration. A theoretical approach, under the assumption that 137Cs in soil is mainly adsorbed at the frayed edge site (FES) and ion exchange of 137Cs with K+ and NH4 + ions is in equilibrium, partly explained the variability in the soil solution 137Cs concentrations under different soil and fertilization conditions and suggested that the major portion of 137Cs in soil would be adsorbed in FES under lower K+ and NH4 + concentrations but fixed in the collapsed interlayer sites under higher K+ and NH4 + concentrations, the ranges of which are typically observed in agricultural soils. Our results indicate that the major factors affecting 137Cs transfer from soil to brown rice would be the 137Cs, K+, and NH4 + concentrations in the soil solution and the time elapsed from the deposition of 137Cs, and emphasize the necessity of including the dynamic 137Cs adsorption and fixation process in soil into the TF prediction models applicable to agricultural soils received with periodical fertilizations.