Statistical model for managing the transfer of radiocesium to rice plants under various soil chemical properties II. Application for risk management

Abstract

Following radiocesium (RCs) release due to the accident at the TEPCO Fukushima Daiichi Nuclear Power Plant in 2011, extra potassium (K) fertilizer has been applied to paddy fields to reduce uptake of RCs by rice plants. Many studies have shown that RCs uptake can be suppressed by sufficient soil concentrations of exchangeable K. However, when exchangeable K concentrations decline, RCs uptake can increase and varies widely between different soils. Therefore, risk assessments of RCs transfer to rice plants are required and need to be performed with consideration of soil properties to inform whether to continue applying K. In our previous study, we developed a statistical model for estimating ¹³⁷Cs concentrations in rice grains from concentrations of soil exchangeable ¹³⁷Cs and K. In this study, we tested the model to inform applications of K. Our model estimated upper prediction intervals for rice grain RCs concentrations under several scenarios of the concentration of soil exchangeable RCs. From the upper boundary of upper prediction intervals, we determined the concentrations of soil exchangeable K required to avoid exceedance of target rice grain RCs concentrations. The required concentrations of soil exchangeable K varied widely depending on assumed soil exchangeable RCs concetrations. This result corresponds to the finding in our previous study that the effect of soil exchangeable ¹³⁷Cs concentration on rice grain 137Cs concentration was nearly equal to that of soil exchangeable K. These results show that the model can be applied for risk management and countermeasure taking account soil properties, by elucidating spatial distributions of soil exchangeable RCs.