Models for Assessment on the Uptake of Radio-cesium by Rice Using Soil Parameters Calibrated for Paddy Fields in Fukushima Prefecture

Abstract

Two recently developed models of radio-cesium (RCs) transfer from soil to rice grains that were parameterized and ready-to-use for paddy fields in Fukushima were reviewed to establish model-based countermeasures for food safety management in Fukushima. A probability density function model of the transfer factor from soil to rice grains based on soil exchangeable potassium (K) was compared with that of a rice grain RCs concentration model on the basis of the concentration of soil exchangeable RCs and soil exchangeable K. The relevance between these two models was demonstrated using soil exchangeable RCs as a quantitative index of the availability of soil RCs and observed data. The results indicate that the probability density of the transfer factor is affected by soil exchangeable RCs and that the use of a log-normal distribution in the model is justified by the observed distribution pattern of soil exchangeable RCs. This finding improves the accountability of the differences in the modeled probability densities for different regions and helps design countermeasures using the two models for different purposes, such as precautions for K fertilization or conservative risk assessment of shipping restrictions.