Estimation of rooting depth of Cs uptake by plants.

Understanding the soil-to-plant transfer process of Cs is essential for predicting the contamination levels of plants in contaminated areas. The rooting depth is considered one of the key factors explaining the difference in the activity concentration of Cs in different plant species. In this study, the distributions of Cs and Cs in soils and plants were investigated, and the plants' rooting depth of Cs uptake was estimated using the Cs/Cs ratios in exchangeable fractions of soils and biological samples. The results showed that different plant species accumulate different levels of Cs and Cs. The Cs/Cs ratios were fairly constant in plants of the same species. The average Cs/Cs ratios in bamboo grasses and ferns were 0.015 ± 0.009 (n = 5) and 0.13 ± 0.04 Bq ng (n = 10) in Yamakiya, respectively. The percentage of Cs in the exchangeable fraction of the uppermost soil layer was lower than that in the deeper soil layers. The activity concentrations of Cs in the soil profiles decreased sharply with depth, whereas the depth distributions of Cs were uniform. Therefore, the Cs/Cs ratios were driven mainly by the Cs activity concentrations in soil. The plants' rooting depths of Cs uptake were estimated on the basis of the relationships between the averaged Cs/Cs ratio in the soil layer and the Cs/Cs ratio in the plant. The results indicate that the deeper-rooted species such as bamboo grasses have a lower accumulation of Cs than the superficial-rooting species such as ferns. The soil-to-plant transfer factors would be determined using rooting depth by calculating the averaged activity concentration of Cs within the estimated rooting depth.