The aim of this study was to evaluate and improve the accuracy of the semi-mechanistic models used in regulatory exposure assessment tools, to describe the transfer factors of ¹³⁷Cs from pasture soils to grass observed in different grazing areas of France between 2004 and 2017. This involved a preliminary parameterization step of the dynamic factor describing the ageing of radiocesium in the root zone using a Bayesian approach. A data set with mid-term (10 years about) and long term (more than 20 years) field and literature data from 4 European countries was used. A double kinetics of the bioavailability decay was evidenced with two half-life periods equal to 0.46 ± 0.11 yr and 9.57 ± 1.12 yr for the fast and slow declining rates respectively. We, then, tested a few existing alternative models proposed in literature. The comparison with field data showed that these models always underestimated the observations by one to two orders of magnitude, suggesting that the solid-liquid partition coefficient (Kd) was overestimated by models. The results suggest that semi mechanistic models might fail in the long-term prediction of the radionuclide transfer from soil-to-plant in the food chain. They highlight the need to calculate Kd using easily exchangeable ¹³⁷Cs (i.e. labile fraction) rather than total soil ¹³⁷Cs.

这项研究的目的是评估和改善用于监管性暴露评估工具的半机械模型的准确性，以描述^137个转移因子。从2004年至2017年在法国不同放牧地区观察到的从牧场土壤到草的Cs。这涉及使用贝叶斯方法描述根部放射性铯老化的动态因子的初步参数化步骤。使用了来自四个欧洲国家的具有中期（大约10年）和长期（超过20年）领域和文献数据的数据集。在两个半衰期分别为快速下降速率和缓慢下降速率分别为0.46±0.11年和9.57±1.12年的情况下，证明了生物利用度衰减的双重动力学。然后，我们测试了文献中提出的一些现有替代模型。与现场数据的比较表明，这些模型总是低估观测值一到两个数量级，这表明固液分配系数（Kd）被模型高估了。结果表明，半机械模型可能无法长期预测食物链中放射性核素从土壤到植物的转移。他们强调需要使用易于交换的¹³⁷ Cs（即不稳定部分）而不是总土壤¹³⁷ Cs计算Kd。