Quantifying the effects of soil and plant characteristics on radiocaesium uptake: A global perspective

After nuclear accidents, radiocaesium can enter the terrestrial environment. Plants growing on caesium (Cs) contaminated agricultural lands, can take up Cs because it is physicochemically analogue to potassium. The availability of Cs to plants is controlled in part by the soil absorption properties for Cs and cation conditions of a soil. If agricultural products contaminated with Cs are ingested, it might be a risk for the health.

Soil-to-plant transfer models were developed based on soil and plant characteristics to predict the fate of Cs in the environment. Currently, decisions concerning agricultural countermeasures are mostly based on semi-mechanistic models that were developed for European conditions in the aftermath of the Chernobyl accident. These models however, did not predict radiocaesium transfer from Japanese soils realistically as post Fukushima experience has shown. Observations indicate the influence of regional characteristics (e.g. climate conditions, soil properties, crop type, land management practices) on Cs bioavailability. As new countries in Asia, Africa and South America are adopting nuclear energy, Cs soil-plant transfer models will be required that can make predictions under diverse environmental conditions (e.g. tropical and arid).

It is hypothesized that radiocaesium mobility and availability to plants are controlled by a unique set of soil parameters, such as clay mineralogy, that can be measured with soil tests. Models using these parameters will be able to predict radiocaesium transfer across different environments with few inputs.

This research is in line with the project coordinated by the International Atomic Energy Agency (IAEA) “Monitoring and predicting radionuclide uptake and dynamics for optimizing of radioactive contamination in agriculture” to improve the robustness of these soil-plant transfer models for the underexplored areas, crops and climates. It aims to better understand radiocaesium mobility and availability to plants in a wide range of soil and plant types, especially in non-European soils. The research findings are used to improve or develop soil-plant transfer models that can predict radiocaesium transfer across environments.

Laboratory pot trials are set up with soils from various origins and with distinct characteristics are collected. The soil mineralogy is quantitatively determined with X-ray diffraction technique. The soils are contaminated with 137Cs and ryegrass is grown. After harvest a 137Cs soil-plant transfer factor is obtained. Empirical relations between the soil mineralogy and characteristics should explain the observed 137Cs transfer factor.

The laboratory results are supplemented by data from previous experiments and data in the literature. A meta-analysis is carried out to select suitable data. The empirical relations and literature data are used to adjust the Cs soil-plant transfer model. By updating the model, Cs soil-plant transfer predictions will be improved which can support decisions after nuclear power plant accidents worldwide.