Availability to and uptake by plants of radionuclides under different environmental conditions∗

Abstract

The availability of radionuclides from the ground depends on many different factors, such as the composition and consistency of the soil, the presence of other metal ions and complexing organic compounds, the local climate and the residence time of the radionuclides in the ground, to mention just a few. Besides there are airborne radionuclides which settle directly on to the plants by dry and wet deposition from nuclear fall‐out. Some of these radionuclides are readily absorbed to various degrees by the plants from the leaves and distributed within the whole plant. This form of contamination is very much faster than the uptake from the soil by the roots since it eliminates the migration of the nuclides through the ground. We have also studied the availability of ²²⁶radium from soil containing 40 x 10³ Bq of radium chloride/kg of soil contaminated about 50 years ago. Our results with this well weathered matrix as compared to freshly prepared radium‐soil mixtures show that the bioavailability of this radionuclide decreases rapidly with time. These results are best fitted by a model of two radium compartments representing a biologically available and another nearly insoluble fraction in the soil. The transfer from soil to plant depends on the properties of the ions, the presence of other competing ions, in the case of radium on the concentrations of other members of the alkaline earth elements, as well as on the plant species. We were able to show that plant species with a high content of calcium, take up more radium than those with a low affinity to this element. Foliar uptake, i.e., incorporation of activity deposited onto the leaves was estimated for cesium, strontium and iodine in selected food plants as a function of time and under different experimental conditions, such as washing the leaves at various intervals after the deposition or applying a chelating agent before the deposition. The amount of incorporated radionuclides could be reduced by washing the leaves a short time after application of the active substances. The chelating agent Prussian Blue was found to inhibit the uptake of cesium.