Foliar contamination of plants with aerosols of ¹³⁷Cs, ⁸⁵Sr,¹³³Ba and ¹²³mTe: Influence of rain

Laboratory of Radioecology and Ecotoxicology, Institute for Radioprotection and Nuclear Safety, DEI/SECRE/LRE, Cadarache, Bd. 186, BP. 3, 13115 St. Paul-lez-Durance Cedex, France

Abstract

Two types of plants (lettuce and radish) were contaminated by dry deposition of radioactive aerosols (¹³⁷Cs, ⁸⁵Sr, ¹³³Ba and ¹²³mTe). Due to the rain efficiency in decreasing radiological contamination of crops, a rain scenario was applied on the two types of plants. These experiments aimed at improving the prediction of the consequences on agricultural products of a nuclear accident occurring on a PWR, and at improving the understanding of the different processes occurring between contamination and harvest. For a plant species at a given stage of its growth cycle, the interception of the four radionuclides was found to be identical and varied from 68% for radish to 75% (at the middle of ripeness stage) or 78% (at the mature plant stage). Using a conceptual model, the predominance between the two processes - washing-off the leaves and absorption through the leaves cuticles allowing translocation - was evidenced. For Cs, Sr and Ba, for both the lettuce and the radish, washing-off on the foliar cover was the most significant during the first rain. The absorption process inside the plant became dominant only from the third rain event. Tellurium had a particular behaviour: it was non-mobile and stayed put on the leaves. The values of the washing-off and absorption coefficients were estimated. The global transfer factor values were dependant on both the radionuclides and the plant species; nevertheless, a higher value was obtained for cesium, regardless of the plant and the rainfall (from 0.06 m².kg^-1 for radish to 0.1 m².kg^-1 for a whole lettuce).