Transfer and translocation of 241Am, 239Pu, 137Cs and 85Sr after partial foliar contamination of bean plants

Bean plants at the flowering development stage were contaminated by soaking their two first leaves for 3 hours in a solution containing one of the actinides 241Am or 239Pu, or both 137Cs and 85Sr. The aim of the study was to assess the adequacy of using the values of Cs/Sr for the foliar transfer parameters of transuranic actinides, as used for example in the ASTRAL code to calculate the contamination of agricultural products after a nuclear accident. Secondly, these experiments were launched to tentatively determine specific values for the foliar transfer parameters for Am and Pu, despite technical limitations due to high radiotoxicity of these isotopes which prevented the contamination of the whole foliage of bean plants. Cs and Sr were used to compare the results with those obtained with other modes of contamination, by dry deposition of aerosols for example. Results showed that the soaking protocol was adequate to compare the foliar transfer of various radionuclides, although it should be difficult to provide specific values because of partial contamination of the foliage. Foliar transfer factors, expressed as Bq.kg-1dwpods/Bq.L-1solution (2.5x10-2) and translocation factors, dimensionless, (2.3x10-3) for Am and for Pu (1.5x10-3 and 7.5x10-5 respectively), compared to those for Sr (respectively 3.6x10-3 and 5.9x10-4) and for Cs (respectively 2.9x10-1 and 1.3x10-1), were studied using this procedure. Transfer and translocation factors for Am were significantly higher than those for Sr, but were smaller than those for Cs. Therefore, Am can be classified as a medium mobile radionuclide in plant. Transfer and translocation of Pu were significantly lower than these for Sr and for Am. Besides, the transfer and translocation factors of Am and Pu only differed from one order of magnitude or less from the one of Sr, which could be in the usual range of variation characterising transfer factors. (author)