Comparison of soil/solution distribution of a fresh radionuclides contamination (137Cs, 129I and 233U) added under organic or water pathways with their natural endogenous isotopes

International audienceDue to nuclear activities, radionuclides (RNs) could bedisseminated in environment following accidental or chronicreleases. In models used to predict their behaviour, theirdistribution in the soil/solution system is often estimated using apartition coefficient (Kd), relating the total concentration of RNin the soil to that present in solution.The use of Kd model assumes that RNs are in equilibriumbetween soil and solution and, if the same value is used for shortto long term modelling, assumes Kd value is not time dependant.However, for some RNs, several studies showed a stabilizationof RNs in soils over time. This stabilization depends on thenature of RN considered, on soil geochemical parameters and/oron the nature of the contamination. For this last point, recentstudies shown that 137Cs water available fraction from soil differsif the contamination is due to contaminated water orcontaminated leaves.Obtaining Kd values in line with the required time scale forlong-term assessment of RNs transfer could be difficult becausethe time scale of prediction is longer than the existingcontamination. To compensate this lack of data, naturalendogenous isotopes of the targeted RNs, could be used to mimiclong term behavior of freshly added radionuclides. However,some biases could exist in this transposition. The major one isthat a part of the natural isotopes could be included in themineral matrix and not available for soil to water transfer. Inaddition to the Kd determination, the objective of this work is todetermine the isotope soil water available fraction and itsassociated Kdavailable, for freshly added RNs and their naturalendogenous isotope.To reach this objective a cocktail of radionuclides havingdifferent soil behaviors (137Cs, 129I, 233U) was added under liquidor organic (from plants that have been previously contaminated)pathways to four soils presenting contrasted geochemicalproperties. Their water available fraction and Kdavailable weredetermined by a successive desorption batch method, whereastheir distribution within the solid phase was studied withchemical sequential extraction experiments. The obtained resultsfor added RNs were compared with their natural endogenous isotopes (133Cs, 127I, 238U)