Radium is a naturally occurring radioactive element and could in certain cases poses environmental and health risks due to its involvement in biological processes and subsequent release of radon gas from its radioactive decay. Interest in the environmental behavior of radium follows from its ubiquitous presence in the context of TE-NORM (Technologically Enhanced Naturally Occurring Radioactive Material) related activities, which mainly originate from uranium mining/milling, fossil fuels, etc… As such, the main scientific challenge calls for identifying its mobility, transport and bioavailability in the environment. The former uranium mining site of Rophin (Lachaux, France) is characterized at the downstream by a wetland area with high concentrations of 238U and its decay products, such as 226Ra [1]. In particular, an inherited layer of soil found at a depth of approximately 15 cm is recording radium concentrations up to 74 kBq.kg-1 of dry mass of soil. The overall adopted scientific approach is then to propose a mechanistic description of the mobility of radium in Rophin wetland soils by coupling laboratory experiments and field investigations with DET (Diffusive Equilibrium in Thin-Films) samplers. The objective was to determine which fraction is labile, i.e. the fraction that is adsorbed on soils and whose resupply in solution is rapid. This was assessed by desorption experiments under representative site conditions by an original methodology involving different solid/liquid ratios. This extensive lab methodology is based on a distribution coefficient (Kd) model allowing to assess the labile fraction of radium and Kd values in soils. DET probes field deployment followed to monitor radium concentrations in pore waters down to a depth of 50 cm. A centimetric-scale Ra profile was obtained from an original analytical strategy developed in Boudias (2022) [2] (see Boudias et al.’s abstract to this conference). Field data were then implemented into the Kd model to evaluate and improve the representativeness of the laboratory results on labile parameters of radium compared to the in natura equilibrium between soils and pore waters [3]. Overall, the labile fraction of radium was found to be very low (from 5 to 12 % for the inherited layer) and was characterized by Kd values of the order of 100 L.kg-1. This study provides access to valuable data essentials for a more detailed description of radium behavior and interactions in wetland soils. To go a step further, a combined DET-DGT (Diffusive Gradients in Thin-Films) approach will be implemented in the Rophin site in order to determine both labile and dissolved fractions from large soil profiles [3]. The ambition of this work will therefore be to directly access to in natura Kd values and associated kinetic parameters for a more accurate characterization of Ra lability and fate in soil layers.