The dynamic technique Diffusive Gradients in Thin films (DGT), that measures metal speciation in situ, has found wide environmental application. Typical interpretation of the metal accumulation in terms of the solution concentration has assumed that trace metals do not penetrate beyond the surface of the binding layer. A methodology using multiple binding layers for the case of a metal without its complexes was developed by Levy and co-workers1 and then extended to cases where complexes penetrate, but not the free metal. After deploying DGT samplers in simple solution, a penetration length can be measured from the accumulation distribution between 2 or 3 binding gels. If the penetration is relevant, perfect-sink conditions do not apply and equations considering kinetic limitations are required to calculate the total concentration estimated from DGT samplers. Although these experimental data are crucial to better understand the functioning of DGT sampler, scarce applications of this methodology are found in the literature. Yet, experimental data indicated penetration of both, uranyl and their inorganic complexes in the resin domain of a Metsorb-DGT sampler2. Here, we used a Monophos®-based DGT sampler, for which we firstly checked its suitability to measure the labile uranium concentration (which was also the total concentration) in moderately basic waters (pH ≈ 8), and then checked the hypothesis of perfect-sink condition. This led to a new model where both the free metal ion (or uranyl, in our system) and its complexes penetrate into the resin domain. DGT validation experiments were performed in a simple solution (10 mmol L-1 NaNO3 and 1 mmol L-1 NaHCO3) for which the main U(VI) species were UO2(CO3)3 4- and UO2(CO3)3 2-. Then,time-series experiments were performed in complex matrices relevant to moderately basic waters in which more U(VI) species i.e., Ca2UO2(CO3)3, CaUO2(CO3)3 2-, MgUO2(CO3)3 2- and/or UO2(CO3)34- are present. DGT uptake of Ca2+ and Mg2+, which may impact U speciation or compete with UO2 2+ for DGT binding sites, was also quantified. After evaluating the DGT performance in the laboratory, a field application was finally performed along the Œuf river (Essonne, France). Results for the Monophos®-based DGT sampler were compared to measurements performed with Chelex- and Metsorb-DGT samplers both in lab and in field. The DGT field samplings have also been successfully combined with elemental and isotopic measurements of U in the river water, opening new perspectives to monitor water quality around uranium processing plants, nuclear facilities or mining areas. Acknowledgements: This work has been supported by the ANR (French National Research Agency), under the “Investissement d’Avenir” framework program [Number ANR-17-CE08-0053]. A financial support for the field campaign through the research project NEPTUNE funded by the French program NEEDS. Support from the Spanish Ministry of Science and Innovation is gratefully acknowledged (MCIN/AEI/10.13039/501100011033, project PID2019-107033GB-C21).