Natural samples of soil, sediment and natural water were collected in the “Parc National du Mercantour” in France. Soil and sediment samples were studied to better understand the behaviors of radionuclides (RNs) in different natural compartments. Considering
Am activities in depth (measured by α- and γ-spectrometries), two types of sediment profiles can be distinguished depending on the origin (Chernobyl accident or atmospheric nuclear weapon tests). Due to difficulties in modeling the dispersion of those RNs in natural samples, even in a protected area, semi-synthetic studies were conducted. Eu(III) was used as an analogue of Am(III). Eu behavior in water was studied by EXAFS and compared to speciation diagrams drawn in similar chemical conditions. Eu is mainly complexed by carbonate and phosphate ions. The mean Eu-O distance (2.46 Å) obtained by EXAFS is in agreement with predominant solid species determined by speciation diagrams and previous published studies.