137Cs in Argentinean soils: Inventory, depth profiles and transport modeling

M. L. MONTES; L. M. S. SILVA; C.S.A. SÁ; J. RUNCO; M. A. TAYLOR; J. DESIMONI

Mar del Plata

Congreso; 1er congreso Internacional de Ciencia y Tecnología Ambiental, 1er Congreso Nacional de la Sociedad Argentina de Ciencia y Tecnología Ambiental; 2012

Vertical distribution and inventories of 137Cs activity were determined in undisturbed soils of neighborhood of La Plata city, Argentina. The study was complemented with determinations of pH, organic carbon, texture and mineralogy of soils. The mean inventories are in accord with the fallout deposit arising from the nuclear weapons atmospheric test performed in the South Hemisphere [1], with a mean value of 891 Bq/m2. Putting together the accessible information of South America[2], it seems that the distribution in latitudinal bands of the inventory is perturbed by the presence of the Cordillera de los Andes, and that the inventory strongly depends of the mean annual precipitation rate. There were significant differences in the 137Cs soil profiles, attributable especially to the illite content. 137Cs profiles were analyzed with the convection-dispersion model, with and without irreversible fixation [3-5]. The data can not be reproduce by the convection-dispersion equation without fixation [3], probably because of the predominance of illite in the studied soil, a receptor of 137Cs in a irreversibly way [6]. In effect, the radiological analysis of the clay showed that the major part of 137Cs is in this fraction. So, the diffusion-sorption-fixation model was used and all the 137Cs profile were succefully reproduced, given rise to effective diffusion coefficient and effective convective velocity values in conformity with those determined for other regions of South Hemisphere. Moreover, the fixation parameter resulted maily dependent on the clay fraction.