Natural radioactivity levels (K, Th, U and Rn) in the Cecita Lake area (Sila Massif, Calabria, Southern Italy): an attempt to discover correlations with soil features on a statistical base

Soils can exhibit a complex range of physical, mineralogical, and chemical features depending on many interrelated factors such as parental rock composition and mineralogy, climate, topography, vegetation amounts and types, water infiltration versus runoff. soil moisture, organic matter, presence and types of anthropogenic contaminants, and many others. Radioactivity as measured on these complex systems is consequently perturbed by several mixed effects. In order to find out a possible (potential) relationship among soil properties and experimental data attributable to radioactivities of K, Th. U and Rn a detailed investigation has been performed in the Cecita Lake basin (Sila Grande, Calabria, Southern Italy). Most of the soil types outcropping in the Cecita Lake surroundings belong to the Entisol and Inceptisol orders [USDA (United States Department of Agriculture), 2006. Keys to Soil Taxonomy. 10th edit., USDA, Soil Survey Staff, Natural Resources Conservation Service, Washington D.C., 333 pp.], representing relatively young, poorly to moderately differentiated soils, showing features strongly dependent on the nature of the parent rock and the climatic conditions. Disintegrations contributed by K, Th, U and Rn measured respectively in % (K), ppm (U and Th) and kBq/m(3) (Rn), have been related to 13 a priori known soil unit groups with well-defined general features and spatial position. The data have been analysed by using graphical and numerical statistical procedures able to manage compositional data in a correct sample space. The paper summarises the results of this research and highlights the conclusions drawn from these investigations, particularly concerning i) the modelling of the high U variability, a behaviour that tends to homogenise the differences potentially attributable to soil features, with the exception of situations where uranium could be enriched due to adsorption onto iron oxi-hydroxides and/or clay minerals or concentrated in argillic horizons due to illuviation; ii) the discovering of the discriminative effect of the K/Th ratio values, particularly for soil groups where Th behaviour, as other tetravalent actinides. is strongly affected by the presence of mineral colloids or where the presence of clays affects the trapping of K; iii) the clustering of the a priori known soil groups in four new sets characterised by internal similarities for Rn values for which the morphology appears to be the most important discriminative effect.