The soil screening levels express the levels of contaminant concentration in the soil,which guide the actions to be taken following investigation to confirm contamination.The list of toxic substances or elements under Brazilian legislation includes organics,volatile organics and metals; but,it does not consider radioactive elements,all potentially carcinogenic and,therefore,necessarily subject to legal control.The National Nuclear Energy Commission,the federal agency currently responsible for legislation regarding the control of Normally Occurring Radioactive Material (NORM) facilities,also does not establish guiding values for intervention in terms of soil activity concentration in the case of contamination with radioactive elements.In mining,the processing and treating of ores such as cassiterite,uranium,phosphate,niobium,rare earths,among others,contribute to the generation of large amounts of NORM residues.Evidently,the improper disposal of these materials may lead to situations that result in soil and groundwater contamination,and unnecessary exposure of the population in general.In order to establish guiding values for soil quality for natural radionuclides,12 units were selected for mapping in the state of Minas Gerais.The study area included the entire state,which has unique characteristics related to the lithology,genesis and morphology of the soils.These have tremendous influence on the pedogeochemistry of trace elements and radionuclides.About 70% of the soils in the state correspond to such highly weathered soils as oxisols,ultisols and nitosols.Approximately 17% of the remaining soils belong to the Cambisol class,which frequently shows oxisol minerology.In these soils,low radioactive clays predominate,for example,kaolinite associated with oxides and hydroxides of iron and aluminum.A total of 122 soil samples were collected and analyzed in order to determine the activity concentration of U and Th activity.In general,it was possible to verify that the activity concentrations of Th-232 are higher than those of U-238,which is a characteristic typical of rocks of igneous origin.The results obtained up to the present time are higher than the reference values for soil quality adopted in other parts of Brazil and the world.