Radiological Survey in Soil of South America

M.L. MONTES; J. DESIMONI

Radioisotopes/Book 1

InTech

Año: 2011; p. 197 - 224

Although the Earth´s crust is naturally radioactive, natural and man-made nuclides have radiobiological implication due they are a significant part of human external radiation exposure and can contributed to the internal exposure by inhalation and ingestion. In the 60´s the nuclear power production and nuclear weapons testing supply achieved a 7% of the total dose, at the present they are a very small fraction of the total dose. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has estimated that exposure to natural sources contributes with more than 98% to the radiation dose to the population (excluding medical exposure). Depending on factors such as height over sea level, amount and type of radionuclides in the soil, air, food, and water, the local doses varies worldwide. In consequence, before assessing the radiation dose to the population, a precise knowledge of the activity of a number of radionuclides is required. Therefore, the determination of radionuclides in environmental samples becomes an important task in protecting human health and to establish regulations. Additionally, the mobility of the radionuclide in the ecosystem involves a number of complex mechanisms and the transfer of radionuclides through the environmental compartments implies multiple interactions between the biotic and abiotic components of the ecosystem, as well as human interferences like the use of fertilizer or the overexploitation of the natural resources. To the identification of these interactions it is necessary to develop and test predictive models describing the radionuclide fluxes from the environment to the man. For South America, the UNSCEAR reports only account values of the activity concentration of the natural nuclide 40K for Argentina. In the Brazilian State of Rio Grande do Norte the average concentrations of 226Ra, 232Th and 40K in unperturbed soils have been determined. In Argentina data of 226Ra and 40K of semi-natural grassland soils of the central part of the country (Province of San Luis) have been accounted. Recently, the first systematic studies to establish baseline activities for the naturally (40K, 238U and 232Th chains) occurring radionuclides in unperturbed soils of inland and coastal areas around La Plata city, Province of Buenos Aires, have been settled on samples taken from the surface down to a depth of 50 cm. Regarding the anthropogenic nuclides, only a few studies dealing with the determination of the activity of the 137Cs, globally presented on the soil because of nuclear weapon tests that have been performed in the Southern Hemisphere. Total inventories and depth distributions of 137Cs were established in the Central and Southerm agricultural sheep-farming regions of Chile. In Venezuela, the 137Cs concentration at two different depth (0 cm -20 cm and 20 cm - 40cm) were measured . In Argentina 137Cs reference activity profile was determined in the Pampa Ondulada region and in the central part of the country in natural and semi-natural grassland regions. Beside the natural chains values, the profiles of 137Cs in the same region of Buenos Aires Province have been settled. Important differences were found, attributed to chemical, physical, mineralogical, edaphic, rainfall rate and climatic factors.