Radiological Survey in Soil of South America

Abstract

When the Earth was formed, the crust and consequently the soil and water were conformed by a wide variety of chemical elements with different concentrations; being some of these radioactives. There are different activity levels of natural radionuclides, as those of the 238U and 232Th decay chains, 40K, 7Be and 14C, etc. along the planet [Cooper et al., 2003]. Among the 80 nuclides found in the environment, the more relevant concerning the radiobiological significance are 40K, and the nuclides belonging to the 238U and 232Th decay chains. The human activities can strongly modify the natural concentrations due to the presence of residues or accumulation of elements caused by the release of effluents to the environment. In the 60 s the nuclear power production and nuclear weapon testing discharge to the environment anthropogenic nuclides. In particular, the Southern Hemisphere was mainly polluted by the debris originated in the South Pacific and middle Atlantic nuclear weapon tests [UNSCEAR, 2008]. Along with the class of anthropogenic gamma emitter nuclides releases, the 137Cs is the most prominent isotope in the Earth crust originated by fission process. It is considered as one of the hazardous environmental contaminant due to the contribution to the external irradiation exposure and its incorporation to the human food chain [Singh et al., 2009]. Regardless, both natural and man-made nuclides have radiobiological implication because they significantly contribute to human external radiation dose and to the internal dose by inhalation and ingestion [Cooper et al., 2003; UNSCEAR, 2008]. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has estimated that exposure to natural sources is approximately 98% of the total radiation dose (excluding medical exposure) [UNSCEAR, 2000; UNSCEAR, 2008]. The dose arising from natural nuclides varies worldwide depending upon factors such as height above sea level, the amount and type of radionuclides in the air, food and water, as well as the concentration of the natural nuclides in the soil and rocks, which in turn depend on the local geology of each region, etc. The information about the presence and migration anthropogenic radionuclides is crucial to fully understand the long-term behaviour in the environment, the uptake by flora and fauna including the human food chain, as well as potential contribution to groundwater. In consequence, before assessing the radiation dose to the population, a precise knowledge of the activity of a number of radionuclides is required [UNSCEAR, 2000;