Natural radionuclides in surface soils from Biritiba-Mirim reservoir, state of São Paulo, Brazil

The Biritiba-Mirim reservoir (23°36'S 46°05'W) is located at the Upper Tiete water basin, which is responsible for water supply in the São Paulo Metropolitan area. Few studies aimed at the analysis of natural radionuclides in surrounding soils of the Brazilian water supply reservoirs, including the reservoirs of the Upper Tiete water basin. Some of this research is part of studies developed by the Laboratório de Radiometria Ambiental from the Instituto de Pesquisas Energéticas e Nucleares (LRA-IPEN) and aimed the evaluation of natural radionuclides activities concentrations in soils and sediments of the neighboring reservoirs (Ponte Nova, Jundiaí and Taiaçupeba). In international literature is possible to find some latest studies that have evaluated the levels of natural radionuclides in soils, however, most of them are focused on the analysis of recognized contaminated areas (e.g. mining activities or nuclear industry operations). The anthropogenic inputs of naturally occurrence radioactive materials should be managed to prevent risks either to humans or the biota, especially in disturbed environments, such as artificial water reservoirs. The main objective of this paper was to evaluate the activity concentrations of ²³⁸U, ²³²Th, ²²⁸Ra, ²²⁸Th, ²²⁶Ra and ⁴⁰K in surface soils from the Biritiba-Mirim reservoir. Moreover, this study aimed to verify the influence of soil physical-chemical parameters (clay, silt, and sand contents, pH, organic matter, cation exchangeable capacity, and total porosity), the lithological composition, and the land use on the activity concentrations of the natural radionuclides. (author)