Uranium isotopes in groundwater occurring at Amazonas State, Brazil

This paper reports the behavior of the dissolved U-isotopes U-238 and U-234 in groundwater providing from 15 cities in Amazonas State, Brazil. The isotope dilution technique accompanied by alpha spectrometry were utilized for acquiring the U content and U-234/U-238 activity ratio (AR) data, 0.01-1.4 mu g L-1 and 1.0-3.5, respectively. These results suggest that the water is circulating in a reducing environment and leaching strata containing minerals with low uranium concentration. A tendency to increasing ARs values following the groundwater flow direction is identified in Manaus city. The AR also increases according to the SW-NE directions: Uarini -> Tefe; Manacapuru -> Manaus; Presidente Figueiredo -> Sao Sebastiao do Uatuma; and Boa Vista do Ramos -> Parintins. Such trends are possibly related to several factors, among them the increasing acid character of the waters. The waters analyzed are used for human consumption and the highest dissolved U content is much lower than the maximum established by the World Health Organization. Therefore, in view of this radiological parameter they can be used for drinking purposes. (C) 2014 Elsevier Ltd. All rights reserved.