title: Uranium isotopes in groundwater occurring at Amazonas State, Brazil.
abstract: This paper reports the behavior of the dissolved U-isotopes (238)U and (234)U 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 (234)U/(238)U activity ratio (AR) data, 0.01-1.4µgL(-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→Tefé; Manacapuru→Manaus; Presidente Figueiredo→São Sebastião do Uatumã; 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.
authors.affiliation: Coordenação de Pesquisas em Clima e Recursos Hídricos, CDAM-INPA, Av. André Araújo, 2936, Petrópolis, CEP 69080971 Manaus, Amazonas, Brazil. Electronic address: marciols@inpa.gov.br.
authors.forename: Márcio Luiz
authors.initials: ML
authors.lastname: da Silva
authors.affiliation: Departamento de Petrologia e Metalogenia, IGCE-UNESP, Av. 24-A, 1515, CP 178, CEP 13506-900 Rio Claro, São Paulo, Brazil. Electronic address: danielbonotto@yahoo.com.br.
authors.forename: Daniel Marcos
authors.initials: DM
authors.lastname: Bonotto
keywords: (234)U/(238)U activity ratio; Amazon area; Dissolved uranium; Groundwater; Tube wells