LEAD SOURCE ASSESSMENT BY ISOTOPIC AND ELEMENTARY COMPOSITION IN THE TRANSITION FROM PRISTINE TO POLLUTED CONDITION OF COASTAL SEDIMENTS / AVALIAÇÃO DAS FONTES DE PB PELAS COMPOSIÇÕES ISOTÓPICAS E ELEMENTARES DE SEDIMENTOS COSTEIROS NA TRANSIÇÃO DE CONDIÇÕES NATURAIS PARA POLUÍDAS

The source assessments of metal contaminants are critical for a consistent management of coastal zones. In this work, lead (Pb) concentration and isotopic composition were determined in sediments from Angra dos Reis coast (Brazil) to evaluate the potential influence of contamination sources on Pb distribution. Estimated Pb enrichment factor superior to 1.64 suggested natural source predominance. Diagrams of 206Pb/207Pb ratio plotted against 208Pb/206Pb and 1/Pb ratios indicated a binary source mixing that was explained by marine and terrigenous influences. Only some specific sites fall close to anthropogenic Pb isotopes signatures (e.g., from urban effluents and gasoline). The lower Pb concentrations were associated with a marine carbonate dilution effect, as indicated by a negative relationship between Pb and Ca. Past dredging activities contributed to explain a diffuse occurrence of anthropogenic Pb isotopic signature. The overall results reveal the beginning of a transition from pristine to slightly-polluted condition. ResumoA avaliação das fontes dos contaminantes metálicos é fundamental para um bom gerenciamento das zonas costeiras. Neste trabalho, as concentrações e composições isotópicas do chumbo (Pb) foram determinadas em sedimentos do litoral de Angra dos Reis (Brasil) para avaliar a potencial influência das fontes de contaminação na distribuição de Pb. Fatores de enriquecimento de Pb de até 1,64 sugeriram predominância de fontes naturais. Diagramas da razão 206Pb/207Pb plotados contra as razões 208Pb/206Pb e 1/Pb indicaram uma mistura binária de fontes, que foi explicada por influências marinhas e terrígenas. Apenas alguns locais específicos possuem assinaturas isotópicas similares às antropogênicas (por exemplo, de efluentes urbanos e gasolina). As concentrações mais baixas de Pb foram associadas a um efeito de diluição pelo carbonato marinho, como indicado por uma relação negativa entre Pb e Ca. Atividades de dragagem no passado contribuíram para explicar uma ocorrência difusa da assinatura isotópica de Pb antropogênico. Os resultados, em geral, revelam o início de uma transição da condição natural para levemente poluída.

Predominance Diagrams of Dissolved Uranium Species and logfO2(g)-pH Diagrams of U-PO43--Nacl-H2O System at 25°C, PCO2=10-3.5 Mpa

To explore the effect of logfO2(g), pH, uranium concentration, phosphate concentration and NaCl concentration on the predominance diagrams of dissolved uranium species and formation of solid phases containing uranium in the U-PO43--NaCl-H2O system at 25 °CandPCO2=10-3.5MPa, the thermodynamic model of this system was constructed. Based on the results of calculation, the logfO2(g)-pH diagrams were drawn. It can be found that: 1) the formation of uraninite needed enough reductive condition (about logfO2(g) < -50 ), while the formation of Na-Autunite needed the strict pH range (5<pH<8) in oxidative condition. 2)The addition of phosphate concentration could promote the formation of Na-Autunite, and inhibit the formation of U4O9(C). 3)The independent increasing of uranium concentration can lead to more kinds of uranium species.4) The variance of NaCl concentration had little impact on the formation of solid phases containing uranium.