Distribuição e mobilidade de arsênio e metais pesados em águas e sedimentos de ribeirões do Quadrilátero Ferrífero, Minas Gerais

• Ano de defesa: 2008
• Autor(a) principal: Varejão, Eduardo Vinícius Vieira
• Orientador(a): Bellato, Carlos Roberto
• Banca de defesa: Neves, Antônio Augusto , Silva, Maria do Carmo Hespanhol da , Queiroz, Maria Eliana Lopes Ribeiro de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Mestrado em Agroquímica
• Departamento: Agroquímica analítica; Agroquímica inorgânica e Físico-química; Agroquímica orgânica
• País: BR
• Palavras-chave em Português: Arsênio; Metais pesados; Sedimento; Extração sequencial
• Palavras-chave em Inglês: Arsenic; Heavy metals; Sediments; Sequencial extraction
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA
• Link de acesso: http://locus.ufv.br/handle/123456789/2047

The aim of this work was to evaluate the arsenic and heavy metal distribution and mobility in water and sediments from the Tripuí and Carmo rivers. The studied area involved part of the rivers course located between the Ouro Preto and Mariana municipalities, southwest region of the Iron Quadrangle, Brazil. The BCR sequential extraction method was used to fractionate As, Cd, Co, Cr, Cu, Ni, Pb and Zn in sediment samples. The total amounts of the elements in the dissolved phase and in suspended particulate matter were determined. The arsenic quantification was carried out by utilizing Hydride Generation Atomic Absorption Spectrometry (HG-AAS). The As (V) reduction before the hydride formation is necessary to As quantification by HGAAS, and it has been obtained by using potassium iodide. However, the BCR protocol utilize oxidizing agents in some extraction steps, and the presence of these extractors in the final solutions interfere on the arsenic reduction due to iodide oxidation. Besides, the iodide oxidation by the extractants leads to production of great quantities of iodine, which may prejudice the formation and release of the hydrides. To avoid these interferences, different reaction conditions were evaluated to As(V) reduction in the BCR extracts. The results showed that quantitative reduction of As(V) can be obtained by the use of KI in association to ascorbic acid, which acts reducing iodine to iodide, allowing the reduction of As(V) to As(III) and the arsenic quantification by HG-AAS. The ascorbic acid concentration in the final solutions varied depending on the sequential extraction step, due to the different oxidizing character of the extractants utilized in each one. So, in the extracts obtained from the four steps of the BCR procedure, the reduction of the As(V) was carried out utilizing 1% (w/v) KI plus ascorbic acid in the subsequent concentrations: 1% (w/v) to the steps 1 and 2; 3% (w/v) to the step 3; and 2% (w/v) to the step 4. This preliminary study allowed the use of HG-AAS to quantify As in the BCR extracts. The analyses of water showed arsenic in concentration between 36,7 and 68,3 µg L-1, above the maximum limit permitted by the Brazilian legislation in water destined to human consumption. Arsenic and heavy metals are present at elevated concentrations in the sediment fractions regarded as potentially available to aquatic medium. Total Mercury in sediments ranged from 179,71 to 690,12 µg kg-1, constituting signal of the recent release of the elemental Hg into the environment from small-scale gold mining activities. Results of water analysis and sediment fractionation reflect the anthropogenic contribution to the element release from the parent minerals and the associated local human health risk.