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O procedimento de extracao em tres etapas sequenciais recomendado pelo Programa de Normas Europeias de Medicoes e Ensaios (SM&T), anteriormente nomeado por Gabinete Comunitario de Referencia (BCR), foi aplicado para a especiacao quimica de metais pesados (Cu, Pb, Cr e Zn) em sedimentos provenientes de diferentes regioes urbanizadas da Cidade de Uberlândia (MG, Brasil). Para obter o balanco de massa, uma quarta etapa, ou seja, a digestao do residuo foi realizada atraves do processo de digestao assistida por micro-ondas em meio acido. Maiores concentracoes dos elementos metalicos foram encontradas em pontos de amostragem que recebem descarga de uma area urbana e uma zona industrial. Todos os metais, exceto Zn, estavam presentes em maiores concentracoes nas fracoes residuais (fortemente associados com as estruturas cristalinas dos minerais), indicando que Cu, Pb e Cr foram menos moveis e potencialmente menos biodisponiveis nesses sedimentos. Em sedimentos de zonas de descargas industriais e urbanas, a sequencia de mobilidade dos metais estudados foi Pb > Zn > Cu > Cr. Maiores concentracoes de Pb foram encontradas nas fracoes residuais no ponto de amostragem localizado no afluente que drena a zona industrial (102 mg kg -1 ), indicando que este elemento metalico foi fortemente ligado aos sedimentos. Portanto, sob os pontos de vista toxicologico e ambiental, o Pb nao causa impacto ao meio ambiente e consequentemente a saude humana. A soma das quatro fracoes (soluvel em acido, redutivel, oxidavel e residual) apresentou boa concordância com o teor total, o que comprova a exatidao do procedimento de extracao por micro-ondas em conjunto com o metodo analitico FAAS. A three-step sequential extraction procedure recommended by the European Standards, Measurements and Testing (SM&T) Program, formerly the Community Bureau of Reference (BCR), was applied to the chemical speciation of heavy metals (Cu, Pb, Cr and Zn) in sediments from different populated zones of Uberlândia City (MG State, Brazil). To obtain a mass balance, a fourth step, i.e., digestion and analysis of the residue, was performed using a microwave-assisted acid digestion procedure. The highest metallic elements concentrations were observed at one of the sampling points which receive discharge from an urban area and an industrial zone. All metals, except Zn, were present at higher concentrations in the residual fractions (strongly associated with the crystalline structures of the minerals) indicating that Cu, Pb and Cr were less mobile and potentially less bioavailable in these sediments. In sediments from industrial and urban discharge zones the mobility sequence of the heavy metals studied was Pb > Zn > Cu > Cr. The highest Pb concentrations were found in the residual fractions at the sampling point located in the tributary stream that drains the industrial district (102 mg kg -1 ), indicating that this metallic element was strongly bound to the sediments. Therefore, under the contamination and toxicological point of view, Pb has no impact to the environment and consequently to the human health. The sum of the four fractions (acid-soluble + reducible + oxidizable + residual) was in good agreement with the total content, which verifies the accuracy of the microwave extraction procedure in conjunction with the FAAS analytical method.

Metal speciation in surface sediments of the Uberabinha river in Uberlândia, MG State, Brazil