Variations in the aquatic environmental conditions can produce a release of heavy metals from the sediment to the water resulting in an increase of their bioavailability and consequent toxicity (Young et al., 1987;Wen and Allen, 1999). This aspect can be further investigated when the samples are analyzed in recent sediments, allowing a detailed study of heavy metals in association with the bioavailable and residual fractions, involving materials of different origins. The distribution and quantification of heavy metals in river sediments are usually based on concentrations obtained from extraction procedures and compared with the natural background levels (Salomons and Förstner, 1984).The Tietê River, with 900 km of extension, is the longest river of the southeast part of Brazil. Its drainage basin, with a population of nearly 25 million people, is important for food and energy production, with more than ten hydroelectric power plants along the main channel of the river and tributaries. Over the years, with the increased population and consequent development of industry and agriculture, the river water and sediment quality deteriorated. In recent years, attention has been focused to the problem of river pollution related to the presence of heavy metals in dissolved and particulate loads (Mortatti and Probst, 2010).This paper aims to characterize the heavy metal distribution in the recent sediments along the Tietê River (from headwater to the mouth) and evaluate the degree of pollution in the river basin, considering a regional background level. (Received March 31, 2011; Accepted September 22, 2011) The distribution of heavy metals in recent sediments deposited along the Tietê River, a highly polluted river in southeast region of Brazil was studied. Around the metropolitan area of São Paulo city (25 million people), the pollution is related to municipal wastes and industrial effluents with reinforced downstream by agricultural activities. The observed increase of heavy metal concentrations is particularly important for Zn in the upper basin and Cu, Co and Cr at mouth. Geo-accumulation index calculation, related to the regional background, showed that the sediments along the basin are seriously polluted by heavy metals of anthropogenic origin, mainly Cu, Co, Cr and Zn. Calculated index suggests medium to very strongly pollution. Heavy metal distribution in recent sedimentsKeywords: heavy metals, Tietê River, sediments, geo-accumulation index, pollution INTRODUCTIONHeavy metals are considered one of the greatest threats to the human health, due to their toxic effects on the environment. They are present in various compartments (atmosphere, water, soil, sediments and living organisms) and their forms are controlled by physical and chemical conditions as well as by biological processes. Natural occurrence of heavy metals is related to distribution of clastic mineral detritus from soil, rock and volcanic eruptions (Sanei et al., 2001;Mortatti and Probst, 2010), and from anthropogenic activities related to agricultu...

The fractionation of heavy metals in riverbed sediments along the Tietê River basin, a highly polluted river in southeast region of Brazil, was investigated using a four-step sequential extraction procedure, in order to determine the concentration and distribution of Cu, Co, Cr, Cd, Zn, Ni and Pb, in the river bottom sediments, related to the potential mobility of geochemical phases. Around the metropolitan area of the City of São Paulo, which has 25 million people, the pollution is associated with municipal wastes and industrial effluents. Potentials of high mobility were observed for Cu and Zn along the entire river basin, associated mainly to the organic fraction, while at the Pirapora and Anhembi stations (upper and middle parts of the basin, respectively) the reactive forms of Ni and Pb were more associated to the Fe and Mn oxides. Near the mouth of the Tietê River, no significant contaminations caused by Cr and Ni in riverbed sediments was verified confirming the presence of these metals in the residual or lithogenous phase.

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, basin of upper Tietê River 10 Sedimento de fundo coletado em perfil de profundidade (A), fatiado e acondicionado em recipientes plásticos prontos para congelamento (B).

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