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Sediment Quality Assessment and Management: Insight and Progress Edited by M. Munawar© 2003 Ecovision World Monograph Series Aquatic Ecosystem Health & Management Society Weakly-bound metals and total nutrient concentrations of bulk sediments from some water reservoirs in São Paulo State, SE Brazil A.A. Mozeto1*, P.F. Silvério1, F.C.F. DePaula1, J.E. Bevilacqua2, E. Patella 3, W. de F. Jardim 4 1Lab. de Biogeoquímica Ambiental, Depto de Química, Universidade Federal de São Carlos, Caixa Postal 676, 13565-905 São Carlos, SP, Brazil.* 2 CETESB, São Paulo, SP, Brazil. 3SABESP, São Paulo, SP, Brazil. 4IQ-UNICAMP, Campinas, SP, Brazil. Keywords: heavy metals, Pinheiros river, Tietê river Introduction Suspended particulates and sediments in lakes are well known for being able to concentrate heavy metals such as Cu, Cd, Pb, Zn and Ni. In many aquatic systems throughout the world, concentrations of heavy metals in sediments are much higher than the background levels and are related to anthropogenic activity. For various reasons even in cases where the metal concentrations are higher than the background level, metal bioavailability can be minimal and adverse effects on biota (detected by laboratory bioassays and field benthic community structure surveys) may not occur (Ankley et al., 1996). Sediment physico- and biogeochemical properties have been identified as the factors responsible for the differential bioavailability of contaminants among different sediment types. As pointed out by Ankley et al. (1994), to predict the occurrence of environmental impacts, i.e., a way of measuring the extent of adverse effects on aquatic biota (information essential to natural resource managers), the fraction of the total metal concentration which is biologically available must be evaluated. 222 For a number of years, there existed a good deal of uncertainty on procedures to measure and validate the bioavailable fraction of metals in sediments. Numerous studies have shown that the acid volatile sulphide (AVS) is the key phase controlling the bioavailability of heavy metals in sediments (e.g., Di Toro et al., 1990). It has also been well documented that a wide variety of aquatic organisms withstand environments with more AVS than metals in sediments. Others studies, however, have shown that even with more metal than AVS, sediment could not be assumed to be toxic (Ankley et al., 1993) since unknown (and/or unmeasured) phases (different from AVS) may sequester metals from the truly dissolved (and truly bioavailable) phase. This phase has been identified as the particulate organic carbon, capable of complexing metal ions, and known as non-bioavailable species (USEPA, 1994; Ankley et al., 1993; Ankley et al., 1996; USEPA, 2000). We report in this work results obtained in 1997 on contaminated and nutrientrich sediments from several reservoirs in the state of São Paulo (SE Brazil). As a first approach to evaluate the partitioning, availability and toxicity of metals in lake sediments, an integrated sediment assessment was developed using determinations of weak-acid extractable concentrations of Cd, Ni, Zn, Cu, Pb and Hg (as well as total Hg concentration), total nutrients (C, N and P) and acid volatile sulphide (AVS) distributions, coupled with EH measurements in sediment cores. Further work is presently being carried out in order to consolidate our knowledge on metal partitioning, bioavailability and toxicity within a larger research project (QualiSed Project), started in 2000, aimed at providing a basis for sediment quality criteria to be used by the state of São Paulo environmental agencies (SABESP and CETESB). Material and methods Sampling locations, coring procedures and field EH measurements Sediment core samples from Billings (BL) (Taquacetuba branch), Guarapiranga (GU) and Rio Grande (RG) Reservoirs (Figure 1) for chemical analyses were collected in June 1997 from the following sampling sites: (a) Billings Reservoir: BL-104 (lower part of reservoir branch), BL-102, BL-101 and BL-103 (upper part of reservoir); these sampling sites are located in an area where the Taquacetuba River discharges into the reservoir, hereafter referred to as the Taquacetuba branch; (b) Guarapiranga Reservoir: GU-101 (close to the dam), GU-104, GU-106 and GU-107 (upper part of reservoir); (c) Rio Grande Reservoir: RG-101 (close to the dam) and RG-104 (upper part of reservoir). 223 Fig. 1. Map of the study area, state of São Paulo - SE Brazil, showing locations of water reservoirs in the upper part of the Tietê river basin: Billings, Guarapiranga and Rio Grande in the metropolitan São Paulo. 224 These reservoirs are located in the Metropolitan S...


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