Critérios para avaliação da qualidade de sedimentos - Estudo de caso: Sub-bacia do Ribeirão Espírito Santo, afluente do Rio São Francisco / Criteria for evaluating sediment quality - Case Study: Sub-Watershed of Espírito Santo Stream; Affluent of the São Francisco River

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Sediment Quality Values Guidelines (SQVG) have been used for evaluating ecological risk associated with the sediment contamination for benthonic organisms. The main objective of this work was to develop methodologies and to collect data that allowed the application of SQVG for the following metals: Cd, Cu, Pb, Ni and Zn. The location chosen for the case study was the sub-watershed of the Espírito Santo Stream, which is part of the Unit Planning and Hydrologic Resources Management UPGRH SF4, of the São Francisco river watershed, located in the area of the city of Três Marias. The life in the sub-watershed is significantly affected by the installation of a waste dam that controls effluents coming from the zinc-ore beneficiation plant. Our studies addressed the biogeochemical characterization of the sediments of those environments through the determination of the concentrations of acid volatile sulfide (AVS), the study of the partitioning of metals among the total sediments and interstitial waters, and the determination of the fraction of metals associated with AVS in the total sediments. The data obtained were analyzed in association with those related to the analysis of the structure of the benthonic community and eco-toxicity tests. The studies also included analysis of the physico-chemical variables and concentration of metals in the samples of the surface water; mineralogical and granulometric analyses, quantity of organic matter and concentration of inorganic contaminants in the samples of sediments. High levels of electrical conductivity and total solids diluted were found in one surface water sample site. The results of a Neutron Activation Analysis (NAA) showed that the chemical elements predominant in the samples were Ti, Al, V, Mn and Fe. The results of the total metal analysis in sediment samples showed that only one point located in the Lavagem stream, situated immediately downstream the dam and before flowing into the Espirito Santo stream, presented concentration values of the evaluated metals (Cd, Cu, Pb, Ni and Zn) above those of the background value. The TEL limits (Threshold Effect Level) and PEL (Probable Effect Level) were not exceeded in any of the sampling campaigns. The Guidelines Interstitial Water Toxic Units (IWTU), established by the USEPA, was violated for all samples. The application of SQVG, based on the equilibrium partition theory, showed that metals are controlled by the sulfide-phase present in sediments. This indicates that the metals presented in the sediments may have low bio-availability. The results of the evaluation of the benthonic community structure indicated a possible influence of the waste dam in the Lavagem stream and in the Espírito Santo stream, downstream the confluence with the Lavagem stream. The results of eco-toxicity tests showed that contaminated sediment can cause only chronic effects.

ASSUNTO(S)

geociencias poluição da água análise por ativação netrônica contamination chemical analysis water quality sedimentos ecosistemas aquatico ribeirão do espírito santo aquatic ecosystems neutron activation analysis contaminação qualidade da água sediments environment water pollution espírito santo stream

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