ANÁLISE GEOQUÍMICA DE ÁGUA E DE SEDIMENTOS AFETADOS POR MINERAÇÕES NA BACIA HIDROGRÁFICA DO RIO CONCEIÇÃO, QUADRILÁTERO FERRÍFERO, MINAS GERAIS - BRASIL.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

An environmental investigation was carried out in basin of the Conceição river, aiming at evaluate the geochemical characteristics of water and sediments, and to determine the influences of human activities in its composition and variations. The study area is located at the District of Santa Bárbara, Minas Gerais state - Brazil. Geologically it is inserted in the northeast portion of the Iron Quadrangle and its lithology is characterized by the units of the Rio das Velhas and the Minas Super groups. This study involved a seasonal determination of the hydrogeochemical and physiochemical parameters of the quality of the River water, as : temperature, hydrogen potential, oxidation-reduction potential, dissolved oxygen, electric conductivity, total dissolved solids, turbidity, alkalinity, and the contents of sulphate and chloride. Also the content of Ca, Na, K, Mg, Fe, Mn, Al, The, Cd, Pb, Co, Ass, Cr, Ni, V and Zn were determined in the water and sediments. For this study 27 samples of water and 25 samples of sediments were collected. The sampling along the river and in its main tributaries in the summer (July and September of 2004) and in the winter (October 2003). In addition to the water and sediments samples, 6 rock and soil samples, collected in the headboards of the Conceição river in May of 2004 were investigated, to establish the correlation between the mineralogy and the geochemistry of the rocks, soils, sediments and the water, and to determine the sources for the main elements Al, Fe, Mg, Mn, K and Ca. The sediments show variable values in the concentrations as welll as for the major elements also as for the trace metals. High concentrations of Zn, Cu, and As were observed in the downstream of the Conceição, river which could be related to the mining activities for gold. This is shown in graphics of the normal distribution. Using the baseline values, the Geoaccumulation Index parameter was calculated, classifying the Conceição river as practically no polluted in the case of the elements Cr, Zn and Cu, only moderately polluted by Pb, but strongly to extremely strongly polluted by As. The main sources for the concentrations of the determined elements in the soils and in the sediments, are the rocks of the Rio das Velhas Super group for the elements Al, K, Mg, Cd and Pb, and the Minas Super group for the elements Ca, Mg and Fe. The results of the water analyses evidenced an increase of turbidity, sulphate and chloride in the proximities of the urban areas, which could be attributed to the release of domestic sewages. In relation to the concentration of the main elements and trace metals in the water, it could be written down, that those concentrations along the whole river are inside of the levels allowed by the resolution of CONAMA 357 (2005) for waters of the classes 1 and 2. Only at the sample points C14, C29 and C27, higher concentrations of Fe, Ni, Pb and Cr were observed, which are related with the mining activities. The concentration of chemical elements in soils, sediments and water is related with the lithology of the Rio das Velhas and Mines Supergroups, also being influenced by antropogenhic activities developed in the region, as the mining.

ASSUNTO(S)

geologia ambiental geoquímica ambiental água hidrogeologia

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