BACKGROUND VALUES FOR CHEMICAL ELEMENTS IN SEDIMENTS OF THE GUALAXO DO NORTE RIVER BASIN, MG, BRAZIL

Resumo

The aim of this study was to establish local background values for Fe, As, Pb, Mn, Ba, Zn and Ni using sediments from cutbanks and alluvial terraces of the Gualaxo do Norte River basin, Minas Gerais State, Brazil. A total of 16 stratigraphic sections were surveyed along the basin and 120 samples were analyzed. To establish background values we took into account mineralogical and grain-size analyses, faciologic interpretations, geochemical evaluations (by means of aqua regia partial digestion and ICP-OES readings), and the application of statistical techniques (boxplot representations, iterative 2σ technique, cumulative frequency curve and calculated distribution function). The results reveal relatively high background values for As, Pb, Mn, Ba, Zn and Ni (respectively 64.2; 43.8; 1636.0; 141.4; 65.3 and 39.0 mg.kg-1). The concentrations of these elements are possibly related to the local geology, being the concentrations higher than these values linked to mining activity in the study region, in special gold mining. On the other hand, the background values established for Fe is lower than the values identified in the majority of the sections analyzed. The background value established for Fe corresponds to a concentration of 8.2%. However, concentrations higher than 48% were identified in the study area. There is a strong evidence of Fe enrichment due to mining at the head of the basin. In conclusion, we can say that the proposed values are important parameters for local environmental/territorial management and may help alerting public managers of the necessity of remediation of certain sites, where anomalous toxic element concentrations are identified.