Avaliação do perfil vertical da concentração de metais em sedimentos do Reservatório da Usina Hidrelétrica de Furnas

Abstract

In this work the concentration of metals was evaluated in the vertical profile of sediment samples and water from the reservoir Hydroelectric Furnas - MG (Compartment Sapucaí). The water was collected with a Van Dorn bottle and a Kajak-Brinkhurst was used for sediment collection. The samples were sliced into 1 cm to a depth of 5 cm also collected a slice of 10 cm. The sediment samples were digested in a cavity microwave oven system using concentrated acid (HNO3) and hydrogen peroxide, as recommended by the Environmental Protection Agency 3051A (EPA). The following metals were analyzed: Cd and Pb by graphite furnace atomic absorption spectrometry; Mn by flame atomic absorption spectrometry; As, Cd, Co, Cu, Mn, Fe, Pb, Ni, Se and Zn by inductively coupled plasma mass spectrometry. Certified Reference Material was employed to evaluate the accuracy of the proposed method and the values were in agreement at 95% confidence level (t-Student test) for most metals, except for manganese. The obtained concentrations for the metals in the water samples indicated no pollution, since most are below the maximum limits recommended by the national council of the environment. The results of the concentration of metals in sediment were similar to the values of the Global Geological Reference Levels, the Threshold Effect Level, the Probable Effect Level as well as the Regional Reference Values. The punctual stratification can be observed in the sediment column, nevertheless the main feature are the heterogeneity of the sediment composition which difficult the profile evaluation. It was also noted that there were difference in the metals concentration between the dry and rainy seasons, causing a dilution in the rainy season.