Distribuição do Mercúrio lábil no sedimento do Reservatório de Balbina - Am/Brasil

Abstract

The association of mercury with the granulometric composition and different geochemical aspects of sediment, can provide important information about the mobility of this element in the environmental compartments. The reservoirs are complex environments being studied, as can be divided into three environmental compartments with them, Fluvial compartment, Transition compartment and Lakeside compartment, however, the interest in studying the association of mercury with the geochemical aspects in reservoirs constructed from impoundment Amazonian rivers is mainly due to the impact these buildings have on the biogeochemical cycle of mercury. Sediment is one of the environmental compartments affected by the flooding of the forest is the river banks, and this flood causes changes in the geochemical composition of this environmental compartment due to the addition of organic matter and metals with toxic potential such as the Mercury. In this sense this study aimed to evaluate the geochemical aspects that favor the distribution of labile mercury in sediment Balbina Reservoir. For both the sediment samples were collected in 10 sampling sites located upstream of the dam during the month of May 2015, seasonal rainy period. In these samples were determined by mercury concentration (HgT) mercury analyzer using Direct Mercury Analyzer (DMA-80). The extraction of labile mercury (HgL), labile iron (FeL), labile aluminum (AlL) and labile manganese (MnL) were made using the U. S 3051st EPA method. The concentration of HCl was determined using atomic fluorescence spectrometer cold vapor, Tekran, model 2600, the FeL concentrations, MnL, and AlL were determined using ICP-OS, Thermo®, iCAP 7600 Series model. The content of organic matter (TMO) was done following the 2540-G of the Standard Methods Online methodology and for particle size analysis, we used the particle size analyzer by laser diffraction Mastersizer 2000 from Malvern. The results were analyzed using the Spearman correction coefficient, simple linear regression (RLS) and chemometric tools Hierarchical Cluster Analysis (HCA) and Analysis of Main Components (ACP). TMO varied in the range from 2.08 to 48.29%, the granulometric composition presented in the following percentage ranges, sand 46.86 to 94.18%, silt from 4.97 to 48.03% and clay from 0.85 to 5 92%. The concentration of HgT ranged from 0.0123 to 0.3072 mg HgT kg-1.Varying the concentration of the extracted metals were 4132.39 to 211,896.20 mg FeL kg-1, 1613.64 to 46437.64 mg AlL kg-1, from 0.0176 to 0.6133 mg MnL kg-1 and from 0.000 to 0.2560 mg HgL kg-1. The percentage of HgL in the sediment ranged from 0 to 83% over the concentration of HgT and this variation was influenced by the geochemical characteristics of each collection point. The Spearman correlation coefficient showed that the HgL has positive strong correlation to the TMO, silt, clay, FeL, MnL and AlL and strong negative to the sand. These correlations were ratified by chemometric study of these variables, so that the AHC and ACP showed the existence of three different sediment groups in the Balbina Reservoir. The concentration of HgL is high in the river compartment (in the river Uatumã and its tributaries), the transition compartment (center of the vessel) there is a decrease in concentration and lacustrine compartment (near the dam) there is an increase in concentration. The RLS showed that concentration of HgT and HgL are strongly correlated and it was found that the HgT follows the same pattern of behavior exhibited by HgL. The lability of mercury in the sediment can be influenced by the high concentration of FeL, AlL, MnL, organic matter and pH.