Avaliação de impactos ambientais por estudo geoquímico na bacia do Córrego Rico, Paracatu – MG

Abstract

The present work has as objective to carry through water and sediments quality analyses of the Rico Stream and with this, recognize and quantify the main anthropical interventions in the area, mainly the deposition of domestic sewer without treatment and the clandestine gold washer activity. The study region is located near the Paracatu city, in the northwest of the Minas Gerais state, 239km from Brasilia, initiating immediately to the north, in the spring of the Rico stream, until its ebb tide, approximately between coordinates 17° 13`01’’ south and 46° 52`17’’ west. For the physical-chemical determination of water parameters, collection techniques and water analysis had been used as described in Standard Methods for the Examination of Water and Wastewater, 1998. Spectrophotometer UV-Visible HACH-DR 2000 was used for the determination of Nitrate, Phosphate, Turbidity and Color. Titulometrical methods had been used for determination of Alkalinity, Consumed Oxygen and Chloride. The pH, conductivity and total dissolved solid had been determined with multi-parameter HACH. Elements Al, Fe, Ca, Mg, P, Zn, Ni, Cu, and Si had been determined using emission spectrometer with optics plasma source (ICP-OES). For analysis of deep sediments, the dry material was bolted to separate the silte/clay fraction. The determination of volatile solids was carried through by loss to the fire and the organic substance was determined by the Waldley-Black method. For analysis of trace and major elements, an acid digestion with HF/HNO3/HClO4/HCl and fusing with LiBO2 was used. The determination had been carried through in spectrometer of plasma emission (ICP/OES). For the determination of mercury, a partial acid opening with HNO3/HCl was used. The Hg concentration was determined by acid extract reduction with SnCl2 5% (m/v) and reading in a spectrometer of atomic absorption with cold vapor generation model Mercury Monitor® 3200 Elemental Mercury Detector. Moreover, microbiological study for detection and analysis of total coliforms and E. coli presence was carried through. The capacity of resilience of the stream was determined too. The physical-chemical water parameters and the chemical elements analyzed in water and sediments had presented normal values, according to legislation. The occurred variations are related with the studied region geology, with the fertilizer use in agriculture and mainly in the deposition of domestic sewer without treatment in the Rico Stream or for the mercury use in the activity. The microbiological test concluded that there is contamination by fecal coliforms of the domestic sewer. With regard to the contamination factor, the majority of the studied points presented values below or equal to controlled points. The calculated indices of geoacumulation for metals present low values, classifying the sediments of the studied region, in a general way, as not polluted the moderately polluted ones. The resilience capacity of the stream gotten edges is low, not arriving 30%. Which these study, we can conclude that the main contaminant agent of the Rico Stream basin is the deposition of domestic sewer without treatment in the stream.