Estudo do monitoramento geoquímico e ambiental da qualidade de águas e sedimentos do baixo curso do rio Doce, Espírito Santo, Brasil

Abstract

The hydrographic basin of the Doce River is notable for its large volume of surface water and territorial area in the states of Minas Gerais and Espírito Santo. Although important to these states, it has been intensely influenced in the process of occupation, transformation, direct and indirect interference of the main channel over the last decades, resulting in negative effects on water and sediment quality, as well as consequences in the flows and geoforms on the course of the river. In this context, the purpose of this study was to monitor and evaluate the water and sediment quality of the lower Doce River, Espírito Santo, in relation to the presence of chemical species (Al, Fe, Ti, K, Ca, P, S, Zr, Mn, Zn, Sr, Cu, Nb, Y, Rb, Ni, Cr, Cd e Pb) and the application of geochemical indexes (Contamination Factor (CF), Pollution Load Index (PLI), Enrichment Factor (EF) and Geochemical Index (GeoI)) to measure the environmental quality of the sediments. Similarly, analyze data and information from agencies (ANA, IEMA, IGAM) concerning the chemical analysis of water. The sediment samples were collected in the Doce River in the municipality of Colatina, Espírito Santo, at nine sites where they are supposed to be minimally affected by anthropogenic contamination, and are places of great importance for the subsistence of the population. The level of the chemical species was determined by the Geosol-Lakefield Laboratory, located in the State of Minas Gerais. In relation to the physical aspects, it was carried out at the Construction Materials Laboratory, Department of Rural Technology, Federal Rural University of Pernambuco. The geoaccumulation index showed that most of the sampled sediments of the lower Doce River do not present contamination problems, being weak to moderately contaminated only by cobalt. For the contamination factor, the Co element presented the highest degree of contamination for all sites and periods analyzed. In relation to the Fe, the Co and Ni elements in the rainy season (at sites P4 and P8) indicate high enrichment. When the PLI is calculated, 33% of the sites are contaminated in the dry period, increasing to 44% in the rainy season. Regarding the water monitoring, the elements Fe, Mn, Al and Pb had the highest concentrations, above the allowable value defined by Brazilian National Environmental Council (CONAMA) Resolution 357/05 for class 2. The elements As, Cr, Ni and Zn reached the guideline value for class 2 only in november 2015 in Baixo Guandu, the beginning of Espirito Santos’ portion of the basin. In this context, the results presented here may direct future studies in relation to the environmental geochemistry of Espirito Santos’ portion of the basin, as well as in the elaboration of a management plan, since it is proven the use of the river’s water for human consumption.