No presente estudo, adaptou-se um PAR para avaliar as condições ambientais do rio Gualaxo do Norte, Leste-Sudeste do Quadrilátero Ferrífero, MG, Brasil. Em seguida o PAR foi aplicado em 31 trechos ao longo do seu curso e, posteriormente, avaliou-se a aplicabilidade/viabilidade do instrumento adaptado utilizando-se informações científicas sobre o histórico e o atual uso e ocupação da bacia do rio Gualaxo do Norte. Os resultados demonstraram que o PAR adaptado foi eficiente na avaliação das condições ambientais do rio sob investigação. Contudo, foi evidenciada a necessidade de se ater para avaliação de parâmetros, que podem ter sua visibilidade influenciada pelo período do ano (estiagem ou cheia) ou pela própria localização na bacia. Essa constatação permitiu concluir que a construção/adaptação dos PARs deve ser um processo contínuo de ajustes e aprimoramentos para que o seu emprego possa cobrir uma gama diversificada de tipologias fluviais, bacias hidrográficas e ecorregiões.

In this study, we adapted a Rapid Assessment Protocol methodology (RAP) to assess the environmental conditions of the Gualaxo do Norte River, East-Southeast of the Quadrilátero Ferrífero, MG, Minas Gerais, Brazil. Then the RAP was applied to 31 sections along its course and the applicability/viability of the adapted instrument using scientific information on the history and current use and occupation of the Gualaxo do Norte River basin was evaluated. The results showed that RAP was effectively adjusted to evaluate environmental conditions of river under investigation. However, it was observed the need to evaluate parameters that can have their appearance appraisal influenced by the season of the year (dry or wet) or by their location in the basin. It was concluded that the implementation/adaptation of RAPs should be a continuous process of adjustments and improvements to the extent that their employment may cover a diverse range of rivers, watersheds and ecoregions.

O estabelecimento de valores de background geoquímico como medida relativa para distinguir concentrações naturais de um elemento (geogênica e/ou biogênica) e a influência das atividades antrópicas nestas concentrações representa um dos assuntos mais importantes das ciências ambientais recentes. A relação entre as alterações naturais e as proporcionadas pela ação antrópica nas espécies químicas é uma questão que envolve implicações importantes nas áreas da geologia, toxicologia e biologia, entre outros campos do conhecimento. Isto é especialmente importante, quando interpretações geoquímicas de elementos tóxicos são requeridas. Assim, o objetivo principal desse artigo é apresentar e discutir as razões pelas quais o estabelecimento de valores de background geoquímico tem implicações nos estudos ambientais. Ao longo desse artigo, são apresentados alguns conceitos de background geoquímico e os principais métodos utilizados para avaliar a concentração background de elementos químicos (métodos direto e indireto). Além disso, são destacados alguns exemplos de estudos desenvolvidos no Brasil. Estudos envolvendo o estabelecimento de valores de background geoquímico são importantes porque permitem avaliar riscos potenciais de contaminação e identificar concentrações naturais de elementos-traço de uma determinada área.

The establishment of background geochemical values as a relative measure to distinguish anthropogenic input from natural (geogenic and/or biogenic) concentrations of elements in different environmental samples, is one of the most important subjects in recent environmental sciences. The relationship between natural and anthropogenically altered concentrations of chemical species is a question that involves many implications in the geological, toxicological, biological and other areas of knowledge. This is especially important when geochemical interpretations of toxic elements are required. Thus, the principal objective of this article is to present and discuss the reasons for which the establishment of background geochemical values has implications in environmental studies. Throughout this article some concepts of the geochemical background used by various authors is presented and the main methods used for assessing background concentration of elements (direct and indirect methods). In addition, some examples of studies developed in Brazil are presented. Studies involving the establishment of background geochemical values are important because they allow the evaluation of potential contamination risks and the identification of natural trace-element concentrations in a determined area.

The gold and iron mining activities in the Velhas River yield considerable amounts of suspended solids as well as metals to the hydrological system of the region. The risks were assessed by sequential extraction procedures. They were carried out in sediment samples, aiming to evaluate the presence of Co, Cr, Cu, Ni, Zn and As. Although being at high levels in some parts of the river (e.g. As 527 mg g-1 and Cr 475 mg g-1) they are associated with the residual fraction. Mobility factors were also calculated and show that these species are enriched along the river, e.g. for As 0.02 at the spring and 0.33 at the high course of the river.

Two samples of residues from iron mining plants have been investigated for their retention capacity of As, Cu, Cr, and Pb. The sample with the higher content of iron oxides showed the highest capacity to retain metals. The adsorption affinity series changes from Pb>Cu>Cr~As to As>Pb>Cu>Cr or As>Cu>Cr>Pb, depending on the material and the concentration of the initial solution. In the competitive environment, the Pb adsorption decreases and the As, Cu and Cr adsorption increases. Sequential extraction procedures, carried out after adsorption batch experiments, showed that the most important adsorption process occurs in the oxide fraction and that the major part of the absorbed metal is remobilized from exchangeable and oxide fractions.