Valores de referência de qualidade e adsorção de metais pesados em solos da Região do Médio Paraíba - RJ

Abstract

The definition of standard values of quality (SVQs) of soils is obtained from the determination of the heavy metals natural levels. They are applied in environment monitoring studies as indicators for assessing environmental impacts of such substances, and for legal intervention, according to local and/or regional conditions. The first chapter aim was to propose the SVQs using the natural concentrations of B, Ba, Co, Cr, Cu, Ni, Pb and Zn in slightly impacted soil from the Region of Médio Paraíba, in Rio de Janeiro State. Forty points were sampled (0-20 and 20-40 cm), the metals were extracted by the method 3051A (USEPA, 1998) and the reading performed in ICP - OES device. The soil variables that best correlated with the metals were Mn, Fe and Mg, used to compose the discriminant function groups. The SVQs were proposed for the 75 percentile in three homogeneous groups formed by cluster analysis. On this percentile, the levels of Co, Cr, Ni, Pb, Zn and Cr were similar to those obtained in other Brazilian states and the contents of B and Ba, were generally high and the Cu levels low. In the second chapter, the objective was to evaluate the sorption of Cd and Pb through the adsorption isotherm model that best described each element. The experimental procedure used was the batch method. For this, there were selected, through cluster analysis, 19 soil samples used in the first chapter study. The experimental results (concentrations of equilibrium and amount adsorbed) were used as data input in the ISOFIT software to obtain the six parameters of the isotherm models. These isotherms were compared by criteria of model selection: Akaike Information Criterion corrected (AICc), Akaike difference ( AIC) and weight of evidence or Akaike weight (AICw). The linear model was the most appropriate to represent the sorption of Cd, and for sorption of Pb the Freundlich model. Through statistical analysis (principal components and Pearson correlation) it was observed that the adsorption of Cd was influenced by pH, Ca, and mostly by Fe. The sorption of Pb was most influenced by Mn, besides pH and Ca.