Mercúrio em solos do Sudeste brasileiro : interações e avaliação da vulnerabilidade perante mercúrio elementar e mercúrio (II)

Abstract

This study aimed to evaluate the influence of physical and chemical soil characteristics of southeastern Brazil, without anthropogenic influence, in the natural mercury content of soils and retention of atmospheric mercury and mercuric ion by soils in order to determine the soil vulnerability to mercury. At first, the natural mercury content of soils was determined employing a direct mercury analyzer (DMA- 80) and correlated with the physical and chemical soil characteristics. The mercury concentration range found was from limit of detection (0.0001 g kg-1) to 215 ± 9 g kg-1. The soil mercury content was correlated mainly with the clay content and pH . Following, Langmuir and Freundlich models were fitted to mercury adsorption data. Moreover, the soils were incubated with Hg2+solution and it was determined the mercury available and total fractions. The levels of the available fraction indicated that the presence of humified organic matter decreases the vulnerability to contamination of the soil by Hg2+ when comparing A and B horizons of the same soil. The most vulnerable soils to Hg2+contamination are CXd-B, LVAd2-B e RQo-C. And the least vulnerable soils are CXbe-B, NVef-A, LVd-A, TCp-B, PVA-A, NVef-B, TCp-A, CXbe-A LVAd1-B and LVAd1-A. To evaluate the role of chemical and physical properties of soils in atmospheric mercury retention and oxidation processes in the soil, the samples were incubated with elemental mercury and then analyzed by TDAAS. Also the mercury available fraction was determined. The retention of gaseous mercury in soils varied widely according to the type of soil in contact with mercury vapor. After incubation, mercury concentration range found was from 0.6 ± 0.2 g g-1 to 735 ± 23 g g-1. Among the characteristics of the soil responsible for the retention of Hg0, it can be distinguished the organic matter, pH and CEC, in that order of importance. Oxidation of elemental mercury occurred in all soil. The factors that influence the increase of soil vulnerability are the same factors as influence atmospheric mercury retention capacity and natural mercury content of the soil, as high pH, CEC and clay content, organic matter and iron and aluminum oxides. The least vulnerable soils to atmospheric mercury contamination are LVd-A, RQo-C and LVad1-B. The most vulnerable soils are CXbe-A, TCp-A and CXbe-B.