Fracionamento geoquímico e bioacessibilidade de mercúrio em solos tropicais

Abstract

Understanding mercury geochemical behavior in soils, including the estimation of its bioaccessible fraction is of high relevance because it makes easier the evaluation of its contamination. Sequential chemical extractions are conducted in order to evaluate the fractionation of Hg in soils using different extracting solutions. In this study, single extractions are performed in tropical soil samples, spiked with Hg, using the same solutions applied in the well established sequential extractions and correlations among them are made. Spiked soil samples were also used and four bioaccessibility tests were used: with dilute nitric acid at room temperature, with dilute nitric acid at body temperature, the SBET methods and the gastric phase of the IVG protocol. For all procedures the influence of clay contents, organic matter content and pH on mercury dynamics is evaluated. Spiked samples revealed that the majority of Hg is prone to be bioaccessible in human stomach and another major part is reduced Hg (Hg (0)) which is prone to volatilization after sequential extraction. The single extraction scheme was a good option in order to evaluate water soluble Hg, bioacessible Hg at pH near human stomach, Hg associated with organic matter, reduced Hg (Hg (0)) and Hg associated to Fe and Al hydr(oxides). Bioacessible contents percentages were higher than 20% on average for the two first tests and higher than 40% on average for the third and fourth tests. The SBET method has a lower variation in bioaccessible contents percentage with Hg concentration. Samples contaminated with Hg (0) in Descoberto after artisanal mining operations in XIX century were also submitted to the same bioaccessibility tests and in general, the methodology with the lowest pH, which is the dilute nitric acid solution together with body temperature, estimated higher bioaccessible contents in soil samples while the SBET method estimated higher bioaccessible contents in sediment samples. At the multivariate analysis, two groups of bioaccessibility tests are formed: one with the two tests with nitric acid and the other with SBET and gastric phase of IVG protocol, probably due to the addition of organic compounds in the last group, better estimating bioaccessible contents of Hg.