RESUMEN
Problems related to specificity and re-precipitation of metals in sequential chemical extractions can impair their routine use. In order to test the efficiency of a sequential chemical procedure, model compounds composed by soil components commonly found in tropical soils such as goethite, Al-goethite, ferrihydrite, hematite, bauxite, and humic acid were incubated with either Hg(NO3)2 or HgSO4 and submitted to chemical extraction. The procedure aims to assess: (i) water soluble Hg; (ii) bioaccessible Hg at pH near human stomach; (iii) Hg associated with organic matter; (iv) reduced Hg; (v) Hg associated with Fe, Al, and Mn oxides; and, (vi) residual Hg. This procedure was also tested via single and sequential extractions using the surface and subsurface samples of two tropical soils, i.e., a Rhodic Acrudox and a Typic Hapludox, with and without lime application. Soil samples were submitted to an adsorption experiment with HgCl2 and a high adsorption percentage was observed. The majority of Hg at both single and sequential procedure was extracted by an acetic acid solution (pH = 2). Liming, soil depth, and soil type were not determinative on Hg extractability. The sequential extraction applied showed a lack specificity of Hg fractions, confirmed by the model components.
Asunto(s)
Mercurio/análisis , Contaminantes del Suelo/análisis , Adsorción , Compuestos de Calcio , Fraccionamiento Químico , Humanos , Óxidos , Suelo/química , AguaRESUMEN
In order to investigate the content and distribution of Hg in soils from Amazon areas not impacted by gold mining activities, the concentration and granulometric distribution of Hg were determined in three different types of soils. Hg speciation data were obtained by a thermodesorption atomic spectrometry system and the role of physico-chemical and mineralogical characteristics on Hg content were also studied. Hg concentrations found in the soil fraction <2000 microm were similar to values found in other Amazon areas without anthropogenic sources. The fine fraction (<53 microm) of podzolized soils had a higher Hg content than clayey soils. Multivariate analysis shows that there are marking differences between Spodosols of two distinct areas (fine fraction Hg contents up to 10-fold as high) indicating the importance of pedogenic processes. All statistical data analysis indicated that organic matter plays an important role in Hg accumulation in the types of soils studied. Thermodesorption analysis revealed the presence of only Hg2+, and the predominance of organically bound Hg in the majority of the studied samples.