Geoquímica e distribuição de metais pesados em solos na região de Unaí, Paracatu e Vazante, MG

• Autor(a) principal: Burak, Diego Lang
• Data de Publicação: 2008
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1587
• topic: Variabilidade espacial; Metais pesados; Geoquímica de superfície; Pedogênese; Spatial variability; Heavy metals; Surface geochemistry; Pedogenesis; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

The study of heavy metals dynamics in the region of Unaí, Paracatu and Vazante was conducted in different study scales, emphasizing the distribution of heavy metals in the landscape, in a representative toposequence of soils in the landscape, and in particle-size fractions these soils toposequence. The purpose of the second Chapter was to evaluate and interpret the spatial patterns of geochemical distribution of heavy metals (Co, Cu, Ni, Pb and Zn) and major elements (Al, Fe, Ti, Mg and Mn) of natural origin in the soils of the regions of Unaí, Paracatu e Vazante, Minas Gerais and the relation with geology and geomorphology. Samples collected at two depths (0-20 and 60-80 cm) were ground and submitted to extraction with aqua-régia and de average of metal contents of the two depths was used. The altitude of the sampled regions ranged from 1040 to 480 m. Descriptive statistical analyses; Pearson s correlation and Principal Components Analysis of the contents of all metals were performed. Subsequently geoestatistical maps were obtained, utilizing ordinary kriging as the interpolator. The Pb, Zn and Mn were strongly associated among themselves as well as the Cu and Fe. The Al, predominantly found in higher altitudes (>900 m), did not show any association with heavy metals. The Pb and Zn had higher contents in soils near dolostone (altitude between 650 to 550 m). The highest contents of Cu were observed over black shales rocks (altitude between 650 to 750 m). Co and Ni were related to the regions of sediments accumulation, in the lower altitudes within the region (550 to 480 m), Even though there is a higher dispersive effect of tropical weathering in the distribution of metals, the Cu, Pb and Zn had the highest contents near their sources as result of the greater affinity of these metals to the Fe and Mn oxides, predominantly formed under tropical conditions and also present near the source of heavy metals. On the other hand, the low affinity of Ni and Co to Fe and Mn oxides and the geomorphology of the region allowed their migration along the channel network from theirs source to the zones of sediments accumulation in lower altitudes. In the third Chapter we had the objective of evaluating the patterns of spatial distribution of Pb and Zn extracted by DTPA (available fraction) and their relation to the contents of Al, Fe, Mn Mg, Pb an Zn extracted by aqua-régia (pseudo-totals). The geomorphology and the geology were also considered. In addition, e evaluated the relations of the contents of Pb and Zn extracted by DTPA with chemical, physical and mineralogical attributes of soils representatives of the region. The amounts of Pb and Zn were low. In general, only the Pb had higher available amounts and the richest in Pb pseudo-total contents in vicinities regions of the dolostone, characterized as Pb sources in the region. In the zones with the highest amounts of Pb extracted by DTPA and aqua-régia, this metal occurs associated with the Mn oxides. The geomorphology affected mainly the dispersion of more available Zn, as revealed by the smaller relation between the patterns of spatial distribution of the amounts on c and subsurface. In addition, the contents of these two layers do not have relations with the pseudo total amounts. High available contents of Zn and Pb on the 60-80 cm layer occur in soils with a lower degree of weathering (soils on black shale) and in soil under the influence of sedimentations processes, where these metals exist in more exchangeable forms. The fourth Chapter aimed to study the relation of the pedogenesis and the distribution of Pb and Zn in physical fractions of soils in Cambisol-Ferrasol toposequence. The total amounts so metals in different particle-size fractions of A and B horizon of Cambisol over dolostone and of a Ferralsol over shales and metasediments were evaluated. Both soils had been collected in a rich heavy metal region. Using the method of agitation in water, the fractions 2000-200 &#956;m, 200-50 &#956;m, 50-20 &#956;m and <20 &#956;m were separated. From these fractions, finer fractions corresponding to coatings and stables microaggregates (not recovered by agitation in water) were obtained by ultrasonic method. The fraction < 20 &#956;m (separated by agitation in water) had highs contents of metals as result of the presence of finer and more reactive fractions. We observed a difference in the amounts of fractions 200 &#956;m, 200-50 &#956;m and 50-20 &#956;m before and after the ultrasonic method. Only the 2000-200 &#956;m, 200-50 &#956;m and 50-20 &#956;m fractions of the Cambisol even after the ultrasonic method, had the high contents of Pb and Zn, indicating the presence of metals-accumulating minerals in this soils. The fractions <20 &#956;m obtained after ultrasonic method and characterized as coatings and microaggregates exhibits higher contents of Pb and Zn. In general, the Pb was enhanced in the coatings together with the Mn oxides and organic carbon. In general, Zn and Pb were more associated with Fe and Al oxides in microaggregates. The Cambisol is a source of Pb and Zn for surrounding region and in this soil the coatings and concretions are the greater Pb accumulating-compartments, whereas in Ferralsol, the formation of stable microaggregates rich in Pb and Zn is the mains pedogenetic process of attenuation of Pb presence in the environment.