RESUMO

In 2015, >50 million cubic meters of Fe mining tailings were released into the Doce River basin from the Fundão dam, raising the question of its consequences on the affected ecosystems. This study aimed to establish a mineralogical-(geo)chemical association of potentially toxic elements (PTEs) from Fe mining tailings from the Fundão dam, collected seven days after the failure, through a multidisciplinary approach combining assessment of the risk to human health, environmental geochemistry, and mineralogy. Thus, eleven tailings samples were collected with the support of the Brazilian Military Police Fire Department. Granulometry, magnetic measurements, optical microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and sequential chemical extraction of PTEs analyses were performed. Contamination indexes, assessment of risk to human health, and Pearson correlation were calculated using the results of sequential chemical extraction of PTEs. The predominance of goethite in Fe oxyhydroxide concentrates from the mud indicates that the major source of hematite may not be from tailings, but from pre-existing soils and sediments, and/or preferential dissolution of hematite in deep flooded zones of the tailings column of the Fundão dam. Moreover, the high correlation of most carcinogenic PTEs with their crystallographic variables indicates that goethite is the primary source of contaminants. Goethites from Fe mining tailings showed high specific surface area and Al-substitution, and due to their greater stability and reactivity, the impacts on PTE sorption phenomena and bioavailability may be maintained for long periods. However, their lower dissolution rate, and the consequent release of heavy metals would promote greater resilience for affected ecosystems, preventing significant PTE inputs under periodic reduction conditions. More specific studies, involving the crystallographic characteristics of Fe oxyhydroxides should be developed since they may provide another critical component of this set of complex and dynamic variables that interfere with the bioavailability of metals in ecosystems.

Assuntos

RESUMO

Fe-rich Oxisols on mafic rocks in Brazil generally have high magnetic susceptibility with high contents of some trace elements. These are taxonomically similar soils; however, differences in magnetic and geochemical properties may affect agricultural or environmental usability and subsequent management. This study investigated the pedogenesis of Fe-rich Oxisols from various parent materials and evaluated the lithogenetic influence on magnetic susceptibility and trace elements contents. Soil samples were collected from Bw horizons in 13 Rhodic Oxisols and a Typic Oxisol developed from several parent materials in Minas Gerais State, Brazil. Soils were analyzed by X-ray diffractometry (XRD) and magnetometry. Soil chemical analyses consisted of sulfuric and total (tri-acid) digestions and selective Fe oxides dissolutions and statistical correlations were determined. Fe-rich Oxisols presented a typical mineralogical composition of highly weathered soils with structural stability. The results confirm the difficulty to identify accurately magnetic minerals in different grain sizes using XRD. However, coarse fractions still exert dominant influence on the magnetic properties of the Fe-rich Rhodic Oxisols. In addition, coarse fractions probably contribute to the enrichment of superparamagnetic particles for the clay fraction. Although highly weathered, Fe-rich Oxisols may have their geochemical attributes still controlled by the parent material, where trace elements seem to be correlated with the magnetic minerals in the coarse fractions. Thus, the natural replacement of some trace elements from soil-solution equilibrium reactions during plant development could be more effective in soils with higher magnetic particles concentrations in the coarse fractions.

Assuntos

RESUMO

Fe-rich Oxisols on mafic rocks in Brazil generally have high magnetic susceptibility with high contents of some trace elements. These are taxonomically similar soils; however, differences in magnetic and geochemical properties may affect agricultural or environmental usability and subsequent management. This study investigated the pedogenesis of Fe-rich Oxisols from various parent materials and evaluated the lithogenetic influence on magnetic susceptibility and trace elements contents. Soil samples were collected from Bw horizons in 13 Rhodic Oxisols and a Typic Oxisol developed from several parent materials in Minas Gerais State, Brazil. Soils were analyzed by X-ray diffractometry (XRD) and magnetometry. Soil chemical analyses consisted of sulfuric and total (tri-acid) digestions and selective Fe oxides dissolutions and statistical correlations were determined. Fe-rich Oxisols presented a typical mineralogical composition of highly weathered soils with structural stability. The results confirm the difficulty to identify accurately magnetic minerals in different grain sizes using XRD. However, coarse fractions still exert dominant influence on the magnetic properties of the Fe-rich Rhodic Oxisols. In addition, coarse fractions probably contribute to the enrichment of superparamagnetic particles for the clay fraction. Although highly weathered, Fe-rich Oxisols may have their geochemical attributes still controlled by the parent material, where trace elements seem to be correlated with the magnetic minerals in the coarse fractions. Thus, the natural replacement of some trace elements from soil-solution equilibrium reactions during plant development could be more effective in soils with higher magnetic particles concentrations in the coarse fractions.(AU)

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RESUMO

A formação de Latossolos com horizonte A húmico (Lhs) no Nordeste é relativamente rara e, geralmente, está associada a ambientes altimontanos, distinguindo-se da região semiárida circundante. Devido a isso, estes solos são intensamente utilizados e importantes para a economia regional. O objetivo deste estudo foi caracterizar Lhs da região Nordeste, bem como avaliar os mecanismos envolvidos no acúmulo do carbono orgânico (CO) em profundidade, visando a determinação da aptidão agrícola para o uso e manejo adequado do solo. O trabalho foi conduzido no município de Brejão, Agreste do Estado de Pernambuco. Foi realizada a caracterização morfológica, física, química e mineralógica de quatro perfis de Latossolos com horizonte A húmico, sob diferentes sistemas de uso da terra (vegetação nativa, capoeira, cultivo e pastagem), com a avaliação da aptidão agrícola e da variação do CO em profundidade. Os solos foram classificados como LATOSSOLOS AMARELOS Distrocoesos húmicos, textura argilosa, todos com horizonte A húmico maior que 100 cm. Todos os perfis apresentaram acidez elevada, alta saturação por alumínio, baixa capacidade de troca de cátions (CTC), caráter coeso e fração argila essencialmente caulinítica. O teor de CO foi alto, independente do uso do solo, e se correlacionou fortemente em profundidade com a argila dispersa, CTC, N e P. A distribuição do CO em profundidade foi favorecida pelos menores teores de argila e pela associação com as formas de Fe pouco cristalinas. A aptidão agrícola das terras enquadrou-se no grupo 2, ou seja, aptidão boa para lavouras de ciclo curto e/ou longo com práticas agrícolas com um médio e alto nível tecnológico. No entanto, essa aptidão é restrita quando utilizado baixo nível tecnológico em razão da exigência de elevadas doses de fertilizantes e corretivos.

The occurrence of Oxisols with a humic A horizon (Lhs) in Northeast Brazil is relatively rare and, generally associated with mountainous environments, quite different from the surrounding semiarid region. Therefore, these soils are intensely used and important for the regional economy. The aim of this study was to characterize the Lhs from Northeast, and assess the mechanisms involved in the accumulation of organic carbon in depth, in order to determine suitability agricultural and use and adequate soil management. The work was carried out in Brejão municipality, Agreste region of Pernambuco State, Brazil. Morphological, physical, chemical and mineralogical properties were determined in four soil profiles, under different management systems (native forest, secondary forest, traditional cropping system and planted pasture), with the assessment of agricultural suitability and variation of organic carbon (OC) in depth, and soil properties were correlated with the soil OC content in depth. All studied soils were classified as Humic Haplustox, with humic A horizon thicker than 100 cm. Furthermore, the soils showed high acidity and aluminum saturation, low cation exchange capacity (CTC), cohesive character and a kaolinitic clay fraction. The values of soil density were inversely correlated with the organic matter content. The OC was considered high, despite the management system. The variation of the OC with depth was strongly correlated with disperse clay, CTC, N and P. The OC distribution with depth was favored by smaller amounts of clay and by the association with poor crystalline Fe compounds. The agricultural suitability from soils framed up in group 2, good suitability for short cycle crops and/or long with agricultural practices with medium and high technological level. However, this ability is restricted when used low technological level due to the high demand for fertilizers and corrective.

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