In this study, the extraction and characterization of aquatic humic substances (AHS) from two blackwater rivers in the Amazon basin was carried out in order to assess the seasonal effects in the AHS structure. In addition, an investigation of the complexing capacities (CC) of the structures containing the metal ions CdII, NiII and PbII was also done. The characterization (of the AHS) was done using UV-Vis, molecular fluorescence, and infrared spectroscopy. AHS from the Negro River showed more aromatic characteristics in its structures and molecular weight, than the AHS from the Carú River. The AHS studied presented a seasonal pattern characterized by higher humification levels during the rainy season. For all the metals, the AHS complexing capacity was higher for the Negro River. The highest complexing capacities were observed for the NiII assays, which were 0.56 and 0.12 µmol NiII mg-1 dissolved organic carbon (DOC), for AHS RN and AHS RC-II, respectively. We concluded that the transport, bioavailability, and toxicity, of these metal species should be higher for Carú River.

The chemical and spectroscopic characteristics of soil organic matter (SOM) isolated from Amazonian dark earth (ADE) and surrounding soil (SR) were evaluated according to the soil depth. The results showed opposite trends for the soils. While ADE featured SOM with a greater aromatic condensation degree and greater hydrophobicity in the top layer, the SR showed more aliphatic and polar SOM. The SOM arrangement from ADE was less hydrophobic, aromatic, and more polar in depth. In contrast, the SOM from SR showed an increase in molecular weight and hydrophobicity. Besides the aromatic protection in the SOM from ADE, there was organo-mineral protection through binding to soil minerals. This suggested that the SOM from ADE was protected by its hydrophobicity and interaction with minerals compared with that from the SR, thereby showing that the combination of both characteristics is important to create new technologies for soil carbon storage.

Vinasse is a residue of ethanol production from sugarcane. In view of the problems associated with its disposal, this study aimed to propose a treatment for vinasse by hydrothermal carbonization. The influence of temperature (100 to 200 ºC), acidity (1.7 to 8.3%) and reaction time (12 to 48 h) on the hydrothermal treatment was evaluated, as well the characteristics of the solid (hydrochar) and liquid (process water) products. For the solid product, two hydrothermal carbonization conditions stood out as leading to higher carbonization and yields. These conditions were 200 ºC, 8.3% acidity and times of 12 and 48 h. For the process water, the carbonization reaction at 200 ºC, 8.3% acidity and 48 h produced the highest discoloration and 77% reduction of total organic carbon. Thus, hydrothermal carbonization proved to be an efficient method to treat vinasse, and the hydrochar presents potential for use as fertilizers / soil conditioners, and also the process water after pre-treatment.

Seasonal concentrations of total, particulate and dissolved Al, Cu, Cd, Cr, Fe, Pb and Ni were analyzed in surface water and total metals in sediment samples from black and whitewater rivers within the Itacoatiara City, Central Amazon. Metals concentrations in water and sediment samples demonstrated that even though urbanization and agricultural practices are common in this region. Metal concentrations in sediments samples are acceptable regarding the recommended levels for protection of aquatic life. From this work, which is the first trace elements study in the main tributaries from Itacoatiara region, we conclude that metals are present in a particulate form, being easier to be transported to other aquatic bodies. During flooding periods an increase of Al, Fe and total organic compound (TOC) in almost water sampling points was observed.

Neste trabalho foi feita a determinação de nove metais em amostras superficiais e testemunhos de sedimentos de cinco locais de amostragens nos rios Preto, Turvo e Grande em períodos chuvoso e seco. Os metais foram determinados por espectrometria de absorção atômica com atomização por chama. Análise de componentes principais dos dados foi feita para avaliar os fatores que controlam as variações nas concentrações de metais. A granulometria e teor de matéria orgânica foram determinantes das concentrações de metais. No rio Preto (área urbana) concentrações elevadas de Zn são provenientes de aporte antrópico, enquanto que no rio Turvo (represamento, área rural) níveis elevados de nitrogênio total, Al, Cr, Cu, Fe, K, Mn e Ni foram decorrentes do escoamento superficial agrícola. Os demais locais mostraram menores concentrações de metais, porém violações dos valores guia de qualidade de sedimento, principalmente para Cr e Mn, indicam a necessidade de estratégias de gerenciamento da Bacia Hidrográfica do Turvo/Grande.

In this work, nine metals were determined in superficial samples and sediment cores obtained from five sampling sites in the Preto, Turvo, and Grande Rivers during the wet and dry seasons. The metals were determined by flame atomization atomic absorption spectrometry. Principal component analysis of the data was performed to evaluate the factors responsible for the variations in metal concentrations. Granulometry and organic matter were the determining factors of metals concentrations. In the Preto River (urban area), high Zn concentrations are due to anthropic sources, whereas the high levels of total nitrogen, Al, Cr, Cu, Fe, K, Mn, and Ni in the Turvo river (damming, rural area) are due to agricultural runoff. Although lower concentrations of metals were observed at the remaining sites, violations of the guide values for sediment quality, particularly for Cr and Mn, indicate the need for management strategies for the Turvo/Grande Hydrographic Basin.

Este estudo teve como objetivo principal avaliar a influência das SHA obtidas a partir de uma área de cultivo de cana de açúcar sobre a influência das espécies de crômio (Cr(III) e Cr(VI)). Foi estudada a capacidade de complexação (CC) das SHA com as espécies de crômio e estas foram caracterizadas por espectrofotometria de UV/Vis, fluorescência molecular, análise elementar e infravermelho. SHA com e sem fracionamento apresentou maior grau de aromaticidade e predominância de ácidos húmicos, e as razões E4/E6 e E2/E4 sugerem a presença de anéis aromáticos e maior contribuição das plantas e lignina. As maiores CC foram observados para a SHA fracionadas, sendo as frações com tamanho molecular < 10 kDa e 10-30 kDa as que apresentaram as maiores capacidades para complexar os íons Cr(III) e Cr(VI), respectivamente. Estes resultados corroboram com os dados de C/H/N e UV/Vis, permitindo concluir que as SHA sem fracionamento têm em sua estrutura maior grupos aromáticos e uma predominância de ácidos húmicos.

This study had as main objectiveto evaluate the influence of AHS obtained from an area under sugarcane cultivation on the dynamics of chromium species (Cr(III) and Cr(VI)). Was studied complexing capacity (CC) with the AHS of chromium species and these were characterized using UV/Vis spectrophotometry, molecular fluorescence, elemental analysis and infrared. AHS with and without fractionation showed a greater aromaticity degree and a predominance of humic acids, and the E4/E6 and E2/E4 ratios suggested aromatic rings and a greater contribution from plants, which indicates lignin structures. The highest CCs were observed for the AHS fractionated, being fraction with molecular-size < 10 kDa and 10-30 kDa showed the highest ability to complex Cr(III) and Cr(VI) ions, respectively. These results are corroborating with C/H/N and UV/Vis data, where we can conclude that the AHS without fractionation had the greatest aromaticity and a predominance of humic acids in their structure.

Este estudo teve como principal objetivo determinar a capacidade de complexação da Matéria Orgânica (MO) de regiões tipicamente agrícolas e urbanas, com os íons de cobre e níquel. As amostras foram coletadas durante as estações de seca e chuva e submetidas ao estudo da capacidade de complexação e da constante de estabilidade condicional da MO com os íons Cu(II) e Ni(II) usando um Espectrofluorímetro de Luminescência e o Sistema de Ultrafiltração de Fluxo Tangencial. Os valores da constante de estabilidade condicional (log Kc) da MO com o íon cobre variaram de 0,04 a 1,35 sendo o maior valor obtido para o local com maior carbono orgânico dissolvido (COD 2,73-2,43 mg L-1) e o menor para local de menor COD, corroborando com o grau de aromaticidade. Conclui que a Matéria Orgânica Dissolvida (MOD) de rios de áreas agrícolas e urbanas continha um número menor de sítios de ligação, quando comparado com outros locais.

This study had as main objective to determine the complexing ability of the Organic Matter (OM) from typical agricultural areas and from urban areas with copper and nickel ions. The samples were collected during the dry and rainy seasons and were subjected to study the complexing capacity and OM conditional stability constant with Cu(II) and Ni(II) ions using a luminescence spectrofluorometer and tangential flow ultrafiltration system. The conditional stability constant values (log Kc) of OM with the copper ion varied from 0.04 to 1.35 with the highest value obtained for the place with the largest dissolved organic carbon (DOC 2.73-2.43 mg L-1) and the lowest for the smallest site DOC, corroborating the degree of aromaticity. We can conclude that the Dissolved Organic Matter (DOM) of the bodies of water in agricultural and urban areas contained a lower number of binding sites when compared with other locations.

Este estudo teve como principal objetivo avaliar o efeito da radiação solar sobre a capacidade de complexação das substâncias húmicas aquáticas (AHS) com as espécies metálicas Al3+, Cr3+, CrO4(2-) e Ni2+. Microcosmos foram montados com AHS extraídas do Rio Preto com concentração de 5,0 mg L-1 de carbono orgânico dissolvido e diferentes concentrações de metais, sendo expostos à radiação solarin situ. As constantes de estabilidade condicional foram de 2,0 × 10-2, 1,1 × 10-5 e 2,6 × 10-2 para os complexos AHS-Cr3+, AHS-Ni2+ e AHS-CrO4(2-), respectivamente. Os resultados mostraram que a radiação solar foi responsável por um decréscimo na capacidade de complexação de 15-26% para AHS-Al3+, 15-72% para AHS-Cr3+, 12-18% para AHS-CrO4(2-) e de 13-42% para AHS-Ni2+. Conclui-se que a radiação solar altera a disponibilidade de metais previamente complexados às AHS, tornando-os disponíveis no corpo aquático.

This study had as main objective to assess the effect of solar radiation on the capacity of the aquatic humic substances (AHS) to complex Al3+, Cr3+, CrO4(2-) and Ni2+. Microcosms were prepared with AHS from Preto River containing 5.0 mg L-1 of dissolved organic carbon and different concentrations of metal species, being exposed to solar radiation, in situ. Conditional stability constants obtained for the AHS-Cr3+, AHS-Ni2+ and AHS-CrO4(2-) complexes were 2.0 × 10-2, 1.1 × 10-5 and 2.6 × 10-2, respectively. The results showed that solar radiation is responsible for decreasing capacity complexation in 15-26% for AHS-Al3+, 15-72% for AHS-Cr3+, 12-18% for AHS-CrO4(2-) and 13-42% for AHS-Ni2+. We can conclude that solar radiation alters metals' availability previously complexed to AHS, making them available in the aquatic body.