César Reis

Sorção e persistência da sorgoleona em um Latossolo Vermelho-Amarelo

The root exudates produced by sorghum contain a biologically active constituent known as sorgoleone. The behavior of sorgoleone in a Red-Yellow Latosol was studied. The sorption model of sorgoleone in soil was better adjusted to the Freundlich equation, through the coefficients Kf (capacity of sorption) and 1/n (linearity of the isotherm). The persistence of sorgoleone in soil and its possible degradation were also evaluated by monitoring their residues in the soil along the time. Recovery rate of sorgoleone from the soil reached 93% after 24h. It was verified that sorgoleone is strongly sorbed in the soil and its half-life is 10 days, under the experimental conditions. The presence of sorgoleone or its metabolites was not detected in the soil after 60 days.

CO2-C losses and carbon quality of selected Maritime Antarctic soils

Abstract Polar Regions are the most important soil carbon reservoirs on Earth. Monitoring soil carbon storage in a changing global climate context may indicate possible effects of climate change on terrestrial environments. In this regard, we need to understand the dynamics of soil organic matter in relation to its chemical characteristics. We evaluated the influence of chemical characteristics of humic substances on the process of soil organic matter mineralization in selected Maritime Antarctic soils. A laboratory assay was carried out with soils from five locations from King George Island. We determined the contents of total organic carbon, oxidizable carbon fractions of soil organic matter, and humic substances. Two in situ field experiments were carried out during two summers, in order to evaluate the CO2-C emissions in relation to soil temperature variations. The overall low amounts of soil organic matter in Maritime Antarctic soils have a low humification degree and reduced microbial activity. CO2-C emissions showed significant exponential relationship with temperature, suggesting a sharp increase in CO2-C emissions with a warming scenario, and Q10 values (the percentage increase in emission for a 10°C increase in soil temperature) were higher than values reported from elsewhere. The sensitivity of the CO2-C emission in relation to temperature was significantly correlated with the humification degree of soil organic matter and microbial activity for Antarctic soils.

Preparation and evaluation of magnetic chitosan particles modified with ethylenediamine and Fe(III) for the removal of Cr(VI) from aqueous solutions

The adsorption of Cr(VI) in aqueous solution by magnetic particles of crosslinked chitosan-ethylenediamine-Fe(III) (MPCh-EDA-FeCL) was studied in a batch system. Fe3+ in the MPCh-EDA-FeCL permitted that adsorption of Cr(VI) occurred with maximum efficiency between pH 3 and 11. The maximum adsorption capacity at pH 7.0 was 81.04 mg g-1 at 25 oC. The adsorption kinetic process was described by the pseudo-second-order model. Thermodynamic parameters indicated spontaneous, exothermic and chemical adsorption nature. The adsorbent was successively regenerated using a 0.1 mol L-1 NaOH solution. Results were satisfactory for treatment of wastewater from the electroplating industry.

Características físico-químicas de ácidos húmicos em diferentes etapas da vermicompostagem

Samples of materials, collected at different stages of vermicompostaging, were submitted to extraction procedures of humic acids. Titration, termogravimetry (DTG), X-ray diffraction, spectrophotometry in the uv/visible and infrared techniques, were used in the study of these materials. The data from the potentiometry titration analysis were submitted to adjustment by non-linear regression, determining thus five values of pKas characteristic of five classes of titrable groups. In the DTG curves two stages can be observed, being the first one characteristic of the separation of aliphatic and/or alycyclic structures and the second of decomposition of aromatic structures. The X-ray diffraction technique exhibed marked differences in the results, mainly in the first three peaks, were a structural reorganization and a polymerization along the vermicompostaging process. The infrared spectra practically no differentiation between the samples. The values for the ratio E4/E6 found are in accordance with the characteristic values for humic acids, but do not supply information that can contribute to the elucidation of the structure and formation of these acids.

Estudo Comparativo da Seletividade de um Método Cinético-Catalítico: a Determinação de Cr(VI) pela Oxidação da o-Dianisidina pelo Peróxido de Hidrogênio

Selectivity studies for the determination of Cr(VI) using the catalytic oxidation of the o-dianisidine by hydrogen peroxide showed two distincts situations. In the first, when interferents were studied by a univariate procedure, Cr(III) and Cu(II) cause serious interferences even at the 2:1 proportion, relative to Cr(VI), while Fe(III) interfered at the 15:1 ratio and EDTA at the 10:1 ratio. On the other hand, when a multivariate investigation was performed, Cr(III) did not present any significant principal effects and its significant interaction effects were negative, in contrast to EDTA, that presented positive interaction effects although, like Cr(III), did not show significant interaction effects. In view of the interferents action it become necessary to separate Cr(VI) by extraction with methylisobutylketone in a chloridric acid medium before its determination in vegetals and in wastewater from a cellulose industry samples. Using this procedure, the method precision is ±0,5% at the 10 ng/mL Cr(VI) concentration level. The detection and quantification limits, calculated by means of absorbance measurements of ten replicates of blank reagents were 1,1 and 3,2 ng/mL, respectively. The results obtained with real samples showed a relative standard deviation between 1,2% and 3,0% relative to their reference values.

MCR-ALS aplicado no monitoramento quantitativo do processo de eletrodegradação da atrazina usando espectros UV : resultados comparativos com HPLC-DAD como um método de referência.

Electrodegradation of atrazine in water was performed using homemade (PA and PB) and purchased (PC) boron-doped diamond anodes. The degradation was monitored off-line by analyzing total organic carbon and high performance liquid chromatography with diode array detector (HPLC-DAD) and at-line by UV spectroscopy. The spectra were recorded every 2 min. The rank deficiency problem was resolved by assembling an augmented column-wise matrix. HPLC was employed to separate the original and byproducts degradation components. Aiming the same goal, multivariate curve resolution - alternating least squares (MCR-ALS) was applied to resolve the UV spectroscopic data. Comparison between HPLC and MCR-ALS separations is presented. By using MCR-ALS the spectra of atrazine and two byproducts were successfully resolved and the resulted concentration profiles properly represented the system studied. The ALS explained variance (R2) for PA, PB and PC was equal to 99.99% for all of them and the lack of fit for PA, PB and PC were 0.39, 0.34 and 0.54 respectively. The correlation (R) between the recovered and pure spectra were calculate for each electrodegradation, validating the MCR-ALS results. The average R was equal to 0.997. The spectral and concentration profiles described with this new approach are in agreement with HPLC-DAD results. The proposed method is an alternative to classical analyses for monitoring of the degradation process, mainly due to the simplicity, fast results and economy.

Caracterização potenciométrica de substâncias húmicas extraídas de solos da Antártica Marítima

Monitoring of soil carbon storage may indicate possible effects of climate change on the terrestrial environment and it is therefore necessary to understand the influence of redox potential and chemical characteristics of humic substances (HS) of Antarctic soil. Five soils from King George Island were used. HS were extracted, quantified and characterized by potentiometry and the content of total carbon and nitrogen determined. HS of these soils had greater aliphatic character, low content of phenolic groups, lower acidity and lower formal standard electrode potential, compared to HS of soils from other regions, suggesting they are more likely to be oxidized.

Multiparametric adjustment program of potentiometric titration curves of humic acids

Tendo em vista a dificuldade de determinacao dos pontos de inflexao na curva de titulacao potenciometrica de acidos humicos, por metodologias tradicionais, foi desenvolvido foi desenvolvido um programa na linguagem Delphi para ajuste multiparametrico de dados de titulacao potenciometrica. Para isso um processo iterativo para estimar as raizes de um polinomio, com base no metodo de Newton-Raphson, foi utilizado. Os dados das titulacoes potenciometricas de acidos humicos usados nas regressoes foram obtidos em um sistema automatizado de titulacao potenciometrica. O programa desenvolvido na linguagem Delphi permite maior versatilidade e facilidade de operacao, com uma interacao mais amigavel com o usuario. As curvas de titulacao potenciometricas ajustadas sobrepuseram-se quase que totalmente as curvas experimentais. Os valores de pKa e as percentagens de grupos titulaveis dos acidos humicos, parâmetros ajustaveis na regressao multiparametrica, apresentaram valores comparaveis com dados da literatura.

Pulp Mill Effluent Treatment Using Plasma Obtained by High Voltage Electrolysis

Effluents from pulp mills have a high organic load and can still contain high organic biorecalcitrant material that is harmful to the aquatic environment, even after undergoing biological treatment in effluent treatment plants. This study presents a novel treatment method tested on effluents (prior to and after biotreatment) from a Brazilian kraft pulp mill, based on hydroxyl radical production and hydrogen peroxide obtained by plasma generated by high-voltage electrolysis. These species present significant oxidation potential that could enable the complete breakdown of the organic matter. From the application of plasma to treat pulp mill effluent for a 7-hour period, it was obtained a chemical oxygen demand (COD) removal between 88.2 and 99.7%, total organic carbon (TOC) removal of 90.3 to 95.6%, and a color removal of 95.0 to 98.0%. The final pH of the treated effluent was 11.6 to 11.9. The results obtained in this study showed that the high-tension plasma treatment, applied on effluent from kraft pulp mills before and after biological treatment, can be an attractive alternative.

Modelling of Lead Migration from Electronic Waste to Mixtures of Kaolinite, Iron Oxides and Organic Matter

Improper disposal of electronic waste in the environment facilitates migration of heavy metals, especially lead, into the soil and can contribute to the bioavailability of this species. Based on a simplex-centroid mixture experimental design, small-scale tests were performed for incubation of printed circuit boards (PCBs) in mixtures containing organic matter (OM), kaolinite (KA) and iron oxides (IO) to verify lead migration. Regression equations were acquired and were adjusted to the obtained responses. Results showed high total content of Pb, ranging from 400 to 4000 mg kg-1, depending on the mixture and incubation time. Mobility and/or bioavailability of lead in the mixtures were evaluated by a three-step sequential extraction. The bioavailability factor (BF) was obtained from the ratio of the sum of exchangeable fraction (F1) and the organically bound fraction (F2) by F1, F2 and the residual fraction (F3) and the values of bioavailability factor for Pb, the heavy metal considered of greatest environmental concern in this study, ranged between 0.16 and 0.52.