Estudo da labilidade de Cu(II), Cd(II), Mn(II) e Ni(II) em substâncias húmicas aquáticas utilizando-se membranas celulósicas organomodificadas

In this work commercial filters papers were organomodified with tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (3-APTS), aiming at the development of a new analytical procedure for in-situ speciation of labile and inert metal species in aquatic systems. Parameters that exert influence on the metal lability such as pH, chelating time, concentration and characteristics of the organic matter were studied in the laboratory using tests for metal recuperation. The results showed slower kinetics for Cu ion than for Ni, Mn and Cd in the absence of aquatic humic substances (AHS). The relative lability observed for complexed metals in aquatic humic substances using organomodified filter papers was Cu>>Cd>Ni>Mn. The pH values, structural characteristics and concentration of AHS exert strong influence on the lability of the metals. The results obtained showed that the utilization of organomodified filter papers can be an interesting and promising alternative for in situ characterization of metal lability in aquatic systems.

Fatores que governam a especiação do cobre em ambientes aquáticos urbanos: evidências da contribuição de sulfetos solúveis

Copper speciation and behavior in different rivers located in the city of Curitiba were evaluated in this work. Sampling locations were selected to cover different levels of urbanization regarding their anthropogenic occupation and land use. Results showed that in highly-developed areas, both organic matter and dissolved sulfides were able to control copper speciation. Dissolved sulfide species were the major complexing agent in areas where dissolved oxygen levels are low. Finally, it was demonstrated that in urban areas anthropogenic factors such as sewage inputs and occupation of the drainage basin are the key aspects controlling copper dynamics and speciation in river waters.

Distribuição e especiação de mercúrio em sedimentos de áreas de garimpo de ouro do quadrilátero ferrífero (MG)

The concentration and thermodesorption speciation of mercury in sediments from four different Iron Quadrangle sites impacted by gold mining activity were determined. The mercury content of some samples was considerably high (ranging from 0.04 to 1.1 µg g-1). Only Hg2+ was found and it was preferably distributed in the silt/clay fraction in all samples. Cluster analysis showed that mercury and manganese can be associated. The occurrence of cinnabar in this region as another mercury source was also discussed, corroborating earlier works showing the importance of natural mercury in the geochemical cycle of the metal in this region.

Ensaios para determinar a (Bio)disponibilidade de chumbo em solos contaminados: revisão

Incidental ingestion of contaminated soils is a major route of Pb uptake by humans, especially by children. Lead speciation in soils controls its bioavailability. Bioavailability assessment requires the determination of the amount of absorbed lead if a contaminated soil is ingested. In vivo tests, which employ animals, are considered the best model to infer absorption of Pb. But they have some logistic limitations and several authors proposed in vitro methods, which simulate conditions of human digestion. Many of them present results which correlate with in vivo essays. Several authors consider in vitro tests a good and reliable alternative to infer lead bioavailability.

Especiação redox de cromo em solo acidentalmente contaminado com solução sulfocrômica

Determination of Cr(VI) and Cr(III) was studied in soil samples accidentally contaminated with sulphochromic solution. Molecular absorption spectrophotometry based on the diphenylcarbazide method was used for the determination of Cr(VI) after its alkaline extraction. The total chromium concentration was determined using ICP OES. The quantification of Cr(III) was accomplished by subtracting the Cr(VI) concentration from the total chromium concentration. Regardless of the known contamination of the soil samples by sulphochromic solution, concentrations of Cr(VI) were below the detection limit. Addition and recovery experiments for Cr(VI) in soil samples with and without organic matter indicated its influence on the reduction of Cr(VI) to Cr(III).

Especiação de cromo em cimentos e derivados de cimento brasileiros

A method for determination of Cr(III) and Cr(VI) in cement and cement-related materials was studied. Molecular absorption spectrophotometry based on 1,5-diphenylcarbazide as chromogenic reagent was used for determination of Cr(VI) after alkaline extraction. The total chromium concentration was determined using flame atomic absorption spectrometry (FAAS) after complete sample decomposition by fusion. The quantification of Cr(III) was accomplished by subtracting the Cr(VI) concentration from the total chromium concentration. The concentration of Cr(III) in the samples ranged from 10.9 to 88.0 mg kg-1, whereas only in few samples the Cr(VI) concentration was higher than the value established by the European Community to this type of sample [2 mg kg-1 Cr(VI)].

Comparação de técnicas de determinação de ésteres em cachaça

An analytical comparison of three different techniques for quantitative profile of esters in cachaça is reported. The Ministério da Agricultura Pecuária e Abastecimento (MAPA) recommends the use of GC/FID or volumetry. Despite being laborious and lacking in chemical speciation, the volumetric technique for total ester content shows to be appropriate, reproducible, and accurate for the analysis of cachaça. However, the GC/FID suggested by MAPA, considering only ethyl acetate, shows inaccuracy, underestimating the total ester content by a median factor of 72%, mainly due to the absence of ethyl lactate analysis. On the other hand, the GC/MS technique that comprises the analysis and speciation of nine esters, including ethyl lactate, proved to be reproducible, simple, fast and accurate for the analysis of total ester content in cachaça. Thus, the total ester content results obtained using GC/FID must be considered with precaution.

Distribuição espacial de compostos orgânicos de estanho em sedimentos costeiros e em Phallusia nigra da Baía de Todos os Santos e litoral norte da Bahia - Brasil

Organic tin compounds were investigated in the sediment of twenty-four stations located in the Todos os Santos Bay and the north coast of Bahia - Brazil. The concentration of these organic tin was also determined in a ascidium species of Phallusia nigra. The speciation and quantification was performed by GC-MS/MS. The highest concentrations were: tributyltin (TBT) 438 ng g-1, dibutyltin (DBT) 207 ng g-1, monobutyltin (MBT) 423 ng g-1, diphenyltin (DPT) 25.8 ng g-1 and monophenyltin (MPT) 55.0 ng g-1. DBT and MBT were found in Phallusia nigra, with highest concentrations of 294.1 and 148.5 ng g-1, respectively.

Avaliação da influência de sulfetos solúveis na complexação do cobre em águas superficiais empregando métodos voltamétricos

In this work a sulfide quantification protocol using voltammetric methods was developed to evaluate the effect of dissolved sulfides on copper complexation. On the basis of pH, sulfide release from the dissociation of specific metal sulfide complexes can be electrochemically measured and then removed (as H2S) by a N2 purge. Cathodic stripping square wave voltammetry (CSSWV) was conducted to quantify Cu sulfides complexes which dissociate at pH < 5.0 during the process of acid titration.

Aplicação da casca de arroz na adsorção dos íons Cu2+, Al3+, Ni2+ e Zn2+

The potential use of rice husk as biosorbent to remove Cu2+, Al3+, Ni2+ and Zn2+ ions from aqueous solutions was investigated under both noncompetitive and competitive conditions. The biosorbent was used in the form of particles with size smaller than 0.5 μm and in the concentration of 500 mg L-1 (dry weight). The experiments were performed using batch adsorption technique for concentrations of 10, 30 and 70 mg L-1 of metal ions at pH 4.0 and 5.0. The chemical speciation of metals in the experimental conditions used in this work was predicted by the software Visual MINTEQ 2.6.

Comparação da labilidade de metais empregando voltametria, difusão em filmes finos por gradiente de concentração (DGT) e modelo computacional

Speciation of metals in a synthetic freshwater was comparatively evaluated using Anodic Stripping Voltammetry, Diffusive Gradients in Thin Films and a Chemical Equilibrium Model. The labile fractions of Cu and Zn quantified by DGT were similar to the ones measured by ASV. The labile species of Cd and Pb could not be determined by both experimental methods due to the formation of inert complexes with organic ligands in the sample. Despite the differences among the methods, the speciation results obtained by the use of DGT and ASV agreed well with predictions made by the chemical equilibrium model.

Pré-concentração de Cr(III) e análise de especiação de cromo empregando montmorilonita saturada com íons potássio

The clay mineral montmorillonite-K10 (MT), treated under acidic medium and saturated with potassium ions (MTK), was employed in sorption and desorption studies aiming the preconcentration of Cr(III) and the speciation analysis of chromium. The sorption process of Cr(III) was close to 100%, suggesting that MTK was a good material for Cr(III) preconcentration, although, the maximum recovery in HNO3 solution was near 89%. On the other hand, Cr(VI) practically was not retained in MTK, suggesting this material as an appropriate mineral phase to be used in speciation analysis of chromium in aqueous medium.

Análise de especiação de cobre e zinco empregando voltametria de redissolução anódica com pulso diferencial

This work describes methodologies for speciation analysis of the metals copper and zinc as total, total dissolved, labile, as well as complexation capacity (conditional stability constants and available ligand concentration), using the same technique, differential pulse anodic stripping voltammetry (DPASV). Several supporting electrolytes were tested, and the results showed that KNO3 and HNO3 resulted in voltamograms without interferences as well as excellent resolution for the total and labile fractions. The methodology using the DPASV technique allows a simple and low cost analysis of copper and zinc speciation, with high precision and sensitivity, with limits of quantification (LOQ) of 1.8 nmol L-1 for copper and 2.1 nmol L-1 for zinc.

Especiação química de arsênio inorgânico no estuário da Laguna dos Patos (RS, Brasil)

This study optimized and validated a method to perform chemical speciation of inorganic arsenic in water samples collected under the Monitoring Program of the Port of Rio Grande-RS in July and October 2010 from the Laguna dos Patos Estuary (RS, Brazil). The flow injection hydride generation atomic absorption spectrometry technique was employed, allowing quantification of As3+ and As5+ present in estuarine water samples. Data interpretation for results generated using the improved method for analyzing water samples collected from Laguna dos Patos Estuary was done by main components analysis.

Zn-edta degradation by catechol-driven fenton reaction

Zn-EDTA degradabilty by catechol-driven Fenton reaction was studied. Response surface methodology central composite design was employed to maximize this complex degradation. Theoretical speciation calculations were in good agreement with the experimental results. Fenton and Fenton type treatments are typically thought to be applicable only in the highly acidic range, representing a major operational constraint. Interestingly, at optimized concentrations, this CAT-driven Fenton reaction at pH 5.5 achieved 100% Zn-EDTA degradation; 60% COD and 17% TOC removals, using tiny amounts of CAT (50 µM), Fe(III) (445 µM) and H2O2 (20 mM) with no evident ferric sludge.