Extratores para avaliação da disponibilidade de metais pesados em solos adubados com vermicomposto de lixo urbano

Os objetivos deste trabalho foram selecionar extratores químicos para avaliação da disponibilidade de metais pesados em solos tratados com vermicomposto de lixo urbano e calcário, e verificar os efeitos destes insumos nos teores disponíveis de metais pesados em solos. Foram realizados dois ensaios em casa de vegetação. Em um deles, foi usado um Latossolo Vermelho distroférrico e, no outro, um Argissolo Vermelho-Amarelo eutrófico, e, em ambos, a alface foi utilizada como planta-teste. O delineamento experimental de cada experimento foi em blocos ao acaso, em esquema fatorial 5x5, com quatro repetições, combinando-se doses de corretivos da acidez para elevar a saturação por bases a 40%, 50%, 60%, 70% e 80%, e o equivalente a 0, 25, 50, 75 e 100 t ha-1 de vermicomposto. Os extratores DTPA e Mehlich 3 detectam aumento nos teores de Ni, Pb, Cu e Zn em solos argiloso e arenoso adubados com vermicomposto de lixo urbano. O DTPA é mais eficiente que os extratores Mehlich 1 e Mehlich 3 na avaliação das alterações nos teores disponíveis dos metais pesados provocadas pelas mudanças no pH no solo argiloso. O Mn é o único elemento cuja disponibilidade é avaliada eficientemente tanto no solo argiloso como no arenoso, pelo DTPA.

Ácidos orgânicos como extratores de metais pesados fitodisponíveis em solos tratados com lodo de esgoto

Ainda não foi desenvolvido um método de extração eficiente para estimar teores fitodisponíveis de metais pesados, porque os extratores utilizados não simulam reações semelhantes às que ocorrem próximo às raízes. O objetivo deste trabalho foi avaliar uma solução de ácidos orgânicos rizosféricos como extratora de teores fitodisponíveis de metais pesados presentes em solos tratados com lodo de esgoto. Os solos utilizados foram: Latossolo Amarelo distrófico, Neossolo Quartzarênico e Latossolo Vermelho distrófico, cultivados com plantas de banana, pupunha e café, respectivamente. A avaliação do extrator (solução composta por ácido acético, cítrico, lático e oxálico em concentrações de 1,00, 0,72, 0,49 e 0,12 mol L-1, respectivamente) foi feita a partir da análise da correlação entre teores de metais pesados (Cd, Cr, Cu, Ni, Pb e Zn) extraídos do solo e os teores nas plantas. As correlações foram significativas, indicando a eficiência do extrator para todos os casos estudados. Entre os metais avaliados, as quantidades extraídas de Pb correlacionaram-se melhor com teor fitodisponível nas três situações investigadas.

Determinação de cádmio, cobre, cromo, níquel, chumbo e zinco em fosfatos de rocha

A preocupação com metais pesados provenientes de fertilizantes minerais deve-se à possibilidade de entrada desses elementos na cadeia alimentar. O objetivo deste trabalho foi determinar o teor de metais pesados e comparar três métodos de extração (Embrapa, USEPA 3051A e USEPA 3050B) de Cd, Cr, Cu, Ni, Pb e Zn em fosfatos de rochas nacionais e importados. A quantificação dos teores desses elementos foi feita em espectrofotômetro de absorção atômica de chama ar-acetileno. Entre os fosfatos estudados, o termofosfato apresentou concentrações significativamente superiores de Cr, Cu, Ni e Zn e o fosfato natural 2, de Cu, Ni, Pb e Zn. O fosfato reativo 3 apresentou a maior quantidade de Cd (145±13 mg kg-1) e o fosfato natural 2, a maior quantidade de Pb (234±9 mg kg-1). Os métodos avaliados podem ser aplicados em estudos de teor de metais pesados em fertilizantes fosfatados.

Organic acids in the rhizosphere and phytoavailability of sewage sludge-borne trace elements

The aim of this work was to quantify low molecular weight organic acids in the rhizosphere of plants grown in a sewage sludge-treated media, and to assess the correlation between the release of the acids and the concentrations of trace-elements in the shoots of the plants. The species utilized in the experiment were cultivated in sand and sewage sludge-treated sand. The acetic, citric, lactic, and oxalic acids, were identified and quantified by high performance liquid chromatography in samples collected from a hydroponics system. Averages obtained from each treatment, concentration of trace elements in shoots and concentration of organic acids in the rhizosphere, were compared by Tukey test, at 5% of probability. Linear correlation analysis was applied to verify an association between the concentrations of organic acids and of trace elements. The average composition of organic acids for all plants was: 43.2, 31.1, 20.4 and 5.3% for acetic, citric, lactic, and oxalic acids, respectively. All organic acids evaluated, except for the citric acid, showed a close statistical agreement with the concentrations of Cd, Cu, Ni, and Zn found in the shoots. There is a positive relationship between organic acids present in the rhizosphere and trace element phytoavailability.

Avaliação de Trichogramma spp. para o controle de Trichoplusia ni

O objetivo deste trabalho foi avaliar as características biológicas dos parasitoides Trichogramma acacioi, T. atopovirilia, T. marandobai, T. demoraesi, T. exiguum (duas linhagens) e T. pretiosum (seis linhagens), criados em ovos de Trichoplusia ni. O experimento foi conduzido em delineamento inteiramente casualizado, com 15 repetições. As características biológicas avaliadas foram: parasitismo, viabilidade, razão sexual e número de indivíduos por ovo. A percentagem de parasitismo variou entre 7,66 e 53%, com maior valor observado para a linhagem Tspd de Trichogramma pretiosum, e o menor para a linhagem Trecife de T. pretiosum. Não houve diferença significativa dessa espécie quanto à viabilidade, que ficou acima de 85%. A razão sexual variou de 0,75 a 1, e a linhagem Tspd apresentou o menor valor. O número de parasitoides por ovo variou entre 2,39 para T. marandobai (linhagem Tm1) e 1,34 para T. exiguum (linhagem Te1). A espécie que apresentou o melhor desempenho em laboratório foi T. pretiosum (Tspd), com os maiores valores observados na percentagem de parasitismo e na emergência.

Zn and K influence in fruit sizes of Valencia orange

In orange commercial farms, Zn deficiencies symptoms and small fruits were observed in Corrientes, Argentine. During four years (1995 to 1998), Valencia orange (Citrus sinensis Osb.) on Rough lemon (C. jambhiri Lush.) rootstock, implanted in 1974 in sandy soil, where six treatments were tested. Treatments varied from 1 to 3 Kg KCl.tree-1.year-1 (applied in April and December) with and without Zineb 80, 0,35%. year-1, 20 L. tree-1 (13,3 g Zn.tree-1 applied in December). The experimental design was a randomized complete block with four replications, with a single tree and borders in the experimental plot. Foliar sample were taken every year in Autumn and Summer, foliar concentrations of Zn and K were determined by atomic spectrum absorption. Harvested fruits were classified into small, medium and big. Analysis of Variance, Tukey test and Pearson correlations between production and foliar concentrations were performed. Higher fertilization levels of K with Zn increased medium and big fruits production (Kg and percentage). Foliar concentrations of K and Zn were positively correlated with big and medium fruit production and negatively correlated with small one. Chemical names used: Ethilenbis-ditiocarbamate of Zn (Zineb).

Desenvolvimento e caracterização de recobrimentos de Ni-Co e de seus óxidos mistos para a produção de oxigênio por eletrólise alcalina da água

This paper describes the development and characterisation of Ni-Co coatings to be used as anodes in water electrolysis. Chemical oxidation of the surface was performed through thermal treatment at 400ºC for 10 h. The resulting surfaces were analysed by X-ray diffraction, EDX, SEM, cyclic voltammetry and constant current electrolysis. The electrochemical oxidation occurring on bare surfaces during electrolysis promotes the formation of thick oxide layers resulting in loss of activity. In oxidised surfaces the chemical Ni-Co oxide grown during the thermal treatment prevents further oxidation thus retaining their activity towards oxygen evolution. An optimum condition for the growth of mixed oxide with high activity was found for the bath containing 50 g L-1 CoSO4.

Emprego de nebulizador pneumático de ICP-MS como câmara de diluição em sistemas de injeção em fluxo para determinações multielementares

An automatic dispenser based on a flow-injection system used to introduce sample and analytical solution into an inductively coupled plasma mass spectrometer through a spray chamber is proposed. Analytical curves were constructed after the injection of 20 to 750 µL aliquots of a multielement standard solution (20.0 µg L-1 in Li, Be, Al, V, Cr, Mn, Ni, Co, Cu, Zn, As, Se, Sr, Ag, Cd, Ba, Tl, Pb) and the acquisition of the integrated transient signals. The linear concentration range could be extended to ca. five decades. The performance of the system was checked by analyzing a NIST 1643d reference material. Accuracy could be improved by the proper selection of the injected volume. Besides good precision (r.s.d. < 2%), the results obtained with the proposed procedure were closer to the certified values of the reference material than those obtained by direct aspiration or by injecting 125 µL of several analytical solutions and samples.

Determinações multi-elementares de metais, Sulfato e Cloreto em amostras de águas por espectrometria de massas com fonte de plasma (ICP-MS)

The multi-element determination of Al, Cr, Mn, Ni, Cu, Zn, Cd, Ba, Pb, SO4= and Cl- in riverine water samples was accomplished by inductively coupled plasma mass spectrometry (ICP-MS). The sample passed through a column containing the anionic resin AG1-X8 and the metals were determined directly. The retained anionic species were eluted and SO4= and Cl- were determined at m/z 48 and 35 correspondent to the ions SO+ and Cl+ formed at the plasma. Accuracy for metals was assessed by analysing the certified reference TM-26 (National Water Research Institute of Canada). Results for SO4= and Cl- were in agreement with those obtained by turbidimetry and spectrophotometry. LOD's of 0.1 µg l-1 for Cd, Ba and Pb; 0.2 µg l-1 for Al, Mn and Cu; 0.5 µg l-1 for Cr; 0.9 for Zn; 2.0 µg l-1for Ni , 60 µg l-1 for S and 200 µg l-1 Cl were attained.

Adsorção de íons Cu2+ em latossolo vermelho-amarelo húmico

In environmental studies it is necessary to know the adsorption behavior of metals by soils, since the unfavorable effects of heavy metals and even the micronutrients at high concentrations in the environment are related to these adsorbents' ability to immobilize them. A sample of a humic yellow red oxisol from Araponga region in the State of Minas Gerais, Brazil, was used to verify the adsorption behavior of Cu2+ ions in this substrate. The mathematical model described by Langmuir's adsorption equation in its linearized form was applied and the values of the maximum capacity b and those of the constant related to the bonding energy a were obtained. Aliquots of copper nitrate solutions containing several concentrations of this metal were added to soil samples, the pH being predetermined for developing the adsorption experiments. The chemical and physical characterization of soil sample were performed by determining the organic carbon, nitrogen and phosphorus concentrations, cation exchange capacity (CEC), pH, concentration of metals (Al, Fe, K, Mg, Ca, Zn, Cu, Ni, Cr, Co, Pb, and Cd), granulometric analysis and X-ray diffraction. Langmuir isotherms presented two distinct adsorption regions at both pH 4 and pH 5, showing that the adsorptive phenomenon occurs in two distinct stages. The adsorption sites for the lower part presented greater bonding energy and low adsorption capacity compared with the adsorption sites of the part of the curve corresponding to higher Cu concentrations in the equilibrating solution.

Substâncias húmicas aquáticas: fracionamento molecular e caracterização de rearranjos internos após complexação com íons metálicos

The aquatic humic substances (AHS) investigated in this study were conventionally isolated from Rio Negro waters - Amazonas State/Brazil by means of the collector XAD 8. A special five-stage tangential-flow ultrafiltration device was used for analytical fractionation of AHS. The fractionation patterns (6 fractions each) showed that metal traces remaining in AHS after their XAD 8 isolation have different size distributions. For instance, the major percentage of traces of Ni, Cu, Zn, Cd and Pb (determined using ICP-AES) was preferably complexed by molecules with relatively high molecular size (30-100 kDa) and the following complexation order was characterized: F2 >> F1 = F4 = F5 > F3 > F6. Moreover, the species formed between AHS and metals prepared by spiking, showed distribution patterns changing as a function of the complexation time (ageing process), indicating a slow transformation process and an inner rearrangements in the binding sites within the AHS molecules.

Síntese, caracterização e estudo das propriedades catalíticas e magnéticas de nanopartículas de Ni dispersas em matriz mesoporosa de SiO2

Nickel nanoparticles supported on amorphous silica ceramic matrix were synthesized by the polymeric precursor method. The nanostructure was characterized by NMR, BET, XRD, SEM, TEM, and flame atomic absorption spectrometry techniques. It was observed a dependence of the crystallite size on the thermal annealing, under a N2 atmosphere. The materials presented a high catalytic activity and selectivity upon the beta-pinene hydrogenation reaction. The magnetic hystereses were also correlated with the morphology of the processed material.

Determinação de Mn, Cu e Zn em matrizes salinas após separação e pré-concentração usando Amberlite XAD-7 impregnada com Vermelho de Alizarina S

The aim of this work was to explore the possibility of the application of a non-ionic resin obtained by impregnation of Alizarin Red S (VAS) in Amberlite XAD-7 for manganese, copper and zinc separation and preconcentration in saline matrices. For these system, the metals were quantitatively retained, in the pH range 8.5-10.0, by using 0.50 g of solid phase, stirring time of five minutes and a total mass up to 200 mug of each cation. The sorbed elements were subsequently eluted and a fifty-fold, ten-fold and ten-fold preconcentration factor for to Zn, Cu and Mn were obtained, respectively.

Distribuição de metais e caracterização das constantes de troca entre espécies metálicas e frações húmicas aquáticas de diferentes tamanhos moleculares

In this work the metal distribution and exchange constants between metal species and aquatic humic fractions with different molecular sizes were studied. The aquatic humic substances (AHS) were extracted by XAD-8 resin from water sample collected from Itapitanguí river, São Paulo State, Brazil. The AHS were fractionated in six fractions with different molecular sizes (>100 - <5 kDa) and characterized by several techniques. Molar ratios H/C suggested higher aromaticity for fractions F1 and F6 whereas molar ratios C/N didn´t show any differences regarding the humification degree between the fractions. The UV-Vis absorbance a254/a436 ratio showed higher results for F4 and F5, probably by less condensed features. FTIR studies showed high similarity in the functional groups in the fractions. The highest percentage of traces of Co, Al, Fe, Mn, Cu, Zn and Ni (determined by ICP-AES) was preferably complexed by fractions F3 and F4 with a greater amount of dissolved organic carbon (DOC). In addition, the exchange constants, determined by ultrafiltration method, showed complexes AHS-Fe and AHS-Al with higher stability than complexes AHS-Co in all fractions.

Catalisadores Ni/Al2O3 promovidos com molibdênio para a reação de reforma a vapor de metano

Mo-promoted Ni/Al2O3 catalysts for the methane steam reforming reaction were studied in this work. The Ni/Al2O3 catalysts were prepared by precipitation and molibdenum was added by impregnation up to 2%wt. The solids were tested using a micro-reactor under two H2Ov/C conditions and were characterized by ICP-OES, XRD, N2 adsoption, H2 chemisorption and TPR. NiO and NiAl2O4 phases were observed and the metallic area decreased with the increase of the Mo content. From the catalytic tests high stability was verified for H2Ov/C=4.0. On the other hand, only the catalyst containing 0,05% Mo stayed stable during 30 hours of the test at H2Ov/C=2.0.