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Ou este artigo descreve dois resultados de uma pesquisa, cujo objetivo foi investigar as contribuições do software GeoGebra 3D para os processos de ensino e de aprendizagem de conteúdos de geometria espacial que não o Ensino Médio, seguindo as pressões teóricas do Modelo Van Hiele. Para todos os procedimentos metodológicos, a pesquisa foi realizada sob a perspectiva da abordagem qualitativa, por meio da pesquisa, em uma segunda edição da série Ensino Médio de uma escola pública localizada em Boa Vista, Roraima, Brasil. Essa intervenção possibilitou a produção de dois dados registrados por meio de questionários, um relatório do observatório de pesquisa, registros fotográficos, arquivos digitais construídos com o softwareO GeoGebra e os registros escritos fornecem as atividades propostas. Os resultados apontam que o uso do software GeoGebra 3D contribuiu efetivamente para promover ou avançar o pensamento geométrico de dois pesquisadores, em relação aos conselhos de Poliedros, do nível 1 (visualização) ao nível 4 (dedução formal) do Modelo Van Hiele.

The present experience report proposes to describe and analyze actions of teaching performance, experienced by the first author, with the implementation of remote teaching at the Militarized State College Luiz Ribeiro de Lima, located in the city of Boa Vista, Roraima. Such actions are the result of the Implementation Plan for Non-Presential Activities for State Public Schools, prepared by State Secretariat for Education and Sport of Roraima (SSES / RR) in the face of the interruption of face-to-face classes to contain the pandemic caused by the new Coronavirus (Covid-19). In this work, concepts of active methodologies, hybrid education and remote teaching are discussed, in order to subsidize and qualify the pedagogical practices adopted in the referred educational establishment, for the development plan for non-classroom activities. The theoretical contribution used consisted of studies by Bacich, Tanzi Neto and Trevisani (2015), Bacich (2017), Moran (2015, 2018, 2019), Pasini, Carvalho and Almeida (2020), among others. To this end, a bibliographical and documentary research was carried out on books, scientific articles, official documents, technical notes, and reports that deal with the topic, as well as data obtained in the lesson plans and reports prepared by teachers who develop out remote activities. It is noteworthy that the data analyzed here are the result of the pedagogical practices adopted in remote education, which are being developed in the discipline of Mathematics, in the High School stage of the Youth and Adult Education (YAE) modality. The results reveal that remote teaching has been a challenge in current pedagogical practices, which require new teaching methodologies, which require digital technologies, but which can transform the role of the teacher and students, giving new meaning to the concepts of teaching and learning The conclusions point out ways to outline actions in the context of remote education that tends to remain even after the reopening of schools to resume face-to-face classes. El presente informe de experiencia se propone describir y analizar acciones de desempeño docente, vividas por el primer autor, con la implementación de la enseñanza remota en el Colegio Estatal Militarizado Luiz Ribeiro de Lima, ubicado en la ciudad de Boa Vista, Roraima. Tales acciones son el resultado del Plan de Implementación de Actividades No Presenciales para las Escuelas Públicas del Estado, preparado por de la Secretaría de Estado de Educación y Deporte de Roraima (SEED / RR) ante la interrupción de las clases presenciales para contener la pandemia provocada por el nuevo Coronavirus (Covid-19). En este trabajo se discuten conceptos de metodologías activas, educación híbrida y enseñanza remota, con el fin de subsidiar y calificar las prácticas pedagógicas adoptadas en el referido establecimiento educativo, para el desarrollo de actividades no presenciales. El aporte teórico utilizado consistió en estudios de Bacich, Tanzi Neto y Trevisani (2015), Bacich (2017), Moran (2015, 2018, 2019), Pasini, Carvalho y Almeida (2020), entre otros. Para ello, se realizó una investigación bibliográfica y documental sobre libros, artículos científicos, documentos oficiales, notas técnicas e informes que abordan el tema, así como datos obtenidos en los planes de lecciones e informes elaborados por los docentes que desarrollan las actividades a distancia. Es de destacar que los datos aquí analizados son el resultado de prácticas pedagógicas adoptadas en educación remota, las cuales se están desarrollando en la disciplina de Matemáticas, en la etapa de Escuela secundaria de la modalidad Educación de Jóvenes y Adultos (EJA). Los resultados revelan que la enseñanza remota ha sido un desafío en las prácticas pedagógicas actuales, que requieren nuevas metodologías de enseñanza, que necesitan tecnologías digitales, pero que puede transformar el rol del docente y los estudiantes, reformulando los conceptos de enseñanza y aprendizaje. Las conclusiones señalan formas de perfilar acciones en el contexto de la educación a distancia que tiende a mantenerse incluso después de la reapertura de las escuelas para retomar las clases presenciales. O presente relato de experiência se propõe a descrever e analisar ações da atuação docente, vivenciadas pela primeira autora, com a implantação do ensino remoto no Colégio Estadual Militarizado Luiz Ribeiro de Lima, localizado na cidade de Boa Vista, Roraima. Tais ações são decorrentes das orientações advindas da Secretaria de Estado da Educação e Desporto de Roraima (SEED/RR) frente ao cenário de interrupção das aulas presenciais para conter a pandemia causada pelo novo coronavírus (Covid-19). Neste trabalho são discutidos conceitos de educação híbrida e ensino remoto, com vistas a subsidiar e qualificar as práticas pedagógicas adotadas no referido estabelecimento de ensino, com a implementação do plano de desenvolvimento de atividades não presenciais. Para tanto, foi realizada uma pesquisa bibliográfica e documental em artigos científicos, documentos oficiais, notas técnicas, e reportagens que tratam sobre o tema, bem como, dados obtidos nos planos de aula e relatórios elaborados pelos professores que desenvolvem atividades remotas. Ressalta-se que os dados aqui analisados são frutos das práticas pedagógicas adotadas no ensino remoto, que estão sendo desenvolvidas na disciplina de Matemática, na etapa do Ensino Médio da modalidade Educação de Jovens e Adultos (EJA). Nas conclusões aponta-se caminhos para delinear ações no contexto do ensino remoto que tende a permanecer mesmo depois da reabertura das escolas para a retomada das aulas presenciais.

Six campaigns were performed in North Channel (CNOR), Barcas Channel (BC) and lower zones (EZ) of Tagus estuary to better understand methylmercury (MMHg) and mercury (Hg) transport and fate. Highest concentrations of particulate and dissolved MMHg were observed in CNOR in bottom waters and in the warmest months. The MMHg distribution coefficients between particulate and dissolved fractions were mainly influenced by particulate matter and dissolved organic carbon. The values were slightly higher in summer than in winter and in CNOR. Overall, results established that the tidal effect is a main driver on the transport and fate of Hg and MMHg from CNOR to outer areas, evidenced by the exportation of the Hg species from CNOR to the upstream station in high tide and to the downstream one in low tide. Therefore, CNOR may be considered a source of Hg and MMHg to the outer estuary.

Neurotoxic methylmercury (MMHg) is formed from inorganic divalent mercury (Hg2+). However, it is poorly understood to what extent different mercury (Hg) pools contribute to existent MMHg levels. In this study, ambient concentrations of total Hg (THg) and MMHg as well as rates of methylation and demethylation were measured simultaneously in sediments with and without salt-marsh plant vegetation, which were collected in Guadiana and Tagus estuaries, Portugal. Concurrent processes of Hg methylation and MMHg demethylation were directly monitored and compared by spiking sediments cores with stable isotope tracers of 199Hg2+ and CH3201Hg+ followed by gas chromatographic separation and isotope-specific detection using inductively coupled plasma mass spectrometry. Compared to the Guadiana estuary, where concentrations were comparatively low, THg and MMHg levels varied between vegetated and non-vegetated sediments collected at the Rosario site (ROS) of the Tagus estuary. Methylation (KM) and demethylation rates (KD) were also different between estuaries being dependent on the presence of vegetation. In addition, the type of macrophyte species influenced KM and KD values. In fact, the highest KM value was found in Sarcocornia fruticosa vegetated sediments at the Castro Marim site in Guadiana (CM, 0.160 day−1) and the lowest KM was observed in non-vegetated sediments at the Alcochete site in Tagus (ALC, 0.009 day−1). KD varied by a factor of three among sites with highest rates of demethylation observed in non-vegetated sediments in Guadiana (12 ± 1.3 day−1, corresponding to a half-life of 1.4 ± 0.2 h). This study clearly shows that the presence of vegetation in sediments favors the formation of MMHg. Moreover, this effect might be site specific and further studies are needed to confirm the findings reported here.

Guided by the question “How can the use of GeoGebra 3D software contribute to the teaching and learning processes of Spatial Geometry contents in High School?”, we present in this article a cut of the educational product developed in an ongoing master's research. This product was developed with the objective of presenting a pedagogical support material aiming to explore constructions carried out through the GeoGebra 3D software, so that students develop spatial visualization skills that can contribute to the mental representation of three-dimensional objects and the formalization of concepts. geometric patterns of polyhedra: prisms and pyramids. We hope that this product can provoke in Mathematics teachers the desire to produce new constructions or adaptations of the activities carried out, using digital technologies common to the students' daily lives. Orientados pela interrogação “De que forma o uso do software GeoGebra 3D pode contribuir nos processos de ensino e de aprendizagem dos conteúdos de Geometria Espacial no Ensino Médio?”, apresentamos neste artigo um recorte do produto educacional desenvolvido em uma pesquisa de mestrado em andamento. Este produto foi elaborado com o objetivo de apresentar um material de apoio didático pedagógico visando explorar construções realizadas através do software GeoGebra 3D, de modo que os alunos desenvolvam habilidades de visualização espacial que possam contribuir para a representação mental dos objetos tridimensionais e a formalização dos conceitos geométricos de poliedros: prismas e pirâmides. Almejamos que esse produto possa provocar nos professores de Matemática o anseio de produzir novas construções ou adaptações das atividades realizadas, utilizando tecnologias digitais comuns ao cotidiano dos alunos.

King George Island, situated in the South Shetland Islands archipelago, is one of the most visited sites in Antarctica. This has contributed to a high density of scientific stations and shelters in the region, especially in Fildes Peninsula. In order to evaluate the natural and anthropogenic sources of trace elements (As, Cd, Cu, Zn, Pb and Hg) soil and moss samples were collected from different sites in January 2013. In general, the results revealed homogeneous concentrations (μg g−1) for each element in the majority of collected samples (As: 3.8 ± 1.4; Cd: 0.4 ± 0.9; Cu: 34 ± 4; Zn: 115 ± 13; Pb: 20 ± 5; Hg; 0.011 ± 0.009). However, some samples in specific areas of Fildes Bay showed the existence of local anthropogenic activities that have contributed to the enrichment of contaminants in soils and moss samples that correlated to one another (e.g. Pb: 1101 μg g−1). Human presence is linked to examples of contamination and environmental perturbation, making essential the implementation of this type of study in order to understand and protect unique places in Antarctica.

Mercury (Hg) dynamics was evaluated in contaminated sediments and overlying waters from Tagus estuary, in two sites with different Hg anthropogenic sources: Cala Norte (CNOR) and Barreiro (BRR). Environmental factors affecting methylmercury (MMHg) production and Hg and MMHg fluxes across sediment/water interface were reported. [THg] and [MMHg] in solids (0.31–125 μg g−1 and 0.76–201 ng g−1, respectively) showed high variability with higher values in BRR. Porewater [MMHg] (0.1–63 ng L−1, 0.5–86% of THg) varied local and seasonally; higher contents were observed in the summer campaign, thus increasing sediment toxicity affecting the sediment/water Hg (and MMHg) fluxes. In CNOR and BRR sediments, Hg availability and organic carbon were the main factors controlling MMHg production. Noteworthy, an upward MMHg diffusive flux was observed in winter that was inverted in summer. Although MMHg production increases in warmer month, the MMHg concentrations in overlying water increase in a higher proportion compared to the levels in porewaters. This opposite trend could be explained by different extension of MMHg demethylation in the water column. The high concentrations of Hg and MMHg and their dynamics in sediments are of major concern since they can cause an exportation of Hg from the contaminated areas up to ca. 14,600 mg year−1 and an MMHg deposition of up to ca. 6000 mg year−1. The results suggest that sediments from contaminated areas of Tagus estuary should be considered as a primary source of Hg for the water column and a sink of MMHg to the sedimentary column.

Intertidal sediments of Tagus estuary regularly experiences complex redistribution due to tidal forcing, which affects the cycling of mercury (Hg) between sediments and the water column. This study quantifies total mercury (Hg) and methylmercury (MMHg) concentrations and fluxes in a flooded mudflat as well as the effects on water-level fluctuations on the air-surface exchange of mercury. A fast increase in dissolved Hg and MMHg concentrations was observed in overlying water in the first 10min of inundation and corresponded to a decrease in pore waters, suggesting a rapid export of Hg and MMHg from sediments to the water column. Estimations of daily advective transport exceeded the predicted diffusive fluxes by 5 orders of magnitude. A fast increase in dissolved gaseous mercury (DGM) concentration was also observed in the first 20-30min of inundation (maximum of 40pg L-1). Suspended particulate matter (SPM) concentrations were inversely correlated with DGM concentrations. Dissolved Hg variation suggested that biotic DGM production in pore waters is a significant factor in addition to the photochemical reduction of Hg. Mercury volatilization (ranged from 1.1 to 3.3ngm-2h-1; average of 2.1ngm-2h-1) and DGM production exhibited the same pattern with no significant time-lag suggesting a fast release of the produced DGM. These results indicate that Hg sediment/water exchanges in the physical dominated estuaries can be underestimated when the tidal effect is not considered.

Sources and transport processes of As, Cu, Cd and Pb were studied in different environmental compartments of Deception Island, an active volcano in the South Shetland Islands, Antarctica. Element concentrations in fresh water samples are consistent with the lowest values reported elsewhere in Antarctica. Interestingly, higher concentration values of As were found in samples collected in or near spring water courses and its transport may be related with processes of lixiviation in underground waters. While in saline waters Cu and Pb had important punctual sources, concentration values for Cd were consistently high pointing to the existence of a natural and diffuse source possibly related with the hydrothermal activity. The high Si/Al ratio, low carbon content, and a non-significant anthropogenic heavy metal input may explain the surprisingly homogeneous heavy metal content found in sediment samples.

The Tagus Estuary is one of the most Hg-contaminated estuaries in SW Europe. Sediment cores were sampled at two low Hg-contaminated sites inside the natural park, Alcochete (ALC) and Vale Frades (VF), and analyzed for mercury and methylmercury. Concentrations of Hg and MeHg in sediments were below 1 μg g−1 and 4.4 ng g−1, respectively. While in summer organic matter and/or excess SO4 2− promotes Hg methylation, in winter, Hg availability is the sole driver for methylation. Diffusive fluxes in the sediment/water interface show a sink of Hg species in the ALC site (ca. 170 mg year−1 of Hg and 60 mg year−1 of MeHg), while in the VF area, a sink of MeHg (ca. 1900 mg year−1) as well as a source of Hg (ca. 2000 mg year−1) is observed. The morphology and hydrodynamic regime of the Tagus Estuary seem to influence Hg dynamics even in areas with low levels of Hg contamination.

Background Technological advances improved the practice of “modern” extracorporeal membrane oxygenation (ECMO). In the present report, we describe the experience of a referral ECMO center using portable miniaturized ECMO systems for H1N1-related severe acute respiratory distress syndrome (ARDS). Methods An observational study of all patients with H1N1-associated ARDS treated with ECMO in Hospital S. Joao (Porto, Portugal) between November 2009 and April 2011 was performed. Extracorporeal membrane oxygenation support was established using either ELS or Cardiohelp systems (Maquet-Cardiopulmonary-AG, Hirrlingen, Germany). Results Ten adult patients with severe ARDS secondary to H1N1 infection (Pa o 2/fraction of inspired oxygen, 69 mm Hg [56-84]; Murray score, 3.5 [3.5-3.8]) were included, and 60% survived to hospital discharge. Five patients were uneventfully transferred on ECMO from referring hospitals to our center by ambulance. Six patients were treated during the first postpandemic influenza season. All patients were treated with oseltamivir, and 1 received in addition zanamivir. Four patients received corticosteroids. Nosocomial infection was the most common complication (40%). Of the 4 deaths, 2 were caused by hemorrhagic shock; 1, by irreversible multiple organ failure; and 1, by refractory septic shock. Conclusion In our experience, ECMO support was a valuable therapeutic option for H1N1-related severe ARDS. The use of portable miniaturized systems allowed urgent rescue of patients from referring hospitals and safe interhospital and intrahospital transport during ECMO support.

The contribution of electrochemical methods to the knowledge of dynamic speciation of toxic trace elements in marine waters is critically reviewed. Due to the importance of dynamic considerations in the interpretation of the electrochemical signal, the principles and recent developments of kinetic features in the interconversion of metal complex species will be presented. As dynamic electrochemical methods, only stripping techniques (anodic stripping voltammetry and stripping chronopotentiometry) will be used because they are the most important for the determination of trace elements. Competitive ligand ex- change-adsorptive cathodic stripping voltammetry, which should be considered an equilibrium technique rather than a dynamic method, will be also discussed because the complexing parameters may be affected by some kinetic limitations if equilibrium before analysis is not attained and/or the flux of the adsorbed complex is in fluenced by the lability of the natural complexes in the water sample. For a correct data interpretation and system characterization the comparison of results obtained from different techniques seems essential in the articulation of a serious discussion of their meaning.

Paralytic shellfish toxins were quantified in whole tissues of the mussel Mytilus galloprovincialis exposed to blooms of the dinoflagellate Gymnodinium catenatum in Portuguese coastal waters. A validated liquid chromatography method with fluorescence detection, involving pre-chromatographic oxidation was used to quantify carbamoyl, N-sulfocarbamoyl and decarbamoyl toxins. In order to test for any matrix effect in the quantification of those toxins, concentrations obtained from solvent and matrix matched calibration curves were compared. A suppression of the fluorescence signal was observed in mussel extract or fraction in comparison to solvent for the compounds dcGTX2 + 3, GTX2 + 3 and GTX1 + 4, while an enhancement was found for C1 + 2, dcSTX, STX, B1, dcNEO and NEO. These results showed that a matrix effect varies among compounds. The difference of concentrations between solvent and matrix matched calibration curves for C1 + 2 (median = 421 ng g⁻¹) exceeded largely the values for the other quantified compounds (0.09-58 ng g⁻¹). Those differences were converted into toxicity differences, using Oshima toxicity equivalence factors. The compounds C1 + 2 and dcNEO were the major contributors to the differences of total toxicity in the mussel samples. The differences of total toxicity were calculated in ten mussel samples collected during a 10-week blooming period in Portuguese coastal lagoon. Values varied between 53 and 218 µg STX equivalents kg⁻¹. The positive differences mean that the estimated toxicity using solvent calibration curves exceed the values taking into account the matrix. For the toxicity interval 200-800 µg STX equivalents kg⁻¹ an increase was found between 44 and 28%.

The suitability of hyphenated USAED with HPLC separation and ET-AAS determination as a new rapid methodology for Se control in Se-enriched food supplements is demonstrated. Total Se determination and Se speciation are accomplished in a single sample treatment using low sample amounts (ca. 10 mg), and low extracting volume (1 mL). The total Se content in seven of the 10 Se-enriched supplements studied was in agreement with the values obtained after microwave pressurized acid digestion, MW, (test t , p = 0.05) . The Se species studied were Se(IV), Se(VI), SeMet, SeMeSeCys, and SeCys 2 , being some of the most common found in the 10 supplements studied. Although SeMet was the Se species expected to be present at the highest concentration in most Se-enriched food supplements, we detected it in only three of the 10 samples studied. In the other seven samples, two of them had Se(IV) as the main Se species. The other five supplements had Se species that did not match with any of the five standards selected by us. We have also systematically demonstrated that ultrasonication does not alter the following Se species: Se(IV), Se(VI), SeMet, SeMeSeCys, and SeCys 2 . The new procedure can be easily adapted to more Se species and can be routinely used for Se control in Se-enriched food supplements. Concerning the supplements studied, our results suggest that stricter control on the Se content in enriched food supplements in terms of Se species will need to become mandatory.

The interaction between nickel and pectin extracted from citrus fruit was studied in 0.10 M KNO(3), at pH 5.5 and 25 degrees C. Differential pulse and/or square wave polarography were used to determine free nickel. For a high coverage degree (theta) of the pectin by the metal ion a good fitting was observed between experimental results and the model that includes both complex species, ML and ML(2) (M for the metal ion and L for the ligand). In the ML(2) species, Ni(II) interacts with two carboxylate groups of different chains, resulting in an inter-chain association. For low theta values, the formation of ML(2) is hindered due to the repulsion between the negative charges of carboxylic groups in two independent segments of pectin. The influence of calcium or copper ions on the free nickel concentration, in the presence of pectin, may lead to a decrease in free nickel concentration, contrary to what would be expected from direct competition between Ca(II) or Cu(II) and Ni(II) for the pectin binding sites. This is due to the partial neutralisation of the negative carboxylic charges by the positive charges of the divalent cations, which favours NiL(2) formation through the association of independent chains.

Remediation of sites contaminated with heavy metals using hyperaccumulators seems a promising alternative to engineering approaches. In this work, we compared cadmium (Cd) accumulation and toleranc...

Due to its potential as sample treatment for Analytical Chemistry, the Ultrasonic-Assisted Enzymatic Digestion (USAED) for total elemental determination and elemental speciation is described under the most recent achievements published in literature, focusing on the variables that critically affect the performance of this relatively new sample treatment, such as the type of enzymes or the type of ultrasonic system used for the acceleration of the solid-liquid extraction process. Moreover, analytical chemists are aware of common errors produced in data interpretation concerning USAED. In addition, a guide for the rapid application of this methodology is also provided along with detailed explanations. Finally, future trends regarding USAED are also given and commented.

Dynamic and static ultrasonic procedures involving ultrasonic bath and tandem focused ultrasound (i.e. two probes were used in the same sample treatment) have been assessed in order to implement a reliable solid–liquid back extraction of mercury from commercial resins (dowex and chelex-100), previously used to concentrate Hg(II) from treated urine. The urine had been previously treated with an advanced oxidation process provided by the conjunction of potassium permanganate, hydrochloric acid and high intensity focused ultrasound, which allowed that organic matter degradation was achieved in less than 3 min. 95 ± 10% of mercury in the certified urine and 97 ± 6% of the spiked methyl-mercury was recovered with the dowex resin plus the static ultrasonic procedure, whilst 96 ± 11% of the spiked mercury was recovered with the dowex resin plus the dynamic procedure, for which ultrasonication was not necessary. The Hg pre-concentration factor used in this work was 8 (20 mL of urine to 2.5 mL of acid), but different volume ratios can be used in order to increase this factor.

Three different ultrasonic-based sample treatment approaches, the automated ultrasonic slurry sampling, the ultrasonic assisted acid solid–liquid extraction (ASLE) and the enzymatic probe sonication (EPS) were compared and discussed for the determination of Cd and Pb by ET–AAS in biological reference materials. The sample mass chosen to perform the analysis was 10 mg and the liquid volume was 1 ml of nitric acid 1 M. The best results were obtained with the slurry procedure with which it was possible accurate and precise determination of the Cd and Pb content in four of the five reference materials studied. Optimum performance (total metal extraction) of ASLE assisted by ultrasound for Cd was only achieved in two of the four materials assessed whereas total Pb recovery was only possible in three of the five samples. Total extraction with the enzymatic probe sonication was only obtained for Cd in oyster tissue. Neither ASLE nor EPS were able to extract Cd or Pb from spruce needles. Pb concentration obtained after EPS was found to be highly dependent from sample centrifugation speed and time.

A new sample treatment was developed for the determination of dissolved cadmium in Tagus estuarine waters, based on focused ultrasound in conjunction with small volumes in the extraction steps for Cd pre-concentration. Cadmium was first pre-concentrated using a classical approach (APDC as the complexing agent and MIBK as the organic phase) and then back-extracted into HNO 3 with the aid of focused ultrasound, which reduced the acid concentration by more than one order of magnitude (from 4 to 0.1 mol L − 3 ). This sample treatment was accomplished in less than 5 min, using low sample volume (20 mL), and low-volume, low-concentration reagents. The pre-concentration factor used in this work was 25, but different sample/organic volume ratios may be used in order to increase that value. The limit of detection and the limit of quantification in Tagus water samples were 0.03 nmol L − 1 and 0.1 nmol L − 3 , respectively. Recoveries from spiked Tagus water were higher than 90%. The procedure was validated using the reference estuarine water NRC-SLEW-3. In the solubilization of Cd particulate, bath ultrasonication was used in conjunction with HNO 3 + HCl, followed by H 2 O 2 , which took about 2 instead of the usual 12 h (cooling included) when high-pressure microwave digestion is used.

Different oxidation methodologies based on ozone and focused ultrasound for the degradation of organic matter and organic-mercury compounds (spiked) present in human urine are discussed. Inorganic and total mercury can be determined in human urine. A flow-injection cold-vapour atomic absorption spectrometer system was used for mercury measurements. Optimization of cold vapour generation was performed with NaBH 4 and SnCl 2 . A two-level full factorial design (2 4 ) was applied to understand the cross-effects among the variables influencing the degradation of organic-mercurials and organic matter in urine by KMnO 4 /HCl/focused ultrasound, namely, KMnO 4 and HCl concentration, ultrasonication time and ultrasonication amplitude. Optimization results showed that all variables were significant. New trends in the application of focused ultrasound and ozone are highlighted. As a result of the optimization procedure, one simple, rapid and accurate method was developed for the determination of total mercury in urine samples The method is based on the ultrasound assisted degradation of organo-mercurials and organic matter in urine in the presence of KMnO 4 /HCl/Focused Ultrasound. The procedure can be accomplished within 3 min, using 50% sonication amplitude provided by a probe ultrasonic device (63 W maximum output power, 22.5 kHz frequency). The method was applied to measure the mercury content in spiked urine from different non-exposed volunteers.

The interaction between Cu(II) and pectin extracted from citrus fruit was studied in KNO3 0.10 mol dm−3 at 25 °C and pH 5.5, using ion selective electrode potentiometry and voltammetry, namely differential pulse polarography and square-wave voltammetry. Although many independent variables may affect Cu(II)-polymer interactions such as charge density, polymer concentration and copper to polymer concentration ratio, a good fitting was observed for the model with ML and ML2 complex species, when M:L total concentration (mol dm−3) ratio varies from 0.2 to 2.7 and the ligand concentration is in the range (0.2 to 1) g dm−3, i.e., (0.4 to 2)×10−3 mol COO− dm−3. The complex parameters found in these conditions were log βCuL=3.5±0.1 and log βCuL2= 8.0±0.2. For lower total ligand and total metal ion concentrations, used in voltammetry, the interaction Cu(II)-pectin is affected by a cooperative mode (increase of metal ion-ligand affinity) when the total metal ion concentration increases and by an anti-cooperative mode when the total ligand concentration increases, possibly due to different conformations of the polymer.

The physico-chemical forms in which the heavy metals occur in the environment, particularly in biological samples, may strongly condition their bioavailability and toxicity. Hence, the distinction between different fractions of the total metal is of interest. Today, the challenge facing the scientific community and regulatory agencies is to assess health risks and/or benefits of low-level exposure to metals and metalloids in the environment, especially in foods. Accordingly, new analytical procedures to enable determination of trace and ultratrace levels of metals/metalloids and their species are needed so that the steps of extraction and separation must be mild enough to liberate the species from the matrix while maintaining their chemical integrity. The combination of enzymatic digestions plus ultrasonication, by either bath or probe, has recently emerged as a promising methodology for metal/metalloid speciation with environmentally acceptable performance. We critically review the state-of-the art of enzymatic digestion in sample treatment for total metal determination and speciation by atomic spectrometry. In addition, we comment on new trends based on the capability of novel sample treatments using enzymes and ultrasonication. We also provide guidelines to implement this analytical methodology in the laboratory.

A method was developed for the generation of mercury vapour by means of cold-vapour flow-injection atomic absorption spectrometry (FI-CV-AAS) from white wine samples after ozonation as sample pre-treatment. Two different reactors designs for sample ozonation were developed and investigated. The limit of detection and the limit of quantification were, respectively, 0.5 and 1.7 microg l(-1), and the relative standard deviation (n=10) was 2% for a concentration of 50 microg l(-1) and 7% for a concentration of 5 microg l(-1). The pre-treatment with ozone has allowed to reduce drastically the amount of chemical reagents (e.g. carrier agent and reducing agent) used in the FI-CV-AAS system. The mercury content of wine samples was also determined by FI-CV-AAS after pre-concentration in the presence of HNO(3) and H(2)O(2). In general, there was no significant difference among data obtained from both methodologies, but pre-treatment with ozone is much faster.

Aims The objective of this study was to investigate the response of Brassica juncea in the presence of Cd, in hydroponic and soil experiments, and to conclude about common and divergent trends in both cultures. Methods We studied the effect of Cd on growth, oxidative damage and antioxidant responses in roots and shoots of B. juncea grown in soil and hydroponic cultures, using typical time-scales for each one. Major ROS-scavenging enzymes such as catalase, ascorbate peroxidase and guaiacol peroxidase were evaluated, as well as lipid peroxidation. Results Small Cd concentrations in the plant led to enhanced plant growth, while large Cd concentrations impaired growth. The increase in lipid peroxidation observed in the presence of Cd was always greater in shoots than in roots. The physiological response to enhanced levels of reactive oxygen species in the presence of Cd included an increase in guaiacol peroxidase, ascorbate peroxidase and catalase activities, but those enzymes were not always enhanced in a similar manner in both cultures. Conclusions The main factors responsible for the differences between the experiments in soil and nutrient solution, were the different Cd content in the plant tissues and the different time-scale of the experiments.

Soluble Pb(II) speciation in a polluted river (Este River, Northern Portugal) was studied using differential pulse anodic stripping voltammetry (DPASV). Three sampling sites were selected: Braga (downstream the pollution sources), Foz (near the river mouth) and an intermediate point called Louro. Studies have been done with samples collected in different times of the year, namely spring, summer, autumn and winter. Centrifuged and filtered samples were titrated with Pb(II) and the labile metal concentration measured by DPASV. Results show that soluble metal complexes are labile, in the time scale of the analytical technique, with DML

Soil pollution with toxic metals has become an important social and environmental challenge. When the polluted area is large and the site poses little immediate risk to health or environment, in situ remediation technologies can be envisaged. Here we used a polyacrylate polymer to immobilize cadmium (Cd) in a sandy soil artificially contaminated with the metal. Growth of perennial ryegrass in pots with 9.5 kg of soil was stimulated in polymer-amended soil. Even in pots with the highest levels of Cd, growth was much less impaired than in pots without polymer. Shoot Cd concentrations were smaller in the plants cultivated in the amended soil. Because water soluble Cd was considerably reduced in the contaminated polymer-amended soil, the effect of the polymer on plant growth was attributed to the decrease of Cd concentration in soil solution.

The influence of UV-B irradiation in estuarine water from the salt marsh of Corroios, Tagus river, was studied in the laboratory in terms of lead speciation. The filtered water was exposed to UV-B irradiation with a intensity of 540 μ W/cm 2 . The effect of UV-B (280–320 nm) was studied from the titration with Pb 2+ , followed by anodic stripping voltammetry in differential-pulse mode, after different periods of irradiation time, from 1 h up to 10 days. It was found that, before UV-B irradiation, Pb 2+ speciation can be interpreted assuming two different types of ligands: one macromolecular, with an heterogeneous behaviour represented by two main groups, while the other is a small ligand, homogeneous in terms of Pb 2+ complexation. Stability constant values indicate that the heterogeneous ligand presents a humic-like behaviour, with minor sites related to phenolic, amino or sulphur type groups, and major sites related to carboxylic type groups. Small homogeneous ligands, probably released by bioorganisms, also present stability constants of carboxylic type groups. From the results it can be observed that UV-B irradiation decreases complexing strength of the medium as well as its heterogeneity, both effects becoming evident after 1 h of irradiation. Even so, for the concentration range studied ( C Pb ≤2×10 −6 M) more than 80% of Pb II still remains complexed to the weaker group of the macromolecular ligand. Since UV-B doses are similar to maximum spring solar intensity, the results suggest both chemical and ecological implications.

Complexation of trace metals by humic matter is an important issue, as it determines to a large extent their bioavailability, toxicity and mobility. In a complexing medium the supply of metal species towards an interface is always related to the kinetics of the complex association/dissociation reactions, irrespective of whether one is dealing with living organisms in natural media, or with an electrode in voltammetry, or with a membrane in a separation process. In voltammetric studies lability criteria have been developed for steady-state and dynamic experiments, for homogeneous and chemically heterogeneous systems. In this work these criteria are reformulated on a more rigorous level and used to investigate the lability of cadmium and lead complexes in different samples of fulvic and humic matter (chemically heterogeneous systems). It is explained how lability varies with the stability of the chemically heterogeneous complex. The discussion further shows that, amongst other things, an increasing degree of chemical heterogeneity leads to a decrease of the lability.

Xavier, José C. et al., Polar marine ecosystems have global ecological and economic importance because of their unique biodiversity and their major role in climate processes and commercial fisheries, among others. Portugal and Spain have been highly active in a wide range of disciplines in marine biology of the Antarctic and the Arctic. The main aim of this paper is to provide a synopsis of some of the results and initiatives undertaken by Portuguese and Spanish polar teams within the field of marine sciences, particularly on benthic and pelagic biodiversity (species diversity and abundance, including microbial, molecular, physiological and chemical mechanisms in polar organisms), conservation and ecology of top predators (particularly penguins, albatrosses and seals), and pollutants and evolution of marine organisms associated with major issues such as climate change, ocean acidification and UV radiation effects. Both countries have focused their polar research more in the Antarctic than in the Arctic. Portugal and Spain should encourage research groups to continue increasing their collaborations with other countries and develop multi-disciplinary research projects, as well as to maintain highly active memberships within major organizations, such as the Scientific Committee for Antarctic Research (SCAR), the International Arctic Science Council (IASC) and the Association of Polar Early Career Scientists (APECS), and in international research projects. © 2013 Elsevier B.V.

This work reports the first integrated mercury study in an Antarctic ecosystem. Sample collection took place in Deception Island, an active volcano in the South Shetland Islands, in several environmental compartments (water, snow, sediments and vegetation) and different locations, during December 2011. The results suggest that volcanic activity is the most important Hg source. Mercury levels in water and sediments sampled at two fumaroles were up to 10,000 times higher than in the other sampling sites. Dissolved methylmercury (MeHg) is below the detection limit in those samples, probably due to the very high temperature found in fumaroles (above 80 °C). On the other hand MeHg accounted for, on average, 23% of total dissolved Hg in the saline waters of Foster bay, which suggests exceptional conditions for Hg methylation. Combined with the high residence time of the water in Foster bay, the results point to the existence of a MeHg pool available for aquatic living organisms.

The diffusion coefficients of humic matter samples (Purified Peat (PP) Moss and Fluka) in solution were obtained by both dynamic light scattering (DLS) and voltammetric methods. The diffusion coefficients from voltammetric measurements are greater than those determined by DLS, due to the different way each technique responds to the size distribution of polydisperse samples. Large aggregates are present in both PP humic acid (HA) and Fluka samples (diameters larger than 30 nm), their size depending on the origin and/or preparation procedure of the sample, as well as on the experimental conditions of pH and ionic strength. The influence of ionic strength on the diffusion coefficient of PPHA was analysed. Similar results were obtained by DLS and voltammetry in samples with low polydispersity up to ionic strength of 0.1 M. For higher ionic strengths aggregation may occur, leading to an increase in the apparent molecular size. The influence of pH on the diffusion coefficient of PPHA shows one population formed by large aggregates (185 nm diameter) at pH 5 in the absence of added salt. When pH is lowered below 2.5, coagulation occurs quickly leading to the precipitation of PPHA. Some irreversible disagreggation (120 nm diameter) is promoted by pH increase up to 10. PPHA samples, initially set to pH 10 and then adjusted to pH between 3 and 5, present somehow different characteristics from samples directly set to the required pH, which stresses the influence of the preparation method on final sample properties.

Humic matter (HM) presents a high affinity to bind lead ions, but complexation is affected by the presence of major ions such as Ca2+, Mg2+, and Al3+, which might have severe consequences in the bi...

Potentiometric and polarographic metal speciation results were compared for a cadmium/humic acid complex system. Three polarographic techniques were used: normal (NPP), differential (DPP) and reverse (RPP) pulse polarography. Satisfactory agreement between potentiometric and polarographic data is obtained for systems with pH below 5. RPP generally shows better agreement than NPP and DPP. The discussion of the results includes lability, effects of heterogeneity and adsorption of humic acids at the mercury electrode.

The complexation of humic matter with lead in natural water conditions was studied by differential pulse anodic stripping voltammetry (DPASV) using a mercury film of a Nafion-coated mercury film as the working electrode. The results clearly show that the Nafion film greatly minimizes the adsorption of humics on the electrode. Besides adsorption, other effects on the voltammetic signal are discussed, such as the degree of lability, ligand heterogeneity, and the metal-to-ligand concentration ratio at the electrode surface.

The competition between calcium and the heavy metals zinc(II) and cadmium(II) in their interaction with humic substances has been studied by differential pulse anodic stripping voltammetry at constant ionic strength. Two experimental methodologies were employed: (1) addition of humic acid to a solution of heavy metal; and (2) addition of heavy metals to a humic acid solution, both using various concentrations of calcium. The former method leads to complexation curves from which an overall mean stability for the heavy metal complex can be obtained. In the latter procedure, mean stability values are obtained at each titration point from the fractions of free and bound heavy metal ions. In the presence of competing ions like calcium, the association of heavy metals with the humic material can be well understood by incorporation of an additional equilibrium reaction for calcium with the humate polyanion. Hence, we are able to obtain information successfully on heavy metal speciation in more complex systems like natural waters, which contain competing cations such as calcium.

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International audience; A set of experiments on the complexation of cadmium and lead with humic acids were performed at pH 5.0 using normal- and reverse-pulse polarography and d.c. and differential-pulse anodic stripping voltammetry. The concentration of deprotonated groups at pH 7.0, the average stability parameter, ($) over bar K, the differential equilibrium function, f(K-DEF), and a parameter, Gamma, proportional to the metal buffer capacity of the system and related to the heterogeneity of the ligand, were calculated. It was concluded that the complexes are labile within the experimental error for the time scale of the techniques; that lead complexes are more stable than cadmium complexes and that the ligand has a more heterogeneous behaviour with respect to lead than to cadmium

Tobacco (Nicotiana tabacum L.) is a tolerant species that accumulates cadmium. We studied the effect of Cd (0, 10, 25, 50, 100 μM) on growth parameters, chlorophyll and proline contents, enzymatic antioxidative response and lipid peroxidation of tobacco plants grown in hydroponic culture for 11 days to clarify the strategy of plant response against oxidative stress caused by this heavy metal. Cadmium accumulated more in roots than in shoots. Plant growth was not significantly affected by the cadmium concentrations used. Young leaves were more affected, showing visible chlorosis and a significant decrease in chlorophyll content at high Cd concentrations. Dry weight of both leaves and roots increased indicating a lower capacity for roots to absorb water. An increase in malondialdehyde levels was observed, indicating that lipid peroxidation occurred as a result of ROS formation. The activity of guaiacol peroxidase in leaves increased, indicating that it was very important in the scavenging of H2O2, while superoxide dismutase activity only increased in old leaves. Ascorbate peroxidase showed constant activity levels in tobacco leaves, suggesting that the ascorbate–glutathione pathway was less important as a defense mechanism.

The kinetics of paralytic shellfish toxins in Mytilus galloprovincialis, previously exposed to Gymnodinium catenatum, was studied under depuration laboratory conditions and over a declining bloom of the dinoflagellate in the field. The variation of the levels observed throughout the laboratory experiment was characterized by a fast depuration of B1, C1 + 2, dcSTX and dcGTX2 + 3, possibly due to the gut evacuation of unassimilated toxins or microalgae cells, or loss during digestive mechanisms. Subsequent enhancements were observed for all compounds with emphasis to dcSTX and dcGTX2 + 3, pointing to biotransformation of the assimilated toxins. Then levels decreased gradually. A first-order depuration kinetic model fitted well to the decrease of B1, C1 + 2 and dcGTX2 + 3 concentrations, but not for dcSTX. Mussels exposed to a declining bloom of Gymnodinium catenatum exhibited a loss of toxins following the same pattern. Despite the low abundance of this dinoflagellate, a similar kinetic model was applied to the field data. The depuration rate of dcGTX2 + 3 in the field experiment (0.153 ± 0.03 day(-1)) significantly exceeded the value calculated in the laboratory (0.053 ± 0.01 day(-1)), while smaller differences were obtained for B1 (0.071 ± 0.02 and 0.048 ± 0.01 day(-1)) and similar values for C1 + 2 (0.082 ± 0.03 and 0.080 ± 0.03 day(-1)). The slower depuration rate of dcGTX2 + 3 in the heavily contaminated mussels at the laboratory may be related to a more effective contribution of C1 + 2 biotransformation.

Ultrasound (US)-assisted extraction has been widely used for metal ion extraction in plants due to its unique properties of decreased extraction time, minimal contamination, low reagent consumption and low cost. However, very few papers present a sound comparison between probe-focussed sonication and conventional stirring in the evaluation of metal ion extraction in plants. In this study, ultrasonic-assisted digestion has been evaluated and compared to magnetic stirring for total copper and cadmium determination by atomic absorption spectrometry in biological samples (plants, plankton and mussels). The same experimental conditions of sample amount and particle size, extractant solution and extraction time were applied for both ultrasound and magnetic stirring-assisted extraction methods in order to truly compare their effect on metal ion solubilisation. To gain further insight in this issue, dried and fresh plants were tested. The results obtained indicated that osmotic tension in cell walls, produced when dried and powdered samples were immersed in the extractant solution, had an important contribution to metal ion solubilisation, the enhancement due to US for the same purpose being negligible.

The effect of cadmium (Cd) on root exudates of sorghum and maize was investigated in order to get further insight into the mechanisms of plant tolerance to Cd. Plants were grown hydroponically and supplemented with: 0, 0.5, and 5.0 mg Cd L− 1. Hydroponic solutions containing exudates were analyzed by high performance liquid chromatography (HPLC). The results showed different exudation patterns by sorghum and maize with cadmium supply. While sorghum enhanced malate exudation over the entire range of applied Cd in the uptake solutions, maize increased mainly citrate. Moreover, malate concentration exuded in sorghum rhizosphere presented higher values than citrate (from maize). With the aid of the HYPERQUAD speciation program, a significant decrease in the bioavailable Cd (free Cd plus Cd chloro-complexes) was found due to the increase of Cd organic complexation in the hydroponic solution. Furthermore, similar metal organic complex concentrations were obtained for both plants, which turned the maize...

The stability constant of ML 2 species for the system lead + nitrilotriacetic acid (NTA) has been determined (log β ML 2 = 17.0 + 0.2) at 25°C in KNO 3 0.1 M from polarographic measurements. The influence of this species was considered in speciation studies of lead in freshwater and seawater conditions, the competition of the Ca 2+ and Mg 2+ ions having been analysed.

A new fast and reproducible approach is described for the application of the enzymatic probe sonication (EPS) methodology [J.L. Capelo, P. Ximenez-Embun, Y. Madrid-Albarran, C. Camara, Anal. Chem. 76 (2004) 233–237] for total selenium determination by electrothermal atomic absorption spectrometry, ET-AAS. Ni(NO3)2 and Pd(NO3)2 were studied as matrix modifiers in conjunction with H2O2, being best results obtained with Pd(NO3)2 plus H2O2. The presence of H2O2 as matrix modifier increases up to 66% the time-life of the graphite tubes, by avoiding the building-up of carbonaceous residues. BCR-414 plankton and ERM-CE 278 mussel tissue reference materials were used for proof-of-the-methodology. Different enzymes, protease XIV, substilisin and trypsin were studied. The use of fresh enzyme was found critical. Good Se recoveries were obtained for oyster tissue, 111%; BCR-414 plankton, 106% and ERM-CE 278 mussel tissue, 93%, when protease XIV was used. Data regarding microwave digestion versus EPS methodology is also presented and discussed.