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Saliva, an easily accessible biofluid, is validated as biomarker of arsenic (As) exposure in several villages of West Bengal, India. Pentavalent arsenic [As(V)] was found to be the predominant species in saliva, with the amount of inorganic As [As(V) and trivalent form, As(III)] being more than half of the total As in the samples. Significant association was found between total daily ingestion of As and As(V) (r = 0.59; p = 0.000), As(III) (r = 0.60; p = 0.000), dimethylarsinous acid (DMA(V)) (r = 0.40; p = 0.000), and monomethylarsonous acid (MMA(V)) (r = 0.44; p = 0.000), implying that these species have mainly been derived from the methylation of the inorganic As in the water that study participants drank and the food they ate. Analysis of confounding effects of age, sex, smoking, body mass index and the prevalence of skin lesion suggests that women and controls with no skin lesion had a higher capacity to methylate the ingested As compared to the rest of the population. Thus, our study demonstrates that As species in saliva can be an useful tool to predict the individual susceptibility where higher As exposure and a lower methylation capacity are implicated in the development of As-induced health effects.
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Arsénico/análisis , Saliva/química , Ácido Cacodílico/análogos & derivados , Ácido Cacodílico/análisis , Cromatografía Líquida de Alta Presión , Femenino , Humanos , India , Modelos Lineales , Masculino , Compuestos Organometálicos/análisisRESUMEN
Saliva is a biological fluid that has not been used extensively as a biomonitoring tool in epidemiological studies. This study presents the arsenic (As) concentrations in saliva and urine samples collected from populations of West Bengal, India who had been previously exposed to high As levels in their drinking water. We found a significant (p < 0.05) association between the Log transformed Daily Ingestion of As (µg day(-1)) and the As concentration in saliva (r = 0.68). Additionally, As concentration of saliva and urine also had a significant positive correlation (r = 0.60, p < 0.05). Male participants, smokers, and cases of skin lesion were independently and significantly associated with an increase in salivary As. Thus our findings show that saliva is a useful biomarker of As exposure in the study population. The study also advocates that measurement of the forms of As in saliva may additionally provide insight into the internal dose and any individual differences in susceptibility to As exposure.
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Arsénico/metabolismo , Exposición a Riesgos Ambientales/análisis , Saliva/metabolismo , Adolescente , Adulto , Anciano , Arsénico/orina , Biomarcadores/metabolismo , Estudios de Casos y Controles , Agua Potable/química , Femenino , Humanos , India , Masculino , Persona de Mediana Edad , Control de Calidad , Análisis de Regresión , Adulto JovenRESUMEN
Selenium (Se) is of key importance to human health with a very narrow concentration range of optimal dietary intake. Due to the inherent analytical challenge linked with the low natural abundance, information on precise and accurate Se speciation in deficient environments is hardly existent. This study presents a novel approach to determine Se species-specifically at ultratraces, by online coupling of a preconcentration (trap) column to an ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) system. It is demonstrated that with this robust and work/time efficient method, the predominant selenium oxyanions, selenite (Se(IV)) and selenate (Se(VI)), can be quantified down to 7.3 and 8.3 picogram total Se, respectively, in an overall analytical time of 420 s, only. The applicability for environmental samples was proven on pristine volcanic ashes collected from seven different volcanoes. The high sensitivity of the novel approach allowed to determine speciation in samples that were strongly depleted in total selenium (<0.05 mg kg(-1) Se) with only minor fractions of Se mobilized (i.e., less than 10% of the total selenium was leached in 10 out of 12 samples). The studied samples showed considerate differences in selenium speciation, with selenite and selenate co-occurring in most samples. The fact that the studied sample leachates had a wide range of pH (3.78-9.55) and major anion/cation composition underlines the versatility and wide potential application range of the method presented.
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Monitoreo del Ambiente/métodos , Espectrometría de Masas/métodos , Sistemas en Línea , Selenio/análisis , Ácido Selénico , Compuestos de Selenio/análisis , Selenito de Sodio/análisisRESUMEN
Background: Ornithine transcarbamylase deficiency (OTCD) is a rare disorder of the urea cycle that obstetricians should be aware of in order to guide management for pregnant carriers of the X-linked gene that causes the condition. Cases: We present the pregnancy management and outcomes of two women with OTCD. The particular manifestations of the disease drive antenatal, intrapartum and postpartum management. Conclusion: Preconception counseling, early prenatal diagnostics and multidisciplinary intrapartum and postpartum management plans contribute to improved outcomes for patients.
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The biogeochemical cycle of arsenic (As) has been extensively studied over the past decades because As is an environmentally ubiquitous, nonthreshold carcinogen, which is often elevated in drinking water and food. It has been known for over a century that micro-organisms can volatilize inorganic As salts to arsines (arsine AsH(3), mono-, di-, and trimethylarsines, MeAsH(2), Me(2)AsH, and TMAs, respectively), but this part of the As cycle, with the exception of geothermal environs, has been almost entirely neglected because of a lack of suited field measurement approaches. Here, a validated, robust, and low-level field-deployable method employing arsine chemotrapping was used to quantify and qualify arsines emanating from soil surfaces in the field. Up to 240 mg/ha/y arsines was released from low-level polluted paddy soils (11.3 ± 0.9 mg/kg As), primarily as TMAs, whereas arsine flux below method detection limit was measured from a highly contaminated mine spoil (1359 ± 212 mg/kg As), indicating that soil chemistry is vital in understanding this phenomenon. In microcosm studies, we could show that under reducing conditions, induced by organic matter (OM) amendment, a range of soils varied in their properties, from natural upland peats to highly impacted mine-spoils, could all volatilize arsines. Volatilization rates from 0.5 to 70 µg/kg/y were measured, and AsH(3), MeAsH(2), Me(2)AsH, and TMAs were all identified. Addition of methylated oxidated pentavalent As, namely monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), to soil resulted in elevated yearly rates of volatilization with up to 3.5% of the total As volatilized, suggesting that the initial conversion of inorganic As to MMAA limits the rate of arsine and methylarsines production by soils. The nature of OM amendment altered volatilization quantitatively and qualitatively, and total arsines release from soil showed correlation between the quantity of As and the concentration of dissolved organic carbon (DOC) in the soil porewater. The global flux of arsines emanating from soils was estimated and placed in the context of As atmospheric inputs, with arsines contributing from 0.9 to 2.6% of the global budget.
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Contaminantes Atmosféricos/análisis , Arsenicales/análisis , Contaminantes del Suelo/análisis , Monitoreo del Ambiente , Suelo/químicaRESUMEN
Synchrotron radiation-induced micro-X-ray analysis were applied to characterize the newly formed phases that precipitate in a passive treatment system using magnesium oxide to remove high concentrations of zinc (ca. 440 mg/L) and other minor metals from neutral pretreated waters in the Iberian Pyrite Belt (SW Iberian Peninsula). Micro-X-ray fluorescence (µ-XRF) maps of polished samples were used to find spatial correlations among metals, pinpointing zones of interest where micro-X-ray diffraction (µ-XRD) data were exploited to identify the mineral phases responsible for metal retention. This coupled technique identified hydrozincite (Zn(5)(CO(3))(2)(OH)(6)) and minor loseyite ((Mn,Zn)(7)(CO(3))(2)(OH)(10)) as the mineral sinks for Zn and also other potentially toxic elements such as Co and Ni. Although hydrozincite retains traces of Mn, this metal is mainly retained by precipitation of loseyite. The precipitation of zinc hydroxy-carbonates and their ability to uptake other metals (Mn, Co, and Ni) is hence of potential interest not only for the treatment of contaminated waters but also for the generation of a solid waste that could be exploited as a new Zn economic resource.
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Residuos Industriales/análisis , Óxido de Magnesio/química , Metales/química , Minería , Eliminación de Residuos Líquidos/métodos , Compuestos de Zinc/química , Precipitación Química , Metales/análisis , Silicio/análisis , Espectrometría por Rayos X , Sincrotrones , Difracción de Rayos XRESUMEN
In the present study, we investigated the possibilities and drawbacks of hollow fiber liquid phase microextraction (HF-LPME) combined with total reflection X-ray fluorescence (TXRF) spectrometry for the determination of low amounts of inorganic arsenic (As) species in water samples. The obtained results showed that a three-phase HF-LPME system was more suitable to be used in combination with TXRF than the two phase configuration, since lower detection limit and better precision for As determination can be attained. Relevant experimental parameters affecting As extraction (i.e. types of extractant, organic solvent, agitation speed, pH and extraction time) and TXRF analysis (deposition volume and drying mode) were systematically evaluated. It was found that As(III) was more efficiently extracted at pH 13, whereas, optimum pH for As(V) extraction was at pH 8.5. Limits of detection (LOD) achieved using the best analytical conditions meet the requirements of current legislation and allow the determination of inorganic As(V) and As(III) in water. The proposed method was also applied to different spiked environmental water samples for the preconcentration and subsequent determination of trace inorganic As species.
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The ability of gypsum, a common sulfate mineral, to host arsenic atoms in its crystalline structure, is demonstrated through experimental structural studies of the solid solutions formed upon synthetic coprecipitation of gypsum (CaSO4 x 2 H2O) and arsenic. Neutron and X-ray diffraction methods show an enlargement of the gypsum unit cell proportional to the concentration of arsenic in the solids and to the pH solution value. The substitution of sulfate ions (SO4(2-)) by arsenate ions is shown to be more likely under alkaline conditions, where the HAsO4(2-) species predominates. A theoretical Density Functional Theory model of the arsenic-doped gypsum structure reproduces the experimental volume expansion. Extended X-ray Absorption Fine Structure (EXAFS) measurements of the local structure around the arsenic atom in the coprecipitated solids confirm solid state substitution and allow some refinement of the local structure, corroborating the theoretical structure found in the simulations. The charge redistribution within the structure upon substitutions of either the protonated or the unprotonated arsenate species studied by means of Mulliken Population Analyses demonstrates an increase in the covalency in the interaction between Ca(2+) and AsO4(3-), whereas the interaction between Ca(2+) and HAsO4(2-) remains predominantly ionic.
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Arseniatos/química , Sulfato de Calcio/química , Modelos Moleculares , Difracción de Neutrones , Difracción de Rayos X , Conformación Molecular , Protones , Electricidad EstáticaRESUMEN
Introduction: the perception of individuals about their own health is a strong indicator of their real state, as well as their behaviors related to the prognosis in case of presence of pathologies, besides being proportional to their motivations to acquire healthy habits. Objective: to describe the motivations of overweight adolescents when participating in a multidisciplinary health promotion program and their perceptions about habits related to physical and emotional well-being. Methods: this is a qualitative study, using the Bardin content analysis technique. The tool used for data collection was the semi-structured interview, analyzed with the help of the software QSR NVivo 11 through grouping of the speech into clusters. These in turn were evaluated in three categories: (1) motivation; (2) food; and (3) physical exercise. Results: the average age of the participants was 13.8 ± 2.4, with an average body mass index of 31.8 ± 8.5 kg/m². Regarding family income, 41.66% had monthly income of 3 to 6 minimum wages. Regarding the educational level of parents, 70.83% of mothers had completed higher education, while 29.16% had completed high school. According to the respondents' answers, the greatest motivation to participate in a multidisciplinary obesity treatment program was weight loss. In category 2, it was observed that adolescents associated the act of eating with feelings such as anxiety and nervousness. In category 3, the impact of the pandemic was found under the modalities of physical exercise practiced. Conclusion: the results prove the importance of understanding the perception of adolescents about their own health and related habits, in order to elaborate effective strategies for health promotion and consequent improvement of the quality of life of these individuals.
Introdução: a percepção dos indivíduos a respeito da própria saúde é um forte indicador do seu real estado, bem como dos seus comportamentos relativos ao prognóstico em caso de presença de patologias, além de ser proporcional às suas motivações para adquirir hábitos saudáveis. Objetivo: descrever as motivações de adolescentes acima do peso ao participarem de um programa multidisciplinar de promoção da saúde e suas percepções a respeito de hábitos relacionados ao bem estar físico e emocional. Métodos: trata-se de estudo de abordagem qualitativa, com emprego da técnica de análise de conteúdo de Bardin. A ferramenta utilizada para coleta de dados foi a entrevista semiestruturada, analisada com auxílio do software QSR NVivo 11 através de agrupamento das falas em clusters. Esses por sua vez foram avaliados em três categorias: (1) motivação; (2) alimentação; e (3) exercício físico. Resultados: a idade média dos participantes foi de 13,8 ± 2,4, com índice de massa corporal médio de 31,8 kg/m² ± 8,5. Em relação à renda familiar, 41,66% apresentaram renda mensal de 3 a 6 salários mínimos. No que tange à escolaridade dos responsáveis, 70,83% das mães possuíam o ensino superior completo, enquanto 29,16% possuíam ensino médio completo. De acordo com as respostas dos entrevistados a maior motivação para participarem de um programa multidisciplinar de tratamento da obesidade foi o emagrecimento. Já na categoria 2 observou-se que os adolescentes associaram o ato de comer com sentimentos como a ansiedade e o nervosismo. Na categoria 3, constatou-se o impacto da pandemia sob as modalidades de exercício físico praticados. Conclusão: os resultados comprovam a importância de entender a percepção dos adolescentes a respeito da própria saúde e hábitos relacionados, a fim de elaborar de estratégias efetivas para promoção da saúde e consequente, melhoria da qualidade de vida desses indivíduos.
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Introduction: there is evidence that multidisciplinary interventions are an efficient approach to achieving weight loss and other health-related goals. However, dropout rates of these programs are high among adolescents. The suggestion is that understanding the motivation of individuals to participate in these projects is fundamental to developing strategies for permanence and, consequently, promoting better results.Objective: the main aim of this study was to describe the motivations of overweight adolescents participating in a multidisciplinary health promotion project.Methods: this qualitative study was conducted from March to July 2021 using the Bardin content analysis technique. The tool used for data collection was the semi-structured interview, analyzed means by the software QSR NVivo 11 by grouping the speech into clusters. These, in turn, were evaluated in three categories: (1) motivation, (2) food, and (3) physical exercise.Results: the age of the participants was 13.8 ± 2.4 years old, with body mass index of 31.8 ± 8.5 kg/m². Regarding family income, 41.66% had a monthly payment of 3 to 6 minimum wages. Regarding parents' educational level, 70.83% of mothers had completed higher education, while 29.16% had completed high school. According to the respondent's answers, weight loss was the greatest motivation to participate in a multidisciplinary obesity treatment program. In category 2, it was observed that adolescents associated the act of eating with feelings such as anxiety and nervousness. In category 3, the impact of the pandemic was found under the modalities of physical exercise practiced.Conclusion: the results describe the motivation of overweight adolescents to participate in a multidisciplinary program, in addition to elucidating participants' perception of their health and related habits, strategies for health promotion, and consequent improvement of the quality of life of these individuals.
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Dissolved organic carbon (DOC) and Fe mineral phases are known to influence the mobility of arsenic (As) in groundwater. Arsenic can be associated with colloidal particles containing organic matter and Fe. Currently, no data is available on the dissolved phase/colloidal association of As in groundwater of alluvial aquifers in West Bengal, India. This study investigated the fractional distribution of As (and other metals/metalloids) among the particulate, colloidal and dissolved phases in groundwater to decipher controlling behavior of organic and inorganic colloids on As mobility. The result shows that 83-94% of As remained in the 'truly dissolved' phases (i.e., <0.05 µm size). Strong positive correlation between Fe and As (r(2) between 0.65 and 0.94) is mainly observed in the larger (i.e., >0.05 µm size) colloidal particles, which indicates the close association of As with larger Fe-rich inorganic colloids. In smaller (i.e., <0.05 µm size) colloidal particles strong positive correlation is observed between As and DOC (r(2)=0.85), which highlights the close association of As with smaller organic colloids. As(III) is mainly associated with larger inorganic colloids, whereas, As(V) is associated with smaller organic/organometallic colloids. Scanning Electron Microscopy and Energy Dispersive X-ray spectroscopy confirm the association of As with DOC and Fe mineral phases suggesting the formation of dissolved organo-Fe complexes and colloidal organo-Fe oxide phases. Attenuated total reflectance-Fourier transform infrared spectroscopy further confirms the formation of As-Fe-NOM organometallic colloids, however, a detailed study of these types of colloids in natural waters is necessary to underpin their controlling behavior.
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Arsénico/análisis , Coloides/química , Agua Potable/química , Agua Subterránea/química , Contaminantes Químicos del Agua/análisis , Arsénico/química , Filtración , India , Hierro/química , Microscopía Electrónica de Rastreo , Tamaño de la Partícula , Espectrometría por Rayos X , Espectrofotometría Atómica , Espectroscopía Infrarroja por Transformada de FourierRESUMEN
Recent technological improvements have led to the widespread adoption of field portable energy dispersive X-ray fluorescence (FP-XRF) by governmental agencies, environmental consultancies and research institutions. FP-XRF units often include analysis modes specifically designed for the quantification of trace elements in soils. Using these modes, X-ray tube based FP-XRF units can offer almost "point and shoot" ease of use and results comparable to those of laboratory based instruments. Nevertheless, FP-XRF analysis is sensitive to spectral interferences as well as physical and chemical matrix effects which can result in decreased precision and accuracy. In this study, an X-ray tube-based FP-XRF analyser was used to determine trace (low ppm) concentrations of As in a floodplain soil. The effect of different sample preparation and analysis conditions on precision and accuracy were systematically evaluated. We propose strategies to minimise sources of error and maximise data precision and accuracy, achieving in situ limits of detection and precision of 6.8 ppm and 14.4%RSD, respectively for arsenic. We demonstrate that soil moisture, even in relatively dry soils, dramatically affects analytical performance with a signal loss of 37% recorded for arsenic at 20 wt% soil moisture relative to dry soil. We also highlight the importance of the use of certified reference materials and independent measurement methods to ensure accurate correction of field values.
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Arsénico/análisis , Contaminantes del Suelo/análisis , Espectrometría por Rayos X , Algoritmos , Calibración , Monitoreo del Ambiente/métodos , Francia , Hierro/análisis , Manganeso/análisis , Espectrometría de Masas , Tamaño de la Partícula , Fotones , Análisis de Regresión , Reproducibilidad de los Resultados , Suelo , Temperatura , Agua/químicaRESUMEN
Arsenic contamination of floodplain soils is extensive and additional fresh arsenic inputs to the pedosphere from human activities are ongoing. We investigate the cumulative effects of repetitive soil redox cycles, which occur naturally during flooding and draining, on a calcareous fluvisol, the native microbial community and arsenic mobility following a simulated contamination event. We show through bioreactor experiments, spectroscopic techniques and modelling that repetitive redox cycling can decrease arsenic mobility during reducing conditions by up to 45%. Phylogenetic and functional analyses of the microbial community indicate that iron cycling is a key driver of observed changes to solution chemistry. We discuss probable mechanisms responsible for the arsenic immobilisation observed in-situ. The proposed mechanisms include, decreased heterotrophic iron reduction due to the depletion of labile particulate organic matter (POM), increases to the proportion of co-precipitated vs. aqueous or sorbed arsenic with α-FeOOH/Fe(OH)3 and potential precipitation of amorphous ferric arsenate.
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Arsénico/química , Inundaciones , Contaminantes del Suelo/química , Suelo/química , Arsénico/análisis , Reactores Biológicos , Carbonato de Calcio/análisis , Carbonato de Calcio/química , Oxidación-Reducción , Contaminantes del Suelo/análisisRESUMEN
A comparative hydrogeochemical study was carried out in West Bengal, India covering three physiographic regions, Debagram and Chakdaha located in the Bhagirathi-Hooghly alluvial plain and Baruipur in the delta front, to demonstrate the control of geogenic and anthropogenic influences on groundwater arsenic (As) mobilization. Groundwater samples (n = 90) from tube wells were analyzed for different physico-chemical parameters. The low redox potential (Eh = -185 to -86 mV) and dominant As(III) and Fe(II) concentrations are indicative of anoxic nature of the aquifer. The shallow (<100 m) and deeper (>100 m) aquifers of Bhagirathi-Hooghly alluvial plains as well as shallow aquifers of delta front are characterized by Ca(2+)HCO3(-) type water, whereas Na(+) and Cl(-) enrichment is found in the deeper aquifer of delta front. The equilibrium of groundwater with respect to carbonate minerals and their precipitation/dissolution seems to be controlling the overall groundwater chemistry. The low SO4(2-) and high DOC, PO4(3-) and HCO3(-) concentrations in groundwater signify ongoing microbial mediated redox processes favoring As mobilization in the aquifer. The As release is influenced by both geogenic (i.e. geomorphology) and anthropogenic (i.e. unsewered sanitation) processes. Multiple geochemical processes, e.g., Fe-oxyhydroxides reduction and carbonate dissolution, are responsible for high As occurrence in groundwaters.
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Agua Subterránea/análisis , Agua Subterránea/química , Purificación del Agua/métodos , Arsénico/química , Carbono/química , Carbonatos/química , Catálisis , Monitoreo del Ambiente/métodos , Compuestos Ferrosos/química , Agua Dulce/química , Geografía , Sedimentos Geológicos , Geología , Hidróxidos/química , India , Hierro/química , Oxidación-Reducción , Oxígeno/química , Lluvia , Ríos , Estaciones del Año , Termodinámica , Contaminantes Químicos del Agua/análisisRESUMEN
The global impact on public health of elevated arsenic (As) in water supplies is highlighted by an increasing number of countries worldwide reporting high As concentrations in drinking water. In Latin America, the problem of As contamination in water is known in 14 out of 20 countries: Argentina, Bolivia, Brazil, Chile, Colombia, Cuba, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Peru and Uruguay. Considering the 10 µg/L limit for As in drinking water established by international and several national agencies, the number of exposed people is estimated to be about 14 million. Health effects of As exposure were identified for the first time already in the 1910s in Bellville (Córdoba province, Argentina). Nevertheless, contamination of As in waters has been detected in 10 Latin American countries only within the last 10 to 15 years. Arsenic is mobilized predominantly from young volcanic rocks and their weathering products. In alluvial aquifers, which are water sources frequently used for water supply, desorption of As from metal oxyhydroxides at high pH (>8) is the predominant mobility control; redox conditions are moderate reducing to oxidizing and As(V) is the predominant species. In the Andes, the Middle American cordillera and the Transmexican Volcanic Belt, oxidation of sulfide minerals is the primary As mobilization process. Rivers that originate in the Andean mountains, transport As to more densely populated areas in the lowlands (e.g. Rímac river in Peru, Pilcomayo river in Bolivia/Argentina/Paraguay). In many parts of Latin America, As often occurs together with F and B; in the Chaco-Pampean plain As is found additionally with V, Mo and U whereas in areas with sulfide ore deposits As often occurs together with heavy metals. These co-occurrences and the anthropogenic activities in mining areas that enhance the mobilization of As and other pollutants make more dramatic the environmental problem.
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Arsénico/toxicidad , Exposición a Riesgos Ambientales , Humanos , América Latina , Medición de Riesgo , Abastecimiento de AguaRESUMEN
Speciation plays a crucial role in elemental mobility. However, trace level selenium (Se) speciation analyses in aqueous samples from acidic environments are hampered due to adsorption of the analytes (i.e. selenate, selenite) on precipitates. Such solid phases can form during pH adaptation up till now necessary for chromatographic separation. Thermodynamic calculations in this study predicted that a pH<4 is needed to prevent precipitation of Al and Fe phases. Therefore, a speciation method with a low pH eluent that matches the natural sample pH of acid rain-soil interaction samples from Etna volcano was developed. With a mobile phase containing 20mM ammonium citrate at pH 3, selenate and selenite could be separated in different acidic media (spiked water, rain, soil leachates) in <10 min with a LOQ of 0.2 µg L(-1) using (78)Se for detection. Applying this speciation analysis to study acid rain-soil interaction using synthetic rain based on H(2)SO(4) and soil samples collected at the flanks of Etna volcano demonstrated the dominance of selenate over selenite in leachates from samples collected close to the volcanic craters. This suggests that competitive behavior with sulfate present in acid rain might be a key factor in Se mobilization. The developed speciation method can significantly contribute to understand Se cycling in acidic, Al/Fe rich environments.
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Lluvia Ácida , Compuestos de Selenio/química , Selenito de Sodio/química , Suelo , Cromatografía Líquida de Alta Presión , Ácido Cítrico/química , Concentración de Iones de Hidrógeno , Hierro/química , Espectrometría de Masas , Compuestos de Amonio Cuaternario/química , Ácido Selénico , Termodinámica , Erupciones VolcánicasRESUMEN
The structural parameters of Hg2+ hydration were studied in 0.225 mol/L solutions of Hg2+ in DNO3/D2O by means of neutron diffraction with isotopic substitution of 199Hg for natHg. It was found that Hg2+ is hydrated by a first solvation shell of six water molecules. The observed Hg-O and Hg-H distances are equal to 2.48+/-0.05 and 3.08+/-0.05 A, respectively. The angle phi between the plane of the water molecule and the cation-water oxygen axis is approximately 35 degrees . The solvation of Hg2+ therefore mimics very closely that of Ca2+ (the Ca-O and Ca-H distances are 2.40 and 3.03 A, respectively) and helps to account for the extreme toxicity of mercury(II). We note also that the Hg-O distance obtained in the neutron diffraction experiment is larger by approximately 0.1 A than that obtained by X-ray diffraction. This difference is consistent with a shift of the oxygen electron density toward the mercury cation due to the covalency of the Hg-O interaction.