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1.
J Environ Manage ; 254: 109768, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31698298

RESUMO

Geochemical behavior of arsenic (As) in rice paddy soils determines the availability and mobility of As in the soils, but little is known about the long-term effects of paddy rice cultivation on As speciation in the soils. In this study, surface soil samples were collected from a rice paddy land and its adjacent dry land with similar soil properties and known cultivation histories. The soils of the paddy land and dry land contained 378 and 423 mg As kg-1, respectively. The predominant As species in the soils were investigated using As K-edge X-ray absorption spectroscopy (XAS) in combination with two sequential chemical fractionation methods. The XAS results showed that the predominant As species in the soils were As(III)- and As(V)-ferrihydrite, As(V)-goethite and scorodite. In comparison to the dry land soil, the paddy land soil contained a higher proportion of As(V)-ferrihydrite and a lower proportion of scorodite. The results of chemical fractionation revealed that As in the paddy land soil was more labile than that in the dry land soil. It is therefore suggested that long-term rice cultivation enhances the mobility and availability of As in paddy soils.


Assuntos
Arsênico , Oryza , Poluentes do Solo , Solo , Espectroscopia por Absorção de Raios X
2.
Nat Commun ; 10(1): 4758, 2019 10 18.
Artigo em Inglês | MEDLINE | ID: mdl-31628305

RESUMO

The outermost surface of insect cuticle is a high-performance interface that provides wear protection, hydration, camouflage and sensing. The complex and inhomogeneous structure of insect cuticle imposes stringent requirements on approaches to elucidate its molecular structure and surface chemistry. Therefore, a molecular understanding and possible mimicry of the surface of insect cuticle has been a challenge. Conventional optical and electron microscopies as well as biochemical techniques provide information about morphology and chemistry but lack surface specificity. We here show that a near edge X-ray absorption fine structure microscope at the National Synchrotron Light Source can probe the surface chemistry of the curved and inhomogeneous cuticle of the African flower scarab. The analysis shows the distribution of organic and inorganic surface species while also hinting at the presence of aragonite at the dorsal protrusion region of the Eudicella gralli head, in line with its biological function.


Assuntos
Escamas de Animais/química , Besouros/química , Espectroscopia por Absorção de Raios X/métodos , Escamas de Animais/anatomia & histologia , Escamas de Animais/ultraestrutura , Animais , Besouros/anatomia & histologia , Besouros/ultraestrutura , Feminino , Flores/parasitologia , Proteínas de Insetos/análise , Proteínas de Insetos/ultraestrutura , Microscopia Eletrônica de Varredura , Propriedades de Superfície , Síncrotrons
3.
J Agric Food Chem ; 67(44): 12172-12181, 2019 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-31609615

RESUMO

Understanding the mechanisms of absorption and transport of foliar nutrition is a key step towards the development of advanced fertilization methods. This study employed X-ray fluorescence (XRF) and X-ray absorption near edge spectroscopy (XANES) to trace the in vivo absorption and transport of ZnO and ZnSO4(aq) to soybean leaves (Glycine max). XRF maps monitored over 48 h showed a shape change of the dried ZnSO4(aq) droplet, indicating Zn2+ absorption. Conversely, these maps did not show short movement of Zn from ZnO. XRF measurements on petioles of leaves that received Zn2+ treatments clarified that the Zn absorption and transport in the form of ZnSO4(aq) was faster that of ZnO. Solubility was the major factor driving ZnSO4(aq) absorption. XANES speciation showed that in planta Zn is transported coordinated with organic acids. Because plants demand Zn during their entire lifecycle, the utilization of sources with different solubilities can increase Zn use efficiency.


Assuntos
Soja/metabolismo , Espectrometria de Fluorescência/métodos , Espectroscopia por Absorção de Raios X/métodos , Zinco/análise , Zinco/metabolismo , Transporte Biológico , Fertilizantes/análise , Folhas de Planta/química , Folhas de Planta/metabolismo , Soja/química
4.
Environ Sci Technol ; 53(21): 12416-12424, 2019 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-31553176

RESUMO

Iodine-129 is one of three key risk drivers at several US Department of Energy waste management sites. Natural organic matter (NOM) is thought to play important roles in the immobilization of aqueous iodide (I-) and iodate (IO3-) in the environment, but molecular interactions between NOM and iodine species are poorly understood. In this work, we investigated iodine and carbon speciation in three humic acid (HA)-I systems using I K-edge XANES and EXAFS and C K-edge XANES spectroscopy: (1) I- in the presence of laccase (an oxidase enzyme) and a mediator, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in a pH 4 buffer, (2) I- in the presence of lactoperoxidase (LPO) and H2O2 in a pH 7 buffer, and (3) IO3- in a pH 3 groundwater. Both oxidase and peroxidase systems could oxidize I- to I2 or hypoiodide (HOI) leading to organo-I formation. However, the laccase-ABTS mediator was the most effective and enhanced I- uptake by HA up to 13.5 mg/g, compared to 1.9 mg/g for the LPO-H2O2. IO3- was abiotically reduced to I2 or HOI leading to an organo-I formation. Pathways for HA iodination include covalent modification of aromatic-type rings by I2 / HOI or iodine incorporation into newly formed benzoquinone species arising from the oxidation of phenolic C species. This study improves our molecular-level understanding of NOM-iodine interactions and stresses the important role that mediators may play in the enzymatic reactions between iodine and NOM.


Assuntos
Iodetos , Iodo , Substâncias Húmicas , Peróxido de Hidrogênio , Oxirredução , Espectroscopia por Absorção de Raios X
5.
Chemosphere ; 237: 124489, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31549638

RESUMO

The present study provides the starch-mediated carbothermal preparation of magnetic-responsible ferrihydrite (MFHP) based on Fe-rich precipitates which is recovered by mine drainage for immobilization of arsenate and antimonate in water. Fe K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) represented partial transformation from ferrihydrite to magnetite in MFHP due to the carbothermal reduction process, resulting in an effective saturation magnetism (= 19.2 emu/g). As and Sb K-edge EXAFS revealed that arsenate ion combines onto the surface of MFHP as inner-sphere binuclear bidentate surface complex, and antimonate forms inner-sphere mononuclear bidentate complex. In addition, the leachability by toxicity characteristic leaching procedure (TCLP) implies the environmental friendly preparation method for preparing magnetic-responsible adsorbents using mining waste.


Assuntos
Antimônio/química , Arseniatos/química , Adsorção , Compostos Férricos/química , Óxido Ferroso-Férrico , Imobilização , Mineração , Análise Espectral/métodos , Espectroscopia por Absorção de Raios X , Raios X
6.
Environ Pollut ; 254(Pt B): 113112, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31479811

RESUMO

Antimony, as the Sb(V) species, often occurs in oxic soils and sediments as coprecipitates with poorly-crystalline Fe(III)-bearing minerals. It is common for these Sb(V)-Fe(III) coprecipitates to also contain varying quantities of co-occurring humic acid (HA). When exposed to reducing conditions, the production of Fe(II) may cause the initial metastable HA-Sb(V)-Fe(III) phases to undergo rapid transformations to more stable phases, thereby potentially influencing the geochemical behavior of coprecipitated Sb(V). However, little is known about the impacts of this transformation on the mobility and speciation of Sb. In this study, we reacted synthetic HA-Sb(V)-Fe(III) coprecipitates (Fe:Sb ratio = 4, and C:Fe molar ratios = 0, 0.3, 0.8 and 1.3) with 0, 1 or 10 mM Fe(II) under O2-free conditions at pH 7.0 for 15 days. Fe K-edge EXAFS spectroscopy revealed that solid-phase Fe(III) in the initial coprecipitates contained a mixture of ∼4/5 ferrihydrite (Fe10O14(OH)2) and ∼1/5 tripuhyite (FeSbO4), regardless of the corresponding amount of coprecipitated HA. Tripuhyite persisted throughout the full experiment duration, while ferrihydrite was partially replaced by goethite (FeOOH) when either 1 or 10 mM Fe(II)aq was added to the coprecipitates. The greatest level of goethite formation (∼55% of solid-phase Fe) was observed in the HA-free/10 mM Fe(II)aq treatment, with ferrihydrite transformation being partially attenuated at higher levels of HA. Mobilisation of aqueous Sb was the greatest for 1 mM Fe(II) treatments at high HA:Fe ratios. Sb K-edge XANES spectroscopy showed that the largest reduction of Sb(V) to Sb(III) (∼37%) and the greatest repartitioning of Sb to the mineral surface (∼7.9-9.8%) occurred in the coprecipitates with the highest HA contents in the presence of 10 mM Fe(II). The results indicate that the amount of HA in HA-Sb(V)-Fe(III) coprecipitates can greatly influence mobility and speciation of Sb in Fe(II)-rich conditions. The results of this study provide new insights into alterations in Sb mobility and retention in response to Fe cycling under organic matter-rich reducing conditions.


Assuntos
Antimônio/química , Compostos Férricos/química , Compostos Ferrosos/química , Substâncias Húmicas , Poluentes do Solo/química , Compostos de Ferro/química , Minerais/química , Oxirredução , Espectroscopia por Absorção de Raios X
7.
Environ Sci Technol ; 53(17): 10131-10138, 2019 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-31418551

RESUMO

Acid-soluble soil phosphorus (P) is a potential resource in P-limited agricultural systems that may become critical as global P sources decrease in the future. The fate of P in three alkaline Vertisols, a major agricultural soil type, after acidic incubation was investigated using synchrotron-based K-edge X-ray absorption near-edge structure (XANES) spectroscopy, geochemical modeling, wet chemistry soil extraction, and a P sorption index. Increases in labile P generally coincided with decreased stability and dissolution of calcium phosphate (CaP) minerals. However, only a minor proportion of the CaP dissolved in each soil was labile. In two moderate-P soils (800 mg P kg-1), XANES indicated that approximately 160 mg kg-1 was repartitioned to sorbed phases at pH 5.1 of one soil and at pH 4.4 of the second; however, only 40 and 28% were labile, respectively. In a high-P soil (8900 mg P kg-1), XANES indicated a decrease in P of 1170 mg kg-1 from CaP minerals at pH 3.8, of which approximately only 33% was labile. Phosphorus mobilized by agricultural practices without concurrent uptake by plants may be repartitioned to sorbed forms that are not as plant-available as prior to acidification.


Assuntos
Poluentes do Solo , Solo , Agricultura , Fosfatos de Cálcio , Fosfatos , Fósforo , Espectroscopia por Absorção de Raios X
8.
Environ Sci Technol ; 53(19): 11486-11495, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31460750

RESUMO

Lead (Pb) exposure from household dust is a major childhood health concern because of its adverse impact on cognitive development. This study investigated the absorption kinetics of Pb from indoor dust following a single dose instillation into C57BL/6 mice. Blood Pb concentration (PbB) was assessed over 24 h, and the dynamics of particles in the lung and gastro-intestinal (GI) tract were visualized using X-ray fluorescence (XRF) microscopy. The influence of mineralogy on Pb absorption and particle retention was investigated using X-ray absorption near-edge structure spectroscopy. A rapid rise in PbB was observed between 0.25 and 4 h after instillation, peaking at 8 h and slowly declining during a period of 24 h. Following clearance from the lungs, Pb particles were detected in the stomach and small intestine at 4 and 8 h, respectively. Analysis of Pb mineralogy in the residual particles in tissues at 8 h showed that mineral-sorbed Pb and Pb-phosphates dominated the lung, while organic-bound Pb and galena were the main phases in the small intestines. This is the first study to visualize Pb dynamics in the lung and GI tract using XRF microscopy and link the inhalation and ingestion pathways for metal exposure assessment from dust.


Assuntos
Poeira , Animais , Disponibilidade Biológica , Camundongos , Camundongos Endogâmicos C57BL , Espectroscopia por Absorção de Raios X , Raios X
9.
Environ Sci Technol ; 53(18): 10723-10731, 2019 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-31436974

RESUMO

Arsenic (As) is reported to be effectively sorbed onto natural organic matter (NOM) via thiol coordination and polyvalent metal cation-bridged ternary complexation. However, the extent of sorption via complexation with oxygen-containing functional groups of NOM is poorly understood. By equilibrating arsenite, arsenate, and monothioarsenate with purified model-peat, followed by As K-edge X-ray absorption spectroscopic analysis, this study shows that complexation with oxygen-containing functional groups can be an additional or alternative mode of As sorption to NOM. The extent of complexation was highest for arsenite, followed by monothioarsenate and arsenate. Complexation was higher at pH 7.0 compared to 4.5 for arsenite and arsenate and vice versa for monothioarsenate because of partial transformation to arsenite at pH 4.5. Modeling of the As K-edge extended X-ray absorption fine structure data revealed that As···C interatomic distances were relatively longer in arsenate- (2.83 ± 0.01 Å) and monothioarsenate-treated peat (2.80 ± 0.02 Å) compared to arsenite treatments (2.73 ± 0.01 Å). This study suggests that arsenite was predominantly complexed with carboxylic groups, whereas arsenate and monothioarsenate were complexed with alcoholic groups of the peat. This study further implies that in systems, where NOM is the major sorbent, arsenate and monothioarsenate can have higher mobility than arsenite.


Assuntos
Arsênico , Arsenitos , Arseniatos , Oxigênio , Espectroscopia por Absorção de Raios X
10.
Environ Sci Technol ; 53(17): 10208-10217, 2019 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-31390183

RESUMO

Peat layers within alluvial sediments are considered effective arsenic (As) sinks under reducing conditions due to the binding of As(III) to thiol groups in natural organic matter (NOM) and the formation of As-bearing sulfide phases. However, their possible role as sources of As for anoxic groundwaters remains unexplored. Here, we perform laboratory experiments to provide evidence for the role of a sediment peat layer in releasing As. Our results show that the peat layer, deposited about 8,000 years ago in a paleomangrove environment in the nascent Mekong Delta, could be a source of As to porewater under reducing conditions. X-ray absorption spectroscopy (XAS) analysis of the peat confirmed that As was bound to NOM thiol groups and incorporated into pyrite. Nitrate was detected in peat layer porewater, and flow-through and batch experiments evidenced the release of As from NOM and pyrite in the presence of nitrate. Based on poisoning experiments, we propose that the microbially mediated oxidation of arsenic-rich pyrite and organic matter coupled to nitrate reduction releases arsenic from this peat. Although peat layers have been proposed as As sinks in earlier studies, we show here their potential to release depositional- and/or diagenetically-accumulated As.


Assuntos
Arsênico , Água Subterrânea , Poluentes Químicos da Água , Sedimentos Geológicos , Oxirredução , Solo , Espectroscopia por Absorção de Raios X
11.
Environ Sci Process Impacts ; 21(9): 1459-1476, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31353376

RESUMO

We investigated the impact of aging-induced structural modifications of carbonate green rust (GR), a mixed valent Fe(ii,iii) (hydr)oxide with a high oxyanion sorption affinity, on the partitioning and binding mode of arsenic (As). Suspensions of carbonate GR were produced in the presence of As(v) or As(iii) (i.e. co-precipitated with As(iii) or As(v)) and aged in anoxic and oxic conditions for up to a year. We tracked aqueous As over time and characterized the solid phase by X-ray absorption spectroscopy (XAS). In experiments with initial As(v) (4500 µg L-1, As/Fe = 2 mol%), the fresh GR suspension sorbed >99% of the initial As, resulting in approximately 14 ± 8 µg L-1 residual dissolved As. Anoxic aging of the As(v)-laden GR for a month increased aqueous As to >60 µg L-1, which was coupled to an increase in GR structural order revealed by Fe K-edge XAS. Further anoxic aging up to a year transformed As(v)-laden GR into magnetite and decreased significantly the aqueous As to <2 µg L-1. The As binding mode was also modified during GR transformation to magnetite from sorption to GR particle edges to As substitution for tetrahedral Fe in the magnetite structure. These GR structural modifications altered the ratio of As partitioning to the solid (µg As/mg Fe) and liquid (µg As per L) phase from 2.0 to 0.4 to 14 L mg-1 for the fresh, month, and year aged suspensions, respectively. Similar trends in GR transformation and As partitioning during anoxic aging were observed for As(iii)-laden suspensions, but occurred on more rapid timescales: As(iii)-laden GR transformed to magnetite after a day of anoxic aging. In oxic aging experiments, rapid GR oxidation by dissolved oxygen to Fe(iii) precipitates required only an hour for both As(v) and As(iii) experiments, with lepidocrocite favored in As(v) experiments and hydrous ferric oxide favored in As(iii) experiments. Aqueous As during GR oxidation decreased to <10 µg L-1 for both As(v) and As(iii) series. Knowledge of this interdependence between GR aging products and oxyanion fate improves biogeochemical models of contaminant and nutrient dynamics during Fe cycling and can be used to design more effective arsenic remediation strategies that rely on arsenic sorption to GR.


Assuntos
Arseniatos/análise , Arsenitos/análise , Poluentes Ambientais/análise , Óxido Ferroso-Férrico/química , Arseniatos/química , Arsenitos/química , Poluentes Ambientais/química , Hidróxidos/química , Oxirredução , Oxigênio/química , Fatores de Tempo , Espectroscopia por Absorção de Raios X
12.
Sci Total Environ ; 689: 958-962, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31280176

RESUMO

Intensive uses of agrochemicals and soil amendments often cause the elevation of Cu and Zn concentrations in vineyard (VY) and orchard soils. The concentration and speciation of Cu and Zn in the soils at millimeter resolution is critical to understanding the risk of transport of these metals via surface runoff and infiltration. The objective of this study was to investigate the concentration and chemical species of Zn and Cu in VY and persimmon (PS) soils at millimeter vertical resolution. The soils were collected with 5 mm increments down to 5 cm depth and with 5 cm increments down to 25 cm depth. The total concentration and chemical species of Zn and Cu were determined by total digestion and X-ray absorption fine structure (XAFS) spectroscopy, respectively. The Zn concentration of VY soil reached a maximum of 290 mg kg-1 at the uppermost layer of the profile (0.5-1.0 cm). The Cu concentration of VY soil reached a maximum of 201 mg kg-1 (10-15 cm). These Zn and Cu concentrations were greater than background levels. Zinc K-edge XAFS spectroscopy determined that the uppermost layer of VY soil (0-0.5 cm) contained 42% Zn associated with humus and lesser extent of Zn associated with gibbsite (37%) and kaolinite (21%). Zinc associated with humus was not observed in the VY soil profiles below 0.5 cm, whereas Zn associated with gibbsite and kaolinite contributed >83% of total Zn species. Copper K-edge XAFS spectroscopy determined the presence of Cu bonded with humus (40-67%) and Cu adsorbed on kaolinite (26-45%) in the entire soil profile. Our study found the remarkable variation of Cu and Zn concentration and speciation within several centimeters from the soil surface in vineyard and orchard landscapes.


Assuntos
Cobre/análise , Monitoramento Ambiental/métodos , Poluentes do Solo/análise , Espectroscopia por Absorção de Raios X/métodos , Zinco/análise , Diospyros/crescimento & desenvolvimento , Fazendas , Solo/química , Vitis/crescimento & desenvolvimento
13.
Environ Pollut ; 252(Pt B): 1439-1447, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31265954

RESUMO

Arsenic (As) and antimony (Sb) are considered as priority environmental pollutants and their accumulation in crop plants particularly in rice has posed a great health risk. This study endeavored to investigate As and Sb contents in paired soil-rice samples obtained from Xikuangshan, the world largest active Sb mining region, situated in China, and to investigate As speciation and location in rice grains. The soil and rice samples were analyzed by coupling the wet chemistry, laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), synchrotron-based micro X-ray fluorescence mapping (µ-XRF) and micro X-ray absorption near-edge structure (µ-XANES) spectroscopy. The results of field survey indicated that the paddy soil in the region was co-polluted by Sb (5.91-322.35 mg kg-1) and As (0.01-57.21 mg kg-1). Despite the higher Sb concentration in the soil, rice accumulated more As than Sb indicating the higher phytoavailability of As. Dimethylarsinic acid (DMA) was the predominant species (>60% on average) in the rice grains while the percentage of inorganic As species was 19%-63%. The µ-XRF mapping of the grain section revealed that the most of As was distributed and concentrated in rice husk, bran and embryo. Sb was distributed similarly to As but was not in the endosperm of rice grain based on LA-ICP-MS. The present results deepened our understanding of the As/Sb co-pollution and their association with the agricultural-product safety in the vicinity of Sb mining area.


Assuntos
Antimônio/análise , Arsênico/análise , Poluição Ambiental/análise , Oryza/química , Poluentes do Solo/análise , China , Mineração , Solo/química , Espectroscopia por Absorção de Raios X
14.
Bull Environ Contam Toxicol ; 103(1): 64-68, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31165189

RESUMO

The molecular-level surface complexation structure of Ca2+ at the goethite/water interface remains unclear. We investigated the sorption of Ca2+ on the surfaces of goethite using classical molecular dynamics (MD) simulations and Ca K-edge X-ray absorption near edge structure (XANES) spectroscopy. The XANES results showed that Ca2+ was sequestered by goethite dominantly via sorption at pH ≤ 9, whereas the Ca(OH)2 surface precipitate formed at pH 10 for an initial Ca2+ concentration of 2 mM. The MD simulations showed that Ca2+ dominantly absorbed on the (100) and (110) surfaces of goethite via bidentate binuclear complexation by forming ≡(Fe-OH)2Ca2+·5H2O species, whereas little Ca2+ adsorbed on the (021) surface. The theoretical Ca K-edge XANES spectrum calculations gave a mean Ca-O interatomic distance of 2.34 Å (2.23-2.55 Å) and a Ca-Fe interatomic distance of 3.80 Å (3.79-3.81 Å) at goethite/water interface. Our results may shed some light on the geochemical cycling of calcium and other related cations and anions.


Assuntos
Cálcio/química , Simulação de Dinâmica Molecular , Adsorção , Compostos de Ferro/química , Minerais/química , Modelos Químicos , Estrutura Molecular , Água/química , Espectroscopia por Absorção de Raios X
16.
Sci Total Environ ; 688: 1-9, 2019 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-31229806

RESUMO

Thermal hydrolysis pretreatment (THP) can improve sludge disintegration and biogas production. Phosphorus (P) is immobilized on hydrochars of sewage sludge (SS). It is critical to understand changes in P speciation in SS hydrochars under different reaction temperatures and reaction times during THP for reclamation and (re)cycling of P. This study combined sequential extraction, 31P liquid and solid-state nuclear magnetic resonance (NMR), and P K-edge X-ray absorption near edge structure (XANES) spectroscopy to systematically analyze variation in P speciation and related metals in hydrochars. The temperature of the THP has more influence on P extraction content than reaction time; the bioavailability of P from hydrochars declined with increasing temperature. A 31P liquid and solid-state NMR analysis demonstrated that orthophosphate was the most abundant phosphate present small deviations in the chemical shift were observed in different samples under different conditions. The results of XANES demonstrated that CaP was more stable than FeP and AlP. LCF results suggested OcataCa proportion raised under stable CaP ratio in samples when the temperature was above 155 °C and duration was 60 min. This study provides a theoretical basis that can meet the practical application of THP for sludge disposal and P reclamation on subsequent anaerobic digestion.


Assuntos
Fósforo/química , Eliminação de Resíduos Líquidos , Poluentes Químicos da Água/química , Hidrólise , Fósforo/análise , Esgotos/química , Temperatura Ambiente , Poluentes Químicos da Água/análise , Espectroscopia por Absorção de Raios X
17.
Environ Sci Pollut Res Int ; 26(23): 23850-23860, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31214887

RESUMO

The environmental fate of iodine is of general geochemical interest as well as of substantial concern in the context of nuclear waste repositories and reprocessing plants. Soils, and in particular soil organic matter (SOM), are known to play a major role in retaining and storing iodine. Therefore, we investigated iodide and iodate sorption by four different reference soils for contact times up to 30 days. Selective sequential extractions and X-ray absorption spectroscopy (XAS) were used to characterize binding behavior to different soil components, and the oxidation state and local structure of iodine. For iodide, sorption was fast with 73 to 96% being sorbed within the first 24 h, whereas iodate sorption increased from 11-41% to 62-85% after 30 days. The organic fraction contained most of the adsorbed iodide and iodate. XAS revealed a rapid change of iodide into organically bound iodine when exposed to soil, while iodate did not change its speciation. Migration behavior of both iodine species has to be considered as iodide appears to be the less mobile species due to fast binding to SOM, but with the potential risk of mobilization when oxidized to iodate.


Assuntos
Iodatos/química , Iodo/química , Solo/química , Adsorção , Iodetos/química , Oxirredução , Espectroscopia por Absorção de Raios X
18.
Chemistry ; 25(53): 12332-12341, 2019 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-31206850

RESUMO

The development of the nuclear industry has raised multiple questions about its impact on the biotope and humans. Proteins are key biomolecules in cell machinery and essential in deciphering toxicological processes. Phosvitin was chosen as a relevant model for phosphorylated proteins because of its important role as an iron, calcium, and magnesium storage protein in egg yolk. A multitechnique spectroscopic investigation was performed to reveal the coordination geometry of two oxocations of the actinide family (actinyl UVI , NpV ) in speciation with phosvitin. IR spectroscopy revealed phosphoryl groups as the main functional groups interacting with UVI . This was confirmed through laser luminescence spectroscopy (U) and UV/Vis absorption spectroscopy (Np). For UVI , X-ray absorption spectroscopy at the LIII edge revealed a small contribution of bidentate binding present, along with predominantly monodentate binding of phosphoryl groups; for NpV , uniquely bidentate binding was revealed. As a perspective to this work, X-ray absorption spectroscopy speciation of UVI and NpV in the extracted yolk of living eggs of the dogfish Scyliorhinus canicula was determined; this corroborated the binding of phosphorous together with a reduction of the actinyl moiety. Such data are essential to pinpoint the mechanisms of heavy metals (actinyls) accumulation and toxicity in oviparous organisms, and therefore, contribute to a shift from descriptive approaches to predictive toxicology.


Assuntos
Gema de Ovo/metabolismo , Fosvitina/metabolismo , Cálcio/metabolismo , Humanos , Ferro/metabolismo , Magnésio/metabolismo , Minerais , Fósforo/química , Fosvitina/química , Espectroscopia por Absorção de Raios X
19.
Environ Sci Technol ; 53(12): 6877-6886, 2019 06 18.
Artigo em Inglês | MEDLINE | ID: mdl-31120750

RESUMO

Fe-bearing clay minerals are abundant in argillaceous rocks as their redox-active structural iron may control the sorption mechanism of redox sensitive elements on the surface of clay minerals. The extent and efficiency of the redox reactions depend on the oxidation state (Fe2+/Fe3+ ratio) and structural distribution of the substituting cations in the TOT-layer of clay minerals. Even smectites with similar structure originating from different locations might have a distinct arrangement of isomorphic substitutions (e.g., individual iron or Fe-Fe pairs). In this study, the proportion of different iron distribution in Milos-, Wyoming-, and Texas-montmorillonite was determined by combining X-ray absorption spectroscopy (XAS) with ab initio calculations. The relaxed atomic structures of the smectite models with different arrangement of individual Fe atoms and Fe-Fe/Fe-Mg clusters served as the basis for the calculations of the XAS spectra. The combination of simulation results and measured Fe K-edge XAS spectra of Wyoming-, Milos- and Texas-montmorillonites suggested that iron is present as Fe3+ in the octahedral sheet. Fe3+ in Texas-montmorillonite has a tendency to form clusters, while no definitive statement about clustering or avoidance of Fe-Fe and Fe-Mg pairs can be made for Milos- and Wyoming-montmorillonite.


Assuntos
Silicatos de Alumínio , Ferro , Silicatos , Texas , Wyoming , Espectroscopia por Absorção de Raios X
20.
Chemosphere ; 228: 619-628, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31059960

RESUMO

The recovery of phosphorus from sewage sludge was critical due to the depletion of phosphate ore. The present research aims to identify the phosphorus speciation and reveal the phosphorus transformation mechanism of dewatered sewage sludge during hydrothermal conversion (HTC) process, as well as to achieve the high efficiency recovery of phosphorus. Multiple analysis of SMT method, VK diagram, XANES and NMR showed that most phosphorus (>80%) was transferred to the hydrochar and presented as inorganic phosphorus (IP) after the HTC process. A dehydration trend was observed of the HTC process with the increase of sub-critical temperature. Ca-associated phosphorus increased significantly as the temperature increased. The Pyro-P gradually transformed to Ortho-P with the increase of HTC temperature and disappeared at 320 °C. The addition of HCl (6.13 and 12.3 mmol/g) in the HTC process resulted in a high percentage (>80%) of phosphorus transferred to the aqueous phase, and the bioavailability of the residual phosphorus increased significantly. The recovery rate of phosphorus could achieve 98.37% at the pH of 7.52, with the struvite purity of 90.41%. The results of this study provide new insights into the selective transfer of phosphorus in dewatered sludge by HTC process, in addition to some efficient ways for the utilisation of the HTC products.


Assuntos
Fósforo/química , Esgotos/química , Eliminação de Resíduos Líquidos/métodos , Espectroscopia de Ressonância Magnética , Estruvita , Temperatura Ambiente , Espectroscopia por Absorção de Raios X
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