Speciation Analysis Research Articles

Separation of Inorganic Forms of Tellurium Using On-Site SPE Followed by ICP-MS or ICP-OES—The Right Solution for Water Monitoring

Tellurium, recognized as one of the technology-critical elements, should be considered as a xenobiotic. Its application, i.a. in the growing photovoltaic industry, raises concerns about Te(IV) and Te(VI) release to the environment. As both forms differ in mobility and toxicity, Te speciation should be included in water monitoring, but problems with speciation changes occurring during sampling, transport, and sample storage require the use of on-site separation of Te forms. A simple procedure based on solid phase extraction (SPE) with the anionic exchange mechanism (SAX, involving commercially available columns), followed by their quantification with elemental techniques, has a high potential for implementation in routine analysis. The proposed SPE-ICP-MS (inductively coupled plasma mass spectrometry) method allows direct analysis of Te(VI) and Te(IV), with Te(IV) determined after elution from the column. The detection limits obtained for the 5.0 mL sample are 0.02 ng mL−1 and 0.05 ng mL−1 for Te(VI) and Te(IV), respectively. Hydride generation inductively coupled plasma optical emission spectrometry (HG-ICP-OES) was used to control possible changes in tellurium speciation occurring during species isolation using SPE. The simple and fast water pretreatment proposed here offers the possibility of separating Te(IV) and Te(VI) at the sampling site, and the elution of Te(IV) does not have to be conducted on-site. Application to the river water and seawater matrix proved the feasibility of incorporating Te speciation analysis into routine water analysis.

Heavy Metals Speciation and Health Risk Analysis of Arable Farmlands In Ardo-Kola, Bali and Wukari Local Government Areas of Taraba State Nigeria

Heavy Metals Speciation and Health Risk Analysis of Arable Farmlands In Ardo-Kola, Bali and Wukari Local Government Areas of Taraba State Nigeria

The role of chloride in calcium precipitation from drinking groundwater

AbstractBACKGROUNDChloride is present in many water sources. In addition, the use of hypochlorite as a disinfectant for drinking water increases its chloride concentration. However, the effect of this prevalent ion on Ca precipitation in drinking water is poorly described, and its effect, as a function of the Ca/Mg ratio, which drives Ca precipitation, has not been studied. Accordingly, Ca precipitation was studied using batch assays at different concentrations of chloride and hypochlorite for Ca/Mg ratios of 4.0 and 1.1. The assays were performed at 20 and 25 °C. Chemical speciation analysis was performed using Visual MINTEQ software, and precipitates derived from the process were analyzed by X‐ray diffraction.RESULTSCa precipitation was influenced by the Cl− concentration, causing an oversaturation of CaCO3 with a trend to a maximum. The highest Ca precipitation was achieved at a Ca/Mg ratio of 4.0, obtained at an initial Cl− concentration of 50 mg L−1, both at 20 and 25 °C. For a Ca/Mg ratio of 1.1, the highest precipitation occurred at initial Cl− concentrations of 10–15 mg L−1 at 20 °C and 20 mg L−1 at 25 °C. In ClO− experiments, Ca precipitation increases proportionally with hypochlorite dosage. Greater Ca precipitation is observed at Ca/Mg = 4.0 compared to Ca/Mg = 1.1. The proportion of aragonite or calcite in the precipitates obtained depends on the presence of Cl− and ClO− as well as on the Ca/Mg ratio.CONCLUSIONChloride affects Ca precipitation by oversaturation, and the precipitation of CaCO3 species depends on the concentration of Mg. © 2024 Society of Chemical Industry (SCI).

Evaluation of Solubility and Complexation Ability of Vanillic, Syringic and Gallic Acids Towards Aluminum Cation

Chelation therapy is currently successfully applied to reduce the aluminum burden and its neurodegenerative consequences. In view of a possible application to aluminum chelation therapy, here we have studied the complexation of hydroxybenzoic acids, namely, vanillic, syringic and gallic acids, towards aluminum ion at physiologically relevant conditions as regards temperature (37 °C) and ionic strength (i.e., 0.16 M NaCl). The solubility values and the protonation constants of the hydroxybenzoic acids were primarily assessed to estimate the competition of these acids towards aluminum and H+ ions. Then, potentiometric titrations were carried out, and the speciation analysis indicated a pH-dependent complexation occurring at a 1:1 hydroxybenzoic acid-to-aluminum ratio for vanillic and syringic, and 1:1, 2:1 and 3:1 ligand-to-Al(III) ratios for gallic. Gallic acid forms more stable complexes with Al(III) ion than vanillic and syringic acids and could therefore represent a good candidate for being used as sequestering agents for Al(III) ion.

Growth substrate limitation enhances anaerobic arsenic methylation by Paraclostridium bifermentans strain EML.

Microbial arsenic methylation is established as a detoxification process under aerobic conditions (converting arsenite to monomethylated arsenate) but is proposed to be a microbial warfare strategy under anoxic conditions due to the toxicity of its main product, monomethylarsonous acid (MMAs(III)). Here we leveraged a paddy soil-derived anaerobic arsenic methylator, Paraclostridium bifermentans strain EML, to gain insights into this process. Strain EML was inoculated into a series of media involving systematic dilutions of Reinforced Clostridial Broth (RCB) with 25 µM arsenite to assess the impact of growth substrate concentration on arsenic methylation. Growth curves evidenced the sensitivity of strain EML to arsenite, and arsenic speciation analysis revealed the production of MMAs(III). Concentrations of MMAs(III) and arsenic methylation gene (arsM) transcription were found to be positively correlated with RCB dilution, suggesting that substrate limitation enhances arsM gene expression and associated anaerobic arsenic methylation. We propose that growth substrate competition among microorganisms may also contribute to an increase in anaerobic arsenic methylation. This hypothesis was further evaluated in an anaerobic co-culture system involving strain EML and either wild-type Escherichia coli K-12 MG1655 (WT) or E. coli expressing the MMAs(III)-resistance gene (arsP) (ArsP E. coli). We observed increased MMAs(III) production in the presence of E. coli than its absence and growth inhibition of WT E. coli to a greater extent than ArsP E. coli, presumably due to the MMAs(III) produced by strain EML. Collectively, our findings suggest an ecological role for anaerobic arsenic methylation, highlighting the significance of microbe-microbe competition and interaction in this process.IMPORTANCEMicrobial arsenic methylation is highly active in rice paddy fields under flooded conditions, leading to increased accumulation of methylated arsenic in rice grains. In contrast to the known detoxification process for aerobic arsenic methylation, the ecological role of anaerobic arsenic methylation remains elusive and is proposed to be an antibiotic-producing process involved in microbial warfare. In this study, we interrogated a rice paddy soil-derived anaerobic arsenic-methylating bacterium, Paraclostridium bifermentans strain EML, to explore the effect of growth substrate limitation on arsenic methylation in the context of the microbial warfare hypothesis. We provide direct evidence for the role of growth substrate competition in anaerobic arsenic methylation via anaerobic prey-predator co-culture experiments. Moreover, we demonstrate a feedback loop, in which a bacterium resistant to MMAs(III) enhances its production, presumably through enhanced expression of arsM resulting from substrate limitation. Our work uncovers the complex interactions between an anaerobic arsenic methylator and its potential competitors.

Method validation and geochemical modelling of chromium speciation in natural waters

The study focuses on validating reference methods such as ICP-OES and ICP-MS for detecting ultra-trace levels of chromium in groundwater, where concentrations are typically very low. Additionally, it verifies a hyphenated technique, IC-ICP-MS, for determining naturally occurring Cr(VI) in tested waters. The validation process involved various chromium analysis variants, including isotopes 52Cr and 53Cr in ICP-MS and IC-ICP-MS techniques, along with specific emission lines in the ICP-OES technique. Statistical data processing revealed that the achieved limits of quantification for Cr in different techniques ranged from 0.053 µg/L to 1.3 µg/L, with the associated measurement uncertainty estimated between 14% and 19% (at a coverage factor k = 2, 95%). For speciation analysis, it was possible to quantitatively determine Cr(VI) at concentrations as low as 0.12 µg/L, with the measurement uncertainty ranging between 10% and 14%. The Kruskal-Wallis test indicated that for the 14 water samples analysed, there was no statistically significant difference in the results obtained using different analytical techniques (p > 0.05). The geochemical modelling approach applied enhances the understanding of chromium speciation in water samples, verifying the accuracy of speciation analysis and identifying specific ion forms in which Cr(III) and Cr(VI) occur. In the analysed water samples, the concentration of Cr(VI) ranges between 0.13 and 35 µg/L, with the primary form identified as the oxoanion CrO42−. Importantly, statistical tests demonstrated no statistically significant differences between the total chromium concentration in water and the concentration of Cr(VI), indicating that the entire concentration of total chromium corresponds to Cr(VI) speciation.

Ecological risk and chemical speciation of heavy metals in surface sediments of the Pearl River Estuary for comprehensive assessment

The Pearl River Estuary, a vital ecological and economic zone in Southern China, has been heavily impacted by industrial discharges, leading to significant heavy metal contamination. To address the ecological implications of different chemical forms of heavy metals, this study systematically evaluated the total concentrations and chemical speciation of Cu, Zn, Cd, and Pb in surface sediments (0–2 cm) collected from 17 sites. Chemical speciation was determined using a modified BCR sequential extraction procedure, and pollution and ecological risks were assessed via the geo-accumulation index (Igeo), potential ecological risk index (RI), and risk assessment code (RAC). The results showed that all four metals exceeded background values, with Cd presenting the highest enrichment (39 times) and contributing 97% of the ecological risk. Speciation analysis revealed that Cd predominantly exists in bioavailable forms, posing severe ecological threats. This study highlights the urgent need for targeted remediation strategies to mitigate Cd contamination and its ecological impact on the estuary.

Enhanced phosphorus bioavailability and reduced water leachability in dairy manure through hydrothermal carbonization: effect of processing temperature and CaO additive

ABSTRACT Dairy manure, a significant source of phosphorus (P), can potentially cause environmental risk due to P runoff when dairy manure is directly applied to cropland. Thus, there is an increasing interest in mitigating P loss from manure prior to land applications. This study aimed to investigate the potential of hydrochar produced by hydrothermal carbonization (HTC) for P recycling from dairy manure with and without the addition of CaO, focusing on the plant bioavailability, stabilization, and transformation of P in the resultant hydrochar. Hydrochar was prepared under different temperatures (180–240°C). The effect of CaO addition (0–10% of raw manure on dry wt. basis) was also evaluated at 220°C. Results showed that water-soluble P (WSP), a key indicator of P runoff loss, was significantly reduced in hydrochar, particularly with CaO addition. In addition, the plant available P in hydrochar increased with HTC temperature increase till 220°C, which accounted for ∼90% of total P content, then decreased with temperatures higher than 220°C. The addition of CaO slightly reduced plant bioavailability when compared to hydrochar produced at 220°C without additive. The P fractionation and speciation analyses indicated the transformation of P into Ca-associated apatite P. Hydrochar produced at 220°C with 10% CaO addition resulted in a high P recovery (∼85%) and a reduced runoff risk by 97%. The results demonstrate the efficacy of P recycling through hydrochar produced from dairy manure through HTC, which offers a sustainable approach to managing dairy waste while mitigating the potential environmental risks of P runoff.

Laboratory-Based X-Ray Emission Spectroscopy (XES) for Determination of Oxidation State and Ligand Species

Identification of oxidation state and ligand species is often challenging, requiring arduous preparation and destructive analytical techniques which inhibit rapid analyses. Advancements in laboratory-based X-ray emission spectrometers (XES) are addressing this issue, facilitating consistent access to element-specific bulk chemical analysis of oxidation state and ligand speciation in users’ own labs. Intended to simplify and expand access to this powerful technique for both new and existing members of the XAS community, everyday analysis is a game-changer which enables researchers to control their experiment like never before. Synchrotron-like data quality is achievable within minutes even on trace elements (few hundred PPM). Utilizing a Rowland-circle geometry, easyXAFS spectrometers support a broad energy range (2-25 keV) capable of XES analysis of over 50 elements ranging from phosphorus through the actinides. Herein we discuss the benefits of XES for determination of oxidation state and ligand speciation highlighting previous and ongoing research in electrocatalysis, cathode coatings, battery charge/discharge operando measurements. Figure 1

Hydride generation smartphone readable colorimetric system for speciation analysis of inorganic antimony without chromatographic separation

Antimony (Sb) was considered as a toxic metalloid element in environmental water system, the concentration of antimony in water sample was required to not be higher than 0.02 μg/mL. Miniaturized/portable analytical systems/devices were needed for on-site analysis of antimony. Herein, hydride generation was combined with a smartphone readable colorimetric method and used for the speciation analysis of inorganic antimony without chromatographic separation. Sb(III) was analyzed when masking reagent was used for Sb(V), total antimony concentration was obtained when Sb(V) was educed to Sb(III) before analysis. The conversion of Sb(Ⅲ) to SbH3 was achieved through hydride generation (HG) reaction, a redox reaction between SbH3 and HAuCl4 occurred with a result of in-situ generation of gold nanoparticles (Au NPs) on test paper, changing color from pale yellow to black and allowing for colorimetric analysis with naked-eye and smartphone RGB mode. Detectable limits of 0.02 μg/mL and 0.01 μg/mL can be recognized by naked-eye and smartphone mode, respectively. This miniaturized and easy-used smartphone readable analytical system was further used for on-site analysis of inorganic antimony in real samples, recoveries of 95–105 % were obtained.

Effects of Large-Scale Wildfires on the Redistribution of Radionuclides in the Chornobyl River System.

Wildfires in radiologically contaminated areas raise significant concerns due to potential radionuclides redistribution and increased public radiation exposure. This study examined the impact of the 2020 Chornobyl wildfire on the redistribution of radionuclides, specifically 137Cs and 90Sr, in the Chornobyl River system. We determined the quantities and speciation of 137Cs and 90Sr in charred residues and soil after wildfires and analyzed the riverine concentrations of these radionuclides based on long-term monitoring data. Our findings indicate that the inventories of 137Cs and 90Sr in the charred residues and soil decreased with increasing distance from the nuclear power plant, which is consistent with the initial deposition patterns. However, the transfer of 137Cs and 90Sr from soil to charred residues did not correspond to the distance, type of contamination source, or fire type. Speciation analysis revealed that the water-soluble fractions of 137Cs and 90Sr in the charred residues were significantly higher than those in the soil, implying increased mobility. Following the wildfires, no significant increase in 137Cs concentration was observed in a river catchment in Chornobyl. However, 90Sr concentrations showed a significant increase, exceeding the permissible levels in drinking water (2 Bq/L) in Ukraine. This increase is attributed to hydrologically driven mobilization processes: (1) during snowmelt in spring and (2) the transport of soluble 90Sr from charred residues and surface soil into the river during high suspended solid concentration events. Collectively, our findings highlight the importance of continuous monitoring of radionuclide dynamics in postwildfire environments to better assess potential radionuclide redistribution and radiation exposure risks. These results provide valuable insights into the behavior of 137Cs and 90Sr in river systems affected by wildfires, contributing to a more accurate understanding of their environmental impacts and potential countermeasures.

Investigating formation water variability in the Búzios oilfield (Santos Basin) using cluster analysis and hydrogeochemical modeling

The characteristics of formation waters play a crucial role in production development projects within Pre-Salt oil fields in the Santos Basin, offshore southeastern Brazil. This study investigated the compositional variations of brines of the Búzios Field (northeast of the Santos Basin), proposing for the first time an extensive hydrochemical mapping of the Pre-Salt aquifers and identifying nuances of connectivity. A comprehensive methodology was employed, including analysis of pressure gradients, cluster analysis, and hydrogeochemical modeling to classify different types of brine and understand their behavior under reservoir conditions. A hydrochemical classification routine was applied to 129 formation water samples, identifying seven distinct clusters using the unsupervised k-means algorithm. This clustering process efficiently differentiated representative, non-representative, and contaminated samples. The hydrochemical composition of the formation waters varied among the four hydraulic compartments identified in the field, with their boundaries defined by permeability barriers. Compared with the central portion of the field (regional aquifer), where salinities predominantly range from 155,000 to 185,000 mg/L of NaCl, enrichment of specific ions was observed at the field's extremities, such as boron (northeast), barium and lithium (north), and bicarbonate (west). These hydrochemical differences lead the brine salinities at the field's extremities to exceed 225,000 mg/L of NaCl. Hydrogeochemical modeling provided insights into the pH levels of each brine under reservoir conditions, showing a decrease of between 23 and 32% compared to surface pH values. The speciation analysis showed positive strontianite and barite saturation indices in certain types of formation water, indicating potential precipitation. These areas are considered critical for inorganic scaling in production equipment.

Unexpected nanoscale CeO2 structural transformations induced by ecologically relevant phosphate species

In the present study, the dissolution and microstructural transformation of CeO2 nanoparticles (NPs) in a phosphate-containing milieu were investigated. The dissolution behaviour of 2 nm and 5 nm CeO2 NPs in phosphate buffer solutions was found to differ markedly from that observed in 0.01 M NaClO4. Through synchrotron X-ray diffraction analysis and X-ray absorption spectroscopy, the interaction between CeO2 NPs and phosphate species was examined, revealing the transformation of the oxide into sodium-cerium double phosphate, with cerium predominantly existing in the Ce(IV) state. According to scanning and transmission electron microscopy observations, thus formed Na-Ce(IV) phosphate consists of spindle-like aggregates of nanocrystalline rods, presumably formed during phosphate anions sorption on the initial CeO2 surface. Pair distribution function analysis revealed that Na-Ce(IV) phosphate has a three-dimensional framework crystal structure, similar to NaTh2(PO4)3, as reported earlier, with large channels along the c-axis containing disordered sodium atoms. This study represents the first detailed analysis of phosphate-induced speciation and microstructural transformation of CeO2 NPs, resulting in the formation of Ce(IV) phosphate. Similar processes may occur in natural ecosystems upon the introduction of CeO2 NPs.

Novel Applications of CE-ICP-MS/MS: Monitoring of Antiaging GHK-Cu Cosmetic Component Encapsulation in Liposomes.

The hyphenation of the separation technique with the high-sensitive mass spectrometry detection is one of the driving forces of modern analysis enabling measurements in complex matrices. In particular, capillary electrophoresis coupled to inductively coupled plasma tandem mass spectrometry allows for speciation analysis of selected analytes with a superior resolution. The mild, physiological-friendly conditions of this separation technique offer the unique advantage of analyzing chemical entities in their intact form, which has been successfully exploited in various areas. Herein, we report the pioneering application of such a hyphenated technique in the cosmetic field to investigate the encapsulation of copper tripeptide complex (GHK-Cu) in liposomes. By monitoring copper and phosphorus signals, the formation of liposomes via a simple ethanol injection method was confirmed, and the concentration of GHK-Cu in the liposomes was assessed. The application of coupling of capillary electrophoresis with inductively coupled plasma tandem mass spectrometry (CE-ICP-MS/MS) in cosmetic studies could lead to the development of diverse liposomal formulations with preferential properties and expand their accessibility.

Chemical Fingerprinting of PM2.5 via Sequential Speciation Analysis Using Electrochemical Mass Spectrometry.

Chemical fingerprinting to characterize the occurrence state and abundance of organic and inorganic constituents within fine particulate matter (PM2.5) is useful in evaluating the associated health risks and tracing pollution sources. Herein, an analytical strategy for the rapid analysis of metal and organic constituents in PM2.5 was developed employing a combination of sequential chemical extraction coupled with mass spectrometry detection. H2O, CH3OH, EDTA-2Na, electrochemical oxidation, and electrochemical reduction were sequentially utilized to extract the chemical constituents in PM2.5 samples on a homemade device employing simultaneous online detection using two linear trap quadrupole mass spectrometers (LTQ-MS) with electrospray ionization (ESI) in positive and negative modes. After a single analytical procedure, dozens of metals (e.g., Pb, Cr, and Cu), organic compounds (e.g., amines, polycyclic aromatic hydrocarbons, and aliphatic acids), and negative ions (e.g., NO3-, NO2-, and Cl-) were comprehensively detected in the water-soluble, liposoluble, insoluble, oxidizable, and reducible fractions of PM2.5 samples, and their physical and chemical relationships were established.

Headspace-single drop microextraction based visual colorimetry for non-chromatographic speciation analysis of nitrite and nitrate in environmental water sample

In this work, a visual colorimetric method based on headspace-single drop microextraction (HS-SDME) was developed for the non-chromatographic speciation analysis of nitrite and nitrate. The method adequately exploited the individual chemical vapor conditions of nitrite and nitrate that were converted to NO by specific reductants. Gaseous NO underwent a diazotization reaction with chromogenic reagent through the HS-SDME process to change from colorless to purplish-red. Instead of using large, time-consuming and relatively complicated chromatographic equipment for separation, the species of nitrite and nitrate could be analyzed by simply changing the reagents. Meanwhile, the extraction method effectively mitigated the matrix interference of solution and improved the sensitivity of method, with intuitive discrimination of color by the naked eye. The limits of detection were 0.07 μg/mL for nitrite and 0.2 μg/mL for nitrate, respectively. This method has been applied to analysis of real environmental water samples, which also effectively extended the application scope of HS-SDME device.

Chemical Characteristics of Zirconium Chloride and Zirconium Oxide Nanoparticles Driving Toxicity on Lemna minor

The increasing global production and utilization of zirconium (Zr) compounds, including zirconium chloride (ZrCl4) and zirconium oxide nanoparticles (NPs-ZrO2), raises concerns about their potential environmental impact. This study investigated the toxicity mechanisms of ZrCl4 and NPs-ZrO2 on the aquatic plant Lemna minor. The physicochemical properties of NPs-ZrO2 in the test medium were characterized, revealing concentration-dependent changes in the hydrodynamic diameter, zeta potential, and solubility over time. The analysis of Zr speciation showed the predominance of Zr(OH)4(aq) species from ZrCl4. Plants of L. minor exposed to ZrCl4 and NPs-ZrO2 exhibited differential Zr bioaccumulation, growth inhibition, oxidative stress, and antioxidant responses. ZrCl4 induced a higher toxicity than NPs-ZrO2, with bioaccumulation strongly correlating with adverse effects. The differential toxicity impact between these two Zr-compounds was also determined by the lowest observed-effect doses for growth and biochemical parameters. The scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirmed internalization of NPs-ZrO2 and Zr uptake in the L. minor plant. Therefore, these findings highlighted the importance of chemical speciation, environmental transformations, and biological responses in assessing the ecological impact of Zr-compounds for effective risk assessment and management strategies for protecting aquatic ecosystems.

Direct ion chromatographic method for speciation micro analysis of arsenic forms in industrial samples with “rich” matrix composition

The speciation analysis of arsenic has consistently been a subject of great interest. However, it remains challenging to analyze complex matrix samples that contain both arsenic and interfering components. In this case, it can be hard to choose the right combinations of different instrumental methods, or a separation method followed by detection, which is usually done using a spectral approach (hybrid methods). In the production control of copper electrorefining, the determination of the concentration of As (III) and As (V) helps to improve the quality of the cathode copper produced. This work investigated the possibility of directly determining both arsenic forms and total As in an electrolyte bath using ion chromatography (IC) with conductometric detection. The use of the ion chromatographic approach for the determination of As(V) in complex matrix samples such as copper electrolyte must take into account the presence of potential interferences from anions such as sulphates, sulfites, selenites, selenates, etc. The results revealed that the method is accurate and precise, with As(V) quantification limits of 15 µg.L-1 and detection limits of 5 µg.L-1. This method is suitable for assessing various types of arsenic in the production of electrolytic copper, with the aim of replacing the current technique that requires liquid-liquid extraction and ICP-OES detection. This led to the following improvements: Enhanced efficiency: The method eliminates the need for extensive and time-consuming sample preparation for the initial separation of arsenic forms. At the same time, the method's characteristics are comparable to those of ICP-OES with liquid-liquid extraction, which is often used in the speciation analysis of arsenic. The method is environmentally friendly as it avoids the use of organic and poisonous extractants. The method can simultaneously analyze other anions (PO43-, SO42-, F-, Cl-, etc.) with arsenates with appropriate calibration.

Selenium speciation analysis of selenium-enriched Shiitake mushrooms (Lentinula edodes) by HPLC-ESI-MS

Selenium (Se) is an essential component of critical enzymes and is intricately linked to human health. Shiitake mushrooms (Lentinula edodes) are considered as good dietary supplements for producing Se-enriched foods due to their high protein content and ability to absorb minerals from growth substrates. In this study, the distribution of soluble Se in Se-enriched L. edodes was analyzed by microwave digestion and hydride generation-atomic fluorescence spectrometry (HG-AFS). In order to evaluate the absorption and conversion effect of Se by L. edodes, the Se-containing compounds in selenized L. edodes were quantitatively and qualitatively analyzed by high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI-MS). It can be shown that L. edodes possessed a good biological transformation ability of organic Se enrichment though the quantitative analysis of three seleno-amino acids, selenocystine (Se-Cys2), methylselenocysteine (Se-MeSeCys) and selenomethionine (Se-Met), in selenized L. edodes. The structures of three unknown Se-containing compounds were identified by qualitative analysis, the results indicated that the possible structures were selenomethylmethionine (C6H14NO2Se), N-Acetyl-selenomethionine (C7H13NO3Se) and Se-methyl-5-selenoadenosinese-oxide (C12H18N5O3Se). The discovery of these Se compounds filled the research gap and provided a theoretical basis for molecular structure identification and mechanism study of organic Se in Se-enriched L. edodes.

Interpretation of vertical migration and enrichment processes of rare earth elements (REEs) in ion-adsorption-type mineralization in Japan based on REE speciation analyses

Typical vertical profiles of ion-adsorption-type rare earth element (REE) deposits discovered in southwest Japan were studied by conducting speciation analyses, including X-ray absorption fine structure and laser-induced fluorescence spectroscopy combined with transmission electron microscopy and adsorption/desorption experiments. The results revealed that REE speciation, migration, and enrichment in weathered granite is largely controlled by soil pH, which in turn controls the variable charges of kaolinite, the REE host phase. Both the distribution coefficient Kd and the soil pH increase with depth. As a result, (i) REE dissolution and migration occur in the near-surface acidic environment of the upper layers, where hydroxyls of kaolinite basal surfaces and edges are deprotonated to a lesser degree, and (ii) REEs accumulate in the relatively high-pH environment below the surface, where hydroxyls of kaolinite basal surfaces and edges are deprotonated to a larger degree, producing REE adsorption sites with variable charges. An increase of soil pH to greater than 6 in deeper layers promotes inner-sphere complexation of REEs. Although inner-sphere complexation inhibits the ion-exchange extraction of REEs, the inner-sphere complexes can be still extracted by lowering the pH of the extraction solution. This fact, which indicates that the adsorption of both inner- and outer-sphere complexes is reversible, is important in terms of both (i) understanding vertical REE profiles in which the pH varies and (ii) the efficient recovery of REEs from REE-enriched layers at all depths in weathered granite.