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PubMed2005

Sulfur speciation and stable isotope trends of water-soluble sulfates in mine tailings profiles.

Sulfur speciation and the sources of water-soluble sulfate in three oxidizing sulfidic mine tailings impoundments were investigated by selective dissolution and stable isotopes. The studied tailings impoundments--Piuquenes, Cauquenes, and Salvador No. 1--formed from the exploitation of the Rio Blanco/La Andina, El Teniente, and El Salvador Chilean porphyry copper deposits, which are located in Alpine, Mediterranean, and hyperarid climates, respectively. The water-soluble sulfate may originate from dissolution of primary ore sulfates (e.g., gypsum, anhydrite, jarosite) or from oxidation of sulfide minerals exposed to aerobic conditions during mining activity. With increasing aridity and decreasing pyrite content of the tailings, the sulfur speciation in the unsaturated oxidation zones showed a trend from dominantly Fe(III) oxyhydroxide fixed sulfate (e.g., jarosite and schwertmannite) in Piuquenes toward increasing presence of water-soluble sulfate at Cauquenes and Salvador No. 1. In the saturated primary zones, sulfate is predominantly present in water-soluble form (mainly as anhydrite and/or gypsum). In the unsaturated zone at Piuquenes and Cauquenes, the delta34S(SO4)values ranged from +0.5 per thousand to +2.0 per thousand and from -0.4 per thousand to +1.4 per thousand Vienna Canyon Diablo Troilite (V-CDT), respectively, indicating a major sulfate source from pyrite oxidation (delta34S(pyrite) = -1.1 per thousand and -0.9 per thousand). In the saturated zone at Piuquenes and Cauquenes, the values ranged from -0.8 per thousand to +0.3 per thousand and from +2.2 per thousand to +3.9 per thousand, respectively. At Cauquenes the 34S enrichment in the saturated zone toward depth indicates the increasing contribution of isotopically heavy dissolved sulfate from primary anhydrite (approximately +10.9 per thousand). At El Salvador No. 1, the delta34S(SO4) average value is -0.9 per thousand, suggesting dissolution of supergene sulfate minerals (jarosite, alunite, gypsum) with a delta34S approximately -0.7 per thousand as the most probable sulfate source. The gradual decrease of delta18O(SO4) values from the surface to the oxidation front in the tailings impoundments at Piuquenes (from -4.5 per thousand to -8.6 per thousand Vienna Standard Mean Ocean Water, V-SMOW) and at Cauquenes (from -1.3 per thousand to -3.5 per thousand) indicates the increasing importance of ferric iron as the main electron acceptor in the oxidation of pyrite. The different delta18O(SO4) values between the tailings impoundments studied here reflect the local climates.

Chile↗
PubMed2005

Changes in zinc speciation in field soil after contamination with zinc oxide.

Recent studies on the speciation of Zn in contaminated soils confirmed the formation of Zn-layered double hydroxide (LDH) and Zn-phyllosilicate phases. However, no information on the kinetics of the formation of those phases under field conditions is currently available. In the present study, the transformation of Zn in a field soil artificially contaminated with ZnO containing filter dust from a brass foundry was monitored during 4 years using extended X-ray absorption fine structure (EXAFS) spectroscopy. Soil sections were studied by micro-X-ray fluorescence (micro-XRF) and micro-EXAFS spectroscopy. EXAFS spectra were analyzed by principal component analysis (PCA) and linear combination fitting (LCF). The results show that ZnO dissolved within 9 months and that half of the total Zn reprecipitated. The precipitate was mainly of the Zn-LDH type (>75%). Only a minor fraction (<25%) may be of Zn-phyllosilicate type. The remaining Zn was adsorbed to soil organic and inorganic particles. No significant changes in Zn speciation occurred from 9 to 47 months after the contamination. Thermodynamic calculations show that both Zn-LDH and Zn-phyllosilicate may form in the presence of ZnO but that the formation of Zn-phyllosilicate would be thermodynamically favored. Thus, the dominance of Zn-LDH found by spectroscopy suggests that the formation of the Zn precipitates was not solely controlled bythermodynamics but also contained a kinetic component. The rate-limiting step could be the supply of Al and Si from soil minerals to the Zn-rich solutions around dissolving ZnO grains.

Absorption↗
PubMed2005

Cryogenic laser induced U(VI) fluorescence studies of a U(VI) substituted natural calcite: implications to U(VI) speciation in contaminated Hanford sediments.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) and imaging spectromicroscopy (TRLFISM) were used to examine the chemical speciation of uranyl in contaminated subsurface sediments from the U.S. Department of Energy (U.S. DOE) Hanford Site, Washington. Spectroscopic measurements for contaminant U(VI) were compared to those from a natural, uranyl-bearing calcite (NUC) that had been found via X-ray absorption spectroscopy (XAS) to include uranyl in the same coordination environment as calcium. Spectral deconvolution of TRLFS measurements on the NUC revealed the unexpected presence of two distinct chemical environments consistent with published spectra of U(VI)-substituted synthetic calcite and aragonite. Apparently, some U(VI) substitution sites in calcite distorted to exhibit a local, more energetically favorable aragonite structure. TRLFS measurements of the Hanford sediments NP4-1 and NP1-6 were similar to the NUC in terms of peak positions and intensity, despite a small CaCO3 content (1.0 to 3.2 mass %). Spectral deconvolution of the sediments revealed the presence of U(VI) in calcite and aragonite structural environments. A third, unidentified U(VI) species was also present in the NP1-6 sediment. TRLFISM measurements at multiple locations in the different sediments displayed only minor variation, indicating a uniform speciation pattern. Collectively, the measurements implied that waste U(VI), long-resident beneath the sampled disposal pond (32 y), had coprecipitated within carbonates. These findings have major implications for the solubility and fate of contaminant U(VI).

Calcium Carbonate↗
PubMed2004

In vivo synchrotron study of thallium speciation and compartmentation in Iberis intermedia.

Thallium (TI) is a metal of great toxicological concern and its prevalence in the natural environment has steadily increased as a result of manufacturing and combustion practices. Due to its low natural abundance and increasing demand, TI is the fourth most expensive metal, thus, recovery and reuse could be a profitable endeavor. The hyperaccumulator Iberis intermedia was examined via in vivo micro-X-ray absorption near edge (micro-XANES) and micro-X-ray fluorescence (micro-XRF) spectroscopies to determine the speciation and distribution of TI within leaves of the plant. I. intermedia plants were cultivated under controlled conditions in 0, 10, and 20 mg TI kg(-1) soil leading to a shoot concentration of up to 13 430 mg TI kg(-1) dry weight plant mass during 10 weeks of growth. Live plant leaves were examined by micro-XANES and micro-XRF which determined aqueous TI(I) to be the model species distributed primarily throughout the vascular network. A direct relationship of vein size to TI concentration was observed. The high uptake of TI and high potential biomass of I. intermedia, combined with knowledge of TI speciation and compartmentation within the plant, are discussed in terms of accumulation/tolerance mechanisms, consequences for potential food chain contamination, and phytomining strategies to reclaim TI-contaminated soils, sediments, and waters.

Biodegradation, Environmental↗
PubMed2004

Arsenic speciation of solvent-extracted leachate from new and weathered CCA-treated wood.

For the past 60 yr, chromate-copper-arsenate (CCA) has been used to pressure-treat millions of cubic meters of wood in the United States for the construction of many outdoor structures. Leaching of arsenic from these structures is a possible health concern as there exists the potential for soil and groundwater contamination. While previous studies have focused on total arsenic concentrations leaching from CCA-treated wood, information pertaining to the speciation of arsenic leached is limited. Since arsenic toxicity is dependent upon speciation, the objective of this study was to identify and quantify arsenic species leaching from new and weathered CCA-treated wood and CCA-treated wood ash. Solvent-extraction experiments were carried out by subjecting the treated wood and the ash to solvents of varying pH values, solvents defined in the EPA's Synthetic Precipitation Leaching Procedure (SPLP) and Toxicity Characteristic Leaching Procedure (TCLP), rainwater, deionized water, and seawater. The generated leachates were analyzed for inorganic As(III) and As(V) and the organoarsenic species, monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), using high-performance liquid chromatography followed by hydride generation and atomic fluorescence spectrometry (HPLC-HG-AFS). Only the inorganic species were detected in any of the wood leachates; no organoarsenic species were found. Inorganic As(V) was the major detectable species leaching from both new and weathered wood. The weathered wood leached relatively more overall arsenic and was attributed to increased inorganic As(III) leaching. The greater presence of As(III) in the weathered wood samples as compared to the new wood samples may be due to natural chemical and biological transformations during the weathering process. CCA-treated wood ash leached more arsenic than unburned wood using the SPLP and TCLP, and ash samples leached more inorganic As(III) than the unburned counterparts. Increased leaching was due to higher concentrations of arsenic within the ash and to the conversion of some As(V) to As(III) during combustion.

Arsenates↗
PubMed2004

Lutetium speciation and toxicity in a microbial bioassay: testing the free-ion model for lanthanides.

The validity of the free-ion model (FIM) for the element lutetium (Lu), a member of the lanthanides, was assessed in experiments with the bacterium Vibrio fischeri. The FIM is mainly based on divalent metals and synthetic ligands and has not yet been validated for the trivalent lanthanides. The bioluminescence response of V. fischeri was studied at different Lu concentrations in the presence and absence of natural and synthetic organic ligands [citrate, malate, oxalate, acetate, ethylenediaminetetraacetate (EDTA), and nitrilotriacetate (NTA)]. All ligands were tested separately to ensure that their concentrations would not cause adverse effects themselves. Free Lu3+ concentrations were calculated with a speciation program, after extension of its database with the relevant Lu equilibria. The results confirmed the FIM for Lu: that is, in contrast to total dissolved Lu concentrations, free Lu3+ concentrations had an apparent relationship with the response of V. fischeri. However, a contribution of minor inorganic Lu complexes cannot be ruled out. In the presence of malate and oxalate, the EC50 for Lu3+ decreased faster in time than for the other ligands, indicating lower elimination rates. With an EC50 of 1.57 microM, Lu3+ is more toxic than La3+, Cd2+, or Zn2+ and approximately equally as toxic as Cu2+. Although the pH increased slightly during the experiments, it was shown that the influence of pH on Lu speciation was limited.

Aliivibrio fischeri↗
PubMed2004

Spectroscopic and diffraction study of uranium speciation in contaminated vadose zone sediments from the Hanford site, Washington state.

Contamination of vadose zone sediments under tank BX-102 at the Hanford site, Washington, resulted from the accidental release of 7-8 metric tons of uranium dissolved in caustic aqueous sludge in 1951. We have applied synchrotron-based X-ray spectroscopic and diffraction techniques to characterize the speciation of uranium in samples of these contaminated sediments. UIII-edge X-ray absorption fine structure (XAFS) spectroscopic studies demonstrate that uranium occurs predominantly as a uranium(VI) silicate from the uranophane group of minerals. XAFS cannot distinguish between the members of this mineral group due to the near identical local coordination environments of uranium in these phases. However, these phases differ crystallographically, and can be distinguished using X-ray diffraction (XRD) methods. As the concentration of uranium was too low for conventional XRD to detect these phases, X-ray microdiffraction (microXRD) was used to collect diffraction patterns on approximately 20 microm diameter areas of localized high uranium concentration found using microscanning X-ray fluorescence (microSXRF). Only sodium boltwoodite, Na(UO2)(SiO3OH) x 1.5H20, was observed; no other uranophane group minerals were present. Sodium boltwoodite formation has effectively sequestered uranium in these sediments under the current geochemical and hydrologic conditions. Attempts to remediate the uranium contamination will likely face significant difficulties because of the speciation and distribution of uranium in the sediments.

Environmental Pollutants↗
PubMed2005

Speciation of Co(II) and Ni(II) in anaerobic bioreactors measured by competitive ligand exchange-adsorptive stripping voltammetry.

Competitive ligand exchange-adsorptive stripping voltammetry is applied to speciation analysis of dissolved Ni(II) and Co(II) in an anaerobic bioreactor and similar batch media. Co and Ni speciation in these media can be measured down to concentration levels of ca. 1 nM. Sulfide interference is avoided via removal as H2S. In methanogenic bioreactors, up to 95% of the dissolved Co and Ni is present in strongly bound forms, with complex stabilities > or =10(8)-10(9) and 10(7)-10(8) mol(-1) L, respectively. In effluent from sulfate-reducing bioreactors, Co is also found to be present in a strongly bound form, and up to micromolar levels of strongly complexing excess ligand was detected. The predominant presence of Co and Ni in strong complexes, with concomitant low free dissolved concentrations, is significant for limitation by these elements in anaerobic bioreactors.

Anaerobiosis↗
PubMed2006

Spatial and temporal variability of arsenic solid-state speciation in historically lead arsenate contaminated soils.

The arsenic (As) solid-state speciation (i.e., oxidation state, precipitates, and adsorption complexes) is one of the most important factors controlling dissolved As concentrations at As contaminated sites. In this case study, two representative subsurface samples (i.e., oxidized and semi-reduced sites) from former lead arsenate contaminated soils in the northeastern United States were chosen to investigate the effects of aging on As retention mechanisms using multiscale spectroscopic techniques. X-ray powder diffraction (XRD), synchrotron based microfocused (micro) XRD, in situ micro-synchrotron based X-ray fluorescence spectroscopy (SXRF), and micro-X-ray absorption near edge structure (XANES) spectroscopy were used to compliment the final bulk X-ray absorption spectroscopy (XAS) analyses. In the sample from an oxic area, As is predominantly (approximately 71%) present as As(V) adsorbed onto amorphous iron oxyhydroxides with a residue (approximately 29%) of an original contaminant, schultenite (PbHAsO4). Contrarily, there is no trace of schultenite in the sample from a semi-reduced area. Approximately 25% of the total As is present as adsorbed phases on amorphous iron oxyhydroxide and amorphous orpiment (As2S3). The rest of the fractions (approximately 46%) were identified as As(V)-Ca coprecipitates. This study shows that aging effects can significantly alter the original chemical constituent (schultenite) in soils, resulting in multi and site-specific As solid-state speciation. The variability in spatial and temporal scale may be important in assessing the environmental risk and in developing in situ remediation technologies.

Arsenates↗
PubMed2006

Mercury speciation in coal-fired power plant plumes observed at three surface sites in the southeastern U.S.

Elemental Hg (Hg0), reactive gaseous Hg (RGM) and fine particulate Hg (Hgp) were measured intermittently at three sites in the southeastern U.S. from June 2001 through November 2004. Simultaneous measurements of SO2 and NOy were used to identify plumes from coal fired power plants (CFPPs). Emission signatures and back trajectories were used to identity specific CFPPs, and to compare observed (i.e., at the site) versus expected (i.e., at the stack) Hg speciation. Results for 41 precipitation-free plume events show that observed RGM:SO2 is substantially lower (by a factor of 2-4) than expected RGM:SO2. Hgp represented 2%, or less, of total-Hg in CFPP plumes, in general agreement with emission estimates. Results for 21 events, where both RGM and Hg0 could be estimated, show that total-Hg (i.e., RGM + Hg0) was essentially conserved from the point of emission to the site, and that Hg0 was the dominant form (average 84%). Emission estimates, based on coal analyses and the EPRI-ICR Hg speciation model, indicate that Hg0 should represent about 42% of Hg in the observed plumes. Possible explanations for these differences include, but are not limited to, in-plume reduction of RGM to Hg0, measurement error, errors in emission estimates, and depositional losses. Further work is needed to confirm these results and to determine if they apply to CFPPs in general, or the limited set of observed CFPPs.

Air Pollutants↗
PubMed2006

Microscopically focused synchrotron X-ray investigation of selenium speciation in soils developing on reclaimed mine lands.

Chemical speciation determines Se solubility and therefore its bioavailability and potential for transport in the environment. In this study we investigated the speciation of Se in soil developed on reclaimed mine sites in the U.S. Western Phosphate Resource Area (WPRA) using micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy and micro-X-ray fluorescence (micro-XRF) mapping. Selenium was nonuniformly distributed in the soils and positively correlated with Fe, Mn, Cu, Zn, and Ni. Sixteen points of interest (POI) from three soil samples were analyzed with micro-XANES spectroscopy. The XANES data indicated that Se is present in the soils in at least three oxidation states, Se(-II, 0), Se(IV), and Se(VI). Selenides or elemental Se dominated 7 of the 16 POI. Selenate was the dominant species at only one of the POI. The remaining eight POI were composed of both Se(IV) and Se(VI), with minor Se(-II, 0) contributions. The results of this research suggest that the reduced Se species in the soil parent material are oxidizing to Se(VI), one of the more mobile species of Se in the environment. This information can be used to better predict and manage Se availability in soils.

Mining↗
PubMed2006

Reduced inorganic sulfur speciation in drain sediments from acid sulfate soil landscapes.

We examined processes regulating reduced inorganic sulfur (RIS) speciation in drain sediments from coastal acid sulfate soil (ASS) landscapes. Pore water sulfide was undetectable or present at low levels (0.6-18.8 microM), consistent with FeS(s) precipitation in the presence of high concentrations of Fe2+ (generally >2 mM). Acid-volatile sulfide (AVS), with concentrations up to 1019 micromol g(-1), comprised a major proportion of RIS. The AVS to pyrite-S ratios were up to 2.6 in sediment profiles containing abundant reactive Fe (up to approximately 4000 micromol g(-1)). Such high AVS:pyrite-S ratios are indicative of inefficient conversion of FeS(s) to pyrite. This may be due to low pore water sulfide levels causing slow rates of pyrite formation via the polysulfide and H2S oxidation pathways. Overall, RIS speciation in ASS-associated drain sediments is unique and is largely regulated by abundant reactive Fe.

Chemical Precipitation↗
PubMed2006

A stochastic regression approach to analyzing thermodynamic uncertainty in chemical speciation modeling.

Chemical speciation modeling is a vital tool for assessing the bioavailability of inorganic species, yet significant uncertainties in thermodynamic parameters and model form limit its potential for decision-making. In this paper we present a novel method for the quantification of thermodynamic parameter uncertainty and ionic strength correction model uncertainty using Bayesian Markov Chain Monte Carlo (MCMC) estimation methods. These methods allow for the inclusion of correlation modeling, which has not been present in previous work. The MCMC simulations are used to model a natural river water to determine the uncertainty in the calculated environmental speciation of ethylenediamenetetraacetate, a chelating agent that has attracted considerable environmental interest. The results indicate that incorporating correlation among related thermodynamic parameters into the uncertainty model is necessary to correctly quantify the overall system uncertainty. This result indicates the superiority of MCMC estimation methods overtraditional Monte Carlo methods when available data are used to estimate parameter uncertainty in systems with closely related model parameters.

Bayes Theorem↗
PubMed2003

Correlations of synthetic, spectroscopic, structural, and speciation studies in the biologically relevant cobalt(II)-citrate system: the tale of the first aqueous dinuclear cobalt(II)-citrate complex.

Synthetic efforts targeting soluble species of Co(II) with the low molecular mass physiological ligand citric acid led to the isolation of the first dinuclear complex [Co(2)(C(6)H(5)O(7))(2)(H(2)O)(4)](2-), at pH approximately 5, in the form of its K+ (1) and Na+ (2) salts. Both 1 and 2 were characterized analytically, spectroscopically (FT-IR, UV/visible, EPR), and magnetically. Complex 1 crystallizes in the monoclinic space group P2(1)/n, with a = 10.348(5) A, b = 11.578(6) A, c = 12.138(6) A, beta = 112.62(2) degrees, V = 1342(1) A(3), and Z = 2. Complex 2 crystallizes in the monoclinic space group P2(1)/c, with a = 9.234(4) A, b = 11.913(4) A, c = 11.728(6) A, beta = 99.93(2) degrees, V = 1271(1) A(3), and Z = 2. X-ray crystallography on 1 and 2 reveals the presence of two Co(II) ions, in a dinuclear assembly, octahedrally coordinated by two citrate ligands in a tridentate fashion. The octahedral environment around each Co(II) is complemented by another singly bonded citrate belonging to the adjacent Co(II) unit and two water molecules. Magnetic susceptibility and EPR studies on 1, in the solid state, corroborate the X-ray results, indicating a weak interaction between the two Co(II) ions. Moreover, EPR and UV/visible studies in solution suggest that 1 does not retain its dimeric structure, yielding a mononuclear octahedral Co(II)-citrate species. Detailed speciation studies suggest the presence of a number of species including the mononuclear complex [Co(C(6)H(5)O(7))](-), optimally present around pH approximately 5. In consonance with EPR and UV/visible spectroscopy, [Co(C(6)H(5)O(7))](-) is likely the scaffolding unit on the basis of which the dimer [Co(2)(C(6)H(5)O(7))(2)(H(2)O)(4)](2-) is isolated from aqueous solutions. Collectively, this comprehensive study offers significant structural insight into the Co(II)-citrate speciation and the elucidation of the role of Co(II) in biological fluids.

Journal Article↗
PubMed2005

Mononuclear titanium(IV)-citrate complexes from aqueous solutions: pH-specific synthesis and structural and spectroscopic studies in relevance to aqueous titanium(IV)-citrate speciation.

Titanium is a metal frequently employed in a plethora of materials supporting medical applications. In an effort to comprehend the involvement of titanium in requisite biological interactions with physiological ligands, synthetic efforts were launched targeting aqueous soluble species of Ti(IV). To this end, aqueous reactions of TiCl(4) with citric acid afforded expediently, under pH-specific conditions, the colorless crystalline materials Na(6)[Ti(C(6)H(4.5)O(7))(2)(C(6)H(5)O(7))].16H(2)O (1) and Na(3)(NH(4))(3)[Ti(C(6)H(4.5)O(7))(2)(C(6)H(5)O(7))].9H(2)O (2). Complexes 1 and 2 were characterized by elemental analysis, FT-IR, (13)C-MAS solid state and solution NMR, cyclic voltammetry, and X-ray crystallography. 1 crystallizes in the triclinic space group P, with a = 15.511(9) A, b = 15.58(1) A, c = 9.848(5) A, alpha = 85.35(2) degrees, beta = 76.53(2) degrees, gamma = 61.97(2) degrees, V = 2042(2) A(3), and Z = 2. 2 crystallizes in the triclinic space group P, with a = 12.437(5) A, b = 12.440(5) A, c = 12.041(5) A, alpha = 83.08(2) degrees, beta = 81.43(2) degrees, gamma = 67.45(2) degrees, V = 1697(2) A(3), and Z = 2. The X-ray structures of 1 and 2 reveal the presence of a mononuclear complex, with Ti(IV) coordinated to three citrate ligands in a distorted octahedral geometry around Ti(IV). The citrates employ their central alkoxide and carboxylate groups to bind Ti(V), while the terminal carboxylates stay away from the Ti(IV)O(6) core. Worth noting in 1 and 2 is the similar mode of coordination but variable degree of protonation of the bound citrates, with the locus of (de)protonation being the noncoordinating terminal carboxylates. As a result, this work suggests the presence of a number of different Ti(IV)-citrate species of the same nuclearity and coordination geometry as a function of pH. This is consistent with the so far existing pool of mononuclear Ti(IV)-citrate species and provides a logical account of the aqueous speciation in the requisite binary system. Such information is vital in trying to delineate the interactions of soluble and bioavailable Ti(IV) forms promoting biological interactions in humans. To this end, chemical properties, structural attributes, and speciation links to potential ensuing biological effects are dwelled on.

Biological Availability↗
PubMed2003

Speciation of selenium compounds from high selenium broccoli is affected by the extracting solution.

The speciation of selenium compounds from high selenium broccoli (876 microg/g) depends on the extraction conditions. Twenty-seven extraction conditions were explored involving nine different buffering systems between pH 1 and pH 9. In nonbuffered extractions of broccoli, more than 40% of the spiked Se-methylselenocysteine was not recovered in the filtered solution. However, in buffered extractions, losses for Se-methylselenocysteine ranged from 10 to 20%. Mass balance indicated that approximately 30% of naturally occurring selenium in broccoli samples was volatilized and lost to the atmosphere when buffered extractions were made. Solid phase extractions indicated that the polarity of selenium compounds in solution was also dependent on the extracting solution. High-pressure liquid chromatography coupled to an inductively coupled plasma mass spectrometer was used to show that selenium compounds extracted from broccoli reacted with the extracting solution. Compound identities were assigned by matching retention times to standards of selenite, selenate, methylseleninic acid, Se-methylselenocysteine, selenomethionine, and the selenonic acids of Se-methylselenocysteine and selenomethionine. Changes in speciation were analyte-, pH-, and buffer-dependent, but generally, a higher pH resulted in more highly oxidized selenium compounds. For valid conclusions to be drawn from the analytical data, the extraction conditions should match the conditions present in the matrix or be specified for a particular application such as a simulated gastrointestinal digestion.

Brassica↗
PubMed2003

Characterization of sulfur speciation in low molecular weight subunits of glutenin after reoxidation with potassium iodate and potassium bromate at different pH values using x-ray absorption near-edge structure (XANES) spectroscopy.

Sulfur speciation in low molecular weight (LMW) subunits of glutenin after reoxidation with potassium iodate and potassium bromate at different pH values, aged subunits of glutenin as well as gluten, and gliadin have been investigated in situ by S K-edge X-ray absorption near-edge structure (XANES) spectroscopy. XANES spectra were analyzed quantitatively using a least-squares fitting routine to provide relative percentage contribution of different sulfur species occurring in the samples. Using potassium iodate and potassium bromate for reoxidation of reduced LMW subunits of glutenin led not only to disulfide states but also to higher oxidation states (sulfoxide state, sulfonic acid state). Strongest oxidation occurred at low pH values. Higher oxidation states were also predominantly detected in the aged subunits of glutenin, whereas the disulfide state was the main sulfur species in gluten and gliadin samples. The results showed that the oxidation state of sulfur prior to oxidation (thiol, disulfide) strongly influences sulfur speciation after oxidation. The choice of the oxidizing reagent seems to be of minor importance.

Bromates↗
PubMed2005

Arsenic speciation in farmed Hungarian freshwater fish.

Arsenic speciation analysis was carried out on freshwater farmed fish collected from an area with elevated groundwater arsenic concentrations in Hungary as well as from outside of the area (control samples). The arsenic species were determined by high-performance liquid chromatography-inductively coupled plasma mass spectrometry on methanol extracts of the muscle tissue from the fish. Catfish (Claries gariepinus) were raised in geothermal water where the average total arsenic concentrations were 167 (contaminated sites) and 15.1 ng As mL(-1) (control); they were all fed an artificial diet containing 2880 microg As kg(-1) total arsenic, mostly present as arsenobetaine. In the catfish, the accumulated total arsenic (2510-4720 microg As kg(-1)) was found mostly in the form of arsenobetaine suggesting that uptake of arsenic was dominated by their diet. Carp (Cyprinus carpio) were cultured in surface lakes with no significant arsenic pollution and had total arsenic concentrations ranging from 62 to 363 microg As kg(-1). The arsenic species found in the carp extracts differed markedly from those in the catfish in that no arsenobetaine was detected. Most samples of carp from the investigated sites contained low concentrations of As(III) (arsenite), As(V) (arsenate), MA (methylarsonate), and DMA (dimethylarsinate), and no other compounds were detected. The four individuals from the control site, however, all contained appreciable levels of oxo-arsenosugar-glycerol and oxo-arsenosugar-phosphate. Indeed, the oxo-arsenosugar-phosphate dominated the speciation pattern for these carp contributing about 75% of the sum of species. The contrast between these two freshwater aquaculture species regarding total arsenic and arsenic species has relevant toxicological aspects in terms of food safety.

Animals↗