Fraction Of Mn Research Articles

Evolution of Cr, Cu, Mn, and Zn during the composting process of chicken manure and their integrated potential ecological risk assessment

The aim of this study was to ascertain the evolution of Cr, Cu, Mn, and Zn during the composting process of chicken manure and their integrated potential ecological risk. This study detected the total amounts of Cr, Cu, Mn, and Zn in 4 samples collected at four different stages in the composting workshop of an intensive chicken farm in Chengdu, China. Furthermore, the chemical fractionation of the four heavy metals was analyzed by the BCR (European Community Bureau of Reference) three-step sequential extraction procedure for each sample. At last, the integrated potential ecological risk of Cr, Cu, Mn, and Zn in the compost at four different stages was evaluated by the procedure of potential ecological risk assessment based on its results of chemical fractionation of Cr, Cu, Zn, and Mn. During the composting process, the total amounts of Cr, Cu, Zn and Mn presented an increasing trend, significantly. Nevertheless, the residual fraction (Res-F) percentage of Cr, Zn, and Cu increased, and the acid extractable fraction (Aci-F) percentage of Mn decreased. The value of integrated potential ecological risk of the four heavy metals in the final product was 9.91. These results indicated the integrated potential ecological risk of the four heavy metals is low. This study provided a support on the promotion and utilization of compost for the intensive chicken farms in China.

Ubiquitous first-order transitions and site-selective vanishing of the magnetic moment in giant magnetocaloric MnFeSiP alloys detected by Mn55 NMR

We report on a study on a representative set of FeP-based MnFePSi samples by means of Mn NMR in both zero and applied magnetic field. The first-order nature of the magnetic transition is demonstrated by truncated order parameter curves with a large value of the local ordered moment at the Curie point, even at compositions where the transition appears second order from magnetic measurements. No weak ferromagnetic order could be detected at Si-poor compositions showing the kinetic arrest phenomenon, but rather the phase separation of fully ferromagnetic domains from volume fractions where Mn spins are fluctuating. The more pronounced decrease of the ordered moment at the $3f$ sites than at the $3g$ sites on approaching ${T}_{C}$, characteristic of the mixed magnetism of these materials, is shown to be driven by the drop of the $3f$ spin density instead of enhanced spin fluctuations. The temperature-driven $3f$ spin extinction is demonstrated to evolve into a truly nonmagnetic state of the $3f$ Mn ions well above ${T}_{C}$, in agreement with theoretical models and in contrast with previous experiments who detected just a partial moment quenching. Besides ``normal'' $3f$ Mn ions undergoing a magnetic to spinless state transition, NMR in Mn-rich compositions detects the disproportionation at $3f$ sites of a significant minority Mn fraction with negligible hyperfine couplings, which retains its diamagnetic character independent of temperature. Such a diamagnetic fraction qualitatively accounts for the reduced average $3f$ moment previously reported at large Mn concentrations.

Dynamics and transformations of micronutrients in agricultural soils as influenced by organic matter build-up: A review

Abstract The dynamics and transformations of micronutrients (Zn, Cu, Fe, Mn, B and Mo) in soils, are governed by various factors like pH, EC, soil organic matter etc. Soil organic matter (SOM) is known to modify different physiochemical reactions that influence the available component of micronutrients. Soil organic matter favors reduced (lower redox potential) environment and enhances the accessibility of micronutrient cations in the soil. Also, SOM has direct and indirect impacts on nutrient transformations. Soil organic matter (SOM) also serves as source of soil organic carbon (SOC) comprising about 60% on a mass basis. Under reduced environment the addition of SOM increased complexed forms of micronutrients. Build-up of SOM in soil converts adsorbed fractions to more plant-accessible forms of micronutrients. Soil organic matter addition increases the water soluble and exchangeable forms of micronutrients in soil which further increase the uptake of micronutrients. High amount of SOM in soils assists the various reactions of micronutrients resulting in formation of more stable complexes of micronutrient. Soil organic matter binds more Zn, Cu, B and Mo compared to Fe and Mn because the former are less sensitive to redox changes. The accretion of organic matter near the soil surface increases transformations (towards adsorbed fractions) of Mn and Fe and possibly decreases the availability of Zn, Cu, B and Mo by causing their redistribution among other complex fractions.

Incorporating bioaccessibility into health risk assessment of heavy metals in particulate matter originated from different sources of atmospheric pollution

Rapid industrialization and urbanization have resulted in widespread pollution of airborne particulate matter (PM) containing various heavy metals with adverse human-health effects. Health risk assessment of PM calls for accurate evaluation of the bioaccessibility, instead of the total content, of heavy metals in PM. Here, we demonstrated that the leachable fraction of particle-bound As, Pb, Cr, Mn, Cd, Cu, Ni and Zn in lung fluid within the typical retention duration of particles in human lungs varied drastically among particles originated from different air pollution sources, including coal combustion, biomass combustion, fugitive dust, road dust, construction dust, cement and soil. Moreover, bioaccessibility of heavy metals, particularly in biomass combustion, cement and soil particles, was strongly dependent on pollution sources, and the particulate Cu, Ni, Pb and Cd appeared to be the primary indicators of the source dependence of heavy metal bioaccessibility. Using total rather than bioaccessible concentrations of particle-bound heavy metals not only led to overestimation of the health risk of source particles, but more importantly, inaccurate identification of the high-risk pollution sources and the priority metal pollutants in the source particles. When considering bioaccessibility of particle-bound heavy metals examined in this study, coal combustion products exhibited the highest carcinogenic and noncarcinogenic risks among all source particles, whereas cement particles would be the source with highest risk based on total metal content. As and Mn appeared to be the main drivers for the noncarcinogenic risks of source particles, while As, Ni and Cr were the major contributors to the carcinogenic risks of source particles, significantly different from those based on total contents. This research underlines the importance of incorporating bioaccessibility into health risk indexes of frequently occurring particle-bound heavy metals from specific air pollution sources, which will facilitate risk-based assessment of source contribution and hence effective source regulation of airborne PM.

Crystal Structure and Magnetic Properties of Non-Stoichiometric Co<sub>2</sub>MnGa Heusler Alloy

Crystal structure and magnetic properties of Heusler-alloy Co2MnGa were examined systematically using non-stoichiometric compositions of Co and Mn element from the Czochralski as-grown single crystal samples. The crystalline structure of each sample was characterized by means of X-ray powder diffraction technique. Each sample was treated with and without heat treatment at 923 K for 10 hours. The effects of Co and Mn excess were observed in the lattice constants for both treatments. The L21-type crystal structure was observed only for the heat-treated samples. The changes in lattice constants are attributed to the substitution of atomic sites. The excess of Co tends to decrease the crystal volume, in opposite to the excess of Mn. In order to investigate the Slater-Pauling rule in the non-stoichiometric samples, the saturation magnetic moments were measured from the field-dependent magnetization measurement for the as-grown samples at 2 K. The deviation from the Slater-Pauling rule was found in the lower concentration of valence electron which associated to the lower total fraction of both Co and Mn. This indicates that the magnetic interactions of these materials cannot only be contributed to the number of valence electron.

Fine scale study of major and trace elements in the Fe-Mn nodules from the South China Sea and their metallogenic constraints

Many marine Fe-Mn polymetallic nodules may contain high concentrations of Mn, Cu, Ni, Zn, Co and rare earth elements plus yttrium (REY). To determine the occurrence and enrichment processes of these metals in the Fe-Mn nodules, we conducted high resolution mineralogical and geochemical studies on the Fe-Mn nodules collected from the South China Sea. In-situ EPMA and LA-ICP-MS analyses and elemental imaging were performed on individual microlayers of the nodules to reveal the major and trace element distributions.The whole-rock mineralogical and chemical compositions of the Fe-Mn nodules indicate a hydrogenetic origin. The Mn mineral phases are mainly composed of nanocrystalline vernadite with interlayered 10 Å and 7 Å phyllomanganates, such as todorokite, birnessite, and buserite. Fe(-Ti) oxides/hydroxides are intergrown and essentially X-ray amorphous feroxyhyte and goethite. We recognize two main types of microlayers: Type-A layer (suboxic diagenetic precipitates) containing a high Mn/Fe ratio and high concentrations of Cu, Ni, Zn, Ba, Li and Mg, and Type-B layer (oxic hydrogenetic accretions) with low fractionation of Mn and Fe and high contents of Co, REY, Ti, Sr and Pb. Furthermore, elemental mapping indicates that the enrichments of Co and REY are mainly associated with Fe mineral phases rather than Mn ones, which are enriched in Mg, Cu, Ni, Zn, Li and Ba. Two mineralization processes and metal distributions in the individual microlayers are identified in the Fe or Mn mineral phases. The occurrence of 10 Å and 7 Å phyllomanganates in Type-A layers are commonly enriched in trace metals such as Ni, Cu, Zn, Li, Ba, and Mg, whereas the metals for the Type-B layers include Co, Ti, Pb, Sr, REY, which may be carried by the intergrowing Fe(-Ti) oxyhydroxides and vernadite. Thus, hydrogenesis and diagenesis facilitate the enrichment of Fe-Co-Ti-Sr-Pb-REY and Mn-Ni-Zn-Cu-Li-Ba-Mg, respectively, during the mineralization of the South China Sea nodules.

Ecodynamics and bioavailability of metal contaminants in a constructed wetland within an agricultural drained catchment

Constructed wetlands are designed to mitigate nutrient and pesticide fluxes from agricultural catchments. Nevertheless, information on their efficiency in removing non-degradable contaminants such as metals is still scarce. This study aimed to explore the metallic signature and fate of metals within the Rampillon wetland (France) receiving water from a drained 355-ha catchment under intensive agriculture. Original monitoring coupling classic, time-integrated and bioaccumulation-based tools was achieved to characterise spatiotemporal dynamics of various metals (As, Cd, Cr, Co, Cu, Mn, Ni, Pb, Sb, Se and Zn). To assess metal inflows and mitigation, samples of dissolved and particulate metals were collected bimonthly at the inlet and outlet of the wetland over 3 months. Simultaneously, time-integrated (sediment traps and passive samplers) and bioaccumulation-based (caged gammarids and biofilms) tools were deployed to monitor temporal changes in metal speciation and bioavailability. To gain insight into the spatial distribution of metals between abiotic and biotic matrices, sediments and indigenous invertebrates with contrasted ecologies were sampled in different cells of the wetland. The results showed time-integrated tools were more suitable than bimonthly samples to quantify metal mitigations because of temporal fluctuations and low contamination levels. Significant mitigations were thus observed in trapped sediments for all metals (ranged 11–23%, except Mn) as well as in the DGT-labile fraction for Cd, Cr, Co, Mn and Ni (ranged 13–51%). Bioaccumulation levels in biofilms also revealed a decrease in metal bioavailability at the outlet. Furthermore, the spatial survey supported the central role of sediments in metal trapping and the beneficial effect of this wetland for local biodiversity in terms of exposure. To conclude, this study provides valuable information on the ecodynamics and bioavailability of metals required for sustainable management of such artificial ecosystems and furthermore, of agricultural areas.

Relation between changes in organic matter structure of poultry litter and heavy metals solubility during composting

Poultry litter (PL) is widely used as fertilizer because of its rich N, P and Ca content. When PL is applied to previously untreated soil, it is a potential contaminant. Composting is an alternative for stabilizing organic and mineral components. This study aimed to elucidate the structural changes and its influence on the solubility of heavy metals in poultry litter during the first 30 d of composting, which is the period when the most intense transformations occur. For this analysis, the transformation dynamics of the organic structures and the availability of mineral elements were studied via spectroscopic characterization, total heavy metal content determination and chemical fractionation at three composting times (0, 15, and 30 d). During composting, the material's aromaticity increased, while its aliphaticity decreased, and the hydrophobicity index increased as the polarity decreased. These results indicate that during the first 30 d, PL composting occurs via transformation of the most labile structures (carbohydrate, peptide and fatty acid fragments), thereby preserving the most stable and least functionalized structures. Composting increased the concentrations of Cu, Cr, Pb and Zn and the transformation of CAlk-O and CAlk-di-O associated with peptides and carbohydrates and favored solubilizing and leaching a water-soluble fraction rich in these compounds. The labile fractions of Fe and the humified organic matter fractions of Cu, Fe, Mn, Zn, and Al increased. The structural changes reduced heavy metal solubility, thus indicating that after 30 d of composting, the heavy metal contamination risk is low.

Determination and In Vitro Bioaccessibility Evaluation of Cu, Fe, Mn, and Zn in Chia (Salvia hispanica L.) Seeds by ICP OES

The objective of this study was to determine the total content and estimate the bioaccessible fraction of Cu, Fe, Mn, and Zn in chia seeds (Salvia hispanica L.) by inductively coupled plasma optical emission spectrometry (ICP OES). For the evaluation of the total content, a method of acid digestion was developed, using a complete factorial design 23, in a digester block with reflux system using cold finger, and the variables chosen were as follows: volume of nitric acid, sulfuric acid, and hydrogen peroxide. Optimization provided the best conditions considering 5.0 mL of HNO3 65% m m−1, 0.5 mL of H2SO4 98% m m−1, and 3.0 mL of H2O2 30% m m−1. The detection limits, in μg g−1, were 0.18 (Cu), 0.22 (Fe), 0.28 (Mn), and 0.37 (Zn). The analyte addition and recovery test were applied to evaluate the accuracy and recovery percentage values ranging from 84 to 114% were obtained, which is considered adequate for quantitative analysis. Precision was expressed as relative standard deviation (% RSD). It was less than or equal to 7.6% (n = 10) for all analytes. The procedure was applied to 10 samples of chia seed commercialized in Salvador (Brazil). The following concentration ranges, in μg g−1, were found: Cu (12–24.2), Fe (53.2–108), Mn (29.8–84.2), and Zn (45.8–77.4). Bioaccessibility was assessed using an in vitro method that takes into account the entire gastrointestinal tract. The following bioaccessible fractions were obtained in percent: Cu (3.6–14), Fe (5.2–5.5), Mn (5.8–29.1), and Zn (< 0.7 μg g−1). The procedure was validated through a mass balance (bioaccessible content + residual fraction compared with the total content), which presented percentages of recovery ranging from 82 to 156%. This new information provides a starting point for more complex evaluations from the nutritional point of view, including the establishment of a recommended daily dietary intake for this frequently consumed seed.

Characteristics of Fe and Mn bearing precipitates generated by Fe(II) and Mn(II) co-oxidation with O2, MnO4 and HOCl in the presence of groundwater ions

In this work, we combined macroscopic measurements of precipitate aggregation and chemical composition (Mn/Fe solids ratio) with Fe and Mn K-edge X-ray absorption spectroscopy to investigate the solids formed by co-oxidation of Fe(II) and Mn(II) with O2, MnO4, and HOCl in the presence of groundwater ions. In the absence of the strongly sorbing oxyanions, phosphate (P) and silicate (Si), and calcium (Ca), O2 and HOCl produced suspensions that aggregated rapidly, whereas co-oxidation of Fe(II) and Mn(II) by MnO4 generated colloidally stable suspensions. The aggregation of all suspensions decreased in P and Si solutions, but Ca counteracted these oxyanion effects. The speciation of oxidized Fe and Mn in the absence of P and Si also depended on the oxidant, with O2 producing Mn(III)-incorporated lepidocrocite (Mn/Fe = 0.01–0.02 mol/mol), HOCl producing Mn(III)-incorporated hydrous ferric oxide (HFO) (Mn/Fe = 0.08 mol/mol), and MnO4 producing poorly-ordered MnO2 and HFO (Mn/Fe > 0.5 mol/mol). In general, the presence of P and Si decreased the crystallinity of the Fe(III) phase and increased the Mn/Fe solids ratio, which was found by Mn K-edge XAS analysis to be due to an increase in surface-bound Mn(II). By contrast, Ca decreased the Mn/Fe solids ratio and decreased the fraction of Mn(II) associated with the solids, suggesting that Ca and Mn(II) compete for sorption sites. Based on these results, we discuss strategies to optimize the design (i.e. filter bed operation and chemical dosing) of water treatment plants that aim to remove Fe(II) and Mn(II) by co-oxidation.

Geochemical Fractionation and Assessment of Probabilistic Ecological Risk of Potential Toxic Elements in Sediments Using Monte Carlo Simulations.

The need for further research into potentially toxic elements in Serbian rivers led to an investigation of distributions, sources, and ecological risks in a sample base of sediments from 15 rivers. The analyses were carried out through both experimental and theoretical methods. Geochemical fractionation of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, As, V, and Zn in sediments was studied using a sequential extraction procedure. Both a Håkanson risk index (RI) and a Monte Carlo simulation (MCS) were used in order to estimate ecological risk, applying the probability distribution of RI values instead of single-point calculations. In order to both further the development of the used method and include additional processes, software for the simulations was developed instead of using proprietary solutions. Metal fractionation showed high percentage recoveries of Cd, Cr, Co, Cu, Fe, Ni, and V in residual fractions. The high content of Pb, Mn, and Zn in mobile fractions might cause serious environmental concerns. In some localities, Cu and Cd could be problematic elements, since their mobility was high. An environmental assessment based on the described criteria provided risk levels varying from low to median (mainly contributed by Cd and Cu).

Accumulation of heavy metals by wild edible mushrooms with respect to soil substrates in the Athens metropolitan area (Greece)

Six wild edible mushroom species, Agaricus bisporus, A. bitorquis, A. gennadii, Coprinus comatus, Psathyrella candolleana and Volvopluteus gloiocephalus, were collected from the Greater Athens area (Greece), together with their soil substrates (two depth-layers) for studying bioaccumulation of heavy metals in a densely populated urban environment. Total and bioavailable Cr, Cu, Fe, Mn, Ni, Pb and Zn concentrations in soils were assessed along with their respective concentrations in mushrooms, and were evaluated in conjunction with soil properties, including K, P and Na content, CaCO3 equivalent percentage, mechanical composition, pH and organic matter. In particular, Cu, Pb, Zn and Ni displayed a high variability in their total and bioavailable concentrations measured in the upper soil layer. Relatively high Pb and Ni contents were measured in mushrooms, while Cu, Zn, Fe and Mn concentrations varied considerably. No significant correlations were detected between total concentrations of heavy metals in soils and mushrooms, whereas bioavailable fractions for several metals were significantly correlated with their respective content in A. bisporus, C. comatus, P. candolleana and V. gloiocephalus. K, Na and P concentrations in soils were associated to the content of several metals in fruit-bodies. The effect of soil texture on metals accumulation by mushrooms was species-dependent since high correlations were found for V. gloiocephalus and C. comatus only. Interactions between metals content in fruit-bodies seem to be species-specific except for Ni vs. Fe and Mn vs. Fe, which are positively correlated in all cases. Overaccumulation of metals in fruit-bodies was established only in respect to the bioavailable fractions of Cu, Mn, Zn and Ni in soil. The levels of toxicity for Pb were exceeded in mushrooms of five species, whereas the rest of the heavy metals (with the exception of Cu) were detected at lower contents than their recommended dietary allowances or tolerable upper intake levels.

An alternative sequential extraction scheme for the determination of trace elements in ferrihydrite rich sediments

Sequential extraction schemes (SES) were evaluated to investigate the fractionation of Al, As, Cd, Cs, Cr, Co, Cu, Fe, Mn, Mo, Pb, Sr, U and Zn between the different mineral phases in iron oxide rich deposits of a former uranium mining site. Ineffective dissolution of iron oxide was observed when applying the BCR sequential extraction scheme. The hydroxylamine hydrochloride reagent in nitric acid could not effectively dissolve the iron oxide phase, even after several consecutive extractions. The use of sodium pyrophosphate to remove organic matter prior to the dissolution of the iron oxides and the use of oxalic acid buffer and dithionite citrate buffer to dissolve the amorphous and crystalline iron oxides was evaluated. An alternative six step SES for iron oxide rich sediments is proposed consisting of F1) Exchangeable-Carbonate fraction using acetic acid/ sodium acetate buffer (pH 5) F2) Labile organic fraction using sodium pyrophosphate, F3) Easily reducible amorphous oxides using an oxalic acid buffer, F4) Organic and Sulfide fraction using hydrogen peroxide, followed by ammonium acetate extraction, F5) Poorly reducible crystalline oxides using sodium dithionite and F6) residual fraction using a microwave digestion step with hydrofluoric acid, nitric acid and hydrochloride acid mixture. A good correspondence between the sum of the sequential extraction steps and total metal concentrations was found. Both the BCR method and new method were also applied to the CRM BCR 701 providing indicative values for non-certified elements with the BCR method and indicative values for the method presented.

Metal distribution in sediments of a drinking water reservoir: influence of reservoir morphometry and hydrodynamics.

Metal(loid)s in the reservoir sediment tend to be released into the water column when encountering disturbances and thus pose threats to the aquatic system. In this study, sediment and pore water samples collected from eight cross sections in the Biliu River Reservoir (Dalian, China) were analyzed to determine the spatial distributions of six metal(loid)s and their associations with reservoir morphometry and hydrodynamics. The results show that total metal concentrations of the sediments are higher at the sites with greater water depths and are influenced by the reservoir morphometry. Mn is of great concern with respect to its increasing total concentration from the upstream sites to the dam sites. According to the improved BCR sequential extraction procedure, the acid-soluble fraction of Mn increases along the thalweg to the dam, implying the soluble Mn2+ in the upstream hypolimnion, and sediment is possible to be transported longitudinally by water currents. For Fe, Mn, Pb, Cu, and Zn, the reducible fraction accounts for more than 15% of the total metal concentration, which suggests that Fe-Mn (hydr)oxides could be important in scavenging these metals. High Mn concentrations in pore waters close to the dam, with an average value of more than 40mg/L, give rise to significant Mn diffusive flux up to 296.1mg/m2/day.

Potential of Equisetum ramosissimum Desf. for remediation of antimony flotation tailings: a case study

A flooding event caused collapsing of the Stolice flotation tailing dam and spilling of large volumes of sludge into environment. Urgent remediation measures have not been applied due to the lack of financial resources. Remediation values for Sb, Zn, and Pb in the flotation tailing samples were exceeded 20.5, 4.2, and 1.15 times, respectively, emphasizing the need for remediation.Plants growing on mine spoils represent useful tools for environmental monitoring and soil remediation. The appearance of Equisetum ramosissimum as a dominant colonizer on the flotation tailings indicates that biological reclamation of the site is possible. Equisetum ramosissimum shows the ability to phytostabilize and immobilize available fractions of Fe, Mn, Zn, Pb, and Sb. Transfer rate of metals from roots to shoots reveals exclusion of elements from the shoots, preventing their further spreading through the food chain. The results of this study show that E. ramosissimum can be an additional tool for environmental monitoring and remediation of flotation tailings after hazardous events.

Determination of total concentration and bioaccessible fraction of metals in infant cereals by MIP OES

The present study provides information about the total concentration and bioaccessible fraction of metals Al, Ba, Bi, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Pb, Ti and Zn in nine different infant cereal samples. An in vitro digestion method was employed to evaluate the bioaccessibility. The determinations were performed by microwave induced plasma optical emission spectrometry (MIP OES). The bioaccessibility varied according to the type of infant cereal sample. The values of bioaccessible fraction (minimum and maximum) for Cu, Fe, Mn, Pb and Zn were 24–68, 1–10, 7–58, 24–100 and 1–7% of the total concentration, respectively. Al and Ti presented bioaccessibility in only two samples: 6% in the multicereal A and 14% in the rice and oat cereal B, respectively. The concentration of Ba, Bi, Cd, and Cr was below the limit of detection for the bioaccessibility method. The obtained concentrations were lower than the daily recommended intake for essential and toxic elements, with exception of Pb in the rice and oat A sample.

Manganese speciation in Mn-rich CaCO3: A density functional theory study

The manganese content of aragonitic bivalve shells is a potential archival indicator of temporal Mn bioavailability in aquatic environments. The Mn speciation mechanism in biogenic aragonite minerals remains elusive because the analog is challenging to synthesize, and the metastable phase has yet to be fully resolved experimentally. In this study, we performed density functional theory (DFT) computations of hypothetical Mn-doped aragonite to examine its local coordination structure and thermodynamic and electronic properties. Our DFT calculations reproduced the experimental crystal structures and solubility product constants (Ksp) of Mn-doped calcite. The magnetic moment of Mn was close to 5 μB in both Mn-doped calcite and Mn-doped aragonite (Ca1−xMnxCO3). The calculated Ksp of Mn-doped aragonite was higher than that of Mn-doped calcite and increased with Mn content, indicative of the unfavorable coprecipitation of Mn with the aragonite phase. We found that the incorporation of a small mole fraction of Mn into aragonite created significant structural distortion around the Mn site, resulting in mixed coordination numbers of Mn (mainly five and seven). Valence-to-core X-ray emission spectroscopy (XES) measurements are useful in determining the coordination environment of Mn complexes. We calculated theoretical XES spectra, with a 1s core hole in Mn, for Mn-doped calcite and four versions of Mn-doped aragonite. The Boltzmann-averaged spectrum for different coordination numbers in Mn-doped aragonite was akin to an experimental XES spectrum of aragonitic bivalve shells. The energy position of the Kβ2,5 band was calculated to be insensitive to Mn speciation in CaCO3; however, the band intensity was relatively sensitive to Mn speciation. The XES spectrum intensity decreased exponentially with increasing Mn–O distance. This quantitative XES relationship we report can reduce uncertainties in the spectral interpretation due to the absence of an Mn-doped aragonite reference spectrum.

Fractionation and release of Cd, Cu, Pb, Mn, and Zn from historically contaminated river sediment in Southern China: Effect of time and pH.

The release of in situ heavy metals (cadmium [Cd], copper [Cu], lead [Pb], manganese [Mn], and zinc [Zn]) from contaminated river sediment near a Cu-iron mine in South China was experimentally studied. The effects of pH values and the kinetics of heavy metal release were investigated. In addition, species of the 5 metals in the sediment were determined as a function of pH and time. Rates and extents of metal desorption were studied over 30 d, and a 3-parameter, 2-compartment model was used to analyze the desorption kinetics. The rate constants (ks ) for the slowly desorbing fraction of heavy metals were found to be 5 to 6 orders of magnitude lower than the corresponding rate constants (kr ) for the rapidly desorbing fraction, suggesting that slow desorption is the rate-limiting step. The partition coefficients (Kd ) varied significantly among metals, on the order Pb > Cu >Zn > Cd > Mn, indicating that the sediment had a much higher retention capability for strongly hydrolyzed metals than for weakly hydrolyzed ones. The amount of metals released from the sediment decreased dramatically at the final pH of 2 to 4 and leveled off in the pH range of 5 to 8. Release time and pH exhibited a varied influence on the fractionation of metals, and had a more remarkable influence on more mobile fractions and hardly any effect on the residual fraction during the desorption process. The fractionation of strongly adsorbing metals like Pb was not as dependent on release time and pH as it was for the weakly bonded metals like Mn and Cd. The results indicate that in situ heavy metals may exhibit a sustainable potential for release and may increase health risks when the pH of the river is lowered. Environ Toxicol Chem 2019;38:464-473. © 2018 SETAC.

Off-line preconcentration and inductively coupled plasma sector field mass spectrometry simultaneous determination of Cd, Co, Cu, Mn, Ni, Pb and Zn mass fractions in seawater: Procedure validation

Despite the ongoing reduction of emissions of contaminants into the environment, the ocean still represents the most anthropogenically impacted ecosystem worldwide. Sound strategies for marine chemical monitoring call for measurement systems capable of producing comparable analytical results with demonstrated quality. An analytical procedure for simultaneous measurements of the Cd, Co, Cu, Pb, Mn, Ni, Pb and Zn mass fractions in open ocean waters was validated. Procedure validation, including systematic combined uncertainty estimations on measurement results, and the traceability of data are described and explained. Off-line analytes pre-concentration and matrix separation was performed with the commercially available automated seaFAST-pico™ system, followed by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) mass fractions determination. The validation approach applied in the present study is in line with the requirements of ISO/IEC 17025 standard and Eurachem guidelines. Selectivity, working range, linearity, recovery (from 93% to 100%, obtained using the NASS-6 CRM from NRC, Canada), repeatability (1.5–3%), intermediate precision (2–%), limits of detection (0.00006–0.004 μg kg−1) were systematically assessed. The relative expanded uncertainties obtained were at range from 7.0% to 14.0% (k = 2). Excellent results were obtained when applying this procedure to the NASS-7 CRM from NRC, Canada. The potential of this analytical procedure was also tested on open seawater samples from different regions of the world. The validated procedure was applied for the characterisation of the ERM®-CA403 candidate certified reference material and obtained results submitted as the IAEA contribution to this certification.

Atomic-scale mechanisms of single crystal plasticity in CoCrFeMnNi high-entropy alloys

The behavior of CoCrFeMnNi high-entropy alloys under mechanical loading was studied within the framework of the molecular dynamics method. The mechanisms of local structural transformations of the crystal lattice responsible for the onset of plasticity at the tension of CoCrFeMnNi single crystals were determined. A crystallographic analysis of the structure and identification of the defects formed was carried out. Irrespectively on stoichiometric composition of samples the plasticity is realized by the nucleation, growth and intersection of intrinsic stacking faults. Rearrangement of fcc lattice to bcc structure in the regions where the local atom fraction of Fe, Mn and Ni is above average was found to be the mechanism of stacking fault formation. The effect of the stoichiometric composition and crystallographic orientation of single-crystal CoCrFeMnNi samples upon the structural rearrangements at the nucleation and development of plastic deformation under tension was studied.