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pH influences the reactivity of iron (II) minerals towards halogenated pollutants like hexachlorocyclohexanes (HCHs). To explore these incompletely understood interactions, we investigated the carbon isotope fractionation of the δ-HCH isomer during dehalogenation by iron sulfide at pHs spanning a pH range across slightly acidic to alkaline domains (5.8–9.6). The δ-1,3,4,5,6-pentachlorocyclohex-1-ene (δ-PCCH) was the intermediate degradation product, while benzene, monochlorobenzene (MCB), but especially 1,2-dichlorobenzene (1,2-DCB), and 1,2,4-trichlorobenzene (1,2,4-TCB), were the main degradation products of δ-HCH. These degradation products suggested dehydrochlorination as the main degradation pathway of δ-HCH by iron sulfide. Different kinetic experiments indicate that the rate constants (k a) during dechlorination of δ-HCH by iron sulfide rose with pH: 0.003 d−1 (pH 5.8) < 0.034 d−1 (pH 8) < 0.085 (pH 9.3) < 0.286 d−1 (pH 9.6). Upon Rayleigh model calculations, an enrichment factor (εC) of −7.8 ± 1.0 ‰ was calculated for δ-HCH dehalogenation by FeS at pH 8.0. This suggests an apparent kinetic isotope effect (AKIE C) value of 1.049 ± 0.006 for dehydrohalogenation. The magnitude of the isotope effect from this paper furthermore supports dehydrohalogenation and opens the possibility to study the degradation of HCHs by iron (II) minerals containing FeS as mackinawite in oxygen-deprived environments. [Display omitted] • Dehydrohalogenation of δ-HCH occurred during degradation with FeS. • δ-pentachlorocyclohexene was the intermediate degradation product. • The rate constants (k a) during dechlorination of δ-HCH by FeS rose with pH. • Dehydrohalogenation of δ-HCH induced a significant isotope fractionation. [ABSTRACT FROM AUTHOR]

The magnitude of isotopic fractionation during sublimation of ice remains poorly constrained. Field and laboratory studies that span decades have persistently shown conflicting results. A better understanding of fractionation during sublimation is needed to improve interpretation of alpine hydrology, glaciology, paleoclimate and planetary histories that rely on stable isotopic records stored in icy reservoirs. At the core of the problem is the question of whether sublimation occurs as a layer-by-layer process with no fractionation or whether diffusion within the ice and vapor-ice exchange generate fractionation. We present results from an experiment where we suspended ice spheres in temperatures ranging from -25 to -10 °C in an unsaturated atmosphere and used aRayleigh distillation model to estimate fractionation of the spheres. A small, yet statistically significant and repeatable, isotope fractionation (103lnα18O of ∼ −0.6 ‰ and 103lnα2H between −3.0 and − 4.0 ‰ or α = 0.999, α = 0.9940 to 0.9970, respectively) was found during the sublimation of ice. The results indicate the presence of fractionation yet the values are an order of magnitude smaller than would be predicted for equilibrium fractionation at this temperature. By assuming a porosity for the ice of 0.0005 % - which is typical for ice frozen under these conditions, we estimate an increase in diffusivity relative to solid ice consistent with the observed fractionation values. The results help to reconcile how fractionation estimates during sublimation could vary between experimental and observational studies where porosity is not controlled for and can vary substantially across a continuum from porous firn layers to low porosity ice deep in glaciers. • Closed porosity within ice can increase the diffusivity generating a small but observable isotope fractionation. • Secondary processes such as ice compaction can affect porosity, thus the magnitude of isotope fractionation may vary depending on ice type. • Isotope fractionation during sublimation is much lower than equilibrium fractionation predictions, yet statistically significant. [ABSTRACT FROM AUTHOR]

Abstract The Xihuashan and Yaogangxian granitic plutons in South China comprise highly evolved multiphase Li‐rich granites and host quartz‐vein‐type tungsten deposits. The δ7Li values of Phase A (early stage), B (middle stage), and C (late stage) from the Xihuashan pluton are 1.0–1.2‰, 1.1–3.0‰, and 2.4–2.8‰ respectively, increasing through chemical evolution. The granites from the Yaogangxian pluton also display gradually enriched in heavy Li isotopes in a later stage, although systematically lighter than those of the Xihuashan pluton. In both plutons, the δ7Li shows good correlations with SiO2 and Li concentrations as well as Rb/Sr, Nb/Ta, and Zr/Hf ratios, indicating Li isotopic fractionation most likely caused by magmatic differentiation. In situ analyses show that the minerals of Xihuashan pluton record a continuous elemental spectrum, reflecting the results of progressive magmatic differentiation. The δ7Li values of quartz, feldspar, mica, and zircon all correlate well with the chemical evolutions of granitic magma, systematically elevated in Phases B and C relative to Phase A. The Li isotope data of the mineral separates further document that the enrichment of 7Li in the residual melt was most likely due to the equilibrium fractionation between the mineral and melts. The data are interpreted to reflect that intense magmatic differentiation was responsible for Li isotopic variations coupled with the enrichment in the Li, F, P, and rare metals in the late‐phase granites of the Xihuashan pluton. The lithium isotope behavior documented in this study provides new insights into magmatic differentiation and associated rare‐metal mineralization.

Significant uranium (U) isotope fractionation has been observed during abiotic reduction of aqueous U, counter to the expectation that uranium isotopes are only fractionated by bioassociated enzymatic reduction. In our experiments, aqueous U is removed from solution by reductive precipitation onto the surfaces of synthetic iron monosulfide. The magnitude of uranium isotopic fractionation increases with decreasing aqueous U removal rate and with increasing amounts of neutrally charged aqueous Ca-U-CO3 species. Our discovery means that abiotic U isotope fractionation likely occurs in any reducing environment with aqueous Ca ≥ 1 mM, and that the magnitude of isotopic fractionation changes in response to changes in aqueous major ion concentrations that affect U speciation. Our results have implications for the study of anoxia in the ancient oceans and other environments.

The fractionation factor in the magnesium-isotope fractionation between aqueous solutions of magnesium and brucite changes sign with increasing temperature, as uncovered by recent experiments. To understand this behavior, the Reduced Partition Function Ratios and isotopic fractionation factors (Δ26/24Mgbrucite-Mg(aq)) are calculated using molecular models of aqueous [Mg(OH2)6]2+ and the mineral brucite at increasing levels of density functional theory. The calculations were carried out on the [Mg(OH2)6]2+·12H2O cluster, along with different Pauling-bond-strength-conserving models of the mineral lattice of brucite. Three conclusions were reached: (i) all levels of theory overestimate 〈Mg–O〉 bond distances in the aqua ion complex relative to Tutton's salts; (ii) the calculations predict that brucite at 298.15 K is always enriched in the heavy isotope, in contrast with experimental observations; (iii) the temperature dependencies of Wimpenny et al. (2014) and Li et al. (2014) could only be achieved by fixing the 〈Mg–O〉 bond distances in the [Mg(OH2)6]2+·12H2O cluster to values close to those observed in crystals that trap the hydrated ion.

The fractionation factor in the magnesium-isotope fractionation between aqueous solutions of magnesium and brucite changes sign with increasing temperature, as uncovered by recent experiments. To understand this behavior, the Reduced Partition Function Ratios and isotopic fractionation factors (Δ26/24Mgbrucite-Mg(aq)) are calculated using molecular models of aqueous [Mg(OH2)6]2+ and the mineral brucite at increasing levels of density functional theory. The calculations were carried out on the [Mg(OH2)6]2+·12H2O cluster, along with different Pauling-bond-strength-conserving models of the mineral lattice of brucite. Three conclusions were reached: (i) all levels of theory overestimate 〈Mg–O〉 bond distances in the aqua ion complex relative to Tutton's salts; (ii) the calculations predict that brucite at 298.15 K is always enriched in the heavy isotope, in contrast with experimental observations; (iii) the temperature dependencies of Wimpenny et al. (2014) and Li et al. (2014) could only be achieved by fixing the 〈Mg–O〉 bond distances in the [Mg(OH2)6]2+·12H2O cluster to values close to those observed in crystals that trap the hydrated ion.

The direct determination of silicate melts iron and silicon isotopes signature remains a major challenge of high-temperature isotope geochemistry. For this reason, melts are often approximated by silicate glasses. Calculation of precise equilibrium Si and Fe isotopes fractionation factors between minerals and melt would indeed allow us to distinguish equilibrium fractionation from diffusion-driven kinetic fractionation involved in the iron and silicon isotopes signatures of Earth and other planets. In this study, we use for the first time, first-principles molecular dynamics based on density functional theory to determine iron and silicon isotope compositions of different silicate melts, namely: iron-rich basalt, iron-depleted basalt, basanite, trachyte and phonolite. The 57Fe/54Fe reduced partition function ratios (β-factors) of the different melts span over a 1.1 ‰ range at 1000 Kelvin (K) while 30Si/28Si β-factors are much less influenced by the melt composition with a 0.5 ‰ fractionation range at the same temperature. The main parameter controlling iron isotope fractionation in silicate melts having similar iron oxidation state is, after temperature, the average Fe-O bond length. The chemical environment around iron (e.g. Fe-Fe distances) is suggested to contribute to Fe isotope fractionation as well. Silicon isotopes fractionation seems also affected, but to a lesser extent, by its local chemical composition with decreasing Si-Fe distances leading to slightly higher Si β-factor in the melt. From these melts Fe and Si β-factors, a new set of equilibrium fractionation factors between a variety of minerals and melts has been calculated. These new Δ57Fe min-melt and Δ30Si min-melt sets allow us to discuss whether processes such as fractional crystallization, partial melting and diffusion could be responsible for the documented Fe and Si isotopes variations in igneous rocks. Our results suggest that: 1) fractional crystallization may explain at least part of the Fe and Si isotopic evolution during magmatic differentiation, for values up to δ57Fe = 0.65 ‰ and δ30Si = -0.1 ‰, respectively, 2) partial melting of the upper mantle can produce the Mid-Ocean Ridge Basalts (MORB) iron isotopes signature. Finally, we calculated that olivine at equilibrium with a basaltic melt could display an iron isotope composition down to −0.1 ‰ for δ57Fe. Hence, the lower isotopic compositions (δ57Fe < -0.1 ‰) observed in natural olivines are most likely due to diffusion-driven kinetic fractionation. [ABSTRACT FROM AUTHOR]

The Rayleigh distillation isotope fractionation (RDIF) model is one of the most popular methods used in isotope geochemistry. Numerous isotope signals observed in geologic processes have been interpreted with this model. The RDIF model provides a simple mathematic solution for the reservoir-limited equilibrium isotope fractionation effect. Due to the reservoir effect, tremendously large isotope fractionations will always be produced if the reservoir is close to being depleted. However, in real situations, many prerequisites assumed in the RDIF model are often difficult to meet. For instance, it requires the relocated materials, which are removed step by step from one reservoir to another with different isotope compositions (i.e., with isotope fractionation), to be isotopically equilibrated with materials in the first reservoir simultaneously. This "quick equilibrium requirement" is indeed hard to meet if the first reservoir is sufficiently large or the removal step is fast. The whole first reservoir will often fail to re-attain equilibrium in time before the next removal starts. This problem led the RDIF model to fail to interpret isotope signals of many real situations. Here a diffusion-coupled and Rayleigh-like (i.e., reservoir-effect included) separation process is chosen to investigate this problem. We find that the final isotope fractionations are controlled by both the diffusion process and the reservoir effects via the disequilibrium separation process. Due to its complexity, we choose to use a numerical simulation method to solve this problem by developing specific computing codes for the working model. According to our simulation results, the classical RDIF model only governs isotope fractionations correctly at the final stages of separation when the reservoir scale (or thickness of the system) is reduced to the order of magnitude of the quotient of the diffusivity and the separation rate. The RDIF model fails in other situations and the isotope fractionations will be diffusion-limited when the reservoir is relatively large, or the separation rate is fast. We find that the effect of internal isotope distribution inhomogeneity caused by diffusion on the Rayleigh-like separation process is significant and cannot be ignored. This method can be applied to study numerous geologic and planetary processes involving diffusion-limited disequilibrium separation processes including partial melting, evaporation, mineral precipitation, core segregation, etc. Importantly, we find that far more information can be extracted through analyzing isotopic signals of such "disequilibrium" processes than those of fully equilibrated ones, e.g., reservoir size and the separation rate. Such information may provide a key to correctly interpreting many isotope signals observed from geochemical and cosmochemical processes. [ABSTRACT FROM AUTHOR]

The biomineralization of CaCO3 often involves the transformation of amorphous precursors into crystalline phases, which is regulated by various proteins and inorganic ions such as Mg2+ ions. While the effects of Mg2+ ions on the polymorph and shape of the crystalline CaCO3 have been observed and studied, the interplay between Mg2+ ions and CaCO3 during the mineralization remains unclear. This work focuses on the mechanism of Mg2+ ion-regulated mineralization of CaCO3. By tracing the Mg isotope fractionation, the different mineralization pathways of CaCO3 under different Mg2+ ion concentrations had been clarified. Detailed regulatory role of Mg2+ ions at the different stages of mineralization had been proposed through combining the fractionation data with the analyses of the CaCO3 polymorph and shape evolution. These results provide a clear view of the Mg-mediated crystallization process of amorphous CaCO3, which can be used to finely control the phase of the crystalline products according to different needs. [ABSTRACT FROM AUTHOR]

Diffusion is a significant driver of isotope fractionation at high temperatures, but its precise role is difficult to evaluate in many situations due to the sparsity of data on the isotopic mass dependence of the diffusion coefficient. Such data are lacking particularly for diffusion in minerals. The ratio of diffusion coefficients of two isotopes of the same element in the same material can be characterized as the inverse mass ratio raised to an empirical exponent β , but experiments to determine β are challenging and few measurements have been reported. Here, a method is developed to empirically determine β based on numerical modelling of the diffusion-controlled elemental and isotopic redistribution between minerals during slow subsolidus cooling, and comparison of the results to data from natural mineral pairs. The method is applied to the Ca redistribution between orthopyroxene (opx) and clinopyroxene (cpx), where the elemental partitioning equilibrium as a function of temperature has been well characterized experimentally and Ca isotope fractionation data are available in natural samples that experienced slow cooling. We show that the Ca isotope fractionation during cooling is insensitive to the initial temperature, cooling rate or grain size over a broad range of conditions, provided that diffusion is sufficient to re-homogenize opx grains at near-peak temperatures during early cooling. Furthermore, we find that the Ca isotope fractionation established during cooling is much more strongly dependent on the value of β in opx than the value of β in cpx, as long as cpx dominates the Ca budget in the system. Transient heating events produce fractionation in the opposite sense to that developed during cooling, which can diminish or reverse the isotope fractionation for samples that experienced such events after cooling. Based on the largest Ca isotope fractionation that has been documented between opx and cpx in natural samples, it is inferred that for Ca, β opx = 0.04(1). Despite the relatively small inferred value of β opx , diffusive fractionation of Ca isotopes between opx and cpx is significant over a broad range of cooling rates. Similar behavior during sub-solidus cooling is anticipated for other elements with temperature-dependent inter-mineral partition coefficients, and the method developed here has the potential to be used to place constraints on β for many elements, even in minerals where experimental measurements are not feasible. [ABSTRACT FROM AUTHOR]

Due to the different sources of raw materials and manufacturing processes, different automotive paint samples have different isotopic signatures, which can be used as the basis for distinguishing similar paint samples. The varnish is the paint applied on the outermost layer of the car, which is easily affected by the storage conditions. Therefore, the isotope ratios of different varnish samples under different storage conditions were analyzed. Ten automotive varnish samples were collected and stored for 6 months at room temperature away from light, high temperature of 60 ℃, low temperature of-20 ℃ and strong ultraviolet light. After that, the samples were analyzed by elemental analyzer-isotope ratio mass spectrometry (EA-IRMS). The carbon, hydrogen and oxygen isotope values were determined. The results showed that the carbon, hydrogen and oxygen isotope ratios of different paint samples can be used to distinguish different samples, the potential of identification and differentiation of paint samples using stable isotopes of carbon, hydrogen and oxygen were demonstrated. The carbon, hydrogen and oxygen isotope fractionation of the paint samples occurred under different storage conditions. The δ13C value of the samples shifted to a negative value after storage at high temperature and low temperature, greater variation of samples occurred at high temperature, and the influence of strong ultraviolet radiation was weak, which meant that UV light had little effect on the δ13C value of the paint samples. The δ²H value shifted to a positive value under the three conditions, which was most affected by ultraviolet radiation, and minimal change in the condition of high temperature. The δ18O value shifted to more negative under the three conditions. But the shift amplitude of the δ18O value was different between samples of different resin types. Among the three resin types of samples, polymethyl methacrylate lipid resin samples had the smallest offset due to the least oxygen content in the molecules, the variation ranges of glyceryl elaidate and sorbitan monostearate paint samples had little difference under the three storage conditions. Stable isotope analysis method can provide high resolution three-dimensional fingerprints for paint samples, which has great potential in paint identification applications, and can be applied to traceability analysis of paint physical evidence. [ABSTRACT FROM AUTHOR]

Tin (Sn) isotope geochemistry has great potential in tracing geological processes. However, lack of equilibrium Sn isotope fractionation factors of various Sn species limits the development of Sn isotope geochemistry. Equilibrium Sn isotope fractionation factors (124Sn/116Sn and 122Sn/116Sn) among various Sn(II, IV) complexes in aqueous solution were calculated using first‐principles calculations. The results show that the oxidation states and the change of Sn(II, IV) species in hydrothermal fluids are the main factors leading to tin isotope fractionation in hydrothermal systems. For the Sn(IV) complexes, Sn isotope fractionation factors depend on the number of H2O molecules. For the Sn(II) complexes, the Sn isotope fractionation between Sn(II)–F, Sn(II)–Cl and Sn(II)–OH complexes is mainly affected by the bond length and the coordination number of anion, whereas the difference in 1000lnβ values of Sn(II)–SO4 and Sn(II)–CO3 complexes is insignificant with the change of anion coordination number. By comparing the 1000lnβ values of all Sn(II, IV) complexes, the enrichment trend in heavy Sn isotopes is Sn(IV) complexes > Sn(II) complexes. The equilibrium Sn isotopic fractionation factors enhance our understanding of the tin transportation and enrichment processes in hydrothermal systems. [ABSTRACT FROM AUTHOR]

15N/14N ratios of meteorites are a powerful tool for tracing the journey of life-essential volatiles like nitrogen (N), carbon and water from nebular solids to the present-day rocky planets, including Earth. The utility of 15N/14N ratios of samples originating from differentiated protoplanets (e.g., iron meteorites) and planets (e.g., Earth's mantle) for tracing this journey could be affected by the fractionation of N isotopes during core-mantle differentiation, which would overprint their primitive compositions. The extent of N isotopic fractionation during core-mantle differentiation and its effect on the 15N/14N ratios of resulting metallic and silicate reservoirs is, however, poorly understood. Using high pressure–temperature experiments, here we show that equilibrium N isotopic fractionation between metallic and silicate melts (Δ15Nalloy–silicate = δ15Nalloy – δ15Nsilicate = –3.3 ‰ to –1.0 ‰) is limited across a wide range of oxygen fugacity and is much smaller than previous estimates. Also, we present ab initio calculations based on the relevant N speciation in metallic and silicate melts confirming both the magnitude and direction of equilibrium N isotopic fractionation predicted by our experimental results. Limited N isotopic fractionation during core-mantle differentiation suggests that the core and mantle relicts largely preserve the N isotopic compositions of their bulk bodies. Based on the δ15N values of non-carbonaceous iron meteorites (as low as –95 ‰), we predict that the extent of variations in the N isotopic compositions of inner solar system protoplanets was larger than that recorded by enstatite chondrites (δ15N = –29 ‰ to –6‰). As most of the Earth grew primarily via the accretion of similar inner solar system protoplanets, a relatively high δ15N value of present-day Earth's primitive mantle (–5‰) cannot be explained by the accretion of enstatite chondrite-like materials alone and necessitates a significant contribution of 15N-rich materials to the Earth's interior. [ABSTRACT FROM AUTHOR]

Accretion of terrestrial planets involved partial or global melting events such as magma oceans or magma ponds. Mars experienced large-scale differentiation very early in its history, as shown by its 146Sm-142Nd and 182Hf-182W record. The broad variations in ε142Nd and ε142W of SNC meteorites highlight the presence of mantle sources that must have remained isolated, at least partly, after the crystallization of a global magma ocean. In this study, we have investigated whether the crystallization of the martian magma ocean could have generated mantle reservoirs characterized by different silicon isotope signatures, as the fractionation of Si isotopes between minerals and melts is known to depend on pressure. Thus, the goal of this study was to investigate whether there were any relationships between magma ocean crystallisation and possible variations in the Si isotope record of SNC meteorites. High resolution silicon isotope measurements were performed on twelve meteorites from the Shergottite, Nakhlite and Chassignite groups using a Neptune Plus MC-ICP-MS in dry plasma mode. The δ30Si values are in good agreement with previous studies but display a narrower range of variations with a mean value at −0.46 ‰ ± 0.07 (2SD). A magma ocean crystallization model shows that the range of δ30Si in SNCs is consistent with that generated by magma ocean crystallisation. In particular, there is a correlation between calculated 147Sm/144Nd for the moderately depleted mantle sources with δ30Si values; this correlation is consistent with the crystallization model if one includes trapped melt in the cumulates. In contrast, enriched shergottites displayed a very homogenous composition in Sm/Nd ratios, despite significant variability in δ30Si. This observation could be related to either fluid-rock interactions or redox effect during magma differentiation. Altogether, silicon isotope compositions of SNC provide new constraints about magma ocean crystallization processes in Mars. [ABSTRACT FROM AUTHOR]

Aerosol ammonium (NH 4 + ) is a critical component of particulate matter that affects air pollution, climate, and human health. Isotope-based source apportionment of NH 4 + is essential for ammonia (NH 3 ) mitigation but the role of kinetic vs equilibrium controls on nitrogen isotope (δ 15 N) fractionation between NH 3 and NH 4 + remains unresolved. Based on concurrent measurements of NH 3 and NH 4 + in winter Beijing, we observed that the difference of δ 15 N between NH 3 and NH 4 + on clean days (3.3 ± 13.3‰) was significantly lower than that during polluted periods (30.2 ± 11.8‰). This difference signified incomplete equilibrium fractionation and that kinetic fractionation may have occurred between NH 3 and NH 4 + , especially during clean days. Assuming that kinetic and equilibrium fractionation occurred successively, the contribution of nonagricultural emissions to NH 4 + was apportioned to 60.3 ± 12.8%, higher than that of 50.4 ± 17.7% considering only equilibrium fractionation. These results indicate that the source apportionment of NH 4 + considering only equilibrium fractionation in the conventional scenario would underestimate the contribution of nonagricultural emissions by 16.4% (up to 33.1% on clean days). Our analysis highlighted the importance in considering both kinetic and equilibrium fractionation scenarios to improve the precision of NH 4 + source apportionment by using nitrogen isotopes.

Cadmium (Cd) isotopes have recently emerged as novel tracers of Cd sources and geochemical processes. Widespread clay minerals play a key role in Cd migration due to their strong adsorption capacity, but the mechanism of Cd isotope fractionation during adsorption onto clay minerals is poorly understood. Here, we experimentally investigated the adsorption mechanisms of Cd on montmorillonite (2:1) and kaolinite (1:1) by using extended X-ray absorption fine structure (EXAFS) spectroscopy. Our results show that lighter Cd isotopes are preferentially adsorbed on clay minerals, with Δ 114/110 Cd dissolved-adsorbed values of 0.03 ± 0.02‰ for montmorillonite and 0.03 ± 0.03‰ for kaolinite. These values are independent of the pH, initial Cd concentration, and ionic strength. EXAFS indicate that the adsorbed Cd forms octahedral outer-sphere surface complexes with an average Cd-O bond length of 2.25-2.26 Å, identical to Cd-O bonding environment in the Cd(NO 3 ) 2 solution. Our results demonstrate that the extent of Cd isotope fractionation is constrained by structural changes (including the bond length and coordination number) in surface complexes. These findings suggest that Cd adsorption on clay minerals has a minimal impact on the variability of Cd isotopic compositions in soils and sediments, implying that variations in Cd isotope ratios in soils and sediments primarily reflect changes in Cd sources.

To better understand zinc and copper regulation and their involvement in various biochemical pathways as it relates to autism spectrum disorder (ASD), isotopic composition of serum zinc and copper were evaluated in both healthy children and children with ASD in North America. No significant difference in isotopic composition of serum zinc or copper with respect to healthy controls and ASD children were identified. However, the isotopic composition of serum copper in boys was found to be enriched in 65Cu in comparison to previously published healthy adult copper isotopic composition. Furthermore, in both boys and girls, the average isotopic composition of serum zinc is heavier than previously published healthy adult isotopic zinc composition. There was also a negative association between total zinc concentrations in serum and the zinc isotopic composition of serum in boys. Finally, children with heavier isotopic composition of copper also showed a high degree of variability in their zinc isotopic composition. While numerous studies have measured the isotopic composition of serum zinc and copper in adults, this is one of the first studies which measured the isotopic composition of serum copper and zinc in children, specifically those diagnosed with ASD. The results of this study showed that age and gender specific normal ranges of isotopic composition must be established to effectively use isotopic composition analysis in studying various diseases including ASD.

Summary: Determining whether isotope fractionation occurs during root water uptake is a prerequisite for using stem or xylem water isotopes to trace water sources. However, it is unclear whether isotope fractionation occurs during root water uptake in gramineous crops.We conducted prevalidation experiments to estimate the isotope measurement bias associated with cryogenic vacuum distillation (CVD). Next, we assessed isotope fractionation during root water uptake in two common agronomic crops, wheat (Triticum aestivum L.) and maize (Zea mays L.), under flooding after postdrought stress conditions.Cryogenic vacuum distillation caused significant depletion of 2H but negligible effects on 18O for both soil and stem water. Surprisingly CVD caused depletion of 2H and enrichment of 18O in root water. Stem and root water δ18O were more than soil water δ18O, even considering the uncertainty of CVD. Soil water 18O was depleted compared with irrigation water 18O in the pots with plants but enriched relative to irrigation water 18O in the pots without plants.These results indicate that isotope fractionation occurred during wheat and maize root water uptake after full irrigation and led to a heavy isotope enrichment in stem water. Therefore, the xylem/stem water isotope approach widely used to trace water sources should be carefully evaluated. [ABSTRACT FROM AUTHOR]

The basis for the δ13C values of plant tissues used to infer past ecological environments is their relationships with modern ecological conditions. A total of 71 pairs of pollen and leaf samples were collected from Pinus yunnanensis, an endemic species of the Yunnan plateau, in northwestern Yunnan, China. Their carbon isotopic composition was examined to investigate the two tissues' difference of stable carbon isotopes, possible factors affecting their δ13C values, and their distinctiveness within Pinus and Pinaceae. Our study showed that pollen δ13C values range from −32.92 to −26.34‰ with an average of −30.88‰, whereas leaf δ13C values vary between −33.79 and −28.96‰ with an average value of −31.2‰, suggesting an isotope fractionation between the two tissues. A statistically significant negative correlation between the pollen δ13C values and altitudes of the sampling sites as well as no significant correlation between the leaf δ13C values and altitudes suggested that pollen may be more sensitive to some climatic parameters than leaf. A comparison of the pollen and leaf δ13C values from Pinus yunnanensis with the available data from other Pinus species and other genus species of Pinaceae indicated that the pollen and leaf δ13C values of Pinus yunnanensis are the lowest, partially due to the effects of water availability. [ABSTRACT FROM AUTHOR]

Temperature dependencies of the oxygen, carbon, magnesium, and calcium β-factors (from 0 to 1500°C with a step of 10°C) have been determined for Ca–Mg carbonates (calcite, magnesite, dolomite, aragonite) by the "frozen phonon" approach of the density functional theory within the harmonic and quasi-harmonic approximations. For calcite, considering the Ca–Mg isomorphism, the temperature dependence of oxygen and carbon β-factors of isotope fractionation is described by the following equations: 103ln β18Ocal = (11.61731 + Δa)x – (0.35444 + Δb)x2 + (0.00908 + Δc)x3, 103ln β13Ccal = (24.74146 + Δa)x – (1.08996 + Δb)x2 + (0.03178 + Δc)x3, where x = 106/T2(K–2); Δa, Δb and Δc are the shifts of the corresponding polynomial coefficients depending on the magnesium content, calculated separately for 18O/16O and 13C/12C. The effect of pressure on oxygen and carbon β-factors for carbonates is calculated. Estimates obtained within the quasi-harmonic approximation do not exceed 1‰ in pressure intervals typical to the Earth's crust conditions. [ABSTRACT FROM AUTHOR]

Metamorphic rocks show much lower mercury (Hg) levels than sedimentary rocks, which may be due to the loss of Hg during high-pressure and high-temperature conditions during metamorphism. To test this hypothesis, we conduct high-pressure and high-temperature experiments on ancient and modern sediments (WH black shale and GSS-4 soil). Under 0.3 GPa, the Hg concentrations decrease while the δ202Hg values increase with rising temperatures (WH black shale: 333–89 ppb, −1.34 to −0.79‰, 250–700 °C; GSS-4: 545–265 ppb, −1.39 to −1.01‰, 400–700 °C), suggesting the loss of isotopically light Hg isotopes under high-temperature conditions. Under constant temperatures of both 200 °C and 500 °C, with increasing pressure (0.5–1.4 GPa), GSS-4 shows only a slight decrease in Hg concentration with no variation in δ202Hg, suggesting that high-pressure conditions restrain the loss of isotopically lighter isotopes. Consistent Δ199Hg and Δ200Hg values were observed in both samples during our experiment, implying no Hg isotope mass-independent fractionation (Hg-MIF) under high-temperature and high-pressure conditions. While results of this imply that metamorphism may lead to the emission of isotopically lighter Hg from sedimentary rocks to the surface environment, the lack of Hg-MIF during metamorphism provides important support for the use of Hg isotopes for paleoenvironment reconstruction. [ABSTRACT FROM AUTHOR]

The Mo stable isotope system has been used to trace material recycling during subduction-related processes, but the behavior of Mo isotopes during magmatic evolution (e.g., crystal–melt fractionation and melt–fluid interaction) remains contentious, especially in high-SiO 2 granites. This study addresses the issue of Mo isotope variation in high-SiO 2 granites by measuring bulk-rock and mineral Mo isotopes of biotite granites (BGs) and garnet-bearing two-mica granites (GBGs) from the well-characterized Zhengga granite pluton (southern Tibet, China). The GBGs have similar Sr–Nd–O isotope compositions to those of the BGs but show higher SiO 2 and lower TiO 2 , MgO, total Fe 2 O 3 , and CaO contents, and represent the products of advanced fractionation of the BG magmas. The BGs have lower Mo contents (0.02–0.07 ppm) and higher δ98/95Mo values (−0.54‰ to 0.22‰) compared with the GBGs (0.029–2.121 ppm and −0.97‰ to −0.41‰, respectively). Analysis of major silicate minerals suggests that substantial segregation of biotite and feldspar with high δ98/95Mo values of 0.00‰ to 0.38‰ and −1.06‰ to 0.57‰ (most within −0.58‰ to 0.13‰) could have driven the GBGs and the late-stage crystalline phase of garnet (−1.22‰ to −0.98‰) towards very low δ98/95Mo values. However, the trend of decreasing δ98/95Mo with indices of magma differentiation is not linear: one group of GBGs show increasing Mo contents and decreasing δ98/95Mo values with decreasing Y, Ho, and Dy contents; while the other group display increasing Mo contents and slightly decreasing δ98/95Mo values with respect to the increasing contents of Y, Ho, and Dy. These two contrasting behaviors can be ascribed to further crystal fractionation and melt–fluid interaction in a closed magmatic–hydrothermal system. This is also evidenced by the formation of two types of garnets with different contents of Mo and rare earth elements in these two groups of GBGs. Closed-system fluid saturation is inferred to have driven the silicate melt to be enriched in 98Mo, which limited the decrease in melt δ98/95Mo caused by crystal fractionation. These observations are supported by quantitative geochemical modeling. We conclude that both fractional crystallization and melt–fluid interaction control Mo isotope fractionation in high-SiO 2 granites and that Mo isotopes are useful for tracing the evolution of high-SiO 2 igneous rocks. [ABSTRACT FROM AUTHOR]

Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study examines the Ca isotope (δ 44/40Ca) geochemistry of Icelandic rivers with the overall aims of improving the δ 44/40Ca tracer, constraining solute sources, and addressing the hypothesis that basalt weathering disproportionately regulates Earth's long-term climate. We report Ca isotope and elemental data for mainstem rivers, tributary streams, thermal and non-thermal springs, basalt, calcite, soil, vegetation, and sediment collected from the Skagafjörður region in North Iceland. Waters and calcite were further analyzed for their carbon isotope (δ13C) composition, and we conducted experiments to characterize δ 44/40Ca values of riverine colloids, the clay-size fraction (<2 µm) of soil, and exchangeable leachates obtained from soil and bedload sediment. The dataset includes analyses of travertine and coexisting water samples collected from a CO 2 -rich spring (Hvanná river) in South Iceland. Samples show a ∼2‰ range, with groundwater, the ultrafiltered fraction of river water, and hydrothermal calcite producing among the highest δ 44/40Ca values and travertine, soil exchangeable Ca, and vegetation the lowest. Riverine δ 44/40Ca values are on average ∼0.20‰ higher than those for basalt, which shows minimal isotopic variability. Mainstem glacial-fed rivers entering the Skagafjörður valley from the soil- and vegetation-free highlands have higher δ 44/40Ca values than direct-runoff tributaries draining catchments to the north where pedogenesis is more pervasive. Riverine δ 44/40Ca values correlate with Sr/Ca and Na/Ca ratios, as well as the saturation index of calcite (SI cal). Riverine δ13C values increase from ∼−8‰ (atmospheric) to ∼−3‰ (calcite) as SI cal values increase from highly-undersaturated to near-equilibrium. One watershed (Svartá river) shows unique trends, where riverine δ 44/40Ca values and Sr/Ca ratios do not correlate, and soil exchangeable leachates produced anomalously high amounts of Ca. Clay-size fractions isolated from three horizons composing a brown andosol show slightly lower δ 44/40Ca values than bulk basalt, but the values overlap with those for primary minerals. Colloids appear to have lower δ 44/40Ca values than truly dissolved Ca. The proxy could be developed as a tracer for colloidal contributions to riverine dissolved loads, especially in soil-mantled catchments where the inputs appear most pronounced. Groundwater δ 44/40Ca values correlate with pH, temperature, distance from the coast, and Sr/Ca ratios, all consistent with fractionation control yielding varying degrees of geochemical evolution. The combined riverine patterns largely reflect three-component mixing between basalt weathering, calcite weathering, and hydrothermal water inputs. Subsurface Ca isotope fractionation indirectly impacts riverine δ 44/40Ca values by elevating the δ 44/40Ca values of groundwater and hydrothermal calcite. This study highlights the significance of hydrothermal water inputs of Ca and HCO 3 to Icelandic rivers, which have been previously underappreciated. Mixing calculations suggest that a maximum of ∼20% of the Ca in mainstem rivers derives from surficial basalt weathering. Small tributaries draining the flanks of the valley show the clearest signals of basalt weathering by atmospheric CO 2 , but these waters have much lower solute concentrations than those employed in previous attempts to estimate basalt weathering rates and parameterize the climate sensitivity of the basalt weathering feedback. [ABSTRACT FROM AUTHOR]

Natural-abundance measurements of nitrate and nitrite (NOx) isotope ratios (δ15N and δ18O) can be a valuable tool to study the biogeochemical fate of NOx species in the environment. A prerequisite for using NOx isotopes in this regard is an understanding of the mechanistic details of isotope fractionation (15ε, 18ε) associated with the biotic and abiotic NOx transformation processes involved (e.g., denitrification). However, possible impacts on isotope fractionation resulting from changing growth conditions during denitrification, different carbon substrates, or simply the presence of compounds that may be involved in NOx reduction as co-substrates [e.g., Fe(II)] remain uncertain. Here we investigated whether the type of organic substrate, i.e., short-chained organic acids, and the presence/absence of Fe(II) (mixotrophic vs. heterotrophic growth conditions) affect N and O isotope fractionation dynamics during nitrate (NO3 -) and nitrite (NO2 -) reduction in laboratory experiments with three strains of putative nitrate-dependent Fe(II)-oxidizing bacteria and one canonical denitrifier. Our results revealed that 15ε and 18ε values obtained for heterotrophic (15ε-NO3 -: 17.6 ± 2.8‰, 18ε-NO3 -:18.1 ± 2.5‰; 15ε-NO2 -: 14.4 ± 3.2‰) vs. mixotrophic (15ε-NO3 -: 20.2 ± 1.4‰, 18ε-NO3 -: 19.5 ± 1.5‰; 15ε-NO2 -: 16.1 ± 1.4‰) growth conditions are very similar and fall within the range previously reported for classical heterotrophic denitrification. Moreover, availability of different short-chain organic acids (succinate vs. acetate), while slightly affecting the NOx reduction dynamics, did not produce distinct differences in N and O isotope effects. N isotope fractionation in abiotic controls, although exhibiting fluctuating results, even expressed transient inverse isotope dynamics (15ε-NO2 -: -12.4 ± 1.3 ‰). These findings imply that neither the mechanisms ordaining cellular uptake of short-chain organic acids nor the presence of Fe(II) seem to systematically impact the overall N and O isotope effect during NOx reduction. The similar isotope effects detected during mixotrophic and heterotrophic NOx reduction, as well as the results obtained from the abiotic controls, may not only imply that the enzymatic control of NOx reduction in putative NDFeOx bacteria is decoupled from Fe(II) oxidation, but also that Fe(II) oxidation is indirectly driven by biologically (i.e., via organic compounds) or abiotically (catalysis via reactive surfaces) mediated processes co-occurring during heterotrophic denitrification. [ABSTRACT FROM AUTHOR]

The transformation of mercury (Hg) in the environment plays a vital role in the cycling of Hg and its risk to the ecosystem and human health. Of particular importance are Hg oxidation/reduction and methylation/demethylation processes driven or mediated by the dynamics of light, microorganisms, and organic carbon, among others. Advances in understanding those Hg transformation processes determine our capacity of projecting and mitigating Hg risk. Here, we provide a critical analysis of major knowledge gaps in our understanding of Hg transformation in nature, with perspectives on approaches moving forward. Our analysis focuses on Hg transformation processes in the environment, as well as emerging methodology in exploring these processes. Future avenues for improving the understanding of Hg transformation processes to protect ecosystem and human health are also explored. [ABSTRACT FROM AUTHOR]

Natural-abundance measurements of nitrate and nitrite (NOx) isotope ratios (δ15N and δ18O) can be a valuable tool to study the biogeochemical fate of NOx species in the environment. A prerequisite for using NOx isotopes in this regard is an understanding of the mechanistic details of isotope fractionation (15ε, 18ε) associated with the biotic and abiotic NOx transformation processes involved (e.g., denitrification). However, possible impacts on isotope fractionation resulting from changing growth conditions during denitrification, different carbon substrates, or simply the presence of compounds that may be involved in NOx reduction as co-substrates [e.g., Fe(II)] remain uncertain. Here we investigated whether the type of organic substrate, i.e., short-chained organic acids, and the presence/absence of Fe(II) (mixotrophic vs. heterotrophic growth conditions) affect N and O isotope fractionation dynamics during nitrate (NO3–) and nitrite (NO2–) reduction in laboratory experiments with three strains of putative nitrate-dependent Fe(II)-oxidizing bacteria and one canonical denitrifier. Our results revealed that 15ε and 18ε values obtained for heterotrophic (15ε-NO3–: 17.6 ± 2.8‰, 18ε-NO3–:18.1 ± 2.5‰; 15ε-NO2–: 14.4 ± 3.2‰) vs. mixotrophic (15ε-NO3–: 20.2 ± 1.4‰, 18ε-NO3–: 19.5 ± 1.5‰; 15ε-NO2–: 16.1 ± 1.4‰) growth conditions are very similar and fall within the range previously reported for classical heterotrophic denitrification. Moreover, availability of different short-chain organic acids (succinate vs. acetate), while slightly affecting the NOx reduction dynamics, did not produce distinct differences in N and O isotope effects. N isotope fractionation in abiotic controls, although exhibiting fluctuating results, even expressed transient inverse isotope dynamics (15ε-NO2–: –12.4 ± 1.3 ‰). These findings imply that neither the mechanisms ordaining cellular uptake of short-chain organic acids nor the presence of Fe(II) seem to systematically impact the overall N and O isotope effect during NOx reduction. The similar isotope effects detected during mixotrophic and heterotrophic NOx reduction, as well as the results obtained from the abiotic controls, may not only imply that the enzymatic control of NOx reduction in putative NDFeOx bacteria is decoupled from Fe(II) oxidation, but also that Fe(II) oxidation is indirectly driven by biologically (i.e., via organic compounds) or abiotically (catalysis via reactive surfaces) mediated processes co-occurring during heterotrophic denitrification.

Toluene is a pollutant frequently detected in contaminated groundwater, mostly due to leakage from underground gasoline storage tanks and pipeline ruptures. Multi-element compound-specific isotope analysis provides a framework to understand transformation processes and design efficient remediation strategies. In this study, we enriched an anaerobic bacterial culture derived from a BTEX-contaminated aquifer that couples toluene and phenol oxidation with nitrate reduction and the concomitant production of carbon dioxide and biomass. The 16S rRNA gene amplicon data indicated that the toluene-degrading consortium was dominated by an Aromatoleum population (87 ± 2 % relative abundance), and metagenome sequencing confirmed that the genome of this Aromatoleum sp. encoded glycyl-radical enzyme benzylsuccinate synthase (BssABC) and phenylphospate synthase (PpsA1BC) homologous genes involved in the first step of toluene and phenol transformation, respectively. Carbon and hydrogen isotopic fractionation were ε bulk, C = - 3.5 ± 0.6 ‰ and ε rp, H = - 85 ± 11 ‰, respectively, leading to a dual C-H isotope slope of ΛH/C = 26 ± 2. This value fits with a previously reported value for a consortium dominated by an Azoarcus species (ΛH/C = 19 ± 5) but differs from that reported for Aromatoleum aromaticum (ΛH/C = 14 ± 1), both of which grow with toluene under nitrate-reducing conditions. Overall, this suggests the existence of different BssABC enzymes with different mechanistic motifs even within the same Aromatoleum genus. [Display omitted] • An enriched bacterial culture couples toluene oxidation with nitrate reduction. • The culture was dominated by an Aromatoleum population. • Significant C and H isotope fractionation during toluene biodegradation. • Dual C-H isotope slope differs from that reported for other Aromatoleum sp. • Calculated Λ allows distinguishing toluene degradation pathways in the field. [ABSTRACT FROM AUTHOR]

[Display omitted] • K, Sr isotopes, and trace element constrain potash origin in the Simao Basin. • K isotope fractionation can occur between secondary and primary sylvite. • The secondary sylvite relatively enriches light K isotope. • As K content increases, Rb/Sr positively correlates to K/Cl, in primary sylvinite. With the advancement of emerging potassium isotope testing techniques, the characteristics of δ 41K in evaporite have garnered increasing attention. Its application in constraining the genesis of potash deposits and tracing the process of potash mineralization holds significant prospects. A comprehensive analysis of the geochemical characteristics of K, Sr isotopes, and trace elements provides an opportunity to address the ongoing debate regarding the mineralization mechanism of potash in the Simao Basin. In this study, we collected 64 potash samples from the Simao and Khorat basins. The analytical results revealed that the major ions in the samples consist of Na+, K+, Mg2+, Ca2+, Cl−, and SO 4 2-, while the trace elements Br, Sr, Rb, B, Li, V, Cr, Mn, Ba, As, and Zn are relatively enriched. The δ 41K values range from −0.12 ‰ to 0.20 ‰ with an average of 0.01 ‰. The 87Sr/86Sr ratios range from 0.707553 to 0.708565 with an average of 0.708020, which is lower than that of the river water in the drainage basin. Additionally, the Br content ranges from 316.3 × 10−6 to 1709.1 × 10−6, with an average of 633.8 × 10−6. These data indicate that the Early Cretaceous Albian-Middle Jurassic Bajocian seawater serves as an important source of potassium for potash deposition in the Simao Basin. The characteristics of the ratios of the Br/Cl (mmol/mol), K/Cl (mmol/mol), Rb/Sr (mol/mol), along with the contents of the Br and Rb, indicate that the most of potash in the Simao Basin is primary origin. Moreover, we have also provided new insight into the geochemical behaviors of K isotopes during the evolution of the evaporites. The precipitation of potash may be accompanied by K isotope fractionation, as evidenced by the lighter K isotope composition of carnallite compared to that of sylvinite. K isotope fractionation occurs between the secondary sylvite and its parent source, and newly precipitated solids are characterized by relatively light K isotope. Episodic freshwater inflow into the evaporative basin stimulates microbial activity, leading to fluctuations in K isotopes in the precipitated potash during the same evaporation stage. Therefore, this work not only provided direct evidence from the K isotopes for determining the origin of the potash in the Simao Basin but also further perceived the geochemical behaviors of K isotopes during the evolution of evaporite. [ABSTRACT FROM AUTHOR]

• Porewater Ni isotope composition (δ60Ni) can be heavier than deep seawater. • Dissolution of detrital materials in marine sediments may supply dNi to pore fluids. • In marine sediments, porewater Ni isotopes are fractionated by active Mn cycling. • Continental margin sediments can supply dissolved Ni with heavy δ60Ni to the ocean. • Heavy benthic δ60Ni may help to resolve the global ocean mass balance of Ni. Nickel (Ni) is a bio-essential element for phytoplankton in the modern oceans, and yet, the global ocean mass balance of Ni has puzzled scientists for decades. Many estimates of total Ni output flux are larger than the total Ni input flux to the ocean. The measurement of Ni stable isotopes (δ60Ni) in earth materials may inform our understanding of ocean biogeochemistry and redox conditions in both the modern ocean and the geological past. An ocean Ni stable isotope imbalance has also concerned scientists, with a global ocean δ60Ni of +1.4 ‰ which is notably heavier than the major source of Ni to the oceans from rivers. Recent efforts to resolve Ni and δ60Ni imbalances have focused on the role which manganese (Mn) oxides play in marine Ni cycling, both in the water column and in marine sediments. Manganese oxide rich marine sediments can supply isotopically heavy dissolved Ni to porewater fluids and seawater, but the source of the isotopically heavy porewater Ni remains unclear. Here we present porewater trace metal concentrations and δ60Ni from two sites from the continental margin off southern California. Porewater Ni concentrations are up to roughly 100-fold higher than deep seawater concentrations (∼1 μM compared to 10 nM, respectively). Porewater δ60Ni is near 0 ‰ in the subsurface region where Ni concentrations are highest, suggesting dissolution of lithogenic material from sediments. Porewater δ60Ni increases dramatically towards the sediment-water interface with values of up to +2.66 ‰, which to our knowledge are the heaviest Ni isotope compositions ever reported for natural materials. Measurements of porewater and sediment Ni and Mn concentrations suggest that Ni is released to porewaters in the Mn-reducing zone, and then removed by newly precipitated Mn oxides as Mn and Ni move towards the oxygenated zone of sediments. A simple Rayleigh model suggests a Ni isotope fractionation of factor of -0.61 ‰ for Ni sorption onto Mn oxides, while a diffusion-reaction model suggests a Ni isotope fractionation of -1.80 to -0.96 ‰, always with preferential adsorption of lighter Ni isotopes. This flux of Ni toward the sediment-water interface, coupled with preferential removal of lighter Ni isotopes in marine sediments, provides evidence supporting an isotopically heavy benthic source of new Ni to the oceans, which we estimate has a magnitude of 0.65 × 108 to 1.66 × 108 moles/year. We find that a benthic flux such as measured here over just 0.27-2.70 % of the ocean seafloor could mix with the river δ60Ni of +0.8 ‰ to achieve the observed deep ocean δ60Ni of +1.4 ‰. This study reveals the similarities in how rivers and continental margin sediments supply heavy Ni isotopes to the ocean. In both continental rivers and margin sediments, terrigenous Ni is released with an δ60Ni near 0.1 ‰, but lighter isotopes are captured by precipitation onto oxides so that the dissolved flux to the ocean is isotopically heavier than the terrigenous material from which Ni was released, and in the case of margin sediments may be heavier than even bulk seawater δ60Ni. We thus recognize continental margin sediments with active Mn cycling as a 'new' source of isotopically heavy dissolved Ni to the ocean. [ABSTRACT FROM AUTHOR]

• Multi-stage carbon isotope fractionation occurs during the deep CBM field degassing. • Multi-stage isotope fractionation indicates the bidisperse pore structure of coal. • Carbon isotope fractionation (CIF) model incorporating multi-scale pore structures and multiple transport mechanisms was established. • Compared to traditional methods, the CIF model has more advantages for evaluating the GIP content of deep CBM. • The in-situ free gas ratio of deep CBM in the southern margin of the Ordos Basin ranges from 13.30% to 32.89%. Gas-in-place (GIP) content and the in-situ free/adsorbed gas ratio are crucial factors for evaluating resource potential and optimizing production strategies of deep coalbed methane (CBM). While the prevailing notion that adsorbed gas predominates is widely accepted in shallow CBM, this idea has been contested in deep CBM. Various numerical models for calculating GIP content based on gas volume data from canister degassing experiments commonly suffer from low accuracy, strong multiplicity, and inability to evaluate critical parameters of free/adsorbed gas ratio. Isotope fractionation is an important tool for studying the occurrence state and transport mechanism of natural gas, and numerical modeling that considers both cumulative degassing content and carbon isotope data has proven effective in determining the GIP content and adsorbed gas ratio in shale. However, the applicability of the existing isotope fractionation models in deep CBM has yet to be demonstrated experimentally and theoretically. In this study, four coal samples from the Shanxi and Taiyuan formations in Ordos Basin were subjected to canister degassing, gas metering, and methane isotopic composition testing. The results revealed significant multi-stage carbon isotope fractionation characteristics throughout deep CBM degassing, reflecting the strong heterogeneous pore structure characteristics within the coal. Existing carbon isotope fractionation (CIF) models are unable to effectively characterize this complex phenomenon. Based on these findings, we innovatively developed a CIF model that considers bidisperse pore structures and multiple transport mechanisms. The model can better characterize the complex isotope fractionation behavior and reveal the mechanisms of carbon isotope transport in series structures of multi-scale pores. Using the model, we calculated the GIP content of four experimental samples from the Shanxi and Taiyuan formations on the southeastern edge of the Ordos Basin, ranging from 27.78 m3/t to 39.13 m3/t, with an average of 31.68 m3/t, and the in-suit free gas ratio ranges from 13.30 % to 32.89 %, with an average of 19.45 %. These research findings provided new insights for assessing the resource potential of deep CBM, screening sweet spots, and predicting gas well performance. [ABSTRACT FROM AUTHOR]

This study concerns wet carbonation of β-C 2 S (Ca 2 SiO 4) in a closed system at 23 °C. The progress of carbonation was detected by quantitative X-ray diffraction (QXRD) and thermogravimetric analysis (TGA). Further measurements of pH and ion concentrations as well as modelling carbon species and saturation indices were done. Additionally, stable carbon isotope ratios (δ 13C) in CO 2 , dissolved inorganic carbon (DIC) and carbonate phases were measured. The aim of this study was to investigate δ 13C isotope values during C 2 S carbonation. If a systematic fractionation of carbon isotopes occurs during the reaction, it can help to quantify the carbonation reaction. During the carbonation process over 48 h, we found carbon isotope distributions from the gaseous phase to the solution and ultimately to the solid phase. Calculations confirm the direct relation of δ 13C values to the carbonation progress. With this, stable isotope measurements offer a promising tool to monitor the reaction progress in-situ. • Use of stable carbon isotopes to track carbonation of β-C 2 S in a closed system. • Fractionation of δ 13C during carbonation reaction. • Carbon isotope distributions from gaseous to fluid and ultimately solid phase. • Stable carbon isotope measurements as tool to monitor carbonation reaction in-situ. [ABSTRACT FROM AUTHOR]

The city of Ostrava, NE Czech Republic, is known for its industrial pollution. It has well-characterized emission sources and stable air movement patterns. These features are conveniently used to generalize on atmospheric NO x and SO 2 oxidation processes. In 2021, we conducted a series of sampling campaigns to assess the isotopic fractionation conducive to NO 3 − and SO 4 2− aerosols in PM 10. These sampling campaigns were timed to capture varying atmospheric conditions, including climatic inversion periods, providing also insights into urban emission dynamics over the course of the year. Gaseous NO x and SO 2 were collected on passive filters, while their oxidized forms, NO 3 − and SO 4 2, were captured on PM 10 particle filters, enabling us to analyze the transformation dynamics of these pollutants. Isotopic analyses distinguished the sources of NO x emissions—coal combustion (δ 15N = −3‰) and vehicular emissions (δ 15N = −7 ‰)—and allowed quantifying isotope fractionation during their conversion to NO 3 − (ε NOx-NO3- = 11.5 ± 1.15 ‰). This fractionation, however, was influenced by seasonal variations, and appears to be notably affected by NH 4 NO 3 decomposition during warmer months. The correlation of the NO 3 − to NO x ratio with PM 10 and atmospheric moisture highlighted the interplay between particulate matter and humidity in relevant atmospheric transformations. Similarly, for SO 2 , primarily emitted from coal combustion (δ 34S = −2‰), we identified distinct fractionation patterns during oxidation to SO 4 2− encompassing both kinetic (ε SO2-H2O = −1.3 ± 0.5‰) and equilibrium (ε SO2- SO42- = 2.24 ± 0.67‰) effects. The SO 4 2−/SO 2 ratio was correlated with PM 10 but showed no dependence on humidity. Significantly, atmospheric inversion conditions accelerated oxidation, modifying the fractionation patterns for both NO x (ε NOx-NO3 - = 7‰) and SO 2 (ε SO2- SO42-= −0.9 ± 0.3‰). Our methodology elucidates pivotal mechanisms in atmospheric pollution transformation, underlined by the tracing of NO x and SO 2 to aerosol conversions via δ 15N and δ 34S isotopic analyses. The isotope fractionation underscores equilibrium processes in oxidation reactions, while the effect of PM 10 and humidity reveals the complexity of these atmospheric oxidative transformations. The role of wet deposition in removing SO 2 highlights an essential pathway in the atmospheric sulfur cycle. • Transmission of NO x and SO 2 sources to aerosols were traced using 15N and 34S data. • Oxidation reactions proceed with a positive (equilibrium) isotope fractionation of 15N and 34S. • The complex mechanism of oxidative transmission is affected by PM 10 concentration and air water content. • Part of atmospheric SO 2 is removed to wet deposition. [ABSTRACT FROM AUTHOR]

Isotope technology is an ideal tool for tracing the sources of certain pollutants or providing insights into environmental processes. In recent years, the advent of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has enabled the precise measurement of various metal stable isotopes. Due to the presence of "fingerprint" properties in various environmental samples, metal stable isotopes have been applied to distinguish the source of contaminants effectively and further understand the corresponding environmental processes. The environmental fate of metal elements is strongly controlled by adsorption, an essential process for the distribution of elements between the dissolved and particulate phases. The adsorption of metal elements on mineral and organic surfaces significantly affects their biogeochemical cycles in the environment. Therefore, it is crucial to elucidate the fractionation characteristics of stable metal isotopes during the adsorption process. In this review, three typical transitional metal elements were selected, considering Mo as the representative of anionic species and Fe and Zn as the representative of cationic species. For Mo, the heavier Mo isotope is preferentially adsorbed in the solution phase, pH has a more significant influence on isotope fractionation, and temperature and ionic strength are relatively insensitive. Differences in coordination environments between dissolved and adsorbed Mo during adsorption, i.e., attachment mode (inner- or outer-sphere) or molecular symmetry (e.g., coordination number and magnitude of distortion), are likely responsible for isotopic fractionation. For Fe, The study of equilibrium/kinetic Fe isotopic fractionation in aqueous Fe(II)-mineral is not simple. The interaction between aqueous Fe(II) and Fe (hydroxyl) oxides is complex and dynamic. The isotope effect is due to coupled electron and atom exchange between adsorbed Fe(II), aqueous Fe(II), and reactive Fe(III) on the surface of Fe (hydroxyl) oxide. For Zn, the heavier Fe isotope preferentially adsorbs on the solid phase, and pH and ionic strength are essential influencing factors. The difference in coordination environment may be the cause of isotope fractionation. [Display omitted] • The analytical techniques of Mo, Fe, and Zn stable isotopes were systematically summarized. • The characteristics and mechanism of Mo, Fe, and Zn stable isotopes fractionation during adsorption process were elaborated. • The prospects for future research issues related to stable metal isotopes were provided. [ABSTRACT FROM AUTHOR]

Biodegradation of lower chlorinated benzenes (tri-, di- and monochlorobenzene) was assessed at a coastal aquifer contaminated with multiple chlorinated aromatic hydrocarbons. Field-derived microcosms, established with groundwater from the source zone and amended with a mixture of lower chlorinated benzenes, evidenced biodegradation of monochlorobenzene (MCB) and 1,4-dichlorobenzene (1,4-DCB) in aerobic microcosms, whereas the addition of lactate in anaerobic microcosms did not enhance anaerobic reductive dechlorination. Aerobic microcosms established with groundwater from the plume consumed several doses of MCB and concomitantly degraded the three isomers of dichlorobenzene with no observable inhibitory effect. In the light of these results, we assessed the applicability of compound stable isotope analysis to monitor a potential aerobic remediation treatment of MCB and 1,4-DCB in this site. The carbon isotopic fractionation factors (ε) obtained from field-derived microcosms were -0.7‰ ± 0.1 ‰ and -1.0‰ ± 0.2 ‰ for MCB and 1,4-DCB, respectively. For 1,4-DCB, the carbon isotope fractionation during aerobic biodegradation was reported for the first time. The weak carbon isotope fractionation values for the aerobic pathway would only allow tracing of in situ degradation in aquifer parts with high extent of biodegradation. However, based on the carbon isotope effects measured in this and previous studies, relatively high carbon isotope shifts (i.e., ∆δ13C > 4.0 ‰) of MCB or 1,4-DCB in contaminated groundwater would suggest that their biodegradation is controlled by anaerobic reductive dechlorination. [Display omitted] [ABSTRACT FROM AUTHOR]

Purpose: Silicon is important for both plant growth and the soil biogeochemical cycle. Si uptake and accumulation ability varies in plants, which are defined as Si accumulators, intermediates, or non-accumulators. However, the processes governing Si uptake and translocation are not fully understood. Stable Si isotopic signatures may offer new perspectives on the processes involved in the Si biogeochemical cycle. Methods: Si isotopic fractionation between different Si pools was analyzed in Si accumulators (rice, maize), intermediates (cucumber), and non-accumulators (tomato) grown in yellow, black, and cinnamon soils using multi-collector inductively coupled plasma mass spectrometry. Results: Plants grown in all soil types exhibited 28Si enrichment relative to the soil solution. The degree of fractionation was negatively correlated with silt, clay, free iron oxide (Fed), and crystalline Fe oxide (Fed-Feo) contents, and positively correlated with sand content. The degree of isotope fractionation was species-specific during uptake, in order of rice > maize > cucumber > tomato, while the reverse was true for root–shoot translocation. In addition, isotope fractionation was absent in tomato shoots, contrasting with the Rayleigh-like behavior of the other species. Conclusion: Fed and Fed-Feo contents affected the H4SiO4 adsorption–desorption process, thereby influencing isotope fractionation between the plants and soil. Species-specific fractionation was attributed to the varying contributions of water flow uptake and the transporter-mediated uptake process. Moreover, the Si transport mechanism within shoots in Si non-accumulators varied from those in accumulators and intermediates. These findings provide insight into Si isotope fractionation dynamics during uptake and translocation. [ABSTRACT FROM AUTHOR]

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Compound specific stable isotope analysis (CSIA) of amino acids from bacterial biomass is a newly emerging powerful tool for exploring central carbon metabolism pathways and fluxes. By comparing isotopic values and fractionations relative to water and growth substrate, the impact of variable flow path for metabolites through different central metabolic pathways, perturbations of these paths, and their resultant consequences on intracellular pools and resultant biomass may be elucidated. Here, we explore the effects that central carbon metabolism and growth rate can have on stable hydrogen (δ²H) and carbon (δ13C) compound specific isotopic values of amino acids, and whether diagnostic isotopic fingerprints are revealed by these paired analyses. We measured d2H and δ13C in amino acids in the wild type Escherichia coli (MG1655) across a range of growth rates in chemostat cultures to address the unknown isotopic consequences as metabolic fluxes are shuffled between catabolic and anabolic metabolisms. Additionally, two E. coli knockout mutants, one with deficiency in glycolysis -pgi (LC1888) and another inhibiting the oxidative pentose phosphate pathway (OPPP) -zwf (LC1889), were grown on glucose and used as a comparison against the wild type E. coli (MG1655) to address the isotopic changes of amino acids produced in these perturbed metabolic pathways. Amino acid δ²H values, which collectively vary in composition by more than 400‰, are altered along with δ13C values demonstrating fundamental shifts in central metabolic pathways and/or fluxes. Within our linear discriminant analysis with a simple model organism to examine potential amino acid fingerprinting, our knockout strains and variable growth rate samples plot across a wider array of organism classification than merely within the boundaries of other bacterial data. [ABSTRACT FROM AUTHOR]

The Titanium (Ti) isotope compositions of felsic rocks are heavier than their mafic counterparts, and alkaline magmas develop heavier Ti isotope compositions compared to other magma series during magmatic differentiation. Both observations are interpreted to reflect the preferential sequestration of light Ti isotopes in Fe-Ti oxides, such as rutile, ilmenite and titanomagnetite. However, such interpretations so far rely on whole rock studies of cogenetic magmatic samples and the detailed mechanics of oxide-melt equilibrium on the Ti isotope composition of magmas is poorly constrained. To address this, we have measured the Ti isotope composition of co-existing Fe-Ti oxides and groundmass or silicate melt in both natural lavas from contrasting tectonic settings (Heard Island and Santorini), and experimental run products (rutile-melt). All Fe-Ti oxide phases are consistently isotopically lighter than their respective host groundmass or silicate melt, with the magnitude of Δ49/47Ti oxide-melt increasing from rutile to ilmenite, and titanomagnetite. The observed difference in Ti isotope fractionation between rutile-melt experiments and ilmenite-groundmass pairs is primarily reflective of small differences in their Ti O bond length, with ilmenite being isotopically lighter (Δ49/47Ti ilmenite-melt extrapolated to 1000 K = −0.600 ± 0.035‰) compared to rutile (Δ49/47Ti rutile-melt at extrapolated to 1000 K = −0.404 ± 0.099‰) due to slightly longer Ti O bonds in ilmenite. In contrast, the variation in Δ49/47Ti observed between titanomagnetite-groundmass pairs increases as a function of increasing TiO 2 content (increasing ulvöspinel component) in titanomagnetite, with Δ49/47Ti titanomagnetite-melt values extrapolated to 1000 K ranging from −0.811 to −1.451‰ in Ti-rich titanomagnetite (21–23 wt.% TiO 2 ; Usp 66-73) from Heard Island compared to −0.673‰ to −0.863 in Santorini (14–15 wt.% TiO 2 ; Usp 45-49). We interpret this to result from a weaker and distorted crystal lattice due to changes in the local cationic environment resulting from exchange of smaller Fe3+ ions with larger Fe2+ ions during magnetite-ulvöspinel solid solution. Our results are consistent with fractionation factors inferred from Ti isotopic analyses of mineral separates and ab-initio calculations. We use these fractionation factors in combination with Ti isotope fractionation factors for silicate minerals recalculated from previous studies, along with petrologic information to model the behaviour of Ti isotopes during partial melting of Earth's mantle as well as reproducing the observed variation in δ49/47Ti of differentiated magmas from distinct geodynamic settings. [ABSTRACT FROM AUTHOR]

Isotope fractionation of fatty acids can reflect the metabolic pathway of fatty acids in organisms, but few studies have been conducted. In this study, stable carbon isotope fractionation of fatty acids in sea cucumber (Apostichopus japonicus) was conducted by feeding experiments of comparing the fatty acid profile and δ13C of fatty acids in body wall to diet. The results showed that the fractionation of δ13C of fatty acids in A. japonicus was −1.588–7.403‰. The fractionation of δ13C of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs) was 1.098–7.403‰, −1.588–2.778‰, and −1.559–5.614‰, respectively. The degree of fractionation of δ13C of SFAs was greater than that of unsaturated fatty acids (UFAs). We simulated the possible metabolic process of fatty acids in A. japonicus based on fatty acid profile and δ13C of fatty acids, indicating that the combination of these two methods could be potentially used in the study of fatty acid metabolism in marine benthic animal of A. japonicus. Our finding provides a new technique for the metabolic pathways of biomolecules in organisms. [ABSTRACT FROM AUTHOR]

This study reports the high-precision silver (Ag) isotopic compositions of the dominant Ag-bearing mineral (galena) in the representative Zhaxikang polymetallic deposit, which experienced a complex ore-forming process that can be divided into two episodes composed of six stages (first episode: Pb–Zn mineralization, stages 1 and 2; second episode: Sb mineralization, stages 3 to 6). The objective of this case study is to investigate the Ag isotopic fractionation mechanisms in a hydrothermal ore-forming system and explore the potential application of Ag isotopes. The earlier-generated stage 2 galena (0.17–6.07‰) has higher δ109AgNIST 978 Ag values with a significantly broader range in comparison to the subsequent stage 3 galena (–3.65 to 2.27‰). The δ109AgNIST 978 Ag values of galena also decrease from deep to shallow along with the trend of orebody V. These temporally and spatially decreasing trends indicate that the second episode of ore-forming fluid overprinted the first episode of mineralization along with the trend of orebodies from deep to shallow within the Zhaxikang orefield. A simple triple-phase separation model captures the temporal and spatial patterning of the data resulting from Ag isotopic fractionation, which is most likely related to the solid–liquid-vapor dynamics of the ore-forming fluid. According to approximate theoretical calculations, there is still great prospecting potential for Ag at depth within the Zhaxikang orefield. In summary, the Ag isotopes have the potential to trace phase changes, monitor ore-forming fluid evolution, constrain ore formation processes, and provide insights into ore exploration. [ABSTRACT FROM AUTHOR]

Compound specific stable isotope analysis (CSIA) of amino acids from bacterial biomass is a newly emerging powerful tool for exploring central carbon metabolism pathways and fluxes. By comparing isotopic values and fractionations relative to water and growth substrate, the impact of variable flow path for metabolites through different central metabolic pathways, perturbations of these paths, and their resultant consequences on intracellular pools and resultant biomass may be elucidated. Here, we explore the effects that central carbon metabolism and growth rate can have on stable hydrogen (δ2H) and carbon (δ13C) compound specific isotopic values of amino acids, and whether diagnostic isotopic fingerprints are revealed by these paired analyses. We measured δ2H and δ13C in amino acids in the wild type Escherichia coli (MG1655) across a range of growth rates in chemostat cultures to address the unknown isotopic consequences as metabolic fluxes are shuffled between catabolic and anabolic metabolisms. Additionally, two E. coli knockout mutants, one with deficiency in glycolysis –pgi (LC1888) and another inhibiting the oxidative pentose phosphate pathway (OPPP) –zwf (LC1889), were grown on glucose and used as a comparison against the wild type E. coli (MG1655) to address the isotopic changes of amino acids produced in these perturbed metabolic pathways. Amino acid δ2H values, which collectively vary in composition by more than 400‰, are altered along with δ13C values demonstrating fundamental shifts in central metabolic pathways and/or fluxes. Within our linear discriminant analysis with a simple model organism to examine potential amino acid fingerprinting, our knockout strains and variable growth rate samples plot across a wider array of organism classification than merely within the boundaries of other bacterial data.