Preferential Removal Research Articles

The Li isotope composition of marine biogenic carbonates: Patterns and mechanisms

Little is known about the fractionation of Li isotopes during formation of biogenic carbonates, which form the most promising geological archives of past seawater composition. Here we investigated the Li isotope composition (δ7Li) and Li/Ca ratios of organisms that are abundant in the Phanerozoic record: mollusks (mostly bivalves), echinoderms, and brachiopods. The measured samples include (i) modern calcite and aragonite shells from various species and natural environments (13 mollusk samples, 5 brachiopods and 3 echinoderms), and (ii) shells from mollusks grown under controlled conditions at various temperatures. When possible, the mollusk shell ultrastructure was micro-sampled in order to assess intra-shell heterogeneity. In this paper, we systematically characterize the influence of mineralogy, temperature, and biological processes on the δ7Li and Li/Ca of these shells and compare with published data for other taxa (foraminifera and corals).Aragonitic mollusks have the lowest δ7Li, ranging from +16 to +22‰, echinoderms have constant δ7Li of about +24‰, brachiopods have δ7Li of +25 to +28‰, and finally calcitic mollusks have the largest range and highest δ7Li values, ranging from +25‰ to +40‰. Measured brachiopods have similar δ7Li compared to inorganic calcite precipitated from seawater (δ7Li of +27 to +29‰), indicating minimum influence of vital effects, as also observed for other isotope systems and making them a potentially viable proxy of past seawater composition. Calcitic mollusks, on the contrary, are not a good archive for seawater paleo–δ7Li because many samples have significantly higher δ7Li values than inorganic calcite and display large inter-species variability, which suggests large vital effects. In addition, we observe very large intra-shell variability, in particular for mixed calcite-aragonite shells (over 20‰ variability), but also in mono-mineralic shells (up to 12‰ variability). Aragonitic bivalves have less variable δ7Li (7‰ variability) compared to calcitic mollusks, but with significantly lower δ7Li compared to inorganic aragonite, indicating the existence of vital effects. Bivalves grown at various temperatures show that temperature has only a minor influence on fractionation of Li isotopes during shell precipitation. Interestingly, we observe a strong correlation (R2 = 0.83) between the Li/Mg ratio in bivalve Mytilus edulis and temperature, with potential implications for paleo-temperature reconstructions.Finally, we observe a negative correlation between the δ7Li and both the Li/Ca and Mg/Ca ratio of calcite mollusks, which we relate to biomineralization processes. To explain this correlation, we propose preferential removal of 6Li from the calcification site of calcite mollusks by physiological processes corresponding to the regulation of the amount of Mg in the calcifying medium. We calculate that up to 80% of the initial Li within the calcification site is removed by this process, leading to high δ7Li and low Li/Ca in some calcite mollusk specimens. Collectively, these results suggest that Mg (and thus [Li]) is strongly biologically controlled within the calcifying medium of calcite mollusks.Overall, the results of this study show that brachiopods are likely to be suitable targets for future work on the determination of paleo-seawater Li isotope composition—an emerging proxy for past weathering and hydrothermal processes.

Fate and behavior of oil sands naphthenic acids in a pilot-scale treatment wetland as characterized by negative-ion electrospray ionization Orbitrap mass spectrometry

Large volumes of oil sands process-affected water (OSPW) are generated during the extraction of bitumen from oil sands in the Athabasca region of northeastern Alberta, Canada. As part of the development of treatment technologies, molecular characterization of naphthenic acids (NAs) and naphthenic acid fraction compounds (NAFC) in wetlands is a topic of research to better understand their fate and behavior in aquatic environments. Reported here is the application of high-resolution negative-ion electrospray Orbitrap-mass spectrometry for molecular characterization of NAs and NAFCs in a non-aerated constructed treatment wetland. The effectiveness of the wetlands to remove OSPW-NAs and NAFCs was evaluated by monitoring the changes in distributions of NAFC compounds in the untreated sample and non-aerated treatment system. After correction for measured evapotranspiration, the removal rate of the classical NAs followed approximately first-order kinetics, with higher rates observed for structures with relatively higher number of carbon atoms. These findings indicate that constructed wetland treatment is a viable method for removal of classical NAs in OSPW. Work is underway to evaluate the effects of wetland design on water quality improvement, preferential removal of different NAFC species, and reduction in toxicity.

Fractionation of Pyrrolic Nitrogen Compounds Compounds during Primary Migration of Petroleum within the Barnett Shale Sequence of Marathon 1 Mesquite Well, Texas

The primary migration of petroleum has been recently described in detail for a thermally mature core of the Barnett Shale with almost nonvariant organofacies and maturity. Here, we use samples from the same well to provide new insights into the fractionation of pyrrolic nitrogen compounds during primary migration. Using gas chromatography–mass spectrometry (GC-MS), a decrease in concentration of carbazoles and benzocarbazoles was observed which correlated with migration distance. However, a preferential removal of individual isomers like benzocarbazole[a] relative to benzocarbazole[c] could not be detected. Enlarging the analytical window, we studied the effect of primary migration on high molecular weight nitrogen-containing compounds using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) combined with electrospray ionization (ESI) in the negative ion mode. Compounds with one or two nitrogen atoms are most abundant. Among the N1 compounds, those with 12, 15, 18, 20, and 23 double b...

Preferential removal of phosphorus using modified steel slag and cement combination for its implications in engineering applications

Abstract Eutrophication is receiving increasing attention globally, and excessive phosphorus (P) discharge is the principal cause. To alleviate this, steel slag, an industrial by-product, was selected to remove P from synthetic solution in this study. High-powered ball grinding technology was used to modify the slag before the experiments, resulting in finer particle size, higher specific surface area and activation, which were characterized by BET, SEM and XRD. Batch experiments were conducted to investigate its adsorption properties. With initial P concentration of 5 mg/L, about 96% of P was removed within 60 min, accompanied by an increase in pH and Ca2+ concentration. The adsorption data was best fitted by the Lagergren pseudo-second-order kinetic model. The Langmuir equation fitted the isotherm data well, with a maximum adsorption capacity of 21.70 mg P/g. When the initial pH was higher than 4.0, P adsorption capacity varied inversely with pH. In a 700 h continuous flow experiment, the cement-slag padding prepared in this study removed around 98.2 % of the influent P, decreasing from 21.0 mg/L to 0.4 mg/L. CaCO3 and amorphous calcium-phosphate compounds generating in the column indicated that the dominant P removal mechanism was through precipitation. The padding proved capable of controlling pH increases, providing a method to prepare slow-release materials containing slag to treat P-contaminated wastewater.

Comprehensive geochemical correlation between surface and subsurface hydrocarbon occurrences in the Batman-Mardin-Şırnak area (SE Turkey)

Abstract Southeast Turkey is the main oil-producing region of the country, located at the northwestern part of the Zagros Basin. In this study, we investigated the geochemical characteristics of both surface and subsurface hydrocarbon occurrences in the Batman-Mardin-Sirnak area in southeast Turkey to determine whether a genetic relationship exists between the two. For this, thirty solid bitumens from twenty-two different veins along with ten heavy oils and thirteen oil seepage samples from nearby oilfields and seeps were studied using diverse geochemical tools. Firstly each of the different hydrocarbon types was considered individually with respect to source organofacies, level of thermal maturity and degree of biodegradation. The results obtained from the source-related parameters demonstrate a marine algal source for all investigated samples. Also, lithology determination based on various diasterane, tricyclic terpane, hopane and homohopane parameters, suggests a carbonate source for all samples, except for the Dadas and Iskar seeps (clastic). Thereafter, considering the influences caused by thermal and biological alteration processes, all heavy oils, less mature solid bitumens as well as the less biodegraded seep oils were selected to be correlated using selected additional parameters. Homohopane distributions reveal that solid bitumens, compared to heavy oils and seeps, are highly enriched in C31- and depleted in higher homologues possibly due to cracking of high molecular weight homologues to lower ones during and/or after solidification processes. Furthermore, the similarities observed for the relative abundances of six series of aromatic hydrocarbons and their alkylated counterparts substantiate strong genetic affinities within the sample set. Finally, compound-specific stable carbon isotopes of individual components show that solid bitumens are more enriched in 13C than the heavy oils which is mainly attributed to the preferential removal of light isotopes (12C) during solidification. Our results strongly confirm that Turkish solid bitumens are genetically related to the nearby heavy oils, thereby providing new information on the petroleum system in this part of the southeast Anatolia.

Areally Extensive Surface Bedrock Exposures on Mars: Many Are Clastic Rocks, Not Lavas.

Areally extensive exposures of intact olivine/pyroxene-enriched rock, as well as feldspar-enriched rock, are found in isolated locations throughout the Martian highlands. The petrogenetic origin(s) of these rock units are not well understood, but some previous studies favored an effusive volcanic origin partly on the basis of distinctive composition and relatively high thermal inertia. Here we show that the regolith development, crater retention, and morphological characteristics for many of these "bedrock plains" are not consistent with competent lavas and reinterpret the high thermal inertia orbital signatures to represent friable materials that are more easily kept free of comminution products through eolian activity. Candidate origins include pyroclastic rocks, impact-generated materials, or detrital sedimentary rocks. Olivine/pyroxene enrichments in bedrock plains relative to surrounding materials could have potentially formed through deflation and preferential removal of plagioclase.

NMR studies on lignocellulose deconstructions in the digestive system of the lower termite Coptotermes formosanus Shiraki

Termites represent one of the most efficient lignocellulose decomposers on earth. The mechanism by which termites overcome the recalcitrant lignin barrier to gain access to embedded polysaccharides for assimilation and energy remains largely unknown. In the present study, softwood, hardwood, and grass lignocellulose diets were fed to Coptotermes formosanus workers, and structural differences between the original lignocellulose diets and the resulting feces were examined by solution-state multidimensional nuclear magnetic resonance (NMR) techniques as well as by complementary wet-chemical methods. Overall, our data support the view that lignin polymers are partially decomposed during their passage through the termite gut digestive system, although polysaccharide decomposition clearly dominates the overall lignocellulose deconstruction process and the majority of lignin polymers remain intact in the digestive residues. High-resolution NMR structural data suggested preferential removal of syringyl aromatic units in hardwood lignins, but non-acylated guaiacyl units as well as tricin end-units in grass lignins. In addition, our data suggest that termites and/or their gut symbionts may favor degradation of C–C-bonded β–5 and resinol-type β–β lignin inter-monomeric units over degradation of ether-bonded β–O–4 units, which is in contrast to what has been observed in typical lignin biodegradation undertaken by wood-decaying fungi.

Transformation of nitrogen-containing compounds in atmospheric residue by hydrotreating

Atmospheric residue from Saudi Arabia light crude oil was subjected to the hydrotreating process in a continuous fixed-bed reactor with hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) catalysts. The detailed molecular composition of the polar heteroatom species in the feedstock and products was determined by electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) combined with other analytical methods. The ESI FT-ICR MS analysis indicates that the N1 class species have the highest relative abundance. In the hydrotreating process, small neutral N1 class species with high aromaticity and short side chains showed the highest relative abundance and were defined as easily removable compounds. High aromaticity and small molecule basic N1 compounds exhibited higher catalytic activity towards hydrogenation. The N1S1 class species were converted to the N1 class species, or even hydrocarbons, by the preferential removal of the sulfur atoms. Most of the N1O1 class species were difficult to remove, because of their stable chemical structure.

Irradiation of nuclear materials with laser-plasma filaments produced in air and deuterium by terrawatt (TW) laser pulses

Be–C–W mixed materials with variable atomic ratios were exposed to high power (TW) laser induced filamentation plasma in air in normal conditions and in deuterium at a reduced pressure of 20 Torr. Morphological and structural investigations were performed on the irradiated zones for both ambient conditions. The presence of low-pressure deuterium increased the overall ablation rate for all samples. From the elemental concentration point of view, the increase of the carbon percentage has led to an increase in the ablation rate. An increase of the tungsten percentage had the opposite effect. From structural spectroscopic investigations using XPS, Raman and FT-IR of the irradiated and non-irradiated sample surfaces, we conclude that deuterium-induced enhancement of the ablation process could be explained by preferential amorphous carbon removal, possibly by forming deuterated hydrocarbons which further evaporated, weakening the layer structure.

The effect of de- and re-polymerization during heat-treatment on the mechanical behavior of Scots pine sapwood under quasi-static load

Loss in strength and ductility is a major drawback for the heat-treatment of solid wood. Previous studies focused mainly on the de-polymerization of cell wall constituents as a cause and the importance of the preferential removal of hemicelluloses. This study tested the hypothesis that the mechanical behavior of wood is additionally affected by re-polymerization reactions within the cell wall matrix during heat-treatment. This was achieved by comparing changes in chemical composition, FT-IR spectra, and mechanical properties of Scots pine sapwood that was heat-treated in either dry state in superheated steam or in wet state using pressurized hot water. Although preferential de-polymerization of hemicelluloses was evident for both heat-treatment techniques, the analysis of the chemical composition and FT-IR spectroscopy indicated additional re-polymerization reactions within the cell wall matrix of dry heat-treated wood. The consequent formation of covalent bonds and cross-links increased the resistance against compression loads and hindered inelastic deformation during bending. This resulted in an additional reduction in bending strength and strain energy density of dry compared to wet heat-treated wood. Re-polymerization reactions during heat-treatments of wood in dry state were suggested as the main cause for the brittle failure under bending loads, while the effect of hemicellulose-removal on brittleness was much smaller than stated previously.

The Competing Effects of Counterface Peaks and Valleys on the Wear and Transfer of Ultra-Low Wear Alumina–PTFE

The wear rates of tribological polymers are strongly influenced by counterface roughness through competing mechanisms such as polymer abrasion by counterface asperities and mechanical engagement of debris into the features of the rough surface. Previous studies have shown that an ultra-low wear (k ~ 10−7 mm3/Nm) alumina–PTFE solid lubricant loses wear resistance and the ability to form stable transfer films when the counterface roughness exceeds a critical magnitude or aligns with the sliding direction. In this paper, we aimed to test the independent effects of counterface peaks and valleys on polymer wear and transfer using this well-studied alumina–PTFE system. Wear tests were performed against 304 stainless steel counterfaces of systematically varied peak height and valley depth. Interrupted microscopy measurements were used to record the details of debris engagement, migration, aggregation, and removal. Preferential removal of the tallest peaks on the counterface helped stabilize the transfer films and dramatically reduced the transient wear volume of the polymer composite even on very rough surfaces. The results illustrate the independent and competing effects of counterface peaks, plateaus, and valleys on the wear and transfer of this ultra-low wear polymer composite. While increased peak height promoted primary material removal from the polymer composite and inhibited the formation of the transfer film, intersecting valleys and smooth plateaus helped nucleate and stabilize transfer films. On rough surfaces with tall peaks, the composite eventually achieved ultra-low wear by gradually removing the tallest asperities to achieve a more favorable topography for transfer film formation.

Parallel loss of introns in the ABCB1 gene in angiosperms

BackgroundThe presence of non-coding introns is a characteristic feature of most eukaryotic genes. While the size of the introns, number of introns per gene and the number of intron-containing genes can vary greatly between sequenced eukaryotic genomes, the structure of a gene with reference to intron presence and positions is typically conserved in closely related species. Unexpectedly, the ABCB1 (ATP-Binding Cassette Subfamily B Member 1) gene which encodes a P-glycoprotein and underlies dwarfing traits in maize (br2), sorghum (dw3) and pearl millet (d2) displayed considerable variation in intron composition.ResultsAn analysis of the ABCB1 gene structure in 80 angiosperms revealed that the number of introns ranged from one to nine. All introns in ABCB1 underwent either a one-time loss (single loss in one lineage/species) or multiple independent losses (parallel loss in two or more lineages/species) with the majority of losses occurring within the grass family. In contrast, the structure of the closest homolog to ABCB1, ABCB19, remained constant in the majority of angiosperms analyzed. Using known phylogenetic relationships within the grasses, we determined the ancestral branch-points where the losses occurred. Intron 7, the longest intron, was lost in only a single species, Mimulus guttatus, following duplication of ABCB1. Semiquantitative PCR showed that the M. guttatus ABCB1 gene copy without intron 7 had significantly lower transcript levels than the gene copy with intron 7. We further demonstrated that intron 7 carried two motifs that were highly conserved across the monocot-dicot divide.ConclusionsThe ABCB1 gene structure is highly dynamic, while the structure of ABCB19 remained largely conserved through evolution. Precise removal of introns, preferential removal of smaller introns and presence of at least 2 bp of microhomology flanking most introns indicated that intron loss may have predominantly occurred through non-homologous end-joining (NHEJ) repair of double strand breaks. Lack of microhomology in the exon upstream of lost phase I introns was likely due to release of the selective constraint on the penultimate base (3rd base in codon) of the terminal codon by the splicing machinery. In addition to size, the presence of regulatory motifs will make introns recalcitrant to loss.

Variations and controls of iron oxides and isotope compositions during paddy soil evolution over a millennial time scale

A paddy soil chronosequence consisting of five profiles derived from calcareous marine sediments with cultivation history from 0 to 1000years was studied to understand the underlying mechanisms and processes controlling the millennial scale Fe evolution. We evaluated the chronosequencial changes in depth distribution of Fe oxide contents and Fe isotopic compositions. Results showed that paddy soil evolution under the influence of periodic flooding and groundwater fluctuation resulted with time in variations of soil moisture regime and redox condition that control Fe mobilization, translocation and redistribution, leading to enhanced profile differentiation of Fe oxides and measurable Fe isotope fractionation. Total Fe and oxide bound Fe as well as their differentiation between surface and subsurface horizons increased as paddy soils age, leading to the formation of diagnostic horizons and features characterizing Fe distribution and redistribution. Selective extractions showed that the weakly-bound, oxide-bound and silicate bound Fe corresponded to 1–16%, 8–46%, and 52–91% of the total Fe, respectively, and these proportions varied with both time and depth due to the redox-related Fe transformation and translocation. δ56Fe values in the studied paddy soil chronosequence ranged from −0.01‰ to 0.18‰ and exhibited a strong negative correlation with the logarithm of total Fe concentrations, suggesting mass-dependent Fe isotope fractionation occurred as a result of the preferential removal of lighter Fe isotopes during long-term paddy soil evolution under the predominant reducing conditions. However, the Fe isotopic ratio of a specific paddy soil horizon was a result of a complex interaction of different processes, which were summarized and interpreted in our proposed conceptual model. Comparison of Fe isotopic compositions in the worldwide soils demonstrated that Fe isotopes can evidence Fe transfer and pinpoint the factors and processes that control Fe mobilization and redistribution particularly in soils with changing moisture regimes and redox conditions. Our findings provide new insights into the behavior and geochemical cycle of Fe at the Earth's surface strongly affected by human activities and contributes to an improved understanding of how anthropedogenesis affects Fe evolution in the Earth's Critical Zone.

Serpentinization of olivine at 300 °C and 500 bars: An experimental study examining the role of silica on the reaction path and oxidation state of iron

The generation of H2 during serpentinization of ultramafic oceanic crust along Earth's mid-ocean ridges provides a key energy source for the deep biosphere and has important implications for metal transport and mineral stability in the subseafloor hydrothermal system. Nonetheless, the driving forces and rates of the coupled processes of Fe partitioning and H2 generation during serpentinization are complicated by many factors, but especially, the activity of SiO2(aq) in the serpentinizing fluid. To examine the role of this key variable in H2 generation and Fe partitioning between magnetite and Fe-serpentine during serpentinization, San Carlos olivine was reacted with a NaCl-SiO2(aq)-bearing fluid at 300°C and 500bars for approximately 90days using flexible gold cell hydrothermal equipment. Time-series changes in solution chemistry and dissolved H2 are coupled with magnetic susceptibility, Mössbauer spectroscopy, and Fe isotope measurements of reactant olivine and coexisting alteration products to provide a complete description of Fe mass transfer and oxidation as a function of reaction progress. Utilization of talc as reactant not only provided a source of SiO2(aq) for serpentinization, but effectively prevented brucite formation, in keeping with constraints imposed by many natural hydrothermal systems, which are inherently open systems. Moreover, this experimental strategy allowed Fe derived from olivine dissolution to transfer completely to serpentine and magnetite, facilitating reaction path modeling. Initial changes in solution chemistry indicate “buffering” of dissolved SiO2(aq), owing to the apparently balanced rates of olivine dissolution and serpentine precipitation. During this stage of reaction, a negligible amount of H2 is generated, suggesting that Fe2+-serpentine is stable and the dominant Fe-bearing product. With continued reaction, the rate of SiO2(aq) production lessens likely due to reduction in surface area of talc, such that the continued hydration and hydrolysis of olivine titrates the previously buffered activity of SiO2(aq), eventually approaching serpentine-brucite coexistence. During this secondary stage of reaction, the rate of H2 generation abruptly increases, which reflects the formation of magnetite and Fe3+-serpentine. Temporal changes in the isotope composition of dissolved Fe, throughout these stages, likely reflect different mineral alteration and formation processes, where initially, 1) preferential mass transfer of isotopically light Fe into solution occurred during olivine alteration, without considerable oxidation, as demonstrated by the low H2 production rate, and, 2) the preferential removal of isotopically light Fe from solution in connection with enhanced magnetite and H2 formation during the later stages of reaction. Post experimental analysis of the Fe isotopic composition of Fe-bearing minerals demonstrates statistically negligible enrichment of δ56Fe of magnetite relative to olivine and serpentine, consistent with observations from natural altered oceanic crust. Observations from this study demonstrate the utility of using coupled chemical, isotopic, and analytical approaches to ascertain time series changes in rates of mass transfer and mechanisms of oxidation of Fe during serpentinization of olivine. Ultimately, these insights provide important constraints for the chemical and Fe isotopic evolution of fluids and minerals in ultramafic hosted hydrothermal systems at mid-ocean ridges.

Dry Sliding Wear Mechanism of WC–13Ni Hard Alloy Irradiated by High-Intensity Pulsed Electron Beam

The wear properties and wear mechanism of WC–13%Ni hard alloy irradiated by high-intensity pulsed electron beam (HIPEB) at energy density of 34 J/cm2 with pulse numbers of 1–10 were investigated by dry sliding wear tests. The phase structure, cross-sectional microstructure and microhardness-depth profiles of the irradiated WC–13Ni hard alloy were examined by using X-ray diffractometer, scanning electron microscopy and Vickers testers, respectively. It was found that HIPEB irradiation induced surface remelting and preferentially ablation of Ni binder phase, resulting in the formation of a modified layer composed of remelted top layer accompany with WC phase transformation and graphite phase precipitation, and shock hardening layer. The specific wear rate of the irradiated samples decreased with the increasing pulse number and reached a minimum value of 3.8 × 10−7 mm3/N m with 10 pulses, only for 32% of the non-irradiated samples. The wear mechanism of surface remelting top layer on the irradiated samples was a homogenous microabrasion wear, which was attributed to the surface remelting and phase transformation, and the wear of the shock hardening layer involved preferential removal of Ni binder phase and detachment of WC grains, but it was restrained by strengthening of Ni binder phase from the deep hardening of HIPEB irradiation.

X-ray photoevaporation’s limited success in the formation of planetesimals by the streaming instability

The streaming instability is often invoked as solution to the fragmentation and drift barriers in planetesimal formation, catalyzing the aggregation of dust on kyr timescales to grow km-sized cores. However there remains a lack of consensus on the physical mechanism(s) responsible for initiating it. One potential avenue is disc photoevaporation, wherein the preferential removal of relatively dust-free gas increases the disc metallicity. Late in the disc lifetime, photoevaporation dominates viscous accretion, creating a gradient in the depleted gas surface density near the location of the gap. This induces a local pressure maximum that collects drifting dust particles, which may then become susceptible to the streaming instability. Using a one-dimensional viscous evolution model of a disc subject to internal X-ray photoevaporation, we explore the efficacy of this process to build planetestimals. Over a range of parameters we find that the amount of dust mass converted into planetesimals is often < 1 M_Earth and at most a few M_Earth spread across tens of AU. We conclude that photoevaporation may at best be relevant for the formation of debris discs, rather than a common mechanism for the formation of planetary cores. Our results are in contrast to a recent, similar investigation that considered an FUV-driven photoevaporation model and reported the formation of tens of M_Earth at large (> 100 AU) disc radii. The discrepancies are primarily a consequence of the different photoevaporation profiles assumed. Until observations more tightly constrain photoevaporation models, the relevance of this process to the formation of planets remains uncertain.

Transport and transformation of riverine neodymium isotope and rare earth element signatures in high latitude estuaries: A case study from the Laptev Sea

Marine neodymium (Nd) isotope and rare earth element (REE) compositions are valuable tracers for present and past ocean circulation and continental inputs. Yet their supply via high latitude estuaries is largely unknown. Here we present a comprehensive dissolved Nd isotope (expressed as εNd values) and REE data set together with seawater stable oxygen isotope (δ18O) compositions of samples from the Laptev Sea recovered in two Arctic summers and one winter.The Laptev Sea is a shallow Siberian Shelf sea characterized by extensive river-runoff, sea-ice production and ice transport into the Arctic Ocean. The large variability in εNd (−6 to −17), REE concentrations (16 to 600 pmol/kg for Nd) and REE patterns is controlled by freshwater supply from distinct riverine sources and open ocean Arctic Atlantic Water. Strikingly and contrary to expectations, except for cerium no evidence for significant release of REEs from particulate phases is found, which is attributed to low amounts of suspended particulate matter and high dissolved organic carbon concentrations present in the contributing rivers. Essentially all shelf waters are depleted in light (L)REEs, while the distribution of the heavy REEs shows a deficiency at the surface and a pronounced excess in the bottom layer. This distribution is consistent with REE removal through coagulation of riverine nanoparticles and colloids starting at salinities near 10 and resulting in a drop of all REE concentrations by ∼30%. With increasing salinity preferential LREE removal is observable reaching ∼75% for Nd at a salinity of 34. Although the delayed onset of dissolved REE removal contrasts with most previous observations from other estuarine environments, it agrees remarkably well with results from recent experiments simulating estuarine mixing of seawater with organic-rich river waters. In addition, melting and formation of sea ice leads to further REE depletion at the surface and strong REE enrichment near the shelf bottom as a function of ice melting and brine transfer, respectively. The ice-related processes significantly affect the distribution of dissolved REEs in high-latitude estuaries and likely also similarly contribute to the redistribution of other dissolved seawater constituents.

Biodiesel production by pervaporation-assisted esterification and pre-esterification using graphene oxide/chitosan composite membranes

Abstract In this study, a series of novel graphene oxide/chitosan (GO/CS) composite membranes was successfully synthesized and fully characterized. The performance of GO/CS composite membrane was then evaluated by integrating with the esterification of acetic acid with ethanol or the pre-esterification of palmitic acid with methanol, both essential in biodiesel production. Typically, esterification and pre-esterification are reversible reactions, which are limited by chemical equilibrium, resulting in a low product yield. In our study, reaction and separation were conducted in two separated steps or in a single one by means of a catalytic membrane. The preferential removal of water through the membrane in a PV-assisted process enhanced the conversion. The results show clearly that temperature, wt% of embedded GO within a polymeric CS-based membrane, and initial ratio of alcohol/acid are important parameters to enhance conversion because it acts on the kinetics of both pervaporation and esterification/pre-esterification. The enhanced catalytic membrane of the PV-assisted pre-esterification can only be observed when a proper amount of Amberlyst-15 catalyst is used. Additionally, the results of PV-assisted esterification/pre-esterification show that the ratio of water removal (by membrane) and water production (by esterification) rates play a significant role in evaluating the catalytic membrane. Under specific conditions, the conversions of PV-assisted esterification and pre-esterification by the catalytic membrane could be higher than those without PV-assisted up to 8% and 20%, respectively. This process could offer a key technology for biodiesel production in the future.

Characterizing fluids associated with the McArthur River U deposit, Canada, based on tourmaline trace element and stable (B, H) isotope compositions

The origin and nature of fluids responsible for U deposits of the Athabasca Basin have been in debate. This study presents the trace element abundances and stable isotope ratios (D/H and 11B/10B) of well characterized tourmaline samples determined by in situ analytical techniques, in order to evaluate the nature of fluids during the mineralization of the McArthur River U deposit, the world's largest high-grade U deposit. Magnesio-foitite, an alkali-deficient Mg-rich tourmaline, is abundant along the 13-km long P2 fault, a reverse structure that controls the location of the McArthur River deposit. Magnesio-foitite contains variable concentrations of rare earth elements (REEs, up to 46ppm in total) and Y (up to 35ppm). Chondrite normalized patterns indicate low light REEs (LREEs) relative to heavy REEs (HREEs) (CeN<YN, Y as a proxy for HREEs) and slight negative Eu anomalies, similar to those of uraninite from the deposit. The data combined with textural evidence suggest that magnesio-foitite and uraninite co-crystallized with LREE-rich aluminum phosphate sulfate minerals. Relatively high REE contents of magnesio-foitite in the ore zone indicates the incursion of a REE-rich basement fluid. Low values of δD (−98 to −41‰) for magnesio-foitite suggests that the mineralizing fluid originated from groundwater. Variably high values of δ11B (+13.1 to +23.2‰) are explained by the dissolution of B from carbonate or evaporitic rocks and preferential removal of 10B by the crystallization of illite and kaolinite. The results of this study support the ascent of a REE-rich basement fluid during mineralization and extensive modification of basinal fluids through the crystallization of clay minerals.

Transgenerational endocrine disruption and neurotoxicity in zebrafish larvae after parental exposure to binary mixtures of decabromodiphenyl ether (BDE-209) and lead

Polybrominated diphenyl ethers (PBDEs) and heavy metals are two key groups of electric and electronic equipment contaminants. Despite their co-occurrence in aquatic environments, their combined effects remain largely unknown, particularly under a chronic exposure regime. In the present study, adult zebrafish (Danio rerio) were exposed to environmentally relevant concentrations of BDE-209 and lead (Pb), or their binary mixtures, for 3 months. After chronic parental exposure, increased transfer of BDE-209 and Pb to the offspring eggs was activated in the coexposure groups, with BDE-197 being the predominant PBDE congener, indicating the dynamic metabolism of BDE-209 in parental zebrafish. In the presence of Pb, culturing the eggs in clean water until 5 days post-fertilization (dpf) further accelerated the debromination of BDE-209 towards BDE-197 in the offspring, caused by the preferential removal of bromine atoms at meta positions. BDE-209 and Pb combinations induced reproductive and thyroid endocrine disruption in adults, which resulted in an imbalanced deposition of hormones in the eggs. However, compared with single chemical exposure, the larval offspring at 5 dpf from the coexposure groups had reversed the adverse influences from maternal origin. In addition, the interaction between BDE-209 and Pb led to transgenerational developmental neurotoxicity in the larval offspring, where inhibited neuronal growth and neurotransmitter signaling, disorganized muscular assembly, and impaired visual function contributed to the observed neurobehavioral deficits. Overall, depending on specific biological events, the complex interaction between BDE-209 and Pb under chronic exposure resulted in significant alterations in their environmental fate and toxicological actions, thus complicating the accurate evaluation of ecological risks and constituting an unquantified threat to environmental safety.