Changes In Speciation Research Articles

In situ arsenic immobilization by natural iron (oxyhydr)oxide precipitates in As–contaminated groundwater irrigation canals

Arsenic-contaminated groundwater is widely used in agriculture. To meet the increasing demand for safe water in agriculture, an efficient and cost-effective method for As removal from groundwater is urgently needed. We hypothesized that Fe (oxyhydr)oxide (FeOOH) minerals precipitated in situ from indigenous Fe in groundwater may immobilize As, providing a solution for safely using As-contaminated groundwater in irrigation. To confirm this hypothesis and identify the controlling mechanisms, we comprehensively evaluated the transport, speciation changes, and immobilization of As and Fe in agricultural canals irrigated using As-contaminated groundwater. The efficiently removed As and Fe in the canals accumulated in shallow sediment rather than subsurface sediment. Linear combination fitting (LCF) analysis of X–ray absorption near edge spectroscopy (XANES) indicated that As(V) was the dominant As species, followed by As(III), and there was no FeAsO4 precipitate. Sequential extraction revealed higher contents of amorphous FeOOH and associated As in shallower sediment than in the subsurface layer. Stoichiometric molar ratio calculations, SEM‒EDS, FTIR, and fluorescence spectroscopy collectively demonstrated that the microbial reductive dissolution of amorphous FeOOH proceeded via reactive dissolved organic matter (DOM) consumption in subsurface anoxic porewater environment facilitating high labile As, whereas in surface sediment, the in situ-generated amorphous FeOOH was stable and strongly inhibited As release via adsorption. In summary, groundwater Fe2+ can efficiently precipitate in benthic surface sediment as abundant amorphous FeOOH, which immobilizes most of the dissolved As, protecting agricultural soil from contamination. This field research supports the critical roles of the phase and reactivity of in situ-generated FeOOH in As immobilization and provides new insight into the sustainable use of contaminated water.

Kinetic Model for Predicting Perfluoroalkyl Acid Degradation During UV-Sulfite Treatment.

Hydrated electron (eaq-) treatment processes show great potential in remediating recalcitrant water contaminants, including perfluoroalkyl and polyfluoroalkyl substances (PFAS). However, treatment efficacy depends upon many factors relating to source water composition, UV light source characteristics, and contaminant reactivity. Here, we provide critical insights into the complex roles of solution parameters on contaminant abatement through application of a UV-sulfite kinetic model that incorporates first-principles information on eaq- photogeneration and reactivity. The model accurately predicts decay profiles of short-chain perfluoroalkyl acids (PFAAs) during UV-sulfite treatment and facilitates quantitative interpretation of the effects of changing solution composition on PFAS degradation rates. Model results also confirm that the enhanced degradation of PFAAs observed under highly alkaline pH conditions results from changes in speciation of nontarget eaq- scavengers. Reverse application of the model to UV-sulfite data collected for longer chain PFAAs enabled estimation of bimolecular rate constants (k2, M-1 s-1), providing an alternative to laser flash photolysis (LFP) measurements that are not feasible due to the water solubility limitations of these compounds. The proposed model links the disparate means of investigating eaq- processes, namely, UV photolysis and LFP, and provides a framework to estimate UV-sulfite treatment efficacy of PFAS in diverse water sources.

Insights into self-discharge processes of Al-graphite batteries

Aluminum graphite dual ion batteries (AGDIB) have been widely explored thanks to abundant electrode materials, a long cycle life and high power density. However, the shelf life of AGDIBs is so far barely understood. This work's detailed self-discharge investigations allow the quantification of capacity losses for up to 4 weeks, confirm a deintercalation mechanism by Raman spectroscopy and X-ray diffraction, and furthermore give insight to influence factors. While a cell employing typical materials such as a natural graphite cathode, Mo current collector and AlCl3/[EMIm]Cl=1.5 ionic liquid electrolyte exhibits a capacity loss of 10 % in 24 h, this value can be significantly reduced to 3 % in 24 h when using a glassy carbon current collector and AlCl3/Et3NHCl=1.5 electrolyte instead. Iron impurities within the electrolyte do not affect battery capacities or self-discharge, since it is deposited on the Al anode within the battery soon after assembly. In general, the instability of the current collector material, gas evolution due to electrolyte oxidation at high cell potentials, and cationic electrolyte species greatly influence the self-discharge independently. Electrolyte speciation changes directly related to self-discharge processes are revealed by IR spectroscopy.

Elemental speciation of the sediments from cold methane seeps on the Laptev Sea shelf

Relevance. The lack of elemental speciation data in the bottom sediments of the Laptev Sea, as well as the absence of its quantitative changes in occurrence forms in response to methane emissions. Aim. To assess changes in the elemental speciation in areas where methane-containing fluids are discharged. Objects. Nine samples of bottom sediments taken from three horizons of one “cold seep” and two background stations of the outer shelf-continental slope of the Laptev Sea during the AMK-82 expedition aboard R/V “Academician M.V. Keldysh” in autumn 2020. Methods. Sequential extraction BCR (the European Community Bureau of Reference) was performed to determine the elemental speciation in surface sediments; the residual fraction was determined by dissolving in nitric acid. The obtained fraction solutions were analyzed by ICP-MS (NexIon 300D, Perkin Elmer, Waltham, MA, USA), Pyrolysis (Rock-Eval 6 Turbo, Vinci Technologies). Results. The trend towards an increase in element mobility has been identified as a result of a shift in geochemical conditions that is presumably caused by the authigenic carbonate and sulfide formation. Moreover, the increase in the recoverable fraction (associated only with Fe oxides/hydroxides) is highlighted. We assume that the process of unloading methane-containing fluids plays a significant role in enrichment of authigenic carbonates U, Ni, Zn Co, oxides Fe – Sn and V, authigenic sulfides – Co, Mn and W. We also assume the potential formation of chalcopyrite as an authigenic sulfide in methane discharge areas.

Leaching characteristics of nutrients in food waste digestate-derived biochar

Food waste anaerobic digestion requires proper utilization of solid digestate, and pyrolysis emerges as an effective method to produce nutrient-rich biochar. This study investigated the leaching characteristics and speciation changes of nutrients in food waste digestate (FWD)-derived biochar pyrolyzed at 350 °C (BC350), 450 °C (BC450), and 550 °C (BC550). BC350 featured inorganic nitrogen, while BC450 and BC550 contained elevated organic nitrogen. Nitrogen, potassium, and dissolved organic carbon were released via a quick surface wash-off process. Polyphosphates prevailed in BC350 and leached through a fast diffusion-controlled process. BC450 and BC550 were dominated by Ca/Mg orthophosphates and released via a slow dissolution-controlled process. Leachates from BC450 and BC550 stimulated the shoot length of wheat seeds. After 5 leaching cycles, there were more aromatic dissolved organics, and BC450 and BC550 exhibited higher abundance of C-N and O-P-O. Overall, pyrolysis of FWD at 450 °C and 550 °C shows potential in producing slow-release biochar fertilizers for resource recycling.

Effects of Phosphate and Arsenate on As Metabolism in Microcystis aeruginosa at Different Growth Phases

Arsenic (As) metabolism in freshwater algae at different growth phases has rarely been documented. To address this gap, this study was conducted to assess the intra- and extracellular As metabolism, along with speciation changes, in Microcystis aeruginosa across three growth phases. The treatment involved varying concentrations of As (0, 0.4, 0.6, 0.8 and 1 mg/L, in the form of arsenate, iAsV) under three phosphorus levels (0.02 mg/L as low, 0.1 mg/L as medium, and 0.5 mg/L as high P in the form of phosphate). The findings revealed that extracellular iAsV remained the dominant As species during the lag and exponential growth phases of M. aeruginosa in the growth media, while intracellular trivalent As (iAsIII) emerged as the pronounced species during the exponential growth phase, but also exhibited a significant negative correlation with the P levels. Moreover, elevated P levels had promoted the formation of intra- and extracellular dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) in the exponential growth phase. During the stationary growth phase, intracellular iAsV was found to decrease with the increasing P levels. During the whole growth phases, P had consistently reduced algal As absorption levels. The significant promotion of algal As absorption in response to iAsV was observed only during the lag growth phase. The As bioaccumulation exhibited a correlational relationship with the algal reproduction. Both low and high P levels (0.02 and 0.5 mg/L) decreased the accumulation of As in algae cells during the exponential and stationary growth phases. The transformation and release rate of As were concomitantly influenced by P, and exhibited the same trends within the growth phase. These trends differed between the exponential and stationary growth phases, with an inhibitory effect being present during the former, while a promotional effect was observed during the latter. This study provides insight into potential As hazards in freshwater lakes with algae bloom.

Root-exuded specialized metabolites reduce arsenic toxicity in maize

By releasing specialized metabolites, plants modify their environment. Whether and how specialized metabolites protect plants against toxic levels of trace elements is not well understood. We evaluated whether benzoxazinoids, which are released into the soil by major cereals, can confer protection against arsenic toxicity. Benzoxazinoid-producing maize plants performed better in arsenic-contaminated soils than benzoxazinoid-deficient mutants in the greenhouse and the field. Adding benzoxazinoids to the soil restored the protective effect, and the effect persisted to the next crop generation via positive plant-soil feedback. Arsenate levels in the soil and total arsenic levels in the roots were lower in the presence of benzoxazinoids. Thus, the protective effect of benzoxazinoids is likely soil-mediated and includes changes in soil arsenic speciation and root accumulation. We conclude that exuded specialized metabolites can enhance protection against toxic trace elements via soil-mediated processes and may thereby stabilize crop productivity in polluted agroecosystems.

Influence of environmental factors on changes in the speciation of Pb and Cr in sediments of Wuliangsuhai Lake, during the ice-covered period.

Ecological pollution caused by heavy metals released from sediments is a worldwide concern. However, the effect of changes in sediment speciation on their release of heavy metals has not been adequately reported. In this study, the research focused on Pb and Cr in the ice period of Wuliangsuhai. This study analyzed changes in the sediment speciation of Pb and Cr before and after a release experiment using four risk assessment methods while varying the temperature, pH, and salinity of the water column. The results indicated that the total concentration of Pb ranged from 11.17 to 24.25mg/kg, while for Cr it ranged from 42.26 to 69.68mg/kg. Both elements exhibited mild contamination. The release of Pb and Cr from sediments increases with increasing water temperature, mainly due to the conversion of the residual fraction of Pb to the Fe-Mn oxide fraction and Cr converting more residual fraction to the organic matter and sulfide fraction. The release of sediment Pb and Cr decreased with increasing pH, with Pb converting more acid extractable fraction to the residual fraction and Cr converting more organic matter and sulfide fraction to the residual fraction. In contrast, the release of Pb and Cr increased and then decreased with increasing salinity. For Pb, the acid extractable fraction was more susceptible to conversion to the residual fraction by environmental influences, whereas for Cr, the organic matter and sulfide fraction were susceptible to conversion to the residual fraction.

Redox cycling of straw-amended soil simultaneously increases iron oxide crystallinity and the content of highly disordered organo-iron(III) solids

Iron speciation in soils is influenced largely by its redox state, but the extent of and controls on Fe speciation during recurrent reduction and oxidation events are not fully understood. To investigate the effects of organic matter (OM) inputs and the frequency and duration of redox oscillations on soil Fe speciation, we conducted redox-oscillation experiments with topsoil from a Fluvisol mixed with rice straw (0, 10, 50 g/kg organic carbon, OC). The soil was initially dominated by short-range ordered (SRO) Fe(III) solids and subjected to 14- and 28-day reduction–oxidation cycles for 112 days, with the time spent under anoxic and oxic conditions maintained at 6:1. Reduction was initiated by flooding reactors with artificial river water. To simulate leaching conditions, soil re-oxidation was achieved by air-drying soil after removal of reacted solutions. Fresh river water was then added for each new redox cycle. We monitored changes in solution composition (Eh, pH, Fe(II), total Fe, OC, and Si) and assessed changes of solid-phase Fe speciation by selective extractions, X-ray absorption spectroscopy, and 57Fe Mössbauer spectroscopy. Dissolved OC and Fe increased with increasing straw addition, but decreased in each treatment through consecutive reduction intervals. Release rates of dissolved Fe and OC were highly correlated, implying that microbial reduction of soil Fe(III) solids was fostered by straw amendments. Reduction-induced losses of OC and Fe from straw amended soil were amplified at high redox frequency. Ferrous Fe did not detectably accumulate in the solid phase upon repeated soil oxidation. Although Fe(III)-poor phyllosilicates gained in relative importance in redox-cycled soils, their fraction was hardly affected during redox cycling. Instead, straw additions led to an enhanced depletion of ferrihydrite during soil redox cycling and a relative enrichment of highly disordered Fe(III) species [‘very SRO (vSRO) Fe(III) solids’], which remained only partially ordered in 5-K Mössbauer spectra and likely consisted predominantly of polynuclear organic Fe complexes. The depletion of ferrihydrite in straw-amended soils after 112 days was greater in the 14-day cycle than in the 28-day cycle experiment and accompanied by a less pronounced enrichment of vSRO Fe(III) solids. The crystallinity of distinct Fe oxides (ferrihydrite, lepidocrocite, and hematite) increased during soil redox cycling especially in straw-amended soils, but without noticeable ferrihydrite conversion into crystalline Fe oxides. The increase in the crystallinity of distinct Fe oxides after 112 days was greater at low redox frequency in straw-free soil, however this frequency effect was suppressed by straw additions. Longer soil redox cycling (112 vs. 56 days) increased the crystallinity of distinct Fe oxides, which was most pronounced at high straw levels and low redox frequency. Our results imply that redox changes in SRO Fe oxide- and OM-rich soils can cause a relative enrichment of more crystalline Fe oxides, while still maintaining a pool of vSRO Fe(III) solids. We conclude that soil redox oscillations can lead to divergent transformation pathways of Fe oxides, which concomitantly increase bulk Fe-oxide crystallinity and generate increasing fractions of highly disordered Fe(III) solids on comparatively short time scales. In addition, our study suggests that faster redox cycling in soils with ample electron donor supply and water leaching leads to higher element exports (e.g., OC, metal(loid)s) from soil due to weekly redox pulsing than more slowly alternating redox conditions.

Iodide, iodate & dissolved organic iodine in the temperate coastal ocean

The surface ocean is the main source of iodine to the atmosphere, where it plays a crucial role including in the catalytic removal of tropospheric ozone. The availability of surface oceanic iodine is governed by its biogeochemical cycling, the controls of which are poorly constrained. Here we show a near two-year time series of the primary iodine species, iodide, iodate and dissolved organic iodine (DOI) in inner shelf marine surface waters of the Western English Channel (UK). The median ± standard deviation concentrations between November 2019 and September 2021 (n=76) were: iodide 88 ± 17 nM (range 61-149 nM), iodate 293 ± 28 nM (198-382 nM), DOI 16 ± 16 nM (<0.12-75 nM) and total dissolved iodine (dIT) 399 ± 30 nM (314-477 nM). Though lower than inorganic iodine ion concentrations, DOI was a persistent and non-negligible component of dIT, which is consistent with previous studies in coastal waters. Over the time series, dIT was not conserved and the missing pool of iodine accounted for ~6% of the observed concentration suggesting complex mechanisms governing dIT removal and renewal. The contribution of excess iodine (I*) sourced from the coastal margin towards dIT was generally low (3 ± 29 nM) but exceptional events influenced dIT concentrations by up to ±100 nM. The seasonal variability in iodine speciation was asynchronous with the observed phytoplankton primary productivity. Nevertheless, iodate reduction began as light levels and then biomass increased in spring and iodide attained its peak concentration in mid to late autumn during post-bloom conditions. Dissolved organic iodine was present, but variable, throughout the year. During winter, iodate concentrations increased due to the advection of North Atlantic surface waters. The timing of changes in iodine speciation and the magnitude of I* subsumed by seawater processes supports the paradigm that transformations between iodine species are biologically mediated, though not directly linked.

The potential of ferrihydrite-synthetic humic-like acid composite as a soil amendment for metal-contaminated agricultural soil: Immobilization mechanisms by combining abiotic and biotic perspectives

In-situ passivation technique has attracted increasing attention for metal-contaminated agricultural soil remediation. However, metal immobilization mechanisms are mostly illustrated based on metal speciation changes and alterations in soil physicochemical properties from a macroscopic and abiotic perspective. In this study, a ferrihydrite-synthetic humic-like acid composite (FH-SHLA) was fabricated and applied as a passivator for a 90-day soil incubation. The heavy metals immobilization mechanisms of FH-SHLA were investigated by combining both abiotic and biotic perspectives. Effects of FH-SHLA application on soil micro-ecology were also evaluated. The results showed that the 5%FH-SHLA treatment significantly decreased the DTPA-extractable Pb, Cd and Zn by 80.75%, 46.82% and 63.63% after 90 days of incubation (P < 0.05), respectively. Besides, 5% FH-SHLA addition significantly increased soil pH, soil organic matter content and cation exchange capacity (P < 0.05). The SEM, FTIR, and XPS characterizations revealed that the abiotic metal immobilization mechanisms by FH-SHLA included surface complexation, precipitation, electrostatic attraction, and cation-π interactions. For biotic perspective, in-situ microorganisms synergistically participated in the immobilization process via sulfide precipitation and Fe mineral production. FH-SHLA significantly altered the diversity and composition of the soil microbial community, and enhanced the intensity and complexity of the microbial co-occurrence network. Both metal bioavailability and soil physiochemical parameters played a vital role in shaping microbial communities, while the former contributed more. Overall, this study provides new insight into the heavy metal passivation mechanism and demonstrates that FH-SHLA is a promising and environmentally friendly amendment for metal-contaminated soil remediation.

Trace metal partitioning in the parnaíba delta in dry season, equatorial coast of Brazil

Trace metal concentrations in the particulate fractions (MP), dissolved fractions (MD) and sediments (MS), such as Ba, Cu, Co, Cr, Pb, Ni and Zn, were determined during the dry season of the largest open sea delta of Americas, the Parnaíba River Delta (Brazil). This study aimed to comprehend the distribution, dynamic changes of metal speciation and environmental quality index of trace metals in the particulate fractions and subsurface sediments in scenario of major marine influence over the delta. The trace metals bound to suspended particulate material (SPM) from weathering the drainage basin exhibited a removal trend under increases in salinity and pH. Desorption influenced the partitioning of BaMP, ZnMP, NiMP, CoMP, CuMP, and the adsorption and precipitation of PbMP and CrMP to the surface sediments. The organic matter contents in the sediments acts as an important geochemical carrier of these contaminants, and the dissolved organic carbon influences the binding of PbMD in the subsurface waters. The geoaccumulation index (Igeo) plays a crucial role in revealing potential contamination with ZnMP contents and weak association to this fraction. These results make possible the assessment of ecological risk by metal contamination and global pollution mitigation in coastal tidal estuaries under intensive physical mixing along the equatorial coast.

Addition of plantation waste to the bioconversion of pig manure by black soldier fly larvae: Effects on heavy metal content and bioavailability

During the conversion of pig manure by black soldier fly larvae (BSFL), the accumulation and speciation changes of heavy metals (HMs) have adverse effects on the environment. In this study, corn straw, rice straw, bamboo chips (BC), wood chips, and rice husk char were added to a bioconversion system to study the accumulation, migration, speciation changes, and microbial correlations of HMs. The results indicated that the addition of BC was most beneficial for the accumulation of HMs (47–72 %) in the BSFL body. In the BC group, the accumulation effect of the BSFL body on zinc (Zn) and arsenic (As) was the most evident (72 and 71 %, respectively). The results of linear fitting (R2 > 0.90) and redundancy analysis (RDA; 90 %) indicated that the bacterium Bacillaceae (Bacillus) was beneficial for increasing the larval weight (LW) of BSFL, and a higher LW accumulated HMs. The addition of BC helped reduce the total amount (6–51 %) of available states (weak acid extraction and reducible states) in the BSFL residue. The RDA results indicated that bacteria (55–92 %) affected the transformation of HM speciation. For example, Zn and cadmium were mainly affected by Firmicutes, whereas copper and chromium were affected by Bacteroidetes. Proteobacteria and Pseudomonas formosensis affected the conversion of lead and As. This study provides important insights into the adsorption of HMs from pig manure by BSFL.

Zinc speciation in highly weathered tropical soils affected by large scale vegetable production

Agriculture in highly weathered tropical soils often requires considerable application of lime and fertilizers to ensure satisfactory plant nutrient levels. The consequences of these continue long-term applications is not well understood may induce changes in soil chemical properties, the abundance, and speciation of potentially toxic trace element and as well as of micronutrients in agriculture soils. In this study, we evaluated the adsorption (at pH 5) and speciation of Zn in tropical soils (both agricultural and native vegetation) as a function of fertilization and contact time using chemical fractionation analyses and X-ray absorption spectroscopy. The soils overall had high Zn adsorption capacities (∼ 700 mg kg-1), but the agricultural soil was approximately 30 % higher than of the soil under native vegetation, and the proportion of Zn in the mobile fraction was 35 % in native vegetation and 21 % in agricultural soils. Zn speciation via linear combination analysis showed a strong relationship with soil mineralogical composition and reveled that Zn associated with organic matter decreased while Zn associated with P increased after the conversion of soils from native vegetation to highly fertilized soil. Aluminosilicate soil minerals were identified as major sinks of soil Zn, accounting for 34 % of total Zn retention regardless of soil origin and land use. Association of Zn with phosphate (i.e., hopeite) was observed in the agricultural soil samples, which might be an unexpected Zn-bearing mineral in highly weathered tropical soils and could have impacts on Zn plant nutrition.

Dynamic changes of zinc chemical speciation and zinc-containing peptides release in oysters (Crassostrea hongkongensis) during enzymatic hydrolysis

Oyster hydrolysates exhibit promising potential as a zinc supplement for its significant amounts of zinc, however, the zinc chemical speciation which determines zinc nutrition in oyster hydrolysates has not been investigated. This study optimized the oyster hydrolysis conditions using the Response surface methodology (RSM) method, and the zinc chemical speciation, the sequence of zinc-containing peptides, and the binding sites of zinc and peptides were further investigated. Results showed that inorganic and organic zinc in oysters were 60.15% and 36.53% of total zinc respectively, while organic zinc in oysters aqueous extract was 4.54% of which 3.56% was present in the polysaccharide fraction. The zinc yield was 84.20% of total zinc under optimal hydrolysis conditions, while the organic zinc increased to 52.93% of which 38.14% existed in the protein/peptides fraction. Zinc in protein/peptide fraction primarily was bound to low-molecular-weight peptides (Mw < 1000 Da). Further, 42 shared zinc-containing peptides (mainly 3–4 peptides) were identified. Molecular docking indicated that Glu, Leu, and Tyr might be the binding sites for zinc and peptides. These findings provided a theoretical basis for the development of novel and safe zinc dietary supplements.

Optimization of liquefaction process based on global meta-analysis and machine learning approach: Effect of process conditions and raw material selection on remaining ratio and bioavailability of heavy metals in biochar

&lt;abstract&gt; &lt;p&gt;Although liquefaction technology has been extensively applied, plenty of biomass remains tainted with heavy metals (HMs). A meta-analysis of literature published from 2010 to 2023 was conducted to investigate the effects of liquefaction conditions and biomass characteristics on the remaining ratio and chemical speciation of HMs in biochar, aiming to achieve harmless treatment of biomass contaminated with HMs. The results showed that a liquefaction time of 1–3 h led to the largest HMs remaining ratio in biochar, with the mean ranging from 84.09% to 92.76%, compared with liquefaction times of less than 1 h and more than 3 h. Organic and acidic solvents liquefied biochar exhibited the greatest and lowest HMs remaining ratio. The effect of liquefaction temperature on HMs remaining ratio was not significant. The C, H, O, volatile matter, and fixed carbon contents of biomass were negatively correlated with the HMs remaining ratio, and N, S, and ash were positively correlated. In addition, liquefaction significantly transformed the HMs in biochar from bioavailable fractions (F1 and F2) to stable fractions (F3) (&lt;italic&gt;P&lt;/italic&gt; &amp;lt; 0.05) when the temperature was increased to 280–330 ℃, with a liquefaction time of 1–3 h, and organic solvent as the liquefaction solvent. N and ash in biomass were positively correlated with the residue state (F4) of HMs in biochar and negatively correlated with F1 or F2, while H, O, fixed carbon, and volatile matter were negatively correlated with F4 but positively correlated with F3. Machine learning results showed that the contribution of biomass characteristics to HMs remaining ratio was higher than that of liquefaction factor. The most prominent contribution to the chemical speciation changes of HMs was the characteristics of HMs themselves, followed by ash content in biomass, liquefaction time, and C content. The findings of this meta-analysis contribute to factor selection, modification, and application of liquefied biomass to reducing risks.&lt;/p&gt; &lt;/abstract&gt;

Experimental determination of freezing point depressions in the CuSO4-H2SO4-H2O system

Limited experimental data of the aqueous ternary CuSO4-H2SO4-H2O system hinders the modelling of its thermodynamic properties. Although different mixing rules for predicting the behavior of mixed electrolyte solutions have been proposed in the literature, significant deviations from them can be expected for systems where e.g., changes in speciation occur. In this work, freezing points of the ternary aqueous solutions were measured using a purpose-built apparatus. The measured samples spanned the concentration range 0.0140 to 0.5534 mol·(kg-H2O)–1 at four different CuSO4–to–H2SO4 ratios. The experimental results were compared with Zdanovskii’s rule predictions.

Sulfur speciation in Sphagnum peat moss modified by mutualistic interactions with cyanobacteria.

Peat moss (Sphagnum spp.) develops mutualistic interactions with cyanobacteria by providing carbohydrates and S compounds in exchange for N-rich compounds, potentially facilitating N inputs into peatlands. Here, we evaluate how colonization of Sphagnum angustifolium hyaline cells by Nostoc muscorum modifies S abundance and speciation at the scales of individual cells and across whole leaves. For the first time, S K-edge X-ray Absorption Spectroscopy was used to identify bulk and micron-scale S speciation across isolated cyanobacteria colonies, and in colonized and uncolonized leaves. Uncolonized leaves contained primarily reduced organic S and oxidized sulfonate- and sulfate-containing compounds. Increasing Nostoc colonization resulted in an enrichment of S and changes in speciation, with increases in sulfate relative to reduced S and sulfonate. At the scale of individual hyaline cells, colonized cells exhibited localized enrichment of reduced S surrounded by diffuse sulfonate, similar to observations of cyanobacteria colonies cultured in the absence of leaves. We infer that colonization stimulates plant S uptake and the production of sulfate-containing metabolites that are concentrated in stem tissues. Sulfate compounds that are produced in response to colonization become depleted in colonized cells where they may be converted into reduced S metabolites by cyanobacteria.

Simulating climate change in a coastal watershed with an integrated suite of airshed, watershed, and estuary models

AbstractIn 2020, the Chesapeake Bay Program moved to offset impacts from climate change for the 30‐year period from 1995 through 2025 by having its seven watershed jurisdictions (Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia, and the District of Columbia) apply additional nutrient pollutant reduction practices. The climate change assessment was performed with integrated models of the Chesapeake watershed, airshed, and estuary. Scenarios run for the years 2025, 2035, 2045, and 2055 estimated effects from the different future climatic conditions. This article presents the results of that assessment and is intended to provide a guide to assist other modeling practitioners in assessing climate change impacts in coastal watersheds. Major influences of climate change that were quantified include increases in precipitation volume, potential evapotranspiration, watershed nutrient loads, tidal water temperature, and sea level. Minor influences quantified in the climate change analysis include changes in nutrient speciation and increases in wet deposition of nitrogen, CO2, rainfall intensity, tidal wetland loss, up‐estuary salt intrusion, and phytoplankton biomass. To offset climate change impacts from 1995 to 2025 on water quality, the scenarios indicate an additional 2.3 million and 0.3 million kg of nitrogen and phosphorus per annum, respectively, will need to be reduced beyond what is called for in the Chesapeake Total Maximum Daily Load.

Determination of organic and inorganic Cl in gaseous ethylene based on gas-liquid equal mass response followed by automatic quick furnace-ion chromatography

Herein, a practical method for the determination of organic and inorganic Cl in gaseous ethylene by liquid standard samples was established; and then, the effects of various speciation and matrices on results were investigated followed by automatic quick furnace-ion chromatography (AQF-IC) analysis. From the evaluation of speciation and matrices, unified equation was explored and the method for accurately determining trace HCl with strong adsorption was also developed. First, summarize regularity that the light oil liquid standards themselves conformed to equal Cl mass response by AQF-IC (R2=0.99993). Then, the actual Cl mass in standard gas at 4 levels with different speciation and matrices were calculated by the same regularity based on the assumption of not affected by speciation or matrix change. The gas mass was accurately calculated based on Van der Waals’ Equation. As a result, combined with the theoretical Cl mass calculated by equation, the recoveries of the organic and inorganic Cl were in the range of 93.0%-101.4% [2.0 µmol/mol of CH3Cl/(N2+ethylene)], 93.4%-104.9% (10.1 µmol/mol of CH3Cl/N2), 101.6%-111.2% (20.2 µmol/mol of CH3Cl/ethylene) and 95.3%-101.0% (11.0 mg/m3 of HCl/N2), respectively, indicating the successful verification of above assumption rather than applying more exploration to rebuild relationships between different systems. As proof of principle and for more verification, system of CH2Cl2/He gas standard sample was prepared to explore the quantitative accuracy in more speciation with recoveries in the range of 91.3%-98.5%. In addition, the detection limit of Cl content based on S/N = 3 for ethylene was 0.06 mg/kg. Intra-day and inter-day relative standard devations (RSDs) were in the range of 9.3%-12.0% (≤1.0 mg/kg) and 2.5%-4.4% (>1.0 mg/kg). Finally, the developed method based on gas-liquid equal mass response was successfully applied in the actual samples of light olefins such as ethylene and propylene.