Inorganic Cl Research Articles

Encapsulating Azolates Within Cationic Metal-Organic Frameworks for High-Energy-Density Materials.

Despite the synthesis of numerous cationic metal-organic frameworks (CMOFs), their counter anions have been primarily limited to inorganic Cl-, NO3 -, ClO4 -, BF4 -, and Cr2O7 2-, which have weak coordination abilities. In this study, a series of new CMOFs is synthesized using azolates with strong coordination abilities as counter anions, which are exclusively employed as ligands for coordinating with metals. Owing to the unique nitrogen-rich composition of azolates, the CMOFs demonstrate significant potential as high-energy-density materials. Notably, CMOF(CuTNPO) has an exceptionally high heat of detonation of 7375kJ kg-1, surpassing even that of the state-of-art CL-20 (6536kJ kg-1). To further validate the advantages of employing azolates as counter anions, analogues with azolates serving as ligands are also synthesized. The comparison study indicates that encapsulating azolates within the cationic frameworks confers both high energy and safety properties. X-ray data and quantum calculations indicate that their enhanced performance stems from stronger H─bonds and π-π interactions. This study introduces new roles for azolates in MOFs and expands possibilities for structural diversity and potential applications of framework materials.

Fate of Na & Cl in kitchen waste during hydrothermal carbonization

Hydrothermal carbonization (HTC) is a sustainable approach to recover nutrients from kitchen waste (KW) to realize the applications of hydrochar as fuel, soil amendment and so on. However, the salt content of KW can be as high as 5 wt%, which brings potential risks for product utilization. Thus, the migration path of endogenous (from ingredients) and exogenous (from condiments) Na & Cl in KW during HTC process was investigated. Results showed that the endogenous and total Na element in KW was 0.03–2.98 wt% and 2.97–4.82 wt%, respectively. The main form of sodium was water-soluble (48–82%). The KW feedstocks and cooking methods had little effect on the migration of Na & Cl. During HTC treatment, all sodium element was transformed into water-soluble state, subsequently about 97% was dissolved into the liquid phase. The content of Na element in hydrochar was only below 0.05 wt%, so its negative effect can be negligible. As for the fate of chlorine, the endogenous and total Cl element in KW was 0.31–1.62 wt% and 1.82–3.19 wt%, respectively, and the main form was inorganic Cl accounting for 83–91%. During HTC treatment, about 40–75% of endogenous organochlorine was converted into inorganic Cl by breaking C-Cl bonds, and all inorganic Cl was leached into the liquid phase. In this pattern, partial organochlorine remained in hydrochar with a content of 0.21–0.32 wt%, which need to be further reduced. Methods of adding Na2CO3 solution or HTC-pyrolysis were effective, and approximately 90% of the organic Cl can be removed. Based on the above findings, this study can provide theoretical guidance for the value-added conversion of solid waste with high moisture and high salinity.

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.

Synergistic Optimization of Buried Interface by Multifunctional Organic–Inorganic Complexes for Highly Efficient Planar Perovskite Solar Cells

HighlightsHighly performed perovskite solar cells are achieved via introducing organic–inorganic CL–NH complex as multifunctional interfacial layer.CL–NH complex not only reduces oxygen vacancies on the surface of SnO2 but also regulates film crystallization, resulting in a superior device efficiency of 23.69%.The resulting device performs excellent stability with 91.5% initial power conversion efficiency retained after 500 h light illumination.

Radical-/non-radical-mediated catalyst activation of peroxymonosulfate for efficient atrazine degradation

Efficient degradation technologies are urgent to be developed to avoid the ecological and healthy hazards brought from atrazine (ATZ). LaCoO3-δ/peroxymonosulfate (PMS) system was proved to have strong degradation capabilities to contaminants. In this work, we intended to investigate the effect of the synthesis method on LaCoO3−δ. However, the hydrothermal method yielded a new material (H–Co) with better catalytic performance than LaCoO3−δ, which showed stable catalytic ability at pH 3.0–9.0 and 5 consecutive cycles. The coexistence of inorganic Cl−, SO42−, NO3−, H2PO4−, HCO3− and organic humic acids exerted little influences on the H–Co/PMS system. In addition, the actual livestock and poultry breeding wastewater could be well degraded and mineralized by the H–Co/PMS system. Free radical burst experiments and EPR characterization were performed to verify the synergistic effects of free radicals and non-free radicals during ATZ degradation. Based on SEM, XRD, O2-TPD, FTIR, XPS, and electrochemistry characterizations, the efficient catalytic ability of H–Co could be attributed to the abundant oxygen vacancies, surface hydroxyl groups, zero-valent cobalt sites and high electronic conductivity. The degradation pathways were proposed based on the detection of degradation intermediates of ATZ by UPLC-MS. Moreover, the toxic of ATZ during the oxidation was evaluated by TEXT and E. coli inhibition assay. This work comprehensively analyzed the catalytic reaction mechanism of the H–Co/PMS system and provided a feasible pathway for the treatment of the actual livestock and poultry breeding wastewater.

Advances in chloride additives for high-efficiency perovskite solar cells: multiple points of view.

Chloride (Cl) additives are rather effective in improving the performance of perovskite solar cells (PSCs) through the modulation of crystallization process and surface morphology. After incorporating Cl-containing additives, the optoelectrical properties of perovskite films, such as the electron/hole diffusion length and carrier lifetime, are greatly enhanced. However, only a trace amount of Cl has been identified in the resultant perovskite film, and the mechanism of efficiency improvement induced by Cl remains unclear. In this review, we discuss organic and inorganic Cl additives systematically from the perspective of their solubility, volatility, cation size and chemical groups. In addition, the roles of residual Cl anions and cations are analyzed in detail. Finally, some valuable future perspectives of Cl additives are proposed.

Formation pathways, gas-solid partitioning, and reaction kinetics of PCDD/Fs associated with baghouse filters operated at high temperatures: A case study

The application of the 3T method during combustion (i.e., a Temperature > 850 °C, a residence Time > 2 s, and sufficient Turbulence) can lead to elevated operating temperature in the baghouse filter for the municipal solid waste incineration (MSWI) systems without sufficient heat exchange capacity, which is potentially detrimental to the emission control of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Herein, a field study focusing on the distribution and variation of PCDD/Fs in gaseous and solid phases in a baghouse filter with high operating temperature (225–230 °C) was carried out. The concentration of PCDD/Fs in gases at the outlet of the baghouse filter was around 1 order of magnitude higher than that in inlet gases (i.e., noticeable memory effect of PCDD/Fs), because of the significant PCDD/Fs formation in filter fly ash (primarily contributed by the precursor pathway) followed by PCDD/Fs desorption. In addition, the mechanisms and factors resulting in the memory effect of PCDD/Fs were identified based on a laboratory study that carefully investigated the formation and desorption of PCDD/Fs at potential operating temperatures of baghouse filters (i.e., 180, 200, and 225 °C). The temperature was identified as the key factor inducing the memory effect of PCDD/Fs, because: i) PCDD/Fs memory effect was not observed for baghouse filters with low operating temperatures of ~150 °C in previous studies; ii) both the formation and desorption of PCDD/Fs were noticeably favored by rising temperature from 180 to 225 °C; iii) increasing temperature appeared to facilitate the transformation from inorganic Cl to organic Cl and the conversion from aliphatic carbon to aromatic carbon or unsaturated hydrocarbons, both of which were favorable to PCDD/Fs formation; and iv) the release rate of PCDD/Fs from fly ash was exponentially dependent on temperature based on the modeling results of reaction kinetics.

Simultaneous harmless ionization of CFC and resource utilization of waste solar panel through one-pot hydrothermal treatment

Chlorofluorocarbons (CFCs), which possess the characteristics of high volatility and destroy ozone layer, are hardly disposed of through traditional methods. With a tightly closed reaction environment and high-temperature water medium, CFCs can react and generate inorganic Cl- and F- under subcritical water conditions, which is very useful to enhance leaching and enrich rare metals. Therefore, in the current study, CFCs and photovoltaic wastes containing gallium arsenide (GaAs) were co-processed for mineralization and enhanced leaching simultaneously. Based on frontier orbital theory and bond energy theory, possible decomposition pathways of CFCs were speculated. Enhanced leaching process was studied in detail. When experimental conditions were 300 °C and 8.8 MPa, the mineralization rates of organofluorine and organochlorine in CFCs were 83.68% and 93.37%, respectively. Leaching agent generated by the hydrothermal treatment of CFCs leached GaAs effectively, and the leaching rates of gallium and arsenic were 95.74% and 99.89%, respectively. Converting CFCs into leaching agent will not only avoid ozone layer depletion but also save the cost of hazardous waste treatment and realize economic benefits. Environmental impact assessment indicated that the proposed Ga recycling route allows remarkable reduction of total environmental impacts compared with published processes.

Hydrogel 3D network derived and in-situ magnetized Fe@C for activation of peroxymonosulfate to degrade ciprofloxacin

Hydrogels possess 3D network with abundant reactive groups, and can bind with active metal ions within their confined 3D structure for fabricating functional materials. In this study, a chitosan grafted polyacrylic acid (CTS-g-PAA) hydrogel was prepared for loading Fe2+, which was then converted into magnetic Fe@C via subsequent pyrolysis process. In Fe@C activated peroxymonosulfate (PMS) (Fe@C/PMS) system, the degradation behaviors of ciprofloxacin (CIP) were systematically investigated, including influencing parameters, reactive oxygen species (ROSs), degradation mechanism and potential eco-toxicity of degradation intermediates. The results showed that CTS-g-PAA supported, in-situ derived magnetic Fe@C had not only stable catalytic ability at pH 3.0–9.0, but also high degradation efficiency in the presence of inorganic Cl− and HCO3− (5–20 mM) as well as organic humid acid (10 and 20 mg/L). Under the optimized conditions, the degradation efficiency of CIP could reach to 96.84 % within 1 h. In Fe@C/PMS system, the main ROSs involved free radicals SO4•−, •OH, O2•− and non-free radical 1O2. Through free radical quantitative experiments, the concentration of SO4•− and •OH at 60 min was determined respectively to be 11.84 µM and 0.14 µM, proving the dominant role of SO4•−. By HPLC-MS analysis, the degradation products were proposed via four degradation pathways, including hydroxylation, defluorination and decarboxylation, as well as the ring opening of quinolone and piperazine. Finally, the potential eco-toxicity of CIP and its degradation intermediates was evaluated by using ECOSAR method based on quantitative structure–activity relationships analysis.

Bottom slag-to-flue gas controls on S and Cl from co-combustion of textile dyeing sludge and waste biochar: Their interactions with temperature, atmosphere, and blend ratio

S and Cl distribution patterns and their evolution pathways were quantified during the co-combustions of textile dyeing sludge (TDS) and waste biochar (BC). S in the flue gas rose from 10.60% at 700 °C to 45.09% at 1000 °C for the mono-combustion of TDS in the air atmosphere. At 1000 °C, S in the bottom slag and flue gas grew by 2.65% and fell by 2.11%, respectively, for the TDS mono-combustion in the 30%O2/70%CO2 atmosphere. The 40% BC addition increased the S retention in the bottom slag by 30.39% and decreased its release to the flue gas by 34.50% by changing the evolution of CaSO4 and enabling more K to fix S as K2SO4. The decomposition of inorganic Cl was the main source of the Cl-containing gases. The 20%O2/80%CO2 atmosphere (36.29%) and 40% BC addition (27.26%) had higher Cl in the bottom slag than did TDS mono-combusted at 1000 °C (25.60%) by inhibiting the decomposition of organic Cl. Our study provides insights into the co-combustion of TDS and BC and controls on S and Cl for a cleaner production. Future research remains to conducted to verify scale-up experiments.

Anion Induced Fluorescence Quenching of Various Aromatic Amino Fluorophores

Fluorescence quenching of 2-amino7-bromofluorine (2ABF) and 4,4-diaminodiphenyl sulphone (4DADPS),) ] by inorganic anions Cl-, Br–, SO42– SO32–, S2O32–, CO32–, NO3–, & HPO42– have been studied in 95% (v/v) water–ethanol mixture medium..The quenching was found to be dynamic in all systems. The plots of log kq values with singlet transition energy (Es) of the fluorophore and with ECTTS of the quencher are linear indicating the presence of electron-transfer quenching mechanism. ΔGTH values for charge transfer quenching have been determined for aminodiphenylsulphone.

Lattice B-doping evolved ferromagnetic perovskite-like catalyst for enhancing persulfate-based degradation of norfloxacin

Series of B-doped perovskite-like materials CeCu0.5Co0.5O3 (B-C3O) were fabricated with unique ferromagnetic property due to partial substitution of non-magnetic 2p-impurities boron in the lattice. Then, B-C3O was used for activating peroxymonosulfate (PMS) for the degradation of norfloxacin (NOR), one kind of emerging pollutants with the concentration level up to mg/L in wastewaters. The results indicated that 5.0% B-C3O exhibited stable catalytic ability at pH 3.0–9.0 and high degradation efficiency in co-existing inorganic Cl−, SO42−, NO3−, H2PO4− and organic humic acid. Non-radical 1O2, radicals •OH and SO4•−, as well as ClO− were detected with synergy effect for NOR degradation. By quantifying free radicals, •OH with 0.52 µM and SO4•− with 10.91 µM were obtained at 180 min, verifying the leading role of SO4•−. The degradation process involved the defluorination and decarboxylation, as well as opening of quinolone and piperazinyl rings. Adopting alfalfa as the model plant, the toxicity effect before and after NOR degradation was finally evaluated with seed germination rate and chlorophyll content as the physiological indicators. In summary, non-metal B-doping not only provides a creative strategy for the development of ferromagnetic perovskite-like materials, but also affords excellent catalysts for aiding the advanced oxidation technology for removal of emerging pollutants in wastewaters.

The redistribution and migration mechanism of chlorine during hydrothermal carbonization of waste biomass and fuel properties of hydrochars

This work investigated the effects of experimental conditions on the chlorine (Cl) behaviour during hydrothermal carbonization (HTC) of three waste biomasses. Temperature was found to be the most critical factor affecting Cl migration. Increasing temperature promoted the conversion of organic Cl to inorganic Cl through nucleophilic substitution and organic C–Cl cleavage reactions. The dechlorination efficiency was approximately 90% at high HTC severity. Specifically, the Cl contents in wheat, straw and eucalyptus hydrochars obtained at 270○C for 120 min drastically declined to 2349 mg/kg, 1943 mg/kg, and 312 mg/kg, respectively. The corresponding dechlorination efficiencies reached 89.93%, 90.81%, and 92.29%, respectively. Based on migration characteristics and theoretical inference, we proposed a Cl migration mechanism in waste biomass during HTC. X-ray photoelectron spectroscopy results revealed abundant oxygen-containing functional groups in the surface of hydrochars obtained at low HTC temperature. In contrast, at severe HTC conditions, the dehydration, decarboxylation, aromatization and polymerization reactions intensely occurred, resulting in lower H/C and O/C atomic ratios and enhanced aromatic C–C and CC. Energy analysis suggested that the natural properties of feedstocks significantly affected the energetic recovery efficiency. This research demonstrated the possibility of converting biomass into low-chlorine and high-energy-grade coal-alternative fuel through the HTC process.

Removal of triclosan from aqueous solution via adsorption by kenaf‐derived biochar: Its adsorption mechanism study via spectroscopic and experimental approaches

Biochars derived from kenaf were synthesized to adsorb triclosan from an aqueous solution. The triclosan adsorption mechanism of the biochars pyrolyzed at various temperatures (300, 400, 600, and 750 °C) was explored using physical/chemical analyses (FE-SEM, EDS, EA, XRF, pHpzc, N2 adsorption-desorption, SAXS, ATR-FTIR, and XPS). The triclosan adsorption by the kenaf biochar increased as the pyrolysis temperature increased, except for 450 °C, which showed the lowest adsorption capacity. The kenaf biochar synthesized at 750 °C (KNF-750) exhibited the highest adsorption capacity owing to its high aromatic moiety and large specific surface area. Kinetic adsorption by KNF-750 was well fitted with the pseudo-second-order model, with equilibrium attained within 3 h. The maximum triclosan adsorption capacity of KNF-750 obtained from the Langmuir model with a high correlation coefficient was 77.4 mg/g. Triclosan adsorption sharply decreased at an initial solution pH of 5 because a final solution pH higher than 9 caused dissociation of triclosan. A 90% removal of triclosan was achieved with 4 g/L of KNF-750. The adsorption of triclosan was endothermic, with an enthalpy change of 32.8 kJ/mol. XPS analysis proved that triclosan was adsorbed on the surface of biochar by the disappearance of inorganic Cl and the appearance of organic Cl.

Highly Stable Bulk Perovskite for Blue LEDs with Anion-Exchange Method

To date, the light emitting diode (LED) based halide perovskite was rapidly developed due to the outstanding property of perovskite materials. However, the blue perovskite LEDs based on the bulk halide perovskites have been rarely researched and showed low efficiencies. The bulk blue perovskite LEDs suffered from insufficient coverage on the substrate due to the low solubility of the inorganic Cl sources or damaged by the structural instability with participation of organic cations. Here, we show the new method of fabricating stable inorganic bulk blue perovskite LEDs with the anion exchange approach to avoid use of insoluble Cl precursors. The devices showed nice operational spectral stability at the desired blue emission peak. The bulk perovskite blue LEDs showed a maximum luminance of 1468 and 494 cd m-2 for the 490 and 470 nm emission peaks, respectively.

Hazardous elements flow during pyrolysis of oily sludge

Oily sludge (OS) is a hazardous waste and pyrolysis is a promising technology to achieve energy recovery and non-hazardous disposal simultaneously. However, the distribution of hazardous elements, including N/S/Cl and heavy metals, in pyrolytic products possibly causes secondary pollution. This study conducted a systematic research on hazardous elements flow during OS pyrolysis under variant temperature. Results showed that N/S/Cl in OS were distributed 44.77–15.51 wt%, 83.29–80.22 wt%, and 78.59–73.41 wt% into the solid residues after pyrolysis, respectively. Elevating pyrolysis temperature facilitated more N/S/Cl flowing into pyrolytic oil and gas. The macromolecular N-/S-/Cl-containing compounds, including amides, amines, nitriles, sulfonates, chloroalkanes, etc., were widely distributed in pyrolytic oil and gas products. The micromolecular N-/S-/Cl-containing pollutants released between 200 and 400 °C included HCN, NH3, NOx, H2S, CH4S, CS2, SO2, and HCl, which originated from the decomposition of the amine N, organic sulfide and sulfone-S, and inorganic Cl, respectively. The main pollutants released at above 400 °C included NH3, HCN, NOx, CS2, and SO2, which were derived from the decomposition of heterocyclic N and inorganic pyritic-S and sulfate-S. Moreover, the solid residues intercepted more than 60.0 wt% of total heavy metals, which should be concerned in the future.

Comparative study on inorganic Cl removal of municipal solid waste fly ash using different types and concentrations of organic acids

In this study, different organic acids—such as citric, acetic, lactic, propionic, and butyric acid—were evaluated to ascertain the optimum leaching solvent for dechlorinating fly ash. Results suggest that the acid type, concentration, and interactions between both parameters contributed significantly to the variations in the efficiency of fly ash dechlorination. Simple main-effect analysis suggested that a higher acid concentration yields better dechlorination efficiency. However, improvements in dechlorination efficiency did not necessarily yield a low chlorine content leaching residue because in a specific acid concentration region, the increased acid concentration may also accelerate the mass reduction rate of the leaching residue. Experimental results also demonstrate that citric and acetic acid yield the highest dechlorination efficiency, followed by propionic and butyric acid. The least dechlorination efficiency of lactic acid could be attributed to the formation of precipitate (i.e. calcium lactate) which might cover the chlorides and reduce the contact area of intimal chlorides with the leaching solvent. Therefore, a specific concentration of organic matter fermentation broth rich in citric and acetic radicals may present itself as an ideal water substitute for fly ash dechlorination.

Efficient degradation of chloramphenicol by zero-valent iron microspheres and new insights in mechanisms

Chloramphenicol (CAP) has been extensively used in the broad-spectrum antibiotic therapy so that its excessive emission has brought about serious contamination in aquatic environments. It is of great concern to find an efficient removal method and understand the transformation pathways. In this study, we developed the zero-valence iron based catalytic technique by synthesizing regular zero-valence iron microspheres (ZVI MPs), which could completely remove the CAP pollutant (20 mg L−1) within 15 min. When the CAP concentration increased to 50 mg L−1, the removal efficiency achieved to 95.5% after 15 min of reaction. The chemical evolutions of iron species on the catalyst surface and changes in components of the solution demonstrated the activation of molecular oxygen and hydrogen ion by ZVI MPs. The generation of OH and H radicals as well as their contributions to CAP degradation were confirmed by electron spin resonance and trapping experiments during the reaction. Further experiments including the intermediates identification revealed a possible degradation pathway. To the best of our knowledge, the mechanism of CAP degradation by ZVI was proposed for the first time involving both reductive and oxidative transformations with a prerequisite of efficient reductive dechlorination. The complete dechlorination of CAP molecules was confirmed by the detection of inorganic Cl– concentration (0.124 mmol L−1 after reaction), which generally lowered the toxicity of the products. These findings not only provided an efficient and economic zero-valent iron technique for eliminating the antibiotic pollutants in water, but also made important contributions to better understand the removal mechanism.

Quantitative speciation of insoluble chlorine in E-waste open burning soil: Implications of the presence of unidentified aromatic-Cl and insoluble chlorides

Open burning of electronic waste (E-waste) produces numerous organochlorine compounds (OCs). Although the presence of unidentified OCs has been suggested, the mass balance of identified and unidentified OCs in E-waste open burning soils (EOBSs) still remains unknown. In this study, the concentrations of Cl bonded with aromatic carbon (aromatic-Cl) and aliphatic carbon (aliphatic-Cl), and inorganic Cl in EOBSs were determined by focusing on chlorine (Cl) in water-insoluble fractions (insoluble Cl) and applying Cl K-edge X-ray absorption spectroscopy in conjunction with combustion ion chromatography. The concentrations of identified Cl (Cl in five individual OCs: polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, chlorinated polycyclic aromatic hydrocarbons and chlorinated benzenes) were calculated from the concentrations previously reported for the same samples. The proportions of identified Cl were less than 1% to aromatic-Cl, indicating the abundance of unidentified OCs. The concentrations of both aromatic-Cl and identified Cl were highest in the sample collected from the site in Vietnam (VN), where wires and cables were mainly burned, suggesting that unidentified aromatic-Cl were produced through pathways similar to those of identified OCs, and the pathway could be related to burning of wires and cables. Further, insoluble Cu (II) compound, Cu2(OH)3Cl were assumed to be present in EOBSs and the concentration was highest in VN, implying that insoluble inorganic chlorides could be related to the formation of aromatic-Cl and identified Cl.

Biological chlorine cycling in the Arctic Coastal Plain

This study explores biological chlorine cycling in coastal Arctic wet tundra soils. While many previous chlorine-cycling studies have focused on contaminated environments, it is now recognized that chlorine can cycle naturally between inorganic and organic forms in soils. However, these pathways have not previously been described for an Arctic ecosystem. We measured soil organic and inorganic Cl pools, characterized soils and plant tissues with chlorine K-edge X-ray absorption near-edge spectroscopy (Cl-XANES), measured dechlorination rates in laboratory incubations, and analyzed metagenomes and 16S rRNA genes along a chronosequence of revegetated drained lake basins. Concentrations of soil organic chlorinated compounds (Clorg) were correlated with organic matter content, with a steeper slope in older soils. The concentration and chemical diversity of Clorg increased with soil development, with Clorg in younger soils more closely resembling that of vegetation, and older soils having more complex and variable Cl-XANES signatures. Plant Clorg concentrations were higher than previously published values, and can account for the rapid accumulation of Clorg in soils. The high rates of Clorg input from plants also implies that soil Clorg pools turn over many times during soil development. Metagenomic analyses revealed putative genes for synthesis (haloperoxidases, halogenases) and breakdown (reductive dehalogenases, halo-acid dehalogenases) of Clorg, originating from diverse microbial genomes. Many genome sequences with close similarity to known organohalide respirers (e.g. Dehalococcoides) were identified, and laboratory incubations demonstrated microbial organohalide respiration in vitro. This study provides multiple lines of evidence for a complex and dynamic chlorine cycle in an Arctic tundra ecosystem.