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PFAS (per- and polyfluoroalkyl substances) are omnipresent in the environment and their transportation and transformation have attracted increased attention. Microplastics are another potential risk substances that can serve as a carrier for ubiquitous pollutants, thus affecting the presence of PFAS in the environment. In this study, the adsorption of perfluorooctane sulfonamide (FOSA) and perfluorooctanoic acid (PFOA) on four microplastics (PE, PVC, PS, and PTFE) and their effect on the photodegradation of FOSA were studied. The adsorption capacity of FOSA by PS was the highest, in similar, PS displayed the highest adsorption capacity in the presence of PFOA. Different effects of pH and salinity on the adsorption of FOSA and PFOA were observed among different microplastics indicating inconsistent interaction mechanisms. Furthermore, FOSA could be photodegraded, with PFOA as the main product, while the presence of microplastics had a negligible effect on the degradation of this contaminant. The results indicated that microplastics could act as PFAS concentrators. Moreover, their photochemical inertias make the pollutants enriched on microplastics more resistant to degradation.

Microbially mediated iron redox processes are of great significance in the biogeochemical cycles of elements, which are often coupled with soil organic matter (SOM) in the environment. Although the influences of SOM fractions on individual reduction or oxidation processes have been studied extensively, a comprehensive understanding is still lacking. Here, using ferrihydrite

Soil organic matter (SOM) comprises a continuum of organic materials from granular organic debris to small organic molecules and contains more organic carbon than global vegetation and the atmosphere combined. It has remarkable effects on soil ecological functions and the global carbon cycle as well as the fate of pollutants in the terrestrial ecosystem. Therefore, characterization of SOM is an important topic in soil science, ecology, and environmental science. Chemical complexity and spatial heterogeneity are by far the two biggest challenges to our understanding of SOM. Recent developments in analytical techniques and methods provide the opportunity to reveal SOM composition at the molecular level and to observe its distribution in soils at micro- and nanoscales, which have greatly improved our understanding of SOM. This paper reviews the outstanding advances in SOM characterization regarding these two issues from target and nontarget analyses comprising molecular marker analysis, ultrahigh-resolution mass spectrometry analysis, and in situ microscopic imaging techniques such as synchrotron-based spectromicroscopy, nanoscale secondary ion mass spectrometry, and emerging electron and optical microscopic imaging techniques. However, current techniques and methods remain far from unlocking the unknown properties of SOM. We systematically point out the limitations of the current technologies and outline the future prospects for comprehensive characterization of SOM at the molecular level and micro- and nanoscales, paying particular attention to issues of environmental concern.

Few-layer black phosphorus (FLBP) is easily degraded under ambient conditions which is problem that hinders the application of FLBP, but its degradation mechanism is not yet well understood. In this work, we surprisingly found that persistent generation of reactive oxygen species (ROS) was involved in FLBP degradation even in the dark. The ROS generation patterns and mechanism were revealed by chemiluminescence (CL) and density functional theory (DFT). Meanwhile, rhodamine B (RhB) and methyl orange (MO) can also be removed by FLBP under dark conditions, which further shows the ROS generation during FLBP self-degradation. This work provides new insights into the FLBP self-degradation mechanism and opens opportunities to practically implement FLBP for green catalytic application.

Minerals are known to protect dissolved organic matter (DOM) against biodegradation and thus play an important role in the long-term persistence of organic carbon (OC) in soils. However, as a super...

The release of root exudates (REs) provides an important source of soil organic carbon. This work revealed the molecular composition of REs of different plant species including alfalfa (Medicago sativa L.), bean (Phaseolus vulgaris L.), barley (Hordeum vulgare L.), maize (Zea mays), wheat (Triticum aestivum L.), ryegrass (Lolium perenne L.) and pumpkin (Cucurbita maxima) using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The combination of positive ion mode (+ESI) and negative ion mode (-ESI) increased the number of the molecules detected by ESI FT-ICR MS, and a total of 8758 molecules were identified across all the samples. In detail, lipids and proteins and unsaturated hydrocarbons were more easily detected in +ESI mode, while aromatic compounds with high O/C were readily ionized in -ESI mode, and only 38% of the total assigned formulas were shared by -ESI and +ESI modes. Multivariate statistical analysis of the formulas indicated that the close related plants species secreted REs with similar molecular components. Moreover, the unsaturation degree and nitrogen content were the two key parameters able to distinguish the similarities and differences of molecular components of REs between plant species. The results provided a feasible analysis method for characterization of the molecular components of REs and for the first time characterized the molecular components of REs of a variety of plant species using ESI FT-ICR MS.

Organic matter (OM) often co-exists with iron oxyhydroxides in soils to form iron-oxyhydroxide-associated OM. Reducing reagents, such as dithionite and hydroxylamine, have been widely used to selec...

Swine manures generally contain high levels of copper (Cu) resulting from its use as a growth promoter in feedstuff. Pyrolysis can further concentrate Cu whereas decrease its available fraction in swine manures. Here we investigated the speciation transformation of Cu and associated elements in swine manures induced by pyrolysis using multiple X-ray absorption spectroscopies. Results showed that over 82% of Cu existed as Cu(I)-S and Cu(I)-thiolate complexes in swine manures, which were transformed into stable Cu(I)

Growing evidence has suggested that microbial biofilms are potential environmental "hotspots" for the production and accumulation of a bioaccumulative neurotoxin, methylmercury. Here, we demonstrate that extracellular polymeric substances (EPS), the main components of biofilm matrices, significantly interfere with mercury sulfide precipitation and lead to the formation of nanoparticulate metacinnabar available for microbial methylation, a natural process predominantly responsible for the environmental occurrence of methylmercury. EPS derived from mercury methylating bacteria, particularly Desulfovibrio desulfuricans ND132, substantially increase the methylation potential of nanoparticulate mercury. This is likely due to the abundant aromatic biomolecules in EPS that strongly interact with mercury sulfide via inner-sphere complexation and consequently enhance the short-range structural disorder while mitigating the aggregation of nanoparticulate mercury. The EPS-elevated bioavailability of nanoparticulate mercury to D. desulfuricans ND132 is not induced by dissolution of these nanoparticles in aqueous phase, and may be dictated by cell-nanoparticle interfacial reactions. Our discovery is the first step of mechanistically understanding methylmercury production in biofilms. These new mechanistic insights will help incorporate microbial EPS and particulate-phase mercury into mercury methylation models, and may facilitate the assessment of biogeochemical cycling of other nutrient or toxic elements driven by EPS-producing microorganisms that are prevalent in nature.

Atmospheric brown carbon (BrC) exerts a key impact on the global radiative balance due to its light-absorbing properties. Maillard-like reactions between carbonyl and amino compounds have been identified as an important pathway for forming secondary BrC. Although optical properties have been widely studied, the molecular composition of secondary BrC generated in Maillard chemistry remains unclear, resulting in a knowledge gap to understand its formation and light-absorbing mechanism. In this study, a combination of optical spectroscopy

Soil is a major sink for per- and perfluoroalkyl substances (PFAS), wherein PFAS may be transferred through the food chain to predators at upper trophic levels, which poses a threat to human health. Herein, the concentrations and distributions of legacy and novel PFAS in topsoil samples from different functional areas in Tianjin were comprehensively investigated. Seventeen PFAS congeners were identified, with concentrations ranging from 0.21 ng/g to 5.35 ng/g, with a mean concentration of 1.25 ng/g. The main PFAS in the topsoil was perfluorooctanoic acid (PFOA). 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA;MDL-1.95 ng/g, mean 0.11 ng/g), as an emerging substitute for perfluorooctane sulfonate (PFOS), was also detected in the topsoil. It showed slightly higher concentrations than PFOS (MDL-1.62 ng/g, mean 0.10 ng/g), indicating it has gradually replaced legacy PFOS in this area. Based on the positive-definite matrix factor (PMF) receptor model, the major PFAS sources was dominated by textile treatment, metal electroplating plants, and some potential precursors of PFAS with longer chains (C8) were the major sources (43.4%), followed by food packaging as well as coating materials (25.5%). In addition, Spearman correlation analysis and the structural equation model showed that population density significantly impacted the PFAS distribution in the topsoil of Tianjin.

The selective sorption of dissolved organic matter (DOM) on minerals is a widespread geochemical process in the natural environment. Recent studies have explored the influence of this process on the molecular fractionation of DOM at water-mineral interfaces. However, it remains unclear how molecular fractionation affects the photochemistry of DOM. Here, we demonstrate that the adsorptive fractionation of DOM on ferrihydrite greatly reduces its photoproduction of reactive oxygen species (ROS) including 1O2, O2•-, and •OH normalized to organic carbon (ROSOC). The ROSOC for 1O2, O2•-, and •OH were positively correlated with the abundances of polyphenols and oxygenated polycyclic aromatics, which were also observed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis to be preferentially sequestered by ferrihydrite. The molecules that preferentially remained in the solution after adsorption displayed low levels of ROSOC. The molecular fractionation of DOM induced by adsorption on ferrihydrite therefore influenced the molecular components and also significantly reduced the photoreactive fractions of DOM in waters. These results are very important in promoting our understanding of the effects of molecular fractionation on the biogeochemical features, behaviors, and implications of DOM in the environment.

Thermal treatment can not only efficiently remove volatile pollutants but also distinctly alter the speciation of organic carbon (C) and the behaviors of residual pollutants in contaminated soils. Here we examined the distribution and bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in industrially contaminated site soils affected by thermal treatment (temperature ranging of 105–650 ℃) using synchrotron-based infrared microspectroscopy and n-butanol extraction (a mild solvent extractant). In the pristine soils, the sequestration and distribution of PAHs were simultaneously controlled by aromatic C, aliphatic C and clay minerals. Desorption efficiency of PAHs was substantially increased with increasing temperature, whereas the residual PAHs were strongly immobilized within their binding sites evidenced by their dramatically decreased bioaccessibility. Aliphatic and carboxylic C were gradually decomposed and/or carbonized with increasing temperature. In contrast, aromatic C remained relatively recalcitrant during the thermal treatment and was the key controlling factor for the desorption of residual PAHs in the soils with either thermal treatment or n-butanol extraction. This study is the first to visualize the changes in the binding sites and bioaccessibility of PAHs induced by thermal treatment, which have important implications for understanding the sequestration mechanisms of organic pollutants in soil and optimizing the remediation technique.

The molecular mechanisms behind the adaptive responses for interactions between organisms and nanoparticles, such as silver nanoparticles (AgNPs), are of great concern. In this study, the transcrip...

Interactions between engineered nanoparticles (ENPs) and plants represent one of the fundamental problems we must face in the rapid development of nanotechnology. Hundreds of studies have addressed this issue in the past decade. This review summarizes recent research progress on the uptake, translocation and transformation of metal-based ENPs in higher plants. The integrated uptake and transport pathways of ENPs in plants are summarized and the key physiological barriers to plant uptake of ENPs are proposed. Transformation of ENPs in the soil–plant system is discussed, paying particular attention to the effects of phyllosphere and rhizosphere processes on the transformation and plant uptake of ENPs. The advances, limitations and challenges of analytical techniques for the qualitative and quantitative analysis for ENPs in plants are addressed. Furthermore, the key challenges in each field are thoroughly assessed and future perspectives are proposed. This review is intended to provide an unambiguous assessment of the present knowledge on the uptake, translocation and transformation of NPs in higher plants, and also to provide guidance for future research.

A consensus on the role of organic carbon moieties as the sorptive domains for nonionic organic compounds in soils is lacking due to the extremely complicated compositions of soil matrices. In this study, synchrotron radiation-based infrared microspectroscopy (IMS) was applied to in situ probe the distributions of four nitroaromatic compounds with varying hydrophobicity (namely, 1,3-dinitrobenzene, 1,5-dinitronapthalene, 3-nitrophenanthrene and 6-nitrobenzo[a]pyrene) and their associations with aliphatic and aromatic organic carbon moieties in soils. The technique revealed that both nitro group (NO2) from the nitroaromatic compounds and organic carbon moieties were unevenly distributed in the soils at the micron scale. The spatial distribution of nitro groups was positively correlated with that of aromatic carbon (C = C) (r > 0.804, p H) in the spatial distribution in the soils. Meanwhile, the nitro groups from 1,3-dinitrobenzene and 1,5-dinitronapthalene exhibited a significant correlation with clay minerals (O H) in their distributions (r > 0.629, p

The bioaccumulation and biotransformation of tetrabromoethylcyclohexane (TBECH) in maize were investigated. Furthermore, the roles of plant biomacromolecules such as lipid transfer proteins (LTPs), CYP and GST enzymes in driving the biological processes of TBECH stereoisomers were explored. The uptake and translocation of TBECH in maize were diastereo- and enantio-selective. Isomerization from α- to δ-TBECH and β- to γ-TBECH, and metabolites of debromination, hydroxylation and TBECH-GSH adducts were identified in maize roots. The gene expressions of LTPs, CYPs and GSTs were extensively changed in maize after exposure to technical TBECH. CYP and GST enzyme activities as well as GST31 and CYP71C3v2 gene expressions were selectively induced or inhibited by TBECH diastereomers over time. TBECH was able to dock into the active sites and bind with specific residues of the typical biomacromolecules ZmLTP1.6, GST31 and CYP71C3v2, indicating their roles in the bioaccumulation and metabolization of TBECH. Binding modes and affinities to biomacromolecules were significantly different between α- and β-TBECH, which contributed to their stereo-selectivity. This study provided a deep understanding of the biological fate of TBECH, and revealed the driving molecular mechanisms of the selectivity of TBECH stereoisomers in plants.

It has been well demonstrated that arbuscular mycorrhizal (AM) symbiosis can improve plant chromium (Cr) tolerance, but the detoxification mechanisms are still unsolved. In the present study the role of AM symbiosis in plant sulfur (S) acquisition and metabolism related to Cr detoxification was investigated. Medicago truncatula plants were cultivated with/without AM fungus Rhizophagus irregularis in Cr(VI) contaminated soils at two soil S and phosphorus (P) concentrations. Sulfur uptake, transport and metabolism by plants were determined by biochemical and molecular methods. Meanwhile, Cr uptake and transformation were characterized by using spectroscopic methods, including synchrotron based X-ray absorption near edge structure (XANES) analysis. The results indicated that mycorrhizal inoculation improved plant S acquisition by up-regulating the expression of high affinity sulfate transporter genes (i.e. MtSULTR1.1, MtSULTR1.2) in plant roots. Mycorrhizal colonization also systematically regulated S transport and metabolism for Cr(VI) detoxification. XANES analysis revealed the Cr immobilization in AM roots by phosphate and histidine-like ligands rather than thiol groups. Correlation analysis further confirmed possible involvement of S metabolites in the relief of Cr induced oxidative stress. Mycorrhizal effects were more pronounced under low P condition. The study allowed a new insight into the mechanisms of enhanced plant Cr tolerance by AM symbiosis.

Humic substances (HSs) are collections of diverse organic compounds with broad redox capacities, which directly or indirectly affect the biogeochemical behaviors and fates of almost all the pollutants in the environment. The present study investigates the relationships between the molecular characteristics of HSs and their reducing capacities or electron-donating capacities (EDCs) by electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), total phenolic assay, and mediated electrochemical oxidation analysis. For decreasing the molecular heterogeneity of bulk HSs, HSs were first separated into three fractions according to their polarities. The results demonstrated that compounds in HS fractions with moderate polarity possessed a high content of total phenols and consistently had high EDCs. A strong linear correlation (R2 = 0.97) existed between EDCs and the total phenolic content, which confirmed that phenols contributed to the EDCs of HSs. Further anal...

Photochemical transformation of dissolved organic matter (DOM) plays a very important role in the cycling of organic carbon in aquatic systems. Increasing release of photoactive nanoparticles such as titanium dioxide nanoparticles (nano TiO2) into surface water may impact this process. The present study employed Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to examine the molecular transformation of natural DOM (peat DOM, DOMp) and anthropogenic DOM (sludge-derived DOM, DOMs) under photo-irradiation as affected by nano TiO2. Differences in molecular components between DOMp and DOMs were observed. DOMs contained more heteroatom formulas (76%) with low aromaticity and low carbon oxidation state than did DOMp (22%). The presence of nano TiO2 resulted in significant decreases in both DOM content and molecular diversity under photo-irradiation. Consistent alterations were observed between DOMp and DOMs such that high molecular weight compounds, high aromaticity and/or heteroatom S-containing compounds were more easily photodegraded in the presence of nano TiO2; whereas the average carbon oxidation state decreased in DOMp but increased in DOMs, likely due to the significant differences in O abundance, especially in the contents of carboxyl moieties, between DOMp and DOMs. The findings of the present study suggest that the release of nano TiO2 into aquatic environment will accelerate the consumption of dissolved organic carbon and the attenuation of molecular diversity for both DOM in waters.

With the rapid increase in the application of biochars as amendments, studies are needed to clarify the possible environmental risks derived from biochars to use safely the biomass resources. This work reported selected dark sides of maize straw- and swine manure-derived biochars pyrolyzed at 300 and 500°C. During the pyrolysis processes, total heavy metals in the biochars were enriched greatly accompanying with considerable emission of the heavy metals into atmosphere and the trends became increasingly obvious with pyrolysis temperature. Meanwhile, the biochars showed distinctly decreased available heavy metals compared with raw feedstocks, which could be mainly attributed to the sorption by the inorganics in the biochars. The water- and acid-washing treatments significantly increased the releasing risks of heavy metals from biochars into the environments. Electron paramagnetic resonance analysis indicated that persistent free radicals, emerged strongly in the biochars as a function of the aromatization of biomass feedstocks, were free from the influence of water-, acid-, or organic-washing of the biochars and could remain stable even after aged in soils for 30days. Dissolved biochars, highly produced during pyrolysis processes, showed distinct properties including lower molecular weight distribution while higher aromaticity compared with soil dissolved organic carbon. The results of this study provide important perspectives on the safe usage of biochars as agricultural/environmental amendments.

Due to its complex composition and structure, many of the properties of natural organic matter (NOM) are poorly understood. In this study, the oxidization-induced chemiluminescence (OCL) of NOM was investigated, and a flow-injection OCL method was developed using alkaline persulfate-H

The reduction of ferric iron (Fe(III)) to ferrous iron (Fe(II)) by dissimilatory iron-reducing bacteria is widespread in anaerobic environments. The oxidation of Fe(II) in aerobic environments has been found to produce hydroxyl radicals (

Manganese (Mn) oxides are ubiquitous in the environment and have strong reactivity to induce the transformation of various contaminants. However, whether reactive oxygen species contribute to their surface reactivity remains unclear. Here, sustainable production of superoxide radicals (O2•-) by various MnO2 polymorphs in the dark was quantified and the mechanisms involved were explored. The results confirm that O2•- was produced through one-electron transfer from surface Mn(III) to adsorbed O2. In contrast, no H2O2 was detected due to its decomposition by Mn oxides to form O2•- and Mn(III), leading to the sustained production of O2•- on Mn oxide surfaces. In addition, the production of O2•- was found to make a clear contribution (4 - 28%) to the transformation of a series of halophenols by MnO2, suggesting that the O2•--mediated surface reaction is an important supplement to the direct electron-transfer mechanism in the reactivity of Mn oxides. These findings advance our understanding of the surface reactivity of Mn oxides and also reveal an important but hitherto unrecognized abiotic source of O2•- in the natural environment.

Microbial dissimilatory iron reduction and aerobic oxidation affect the biogeochemical cycles of many elements. Although the processes have been widely studied, the underlying mechanisms, and especially how the surface structures of iron oxides affect these redox processes, are poorly understood. Therefore, {001} facet-dominated hematite nanoplates (HNP) and {100} facet-dominated hematite nanorods (HNR) were used to explore the effects of surface structure on the microbial dissimilatory iron reduction and aerobic oxidation processes. During the reduction stage, the production of total Fe(II) normalized by specific surface area (SSA) was higher for HNP than HNR due to steric effects and the ligand-bound conformation of the connection between iron on different exposed facets and electron donors from microorganisms. However, during the aerobic oxidation stage, both the SSA- and Fe(II)-normalized reactive oxygen species (ROS), including hydrogen peroxide (H2O2) and hydroxyl radical (•OH), were higher for HNR than HNP. Theoretical calculation results showed that the {100} facets exhibited a lower activation energy barrier for oxygen reduction reaction than {001} facets, supporting the experimental observation that {100} facet-dominated HNR had a higher ROS production efficiency than {001} facet-dominated HNP. These results indicated that surface characteristics not only mediated the microbial reduction of Fe(III) but also affected the aerobic oxidation of microbially reduced Fe(II). Accessibility of electron donors to surface iron atom determined the reduction of Fe(III), and activation energy barrier for oxygen reduction by surface Fe(II) dominated the ROS production during the redox processes. This study advances our understanding of the mechanisms through which ROS are produced by iron (oxyhydr)oxides during microbial dissimilatory iron reduction and aerobic oxidation processes.

Characterization of dissolved organic matter (DOM) at the molecular level will greatly improve our understanding of its bio-geochemical role in controlling the fate of contaminants in the environment, and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is the most powerful analytical technique for this purpose. Before FT-ICR-MS analysis, isolation, desalination and concentration of DOM are necessary, and solid-phase extraction (SPE) is the most widely applied pretreatment procedure. However, some molecular information is lost using conventional SPE methods. Here, we propose a novel strategy of SPE enrichment using stepwise elution (SPE-SE). Compounds in DOM were divided into three fractions by this SPE-SE procedure according to their polarity and ionization efficiency. The diversity of DOM molecules identified by ESI-FT-ICR-MS using SPE-SE exceeded those using conventional SPE methods by more than 50%. This method is feasible and has the potential to be used as a pretreatment strategy for complex DOM matrixes prior to ESI-FT-ICR-MS analysis, especially for those rich in nitrogenous molecules, carbohydrates, lipids and/or aromatic compounds.

Arbuscular mycorrhizal (AM) fungi can enhance plant Cr tolerance through immobilizing Cr in mycorrhizal roots. However, the detailed processes and mechanisms are unclear. The present study focused on cellular distribution and speciation of Cr in both extraradical mycelium (ERM) and mycorrhizal roots exposed to Cr(VI) by using field emission scanning electron microscopy equipped with energy dispersive X-ray spectrometer (FE-SEM-EDS), scanning transmission soft X-ray microscopy (STXM) and X-ray absorption fine structure (XAFS) spectroscopy techniques. We found that amounts of particles (possibly extracellular polymeric substances, EPS) were produced on the AM fungal surface upon Cr(VI) stress, which contributed greatly to Cr(VI) reduction and immobilization. With EDS of the surface of AM fungi exposed to various Cr(VI) levels, a positive correlation between Cr and P was revealed, suggesting that phosphate groups might act as counter ions of Cr(III), which was also confirmed by the XAFS analysis. Besides, STXM and XAFS analyses showed that Cr(VI) was reduced to Cr(III) in AM fungal structures (arbuscules, intraradical mycelium, etc.) and cell walls in mycorrhizal roots, and complexed possibly with carboxyl groups or histidine analogues. The present work provided evidence of Cr immobilization on fungal surface and in fungal structures in mycorrhizal roots at a cellular level, and thus unraveled the underlying mechanisms by which AM symbiosis immobilize Cr.

The phytotoxicities of TBECH diastereomers to plants at the biochemical and molecular levels were investigated in a hydroponic study by using maize as a model plant. The results showed that TBECH could induce the production of two species of reactive oxygen species (ROS), O2•- and H2O2, in maize tissues. The accumulation of ROS was the highest when maize was exposed to β-TBECH. TBECH enhanced the phosphorylation of plant histone, and the contents of γ-H2AX in maize followed the order β-TBECH > αβ-TBECH > γδ-TBECH > γ-TBECH. Transcriptome profiling revealed that antioxidant enzyme genes (AEGs) were over-expressed in maize when stressed by technical grade TBECH. The RT-PCR detection further validated that three typical AEGs, including CAT, SOD, and POD genes, were time-dependent and selectively expressed under the influence of TBECH diastereomers. Molecular compositions of maize root exudates characterized by FT-ICR-MS were significantly different among the four groups of TBECH diastereomer treatments. TBECH diastereomers specifically affected the chemical diversity and abundance of root exudates. New insights into the biochemical effects of TBECH on plants are provided in this work, which is helpful to deepening the understanding of their stereo-selectivity.

In vitro biotransformation of HBCDs by maize cytochrome P450 (CYP) enzymes, responses of CYPs to HBCDs at protein and transcription levels, and in silico simulation of interactions between CYPs and HBCDs were investigated in order to elucidate the roles of CYPs in the metabolism of HBCDs in maize. The results showed that degradation reactions of HBCDs by maize microsomal CYPs followed the first-order kinetics and were stereo-selective, with the metabolic rates following the order (-)γ- (+)γ- (+)α- (-)α-HBCD. The hydroxylated metabolites OH-HBCDs, OH-PBCDs and OH-TBCDs were detected. (+)/(-)-α-HBCDs significantly decreased maize CYP protein content and inhibited CYP enzyme activity, whereas (+)/(-)-γ-HBCDs had obvious effects on the induction of CYPs. HBCDs selectively mediated the gene expression of maize CYPs, including the isoforms of CYP71C3v2, CYP71C1, CYP81A1, CYP92A1 and CYP97A16. Molecular docking results suggested that HBCDs could bind with these five CYPs, with binding affinity following the order CYP71C3v2 CYP81A1 CYP97A16 CYP92A1 CYP71C1. The shortest distances between the Br-unsubstituted C atom of HBCD isomers and the iron atom of heme in CYPs were 4.18-11.7 Å, with only the distances for CYP71C3v2 being shorter than 6 Å (4.61-5.38 Å). These results suggested that CYP71C3v2 was an efficient catalyst for degradation of HBCDs. For (+)α- and (-)γ-HBCDs, their binding affinities to CYPs were lower and the distances to the iron atom of heme in CYPs were shorter than their corresponding antipodes, consistent with the in vitro experimental results showing that they had shorter half-lives and were more easily hydroxylated. This study provides solid evidence for the roles of maize CYPs in the metabolism of HBCDs, and gives insight into the molecular mechanisms of the enantio-selective metabolism of HBCDs by plant CYPs.

Dissolved black carbon (DBC) involves in many biogeochemical processes in both terrestrial and aquatic environments. About 26.5 Tg of charcoal- or black carbon-derived DBC was released into aquatic environments annually, accounting to ∼10% of the global riverine flux of dissolved organic carbon (DOC). Yet the sorption behaviors of DBC and their effects on water quality in soil-water environment are poorly understood. Here we examined the molecular composition variations of DOC induced by the sorption of two biochar-derived DBCs (pyrolyzed at 300 °C and 500 °C) on three contrasting soils. The DBCs were adsorbed mainly through competitive displacement of soil surface functional groups and co-sorption with soil indigenous DOC, which varied with soil properties and the aromaticity of the DBCs. Ultrahigh resolution mass spectrometry analysis indicated that compounds with rich oxygen content or unsaturated structures such as tannins and unsaturated aromatics from both DBC and soil DOC, were preferentially adsorbed on the soils in the presence of DBC. In contrast, compounds with high aromatic structures including condensed aromatics and lignins were concentrated in the aquatic phase. Molecular fractionation also occurred to the heteroatomic compounds during the sorption, and the heteroatomic dissolved organic sulphur in the DBCs was easier to be adsorbed relative to dissolved organic nitrogen. Our results suggest that DBC sorption in soil-water environment could have important implications for water quality by altering DOC molecular composition and decreasing DOC molecular diversity at the soil-water interface. This study provides essential information for understanding the behavior of DBC in the environments.

Interactions between dissolved organic matter (DOM) and iron oxyhydroxides have important environmental and geochemical implications. The present study employed two hematite nanocrystals to investigate the adsorption and molecular fractionation of two typical humic substances (HSs) using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Hematite with a predominant exposure of {100} facets induced more pronounced adsorption and molecular fractionation of HSs than {001} facets, indicating that the interfacial adsorptive fractionation process of HSs was mediated by exposed facets of hematite. Further exploration of the surface OH groups of the two hematite nanocrystals confirms that the facet-mediated molecular fractionation of HSs was attributable to the abundance of singly iron-atom coordinated -OH sites on the hematite surfaces. Molecules with a high oxidation state and high aromaticity such as oxidized black carbon, polyphenol-like, and tannic-like compounds preferentially formed ligand-exchange complexes with singly coordinated -OH groups on the hematite surfaces, inducing the selective binding and molecular fractionation of HSs at the mineral-water interface. These results demonstrate that singly iron-atom coordinated -OH sites determine DOM adsorption and mediate molecular fractionation on hematite surfaces, and this contributes substantially to our understanding of the molecular mechanisms of iron oxyhydroxide-mediated molecular exchange of DOM in soils and/or sediments.

Perfluorooctane sulfonate (PFOS) precursors have been found extensively in sewage sludge and biosolids-amended soils. The degradation of these precursors are regarded as a significant source of PFOS in the environment. In this study, the accumulation of N-ethyl perfluorooctane sulfonamido acetic acid (N-EtFOSAA) in the plants of seven species, namely alfalfa, lettuce, maize, mung bean, radish, ryegrass, and soybean from biosolids-amended soil, and the degradation kinetics of N-EtFOSAA in soil-plant microcosms were evaluated over 60 days. N-EtFOSAA was found in the roots of all plant species, while was not in stems and leaves. The root concentration factors of N-EtFOSAA ranged 0.52–1.37 (pmol/groot)/(pmol/gsoil). Stepwise multiple regression analysis was used to elucidate the accumulation of N-EtFOSAA in the roots of plants. The results showed that the root protein and lipid contents explain 85.0% of the variation in root N-EtFOSAA levels (P

Adsorption by minerals is a common geochemical process of dissolved organic matter (DOM) which may induce fractionation of DOM at the mineral-water interface. Here, we examine the molecular fractionation of DOM induced by adsorption onto three common iron oxyhydroxides using electrospray ionization coupled with Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Ferrihydrite exhibited higher affinity to DOM and induced more pronounced molecular fractionation of DOM than did goethite or lepidocrocite. High molecular weight (500 Da) compounds and compounds high in unsaturation or rich in oxygen including polycyclic aromatics, polyphenols and carboxylic compounds had higher affinity to iron oxyhydroxides and especially to ferrihydrite. Low molecular weight compounds and compounds low in unsaturation or containing few oxygenated groups (mainly alcohols and ethers) were preferentially maintained in solution. This study confirms that the double bond equivalence and the number of oxygen atoms are valuable parameters indicating the selective fractionation of DOM at mineral and water interfaces. The results of this study provide important information for further understanding the behavior of DOM in the natural environment.

Behaviors of BDE-28 and BDE-47 in two distinct soils (Phaeozem and Acrisol) as affected by the separate addition of root exudate components (i.e., oxalic acid, glycine, and fructose) were investigated by a soil microcosm incubation experiment. The results showed that root exudate components promoted the desorption of BDE-28 (57.6–235.0 %) and BDE-47 (56.9–223.7 %) from the soils due to the enhancement of their water solubilities. The addition of root exudate components increased the n-butanol extractability of BDE-28 and BDE-47 by 20.3–72.5 and 48.6–169.2 %, respectively, which had a positive correlation with the concentrations of dissolved organic carbon (DOC) in the soils (p

Engineered nanomaterials such as ZnO nanoparticles (NPs) will inevitably enter the environment because of the large quantities produced and their widespread application. Plants comprise a fundamental living component of terrestrial ecosystems; thus, understanding the interaction between ENMs and plants is important. In the present study we conducted an integrated study by employing a combination of microscopic and spectroscopic techniques to comparatively investigate the uptake of ZnO NPs and Zn2+ ions by maize in order to further elucidate plant uptake pathways of ZnO NPs. The results demonstrate that the majority of Zn taken up was derived from Zn2+ released from ZnO NPs, and Zn accumulated in the form of Zn phosphate. ZnO NPs were observed mainly in the epidermis, a small fraction of ZnO NPs were present in the cortex and root tip cells, and some further entered the vascular system through the sites of the primary root-lateral root junction. However, no ZnO nanoparticle was observed to translocate to shoots, possibly due to the dissolution and transformation of ZnO NPs inside the plants.

Sorption of organic compounds on fresh black carbons (BCs) can be greatly attenuated in soil over time. We examined herein the changes in surface properties of maize straw-derived BCs (biochars) after aged in a black soil and their effects on the sorptive behaviors of naphthalene, phenanthrene and 1,3-dinitrobenzene. Dissolved fulvic and humic acids extracted from the soil were used to explore the role of dissolved organic carbon (DOC) in the aging of biochars. Chromatography analysis indicated that DOC molecules with relatively large molecular weight were preferentially adsorbed on the biochars during the aging processes. DOC sorption led to blockage of the biochar's micropores according to N2 and CO2 adsorption analyses. Surface chemistry of the biochars was also substantially modified, with more O-rich functional groups on the aged biochars compared to the original biochars, as evidenced by Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. The changes in both the physical and chemical surface properties of biochars by DOC led to significant attenuation of the sorption capacity and nonlinearity of the nonionic organic compounds on the aged biochars. Among the tested organic compounds, phenanthrene was the most attenuated in its sorption by the aging treatments, possibly because of its relatively large molecular size and hydrophobicity. The information can help gain a mechanistic understanding of interactions between BCs and organic compounds in soil environment.

Recent studies have revealed that zinc phosphate is an important transformation product of zinc oxide nanoparticles (ZnO NPs) in the environment, and the role of soluble phosphate in the transformation of ZnO NPs to zinc phosphate has been confirmed. However, whether insoluble phosphate that exists widely in the environment can induce chemical transformation of ZnO NPs has not been addressed. Therefore, transformation of ZnO NPs in the presence of hydroxyapatite (HAP), selected as representative of insoluble phosphate, at different pH was investigated in the present study. Transformation products were identified by employing X-ray diffraction and synchrotron based X-ray absorption fine structure spectroscopy. The results indicate that under acidic condition (pH 5) phosphate ion (PO43-) and calcium anion (Ca2+) were released from HAP in aqueous solution, inducing a rapid transformation of about 80% ZnO NPs to scholzite within 4 h. Under neutral or basic conditions (pH 7 and 9) the adsorption of Zn2+ on HAP resulted in a slow transformation of about 60% ZnO NPs to amorphous inner-sphere Zn adsorption complexes within 30 days. This work suggests the important role of HAP in the transformation of ZnO NPs and may affect the behavior, fate and toxic effects of ZnO NPs in the environment. (C) 2014 Elsevier B.V. All rights reserved.

The adsorption kinetics, isotherms and thermodynamics of Cr(III) on graphene oxide (GO) were studied. The adsorption kinetic data were well described with pseudo-second-order model and the equilibrium data were well fitted by Langmuir model. The calculated thermodynamic parameters indicated that the adsorption of Cr(III) on GO was spontaneous and endothermic. The maximum adsorption capacity of Cr(III) on GO at pH 5.0 and T=296 K was about 92.65 mg g(-1), which was higher than other reported adsorbents. It was found that the adsorption of Cr(III) on GO was strongly dependent on solution pH, but weakly dependent on ionic strength. Fourier transform infrared (FTIR) spectra suggested that Cr(III) was adsorbed on GO mainly through the formation of inner-sphere complexes with the O-containing functional groups on GO surface. Results in this study suggested that GO was a suitable material for the preconcentration and removal of Cr(III) from water. (C) 2014 Elsevier B.V. All rights reserved.

Sulfur speciation under the influence of sample pretreatment and sewage sludge (SS) application in a continuously SS-amended soil was assessed by wet-chemical fractionation and S K-edge XANES spectroscopy. Distinct differences in S speciation among the following pretreatments including fresh, air-drying, anoxic freeze-drying, oven-drying, and conditioning (incubation at room temperature and 75% of water holding capacity for 2 wk) were detected in both topsoils and subsoils. Air-drying significantly increased available S content but decreased C-bonded S content in the soils compared with anoxic freeze-drying. Oven-drying and conditioning pretreatments showed a similar effect on S fractions to air-drying in the soils but to a lesser extent. X-ray adsorption near-edge structure analysis showed that both reduced and intermediate organic S tended to decrease while oxidized S obviously increased in the air-dried samples. In contrast, the conditioning pretreatment facilitated the transformation of intermediate S into reduced organic S. Continuous application of SS significantly increased total soil S, C-bonded S, and residual S contents but decreased available S content in the topsoil. Meanwhile, XANES analysis indicated that reduced organic S was markedly increased (over 50% of total S) in the SS-amended topsoil. No obvious effect of the application of SS on S speciation in the subsoil was observed except for the facilitated transportation of S into lower depth. Overall, our results suggest that anoxic atmospheres during the entire pretreatment process from sampling to drying, grinding, and analysis is crucial for the accurate speciation analysis of S in soils, and the anoxic freeze-drying is, therefore, highly recommended.

Dissolved organic carbon (DOC) has a major influence upon sorption/desorption and transport of hydrophobic organic contaminants (HOCs) in soil environments. However, the molecular mechanisms of DOC sorption and its effects on aged HOC desorption in contaminated soils still remain largely unclear. Here, effects of three different DOC (one from commercial peat and two from biochars produced at 300 °C and 500 °C pyrolysis temperatures, respectively) and oxalate (as a reference) on abiotic desorption behavior of aged phenanthrene from three agricultural soils were investigated. Results showed that desorption of aged phenanthrene from soils was predominantly dependent on soil organic carbon content. The presence of DOC and oxalate resulted in higher desorption of phenanthrene compared to water alone, and the effects were positively related to soil organic carbon content and DOC/oxalate concentration. The facilitating effects of DOC were further increased during the second consecutive desorption, whereas oxalate had no such effect. Ultra-high-resolution Fourier transform-ion cyclotron resonance-mass spectrometry confirmed the molecular fractionation of DOC at the soil-water interface during DOC sorption. Specifically, the DOC molecules with O-rich moieties were preferentially adsorbed, whereas the molecules with phenolic and aromatic structures were selectively retained in the soil solutions through competitive displacement and co-sorption reactions during sorption. The enriched phenyl structures in the retained DOC facilitated its association with phenanthrene in the solutions and thus the release of phenanthrene from the soils. In contrast, oxalate replaced some organic carbon from the soils and thus released the associated phenanthrene into the solutions. Our findings highlight the importance of the molecular composition and structure of DOC for the desorption of phenanthrene in soil-water environments, which may help improve our understanding of the release and transport of organic compounds in the environments.

Natural organic matter (NOM) is a complex organic mixture and plays a crucial role in environmental processes. By using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), detailed molecular information on NOM could be achieved. In this paper, ion accumulation time (IAT), a key parameter of FTICR-MS for complex mixture detection, was the focus, and its effect on the molecular characterization of NOM by FTICR-MS was systematically investigated. A notable feature of selective detection of NOM molecules by FTICR-MS with different IAT was observed. Most of the polar molecules with high O/C ratio (O/C ratio0.5) could be easily detected by FTICR-MS with a short IAT, but extending IAT led to the ion intensities of these molecules decreasing or even disappearing. Meanwhile, a large number of unsaturated and aromatic molecules with low O/C ratio (O/C ratio0.6) and low polarity, all of which could not be observed with a short IAT, were remarkably detected by extending IAT. Results also revealed that the unsaturated and aromatic molecules, which could only be observed by extending the IAT, were not generated by the fragmentation of molecules in NOM or from the dissociation of NOM aggregations but originally existed in NOM samples. The selective detection of NOM molecules caused by IAT extension was possibly attributed to their different polarity and different stability in the collision cell. On the basis of these results, a novel strategy of combining mass spectrometric data of NOM obtained with different IAT by FTICR-MS was proposed. With this strategy, more than 4715 CHO-molecular formulas were assigned, where about 2000 more formulas were obtained in comparison with using a short IAT (2733 CHO-molecular formulas identified) solely. The strategy is simple and robust and can be used as an alternative method to obtain more molecular information on NOM in the environment.

Diastereomer- and enantiomer-specific accumulation and biotransformation of hexabromocyclododecane (HBCD) in maize (Zea mays L.) were investigated. Molecular interactions of HBCD with plant enzymes were further characterized by homology modeling combined with molecular docking. The (-)α-, (-)β-, and (+)γ-HBCD enantiomers accumulated to levels in maize significantly higher than those of their corresponding enantiomers. Bioisomerization from (+)/(-)-β- and γ-HBCDs to (-)α-HBCD was frequently observed, and (-)γ-HBCD was most easily converted, with bioisomerization efficiency of 90.5 ± 8.2%. Mono- and dihydroxyl HBCDs, debrominated metabolites including pentabromocyclododecene (PBCDe) and tetrabromocyclododecene (TBCDe), and HBCD-GSH adducts were detected in maize roots. Patterns of hydroxylated and debrominated metabolites were significantly different among HBCD diastereomers and enantiomers. Three pairs of HBCD enantiomers were selectively bound into the active sites and interacted with specific residues of maize enzymes CYP71C3v2 and GST31. (+)α-, (-)β-, and (-)γ-HBCDs preferentially bound to CYP71C3v2, whereas (-)α-, (-)β-, and (+)γ-HBCDs had strong affinities to GST31, consistent with experimental observations that (+)α-, (-)β-, and (-)γ-HBCDs were more easily hydroxylated, and (-)α-, (-)β-, and (+)γ-HBCDs were more easily isomerized and debrominated in maize compared to their corresponding enantiomers. This study for the first time provided both experimental and theoretical evidence for stereospecific behaviors of HBCD in plants.