Suwannee River Fulvic Acid Research Articles

Online LC-Orbitrap MS method for the rapid molecular characterization of dissolved organic matter.

High-resolution mass spectrometry (HRMS) combined with electrospray ionization (ESI) has been the most useful technique for molecular characterization of dissolved organic matter (DOM) derived from diverse sources. However, the comprehensive detection of DOM composition was hindered by ionization suppression observed in ESI sources. HRMS coupled with liquid chromatography (LC) is a potential tool for comprehensive molecular characterization of DOM. The Suwannee River fulvic acids (SRFAs) and two DOM samples from seawater and refinery wastewater extracted by solid phase extraction (SPE) were analyzed by LC-Orbitrap MS coupled with ESI. The mobile phases, solvent composition, and gradient in the LC-Orbitrap MS analysis were optimized. The number of detected molecular formulae of SRFAs by online LC-Orbitrap MS was significantly increased by approximately 40% compared to direct injection. These additional detected compounds are mainly protein and lignin-like compounds, with a low O/C ratio and high H/C ratio. For the SRFAs, the relative standard deviations (%) of reproducibility are 5.51, 2.33, 7.97, and 1.80 for average O/C, H/C, double bond equivalent, and modified aromaticity index, respectively. This study proposed a simple and rapid method based on LC-Orbitrap MS for an in-depth analysis of the molecular composition of DOM, achieving a remarkable analysis time of only 5 min per sample. The rapid method provides a dependable and efficient approach for the molecular characterization of DOM, thereby advancing our comprehension and investigation of DOM across diverse ecosystems.

Nontargeted Analysis of Reactive Nitrogenous Compounds in Suwannee River Standard Reference Materials and Authentic River Water Samples.

Concerns over toxic nitrogenous disinfection byproducts (N-DBPs) necessitate identifying their precursors in source water. Natural organic amino compounds are known precursors to N-DBPs. Three Suwannee River (SR) standard reference materials (SRMs), humic acids (HA), fulvic acids (FA), and natural organic matter (NOM), are commonly used to study DBP formation, but the chemical makeup of amino compounds in SRSRMs remains largely unknown. To address this, we combined stable hydrogen/deuterium isotope labeling, HDPairFinder bioinformatics, and nontargeted high-performance liquid chromatography-high-resolution mass spectrometry (HPLC-HRMS) to characterize these compounds in SRSRMs. This method classifies reactive amines, provides accurate masses and MS/MS spectra, and quantifies intensities. We identified 2707 high-quality features with primary and/or secondary amines in SRSRMs and 75% of them having an m/z < 300. Across all three SRSRMs, 327 amino features were detected, while 856, 794, and 200 unique features were found in SRNOM, SRHA, and SRFA, respectively. In North Saskatchewan River (NSR) samples, a total of 6449 amino features were detected, 818 of them matched those in SRSRMs, and 87% of them were different between the two rivers. Using chemical standards, we confirmed 10 compounds and tentatively identified 5 more. This study highlights similarities and differences in reactive N-precursors in SRSRMs and local river water, enhancing the understanding of geo-differences in reactive N-precursors in different source waters.

Photolytic Mass Loss of Humic Substances Measured with a Quartz Crystal Microbalance.

Laboratory studies have shown that photolytic mass loss can be a significant sink for secondary organic aerosol (SOA). Here, we use a quartz crystal microbalance to measure mass loss of Suwannee River Humic Acid (SRHA) and Suwannee River Fulvic Acid (SRFA), surrogates for SOA, exposed to 254, 300, and 405 nm radiation over the course of 24 h. We find that the photolytic mass loss rates of these materials are comparable to those for laboratory-generated limonene and toluene SOA material from the study of Baboomian et al, ACS Earth Space Chem. 2020, 4, 1078. Scaling our results to ambient conditions, we estimate that humic substances in aerosols can lose as much as 8% by mass in the first day of exposure in the atmosphere, equivalent to 0.025% of J NO2 , the photolysis rate of nitrogen dioxide. By using zero air instead of nitrogen, we also find that the presence of oxygen accelerates the photolytic mass loss rate by a factor of 2 to 4 at all wavelengths suggesting a potential role for reactive oxygen species. UV photolysis of an aqueous SRFA solution demonstrated both photobleaching at UV wavelengths and photoenhancement at visible wavelengths. Ultrahigh-resolution mass spectrometric analysis showed that condensed-phase SRFA photolysis led to decreased intensity in the 100-300 m/z range while aqueous SRFA photolysis resulted in an increase in intensity in the same range. This work reaffirms that photolytic mass loss is a potentially significant sink for SOA, but only on the time scale of a day or two and demonstrates that SRHA and SRFA are suitable surrogates for atmospheric SOA with respect to photolytic mass loss.

Characterization of Low-Molecular-Weight Dissolved Organic Matter Using Optional Dialysis and Orbitrap Mass Spectrometry.

Low-molecular-weight (LMW, <1000 Da) dissolved organic matter (DOM) plays a significant role in metal/organic pollutant complexation, as well as photochemical/microbiological processes in freshwater ecosystems. The micro size and high reactivity of LMW-DOM hinder its precise characterization. In this study, Suwannee River fulvic acid (SRFA), a commonly used reference material for aquatic DOM, was applied to examine the optical features and molecular composition of LMW-DOM by combining membrane separation, ultraviolet-visible absorption and Orbitrap mass spectrometry (MS) characterization. The 100-500 Da molecular weight cut-off (MWCO) membrane had a better performance in regard to separating the tested LMW-DOM relative to the 500-1000 Da MWCO membrane. The ultraviolet-visible absorbance decreased dramatically for the retentates, whereas it increased for the dialysates. Specifically, carbohydrates, lipids and peptides exhibited high selectivity to the 100-500 Da MWCO membrane in early dialysis. Lignins, tannins and condensed aromatic molecules displayed high permeability to the 500-1000 Da MWCO membrane in late dialysis. Overall, the retentates were dominated by aromatic rings and phenolic hydroxyls with high O/Cwa (weighted average of O/C) and low H/Cwa. Conversely, such dialysates had numerous aliphatic chains with high H/Cwa and low O/Cwa compared to SRFA. In particular, LMW-DOM below 200 Da was identified by Orbitrap MS. This work provides an operational program for identifying LMW-DOM based on the SRFA standard and MS analysis.

A Gated TIMS FTICR MS Instrument to Decipher Isomeric Content of Complex Organic Mixtures.

Modern research faces increasingly complex materials with a constant need for new analytical strategies that can provide deeper levels of chemical insight. Ultrahigh resolution mass spectrometry (MS), particularly Fourier transform ion cyclotron resonance (FTICR) MS, has provided a robust analytical foundation. However, MS alone offers limited structural information. Here, we present the first implementation and results from an FTICR MS with fully integrated dual accumulation analysis with gated trapped ion mobility spectrometry (gTIMS) capability. The drastically extended charge capacity and parallel accumulation facilitate the analysis of complex mixtures. We achieved a high dynamic range of 4 orders of magnitude within a single FTICR acquisition event. Simultaneously, the valuable linear relationship between the TIMS elution voltage and reduced mobility was retained over a wide mobility range. Benchmarking the instrument performance with Suwannee River fulvic acid (SRFA) by variable ramp gTIMS analysis allowed separation and unambiguous assignment of different charge state distributions. Application to bio-oils has proven the capability to distinguish the isomeric diversity in these ultracomplex samples, while maintaining the expected FTICR MS resolving power and mass accuracy. Valuable information about the molecular distribution, isomeric diversity, and main molecular differences could directly be extracted within the analysis time of a classical "dilute and shoot" direct infusion experiment. The development of this fully integrated and flexible gTIMS with FTICR MS analysis possesses the potential to significantly change the current landscape of high-resolution mass spectrometric analysis of complex mixtures through the added insight of isomeric complexity afforded by TIMS. The exploration of the added IMS dimension promises transformative effects across diverse fields including energy transition, environmental studies, and biological research.

Inferring the Molecular Basis for Dissolved Organic Matter Photochemical and Optical Properties.

Despite the widespread use of photochemical and optical properties to characterize dissolved organic matter (DOM), a significant gap persists in our understanding of the relationship among these properties. This study infers the molecular basis for the optical and photochemical properties of DOM using a comprehensive framework and known structural moieties within DOM. Utilizing Suwannee River Fulvic Acid (SRFA) as a model DOM, carboxylated aromatics, phenols, and quinones were identified as dominant contributors to the absorbance spectra, and phenols, quinones, aldehydes, and ketones were identified as major contributors to radiative energy pathways. It was estimated that chromophores constitute ∼63% w/w of dissolved organic carbon in SRFA and ∼47% w/w of overall SRFA. Notably, estimations indicate the pool of fluorescent compounds and photosensitizing compounds in SRFA are likely distinct from each other at wavelengths below 400 nm. This perspective offers a practical tool to aid in the identification of probable chemical groups when interpreting optical and photochemical data and challenges the current "black box" thinking. Instead, DOM photochemical and optical properties can be closely estimated by assuming the DOM is composed of a mixture of individual compounds.

Effect of dissolved organic matter on bacterial regrowth and response after ultraviolet disinfection

The effect of dissolved organic matter (DOM) on bacterial regrowth in water after disinfection using ultraviolet (UV) light emitting diodes (UVLEDs) is still unclear. Herein, the regrowth and responses of Vibrio parahaemolyticus and Bacillus cereus were investigated after being exposed to UVLEDs at combined wavelengths (265 and 280 nm) in a phosphate-buffered saline consisting of Suwannee River natural organic matter (SRNOM) and Suwannee River fulvic acid (SRFA). Low-molecular-weight (MW) organic compounds, which may form into intermediary photoproducts, and indicate bacterial repair metabolism, were characterized through non-target screening using orbitrap mass spectrometry. This study demonstrates the ability of the UVLEDs-inactivated cells to regrow. After UV exposure, a considerable upregulation of RecA was observed in two strains. With increasing the incubation time, the expression levels of RecA in V. parahaemolyticus increased, which may be attributed to the dark repair mechanism. Coexisting anionic DOM affects both the disinfection and bacterial regrowth processes. The time required for bacterial regrowth after UV exposure reflects the time needed for the individual cells to reactivate, and it differs in the presence or absence of DOM. In the presence of DOM, the cells were less damaged and required less time to grow. The UVLEDs exposure results in the occurrence of low-MW organic compounds, including carnitine or acryl-carnitine with N-acetylmuramic acid, which are associated with bacterial repair metabolism. Overall, the results of this study expand the understanding of the effects of water matrices on bacterial health risks. This can aid in the development of more effective strategies for water disinfection.

Spectroscopic studies of the role of dissolved organic matter in acenaphthene photodegradation in liquid water and ice

The effect of concentration and origin of dissolved organic matter (DOM) on acenaphthene (Ace) photodegradation in liquid water and ice was investigated, and the components in DOM which were involved in Ace photodegradation were identified. The DOM samples included Suwannee River fulvic acid (SRFA), Elliott soil humic acid (ESHA), and an effluent organic matter (EfOM) sample. Due to the production of hydroxyl radical (•OH) and triplet excited-state DOM (3DOM*) which react with Ace, DOM had promotion effects on Ace photodegradation. However, the promotion effects of DOM were prevailed over by their suppressing effect of DOM including screening light effect, intermediates reducing effect and RS quenching effect, and thus, the photodegradation rates of Ace decreased in the presence of the three DOM with concentrations of 0.5–7.5 mg C/L in liquid water and ice. ESHA had higher light absorption and thus had higher screening light effect on Ace photodegradation in liquid water than SRFA and EfOM. At each DOM concentration, ESHA exhibited higher promotion effect on Ace photodegradation than SRFA and EfOM, in liquid water and ice. The binding of Ace with DOM was indicated by decreases in fluorescence intensity of Ace when coexisted with DOM. However, the binding of Ace to DOM played an unimportant role in suppressing Ace photodegradation. The photodegradation behavior of fluorophores in Ace with DOM present in ice was not similar to that in liquid water. C–O, C═O, carboxyl groups O–H and aliphatic C–H functional groups in DOM were involved in the interaction of DOM with Ace. The presence of Ace seemed to have no influence on the photodegradation behavior of functional groups in DOM.

Controls of Mineral Solubility on Adsorption-Induced Molecular Fractionation of Dissolved Organic Matter Revealed by 21 T FT-ICR MS.

Mineral adsorption-induced molecular fractionation of dissolved organic matter (DOM) affects the composition of both DOM and OM adsorbed and thus stabilized by minerals. However, it remains unclear what mineral properties control the magnitude of DOM fractionation. Using a combined technique approach that leverages the molecular composition identified by ultrahigh resolution 21 T Fourier transform ion cyclotron resonance mass spectrometry and adsorption isotherms, we catalogue the compositional differences that occur at the molecular level that results in fractionation due to adsorption of Suwannee River fulvic acid on aluminum (Al) and iron (Fe) oxides and a phyllosilicate (allophane) species of contrasting properties. The minerals of high solubility (i.e., amorphous Al oxide, boehmite, and allophane) exhibited much stronger DOM fractionation capabilities than the minerals of low solubility (i.e., gibbsite and Fe oxides). Specifically, the former released Al3+ to solution (0.05-0.35 mM) that formed complexes with OM and likely reduced the surface hydrophobicity of the mineral-OM assemblage, thus increasing the preference for adsorbing polar DOM molecules. The impacts of mineral solubility are exacerbated by the fact that interactions with DOM also enhance metal release from minerals. For sparsely soluble minerals, the mineral surface hydrophobicity, instead of solubility, appeared to be the primary control of their DOM fractionation power. Other chemical properties seemed less directly relevant than surface hydrophobicity and solubility in fractionating DOM.

The dependence in microcystin removal with powdered activated carbon on variant properties, carbon properties, and dissolved organic matter

Powdered activated carbon (PAC) is commonly used by water treatment plants to remove harmful cyanotoxins such as microcystins (MCs) produced during seasonal harmful algal blooms. MC removal by PAC depends upon the properties of the PAC, the properties of the MC variant, and the presence and properties of dissolved organic matter (DOM). To identify which of these factors has the greatest impact on the removal of MC by PAC, we evaluated the removal of four different MC variants (MC-LR, MC-LA, MC-RR and desmethylated MC-RR) by three different PAC types (wood-based, coal-blend and coal-based). The role of DOM properties was evaluated using DOM isolated from two different sources, a terrestrial source (Suwannee River Fulvic Acid, SRFA) and a microbial source (Grand Lake St Marys DOM, GLSM). The results of adsorption experiments conducted over a period of 72 h demonstrated the wood-based PAC, which had the highest surface area and mesopore volume of the PAC tested, had the highest adsorption rate and capacity for all four MC variants. Of the variants studied, neutrally charged MC-RR was adsorbed more rapidly and to a greater extent on all of the PAC types than were the other variants. Although MC-LA and MC-LR had the greatest hydrophobicity, their negative charges resulted in their being adsorbed the least. As expected, DOM inhibited microcystin adsorption to PAC. The degree of inhibition, however, did not significantly vary for the two DOM types evaluated, indicating the properties of the DOM on MC adsorption to PAC was less important than the PAC properties or MC variant properties. Overall, PAC properties were a more important factor in MC removal than were the MC properties or DOM conditions.

Ligand exchange provides new insight into the role of humic substances in the marine iron cycle

Organic complexation of iron plays a crucial role in preventing its precipitation, facilitating its transport, and modulating its reactivity and bioavailability in natural waters. Although humic substances (HS) complexes serve as the primary source of terrestrial iron reaching ocean waters, the transition from Fe-HS species to other forms of organic complexation with ocean autochthonous ligands has not yet been properly described. Taking advantage of the electrolability of Fe-HS complexes, we monitored the ligand exchange of iron-saturated Suwannee River fulvic and humic acids (SRFA and SRHA) after the addition of desferrioxamine B (DFOB) and other ligands for comparison. We observed that Fe-HS concentrations gradually decreased until reaching an apparent steady state, typical of a reversible reaction within 1 to 15 h. The dissociation kinetics and species partitioning of Fe-SRHS complexes at the equilibrium showed some features contrary to the current paradigm of HS iron complexation. The affinity of SRFA to bind iron is close to that of DFOB and for SRHA is even higher. The heterogeneity of the HS iron binding groups was confirmed, although experiments in NaCl solutions revealed that in seawater it is substantially caused by the interaction of major divalent ions. The different dissociation kinetics of Fe-SRHS complexes obtained with different competing ligands and the absence of Fe-DFOB dissociation in the presence of iron-free SRFA indicate an intimate associative mechanism of ligand exchange, with the presence of a ternary complex (SRHS-Fe-DFOB) that does not form if the departing complex is Fe-DFOB. We hypothesize that at the concentrations of HS and siderophores found in the open ocean, iron ligand exchange is limited and organic iron speciation will be close to being regulated on a “first come, first served” basis. Experiments conducted under saturation of all iron complexes support the formation of a permanent concentration of a ternary complex. Our findings show the real complexity of cation-ligand interactions in seawater, with implications for the interpretation of recent chromatographic and electrochemical measurements and for the understanding of iron partitioning in the presence of ubiquitous HS.

Changes in Fe-redox and Fe-species across the end-Permian ‘Dead Zone’ in the Sydney Basin, Australia (252.10 ± 0.06 Ma): Evidence from X-ray absorption spectroscopy

The end-Permian mass extinction event is traceable across several non-marine basins in Australia. In the Sydney Basin, the lithological succession is characterized by a change from coal seams to mudstones and sandstones, recording a major environmental change following the disappearance of the Permian vegetation. A few millimeter-thick iron-rich ‘rusty’ layer occurs between the uppermost Permian coal seam and the mudstone, a layer that extends laterally across the basin and which has also been documented from coeval successions in Antarctica. This layer is overlain by the <1.5-m-thick Frazer Beach Member, whose basal 10-cm-thick microbreccia bed comprises 99% kaolinite and quartz, and is dated as 252.10 ± 0.06 Ma. The Frazer Beach Member corresponds to the so-called end-Permian ‘Dead Zone’ lacking fossil pollen and leaves. This distinctive member was deposited directly following the extinction of the Permian peat-forming forests.Here we identify, through X-ray absorption spectroscopy, a drastic redox shift across the extinction interval with increasing amount of reduced Fe-species followed by highly oxidized Fe-species, most resembling Fe(III) complexed with organic matter. Values subsequently normalise in younger samples through the ‘Dead Zone’, attaining only slightly higher redox-levels than before the event. The organically complexed Fe-species in the event bed is consistent with the standard Suwannee River fulvic acid, an acid Fe-complex with iron bound to organic matter, whereas the samples above and below the extinction layer yield spectra predominantly resembling magnetite (Fe3O4) mineral phase. We consider that the iron redox fluctuation marking the extinction interval is related to significant environmental changes with accumulation of organic matter following the mass extinction. The highly reduced iron in the extinction layer may relate to methane release from bacterial degradation, or emissions from clathrates. The presence of fulvic acid in the distinct iron-rich extinction layer indicates that an abrupt onset of the process of degradation of plant matter, lipids and calcium hydroxide (CaOH) took place, resulting in this ‘Death layer’. This was followed by millions of years of erosive conditions before new, complex vegetation could establish.

Effect of dissolved organic matter on sulfachloropyridazine photolysis in liquid water and ice

Dissolved organic matter (DOM) is an ubiquitous component of environmental snow and ice, which can absorb light and produce reactive species (RS) and thus is of importance in ice photochemistry. The photodegradation of sulfachloropyridazine (SCP) without and with DOM present in liquid water and ice were investigated in this study. The photodegradation rate constants for SCP without DOM present was enhanced by 52.5 % in ice relative to liquid water, likely due to the enhanced role of SCP self-sensitized RS in ice. DOM significantly promoted SCP photolysis in both liquid water and ice, which was mainly attributed to roles of singlet oxygen (1O2) and triplet excited-state DOM (3DOM*) generated from DOM. 1O2 production from DOM was significantly enhanced in ice relative to liquid water. Hydroxyl radical (•OH) production from DOM in ice was similar to those in liquid water. Enhancement in 3DOM* production in ice was observed at low DOM concentrations. Suwannee River Fulvic Acid (SRFA) and Elliott Soil Humic Acid (ESHA) exhibited differences in RS production in liquid water and ice, as well as in enhancement of 1O2 and 3DOM* produced in ice relative to liquid water. DOM induced reaction pathways of SCP different from those without DOM present, and therefore affected toxicity of SCP photoproducts. There were differences in photodegradation pathways of SCP as well as in toxicity of SCP photoproducts between liquid water and ice.

Eco-Corona Formation on Plastics: Adsorption of Dissolved Organic Matter to Pristine and Photochemically Weathered Polymer Surfaces.

Plastic fate in freshwater systems is dependent on particle size, morphology, and physicochemical surface properties (e.g., charge, surface roughness, and hydrophobicity). Environmental aging processes, such as photochemical weathering and eco-corona formation due to dissolved organic matter (DOM) adsorption on plastic surfaces, can alter their physicochemical properties, affecting fate and transport. While plastic aging has been studied from a materials science perspective, its specific implications in environmental contexts remain less understood. Although photochemical weathering and eco-corona formation occur simultaneously in the environment, in this work, we systematically assessed the effects of photochemical weathering on the physicochemical properties of polymers (polyethylene, polypropylene, polyethylene terephthalate, and polystyrene) and how this influences the adsorption of DOMs (Suwannee River humic acid, fulvic acid, and natural organic matter) relative to pristine polymers. Pristine polymers initially had different and distinct physicochemical surface properties, but upon aging, they became more similar in terms of surface properties. Photochemical weathering resulted in a decrease in polymer film thickness, an increase in surface roughness, and hydrophilicity. DOM adlayers on the polymer surfaces resulted in more comparable wettability, effectively masking the initial polymer properties. Collectively, this study explores the physiochemical changes polymers undergo in laboratory studies mimicking environmental conditions. Understanding these changes is the initial step to rationalizing and predicting processes and interactions such as heteroaggregation that dictate the fate of plastics in the environment.

Rigidity and Flexibility: Unraveling the Role of Fulvic Acid in Uranyl Sorption on Graphene Oxide Using Molecular Dynamics Simulations.

Using molecular dynamics simulations, this work targets a molecular understanding on the rigidity and flexibility of fulvic acid (FA) in uranyl sorption on graphene oxide (GO). The simulations demonstrated that both rigid Wang's FA (WFA) and flexible Suwannee River FA (SRFA) can provide multiple sites to cooperate with GO for uranyl sorption and act as "bridges" to connect uranyl and GO to form GO-FA-U (type B) ternary surface complexes. The presence of flexible SRFA was more beneficial to uranyl sorption on GO. The interactions of WFA and SRFA with uranyl were primarily driven by electrostatics, and the electrostatic interaction of SRFA-uranyl was significantly stronger owing to the formation of more complexes. The flexible SRFA could markedly enhance the bonding strength of uranyl with GO by folding itself to provide more sites to coordinate with uranyl. The rigid WFAs tended to be adsorbed on the GO surface in parallel due to π-π interactions, whereas the flexible SRFAs took more slant configurations resulting from intermolecular hydrogen bonds. This work provides new insights into the sorption dynamics, structure, and mechanism and addresses the effect of molecular rigidity and flexibility, with great significance for FA-based remediation strategies of uranium-contaminated sites.

Factors Affecting the Adsorption of Per- and Polyfluoroalkyl Substances (PFAS) by Colloidal Activated Carbon

The immobilization of per- and polyfluoroalkyl substances (PFAS) by colloidal activated carbon (CAC) barriers has been proposed as a potential in-situ method to mitigate the transport of plumes of PFAS in the subsurface. However, if PFAS are continuously released from a source zone, the adsorptive sites on CAC will eventually become saturated, upon which point the breakthrough of PFAS in the barrier will occur. To predict the long-term effectiveness of CAC barriers, it is important to evaluate the factors that may affect the adsorption of PFAS on CAC. In this study, the adsorption of 7 PFAS on a polymer-stabilized CAC (i.e., PlumeStop®) and on a polymer-free CAC was investigated using batch experiments. The adsorption affinity of PFAS to CAC was in the following order: PFOS > 6:2 FTS > PFHxS > PFOA > PFBS > PFPeA > PFBA. This result indicates that hydrophobic interaction was the predominant adsorption mechanism, and that hydrophilic compounds such as PFBA and PFPeA will break through CAC barriers first. The partition coefficient Kd for the adsorption of PFAS on the polymer-stabilized CAC was 1.3 - 3.5 times smaller than the Kd for the adsorption of PFAS on the polymer-free CAC, suggesting that the polymers decreased the adsorption, presumably due to competitive sorption. Thus, the PFAS adsorption capacity of PlumeStop CAC barriers is expected to increase once the polymers are biodegraded and/or washed away. The affinity of PFOS and PFOA to CAC increased when the ionic strength of the solution increased from 1 to 100 mM, or when the concentration of Ca2+ increased from 0 to 2 mM. In contrast, less PFOS and PFOA were adsorbed in the presence of 1 - 20 mgC/L Suwannee River Fulvic Acid, which represented dissolved organic carbon, or in the presence of 10 - 100 mg/L diethylene glycol butyl ether (DGBE), which is an important component in some aqueous film-forming foam (AFFF) formulations. The presence of 0.5 - 4.8 mg/L benzene or 0.5 - 8 mg/L trichloroethylene, the co-contaminants that may comingle with PFAS at AFFF-impacted sites, diminished PFOS adsorption but had no effect or even slightly enhanced PFOA adsorption. When the initial concentration of TCE was 8 mg/L, the Kd (514 ± 240 L/g) for the adsorption of PFOS was approximately 20 times lower than that in the TCE-free system (Kd = 9,579 ± 829 L/g). The results of this study provided insights into some key factors that may affect the adsorption of PFAS in in-situ CAC barriers.

Quantitative Separation of Unknown Organic-Metal Complexes by Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry.

Dissolved organic matter (DOM) is widely recognized to control the solubility and reactivity of trace metals in the environment. However, the mechanisms that govern metal-DOM complexation remain elusive, primarily due to the analytical challenge of fractionating and quantifying metal-organic species within the complex mixture of organic compounds that comprise DOM. Here, we describe a quantitative method for fractionation and element-specific detection of organic-metal complexes using liquid chromatography with online inductively coupled plasma mass spectrometry (LC-ICP-MS). The method implements a post-column compensation gradient to stabilize ICP-MS elemental response across the LC solvent gradient, thereby overcoming a major barrier to achieving quantitative accuracy with LC-ICP-MS. With external calibration and internal standard correction, the method yields concentrations of organic-metal complexes that were consistently within 6% of their true values, regardless of the complex's elution time. We used the method to evaluate the effects of four stationary phases (C18, phenyl, amide, and pentafluoroylphenyl propyl) on the recovery and separation of environmentally relevant trace metals (Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in Suwannee River Fulvic Acid and Suwannee River Natural Organic Matter. The C18, amide, and phenyl phases generally yielded optimal metal recoveries (>75% for all metals except Pb), with the phenyl phase separating polar species to a greater extent than C18 or amide. We also fractionated organic-bound Fe, Cu, and Ni in oxidized and reduced soils, revealing divergent metal-DOM speciation across soil redox environments. By enabling quantitative fractionation of DOM-bound metals, our method offers a means for advancing a mechanistic understanding of metal-organic complexation throughout the environment.

Sunlight-Mediated Reductive Transformation of Thallium(III) in Acidic Natural Organic Matter Solutions: Mechanisms and Kinetic Modeling.

Thallium (Tl) redox state determines its speciation and fate in aqueous environments. Despite the high potential of natural organic matter (NOM) providing the reactive groups to complex and reduce Tl(III), the kinetics and mechanisms by which NOM influences the Tl redox transformation have remained insufficiently understood. Here, we studied the reduction kinetics of Tl(III) in acidic Suwannee River fulvic acid (SRFA) solutions under dark and solar-irradiated conditions. Our results show that the thermal Tl(III) reduction occurs by the reactive organic moieties in SRFA, with the electron-donating capacities of SRFA increased with pH and decreased with [SRFA]/[Tl(III)] ratios. Solar irradiation promoted Tl(III) reduction in SRFA solutions as a result of ligand-to-metal charge transfer (LMCT) within the photoactive Tl(III) species as well as an additional reduction process mediated by a photogenerated superoxide. We demonstrated that the formation of Tl(III)-SRFA complexes decreased the reducibility of Tl(III), with the kinetics dependent on the nature of the binding component and SRFA concentrations. A "three ligand class" kinetics model has been developed and satisfactorily describes Tl(III) reduction kinetics over a range of experimental conditions. The insights presented here should assist in understanding and predicting the NOM-mediated speciation and redox cycle of Tl in a sunlit environment.

Dark repair of sunlight-inactivated tetracycline-resistant bacteria: Mechanisms and important role of bacteria in viable but non-culturable state

The spread of antibiotic resistant bacteria (ARB) in the environment poses a potential threat to human health, and the reactivation of inactivated ARB accelerated the spread of ARB. However, little is known about the reactivation of sunlight-inactivated ARB in natural waters. In this study, the reactivation of sunlight-inactivated ARB in dark conditions was investigated with tetracycline-resistant E. coli (Tc-AR E. coli) as a representative. Results showed that sunlight-inactivated Tc-AR E. coli underwent dark repair to regain tetracycline resistance with dark repair ratios increasing from (0.124 ± 0.012)‱ within 24 h dark treatment to (0.891 ± 0.033)‱ within 48 h. The presence of Suwannee River fulvic acid (SRFA) promoted the reactivation of sunlight-inactivated Tc-AR E. coli and tetracycline inhibited their reactivation. The reactivation of sunlight-inactivated Tc-AR E. coli is mainly attributed to the repair of the tetracycline-specific efflux pump in the cell membrane. Tc-AR E. coli in a viable but non-culturable (VBNC) state was observed and dominated the reactivation as the inactivated ARB remain present in the dark for more than 20 h. These results explained the reason for distribution difference of Tc-ARB at different depths in natural waters, which are of great significance for understanding the environmental behavior of ARB.

Characterization of a Newly Available Coastal Marine Dissolved Organic Matter Reference Material (TRM-0522).

Recent methodological advances have greatly increased our ability to characterize aquatic dissolved organic matter (DOM) using high-resolution instrumentation, including nuclear magnetic resonance (NMR) and mass spectrometry (HRMS). Reliable DOM reference materials are required for further method development and data set alignment but do not currently exist for the marine environment. This presents a major limitation for marine biogeochemistry and related fields, including natural product discovery. To fill this resource gap, we have prepared a coastal marine DOM reference material (TRM-0522) from 45 m deep seawater obtained ∼1 km offshore of Sweden's west coast. Over 3000 molecular formulas were assigned by direct infusion HRMS, confirming sample diversity, and the distribution of formulas in van Krevelen space was typical for a marine sample, with the majority of formulas in the region H/C 1-1.5 and O/C 0.3-0.7. The extracted DOM pool was more nitrogen (N)- and sulfur (S)-rich than a typical terrestrial reference material (SRFA). MZmine3 processing of ultrahigh-performance liquid chromatography (UPLC)-HRMS/MS data revealed 494 resolvable features (233 in negative mode; 261 in positive mode) over a wide range of retention times and masses. NMR data indicated low contributions from aromatic protons and, generally speaking, low lignin, humic, and fulvic substances associated with terrestrial samples. Instead, carboxylic-rich aliphatic molecules were the most abundant components, followed by carbohydrates and aliphatic functionalities. This is consistent with a very low specific UV absorbance SUVA254 value of 1.52 L mg C-1 m-1. When combined with comparisons with existing terrestrial reference materials (Suwannee River fulvic acid and Pony Lake fulvic acid), these results suggest that TRM-0522 is a useful and otherwise unavailable reference material for use in marine DOM biogeochemistry.