Aquatic Natural Organic Matter Research Articles

Adsorption of Se(IV) on kaolinite and montmorillonite in the presence of fulvic acid

This study investigates the influence of fulvic acid, a representative of aquatic natural organic matter (NOM), on the pH-dependent adsorption of Se(IV) on kaolinite and montmorillonite. Given their negative charges in aqueous solutions, Se(IV) and fulvic acid compete for the limited and identical adsorptive sites of clay minerals, particularly in neutral to alkaline environments. This competition was most pronounced under acidic conditions, where both Se(IV) and fulvic acid adsorption are favored. At pH 3, the presence of 20–80 mg·L−1 fulvic acid reduced the Se(IV) adsorption by up to half on both clay adsorbents. However, in near-neutral to alkaline pH regions (pH 6 to 10), the competitive interaction between Se(IV) and fulvic acid was less pronounced, since the adsorption of both fulvic acid and Se(IV) decreased. In particular for kaolinite, a rise in Se(IV) adsorption was evident at lower fulvic acid concentrations (20 mg·L−1). This phenomenon arises from the absence of aqueous complexes between Se(IV) and fulvic acid under acidic conditions, contrasting with their strong interaction under alkaline conditions as observed in the ATR-FTIR spectra. This study sheds light on the influence of NOM on the mobility of Se(IV) in natural waters, an aspect yet to be thoroughly explored.

Molecular weight fraction-specific transformation of natural organic matter during hydroxyl radical and sulfate radical oxidation

Aquatic natural organic matter (NOM) is one of the main scavengers of reactive species (e.g., •OH and SO4•−) during oxidation processes and undergoes complex transformations. Here, the organic content, optical properties, and redox state in various MW fractions and bulk Suwannee River NOM (SRNOM) were simultaneously evaluated during •OH and SO4•− oxidation processes for the first time. The SRNOM transformation pathways were specific to radical species and MW fractions, which was evidenced by a proportional decrease in electron-donating moieties and chromophores during •OH oxidation but a higher decrease in electron-donating moieties than chromophores during SO4•− oxidation, particularly in lower MW fractions (<3 kDa). The •OH decomposed reactive moieties mainly via aromatic ring opening or depolymerization in all MW fractions. SO4•− oxidation followed a similar pathway in higher MW fractions (>3 kDa) but mainly formed compounds with UV-absorbing properties (e.g., quinones) in lower MW fractions (<3 kDa). With competitive kinetics and depolymerization model, •OH was quantified as approximately 10 times more reactive towards MW fractions than SO4•−. However, the SO4•− concentrations were approximately 10 times those of •OH, resulting in comparable performance to •OH oxidation. SRNOM depolymerization by •OH and SO4•− resulted in formation of more precursors of disinfection byproducts than the parent constituents, especially for •OH. This work improves our understanding of the transformation of specific SRNOM fractions during radical oxidation processes.

Thorough Validation of Optimized Size Exclusion Chromatography-Total Organic Carbon Analysis for Natural Organic Matter in Fresh Waters.

Size exclusion chromatography with total organic carbon detection (HPSEC-TOC) is a widely employed technique for characterizing aquatic natural organic matter (NOM) into high, medium, and low molecular weight fractions. This study validates the suitability of HPSEC-TOC for a simplified yet efficient routine analysis of freshwater and its application within drinking water treatment plants. The investigation highlights key procedural considerations for optimal results and shows the importance of sample preservation by refrigeration with a maximum storage duration of two weeks. Prior to analysis, the removal of inorganic carbon is essential, which is achieved without altering the NOM composition through sample acidification to pH 6 and subsequent N2-purging. The chromatographic separation employs a preparative TSK HW-50S column to achieve a limit of detection of 19.0 µgC dm-3 with an injection volume of 1350 mm-3. The method demonstrates linearity up to 10,000 µgC dm-3. Precision, trueness and recovery assessments are conducted using certified reference materials, model compounds, and real water samples. The relative measurement uncertainty in routine analysis ranges from 3.22% to 5.17%, while the measurement uncertainty on the bias is 8.73%. Overall, the HPSEC-TOC represents a reliable tool for NOM fractions analysis in both treated and untreated ground and surface water.

Electro-sorption and -desorption characteristics of electrically conductive polyacrylonitrile membranes to remove aqueous natural organic matter in dead-end ultrafiltration system

Electrically conductive (EC) membranes have emerged as an innovative approach in removing natural organic matter (NOM) by electro-sorption (e-sorption) when external anodic potential (AP) is applied. In this study, the EC membranes were established by a forming a porous nanolayer of Pt nanoparticles via magnetron sputtering on both sides of virgin and chemically modified PAN ultrafiltration (UF) membranes. The modified PAN membranes were functionalized with ethylenediamine (PAN-EDA) and sodium hydroxide (PAN-NaOH). The virgin PAN membrane material contains nitrile group and demonstrated a negative zeta potential in the analyzed pH range. The PAN-EDA membrane owned amidine and amine groups, whereas PAN-NaOH membrane possessed carboxyl and amide groups in the membrane matrix. The PAN-NaOH and PAN-EDA membranes exhibited isoelectric points at 3.7 and 7.8, respectively. Electrical field-assisted UF experiments were conducted with Suwannee River NOM in dead-end mode and NOM removal was monitored using different methods of NOM characterization (e.g., SEC, DOC and UV254 absorbance). The results revealed that the non-electrically conductive (NEC) and EC virgin PAN membranes exhibited almost no intrinsic adsorption (at 0 V external potential) and e-sorption of NOM at 2.5 V AP respectively. However, NEC PAN-NaOH and PAN-EDA membranes showed DOC intrinsic sorption loadings of 17 mg·m−2 and 258 mg·m−2 at permeate flux 100 L·m−2·h−1 and pH 7 respectively. In comparison, the DOC e-sorption loadings of the EC PAN-NaOH and EC PAN-EDA membranes at 2.5 V AP were 197 mg·m−2 and 525 mg·m−2 under same test conditions respectively. The NOM e-desorption characteristics of the EC modified PAN membranes were also investigated to regenerate membranes for a sustainable filtration process. The results indicated that the EC PAN-NaOH and PAN-EDA membranes can be regenerated by reversing the electrical polarity almost completely. In conclusions, the outcomes of this work confirm that the presence of the derivatives of amines (e.g., amines, amidine and amide groups) and carboxyl group are necessary in the membrane matrix to induce e-sorption and -desorption characteristics.

Quantitative source tracking for organic foulants in ultrafiltration membrane using stable isotope probing approach

Quantitatively identifying the primary sources of organic membrane fouling is essential for the effective implementation of membrane technology and optimal water resource management prior to the treatment. This study leveraged carbon stable isotope tracers to estimate the quantitative contributions of various organic sources to membrane fouling in an ultrafiltration system. Effluent organic matter (EfOM) and aquatic natural organic matter (NOM), two common sources, were combined in five different proportions to evaluate their mixed effects on flux decline and the consequent fouling behaviors. Generally, biopolymer (BP) and low molecular weight neutral (LMWN) size fractions - abundantly present in EfOM - were identified as significant contributors to reversible and irreversible fouling, respectively. Fluorescence spectroscopy disclosed that a protein-like component notably influenced overall membrane fouling, whereas humic-like components were predominantly responsible for irreversible fouling rather than reversible fouling. Fluorescence index (FI) and biological index (BIX), common fluorescence source tracers, showed promise in determining the source contribution for reversible foulants. However, these optical indices were insufficient in accurately determining individual source contributions to irreversible fouling, resulting in inconsistencies with the observed hydraulic analysis. Conversely, applying a carbon stable isotope-based mixing model yielded reasonable estimates for all membrane fouling. The contribution of EfOM surpassed 60 % for reversible fouling and increased with its content in DOM source mixtures. In contrast, aquatic NOM dominated irreversible fouling, contributing over 85 %, regardless of the source mixing ratios. This study emphasizes the potential of stable isotope techniques in accurately estimating the contributions of different organic matter sources to both reversible and irreversible membrane fouling.

Natural organic matter flocculation behavior controls lead phosphate particle aggregation by mono- and divalent cations

Phosphate addition is commonly applied to remediate lead contaminated sites via the formation of lead phosphate particles with low solubility. However, the effects of natural organic matter (NOM) with different properties, as well as the contributions of specific interactions (particle-particle, particle-NOM, and NOM-NOM) in enhanced stabilization or flocculation of the particles, are not currently well understood. This study investigates the influence of two aquatic NOM and two soil or coal humic acid (HA) extracts on the aggregation behavior of lead phosphate particles and explores the controlling mechanisms. All types of NOM induced disaggregation and steric stabilization of the particles in the presence of Na+ (100 mM) or low (1 mM) Ca2+ concentrations, as well as at low NOM concentrations (1 mgC/L). However, for the soil and coal HA, a threshold at NOM concentrations of 10 mgC/L and high (3 mM) Ca2+ concentrations was observed where bridging flocculation (rather than steric stabilization) occurred. In situ attenuated total reflectance – Fourier transform infrared characterization confirmed adsorption of the soil and coal humic acid extracts (10 mgC/L) onto the surface of the lead phosphate particles in 3 mM Ca2+, whereas dynamic and static light scattering demonstrated extensive HA flocculation that dominated the overall scattered light intensities. These results imply that the accelerated aggregation was induced by a combination of HA adsorption and bridging flocculation by Ca2+. Overall, this research demonstrates that the type of NOM is critical to predict the colloidal stability of lead phosphate particles. Aquatic NOM stabilized the particles under all conditions evaluated, but soil or coal HA with higher molecular weight and aromaticity showed highly variable stabilization or flocculation behavior depending on the HA and Ca2+ concentrations available to adsorb to the particles and participate in bridging. These results provide new mechanistic insights on particle stabilization or destabilization by NOM.

The estimation of DBPs formation potential depending on the molecular structure of natural organic matter

Objectives:Since natural organic matter(NOM) is generated from an ecosystem, it has various characteristics depending on its origin. Especially, aquatic NOM reduces an efficiency of water treatment system and forms disinfection-by-products(DBPs) as a precursor. In this study, DBP formation potential was estimated according to the molecular structure of NOMs resulted by pyrolysis-gas chromatography-mass spectrometer(py-GC-MS). Methods:Five NOM samples were characterized: Suwannee River NOM(SRNOM), Mississippi River NOM(MRNOM), Nakdong River NOM(NR), NOM in effluent of Jinhae wastewater treatment plant(WP), and NOM in a small stream(SG) in Changwon city. The various analytical instruments were used including TOC analyzer, UV spectrometer, fluorescence spectrometer, and size-exclusion chromatography. After freeze drying of NOMs, molecular structure of samples was identified by py-GC-MS. Results and Discussion:Molecular weights of SRNOM and MRNOM were similar each other (~1400Da). The others(NR,WP,SG) were larger than the SRNOM and MRNOM. Hydrophobicity of the samples followed the order: SRNOM≒MRNOM &gt; NR &gt; WP &gt; SG. Py-GC-MS results showed that SRNOM and MRNOM contain high portion of humic components. Otherwise, NR, WP, SG have protein which is originated from microbials. The DBP formation potential of SRNOM and MRNOM were the highest.Conclusion:This research shows the different characteristics of NOMs originated from different source. The results confirmed that NOM contained high portion of humic components results in the formation of high concentration of DBPs.

Ions play different roles in virus removal caused by different NOMs in UF process: Removal efficiency and mechanism analysis

In this study, we investigated the effect of different compositions of aquatic natural organic matter (NOM) and ions on virus removal by ultrafiltration (UF). MS2 bacteriophage was used as a surrogate. Humic acid (HA) improved the MS2 removal rate from 1.95 ± 0.09 LRV to 2.40 ± 0.03 LRV at the HA dosage of 9 mg/L through the combined mechanisms of size exclusion, electrostatic repulsion and hydrophobicity. MS2 removal rate further increased to 3.10 ± 0.05 LRV by 10 mmol/L Na+ dosage and 3.19 ± 0.12 LRV by Ca2+ 1 mmol/L in the HA-containing UF system. Size exclusion turned into the dominant virus removal mechanism according to the results of the fouling model fitting and the weakening of electrostatic repulsion and hydrophobicity. The complexation of Ca2+ also played a role in MS2 removal based on the analysis of interaction force. MS2 removal rate by bovine serum albumin (BSA) was poor, which was 2.07 ± 0.06 LRV at the BSA dosage of 9 mg/L. Hydrophobicity was greatly reduced and the dominant virus removal mechanisms were size exclusion and electrostatic repulsion. 10 mmol/L Na+ in the presence of BSA deteriorated MS2 removal rate to 2.02 ± 0.07 LRV by the weakening of electrostatic repulsion, hydrophobicity and size exclusion. Electrostatic repulsion severely decreased by 1 mmol/L Ca2+ and the enhanced adsorption barrier represented competitive adsorption of Ca2+ by BSA and MS2 contributed for MS2 removal further decline (1.99 ± 0.05 LRV). Complex components in water will have different effects on virus removal due to their properties and interactions. This study can provide references for selecting more efficient water treatment methods according to the different compositions of raw water in actual water treatment applications during the UF process. Moreover, the retention of virus by UF can be predicted based on our study results.

A fluorescence indicator for source discrimination between microplastic-derived dissolved organic matter and aquatic natural organic matter

Recently, studies have increasingly focused on the occurrence of plastic leachate and its effects on aquatic environments. However, few studies have aimed to identify microplastic-derived dissolved organic matter (MP-DOM) from environmental samples that are often enriched with natural organic matter (NOM). In this study, three MP-DOM (EPS-DOM, PVC-DOM, and PET-DOM) and eight aquatic NOM samples, and their mixtures, were used to identify a unique optical surrogate for MP-DOM within background NOM. Three major fluorescence peaks (peaks P, H, and L) were identified in the excitation emission matrix (EEM) spectra of both DOM sources (i.e., MP-DOM and NOM). The first two peaks were more pronounced for MP-DOM than for aquatic NOM, whereas peak L showed the opposite trend. The summed intensity ratio of the ranges of the first two peaks relative to peak L, namely, (H + P)/L, clearly distinguished between MP-DOM and NOM samples. The MP-DOM source discrimination capability was compared for several selected spectroscopic indices by tracking their changes in the mixtures of two source groups with increasing fraction of MP-DOM via end-member mixing analysis. This was further evaluated based on the three criteria built on the significance of the difference between the two groups, the correlation coefficients of the regressions, and the minimum fraction of MP-DOM in mixtures that can be distinguished from 100% NOM samples. Irrespective of the plastic type and leaching conditions (i.e., UV-irradiated or not), the new optical index, (H + P)/L, was superior at distinguishing MP-DOM from the mixtures when compared to other commonly used optical indices. The new index can serve as a sensitive, robust, and reliable fluorescence indicator with minimal interference from NOM for detecting plastic leachate in aquatic samples.

Molecular insights into the reactivity of aquatic natural organic matter towards hydroxyl (•OH) and sulfate (SO4•−) radicals using FT-ICR MS

The higher scavenging capacity of natural organic matter (NOM) to hydroxyl radical (•OH) than sulfate radical (SO4•−) has been long-acknowledged. However, the difference in reactivity and the influence of initial characteristics, especially at the molecular-level, remain unaddressed. In this study, the reactivities of different NOM isolates to •OH and SO4•− were compared based on the determined second-order rate constants following the depletion of UV254-absorbing moieties. Three NOM isolates with varying characteristics were selected to investigate the influence of initial characteristics on their reactivities. With the identified reactive molecules using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), the distinct reactivity between the radicals and the influence of the initial characteristics were illustrated. The reactivity towards SO4•− was dominated by the electron density of the molecules (i.e., double bond equivalent (DBE)), while that of •OH was also shaped by molecular size (i.e., m/z) and composition (i.e., N- or S-incorporation). The examination on the exclusively reactive molecules (accounting for 10–20%) reflected a preferred H-abstraction by •OH and decarboxylation by SO4•−. Moreover, the analysis on the shared reactive molecules (80–90%) based on the UV254 versus electron-donating capacity (EDC) dependency revealed a prevalent •OH addition while single electron transfer to SO4•−. The different reaction rates associated with the proposed transformation pathways supported the observed higher reactivity of NOM to •OH than SO4•−.

Influence of humic substances on the transport of indium and gallium in porous media

Indium and gallium are used widely in modern industry, mostly for the production of semiconductors. They are considered as Technology-Critical Elements and have therefore received growing attention in the past few years. We investigated the influence of different types of humic substances on the transport of indium and gallium in laboratory-scale, saturated column experiments, to gain understanding of their mobility in natural environments. We evaluated the effect of different humic substances on the transport of indium and gallium in quartz sand: a commercial humic acid (Aldrich Humic Acid, AHA), a fulvic acid (Suwannee River Fulvic Acid, SRFA) and an aquatic natural organic matter (Suwannee River Natural Organic Matter, SRNOM). The impact of the flow rate and the influence of different concentrations of organic matter were also investigated. Indium was shown to be more mobile than gallium in the presence of humic substances. The mobility of indium in sand was highest for SRNOM, followed by SRFA and then AHA, while for gallium the order was SRFA > SRNOM > AHA. These results can be significant in understanding the mobility of indium and gallium in soils with various compositions of organic matter.

Impact of origin and structure on the aggregation behavior of natural organic matter

The intermolecular interactions of natural organic matter (NOM) play a key role in the fate and transport of organic carbon and pollutants in environmental and engineered systems. In this study, the impact of origin and structure on the aggregation behavior of NOM was investigated in the presence of naturally abundant cations. The physicochemical properties of NOM were quantified using a range of indices. Thermodynamic analysis suggests that the colloidal stability of NOM was mainly determined by its hydrophobicity (i.e., Lewis acid-base interactions). All NOM can be coagulated by Ca2+ owing to the strong cation-NOM interactions, which lead to bridging effect and lower Lewis acid-base interactions. Terrestrial NOM can be coagulated by Mg2+ while aquatic NOM cannot, owing to their different hydrophobicity. The critical coagulation concentrations of tested terrestrial NOM in the presence of Ca2+ (CCC–Ca) were quite similar at 1.94–4.88 mM despite their different structural properties. The CCC-Ca of tested aquatic NOM varied significantly from 46.89 mM to 110.40 mM depending on their structure. The optical indices including E2/E3, FI, and HIX can be potentially used as convenient indicators for assessing the colloidal stability of aquatic NOM for water treatment and risk assessment purposes.

Specific ion effects on the aggregation behavior of aquatic natural organic matter

Specific ion effects on the aggregation behavior of a reference aquatic natural organic matter (NOM), Suwannee River NOM (SRNOM), were investigated using kinetic, titration, calorimetric, and surface tension methods. Monovalent cations induced structural compacting of SRNOM, but not its aggregation. Their ability to induce structural compacting follows the order: Cs+ > Rb+ > K+ > Na+ > Li+. Divalent cations except Mg2+ can readily induce SRNOM aggregation. Their critical coagulation concentrations (CCC) follow the order: CCCSr > CCCCa > CCCBa. Electrokinetic, titration, and calorimetric data suggest that monovalent cations have weak interactions with SRNOM, while divalent cations strongly interact with SRNOM. Overall, the cation specificity in aggregation is determined by cation-NOM interactions and their ability to modulate surface tension. Specific ion effects of monovalent cations correlate to their hydration free energy, while that of divalent cations correlate to the ratio of the hydration entropy of cation to the enthalpy change of cation-NOM interactions. The cation specificity is consistent with the extended Derjaguin-Landau-Verwey-Overbeek theory, and the intermolecular interaction energy is dominated by the Lewis acid-base interactions. Our results suggest that specific cations should be targeted to predict or manipulate intermolecular interactions of aquatic NOM in natural and engineered settings.

Peroxymonosulfate Oxidizes Amino Acids in Water without Activation.

A variety of peptidic and proteinaceous contaminants (e.g., proteins, toxins, pathogens) present in the environment may pose risk to human health and wildlife. Peroxymonosulfate is a strong oxidant (EH0 = 1.82 V for HSO5-, the predominant species at environmental pH values) that may hold promise for the deactivation of proteinaceous contaminants. Relatively little quantitative information exists on the rates of peroxymonosulfate reactions with free amino acids. Here, we studied the oxidation of 19 of the 20 standard proteinogenic amino acids (all except cysteine) by peroxymonosulfate without explicit activation. Reaction half-lives at pH 7 ranged from milliseconds to hours. Amino acids possessing sulfur-containing, heteroaromatic, or substituted aromatic side chains were the most susceptible to oxidation by peroxymonosulfate, with rates of transformation decreasing in the order methionine > tryptophan > tyrosine > histidine. The rate of tryptophan oxidation did not decrease in the presence of an aquatic natural organic matter. Singlet oxygen resulting from peroxymonosulfate self-decomposition, while detected by electron paramagnetic resonance spectroscopy, was unlikely to be the principal reactive species. Our results demonstrate that peroxymonosulfate is capable of oxidizing 19 amino acids without explicit activation and that solvent-exposed methionine and tryptophan residues are likely initial targets of oxidation in peptides and proteins.

Differential absorbance study of interactions between europium, soil and aquatic NOM and model compounds

This study compared the binding of europium by soil and aquatic natural organic matter (NOM) exemplified by Pahokee Peat humic acid (PPHA) and Northern Reservoir NOM, respectively. NOM/Eu3+ interactions were measured based on the differential absorbance approach. The experimental results show that the binding of Eu3+ by humic acid isolated from agricultural soil results in several features of the differential spectra that are distinct from those observed for aquatic NOM. These features may be associated with the presence in soil NOM of functional groups similar to gallic acid. The binding of Eu3+ by NOM was modeled using a phenomenological approach that accounted for the involvement of dissimilar metal-binding functionalities. This study also introduced the concept of integrated differential absorbance; the use of that parameter allowed achieving a close fit between the experimental and model data. This study presents an alternative approach to ascertain mechanisms of, and differences in the interactions of europium with model compounds and natural organic matter with the provenance from soil and surface water.

Prediction of Apolar Compound Sorption to Aquatic Natural Organic Matter Accounting for Natural Organic Matter Hydrophobicity Using Aqueous Two-Phase Systems.

The equilibrium partitioning of organic compounds to natural organic matter (NOM) plays a key role in their environmental fate as well as bioavailability. In this study, a prediction model for organic compound sorption to NOM was theoretically derived based on two-phase systems. In this model, the hydrophobicity of NOM was scaled by their partition coefficients in an aqueous two-phase system (KATPS) and that of organics was scaled by their octanol-water partition coefficients (KOW). The model uses only KATPS and KOW as variables. Coefficients in the model were determined using a data set including the organic carbon-water partition coefficient (KOC) of four polycyclic aromatic hydrocarbons (PAHs) sorption to 10 NOM samples collected from surface waters. The resulting model was validated using additional NOM samples and reference NOM, which suggested good prediction power for PAH sorption to aquatic NOM. The model performance was compared with commonly used linear free energy relationship models, and its applicability was discussed. Sorption behavior unexpected by this model is attributed to additional sorption mechanisms other than partitioning. Overall, this approach allows prediction of KOC for apolar organic compound sorption to aquatic NOM simply using their respective partition coefficients in two-phase systems based on a specific model.

Removal of natural organic matter from Lake Terkos by EC process: Studying on removal mechanism by floc size and zeta potential measurement and characterization by HPSEC method

The performance of electrocoagulation (EC) process via aluminium and iron plate anodes were evaluated for removal of aquatic natural organic matter (NOM). The effect of current density (j), operation time (tEC), initial pH (pHi), charge loading and electrode types were investigated. The NOM removal efficiencies were measured with respect to dissolved organic carbon (DOC), UV254/VIS436 and specific UV-absorbance (SUVA) with initial value 6.58 mg DOC/L, 0.1363 1/cm, 0.004 1/cm and 2.07 L/(m mg), respectively. The experimental results showed that the effective removal of NOM (63.7% for DOC, 79.7% for UV254 and 76.7% for VIS436 (color) was obtained by iron electrode at original pHi of lake water (7.74±0.02) at 60 min. The adsorption capacity, qt, (mg DOC per g produced Al and Fe or coulomb) were calculated at a specific electrolysis time. At 6 mA/cm2 of optimum current density, 8.2 mg of DOC was removed per g in-situ produced Fe at original pHi of water. In addition the zeta potential and floc size analysis’ were used to explicate the removal mechanism of NOM. The results of the size exclusion chromatography showed that the affinity of EC process is higher for the aromatic fraction of NOM during electrolysis time.

Binding of Cu, Co, and Cs to fluorescent components of natural organic matter (NOM) from three contrasting sites.

Aqueous natural organic matter (NOM) contains different types of functional groups (carboxylic, phenolic, sulfidic, etc.), and hence could change the speciation of metals in environmental systems. This work is a proof-of-concept study on the interaction of three metals (Cu, Co, and Cs) with NOM using fluorescence spectroscopy. The specific aim was to determine the conditional stability constants for these three metals with NOM optical components, obtained from the quenching of fluorescence signals. Three contrasting water types were sampled in Northern Ontario: a pristine source (Cross Rd.), an urban-impacted source (Junction Creek), and an industrially impacted creek (Copper Cliff creek). In this investigation, Cu2+ was used as a benchmark, whereas Co2+ and Cs+ analyses were novel applications of this technique. Humic-like (H-like; terrestrial and microbial), fulvic-like (F-like), and protein-like (P-like) fluorescence components were found in various proportions at the three sampling sites. For these samples, the fluorescence signals of the H-, F-, and P-like components were quenched upon additions of Cu2+. The computed conditional stability constants (as log Kc) ranged from 4.46 to 6.06. In contrast, Kc values with Co2+ were measurable only for the two H-like components of the pristine sample (log Kc 3.02-4.05). Cesium (Cs+) induced quenching only for the P-like component at the industrial-impacted site (log Kc 4.82-5.03). While this study corroborates earlier reports that Cu2+-NOM interactions can be measured by fluorescence, we are showing for the first time a direct chemical interaction of Co2+ and Cs+ with specific NOM components, as reported by fluorescence quenching.

Molecular Size Distribution of Fluorophores in Aquatic Natural Organic Matter: Application of HPSEC with Multi-Wavelength Absorption and Fluorescence Detection Following LPSEC-PAGE Fractionation.

Analytical high performance size exclusion liquid chromatography (HPSEC) with multiwavelength absorbance and fluorescence detections was used for the analysis of molecular size distribution and optical properties of dissolved natural organic matter. Experiments were conducted on Suwannee River organic matter (SRNOM) and its fractions A, B, C+D preliminary obtained by combination of preparative low pressure size exclusion chromatography and polyacrylamide gel electrophoresis (LPSEC-PAGE) and purified by dialysis on membrane with nominal cutoff 10 kDa, the fractions molecular size varied in order A > B > C + D > 10 kDa. The multistep fractionation of SRNOM enabled the size-separation of at least five types of humic-like fluorophores within NOM showing emission maxima at 465, 450, 435, 420, and 405 nm. The decrease of the humic-like emission maxima paralleled the decrease of the nominal molecular size of fluorescent SRNOM. The protein-like fluorescence was split into tyrosine-like and tryptophan-like fluorophores and only detected in fractions A and B. This work provides new data on the optical properties of size-fractionated NOM, which consistent with the formation of supramolecular NOM assemblies, likely controlled by association of low-molecular size components. It is clearly observed for the high molecular size fraction A, containing free amino acids or short peptides. The combination of several different fractionation procedures is very useful for obtaining less complex NOM compounds and understanding the NOM function in the environment.

Ferrous-activated peroxymonosulfate oxidation of antimicrobial agent sulfaquinoxaline and structurally related compounds in aqueous solution: kinetics, products, and transformation pathways.

Sulfaquinoxaline (SQX) is a coccidiostatic drug widely used in poultry and swine production and has been frequently detected in various environmental compartments such as surface water, groundwater, soils, and sediments. In the present study, degradation of SQX by ferrous ion-activated peroxymonosulfate oxidation process (Fe(II)/PMS), a promising in situ chemical oxidation (ISCO) technique, was systematically investigated. Experimental results showed that Fe(II)/PMS process appeared to be more efficient for SQX removal relative to Fe(II)/persulfate process (Fe(II)/PS). An optimal Fe(II):PMS molar ratio of 1:1 was found to be necessary for efficient removal of SQX. Increasing the solution pH hampered the degradation of SQX, and no enhancement in SQX degradation was observed when chelating agents S,S'-ethylenediamine-N,N'-disuccinic acid (EDDS) and citrate were present. The presence of Suwannee River fulvic acid (SRFA), as a representative of aquatic natural organic matter (NOM), could inhibit the degradation of SQX. SQX was more susceptible to Fe(II)/PMS oxidation in comparison to its substructural analog 2-amino-quinoxaline (2-AQ) and other sulfonamides, i.e., sulfapyridine (SPD) and sulfadiazine (SDZ). Transformation products of SQX were enriched by solid-phase extraction (SPE) and identified by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MS/MS). On the basis of the TPs identified, detailed reaction pathways for SQX degradation including sulfonamide bond cleavage, SO2 extrusion, and aniline moiety oxidation were proposed. Our contribution may provide some useful information for better understanding the kinetics and mechanisms of SQX degradation by sulfate radical-based advanced oxidation processes (SR-AOPs).