Suwannee River Natural Organic Matter Research Articles

Characterizing Macroporous Ion Exchange Membrane Adsorbers for Natural Organic Matter (NOM) Removal—Adsorption and Regeneration Behavior

Addressing the characterization of Natural Organic Matter (NOM) removal by functionalized membranes in water treatment, this study evaluates the effectiveness of two commercial ion-exchange membrane adsorbers: Sartobind® Q (with quaternary amines) and D (with tertiary amines). Using Suwannee River NOM (SRNOM) as a surrogate, Langmuir adsorption isotherms revealed maximum capacities (Qmax) of 2966 ± 153 mg C/m2 and 2888 ± 112 mg C/m2, respectively. Variations in flux from 50 to 500 LMH had a minimal impact on breakthrough times, proving low diffusion limitations. The macroporous (3–5 µm) functionalized cellulose-based membranes exhibited high permeabilities of 10800 L/(h m2 bar). Q maintained positive zeta potential vs. pH, while D’s zeta potential decreased above pH 7 due to amine deprotonation and turning negative above an isoelectric point of 9.1. Regeneration with 0.01 M NaOH achieved over 95% DOC regeneration for Sartobind® D, characterizing reversibility through a pH-swing. Cyclic adsorption showed that Q maintained its capacity with over 99% DOC regeneration, while D required acidic conditioning after the first regeneration cycle to mitigate capacity reduction and re-deprotonate the adsorber. These results have demonstrated the potential suitability of adsorber membranes, designed originally for biotechnological purposes, for the possible removal of disinfection byproduct precursors in drinking water treatment.

Resolving Uncertainties in the Quantification of Trace Elements within Organic-Rich Boreal Rivers for AF4-UV-ICP-MS Analysis.

Over the past few decades, asymmetric flow field-flow fractionation (AF4) has emerged as a robust technique for the separation of colloid-associated trace elements (TEs) in aqueous samples. Nevertheless, little is known about potential artifacts and how to control them when measuring the concentrations of colloid-associated elements at low (μg L-1) or ultralow concentrations (ng L-1) using AF4-UV-ICP-MS. Water from a boreal river was selected as a challenging test material due to its high concentrations of dissolved organic matter (DOM) and Fe-rich colloids. These colloids are expected to be significant contributors to artifact occurrence, even in a metal-free, ultraclean laboratory. The results show that the adsorption of Mn, Co, Ni, Cu, and Pb onto acid-cleaned, non-channel surfaces (such as connection tubing and autosampler) accounted for up to 48% of TE loss. These losses on non-channel surfaces also represent potential sources of cross-contamination for Co, Ni, Cu, and Pb. New, uncleaned poly(ether sulfone) membranes are also sources of contamination for Ni and Cu. Analytical bias may exist in the measured concentrations of TEs, primarily due to the potential carryover of weakly adsorbed TEs (e.g., Ni and Cu) on the system surfaces by colloids in the samples (e.g., DOM). On the other hand, colloids in the samples can also act to gradually remove contaminants from the surfaces. For these types of DOM-rich waters, preconditioning the AF4 system using 40 mg C L-1 of Suwannee River Natural Organic Matter (SRNOM, pH = 7) is recommended to mitigate the impact of membrane fouling and carryover. A comprehensive strategy for minimizing instrumental artifacts is presented and discussed.

Photochemical fate of β-blocker pindolol in riverine and its downstream coastal waters

Pindolol (PIN) is a commonly used β-blocker drug and has been frequently detected in various natural waters. Comprehensive understanding of its environmental photochemical transformation is necessary to assess its environmental risk. In this study, the photodegradation kinetics and mechanisms of PIN in both freshwater and coastal water were investigated for the first time. The photodegradation experiments were carried out by steady-state photochemical experiment under simulated sunlight irradiation. The results showed that the photodegradation rate of PIN in the freshwater of the Pearl River estuary was significantly faster than that in its downstream coastal water. In river water, PIN can undergo both direct photolysis and indirect photolysis induced by riverine dissolved organic matter (DOM) mainly through excited triplet-state of DOM and singlet oxygen, while direct photolysis dominated its degradation in coastal water. The promotion effect was found to be much greater for Suwannee River Natural Organic Matter (SRNOM) than that of the sampled riverine DOM, due to its high steady-state concentrations of reactive species. Interestingly, coastal DOM in northern and southern China were found to have similar promotion effects on PIN photodegradation for the first time, but both less than that of riverine DOM. A total of seven degradation products of PIN resulting from hydroxylation, hydrogen abstraction and cleavage of ether bond were identified. Biological toxicity of one products were found to be higher than that of PIN. These results are of significance for knowing the persistence and ecological risk of PIN in natural waters.

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.

Indirect photodegradation of zinc pyrithione: The effect of chromophoric dissolved organic matter components and seawater factors

Chromophoric dissolved organic matter (CDOM) is the main photosensitizer in seawater. CDOM can absorb solar radiation extensively and generate reactive intermediates (RIs), including singlet oxygen (1O2), hydroxyl radicals (HO·), and CDOM triplet states (3CDOM*), that are favorable for indirect photodegradation of organic pollutants. In the current study, the effect and mechanism of CDOM components on zinc pyrithione (ZnPT) indirect photodegradation were studied. Among the three CDOM isolates (humic acid (JKHA), Suwannee River humic acid (SRHA), and Suwannee River natural organic matter (SRNOM)), JKHA had the highest fluorescence intensity per gram of carbon and the fastest indirect photodegradation rate for ZnPT. Furthermore, the fluorescent components were divided into four terrestrial humic-like components: C1, C2, C3, and C4, by using excitation–emission matrix spectroscopy combined with parallel factor analysis. A notable relationship was found between the four fluorescent components of CDOM and ZnPT indirect photodegradation. The indirect photodegradation rate of ZnPT varied in different types of CDOM solutions, which may be attributed to the different compositions of CDOM. The relative contents of C1 and C4 were significantly higher in JKHA than in the other two CDOMs, and they were the major contributors to the production of 3CDOM* and 1O2, which promoted ZnPT indirect photodegradation. The impact of seawater factors on ZnPT indirect photodegradation was also investigated. The ZnPT indirect photodegradation rate initially decreased and then increased as the pH increased from 5.00 to 11.00. The lowest rate of indirect photodegradation of ZnPT was observed at pH = 9.00. As the salinity was <25‰, in salinity the ZnPT indirect photodegradation rate increased concomitantly with an increase, and pronounced inhibition of ZnPT indirect photodegradation was observed when the salinity was >25‰. Nitrate had a promoting influence on ZnPT indirect photodegradation, whereas HCO3−, halogen ions, and metal ions all inhibited it.

Transformation of 2,4,6-tribromophenol in the acetylperoxyl radical based oxidation process and formation of brominated byproducts

Acetylperoxyl radical (CH3C(O)OO•), as a peracetic acid (PAA) derived specific radical, has a promising future in environmental remediation. However, the research about the transformation mechanism of halogenated organics with CH3C(O)OO• and the subsequent formation of disinfection byproducts (DBPs) is still in the gap stage. 2,4,6-tribromophenol (2,4,6-TBP) was chosen as a target brominated compound to study its transformation and the formation mechanism of brominated byproduct in the neutral Co(II)/PAA system. The results showed that 94.7 % of 2,4,6-TBP with 50 µM was transformed and its corresponding pseudo-first-order kinetic constant is about 0.540 min−1. Interestingly, CH3C(O)OO• and reactive bromine species were found to dominate 2,4,6-TBP transformation. 2,4,6-TBP had the best transformation under neutral conditions· H2O2, HCO3–, and natural organic matter (NOM) significantly inhibited 2,4,6-TBP transformation, while Cl− had little effect on 2,4,6-TBP transformation. In addition, the main transformation pathways of 2,4,6-TBP, including debromination, C–C coupling, self-coupling, and CH3C(O)OO• cross-coupling were proposed based on the analysis of transformation products by LC-MS/MS and DFT theoretical calculations. In identified intermediates, there are some DBPs, including bromate, bromoform, and dibromoacetic acid. These DBPs increased gradually in approximately 24 h, moreover, Suwannee River NOM improved DBPs production. Therefore, the formation mechanism of DBPs during the treatment of brominated organics with CH3C(O)OO• was proposed for the first time, which extended the theory of the formation mechanism of DBPs in CH3C(O)OO•-based water treatment.

Applying the modified UV-activated TOP assay to complex matrices impacted by aqueous film-forming foams

Per- and polyfluoroalkyl substances (PFAS) are a large chemical family, and numerous chemical species can co-exist in environmental samples, especially those impacted by aqueous film-forming foams (AFFFs). Given the limited availability of chemical standards, capturing the total amount of PFAS is challenging. Thus, the total oxidizable precursor (TOP) assay has been developed to estimate the total amount of PFAS via the oxidative conversion of precursors into perfluorocarboxylic acids (PFCAs). This study aims to enhance the robustness of the TOP assay by replacing heat activation with UV activation. We evaluated the molar yields of known precursors in water in the presence of varying levels of Suwannee River natural organic matter (SRNOM) and in two soils. The impact of UV activation was also evaluated in two soils spiked with three well-characterized AFFFs, six AFFF-impacted field soils, and nine rinse samples of AFFF-impacted stainless-steel pipe. In the presence of 100 mg/L SNROM, 6:2 fluorotelomer sulfonate (FTS), 8:2 FTS, and N-ethyl perfluorooctane sulfonamidoacetic acid (N-EtFOSAA) in deionized water had good molar recovery as PFCAs (average of 102 ± 9.8 %); at 500 mg/L SNROM, the recovery significantly dropped to an average of 51 ± 19 %. In two soils (with 4 % and 8.8 % organic matter) with individual precursor spikes, the average molar recovery was 101 ± 9.4 %, except N-EtFOSAA, which had a reduced recovery in the soil with 8.8 % organic matter (OM). UV-activated assays outperformed heat-activated ones, especially in AFFF-impacted soils and pipe extract samples, with an average of 1.4–1.5× higher PFCA recovery. In almost all test samples, UV activation resulted in a notable shift towards longer PFCA chain lengths, particularly for samples with high OM content. The study confirmed the advantages of UV activation, including a significantly shortened exposure time (1 h vs. 6 h) and reduced matrix effects from OM due to the dual functions of UV in activating persulfate and photodegrading OM.

Elucidating the inhibitory effects of natural organic matter on the photodegradation of organic micropollutants: Atrazine as a probe compound

Natural organic matter (NOM) is a complex mixture of heterogeneous compounds with varying functional groups and molecular sizes. Understanding the impact of NOM on the generation of photochemically produced reactive intermediates (PPRIs) and their potential inhibitory effects on photolysis has remained challenging due to the variations in the reactivities and concentrations of these functional groups. To address this gap, tannic acid (TA), gallic acid (GA), catechin (CAT), and tryptophan (Trp), were chosen as potential substitutes for NOM. Their effects on the photochemical transformation process were evaluated and compared with the widely used Suwannee River NOM (SRNOM). Atrazine (ATZ) was selected as a probe organic micropollutant (OMP). In this investigation, a significantly higher concentration of HO• was observed compared to O21, and the triplet excited state ( NOM*3). The findings suggest that the substituted phenols, particularly those with carboxylate-substitutions, played a substantial role in HO• formation, while electron-rich moieties acted as antioxidants, consuming NOM*3. Hydroxyl, carboxylic, and amino acid were the active groups for O21 formation. However, the inhibitory effects induced by the NOM surrogates were significant and mainly attributed to the direct photolysis inhibition caused by the inner filter effect. The scope of this work was further extended to include SRNOM, where similar trends with less pronounced formation of PPRIs and inner filter effects were observed. Therefore, this study sheds some light on the role of the functional groups in NOM during photochemical transformations of OMPs, thereby deepening our understanding of their fate in aqueous systems.

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.

Singlet Oxygen Quantum Yields of Pyrogenic Dissolved Organic Matter from Lab-Prepared and Wildfire Chars.

Wildfires or prescribed fires release pyrogenic dissolved organic matter (pyDOM) into the environment, which can photochemically produce singlet oxygen (1O2) in sun-lit surface waters. 1O2 quantum yields (ΦΔ) are well-studied for non-pyrogenic DOM, but little is understood about the 1O2 generation from pyDOM, especially the ΦΔ values from real wildfire samples and their wavelength dependence. In this study, time-resolved 1O2 phosphorescence was used to determine the wavelength-dependent ΦΔ values for pyDOM generated from wildfire char and a series of lab-prepared chars produced by combusting oak and pine wood. Wildfire and most lab-prepared pyDOM generally had similar ΦΔ values (2.1-2.7%) at 365 nm compared to the reference Suwannee River Natural Organic Matter (SRNOM) isolate (2.4%). Interestingly, pyDOM from the highest combustion temperature char was found to possess extremely low ΦΔ values compared to SRNOM and other pyDOM at all excitation wavelengths. In addition, it was revealed that the predicted steady-state concentration of 1O2 from pyDOM was similar to that from SRNOM, indicating that the addition of pyDOM from wood chars may not strongly impact surface water photochemistry.

Using multilinear regressions developed from excitation-emission matrices to estimate the wastewater content in urban streams impacted by sanitary sewer leaks and overflows

Failing sewer infrastructure introduces unknown quantities of raw wastewater into urban streams, raising human and ecological health concerns. To address this problem, we developed multilinear regressions that relate fluorescent dissolved organic matter to wastewater content. The models were constructed with the area-normalized regional volumes of excitation-emission matrices measured for mixtures of deionized water, surface water from a wastewater-impacted stream, wastewater from a sanitary sewer adjacent to the stream, and Suwannee River natural organic matter. The best performing multilinear regression had a standard error of 0.55 % wastewater. A matrix-matched calibration was used to internally validate the approach and confirm the wastewater content of select samples. The multilinear model was externally validated through (i) comparison to concentrations of contaminants of emerging concern in surface water and wastewater and (ii) extension to samples from previous campaigns that employed alternative wastewater indicators. Using the validated model, we estimated an average wastewater content of 2.4 ± 4.0 % in 165 samples collected from 14 locations in the Gwynns Falls watershed (USA) between April 2019 and April 2023. The maximum wastewater content was 35 % at a site where sanitary sewer leaks and overflows have been previously documented. The reported approach represents a cost-effective and scalable technique to estimate wastewater content in urban streams through analysis of fluorescent dissolved organic matter.

Microcystin-LR Removal by Ozone (O3) and Vacuum-UV (VUV): The Effect of Chloride Ions

ABSTRACT Removal of microcystin-LR (MC-LR) by ozone (O3), vacuum-UV (VUV), and their combination was investigated in the presence of chloride as one of the main solutes present in water. In general, the combined VUV/O3 process provided the greatest MC-LR removal, with the presence of chloride enhancing the removal efficacy. Formation of chlorine radical species was the primary reason for the observed improvement. The order of MC-LR removal by different processes using UV fluence of around 300 mJ cm−2, ozone dose of 0.1 mg L−1, and chloride concentration of 120 mg L−1 was as follows: VUV/O3/Chloride > VUV/O3 > VUV/Chloride > VUV > O3. Comparing MC-LR removal by O3, VUV and VUV/O3 in synthetic lab samples, spiked with Suwannee River NOM and natural water samples of the same organic concentration, showed the significance of background organics in scavenging ozone in the process. For a given ozone dosage, MC-LR removal by O3 or VUV/O3 in natural water was lower than that in the synthetic water samples. The standalone VUV was not affected and the MC-LR removals were identical in both synthetic and natural waters.

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.

New Insights into the Role of Natural Organic Matter in Fe-Cr Coprecipitation: Importance of Molecular Selectivity.

Coprecipitation of Fe/Cr hydroxides with natural organic matter (NOM) is an important pathway for Cr immobilization. However, the role of NOM in coprecipitation is still controversial due to its molecular heterogeneity and diversity. This study focused on the molecular selectivity of NOM toward Fe/Cr coprecipitates to uncover the fate of Cr via Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS). The results showed that the significant effects of Suwannee River NOM (SRNOM) on Cr immobilization and stability of the Fe/Cr coprecipitates did not merely depend on the adsorption of SRNOM on Fe/Cr hydroxides. FT-ICR-MS spectra suggested that two pathways of molecular selectivity of SRNOM in the coprecipitation affected Cr immobilization. Polycyclic aromatics and polyphenolic compounds in SRNOM preferentially adsorbed on the Fe/Cr hydroxide nanoparticles, which provided extra binding sites and promoted the aggregation. Notably, some specific compounds (i.e., polyphenolic compounds and highly unsaturated phenolic compounds), less unsaturated and more oxygenated than those adsorbed on Fe/Cr hydroxide nanoparticles, were preferentially incorporated into the insoluble Cr-organic complexes in the coprecipitates. Kendrick mass defect analysis revealed that the insoluble Cr-organic complexes contained fewer carbonylated homologous compounds. More importantly, the spatial distribution of insoluble Cr-organic complexes was strongly related to Cr immobilization and stability of the Fe/Cr-NOM coprecipitates. The molecular information of the Fe/Cr-NOM coprecipitates would be beneficial for a better understanding of the transport and fate of Cr and exploration of the related remediation strategy.

Comparison of molecular characteristics between commercialized and regional natural organic matters

Natural organic matter (NOM) is a ubiquitous substance in natural aquatic ecosystems that is a significant component in any experiment involving water. However, experimentally simulating the aquatic conditions using NOMs from natural sources remains difficult. As a result, previous experimental studies have predominantly relied on commercialized NOMs. This study aimed to comprehensively compare the characteristics of two commercialized NOMs (Suwannee River NOM: SRNOM, Mississippi River NOM: MRNOM) and two regional NOMs (Nakdong River NOM: NDNOM, effluent organic matter: EfOM) using various analytical methods during water dissolution. Both commercialized NOMs showed low conductivity (SRNOM: 28.6 &lt;i&gt;μ&lt;/i&gt;S/cm, MRNOM: 35.4 &lt;i&gt;μ&lt;/i&gt;S/cm) and were highly humidified (SRNOM: HIX 14.22, MRNOM: HIX 11.44), whereas NOMs from natural water had relatively higher conductivity (NDNOM: 365.7 &lt;i&gt;μ&lt;/i&gt;S/cm, EfOM: 398.8 &lt;i&gt;μ&lt;/i&gt;S/cm) and lower humification (NDNOM: HIX 2.47, EfOM: HIX 2.50). The SRNOM and MRNOM contained large amounts of tannin-like substances (SRNOM: 43.5%, MRNOM: 43.1%). The NDNOM had a humidification state similar to that of the EfOM, except for the portion of protein-like biopolymer, which was smaller. The different characteristics of the samples can be critical in selecting appropriate NOMs for use in future studies because they can significantly influence the experimental chemical reaction.

Aquatic plant root exudates: A source of disinfection byproduct precursors in constructed wetlands

Aquatic plant-derived dissolved organic matter (DOM) in water bodies is an important source of disinfection byproduct (DBP) precursors. It is therefore very important to investigate DBP formation, and the main DBP precursors that enter drinking water during treatment processes. In this study, Lythrum salicaria root extract (LSRE) and Acorus calamus root extract (ACRE) were analyzed. The LSRE and ACRE were chlorinated and disinfected to generate trihalomethanes, haloacetic acids, haloketones, and haloacetaldehydes. The DBP formation potential of LSRE, dominated by humus, was higher than that of Suwannee River natural organic matter (SRNOM), and trichloroacetic acid was the main DBP. It was calculated that 2.09 % of the increased DOC brought by the surface flow wetland planted with emergent aquatic plants, and the contribution rates of TCMFP, DCAAFP and TCAAFP in effluent were 3.34 %, 3.23 % and 3.05 %, respectively. A total of 706 chlorinated-formula were detected by FTICR-MS, among which mono- and di-chlorinated formulae were the most abundant. Macromolecular hydrophobic organics and tannins were the main precursors for LSRE. Unlike LSRE, the DOM composition of ACRE was dominated by protein or aliphatic compounds; therefore, the risk of DBP formation was not as high as that for LSRE. This study is the first to determine the risk of DBP formation associated with aquatic plant root extracts, and confirmed that tannins in plant-derived DOM are more important DBP precursors than lignins.

Assess the formation of disinfection by-products from pyrogenic dissolved organic matter (pyDOM): impact of wildfire on the water quality of forest watershed

Wildfires can release pyrogenic dissolved organic matter (pyDOM) into the forest watershed, which may pose challenges for water treatment operations downstream due to the formation of disinfection by-products (DBPs). In this study, we systematically assessed the physio-chemical properties of pyDOM (e.g., electron-donating and -accepting capacities; EDC and EAC) and their contributions to DBP formation under different disinfection scenarios using (1) ten lab samples produced from various feedstocks and pyrolysis temperatures, and (2) pre- and post-fire field samples with different burning severities. A comprehensive suite of DBPs—four trihalomethanes (THMs), nine haloacetic acids (HAAs), and seven N-nitrosamines—were included. The formations of THM and HAA showed an up to 5.7- and 8.9-fold decrease as the pyrolysis temperature increased, while the formation of N-nitrosamines exhibited an up to 6.6-fold increase for the laboratory-derived pyDOM. These results were supported by field pyDOM samples, where the post-fire samples consistently showed a higher level of N-nitrosamine formation (i.e., up to 5.3-fold), but lower THMs and HAAs compared to the pre-fire samples. To mimic environmental reducing conditions, two field samples were further reduced electrochemically and compared with Suwannee River natural organic matter (SRNOM) to evaluate their DBP formation. We found increased DBP formation in pyDOM samples following electrochemical reduction but not for SRNOM, which showed increased N-nitrosamines but decreased THMs and HAAs post-electrochemical reduction. Furthermore, this study reported for the first time the formation of two previously overlooked N-nitrosamines (i.e., nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA)) in both laboratory and field pyDOM samples, raising concerns for drinking water safety given their higher toxicity as compared to the regulated counterparts. Results from this study provide new insights for DBP mitigation during post-fire recovery, which are particularly relevant to communities that rely on forest watersheds as their drinking water sources.

Experimental measurements and numerical simulations of the transport and retention of nanocrystal CdSe/ZnS quantum dots in saturated porous media: Effects of electrolytes, organic ligand, and natural organic matter

This study explores the transport and retention of CdSe/ZnS quantum dot (QD) nanoparticles in water-saturated sand columns as a function of electrolytes (Na+ and Ca2+), ionic strength, organic ligand citrate, and Suwannee River natural organic matter (SRNOM). Numerical simulations were carried out to understand the mechanisms that govern the transport and interactions of QDs in porous media and to assess how environmental parameters impact these mechanisms. An increase in the ionic strength of NaCl and CaCl2 increased QDs retention in porous media. The reduction of the electrostatic interactions screened by dissolved electrolyte ions and the increase of divalent bridging effect are the causes for this enhanced retention behavior. Citrate or SRNOM enhanced QDs transport in NaCl and CaCl2 systems by either increasing the repulsion energy barrier or inducing the steric interactions between QDs and the quartz sand collectors. A non-exponential decay characterized the retention profiles of QDs along the distance to the inlet. The modeling results indicated the four models containing the attachment, detachment, and straining terms – Model 1: M1-attachment, Model 2: M2-attachment and detachment, Model 3: M3-straining, and Model 4: M4-attachment, detachment, and straining – closely simulated the observed breakthrough curves (BTCs) but inadequately described the retention profiles.

Inhibition of photosensitized degradation of organic contaminants by copper under conditions typical of estuarine and coastal waters

Dissolved organic matter (DOM) driven-photochemical processes play an important role in the redox cycling of trace metals and attenuation of organic contaminants in estuarine and coastal ecosystems. In this study, we evaluate the effect of Cu on 4-carboxybenzophenone (CBBP) and Suwannee River natural organic matter (SRNOM)-photosensitized degradation of seven target contaminants (TCs) including phenols and amines under pH conditions and salt concentrations typical of those encountered in estuarine and coastal waters. Our results show that trace amounts of Cu(II) (25 −500 nM) induce strong inhibition of the photosensitized degradation of all TCs in solutions containing CBBP. The influence of TCs on the photo-formation of Cu(I) and the decrease in the lifetime of transformation intermediates of contaminants (TC•+/ TC•(-H)) in the presence of Cu(I) indicated that the inhibition effect of Cu was mainly due to the reduction of TC•+/ TC•(-H) by the photo-produced Cu(I). The inhibitory effect of Cu on the photodegradation of TCs decreased with the increase in Cl− concentration since less reactive Cu(I)−Cl complexes dominate at high Cl− concentrations. The impact of Cu on the SRNOM-sensitized degradation of TCs is less pronounced compared to that observed in CBBP solution since the redox active moieties present in SRNOM competes with Cu(I) to reduce TC•+/ TC•(-H). A detailed mathematical model is developed to describe the photodegradation of contaminants and Cu redox transformations in irradiated SRNOM and CBBP solutions.

Chlorpyrifos fate in the Arctic: Importance of analyte structure in interactions with Arctic dissolved organic matter

The insecticide and current use pesticide chlorpyrifos (CLP) is transported via global distillation to the Arctic where it may pose a threat to this ecosystem. CLP is readily detected in Arctic environmental compartments, but current research has not studied its partitioning between water and dissolved organic matter (DOM) nor the role of photochemistry in CLP's fate in aquatic systems. Here, the partition coefficients of CLP were quantified with various types of DOM isolated from the Arctic and an International Humic Substances Society (IHSS) reference material Suwannee River natural organic matter (SRNOM). While CLP readily partitions to DOM, CLP exhibits a significantly higher binding constant with Arctic lacustrine DOM relative to fluvial DOM or SRNOM. The experimental partitioning coefficients (KDOC) were compared to a calculated value estimated using poly parameter linear free energy relationship (pp-LFER) and was found to be in good agreement with SRNOM, but none of the Arctic DOMs. We found that Arctic KDOC values decrease with increasing SUVA254, but no correlations were observed for the other DOM compositional parameters. DOM also mediates the photodegradation of CLP, with stark differences in photo-kinetics using Arctic DOM isolated over time and space. This work highlights the chemo-diversity of Arctic DOM relative to IHSS reference materials and highlights the need for in-depth characterization of DOM that transcends the current paradigm based upon terrestrial and microbial precursors.