Changes in dissolved organic matter during the treatment processes of a drinking water plant in Sweden and formation of previously unknown disinfection byproducts

Development and Application of a High-Precision Algorithm for Nontarget Identification of Organohalogens Based on Ultrahigh-Resolution Mass Spectrometry

Brominated and/or chlorinated organic compounds (referred to as organohalogens) are frequently detected in natural and engineered environments. However, ultrahigh-resolution mass spectrometry (UHR-MS)-based nontargeted identification of organohalogens remains challenging because of the coexistence of a vast number of halogenated and nonhalogenated organic molecules. In this study, a new algorithm, namely, the NOMDBP code, was developed to simultaneously identify organohalogens and non-organohalogens from the UHR-MS spectra of natural and engineered waters. In addition to isotopic patterns, for the first time, three optional filter rules [i.e., selection for minimum nonoxygen heteroatoms, inspection of the presence of newly formed halogenated disinfection byproducts (Xn-DBPs), and of their precursors] were incorporated into our code, which can accurately identify DBP-associated peaks and further elucidate Xn-DBP generation and transformation mechanisms. The formula assignment ratio against 2815 previously reported organohalogens, and their 11,583 isotopologues exceeded 97%. Application of our algorithm to disinfected natural organic matter indicated that oxygen-containing Xn-DBP species accounted for a majority of the Xn-DBPs. Furthermore, brominated Xn-DBPs (Br-DBPs) were characterized by a higher degree of unsaturation compared to chlorinated Xn-DBPs. In addition to electrophilic substitution and electrophilic addition reactions, the decomposition/transformation pathway was found to be another important mechanism in Br-DBP formation. The results of this study highlight the superior potential of our code for the efficient detection of yet unknown organohalogens (including organohalogens bearing nonoxygen heteroatoms) in a nontargeted manner and for the identification of their generation mechanism occurring during the disinfection process.

Exploring the relative changes in dissolved organic matter for assessing the water quality of full-scale drinking water treatment plants using a fluorescence ratio approach

This study aims to extend and demonstrate the application of fluorescence spectroscopy for monitoring the water quality of three differently operated full-scale drinking water treatment plants located in the Shenzhen city (China). A ratio of fluorescent dissolved organic matter (FDOM), which describes relative changes in humic-like to protein-like fluorescence, was used to explain mechanisms behind the physicochemical processes. The fluorescence components obtained through individual and combined parallel factor analysis (PARAFAC) modeling revealed the presence of humic-like (C1) and protein-like (C2) structures in the DOM. The C1/C2 ratio provided a direct relationship between the seasonal variations and DOM composition. Wet season generated DOM enriched with humic-like fluorescence, while dry season caused a higher release of protein-like fluorescence. The fluorescence ratio presented unique patterns of DOM in treatment trains. The chemical pretreatment and disinfection unit processes showed a higher tendency to remove the humic-like fluorescence. However, the C1/C2 ratio increased during physical treatment processes such as coagulation-precipitation and sand filtration, indicating preferential removal of protein-like fluorescence. The DOM composition in influent directly (R² = 0.77) influenced the relative intensities of fluorescence components in the treated water. Compared to the dry season, the wet season caused significant changes in DOM composition and produced treated water enriched with humic-like fluorescence. This fluorescence ratio offers an approach to explore the role of different treatment units and determine the factors affecting the composition of DOM in the surface water and drinking water treatment plants.

Untargeted characterisation of dissolved organic matter contributions to rivers from anthropogenic point sources using direct-infusion and high-performance liquid chromatography/Orbitrap mass spectrometry

RATIONALE

Anthropogenic organic inputs to freshwaters can exert detrimental effects on aquatic ecosystems, raising growing concern for both environmental conservation and water security. Current regulation by the EU water framework directive (European Union, 2000/60/EC) relates to organic pollution by monitoring selected micropollutants; however, aquatic ecosystem responses require a comprehensive understanding of dissolved organic matter (DOM) composition. The introduction of high-resolution mass spectrometry (HRMS) is set to greatly increase our understanding of the composition of DOM of both natural and anthropogenic origin derived from diffuse and point sources.

METHODS

DOM was extracted from riverine and treated sewage effluent using solid-phase extraction (SPE) and analysed using dissolved organic carbon analysis, direct-infusion high-resolution mass spectrometry (DI-HRMS) and high-performance liquid chromatography (HPLC)/HRMS. The data obtained were analysed using univariate and multivariate statistics to demonstrate differences in background DOM, anthropogenic inputs and in-river mixing. Compound identifications were achieved based on MS2 spectra searched against on-line databases.

RESULTS

DI-HRMS spectra showed the highly complex nature of all DOM SPE extracts. Classification and visualisation of extracts containing many thousands of individual compounds were achieved using principal component analysis (PCA) and hierarchical cluster analysis. Kruskal-Wallis analyses highlighted significant discriminating ions originating from the sewage treatment works for more in-depth investigation by HPLC/HRMS. The generation of MS2 spectra in HPLC/HRMS provided the basis for identification of anthropogenic compounds including; pharmaceuticals, illicit drugs, metabolites and oligomers, although many thousands of compounds remain unidentified.

CONCLUSIONS

This new approach enables comprehensive analysis of DOM in extracts without any preconceived ideas of the compounds which may be present. This approach has the potential to be used as a high throughput, qualitative, screening method to determine if the composition of point sources differs from that of the receiving water bodies, providing a new approach to the identification of hitherto unrecognised organic contribution to water bodies.

Effects of ascorbate and carbonate on the conversion and developmental toxicity of halogenated disinfection byproducts during boiling of tap water

Chlorine disinfection inactivates pathogens in drinking water, but meanwhile it causes the formation of halogenated disinfection byproducts (DBPs), which may induce adverse health effects. Humans are unavoidably exposed to halogenated DBPs via tap water ingestion. Boiling of tap water has been found to significantly reduce the concentrations of halogenated DBPs. In this study, we found that compared with boiling only, adding ascorbate (vitamin C) or carbonate (baking soda) to tap water and then boiling the water further reduced the level of total organic halogen (a collective parameter for all halogenated DBPs) by up to 36% or 28%, respectively. Adding ascorbate removed the chlorine residual in tap water and thus prevented the formation of more halogenated DBPs in the boiling process. Adding carbonate elevated pH of tap water and consequently enhanced the hydrolysis (dehalogenation) of halogenated DBPs or led to the formation of more trihalomethanes that might volatilize to air during the boiling process. The comparative developmental toxicity of the DBP mixtures in the water samples was also evaluated. The results showed that adding a tiny amount of sodium ascorbate or carbonate (2.5-5.0 mg/L) to tap water followed by boiling for 5 min reduced the developmental toxicity of tap water to a substantially lower level than boiling only. The addition of sodium ascorbate or carbonate to tap water in household could be realized by preparing them in tiny pills. This study suggests simple and effective methods to reduce the adverse effects of halogenated DBPs on humans through tap water ingestion.

Molecular-Level Transformation of Dissolved Organic Matter during Oxidation by Ozone and Hydroxyl Radical

Ozonation of drinking and wastewater relies on ozone (O₃) and hydroxyl radical (^•OH) as oxidants. Both oxidants react with dissolved organic matter (DOM) and alter its composition, but the selectivity of the two oxidants and mechanisms of reactivity with DOM moieties are largely unknown. The reactions of O₃ and ^•OH with two DOM isolates were studied by varying specific ozone doses (0.1-1.3 mg-O₃/mg-C) at pH 7. Additionally, conditions that favor O₃ (i.e., addition of an ^•OH scavenger) or ^•OH (i.e., pH 11) were investigated. Ozonation decreases aromaticity, apparent molecular weight, and electron donating capacity (EDC) of DOM with large changes observed when O₃ is the main oxidant (e.g., EDC decreases 63-77% for 1.3 mg-O₃/mg-C). Both O₃ and ^•OH react with highly aromatic, reduced formulas detected using high-resolution mass spectrometry (O:C = 0.48 ± 0.12; H:C = 1.06 ± 0.23), while ^•OH also oxidizes more saturated formulas (H:C = 1.64 ± 0.26). Established reactions between model compounds and O₃ (e.g., addition of one to two oxygen atoms) or ^•OH (e.g., addition of one oxygen atom and decarboxylation) are observed and produce highly oxidized DOM (O:C > 1.0). This study provides molecular-level evidence for the selectivity of O₃ as an oxidant within DOM.

Role of Reactive Halogen Species in Disinfection Byproduct Formation during Chlorine Photolysis

The multiple reactive oxidants produced during chlorine photolysis effectively degrade organic contaminants during water treatment, but their role in disinfection byproduct (DBP) formation is unclear. The impact of chlorine photolysis on dissolved organic matter (DOM) composition and DBP formation is investigated using lake water collected after coagulation, flocculation, and filtration at pH 6.5 and pH 8.5 with irradiation at three wavelengths (254, 311, and 365 nm). The steady-state concentrations of hydroxyl radical and chlorine radical decrease by 38-100% in drinking water compared to ultrapure water, which is primarily attributed to radical scavenging by natural water constituents. Chlorine photolysis transforms DOM through multiple mechanisms to produce DOM that is more aliphatic in nature and contains novel high molecular weight chlorinated DBPs that are detected via high-resolution mass spectrometry. Quenching experiments demonstrate that reactive chlorine species are partially responsible for the formation of halogenated DOM, haloacetic acids, and haloacetonitriles, whereas trihalomethane formation decreases during chlorine photolysis. Furthermore, DOM transformation primarily due to direct photolysis alters DOM such that it is more reactive with chlorine, which also contributes to enhanced formation of novel DBPs during chlorine photolysis.

Identification of the production and biotransformational changes of soluble microbial products (SMP) in wastewater treatment processes: A short review

While the definition of soluble microbial products (SMP) remains somewhat contentious, they have been widely accepted to be the pool of organic compounds which are released by cells into their surroundings (liquid or otherwise) due to substrate metabolism and biomass decay. SMPs are also potential precursors of disinfection by-products, and are known to be important in membrane fouling. With recent developments in analytical methodologies, many of the low molecular weight (MW) compounds can now be identified, although they are often incorrectly identified as recalcitrant compounds present in the influent. The old hypothesis of "microbial infallibility" suggested that all organic compounds produced by bacteria will eventually be degraded by microorganisms. However, there are some limitations to this hypothesis due to; the time available for degradation, the rate of activity of the microorganisms themselves, synergistic effects, as well as the degree of complexity of the chemical substance. Therefore, it is important to identify and characterise the SMPs involved in these processes, which can then in turn support the research and development of improving wastewater treatment efficiency and effectiveness, and eventually reduce environmental damage. In addition, it is still unclear what the evolutionary purpose of these compounds are. This paper reviews the work that has been done on the production and biotransformation of chemical compounds up to now and which were reported to be found in wastewater treatment systems.

Identification, formation and control of polar brominated disinfection byproducts during cooking with edible salt, organic matter and simulated tap water

Edible salt is essential to the health of humans and serves as a seasoning universally. Besides chloride, edible salt also contains other anions such as bromide, fluoride, sulfate, and carbonate due to incomplete removal during raw salt refinement. In a household cooking (e.g., soup making) process, a chlorine/monochloramine residual in tap water could react with bromide in edible salt and organic matter in food (e.g., rice, wheat) to form numerous brominated disinfection byproducts (Br-DBPs) at significant levels, which might induce adverse health effects to human beings. In this study, we solicited 20 edible salts of different types (i.e., sea salts, well and rock salts, lake salts, and bamboo salts) from nine countries and determined their bromide levels to be 67-375 mg/kg, with an average level of 173 mg/kg. A total of 25 polar Br-DBPs were detected and identified with structures/formulae in cooking water samples using ultra performance liquid chromatography/electrospray ionization-triple quadruple mass spectrometry (UPLC/ESI-tqMS) and high-resolution mass spectrometry. Effects of cooking conditions (e.g., disinfectant type and level, edible salt dose, organic matter type and dose, sequence and time interval of adding organic matter and salt, etc.) on the formation of polar Br-DBPs were investigated, and optimized cooking conditions with minimized formation of polar Br-DBPs were determined. Further aided with an Hep G2 cell cytotoxicity assay, it was found that the overall cytotoxicity of chlorinated and chloraminated cooking water samples prepared after cooking condition optimization was reduced by 57% and 22%, respectively, compared with those prepared before cooking condition optimization.

Validation and Evaluation of High-Resolution Orbitrap Mass Spectrometry on Molecular Characterization of Dissolved Organic Matter

Molecular composition of dissolved organic matter (DOM) is a hot topic in subjects such as environmental science and geochemistry. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been applied to molecular composition characterization of DOM successfully. However, high instrument and maintenance costs have constrained its wider application. A high-resolution Orbitrap mass spectrometer (Orbitrap MS) can provide approximately 500,000 resolving power (at m/z 200), which is potentially capable of characterizing the molecular composition of DOM. In this paper, the application of high-resolution Orbitrap MS was evaluated by comparing with FT-ICR MS in the aspect of resolution, mass distribution, detection dynamic range, and isotopic peak intensity ratio. The impact of instrument parameters of Orbitrap MS was further investigated, which includes ionization, ion transfer, and mass detection. The result shows that the high-resolution Orbitrap MS is capable or even preferable for molecular characterization of DOM. However, the peak intensity distributions are dependent on the instrument parameters, which could affect the environmental impact assessment caused by the sample itself. The result indicates that development of a universal and comparable method is of great demand.

Chemical Alterations of Dissolved Organic Matter by Permanganate Oxidation

Dissolved organic matter (DOM) is ubiquitous in raw drinking water and can efficiently scavenge oxidants, such as permanganate. Here, changes to DOM induced by permanganate oxidation under typical drinking water treatment conditions (6 μM, 1 h) to bulk DOM properties, DOM functional groups, and DOM chemical formulae were examined for two DOM isolate types (terrestrial and microbial). Permanganate oxidation did not mineralize DOM, rather changes were compositional in nature. Optical properties suggest that permanganate oxidation decreased DOM aromaticity (decreased SUVA-254), decreased DOM electron-donating capacity, and decreased DOM average molecular weight (increased E2/E3 ratios). Fourier-transform-infrared spectroscopy second derivative analyses revealed that permanganate does not oxidize DOM alkene groups, suggesting permanganate access to functional groups may be important. Four ionization techniques were used with ultrahigh-resolution mass spectrometry: negative and positive ion mode electrospray ionization and negative and positive ion mode laser/desorption ionization. The results from all four techniques were combined to understand changes in DOM chemical formulae. It was concluded that nitrogen-containing aromatic compounds and alkylbenzenes were oxidized by permanganate to form nitrogen-containing aliphatic compounds and benzoic acid-containing compounds. This work highlights how multiple ionization techniques coupled with UHR-MS can enable a more detailed characterization of DOM.

Characterization of Carbonyl Disinfection By-Products During Ozonation, Chlorination, and Chloramination of Dissolved Organic Matters

Carbonyl compounds are an important class of by-products that are generated in disinfection reactions. These chemicals are ingredients contributing to toxicology in the drinking water system, the compositions and structures of which are worthy of attention. In this study, a chemical derivatization method based on simultaneous light/heavy isotope labeling was established for general recognition of carbonyl compounds and carbonyl disinfection by-products (DBPs) as per the humic substance reference standard (Suwannee river fulvic acid II, SRFA) before and after ozonation, chlorination, and chloramination. Decomposition of macromolecular components into polar carbonyl species was observed to be the most prominent pathway in ozone treatment due to the efficient reactivity of ozone with phenols and alkoxy aromatic rings. As a result, alteration of molecular characteristics was noticed. For instance, ozone-induced carbonyl DBPs in the highly oxygenated compound classes (0.67 ≤ O/C ≤ 1.2, 0.6 < H/C ≤ 1.5) possessed higher O/C but contained less oxygen numbers and carbon numbers. Cl/Br-carbonyl-DBPs were identified after chlorination and chloramination, and I-carbonyl-DBPs were found in ozone and chloramine treatments. Several major halogenated carbonyl homologues were further recognized, including halogenated 4-oxobutenoic acid analogues, halogenated 2,5-dioxohex-3-enoic acid analogues, and halogenated 4-cyclopentene-1,3-diones analogues. These findings illustrate the presence of abundant carbonyl DBPs in water disinfection, and hence their impacts on human health deserve further investigation.

Nonhalogenated Aromatic DBPs in Drinking Water Chlorination: A Gap between NOM and Halogenated Aromatic DBPs

Halogenated disinfection byproducts (DBPs) are generated via reactions with natural organic matter (NOM) in chlorine disinfection of drinking water. How large NOM molecules are converted to halogenated aliphatic DBPs during chlorination remains a fascinating yet largely unresolved issue. Recently, many relatively toxic halogenated aromatic DBPs have been identified in chlorinated drinking waters, and they behave as intermediate DBPs to decompose to halogenated aliphatic DBPs. There is still one gap between NOM and halogenated aromatic DBPs. In this study, nine nonhalogenated aromatic compounds were identified as new intermediate DBPs in chlorination, including 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 3-formyl-4-hydroxybenzoic acid, salicylic acid, 5-formyl-2-hydroxybenzoic acid, 4-hydroxyphthalic acid, 4'-hydroxyacetophenone, 4-methylbenzoic acid, and 4-hydroxy-3-methylbenzaldehyde. These nonhalogenated aromatic DBPs formed quickly and reached the maximum levels at relatively low chlorine doses within a short contact time, and their formation pathways were proposed. The formation kinetics of three nonhalogenated aromatic DBPs and their corresponding monochloro-/dichloro-substitutes during chlorination were then modeled. The nonhalogenated aromatic DBPs contributed up to 84% of the formed monochloro-substitutes and 22% of the formed dichloro-substitutes, demonstrating that they somewhat acted as intermediates between NOM and halogenated aromatic DBPs. Furthermore, the formed nonhalogenated aromatic DBPs were found to be removed by >50% by granular activated carbon adsorption.

Molecular Characteristics of Dissolved Organic Nitrogen and Its Interaction with Microbial Communities in a Prechlorinated Raw Water Distribution System

Dissolved organic nitrogen (DON) represents a unique challenge in prechlorinated raw water distribution systems (PRWDSs) because of its contribution to the formation of harmful nitrogen-disinfection byproducts, influence upon biogeochemical processes, and unclear molecular characteristics. Here, Fourier transform ion cyclotron resonance mass spectrometry in combination with high-throughput sequencing was applied to elucidate the molecular changes of DON and biofilm microbial communities in a PRWDS in Yixing, China. Our study revealed that dynamic characteristics of DON are significantly correlated with the biofilm. The accumulation of refractory lignin-like compounds and C_nH_mO_pN₁ contributes to the higher recalcitrance molecular characteristics of DON in the effluent associated with Alphaproteobacteria, Planctomycetes, and Bacteroidetes. Additionally, with the help of prechlorination, the biofilm may change the DON characteristics and lead to higher oxygenation, higher m/z, and lower saturation during transportation. Despite the promotion of C_nH_mO_pN₁ and C_nH_mO_pN₃ at the early stage, we suggest that appropriate concentration of chlorine can add to the front end of raw water distribution pipes. Prechlorination may control the nitrification process and stabilize the rapid growth of diversity and concentration of low molecular weight DON, especially the refractory C_nH_mO_pN₁ in the effluent, which may help to improve treatment efficiency of drinking water treatment plants.

Freezing-Induced Bromate Reduction by Dissolved Organic Matter and the Formation of Organobromine Compounds

The freezing-induced acceleration of bromate reduction by humic substances (HS) contributes to HS bromination and the formation of organobromine compounds (OBCs). Herein, we report the enhanced reduction of bromate by dissolved organic matter and the formation of large amounts of OBCs in freezing solutions. After 48 h of freezing process, 78.1-100% of bromate was reduced by DOM at different initial concentrations of bromate and DOM in acidic solutions (pH 3 and 4). Bromide was one of the main reduction products, and it accounted for 30.9-47.8% of the total bromine content. Except for bromide, a large amount of OBCs formed by brominating DOM with reactive bromine species, like hypobromite, were detected. The conversion of bromate to OBCs, calculated as the total organobromine content to the initial bromate content, ranged from 28.2 to 52.5% and was mainly dependent on the bromate/DOM content. About 110-603 species of OBCs were detected by Fourier transform ion cyclotron resonance mass spectrometry, and they were primarily highly unsaturated and phenolic compounds. By analyzing the spectral variation before and after the freezing process, we found the disappearance of 900 compounds containing only C, H, and O with a low carbon oxidation state that was regarded as the main reductant of bromate. Our findings call for further investigation of the processes and the effects of bromate formation in aqueous environments.

Spatiotemporal variations of spectral characteristics of dissolved organic matter in river flowing into a key drinking water source in China

The characteristics of dissolved organic matter (DOM) in inflowing river, flowing into drinking water, have profound influences on the quality and safety of water. Here, ultraviolet-visible (UV-vis) spectroscopy and three-dimensional fluorescence (EEM) spectroscopy were combined to investigate the spatiotemporal variations of DOM in Nanfei River flowing into Chaohu Lake in China. 24 water samples and 24 surface sediments samples (including dry-to-wet transition season and wet season in 2018) were collected from different types of outlets. Parallel factor analysis (PARAFAC) model and correlation analysis were conducted to identify the primary sources of DOM. Two humic-like components (C1 235-250 nm/385-430 nm and C3 255-270 nm/455-510 nm) and one tryptophan-like component (C2 270-290 nm/320-350 nm) were effectively identified by PARAFAC model. The results showed DOM concentration presented significant spatiotemporal variations. The concentration was much lower in water than in surface sediments in dry-to-wet transition season, but higher in the wet season. Fluorescence index (FI), biological index (BIX) and humification index (HIX) were used to judge characteristic of DOM origination. These indexes indicated that, DOM in Nanfei River had both the characteristics of humus and autogenous, but neogene autogenic feature was stronger, which was largely due to mixture of water, resuspension and desorption of DOM in sediments and photochemical degradation. In addition, the characteristic parameter of molecular mass of DOM (the values of M) had an obvious linear relationship with the fluorescence intensity ratio of fulvic acid-like to humic acid-like (C1/C3), indicating that macromolecular substances could be removed by adding or improving membrane treatment. These provided technical support for improving quality and comprehensive treatment of drinking water sources.

Identification of novel disinfection byproducts in pool water: Chlorination of the algaecide benzalkonium chloride

The maintenance of public swimming pools requires numerous technological steps. One of the most important issues involves microbiological safety. Benzalkonium chloride (BAC) encompasses homologous alkylbenzyldimethylammonium chlorides with various alkyl chains, in particular C12 and C14, and is known as a popular algaecide for keeping water clean. In addition to BAC, NaOCl and UV-irradiation are also used to treat pool water as additional technological steps. Therefore, BAC itself can become a precursor of disinfection byproducts (DBPs). High-performance liquid chromatography - tandem mass spectrometry (HPLC-MS/MS), with accurate mass measurements, has allowed the discovery of several groups of DBPs that are related to BAC in public pool water in Arkhangelsk (Russia). These DBPs include numerous isomeric monochlorinated derivatives ([C₂₁H₃₇ClN]⁺ and [C₂₃H₄₁ClN]⁺), hydroxyl derivatives ([C₂₁H₃₈NO]⁺ and [C₂₃H₄₂NO]), carbonyl ([C₂₁H₃₆NO]⁺ and [C₂₃H₄₀NO]⁺), and dicarbonyl derivatives ([C₂₁H₃₄NO₂]⁺ and [C₂₃H₃₈NO₂]⁺). In addition, chlorinated alcohols, ketones and ketoalcohols of BAC were also detected, including [C₂₁H₃₅ClNO]⁺, [C₂₁H₃₇ClNO]⁺ and [C₂₁H₃₅ClNO₂]⁺ for BAC-12; and [C₂₃H₃₉ClNO]⁺, [C₂₃H₄₁ClNO]⁺ and [C₂₃H₃₉ClNO₂]⁺ for BAC-14. MS/MS allowed reliable elucidation of the structures of novel DBPs, proving that chlorination starts via radical substitution in the long aliphatic chains of BAC. UV-irradiation dramatically accelerates the reaction completely destroying the original compounds in less than an hour, while the array of the intermediate products remains the same as in the dark. The formation of other DBPs proceeds due to further reactions of these primary products. The concentrations of novel DBPs in pool water reach μg L^-1 levels. These conclusions were proved by conducting model reactions of BAC with NaOCl.

Identification, Formation, and Predicted Toxicity of Halogenated DBPs Derived from Tannic Acid and Its Biodegradation Products

Humic substances are commonly known disinfection byproduct (DBP) precursors. Tannic acid is one precursor of humic substances in organic degradation, and it occurs ubiquitously in both source water and wastewater. In this study, the biological degradation process was simulated under laboratory conditions, and the characteristics of DBP formation generated from the chlorination of tannic acid samples with different biodegradation times were explored. Twenty-six emerging halogenated DBPs were identified, and the formation pathways of the tannic acid-derived DBPs were tentatively proposed. Moreover, results demonstrated that the profile of the chlorinated DBP formation was significantly different from its brominated counterpart during biodegradation, and a general increasing trend of the ratio of TOBr/TOX or TII_PIS79/(TII_PIS79+TII_PIS35) as biodegradation time increasing was noticeable. The observed trend could be mainly ascribed to the reactive sites of tannic acid shifting from relatively fast to slow sites during biodegradation. In addition, the comparative toxicity of the detected DBPs derived from tannic acid was predicted by using two quantitative structure-activity relationship models established previously. On the basis of both the two toxicity metrics (involving developmental toxicity and growth inhibition potency), the predicted toxicity data indicated that the emerging DBP group trihalo-(di)hydroxycyclopentane-1,3-diones may possess extremely high toxic potencies.

Molecular characteristics of dissolved organic matter transformed by O3 and O3/H2O2 treatments and the effects on formation of unknown disinfection by-products

We investigated semiquantitative changes in almost 1000 dissolved organic matter (DOM) features during oxidation with 1 mg of O₃ per liter (mg O₃/L), 4 mg O₃/L, or 4 mg O₃/L + 2.5 mg of H₂O₂ per liter (advanced oxidation process, AOP) by unknown screening analysis with Orbitrap mass spectrometry. The consequential effects on formation of unknown disinfection by-products (DBPs) by chlorination were evaluated in laboratory-scale experiments. Several hundred unsaturated DOM features with positive oxygen-subtracted double bond equivalents per carbon ((DBE-O)/C) were decomposed by the ozone-only treatment and AOP. The AOP decomposed some saturated (negative (DBE-O)/C)) and reduced molecules, which had negative carbon oxidation states (C_os). Several hundred saturated oxidation by-products were detected after ozonation and the AOP. After chlorination, the samples pre-treated with ozone alone resulted in higher formation of unknown DBPs than the AOP pre-treated sample or the sample without oxidation. Over half of the DBP precursors, estimated by electrophilic substitution, were not totally decomposed by any oxidation process, but they were increased after the ozone-only process and AOP. DBP precursors produced by the ozone-only process or AOP formed unique unknown DBPs. Therefore, post-treatment processes after oxidation and before chlorination are important to minimize formation of unknown DBPs.

Formation of Brominated Organic Compounds and Molecular Transformations in Dissolved Organic Matter (DOM) after Ballast Water Treatment with Sodium Dichloroisocyanurate Dihydrate (DICD)

Estuarine water treated with a ballast water management system (BWMS) using a solution of dissolved dichloroisocyanurate dihydrate (DICD) resulted in the formation of newly described brominated disinfection byproducts (Br-DBPs). Analysis of dissolved organic matter (DOM) in untreated water with ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) identified 3897 m/z ions and their exact molecular formulas. After DICD treatment, a total of 213 halogenated molecular ions with relative abundance of at least 1% were assigned and confirmed using isotope simulation. Halogenated ions were assigned in four DBP elemental groups including CHOBr (180), CHONBr (13), CHOCl (16), and CHOBrCl (4). Forty-nine of the 197 brominated formulas have not been previously reported. We also were able to tentatively assign possible structures to the formula C₃HBr₃N₂ due to very limited isomeric possibilities. The tentatively assigned compound found at 6.4% relative abundance was identified as either tribromoimidazole or tribromopyrazole. Our results show the formation of complex halogenated DBPs that are formed in the treatment of water with a novel BWMS that employs granular DICD as a biocide. The toxicological and mutagenic properties as well as the fate of these newly identified brominated DBPs are unknown.

Transformation and fate of dissolved organic nitrogen in drinking water supply system: A full scale case study from Yixing, China

The transformation of dissolved organic nitrogen (DON) in the drinking water treatment plants could be closely associated with nitrogenous disinfection by-product (N-DBP) formation. In this study, we have assessed the molecular transformation of DON and its impact on N-DBP formation in a full scale drinking water treatment plant. Based on the result of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis, DON compounds with low molecular weight (<1 kDa) were classified as CHON, CHON₂ and CHON₃ according to the number of nitrogen atoms. Via the analytical window of van Krevelen diagrams, we found that the molecular structural features of CHON, CHON₂ and CHON₃ were not altered before the chlorination process. In detail, the CHON₂ and CHON₃ compositions were concentrated on the regions assigned to a lignin-structure while CHON compositions were also distributed in other compounds including proteins, carbohydrates and tannin. Furthermore, CHON formation was more difficult to be removed before the V-filter process. For N-DBP, chlorine-containing DON (Cl-DON) composition was likely to be removed through flocculation and sedimentation processes, whereas N-nitrosamine compounds were removed in V-filter and biological activated carbon filter processes. The health risks of aromatic structure N-nitrosamines due to the pre-chlorination of the raw water should be further studied.

Application of (LC/)MS/MS precursor ion scan for evaluating the occurrence, formation and control of polar halogenated DBPs in disinfected waters: A review

Water disinfection can result in the unintended formation of halogenated disinfection byproducts (DBPs), which have been the subject of intensive investigation over the past 40 years. Robust methods for evaluating and characterizing the formation of halogenated DBPs are prerequisites for ultimately controlling the formation of DBPs and ensuring quality and safe disinfected water. Only a fraction of the total organic halogen (TOX) formed during disinfection has been chemically identified or even well characterized by the classical (derivatization-)gas chromatography/mass spectrometry (GC/MS) method. Such a method may not be amenable to the detection of polar halogenated DBPs, which constitute a major portion of the TOX that is still unaccounted for. Accordingly, a novel precursor ion scan (PIS) method using (liquid chromatography/) electrospray ionization-triple quadrupole mass spectrometry was developed for the rapid selective detection of all polar halogenated DBPs-no matter whether the DBPs are known or unknown-in water. This article reviews recent literature on the application of the PIS method for evaluating the occurrence, formation and control of polar halogenated DBPs in disinfected waters. The challenges in developing the PIS method were briefly summarized. Application of the powerful method pinpointed >150 previously unknown DBPs and revealed the formation, speciation and transformation of halogenated DBPs in disinfected drinking water, wastewater effluents, and swimming pool water. For the same source water, positive correlations were found between the total ion intensity (TII) levels in the PIS spectra of m/z 35/79/126.9 and the total organic chlorine/bromine/iodine levels in the disinfected water sample, and a disinfected sample with a higher TII level generally showed a higher toxic potency. Accordingly, the TII value can be used as a surrogate to comparatively reflect the water quality and assess the efficiency of a DBP control approach. To achieve a more comprehensive and systematic understanding of the DBP compositions in different waters and thus better control the DBP formation and reduce their overall toxicity, topics for future work were discussed.

The chemodiversity of algal dissolved organic matter from lysed Microcystis aeruginosa cells and its ability to form disinfection by-products during chlorination

Algal-derived dissolved organic matter (ADOM) originating from lysed Microcystis aeruginosa cells was investigated as precursor material to form disinfection by-products upon disinfection with free chlorine. Non-targeted ultrahigh resolution 12 T negative mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed high molecular diversity in solid-phase extracted and ionizable components of Microcystis aeruginosa ADOM. The toxin microcystin LR was effectively degraded by free chlorine, which was expected. However, we found a high diversity of disinfection by-products associated with the addition of free chlorine to the water-soluble and solid-phase extractable fraction of ADOM and of double-bond moieties in abundant and known unsaturated fatty acids. Aromatic DOM precursors were absent from known metabolites of Microcystis aeruginosa and no evidence for aromatic disinfection by-products (DBPs) was found, despite N-containing compounds. A large diversification of N-containing molecular formulas was observed after chlorination, which seems indicative for the breakdown and oxidation of larger peptides. Additionally, a diverse group of N-compounds with presumed chloramine functional groups was observed. This study highlights the importance to evaluate ADOM and its ability to form different DBPs when compared to allochthonous or terrestrially-derived DOM.

Innovative drinking water treatment techniques reduce the disinfection-induced oxidative stress and genotoxic activity

Disinfection of drinking water using chlorine can lead to the formation of genotoxic by-products when chlorine reacts with natural organic matter (NOM). A vast number of such disinfection by-products (DBPs) have been identified, making it almost impossible to routinely monitor all DBPs with chemical analysis. In this study, a bioanalytical approach was used, measuring oxidative stress (Nrf2 activity), genotoxicity (micronucleus test), and aryl hydrocarbon receptor (AhR) activation to evaluate an innovative water treatment process, including suspended ion exchange, ozonation, in-line coagulation, ceramic microfiltration, and granular activated carbon. Chlorination was performed in laboratory scale after each step in the treatment process in order to investigate the effect of each treatment process to the formation of DBPs. Suspended ion exchange had a high capacity to remove dissolved organic carbon (DOC) and to decrease UV absorbance and Nrf2 activity in non-chlorinated water. High-dose chlorination (10 mg Cl₂ L^-1) of raw water caused a drastic induction of Nrf2 activity, which was decreased by 70% in water chlorinated after suspended ion exchange. Further reduction of Nrf2 activity following chlorination was achieved by ozonation and the concomitant treatment steps. The ozonation treatment resulted in decreased Nrf2 activity in spite of unchanged DOC levels. However, a strong correlation was found between UV absorbing compounds and Nrf2 activity, demonstrating that Nrf2 inducing DBPs were formed from pre-cursors of a specific NOM fraction, constituted of mainly aromatic compounds. Moreover, high-dose chlorination of raw water induced genotoxicity. In similarity to the DOC levels, UV absorbance and Nrf2 activity, the disinfection-induced genotoxicity was also reduced by each treatment step of the innovative water treatment technique. AhR activity was observed in the water produced by the conventional process and in the raw water, but the activity was clearly decreased by the ozonation step in the innovative water treatment process.

Fe(VI)-Mediated Single-Electron Coupling Processes for the Removal of Chlorophene: A Combined Experimental and Computational Study

Potassium ferrate [Fe(VI)] is a promising oxidant widely used in water treatment for the elimination of organic pollutants. In this work, the reaction kinetics, products, and mechanisms of the antimicrobial agent chlorophene (CP) undergoing Fe(VI) oxidation in aqueous solutions were investigated. CP is very readily degraded by Fe(VI), with the apparent second-order rate constant, k, being 423.2 M^-1 s^-1 at pH 8.0. A total of 22 oxidation products were identified using liquid chromatography-quadrupole time-of-flight-mass spectrometry , and their structures were further elucidated using tandem mass spectrometry. According to the extracted peak areas in mass spectra, the main reaction products were the coupling products (dimers, trimers, and tetramers) that formed via single-electron coupling. Theoretical calculations demonstrated that hydrogen abstraction should easily occur at the hydroxyl group to produce reactive CP· radicals for subsequent polymerization. Cleavage of the C-C bridge bond, electrophilic substitution, hydroxylation, ring opening, and decarboxylation were also observed during the Fe(VI) oxidation process. In addition, the degradation of CP by Fe(VI) was also effective in real waters, which provides a basis for potential applications.

Flux, Impact, and Fate of Halogenated Xenobiotic Compounds in the Gut

Humans and their associated microbiomes are exposed to numerous xenobiotics through drugs, dietary components, personal care products as well as environmental chemicals. Most of the reciprocal interactions between the microbiota and xenobiotics, such as halogenated compounds, occur within the human gut harboring diverse and dense microbial communities. Here, we provide an overview of the flux of halogenated compounds in the environment, and diverse exposure routes of human microbiota to these compounds. Subsequently, we review the impact of halogenated compounds in perturbing the structure and function of gut microbiota and host cells. In turn, cultivation-dependent and metagenomic surveys of dehalogenating genes revealed the potential of the gut microbiota to chemically alter halogenated xenobiotics and impact their fate. Finally, we provide an outlook for future research to draw attention and attract interest to study the bidirectional impact of halogenated and other xenobiotic compounds and the gut microbiota.

High Frequency Data Exposes Nonlinear Seasonal Controls on Dissolved Organic Matter in a Large Watershed

We analyzed a five year, high frequency time series generated by an in situ fluorescent dissolved organic matter (fDOM) sensor installed near the Connecticut River's mouth, investigating high temporal resolution DOM dynamics in a larger watershed and longer time series than previously addressed. We identified a gradient between large, saturating summer fDOM responses to discharge and linear, subdued responses during colder months. Seasonal response patterns were not consistent with multiple linear regression. Alternatively, we binned measurements across the yearly cycle using environmental indices, such as temperature, and applied moving regression, a novel approach which produced superior fits to calendar day binning. Spatially averaged watershed soil temperature at 10 cm was the best overall index of discharge-fDOM response. DOM fractionation showed fDOM was primarily a surrogate for hydrophobic organic acid (HPOA) concentrations. HPOAs were highly correlated with discharge, but hydrophilics (HPIs) were not. Discharge dependent DOM concentrations driven by the HPOA fraction may be controlled by soil temperature and water table position relative to organic and mineral soil horizons. HPI concentrations were correlated with average watershed soil temperature at 10 cm but were rather stationary throughout the year, further indicating a consistent groundwater source for this nonfluorescent DOM. We present a resolved subseasonal empirical model of DOM concentrations and fluxes, showing that riverine DOM flux and quality depend heavily on seasonal terrestrial carbon dynamics and hydrologic flow paths. High frequency monitoring reveals readily discernible patterns demonstrating that upland biogeochemical signals are maintained even at this large watershed scale.

Abiotic formation of organoiodine compounds by manganese dioxide induced iodination of dissolved organic matter

Iodination of dissolved organic matter (DOM) initiated by manganese oxide may represent an important source of organoiodine compounds (OICs) for iodide-containing waters. Here, Suwannee River natural organic matter was selected as model DOM, the OICs formation in simulated freshwater samples from iodinated DOM induced by manganese oxide (δ-MnO₂) was investigated at different pHs and concentrations of iodide and δ-MnO₂ by using negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS). While no OIC was observed in DOM control samples without δ-MnO₂, hundreds of OICs were detected in the presence of δ-MnO₂, suggesting the enhanced role of δ-MnO₂ played in DOM iodination. The relative abundance was defined as the value of dividing the peak intensity of OICs by the highest m/z peak intensity constantly occurred in each mass spectrum, and selected as a parameter for partly reflecting the real level of OICs. The relative abundance of most OICs were around or greater than 1%, and several OICs with higher relative abundance were identified as diiodo-5-hydroxy-4-cyclopentene-1,3-dione, diiodomethane and diiodoacetic acid. The numbers of the formed OICs increased with the increase concentrations of iodide/δ-MnO₂ and the decrease of pH, and nearly all OICs formed at lower levels of iodide/δ-MnO₂ and/or higher pH were overlapped by that at higher levels of iodide/δ-MnO₂ and/or lower pH, indicating the reliability of FT-ICR MS analysis techniques and data processing method. The OICs were formed mainly from the iodination of typical lignin-like and tannin-like compounds, as well as the precursor compounds with higher relative abundance through substitution reactions. Our findings demonstrate that the OICs formation by δ-MnO₂-initiated DOM iodination should receive more attention and the concentration, exact structure and toxicity of the OICs need to be further investigated.

Changes in Dissolved Organic Matter Composition and Disinfection Byproduct Precursors in Advanced Drinking Water Treatment Processes

Molecular changes in dissolved organic matter (DOM) from treatment processes at two drinking water treatment plants in Japan were investigated using unknown screening analysis by Orbitrap mass spectrometry. DOM formulas with carbon, hydrogen and oxygen (CHO-DOM) were the most abundant class in water samples, and over half of them were commonly found at both plants. Among the treatment processes, ozonation induced the most drastic changes to DOM. Mass peak intensities of less saturated CHO-DOM (positive (oxygen subtracted double bond equivalent per carbon (DBE-O)/C)) decreased by ozonation, while more saturated oxidation byproducts (negative (DBE-O)/C) increased and new oxidation byproducts (OBPs) were detected. By Kendrick mass analysis, ozone reactions preferred less saturated CHO-DOM in the same alkylation families and produced more saturated alkylation families of OBPs. Following ozonation, biological activated carbon filtration effectively removed <300 Da CHO-DOM, including OBPs. Following chlorination, over 50 chlorinated formulas of disinfection byproducts (DBPs) were found in chlorinated water samples where at least half were unknown. Putative precursors of these DBPs were determined based on electrophilic substitutions and addition reactions. Ozonation demonstrated better decomposition of addition reaction-type precursors than electrophilic substitution-type precursors; over half of both precursor types decreased during biological activated carbon filtration.

Optical properties and composition changes in chromophoric dissolved organic matter along trophic gradients: Implications for monitoring and assessing lake eutrophication

Chromophoric dissolved organic matter (CDOM) is an important optically active substance in aquatic environments and plays a key role in light attenuation and in the carbon, nitrogen and phosphorus biogeochemical cycles. Although the optical properties, abundance, sources, cycles, compositions and remote sensing estimations of CDOM have been widely reported in different aquatic environments, little is known about the optical properties and composition changes in CDOM along trophic gradients. Therefore, we collected 821 samples from 22 lakes along a trophic gradient (oligotrophic to eutrophic) in China from 2004 to 2015 and determined the CDOM spectral absorption and nutrient concentrations. The total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chla) concentrations and the Secchi disk depth (SDD) ranged from 0.02 to 24.75 mg/L, 0.002-3.471 mg/L, 0.03-882.66 μg/L, and 0.05-17.30 m, respectively. The trophic state index (TSI) ranged from 1.55 to 98.91 and covered different trophic states, from oligotrophic to hyper-eutrophic. The CDOM absorption coefficient at 254 nm (a(254)) ranged from 1.68 to 92.65 m^-1. Additionally, the CDOM sources and composition parameters, including the spectral slope and relative molecular size value, exhibited a substantial variability from the oligotrophic level to other trophic levels. The natural logarithm value of the CDOM absorption, lna(254), is highly linearly correlated with the TSI (r² = 0.92, p < .001, n = 821). Oligotrophic lakes are distinguished by a(254)<4 m^-1, and mesotrophic and eutrophic lakes are classified as 4 ≤ a(254)≤10 and a(254)>10 m^-1, respectively. The results suggested that the CDOM absorption coefficient a(254) might be a more sensitive single indicator of the trophic state than TN, TP, Chla and SDD. Therefore, we proposed a CDOM absorption coefficient and determined the threshold for defining the trophic state of a lake. Several advantages of measuring and estimating CDOM, including rapid experimental measurements, potential in situ optical sensor measurements and large-spatial-scale remote sensing estimations, make it superior to traditional TSI techniques for the rapid monitoring and assessment of lake trophic states.

Carbonaceous and nitrogenous disinfection byproduct precursor variation during the reversed anaerobic-anoxic-oxic process of a sewage treatment plant

Disinfection byproduct (DBP) precursors in wastewater during the reversed anaerobic-anoxic-oxic (A²/O) process, as well as their molecular weight (MW) and polarity-based fractions, were characterized with UV scanning, fluorescence excitation emission matrix, Fourier transform infrared and nuclear magnetic resonance spectroscopy. Their DBP formation potentials (DBPFPs) after chlorination were further tested. Results indicated that the reversed A²/O process could not only effectively remove the dissolved organic carbon (DOC) and dissolved total nitrogen in the wastewater, but also affect the MW distribution and hydrophilic-hydrophobic properties of dissolved organic matter (DOM). The accumulation of low MW and hydrophobic (HPO) DOM was possibly due to the formation of soluble microbial product-like (SMP-like) matters in the reversed A²/O treatment, especially in the anoxic and aerobic processes. Moreover, DOM in the wastewater displayed a high carbonaceous disinfection byproduct formation potential (C-DBPFP) in the fractions of MW>100kDa and MW<5kDa, and revealed an increasing tendency of nitrogenous disinfection byproduct formation potential (N-DBPFP) with decrease of MW. For polarity-based fractions, the HPO fraction of wastewater showed significantly higher C-DBPFP and N-DBPFP than hydrophilic and transphilic fractions. Therefore, although the reversed A²/O process could remove most DBP precursors by DOC reduction, it led to the enhancement of DBPFP with the formation and accumulation of low MW and HPO DOM. In addition, strong correlations between C-DBPFPs and SUVA, and between N-DBPFPs and DON/DOC, were observed in the wastewater, which might be helpful for DBPFP prediction in wastewater and reclaimed water chlorination.

Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: Multidisciplinary Challenges and Opportunities

While drinking water disinfection has effectively prevented waterborne diseases, an unintended consequence is the generation of disinfection byproducts (DBPs). Epidemiological studies have consistently observed an association between consumption of chlorinated drinking water with an increased risk of bladder cancer. Out of the >600 DBPs identified, regulations focus on a few classes, such as trihalomethanes (THMs), whose concentrations were hypothesized to correlate with the DBPs driving the toxicity of disinfected waters. However, the DBPs responsible for the bladder cancer association remain unclear. Utilities are switching away from a reliance on chlorination of pristine drinking water supplies to the application of new disinfectant combinations to waters impaired by wastewater effluents and algal blooms. In light of these changes in disinfection practice, this article discusses new approaches being taken by analytical chemists, engineers, toxicologists and epidemiologists to characterize the DBP classes driving disinfected water toxicity, and suggests that DBP exposure should be measured using other DBP classes in addition to THMs.

Molecular characterization of effluent organic matter in secondary effluent and reclaimed water: Comparison to natural organic matter in source water

Municipal wastewater reclamation is becoming of increasing importance in the world to solve the problem of water scarcity. A better understanding of the molecular composition of effluent organic matter (EfOM) in the treated effluents of municipal wastewater treatment plants (WWTPs) is crucial for ensuring the safety of water reuse. In this study, the molecular composition of EfOM in the secondary effluent of a WWTP in Beijing and the reclaimed water further treated with a coagulation-sedimentation-ozonation process were characterized using a non-target Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) method and compared to that of natural organic matter (NOM) in the local source water from a reservoir. It was found that the molecular composition of EfOM in the secondary effluent and reclaimed water was dominated by CHOS formulas, while NOM in the source water was dominated by CHO formulas. The CHO formulas of the three samples had similar origins. Anthropogenic surfactants were responsible for the CHOS formulas in EfOM of the secondary effluent and were not well removed by the coagulation-sedimentation-ozonation treatment process adopted.

Effect of ozonation on the characteristics of effluent organic matter fractions and subsequent associations with disinfection by-products formation

Ozonation could be used in advanced wastewater treatment plants to reduce the precursors of disinfection by-products (DBPs), or for disinfection and oxidation of trace organic compounds. Detailed analysis of effluent organic matter (EfOM) is intrinsic to the understanding of impact of ozonation on the characterization variation of EfOM, which is closely related with DBPs formation during subsequent chlorination. In this study, the raw as well as oxidized EfOM with ozone were fractionated into hydrophobic acids, neutrals and bases, and hydrophilic acids, neutrals and bases. Results indicated that ozonation increased the proportion of hydrophilic fractions in EfOM, especially of hydrophilic acids, which resulted in increased specific haloacetic acids formation potential (HAAFP) in the subsequent chlorination. Although ozonation decreased the total organic carbon and SUVA₂₅₄ of EfOM and most isolated fractions, further ozonation increased the SUVA of hydrophilic acids after the initial decrease. This was in accordance with the chemical structures analysis with FTIR, which showed the relative abundance of unsaturated structures such as CO bonds in hydrophilic fractions increased with further ozonation. Furthermore, specific trihalomethanes formation potential (THMFP) of each fraction decreased after initial pre-ozonation but increased with different extent with further ozonation. While for HAAs, pre-ozonation of hydrophilic acids significantly increased the dichloroacetic acid (DCAA) formation potential. In brief, EfOM containing a relatively high content of aromatic structures i.e. SUVA₂₅₄ and aliphatic structures yielded a remarkably high specific DBPFP. Further mineralization of organic fractions and specific increased formation of aliphatic CH structures by further ozonation caused the increased DBPFPs especially DCAAFP during subsequent chlorination.

Tracking changes in composition and amount of dissolved organic matter throughout drinking water treatment plants by comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry

Dissolved organic matter (DOM) can affect the performance of water treatment processes and produce undesirable disinfection by-products during disinfection. Several studies have been undertaken on the structural characterization of DOM, but its fate during drinking water treatment processes is still not fully understood. In this work, the nontargeted screening method of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC×GC-qMS) was used to reveal the detailed changes of different chemical classes of compounds in DOM during conventional and advanced drinking water treatment processes at three drinking water treatment plants in China. The results showed that when the dissolved organic carbon removal was low, shifts in the DOM composition could not be detected with the specific ultraviolet absorbance at 254nm, but the changes were clear in the three-dimensional fluorescence excitation-emission matrix or GC×GC-qMS analyses. Coagulation-sedimentation processes selectively removed 37-59% of the nitrogenous compounds, alcohols and aromatic hydrocarbons but increased the concentrations of halogen-containing compounds by 17-26% because of the contact time with chlorine in this step. Filtration was less efficient at removing DOM but preferentially removed 21-60% of the acids. However, other organic matter would be released from the filter (e.g., nitrogenous compounds, acids, and aromatic hydrocarbons). Biological activated carbon (BAC) treatment removed most of the compounds produced from ozonation, particularly ketones, alcohols, halogen-containing compounds and acids. However, it should be noted that certain highly polar or high molecular weight compounds not identified in this study might be released from the BAC bed. After the whole treatment processes, the concentrations of nitrogenous compounds, alcohols, alkenes, aromatic hydrocarbons and ketones were decreased more by the advanced treatment processes than by the conventional treatment processes. Alcohol and ketone removals were probably related to the reduction in protein-like materials. Alkane removal was probably related to the reduction in fulvic acid-like and humic acid-like materials.

Halogenated fatty amides - A brand new class of disinfection by-products

An array of similar halogenated nitrogen-containing compounds with elemental composition C_nH_2nNO₂X, C_nH_2n-2NO₂X and C_nH_2n-1NOX₂ (X = Cl, Br; n = 16, 18, 22) was detected in drinking water with high performance liquid chromatography - high resolution mass spectrometry (HPLC-HRMS) method. Compounds of this type were never mentioned among disinfection by-products. Tandem mass spectrometry allowed referring them to halohydrines or dihalogenated fatty amides, the products of conjugated electrophilic addition of halogens to the double bonds of unsaturated fatty amides. The proposed structures were confirmed by conducting aqueous chlorination with standard solution of oleamide. These compounds may be considered as a brand new class of disinfection by products, while their toxicities require special study.

Characterizing spatiotemporal variations of chromophoric dissolved organic matter in headwater catchment of a key drinking water source in China

Natural surface drinking water sources with the increasing chromophoric dissolved organic matter (CDOM) have profound influences on the aquatic environment and drinking water safety. Here, this study investigated the spatiotemporal variations of CDOM in Fengshuba Reservoir and its catchments in China. Twenty-four surface water samples, 45 water samples (including surface water, middle water, and bottom water), and 15 pore water samples were collected from rivers, reservoir, and sediment of the reservoir, respectively. Then, three fluorescent components, namely two humic-like components (C1 and C2) and a tryptophan-like component (C3), were identified from the excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) for all samples. For spatial distributions, the levels of CDOM and two humic-like components in the reservoir were significantly lower than those in the upstream rivers (p < 0.01), indicating that the reservoir may act as a reactor to partly reduce the levels of exogenous input including CDOM and humic-like matters from the surrounding catchment. For temporal variations, the mean levels of CDOM and three fluorescent components did not significantly change in rivers, suggesting that perennial anthropic activity maybe an important factor impacting the concentration and composition of river CDOM but not the precipitation and runoff. However, these mean values of CDOM for the bulk waters of the reservoir changed markedly along with seasonal variations, indicating that the hydrological processes in the reservoir could control the quality and quantity of CDOM. The different correlations between the fluorescent components and primary water parameters in the river, reservoir, and pore water samples further suggest that the reservoir is an important factor regulating the migration and transformation of FDOM along with the variations of different environmental gradients.

Formation of known and unknown disinfection by-products from natural organic matter fractions during chlorination, chloramination, and ozonation

Natural organic matter (NOM) is the main precursor of disinfection by-products (DBPs) formed during drinking water treatment processes. Previous studies of the relationships between DBP formation and NOM fractionation have mainly been focused on currently regulated DBPs and a few certain emerging DBPs. In this work, the Suwannee River NOM solution was fractionated into groups with different hydrophobicities using DAX-8 resins, and volatile and semi-volatile DBPs formed during the chlorination, chloramination and ozonation of the NOM fractions were examined by a nontargeted screening of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry procedure. The results showed that a total of 302 DBPs representing nine chemical classes were detected, of which 266 were possibly newly detected, based on library searching with NIST 08 library (using similarity and reverse values of at least 600 and 700, respectively) and linear retention indices. The characterization of DBP precursors suggests that hydrophobic (HPO) NOM contains the major fraction of precursor for the formation of nitrogenous DBPs (contributing about 60% of the total nitrogenous DBPs) during all three disinfection processes. Much larger amounts of heterocyclic DBPs were formed from the HPO fraction than from the hydrophilic fraction during chlorination. During chloramination and ozonation, 5-15 times more ketones were formed from the hydrophilic fraction than from the HPO fraction. During ozonation, more than twice the amounts of esters and alcohols were formed from the hydrophilic fraction than from the HPO fraction. Three-dimensional excitation-emission matrix spectra suggest that similar to the formation of regulated DBPs, humic acid-like substances are probably the precursors of halogen-containing DBPs. Relatively higher nitrogenous DBPs formation from the HPO fraction might be because of the existence of protein-like materials.

Probing and Comparing the Photobromination and Photoiodination of Dissolved Organic Matter by Using Ultra-High-Resolution Mass Spectrometry

Photochemical halogenation of dissolved organic matter (DOM) may represent an important abiotic process for the formation of natural organobromine compounds (OBCs) and natural organoiodine compounds (OICs) within surface waters. Here we report the enhanced formation of OBCs and OICs by photohalogenating DOM in freshwater and seawater, as well as the noticeable difference in the distribution and composition pattern of newly formed OBCs and OICs. By using negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry, various OBCs and OICs were identified during the photohalogenation processes in sunlit waters. The respective number of OBCs and OICs formed in artificial seawater (ASW) under light radiation was higher than that in artificial freshwater (AFW), suggesting a possible role of the mixed reactive halogen species. OBCs were formed mainly via substitution reactions and addition reactions accompanied by other reactions and distributed into three classes: unsaturated hydrocarbons with relatively low oxygen content, unsaturated aliphatic compounds, and saturated fatty acids and carbohydrates with relatively high hydrogen content. Unlike the OBCs, OICs were located primarily in the region of carboxylic-rich alicyclic molecules composed of esterified phenolic, carboxylated, and fused alicyclic structures and were generated mainly through electrophilic substitution of the aromatic proton. Our findings call for further investigation on the exact structure and toxicity of the OBCs and OICs generated in the natural environment.

Halogenated Organic Compounds Identified in Hydraulic Fracturing Wastewaters Using Ultrahigh Resolution Mass Spectrometry

Large volumes of water return to the surface following hydraulic fracturing of deep shale formations to retrieve oil and natural gas. Current understanding of the specific organic constituents in these hydraulic fracturing wastewaters is limited to hydrocarbons and a fraction of known chemical additives. In this study, we analyzed hydraulic fracturing wastewater samples using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) as a nontargeted technique to assign unambiguous molecular formulas to singly charged molecular ions. Halogenated molecular formulas were identified and confirmed using isotopic simulation and MS-MS fragmentation spectra. The abundance of halogenated organic compounds in flowback fluids rather than older wastewaters suggested that the observed molecular ions might have been related to hydraulic fracturing additives and related subsurface reactions, such as through the reaction of shale-extracted chloride, bromide, and iodide with strong oxidant additives (e.g., hypochlorite, persulfate, hydrogen peroxide) and subsequently with diverse dissolved organic matter. Some molecular ions matched the exact masses of known disinfection byproducts including diiodoacetic acid, dibromobenzoic acid, and diiodobenzoic acid. The identified halogenated organic compounds, particularly iodinated organic molecules, are absent from inland natural systems and these compounds could therefore play an important role as environmental tracers.

Linking the mobilization of dissolved organic matter in catchments and its removal in drinking water treatment to its molecular characteristics

Drinking water reservoirs in the Northern Hemisphere are largely affected by the decadal-long increase in riverine dissolved organic carbon (DOC) concentrations. The removal of DOC in drinking water treatment is costly and predictions are needed to link DOC removal efficiency to its mobilization in catchments, both of which are determined by the molecular composition. To study the effect of hydrological events and land use on the molecular characteristics of dissolved organic matter (DOM), 36 samples from three different catchment areas in the German low mountain ranges, with DOC concentrations ranging from 3 to 32 mg L^-1, were examined. Additionally, nine pairs of samples from downstream drinking water reservoirs were analyzed before and after flocculation. The molecular composition and the age of DOM were analyzed using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and radiocarbon (¹⁴C) analysis. At elevated discharge in a forested catchment comparatively younger, more oxygenated and unsaturated molecules of higher molecular weight were preferentially mobilized, likely linked to the reductive mobilization of iron. DOM with highly similar molecular characteristics (O/C ratio > 0.5, m/z > 500) could also be efficiently removed through flocculation in drinking water treatment. The proportion of DOM removed through flocculation ranged between 43% and 73% of DOC and was highest at elevated discharge. In catchment areas with a higher percentage of grassland and agriculture a higher proportion of DOM molecules containing sulfur and nitrogen was detected, which in turn could be less efficiently flocculated. Altogether, it was shown that DOM that is released during large hydrological events can be efficiently flocculated again, suggesting a reversal of similar chemical mechanisms in both processes. Since the occurrence of heavy rainfall events is predicted to increase in the future, event-driven mobilization of DOC may continue to challenge drinking water production.

Molecular Composition and Photochemical Reactivity of Size-Fractionated Dissolved Organic Matter

The photochemical production of reactive species, such as triplet dissolved organic matter (³DOM) and singlet oxygen (¹O₂), contributes to the degradation of aquatic contaminants and is related to an array of DOM structural characteristics, notably molecular weight. In order to relate DOM molecular weight, optical properties, and reactive species production, Suwannee River (SRFA) and Pony Lake fulvic acid (PLFA) isolates are fractionated by sequential ultrafiltration, and the resultant fractions are evaluated in terms of molecular composition and photochemical reactivity. UV-visible measurements of aromaticity increase with molecular weight in both fulvic acids, while PLFA molecular weight fractions are shown to be structurally similar by Fourier-transform ion cyclotron resonance mass spectrometry. In addition, Bray-Curtis dissimilarity analysis of formulas identified in the isolates and their size fractions reveal that SRFA and PLFA have distinct molecular compositions. Quantum yields of ³DOM, measured by electron and energy transfer probes, and ¹O₂ decreased with molecular weight. Decreasing [³DOM]_ss with molecular weight is shown to derive from elevated quenching in high molecular weight fractions, rather than increased ³DOM formation. This work has implications for the photochemistry of waters undergoing natural or engineered treatment processes that alter DOM molecular weight, such as photooxidation and biological degradation.

Photoconversion of Chlorinated Saline Wastewater DBPs in Receiving Seawater is Overall a Detoxification Process

Chlorine disinfection of wastewater effluents rich in bromide and iodide ions results in the formation of relatively toxic bromo- and iodo-disinfection byproducts (DBPs), especially highly toxic bromophenolic and iodophenolic DBPs, which could harm the marine ecosystem when they are discharged into receiving seawater along with the wastewater effluents. In this study, we investigated the conversion of three individual halophenolic DBPs (5-bromosalicylic acid, 2,5-dibromohydroquinone, and 2,4,6-triiodophenol) and two chlorinated saline wastewater DBP mixtures in seawater. The conversion products were analyzed with ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, and the conversion of overall halo-DBPs in the wastewater DBP mixtures was monitored by measuring total organic halogen. The photoconversion-induced variations in the toxicity were evaluated using the embryos of a marine polychaete. Halophenolic DBPs were found to undergo photoconversion in seawater. The conversion was triggered by photonucleophilic substitution: bromophenolic and iodophenolic DBPs were converted to their chlorophenolic or hydroxyphenolic analogues, via substituting the bromine and iodine atoms with chloride or hydroxide ions in seawater; chlorophenolic DBPs were converted to their hydroxyphenolic analogues, via substituting the chlorine atoms with hydroxide ions in seawater. The hydroxyphenolic analogues thus formed further decomposed and finally cleaved to aliphatic compounds. The photoconversion of chlorinated saline wastewater DBPs in receiving seawater was overall a dehalogenation and detoxification process.

Molecular characterization of low molecular weight dissolved organic matter in water reclamation processes using Orbitrap mass spectrometry

Reclaimed water has recently become an important water source for urban use, but the composition of dissolved organic matter (DOM) in reclaimed water has rarely been characterized at the compound level because of its complexity. In this study, the transformation and changes in composition of low molecular weight DOM in water reclamation processes, where secondary effluent of the municipal wastewater treatment plant was further treated by biofiltration, ozonation and chlorination, were investigated by "unknown" screening analysis using Orbitrap mass spectrometry (Orbitrap MS). The intense ions were detected over an m/z range from 100 to 450. In total, 2412 formulae with various heteroatoms were assigned, and formulae with carbon (C), hydrogen (H) and oxygen (O) only and C, H, O and sulfur (S) were the most abundant species. During biofiltration, CHO-only compounds with relatively high hydrogen to carbon (H/C) ratio or with saturated structure were preferentially removed, while CHOS compounds were mostly removed. Ozonation induced the greatest changes in DOM composition. CHOS compounds were mostly decreased after ozonation while ozone selectively removed CHO compounds with relatively unsaturated structure and produced compounds that were more saturated and with a higher degree of oxidation. After chlorination, 168 chlorine-containing formulae, chlorinated disinfection by-products (DBPs), were additionally detected. Candidate DBP precursors were determined by tracking chlorinated DBPs formed via electrophilic substitution, half of which were generated during the ozonation.