Nontargeted identification of chlorinated disinfection byproducts formed from natural organic matter using Orbitrap mass spectrometry and a halogen extraction code

Database and review of disinfection by-products since 1974: Constituent elements, molecular weights, and structures

Since trihalomethanes were discovered in 1974, disinfection by-products (DBPs) in drinking water have attracted extensive attention. In 2011, more than 600 known DBPs were compiled; however, newly reported DBPs have not been integrated. The rapid development of mass spectrometry has led to a significant increase in the number of DBPs, therefore, there is a need to develop a database of all DBPs and their properties. Herein, a database including 6310 DBPs (651 confirmed, 1478 identified and 4142 proposed) reported between 1974 and 2022 was constructed and made available for public use at https://dbps.com.cn/main. This database can be a tool in screening new DBPs, comprehensively reviewing, and developing predictive models. In this paper, to demonstrate the functions of the database and provide useful information for this area, the origin of the collected DBPs was presented, and some basic information, including elemental composition, molecular weight, functional groups, and carbon frameworks, were comparatively analyzed. The results showed that the proportion of DBPs verified by standard compounds and frequently detected in real water is less than 7.0%, and most of DBPs remained to be identified. Approximately 88% of DBPs contain halogens, and brominated -DBPs occupied a similar ratio to chlorinated -DBPs in real water. Acids were the main functional groups of DBPs, aliphatic and aromatic compounds are the two major carbon frameworks, and the molecular weights of most DBPs ranged from 200 to 400 Da. In addition, 4142 proposed DBPs as obtained using high-resolution mass spectrometry, were characterized based on the modified van Krevelen diagram and adjusted indexes with halogens. Most of the proposed DBPs featured lignin and tannin structures, and phenolic/highly unsaturated DBPs account for the majority.

Recent progress in identification of water disinfection byproducts and opportunities for future research

Numerous disinfection by-products (DBPs) are formed from reactions between disinfectants and organic/inorganic matter during water disinfection. More than seven hundred DBPs that have been identified in disinfected water, only a fraction of which are regulated by drinking water guidelines, including trihalomethanes, haloacetic acids, bromate, and chlorite. Toxicity assessments have demonstrated that the identified DBPs cannot fully explain the overall toxicity of disinfected water; therefore, the identification of unknown DBPs is an important prerequisite to obtain insights for understanding the adverse effects of drinking water disinfection. Herein, we review the progress in identification of unknown DBPs in the recent five years with classifications of halogenated or nonhalogenated, aliphatic or aromatic, followed by specific halogen groups. The concentration and toxicity data of newly identified DBPs are also included. According to the current advances and existing shortcomings, we envisioned future perspectives in this field.

Characteristics in dissolved organic matter and disinfection by-product formation during advanced treatment processes of municipal secondary effluent with Orbitrap mass spectrometry

Dissolved organic matter (DOM) is reported to be a precursor to disinfection by-products (DBPs), which have adverse effects on human health. Therefore, it is crucial to effectively remove DOM before water disinfection. Characteristics of DOM and DBPs formation during advanced treatment processes including coagulation, adsorption, ultraviolet (UV) irradiation, and ozone (O3) oxidation in municipal secondary effluent were investigated in this research. DOM was characterized by Fourier transform infrared spectroscopy (FTIR), excitation-emission matrix fluorescence spectroscopy (EEM), and Orbitrap mass spectrometry (Orbitrap MS). Moreover, DBPs formation potential under different advanced treatment processes was also discussed. FTIR results indicated that various functional groups existing in DOM may react with the disinfectant to form toxic DBPs. EEM analysis indicated that DOM in all water samples was dominated by soluble microbial product-like (SMPs) and humic acid-like (HA) substances. The municipal secondary effluent was abundant with DOM and rich in carbon, hydrogen, oxygen, and nitrogen atoms, contained a certain dosage of phosphorus and sulfur atoms, and the highest proportion is lignin. Most of the precursors (CHO features) had positive double bond equivalent subtracted oxygen per carbon [(DBE-O)/C] and negative carbon oxidation state (Cos) in all four different advanced treatment processes. DBPs formation potential (DBPFP) of coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes were 487 μg L-1, 586 μg L-1, 597 μg L-1, and 308 μg L-1, respectively. And the DBPs precursors removal efficiency of coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes were 50.8%, 40.8%, 39.8%, and 69.0%, respectively. This study provides in-depth insights into the changes of DOM in municipal secondary effluent at the molecular level and the removal efficiency of DBPs precursors during coagulation, adsorption, UV irradiation, and O3 oxidation advanced treatment processes.

Transformation of dissolved organic matter at a full-scale petrochemical wastewater treatment plant

Transformation of dissolved organic matter (DOM) in petrochemical wastewater (PCW) treatment has rarely been studied. In this work, low- and high-salinity PCW were collected from a treatment plant and the transformations of DOM at molecular level along the treatment processes of both PCW were comparatively investigated. By using Orbitrap MS, the polar DOM constituents were categorized into five molecular classes namely saturated compounds, aliphatics, highly unsaturated and phenolic compounds (Huph), polyphenols and condensed polycyclic aromatics (Cpla). Aliphatics (58.62%) with low molecular weight (150-250 Da) and O/C (0-0.2) were dominant in raw low-salinity PCW; while Huph (65.03%) with O/C at 0.2-0.8 were rich in raw high-salinity PCW. After full-scale treatment, differentiated DOM constituents in both raw PCWs were transformed into aliphatics and Huph with O/C at 0.3-0.5. Anoxic/Oxic treatment of low-salinity system (L-A/O) removed a high fraction of aliphatics (53.05%); while Huph with low O/C (0.1-0.3) (65.68%) in the effluent of L-A/O were further mineralized by ozonation of low-salinity system (L-ozonation). In comparison, anoxic/oxic treatment of high-salinity system (H-A/O) mainly removed unsaturated Huph (34.10%) and aliphatics (30.86%). This resulted in a decrease of dissolved organic carbon as indicated via Spearman correlation. Different from L-ozonation, ozonation of high-salinity system (H-ozonation) degraded aliphatics (26.09%) and Huph (41.85%) with a relatively high O/C (0.2-1.2). After L-A/O and L-ozonation treatments, remaining saturated compounds that were originated from raw low-salinity PCW, were removed by subsequent biological aerated filter. Comparatively, after H-A/O and H-ozonation treatments, residual Huph and aliphatics which were mainly bio-derivates and ozonated intermediates, were further removed by air flotation filter. Hence, DOM transformation of different PCWs along similar treatments varied significantly. This study provides in-depth insights on DOM transformation along a full-scale PCW treatment process.

Transformation of Graphitic Carbon Nitride by Reactive Chlorine Species: "Weak" Oxidants Are the Main Players

Graphitic carbon nitride (g-C₃N₄) nanomaterials hold great promise in diverse applications; however, their stability in engineering systems and transformation in nature are largely underexplored. We evaluated the stability, aging, and environmental impact of g-C₃N₄ nanosheets under the attack of free chlorine and reactive chlorine species (RCS), a widely used oxidant/disinfectant and a class of ubiquitous radical species, respectively. g-C₃N₄ nanosheets were slowly oxidized by free chlorine even at a high concentration of 200-1200 mg L^-1, but they decomposed rapidly when ClO· and/or Cl₂^•- were the key oxidants. Though Cl₂^•- and ClO· are considered weaker oxidants in previous studies due to their lower reduction potentials and slower reaction kinetics than ·OH and Cl·, our study highlighted that their electrophilic attack efficacy on g-C₃N₄ nanosheets was on par with ·OH and much higher than Cl·. A trace level of covalently bonded Cl (0.28-0.55 at%) was introduced to g-C₃N₄ nanosheets after free chlorine and RCS oxidation. Our study elucidates the environmental fate and transformation of g-C₃N₄ nanosheets, particularly under the oxidation of chlorine-containing species, and it also provides guidelines for designing reactive, robust, and safe nanomaterials for engineering applications.

Critical assessment of the Kendrick mass defect analysis as an innovative approach to process high resolution mass spectrometry data for environmental applications

The growing application of high resolution mass spectrometry (HRMS) over the last decades has dramatically improved our knowledge about the occurrence of environmental contaminants. However, most of the compounds detected remain unknown and the large volume of data generated requires specific processing approaches. Therefore, this study presents the concepts of mass defect (MD), Kendrick mass (KM) and Kendrick mass defect (KMD) to the expert and non-expert reader along with relevant examples of applications in environmental HRMS data processing. A preliminary bibliometric overview indicates that the potential benefits of KMD analysis are rather overlooked in environmental science. In practice, a simple calculation allows transforming a mass from the IUPAC system (normalized so that the mass of ¹²C is exactly 12) to its corresponding KM normalized on a specific moiety such as CH₂ (the mass of CH₂ is exactly 14). Then, plotting the KMD according to the nominal KM allows revealing groups of compounds that differ only by their number of CH₂ moieties. For instance, data processing using KM and KMD was proven particularly useful to characterize natural organic matter in a sample, to reveal the occurrence of polymers as well as poly/perfluorinated alkylated substances (PFASs), and to search for transformation products (TPs) of a given chemical.

First Discovery of Iodinated Polyfluoroalkyl Acids by Nontarget Mass-Spectrometric Analysis and Iodine-Specific Screening Algorithm

Per- and polyfluoroalkyl acids (PFAAs) including polyfluoroalkyl carboxylic acids and polyfluoroalkyl sulfonic acids are a large category of crucial environmental pollutants of global concern. Besides known PFAAs, numerous unknown species may exist in the environment, urgently needing discovery and characterization. This study implemented nontarget analysis for a group of novel PFAA pollutants, viz., iodinated PFAAs (I-PFAAs) in wastewater from a fluorochemical manufacturing park by liquid chromatography-high-resolution mass spectrometry in combination with an iodine-specific data-processing algorithm. The algorithm took into account the diagnostic fragment iodine ion (I-) together with carbon and sulfur isotopologue distributions. In total, 18 I-PFAA formulas involving 21 congeners were identified. Semiquantification was conducted, and the total concentrations of I-PFAAs were 1.9-274.7 μg/L, indicating severe pollution of I-PFAAs in the wastewater. The determined concentrations along with predicted environmental behaviors and toxicities demonstrate that I-PFAAs merit further in-depth investigation. The analytical method including the instrumental analysis and data-processing algorithm can be extended to screening and identification of I-PFAAs in other matrices. Furthermore, the analysis results for the first time provide recognition on the occurrence, distribution features, and pollution status of I-PFAAs in the environment.

Non targeted screening of nitrogen containing disinfection by-products in formation potential tests of river water and subsequent monitoring in tap water samples

The generation of disinfection by-products during water chlorination is a major concern in water treatment, given the potential health risks that these substances may pose. In particular, nitrogen-containing DBPs are believed to have greater toxicological significance than carbon-based DBPs. Hence, high performance liquid chromatography coupled to high-resolution mass spectrometry (HPLC-HRMS) in positive mode was employed to identify new non-volatile nitrogen containing disinfection by-products (DBPs) and to assess their presence in potable water. Nine water samples were taken in the Llobregat river, in the context of a water reuse trial, near the catchment of a drinking water treatment plant (DWTP) in 2019. River samples were disinfected with chlorine under controlled formation potential tests conditions and analysed with a non-target approach. The peak lists of raw and chlorinated samples were compared exhaustively, resulting in an extensive list of 495 DBPs that include bromine and/or chlorine atoms. 172 of these species were found frequently, in three or more chlorinated samples. The empirical formulae of these DBPs were unambiguously annotated on the basis of accurate m/z measurements, isotopic patterns and common heuristic rules. Most of the annotated species (310) contained bromide, which is consistent with the relatively high bromide content of the Llobregat basin (>0.3 mg/l). Drinking water samples were taken at the outlet of the DWTP during the same sampling period. According to their analysis, a large portion of the DBPs detected after the formation potential tests do not reach real-life drinking water, which suggests that the treatment train successfully removes a significant fraction of DBP precursors. However, 131 DBPs could still be detected in the final product water. A larger sampling was carried in the Barcelona water distribution network, during six consecutive weeks, and it revealed the presence of 78 halogenated DBPs in end-consumer water, most of which were nitrogen-containing. MS/MS fragmentation and retention times were employed to tentatively suggest molecular structure for these recalcitrant DBPs.

Underlying mechanisms of promoted formation of haloacetic acids disinfection byproducts after indometacin degradation by non-thermal discharge plasma

Indometacin (IDM), as a kind of non-steroidal anti-inflammatory drugs, has ecological and health risks, which is the potential precursor of chlorination disinfection byproducts (DBPs). Non-thermal discharge plasma was attempted to eliminate IDM and control subsequent DBPs formation. Satisfactory removal performance for IDM was realized by the plasma oxidation; almost 100% of IDM was removed within 2 min. Relatively greater removal efficiency was gained at a higher plasma voltage and a lower pH level. Electron paramagnetic resonance spectrometer revealed that reactive species ·OH, O₂·^-, and ¹O₂ were responsible for IDM decomposition. Based on analyses of Fourier transform infrared spectroscopy, two-dimensional correlation spectroscopy, three-dimensional fluorescence spectrum, and gas chromatography-mass spectrometer, attacks of reactive species resulted in sequence breakages in functional groups of IDM, leading to production of small molecular alcohols, acids, and amines. Possible decomposition pathways of IDM were proposed. The produced acetamide and 1H-indol-5-ol were important precursors of DBPs. Formation and toxicity of nitrogen-containing DBPs were dramatically inhibited after IDM degradation; however, those of haloacetic acids were strengthened. The relevant roadmaps among DBPs and degradation intermediates were figured out. This study revealed the underlying mechanisms of IDM degradation by discharge plasma and its potential risks in chlorination disinfection.

Effects of chlorine dose on the composition and characteristics of chlorinated disinfection byproducts in reclaimed water

During chlorination of reclaimed water, the dose of chlorine used can influence the formation of chlorinated disinfection by-products (Cl-DBPs). We used non-targeted screening by Orbitrap mass spectrometry to identify Cl-DBPs in samples of chlorinated reclaimed water, and found that chlorination was likely to form slightly oxidized unsaturated aliphatic compounds and polycyclic aromatic compounds. Increasing the chlorine dose increased the proportion of polycyclic aromatic Cl-DBPs containing one chlorine atom (Cl₁-DBPs) and highly oxidized unsaturated aliphatic Cl-DBPs containing two chlorine atoms (Cl₂-DBPs). In addition, increasing the chlorine dose first decreased and then increased the proportion of Cl₁-DBPs with aromatic index values >0.5 and increased the proportion of Cl₂-DBPs with aromatic index values <0.5. Increasing the chlorine dose increased double bond equivalent minus oxygen values of Cl₁-DBPs and decreased the double bond equivalent minus oxygen values of Cl₂-DBPs, while the nominal oxidant state of carbon decreased for Cl₁-DBPs and increased for Cl₂-DBPs. In considering the possible precursors of Cl-DBPs and their reaction pathways, substitution reactions occurred more readily with aliphatic compounds and addition reactions occurred more readily with aromatic precursors. When the chlorine dose is increased, more Cl₂-DBPs may be formed by substitution. Overall, the chlorine dose influences Cl-DBP formation and composition and should be taken into account during water treatment.

Novel chlorinated disinfection byproducts from tannic acid: nontargeted identification, formation pathways, and computationally predicted toxicity

Tannic acid is ubiquitously present in various simulated and real water sources and in wastewater. Various chlorinated disinfection byproducts (Cl-DBPs) are generated via reactions with tannic acid during disinfection with chlorine. We used high-resolution mass spectrometry in combination with our self-developed halogen extraction code to selectively identify Cl-DBPs. Our strategy enabled successful detection of 35 Cl-DBP formulas formed by chlorination of tannic acid, and we identified 26 of these structures. The structures of 17 novel Cl-DBPs are firstly reported here. The reaction pathways of these Cl-DBPs were tentatively proposed. These Cl-DBPs are likely to be generated during chlorination at various chlorine doses, from 0.0 to 10.0 mg-Cl₂/L, and 14 of the 26 Cl-DBPs were detected in simulated drinking water, which implies a relatively high probability of incidence. Quantitative structure-activity relationship toxicity analyses predicted that most of these Cl-DBPs would exhibit much higher acute toxicity than the common DBPs trichloromethane and monochloroacetic acid and that some of these compounds would induce developmental toxicity and be mutagenic, which further emphasizes that these Cl-DBPs should raise concerns. This study broadens our understanding of the Cl-DBPs formed from tannic acid and should prompt wider application of our analytical strategy in environmental matrices.

Combining high resolution mass spectrometry with a halogen extraction code to characterize and identify brominated disinfection byproducts formed during ozonation

Ozonation is widely used during water treatment but can generate a variety of toxic disinfection byproducts, especially in the presence of bromide. In the present study, our halogen extraction code was extended and modified to identify bromine isotopic patterns and combined with the R package MFAssignR in selectively identifying brominated disinfection byproducts (Br-DBPs) from high resolution mass spectra. In total, 127 Br-DBPs formed from a Suwannee River natural organic matter (SRNOM) solution were successfully detected from tens of thousands of mass spectrometry peaks. Kendrick mass defect analysis and structural characterization identified 17 structures, 15 of which were identified as brominated carboxylic acids and firstly reported here. Computational model predictions indicated that these brominated carboxylic acids may possess high toxic potencies and raise valid concerns. The adapted halogen extraction code described in this study is a powerful tool for a wider application of analyzing Br-DBPs in complex water matrices and provides an effective technique to characterize and identify these compounds in future studies.