Unraveling the chemodiversity of halogenated disinfection by-products formed during drinking water treatment using target and non-target screening tools

Chemodiversity in freshwater health

Dissolved organic matter may offer a way to track and restore the health of fresh waters.

Integrating different tools and technologies to advance drinking water quality exposure assessments

Contaminants in drinking water are a major contributor to the human exposome and adverse health effects. Assessing drinking water exposure accurately in health studies is challenging, as several of the following study design domains should be addressed as adequately as possible. In this paper, we identify the domains Time, Space, Data Quality, Data Accessibility, economic considerations of Study Size, and Complex Mixtures. We present case studies for three approaches or technologies that address these domains differently in the context of exposure assessment of drinking water quality: regulated contaminants in monitoring databases, high-resolution mass spectrometry (HRMS)-based wide-scope chemical analysis, and effect-based bioassay methods. While none of these approaches address all the domains sufficiently, together they have the potential to carry out exposure assessments that would complement each other and could advance the state-of-science towards more accurate risk analysis. The aim of our study is to give researchers investigating health effects of drinking water quality the impetus to consider how their exposure assessments relate to the above-mentioned domains and whether it would be worthwhile to integrate the advanced technologies presented into planned risk analyses. We highly suggest this three-pronged approach should be further evaluated in health risk analyses, especially epidemiological studies concerning contaminants in drinking water. The state of the knowledge regarding potential benefits of these technologies, especially when applied in tandem, provides more than sufficient evidence to support future research to determine the implications of combining the approaches described in our case studies in terms of protection of public health.

Effect-Directed Analysis Combined with Nontarget Screening to Identify Unmonitored Toxic Substances in the Environment

Effect-directed analysis (EDA) combined with nontarget screening (NTS) has established a valuable tool for the identification of unmonitored toxic substances in environmental samples. It consists of three main steps: (1) highly potent fraction identification, (2) toxicant candidate selection, and (3) major toxicant identification. Here, we discuss the methodology, current status, limitations, and future challenges of EDA combined with NTS. This method has been applied successfully to various environmental samples, such as sediments, wastewater treatment plant effluents, and biota. We present several case studies and highlight key results. EDA has undergone significant technological advancements in the past 20 years, with the establishment of its key components: target chemical analysis, bioassays, fractionation, NTS, and data processing. However, it has not been incorporated widely into environmental monitoring programs. We provide suggestions for the application of EDA combined with NTS in environmental monitoring programs and management, with the identification of further research needs.

Nontarget Analysis and Comprehensive Characterization of Iodinated Polyfluoroalkyl Acids in Wastewater and River Water by LC-HRMS with Cascade Precursor-Ion Exclusions and Algorithmic Approach

Poly- and perfluoroalkyl acids (PFAAs) are a large family of widespread contaminants of worldwide concern and well-known as "forever chemicals". Direct emission of PFAAs from the fluorochemical industry is a crucial source of PFAA pollutants in the environment. This study implemented nontarget analysis and comprehensive characterization for a category of new PFAA contaminants, i.e., iodinated PFAAs (IPFAAs), in fluorochemical industry wastewater and relevant contaminated river water by liquid chromatography-high-resolution mass spectrometry with a cascade precursor ion exclusion (PIE) strategy and in-house developed data extraction and processing algorithms. A total of 26 IPFAAs (including 2 isomers of an IPFAA) were found and identified with tentative molecular structures. Semiquantification of the IPFAAs was implemented, and the total concentrations of IPFAAs were 0.16-285.52 and 0.15-0.17 μg/L in wastewater and river water, respectively. The high concentrations in association with the predicted ecotoxicities and environmental behaviors demonstrate that these IPFAAs are worthy of more concern and further in-depth research. The cascade PIE strategy along with the data extraction and processing algorithms can be extended to nontarget analysis for other pollutants beyond IPFAAs. The nontarget identification and characterization outcomes provide new understanding on the environmental occurrence and pollution status of IPFAAs from a comprehensive perspective.

Characterization of halogenated organic compounds by the Fourier transform ion cyclotron resonance mass spectrometry: A critical review

Halogenated organic compounds (HOCs), widely present in various environments, are generally formed by natural processes (e.g., photochemical halogenation) and anthropogenic activities (e.g., water disinfection and anthropogenic discharge of HOCs), posing health and environmental risks. Therefore, in-depth knowledge of the molecular composition, transformation, and fate of HOCs is crucial to regulate and reduce their formation. Because of the extremely complex nature of HOCs and their precursors, the molecular composition of HOCs remains largely unknown. The Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers the most powerful resolution and mass accuracy for the simultaneous molecular-level characterization of HOCs and their precursors. However, there is still a paucity of reviews regarding the comprehensive characterization of HOCs by FT-ICR MS. Based on the FT-ICR MS, the formation mechanism, sample pretreatment, and analysis methods were summarized for two typical HOCs classes, namely halogenated disinfection byproducts and per- and polyfluoroalkyl substances in this review. Moreover, we have highlighted data analysis methods and some typical applications of HOCs using FT-ICR MS and proposed suggestions for current issues. This review will deepen our understanding of the chemical characterization of HOCs and their formation mechanisms and transformation at the molecular level in aquatic systems, facilitating the application of the state-of-the-art FT-ICR MS in environmental and geochemical research.

Nontarget Insights into the Fate of Cl-/Br-Containing DOM in Leachate during Membrane Treatment

Halogenated organic compounds in wastewater are persistent and bioaccumulative contaminants of great concern, but few are known at the molecular level. Herein, we focus on nontarget screening of halogenated dissolved organic matter (DOM) in highly concentrated organic matrices of waste leachates and their concentrates. Solid-phase extraction (SPE) was optimized before capturing halogenated signatures via HaloSeeker 2.0 software on mining full-scan high-resolution mass spectrometry (HRMS) fingerprints. This study identified 438 Cl-/Br-containing DOM formulas in 21 leachates and membrane concentrates. Among them, 334 formulas were achieved via SPE with mixed-sorbent cartridges (mixed-SPE), surpassing the 164 formulas achieved through Bond Elut PPL cartridges (PPL-SPE). Herein, only four samples identified via PPL-SPE exhibited a resolution of >50% for extracted Cl-/Br-containing DOM by either SPE. The halogenated DOM constituted 6.87% of the total DOM mass features. Nevertheless, more abundant adsorbable organic halogens deciphered waste leachates and highly concentrated waste streams as reservoirs for halogenated contaminants. Remarkably, 75.7-98.1% of Cl-/Br-containing DOM in primary membrane concentrates remained stable through the secondary membrane treatment, indicating the persistence of these unknown contaminants even post-treatment.

Genotoxicity and endocrine disruption potential of haloacetic acids in human placental and lung cells

Chlorination of water results in the formation of haloacetic acids (HAAs) as major disinfection byproducts (DBPs). Previous studies have reported some HAAs species to act as cytotoxic, genotoxic, and carcinogenic. This work aimed at further exploring the toxicity potential of the most investigated HAAs (chloroacetic (CAA), bromoacetic (BAA), iodoacetic (IAA) acid) and HAAs species with high content of bromine (tribromoacetic acid (TBAA)), and iodine in their structures (chloroiodoacetic (CIAA) and diiodoacetic acid (DIAA)) to human cells. Novel knowledge was generated regarding cytotoxicity, oxidative stress, endocrine disrupting potential, and genotoxicity of these HAAs by using human placental and lung cells as in vitro models, not previously used for DBP assessment. IAA showed the highest cytotoxicity (EC₅₀: 7.5 μM) and ability to generate ROS (up to 3-fold) in placental cells, followed by BAA (EC₅₀: 20-25 μM and 2.1-fold). TBAA, CAA, DIAA, and CIAA showed no significant cytotoxicity (EC₅₀ > 250 μM). All tested HAAs decreased the expression of the steroidogenic gene hsd17b1 up to 40 % in placental cells, and IAA and BAA (0.01-1 μM) slightly inhibited the aromatase activity. HAAs also induced the formation of micronuclei in A549 lung cells after 48 h of exposure. IAA and BAA showed a non-significant increase in micronuclei formation at low concentrations (1 μM), while BAA, CAA, CIAA and TBAA were genotoxic at exposure concentrations above 10 μM (100 μM in the case of DIAA). These results point to genotoxic and endocrine disruption effects associated with HAA exposure at low concentrations (0.01-1 μM), and the usefulness of the selected bioassays to provide fast and sensitive responses to HAA exposure, particularly in terms of genotoxicity and endocrine disruption effects. Further studies are needed to define thresholds that better protect public health.

The transformation of dissolved organic matter and formation of halogenated by-products during electrochemical advanced oxidation pretreatment for shale gas produced water

Electrochemical advanced oxidation processes (EAOPs) have shown great potential for the treatment of shale gas produced water (SGPW). In this study, we investigated the transformation of dissolved organic matter (DOM) during EAOPs of SGPW and the formation of toxic halogenated by-products at various current densities, using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. We found that the priority of DOM removal was terrestrial humic-like > microbial humic-like > protein-like substances. Non-Halogenated organic compounds (non-HOCs) and HOCs were predominantly CHO, and CHOCl/CHOBr compounds in EAOP-treated SGPW, respectively. As applied current density and treatment time increased, the production of oxyhalides increased, with chlorate > bromate > perchlorate. Meanwhile, most DOM was mineralized, resulting in residual products with higher modified aromaticity index (AI_mod) and nominal oxidation state of carbon (NOSC). The resistants had lower mass-to-charge ratio (m/z), AI_mod, NOSC, and double bond equivalent minus oxygen per carbon ((DBE-O)/C). The dominant reactions were the addition of tri-oxygen and deallyl. Bromine addition dominated the reactions of halogenating addition, while chlorine addition took second place. Furthermore, the acute toxicity of SGPW was positively correlated with inorganic halogenated by-products. This study contributes to the understanding and improvement of EAOPs for the treatment of SGPW.

Enhanced selectivity for acidic contaminants in drinking water: From suspect screening to toxicity prediction

A novel analytical workflow for suspect screening of organic acidic contaminants in drinking water is presented, featuring selective extraction by silica-based strong anion-exchange solid-phase extraction, mixed-mode liquid chromatography-high resolution accurate mass spectrometry (LC-HRMS), peak detection, feature reduction and compound identification. The novel use of an ammonium bicarbonate-based elution solvent extended strong anion-exchange solid-phase extraction applicability to LC-HRMS of strong acids. This approach performed with consistently higher recovery and repeatability (88 ± 7 % at 500 ng L^-1), improved selectivity and lower matrix interference (mean = 12 %) over a generic mixed-mode weak anion exchange SPE method. In addition, a novel filter for reducing full-scan features from fulvic and humic acids was successfully introduced, reducing workload and potential for false positives. The workflow was then applied to 10 London municipal drinking water samples, revealing the presence of 22 confirmed and 37 tentatively identified substances. Several poorly investigated and potentially harmful compounds were found which included halogenated hydroxy-cyclopentene-diones and dibromomethanesulfonic acid. Some of these compounds have been reported as mutagenic in test systems and thus their presence here requires further investigation. Overall, this approach demonstrated that employing selective extraction improved detection and helped shortlist suspects and potentially toxic chemical contaminants with higher confidence.

The chlorination of glycine and α-alanine at excess HOCl: Kinetics and mechanism

The chlorination of the two simplest amino acids at HOCl excess was studied by stopped-flow, conventional spectrophotometric and time resolved ¹H NMR kinetic methods at 25 °C. These reactions show distinct characteristics under neutral and alkaline conditions. At high pH, the common feature of the two systems is that the N-dichloroamino carboxylate ion does not form and the overall process is controlled by the initial decomposition of the N-monochloro derivative. Under such conditions, carbanions form in equilibrium acid - base processes and open alternative reaction paths, resulting in enhanced complexity of the corresponding mechanisms. In the case of α-alanine, the formation of acetonitrile and N-chloro acetamide as main products; acetate ion, acetaldehyde, chloroacetaldehyde, chloroform as byproducts; acetamide and N-chloro ethanimine as intermediates was confirmed. In the case of glycine, the final products are formamide and OCN^-. Under neutral conditions, monochloroamino acid forms immediately upon mixing the reactants, and subsequently it is converted into dichloroamino acid by Cl₂O in a fast process. In considerably slower further reaction steps, acetonitrile and acetate ion form as final products in the α-alanine system, while the chlorination of glycine proceeds to full mineralization. The detailed mechanisms suggested for these reactions postulate the formation of various imines and N-chloro imines which are involved in decarboxylation, dechlorination, hydration and hydrolytic reaction steps.

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.

Uncertainty estimation strategies for quantitative non-targeted analysis

Non-targeted analysis (NTA) methods are widely used for chemical discovery but seldom employed for quantitation due to a lack of robust methods to estimate chemical concentrations with confidence limits. Herein, we present and evaluate new statistical methods for quantitative NTA (qNTA) using high-resolution mass spectrometry (HRMS) data from EPA's Non-Targeted Analysis Collaborative Trial (ENTACT). Experimental intensities of ENTACT analytes were observed at multiple concentrations using a semi-automated NTA workflow. Chemical concentrations and corresponding confidence limits were first estimated using traditional calibration curves. Two qNTA estimation methods were then implemented using experimental response factor (RF) data (where RF = intensity/concentration). The bounded response factor method used a non-parametric bootstrap procedure to estimate select quantiles of training set RF distributions. Quantile estimates then were applied to test set HRMS intensities to inversely estimate concentrations with confidence limits. The ionization efficiency estimation method restricted the distribution of likely RFs for each analyte using ionization efficiency predictions. Given the intended future use for chemical risk characterization, predicted upper confidence limits (protective values) were compared to known chemical concentrations. Using traditional calibration curves, 95% of upper confidence limits were within ~tenfold of the true concentrations. The error increased to ~60-fold (ESI+) and ~120-fold (ESI-) for the ionization efficiency estimation method and to ~150-fold (ESI+) and ~130-fold (ESI-) for the bounded response factor method. This work demonstrates successful implementation of confidence limit estimation strategies to support qNTA studies and marks a crucial step towards translating NTA data in a risk-based context.

Chemical and biological assessments of environmental mixtures: A review of current trends, advances, and future perspectives

Considering the chemical complexity and toxicity data gaps of environmental mixtures, most studies evaluate the chemical risk individually. However, humans are usually exposed to a cocktail of chemicals in real life. Mixture health assessment remains to be a research area having significant knowledge gaps. Characterization of chemical composition and bioactivity/toxicity are the two critical aspects of mixture health assessments. This review seeks to introduce the recent progress and tools for the chemical and biological characterization of environmental mixtures. The state-of-the-art techniques include the sampling, extraction, rapid detection methods, and the in vitro, in vivo, and in silico approaches to generate the toxicity data of an environmental mixture. Application of these novel methods, or new approach methodologies (NAMs), has increased the throughput of generating chemical and toxicity data for mixtures and thus refined the mixture health assessment. Combined with computational methods, the chemical and biological information would shed light on identifying the bioactive/toxic components in an environmental mixture.

Activation of hydrogen peroxide, persulfate, and free chlorine by steel anode for treatment of municipal and livestock wastewater: Unravelling the role of oxidants speciation

Despite the extensive application of electrochemical advanced oxidation processes (EAOPs) in wastewater treatment, the exact speciation of oxidants and their effects on pollutants removal efficiency, by-products formation, and effluent toxicity are largely unknown. In this study, galvanostatic steel anodes were used to drive the electrochemical activation of hydrogen peroxide (EAHP), persulfate (EAP), and free chlorine (EAFC), for industrial-scale treatment of municipal and livestock wastewater with a focus on micropollutants and transformation products (MTPs) and effluent toxicity. Response surface methodology determined the optimized conditions for each treatment towards total organic carbon ([TOC]₀ = 180 mg/L) removal at pH 3.0: persulfate dose = 0.12 mmol/min, 26.5 mA/cm²; free chlorine dose = 0.29 mmol/min, 37.4 mA/cm²; H₂O₂ dose = 0.20 mmol/min, 45 mA/cm². Probe-compound degradation revealed that HO^•, SO₄^•- and Fe^IVO²⁺ species were simultaneously generated in EAP, whereas HO^• and Fe^IVO²⁺ were the principal oxidants in EAHP and EAFC, respectively. Samples were analyzed via liquid and gas chromatography in non-target screening (NTS) mode to monitor the generation or removal of MTPs and by-products including compounds that have not been reported previously. The speciation of oxidants, shifted in presence of halide ions (Cl^-, Br^-) in real wastewater samples, significantly affected the mineralization efficiency and by-product formation. The production of halogenated by-products in EAFC and EAP substantially increased the effluent toxicity, whereas EAHP provided non-toxic effluent and the highest mineralization efficiency (75 - 80%) to be nominated as the best strategy.

Occurrence and transformation of unknown organochlorines in the wastewater treatment plant using specific Fragment-Based method with LC Q-TOF MS

Wastewater treatment plants (WWTPs) are important point sources of organochlorines in surface waters. However, comprehensive molecular-level understanding of the occurrence and transformation of organochlorines in WWTPs remains elusive. In this study, a specific fragment-based screening method with SWATH of LC Q-TOF MS was established to better understand the molecular composition of organochlorines. This method effectively excludes the non-chlorinated signals and provides multi-dimensional information (e.g., retention time, precursor ion mass, product ions, and molecular formula) with one injection to identify the possible structures of organochlorines. Eighty-seven organochlorines were successfully screened in practical wastewater samples, where 8 chlorinated sulfonic acids, 4 chlorophenols, 4 chlorinated benzenediols, and 6 chlorinated benzoic acids were further (tentatively) identified. Relative abundance of organochlorines showed that their occurrence was associated with the treatment units. In particular, anaerobic biological and NaClO treatment units contributed to the formation of chlorinated by-products. Most chlorinated by-products were substituted with more chlorine atoms than organochlorines from the influent. Furthermore, the relative abundance indicated that the fate of organochlorines were related to their structures. Chlorinated benzene sulfonic acids would be removed by adsorption on activated sludge. Most chlorinated benzoic acids were refractory, but some were likely to be chlorinated during the anaerobic process. Chlorophenols and chlorinated benzenediols might undergo chlorination, dealkylation/C-O bond breakage, and bromination. Our study offers a new tool to gain molecular information on organochlorines in complex environmental samples and highlights the importance of molecular structures when evaluating the fate of organochlorines and managing effluent discharge to surrounding waters.

Disinfection byproducts formed during drinking water treatment reveal an export control point for dissolved organic matter in a subalpine headwater stream

Changes in climate, season, and vegetation can alter organic export from watersheds. While an accepted tradeoff to protect public health, disinfection processes during drinking water treatment can adversely react with organic compounds to form disinfection byproducts (DBPs). By extension, DBP monitoring can yield insights into hydrobiogeochemical dynamics within watersheds and their implications for water resource management. In this study, we analyzed temporal trends from a water treatment facility that sources water from Coal Creek in Crested Butte, Colorado. These trends revealed a long-term increase in haloacetic acid and trihalomethane formation over the period of 2005-2020. Disproportionate export of dissolved organic carbon and formation of DBPs that exceeded maximum contaminant levels were consistently recorded in association with late spring freshet. Synoptic sampling of the creek in 2020 and 2021 identified a biogeochemical hotspot for organic carbon export in the upper domain of the watershed that contained a prominent fulvic acid-like fluorescent signature. DBP formation potential analyses from this domain yielded similar ratios of regulated DBP classes to those formed at the drinking water facility. Spectrometric qualitative analyses of pre and post-reacted waters with hypochlorite indicated lignin-like and condensed hydrocarbon-like molecules were the major reactive chemical classes during chlorine-based disinfection. This study demonstrates how drinking water quality archives combined with synoptic sampling and targeted analyses can be used to identify and understand export control points for dissolved organic matter. This approach could be applied to identify and characterize analogous watersheds where seasonal or climate-associated organic matter export challenge water treatment disinfection and by extension inform watershed management and drinking water treatment.

Changes in molecular dissolved organic matter and disinfection by-product formation during granular activated carbon filtration by unknown screening analysis with Orbitrap mass spectrometry

The minimization of disinfection by-product (DBP) formation by the removal of its precursors before water disinfection is a highly effective approach. Granular activated carbon (GAC) filtration is widely used for water treatment, but our understanding of molecular dissolved organic matter (DOM) remains insufficient. This research investigates the removal of DOM and the minimization of DBP formation by pilot-scale coal- and coconut-based granular activated carbon filtrations (coAC and ccAC, respectively) using unknown screening analysis with Orbitrap mass spectrometry. DOM adsorption rates by both GACs were fitted with pseudo-second order models with initial adsorption rates of 0.005 mg g^-1 min^-1 and 0.022 mg g^-1 min^-1 for ccAC and coAC, respectively. Based on observations, ccAC was more effective in the removal of dissolved organic carbon and prolonged adsorption longer than coAC, as the breakthrough of coAC was found on Day 10. ccAC removed compounds with carbon, hydrogen, and oxygen (CHO features) with a wide range of oxidation states, as indicated by the carbon oxidation state (C_os), and a wide range of unsaturation, as indicated by oxygen subtracted double bond equivalent per carbon ([DBE-O]/C), while coAC selectively removed only those CHO features with less oxidized characters. Less oxidized compounds (low C_os) were preferentially removed with less contact time, while more oxidized compounds needed more contact time to adsorb on the GACs. A biofilm was developed on Day 60, and many CHO features were found to have increased after GAC treatment on Day 60, indicating the formation of microbial products. Chlorination resulted in a decrease in many CHO and CHO with Cl atom (CHOCl) features and the formation of CHOCl DBPs more than CHO DBP features. ccAC was effective in the minimization of trihalomethane (THM) and CHOCl DBP feature formations on Day 10 and Day 60, while coAC was found to be much less effective.

Characterization of dissolved organic carbon and disinfection by-products in biochar filter leachate using orbitrap mass spectrometry

Biochar is a low-cost adsorbent with considerable potential for utilization as a water filtration medium; however, organic matter leaching from biochar can lead to the formation of disinfection by-products (DBPs). This study investigated the leaching of dissolved organic carbon (DOC) from eucalyptus-derived biochar and the formation of DBPs generated by chlorination and chloramination. Column experiments with empty bed contact times (EBCTs) of 10 and 30 min were conducted for 200 bed volumes (BVs). The highest DOC concentration (3.5 µg-C/g-biochar) was detected with an EBCT of 30 min. Chloroform (49 µg/L) and dichloroacetonitrile (7 µg/L) because of chlorination were found during the first five BVs, but were reduced thereafter. During the first 10 BVs, unknown chlorinated DBPs generated (CHOCl) by chlorination and chloramination (193 and 152 formulae, respectively) were tentatively identified via an unknown screening analysis. The release of DBP precursors from biochar tentatively identified in this study will impact water filtration applications.

Sulfur(IV) assisted oxidative removal of organic pollutants from source water

The removal of organic pollutants presents a major challenge for drinking water treatment plants. The chemical oxygen demand (COD) is essentially the measure of oxidizable organic matter in source waters. In this study, we report that COD can efficiently be decreased by adding Fe(II)/Fe(III) and sulfite ion to the source water while purging it with air. In this process, oxygen is activated to oxidize the main constituents of COD, i.e. organic substrates, via the generation of reactive inorganic oxysulfur radical ions. In the end, the total amount of sulfur(IV) is converted to the non-toxic sulfate ion. It has been explored how the COD removal efficiency depends on the concentration of S(IV), the total concentration of iron species, the concentration ratio of Fe(II) and Fe(III), the purging rate and the contact time by using source water from a specific location (Királyhegyes, Hungary). The process has been optimized by applying the Response Surface Methodology (RSM). Under optimum conditions, the predicted and experimentally found COD removal efficiencies are in excellent agreement: 85.4% and 87.5%, respectively. The robustness of the process was tested by varying the optimum values of the parameters by ± 20%. It was demonstrated that the method is universally applicable because a remarkable decrease was achieved in COD, 62.0-88.5%, with source waters of various compositions acquired from 9 wells at other locations using the same conditions as in the case of Királyhegyes.

Synergistic cytotoxicity of bromoacetic acid and three emerging bromophenolic disinfection byproducts against human intestinal and neuronal cells

Halogenated disinfection byproducts (halo-DBPs) are drinking water contaminants of great public health concern. Nine haloaliphatic DBPs have been regulated by the U.S. Environmental Protection Agency and various halophenolic compounds have been identified as emerging DBPs. In this study, we evaluated the cytotoxic interactions of the regulated bromoacetic acid and three emerging bromophenolic DBPs, i.e., 2,4,6-tribromophenol, 3,5-dibromo-4-hydroxybenzoic acid, and 3,5-dibromo-4-hydroxybenzaldehyde. Cytotoxicity was measured for each DBP individually as well as each of their mixtures using in vitro human epithelial colorectal adenocarcinoma (Caco-2) and neuroblastoma (SH-SY5Y) cells. Concentration addition (CA) model and isobolographic analysis were employed to characterize the interactions among the DBPs. Our results show that the cytotoxicity of four bromo-DBPs against both cell-types followed the descending rank order of bromoacetic acid > 2,4,6-tribromophenol > 3,5-dibromo-4-hydroxybenzaldehyde > 3,5-dibromo-4-hydroxybenzoic acid. Compared with the toxicity data in literature, our finding that bromoacetic acid showed higher cytotoxicity than bromophenolic DBPs was consistent with the results from Chinese hamster ovary cells (a commonly used in vitro model of DBP toxicological studies); but different from the results obtained from in vivo biological models. Significantly, with CA model prediction, we found that mixtures of four bromo-DBPs exhibited synergistic cytotoxic effects on both human cell types. Isobolographic analysis of binary DBP mixtures revealed that, for Caco-2 cells, bromoacetic acid, 2,4,6-tribromophenol, and 3,5-dibromo-4-hydroxybenzoic acid induced synergism; for SH-SY5Y cells, bromoacetic acid induced synergism with all three bromophenolic DBPs. The production of reactive oxidative species (ROS) induced by DBP mixtures could be an important reason for the synergistic cytotoxicity.

What's in the water? - Target and suspect screening of contaminants of emerging concern in raw water and drinking water from Europe and Asia

There is growing worry that drinking water can be affected by contaminants of emerging concern (CECs), potentially threatening human health. In this study, a wide range of CECs (n = 177), including pharmaceuticals, pesticides, perfluoroalkyl substances (PFASs) and other compounds, were analysed in raw water and in drinking water collected from drinking water treatment plants (DWTPs) in Europe and Asia (n = 13). The impact of human activities was reflected in large numbers of compounds detected (n = 115) and high variation in concentrations in the raw water (range 15-7995 ng L^-1 for ∑₁₇₇CECs). The variation was less pronounced in drinking water, with total concentration ranging from 35 to 919 ng L^-1. Treatment efficiency was on average 65 ± 28%, with wide variation between different DWTPs. The DWTP with the highest ∑CEC concentrations in raw water had the most efficient treatment procedure (average treatment efficiency 89%), whereas the DWTP with the lowest ∑₁₇₇CEC concentration in the raw water had the lowest average treatment efficiency (2.3%). Suspect screening was performed for 500 compounds ranked high as chemicals of concern for drinking water, using a prioritisation tool (SusTool). Overall, 208 features of interest were discovered and three were confirmed with reference standards. There was co-variation between removal efficiency in DWTPs for the target compounds and the suspected features detected using suspect screening, implying that removal of known contaminants can be used to predict overall removal of potential CECs for drinking water production. Our results can be of high value for DWTPs around the globe in their planning for future treatment strategies to meet the increasing concern about human exposure to unknown CECs present in their drinking water.

Emission of (chlorinated) reclaimed water into a Mediterranean River and its related effects to the dissolved organic matter fingerprint

High resolution mass spectrometry (HRMS) was used to investigate the dissolved organic matter (DOM) profile of a reclamation water trial performed in the Llobregat River (Spain) during summer 2019. 23 water samples (including tertiary effluents, surface river and drinking water), taken during five sampling campaigns, were analyzed and their van Krevelen diagrams were compared. The reclaimed water fingerprint was substantially different from the natural profile of the river, showing a higher number of heteroatomic signals (i.e. CHON, CHOS and CHONS) and the presence of high-intensity S-containing features. As a result, reclaimed water discharge introduced substantial changes in the signature of the lignin-like and soot-like compositional-spaces of the river DOM fingerprint. However, the effect on the drinking water fingerprint was, ultimately, very limited. Only a limited number of features (up to 34) were detected as exclusively emitted with the reclaimed water. During the second phase of the trial, the tertiary effluent was chlorinated for disinfection purposes. This process triggered the unexpected formation of a myriad of new features along the Llobregat River. Notably, 109 brominated/chlorinated features were detected, probably generated as a consequence of the photochemical decay of the emitted chloramines and their free-radical reaction with DOM, and three of them persisted in the final drinking water. The formation of halogenated species in situ in the Llobregat River entails uncertainty at ecological and water treatment levels and should be studied carefully to fully disclose the risks associated to wastewater effluent disinfection.