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Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder characterized by abnormal lipid deposition, with oxidative stress being a risk factor in its onset and progression. Haloacetamides (HAcAms), as unregulated disinfection by-products in drinking water, may alter the incidence and severity of NAFLD through the production of oxidative stress. We explored whether HAcAms at 1, 10, and 100-fold concentrations in Shanghai drinking water perturbed lipid metabolism in normal human liver LO-2 cells. CRISPR/Cas9 was used to construct a LO-2 line with stable NRF2 knock-down (NRF2-KD) to investigate the mechanism underlying abnormal lipid accumulation and hepatocyte damage caused by mixed exposure to HAcAms. At 100-fold real-world concentration, HAcAms caused lipid deposition and increased triglyceride accumulation in LO-2 cells, consistent with altered de novo lipogenesis. Differences in responses to HAcAms in normal and NRF2-KD LO-2 cells indicated that HAcAms caused hepatocyte lipid deposition and triglyceride accumulation by activation of the NRF2/PPARγ pathway and aggravated liver cell toxicity by inducing ferroptosis. These results indicate that HAcAms are important risk factors for NAFLD. Further observations and verifications of the effect of HAcAms on NAFLD in the population are warranted in the future.

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We investigated short (first post-fire precipitation)- and long-term (11-month) impacts of the Caldor and Mosquito Fires (2021 and 2022) on water quality, dissolved organic matter, and disinfection byproduct (DBP) precursors in burned and adjacent unburned watersheds. Both burned watersheds experienced water quality degradation compared to their paired unburned watersheds, including increases in dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and DBP precursors from precipitation events. DBP precursor concentrations during storm events were greater in the Caldor Fire's burned watershed than in the unburned watershed; precursors of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloacetamides (HAMs) were 533 µg/L, 1,231 µg/L, 64 and 58 µg/L greater. The burned watershed of the Mosquito Fire also had greater median concentrations of THM (44 µg/L), HAA (37 µg/L), HAN (7 µg/L), and HAM (13 µg/L) precursors compared to the unburned watershed during a storm immediately following the fire. Initial flushes from both burned watersheds formed greater concentrations of more toxic DBPs, such as HANs and HAMs. The Caldor Fire burn area experienced a rain-on-snow event shortly after the fire which produced the greatest degradation of water quality of all seasons/precipitation events/watersheds studied. Over the long term, statistical analysis revealed that DOC and DON values in the burned watershed of the Caldor Fire remained higher than the unburned control (0.98 mg C/L and 0.028 mg N/L, respectively). These short and long-term findings indicate that wildfires present potential treatment challenges for public water systems outside of the two studied here.

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The formation characteristics of trihalomethanes (THMs) and haloacetamides (HAcAms) from dissolved organic matter and its fractions were investigated during chlorine-based disinfection processes. The relationships between water quality parameters, fluorescence parameters, and the formation levels of THMs and HAcAms were analyzed. The fractions contributing most to the acute toxicity were identified. The trichloromethane (TCM) generation level (72 h) generally followed the order of Cl2 > NH2Cl > NHCl2 process. The NHCl2 process was superior to the NH2Cl process in controlling TCM formation. Hydrophobic acidic substance (HOA), hydrophobic neutral substance (HON), and hydrophilic substance (HIS) were identified as primary precursors of 2,2-dichloroacetamide and trichloroacetamide during chlorination and chloramination. The formation of TCM mainly resulted from HOA, HON and HIS fractions relatively uniformly, while HOA and HIS fractions contributed more to the formation of bromodichloromethane and dibromomonochloromethane. UV254 could be used as an alternative indicator for the amount of ΣTHMs formed during chlorination and chloramination processes. Dissolved organic nitrogen was a potential precursor of 2,2-dichloroacetamide during chlorination process. The fractions with the highest potential acute toxicity after the chlorination were water-dependent.

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Disinfection byproduct (DBP) pre-formation is a major issue when prechlorination is used before or during advanced treatment of impacted drinking water sources. Control strategies for pre-formed DBPs before final disinfection, especially for currently nonregulated although highly toxic DBP species, are not yet established. This study evaluated the biodegradation potential of pre-formed DBPs, including haloacetonitriles (HANs), haloacetamides (HAMs), and haloacetaldehydes (HALs), during biofiltration with sand, anthracite, and biological activated carbon of three wastewater effluents under potable reuse conditions. Up to 90%+ removal of di- and trihalogenated HANs, HAMs, and HALs was observed, and removal was associated with active heterotrophic biomass and removal of biodegradable organic carbon. Unlike the microbial dehalogenation pathway of haloacetic acids (HAAs), removal of HANs and HAMs appeared to result from a biologically mediated hydrolysis pathway (i.e., HANs to HAMs and HAAs) that may be prone to inhibition. After prechlorination, biofiltration effectively controlled pre-formed DBP concentrations (e.g., from 271 µg/L to as low as 22 µg/L in total) and DBP-associated calculated toxicity (e.g., 96%+ reduction). Abiotic residual adsorption capacity in biological activated carbon media was important for controlling trihalomethanes. Overall, the toxicity-driving DBP species exhibited high biodegradation potential and biofiltration showed significant promise as a pre-formed DBP control technology.

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Organic matter reacts with chlorine forming disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetamides (HAMs), haloacetic acids (HAAs), and haloacetonitriles (HANs). Filter backwash water (FBW) is either released back to the environment or recycled to the head of the treatment plant after solids settling and the remaining dissolved organic matter is a significant pool of DBP precursors that are not well understood. We characterized dissolved organic matter in FBW from 10 treatment plants and low molecular weight (MW < 1 kDa) organic matter contributed the most to DBP formation. We demonstrated overall similarity of the molecular composition (e.g., elemental ratios, m/z, DBE) of the 10 samples of FBW by Fourier transform ion cyclotron resonance mass spectrometry. Aromatic and more highly oxidized compounds preferentially reacted with chlorine, forming DBPs. Low MW (<450 Da) aliphatic compounds, and highly unsaturated and phenolic compounds were the primary precursors of THMs, HANs, and HAMs, and the formation potentials (FPs) of these groups of DBPs were correlated with multiple individual molecular formulae. HAA FPs were correlated with low MW, highly unsaturated and phenolic compounds. These advances in the understanding of the molecular composition of DBP precursors in FBW may develop the effective strategies to control DBP formation and limit impacts on the quality of finished water, and can be expanded to understanding DBP precursors in drinking water sources.

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It is important to study the stress effects and mechanisms of haloacetamide (HAcAm) disinfection byproducts to reveal their health hazards. In this context, toxicological g was applied to evaluate the effects of four HAcAms, revealing the status of gene expression on Escherichia coli in different stress response types (oxidative, protein, membrane, general, DNA). This study revealed that the main toxic action modes of these HAcAms were general and membrane stresses by high-resolution, real-time gene expression profiling combined with clustering analysis. The results of time-gene evaluation showed that the presence of chloroacetamide (CAcAm) and bromoacetamide (BAcAm) generated more reactive oxygen species, thus activating oxidative stress. Trichloroacetamide (tCAcAm) induced altered expression of glutathione marker genes and membrane stress-related genes, and iodoacetamide (IAcAm) caused severe DNA damage by damaging DNA strands and individual nucleotides mainly through damage to nucleic acids and bases. Furthermore, quantitative structure-activity relationship (QSAR) modelling results indicated that the biological activities of HAcAms were related to their quantum chemical and topological properties.

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Haloacetonitriles (HANs) are an emerging class of nitrogenous disinfection by-products (DBPs) formed in disinfected drinking water and have been reported to be more cyto- and genotoxic than the regulated DBPs. HANs are also known to hydrolyze under neutral pH and normal room temperature. However, the stability of HANs has not been well characterized in DBP toxicological assessments. Most toxicological assessments expose DBPs up to several days which may result in a mixture of HANs and degradation products that might have underestimated HAN toxicity. In this study, HANs stability was characterized in 1) a buffer solution in sealed vials, 2) cell culture media (CCM) in sealed vials, and 3) CCM in 96 sealed well plates with 5% CO2. Solutions were incubated at 37 °C for 3 days. MonoHANs were found to be stable in buffer and CCM except when HANs were incubated in CCM in plates where they could possibly be affected by volatilization and photodegradation during sample handling. However, di- and tri- HANs degraded between 70 and 100% in both buffer solution and CCM. They were also found to be less stable in CCM than in buffer solution possibly from HANs reacting with nucleophiles present in CCM (i.e., amino acids). Identified degradation products include corresponding haloacetamides and haloacetic acids for buffer solutions and only haloacetic acids and an unknown brominated compound for CCM. Results of this study suggests that reported toxicity values might have been underestimated and should consider changing CCM and DBP on a daily basis for a more accurate toxicity measurement.

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Background The concentrations of disinfection by-products (DBPs) are varied by different water sources, disinfectants, or treatment processes in Wuxi, and the associated health risks are also different. Objective To understand the levels of trihalomethanes (THMs) and haloacetamides (HAcAms) in drinking water in Wuxi, and their variations by water sources, seasons, disinfectants or treatment processes, aiming to provide technical support for ensuring the safety of drinking water. Methods In dry period (December 2019) and wet period (July 2020), the finished water and tap water (from the beginning, middle, and end of the drinking water distribution network) from 12 centralized water treatment plants in Wuxi were collected to detect the concentrations of THMs and HAcAms in water samples. A purge and trap-gas chromatography-mass spectrometry method was applied to detect trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and tribromomethane (TBM), and a solid-phase extraction-gas chromatography-mass spectrometry method to detect dichloroacetamide (DCAcAm), trichloroacetamide (TCAcAm), bromochloroacetamide (BCAcAm), dibromoacetamide (DBAcAm), bromodichloroacetamide (BDCAcAm), dibromochloroacetamide (DBCAcAm), and tribromoacetamide (TBAcAm). Analyses and comparisons were made on the concentrations of THMs and HAcAms in drinking water by water sources (the Yangtze River/the Taihu Lake/reservoir), wet/dry seasons, disinfection methods (liquid chlorine/sodium hypochlorite), and treatment processes (conventional treatment/conventional+advanced treatment). Results A total of 96 drinking water samples were collected in Wuxi. THMs were positive in all the water samples (100%), with concentration ranging from 1.027 to 40.225 μg·L−1 and the M (P25, P75) concentration being 24.782 (17.784, 30.932) μg·L−1. None of the 4 THMs exceeded the standard limit of the Standards for drinking water quality (GB 5749-2022 ), and the order of the 4 THMs concentrations from high to low was TCM > BDCM > DBCM > TBM. Five of the 7 HAcAms were detected, the total concentration ranged from 0.137 to 3.288 μg·L−1, and the M (P25, P75) was 0.808 (0.482, 1.704) μg·L−1. The DCAcAm concentration was the highest (2.448 μg·L−1), followed by BCAcAm, while TCAcAm and DBCAcAm were not detected. The M (P25, P75) of the total concentration of THMs in the drinking water from the Taihu Lake was 33.353 (26.649, 36.217) μg·L−1, that of the Yangtze River was 27.448 (24.312, 31.393) μg·L−1, and both were higher than the level of the reservoir [16.359 (2.305, 21.553) μg·L−1] (P<0.05), while the M (P25, P75) of the total concentration of HAcAms in the drinking water from the Taihu Lake was 0.616 (0.363, 0.718) μg·L−1, which was lower than those of the Yangtze River [0.967 (0.355, 2.283) μg·L−1] and the reservoir [1.071 (0.686, 1.828) μg·L−1] (P<0.05). There were no statistically significant differences in the total concentrations of THMs and HAcAms between wet season and dry season, or between different disinfection methods (P>0.05). The M (P25, P75) concentrations of THMs and HAcAms in drinking water after advanced treatment process involving ozone, activated carbon, and membrane were 20.565 (3.316, 27.185) μg·L−1 and 0.623 (0.452, 1.286) μg·L−1 respectively, and were lower than the corresponding values after conventional treatment process, 28.740 (23.431, 35.085) μg·L−1 and 0.934 (0.490, 2.116) μg·L−1 respectively (P＜0.05). Conclusion The concentrations of THMs and HAcAms in drinking water in Wuxi are generally at a low level. The levels of controlled THMs meet the requirements of national standards, and the levels of uncontrolled HAcAms as new DBPs are up to μg·L−1. The concentrations of the two kinds of DBPs in drinking water vary by water sources. The concentrations of THMs and HAcAms produced by the advanced treatment process are lower than that by the conventional treatment process.

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OBJECTIVE: To establish a liquid-liquid extraction and gas chromatography method for the determination of 7 kinds of haloacetaldehydes, 7 kinds of haloacetonitriles, 7 kinds of halonitromethanes and 4 kinds of haloacetamides in drinking water. METHODS: A liquid-liquid extraction gas chromatography technique was employed. Experimental parameters, such as capillary column type, inlet temperature, concentration of salting out reagent and sample pH were optimized to develop an analytical method, and then method validation was conducted. RESULTS: HP-5 MS UI column(30 m×0.25 mm, 0.25 µm), inlet temperature at 180 ℃, addition of 8 g sodium chloride in 50 mL water sample and pH 4-5 were chosen as the final parameters. Good correlation coefficients were obtained in the linear range of 0.20-15 µg/L, with r greater than 0.999.Methods detection limits were between 0.008-0.088 µg/L. When spiked concentration was 1.0 µg/L for pure water and tap water, the recoveries were 81%-106% and 75%-117%, respectively, and relative standard deviations were both less than 4%. When spiked concentration was 12 µg/L for pure water and tap water, the recoveries were 92%-101% and 86%-106%, respectively, and relative standard deviations were less than 4% and 2%, respectively. CONCLUSION: This method is simple, sensitive, and effective. It is suitable for simultaneous determination of 25 disinfection byproducts in drinking water.

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Haloacetonitriles (HANs) and haloacetamides (HAMs) are nitrogenous disinfection byproducts that are present in filter backwash water (FBW) and sedimentation sludge water (SSW). In many cases FBW and SSW are recycled to the head of drinking water treatment plants. HAN and HAM concentrations in FBW and SSW, without additional oxidants, ranged from 6.8 to 11.6 nM and 2.9 to 3.6 nM of three HANs and four HAMs, respectively. Upon oxidant addition to FBW and SSW under formation potential conditions, concentrations for six HANs and six HAMs ranged from 92.2 to 190.4 nM and 42.2 to 95.5 nM, respectively. Therefore, at common FBW and SSW recycle rates (2 to 10% of treated water flows), the precursor levels in these recycle waters should not be ignored because they are comparable to levels present in finished water. Brominated HAN and chlorinated HAM were the dominant species in FBW and SSW, respectively. The lowest molecular weight ultrafiltration fraction (< 3 kDa) contributed the most to HAN and HAM formations. The hydrophilic (HPI) organic fraction contributed the greatest to HAN precursors in sand-FBW and SSW and were the most reactive HAM precursors in both sand- or carbon-FBWs. Fluorescence revealed that aromatic protein-like compounds were dominant HAN and HAM precursors. Therefore, strategies that remove low molecular weight hydrophilic organic matter and aromatic protein-like compounds will minimize HAN and HAM formations in recycled FBW and SSW.

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Drinking water disinfection may result in the formation of different classes of toxic disinfection by-products (DBPs). Haloacetamides (HAcAms) are an emerging class of nitrogenous DBPs (N-DBPs), which are generally more prevalent at lower concentrations in disinfected water than carbonaceous DBPs. Herein a fast, convenient, and effective method of analyzing 10 HAcAms in drinking water samples was demonstrated. This method was developed using gas chromatography /electron capture detection (GC/ECD) supplemented with automated solid phase extraction (auto-SPE). The variables for automated SPE procedures were further optimized, including the selection of SPE sorbents, types and volumes of extraction solvents, SPE washing solvents and wash times. Under optimized conditions, the instrumental linearity range was 0.5-150 µg L-1 with correlation coefficients>0.9975. The limits of detection and quantification of this method were 0.002-0.003 µg L-1 and 0.005-0.010 µg L-1, respectively. The recovery values ranged from 72.4% to 108.5%, and the relative standard deviations ranged from 3.3% to 9.1%. Therefore, the auto-SPE-GC-ECD method showed acceptable linearity and repeatability and was subsequently validated and applied to analyze 10 HAcAms in drinking water.

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This study examined the potential of six aliphatic and aromatic amides, commonly found in natural waters or used as chemical aids in water treatment, to act as organic precursors for nine haloacetamides (HAcAms), five haloacetonitriles (HANs), regulated trihalomethanes (THMs) and haloacetic acids (HAAs) upon chlorination and chloramination. The impact of key experimental conditions, representative of drinking water, including pH (7 & 8), retention time (4 & 24 h) and bromide levels (0 & 100 µg/L), on the generation of the target DBPs was investigated. The highest aggregate DBP yields upon chlor(am)ination were reported for the aromatic and hydrophobic hydroxybenzamide; 2.7% ± 0.1% M/M (chlorination) and 1.7% M/M (chloramination). Increased reactivity was observed in aliphatic and hydrophilic compounds, acrylamide (2.5 ± 0.2% M/M) and acetamide (1.3 ± 0.2% M/M), in chlorination and chloramination, respectively. The addition of bromide increased average DBP yields by 50-70%. Relative to chlorination, the application of chloramines reduced DBP formation by 66.5% (without Br-) and by 46.4% (with Br-). However, bromine incorporation in HAAs and HAcAms was enhanced following chloramination, of concern due to the higher toxicological potency of brominated compounds.

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Haloacetic acids (HAAs) are the second largest class of disinfection by-products (DBPs) by weight in water and are more cytotoxic and genotoxic to mammalian cells than trihalomethanes, the first largest class of DBPs. Gas chromatography (GC) is the most widely used technique for determining HAAs. Due to their polar nature, derivatization prior to GC analysis is required. Typically, derivatization is undertaken with acidic methanol, which converts HAAs to the corresponding methyl ester (haloacetic acid methyl esters, abbreviated as HAAMEs), and HAAs are quantified by measuring HAAMEs. In this study, the interference from two other groups of DBPs, the haloacetonitriles (HANs) and haloacetamides (HAMs), on the determination of HAAs was investigated. HANs and HAMs at a range of concentrations (0, 20, 40, 60, 80, and 100 µg/L) were subjected to the same derivatization and analytical procedures as HAAs. The stability of HANs and HAMs under strongly acidic conditions was assessed and the operative mechanism of interference was investigated. The results showed that HAMs significantly interfered with the determination of the corresponding HAAs and the transformation rates of HAMs (representing the extent of HAMs transforming to corresponding HAAMEs) ranged from 6.5 to 45.7%, while the impact of HANs can be neglected. The stability of HANs and HAMs under strongly acidic conditions indicated that hydrolysis was not the cause of the interference. Instead, it was proposed that HAMs react with methyl alcohol, to generate the same corresponding HAAMEs that was generated when HAAs reacted with methyl alcohol. A method for revising HAA concentrations in the presence of HAMs is suggested.

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Humans are exposed to disinfection by-products (DBPs) mainly through drinking water ingestion and dermal contact. As an emerging class of nitrogenous DBPs (N-DBPs), haloacetamides (HAcAms) have been found to have significantly higher cytotoxicity than regulated DBPs. In this study, we investigated the cytotoxicity of HAcAms on two exposure pathway-related cell lines: human gastric epithelial GES-1 cells and immortalized keratinocytes HaCaT. Our results showed that the ranking order of cytotoxicity of 13 HAcAms was different between HaCaT and GES-1 cells. In addition, the 50% inhibitive concentration in HaCaT was 1.01-3.29 times that in GES-1. Further comparison among GES-1, HaCaT and CHO cell lines confirmed that different cell lines exhibited different sensitivity to the same compound. Importantly, HAcAms showed 5.83-7.13 × 104 times higher toxicity than the well-clarified DBP chloroform, clearly demonstrating the increased toxicity of HAcAms. Finally, using a novel high-content screening (HCS) analysis, we found that 39.29% of chlorinated HAcAms, 42.86% of brominated HAcAms and 16.07% of iodinated HAcAms significantly affected at least one of the cell-health parameters, such as nuclear size, membrane permeability, mitochondrial membrane potential, or cytochrome c release, in GES-1 or HaCaT cells. Thus, brominated HAcAms appear to have stronger effects under the sublethal exposure dose, possibly causing cytotoxicity via apoptosis. Together, our study provides new insights to the toxicity of HAcAms and a comprehensive toxicology dataset for health risk assessment.

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The possibility of using amides of halogen-substituted acetic acids as acyl donors in penicillin acylase-catalyzed reactions has been investigated, and the ability of this group of compounds to inactivate enzymes in the course of the catalytic conversion has been established. The strongest inactivating effect was demonstrated by iodoacetamide and bromoacetamide. However, the negative contribution of this side activity can be minimized by decreasing the temperature, when the rate of acyl donor conversion by penicillin acylases is still high enough, but the impact of enzyme inactivation becomes less significant. The catalytic activity of penicillin acylase from Alcaligenes faecalis in the conversion of 2-haloacetamides was significantly (5-8 times) higher than that of penicillin acylase from Escherichia coli.

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Nitrogenous disinfection by-products (N-DBPs) in chlorinated drinking water are receiving increasing attention due to their elevated toxicities. An effective strategy to control the formation of N-DBPs is to reduce their nitrogenous precursors (e.g., amino acids [AAs], believed to be the important N-DBP precursors) before disinfection. So far, little information is available about the effectiveness of conventional microbial degradation at controlling the formation of N-DBPs. In this study, the biodegradability of 20 AAs was investigated, and the impacts of microbial degradation for the selected 6 typical AAs on the formation of N-DBPs (haloacetonitriles and haloacetamides) and traditional carbonaceous DBP (chloroform) were investigated. The results indicated that glycine, arginine, aspartic acid, asparagine, alanine and serine were susceptible to biodegradation, and the formation potentials (FPs) of DBPs were remarkably reduced after biodegradation. The highest chloroform FP reduction rates from tryptophan and tyrosine were 85.4% and 56.2%, respectively. The FPs of dichloroacetonitrile and trichloroacetamide were also reduced after biodegradation of the all selected AA samples during chlor(am)ination. Dichloroacetamide FPs decreased continuously with incubation time during chlorination for phenylalanine, asparagine, aspartic acid, and the mixed AAs, and the highest reduction rates were 78.7%, 74.6%, 46.7% and 35.3% respectively. The results of integrated toxicity analysis indicated that the pre-treatment of microbial degradation significantly decreased the integrated toxicity of DBPs formed from AAs. Moreover, the microbial community analysis revealed that Proteobacteria was predominant at phylum level in the mixed AA sample, and the dominant genera were Acinetobacter and Pseudomonas. Proteobacteria may play an important role in controlling DBP precursor.

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Nitrogenous classes of disinfection by-products (DBPs), such as haloacetamides (HAAms), haloacetonitriles (HANs) and halonitromethanes (HNMs), while generally present at lower concentrations in disinfected waters than carbonaceous DBPs, such as trihalomethanes or haloacetic acids, have been shown to be more detrimental to human health. While several methods have been shown to be suitable for the analysis of some nitrogenous DBPs (N-DBPs) in disinfected waters, many are unable to quantify HAAms, the most detrimental to health of these three N-DBP classes. Here, we report the first method for the simultaneous analysis of twenty-five N-DBPs (nine HANs, nine HNMs and seven HAAms) in disinfected waters using liquid-liquid extraction followed by gas chromatography-mass spectrometry. The use of a programmable temperature vaporiser injector minimises degradation of the thermally labile HNMs, while avoiding the concomitant decreases in HANs and HAAms which occur when using lower injector temperatures. Extraction parameters, including sample pH, solvent volume, salt addition and sample pre-concentration, were investigated to determine the optimal conditions across all target N-DBPs. Good detection limits were achieved for all analytes (0.8-1.7 µg L-1) and both laboratory and instrumental runtimes were significantly reduced compared to previous methods. The method was validated for the analysis of N-DBPs in drinking, swimming pool and spa waters, and concentrations of up to 41 µg L-1 of some N-DBPs were measured in some pools.

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Haloacetamides (HAMs), an emerging class of disinfection by-products, have received increasing attention due to their elevated cyto- and genotoxicity. However, only limited information is available regarding the iodinated analogues. This study investigated the formation and speciation of iodinated haloacetamides (I-HAMs) and their chlorinated/brominated analogues during the chloramination of bromide and/or iodide-containing waters and a model compound solution over various time periods. The rapid formation of diiodoacetamide (DIAM) was observed during chloramination of three simulated samples, whereas brominated (Br-HAMs) and chlorinated haloacetamides (Cl-HAMs) increased slowly with increasing reaction time. To further understand the differences in the formation of HAMs containing different halogens, experiments with the model compound asparagine in the presence/absence of iodide were conducted. Moreover, iodine utilisation factors and iodine incorporation factors were observed to increase significantly faster and were substantially higher than those of bromine. This implied that, compared with bromide, iodide has substantially greater potential to be transformed to the corresponding HAMs during chloramination, similar to that of other classes of DBPs. That is, I-HAMs formed faster than the other species investigated, including Cl-HAMs and Br-HAMs, in the early reaction stages (0-3 h). The effect of the bromide/iodide ratio (i.e., constant iodide, increasing bromide) on I-HAM formation was also examined. With increasing bromide/iodide ratio, the formation of Br-HAMs increased and dichloroacetamide decreased, but the formation of DIAM was largely unchanged. This was consistent with the constant level of iodide in spite of the increasing bromide. Chlorine and ammonia are applied separately during chloramination in water treatment, so the effect of pre-chlorination (before adding ammonia) on the formation and speciation of I-HAMs during in situ chloramination was also evaluated. Effective mitigation of DIAM formation with in situ chloramination was achieved, and the efficiency improved with increasing pre-chlorination time, where iodide was oxidised to iodate. The HAM-associated cytotoxicity was calculated to determine the change in toxicity at different reaction times, bromide/iodide ratios, and pre-chlorination times. A similar trend as the formation of I-HAMs was observed, which increased rapidly in the first 3 h, but decreased somewhat subsequently. When the bromide/iodide ratio and pre-chlorination time was increased, the calculated toxicity of the HAMs increased (due to more formation of Br-HAMs and less Cl-HAMs) and decreased (due to less DIAM formation), respectively.

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Iodinated haloacetamides (I-HAcAms) are emerging disinfection by-products and have received great concern due to their extremely high health risk. Previous studies have demonstrated the cytotoxicity of I-HAcAms, but the biological mechanism remained unclear. In this study, cytotoxicity mechanisms of 4 I-HAcAms species were preliminarily examined using HepG-2 cells. The results showed that the cytotoxicity could be ranked as follows: diiodoacetamide (DIAcAm)> iodoacetamide (IAcAm)> bromoiodoacetamide (BIAcAm)> chloroiodoacetamide (CIAcAm). Reactive oxygen species (ROS) and apoptosis played an important role in the cytotoxicity for all I-HAcAms species. Moreover, the ROS and cytotoxicity could be completely reversed by the addition of an antioxidant (N-acetylcysteine (NAC)), but the apoptosis could not. Specifically, the apoptosis induced by DIAcAm and IAcAm was partially reversed by NAC, suggesting that in addition to ROS, other pathways were also possible; While For BIAcAm and CIAcAm, the apoptosis was not reversed by NAC at all, which is potentially due to ROS-independent pathways. The apoptosis mechanisms were further analyzed via Bax and Bcl-2 gene expression and the corresponding protein expression in HepG-2 cells, that mitochondrial pathway was important in the apoptosis of HepG-2 cells induced by all I-HAcAms species. Overall, the mitochondrial pathway provided a potential explanation for BIAcAm and CIAcAm-induced apoptosis, while both ROS and mitochondrial pathways explained DIAcAm and IAcAm-induced apoptosis.

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The effective removal of haloacetamides (HAMs) as a group of emerging disinfection by-products is essential for drinking water safety. This study investigated the degradation of 10 HAMs, including chlorinated, brominated, and iodinated analogues, by sodium sulfite (S(IV)) and the mechanism behind it. The results indicated that all HAMs, excluding chlorinated HAMs, decomposed immediately when exposed to S(IV). The reductive dehalogenation kinetics were well described by a second-order kinetics model, first-order in S(IV) and first-order in HAMs. The degradation rates of HAMs increased with the increase of pH and they were positively correlated with sulfite concentration, indicating that the reaction of S(IV) with HAMs mainly depends on sulfite. The rank order and relative activity of the reaction of sulfite with HAMs depends on bimolecular nucleophilic substitution reaction reactivity. The order of the reductive dehalogenation rates of HAMs versus the substitution of halogen atoms was iodo- > bromo- >> chloro-. During reductive dehalogenation of HAMs by sulfite, the α-carbon bound to the amide group underwent nucleophilic attack at 180° to the leaving group (halide). As a consequence, the halide was pushed off the opposite side, generating a transition state pentacoordinate. The breaking of the C-X bond and the formation of the new C-S bond occurred simultaneously and HAM sulfonate formed as the immediate product. Results suggest that S(IV) can be used to degrade brominated and iodinated HAMs in drinking water and therefore should not be added as a quenching agent before HAM analysis to accurately determine the HAM concentrations produced during water disinfection.

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