Nonadditive Cytotoxicity in Select Disinfection Byproducts and Disinfected Secondary Effluents.

Toxicity studies of water disinfection byproducts (DBPs) typically assume additive interactions. Coupling results from both the bottom-up cytotoxicity interaction approach by selecting six common DBPs and the top-down cytotoxicity fractionating the disinfected secondary effluent containing a much broader DBP selection, we demonstrated a novel effect of clear, nonadditive cytotoxicity at low chemical concentrations regardless of the number of DBP types involved. We revealed that the cytotoxicity interactions were influenced by the chemical's type, concentration factor, and mixing ratio. For the bottom-up approach, the average combination indices (CIs) were 1.61 (chloracetamide + chloroacetonitrile, antagonism), 1.03 (bromoacetamide+bromoacetonitrile, near additivity), and 0.69 (iodoacetamide + iodoacetonitrile, synergism) across the DBPs' concentration range of 10-4-10-7 M. These cytotoxicity interactions also varied with the components' mixing ratios. For the top-down approach, we obtained two fractions of DBP mixtures from the disinfected secondary effluent using solvents of different polarities. The effect of the concentration on CI values was significant, with a maximum 43.1% relative deviation in CI from LC5 to LC95. The average CI values across the sample concentration range of 1-50 × (concentration factor) varied from 1.68 (antagonism) to 0.89 (slight synergism) as the ratio of mixture A increased. These results call for further research in prioritizing the forcing DBPs in mixtures.

Determining high priority disinfection byproducts based on experimental aquatic toxicity data and predictive models: Virtual screening and in vivo study.

Only about 100 disinfection byproducts (DBPs) have been tested for their potential aquatic toxicity. It is not known which specific DBPs, DBP main groups, and DBP subgroups are more toxic due to the lack of experimental toxicity data. Herein, high priority specific DBPs, DBP main groups, DBP subgroups, most sensitive model aquatic species, potential PBT and PMT (persistent, bioaccumulative/mobile, and toxic) DBPs were virtually screened for 1187 updated DBPs inventory. Priority setting based on experimental and predicted acute and chronic aquatic toxicity data found that the aromatic and alicyclic DBPs in four DBPs main groups showed high priority because larger proportions of aromatic and alicyclic DBPs are in high hazard categories (i.e. Acute and/or Chronic Toxic-1 or Toxic-2) according to the criteria in GHS system compared to the aliphatic and heterocyclic DBPs. The halophenols, estrogen-DBPs, nonhalogenated esters, and nonhalogenated aldehydes were recognized as high priority DBPs subgroups. For specific DBPs, 19 and 31 DBPs should be highly concerned in the future study because both acute and chronic toxicity of those DBPs to all of the three aquatic life (algae, Daphnia magna, fish) were classified as Toxic-1 and Toxic-2, respectively. The Daphnia magna and algae were sensitive to the acute toxicity of DBPs, while the fish and Daphnia magna were sensitive to the chronic toxicity of DBPs. One potential PBT (Tetrachlorobisphenol A) and four potential PMT DBPs were identified. For verification, the acute toxicity of four DBPs on three aquatic organism were performed, and their tested acute toxicity data to three aquatic organisms were consistent with the predictions. Our results could be beneficial to government regulators to adopt effective measures to limit the discharge of high priority DBPs and help the scientific community to develop or improve disinfection processes to reduce the production of high priority DBPs.

Nontargeted Analysis of Reactive Nitrogenous Compounds in Suwannee River Standard Reference Materials and Authentic River Water Samples.

Concerns over toxic nitrogenous disinfection byproducts (N-DBPs) necessitate identifying their precursors in source water. Natural organic amino compounds are known precursors to N-DBPs. Three Suwannee River (SR) standard reference materials (SRMs), humic acids (HA), fulvic acids (FA), and natural organic matter (NOM), are commonly used to study DBP formation, but the chemical makeup of amino compounds in SRSRMs remains largely unknown. To address this, we combined stable hydrogen/deuterium isotope labeling, HDPairFinder bioinformatics, and nontargeted high-performance liquid chromatography-high-resolution mass spectrometry (HPLC-HRMS) to characterize these compounds in SRSRMs. This method classifies reactive amines, provides accurate masses and MS/MS spectra, and quantifies intensities. We identified 2707 high-quality features with primary and/or secondary amines in SRSRMs and 75% of them having an m/z < 300. Across all three SRSRMs, 327 amino features were detected, while 856, 794, and 200 unique features were found in SRNOM, SRHA, and SRFA, respectively. In North Saskatchewan River (NSR) samples, a total of 6449 amino features were detected, 818 of them matched those in SRSRMs, and 87% of them were different between the two rivers. Using chemical standards, we confirmed 10 compounds and tentatively identified 5 more. This study highlights similarities and differences in reactive N-precursors in SRSRMs and local river water, enhancing the understanding of geo-differences in reactive N-precursors in different source waters.

New Species and Cytotoxicity Mechanism of Halohydroxybenzonitrile Disinfection Byproducts in Drinking Water.

Recently, seven dihalohydroxybenzonitriles (diHHBNs) have been determined as concerning nitrogenous aromatic disinfection byproducts (DBPs) in drinking water. Herein, eight new monohalohydroxybenzonitriles (monoHHBNs), including 3-chloro-2-hydroxybenzonitrile, 5-chloro-2-hydroxybenzonitrile, 3-chloro-4-hydroxybenzonitrile, 3-bromo-2-hydroxybenzonitrile, 5-bromo-2-hydroxybenzonitrile, 3-bromo-4-hydroxybenzonitrile, 5-iodo-2-hydroxybenzonitrile, and 3-iodo-4-hydroxybenzonitrile, were detected and identified in drinking water for the first time. Thereafter, the relative concentration-cytotoxicity contribution of each HHBN was calculated based on the acquired occurrence level and cytotoxicity data in this study, the genome-scale cytotoxicity mechanism was explored, and a quantitative structure-activity relationship (QSAR) model was developed. Results indicated that new monoHHBNs were present in drinking water at concentrations of 0.04-1.83 ng/L and exhibited higher cytotoxicity than some other monohalogenated aromatic DBPs. Notably, monoHHBNs showed concentration-cytotoxicity contribution comparable to diHHBNs, which have been previously identified as potential toxicity drivers in drinking water. Transcriptomic analysis revealed immunotoxicity and genotoxicity as dominant cytotoxicity mechanisms for HHBNs in Chinese hamster ovary (CHO-K1) cells, with potential carcinogenic effects. The QSAR model suggested oxidative stress and cellular uptake efficiency as important factors for their cytotoxicity, highlighting the importance of potential iodinated HHBNs in drinking water, such as 3,5-diiodo-2-hydroxybenzonitrile, for future studies. These findings are meaningful for better understanding the health risk and toxicological significance of HHBNs in drinking water.

Nanoplastics enhanced the developmental toxicity of aromatic disinfection byproducts to a marine polychaete at non-feeding early life stage.

Micro/nanoplastics can act as vectors for organic pollutants and enhance their toxicity, which has been attributed to the ingestion by organisms and the "Trojan horse effect". In this study, we disclosed a non-ingestion pathway for the toxicity enhancement effect of nanoplastics. Initially, the combined toxicity of polystyrene microplastics (40 µm) or nanoplastics (50 nm) with three disinfection byproducts (DBPs) to a marine polychaete, Platynereis dumerilii, was investigated. No toxic effect was observed for the micro/nanoplastics alone. The microplastics showed no effect on the toxicity of the three DBPs, whereas the nanoplastics significantly enhanced the toxicity of two aromatic DBPs when the polychaete was in its non-feeding early life stage throughout the exposure period. The microplastics showed no interaction with the P. dumerilii embryos, whereas the nanoplastics agglomerated strongly on the embryonic chorion and fully encapsulated the embryos. This could contribute to higher actual exposure concentrations in the microenvironment around the embryos, as the concentrations of the two aromatic DBPs on the nanoplastics were 1200 and 120 times higher than those in bulk solution. Our findings highlight an important and previously overlooked mechanism by which nanoplastics and organic pollutants, such as DBPs, pose a higher risk to marine species at their vulnerable early life stages. This study may contribute to a broader understanding of the environmental impacts of plastic pollution and underscore the necessity to mitigate their risks associated with DBPs.

Efficient trihalomethane quantification in drinking water for minimally-equipped water treatment plants labs.

Chlorine is a common disinfectant used in water treatment. However, its reaction with organic matter can lead to the formation of harmful byproducts, such as trihalomethanes (THMs), which are potentially carcinogenic. To address this issue, the aim of this work was to enhance a colorimetric method capable of quantifying THMs in drinking water through UV/Vis Spectrophotometry, using cost-effective equipment, and validate this methodology for the first time according to established validation protocols. The method's innovation involved replacing the solvent pentane with the more common hexane, along with adjusting the heating ramp, elucidating the mechanisms involved in the process. This method involves the reaction between THMs, pyridine, and NaOH to produce a colored compound, which is then monitored through molecular absorption spectroscopy in the visible region. The method was thoroughly validated, achieving a limit of detection of 13.41 µg L-1 and a limit of quantification of 40.65 µg L-1. Recovery assays ranged from 86.1 % to 90.7 %, demonstrating high accuracy. The quality of the linear fit for the analytical curve exceeded R2 > 0.98. The method was applied to real samples, revealing concentrations ranging from 13.58 to 55.46 µg L-1, all way below the legal limit in Brazil (Maximum Contaminant Levels (MCL) = 100 µg L-1). This cost-effective and straightforward method is suitable for integration into water treatment plant laboratories.

Effects of UV light on physicochemical changes in thermoplastic polyurethanes: Mechanism and disinfection byproduct formation.

The presence of microplastics (MPs) products and particles in the environment can significantly impact the human body. Most MPs that enter the environment also enter the water cycle. During sunlight light irradiation (especially ultraviolet (UV) part) or UV disinfection, many of these MPs, particularly those rich in surface functional groups like thermoplastic polyurethanes (TPU), undergo physicochemical changes that can affect the formation of disinfection byproducts (DBPs). This study investigates the physicochemical changes of TPU in water after exposure to UV irradiation and incubation in the dark, as well as the formation of DBPs after chlorination. The results show that TPU undergo chain breakage, oxidation, and cross-linking when exposed to UV irradiation in an aqueous system. This leads to fragmentation into smaller particles, which facilitates the synthesis of DBPs. Subsequent research has demonstrated that the TPU leaching solution produces a significantly higher DBP content than the chlorination of TPU MPs, particularly at high concentrations of CHCl3. Therefore, it is important to give greater consideration to the soluble DBP precursors released by TPU.

The investigation of quenching conditions for the analysis of total organic halogen, aliphatic and aromatic halogenated disinfection byproducts formed from chlor(am)ination.

Total organic halogen (TOX) is used to describe total amount of halogenated DBPs. Typically, once a chlor(am)inated water sample is collected, it is necessary to add a quenching agent to quench the residual disinfectant so that further reactions to form more DBPs during the holding time can be prevented. In this study, we evaluated the effects of four quenching agents: ammonium chloride (NH4Cl), ascorbic acid, sodium sulfite (Na2SO3), and sodium thiosulfate (Na2S2O3) on the decomposition of TOX, aliphatic and aromatic halogenated DBPs under various quenching conditions (quenching time, pH, quenching ratio, temperature). The results showed that ascorbic acid had the least impact on TOX. Ascorbic acid appeared to be the most suitable quenching agent for aliphatic halogenated DBPs, especially since it could preserve more haloacetonitriles than other quenching agents. Both ascorbic acid and Na2SO3 could be used for the analysis of aromatic halogenated DBPs. The lower pH (pH 6.0), not excessive quenching agents and lower temperature (4 ºC) were all conducive to the preservation of TOX and halogenated DBPs. Importantly, unknown TOX (UTOX) also contained significantly toxic components. It was also found that addition of quenching agents might lead to underestimation of UTOX by researchers. SYNOPSIS: The quenching agents and quenching conditions for the analysis of total organic halogen, aliphatic and aromatic halogenated DBPs formed from chlor(am)ination were investigated.

Unexpected weakened formation of disinfection byproducts and enhanced production of halates by cupric oxide during chlorination of peptide-bound aspartic acid.

Under the condition that the residual chlorine is guaranteed, the biofilm still thrives in drinking water distribution systems through secreting a large number of extracellular polymeric substances (EPS), in which protein components are the primary precursor of disinfection byproducts (DBPs), mostly in the form of combined amino acids. The aim of this study is to investigate the action of CuO on the formation of halates (XO3-, ClO3- and BrO3-) and DBPs (trihalomethanes, THMs; haloacetonitriles, HANs) with aspartic acid tetrapeptide (TAsp) as protein surrogate. The presence of CuO promoted the self-decay rather than TAsp-induced decay of oxidants, resulting in an increase in XO3- yield and a decrease in DBPs yield. It was CuO-induced weaker production of cyanoacetic acid and 3-oxopropanoic acid that induced the decreased yields of HANs and THMs, respectively. The FTIR and Raman spectra indicate a weak complexation between CuO and TAsp. Given this, the CuO-HOX/OX- complexes were inferred to be reactive to HOX/OX- but less reactive to TAsp. The study helps to better understand the formation of XO3- and DBPs during the chlorination of EPS, and propose precise control strategies when biofilm boosts in water pipes.

The ideal model for determination the formation potential of priority DBPs during chlorination of free amino acids.

Amino acids (AAs) account for about 15-35% of dissolved organic nitrogen (DON), and are known as the important precursors of nitrogenous disinfection by-products (N-DBPs). Determining the formation potential (FP) of AAs to DBPs is used to reveal the key precursors of DBPs for further control, while the ideal method for N-DBPs FP of AAs during chlorination is not revealed. In this study, the ideal FP test models for five classes of priority DBPs during chlorination of four representative AAs (accounted for about 35% of total AAs) were analyzed. For haloaldehydes (HALs), haloketones (HKs), haloacetonitriles (HANs), haloacetamides (HAMs), and halonitromethanes (HNMs), their FPs during chlorination of four AAs were 0.1-13.0, 0.01-1.1, 0.1-104, not detectable (nd)-173, and nd-0.4 µg/mg, respectively. The FPs of priority DBPs had significant deviations between different FP test models and different tested AAs. For HALs, the model, whose chlorine dosage was determined by 15 × molar concentration of AAs [Cl (mM) = 15 × M](named: model II), was the ideal model. For HKs, model II was also the ideal FP test model for AAs with ≤3 carbons, while for AAs with 4 carbons, the model, whose chlorine dosage was determined by keeping the residual chlorine at 1 ± 0.2 mg/L after 24 h of reaction (named: model 4), was the ideal model. For HANs and HNMs, model 4 was the ideal FP test model for most of the studied AAs. The performance of HAMs during chlorination of amino acids was totally different from other P-DBPs, and model 3 was recommended to be the ideal model, in which chlorine dosage was determined by 3 × mass concentration of AAs [Cl (mg/L) = X × DOC]. This study is a reference that helps researchers select an ideal model for N-DBPs FP study of AAs.

Molecularly imprinted polymers and porous organic frameworks based analytical methods for disinfection by-products in water and wastewater.

Disinfection by-products (DBPs) with heritage toxicity, mutagenicity and carcinogenicity are one kind of important new pollutants, and their detection and removal in water and wastewater has become a common challenge facing mankind. Advanced functional materials with ideal selectivity, adsorption capacity and regeneration capacity provide hope for the determination of DBPs with low concentration levels and inherent molecular structural similarity. Among them, molecularly imprinted polymers (MIPs) are favored, owing to their predictable structure, specific recognition and wide applicability. Also, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) with unique pore structure, large specific surface area and easy functionalization, attract increasing interest. Herein, we review recent advances in analytical methods based on the above-mentioned three functional materials for DBPs in water and wastewater. Firstly, MIPs, MOFs and COFs are briefly introduced. Secondly, MIPs, MOFs and COFs as extractants, recognition element and adsorbents, are comprehensively discussed. Combining the latest research progress of solid-phase extraction (SPE), sensor, adsorption and nanofiltration, typical examples on MIPs and MOFs/COFs based analytical and removal applications in water and wastewater are summarized. Finally, the application prospects and challenges of the three functional materials in DBPs analysis are proposed to promote the development of corresponding analytical methods.

Recognizing high-priority disinfection byproducts based on experimental and predicted endocrine disrupting data: Virtual screening and in vitro study.

So far, about 130 disinfection by-products (DBPs) and several DBPs-groups have had their potential endocrine-disrupting effects tested on some endocrine endpoints. However, it is still not clear which specific DBPs, DBPs-groups/subgroups may be the most toxic substances or groups/subgroups for any given endocrine endpoint. In this study, we attempt to address this issue. First, a list of relevant DBPs was updated, and 1187 DBPs belonging to 4 main-groups (aliphatic, aromatic, alicyclic, heterocyclic) and 84 subgroups were described. Then, the high-priority endocrine endpoints, DBPs-groups/subgroups, and specific DBPs were determined from 18 endpoints, 4 main-groups, 84 subgroups, and 1187 specific DBPs by a virtual-screening method. The results demonstrate that most of DBPs could not disturb the endocrine endpoints in question because the proportion of active compounds associated with the endocrine endpoints ranged from 0 (human thyroid receptor beta) to 32% (human transthyretin (hTTR)). All the endpoints with a proportion of active compounds greater than 10% belonged to the thyroid system, highlighting that the potential disrupting effects of DBPs on the thyroid system should be given more attention. The aromatic and alicyclic DBPs may have higher priority than that of aliphatic and heterocyclic DBPs by considering the activity rate and potential for disrupting effects. There were 2 (halophenols and estrogen DBPs), 12, and 24 subgroups that belonged to high, moderate, and low priority classes, respectively. For individual DBPs, there were 23 (2%), 193 (16%), and 971 (82%) DBPs belonging to the high, moderate, and low priority groups, respectively. Lastly, the hTTR binding affinity of 4 DBPs was determined by an in vitro assay and all the tested DBPs exhibited dose-dependent binding potency with hTTR, which was consistent with the predicted result. Thus, more efforts should be performed to reveal the potential endocrine disruption of those high research-priority main-groups, subgroups, and individual DBPs.

Insight into the effect of UVC-based advanced oxidation processes on the interaction of typical microplastics and their derived disinfection byproducts during disinfection.

The 10 µm polystyrene and polyethylene-terephthalate microplastics (MPs), prevalent in finished drink water, were employed to investigate the effect of normal dosage UVC-based advanced-oxidation-processes (UVC-AOPs) on the interaction between MPs and their derived disinfection-byproducts (DBPs) during subsequent chlorination-disinfection, in the presence of Br-, for the first time. The results indicated that UVC/H2O2 caused higher leaching of microplastic-derived dissolved-organic-matter (MP-DOM), with smaller and narrower molecular-weight-distribution than UVC and UVC/peroxymonosulfate (UVC/PMS). The trihalomethanes (as dominant DBPs) molar-formation-potentials (THMs-MFPs) for MP-DOM leached in different UVC-AOPs followed the order of UVC/H2O2>UVC/PMS>UVC. The adsorption of formed THMs, especially Br-THMs, back on MPs was observed in all MPs suspensions with or without UVC-AOPs pre-treatment. The Cl-THMs adsorption by MPs is more sensitive to UVC-AOPs than Br-THMs. The adsorption experiments showed that UVC-AOPs reduce the capacity but increase the rate of THMs adsorption by MPs, suggesting the halogen and hydrogen bonding forces governed the THMs adsorption rate while hydrophobic interaction determines their adsorption capacity. The UVC-AOPs pre-treatment sharply increased the total yield of THMs via both indirectly inducing MP-DOM leaching and directly increasing the THMs-MFPs of MPs by oxidation. 21.36-41.96% of formed THMs adsorbed back on the UVC-AOPs-pretreated MPs, which might increase the toxicity of MPs.

Reaction mechanisms of chlorinated disinfection byproducts formed from nitrophenol compounds with different structures during chlor(am)ination and UV/post-chlor(am)ination.

Nitrophenol compounds (NCs) have high formation potentials of disinfection byproducts (DBPs) in water disinfection processes, however, the reaction mechanisms of DBPs formed from different NCs are not elucidated clearly. Herein, nitrobenzene, phenol, and six representative NCs were used to explore the formation mechanisms of chlorinated DBPs (Cl-DBPs) during chlor(am)ination and UV/post-chlor(am)ination. Consequently, the coexistence of nitro and hydroxy groups in NCs facilitated the electrophilic substitution to produce intermediates of Cl-DBPs, and the different positions of nitro and hydroxy groups also induced different yields and formation mechanisms of Cl-DBPs during the chlorination and UV/post-chlorination processes. Besides, the amino, chlorine, and methyl groups significantly influenced the formation mechanisms of Cl-DBPs during the chlorination and UV/post-chlorination processes. Furthermore, the total Cl-DBPs yields from the six NCs followed a decreasing order of 2-chloro-3-nitrophenol, 3-nitrophenol, 2-methyl-3-nitrophenol, 2-amino-4-nitrophenol, 2-nitrophenol, and 4-nitrophenol during chlorination and UV/post-chlorination. However, the total Cl-DBPs yields from the six NCs during chloramination and UV/post-chloramination followed a quite different order, which might be caused by additional reaction mechanisms, e.g., nucleophilic substitution or addition might occur to NCs in the presence of monochloramine (NH2Cl). This work can offer deep insights into the reaction mechanisms of Cl-DBPs from NCs during the chlor(am)ination and UV/post-chlor(am)ination processes.

Comparative analysis of chlorinated disinfection byproducts formation from 4-nitrophenol and 2-amino-4-nitrophenol during UV/post-chlorination.

Nitrophenol compounds (NCs) are widely distributed in water environments and regarded as important precursors of disinfection byproducts (DBPs). Herein, 4-nitrophenol and 2-amino-4-nitrophenol were selected as representative NCs to explore chlorinated DBPs (Cl-DBPs) formation during UV/post-chlorination. Dichloronitromethane (DCNM), trichloronitromethane (TCNM), dichloroacetonitrile (DCAN), and trichloromethane (TCM) were formed from 4-nitrophenol and 2-amino-4-nitrophenol during UV/post-chlorination, and the yields of individual Cl-DBPs from 2-amino-4-nitrophenol were higher than those from 4-nitrophenol. Meantime, increasing chlorine contact time, UV fluence, and free chlorine dose could enhance Cl-DBPs formation, while much higher values of the three factors might decrease the yields of Cl-DBPs. Besides, alkaline pH could decrease the yields of halonitromethane (HNMs) and DCAN but increase the yields of TCM. Also, higher concentrations of 4-nitrophenol and 2-amino-4-nitrophenol would induce more Cl-DBPs formation. Subsequently, the possible formation pathways of DCNM, TCNM, DCAN, and TCM form 4-nitrophenol and 2-amino-4-nitrophenol during UV/post-chlorination were proposed according to transformation products (TPs) and density functional theory (DFT) calculation. Notably, Cl-DBPs formed from 2-amino-4-nitrophenol presented higher toxicity than those from 4-nitrophenol. Among these generated Cl-DBPs, DCAN and TCNM posed higher cytotoxicity and genotoxicity, respectively. Furthermore, 4-nitrophenol, 2-amino-4-nitrophenol, and their TPs exhibited ecotoxicity. Finally, 4-nitrophenol and 2-amino-4-nitrophenol presented a high potential to produce DCNM, TCNM, DCAN, and TCM in actual waters during UV/post-chlorination, but the Cl-DBPs yields were markedly different from those in simulated waters. This work can help better understand Cl-DBPs formation from different NCs during UV/post-chlorination and is conducive to controlling Cl-DBPs formation.

Cytotoxicity of emerging halophenylacetamide disinfection byproducts in drinking water: Mechanism and prediction.

Halophenylacetamides (HPAcAms) have been identified as a new group of nitrogenous aromatic disinfection byproducts (DBPs) in drinking water, but the toxicity mechanisms associated with HPAcAms remain almost completely unknown. In this work, the cytotoxicity of HPAcAms in human hepatoma (HepG2) cells was evaluated, intracellular oxidative stress/damage levels were analyzed, their binding interactions with antioxidative enzyme were explored, and a quantitative structure-activity relationship (QSAR) model was established. Results indicated that the EC50 values of HPAcAms ranged from 2353 µM to 9780 µM, and the isomeric structure as well as the type and number of halogen substitutions could obviously induce the change in the cytotoxicity of HPAcAms. Upon exposure to 2-(3,4-dichlorophenyl)acetamide (3,4-DCPAcAm), various important biomarkers linked to oxidative stress and damage, such as reactive oxygen species, 8­hydroxy-2-deoxyguanosine, and cell apoptosis, exhibited a significant increase in a dose-dependent manner. Moreover, 3,4-DCPAcAm could directly bind with Cu/Zn-superoxide dismutase and induce the alterations in the structure and activity, and the formation of complexes was predominantly influenced by the van der Waals force and hydrogen bonding. The QSAR model supported that the nucleophilic reactivity as well as the molecular compactness might be highly important in their cytotoxicity mechanisms in HepG2 cells, and 2-(2,4-dibromophenyl)acetamide and 2-(3,4-dibromophenyl)acetamide deserved particular attention in future studies due to the relatively higher predicted cytotoxicity. This study provided the first comprehensive investigation on the cytotoxicity mechanisms of HPAcAm DBPs.

Effects of cupric ions on the formation of chlorinated disinfection byproducts from nitrophenol compounds during UV/post-chlorination.

Cupric ions (Cu2+) are ubiquitous in surface waters and can influence disinfection byproducts (DBPs) formation in water disinfection processes. This work explored the effects of Cu2+ on chlorinated DBPs (Cl-DBPs) formation from six representative nitrophenol compounds (NCs) during UV irradiation followed by a subsequent chlorination (i.e., UV/post-chlorination), and the results showed Cu2+ enhanced chlorinated halonitromethane (Cl-HNMs) formation from five NCs (besides 2-methyl-3-nitrophenol) and dichloroacetonitrile (DCAN) and trichloromethane (TCM) formation from six NCs. Nevertheless, excessive Cu2+ might reduce Cl-DBPs formation. Increasing UV fluences displayed different influences on total Cl-DBPs formation from different NCs, and increasing chlorine dosages and NCs concentrations enhanced that. Moreover, a relatively low pH (5.8) or high pH (7.8) might control the yields of total Cl-DBPs produced from different NCs. Notably, Cu2+ enhanced Cl-DBPs formation from NCs during UV/post-chlorination mainly through the catalytic effect on nitro-benzoquinone production and the conversion of Cl-DBPs from nitro-benzoquinone. Additionally, Cu2+ could increase the toxicity of total Cl-DBPs produced from five NCs besides 2-methyl-3-nitrophenol. Finally, the impacts of Cu2+ on Cl-DBPs formation and toxicity in real waters were quite different from those in simulated waters. This study is conducive to further understanding how Cu2+ affected Cl-DBPs formation and toxicity in chlorine disinfection processes and controlling Cl-DBPs formation in copper containing water.

Degrading surface-water-based natural organic matter and mitigating haloacetonitrile formation during chlorination: Comparison of UV/persulfate and UV/hydrogen peroxide pre-treatments.

Haloacetonitriles (HANs) are unregulated disinfection by-products that are more toxic than regulated species. Therefore, efficient decomposition of HAN precursors prior to disinfection is crucial for allaying the potential HAN-induced health risks. This study investigated the key roles of ultraviolet-activated persulfate (UV/PS) treatment in alleviating HAN formation. The effects of UV/PS treatment were evaluated by correlating with the characteristics of organic matter in surface water and comparing with conventional UV/H2O2 treatment. Upon irradiating raw water samples and a Suwannee River humic acid solution spiked with 10 mM PS or H2O2 with 254 nm UV light, UV/PS treatment was found to be more potent than UV/H2O2 in mitigating the HAN production and degrading organic substances; moreover, UV/PS treatment effectively decreased the dissolved organic nitrogen (DON) content. In contrast, UV/H2O2 treatment did not induce any noticeable reduction in DON level. Furthermore, both UV/PS and UV/H2O2 treatments reduced the dichloroacetonitrile (DCAN) formation potential (FP), leading to strong correlations with the degradation of aromatic and humic-acid-like compounds. Notably, UV/PS treatment efficiently decreased the FP of bromochloroacetonitrile (BCAN) and dramatically reduced that of dibromoacetonitrile (DBAN) after a sharp increase; however, UV/H2O2 treatment gradually increased the DBAN-FP. Bromide was activated by sulfate radicals during UV/PS treatment, negatively correlating with the BCAN-FP and DBAN-FP, indicating that the formation of reactive bromine species increased the DBAN-FP; however, excessive oxidation possibly led to the recovery of inorganic bromine for decreasing the BCAN-FP and DBAN-FP. Additionally, UV/PS treatment effectively suppressed toxicity owing to its high reduction rate for brominated HANs; in contrast, UV/H2O2 treatment resulted in less significant BCAN and DBAN reductions, leading to minimal net reduction in toxicity. Overall, UV/PS treatment was remarkably effective at diminishing the toxicity of brominated HANs, underscoring its potential to mitigate drinking-water-related health risks.

Impact of climate change on formation of nitrogenous disinfection by-products. Part II: water blooming and enrichment by humic substances.

Climate change affects the concentration and characteristics of dissolved organic matter (DOM) in surface water. The changes in composition of DOM have many implications to drinking water quality, especially in the case of formation of disinfection by-products (DBPs). The aim of this study was to investigate the formation of nitrogenous DBPs (N-DBPs) during chlorination and chloramination, caused by the alternation of surface water's DOM driven by climate change. For this reason, two different cases were examined: (a) rise of algal organic matter (AOM) due to water blooming and (b) water enrichment by humic substances. The target compounds were haloacetonitriles (HANs), haloacetamides (HAcAms), and halonitromethane (TCNM). The results showed that Anabaena appears to be a major precursor for HAcAms and TCNM, while humic acids are precursors for HANs. The results of the mixtures presented the same pattern. During the water blooming case, HAcAms and TCNM formation are in favor, while during water enrichment by humic substances case, HANs is the N-DBP group with higher formation yield. Cloraminated samples presented higher values of cytotoxicity and genotoxicity compared to the chlorinated.

Formation of halogenated forms of bisphenol A (BPA) in water: Resolving isomers with ion mobility - mass spectrometry and the role of halogenation position in cellular toxicity.

Halogenated BPA (XBPA) forms resulting from water chlorination can lead to increased toxicity and different biological effects. While previous studies have reported the occurrence of different XBPAs, analytical limitation have hindered the analysis and differentiation of the many potential isomeric forms. Using online solid-phase extraction - liquid chromatography - ion-mobility - high-resolution mass spectrometry (OSPE-LC-IM-HRMS), we demonstrated a rapid analysis method for the analysis of XBPA forms after water chlorination, with a total analysis time of less than 10 min including extraction and concentration and low detection limits (∼5-80 ng/L range). A multi in-vitro bioassay testing approach for the identified products revealed that cytotoxicity and bioenergetics impacts were largely associated with the presence of halogen atoms at positions 2 or 2' and the overall number of halogens incorporated into the BPA molecule. Different XBPA also showed distinct impacts on oxidative stress, peroxisome proliferator-activated receptor gamma - PPARγ, and inflammatory response. While increased DNA damage was observed for chlorinated water samples (4.14 ± 1.21-fold change), the additive effect of the selected 20 XBPA studied could not explain the increased DNA damage observed, indicating that additional species or synergistic effects might be at play.