Occurrence and Cytotoxicity of Aliphatic and Aromatic Halogenated Disinfection Byproducts in Indoor Swimming Pool Water and Their Incoming Tap Water

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.

Revealing the impact of sample enrichment method on concentration and cytotoxicity of volatile disinfection byproducts in drinking water: A quantitative study for liquid-liquid extraction

Liquid-liquid extraction (LLE) combined with the N2 blow-down method is a promising tool for bioanalysis of drinking water. However, detailed information on which disinfection byproduct (DBP) classes are retained in LLE extracts is currently unavailable. In this study, the recovery of seven classes of volatile DBPs and total adsorbable organic halogens (TOX) during the LLE method, combined with three common N2 blow-down methods, for bioanalysis in real tap water was analyzed at a 2-L scale, along with their corresponding cytotoxicity. The total concentration of seven classes of volatile DBPs in drinking water in Suzhou ranged from 64.6 to 83.0 µg/L, with the majority contributed by trihalomethanes (THMs: 59.9 µg/L), haloaldehydes (HALs: 5.4 µg/L), haloacetamides (HAMs: 3.4 µg/L), and haloacetonitriles (HANs: 3.2 µg/L). During the LLE - N2 blow-down process for bioanalysis, about 69-85 % of targeted volatile DBPs and 64-75 % of TOX were lost, respectively. Seven classes of volatile DBPs accounted for 52.8-64.3 % and 23.8-61.3 % of TOX in tap water and LLE - N2 blow-down samples, respectively, suggesting that targeted aliphatic DBPs are the key contributors to TOX. Furthermore, although LLE - solvent exchange had a better recovery performance than other N2 blow-down methods, the recoveries of volatile DBPs using this method were still not ideal. For example, HALs and HAMs had a slightly better recovery (>50 %), while most volatile DBPs had a poor recovery, including iodo-trihalomethanes (I-THMs, 0 %), haloketones (28 %), THMs (26 %), halonitromethanes (33 %), and HANs (38 %). During LLE - solvent exchange, 31 % and 36 % of targeted DBPs and TOX, respectively, in real tap water can be retained, which shows better performance than non-ionic macroporous copolymers (XAD). More importantly, the water volume required in this method for cytotoxicity analysis is 2 L, which greatly reduces the burden of water sample collection, transport, and pre-treatment compared to XAD (which typically requires 5 or 10 L). In general, this paper reveals the fate of volatile DBPs during LLE - N2 blow-down and indicates that LLE - solvent exchange is a good substitute for the XAD method in bioanalysis.

Halobenzoquinone-induced potential carcinogenicity associated with p53-mediated cell cycle pathway

2,6-Dibromo-1,4-benzoquinone (2,6-DBBQ) and 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), two emerging halobenzoquinones (HBQs), have the highest detection frequencies and levels in drinking water among all HBQs. They are more toxic than the regulated disinfection byproducts. Quantitative structure toxicity relationship analysis predicted that HBQs are a class of potential bladder carcinogens. However, direct experimental evidence for the carcinogenicity of 2,6-DBBQ and 2,6-DCBQ is lacking and the associated toxicity mechanisms remain unclear. In this study, we confirmed the potential carcinogenicity of 2,6-DBBQ and 2,6-DCBQ using an in vitro malignant transformation assay, evaluated their cytotoxicity and genotoxicity, and investigated their toxicity mechanisms. The results showed that 2,6-DBBQ and 2,6-DCBQ significantly decreased the viability of human uroepithelial SV-HUC-1 cells and induced DNA damage in SV-HUC-1 cells, and chromosomal damage in HepG2 cells, and malignant transformation of SV-HUC-1 cells. Moreover, transcriptome sequencing revealed that 2,6-DBBQ and 2,6-DCBQ activated the p53-mediated cell cycle pathway in bladder cancer. In the p53-mediated cell cycle pathway, 2,6-DBBQ and 2,6-DCBQ induced cell cycle arrest at the S phase by downregulating p53 and upregulating p21. Additionally, 2,6-DBBQ and 2,6-DCBQ may have produced excessive reactive oxygen species, damaging DNA and chromosomes. These results not only first confirm the potential carcinogenicity of 2,6-DBBQ and 2,6-DCBQ but also provide an important reference for exploring the cytotoxicity and genotoxicity mechanisms of these HBQs.

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.

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.

Characteristics of disinfection byproducts from dissolved organic matter during chlor(am)ination of source water in Tibetan Plateau, China

The Tibetan Plateau, a typical high-altitude area, is less affected by human activities such as industrial development, and the external pollution to water sources is extremely low. Then it is also an important source of water samples for exploring the molecular characteristics of precursors in the dissolved organic matter (DOM) of disinfection byproducts (DBPs) in drinking water. Research data on DBPs in drinking water on the Tibet Plateau remains insufficient, leading to uncertainty about DBP contamination in the area. This study explores the formation potential of 35 typical DBPs, including 6 trihalomethanes (THMs), 9 haloacetic acids (HAAs), 2 halogenated ketones (HKs), 9 nitrosamines (NAs), and 9 aromatic DBPs, during chlorination and chloramination of typical source water samples in the Tibet Plateau of China. Moreover, in order to further investigate the characteristics of the generation of DBPs, the molecular composition of DOM in the collected water samples was characterized by Fourier transform ion cyclotron resonance mass spectrometry. The findings reveal that, for chlorination and chloramination, the average concentration of the five classes of DBPs was ranked as follows (chlorination, chloramination): HAAs (268.1 μg/L, 54.2 μg/L) > THMs (44.0 μg/L, 2.0 μg/L) > HKs (0.7 μg/L, 1.8 μg/L) > NAs (26.5 ng/L, 74.6 ng/L) > Aromatics (20.4 ng/L, 19.5 ng/L). The dominant compounds in THMs, HAAs, and NAs are trichloromethane, dichloroacetic acid, trichloroacetic acid, and nitrosopyrrolidine, respectively. This study highlights a significant positive correlation between DBP generation and UV254, SUV254, and the double bond equivalents of DOM in the source water. It systematically elucidates DOM molecular composition characteristics and DBP formation potential in high-altitude water sources, shedding light on key factors influencing DBP generation at the molecular level in high-altitude areas.

Disinfection byproducts and their cytotoxicity contribution from dissolved black carbon in source water during chlor(am)ination

Dissolved black carbon (DBC), the soluble component of black carbon, which mainly comes from the incomplete combustion of fossil fuels or biomass, is widely spread in source water and significantly contributes to the formation of dissolved organic matter (DOM). However, the origin of DBC in different types of source water in China has not been well studied, as well as its subsequent transformation and toxicity contribution during disinfection of source water DOM by chlor(am)ine. In this study, DBC from 17 different source water in East China at different seasons was collected. The δ13C compositions indicated that straw burning was the main origin of DBC in source water. After simulated chlor(am)ination of DBC, 5 categories of aliphatic disinfection byproducts (DBPs) including trihalomethanes, haloacetic acids, haloacetonitriles, haloketones, halonitromethanes and 6 categories of aromatic DBPs including halophenols, halonitrophenols, halohydroxybenzaldehyde, halohydroxybenzoic acid, halobenzoquinones and haloaniline were detected. Compared with chlorination of DBC, higher levels of nitrogenous DBPs and aromatic DBPs were generated during chloramination. Detected DBPs accounted for 42 % of total organic halogen. What's more, Chinese hamster ovary cells cytotoxicity tests showed that the cytotoxicity of DBPs formed by chlor(am)ination of DBC was 4 times higher than that by chlor(am)ination of DOM. Haloacetonitriles contributed to the highest cytotoxicity in the chloramination of DBC, and haloacetic acids contributed to the highest cytotoxicity in chlorination. 67 % of the total cytotoxicity attributed to the undetected DBPs. As a result, DBPs generated from DBC contributed to 11.7 % of the total cytotoxicity in the chlor(am)ination of the source water DOM although DBC only took up 2 % of DOC in the source water. Results obtained from this study systematically revealed the DBPs formation from DBC and their potential cytotoxicity contribution in the chlor(am)ination of source water DOM, which should not be ignored in drinking water treatment.

Dihalogenated nitrophenols in drinking water: Prevalence, resistance to household treatment, and cardiotoxic impact on zebrafish embryo

Dihalogenated nitrophenols (2,6-DHNPs), an emerging group of aromatic disinfection byproducts (DBPs) detected in drinking water, have limited available information regarding their persistence and toxicological risks. The present study found that 2,6-DHNPs are resistant to major drinking water treatment processes (sedimentation and filtration) and households methods (boiling, filtration, microwave irradiation, and ultrasonic cleaning). To further assess their health risks, we conducted a series of toxicology studies using zebrafish embryos as the model organism. Our findings reveal that these emerging 2,6-DHNPs showed lethal toxicity 248 times greater than that of the regulated DBP, dichloroacetic acid. Specifically, at sublethal concentrations, exposure to 2,6-DHNPs generated reactive oxygen species (ROS), caused apoptosis, inhibited cardiac looping, and induced cardiac failure in zebrafish. Remarkably, the use of a ROS scavenger, N-acetyl-l-cysteine, considerably mitigated these adverse effects, emphasizing the essential role of ROS in 2,6-DHNP-induced cardiotoxicity. Our findings highlight the cardiotoxic potential of 2,6-DHNPs in drinking water even at low concentrations of 19 μg/L and the beneficial effect of N-acetyl-l-cysteine in alleviating the 2,6-DHNP-induced cardiotoxicity. This study underscores the urgent need for increased scrutiny of these emerging compounds in public health discussions.

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, 8‑hydroxy-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.

New mechanistic insights into halogen-dependent cytotoxic pattern of monohaloacetamide disinfection byproducts

As highly toxic nitrogenous disinfection byproducts (DBPs), monohaloacetamides (monoHAcAms) generally exhibited a cytotoxic rank order of iodoacetamide ˃ bromoacetamide ˃ chloroacetamide. However, the mechanisms underlying the halogen-dependent cytotoxic pattern remain largely veiled as yet. In this work, oxidative stress/damage levels in monoHAcAm-treated Chinese hamster ovary cells were thoroughly analyzed, and binding interactions between monoHAcAms and antioxidative enzyme Cu/Zn-superoxide dismutase (Cu/Zn-SOD) were investigated by multiple spectroscopic techniques and molecular docking. Upon exposure to monoHAcAms, the intracellular levels of key biomarkers associated with oxidative stress/damage, including reactive oxygen species, malondialdehyde, lactate dehydrogenase, 8-hydroxy-2-deoxyguanosine, cell apoptosis, and G1 cell cycle arrest, were all significantly increased in a dose-response manner with the same halogen-dependent rank order as their cytotoxicity. Moreover, this rank order was also determined to be applicable to the monoHAcAm-induced alterations in the conformation, secondary structure, and activity of Cu/Zn-SOD, the microenvironment surrounding aromatic amino acid residues in Cu/Zn-SOD, as well as the predicted binding energy of SOD-monoHAcAm interactions. Our results revealed that the halogen-dependent cytotoxic pattern of monoHAcAms was attributed to their differential capacity to induce oxidative stress/damage and their interaction with antioxidative enzyme, which contribute to a better understanding of the halogenated DBP-induced toxicological mechanisms.

Formation of halonitromethanes from benzylamine during UV/chlorination: Impact factors, toxicity alteration, and pathways

Halonitromethanes (HNMs), a representative nitrogen-containing disinfection byproduct, have gained significant concerns due to their higher cytotoxicity and genotoxicity. UV/chlorination is considered a promising alternative disinfection technology for chlorination. This study aimed to investigate the HNMs formation from benzylamine (BZA) during UV/chlorination. The experimental results revealed that the yields of HNMs initially raised to a peak then dropped over time. Higher chlorine dosage and BZA concentration promoted the formation of HNMs, whereas alkaline pH inhibited their formation. The presence of bromine ion (Br-) not only converted chlorinated-HNMs (Cl-HNMs) to brominated (chlorinated)-HNMs Br (Cl)-HNMs) and brominated-HNMs (Br-HNMs) but also enhanced the total concentration of HNMs. Besides, the calculated cytotoxicity index (CTI) and genotoxicity index (GTI) of HNMs were elevated by 68.97% and 60.66% as Br- concentration raised from 2 to 6 µM. The possible formation pathways of HNMs from BZA were proposed based on the intermediates identified by a gas chromatography/mass spectrometry (GC/MS). In addition, the formation rules of HNMs in actual water verified the results in deionized water during UV/chlorination. The results of this study provide basic data and a theoretical basis for the formation and control of HNMs, which is conducive to applying UV/chlorination.

Chloro- and bromo-benzoquinone formation and transformation mechanisms in a drinking water-distribution system

Halogenated benzoquinones (HBQs) are frequently detected in tap water. HBQ levels are correlated with water age. As the water-transmission distance (water age) increases, the levels of bromo-benzoquinones (Br-BQs) decreased and those of chloro-benzoquinones (Cl-BQs) remained relatively stable in drinking water-distribution system in the presence of residual chlorine. 2,3,5,6-Tetrachloro-1,4-benzoquinone (TCBQ) and 2,6-dibromo-1,4-benzoquinone (DBBQ) were the most abundant Cl-BQ and Br-BQ, with maximum concentrations of 60.2 and 181.4 ng/L, respectively. TCBQ and DBBQ were chosen as representatives of HBQs to investigate their reactions with chlorine, including kinetics, pathways, and changes in toxicity. The hydrolysis and chlorination rates of HBQs were significantly pH-dependent, and the kinetic rates of DBBQ were faster than TCBQ in the pH range of 5-10. Chlorination converted highly toxic TCBQ and DBBQ to less-toxic chlorinated/brominated aliphatic disinfection by-products (DBPs), thereby reducing the overall toxicity of water bodies. This study provides comprehensive insights into the distinct life cycles of TCBQ and DBBQ in drinking water, covering formation, transformation, and toxicity. These findings provide a nuanced understanding of the risks posed by HBQs at various locations within the drinking water distribution system, offering valuable guidance for improving the control of DBPs in drinking water.

Gastrointestinal Degradation and Toxicity of Disinfection Byproducts in Drinking Water Using In Vitro Models and the Roles of Gut Microbiota

Disinfection byproducts (DBPs) in drinking water are mainly exposed to the human body after oral ingestion and degradation in the gastrointestinal tract. The role of gastrointestinal degradation in the toxic effects of DBPs still needs further investigation. In this study, the degradation of five categories of DBPs (22 DBPs) in the stomach and small intestine was investigated based on a semicontinuous steady-state gastrointestinal simulation system, and 22 DBPs can be divided into three groups based on their residual proportions. The degradation of chloroacetonitrile (CAN), dibromoacetic acid (DBAA), and tetrabromopyrrole (FBPy) was further analyzed based on the Simulator of the Human Intestinal Microbial Ecosystem inoculating the gut microbiota, and approximately 60% of CAN, 45% of DBAA, and 80% of FBPy were degraded in the stomach and small intestine, followed by the complete degradation of remaining DBPs in the colon. Meanwhile, gastrointestinal degradation can reduce oxidative stress-mediated DNA damage and apoptosis induced by DBPs in DLD-1 cells, but the toxicity of DBPs did not disappear with the complete degradation of DBPs, possibly because of their interferences on gut microbiota. This study provides new insights into investigating the gastrointestinal toxic effects and mechanisms of DBPs through oral exposure.

Potential and mechanism of disinfection by-products removal in drinking water by bubbling corona discharge

Disinfection by-products (DBPs) with significant teratogenic and carcinogenic properties have become a growing concern among the public. As an efficient and environmentally friendly technology, non-thermal plasma offers potential for removing emerging micro-pollutants. In this study, the degradation performance of bubbling corona discharge was evaluated on 24 halogenated alicyclic and aliphatic DBPs present in drinking water at concentrations ranging from ng/L to μg/L. The degradation of DBPs followed pseudo-first-order kinetics with rate constants (kobs) in the descending order of halonitromethanes (HNMs), halogenated benzoquinones (HBQs), haloacetonitriles, trihalomethanes (THMs), haloketones, halogenated aldehydes, and haloacetic acids (HAAs). THMs, HNMs, and HBQs were effectively removed within 5 min under a discharge power of 28 W. Degradation rates achieved by plasma treatment surpass those of other conventional treatment technologies. The required energy consumption was in the range of 5-30 kW·h/m3/order. Furthermore, the study investigated the effects of discharge power, initial concentration, and economic analysis on the degradation of four selected DBPs as representatives of mono-, di- and multi-carbon-containing DBPs, namely chloroform (TCM) and bromoform (TBM), tribromoacetic acid (TBAA), and 2,3,5,6-tetrachloro-1,4-benzoquinone (TetraC-BQ). Reactive radicals in the plasma system were investigated using electron paramagnetic resonance, optical emission spectroscopy, fluorimetry, and radical scavengers. Hydrated electrons and hydroxyl radicals played an important role in the removal of DBPs. The intermediates generated during the degradation of TCM, TBM, TBAA, and TetraC-BQ were identified, and the possible degradation pathways for mono- and binary C-DBPs and HBQs were deduced. The breakdown of HBQs did not produce secondary contamination with aliphatic DBPs. The carbon in DBPs was primarily converted to formic acid, acetic acid, and oxalic acid, and the halogens were mainly converted to halogen ions. Additionally, luminescent bacteria toxicity testing confirmed that plasma treatment could reduce the acute toxicity of water samples. These findings demonstrate the potential of plasma treatment as a post-treatment device at the household level.

Unveiling the occurrence, distribution, removal, and environmental impacts of 65 emerging contaminants in neglected fresh leachate from municipal solid waste incineration plants

Emerging contaminants (ECs) are commonly found in environmental media. Yet leachate from municipal solid waste incineration plants (MSWIPs), which can serve as a reservoir for various contaminants, including ECs, has received little investigation. To address this gap, 65 ECs were analyzed in the fresh leachate and biological effluent from three major MSWIPs in Shanghai. Results indicated that over half (56%) of the 65 ECs were detected in fresh leachate. Different ECs would be removed to varying degrees after biological treatment, including polycyclic aromatic hydrocarbons (PAHs) (65%), polybrominated diphenyl ethers (PBDEs) (51%), phthalate esters (PAEs) (36%), and organophosphorus pesticides (OPPs) (34%). Notably, for tetrabromobisphenol A (TBBPA), a PBDE substitute, only 2% was removed after biological treatment, while polychlorinated biphenyls (PCBs) were effectively removed at 83%. Water solubility and the octanol-water partition coefficient are key factors influencing the distribution and removal of ECs in leachate. the effluent will still contain refractory ECs even after the biological treatment. These residual ECs discharged to sewers can impact wastewater treatment plants or contaminate surface water and groundwater. These findings provide insights into the leachate contamination by ECs, their environmental fate, factors affecting their behavior, and potential environmental impacts.

Full-scale multisampling and empirical modeling of DBPs in water and air of indoor pools

Disinfection by-products (DBPs) are formed in the water in swimming pools due to reactions between disinfectants (chlorine, bromine, ozone) and the organic matter introduced by bathers and supply water. High concentrations of DBPs are also reported in the air of indoor swimming pools. Based on a robust multisampling program, the levels and variations of DBPs in the air (trichloramine [TCAM] and trihalomethanes [THMs]) and water (THM) were assessed, as well as their precursors (total organic carbon, water temperature, pH, free, and total chlorine) and proxies (CO2 and relative humidity) in four indoor chlorinated swimming pools. High-frequency sampling was conducted during one high-attendance day for each pool. This study focused on parameters that are easy to measure in order to develop models for predicting levels of THMs and TCAM in the air. The results showed that the number of bathers had an important impact on the levels of THMs and TCAM, with a two-to-three-fold increase in air chloroform (up to 110 μg/m3) and a two-to-four-fold increase in TCAM (up to 0.52 mg/m3) shortly after pools opened. The results of this study for the first time showed that CO2 and relative humidity can serve as proxies for monitoring variations in airborne THMs and TCAM. Our results highlight the good predictive capacity of the developed models and their potential for use in day-to-day monitoring. This could help optimize and control DBPs formation in the air of indoor swimming pools and reduce contaminant exposure for both pool employees and users.

Overlooked inorganic DBPs in trichloroisocyanuric acid (TCCA) disinfected indoor swimming pool: Evidences from concentration, cytotoxicity, and human health risk

Trichloroisocyanuric acid (TCCA) is a popular disinfectant for swimming pools in China. However, the occurrence and importance of regulated disinfection byproducts (DBPs) in TCCA-disinfected swimming pools are less understood. This study analyzed 12 regulated DBPs (4 trihalomethanes (THMs), 5 haloacetic acid (HAAs), bromate, chlorate, and chlorite) in 85 swimming pool water samples and 17 input tap water samples from one swimming pool for 17 days continuously. Considering water temperature, pH, free chlorine, total chlorine, and urea, approximately 88%, 49%, 97%, 55%, and 97% of swimming pool water samples were within the water quality limits for China. Total concentrations of THMs, HAAs, and inorganic DBPs of 20.4-42.2, 82.0-229, and 100-729 μg/L in the swimming pool, and 16.6-28.3, 8.2-12.8, and 64.4-95.6 μg/L in the tap water, indicating inorganic DBPs are the dominant swimming pool and drinking water pollutants. Cancer risk values of regulated DBPs in swimming pools and input tap water are 2.7E-05 and 8.1E-05, respectively, and exceed the US EPA's threshold (1.0E-06). The non-cancer risk is below the US EPA's threshold. Following TCCA disinfection, the concentration and calculated cytotoxicity of regulated DBPs had a 3.6-fold and 1.9-fold increase, respectively. Inorganic DBPs contribute to the calculated concentration and cancer risks of DBPs in swimming pools and tap water at sufficient concentrations warranting regulation. This study provides data on 12 regulated DBPs in TCCA-disinfected indoor swimming pools, highlighting the importance of inorganic DBPs from evidences of concentration, cytotoxicity, and cancer risk for the first time.

Advances and research needs for disinfection byproducts control strategies in swimming pools

The control of disinfection byproducts (DBPs) in swimming pools is of great significance due to the non-negligible toxicity and widespread existence of DBPs. However, the management of DBPs remains challenging as the removal and regulation of DBPs is a multifactorial phenomenon in pools. This study summarized recent studies on the removal and regulation of DBPs, and further proposed some research needs. Specifically, the removal of DBPs was divided into the direct removal of the generated DBPs and the indirect removal by inhibiting DBP formation. Inhibiting DBP formation seems to be the more effective and economically practical strategy, which can be achieved mainly by reducing precursors, improving disinfection technology, and optimizing water quality parameters. Alternative disinfection technologies to chlorine disinfection have attracted increasing attention, while their applicability in pools requires further investigation. The regulation of DBPs was discussed in terms of improving the standards on DBPs and their preccursors. The development of online monitoring technology for DBPs is essential for implementing the standard. Overall, this study makes a significant contribution to the control of DBPs in pool water by updating the latest research advances and providing detailed perspectives.