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Acetaminophen is widely used to treat mild to moderate pain and to reduce fever. Under the worldwide COVID-19 pandemic, this over-the-counter pain reliever and fever reducer has been drastically consumed, which makes it even more abundant than ever in municipal wastewater and drinking water sources. Chlorine is the most widely used oxidant in drinking water disinfection, and chlorination generally causes the degradation of organic compounds, including acetaminophen. In this study, a new reaction pathway in the chlorination of acetaminophen, i.e., oxidative coupling reactions via acetaminophen radicals, was investigated both experimentally and computationally. Using an ultraperformance liquid chromatograph coupled to an electrospray ionization-triple quadrupole mass spectrometer, we detected over 20 polymeric products in chlorinated acetaminophen samples, some of which have structures similar to the legacy pollutants "polychlorinated biphenyls". Both C-C and C-O bonding products were found, and the corresponding bonding processes and kinetics were revealed by quantum chemical calculations. Based on the product confirmation and intrinsic reaction coordinate computations, a pathway for the formation of the polymeric products in the chlorination of acetaminophen was proposed. This study suggests that chlorination may cause not only degradation but also upgradation of a phenolic compound or contaminant.

Chlorine disinfection of saline wastewater effluents rich in bromide and iodide forms relatively toxic brominated and iodinated disinfection byproducts (DBPs). Ultrasonication is a relatively new water treatment technology, and it is less sensitive to suspended solids in wastewaters. In this study, we examined the effects of ultrasonication (in terms of reactor type and combination mode with chlorination) on the DBP formation and toxicity in chlorinated primary and secondary saline wastewater effluents. Compared with the chlorinated wastewater effluent samples without ultrasonication, ultrasonic horn pretreatment of the wastewater effluent samples reduced the total organic halogen (TOX) levels in chlorination by ∼30%, but ultrasonic bath pretreatment of the wastewater samples did not significantly change the TOX levels in chlorination, which might be attributed to the higher energy utilization and decomposition extent of organic DBP precursors in the ultrasonic horn reactor. Moreover, the TOX levels in the chlorinated samples with ultrasonic horn pretreatment (USH-chlorination), simultaneous treatment (chlorination+USH) and subsequent treatment (chlorination-USH) were also significantly reduced, with the maximum TOX reductions occurring in the samples with ultrasonic horn pretreatment. A toxicity index was calculated by weighting and summing the levels of total organic chlorine, total organic bromine and total organic iodine in each treated sample. The calculated toxicity index values of the chlorinated wastewater effluent samples followed a descending rank order of "chlorination""chlorination+USH""chlorination-USH""USH-chlorination", with the lowest toxicity occurring in the samples with ultrasonic horn pretreatment. Then, a developmental toxicity bioassay was conducted for each treated sample. The measured toxicity index values of the chlorinated wastewater samples followed the same descending rank order.

Increasing chemical pollution of aquatic environments is a growing concern with global relevance. A large number of organic chemicals are termed as "micropollutants" due to their low concentrations, and long-term exposure to micropollutants may pose considerable risks to aquatic organisms and human health. In recent decades, numerous treatment methods and technologies have been proposed to remove micropollutants in water, and typically several micropollutants were chosen as target pollutants to evaluate removal efficiencies. However, it is often unclear whether their toxicity and occurrence levels and frequencies enable them to contribute significantly to the overall chemical pollution in global aquatic environments. This review intends to answer an important lingering question: Which micropollutants or class of micropollutants deserve more attention globally and should be removed with higher priority? Different risk-based prioritization approaches were used to address this question. The risk quotient (RQ) method was found to be a feasible approach to prioritize micropollutants in a large scale due to its relatively simple assessment procedure and extensive use. A total of 83 prioritization case studies using the RQ method in the past decade were compiled, and 473 compounds that were selected by screening 3466 compounds of three broad classes (pharmaceuticals and personal care products (PPCPs), pesticides, and industrial chemicals) were found to have risks (RQ0.01). To determine the micropollutants of global importance, we propose an overall risk surrogate, that is, the weighted average risk quotient (WARQ). The WARQ integrates the risk intensity and frequency of micropollutants in global aquatic environments to achieve a more comprehensive priority determination. Through metadata analysis, we recommend a ranked list of 53 micropollutants, including 36 PPCPs (e.g., sulfamethoxazole and ibuprofen), seven pesticides (e.g., heptachlor and diazinon), and 10 industrial chemicals (e.g., perfluorooctanesulfonic acid and 4-nonylphenol) for risk management and remediation efforts. One caveat is that the ranked list of global importance does not consider transformation products of micropollutants (including disinfection byproducts) and new forms of pollutants (including antibiotic resistance genes and microplastics), and this list of global importance may not be directly applicable to a specific region or country. Also, it needs mentioning that there might be no best answer toward this question, and hopefully this review can act as a small step toward a better answer.

Chlorine is extensively used in disinfection processes in water and wastewater treatment processes. The chlorine is typically dosed by jet mixing, and yet no systematic study of chlorine jets has been conducted. In the Stonecutters Island Sewage Treatment Works (SCISTW) of the Hong Kong Harbour Area Treatment Scheme (HATS), concentrated chlorine solution (in sodium hypochlorite form) is injected into primary treated effluent in the form of turbulent dense jets. In view of the importance of sewage disinfection to the environmental impact, it is essential to understand the mixing and reaction of chlorine with ammonia nitrogen for disinfection dosage optimization. In this study, an integral buoyant jet model is developed for a chlorine jet reacting with ammonia nitrogen in CEPT sewage. The jet mixing and chlorine demand is studied by accounting for the stoichiometric reaction of chlorine and ammonia including breakpoint chlorination. Based on experiments of chlorine jet in ammonia solution, the stoichiometric mass ratio of chlorine to ammonia under dynamic mixing process is found to be 7.48. The chlorination kinetics model is then incorporated in a general model of a chlorine jet discharging into a coflowing primary treated sewage effluent, with the reaction ratio calibrated based on experimental measurements for the stagnant case. Significant chlorine demand can occur within a short distance (in the order of 0.1 m, or 1 s or less of travel time) from the dosing point due to the turbulent mixing and reaction with ammonia nitrogen and organic impurities. The chlorine demand of CEPT effluent increases with jet dosing total residual chlorine (TRC) concentration. At TRC 60%), while for TRC ≫ 2000 mg/L, up to two thirds of chlorine demand can be induced by the oxidation of organic debris. Model predictions of chlorine demand and concentration agree well with laboratory experiments and field data.

The Khorat Plateau is one of the largest potash deposits in the world. In recent years, exploitation of potash resources accompanied by leakage of underground brines (UB) in potassium-bearing strata has threatened mining safety. However, there is little research on origin of UB in Laos. In this study, twelve samples of UB, salt springs (SS) and river waters were collected in Khammouane mining area, central Laos and analyzed for ionic and boron isotopic compositions. The results show that both of UB, dominated by K+, Mg2+, Na+ and Cl– ions, and SS, enriched in Na+ and Cl–, are chloride-type brines, while river waters abundant in Ca2+ and HC$${\text{O}}_{3}^{ - }$$ ions are carbonate-type waters. K+ (35.1–53.7 g/L) and Rb+ (12.9–16.6 mg/L) concentrations of UB are higher than the peak (25.9 g/L, 9.4 mg/L) of seawater evaporation trajectories (SET). UB is also characterized by high Mg2+ (32.7–68.0 g/L) and Br– (1795.2–2801.3 mg/L) concentrations and its lg(Cl/Br) ratios (1.9–2.1) deviate from the halite dissolution line. These comparisons indicate that the water chemistries of UB are mainly influenced by dissolution of carnallite and sylvite. High Sr2+ concentrations (31.8–58.6 mg/L) in UB might be simultaneously associated with dissolution of potash salt and Ca-bearing minerals (carbonate and anhydrite). The negative saturation indices (SI) of different salt minerals in UB suggest that salt minerals are unsaturated in UB. Meanwhile, boron (B) concentrations (396.0–426.0 mg/L) and δ11B values (+19.8–+21.0‰) of UB fall in between low B–δ11B end member (0.02 mg/L, +2.31‰) of river water and high B-δ11B end member (126.7–890.8 μg/g, +25.94–+32.94‰) of evaporitic minerals. The comparison implies that UB was influenced and mixed by two end members. Therefore, combining with major and trace ionic concentrations, isotopic compositions and lithologies of salt-bearing strata revealed by drillings in mining area, we conclude that the major solute source in UB is derived from dissolution of carnallite and sylvite. These geochemical evidences provide insights into dealing with leakage of underground brines occurred in the underground mining of potash deposits in Laos.

Chlorine-disinfected sewage effluents are typically dechlorinated by using NaHSO3, Na2SO3, or Na2S2O3, as chlorine residual could be harmful to aquatic organisms upon discharge of sewage effluents into receiving marine water. In this study, we systematically investigated the effects of dechlorination-related factors on the developmental toxicity of a chlorinated saline primary sewage effluent, via direct exposure of the embryos of a marine polychaete to the effluent. The results showed that dechlorination ratio (i.e., the ratio of the dosed amount to the requisite stoichiometric amount of a dechlorination agent) and mixing condition were critical factors affecting the toxicity of the effluent. The toxicity of the effluent under insufficient dechlorination conditions was mainly caused by residual chlorine, especially monochloramine. Although the three dechlorination agents generally performed similarly, dechlorination with Na2S2O3 required a more vigorous mixing condition than that with NaHSO3 or Na2SO3, as the relatively high density of Na2S2O3 might affect the mixing efficiency. Under insufficient mixing conditions, a prolonged dechlorination time was beneficial to achieving complete dechlorination and thus lowered the toxicity of the effluent. Moreover, because disinfection byproducts (DBPs) may have chronic effects on aquatic organisms, the developmental toxicity of the DBP mixtures in the chlorinated effluent in different dechlorination scenarios was also evaluated. The results indicated that increasing the dechlorination ratio reduced the developmental toxicity of the DBP mixture in the chlorinated saline sewage effluent, which might be ascribed to the decrease of the levels of overall brominated and iodinated DBPs; the dechlorination agent (NaHSO3 or Na2S2O3) might act as a nucleophile in the nucleophilic substitution and cause the substitution of bromine or iodine atoms in brominated and iodinated DBPs. The results from this study might aid in the design and operation of dechlorination facilities in sewage treatment plants.

Ozonation is widely used in wastewater treatment but the associated byproduct formation is a concern. When ozonation is used in the presence of bromide, bromate is generally considered as a major byproduct, and few studies have examined the toxicity of organic byproducts. This study was designed to investigate the cytotoxicity, genotoxicity and DNA/RNA oxidative damage to Chinese hamster ovary (CHO) cells of organic extracts from ozonated wastewater in the absence or presence of bromide. Ozonation effectively detoxified secondary effluents containing no bromide. However, ozonation significantly increased the cytotoxicity and genotoxicity of the effluents spiked with a bromide concentration as low as 100 μg/L, compared with the bromide-free effluent. When the bromide concentration in the effluent was increased to 2000 μg/L, ozonation resulted in 1.4–1.5 times the cytotoxicity and 1.5–5.0 times the genotoxicity of the non-ozonated secondary effluent. Besides, the oxidative stress (including reactive oxygen species and reactive nitrogen species) and DNA/RNA oxidative damage also became more severe and a high level of 8-hydroxy-(deoxy)guanosine was detected in the CHO cell nucleus in the presence of bromide. Cytotoxicity and genotoxicity were found to increase with the formation of total organic bromine (TOBr). When the CHO cells were exposed to both the organic byproducts and bromate formed from wastewater containing 500 and 2000 μg/L bromide, bromate significantly increased oxidative stress and DNA/RNA oxidative damage at relatively high concentration factors, suggesting both organic byproduct and bromate can contribute to toxicity increase. During ozonation of the effluent containing bromide, particular attention should be paid to the organic byproducts such as TOBr.

Disinfection byproducts (DBPs) are produced during the process of disinfecting drinking water. Toxicological and epidemiological studies have indicated that DBPs may pose adverse effects on human health, which is why their ubiquitous existence in drinking water supplies has aroused increasing concerns. With hundreds of known DBPs and many still unaccounted for, a variety of analytical methods are essential for investigating their formation and occurrence in drinking water. This review discusses current analytical methods and challenges associated with the identification and measurement of DBPs mainly published in the last two years.

Although700 disinfection byproducts (DBPs) have been identified,50% of the total organic halogen (TOX) in drinking water chlorination is unknown, and the DBPs responsible for the chlorination-associated health risks remain largely unclear. Recent studies have revealed numerous aromatic halo-DBPs, which generally present substantially higher developmental toxicity than aliphatic halo-DBPs. This raises a fascinating and important question: how much of the TOX and developmental toxicity of chlorinated drinking water can be attributed to aromatic halo-DBPs? In this study, an effective approach with ultraperformance liquid chromatography was developed to separate the DBP mixture (from chlorination of bromide-rich raw water) into aliphatic and aromatic fractions, which were then characterized for their TOX and developmental toxicity. For chlorine contact times of 0.25-72 h, aromatic fractions accounted for 49-67% of the TOX in the obtained aliphatic and aromatic fractions, which were equivalent to 26-36% of the TOX in the original chlorinated water samples. Aromatic halo-DBP fractions were more developmentally toxic than the corresponding aliphatic fractions, and the overall developmental toxicity of chlorinated water samples was dominated by aromatic halo-DBP fractions. This might be explained by the considerably higher potentials of aromatic halo-DBPs to bioconcentrate and then generate reactive oxygen species in the organism.

Advances in the ultra-high-resolution mass spectroscopy lead to a deep insight into the molecular characterization of natural organic matter (NOM). Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) has been used as one of the most powerful tools to decipher NOM molecules. In FTICR-MS analysis, the matrix effects caused by the co-occurring inorganic substances in water samples greatly affect the ionization of NOM molecules. The inherent complexity of NOM may hinder its component classification and formula assignment. In this study, basic principles and recent advances for sample separation and purification approaches, ionization methods, and the evolutions in formula assignment and data exploitation of the FTICR-MS analysis were reviewed. The complementary characterization methods for FTICR-MS were also reviewed. By coupling with other developed/developing characterization methods, the statistical confidence for inferring the NOM compositions by FTICR-MS was greatly improved. Despite that the refined separation procedures and advanced data processing methods for NOM molecules have been exploited, the big challenge for interpreting NOM molecules is to give the basic structures of them. Online share of the FTICR-MS data, further optimizing the FTICR-MS technique, and coupling this technique with more characterization methods would be beneficial to improving the understanding of the composition and property of NOM.

Granular activated carbon (GAC) adsorption has been traditionally used to remove natural organic matter (NOM), the major precursor of halogenated disinfection byproducts (DBPs), in drinking water treatment plants. Recently, a new approach has been developed to effectively control the formation of trihalomethanes, haloacetic acids, and total organic halogen (TOX) in chlorinated drinking water by targeting intermediate aromatic halogenated DBPs instead of NOM using GAC adsorption. However, the applicability of this new approach to different source water matrices and disinfection conditions remained unclear. In this study, the effects of bromide and contact time on the performance of the new approach for DBP control were investigated. Same source waters were also treated with the traditional approach (i.e., using GAC to remove NOM prior to chlorination) and with chlorination only for comparison. With increasing the initial bromide level from 0 to 2 mg/L, the TOX removal with the new approach increased from 52% to 74%, while the removal with the traditional approach increased from 18% to 37%. Besides, as the chlorine contact time increased from 0.5 to 3.0 h, the TOX removal with the new approach increased from 61% to 75%, while the removal with the traditional approach increased from 21% to 36%. Increasing the bromide level and chlorine contact time enhanced the halogenated DBP removal with both new and traditional approaches, but the removal with the new approach was always two times higher or more than that with the traditional approach, which justified the superiority of the new approach. Moreover, various intermediate aromatic halogenated DBPs were detected in the chlorinated water samples and their levels were significantly decreased after the GAC adsorption, which further corroborated the effectiveness of the new approach for DBP control.

This study characterized the dissolved organic matter (DOM) and byproducts generated after the exposure of activated sludge to ozone and NaClO in ceramic MBR. It was found that NaClO triggered more significant release of DOM than ozone. Proteins with the molecular weight greater than 20 kDa and humic acid like-substances were the principal components of DOM generated by NaClO, while ozone was found to effectively degrade larger biopolymers to low molecular weight substances. The results showed that more than 80% of DOM generated by NaClO and ozone could pass through the 0.2-μm ceramic membrane. Furthermore, total organic chlorine (TOCl) was determined to be the principal species of halogenated byproducts in both cases, while the generation of TOCl by NaClO was much more significant than that by ozone. Only a small fraction of TOCl was removed by the 0.2-μm ceramic membrane. More importantly, the toxic bioassays further revealed that the supernatant of sludge suspension and permeate in the MBR with NaClO cleaning exhibited higher developmental toxicity to the polychaete embryos than those by ozone. The results clearly showed that on-line chemical cleaning with ozone should be a more eco-friendly and safer approach for sustaining long-term membrane permeability in ceramic MBR.

The unintended formation of disinfection byproducts (DBPs) may compromise the safety of drinking water. Since no specified DBPs have been found to be responsible for the overall adverse effects and over half of total organic halogen (TOX) remains unidentified, DBP mixture toxicity is gaining increasing interest as a potential indicator of how risky drinking water might be. In this study, a new approach to evaluating the toxicity of drinking water DBP mixtures was developed by combining freeze-drying or rotoevaporation pretreatment with an in vivo high-salinity-tolerance bioassay with the embryos of a marine polychaete Platynereis dumerilii. The DBP recoveries by freeze-drying or rotoevaporation were compared with those by commonly applied liquid-liquid-extraction (LLE). For drinking water subjected to typical disinfection processes (i.e., chlorination, chloramination, chlorine dioxide treatment, and ozonation with or without postchlorination), LLE led to the lowest TOX recovery (11-18%) and the loss of all inorganic DBPs, while freeze-drying and rotoevaporation recovered 28-58% and 35-61% of TOX, respectively, and effectively recovered 81-99% and 85-104% of inorganic DBPs, respectively. Thus, LLE caused an underestimation of the toxicity of DBP mixtures compared with freeze-drying and rotoevaporation. Besides, the comparative toxicity varied significantly for water samples pretreated with different methods due to the effect of inorganic DBPs and a synergistic effect of organic and inorganic DBPs. The new approach revealed that the bromide-rich source water disinfected with ozone caused the highest developmental toxicity, followed by those disinfected with chlorine, chlorine dioxide, and chloramine in that order.

When a bromide-containing water is treated by the ultraviolet (UV)/chlorine process, hydroxyl radicals (HO) and halogen radicals such as Cl or Br are formed due to the UV photolysis of free halogens. These reactive species may induce the formation of bromate, which is a probable human carcinogen. Bromate formation in the UV/chlorine process using low pressure (LP) and medium pressure (MP) lamps in the presence of bromide was investigated in the present study. The UV/chlorine process significantly enhanced bromate formation as compared to dark chlorination. The bromate formation was elevated with increasing UV fluence, bromide concentration, and pH values under both LP and MP UV irradiations. It was significantly enhanced at pH 9 compared to those at pH 6 and 7 with MP UV irradiation, while it was slightly enhanced at pH 9 with LP UV. The formation by UV/chlorine process started with the formation of free bromine (HOBr/OBr-) through the reaction of chlorine and bromide, followed by a subsequent oxidation of free bromine and formation of BrO and bromate by reacting with radicals.

On-line chemical cleaning with sodium hypochlorite (NaClO) has been extensively practiced for maintaining the stable permeability of membrane bioreactor (MBR), during which activated sludge is inevitably exposed to NaClO. The authors previously reported the NaClO-induced generation of dissolved organic matter (DOM) and halogenated byproducts, however their fate in terms of biodegradability and removability in MBR has been unknown. Therefore, this study investigated the removal mechanisms of generated DOM and byproducts in an aerobic MBR. It was found that about 39% of DOM produced was removed through biodegradation and membrane rejection. The fluorescence excitation-emission matrix (EEM) coupled with parallel factor analysis (PARAFAC) also revealed that protein-like substances were more readily biodegradable than humic-like substances. Moreover, 25 kinds of chlorinated and brominated byproducts were detected after the contact of biomass with NaClO by ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, while nine of which were confirmed with standard compounds. 62.4–84.5% halogenated byproducts were ended up in permeate of MBR chemically cleaned with 5–20 mg/L of NaClO. This study raises a serious concern on reusing and recycling of such MBR permeate.

Chlorine dioxide (ClO2) is a widely used alternative disinfectant due to its high biocidal efficiency and low-level formation of trihalomethanes and haloacetic acids. A major portion of total organic halogen (TOX), a collective parameter for all halogenated DBPs, formed in ClO2-treated drinking water is still unknown. A commonly used pretreatment method for analyzing halogenated DBPs in drinking water is one-time liquid-liquid extraction (LLE), which may lead to a substantial loss of DBPs prior to analysis. In this study, characterization and identification of polar halogenated DBPs in a ClO2-treated drinking water sample were conducted by pretreating the sample with multiple extractions. Compared to one-time LLE, the combined four-time LLEs improved the recovery of TOX by 2.3 times. The developmental toxicity of the drinking water sample pretreated with the combined four-time LLEs was 1.67 times higher than that pretreated with one-time LLE. With the aid of ultra-performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, a new group of polar halogenated DBPs, trihalomethanols, were detected in the drinking water sample pretreated with multiple extractions; two of them, trichloromethanol and bromodichloromethanol, were identified with synthesized standard compounds. Moreover, these trihalomethanols were found to be the transformation products of trihalomethanes formed during ClO2 disinfection. The results indicate that multiple LLEs can significantly improve extraction efficiencies of polar halogenated DBPs and is a better pretreatment method for characterizing and identifying new polar halogenated DBPs in drinking water.

Chlorination is extensively applied for disinfecting sewage effluents, but it unintentionally generates disinfection byproducts (DBPs). Using seawater for toilet flushing introduces a high level of bromide into domestic sewage. Chlorination of sewage effluent rich in bromide causes the formation of brominated DBPs. The objectives of achieving a disinfection goal, reducing disinfectant consumption and operational costs, as well as diminishing adverse effects to aquatic organisms in receiving water body remain a challenge in sewage treatment. In this study, we have demonstrated that, with the same total chlorine dosage, a three-step chlorination (dosing chlorine by splitting it into three equal portions with a 5-min time interval for each portion) was significantly more efficient in disinfecting a primary saline sewage effluent than a one-step chlorination (dosing chlorine at one time). Compared to one-step chlorination, three-step chlorination enhanced the disinfection efficiency by up to 0.73-log reduction of Escherichia coli. The overall DBP formation resulting from one-step and three-step chlorination was quantified by total organic halogen measurement. Compared to one-step chlorination, the DBP formation in three-step chlorination was decreased by up to 23.4%. The comparative toxicity of one-step and three-step chlorination was evaluated in terms of the development of embryo-larva of a marine polychaete Platynereis dumerilii. The results revealed that the primary sewage effluent with three-step chlorination was less toxic than that with one-step chlorination, indicating that three-step chlorination could reduce the potential adverse effects of disinfected sewage effluents to aquatic organisms in the receiving marine water.

Halogenated disinfection byproducts (DBPs) are generated via reactions with natural organic matter (NOM) in chlorine disinfection of drinking water. How large NOM molecules are converted to halogenated aliphatic DBPs during chlorination remains a fascinating yet largely unresolved issue. Recently, many relatively toxic halogenated aromatic DBPs have been identified in chlorinated drinking waters, and they behave as intermediate DBPs to decompose to halogenated aliphatic DBPs. There is still one gap between NOM and halogenated aromatic DBPs. In this study, nine nonhalogenated aromatic compounds were identified as new intermediate DBPs in chlorination, including 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 3-formyl-4-hydroxybenzoic acid, salicylic acid, 5-formyl-2-hydroxybenzoic acid, 4-hydroxyphthalic acid, 4'-hydroxyacetophenone, 4-methylbenzoic acid, and 4-hydroxy-3-methylbenzaldehyde. These nonhalogenated aromatic DBPs formed quickly and reached the maximum levels at relatively low chlorine doses within a short contact time, and their formation pathways were proposed. The formation kinetics of three nonhalogenated aromatic DBPs and their corresponding monochloro-/dichloro-substitutes during chlorination were then modeled. The nonhalogenated aromatic DBPs contributed up to 84% of the formed monochloro-substitutes and 22% of the formed dichloro-substitutes, demonstrating that they somewhat acted as intermediates between NOM and halogenated aromatic DBPs. Furthermore, the formed nonhalogenated aromatic DBPs were found to be removed by >50% by granular activated carbon adsorption.

Chlorine disinfection is a vital treatment process to inactivate pathogens, but it also generates numerous halogenated disinfection byproducts (DBPs) via reactions with halides and natural organic matter (NOM). Epidemiological studies have shown that consumption of chlorinated drinking water with halogenated DBPs is related to increased spontaneous abortions, stillbirth, birth defects, and bladder and colorectal cancers. To control DBPs, efforts have been devoted to minimizing the formation of DBPs by removing the major DBP precursor, NOM, or by adopting alternative disinfectants. Notably, the precursor removal may not be very effective and the application of alternative disinfectants may generate their own sets of DBPs. It has remained a grand challenge to develop a new DBP control strategy which can effectively decrease the DBP formation and reduce the health risks of chlorinated drinking water. To solve this problem, Zhang’s group reported a new approach to effectively control halogenated DBPs by removing intermediate aromatic halogenated DBPs, which were formed from chlorine disinfection, via granular activated carbon (GAC) adsorption.

On-line chemical cleaning with sodium hypochlorite (NaOCl) is widely employed for sustaining MBR permeability, during which the inevitable contact between activated sludge and NaOCl had been shown to trigger substantial release of dissolved organic matter (DOM). Therefore, this work further explored the formation mechanisms of such DOM by looking into the respective reactions of intracellular organic matter (IOM) and cell debris in activated sludge with NaOCl. The results showed that DOM was primarily produced from the dissolution of cell wall, while IOM release was insignificant at the NaOCl concentration of 25 mg/L as Cl2. On the basis of experimental observations, a three-step mechanism was proposed for elucidating the DOM formation from activated sludge upon NaOCl exposure: (i) NaOCl first damaged cells by perforating cellular wall, producing a considerable amount of humic-like substances and low-molecular-weight halogenated byproducts; (ii) IOM was released but rapidly degraded and humified by NaOCl, accompanied with the formation of relatively high-molecular-weight halogenated byproducts; (iii) the residual NaOCl and combined chlorine continued to react with cell wall or likely diffused into cells leading to the deactivation of DNA/enzymes. Consequently, this study offers mechanistic insights into the origination of emerging contaminants during on-line membrane cleaning of practical MBR.

The interaction of chlorine with nitrogenous constituents in water is being concerned due to the formation of relatively toxic nitrogenous disinfection byproducts during chlorine disinfection. In this study, the transformation pathways of the chlorination of adenine and cytosine are proposed based on the products analysis using a collision-energy-dependent method on triple quadrupole mass spectrometry coupled with electrospray ionization. Products with multiple chlorine addition on the heterocyclic ring and on the aliphatic amine were observed during the chlorination of adenine and cytosine. The primary amine functional group in adenine and cytosine can undergo chlorine substitution to form N-chloramine and undergo hydrolysis of the C-N bond to form carbonyl derivative. The transformation of adenine and cytosine depends on pH and the chlorine to precursor (Cl/P) ratio. An 8-chloro derivative of adenine was observed at pH 4, but not at pH 7. Substitution of 1-2 chlorine atoms for the hydrogen atoms in the N-heterocyclic ring was observed during adenine chlorination compared to substitution of 1-4 chlorine atoms during cytosine chlorination. Chlorination of adenine also led to ring cleavage products. Both 5-chlorocytosine and 4-N-chlorocytosine were identified as cytosine transformation products. At pH 7 and a Cl/P molar ratio of 2, the major products of chlorination of cytosine were found to be aromatic chloro-compounds, not aliphatic N-chloramine. The results of this study are significant for understanding the transformation mechanisms of compounds containing both N-heterocyclic and primary amines due to chlorination.

Water disinfection can result in the unintended formation of halogenated disinfection byproducts (DBPs), which have been the subject of intensive investigation over the past 40 years. Robust methods for evaluating and characterizing the formation of halogenated DBPs are prerequisites for ultimately controlling the formation of DBPs and ensuring quality and safe disinfected water. Only a fraction of the total organic halogen (TOX) formed during disinfection has been chemically identified or even well characterized by the classical (derivatization-)gas chromatography/mass spectrometry (GC/MS) method. Such a method may not be amenable to the detection of polar halogenated DBPs, which constitute a major portion of the TOX that is still unaccounted for. Accordingly, a novel precursor ion scan (PIS) method using (liquid chromatography/) electrospray ionization-triple quadrupole mass spectrometry was developed for the rapid selective detection of all polar halogenated DBPs-no matter whether the DBPs are known or unknown-in water. This article reviews recent literature on the application of the PIS method for evaluating the occurrence, formation and control of polar halogenated DBPs in disinfected waters. The challenges in developing the PIS method were briefly summarized. Application of the powerful method pinpointed >150 previously unknown DBPs and revealed the formation, speciation and transformation of halogenated DBPs in disinfected drinking water, wastewater effluents, and swimming pool water. For the same source water, positive correlations were found between the total ion intensity (TII) levels in the PIS spectra of m/z 35/79/126.9 and the total organic chlorine/bromine/iodine levels in the disinfected water sample, and a disinfected sample with a higher TII level generally showed a higher toxic potency. Accordingly, the TII value can be used as a surrogate to comparatively reflect the water quality and assess the efficiency of a DBP control approach. To achieve a more comprehensive and systematic understanding of the DBP compositions in different waters and thus better control the DBP formation and reduce their overall toxicity, topics for future work were discussed.

Chlorine disinfection of wastewater effluents rich in bromide and iodide ions results in the formation of relatively toxic bromo- and iodo-disinfection byproducts (DBPs), especially highly toxic bromophenolic and iodophenolic DBPs, which could harm the marine ecosystem when they are discharged into receiving seawater along with the wastewater effluents. In this study, we investigated the conversion of three individual halophenolic DBPs (5-bromosalicylic acid, 2,5-dibromohydroquinone, and 2,4,6-triiodophenol) and two chlorinated saline wastewater DBP mixtures in seawater. The conversion products were analyzed with ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, and the conversion of overall halo-DBPs in the wastewater DBP mixtures was monitored by measuring total organic halogen. The photoconversion-induced variations in the toxicity were evaluated using the embryos of a marine polychaete. Halophenolic DBPs were found to undergo photoconversion in seawater. The conversion was triggered by photonucleophilic substitution: bromophenolic and iodophenolic DBPs were converted to their chlorophenolic or hydroxyphenolic analogues, via substituting the bromine and iodine atoms with chloride or hydroxide ions in seawater; chlorophenolic DBPs were converted to their hydroxyphenolic analogues, via substituting the chlorine atoms with hydroxide ions in seawater. The hydroxyphenolic analogues thus formed further decomposed and finally cleaved to aliphatic compounds. The photoconversion of chlorinated saline wastewater DBPs in receiving seawater was overall a dehalogenation and detoxification process.

Natural organic matter (NOM) is present in source water worldwide, and it is composed of numerous organic compounds produced in natural processes. NOM has been drawing increasing concerns because it not only affects drinking water treatment on many aspects (e.g., the performance of treatment techniques, necessity of advanced treatment, the dose of treatment chemicals, etc.), but also acts as the main precursor of hazardous drinking water disinfection byproducts (DBPs). Accordingly, to optimize treatment processes and to control the formation of DBPs, it is vital to analyze and characterize NOM for a better understanding of its property and reactivity. In this review, a summary of methods used in NOM analysis and characterization during drinking water treatment was provided, including analysis methods for general parameters (e.g., dissolved organic carbon, dissolved organic nitrogen, (specific) ultraviolet absorbance, fluorescence, polarity, and zeta potential) and characterization methods for elemental and structural identification (e.g., elemental analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, pyrolysis-gas chromatography/mass spectrometry, liquid chromatography/mass spectrometry, and Fourier transform ion cyclotron resonance mass spectrometry). In addition, preparation and pretreatment methods for NOM were also covered in this review, including isolation and concentration methods (reverse osmosis, pressure-reducing evaporation, freeze-drying, and electrodialysis) as well as fractionation methods (size exclusion chromatography, resin fractionation, membrane filtration, polarity rapid assessment, field-flow fractionation, and reversed-phase high performance liquid chromatography).

Disinfection byproducts (DBPs) are a class of compounds generated during chemical disinfection processes. Their wide distribution in potable water supply systems and environmental waters has aroused concerns for both human health and aquatic organisms. Recent toxicological studies have demonstrated that most of the emerging DBPs are significantly more toxic than the regulated DBPs. Analysis techniques are prerequisites for fully understanding DBPs, as they involve identifying and quantifying DBPs, and studying their occurrence and toxicity. Accordingly, this paper reviews current trends in the analysis and identification of emerging DBPs produced in artificial water samples with model substances (e.g., natural organic matter and anthropogenic contaminants) and in real environmental waters (e.g., drinking water, wastewater effluents, swimming pool water, ballast water, cooling water from power stations, and brine reject from desalination plants).

Chlorine disinfection is required to inactivate pathogens in drinking water, but it inevitably generates potentially toxic halogenated disinfection byproducts (halo-DBPs). A previous study has reported that the addition of ascorbate to tap water before boiling could significantly decrease the concentration of overall halo-DBPs in the boiled water. Since the fruit lemon is rich in vitamin C (i.e., ascorbic acid), adding it to tap water followed by heating and boiling in an effort to decrease levels of halo-DBPs was investigated in this study. We examined three approaches that produce lemon water: (i) adding lemon to tap water at room temperature, termed “Lemon”; (ii) adding lemon to boiled tap water (at 100 °C) and then cooling to room temperature, termed “Boiling + Lemon”; and (iii) adding lemon to tap water then boiling and cooling to room temperature, termed “Lemon + Boiling”. The concentrations of total and individual halo-DBPs in the resultant water samples were quantified with high-performance liquid chromatography-tandem mass spectrometry and the cytotoxicity of DBP mixtures extracted from the water samples was evaluated using human epithelial colorectal adenocarcinoma Caco-2 cells and hepatoma HepG2 cells. Our results show that the “Lemon + Boiling” approach substantially decreased the concentrations of halo-DBPs and the cytotoxicity of tap water. This strategy could be applied to control halo-DBPs, as well as to lower the adverse health effects of halo-DBPs on humans through tap water ingestion.

Chlorine disinfection inactivates pathogens in drinking water, but meanwhile it causes the formation of halogenated disinfection byproducts (DBPs), which may induce adverse health effects. Humans are unavoidably exposed to halogenated DBPs via tap water ingestion. Boiling of tap water has been found to significantly reduce the concentrations of halogenated DBPs. In this study, we found that compared with boiling only, adding ascorbate (vitamin C) or carbonate (baking soda) to tap water and then boiling the water further reduced the level of total organic halogen (a collective parameter for all halogenated DBPs) by up to 36% or 28%, respectively. Adding ascorbate removed the chlorine residual in tap water and thus prevented the formation of more halogenated DBPs in the boiling process. Adding carbonate elevated pH of tap water and consequently enhanced the hydrolysis (dehalogenation) of halogenated DBPs or led to the formation of more trihalomethanes that might volatilize to air during the boiling process. The comparative developmental toxicity of the DBP mixtures in the water samples was also evaluated. The results showed that adding a tiny amount of sodium ascorbate or carbonate (2.5–5.0 mg/L) to tap water followed by boiling for 5 min reduced the developmental toxicity of tap water to a substantially lower level than boiling only. The addition of sodium ascorbate or carbonate to tap water in household could be realized by preparing them in tiny pills. This study suggests simple and effective methods to reduce the adverse effects of halogenated DBPs on humans through tap water ingestion.

Halogenated disinfection byproducts (DBPs) are formed during chlorine disinfection of drinking water. The complicated natural organic matter in source water causes the formation of an even more complicated mixture of DBPs. To evaluate the toxicity of a DBP mixture in a disinfected water sample, the sample needs to be pretreated in order to attain an observable acute adverse effect in the toxicity test. During sample pretreatment, volatile DBPs including trihalomethanes, haloacetonitriles and haloketones may be lost, which could affect the toxicity evaluation of the DBP mixture. In this study, we intentionally prepared “concentrated” simulated drinking water samples, which contained sufficiently high levels of volatile and nonvolatile DBPs and thus enabled directly evaluating the toxicity of the DBP mixtures without sample pretreatment. Specifically, the natural organic matter and bromide concentrations and the chlorine dose in the concentrated water samples were 250 times higher than those in a typical drinking water sample. Each concentrated water sample was divided into two aliquots, and one of them was nitrogen sparged to eliminate volatile DBPs; then, both aliquots were used directly in a well-established developmental toxicity test. No significant difference (p > 0.10) was found between the developmental toxicity indexes of each concentrated water sample without and with nitrogen sparging, indicating that the contribution of volatile DBPs to the developmental toxicity of the DBP mixture might be marginal. A reasonable interpretation is that nonvolatile halogenated DBPs (especially the aromatic ones) in the DBP mixture could be the major developmental toxicity contributor that warrants more attention.

Cadmium (Cd) precipitation and dissolution in pore water is associated with dissolved organic carbon (DOC)-induced reduction-oxidation of sulfur (S) under waterlogging and is vital for controlling the bioavailability in paddy soil. A 120-day soil incubation experiment, including application of sulfur (S, 30 mg kg−1) and wheat straw (W, 1.0%) alone or in combination (W + S) into Cd-contaminated paddy soil under waterlogging, was conducted to investigate the dynamic of dissolved Cd and its relationship with DOC, S2−, Fe2+, pH, Eh and pe + pH in soil pore water. The results showed that the lowest dissolved Cd concentration was observed in the W + S-treated soil pore water among all treatments when the soil Eh remained at lower values during the period of 15–60 days of incubation, which could be attributed to CdS precipitation and/or co-precipitation of Cd absorbed by FeS2 because of the reduction in sulfur. The application of S resulted in a Cd rebound in the pore water irrespective of W addition when the Eh began to increase from its lowest values during the period of 45–75 days of incubation, and SOB genera were observed in the S added soil. This could be attributed to re-dissolution of the precipitated Cd in soils under the SOB-driven oxidation of sulfide such as CdS and FeS2. In conclusion, DOC-driven reduction-oxidation of sulfur controls Cd dissolution in the pore water of Cd-contaminated paddy soil under waterlogging conditions. Further studies are required to investigate the interaction of sulfur and SOM-induced DOC on Cd bioavailability in rice-planted paddy soils.

Haloacetic acids (HAAs) are the major disinfection byproducts (DBPs) that are formed during chlorination of drinking water. In this paper, the conversion of HAAs to amino acids (e.g., glycine) via ammonolysis was studied. First, a new and sensitive method for detecting glycine was developed by setting selected ion recording m/z 76 in positive electrospray ionization mass spectrometry coupled with ultra performance liquid chromatography. Second, among the mono-HAAs under the same test conditions, iodoacetic acid (49.3%) showed a considerably higher conversion to glycine during ammonolysis than chloroacetic acid (4.2%) and bromoacetic acid (27.7%). The conversion of iodoacetic acid to glycine increased with increasing temperature, increasing reaction time, or decreasing the ratio of (NH4)2CO3 to NH3·H2O in the aminating agent. Hydrolysis of iodoacetic acid to glycolic acid was also observed during ammonolysis, and it accounted for at most 50% of the iodoacetic acid conversion. The conversion to amino acids and the hydrolysis were the two major pathways during ammonolysis of HAAs. Third, compared with the iodoacetic acid sample and the simulated tap water sample without ammonolysis, the developmental toxicity of the corresponding samples with ammonolysis decreased by up to 10.4% and 32.1%, respectively. The ammonolysis was thus demonstrated to be a detoxification process for both individual HAAs and DBP mixture in chlorinated tap water. In practice, the ammonolysis of haloacid DBPs in tap water may be realized by simply adding an appropriate amount of an aminating agent during cooking.

Flushing toilet with seawater is an effective method for preserving freshwater resources, but it introduces iodide and bromide ions into domestic wastewater. During chlorine disinfection, iodide and bromide ions in the saline wastewater effluent lead to the formation of iodinated and brominated aromatic disinfection byproducts (DBPs). Examples of aromatic DBPs include iodophenolic, bromophenolic and chlorophenolic compounds, which generally display substantially higher toxicity than haloaliphatic DBPs. This paper presented for the first time the rates of phototransformation of 21 newly identified halophenolic DBPs in seawater, the receiving waterbody of the wastewater effluent. The phototransformation rate constants (k) were in the range from 7.75 × 10−4 to 4.62 × 10−1 h−1, which gave half-lives of 1.5–895 h. A quantitative structure−activity relationship was established for the phototransformation of halophenolic DBPs as log k = − 0.0100 × Δ G f 0 + 5.7528 × log M W + 0.3686 × p K a − 19.1607 , where ΔGf0 is standard Gibbs formation energy, MW is molecular weight, and pKa is dissociation constant. This model well predicted the k values of halophenolic DBPs. Among the tested DBPs, 2,4,6-triiodophenol and 2,6-diiodo-4-nitrophenol were found to exhibit relatively high risks on marine organisms, based on toxicity indices and half-lives. In seawater, the two DBPs underwent photonucleophilic substitutions by bromide, chloride and hydroxide ions, resulting in the conversion to their bromophenolic and chlorophenolic counterparts (which are less toxic than the parent iodophenolic DBPs) and to their hydroxyphenolic counterparts (iodo(hydro)quinones, which are more toxic than the parent iodophenolic DBPs). The formed iodo(hydro)quinones further transformed to hydroxyl-iodo(hydro)quinones, which have lower toxicity than the parent compounds.

Toilet flushing with seawater results in saline wastewater, which may contain approximately 33-50% seawater. Halogenated disinfection byproducts (DBPs), especially brominated and iodinated DBPs, have recently been found in chlorinated saline wastewater effluents. With the occurrence of brominated and iodinated DBPs, the adverse effects of chlorinated saline wastewater effluents to marine ecology have been uncertain. By evaluating the developmental effects in the marine polychaete Platynereis dumerilii directly exposed to chlorinated saline/freshwater wastewater effluents, we found surprisingly that chlorinated saline wastewater effluents were less toxic than a chlorinated freshwater wastewater effluent. This was also witnessed by the marine alga Tetraselmis marina. The toxicity of a chlorinated wastewater effluent to the marine species was dominated by its relatively low salinity compared to the salinity in seawater. The organic matter content in a chlorinated wastewater effluent might be partially responsible for the toxicity. The adverse effects of halogenated DBPs on the marine species were observed pronouncedly only in the "concentrated" chlorinated wastewater effluents. pH and ammonia content in a wastewater effluent caused no adverse effects on the marine species. The results suggest that using seawater to replace freshwater for toilet flushing might mitigate the "direct" acute detrimental effect of wastewater to the marine organisms.

When bromide/iodide is present in source water, hypobromous acid/hypoiodous acid will be formed with addition of chlorine, chloramine, or other disinfectants. Hypobromous acid/hypoiodous acid undergoes reactions with natural organic matter in source water to form numerous brominated/iodinated disinfection byproducts (DBPs). In this study, tap water samples were collected from eight cities in China. With the aid of electrospray ionization-triple quadrupole mass spectrometry by setting precursor ion scans of m/z 35, m/z 81, and m/z 126.9, whole pictures of polar chlorinated, brominated, and iodinated DBPs in the tap water samples were revealed for the first time. Numerous polar halogenated DBPs were detected, including haloacetic acids, newly identified halogenated phenols, and many new/unknown halogenated compounds. Total organic chlorine, total organic bromine, and total organic iodine were also measured to indicate the total levels of all chlorinated, brominated, and iodinated DBPs in the tap water samples. The total organic chlorine concentrations ranged from 26.8 to 194.0 μg·L−1 as Cl, with an average of 109.2 μg·L−1 as Cl; the total organic bromine concentrations ranged from below detection limit to 113.3 μg·L−1 as Br, with an average of 34.7 μg·L−1 as Br; the total organic iodine concentrations ranged from below detection limit to 16.4 μg·L−1 as I, with an average of 9.1 μg·L−1 as I; the total organic halogen concentrations ranged from 31.3 to 220.4 μg·L−1 as Cl, with an average of 127.2 μg·L−1 as Cl.

There are two types of wastewater in Hong Kong, non-saline and saline wastewaters. When it comes to disinfection, iodide is an important inorganic ion in concern because it may involve in the formation of iodinated disinfection byproducts, which show significantly higher toxicity than their brominated and chlorinated analogues. In this study, it was found that a non-saline wastewater in Hong Kong contained an unexpected high level of iodine. To trace the iodine sources of this non-saline wastewater, the information of the corresponding area was collected to find the possible iodine sources; then, the water samples from the possible iodine sources were collected; the concentrations of iodine species (iodide, iodate and organic iodine) in these collected water samples were determined; finally, the contribution percentages of iodine species from different sources were calculated. The results revealed that a specific domestic wastewater was the major iodine source, contributing to 68.6% of total iodine, 66.3% of iodide, 57.0% of iodate, and 112% of organic iodine in the non-saline wastewater, while landfill leachate, industrial and hospital wastewaters were the minor iodine sources, contributing to 6.6%, 3.1%, and 3.0% of total iodine in the non-saline wastewater, respectively. Furthermore, it was found that the extensive use of salt might result in high levels of iodine in the domestic wastewater and thus lead to the high level of iodine in the non-saline wastewater.

Aromatic iodinated disinfection byproducts (DBPs) are a newly identified category of highly toxic DBPs. Among the identified aromatic iodinated DBPs, 2,4,6-triiodophenol and 2,6-diiodo-4-nitrophenol have shown relatively widespread occurrence and high toxicity. In this study, we found that 4-iodophenol underwent transformation to form 2,4,6-triiodophenol and 2,6-diiodo-4-nitrophenol in the presence of monochloramine. The transformation pathways were investigated, the decomposition kinetics of 4-iodophenol and the formation of 2,4,6-triiodophenol and 2,6-diiodo-4-nitrophenol were studied, the factors affecting the transformation were examined, the toxicity change during the transformation was evaluated, and the occurrence of the proposed transformation pathways during chloramination of source water was verified. The results revealed that 2,4,6-triiodophenol and 2,6-diiodo-4-nitrophenol, which could account for 71.0% of iodine in the transformed 4-iodophenol, were important iodinated transformation products of 4-iodophenol in the presence of monochloramine. The transformation pathways of 4-iodophenol in the presence of monochloramine were proposed and verified. The decomposition of 4-iodophenol in the presence of monochloramine followed a pseudo-second-order decay. Various factors including monochloramine dose, pH, temperature, nitrite concentration, and free chlorine contact time (before chloramination) affected the transformation. The cytotoxicity of the chloraminated 4-iodophenol samples increased continuously with contact time. The proposed transformation pathways occurred during chloramination of source water.

The formation of brominated disinfection byproducts (Br-DBPs), which are generally significantly more cytotoxic and genotoxic than their chlorinated analogues, in chloramination has not been fully examined. In this work, the formation of new polar Br-DBPs in simulated drinking waters was examined using state-of-the-art ultraperformance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry. As many as 29 aliphatic, aromatic, or nitrogenous polar Br-DBPs were detected in chloramination, and five of them (including 2,4,6-tribromoresorcinol, 2,6-dibromo-4-nitrophenol, 2,2,4-tribromo-5-hydroxy-4-cyclopentene-1,3-dione, 2,2,4-dibromochloro-5-hydroxy-4-cyclopentene-1,3-dione, and 2,2,4-bromodichloro-5-hydroxy-4-cyclopentene-1,3-dione) were tentatively identified. Unlike chlorination, chloramination favored the formation of aromatic and nitrogenous polar Br-DBPs and was mild enough to allow polar intermediate Br-DBPs to accumulate. To further explore the formation mechanism of Br-DBPs in chloramination, a quantitative empirical model involving 33 major reactions was developed to describe the overall kinetics. According to the modeling results, bromochloramine and monobromamine were the major species responsible for 54.2-58.1% and 41.7-45.7%, respectively, of the formed Br-DBPs, while hypobromous acid accounted for only 0.2% of the formed Br-DBPs; direct reactions between monochloramine and natural organic matter accounted for the majority of the formed chlorinated DBPs (93.7-95.1%); hypochlorous acid and hypobromous acid in the chloramination were at ng/L or subng/L levels, which were not enough to cause polar intermediate Br-DBPs to decompose.

Using seawater for toilet flushing may introduce high levels of bromide and iodide into a city's sewage treatment works, and result in the formation of brominated and iodinated disinfection byproducts (DBPs) during chlorination to disinfect sewage effluents. In a previous study, the authors' group has detected the presence of many brominated DBPs and identified five new aromatic brominated DBPs in chlorinated saline sewage effluents. The presence of brominated DBPs in chlorinated saline effluents may pose adverse implications for marine ecology. In this study, besides the detection and identification of another seven new aromatic halogenated DBPs in a chlorinated saline sewage effluent, their developmental toxicity was evaluated using the marine polychaete Platynereis dumerilii. For comparison, the developmental toxicity of some commonly known halogenated DBPs was also examined. The rank order of the developmental toxicity of 20 halogenated DBPs was 2,5-dibromohydroquinone2,6-diiodo-4-nitrophenol ≥ 2,4,6-triiodophenol4-bromo-2-chlorophenol ≥ 4-bromophenol2,4-dibromophenol ≥ 2,6-dibromo-4-nitrophenol2-bromo-4-chlorophenol2,6-dichloro-4-nitrophenol2,4-dichlorophenol2,4,6-tribromophenol3,5-dibromo-4-hydroxybenzaldehydebromoform ≥ 2,4,6-trichlorophenol2,6-dibromophenol2,6-dichlorophenoliodoacetic acid ≥ tribromoacetic acidbromoacetic acidchloroacetic acid. On the basis of developmental toxicity data, a quantitative structure-activity relationship (QSAR) was established. The QSAR involved two physical-chemical property descriptors (log P and pKa) and two electronic descriptors (the lowest unoccupied molecular orbital energy and the highest occupied molecular orbital energy) to indicate the transport, biouptake, and biointeraction of these DBPs. It can well predict the developmental toxicity of most of the DBPs tested.

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX measurement involves concentration of halogenated organic DBPs by adsorption onto activated carbon. Prior to activated carbon adsorption, quenching the chlorine residual in a water sample is an indispensable step to eliminate the positive interference resulting from continued chlorination with organic compounds adsorbed on the activated carbon surface or with the activated carbon surface itself. Arsenite is generally applied as the quenching agent. In this study, the arsenite quenching agent dose that was 100% of the stoichiometric amount of the chlorine residual in a water sample was demonstrated to be most appropriate. In practice, to ensure complete reduction of chlorine residual, slight overdose of arsenite is often recommended, but this was found to cause negative interferences in the TOX measurement due to two reasons. First, the competi...

Bromide is naturally present in source waters worldwide. Chlorination of drinking water can generate a variety of chlorinated and brominated disinfection byproducts (DBPs). Although substantial efforts have been made to examine the effect of bromide concentration on the formation and speciation of halogenated DBPs, almost all previous studies have focused on trihalomethanes and haloacetic acids. Given that about 50% of total organic halogen formed in chlorination remains unknown, it is still unclear how bromide concentration affects the formation and speciation of the new/unknown halogenated DBPs. In this study, chlorinated drinking water samples with different bromide concentrations were prepared, and a novel approach-precursor ion scan using ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry-was adopted for the detection and identification of polar halogenated DBPs in these water samples. With this approach, 11 new putative aromatic halogenated DBPs were identified, and they were classified into four groups: dihalo-4-hydroxybenzaldehydes, dihalo-4-hydroxybenzoic acids, dihalo-salicylic acids, and trihalo-phenols. A mechanism for the formation of the four groups of new aromatic halogenated DBPs was proposed. It was found that increasing the bromide concentration shifted the entire polar halogenated DBPs as well as the four groups of new DBPs from being less brominated to being more brominated; these new aromatic halogenated DBPs might be important intermediate DBPs formed in drinking water chlorination. Moreover, the speciation of the four groups of new DBPs was modeled: the speciation patterns of the four groups of new DBPs well matched those determined from the model equations, and the reactivity differences between HOBr and HOCl in reactions forming the four groups of new DBPs were larger than those in reactions forming trihalomethanes and haloacetic acids.

On-line chemical cleaning of membranes with sodium hypochlorite (NaClO) has been commonly employed for maintaining a constant permeability of membrane bioreactor (MBR) due to its simple and efficient operation. However, activated sludge is inevitably exposed to NaClO during this cleaning process. In spite of the broad applications of on-line chemical cleaning in MBR such as chemical cleaning-in-place (CIP) and chemical enhanced backwash (CEB), little information is currently available for the release of emerging dissolved organic matter (DOM) and byproducts from this prevalent practice. Therefore, in this study, activated sludge suspended in a phosphate buffered saline solution was exposed to different doses of NaClO in order to determine the generation of potential DOM and byproducts. The results showed the occurrence of significant DOM release (up to 24.7 mg/L as dissolved organic carbon) after exposure to NaClO for 30 min. The dominant components of the released DOM were characterized to be humic acid-like as well as protein-like substances by using an excitation-emission matrix fluorescence spectrophotometer. Furthermore, after the contact of activated sludge with NaClO, 19 kinds of chlorinated and brominated byproducts were identified by ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, eight of which were confirmed and characterized with standard compounds. Many byproducts were found to be halogenated aromatic compounds, including halopyrroles and halo(hydro)benzoquinones, which had been reported to be significantly more toxic than the halogenated aliphatic ones. Consequently, this study offers new insights into the practice of on-line chemical cleaning, and opens up a window to re-examine the current operation of MBR by looking into the generation of micropollutants.

Our hypothesis that longer-chained perfluoroalkyl acids (PFAAs) outcompete shorter-chained PFAAs during adsorption was tested in this study, wherein the adsorption interactions of six frequently detected PFAAs with kaolinite clay were modeled and examined experimentally using various suspension compositions. Competitive adsorption of PFAAs on the kaolinite surface was observed for the first time, and longer-chained PFAAs outcompeted those with a shorter chain. The electrostatic repulsion between adsorbed PFAA molecules is a primary inhibitory factor in PFAA adsorption. An increase in aqueous sodium or hydrogen ion concentration weakened electrostatic repulsions and changed the adsorption free energy. Therefore, the adsorption of a shorter-chained PFAA with weaker hydrophobicity could occur at high sodium or hydrogen ion concentrations. The experimental and modeling data suggest that the adsorption of shorter-chained PFAAs (≤4 perfluorinated carbons) in freshwater with a typical ionic strength of 10(-2.5) is not thermodynamically favorable. Furthermore, by measuring the electrokinetic potential of kaolinite suspension in the presence of PFAAs, we found that the kaolinite surface became more negatively charged because of the adsorption of PFAAs. This observation indicates that the adsorbed PFAA molecules were within the electrical double layer of the kaolinite surface and that they contributed to the potential at the slipping plane. The possible alignments of adsorbed PFAA molecules on the kaolinite surface were then proposed.

Brominated disinfection byproducts (Br-DBPs) are generally more cytotoxic and genotoxic than their chlorinated analogues. A great portion of total organic bromine in chlorinated drinking water is still unknown and may be ascribed to polar Br-DBPs. In this work, a novel approach, precursor ion scan using ultra-performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry, was adopted and further developed for selective detection and identification of polar Br-DBPs, which made it possible to reveal the whole picture of the formation and decomposition of polar Br-DBPs during chlorination. Simulated drinking water samples with chlorine contact times from 1 min to 7 d were analyzed. Many new polar aromatic and unsaturated aliphatic Br-DBPs were detected and tentatively proposed with chemical structures, of which 2,4,6-tribromophenol, 3,5-dibromo-4-hydroxybenzoic acid, 2,6-dibromo-1,4-hydroquinone, and 3,3-dibromopropenoic acid were confirmed or identified with authentic standards. It was found that various polar Br-DBPs formed and reached the maximum levels at different chlorine contact times; high molecular weight Br-DBPs might undergo decomposition to relatively low molecular weight Br-DBPs or even finally to haloacetic acids and trihalomethanes. The decomposition of newly detected intermediate Br-DBPs (including molecular ion cluster m/z 345/347/349/351, 2,4,6-tribromophenol, and 3,5-dibromo-4-hydroxybenzoic acid) during chlorination was investigated in detail. The "black box" from the input of "humic substances + bromide + chlorine" through the output of "haloacetic acids + trihalomethanes" was opened to a significant extent.

Precursor ion scans using electrospray ionization-triple quadrupole mass spectrometry with or without ultra performance liquid chromatography preseparation were employed to examine the effects of enhanced/conventional coagulation on the formation of polar halogenated disinfection byproducts (DBPs) during chlorination. It is of interest that many new polar halogenated DBPs were generated as a consequence of enhanced or conventional coagulation, and a number of them were nitrogenous DBPs and/or had m/z values larger than 250. Some of the new polar halogenated DBPs showed up only in samples with enhanced coagulation but not in samples with conventional coagulation, although enhanced coagulation was better for controlling the overall DBP formation. The results suggest that the fraction of natural organic matter resistant to be removed by coagulation should have a low reaction potential with halogens; after enhanced or conventional coagulation, halogens are forced to react with the remaining fraction of natural organic matter, producing new polar (nitrogenous) halogenated DBPs. In addition, enhanced coagulation altered the speciation of halogenated DBPs by elevating the ratio of bromine-containing to chlorine-containing DBPs; this phenomenon was observed for both polar and apolar halogenated DBPs, but polar DBPs were more susceptible to be altered.

Understanding the erosion and deposition rates is very important for designing soil and water conservation measures. However, existing methods of assessing the rates of soil loss present many limitations and are difficult to apply to in karst areas, and there is still very little data in this areas. Karst depressions comprise geomorphologically important sources and sinks for sediments and can provide the long-term history records of environmental changes. But there have been few similar studies focused on its sediments in the world. In this paper, the Cs-137 technique was employed to estimate the sediment deposition rate of karst depression to assess the surface erosion. The results indicate that the average deposition rate, deposition amount and specific deposit yield for the Yongkang catchments since 1963 were estimated to be 4.32 mm y(-1), 3.16 t y(-1) land 20.53. t km(-2) y(-1), respectively. The results obtained were consistent with the actual monitoring data of local runoff plots, and confirm the validity of the overall approach. So it was suggested that the mean specific sediment yields of 20 t km(-2) y(-1) can be representative of the soil loss rates in the regions. Copyright (c) 2010 John Wiley & Sons, Ltd.

Batch ozonation experiments were conducted to investigate the effects of various operating options (i.e. additions of acid, ethanol, ammonium ion, and hydrogen peroxide) on the formation of disinfection byproducts (DBPs) in six different source waters. Formation of bromate, total organic bromines, total aldehydes (the sum of 13 aldehydes) was evaluated, assuming they represent three different types of DBPs during ozonation (i.e. inorganic bromine DBPs, organobromine DBPs, and non-brominated organic DBPs, respectively). Among the tested options, acid addition was found to be the best one to control all the three types of DBPs simultaneously on an ozone exposure basis.

The effect of natural organic matter (NOM) on arsenic adsorption by a commercial available TiO2 (Degussa P25) in various simulated As(III)-contaminated raw waters was examined. Five types of NOM that represent different environmental origins were tested. Batch adsorption experiments were conducted under anaerobic conditions and in the absence of light. Either with or without the presence of NOM, the arsenic adsorption reached steady-state within 1 h. The presence of 8 mg/L NOM as C in the simulated raw water, however, significantly reduced the amount of arsenic adsorbed at the steady-state. Without NOM, the arsenic adsorption increased with increasing solution pH within the pH range of 4.0–9.4. With four of the NOMs tested, the arsenic adsorption firstly increased with increasing pH and then decreased after the adsorption reached the maximum at pH 7.4–8.7. An appreciable amount of arsenate (As(V)) was detected in the filtrate after the TiO2 adsorption in the simulated raw waters that contained NOM. The absolute amount of As(V) in the filtrate after TiO2 adsorption was pH dependent: more As(V) was presented at pH > 7 than that at pH 7 . The arsenic adsorption in the simulated raw waters with and without NOM were modelled by both Langmuir and Frendlich adsorption equations, with Frendlich adsorption equation giving a better fit for the water without NOM and Langmuir adsorption equation giving a better fit for the waters with NOM. The modelling implies that NOM can occupy some available binding sites for arsenic adsorption on TiO2 surface. This study suggests that in an As(III)-contaminated raw water, NOM can hinder the uptake of arsenic by TiO2, but can facilitate the As(III) oxidation to As(V) at TiO2 surface under alkaline conditions and in the absence of O2 and light. TiO2 thus can be used in situ to convert As(III) to the less toxic As(V) in NOM-rich groundwaters.

The use of chlorine and chloramines in drinking water disinfection may produce innumerable halogenated disinfection byproducts (DBPs). Because of the impossibility of measuring the concentration and evaluating the toxicity of each individual halogenated DBP in a water sample, total organic halogen (TOX) as a collective parameter and a toxicity indicator for all the halogenated DBPs has been gaining popularity in recent years. TOX can be divided into total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI). Previously, the authors' group studied the formation kinetics of TOCl and TOBr in chlor(am)ination using two models. In this study, we further explored the formation kinetics of TOI as well as TOCl and TOBr during chlor(am)ination by carefully selecting a series of iodine-related reactions and incorporating them into the two kinetic models. The models well predicted the levels of TOCl, TOBr, TOI, and total chlorine residual during chlorination and chloramination of simulated raw waters. According to the modeling results, 57.1–73.6% of the total generated iodinated DBPs in chlorination was converted to their chlorinated and brominated analogues by the substitution with hypochlorous acid and hypobromous acid; while in chloramination, with the presence of excessive monochloramine, the formed hypoiodous acid might react with monochloramine to form an iodine-substituted intermediate (proposed as chloroiodamine), which was responsible for 41.4–49.8% of the total generated iodinated DBPs, and meantime 51.9–52.6% of the total generated iodinated DBPs underwent deiodination via the base-catalyzed hydrolysis. The models were successfully applied in determining the lag time between the dosages of chlorine and ammonia, a challenging issue in chlorine–chloramine sequential treatment. This study provided important insights into kinetic reactions that control the formation of overall halogenated DBPs in chlor(am)ination.

Coagulation has been proposed as a best available technology for controlling natural organic matter (NOM) during drinking water treatment. The presence of heavy metals such as copper(II) in source water, which may form copper-NOM complexes and/or interact with a coagulant, may pose a potential challenge on the coagulation of NOM. In this work, the effect of copper(II) on NOM removal by coagulation using alum or PAX-18 (a commercial polymerized aluminum chloride from Kemiron Inc., Bartow, Florida) was examined. The results show that the presence of 1 to 10 mg/L of copper(H) in the simulated waters improved the total organic carbon (TOC) removal by up to 25% for alum coagulation and by up to 22% for PAX-18 coagulation. The increased NOM removal with the presence of copper(II) in the waters can most likely be ascribed to the formation copper-NOM complexes that may be more adsorbable on aluminum precipitates and to the formation of copper(II) co-precipitates that may also adsorb NOM. The presence of 1 to 5 mg/L of copper(I) in the waters containing 3 mg/L NOM as carbon was reduced below the maximum contaminant level goal (1.3 mg/L as copper) using either coagulant. The results suggest that the presence of copper(H) in source water may not adversely affect the NOM removal by coagulation. A good linear correlation was observed between the TOC removal efficiency and the log-total moles of the precipitated metals, which include the metal ion from a coagulant and the divalent metal ion(s) in source water.

Linear alkylbenzene sulfonates (LAS) are an important group of organic pollutants in urban wastewater effluents. The practice of using seawater for toilet flushing results in saline wastewater effluents, which contain high levels of bromide ions. Chlorine is most commonly used in wastewater disinfection. During chlorination of freshwater or saline wastewater effluents, some halogenated disinfection byproducts (DBPs) resulting from LAS could be formed. In this study, the overall formation of halogenated DBPs resulting from LAS was quantified by total organic halogen (TOX) measurement. Polar halogenated DBPs resulting from LAS were detected with a novel precursor ion scan method. The structures and formation pathways of the major ones were tentatively proposed. The overall toxicity of different scenarios of LAS samples was evaluated with embryos of a marine polychaete Platynereis dumerilii. The results demonstrate that chlorinated DBPs were generated during chlorination of LAS without bromide, while brominated DBPs were generated during chlorination of LAS with bromide. The TOX concentrations were relatively low, indicating that LAS were not quite reactive with halogen. The major polar chlorinated and brominated DBPs resulting from LAS were proposed to be 2,6-dichloro-3,5-dihydroxy-4-dodecylbenzenesulfonic acid and 2,6-dibromo-3,5-dihydroxy-4-dodecylbenzenesulfonic acid, which belong to a group of DBPs with similar structures but different halogen atoms, and their formation pathways were tentatively proposed. The results also reveal that the undisinfected LAS sample was the least toxic, followed by the chlorinated LAS sample without bromide, and the chlorinated LAS sample with bromide was the most toxic.