Typical Disinfection Byproducts Research Articles

Role of iron homeostasis in the mutagenicity of disinfection by-products in mammalian cells

Disinfection by-products (DBPs) generated from water treatment have serious adverse effects on human health and natural ecosystems. However, research on the mutagenicity of DBPs with different chemical structures is still limited. In the present study, we compared the mutagenicity of 8 typical DBPs in human-hamster hybrid (AL) cells and clarified the mechanisms involved. Our data displayed that the rank order for mutagenicity was as follows: iodoacetamide (IAcAm) > iodoacetonitrile (IAN) > iodoacetic acid (IAA) > bromoacetamide (BAcAm) ≈ bromoacetonitrile (BAN) > bromoacetic acid (BAA), which was confirmed by DNA double strand breaks and oxidative DNA damage. In contrast, bromoform (TBM) and iodoform (TIM) had minimal mutagenicity. The mutation spectrum analysis further revealed that IAN, IAcAm, and IAA could induce multilocus deletions in mammalian cells. Interestingly, nitrogenous DBPs (N-DBPs) and IAA were found to cause varying degrees of iron overload and lipid peroxidation, which was mediated by the activation of the Nrf2/HO-1 signaling pathway. Moreover, the presence of deferoxamine (DFO), an iron ion inhibitor, effectively reduced γ-H2AX and 8-OHdG induced by N-DBPs and IAA. These results indicated that the variations in genotoxicity among DBPs with different structures were associated with their ability to disrupt iron homeostasis. This study provided new insights into the mechanisms underlying the structure-dependent toxicity of DBPs and established a foundation for a more comprehensive understanding and intervention of the health risks associated with DBPs.

Health Risk Assessment of Employees Exposed to Chlorination By-products of Recreational Water in Large Amusement Parks in Shanghai

Objective Chlorination is often used to disinfect recreational water in large amusement parks; however, the health hazards of chlorination disinfection by-products (DBPs) to occupational populations are unknown. This study aimed to assess the exposure status of chlorinated DBPs in recreational water and the health risks to employees of large amusement parks.Methods Exposure parameters of employees of three large amusement parks in Shanghai were investigated using a questionnaire. Seven typical chlorinated DBPs in recreational water and spray samples were quantified by gas chromatography, and the health risks to amusement park employees exposed to chlorinated DBPs were evaluated according to the WHO's risk assessment framework.Results Trichloroacetic acid, dibromochloromethane, bromodichloromethane, and dichloroacetic acid were detected predominantly in recreational water. The carcinogenic and non-carcinogenic risks of the five DBPs did not exceed the risk thresholds. In addition, the carcinogenic and non-carcinogenic risks of mixed exposure to DBPs were within the acceptable risk limits.Conclusion Typical DBPs were widely detected in recreational water collected from three large amusement parks in Shanghai; however, the health risks of DBPs and their mixtures were within acceptable limits.

Adequate nutrient intake mitigate the toxic effects of bromate on the rotifer Brachionus calyciflorus.

Bromate is receiving increased attention as a typical disinfection by-product in aquatic environments, but bromate toxicity tests on invertebrate such as Brachionus calyciflorus rotifer are inadequate. In the present study, the long-term toxicity tests on B. calyciflorus were performed during 21 days under the exposure of different bromate concentrations and two algal density conditions. Furthermore, we evaluated the feeding behaviors of the rotifers under the impact of bromate. The maximum population density of rotifers was significantly reduced at 100 and 200 mg/L bromate exposure at the two algal density conditions. However, we observed that the maximum population density and population growth rate of rotifers were higher at 3.0 × 106 cells/mL algal density than those at 1.0 × 106 cells/mL under the same conditions of bromate exposure. These results suggest that higher food density may have alleviated the negative effects of bromate on rotifers. Meanwhile, the ingestion rate at an algal density of 3.0 × 106 cells/mL was higher than that at 1.0 × 106 cells/mL. The present study provides a basic reference to comprehensively evaluate the toxic effects of bromate on aquatic organisms.

Caffeine degradation via UV/trichloroisocyanuricacid: Kinetic, influencing parameters and chlorinated disinfection byproducts

The combination of ultraviolet (UV) and chlorine-based disinfectants has garnered significant attention in recent years. Trichloroisocyanuricacid (TCCA), an attractive alternative to chlorine, has been widely used in swimming pools. The combination of UV and TCCA (UV/TCCA) may be an emerging treatment for removing micropollutants in swimming pools. However, the performance of UV/TCCA on degrading micropollutants has not been investigated. In this study, the kinetic, influencing parameters, and disinfection byproducts during the degradation of caffeine (CAF) in UV/TCCA system were investigated. CAF was significantly removed by UV/TCCA process (over 94.6 % within 15 min), which was mainly attributed to the contribution of reactive chlorine species (77.1 %) and •OH (22.9 %). As pH was increased from 6.0 to 9.0, the reaction rate constant of CAF demonstrated an initial upward trend followed by a subsequent decline, reaching its peak value at pH 7.2. Higher TCCA dosage significantly promoted the degradation of CAF, while the high concentrations of body fluid analogue and inorganic anions (i.e., HCO3−, SO42−, Br−, Cl−) inhibited the degradation of CAF. Furthermore, UV/TCCA effectively controlled the formation of typical disinfection byproducts and maintained higher free chlorine concentration compared to UV/NaClO under similar reaction conditions. This study filled the knowledge gaps on UV/TCCA process, providing comprehensive evidence for the potential application of UV/TCCA.

Exploring the ignored role of escaped algae in a pilot-scale DWDS: Disinfectant consumption, DBP yield and risk formation

Insufficient treatments during bloom-forming seasons allow algae to enter the subsequent drinking water distribution system (DWDS). Yet, scarce information is available regarding the role escaped algae to play in the DWDS, and how they interact with the system. Thus, three scenarios were conducted: a pilot DWDS with algae (a), pipe water (b), and pipe water with algae (c). Experimental results showed that, compared to biofilm and bulk water, escaped algae required fewer disinfectants. Competition for disinfectants varied with algal strains (Microcystis aeruginosa, MA; Pseudanabaena sp., PS) and disinfectant types (chlorine, Cl2; chloriamine, NH2Cl). Algae in the MA-Cl2 group showed the highest demand (6.25%–36.02%). However, the low-concentration disinfectants distributed to algae could trigger distinct algal status alternations. Cl2 diffused into intact MA cells and reacted with intracellular compositions. Damaged PS cells reached 100% within 2 h. Typical disinfection byproducts (DBPs), including trihalomethanes (THMs), haloacetic acids and halogenated acetonitriles were examined. Disinfectant types and algal strains affected DBP yield and distribution. Although disinfectants consumed by algae might not promote dissolved DBP formation, especially for THMs. DBP formation of the other components was affected by escaped algae via changing disinfectant assignment (reduced by 45.45% for MA-Cl2) and transformation efficiency (by 34.52%). The cytotoxicity risks were estimated. Dissolved DBP-induced risks were not added when escaped algae occurred, whereas disruption and release of intracellular substances increased risks; the maximum cytotoxicity did not occur at 12 h rather than at the end (24 h). Overall, this study provided an innovative perspective on algal-related water quality issues in water systems.

Investigation on toxicity mechanism of halogenated aromatic disinfection by-products to zebrafish based on molecular docking and QSAR model

Halogenated aromatic disinfection by-products (DBPs) are a new type of DBPs that have been detected in various water bodies. Previous studies have shown that most of them can induce in vivo toxicity in aquatic organisms. In this study, in order to further investigate the toxic effects and mechanisms of aromatic DBPs, the toxicity and ecological risks of 10 halogenated aromatic DBPs were assessed using the model organism zebrafish. It was found that the toxicity of DBPs was related to the number, type, and position of halogen and the type of substituent, and the 24 h-toxicity value of DBPs in this experiment could replace their 96 h-toxicity value to reduce the test time and save the test cost. Halogenated phenol and halogenated nitrophenol were more toxic, but the current ecological risks of DBPs were relatively low. In addition, the toxicity mechanism of DBPs was analyzed based on molecular docking and quantitative structure-activity relationship (QSAR) models. The molecular docking results showed that all 10 DBPs could bind to zebrafish's catalase (CAT), cytochrome P450 (CYP450), p53, and acetylcholinesterase (AChE), thereby affecting their normal life activities. QSAR models indicated that the toxicity of halogenated aromatic DBPs to zebrafish mainly depended on their hydrophobicity (log D), the interaction with CAT (ECAT), and hydrogen bonding acidity (A).

A Review of Traditional and Emerging Residual Chlorine Quenchers on Disinfection By-Products: Impact and Mechanisms.

Disinfection by-products (DBPs) are the most common organic contaminants in tap water and are of wide concern because of their highly developmental toxic, cytotoxic, and carcinogenic properties. Typically, to control the proliferation of pathogenic microorganisms, a certain concentration of residual chlorine is retained in the factory water, which reacts with the natural organic matter and the disinfection by-products that have been formed, thus affecting the determination of DBPs. Therefore, to obtain an accurate concentration, residual chlorine in tap water needs to be quenched prior to treatment. Currently, the most commonly used quenching agents are ascorbic acid, sodium thiosulfate, ammonium chloride, sodium sulfite, and sodium arsenite, but these quenching agents can cause varying degrees of DBPs degradation. Therefore, in recent years, researchers have attempted to find emerging chlorine quenchers. However, no studies have been conducted to systematically review the effects of traditional quenchers and new ones on DBPs, as well as their advantages, disadvantages, and scope of application. For inorganic DBPs (bromate, chlorate, and chlorite), sodium sulfite has been proven to be the ideal chlorine quencher. For organic DBPs, although ascorbic acid caused the degradation of some DBPs, it remains the ideal quenching agent for most known DBPs. Among the studied emerging chlorine quenchers, n-acetylcysteine (NAC), glutathione (GSH), and 1,3,5-trimethoxybenzene are promising for their application as the ideal chlorine quencher of organic DBPs. The dehalogenation of trichloronitromethane, trichloroacetonitrile, trichloroacetamide, and bromochlorophenol by sodium sulfite is caused by nucleophilic substitution reaction. This paper takes the understanding of DBPs and traditional and emerging chlorine quenchers as a starting point to comprehensively summarize their effects on different types of DBPs, and to provide assistance in understanding and selecting the most suitable residual chlorine quenchers during DBPs research.

Fluorescence and molecular weight dependence of disinfection by-products formation from extracellular organic matter after ultrasound irradiation

Algal blooms have a negative impact on the safety of drinking water. Ultrasonic radiation technology is an “environment-friendly” technology that is widely used in algae removal. However, this technology leads to the release of intracellular organic matter (IOM), which is an important precursor of disinfection by-products (DBPs). This study investigated the relationship between the release of IOM in Microcystis aeruginosa and the generation of DBPs after ultrasonic radiation as well as analyzed the generation mechanism of DBPs. Results showed that the content of extracellular organic matter (EOM) in M. aeruginosa increased in the order of 740 kHz >1120 kHz >20 kHz after 2 min of ultrasonic radiation. Organic matter with a molecular weight (MW) greater than 30 kDa increased the most, including protein-like, phycocyanin (PC) and chlorophyll a, followed by small-molecule organic matter less than 3 kDa, mainly humic-like substances and protein-like. DBPs with an organic MW range of less than 30 kDa were dominated by trichloroacetic acid (TCAA), while those with an MW greater than 30 kDa had the highest trichloromethane (TCM) content. Ultrasonic irradiation changed the organic structure of EOM, affected the amount and type of DBPs, and tended to generate TCM.

Formation of typical disinfection by-products (DBPs) during chlorination and chloramination of polymyxin B sulfate.

Disinfection by-products (DBPs) formed in chlorination and chloramination are proved to be cytotoxic and genotoxic and arouse increasing attention. However, previous studies of DBP precursors mainly focused on free amino acids (AAs) and few papers evaluated DBPs' formation potential of combined AAs. This study demonstrated that typical carbonaceous (C-) DBPs, trihalomethanes (THMs) and typical nitrogenous (N-) DBPs, dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN) and trichloronitromethane (TCNM) could be formed during chlorination and chloramination of polymyxin B sulfate (PBS), a common polypeptide antibiotic working against Gram-negative bacterial infections. The effects of major parameters, including disinfectant dose, contact time, solution pH, temperature, bromide concentration and chloramination mode were evaluated in batch experiments. Different kinds of DBPs exhibited different characteristics as disinfectant dose or contact time increased. Solution pH and temperature affected the formation of DBPs greatly. The formation pathways of different DBPs from chlor(am)ination of PBS were also proposed. Combined AAs, such as PBS, were proved to be important precursors of DBPs during disinfections.

The molecular interaction of three haloacetic acids with bovine serum albumin and the underlying mechanisms

As typical disinfection byproducts, monohaloacetic acids (monoHAAs) were reported to be cytotoxic and genotoxic with the order of iodoacetic acid (IAA) > bromoacetic acid (BAA) ≫ chloroacetic acid (CAA). However, it remains unknown for the toxicity of monoHAAs to biomacromolecules and the detailed molecular mechanisms. Consequently, the structural and functional responses of bovine serum albumin (BSA) to three monoHAAs (CAA, BAA and IAA) were compared by investigating their interactions using multi-spectroscopic methods, esterase-like activity assays and molecular docking simulations. Results found that monoHAAs stimulated the esterase-like activity of BSA to different levels with the order of CAA > IAA > BAA. The binding of monoHAAs affected the secondary structures, peptide skeleton and aggregation state of BSA. The interactions of BSA with CAA, BAA and IAA are dominated by van der Waals forces and hydrogen bonds, hydrophobic forces and electrostatic forces, respectively. The binding of CAA directly interferes the key residues Arg 254 and Tyr 147 to the activity but BAA and IAA do not. BAA and IAA interacted with Tyr residues by static and dynamic quenching, respectively. The binding constant suggested a relatively weak binding affinity for the interaction of BSA with BAA and with IAA. While CAA barely changed the fluorescence of BSA with the increase of exposure concentrations. Accordingly, this study provides a comprehensive view on the molecular toxicity of monoHAAs interacting with BSA.

Toxicity warning and online monitoring of disinfection by-products in water by electroautotrophic biocathode sensors

As a result of the 2019 coronavirus pandemic, disinfection byproducts generated by the extensive use of chlorine disinfectants have infiltrated the aquatic environment, severely threatening ecological safety and human health. Therefore, the accurate monitoring of the biotoxicity of aqueous environments has become an important issue. Biocathode sensors are excellent choices for toxicity monitoring because of their special electroautotrophic respiration functions. Herein, a novel electroautotrophic biosensor with rapid, sensitive, and stable response and quantifiable output was developed. Its toxicity response was tested with typical disinfection byproducts dichloromethane, trichloromethane, and combinations of both, and corresponding characterization models were developed. Repeated toxicity tests demonstrated that the sensor was reusable rather being than a disposable consumable, which is a prerequisite for its long-term and stable operation. Microbial viability confirmed a decrease in sensor sensitivity due to microbial stress feedback to the toxicants, which is expected to be calibrated in the future by the standardization of the biofilms. Community structure analysis indicated that Moheibacter and Nitrospiraceae played an important role in the toxic response to chlorine disinfection byproducts. Our research provides technical support for protecting the environment and safeguarding water safety for human consumption and contributes new concepts for the development of novel electrochemical sensors.

The effects of polypropylene microplastics on the DBP formation under the chlorination and chloramination processes.

With the increased use of microplastics in modern society, tonnes of various microplastics (MPs) end up in natural and engineered water systems if not properly handled. Being a class of organics, the role of MPs during the disinfection of water treatment systems is still unclear at this stage. In the current experimental study, the formation of 6 typical disinfection by-products (DBPs) was investigated using varying concentrations of polypropylene (PP) MPs under various aquatic chemistry conditions and disinfectants. All investigated DBPs were detected, during the chlorination of PP, with an average CHCl3 concentration of 378μg/g, and other DBPs, including CHCl2Br, TCA, DCAN, 1,1-DCP, and TCNM, were present in less than 60μg/g, on average. When PP coexisted with Suwannee River Fulvic acid (SRFA), a suppression of DBP formation was observed with a 56% net reduction compared with a condition of PP alone. The dynamic balance of being a DBP precursor, or a scavenger, by absorbing the organics of PP is subjected to aquatic chemistry. Increasing the pH decreases the HOCl concentrations, reducing the PP oxidation capacity and DBP formation. As salinity increases, the aggregation of PP can reduce the reaction sites on the surface of PP and enhance the adsorption of SRFA, hence lowering the formation of DBPs.

Low-concentration of trichloromethane and dichloroacetonitrile promote the plasmid-mediated horizontal transfer of antibiotic resistance genes

Disinfection by-products (DBPs) are one of the unintended consequences of water disinfection that are commonly detected in various water environments. Although DBPs are known to induce antimicrobial resistance via stimulation of chromosomal mutations, it remains unclear whether low-concentration of DBPs could stimulate the conjugative transfer of antibiotic resistance genes (ARGs). The present study aimed to investigate the effect of two typical DBPs, namely trichloromethane (TCM) and dichloroacetonitrile (DCAN), on the conjugative transfer of RP4 plasmid in Escherichia coli genera. The results of the study demonstrated that exposure to low concentrations of TCM and DCAN significantly stimulated conjugative transfer of ARGs, wherein application of 25 μg/L of TCM and 10 μg/L of DCAN resulted in maximum fold change of ~5.5– and ~6.0–fold, respectively, at 16 h of exposure. Further, assessment of underlying mechanisms revealed the involvement of intracellular reactive oxygen species generation, SOS response, increase in cell membrane permeability, upregulation of expression of genes and proteins related to pilus generation, ATP synthesis, and RP4 gene expression. Our findings provided a better understanding of the hidden biological effects and the ecological risks of DBPs in the water environment, especially concerning their effect on the spread of antibiotic resistance.

Dummy template based molecularly imprinted solid-phase microextraction coating for analysis of trace disinfection by-product of 2,6-dichloro-1,4-benzoquinone using high-performance liquid chromatography

Trace disinfection by-products (DBPs) produced during the disinfection of drinking water are potentially carcinogenic, teratogenic and mutagenic, which has aroused much attention recently. In this study, a molecularly imprinted (MIP) solid -phase microextraction (SPME) fiber coating was prepared by an in-situ polymerization method using a dummy template molecule for the analysis of trace 2,6-dichloroindole-1,4-benzoquinone (2,6-DCBQ), a typical DBP. The characterization results suggested that this monolithic SPME fiber under the optimized conditions had the porous structure, large surface area and good thermal stability. Due to the strong structural recognition and molecular interaction between MIP SPME coating and target molecule, it showed good extraction selectivity and capacity to trace 2,6-DCBQ with an imprinting factor of 4.7. Then, coupling with high-performance liquid chromatography (HPLC)-ultraviolet (UV) detection, a sensitive analytical method for trace 2,6-DCBQ in water samples was successfully established with a detection limit down to 2.3 ng/mL. The recoveries of the proposed method were in range of 84.4–122% with the relative standard deviations of 1.0–13% (n = 3). The results showed that this MIP SPME-HPLC-UV method possessed high analytical selectivity and sensitivity for trace 2,6-DCBQ in water, which would benefit the improvement of the practicability of DBPs monitoring and detection methodology.

Iron particle formation under chlorine disinfection considering effects of deoxidizers in drinking water

Iron oxidation inevitably occurs in drinking water distribution systems (DWDSs) and can cause water quality problems such as increased turbidity and discoloration of tap water. Considering that chlorine disinfection is also widely used in DWDSs, the role of disinfectant and disinfection byproducts (DBPs) in iron oxidation should not be neglected. Interestingly, here the well-known deoxidizer ascorbic acid (VC), which is also a food additive, could induce the formation of Fe3O4 besides FeOOH resulting in the color change from yellow to black in the presence of trichloroacetic acid (TCA, one of the most typical DBPs) and NaClO (disinfectant). The oxygen-containing functional groups in TCA and VC may bind Fe(II) to guide the crystal growth. Though the particles generated in the presence of TCA and NaClO together with VC had higher content Fe3O4 which would be more difficult to suspend, once disturbance happened, these particles could increase the turbidity and color of water into higher value than the particles formed without VC and those generated in the absence of TCA and NaClO. Therefore, the deoxidizer VC may control “yellow water” without disinfectant, but may deteriorate the water quality under disinfection conditions.

Effect of trichloroacetic acid on iron oxidation: Implications on the control of DBPs and deposits in drinking water

In drinking water distribution system (DWDS), disinfection byproducts (DBPs) have a large possibility of participating in iron oxidation by dissolved oxygen (DO), which may induce particle structure transformations and increase unknown risks. In this work, the influence of trichloroacetic acid (TCAA, one of the most typical DBPs) on iron oxidation processes was studied, and the potential effects of the resulting α-FeOOH particles were evaluated through two aspects: (i) influence on the bacterial community and (ii) toxicity to human cells. TCAA promoted iron oxidation process through an Fe−O−C linkage, which led to a sharper surface of the particles (TCAA-mediated Fe oxide particles, TFOP) than that without TCAA (Fe oxide particles, FOP). Interestingly, the influence of particles on the richness of bacterial community of drinking water was different under anaerobic and aerobic conditions: under anaerobic conditions, the richness of bacterial community increased with the addition of particles, while under aerobic conditions, the richness of bacterial community decreased. The higher affinity of TFOP for electron-accepting DO than FOP indicated the role of DO on TFOP under aerobic conditions. TFOP exhibited the strongest cytotoxicity among FOP and the actual deposits. DFT calculations confirmed that TCAA in iron particles promoted the adsorption and dissociation of H2O2 to generate more •OH with an obvious decrease in the energy barrier from 1.51 to 0.80 eV. This study indicates the high potential of adverse effects of DBPs on loose deposits in DWDS and gives implications for the control of DBPs and deposits in drinking water.

Insights into chloroacetaldehydes degradation by 254 nm ultraviolet: Kinetics, products, and influencing factors

Haloacetaldehydes (HALs) are a type of disinfection byproducts (DBPs) frequently found in disinfected drinking water, and their effective control is important to safeguard human health. To evaluate the appropriateness of using ultraviolet technology for drinking water treatment, this study comparatively examines the photolysis of three chlorinated HALs (Cl-HALs), including monochloroacetaldehyde (MCAL), dichloroacetaldehyde (DCAL), and trichloroacetaldehyde (TCAL), under varying operational and environmental conditions by 254 nm ultraviolet (UV254). Results show that they can be degraded within 2 h at an initial concentration of 20 μg/L with pseudo-first-order reaction rates ranked as MCAL > DCAL > TCAL. Chloride was the major product and total organic carbon decreased substantially, indicating that UV irradiation of Cl-HALs mainly underwent mineralization. MCAL was not formed during photolysis of DCAL or TCAL, suggesting that the carbon-chloride bonds in Cl-HALs were cleaved simultaneously rather than sequentially. In terms of influencing factors, adding free chlorine into solution apparently enhanced Cl-HALs photolysis, whereas increasing Cl-HALs dosage, nitrate, bromide, or iodide inhibited Cl-HAL photolysis. Under their combined effects, the photolysis rates of Cl-HALs dosed into tap and swimming pool waters were lower than those dosed into ultrapure water. These findings hence provide insights for better understanding the treatability of UV254 for Cl-HALs control.

Cobalt doped iron oxychloride as efficient heterogeneous Fenton catalyst for degradation of paracetamol and phenacetin

Cobalt doped iron oxychloride (Co-FeOCl) was synthesized and employed as catalyst in Fenton degradation of paracetamol (APAP) and phenacetin (PNCT) for the first time. The catalytic performance was evaluated by means of various parameters including catalyst load, hydrogen peroxide (H2O2) dose and pH value. The high removal of APAP (87.5%) and PNCT (76.0%) was obtained under conditions of 0.2 g/L Co-FeOCl and 0.5 mM H2O2 at pH 7.0, with calculated pseudo-first order kinetic constants of 0.031 min−1 for APAP and 0.023 min−1 for PNCT. Particularly, quenching tests and in situ electron spin resonance (ESR) tests were employed for the identification of the reactive oxygen species (ROS) in system. Hydroxyl radical (·OH) and superoxide radical (O2−·) were the primary ROS in Co-FeOCl/H2O2 system. A possible mechanism for H2O2 activation by Co-FeOCl catalyst was proposed as well. Finally, the formation of typical disinfection by-products (DBPs) decreased slightly in Co-FeOCl/H2O2 pre-oxidation. However, stability and reusability of Co-FeOCl were deactivated in the consecutive three cycles.

To regulate or not to regulate? What to do with more toxic disinfection by-products?

Since the first regulation of disinfection by-products (DBPs) in the 1970s, >700 DBPs have been identified, and many of these are much more toxic than those regulated. Moreover, drinking water today is not the same as it was in the past, with increasing use of alternative disinfectants like chloramine, ozone, chlorine dioxide, and UV (which can form other types of DBPs), as well as new impacts on our source waters from climate change, population increases, wastewater intrusion, and energy exploration. The question today is whether we are regulating the right DBPs to protect human health, and if not, what should be done. New approaches may involve (1) the use of in vitro data and a Precautionary Principle approach, (2) using surrogate metrics of finished waters, such as total organic bromine/iodine, total nitrosamines, or total organic nitrogen rather than creating longer lists of regulated DBPs, and (3) using toxicity assays for whole drinking water extracts to pinpoint potential problems, then using chemical analyses to identify the toxic agents, and finally, (4) invoking different treatment strategies to reduce the toxicity. While the early regulations likely significantly improved the safety of drinking water, DBP exposure is a constant in modern life, and there is more that we can do.

In vitro toxicity and molecular interacting mechanisms of chloroacetic acid to catalase.

Chloroacetic acid (CAA), one of typical disinfection by-products (DBPs), has attracted considerable concerns for its biological safety. Antioxidant enzyme catalase (CAT) plays a crucial part in the regulation of redox state balance. Herein, CAA was used to test its adverse effects on CAT and explore the underlying mechanism. The cell viability of mouse primary hepatocytes decreased under CAA exposure. A bell-shaped response to CAA exposure was observed in intracellular CAT activity, whose change was partly influenced by molecular CAT activity. CAA binds to CAT mainly via van der Waals forces and hydrogen bonds with a stoichiometry of 9.2. The binding caused structural changes in CAT with the unfolding of polypeptide chains and the decrease of α-helical content. CAA interacts with the amino acid residues surrounding the active sites and substrate channel of CAT. These interactions result in the decrease of molecular CAT activity, which could be restored by high ionic strength. This study has provided a combined molecular and cellular tactics for studying the adverse effects of DBPs on biomarkers and the underlying mechanisms.