Evaluating Evidence for Association of Human Bladder Cancer with Drinking-Water Chlorination Disinfection By-Products

Reduced formation of brominated trihalomethanes during chlorination of bromide-containing waters in the presence of Mn(II)

Manganese(II) (Mn(II)) and bromide (Br-) are common in natural waters. This study investigated the effect of in-situ Mn(II) oxidation and preformed MnOx on the brominated trihalomethane (Br-THM) formation during chlorination of bromide-containing waters. The results showed Br-THM formation could be substantially inhibited by in-situ Mn(II) oxidation, but the addition of preformed MnOx had limited influence on Br-THM formation during chlorination of bromide-containing waters. Analysis of bromine species showed that about 30 % bromine species were incorporated into the MnOx particles and formed MnOx-Br during the in-situ Mn(II) oxidation process. Consequently, the availability of reactive bromine species for the reaction with dissolved organic matter (DOM) reduced, leading to less Br-THM formation. X-ray diffraction (XRD) analysis of in-situ Mn(II) oxidation product indicated the presence of Br- decreased the crystallinity of Mn oxides, verifying the bromine species entered MnOx crystal. However, the adsorptive uptake of bromine species by preformed MnOx was negligible and had no impact on Br-THM formation. Inhibition rate of Mn(II) oxidation on THM formation decreased with increasing specific ultraviolet absorbance (SUVA254) value of filtered water, showing SUVA254 could be a good indicator of DOM competition ability for oxidant with Mn(II). In addition, Excitation/Emission Matrix indicated that Mn(II) could form complexes with humic substances, which might also retard the reaction between humic substances and oxidant to form Br-THMs. This study highlighted the inhibiting effect of in-situ Mn(II) oxidation on Br-THM formation during chlorination of bromide-containing waters.

Assessment of drinking water quality and health risk using water quality index and multiple computational models: a case study of Yangtze River in suburban areas of Wuhan, central China, from 2016 to 2021

Water quality, increasingly recognized for its significant impact on health, is garnering heightened attention. Previous studies were limited by the number of water quality indicators and the duration of analysis. This study assessed the drinking water quality and its associated health risk in suburban areas of Wuhan, a city in central China, from 2016 to 2021. We collected 368 finished water samples and 1090 tap water samples and tested these for 37 different indicators. The water quality was evaluated using the water quality index, with trends over time analyzed via the Mann-Kendall test. Furthermore, an artificial neural network model was employed for future water quality prediction. Our findings indicated that the water quality in rural Wuhan was generally good and had an improvement from 2016 to 2021. The qualification and excellent rates were 98.91% and 86.81% for finished water, and 97.89% and 78.07% for tap water, respectively. The drinking water quality was predicted to maintain satisfactory in 2022 and 2023. Additionally, principal component analysis revealed that the primary sanitary issues in the water were poor sensory properties, elevated metal contents, high levels of dissolved solids, and microbial contamination. These issues were likely attributable to domestic and industrial waste discharge and aging water pipelines. The health risks associated with the long-term consumption of this water have been steadily decreasing over the years, underscoring the effectiveness of Wuhan's ongoing water management efforts.

2,2-Dichloroacetamide exposure induces behavior and memory disorders in mice: Detrimental effects of long-term dietary restriction on neurotoxicity

2, 2-dichloroacetamide (DCAcAm), a nitrogen-containing disinfection byproduct (DBPs), is commonly found in potable water. This study aimed to compare the neurotoxicity of DCAcAm in C57/BL6 mice at both environmentally relevant and higher doses through oral exposure over a 28-day period. Furthermore, the potential effects of dietary restriction (DR) on the cerebral toxicity induced by 20 ppb DCAcAm were examined. The findings indicated that DCAcAm exposure and DR treatment resulted in reduced memory retention and cognitive adaptability in mice. Additionally, higher doses of DCAcAm exposure induced severe brain inflammation and oxidative stress. Metabolic profiling revealed disruptions in fatty acid, energy, and amino acid metabolism in the brain. Remarkably, the negative impacts of 20 ppb DCAcAm on the mice brain were worsened by DR treatment. Analysis of 16S rRNA sequencing revealed notable changes in the composition and structure of intestinal microorganisms after exposure to DCAcAm. This study discovered that DCAcAm has both direct effects on the brain and indirect effects through the microbial-brain-intestinal axis, which collectively result in neurotoxicity and dietary restriction exacerbates these effects. This study provides emerging views on the assessment of the toxicity of nitrogen containing DBPs.

The alternation of halobenzoquinone disinfection byproduct on toxicogenomics of DNA damage and repair in uroepithelial cells

Halobenzoquinones (HBQs) were recently discovered as an emerging class of drinking water disinfection byproducts with carcinogenic concern. However, the molecular mechanism underlying HBQs-induced DNA damage is not clear. In this study, we integrated in vitro genotoxicity, computational toxicology, and the quantitative toxicogenomic analysis of HBQs on DNA damage/repair pathways in human bladder epithelial cells SV-HUC-1. The results showed that HBQs could induce cytotoxicity with the descending order as 2,6-DIBQ > 2,6-DCBQ ≈ 2,6-DBBQ. Also, HBQs can increase DNA damage in SV-HUC-1 cells and thus generate genotoxicity. However, there is no significant difference in genotoxicity among the three HBQs. The results of molecular docking and molecular dynamics simulation further confirmed that HBQs had high binding fractions and stability to DNA. Toxicogenomic analysis indicated that HBQs interfered with DNA repair pathways, mainly affecting base excision repair, nucleotide excision repair and homologous recombination repair. These results have provided new insights into the underlying molecular mechanisms of HBQs-induced DNA damage, and contributed to the understanding of the relationship between exposure to DBPs and risks of developing bladder cancer.

Effects of alternative disinfection methods on the characteristics of effluent organic matter and the formation of disinfection byproducts

The characteristics of effluent organic matter (EfOM) and the type of disinfection methods are closely related to the formation of disinfection byproducts (DBPs) in reclaimed water. In this study, five disinfection methods, i.e., chlorination, ultraviolet (UV) followed by chlorination (UV + Cl), UV/chlorine (UV/Cl), chloramination, and chlorine dioxide (ClO2), were applied to investigate the changes in the properties of EfOM, the formation of DBPs, and the relationship between EfOM properties and DBP formation during the disinfection of four secondary biological effluents. The results showed that EfOM with medium molecular weight (MW) (0.5-6 kDa) was the dominant fraction for all WWTPs. From a fluorescence perspective, the EfOM of the AAO process was rich in humic matter, while the EfOM of the oxidation ditch (OD) process was rich in protein matter. Disinfectants tended to transfer EfOM with high molecular weight (MW) (>6 kDa) to those with low MW (<0.5 kDa). Chlorination, UV + Cl and UV/Cl were more reactive to humic matter, while chloramination and chlorine dioxide were more reactive to protein matter. The formation of known DBPs was mainly dependent on humic matter, while protein matter was more likely to generate unknown DBPs. N-DBPs only accounted for 5.7%-17.7% of the total DBPs, but contributed more than 70% of the calculated toxicity, among which bromochloroacetonitrile (BCAN), dichloroacetonitrile (DCAN), and monobromoacetamide (MBAcAm) were the most important contributors to the calculated cytotoxicity. Monobromoacetic acid (MBAA) and MBAcAm were the primary drivers of the calculated genotoxicity. Overall, UV + Cl was the suggested optimal disinfection method for WWTPs.

Occurrence, stability and cytotoxicity of halobenzamides: A new group of nitrogenous disinfection byproducts in drinking water

Exploring disinfection byproducts (DBPs) with adverse health effects in drinking water is a constant challenge. Halobenzamides (HBZAMs) are suspected to be a new group of nitrogenous DBPs but have not been reported in drinking water to date. In this study, by coupling SPE and UPLC‒MS/MS, a sensitive method was established to detect eight HBZAMs in drinking water with recoveries and limits of detection of 80-103% and 0.01-0.04 ng/L, respectively. Subsequently, distinct fragments of HBZAMs were extended to the development of a pseudotargeted method for the analysis of the fourteen HBZAMs that were speculated and lack chemical standards. Using the developed method, eight HBZAMs were quantified in ten drinking water samples with concentrations ranging from 2.4 to 7.2 ng/L and a detection frequency of 100%, among which five HBZAMs were stable with half-lives over 72 h under real chlorine levels. Twelve HBZAMs without standards were identified in three to ten drinking water samples with comparable levels. The cytotoxicity of eight quantified HBZAMs in CHO-K1 cells varied with disparity, in which the cytotoxicity of 3,5-DBBZAM was over 10-fold higher than that of aliphatic dichloroacetamide. Considering their diversity, toxicity and stability, the occurrence of HBZAMs in drinking water deserves attention.

Temporal and spatial variations of disinfection by-products in South Taihu's drinking water, Zhejiang Province, China

Some disinfection by-products (DBPs) in drinking water present a potential safety concern. This study focuses on the elements influencing DBPs formation. A total of 120 water samples were collected from 10 different drinking water facilities spanning 5 counties within Huzhou, Zhejiang Province, China. Concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) were observed to be 14.5 and 27.4 μg/L, respectively, constituting 34 and 64% of the total DBPs. Seasonal fluctuations demonstrated that HAAs, THMs, halonitromethanes (HNMs), and haloacetonitriles (HANs) followed a similar pattern with higher levels in summer or autumn compared to spring. Importantly, the concentrations of HAAs and THMs were markedly higher in Taihu-sourced water compared to other sources. Geographically, Nanxun exhibited the highest levels of total DBPs, HAAs, and THMs, while Deqing and Changxing demonstrated significantly lower levels. Correlation studies between water quality parameters and DBPs revealed that factors such as chloride content, temperature, and residual chlorine positively influenced DBPs formation, whereas turbidity negatively affected it. Principal component analysis suggested similar formation processes for HANs, haloketones (HKs), HNMs, and THMs. Factors such as temperature, chemical oxygen demand (COD), and residual chlorine were identified as significant contributors to the prevalence of HAAs.

Oxidative stress as a key event in 2,6-dichloro-1,4-benzoquinone-induced neurodevelopmental toxicity

2,6-dichloro-1,4-benzoquinone (DCBQ) has been identified as an emerging disinfection byproducts (DBPs) in drinking water and has the potential to induce neurodevelopmental toxicity. However, there is rarely a comprehensive toxicological evaluation of the neurodevelopmental toxicity of DCBQ. Here, neural differentiating SH-SY5Y cells were used as an in vitro model. Our results have found that DCBQ has decreased cell viability and neural differentiation, generated higher level of reactive oxygen species (ROS), increased the percentage of apoptosis and lowered the level of mitochondrial membrane potential, suggesting the neurodevelopmental toxicity of DCBQ. In addition, antioxidant N-acetyl-L-cysteine (NAC) could significantly attenuate these DCBQ-induced neurotoxic effects, supporting our hypothesis that the neurodevelopmental toxicity may be related with oxidative stress induced by DCBQ. We further demonstrated that DCBQ-induced neurodevelopmental toxicity could promote the mitochondrial apoptosis pathway and inhibit the prosurvival PI3K/AKT/mTOR pathway through inducing ROS, which ultimately inhibited cell proliferation and induced apoptosis in neural differentiating SH-SY5Y cells. These findings have provided novel insights into the risk of neurodevelopmental toxic effects associated with DCBQ exposure, emphasizing the importance of assessing the potential neurodevelopmental toxicity of DBPs.

Health risk assessment of heavy metals and disinfection by-products in drinking water in megacities in China: A study based on age groups and Monte Carlo simulations

Heavy metal(loid)s (HMs) and disinfection by-products (DBPs) in drinking water pose risks to human health and jeopardize drinking water. Water-related behaviors vary significantly among different age groups and regions. In this study, the carcinogenic and non-carcinogenic risks of HMs (As, Cd, Cr6+, Cu, Pb, and Zn) and DBPs (bromodichloromethane (BDCM), bromoform, chloroform, dibromochloromethane (DBCM), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA)) in drinking water in two Chinese megacities (Beijing in North China and Guangzhou in South China) via multiple exposure pathways were assessed. The results showed that children aged 9 months to 2 years had a total carcinogenic risk (TCR) and hazard index (HI) above acceptable levels, indicating that despite the drinking water quality in the selected megacities meeting the current Chinese national standards (GB 5749-2022), the health risks of exposure to HMs and DBPs in drinking water for local young children should not be neglected. Specifically, the carcinogenic risk (CR) of exposure to As in drinking water for children < 18-years-old, who were divided into different age groups, was 1.5-2.0- and 4.5-5.9-times higher than the TCR of exposure to DBPs in Beijing and Guangzhou, respectively. Regarding children aged 9 months to 2 years, the exposure to TCAA accounted for the largest proportion (35.6 %) of the TCR of exposure to DBPs in Beijing drinking water, 5.4-times higher than that in Guangzhou; whereas, the TCR of exposure to DBPs in Guangzhou drinking water was predominantly caused by exposure to chloroform, accounting for 40.6 % of the TCR and 1.5-times higher than that in Beijing. In addition, the CR of exposure to DCAA in drinking water in both megacities accounted for a large proportion of the TCR for children aged 9 months to 2 years. Monte Carlo simulations showed that 62.2 % and 42.6 % of the TCR of simultaneous exposure to As and DBPs in drinking water exceeded the acceptable level for sensitive populations, that is, children aged 1-2 years in Beijing (95th percentile = 4.2 × 10-4) and children aged 9-12 months in Guangzhou (95th percentile = 5.2 × 10-4), respectively. This elaborate health risk assessment sheds light on improving the water quality indices to guarantee drinking water safety in China.

Comparative assessment of embryotoxicity of 2,4,6-triiodophenol to mouse blastoid and pre-implantation embryo models

Embryonic developmental effects of disinfection by-products, which are generated during drinking water treatment and widely detected in environment, have gained more and more attention nowadays, calling for construction of in vitro research models which can mimic early embryonic development to evaluate the embryotoxicity. The embryonic stem cell test offers a promising assay to predict embryotoxicity of environmental pollutions. However, it is not appropriate for the toxicological study of preimplantation embryos. Here, we used mouse extended stem cells (mEPS) to reconstruct embryo-like structures (blastoid), furtherly attempting to evaluate the reliability of this model for the prediction of possible developmental toxicity of 2,4,6-triiodophenol (TIP, 5-50 μM), a novel halogenated disinfection byproduct widely detected in water and even drinking water, to mammalian preimplantation embryo. To verify this, we treated mouse embryo derived from in vitro fertilization (IVF-embryo) as reference. The results showed that mEPS-blastoid was like natural blastocyst in morphology, cell composition, and could recapitulate key developmental events happened during mouse preimplantation stage. When blastoid and IVF-embryo models were separately exposed to TIP, their final blastocyst formation rates were not impaired, according to morphological features, meanwhile that TIP exposure caused slight cell apoptosis. Besides, TIP induced an ICM cell bias in cell fate decision, resulting in cell proportion change, which implied abnormal developmental potential. Though we could not evaluate TIP's embryotoxicity before 8-cell stage using blastoid model, its viability as a novel and high-throughput assessment platform for increasing environmental pollutants was still recognized.

Genotoxic effects of chlorinated disinfection by-products of 1,3-diphenylguanidine (DPG): Cell-based in-vitro testing and formation potential during water disinfection

1,3-diphenylguanidine (DPG) is a commonly used rubber and polymer additive, that has been found to be one of the main leachate products of tire wear particles and from HDPE pipes. Its introduction to aquatic environments and potentially water supplies lead to further questions regarding the effects of disinfection by-products potentially formed. Using different bioassay approaches and NGS RNA-sequencing, we show that some of the chlorinated by-products of DPG exert significant toxicity. DPG and its chlorinated by-products also can alter cell bioenergetic processes, affecting cellular basal respiration rates and ATP production, moreover, DPG and its two chlorination products, 1,3-bis-(4-chlorophenyl)guanidine (CC04) and 1-(4-chlorophenyl)-3-(2,4-dichlorophenyl)guanidine (CC11), have an impact on mitochondrial proton leak, which is an indicator of mitochondria damage. Evidence of genotoxic effects in the form of DNA double strand breaks (DSBs) was suggested by RNA-sequencing results and further validated by an increased expression of genes associated with DNA damage response (DDR), specifically the canonical non-homologous end joining (c-NHEJ) pathway, as determined by qPCR analysis of different pathway specific genes (XRCC6, PRKDC, LIG4 and XRCC4). Immunofluorescence analysis of phosphorylated histone H2AX, another DSB biomarker, also confirmed the potential genotoxic effects observed for the chlorinated products. In addition, chlorination of DPG leads to the formation of different chlorinated products (CC04, CC05 and CC15), with analysed compounds representing up to 42% of formed products, monochloramine is not able to effectively react with DPG. These findings indicate that DPG reaction with free chlorine doses commonly applied during drinking water treatment or in water distribution networks (0.2-0.5 mg/L) can lead to the formation of toxic and genotoxic chlorinated products.

Estimating National Exposures and Potential Bladder Cancer Cases Associated with Chlorination DBPs in U.S. Drinking Water

BACKGROUND

Disinfection byproducts (DBPs) in public water systems (PWS) are an unintended consequence resulting from reactions between mostly chlorine-based disinfectants and organic and inorganic compounds in source waters. Epidemiology studies have shown that exposure to DBP (specifically trihalomethanes) was associated with an increased risk of bladder cancer.

OBJECTIVE

Our goal was to characterize the relative differences in exposures and estimated potential bladder cancer risks for people served by different strata of PWS in the United States and to evaluate uncertainties associated with these estimates.

METHODS

We stratified PWS by source water type (surface vs. groundwater) and population served (large, medium, and small) and calculated population-weighted mean trihalomethane-4 (THM4) concentrations for each stratum. For each stratum, we calculated a population attributable risk (PAR) for bladder cancer using odds ratios derived from published pooled epidemiology estimates as a function of the mean THM4 concentration and the fraction of the total U.S. population served by each stratum of systems. We then applied the stratum-specific PARs to the total annual number of new bladder cancer cases in the U.S. population to estimate bladder cancer incidence in each stratum.

RESULTS

Our results show that approximately 8,000 of the 79,000 annual bladder cancer cases in the United States were potentially attributable to DBPs in drinking water systems. The estimated attributable cases vary based on source water type and system size. Approximately 74% of the estimated attributable cases were from surface water systems serving populations of > 10,000 people. We also identified several uncertainties that may affect the results from this study, primarily related to the use of THM4 as a surrogate measure for DBPs relevant to bladder cancer.

DISCUSSION

Despite significant reductions in exposure over the past several decades, our study suggests that ∼ 10 % of the bladder cancer cases in the United States may still be attributed to exposure to DBPs found in drinking water systems. https://doi.org/10.1289/EHP9985.

Smart Rainwater Harvesting for Sustainable Potable Water Supply in Arid and Semi-Arid Areas

This paper presents a smart rainwater harvesting (RWH) system to address water scarcity in Palestine. This system aims to improve the water harvesting capacity by using a shared harvesting system at the neighborhood level and digital technology. The presentation of this system is organized as follows: (i) identification of the challenges of the rainwater harvesting at the neighborhood level, (ii) design of the smart RWH system architecture that addresses the challenges identified in the first phase, (iii) realization of a simulation-based reliability analysis for the smart system performance. This methodology was applied to a residential neighborhood in the city of Jenin, Palestine. The main challenges of smart water harvesting included optimizing the shared tank capacity, and the smart control of the water quality and leakage. The smart RWH system architecture design is proposed to imply the crowdsourcing-based and automated-based smart chlorination unit to control and monitor fecal coliform and residual chlorine: screens, filters, and the first flush diverter address RWH turbidity. Water level sensors/meters, water flow sensors/meters, and water leak sensors help detect a water leak and water allocation. The potential time-based reliability (Re) and volumetric reliability (Rv) for the smart RWH system can reach 38% and 41%, respectively. The implication of the smart RWH system with a dual water supply results in full reliability indices (100%). As a result, a zero potable water shortage could be reached for the dual water supply system, compared to 36% for the municipal water supply and 59% for the smart RWH system. Results show that the smart RWH system is efficient in addressing potable water security, especially when combined with a dual water supply system.

Quantitative identification of halo-methyl-benzoquinones as disinfection byproducts in drinking water using a pseudo-targeted LC-MS/MS method

Halobenzoquinones (HBQs) as disinfection byproducts (DBPs) in drinking water is prioritized for research due to their prevalent occurrence and high toxicity. However, only fifteen HBQs can be identified among a high diversity using targeted LC-MS/MS analysis in previous studies due to the lack of chemical standards. In this study, we developed a pseudo-targeted LC-MS/MS method for detecting and quantifying diverse HBQs. Distinct fragment characteristics of HBQs was observed according to the halogen substituent effects, and extended to the development of a multiple-reaction-monitoring (MRM) method for the quantification of the 46 HBQs that were observed in simulated drinking water using non-targeted analysis. The fragmentation mechanism was supported by the changes of Gibbs free energy (ΔG), and a linear relationship between the ΔG and the ionization efficiency of analytes was developed accordingly for quantification of these 46 HBQs, 30 of which were lack of chemical standards. It is noted that 29 of the 30 newly-identified HBQs were halo-methyl-benzoquinones (HMBQs), which were predicted to be carcinogens related with drinking-water bladder cancer risk and be more toxic than non-methyl HBQs. Using the new method, twelve HMBQs were detected in actual drinking water samples with concentrations up to 100.4 ng/L, 3 times higher than that reported previously. The cytotoxicity in CHO cells of HMBQs was over 1-fold higher than that of non-methyl-HBQs. Therefore, HMBQs are an essential, highly toxic group of HBQs in drinking water, which deserve particular monitoring and control.

Immune dysfunction induced by 2,6-dichloro-1,4-benzoquinone, an emerging water disinfection byproduct, due to the defects of host-microbiome interactions

2,6-dichloro-1,4-benzoquinone (DCBQ), as an emerging water disinfection byproducts (DBPs), has posed potential risks via the digestion system. However, little is known about the toxicity of DCBQ on the gut microbiome, which plays a critical role on human health. This study has comprehensively investigated the impact of DCBQ on the intestinal microbiome, metabolic functions, and immunity after the mice orally exposure to DCBQ at the concentration of 31.25, 62.5 and 125 mg/kg body weight for 28 days. Our results indicated that DCBQ exposure has perturbed the balance between T helper (Th) 1 mediated pro-inflammatory response and Th2 mediated anti-inflammatory response in mice, especially inducing the activation of immune system toward a Th2 response. DCBQ group has induced gut microbiota dysbiosis, and at phylum level, Proteobacteria was relatively less abundant compared with that in the control group. Furthermore, DCBQ exposure has dramatically perturbed metabolites profiles which were involved in 28 metabolic pathways, such as amino acids biosynthesis and metabolism, lipid metabolism. In particular, the altered gut microbiota showed strong correlations with both the altered metabolites and the altered immunological variables after DCBQ exposure. This study provides evidence on the adverse effects and mechanisms of water disinfection byproduct DCBQ through the interaction of immune-microbiome-metabolome, highlighting the importance to assess DBPs-associated risks.

[Determination of Haloacetic Acids, Disinfection Byproducts, in Tap Water with Reversed-Phase Ultra-Performance Liquid Chromatography-High Resolution Mass Spectrometry]

Objective

To establish a method for quantitative analysis of haloacetic acids (HAAs), disinfection byproducts, in tap water with reversed-phase ultra-performance liquid chromatography-quadrupole-orbitrap high resolution mass spectrometry.

Methods

Tap water samples were collected and 0.70 g/L ascorbic acid was added to eliminate residual chlorine. Then, the water samples were directly injected into the instrument for analysis after filtration. After separation on a pentafluorobenzene (PFP) column with an inner diameter of 1.0 mm at a higher linear velocity and a lower volume flow rate compared with those of a narrow-bore column, nine HAAs, namely, monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), dichloroacetic acid (DCAA), bromochloroacetic acid (BCAA), dibromoacetic acid (DBAA), trichloroacetic acid (TCAA), bromodichloroacetic acid（BDCAA), chlorodibromoacetic acid (CDBAA) and tribromoacetic acid (TBAA), were examined by negative electrospray ionization and full MS/dd-MS 2 acquisition mode. In order to adjust for the matrix effect, matrix matching calibration curves were used to quantitate the nine HAAs.

Results

Good linearity was obtained for each of the nine HAAs within their respective linear ranges. The detection limits and quantification limits of the method were 0.020-1.0 μg/L and 0.060-3.0 μg/L. The recoveries were 69.8%-119%.

Conclusion

The proposed method showed strengths in separation speed and qualitative accuracy. It did not require for complicated pretreatment procedures and can meet the need of tap water sample analysis.

Formation of trihalomethanes and haloacetic acids from 2,6-dichloro-1,4-benzoquinone during chlorination: Decomposition kinetics, conversion rates, and pathways

As a typical aromatic disinfection byproduct (DBP), 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) attracts much concern due to the potential toxicity. To further evaluate the role of 2,6-DCBQ as an intermediate DBP in water with or without chlorine, their decomposition characteristics and transformation potential to the regulated DBPs (i.e., trihalomethanes (THMs) and haloacetic acids (HAAs)) were investigated under different chlorine doses, pH values, temperatures, contact times, and bromide levels. The decomposition of 2,6-DCBQ under different conditions all fit apparent first-order kinetics. The hydrolysis rate constants of 2,6-DCBQ significantly increased with pH. The half-live values of 2,6-DCBQ were 108.3-568.7 h at pH 6.0-6.5, and 1.8-31.1 h at pH 7.0-8.5. During the hydrolysis of 2,6-DCBQ, there was no THMs and HAAs generated. During chlorination, 2,6-DCBQ decayed rapidly accompanied by the fast formation of trichloromethane (TCM) and the gradual generation of dichloroacetic acid and trichloroacetic acid. The molar conversion rates of 2,6-DCBQ-to-THMs (i.e., TCM) and 2,6-DCBQ-to-HAAs were 2.9-10.0% and 0.1-2.2% under different conditions. The presence of bromide increased the conversion rates of 2,6-DCBQ-to-THMs and caused the generation of brominated THMs and HAAs. According to the decomposition characteristics of 2,6-DCBQ and the formation trends of THMs and HAAs under different conditions, multiple formation pathways from 2,6-DCBQ to THMs and HAAs were proposed.

Formation and Cytotoxicity of Halophenylacetamides: A New Group of Nitrogenous Aromatic Halogenated Disinfection Byproducts in Drinking Water

Nitrogenous aromatic halogenated disinfection byproducts (DBPs) in drinking water have received considerable attention recently owing to their relatively high toxicity. In this study, a new group of nitrogenous aromatic halogenated disinfection byproducts, halophenylacetamides (HPAcAms), were successfully identified for the first time in both the laboratory experiments and realistic drinking water. The formation mechanism of HPAcAms during chlorination of phenylalanine in the presence of Br^- and I^-, occurrence frequencies, and concentrations in authentic drinking water were investigated, and a quantitative structure-activity relationship (QSAR) model was developed based on the acquired cytotoxicity data. The results demonstrated that HPAcAms could be formed from phenylalanine in chlorination via electrophilic substitution, decarboxylation, hydrochloric acid elimination, and hydrolysis. The HPAcAm yields from phenylalanine were significantly affected by contact time, pH, chlorine dose, and temperature. Nine HPAcAms with concentrations in the range of 0.02-1.54 ng/L were detected in authentic drinking water samples. Most tested HPAcAms showed significantly higher cytotoxicity compared with dichloroacetamide, which is the most abundant aliphatic haloacetamide DBP. The QSAR model demonstrated that the cellular uptake efficiency and the polarized distributions of electrons of HPAcAms play essential roles in their cytotoxicity mechanisms.

Molecular composition of halobenzoquinone precursors in natural organic matter in source water

Halobenzoquinones (HBQs) are emerging disinfection byproducts generated during the reaction of chlorine disinfectant with natural organic matter (NOM) in source water. In this study, the correlations between molecular weight and HBQs generation of river NOM was evaluated. The compositional and functional characteristics of primary HBQs precursors were revealed by using Orbitrap mass spectrometry combined with molecular tagging. The NOM fraction larger than 50 kDa resulted in approximately 9 times more HBQs (50.9 ± 2.7 ng/mgC) than low molecular weight fractions. Significant correlations were found between the yields of HBQs and lignin-like and highly oxygen compounds in NOM, suggesting their critical roles in HBQs formation. Derivatizating the aldehydes, ketones, hydroxyl and carboxyl groups in NOM could reduce HBQs yields by 90.7%-100%. Unraveling the molecular characteristics of HBQs precursors in NOM would greatly benefit the prediction of HBQs yields of different source water, and develop more efficient disinfection byproduct control strategies.

Fluorescent probe for the detection of hypochlorous acid in water samples and cell models

Hypochlorous acid (HClO) is a special kind of reactive oxygen species, which plays an important role in resisting pathogen invasion and maintaining cell redox balance and other physiological processes. In addition, HClO is commonly used in daily life as a bleaching and disinfectant agent. Its excessive use can also lead to death of water animals and serious respiratory and skin diseases in humans. Therefore, it is of great significance to develop a quick and convenient tool for detecting HClO in the environment and organisms. In this paper, we utilize the specific reaction of HClO with dimethylthiocarbamate to develop a novel naphthalene derivative fluorescent probe (BNA-HClO), it was designed and synthesized by using 6-(2-benzothiazolyl)-2-naphthol as the fluorophore and N,N-dimethylthiocarbamate as the recognition group. BNA-HClO shows large fluorescence enhancement (374-fold), high sensitivity (a detection limit of 37.56 nM), rapid response (<30 s), strong anti-interference ability and good specificity in vitro. Based on the outstanding in vitro sensing capability of BNA-HClO, it has been successfully used to detect spiked HClO in tap water, medical wastewater and fetal bovine serum with good recovery. BNA-HClO has also been successfully used as a portable test strip for the in situ semi-quantitative detection of HClO in tap water solutions. In addition, BNA-HClO can successfully enable the detection and imaging of exogenous and endogenous HClO in living cells. This work provides a simple and effective tool for the detection and imaging of HClO in environmental and biological systems, and provides some theoretical guidance for future exploration of biological and pathological studies related to HClO.

A new fluorescence probe was successfully applied to test strips and imaging analysis of exogenous and endogenous hypochlorite in living cells.

Haloquinone Chloroimides as Toxic Disinfection Byproducts Identified in Drinking Water

Haloquinone chloroimides (HQCs) are suspected to be highly toxic contaminants, and their production during drinking water disinfection is predicted. However, HQC disinfection byproducts (DBPs) have not been reported in drinking water to date because of analytical limitations. In this study, we developed an analytical method to detect five HQCs, including 2,6-dichloroquinone-4-chloroimide (2,6-DCQC), 2,6-dibromoquinone-4-chloroimide (2,6-DBQC), 2-chloroquinone-4-chloroimide (2-CQC), 3-chloroquinone-4-chloroimide (3-CQC), and 2,6-dichloroquinone-3-methyl-chloroimide (2,6-DCMQC). This method combined a derivatization reaction of HQCs with phenol in alkaline solutions to produce halogenated indophenols, a solid-phase extraction pretreatment using hydrophilic-lipophilic balanced (HLB) cartridges, and a multiple reaction monitoring (MRM) method for quantification. The method was demonstrated to be sensitive and accurate with recoveries of 71-85% and limits of detection of 0.1-0.2 ng/L for the five tested HQCs. Using this method, five tested HQCs were identified in drinking water samples from nine water treatment plants and water distribution systems as new DBPs at concentrations of up to 23.1 ng/L. The cytotoxicity of the five tested HQCs in HepG2 cells was higher than or comparable to that of 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), an emerging DBP that was hundreds to thousands of times more toxic than regulated DBPs. This study presents the first analytical method for HQC DBPs in drinking water and the first set of occurrence and cytotoxicity data of HQC DBPs.

Pilot-scale expanded assessment of inorganic and organic tapwater exposures and predicted effects in Puerto Rico, USA

A pilot-scale expanded target assessment of mixtures of inorganic and organic contaminants in point-of-consumption drinking water (tapwater, TW) was conducted in Puerto Rico (PR) to continue to inform TW exposures and corresponding estimations of cumulative human-health risks across the US. In August 2018, a spatial synoptic pilot assessment of than 524 organic and 37 inorganic chemicals was conducted in 14 locations (7 home; 7 commercial) across PR. A follow-up 3-day temporal assessment of TW variability was conducted in December 2018 at two of the synoptic locations (1 home, 1 commercial) and included daily pre- and post-flush samples. Concentrations of regulated and unregulated TW contaminants were used to calculate cumulative in vitro bioactivity ratios and Hazard Indices (HI) based on existing human-health benchmarks. Synoptic results confirmed that human exposures to inorganic and organic contaminant mixtures, which are rarely monitored together in drinking water at the point of consumption, occurred across PR and consisted of elevated concentrations of inorganic contaminants (e.g., lead, copper), disinfection byproducts (DBP), and to a lesser extent per/polyfluoroalkyl substances (PFAS) and phthalates. Exceedances of human-health benchmarks in every synoptic TW sample support further investigation of the potential cumulative risk to vulnerable populations in PR and emphasize the importance of continued broad characterization of drinking-water exposures at the tap with analytical capabilities that better represent the complexity of both inorganic and organic contaminant mixtures known to occur in ambient source waters. Such health-based monitoring data are essential to support public engagement in source water sustainability and treatment and to inform consumer point-of-use treatment decision making in PR and throughout the US.

Analytical discovery of water disinfection byproducts of toxicological relevance: highlighting halobenzoquinones

Analytical advancement enables discoveries in water research, and challenges in the identification and determination of a wide range of trace level toxic compounds in water drives the development of new analytical platforms and tools. The identification of toxic disinfection byproducts (DBPs) in disinfected drinking water is an excellent example. Water disinfection is necessary to protect the public from waterborne disease. However, an unintentional consequence is the formation of DBPs resulting from reactions of disinfectants with natural organic matter in source water. To date, regulated DBPs do not account for the increased bladder cancer risk estimated in epidemiological studies. The majority of halogenated DBPs remain unidentified and the discovery of unknown DBPs of toxicological relevance continues to be a major focus of current water research. This review will highlight halobenzoquinones as a class of DBPs that serves as an example of analytical development and toxicological studies. We will feature recent trends and gaps in analytical technologies for identification of unknown DBPs and bioassays for evaluation of the toxicological effects of specific DBPs and their mixtures.

Roles and Knowledge Gaps of Point-of-Use Technologies for Mitigating Health Risks from Disinfection Byproducts in Tap Water: A Critical Review

Due to rising concerns about water pollution and affordability, there is a rapidly-growing public acceptance and global market for a variety of point-of-use (POU) devices for domestic uses. However, the efficiencies and mechanisms of POU technologies for removing regulated and emerging disinfection byproducts (DBPs) are still not systematically known. To facilitate the development of this field, we summarized performance trends of four common technologies (i.e., boiling, adsorption, membrane filtration, and advanced oxidation) on mitigating preformed DBPs and identified knowledge gaps. The following highest priority knowledge gaps include: 1) data on DBP levels at the tap or cup in domestic applications; 2) certainty regarding the controls of DBPs by heating processes as DBPs may form and transform simultaneously; 3) standards to evaluate the performance of carbon-based materials on varying types of DBPs; 4) long-term information on the membrane performance in removing DBPs; 5) knowledge of DBPs' susceptibility toward advanced redox processes; 6) tools to monitor/predict the toxicity and diversity of DBPs formed in waters with varying precursors and when implementing different treatment technologies; and 7) social acceptance and regulatory frameworks of incorporating POU as a potential supplement to current centralized-treatment focused DBP control strategies. We conclude by identifying research needs necessary to assure POU systems protect the public against regulated and emerging DBPs.

Treatment of iodine-containing water by the UV/NH2Cl process: Dissolved organic matters transformation, iodinated trihalomethane formation and toxicity variation

UV/NH₂Cl process is becoming increasingly important for water treatment, while its impact on iodine-containing water remains unknown. In this study, the structure transformation of dissolved organic matters (DOMs), generation of iodinated trihalomethanes (I-THMs), and variation of acute toxicity were evaulated during the UV/NH₂Cl treatment of iodine-containing water. The combination of exciation emission matrix-parallel factor analysis and two-dimensional correlation spectroscopy integrated with synchronous fluorescence and infrared absorption spectroscopy showed that fulvic-like fraction of DOM was more susceptible to UV/NH₂Cl process and particularly iodo and polysaccharide groups gave the fastest resopnses. Consequently, UV fluence lower than 60 mJ/cm² promoted the production of I-THMs, while excessive UV exhausted NH₂Cl and reactive iodine species and subsequently reduced I-THM generation. Moreover, DOM concentration and source, NH₂Cl dosage, and I^- concentration had significant impacts on I-THM formation in the UV/NH₂Cl process. Additionally, a positive correlation was found between acute toxicity variation and I-THM formation when treating iodine-containing waters with UV/NH₂Cl. These results together provide a comprehensive understanding on UV/NH₂Cl treatment of iodine-containing water.

Public and private tapwater: Comparative analysis of contaminant exposure and potential risk, Cape Cod, Massachusetts, USA

BACKGROUND

Humans are primary drivers of environmental contamination worldwide, including in drinking-water resources. In the United States (US), federal and state agencies regulate and monitor public-supply drinking water while private-supply monitoring is rare; the current lack of directly comparable information on contaminant-mixture exposures and risks between private- and public-supplies undermines tapwater (TW) consumer decision-making.

METHODS

We compared private- and public-supply residential point-of-use TW at Cape Cod, Massachusetts, where both supplies share the same groundwater source. TW from 10 private- and 10 public-supply homes was analyzed for 487 organic, 38 inorganic, 8 microbial indicators, and 3 in vitro bioactivities. Concentrations were compared to existing protective health-based benchmarks, and aggregated Hazard Indices (HI) of regulated and unregulated TW contaminants were calculated along with ratios of in vitro exposure-activity cutoffs.

RESULTS

Seventy organic and 28 inorganic constituents were detected in TW. Median detections were comparable, but median cumulative concentrations were substantially higher in public supply due to 6 chlorine-disinfected samples characterized by disinfection byproducts and corresponding lower heterotrophic plate counts. Public-supply applicable maximum contaminant (nitrate) and treatment action (lead and copper) levels were exceeded in private-supply TW samples only. Exceedances of health-based HI screening levels of concern were common to both TW supplies.

DISCUSSION

These Cape Cod results indicate comparable cumulative human-health concerns from contaminant exposures in private- and public-supply TW in a shared source-water setting. Importantly, although this study's analytical coverage exceeds that currently feasible for water purveyors or homeowners, it nevertheless is a substantial underestimation of the full breadth of contaminant mixtures documented in the environment and potentially present in drinking water.

CONCLUSION

Regardless of the supply, increased public engagement in source-water protection and drinking-water treatment, including consumer point-of-use treatment, is warranted to reduce risks associated with long-term TW contaminant exposures, especially in vulnerable populations.

Why We Will Continue to Lose Our Battle with Cancers If We Do Not Stop Their Triggers from Environmental Pollution

Besides our current health concerns due to COVID-19, cancer is a longer-lasting and even more dramatic pandemic that affects almost a third of the human population worldwide. Most of the emphasis on its causes has been posed on genetic predisposition, chance, and wrong lifestyles (mainly, obesity and smoking). Moreover, our medical weapons against cancers have not improved too much during the last century, although research is in progress. Once diagnosed with a malignant tumour, we still rely on surgery, radiotherapy, and chemotherapy. The main problem is that we have focused on fighting a difficult battle instead of preventing it by controlling its triggers. Quite the opposite, our knowledge of the links between environmental pollution and cancer has surged from the 1980s. Carcinogens in water, air, and soil have continued to accumulate disproportionally and grow in number and dose, bringing us to today's carnage. Here, a synthesis and critical review of the state of the knowledge of the links between cancer and environmental pollution in the three environmental compartments is provided, research gaps are briefly discussed, and some future directions are indicated. New evidence suggests that it is relevant to take into account not only the dose but also the time when we are exposed to carcinogens. The review ends by stressing that more dedication should be put into studying the environmental causes of cancers to prevent and avoid curing them, that the precautionary approach towards environmental pollutants must be much more reactionary, and that there is an urgent need to leave behind the outdated petrochemical-based industry and goods production.

A New Group of Heterocyclic Nitrogenous Disinfection Byproducts (DBPs) in Drinking Water: Role of Extraction pH in Unknown DBP Exploration

pH adjustment prior to extraction is an important step in water sample pretreatment processes for exploration of new/unknown disinfection byproducts (DBPs) in drinking water. To achieve a better extraction efficiency, the pH of a water sample is usually adjusted to a low level (e.g., < 0.5) to ensure that target DBPs are in their neutral forms. However, such a practice may elude some amphoteric DBPs (especially those nitrogenous DBPs with multiple functional groups), which can accept protons at a low pH and lose protons at a high pH. In this study, with careful extraction pH selection and optimization, we first report the detection and identification of a new group of heterocyclic nitrogenous DBPs, halogenated pyridinols, in simulated drinking water using ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry and time-of-flight mass spectrometry, including 5-chloro-3-pyridinol, 2-bromo-3-pyridinol, 2,6-dichloro-4-pyridinol, 2,6-dibromo-3-pyridinol, 3-bromo-2-chloro-5-pyridinol, 5-bromo-2-chloro-3-pyridinol, 3,5,6-trichloro-2-pyridinol, and 2,4,6-tribromo-3-pyridinol. On the basis of the speciation of dissociated chemical species and recovery tests at different extraction pH values, it was found that, only at a pH of 3.0, all the eight new DBPs could achieve recoveries of >50%. With subsequent instrumental parameter optimization, the method detection and quantitation limits of the eight new DBPs were determined to be 0.04-1.58 and 0.15-4.11 ng/L, respectively. The optimized method enabled an accurate detection of the eight new DBPs in two real drinking water samples. Further aided with in vivo developmental and acute toxicity assays using zebrafish embryos, the developmental and acute toxicity of the new DBPs were found to be slightly lower than those of halogenated benzoquinones but dozens of times higher than those of commonly known DBPs such as tribromomethane and iodoacetic acid.

Use of trihalomethanes as a surrogate for haloacetonitrile exposure introduces misclassification bias

Epidemiologists have used trihalomethanes (THMs) as a surrogate for overall disinfection byproduct (DBP) exposure based on the assumption that THM concentrations are proportional to concentrations of other DBP classes. Toxicological evidence indicates THMs are less potent toxins than unregulated classes like haloacetonitriles (HANs). If THMs are not proportional to the DBPs driving toxicity, the use of THMs to measure exposure may introduce non-trivial exposure misclassification bias in epidemiologic studies. This study developed statistical models to evaluate the covariance and proportionality of HAN and THM concentrations in a dataset featuring over 9500 measurements from 248 public water systems. THMs only explain ∼30% of the variance in HANs, whether the data is pooled in a classic linear regression or hierarchically grouped by water system in a multilevel linear regression. The 95% prediction interval on HANs for the median THM concentration exceeds the interquartile range of HANs. Mean HAN:THM ratios range from ∼2.4% to ∼80% across water systems, and varied with source water category, season, disinfectant sequence and distribution system location. The HAN:THM ratio was 265% higher in groundwater systems than in surface water systems and declined by ∼40% between finished effluent and maximum residence times in surface water systems with chlorine-chlorine disinfection. A maximum likelihood approach was used to estimate the misclassification bias that may result from using THMs to construct risk-ratios, assuming that HANs represent the "true" DBP exposure risk. The results indicate an odds ratio of ∼2 estimated with THM concentrations could correspond to a true odds ratio of 4-5. These findings demonstrate the need for epidemiologic studies to evaluate exposure by measuring DBPs that are likely to drive toxicity.

Comparative cytotoxicity studies of halophenolic disinfection byproducts using human extended pluripotent stem cells

2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP) and 2,4,6-triiodophenol (TIP) are a new class of halophenolic disinfection byproducts (DBPs) which have been widely detected in drinking water. In recent years, their developmental toxicity has got increasing public attention due to their potential toxic effects on embryo development towards lower organisms. Nonetheless, the application of human embryos for embryonic toxicologic studies is rendered by ethical and moral considerations, as well as the technical barrier to sustaining normal development beyond a few days. Human extended pluripotent stem (EPS) cells (novel totipotent-like stem cells) represent a much more appropriate cellular model for studying human embryo development. In this study, we utilized human EPS cells to study the developmental toxicity of TCP, TBP and TIP, respectively. All three halophenolic DBPs showed cytotoxicity against human EPS cells in an obvious dose-dependent manner, among which TIP was the most cytotoxic one. Notably, the expression of pluripotent genes in human EPS cells significantly declined after 2,4,6-trihalophenol exposure. Meanwhile, 2,4,6-trihalophenol exposure promoted ectodermal differentiation of human EPS cells in an embryoid bodies (EBs) differentiation assay, while both endodermal and mesodermal differentiation were impaired. These results implied that phenolic halogenated DBPs have specific effects on human embryo development even in the early stage of pregnancy. In summary, we applied human EPS cells as a novel research model for human embryo developmental toxicity study of environmental pollutants, and demonstrated the toxicity of phenolic halogenated DBPs on early embryo development of human beings.

Low-concentration of dichloroacetonitrile (DCAN) in drinking water perturbs the health-associated gut microbiome and metabolic profile in rats

Dichloroacetonitrile (DCAN) is one of the emerging nitrogenous disinfection by-products (DBPs) in drinking water. However, its potential toxicological effects remain poorly understood, especially at a low concentration found in the environment. In the present study, we investigated whether the consumption of low-concentration DCAN through drinking water would produce significant effects in male SD rats, with particular focus on their physiological traits and changes in their gut microbiome and metabolite profiles. After a 4-weeks DCAN intervention, significant changes were observed in the body weight, blood indices, and histology in DCAN-treated (100 μg/L) group. Proteobacteria was relatively less abundant in 20 and 100 μg/L DCAN-treated groups compared with that in the control group at phylum level. At genus level, Parasutterella and Anaerotruncus were significantly less abundant in both 20 and 100 μg/L DCAN-treated groups than that in the control group. Furthermore, the gut microbiota-related metabolites were dramatically perturbed after DCAN consumption. In the 20 and 100 μg/L DCAN-treated groups, there were 48 and 95 altered metabolites, respectively, and were found to be involved in sphingolipid signaling pathway, fatty acid biosynthesis, and cGMP-PKG signaling pathway. In summary, we demonstrated that consumption of low-concentration DCAN through drinking water could impair host health and induce gut microbiota dysbiosis and gut microflora-related metabolic disorders in male SD rats. Our findings highlight the potential toxicity of low-concentration DBPs and provide new insight into potential causal relationship between low concentration DBPs found in the drinking water and the host health.

Identification of N-Nitrosamines and Nitrogenous Heterocyclic Byproducts during Chloramination of Aromatic Secondary Amine Precursors

With diminishing pristine water, wastewater-affected waters that contain complex anthropogenic compounds are becoming important sources of drinking water and the compounds will inevitably react with disinfectants to form disinfection byproducts (DBPs). Secondary amines such as diphenylamine (DPA) analogues are considered as potential precursors of N-nitrosamines. In this study, an in situ ¹⁴N/¹⁵N-labeling and screening workflow was used to systematically investigate the formation of nitrogenous DBPs (N-DBPs) and putative reaction pathways. Twenty-four pairs of N-DBPs were generated and identified from chloramination of DPA through two main pathways, in which chloramines reacted with the amino and phenyl functional groups to form N-nitrosodiphenylamine and monochlorinated 5,10-dihydro-phenazine (Cl-DiH-Phe), respectively. Cl-DiH-Phe could further produce phenazine and the coupling products with another DPA molecule. Selective N-DBP formation was pH and dose-dependent, and the same reactions were observed for additional two aromatic DPA analogues. Effects of alkyl substituents on the formation pathways were investigated using a series of dialkyl and N-alkyl aromatic analogues. Only the amino pathway to form nitrosamines was noticed for dialkyl amines, nevertheless, both the main reactions occurred for N-alkyl aromatic amines. These findings suggested that the reaction with chloramines through a phenyl pathway was likely to be crucial for novel nitrogenous heterocyclic byproducts.

Evaluation of hypopigmentation in embryonic zebrafish induced by emerging disinfection byproduct, 3, 5-di-I-tyrosylalanine

Halogenated dipeptides, 3, 5-di-I-tyrosylalanine (DIYA), have been identified as novel disinfection byproducts (DBPs), following chloramination of authentic water. However, little is known about their toxicity. Zebrafish embryos were used to assess the toxicity of novel iodinated DBPs (I-DBPs). Although DIYA did not exhibit high acute toxicity to embryonic zebrafish (LC₅₀ > 2 mM), it significantly inhibited pigmentation of melanophores and xanthophores on head, trunk and tail at 500 μM as determined by photographic analysis. Whereas N-phenylthiourea (PTU) as a pigment inhibitor did not inhibit development of yellow pigments. Colorimetric detection of melanin further confirmed these results. Quantitative real time polymerase chain reaction (qRT-PCR) measurements indicated that genes (dct, slc24a5, tyr, tyrp1a, tyrp1b, silva) associated with the melanogenesis pathway were dramatically down-regulated following exposure to 500 μM DIYA. In addition, enzymatic activity of tyrosinase (TYR) decreased, also demonstrating that the underlying mechanism of hypopigmentation was attributed to the disruption of melanogenesis pathway. Transcription levels of xanthophore genes (gch2, bnc2, csf1a, csf1b, pax7a and pax7b) were also monitored by qRT-PCR assay. DIYA exposure up-regulated expression of gch2 and bnc2, but not csf1 and pax7. Tested DIYA analogues, brominated tyrosine was unlikely to inhibit pigmentation, indicating that the iodine substitution and dipeptides structure are of important structural feature for the inhibition of pigmentation. In this study, we observed that DIYA inhibited melanogenesis related genes, which might contribute to pigmentation defects. Moreover, as an emerging I-DBPs, the developmental toxicity of aromatic dipeptides should be further studied.

Predicting unregulated disinfection by-products in small water distribution networks: an empirical modelling framework

Disinfection is used to deactivate pathogens in drinking water. However, disinfectants react with natural organic matter present in water to form disinfection by-products (DBPs). While a few of these DBPs have been studied extensively and are regulated in many countries, new unregulated DBPs (UR-DBPs) have also recently been identified in drinking water. The UR-DBPs are considered to be more toxic than regulated DBPs (R-DBPs). To understand the occurrence of UR-DBPs in a water distribution network (WDN), this research presents an approach to predicting the behaviour of emerging UR-DBPs such as dichloroacetonitrile (DCAN), trichloropropanone (TCP), and trichloronitromethane (TCNM) in WDNs. Water quality data, generated by sampling and laboratory analysis of 12 small communities, was used to develop predictive models. A framework was also proposed alongside the predictive models to estimate the concentration of emerging UR-DBPs under limited water quality sampling information. Moreover, the relationship between emerging UR-DBP concentrations and their identified predictors was further observed and evaluated by developing contour profiles. DCAN and TCP predictive models have coefficient of determination (R²) > 85%, whereas for TCNM model, the R² was > 65%. Water quality parameters including water temperature, turbidity, conductivity, and dissolved organic carbon concentrations were identified as key predictors. Similarly, trichloroacetic acid and bromodichloromethane were identified as key predictors among DBP families, to predict the occurrence of emerging UR-DBPs. Developed models and relationships between the UR-DBPs and predictors can help water utilities and regulators to manage the occurrence of UR-DBPs in small WDNs.

Cytotoxicity of Halogenated Tyrosyl Compounds, an Emerging Class of Disinfection Byproducts

Halogenated amino acids and peptides are an emerging class of disinfection byproducts (DBPs), having been detected in drinking water and in washed food products. However, the toxicological significance of these emerging DBPs remains unclear. In this study, the cytotoxicity of eight halogenated tyrosyl compounds was investigated in Chinese hamster ovary (CHO) cells using real-time cell analysis (RTCA). Dihalogenated tyrosyl compounds are more cytotoxic than their monohalogenated analogues. The cytotoxicity of the dihalogenated compounds is associated with their ability to induce intracellular reactive oxygen species (ROS), suggesting that oxidative stress is an important toxicity pathway of these compounds. Pearson correlation analysis of the cytotoxicity (IC₅₀ values) of these compounds with eight physicochemical parameters showed strong associations with their lipophilicity (logP) and reactivity (polarizability, E_LUMO). Finally, cytotoxicity testing of the concentrated extracts of a chloraminated mixture of eight dipeptides with bromide or iodide showed the cytotoxicity of these mixtures in the order: iodinated peptides > brominated peptides ≥ chlorinated peptides. These results demonstrate that halogenated peptide DBPs are toxicologically relevant, and further research is needed to understand the implications of long-term exposure for human health.

Carvacrol encapsulation into nanostructures: Characterization and antimicrobial activity against foodborne pathogens adhered to stainless steel

Carvacrol is a natural antimicrobial capable of inhibiting several microorganisms. The encapsulation of this compound may increase its stability, water solubility and provide controlled release. In this study, carvacrol encapsulated into nanoliposomes (NLC) and polymeric Eudragit® nanocapsules (NCC) was tested against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Salmonella spp. adhered to stainless steel. NLC showed an average diameter of 270.8 nm, zeta potential of +8.64 mV, and encapsulation efficiency of 98%. Minimum Bactericidal Concentration (MBC) of NLC was 3.53 mg/mL against Salmonella and 5.30 mg/mL against the other bacteria. NCC presented an average diameter of 159.3 nm, zeta potential of +44.8 mV, and encapsulation efficiency of 97%. MBC of NCC was 4.42 mg/mL against E. coli and 3.31 mg/mL against the other bacteria. After 2 h incubation with NCC at carvacrol concentration equivalent to ½ MBC, viable counts of Salmonella and E. coli were below the detection limit (1.69 CFU/mL). The population of L. monocytogenes and S. aureus was reduced by 2 log CFU/mL in 6 h. Afterwards, pools of each bacterium were separately adhered to stainless steel coupons (initial population 6.5 CFU/cm²). Salmonella and E. coli were inhibited below the detection limit using the NCC at concentration equivalent to MBC, while L. monocytogenes and S. aureus were reduced by 4 log CFU/cm² and 3.5 log CFU/cm², respectively. Although free carvacrol presented better results than encapsulated one in all tests performed, using encapsulated carvacrol could be more interesting for food applications by masking the strong aroma of the compound, in addition to a controlled release of carvacrol. The results suggest that NCC have potential for use in food contact surfaces in order to avoid bacterial adhesion and subsequent biofilm formation.

Interference from haloacetamides during the determination of haloacetic acids using gas chromatography

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

Occurrence, Formation, and Oxidative Stress of Emerging Disinfection Byproducts, Halobenzoquinones, in Tea

Halobenzoquinones (HBQs) are frequently detected disinfection byproducts (DBPs) in drinking water with high toxicity and relevance to public health. In this study, we characterized the occurrence, formation, and oxidative stress of the HBQs in tea. 2,6-DCBQ and TetraC-1,2-BQ were identified in all prepared teas at total concentrations of 1.3-2.0 ng/L. 2,6-DCBQ originated from drinking water DBPs, while TetraC-1,2-BQ originated from tea leaves or were generated during tea polyphenol chlorination. HBQs in tea induced the formation of reactive oxygen species and semiquinone radicals, and the oxidative stress could be depleted by tea polyphenols, e.g., (-)-epigallocatechin gallate (EGCG). High-resolution mass spectrometry analysis indicated that the HBQs combined with EGCG and formed adducts at a ratio of 1:1 or 2:1 with the binding sites on the A ring and B ring of EGCG. The viability of HepG2 cells exposed to 50 μM 2,6-DCBQ was increased from 20.0% to 65.2% when 50 μM of EGCG was added. These results demonstrated that various HBQs can occur in tea due to the HBQ DBPs in drinking water, the leachate from tea leaves, and the chlorination of tea polyphenols; furthermore, the oxidative stress and cellular toxicity induced by HBQs in tea could be decreased by tea polyphenols. This is the first study to report HBQs in tea, elucidate the sources of HBQs, and assess relevant health risks.

Occurrence of disinfection by-products in sewage treatment plants and the marine environment in Hong Kong

Disinfection byproducts (DBPs) are generated by disinfectants reacting with organic matters. Previous studies have focused on DBPs in drinking water, but they have not paid sufficient attention to DBPs in sewage treatment plants (STPs), where the sources and compositions of DBPs are much more complicated, and there is a likelihood of more toxic DBPs being formed. In this study, the occurrence of DBPs in six STPs in Hong Kong and the potential impact of the effluents from the STPs on the marine environment were investigated. In STPs, the mean concentrations of the total DBPs ranged from 1160 to 17,019 ng/L, 1562 to 20,795 ng/L, and 289 to 1037 ng/L in the influent, effluent, and seawater, respectively. Trihalomethanes, haloacetonitriles, and trihalophenols were the most commonly detected DBPs, whereas hexachloro-1,3-butadiene and halocarbazoles were not detected in the STPs and in the marine environment in Hong Kong. Secondary treatment efficiently removed DBPs and DBP precursors. Regarding disinfection techniques, UV irradiation showed little effect on the concentrations of DBPs, whereas sodium hypochlorite significantly elevated the levels of both traditional and emerging DBPs. The effluents from two selected STPs that use chlorination have an obvious impact on the marine environment. This work presents the potential sources of DBPs in sewage, the influence of the treatment processes and disinfection techniques employed in STPs on the removal/formation of DBPs, and the impact of the effluents from the STPs on the marine environment. This work also highlights the need for investigating the emerging DBPs generated in STPs and their related environmental concerns.

Effects of 2,2-dichloroacetamide (DCAcAm), an emerging disinfection by-product in drinking water, on the intestinal microbiota of adult zebrafish

The presence of disinfection by-products (DBPs) increases the mutagenicity of water and may pose adverse health effects. Gut microbiota exerts a fundamental role on host physiology, and how extrinsic perturbations influence its composition has been increasingly examined. However, the effect of DBPs on gut microbiota is still poorly understood. In the present study, adult zebrafish were exposed to different concentrations of dichloroacetamide (DCAcAm, an emerging nitrogenous DBP) for 30 days. Sequencing of 16S rRNA amplicons revealed a significant change in the richness and diversity of microbiota in the gut of DCAcAm-exposed zebrafish. At the phylum level, the abundance of Proteobacteria decreased and the abundance of Fusobacteria and Firmicutes increased significantly in the gut after exposure to 100 and 500 μg/L DCAcAm. At the genus level, the abundances of several bacteria which are considered pathogens or opportunistic pathogens in fish and closely related to fish metabolism, disease and inflammation (Aeromonas, Stenotrophomonas, Bacteroides and Ralstonia) increased in the DCAcAm-treated groups. Our results reveal that DBPs in drinking water potentially affect gut microbiota composition, which may contribute to the toxicity assessment of DBPs in future and provide new insight into the complex interactions between the DBPs in drinking water and host health.

Health risk assessment of trihalomethanes in water treatment plants in Jiangsu Province, China

Probabilistic lifetime cancer risks and non-cancer risks of trihalomethanes (THMs) through ingestion, dermal contact, and inhalation exposure in 88 drinking water treatment plants (WTPs) with raw waters from five water systems (WSs) in Jiangsu Province were analyzed and compared. Concentrations of THMs in finished water of study WTPs varied, ranging from 18.81 to 38.96 μg/L, which are lower than the maximum of 80 μg/L recommended by USEPA. The results of health risk assessment indicated that cancer risk as well as non-cancer risks of THMs in WTPs sourced from five water systems decreased in the order of WS3 > WS5 > WS2 > WS1 > WS4. The comparison among multiple exposure routes indicated that when non-boiled drinking water is consumed, ingestion has the highest exposure route, with exposure values greater than dermal contact and inhalation for WTPs with raw water from all five water systems. However, when drinking boiled water, dermal contact is the major risk source for WTPs with raw water from WS1 and WS2, instead of dermal contact, inhalation becomes the major risk source for WTPs with raw water from WS3, WS4, and WS5. In WTPs with raw water from water systems WS1, WS3, WS4, and WS5, dibromochloromethane (DBCM) in THMs has the highest contribution to cancer risk, while chloroform in THMs has the highest contribution to non-cancer risk. However, in WTPs with raw water from water system WS2, bromodichloromethane (BDCM) has the highest contribution to both cancer risk and non-cancer risk. The results also indicated that females are prone to cancer risk induced by THMs since Chinese people are accustomed to drinking boiled water. The results supply valuable information for health departments to put forward more specific and efficient policies to control water borne diseases.

Formation, Identification, and Occurrence of New Bromo- and Mixed Halo-Tyrosyl Dipeptides in Chloraminated Water

Dipeptides are widely present in surface water and serve as precursors to form disinfection byproducts (DBPs) during disinfection (e.g., chloramination). Bromide (Br^-) and iodide (I^-) are common in many source waters, enhancing Br- and I-DBP formation. Recently Cl-, I-, and Cl-I-dipeptides were identified after chloramination of tyrosyl dipeptides in the presence of I^- and were detected in authentic disinfected drinking water samples. However, the formation and occurrence of Br- and mixed halogen (Cl, Br, and/or I)-dipeptides in disinfected water have not been studied. Here we investigated the formation of halogenated dipeptides from three aromatic dipeptides, phenylalanylglycine (Phe-Gly), tyrosylalanine (Tyr-Ala), and tyrosylglycine (Tyr-Gly), under chloramination in the presence of Br^- and I^- at environmentally relevant levels ([Br^-] and [I^-], 0 and 0 μg L^-1, 6 and 30 μg L^-1, 30 and 30 μg L^-1, 150 and 30 μg L^-1, 300 and 30 μg L^-1, and 900 and 30 μg L^-1, respectively). For the first time, N-Br- and N,N-di-Br- as well as N-Br- N-Cl- and N-Br-3-I-tyrosyl dipeptides were identified using infusion electrospray quadrupole time-of-flight mass spectrometry. Tyrosyl dipeptides produced N-Cl-, 3-I-/3,5-di-I-, and N-Cl-3-I-tyrosyl dipeptides, while Phe-Gly formed only N-Cl-/ N, N-di-Cl-Phe-Gly. To determine halogenated dipeptides in authentic water samples, we developed a new method of solid phase extraction and high-performance liquid chromatography with quadrupole ion trap mass spectrometry using reaction monitoring. 3,5-Di-I-Tyr-Ala and N-Br-Tyr-Ala were detected in treated water but not in the corresponding raw water, warranting further investigation into the occurrence of halogenated peptides in other drinking water systems.

National Trends of Bladder Cancer and Trihalomethanes in Drinking Water: A Review and Multicountry Ecological Study

We examined trends in incidence of bladder cancer in 8 countries in the 45+ years since trihalomethanes (THMs) were detected in chlorinated drinking water. Total trihalomethanes (TTHMs) are the principal regulated disinfection by-products (DBPs) along with halogenated acetic acids (HAAs). Numerous epidemiological studies have examined exposure to TTHMs and associations with bladder cancer. Concentrations of TTHM have declined in most of the 8 countries that were studied as has smoking prevalence. Incidences of bladder cancer have usually stayed relatively flat, especially for females, with some variations. Since THMs are not carcinogens in whole animal tests, they may not be appropriate surrogates for studying potential cancer risks in drinking water. Etiology of bladder cancer is complex; incidence correlates with age. Previously identified risk factors include smoking, type 2 diabetes, sex, ethnicity, arsenic, aromatic amines, and occupations. As a predominant risk factor, smoking trends may dominate incidence rates, but additional time might be required to determine whether a DBP risk exists due to long latency periods. Causal drinking water-related bladder cancer risks remain questionable and likely small compared to other factors, although surrogate-based DBP management is an appropriate strategy for maintaining drinking water quality as long as it does not compromise microbial disinfection.

Prioritization of unregulated disinfection by-products in drinking water distribution systems for human health risk mitigation: A critical review

Water disinfection involves the use of different types of disinfectants, which are oxidizing agents that react with natural organic matter (NOM) to form disinfection by-products (DBPs). The United States Environmental Protection Agency (USEPA) has established threshold limits on some DBPs, which are known as regulated DBPs (R-DBPs). The human health risks associated with R-DBPs in drinking water distribution systems (DWDSs) and application of stricter regulations have led water utilities to switch from conventional disinfectant (i.e., chlorination) to alternative disinfectants. However, the use of alternative disinfectants causes formation of a new suit of DBPs known as unregulated DBPs (UR-DBPs), which in many cases can be more toxic. There is a growing concern of UR-DBPs formation in drinking water. This review prioritizes some commonly occurring UR-DBP groups and species in DWDSs based on their concentration level, reported frequency, and toxicity using an indexing method. There are nine UR-DBPs group and 36 species that have been identified based on recent published peer-reviewed articles. Haloacetonitriles (HANs) and haloacetaldehydes (HALs) are identified as important UR-DBP groups. Dichloroacetonitrile (DCAN) and trichloroacetaldehye (TCAL) are identified as critical UR-DBPs species. The outcomes of this review can help water regulators to identify the most critical UR-DBPs species in the context of drinking water safety and provide them with useful information to develop guidelines or threshold limits for UR-DBPs. The outcomes can also help water utilities in selecting water treatment processes for the mitigation of human health risk posed by UR-DBPs through drinking water.