In Vitro Cytotoxicity and Adaptive Stress Responses to Selected Haloacetic Acid and Halobenzoquinone Water Disinfection Byproducts

Effects of halobenzoquinone and haloacetic acid water disinfection byproducts on human neural stem cells

Human neural stem cells (hNSCs) are a useful tool to assess the developmental effects of various environmental contaminants; however, the application of hNSCs to evaluate water disinfection byproducts (DBPs) is scarce. Comprehensive toxicological results are essential to the prioritization of DBPs for further testing and regulation. Therefore, this study examines the effects of DBPs on the proliferation and differentiation of hNSCs. Prior to DBP treatment, characteristic protein markers of hNSCs from passages 3 to 6 were carefully examined and it was determined that hNSCs passaged 3 or 4 times maintained stem cell characteristics and can be used for DBP analysis. Two regulated DBPs, monobromoacetic acid (BAA) and monochloroacetic acid (CAA), and two emerging DBPs, 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ) and 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), were chosen for hNSC treatment. Both 2,6-DBBQ and 2,6-DCBQ induced cell cycle arrest at S-phase at concentrations up to 1μmol/L. Comparatively, BAA and CAA at 0.5μmol/L affected neural differentiation. These results suggest DBP-dependent effects on hNSC proliferation and differentiation. The DBP-induced cell cycle arrest and inhibition of normal hNSC differentiation demonstrate the need to assess the developmental neurotoxicity of DBPs.

Behavior of non-regulated disinfection by-products in water following multiple chlorination points during treatment

In this study, the behavior of regulated (trihalomethanes-THMs, haloacetic acids-HAAs) and non-regulated (haloacetonitriles-HANs, haloketones-HKs, chloropicrin-CPK) disinfection by-products (DBPs) was investigated during treatment and distribution in a municipal drinking water system that adds chlorine at multiple points within the water treatment plant (WTP). Three to eight locations in the WTP and four locations in the distribution network were sampled weekly for DBP measurements during the warmest period of the year. The results show that most DBPs found in the study area are formed during treatment, not distribution. However, the DBP species studied behave differently during treatment and distribution. Moreover, the location where DBP concentration is the highest in the distribution network differs among species of the same family, especially HAAs and HKs, and between the sampling campaigns. As a result, the relevance of using the sum of the concentrations of the species of the same DBP family to select sampling sites for DBP monitoring is questionable. This study illustrates the difficulties that drinking water supply managers must face to control and monitor the presence of DBPs.

In vitro bioacessibility and transport across Caco-2 monolayers of haloacetic acids in drinking water

Water disinfection plays a crucial role in water safety but it is also a matter of concern as the use of disinfectants promotes the formation of disinfection by-products (DBPs). Haloacetic acids (HAAs) are one of the major classes of DBPs since they are frequently found in treated water, are ubiquitous, pervasive and have high water solubility, so a great concern emerged about their formation, occurrence and toxicity. Exposure to HAAs is influenced by consumption patterns and diet of individuals thus their bioavailability is an important parameter to the overall toxicity. In the current study the bioacessibility of the most representative HAAs (chloroacetic acid - MCAA, bromoacetic acid - MBAA, dichloroacetic acid - DCAA, dibromoacetic acid - DBAA, and trichloroacetic acid - TCAA) after simulated in vitro digestion (SIVD) in tap water and transport across Caco-2 monolayers was evaluated. Compounds were monitored in 8 points throughout the digestion phases by an optimized LC-MS/MS methodology. MCAA and MBAA were not bioaccessible after SIVD whereas DCAA, DBAA and TCAA are highly bioaccessible (85 ± 4%, 97 ± 4% and 106 ± 7% respectively). Concerning transport assays, DCAA and DBAA were highly permeable throughout the Caco-2 monolayer (apparent permeability and calculated fraction absorbed of 13.62 × 10(-6) cm/s and 90% for DCAA; and 8.82 × 10(-6) cm/s and 84% for DBAA), whereas TCAA showed no relevant permeability. The present results may contribute to efficient risk analysis studies concerning HAAs oral exposure from tap water taking into account the different biological behaviour of these chemically similar substances.

An insight of disinfection by-product (DBP) formation by alternative disinfectants for swimming pool disinfection under tropical conditions

Sodium hypochlorite (NaClO) is the most commonly used disinfectant in pool treatment system. Outdoor pools usually suffer from the strong sunlight irradiation which degrades the free chlorine rapidly. In addition, more pools start to adopt the recirculation of swimming pool water, which intensifies the disinfection by-product (DBP) accumulation issue. Given these potential drawbacks of using NaClO in the tropical environment, two alternative organic-based disinfectants, trichloroisocyanuric acid (TCCA, C3Cl3N3O3) and bromochlorodimethylhydantoin (BCDMH, C5H6BrClN2O2), were investigated and compared to NaClO in terms of their self-degradation and the formation of DBPs, including trihalomethanes (THMs) and haloacetic acids (HAAs), under simulated tropical climate conditions. The result reveals that halogen stabilizer, TCCA, had the advantages of slower free chlorine degradation and lower DBP concentration compared to NaClO, which makes it a good alternative disinfectant. BCDMH was not recommended mainly due to the highly reactive disinfecting ingredient, hypobromous acid (HBrO), which fails to sustain the continuous disinfection requirement. Total disinfectant dosage was the main factor that affects residual chlorine/bromine and THM/HAA formation regardless of different disinfectant dosing methods, e.g. shock dosing (one-time spiking) in the beginning, and continuous dosing during the whole experimental period. Two-stage second-order-kinetic-based models demonstrate a good correlation between the measured and predicted data for chlorine decay (R(2) ≥ 0.95), THM (R(2) ≥ 0.99) and HAA (R(2) ≥ 0.83) formation. Higher temperature was found to enhance the DBP formation due to the temperature dependence of reaction rates. Thus, temperature control of pools, especially for those preferring higher temperatures (e.g. hydrotherapy and spa), should take both bather comfort and DBP formation potential into consideration. It is also observed that chlorine competition existed between different precursors from natural organic matters (NOM) in filling water and body fluid analogue (BFA). Among the composition of BFA, uric acid, citric acid and hippuric acid were found to be the main precursors for HAA formation.

Rh-Catalyzed Reactions of 1,4-Benzoquinones with Electrophiles: C-H Iodination, Bromination, and Phenylselenation

Under Rh-catalyzed conditions, typically electrophilic 1,4-benzoquinones exhibit nucleophilic reactivity, such that exposure to appropriate electrophiles generates products of C-H iodination, bromination, and phenylselenation. This provides a mild and general method for direct halofunctionalization, and the first method that can achieve direct C-H phenylselenation of this compound class. The scope and limitations of the new protocols are outlined, and representative derivatizations are highlighted.

Emerging Disinfection Byproducts, Halobenzoquinones: Effects of Isomeric Structure and Halogen Substitution on Cytotoxicity, Formation of Reactive Oxygen Species, and Genotoxicity

Halobenzoquinones (HBQs) are a structurally diverse class of water disinfection byproducts. Here, we report a systematic study on the effects of isomeric structure and the type and number of halogen substitutions of HBQs on their cytotoxicity, formation of reactive oxygen species (ROS), and genotoxicity. Dynamic responses and IC50 histograms were obtained using real-time cell analysis, clearly ranking the cytotoxicity of the HBQs in Chinese hamster ovary (CHO-K1) cells. Strong isomeric structure effects were shown with 2,5-HBQ isomers inducing greater cytotoxicity than their corresponding 2,6-HBQ isomers (P < 0.05). HBQ-halogen substitution groups also influence cytotoxicity, as cytotoxicity increases across the dihalogenated HBQs: iodo- > bromo- > chloro-HBQs (P < 0.05). Determination of HBQ-induced ROS further supports isomeric structure and halogen substitution effects. HBQ-induced genotoxicity was shown as increased levels of 8-hydroxy-2'-deoxyguanosine and p53 protein. Pearson correlation analysis of the HBQ toxicity measurements with their physicochemical parameters demonstrates that dipole moment and the lowest unoccupied molecular orbital energy are two major structural influences on toxicity (r = -0.721 or -0.766, P < 0.05). Dipole moment also correlates with isomer toxicity. This study suggests that formation and occurrence of highly toxic iodo-HBQs and 2,5-HBQs warrant further investigation to fully assess the impact of HBQs in drinking water.