Effects of Fe(III) on the formation and toxicity alteration of halonitromethanes, dichloroacetonitrile, and dichloroacetamide from polyethyleneimine during UV/chlorine disinfection.

Trace iron ions (Fe(III)) are commonly found in water and wastewater, where free chlorine is very likely to coexist with Fe(III) affecting the disinfectant's stability and N-DBPs' fate during UV/chlorine disinfection, and yet current understanding of these mechanisms is limited. This study investigates the effects of Fe(III) on the formation and toxicity alteration of halonitromethanes (HNMs), dichloroacetonitrile (DCAN), and dichloroacetamide (DCAcAm) from polyethyleneimine (PEI) during UV/chlorine disinfection. Results reveal that the maxima concentrations of HNMs, DCAN, and DCAcAm during UV/chlorine disinfection with additional Fe(III) were 1.39, 1.38, and 1.29 times higher than those without additional Fe(III), instead of being similar to those of Fe(III) inhibited the formation of HNMs, DCAN and DCAcAm during chlorination disinfection. Meanwhile, higher Fe(III) concentration, acidic pH, and higher chlorine dose were more favorable for forming HNMs, DCAN, and DCAcAm during UV/chlorine disinfection, which were highly dependent on the involvement of HO· and Cl·. Fe(III) in the aquatic environment partially hydrolyzed to the photoactive Fe(III)­hydroxyl complexes Fe(OH)2+ and [Fe(H2O)6]3+, which undergone UV photoactivation and coupling reactions with HOCl to achieve effective Fe(III)/Fe(II) interconversion, a process that facilitated the sustainable production of HO·. Extensive product analysis and comparison verified that the HO· production enhanced by the Fe(III)/Fe(II) internal cycle played a primary role in increasing HNMs, DCAN, and DCAcAm productions during UV/chlorine disinfection. Note that the incorporation of Fe(III) increased the cytotoxicity and genotoxicity of HNMs, DCAN, and DCAcAm formed during UV/chlorine disinfection, and yet Fe(III) did not have a significant effect on the acute toxicity of water samples before, during, and after UV/chlorine disinfection. The new findings broaden the knowledge of Fe(III) affecting HNMs, DCAN, and DCAcAm formation and toxicity alteration during UV/chlorine disinfection.

Formation and toxicity alteration of halonitromethanes from Chlorella vulgaris during UV/chloramination process involving bromide ion.

Frequent algal blooms cause algal cells and their algal organic matter (AOM) to become critical precursors of disinfection by-products (DBPs) during water treatment. The presence of bromide ion (Br-) in water has been demonstrated to affect the formation laws and species distribution of DBPs. However, few researchers have addressed the formation and toxicity alteration of halonitromethanes (HNMs) from algae during disinfection in the presence of Br-. Therefore, in this work, Chlorella vulgaris was selected as a representative algal precursor to investigate the formation and toxicity alteration of HNMs during UV/chloramination involving Br-. The results showed that the formation concentration of HNMs increased and then decreased during UV/chloramination. The intracellular organic matter of Chlorella vulgaris was more susceptible to form HNMs than the extracellular organic matter. When the Br-: Cl2 mass ratio was raised from 0.004 to 0.08, the peak of HNMs total concentration increased 33.99%, and the cytotoxicity index and genotoxicity index of HNMs increased 67.94% and 22.80%. Besides, the formation concentration and toxicity of HNMs increased with increasing Chlorella vulgaris concentration but decreased with increasing solution pH. Possible formation pathways of HNMs from Chlorella vulgaris during UV/chloramination involving Br- were proposed based on the alteration of nitrogen species and fluorescence spectrum analysis. Furthermore, the formation laws of HNMs from Chlorella vulgaris in real water samples were similar to those in deionized water samples. This study contributes to a better comprehension of HNMs formation from Chlorella vulgaris and provides valuable information for water managers to reduce hazards associated with the formation of HNMs.

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

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

Formation of halonitromethanes from glycine during LED-UV265/chlorine disinfection.

LED-UV265/chlorine is a promising alternative disinfection technology that emits mono-wavelength light for high germicidal efficiency. Halonitromethanes (HNMs) are highly cytotoxic and genotoxic disinfection byproducts that can be formed during LED-UV265/chlorine disinfection. Thus, this work aimed to investigate the HNMs formation from glycine (Gly) during LED-UV265/chlorine disinfection. The results indicated that the concentrations of chlorinated-HNMs (Cl-HNMs) increased first and then decreased as the reaction proceeded. Besides, the effects of operating parameters (UV intensity, free chlorine dosage, and pH) and coexisting ions (Cu2+ and Br-) on HNMs formation were investigated. It was found that the formation concentrations of Cl-HNMs increased with the increase of LED-UV265 intensity and free chlorine dosage but decreased with increased pH. The presence of Cu2+ promoted the formation of Cl-HNMs. The total concentration of HNMs (at 3 min) with adding 1.5 mg/L Cu2+ was 30.90% higher than that without Cu2+. Notably, nine species of HNMs were detected after adding Br-, and the total concentrations of HNMs were enhanced. Moreover, Cl-HNMs were gradually transformed into brominated (chlorinated)-HNMs and brominated-HNMs as Br- concentration increased. According to the findings, the possible formation mechanism of HNMs from Gly during LED-UV265/chlorine disinfection was deduced. Finally, it was demonstrated that the formation laws of HNMs from Gly in real water samples were basically consistent with those in simulated water. Insights obtained in this study help to comprehend the HNMs formation from Gly and provide strategies for controlling the production of HNMs during LED-UV265/chlorine disinfection.

Chloramination of Nitromethane: Incomplete Chlorination and Unexpected Substitution Reaction.

Ozone is commonly used as a predisinfectant in potable water reuse treatment trains. Nitromethane was recently found as a ubiquitous ozone byproduct in wastewater, and the key intermediate toward chloropicrin during subsequent secondary disinfection of ozonated wastewater effluent with chlorine. However, many utilities have switched from free chlorine to chloramines as a secondary disinfectant. The reaction mechanism and kinetics of nitromethane transformation by chloramines, unlike those for free chlorine, are unknown. In this work, the kinetics, mechanism, and products of nitromethane chloramination were studied. The expected principal product was chloropicrin, because chloramines are commonly assumed to react similarly to, although more slowly than, free chlorine. Different molar yields of chloropicrin were observed under acidic, neutral, and basic conditions, and surprisingly, transformation products other than chloropicrin were found. Monochloronitromethane and dichloronitromethane were detected at basic pH, and the mass balance was initially poor at neutral pH. Much of the missing mass was later attributed to nitrate formation, from a newly identified pathway involving monochloramine reacting as a nucleophile rather than a halogenating agent, through a presumed SN2 mechanism. The study indicates that nitromethane chloramination, unlike chlorination, is likely to produce a range of products, whose speciation is a function of pH and reaction time.

Analysis of degradation kinetic modeling and mechanism of chlorinated-halonitromethanes under UV/monochloramine treatment.

Chlorinated-halonitromethanes (Cl-HNMs) including chloronitromethane (CNM), dichloronitromethane (DCNM), and trichloronitromethane (TCNM) are nitrogenous disinfection by-products, which have high cytotoxicity and genotoxicity to human. This study aimed to investigate the degradation kinetic modeling and mechanism of Cl-HNMs under monochloramine activated by ultraviolet of 254 nm (UV/NH2Cl) treatment. The first-principle kinetic model of UV/NH2Cl process was developed to simulate Cl-HNMs degradation. Of note, the second-order rate constants of Cl-HNMs reacting with HO• (∼108 M-1 s-1), Cl• (kCl•,CNM or DCNM = âˆ¼1010 M-1 s-1, kCl•,TCNM = âˆ¼102 M-1 s-1), Cl2•- (kCl•,CNM or DCNM = âˆ¼109 M-1 s-1, kCl•,TCNM = âˆ¼101 M-1 s-1), ClO• (∼105-106 M-1 s-1) and CO3•- (∼106-107 M-1 s-1) were obtained by the first-principle kinetic model. Overall, Cl-HNMs degradation under UV/NH2Cl treatment was successfully predicted by the kinetic model under various conditions. It was found that UV (>60%) was dominant in Cl-HNMs degradation, followed by HO• (3.8%-24.5%), reactive chlorine species (RCS, 0.9%-28.8%) and CO3•- (0-26.1%). Among the contributions of RCS, Cl• and Cl2•- were main radicals in the degradation of CNM and DCNM, while ClO• was responsible for the abatement of TCNM. The minimum EE/O values under UV/NH2Cl treatment were approximately 30% lower than those under UV treatment. Finally, the possible degradation pathways were proposed, including hemolytic/heterolytic cleavage of Cl-HNMs by UV irradiation, hydrogen abstraction/electron transfer of CNM and DCNM and adduct reaction of TCNM by free radicals. This study based on the kinetic model is beneficial to predict and control the concentrations of Cl-HNMs under UV/NH2Cl treatment.

Effects of bromide ion on the formation and toxicity alteration of halonitromethanes from nitrate containing humic acid water during UV/chlor(am)ine disinfection.

UV/chlor(am)ine are efficient for achieving multiple-barrier disinfection and maintaining residuals, while bromide (Br-) has notable impacts on the formation and toxicity of halonitromethanes (HNMs) during UV/chlor(am)ine disinfection. This study investigated the effects of Br- on HNMs formation and toxicity alteration during UV/chlor(am)ine disinfection of nitrate containing humic acid (HA) water. Results reveal that the maximum concentration of HNMs during UV/chlorine disinfection was 12.03 µg L-1 with 0.2 mg L-1 Br-, which was 22.5% higher than that without Br-, and the predominant species of HNMs were converted from trichloronitromethane (TCNM) to dibromonitromethane (DBNM) and tribromonitromethane (TBNM). However, the maximum concentration of HNMs during UV/chloramine disinfection was 3.69 µg L-1 with 0.2 mg L-1 Br-, which was increased by 26.0% than that without Br-, and the predominant species of HNMs were converted from dichloronitromethane (DCNM) to bromochloronitromethane (BCNM) and DBNM. Notably, the HNMs species and yields during UV/chloramine disinfection were less than those during UV/chlorine disinfection, primarily due to the higher concentrations of HO· and reactive chlorine/bromine species in UV/chlorine. Also, in the ranges of the Br-:Cl2 molar ratio from 0 to 0.32 and pH from 6.0 to 8.0, the Br-:Cl2 molar ratio of 0.16 and acidic pH contributed to the HNMs formation during UV/chlorine disinfection, and a high Br-:Cl2 molar ratio and neutral pH contributed to the HNMs formation during UV/chloramine disinfection. Note that the incorporation of Br- significantly improved the calculated cytotoxicity (CTI) and genotoxicity (GTI) of HNMs formed, and the calculated CTI and GTI of HNMs formed during UV/chloramine disinfection were 28.19 and 48.90% of those during UV/chlorine disinfection. Based on the diversity of nitrogen sources, the possible formation pathways of HNMs from nitrate containing HA water were proposed during UV/chlor(am)ine disinfection in the presence of Br-. Results of this study indicated that UV/chloramine can reduce the formation and toxicity of HNMs efficiently.

Structural and functional alterations of intestinal flora in mice induced by halonitromethanes exposure.

Halonitromethanes (HNMs) as one typical class of nitrogenous disinfection byproducts (DBPs) have been widely found in drinking water and are receiving more and more attentions because of their high cytotoxicity, genotoxicity, and developmental toxicity. However, the effects of HNMs exposure on the intestinal tract and intestinal flora remain unknown. This study comprehensively determined the effects of trichloronitromethane, bromonitromethane, and bromochloronitromethane exposure on the intestinal tract and intestinal flora. Results showed that the three HNMs induced intestinal oxidative stress and inflammatory response. Further, HNMs exposure could change the diversities and community structure of intestinal flora, thereby triggering intestinal flora dysbiosis, which might be associated with the intestinal damage such as oxidative stress and inflammation. The intestinal flora dysbiosis was accompanied with mark alterations in function of intestinal flora, such as carbohydrate, lipid, and amino acid metabolisms. This research provides a new insight into studying the toxicity of HNMs exposure based on intestinal flora, which will further improve the health risk assessment of DBPs in drinking water.

Formation and transformation of halonitromethanes from dimethylamine in the presence of bromide during the UV/chlorine disinfection.

Halonitromethanes (HNMs) is a typical class of nitrogenous disinfection byproducts with high toxicity. The effect of Br- on the formation and transformation of HNMs from dimethylamine (DMA) during the ultraviolet (UV)/chlorine disinfection has been investigated in current study. Results reveal that only chloronitromethane, dichloronitromethane and trichloronitromethane (TCNM) could be found during the UV/chlorine disinfection. Whereas in the presence of Br-, nine species of HNMs could be observed simultaneously. When Br- concentration increased from 0 to 15.0 mg L-1, the predominant species of HNMs were gradually changed from TCNM to dibromonitromethane and tribromonitromethane, which contributed to 23.37% and 31.07% of total HNMs concentration at 15 mg L-1 Br-, respectively. The presence of Br- not only shifted the chlorinated-HNMs (Cl-HNMs) towards brominated-HNMs (Br-HNMs) but also affected the dominant species and total concentration of HNMs. When Br- concentration was 4.0 mg L-1, the formation of HNMs decreased with the increase of pH from 6.0 to 8.0 and increased with the increase of free chlorine and DMA. When free chlorine concentration rose from 0.25 to 1.1 mmol L-1, Br-HNMs were shifted to Br(Cl)-HNMs and then to Cl-HNMs. According to the findings, possible formation and transformation pathways of HNMs from DMA were proposed in the presence of Br- during the UV/chlorine disinfection. Finally, it was proved that the effect of Br- on the trend of HNMs in real water was similar to that in deionized water, but higher HNMs concentrations and delayed peak time were observed in real water. This study can provide the scientific evidence and fundamental data for the applications of UV/chlorine disinfection in the treatment of water containing Br-.

[Determination of 25 disinfection by-products in drinking water using liquid-liquid extraction and gas chromatography].

OBJECTIVE: To establish a liquid-liquid extraction and gas chromatography method for the determination of 7 kinds of haloacetaldehydes, 7 kinds of haloacetonitriles, 7 kinds of halonitromethanes and 4 kinds of haloacetamides in drinking water. METHODS: A liquid-liquid extraction gas chromatography technique was employed. Experimental parameters, such as capillary column type, inlet temperature, concentration of salting out reagent and sample pH were optimized to develop an analytical method, and then method validation was conducted. RESULTS: HP-5 MS UI column(30 m×0.25 mm, 0.25 µm), inlet temperature at 180 ℃, addition of 8 g sodium chloride in 50 mL water sample and pH 4-5 were chosen as the final parameters. Good correlation coefficients were obtained in the linear range of 0.20-15 µg/L, with r greater than 0.999.Methods detection limits were between 0.008-0.088 µg/L. When spiked concentration was 1.0 µg/L for pure water and tap water, the recoveries were 81%-106% and 75%-117%, respectively, and relative standard deviations were both less than 4%. When spiked concentration was 12 µg/L for pure water and tap water, the recoveries were 92%-101% and 86%-106%, respectively, and relative standard deviations were less than 4% and 2%, respectively. CONCLUSION: This method is simple, sensitive, and effective. It is suitable for simultaneous determination of 25 disinfection byproducts in drinking water.

Formation and influence factors of halonitromethanes in chlorination of nitro-aromatic compounds.

Halonitromethanes (HNMs), typical nitrogenous disinfection byproducts generated during disinfection of chlorination and chloramination, are widely detected in drinking water. This study investigated the formation of two dominant HNMs, trichloronitromethane (TCNM) and dichloronitromethane (DCNM) during chlorination/chloramination of ten nitro-aromatic compounds (NACs), including six aromatic mono-nitro compounds, three aromatic di-nitro compounds and one aromatic tri-nitro compound. The results showed that 2-nitrophenol and 3-nitrophenol could be the main precursors of TCNM and DCNM, and the yields of TCNM were one order of magnitude higher than that of DCNM. HNMs formation in chlorination was much higher than that in chloramination. However, HNMs were hardly produced during chlorination and chloramination of the other eight NACs. In chlorination of 2-nitrophenol, a pH range of 5.0-7.0 facilitated the TCNM formation. Besides, the concentration of ferric and manganese ions had different influences on TCNM formation. While the concentration ranges were 0-2 mg/L, ferric ion significantly decreased TCNM formation but manganese ion had not any influence on TCNM formation. Contrary to a previous finding, nitrite significantly reduced TCNM formation, which implied that nitrite has different effects on TCNM formation from various precursors. Moreover, dissolved organic matter (DOM, 0-5 mg/L as C) significantly influenced the formation of TCNM in chlorination of 2-nitrophenol despite the low TCNM formation in chlorination of DOM. Several chlorinated intermediates were detected and identified as mono/di/tri-chloro-2-nitrophenol during chlorination of 2-nitrophenol. It is effectively to reduce the production of TCNM and DCNM formation from chlorination of 2-nitrophenol by controlling disinfection conditions in drinking water.

Kinetics of the formation and degradation of carbonaceous and nitrogenous disinfection by-products in Bangkok and Songkhla source waters.

The kinetics of the formation and degradation of disinfection by-products (DBPs) in the treated water from the Bangkhen and Hatyai water treatment plants in Thailand were investigated. The DBPs studied included trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), and trichloronitromethane (TCNM). When the chlorination time was increased, the levels of TCM, BDCM, DBCM, and TCNM increased, while the levels of TCAN, DCAN, and BCAN decreased. The kinetic rates of DBPs' formation were assessed based on the formation and degradation rates, which were best described by first-order kinetics. TCM had the highest formation rate with a range of rate constants from 5.5 × 10-3 to 7.3 × 10-3 h-1. TCAN had the lowest degradation rate with a range of rate constants from 0.6 × 10-3 to 2.9 × 10-3 h-1. Good correlations were observed between chlorination time and DBPs' formation normalized by LC50, lowest cytotoxicity, and lowest genotoxicity. A high formation rate of TCM and a low degradation rate of TCAN normalized by their toxicity were observed. The optimal retention time providing low DBPs' formation together with high DBPs' degradation was determined. The retention time of three days decreased the sum of the DBPs/LC50, DBPs/lowest cytotoxicity, and DBPs/lowest genotoxicity from a retention time of one day by 40-60%, 45-65%, and 25-36%, respectively.

Simultaneous analysis of haloacetonitriles, haloacetamides and halonitromethanes in chlorinated waters by gas chromatography-mass spectrometry.

Nitrogenous classes of disinfection by-products (DBPs), such as haloacetamides (HAAms), haloacetonitriles (HANs) and halonitromethanes (HNMs), while generally present at lower concentrations in disinfected waters than carbonaceous DBPs, such as trihalomethanes or haloacetic acids, have been shown to be more detrimental to human health. While several methods have been shown to be suitable for the analysis of some nitrogenous DBPs (N-DBPs) in disinfected waters, many are unable to quantify HAAms, the most detrimental to health of these three N-DBP classes. Here, we report the first method for the simultaneous analysis of twenty-five N-DBPs (nine HANs, nine HNMs and seven HAAms) in disinfected waters using liquid-liquid extraction followed by gas chromatography-mass spectrometry. The use of a programmable temperature vaporiser injector minimises degradation of the thermally labile HNMs, while avoiding the concomitant decreases in HANs and HAAms which occur when using lower injector temperatures. Extraction parameters, including sample pH, solvent volume, salt addition and sample pre-concentration, were investigated to determine the optimal conditions across all target N-DBPs. Good detection limits were achieved for all analytes (0.8-1.7 µg L-1) and both laboratory and instrumental runtimes were significantly reduced compared to previous methods. The method was validated for the analysis of N-DBPs in drinking, swimming pool and spa waters, and concentrations of up to 41 µg L-1 of some N-DBPs were measured in some pools.

Rapid and complete dehalogenation of halonitromethanes in simulated gastrointestinal tract and its influence on toxicity.

Halonitromethanes (HNMs) as one typical class of nitrogenous disinfection byproducts in drinking water and wastewater are receiving attentions due to their high toxicity. This study applied a simulator of the human gastrointestinal tract to determine the dehalogenation processes of trichloronitromethane, bromonitromethane and bromochloronitromethane for the first time. Influence of digestion process of HNMs on gut microbiota and hepatotoxicity was further analyzed. Results showed that the three HNMs were rapidly and completely dehalogenated in the gastrointestinal tract, especially in the stomach (2 h retention Time) and small intestine (4 h retention Time). Mucin, cysteine, pancreatin and bile salts in the digestive juice played major roles in the dehalogenation process. HNMs and their dehalogenation products in the resulting fluids of stomach induced the highest toxicity followed by those in intestine and colon, exhibiting dose-dependent effects. Although most HNMs were degraded in the stomach and small intestine, residual HNMs entered into colon changed the microbial community. Abundance of several genera, such as Bacteroides, Lachnospiraceae_unassigned and Lactobacillus had high correlation with exposure concentration of HNMs. This study sheds new light on dehalogenation and toxic processes of HNMs by oral exposure, which provides basic data for their human health risk assessment.

Formation and control of nitrogenous DBPs from Western Australian source waters: Investigating the impacts of high nitrogen and bromide concentrations.

We studied the formation of four nitrogenous DBPs (N-DBPs) classes (haloacetonitriles, halonitromethanes, haloacetamides, and N-nitrosamines), as well as trihalomethanes and total organic halogen (TOX), after chlorination or chloramination of source waters. We also evaluated the relative and additive toxicity of N-DBPs and water treatment options for minimisation of N-DBPs. The formation of halonitromethanes, haloacetamides, and N-nitrosamines was higher after chloramination and positively correlated with dissolved organic nitrogen or total nitrogen. N-DBPs were major contributors to the toxicity of both chlorinated and chloraminated waters. The strong correlation between bromide concentration and the overall calculated DBP additive toxicity for both chlorinated and chloraminated source waters demonstrated that formation of brominated haloacetonitriles was the main contributor to toxicity. Ozone-biological activated carbon treatment was not effective in removing N-DBP precursors. The occurrence and formation of N-DBPs should be investigated on a case-by-case basis, especially where advanced water treatment processes are being considered to minimise their formation in drinking waters, and where chloramination is used for final disinfection.

In vitro studies on the tumorigenic potential of the halonitromethanes trichloronitromethane and bromonitromethane.

Epidemiological data indicate that chronic exposure to water disinfection by-products (DBPs) may result in increased risk of cancer. However, the real carcinogenic potential of individual DBPs is not well known. In this study, we assessed the in vitro carcinogenic potential of trichloronitromethane (TCNM) and bromonitromethane (BNM), two halonitromethanes (HNMs) commonly found in DBPs' mixtures at comparably high concentrations. Human lung BEAS-2B cells were exposed for 8weeks to TCNM and BNM, and the acquisition of different in vitro cancer-like features was evaluated. The results indicate that long-term exposure to non-cytotoxic doses of TCNM and BNM did not cause carcinogenic transformation as indicated by the absence of morphological changes, no effects on cell growth, no changes in the level of matrix metalloproteinases (MMPs) secretion, and no increased anchorage-independent cell growth capacity. Furthermore, TCNM- and BNM-exposed BEAS-2B cells were unable to enhance tumour growth directly or by indirect influence of the surrounding stroma. Our results indicate that the carcinogenic effects of DBP mixtures cannot be attributed to the evaluated HNMs. This is the first study evaluating the cell transformation effects of TCNM and BNM under a long-term exposure scenario using suitable hallmarks of the cancer process.

Comparative toxicity of chloro- and bromo-nitromethanes in mice based on a metabolomic method.

Halonitromethanes (HNMs) as one typical class of nitrogenous disinfection byproducts have been widely found in drinking water. In vitro test found HNMs could induce higher cytotoxicity and genotoxicity than trihalomethanes and haloacetic acids. However, data on toxic effect from in vivo experiment is limited. In this study, bromonitromethane (BNM), bromochloronitromethane (BCNM) and trichloronitromethane (TCNM) were chosen as target HNMs, and exposed to mice for 30 d. Hepatic toxicity and serum metabolic profiles were determined to reveal toxic effects and mechanisms of the three HNMs. Results showed the three HNMs significantly decreased relative liver weight, indicating liver is one of the target organs. Further, the three HNMs exposure damaged hepatic antioxidant defense system, and increased oxidative DNA damage. Nuclear magnetic resonance based metabolomics analysis found amino acid metabolism and carbohydrate metabolism were disturbed by HNMs exposure. Some metabolites in these metabolisms are related to oxidative stress and damage. Combined with above results, BNM had the highest toxicity, followed by BCNM and TCNM, indicating bromo-HNMs had higher toxicity than chloro-HNMs. Induction of oxidative stress is one of the toxicity mechanisms of HNMs. This study firstly provides the insight into in vivo toxicity of HNMs and their underlying mechanisms based on metabolomics methods, which is very useful for their health risk assessment in drinking water.

Degradation of chloramphenicol by UV/chlorine treatment: Kinetics, mechanism and enhanced formation of halonitromethanes.

Ultraviolet (UV)/chlorine process is considered as an emerging advanced oxidation process for the degradation of micropollutants. This study investigated the degradation of chloramphenicol (CAP) and formation of disinfection by-products (DBPs) during the UV/chlorine treatment. It was found that CAP degradation was enhanced by combined UV/chlorine treatment compared to that of UV and chlorination treatment alone. The pseudo-first-order rate constant of the UV/chlorine process at pH 7.0 reached 0.016 s-1, which was 10.0 and 2.0 folds that observed from UV and chlorination alone, respectively. The enhancement can be attributed to the formation of diverse radicals (HO and reactive chlorine species (RCSs)), and the contribution of RCSs maintained more stable than that of HO at pH 5.5-8.5. Meanwhile, enhanced DBPs formation during the UV/chlorine treatment was observed. Both the simultaneous formation and 24-h halonitromethanes formation potential (HNMsFP) were positively correlated with the UV/chlorine treatment time. Although the simultaneous trichloronitromethane (TCNM) formation decreased with the prolonged UV irradiation, TCNM dominated the formation of HNMs after 24 h (>97.0%). According to structural analysis of transformation by-products, both the accelerated CAP degradation and enhanced HNMs formation steps were proposed. Overall, the formation of diverse radicals during the UV/chlorine treatment accelerated the degradation of CAP, while also enhanced the formation of DBPs simultaneously, indicating the need for DBPs evaluation before the application of combined UV/chlorine process.

Degradation of nitro-based pharmaceuticals by UV photolysis: Kinetics and simultaneous reduction on halonitromethanes formation potential.

This study investigated the degradation kinetics and halonitromethanes formation potential (HNMsFP) of two nitro-based pharmaceuticals (i.e., ranitidine (RNTD) and nizatidine (NZTD)) during ultraviolet (UV) photolysis. It was found that the degradation kinetics of RNTD and NZTD exhibited pH-dependent trends, in accordance with their deprotonation equilibria. The neutral species of RNTD and NZTD were more photo-reactive than their corresponding deprotonated species, with their specific fluence-based first-order rate constants varying in the range of 5.64-31.90 m2 E-1. Both the RNTD and NZTD were prone precursors of HNMs (with molar yields of 5.6± 0.3% and 4.7± 0.4%, respectively at pH 7.0). Acidic and neutral circumstances facilitated the HNMs formation. The UV photolysis of RNTD and NZTD could reduce their HNMsFP simultaneously. Positive linear relationships between residual RNTD or NZTD concentration and HNMsFP were observed and the denitration during the UV photolysis accounted for the HNMsFP reduction. With the mandatory UV disinfection fluences in China (i.e. 20-80 mJ cm-2), the effective abatement of RNTD and NZTD and their HNMsFP could not be fully achieved, highlighting the necessity of increasing UV fluence or developing UV-based advanced oxidation process in future.

Monitoring trihalomethanes and nitrogenous disinfection by-products in blending desalinated waters using solid-phase microextraction and gas chromatography.

A simple and efficient method has been developed for the extraction and determination of 16 common volatile halogenated disinfection by-products (DBPs) (four trihalomethanes, six haloacetonitriles, and six halonitromethanes) in blending desalinated waters, using headspace solid-phase microextraction and gas chromatography with flame ionization detector (HS-SPME/GC-FID). After the optimization using factorial designs of the HS-SPME parameters (optimum: carboxen/polydimethylsiloxane such as fiber, extraction time of 60 min at 30°C, pH 7, addition of 40% (w/v) of sodium chloride, and desorption time of 2 min at 250°C), quantification limits ranged from 3.03 to 40.8 µg L-1, and relative standard deviation (inter-day) were lower than 9.7% for all the target DBPs. Adequate relative recoveries (with the exception of chloronitromethane) were obtained even when spiking waters at low levels (25 µg L-1), with values between 83.1% and 119% for ultrapure water, and between 87.4% and 115% for blending desalinated waters, supporting in this way the applicability of the method. The influence of various dechlorinating agents on the stability of 16 DBPs in water was evaluated, with ammonium chloride being the most suitable inhibitor of residual chlorine and carrying out the analytical determination of DBPs within 48 h after sampling. Different blending desalinated water samples collected in the South of Tenerife Island (Spain) were successfully analyzed.