Nitrogenous Disinfection By-products Research Articles

The Adverse Outcome Pathway (AOP) concept as a basis for the development of mechanism-based animal sparing approaches: Kidney toxicity due to lysosomal overload and inhibition of mtDNA polymerase-γ as case studies

Humans are exposed to disinfection by-products (DBPs) mainly through drinking water ingestion and dermal contact. As an emerging class of nitrogenous DBPs (N-DBPs), haloacetamides (HAcAms) have been found to have significantly higher cytotoxicity than regulated DBPs. In this study, we investigated the cytotoxicity of HAcAms on two exposure pathway-related cell lines: human gastric epithelial GES-1 cells and immortalized keratinocytes HaCaT. Our results showed that the ranking order of cytotoxicity of 13 HAcAms was different between HaCaT and GES-1 cells. In addition, the 50% inhibitive concentration in HaCaT was 1.01–3.29 times that in GES-1. Further comparison among GES-1, HaCaT and CHO cell lines confirmed that different cell lines exhibited different sensitivity to the same compound. Importantly, HAcAms showed 5.83–7.13 × 104 times higher toxicity than the well-clarified DBP chloroform, clearly demonstrating the increased toxicity of HAcAms. Finally, using a novel high-content screening (HCS) analysis, we found that 39.29% of chlorinated HAcAms, 42.86% of brominated HAcAms and 16.07% of iodinated HAcAms significantly affected at least one of the cell-health parameters, such as nuclear size, membrane permeability, mitochondrial membrane potential, or cytochrome c release, in GES-1 or HaCaT cells. Thus, brominated HAcAms appear to have stronger effects under the sublethal exposure dose, possibly causing cytotoxicity via apoptosis. Together, our study provides new insights to the toxicity of HAcAms and a comprehensive toxicology dataset for health risk assessment.

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.

Single and combined effects of selected haloacetonitriles in a human-derived hepatoma line

Haloacetonitriles (HANs) are nitrogenous disinfection byproducts (N-DBPs) detected in drinking water that have high toxicity and are a high risk to human health. The cytotoxicity and genotoxicity as well as the oxidative stress of five HANs, namely chloroacetonitrile (CAN), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), bromoacetonitrile (BAN), and dibromoacetonitrile (DBAN) on a hepatoma cell line (HepG2) were determined by single, binary or ternary exposure. The median effective concentrations, based on cell viability, ranged from 0.8360 mg/L for BAN to 256.9 mg/L for DCAN, with a cytotoxicity order of BAN > DBAN > CAN > TCAN > DCAN. The lowest observed effective concentrations regarding DNA damage were 0.01 mg/L for CAN and DCAN, 0.1 mg/L for DBAN and TCAN, and 1 mg/L for BAN. The DNA damage induced by CAN, DCAN and TCAN was repaired to about 80% in 30 min, and when induced by BAN and DBAN, it was repaired completely in 60 min. The intracellular reactive oxygen species (ROS) levels were significantly increased by the five HANs, and bromo-acetonitrile produced a stronger oxidative stress than chloro-acetonitrile. Co-exposure of DCAN, TCAN and DBAN significantly inhibited cell viability, induced DNA damage and facilitated ROS generation in HepG2 cells. However, the interactive effects were inconsistent for the different endpoints, which seemed to be antagonism for cell viability but synergy for ROS generation.

The stability of chlorinated, brominated, and iodinated haloacetamides in drinking water

Haloacetamides (HAMs), a group of nitrogenous disinfection byproducts (N-DBPs), can decompose to form corresponding intermediate products and other DBPs. The stability of ten different HAMs, including two chlorinated, five brominated, and three iodinated species was investigated with and without the presence of chlorine, chloramines, and reactive solutes such as quenching agents. The HAM basic hydrolysis and chlorination kinetics were well described by a second-order kinetics model, including first-order in HAM and hydroxide and first-order in HAM and hypochlorite, respectively, whereas the HAM neutral hydrolysis kinetic was first-order in HAM. Furthermore, HAMs decompose instantaneously when exposed to hypochlorite, which was almost two and nine orders of magnitude faster than HAM basic and neutral hydrolysis, respectively. In general, HAM hydrolysis and chlorination rates both increased with increasing pH and the number of halogens substituted on the methyl group. Moreover, chlorinated HAMs are more unstable than their brominated analogs, followed by the iodinated ones, due to the decrease in the electron-withdrawing inductive effect from chlorine to iodine atom. During hydrolysis, HAMs mainly directly decompose into the corresponding haloacetic acids (HAAs) via a nucleophilic reaction between the carbonyl carbon and hydroxide. For HAM chlorination reactions, hypochlorite reacts with HAMs to form the N-chloro-HAMs (N-Cl-HAMs) via Cl+ transfer from chlorine to the amide nitrogen. N-Cl-HAMs can further degrade to form HAAs via hypochlorous acid addition. In contrast, the reactions between chloramines and HAMs were found to be insignificant. Additionally, four common quenching agents, including sodium sulfite, sodium thiosulfate, ascorbic acid, and ammonium chloride, were demonstrated to expedite HAM degradation, whereas ammonium chloride was the least influential among the four. Taft linear free energy relationships were established for both HAM hydrolysis and chlorination reactions, based on which the hydrolysis and chlorination rate constants for three monohaloacetamides were estimated. The hydrolysis and chlorination rates of 13 HAMs decreased in the following order: TCAM > BDCAM > DBCAM > TBAM > DCAM > BCAM > DBAM > CIAM > BIAM > DIAM > MCAM > MBAM > MIAM (where C = chloro, B = bromo, I = iodo, T = tri, D = di, M = mono). Lastly, using the HAM kinetic model established in this study, HAM half-lifes in drinking water distribution systems can be predicted on the basis of pH and residual chlorine concentration.

Removal of precursors of typical nitrogenous disinfection byproducts in ozonation integrated with biological activated carbon (O3/BAC)

The O3/BAC process has been widely used in drinking water treatment to improve the removal of dissolved organic matters (DOMs), including the precursors of nitrogenous disinfection byproducts (N-DBPs). In this study, the removal of N-DBP precursors by biological activated carbon (BAC) filters with different usage time of granular activated carbon (GAC) was investigated. Results showed that the BAC filter with 6 years of usage time of GAC (old BAC filter) had a poor performance in the removal of precursors of N-DBPs such as dichloroacetonitrile (DCAN; an average of only 4.7%), dichloroacetamide (DCAcAm), and trichloronitromethane (TCNM) when compared with the BAC filter with 1 year of usage time of GAC (new BAC filter). Particularly, the organic fraction >10 kDa and the percentage of autochthonous substances were increased in the effluent of the old BAC filter. The red shift of the fluorescence peaks was evident in the excitation–emission matrix spectrum of the effluent from the old BAC filter. The abiotic adsorption of precursors by the old BAC filter was less. In addition, less amino acids and polysaccharides were removed, but more amino sugars and proteins were produced because of microbial metabolism. The metabolism strength of the attached biofilm decreased with increased operation time of the BAC filter. The relative abundance of Sphingomonas significantly decreased in the biofilm of the old BAC filter. The diversity of microbial community in the old BAC filter was higher, but the equitability was lower than those of the new BAC filter. The less removal of N-DBP precursors by the old BAC filter was attributed to the changes in abiotic adsorption capacity and microbial metabolism properties, in which soluble microbial products played an important role.

Reductive dechlorination of haloacetamides in drinking water by Cu/Fe bimetal

Abstract Haloacetamides (HAcAms), a class of highly toxic nitrogenous disinfection by-products (N-DBPs), have been widely detected in drinking water. The control of DBPs is an important measure to ensure the safety of drinking water. Due to the presence of residual chlorine and organic compounds that failed to be effectively removed, HAcAms could be formed in the finished drinking water distribution systems. In the study, Cu/Fe bimetal with different molar ratios of Cu to Fe was synthesized. This study reported that Cu/Fe bimetal reduced trichloroacetamide (TCAcAm) to dichloroacetamide (DCAcAm) and monoacetamide (MCAcAm), and the reduction ability of Fe was greatly improved due to the incorporation of Cu. The optimal HAcAm removal was achieved when the molar ratio of Cu to Fe was 2.0%, Cu/Fe bimetal could reach complete degradation of TCAcAm within 1 h. With the increase of Cu/Fe bimetal dose or the decrease of solution pH, the reduction ability of Cu/Fe bimetal for HAcAm removal also increased. The calculated integrated toxicity values from HAcAms, which was used to reflect the comprehensive control effect of Cu/Fe bimetal for HAcAms, were also reduced with the decrease of solution pH and the increase of bimetal dose. The release of Cu2+ was not detected during the whole treatment process, Cu/Fe bimetal may be an excellent material for controlling DBPs as the end – control methods in tap water.

Oxidation of theophylline by Ferrate (VI) and formation of disinfection byproducts during subsequent chlorination

Abstract This work investigated the degradation of theophylline (TPL) of environmental concerns by ferrate (Fe(VI)) and the effect of Fe(VI) pre-oxidation on formation of disinfection by-products (DBPs) from TPL during subsequent chlorination. TPL exhibited an appreciable reactivity toward Fe(VI) with apparent second-order rate constants (kapp) ranging from 5.7 to 2480 M−1 s−1 in the pH range from 6 to10. The pH-dependence of kapp could be well simulated by a proposed kinetic model including the generation of an intermediate between Fe(VI) and TPL. A tentative transformation pathway was proposed including the hydroxylation of the imidazole ring as well as the cleavage of C N and C N bonds. The presence of humic acid (HA) apparently reduced the degradation rates of TPL with Fe(VI) even considering the competitive consumption for Fe(VI) by HA. A two channel model successfully explained the effect of HA on the TPL degradation by Fe(VI), where oxidation intermediate of TPL was either reduced back to parent by HA or irreversibly transformed to final products. Compared to direct chlorination of TPL, Fe(VI) pre-oxidation at low dosage enhanced the formation of carbonaceous disinfection by-products (C-DBPs, e.g., 1,1-dichloro-2-propanone, 1,1,1-trichloro-2-propanone, and dichloroacetic acid) during subsequent chlorination. However, a high dosage of Fe(VI) pre-oxidation could decrease the formation of C-DBPs and nitrogenous disinfection by-products (N-DBPs, e.g., dichloroacetonitrile, trichloronitromethane). The effectiveness of Fe(VI) for elimination of TPL in natural water was confirmed, and Fe(VI) pre-oxidation at high doses reduced the formation of DBPs in natural water during subsequent chlorination.

Water Quality in the Henan Intake Area of the South-to-North Water Diversion Project

The molecular weights, as well as the hydrophobicity composition of natural organic matter (NOM) in raw water, were investigated in the Henan intake area of the South-to-North Water Diversion Project. This study also discusses the formation of carbonaceous disinfection by-products and nitrogenous disinfection by-products during chlorination and chloramination of raw water in this area. Most of the NOM in raw water were small molecules and hydrophobic fractions. The molecular weight fractions of <1×103 were the most abundant, accounting for 57% of the NOM. The hydrophobic fractions were the most abundant and accounted for 50% of the NOM. Two kinds of C-DBPs (CF and DCBM) and two kinds of N-DBPs (DCAN and TCNM) were mainly produced after chlorination and chloramination, and the formation potential of CF was about 120 μg·L-1 after chlorination. Results of chloramination showed that the productions of CF and DCBM by this process were about 90% and 84.9% lower than that by chlorination. However, the amount of N-DBPs increased, and among them the amount of DCAN increased by about 2.3 times, but the overall N-DBPs formation potential was still low and less than 6 μg·L-1. The results of this study can provide theoretical and technical support for the process selection and optimization of the waterworks in the Henan intake area of the South-to-North Water Diversion Project.

Activation of permanganate with hydrogen sulfite for enhanced oxidation of a typical amino acid

ABSTRACTDissolved organic nitrogen (DON) has drawn more attention from research into drinking water treatment because of its potential to form nitrogenous disinfection byproducts. Amino acids are important DON constituents that are difficult to remove by conventional water treatment. The permanganate/hydrogen sulfite (PM/BS) system, a novel oxidation process, is used to remove a typical amino acid, glutamate. The factors that affect removal mechanism and the degradation pathways were studied. The results show that the rates of DON and glutamate removal in the PM/BS system within 10 min were 55% and 90%, respectively. The optimum pH for glutamate degradation was 5, and the optimal dosages of KMnO4 and NaHSO3 were 1 mM and 5 mM, respectively. Activation of by resulted in the oxidation of glutamate at very high rates. As shown by electronic spin resonance (ESR) experiments, Mn (III), , and •OH were involved in the degradation process. The oxidation products suggest that most of the glutamate undergoes oxidation to ammonia nitrogen within 10 min, eventually forming N2 in the process. No evidence shows that and formed during the entire process. High-performance liquid chromatography–mass spectrometry results reveal that glutamate degradation consists of two separate pathways involving Mn(III), , and •OH, both of which convert –NH2 into or directly to N2. It can be indicated that nitrogenous disinfection by-products (N-DBPs) formation decreased in the degradation process, as shown by gas chromatograph detection.

Removal of haloacetamides and their precursors at water purification plants applying ozone/biological activated carbon treatment

Haloacetamides (HAcAms) are nitrogenous disinfection byproducts in drinking water. The profiles of six HAcAms and their formation potentials (FPs) upon chlorination at water purification plant 1 (WPP-1) in September 2016 and at WPP-2 in September 2016 and January 2017 were investigated. HAcAms were removed effectively when they were formed via intermediate chlorination during water purification processes. Removal of total HAcAm-FPs ranged from 50% to 75%. Coagulation/flocculation/sand filtration showed the highest removal of total HAcAm-FPs. As for individual HAcAms, while chlorinated acetamide-FPs were removed, brominated acetamide-FPs, particularly 2,2-dibromoacetamide, remained. The bromine incorporation factors increased during all water purification processes except ozonation and the ozone/hydrogen peroxide process for diHAcAms (2,2-dichloroacetamide, 2-bromo-2-chloroacetamide, and 2,2-dibromoacetamide). The trends in relationships between DOM indices (fractions of dissolved organic matter, ultraviolet absorbance at 260 nm, and fluorescence intensities representing humic-like and tryptophan-like compounds) and total HAcAm-FPs during ozonation and ozone/hydrogen peroxide process were different from those during other processes.

Evaluation of disinfection by-products (DBPs) formation potential in ANAMMOX effluents.

Disinfection by-products (DBPs), major health concerns in the potable reuse of municipal wastewater effluent, are process-related in wastewater treatment systems. Anammox is a promising and increasingly-applied technology for nitrogen removal in wastewater. In this study, the relationship between DBP formation potential and the anammox process has been investigated based on a lab-scale sequencing batch reactor (SBR). Excitation and emission matrix (EEM) fluorescence spectroscopy was employed to identify the compositions of the DBP precursors. The results showed that the effluents from the anammox SBR could yield both carbonaceous and nitrogenous DBPs after chlorination. Trichloromethane (TCM) was the dominant product among all DBPs detected. The anammox effluent has a low specific TCM formation potential of 0.778 μmol/mmol C and a trichloronitromethane (TCNM) formation potential of 0.0725 μmol/mmol C, leading to a TCM and TCNM formation potential ratio of 10.7. We found that substrate utilization of anammox did not enhance DBP yields, and the DBP formation potential decreased after 10 hour starvation. High pH conditions stimulated the production of TCM precursors in the anammox reactor. Humic acid-like and protein-like substances were identified in the EEM spectra of anammox effluents.

Impact of ClO2 pre-oxidation on the formation of CX3R-type DBPs from tyrosine-based amino acid precursors during chlorination and chloramination

ClO2 is frequently used as a pre-oxidant in water treatment plants. However, the effects of ClO2 pre-oxidation on disinfection by-product (DBP) formation, especially the highly toxic nitrogenous DBPs, during subsequent chlor (am)ination have not been studied thoroughly. There is also limited information about DBP formation from combined amino acids (AAs), which are more abundant than free AAs in source waters. Many typical DBPs (including representative N-DBPs) have a similar structure of “CX3R” (X = H, Cl, Br or I). In the study, tyrosine and forms representing its reactivity in combined AAs (tyrosine tert-butyl ester and Boc-tyrosine) were selected as model precursors. The formation of various regulated and unregulated CX3R-type DBPs from ClO2 pre-oxidation and subsequent chlor (am)ination were studied at a wide-range of ClO2 and chlor (am)ine doses (ClO2/precursors and chlor (am)ine/precursors are at the range of 0–2.5 and 1–20 [Mol/Mol], respectively). Chloroform and chloral hydrate (CH) yields increased with chlorine dose, while haloacetonitrile and haloacetamide maximized at median chlorine dose (Cl2/Precursors = 10). All DBP yields increased with chloramine dose. ClO2 pre-oxidation increased chloroform, haloacetonitrile, trichloronitromethane and CH yields during chlorination, but ClO2 increased chloroform, CH, trichloroacetamide while decreased dichloroacetonitrile and trichloronitromethane yields during chloramination. The overall toxicity of the formed DBPs was evaluated by cytotoxicity index (CTI). ClO2 pre-oxidation increased CTI from all precursors during post-chlorination while reduced it during post-chloramination. Results imply that ClO2 is probably more suitable for use in combination with chloramination disinfection, rather than chlorination, in the integrated control of CX3R-type DBPs from source waters abundant in AAs.

Role of ammonia on haloacetonitriles and halonitromethanes formation during Ultraviolet irradiation followed by chlorination/chloramination

Combination of ultraviolet (UV) disinfection and chlorination became a common multi-barrier approach taken by water utilities against microbial pathogens in drinking water disinfection. Halogenated disinfection byproducts (DBPs) have been monitored and regulated in drinking water under various jurisdictions around the world for decades. More recently, several nitrogenous DBPs (N-DBPs), like haloacetonitriles (HANs) and halonitromethanes (HNMs), have been identified in chlorinated drinking waters, whose precursors are N-containing organic compounds of various origins and structures. Rising concerns over the N-DBPs formation due to their more potent genotoxic and cytotoxic activity than the regulated carbonaceous-DBPs have prompted extensive research on drinking water disinfection processes. To examine the effect of ammonia nitrogen (NH3-N) on N-DBPs formation during UV disinfection of drinking water followed by chlorination/chloramination, as a first attempt, synthetic waters prepared by humic acid with different NH3-N concentrations were exposed to UV dose up to 300 mJ/cm2 from either low pressure (LP) or medium pressure (MP) lamps, followed by chlorination/chloramination. To investigate trends, the study employed synthetic waters with elevated precursor concentrations and disinfectant exposures to generate significant byproduct formation possible. LP UV treatment had no obvious effect on N-DBP formation, whereas MP UV irradiation produced more dichloroacetonitrile (DCAN). The existence of ammonia (≤1 mg/L-N) increased DCAN concentration in high organics synthetic waters under varying MP UV doses, respectively. In high organics synthetic water samples exposed to a MP UV dose of 300 mJ/cm2 DCAN reached a maximum yield of 13.7 μg/L in the presence of 0.5 mg/L NH3-N, whereas lower yields were observed at NH3-N ≥ 2 mg/L, i.e. 2.9 μg /L and 1.8 μg/L at 2 and 10 mg/L NH3-N, respectively.

Impact of pre-oxidation on nitrosamine formation from a source to drinking water: A perspective on cancer risk assessment

Abstract Given the carcinogenicity of nitrosamines as nitrogenous disinfection byproducts, this study investigated the impacts of different pre-oxidation technologies on nitrosamine formation through different full-scale treatment approaches from a health risk assessment perspective. The cancer risk posed by six nitrosamines and their formation potentials (FPs) in a surface water source and three subsequent plants with comparable treatment approaches in southern Taiwan were estimated to investigate the total toxicity variations through different treatments. In the results, sufficient environmental exposure suppressed the risks by nitrosamine-FPs in the source, with appreciable risks (the median ranging from 6.4 × 10−5 to 1.0 × 10−4) present in the water near the intake. In three treatment plants, the risks decreased through the treatment processes (1%–84% reduction). Pre-chlorination suppressed the risk by nitrosamine formation during post-chlorination (dropped by 58%–86%), whereas pre-ozonation elevated the risk in the next oxidation steps. Removal of organic matter before ozonation reduces the risk increase during oxidation. Total organic carbon (TOC) (r = −0.89) or dissolved organic carbon (DOC) variations (r = −0.86) were negatively associated with the cancer risk variations in three DWTPs. The discrepancy between the risks estimated by using different toxicity data sources occurred. Effectively minimizing the formation of nitrosamines with proper source water quality, treatment approaches, and correct parameters to monitor are critical for minimizing the toxicity posed by various nitrosamines in drinking water.

Comparison of drinking water treatment processes combinations for the minimization of subsequent disinfection by-products formation during chlorination and chloramination

Micro-ozone, permanganate, ferrate, and chlorine dioxide were applied as pre-oxidants to meet conventional requirements for water quality and algal control. The formation of typical carbonaceous disinfection by-products (C-DBPs) and emerging nitrogenous disinfection by-products (N-DBPs) during both chlorination and chloramination were investigated with combinations of different processes: (i) coagulation-sedimentation-filtration (CSF), (ii) pre-KMnO4/O3/K2FeO4/ClO2 matched with CSF, and (iii) pre-KMnO4/O3/K2FeO4/ClO2 coupled with CSF and followed by granular activated carbon (GAC)/O3-GAC advanced treatment. All conventional water quality indexes met the requirements of the national standards for drinking water quality of China (GB5749-2006) when the system was under stable operation; only NH4+-N, which only met the requirement with either pre-oxidation or post-ozonation, failed to do so. Micro-ozone pre-treatment coupled with CSF and O3-GAC showed the best performance in removing chloroform (CF) and dichloracetonitrile (DCAN) precursors. Pre-oxidation had a negative impact on chloropicrin (TCNM) and chloral hydrate formation, but a positive effect on DCAN. The trade-off analysis based on the toxicity of the selected DBPs indicated that pre-oxidation (KMnO4, O3, K2FeO4, and ClO2) had a positive influence on the control of overall cytotoxicity, and O3 pre-oxidation coupled with CSF followed by O3-GAC performed the best. However, for the control of overall genotoxicity, the ClO2 pre-treatment showed best results, whether or not GAC or O3-GAC was involved. These results are important for optimizing the design of the treatment processes in drinking water treatment plants using eutrophic lake water where precursors for regulated C-DBP and unregulated N-DBP formation are prevalent.

Removal of the precursors of N-nitrosodiethylamine (NDEA), an emerging disinfection byproduct, in drinking water treatment process and its toxicity to adult zebrafish (Danio rerio)

N-nitrosodiethylamine (NDEA) is one of the emerging nitrogenous disinfection byproducts with probable cytotoxicity, genotoxicity, and carcinogenesis. Its potential toxicological effects have received extensive attention but remain to be poorly understood. In this study, changes in NDEA precursors in drinking water treatment process were studied using the trial of its formation potential (FP), and the toxicity induced by NDEA to adult zebrafish was investigated. NDEA FP in the raw water of Taihu Lake ranged from 46.9 to 68.3 ng/L. The NDEA precursors were removed effectively by O3/BAC process. Hydrophilic fraction and low-molecular-weight fraction (<1 kDa) had the highest NDEA FP. The toxicity results demonstrated that the acute lethal concentration of NDEA causing 50% mortality in 96 h (96-h LC50) was 210.4 mg/L, and NDEA was more likely to be accumulated in kidney, followed by liver and gill. NDEA induced oxidative stress and antioxidant defense to zebrafish metabolism system at concentrations over 5 μg/L. After a 42-day exposure, a significant DNA damage was observed in zebrafish liver cells at NDEA concentrations beyond 500 μg/L. This study investigated NDEA properties in both engineering prospective and toxicity evaluation, thus providing comprehensive information on its control in drinking water treatment process and its toxicity effect on zebrafish as a model animal.

Determination of several common disinfection by-products in frozen foods

ABSTRACTDisinfected water and/or disinfectants are commonly used by the freezing industry in such processes as sanitising, washing, blanching, cooling and transporting the final product. For this reason, disinfection by-products (DBPs) can be expected in frozen foods. This study focused on the presence of DBPs in a wide variety of frozen vegetables, meats and fish. For this purpose, the 14 halogenated DBPs more prevalent in disinfected water were selected (four trihalomethanes, seven haloacetic acids, two haloacetonitriles and trichloronitromethane). Up to seven DBPs were found in vegetables, whereas only four DBPs were present in meats and fish, and at lower concentrations, since their contact with disinfected water is lower than in frozen vegetables. It is important to emphasise that trichloronitromethane (the most abundant nitrogenous DBP in disinfected water) was found for the first time in foods. Finally, it was concluded that the freezing process can keep the compounds stable longer than other preservation processes (viz. sanitising, canning) and, therefore, frozen foods present higher DBP concentrations than other food categories (minimally processed vegetables, or canned vegetables and meats).

Optimization of the precursor removal of dichloroacetonitrile (DCAN), an emerging nitrogenous disinfection by-product, in an up-flow BAC filter

The process parameters of the up-flow biological activated carbon filter (UBACF) were optimized in a pilot-scale trial for controlling the precursor of dichloroacetonitrile (DCAN), an emerging nitrogenous disinfection by-product. The experiments were performed using a central composite design (CCD) with the response surface methodology (RSM). The results showed that the removal efficiencies of formation potentials (FP) of DCAN increased from 28.9% to 64.4% with the optimized ozone dose, expansion rate of BAC and backwashing cycle, being scheduled to 1.52 mg/L, 27% and 9.5 d, respectively. Excitation and emission matrix (EEM) spectra indicated that the fluorescence peaks of aromatic protein (AP) and soluble microbial products-like (SMPs)-like region were weakened significantly in the effluent of improved process (IP) with optimization, which were main precursors of DCAN. The bacterial community before and after the optimization of UBACF was determined using the high-throughput sequencing technology. The class and genus of microorganism demonstrated that the IP had a more diverse microbial community and more even distribution of species in BAC filter. It was favor of the growth of Alphaproteobacteria, Bacilli and Betaproteobacteria attached to the BAC particles, which could biodegrade effectively the precursors of DCAN.

Occurrence of nitrogenous and carbonaceous disinfection byproducts in drinking water distributed in Shenzhen, China

A 12-month sampling program was conducted throughout a drinking water distribution system in Shenzhen and the data from 251 samples provide a comprehensive picture of the spatial and seasonal variability of 17 species disinfection by-products (DBPs) in a city with subtropical monsoon climate. The carbonaceous disinfection by-product (C-DBPs) included four trihalomethanes (THMs), three trihaloacetaldehydes (THAs) and two haloketones (HKs). Their median concentrations over the entire period were 19.9 μg/L, 3.4 μg/L and 1.4 μg/L, respectively. The nitrogenous DBPs (N-DBPs) monitored were four haloacetonitriles (HANs) and four haloacetamides (HAcAms). Their median levels were 2.0 μg/L and 1.5 μg/L, respectively. Low levels of brominated DBP species (bromine substitution factors ≤ 0.5) were observed. The BSF of each DBP class followed the trend: THMs ≈ DHAcAms > DHANs > THAs. All the DBP concentrations showed clear seasonal variations with the highest average concentrations in spring. Correlation analyses showed that the THMs and CH levels in Shenzhen drinking water could be used as statistical indicators of the levels of unregulated N-DBPs (0.4 < r < 0.7, p < 0.5). The results supplement the database of DBP occurrence in drinking water in China, and provide an important reference data set for DBP occurrence in cities with a subtropical monsoon climate around the world.

Tolerance to dichloroacetonitrile-induced neurotoxicity in streptozotocin-induced diabetic rats

Diabetes mellitus has potential to alter the toxicity of hazardous chemicals. Dichloroacetonitrile (DCAN) is one of high-risk nitrogenous disinfection by-products. This study evaluated the neurotoxicity of DCAN (11, 44 and 88mg/kg) in normoglycaemic and streptozotocin (STZ)-induced diabetic rats via orally for 28days. STZ diabetes prolonged the median survival time and total lethal time after DCAN (88mg/kg) exposure when compared with that observed in normoglycaemic rats. DCAN altered motor activity and induced anxiety behaviour in normoglycaemic rats; but it did not exaggerate behavioural changes in STZ diabetic rats. DCAN –induced brain oxidative damage by compensatory increase glutathione content and decrease malonaldehyde levels; but it did not induce oxidative damage in diabetic rats. STZ diabetes slowed down the pathological pace of DCAN-induced brain mitochondrial dysfunction by decreasing reactive oxygen species and increasing cytochrome C oxidase activity. In conclusion, the present study indicated that STZ diabetic rats are resistant to DCAN-induced neurotoxicity at the dosage and with the dosage schedule in 28-day subacute toxicity test.