Dichloroacetonitrile Research Articles

Peroxidation of High Algae-laden Water by Ozone: Algae Organic Matter Transformation and Disinfection By-products Formation

Formation characteristics and transferring feature of nitrogenous/carbonaceous disinfection by-products have been observed under different ozone dosages and pH conditions, and essential nature conversion of Algae organic matters has been also studied concurrently, based on high algae-laden water. The results showed as follows:reduction of Microcystis aeruginosa could reach 36% at the ozonation concentration of 28.92 mg·L-1. Humic acid-like compounds first increased and then decreased with continuing addition of ozone dosage, whereas soluble microbial products, fulvic acids and aromatic protein substance all diminished. Low dosage of ozone had certain effect on control of dichloroacetonitrile(DCAN) and trichloroacetonitrile (TCAN) formation potential, yet augmented the yield of trichloronitromethane (TCNM) and 1,1,1-trichloroacetone(1,1,1-TCP) precursors, and N-DBPs formation potential was promoted with the increase of ozone dosage. Algae removal efficiency was relatively the best under the acidic condition, meanwhile, UV254 and DOC increased with the rise of pH, though the change was not outstanding. Humic acid-like compounds decreased with the rise of pH; ozonation could degrade the soluble microbial products and the consequence was affected little by the change of pH. DCAN and TCAN formation potential decreased with the rise of pH; TCNM formation potential appeared to be the highest when the pH was 10, whereas the highest 1,1,1-TCP formation potential was found at pH 7.

UV/chlorine as an advanced oxidation process for the degradation of benzalkonium chloride: Synergistic effect, transformation products and toxicity evaluation

Benzalkonium chlorides (BACs), as typical cationic surfactants and biocides widely applied in household and industrial products, have been frequently detected as micropollutants in many aquatic environments. In this study, the combination of UV irradiation and chlorine (UV/chlorine), a newly interested advanced oxidation process, was used to degrade dodecylbenzyldimethylammonium chloride (DDBAC). UV/chlorine showed synergistic effects on DDBAC degradation comparing to UV irradiation or chlorination alone. Radical quenching experiments indicated that degradation of DDBAC by UV/chlorine involved both UV photolysis and radical species oxidation, which accounted for 48.4% and 51.6%, respectively. Chlorine dosage and pH are essential parameters affecting the treatment efficiency of UV/chlorine. The pseudo first order rate constant (kobs, DDBAC) increased from 0.046 min−1 to 0.123 min−1 in response to chlorine dosage at 0–150 mg/L, and the degradation percentage of DDBAC within 12 min decreased from 81.4% to 56.6% at pH 3.6–9.5. Five main intermediates were identified and semi-quantified using HPLC-MS/MS and a possible degradation pathway was proposed. The degradation mechanisms of DDBAC by UV/chlorine included cleavage of the benzyl-nitrogen bond and hydrogen abstraction of the alkyl chain. Trichloromethane (TCM), chloral hydrate (CH), trichloropropanone (TCP), dichloropropanone (DCP) and dichloroacetonitrile (DCAN) were detected using GC-ECD. The formation of chlorinated products increased rapidly initially, then decreased (TCM, TCP, DCP and DCAN) or remained stable (CH) with extended treatment. The actual formation of TCM peaked at 30 min (50.3 μg/L), while other chlorinated products did not exceed 10 μg/L throughout the process. Based on the luminescent bacterial assay, DDBAC solution underwent almost complete detoxification subjected to UV/chlorine treatment for 120 min, which is more effective than UV irradiation or chlorination alone.

Impact of pre-oxidation using H2O2 and ultraviolet/H2O2 on disinfection byproducts generated from chlor(am)ination of chloramphenicol

Hydrogen peroxide with and without activation by ultraviolet irradiation (UV/H2O2 and H2O2, respectively) has been investigated to degrade emerging contaminants in drinking water. The antibiotic chloramphenicol (CAP) and its analogues (thiamphenicol and florfenicol), referred to collectively as CAPs, can produce a range of disinfection by-products (DBPs) during chlorination or chloramination (chlor(am)ination). The impact of unactivated and activated H2O2 pre-oxidation on the formation of nitrogenous and carbonaceous DBPs from the chlor(am)ination of CAP model precursors was investigated. A theoretical estimated toxicity evaluation was also carried out based on the DBPs that formed. H2O2 pretreatment alone did not affect organic carbon and nitrogen concentrations, but significantly reduced the formation of trichloromethane (TCM) during chlorination and trichloronitromethane (TCNM) during chloramination, and enhanced dichloroacetonitrile (DCAN) yields during chloramination. These significant changes in DBP yields caused by H2O2 pre-oxidation are attributable to the transformation of the three CAPs into more reactive precursor structures. The three CAPs did not form DCAN and TCNM during chlorination, regardless of whether H2O2 pre-oxidation was used. However, UV/H2O2 pretreatment resulted in the unexpected formation of TCNM during chlorination. Furthermore, UV/H2O2 pre-oxidation increased the formation of DCAN and TCNM, whereas it had little effect on TCM formation during chloramination. A preliminary estimated toxicity evaluation demonstrated that UV/H2O2 pre-oxidation at low doses, followed by chlorination, resulted in the lowest estimated toxicity from a range of DBPs. Conversely, the estimated toxicity evaluation showed that unactivated H2O2 (high dose) was preferable to UV activated H2O2 for overall control of these investigated DBPs during chloramination.

Formation and Occurrence of N-Chloro-2,2-dichloroacetamide, a Previously Overlooked Nitrogenous Disinfection Byproduct in Chlorinated Drinking Waters.

Haloacetamides (HAMs) are a class of newly identified nitrogenous disinfection byproducts (N-DBPs) whose occurrence in drinking waters has recently been reported in several DBP surveys. As the most prominent HAM species, it is commonly acknowledged that 2,2-dichloroacetamide (DCAM) is mainly generated from dichloroacetonitrile (DCAN) hydrolysis because the concentrations of these two compounds are often well correlated. Instead of DCAM, a previously unreported N-DBP, N-chloro-2,2-dichloroacetamide (N-Cl-DCAM), was confirmed in this study as the actual DCAN degradation product in chlorinated drinking waters. It is suspected that N-Cl-DCAM has been erroneously identified as DCAM, because its nitrogen-bound chlorine is readily reduced by most commonly used quenching agents. This hypothesis is supported by kinetic studies that indicate almost instantaneous N-chlorination of DCAM even at low chlorine residuals. Therefore, it is unlikely that DCAM can persist as a long-lived DCAN decomposition product in systems using free chlorine as a residual disinfectant. Instead, chlorination of DCAM will lead to the formation of an equal amount of N-Cl-DCAM by forming a hydrogen bond between hypochlorite oxygen and amino hydrogen. Alternatively, N-Cl-DCAM can be produced directly from DCAN chlorination via nucleophilic addition of hypochlorite on the nitrile carbon. Due to its relatively low pKa value, N-Cl-DCAM tends to deprotonate under typical drinking water pH conditions, and the anionic form of N-Cl-DCAM was found to be very stable in the absence of chlorine. N-Cl-DCAM can, however, undergo acid-catalyzed decomposition to form the corresponding dichloroacetic acid (DCAA) when chlorine is present, although those acidic conditions that favor N-Cl-DCAM degradation are generally atypical for finished drinking waters. For these reasons, N-Cl-DCAM is predicted to have very long half-lives in most distribution systems that use free chlorine. Furthermore, an analytical method using ultra performance liquid chromatography (UPLC)/negative electrospray ionization (ESI-)/quadrupole time-of-flight mass spectrometry (qTOF) was developed for the detection of a family of seven N-chloro-haloacetamides (N-Cl-HAMs). Combined with solid phase extraction (SPE), the occurrence of N-Cl-DCAM and its two brominated analogues (i.e., N-chloro-2,2-bromochloroacetamide and N-chloro-2,2-dibromoacetamide) was quantitatively determined for the first time in 11 real tap water samples. The discovery of N-Cl-DCAM or, more broadly speaking, N-Cl-HAMs in chlorinated drinking waters is of significance because they are organic chloramines, a family of compounds that is perceived to be more toxicologically potent than halonitriles (e.g., DCAN) and haloamides (e.g., DCAM), and therefore they may pose greater risks to drinking water consumers given their widespread occurrence and high stability.

Production of trihalomethanes, haloacetaldehydes and haloacetonitriles during chlorination of microcystin-LR and impacts of pre-oxidation on their formation

Microcystins (MCs) in drinking water have gained much attention due to their adverse health effects. However, little is known about the impact of pre-oxidation in the formation of disinfection by-products (DBPs) during the downstream chlorination of MCs. The present study examined the formation of both carbonaceous and nitrogenous DBPs from chlorination of MC-LR (the most abundant MC species) and evaluated the impact of permanganate (PM), hydrogen peroxide (H2O2) and chlorine dioxide (ClO2) pre-oxidation on the DBP formation in chlorination. Higher yields of chloroform (CF) (maximum 43.0%) were observed from chlorination of MC-LR than free amino acids which are included in MC-LR structure. Chloral hydrate (CH) and dichloroacetonitrile (DCAN) were also produced from the chlorination of MC-LR, and the latter one was formed probably due to the chlorination of peptide bonds. A high pH favored the production of CF and CH, but inhibited the formation of DCAN. In the presence of bromide, bromo-DBPs could be produced to pose a threat. For example, 0.58μg/L of tribromoacetaldehyde was produced from the chlorination of MC-LR at Br−=200μg/L. PM and ClO2 pre-oxidation could both reduce the DBP formation from MC-LR. In contrast, H2O2 appeared not to significantly control the DBP formation.

Detection of genotoxic effects of drinking water disinfection by-products using Vicia faba bioassay

Plant-based bioassays have gained wide use among the toxicological and/or ecotoxicological assessment procedures because of their simplicity, sensitivity, low cost, and reliability. The present study describes the use of Vicia faba (V. faba) micronucleus (MN) test and V. faba comet assay in the evaluation of the genotoxic potential of disinfection by-products (DBPs) commonly found in chlorine-disinfected drinking water. Five haloacetic acids and three halogenated acetonitriles were chosen as representatives of DBPs in this study because they are of potentially great public health risk. Results of the MN test indicated that monochloroacetic acid (MCA), monobromoacetic acid (MBA), dichloroacetic acid (DCA), dibromoacetic acid (DBA), trichloroacetic acid (TCA), and trichloroacetonitrile (TCAN) caused a statistically significant increase in MN frequency in V. faba root tip cells. However, no genotoxic response was observed for dichloroacetonitrile (DCAN) and dibromoacetonitrile (DBAN). Results of the comet assay showed that all tested DBPs induced a statistically significant increase in genomic DNA damage to V. faba root tip cells. On considering the capacity to detect genomic damage of a different nature, we suggest that a combination of V. faba MN test and V. faba comet assay is a useful tool for the detection of genotoxic effects of DBPs. It is worthy of assessing the feasibility of using V. faba comet assay combined with V. faba MN test to screen for the genotoxic activity of chlorinated drinking water in future work.

Factors affecting the formation of nitrogenous disinfection by-products during chlorination of aspartic acid in drinking water

The formation of emerging nitrogenous disinfection by-products (N-DBPs) from the chlorination of aspartic acid (Asp) was investigated. The yield of dichloroacetonitrile (DCAN) was higher than other N-DBPs, such as dichloroacetamide(DCAcAm) and chloropicrin (TCNM) during the chlorination of Asp. The formation of DCAN, DCAcAm, and TCNM all showed a trend of first increasing and then decreasing during the chlorination of Asp with increasing contact time. The dosage of chlorine had an impact on the formation of DCAN, DCAcAm, and TCNM. The highest yields of DCAN and DCAcAm appeared when the Cl2/Asp molar ratio was about 20, the yield of TCNM increased with increasing the Cl2/Asp molar ratio from 5 to 30 and TCNM was not produced when the ratio was less than 5. Cyanogen chloride (CNCl) was detected when the Cl2/Asp molar ratio was lower than 5. N-DBPs formation was influenced by pH. DCAN formation increased with increasing pH from 5 to 6 and then decreased with increasing pH from 6 to 9, but DCAcAm and TCNM increased with increasing pH from 5 to 8 and then decreased. Higher temperatures reduced the formation of DCAN and DCAcAm, but increased TCNM formation. DCAN and DCAcAm formation decreased, and relatively stable TCNM formation increased, with increasing free chlorine contact time during chloramination. N-nitrosodimethylamine (NDMA) was produced during chloramination of Asp and increased with prolonged chloramination contact time. The presence of bromide ions enhanced the yields of haloacetonitriles and shifted N-DBPs to more brominated species.

DBPs formation and genotoxicity during chlorination of pyrimidines and purines bases

Soluble microbial products (SMPs) are an important component in wastewater effluents, and consist of proteins, polysaccharides, humic acids, and DNA, etc. Pyrimidines and purines bases, the nitrogenous components of DNA, could act as the precursors of disinfection by-products (DBPs) during wastewater chlorination. This study investigated DBPs formation and the genotoxicity of pyrimidines bases (cytosine, uracil and thymine) and purines bases (adenine and guanine) during chlorination. Among the five bases, pyrimidines bases generated higher levels of DBPs than purines. Uracil generated the highest level of DBPs, while cytosine produced the highest level of nitrogenous DBPs (N-DBPs) including dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN) and trichloronitromethane (TCNM). None of N-nitrosamines were detected during chlorination of the five bases. The genotoxicity of chlorinated pyrimidines bases was higher than that of purines bases, and the genotoxicity of chlorinated uracil and cytosine was higher than that of glycine (the most common amino acid in wastewater). Formation pathways of three N-DBPs (DCAN, TCAN and TCNM) and two haloacetic acids (dichloroacetic acid and trichloroacetic acid) were tentatively proposed during chlorination of cytosine. The chemical structures of new intermediates generated during chlorination of cytosine were identified using an electrospray time-of-flight mass spectrometer, and the reaction site of intermediates was calculated by the frontier electron density (FED). The content of the formed intermediates under different chlorine dosages was also investigated to further illustrate the reasonability of the hypothesized reaction pathways.

Acute toxicity of dichloroacetonitrile (DCAN), a typical nitrogenous disinfection by-product (N-DBP), on zebrafish (Danio rerio)

Dichloroacetonitrile (DCAN) is a typical nitrogenous disinfection by-product (N-DBP) and its toxicity on aquatic animals is investigated for the first time. The present study was designed to investigate the potential adverse effects of DCAN on zebrafish. DCAN could induce developmental toxicity to zebrafish embryos. A significant decrease in hatchability and an increase in malformation and mortality occurred when DCAN concentration was above 100µg/L. Heart function alteration and neuronal function disturbance occurred at concentration higher than 500 and 100µg/L, respectively. Further, DCAN was easily accumulated in adult zebrafish. The rank order of declining bioconcentration factor (BCF) was liver (1240–1670)> gill (1210–1430)> muscle (644–877). DCAN caused acute metabolism damage to adult zebrafish especially at 8 days exposure, at which time the “Integrated Biomarker Response” (IBR) index value reached 798 at 1mg/L DCAN dose. Acute DNA damage was induced to adult zebrafish by DCAN even at 10µg/L dose.

Formation of disinfection by-products during chlorine dioxide pre-oxidation of chironomid larvae metabolites followed by chlorination

The objective of this research was to investigate the formation of disinfection by-products (DBPs) during chlorine dioxide pre-oxidation of chironomid larvae metabolites followed by chlorination. The mode of action of chlorine dioxide/chlorine combination was clarified, including the impact of different factors on DBP formation. The results indicated that pre-oxidation suppressed the production of most DBPs such as trihalomethanes, haloacetic acids, haloacetonitriles, and haloketones, compared to when chlorination was used alone. The concentrations of trichloromethane (TCM), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), dichloroacetonitrile (DCAN), and 1,1-dichloro-2-propanone (1,1-DCP) decreased with prolonged pre-oxidation times, with the highest yields observed for DCAA and TCAA. The solution pH had a distinct influence on DBP formation, with the concentrations of DCAA, TCAA, DCAN, 1,1-DCP, and 1,1,1-trichloro-2-propanone (1,1,1-TCP) initially increasing and then decreasing with increasing pH. The maximum concentrations of DCAA and TCAA were observed at pH 7–8, whereas the TCM content increased continuously on increasing the pH up to 8–9. Other DBPs reached their maxima at pH 6–7. Regarding thermal effects, the formation of 1,1,1-TCP enhanced at higher temperatures, while the concentrations of DCAN, 1,1,-DCP, and TCM first increased between 10 and 20°C and then decreased between 20 and 30°C. The concentrations of DCAA and TCAA decreased from 10 to 20°C and then increased between 20 and 30°C.

Kinetics and mechanisms of degradation of chloroacetonitriles by the UV/H2O2 process

Haloacetonitriles (HANs) are emerging disinfection by-products (DBPs) that are more toxic than the regulated DBPs and widely found in the chlorinated/chloraminated water. This paper studied kinetics and mechanisms of the degradation of chloroacetonitriles (CANs) by the UV/H2O2 process at pH 6 and 7.5 and H2O2 concentrations of 1 × 10−3 M, 5 × 10−3 M and 1 × 10−2 M. The degradation followed pseudo first-order degradation kinetics. The degradation rate of monochloroacetonitrile (MCAN) remained similar, while those of dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) increased with increasing pH and H2O2 concentrations. The different trends were attributed to the changing contributions of the two major mechanisms: the nucleophilic attack by hydroperoxide ions (HO2−) and the hydroxyl radical (•OH) oxidation. The second-order rate constants of HO2− towards MCAN, DCAN and TCAN were determined to be 11.8 (±0.62), 4.83 (±0.01) × 103, and 2.54 (±0.23) × 105 M−1 s−1, respectively, while that of •OH were 8.7 × 106, 4.4 × 106, and < 106 M−1 s−1, respectively. The degradation of TCAN was mainly attributed to the HO2− nucleophilic attack, while that of MCAN was dominated by the •OH oxidation. DCAN was degraded by both mechanisms. The nucleophilic attack increased linearly with increasing HO2− concentration as a result of increasing H2O2 concentration and/or pH, while the •OH oxidation was less dependent on H2O2 concentrations and/or pH. The nucleophilic attack mainly transformed HANs to haloacetamides, while the •OH oxidation dechlorinated HANs. This paper firstly illustrated the importance of the HO2− nucleophilic attack, in addition to the •OH oxidation, on the CAN degradation in the UV/H2O2 process.

Photodegradation of haloacetonitriles in water by vacuum ultraviolet irradiation: Mechanisms and intermediate formation

Photodegradation of haloacetonitriles (HANs), highly carcinogenic nitrogenous disinfection by-products, in water using vacuum ultraviolet (VUV, 185 + 254 nm) in comparison with ultraviolet (UV, only 254 nm) was investigated. Monochloroacetonitrile (MCAN), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), and dibromoacetonitrile (DBAN) were species of HANs studied. The effect of gas purging and intermediate formation under VUV were examined. The results show that the pseudo first order rate constants for the reduction of HANs under VUV were approximately 2–7 times better than UV. The order of degradation efficiency under VUV and UV was MCAN < DCAN < TCAN < DBAN. The degradation efficiencies of individual HANs under VUV were higher than those of mixed HANs, suggesting competitive effects among HANs. Under nitrogen purging, the removal rate constants of mixed HANs was much higher than that of the aerated condition by 34.4, 34.9, 10.1, and 3.8 times for MCAN, DCAN, TCAN, and DBAN, respectively. The major degradation mechanism for HANs was different depending on HANs species. Degradation intermediates of HANs such as 2-chloropropionitrile, 2,2-dimethylpropanenitrile, and fumaronitrile were produced from the substitution, addition, and polymerization reactions. In addition, chlorinated HANs with lower number of chlorine atom including MCAN and DCAN were found as intermediates of DCAN and TCAN degradation, respectively.

Elimination of disinfection byproduct formation potential in reclaimed water during solar light irradiation

Ecological storage of reclaimed water in ponds and lakes is widely applied in water reuse. During reclaimed water storage, solar light can degrade pollutants and improve water quality. This study investigated the effects of solar light irradiation on the disinfection byproduct formation potential in reclaimed water, including haloacetonitriles (HANs), trichloronitromethane (TCNM), trihalomethanes (THMs), haloketones (HKs) and chloral hydrate (CH). Natural solar light significantly decreased the formation potential of HANs, TCNM, and HKs in reclaimed water, but had a limited effect on the formation potential of THMs and CH. Ultraviolet (UV) light in solar radiation played a dominant role in the decrease of the formation potential of HANs, TCNM and HKs. Among the disinfection byproducts, the removal kinetic constant of dichloroacetonitrile (DCAN) with irradiation dose was much larger than those for dichloropropanone (1,1-DCP), trichloropropanone (1,1,1-TCP) and TCNM. During solar irradiation, fluorescence spectra intensities of reclaimed water also decreased significantly. The removal of tyrosine (Tyr)-like and tryptophan (Trp)-like protein fluorescence spectra intensity volumes was correlated to the decrease in DCAN formation potential. Solar irradiation was demonstrated to degrade Trp, Tyr and their DCAN formation potential. The photolysis products of Trp after solar irradiation were detected as kynurenine and tryptamine, which had chloroform, CH and DCAN formation potential lower than those of Trp.

Precursors and factors affecting formation of haloacetonitriles and chloropicrin during chlor(am)ination of nitrogenous organic compounds in drinking water

This study investigated the precursors and factors affecting formation of haloacetonitriles (HANs) and chloropicrin (TCNM) during chlorination/chloramination of eight amino acids in the effluent water of V-type clarifying filtration from a drinking water treatment plant. The yields of trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN) and TCNM were higher during chlorination than during chloramination. Tyrosine and tryptophan produced the greatest amount of DCAN and also generated a small amount of TCAN during chlorination process. Besides, the yields of DCAN were higher than TCNM during chlorination/chloramination. Contact time, Cl2:org-N molar ratios, pH, temperature and bromide ion affected nitrogenous disinfection by-products (N-DBPs) formation during chlorination of tryptophan in different degrees. TCAN, DCAN and TCNM formation showed the increasing and then decreasing with prolonged contact time. Higher Cl2:org-N molar ratios improved N-DBPs formation within a certain range. The pH affected N-DBPs formation differently. HANs increased with increasing pH from 5 to 6 and decreased with increasing pH from 6 to 9, while TCNM increased with increasing pH from 5 to 9. Higher temperatures enhanced TCNM formation, but reduced the formation of TCAN and DCAN. The presence of bromide ions improved the yields of HANs and TCNM and shifted N-DBPs to more brominated ones.

Removal of haloacetonitrile by adsorption on thiol-functionalized mesoporous composites based on natural rubber and hexagonal mesoporous silica

Haloacetonitriles (HANs) are nitrogenous disinfection by-products (DBPs) that have been reported to have a higher toxicity than the other groups of DBPs. The adsorption process is mostly used to remove HANs in aqueous solutions. Functionalized composite materials tend to be effective adsorbents due to their hydrophobicity and specific adsorptive mechanism. In this study, the removal of dichloroacetonitrile (DCAN) from tap water by adsorption on thiol-functionalized mesoporous composites made from natural rubber (NR) and hexagonal mesoporous silica (HMS-SH) was investigated. Fourier-transform infrared spectroscopy (FTIR) results revealed that the thiol group of NR/HMS was covered with NR molecules. X-ray diffraction (XRD) analysis indicated an expansion of the hexagonal unit cell. Adsorption kinetic and isotherm models were used to determine the adsorption mechanisms and the experiments revealed that NR/HMS-SH had a higher DCAN adsorption capacity than powered activated carbon (PAC). NR/HMS-SH adsorption reached equilibrium after 12 hours and its adsorption kinetics fit well with a pseudo-second-order model. A linear model was found to fit well with the DCAN adsorption isotherm at a low concentration level.

Occurrence and health risk assessment of halogenated disinfection byproducts in indoor swimming pool water

Swimming pool disinfection byproducts (DBPs) have become a concern in many countries all over the world. In this study, the concentrations of several categories of DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), haloketones (HKs) and trichloronitromethane (TCNM), in 13 public indoor swimming pools in Nanjing, China were determined, the correlations between DBPs and water quality parameters as well as between different DBP categories were evaluated, and the health risks of the DBPs to human were examined. The results indicate that the DBP levels in the swimming pools in Nanjing were relatively high, with HAAs as the most dominant category, followed by THMs, HANs, HKs and TCNM sequentially. Bromochloroacetic acid (BCAA), trichloromethane (TCM), dichloroacetonitrile (DCAN), and 1,1,1-trichloropropanone (1,1,1-TCP) were the most dominant species among HAAs, THMs, HANs, and HKs, respectively. For all the different categories of DBPs, the concentrations in the pool disinfected with ozonation/chlorination were lower than those in the pool disinfected with chlorination. The DBP levels were generally not affected by the number of swimmers and the DBP levels on different dates were relatively stable. Besides, the chlorine residual seemed to be a critical concern in most of the swimming pools in this study. Moreover, there were some correlations between DBPs and water quality parameters as well as between different DBP categories. It is to be noted that the predicted cancer and health risks of the DBPs in these swimming pools were generally higher than the regulatory limits by USEPA, and thus DBPs in these swimming pools should be concerned.

Formation of haloacetonitriles and haloacetamides and their precursors during chlorination of secondary effluents.

The formation of dichloroacetonitrile (DCAN), dichloroacetamide (DCAcAm) and trichloroacetamide (TCAcAm) during chlorination of secondary effluents was evaluated under different conditions. The formation of DCAN and DCAcAm increased, then decreased with increasing contact time and chlorine dose, while TCAcAm formation increased continually, exceeding DCAcAm formation after a relatively long contact time or in response to a relatively high chlorine dose (20-80 mg L(-1)). Increasing the sample pH from 6 to 9 reduced the formation of DCAN and TCAcAm, while DCAcAm formation was highest at pH 8. Precursors in the secondary effluent were characterized by separating the organic matter into several fractions using membrane filtration and XAD resins and then measuring the formation of DCAN, DCAcAm and TCAcAm from each fraction during chlorination. Dissolved organic matter (DOM) with a molecular weight less than 1 kDa dominated the formation of DCAcAm and TCAcAm. However, particle-associated DCAN precursors were detected in addition to potent DCAN precursors in the DOM fractions. Among the XAD fractions of DOM, the hydrophilic neutral fraction prevailed in the secondary effluent and produced the most DCAN, DCAcAm and TCAcAm per volume, and the hydrophilic basic fraction with a low organic content had the highest yields of DCAN, DCAcAm and TCAcAm on a DOC basis, so their dominant precursors were associated with hydrophilic matter.

Comparative cytotoxic and genotoxic potential of 13 drinking water disinfection by-products using a microplate-based cytotoxicity assay and a developed SOS/umu assay.

The implications of disinfection by-products (DBPs) present in drinking water are of public health concern because of their potential mutagenic, carcinogenic and other toxic effects on humans. In this study, we selected 13 main DBPs found in drinking water to quantitatively analyse their cytotoxicity and genotoxicity using a microplate-based cytotoxicity assay and a developed SOS/umu assay in Salmonella typhimurium TA1535/pSK1002. With the developed SOS/umu test, eight DBPs: 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-fura3-chloro-4-(dichloromethyl)-5-hydroxy-2-[5H]-furanone (MX), dibromoacetonitrile (DBN), iodoacetic acid (IA), bromochloroacetonitrile (BCN), bromoacetic acid (BA), trichloroacetonitrile (TCN), dibromoacetic acid (DBA) and dichloroacetic acid (DCA) were significantly genotoxic to S. typhimurium. Three DBPs: chloroacetic acid (CA), trichloroacetic acid (TCA) and dichloroacetonitrile (DCN) were weakly genotoxic, whereas the remaining DBPs: chloroacetonitrile (CN) and chloral hydrate (CH) were negative. The rank order in decreasing genotoxicity was as follows: MX > DBN > IA > BCN > BA > TCN > DBA > DCA > CA, TCA, DCN > CN, CH. MX was approximately 370 000 times more genotoxic than DCA. In the microplate-based cytotoxicity assay, cytotoxic potencies of the 13 DBPs were compared and ranked in decreasing order as follows: MX > IA > DBN > BCN > BA > TCN > DCN > CA > DCA > DBA > CN > TCA > CH. MX was approximately 19 200 times more cytotoxic than CH. A statistically significant correlation was found between cytotoxicity and genotoxicity of the 13 DBPs in S. typhimurium. Results suggest that microplate-based cytotoxicity assay and the developed SOS/umu assay are feasible tools for analysing the cytotoxicity and genotoxicity of DBPs, particularly for comparing their toxic intensities quantitatively.

Comparison of free amino acids and short oligopeptides for the formation of trihalomethanes and haloacetonitriles during chlorination: Effect of peptide bond and pre-oxidation

There has been a series of research work on exploring how disinfection by-products (DBPs) are formed from free amino acids (AAs) during chlorination in drinking water. Yet there is very limited information about the formation of carbonaceous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs) from the chlorination of those AAs in combined forms which are more abundant than free AAs in source waters. In this study, we compared the differences on the formation of trihalomethanes (THMs, representing C-DBPs) and haloacetonitriles (HANs, representing N-DBPs) from free AAs and combined AAs (short oligopeptides) during chlorination. And, the influence of the selected pre-oxidation processes (permanganate, persulfate, hydrogen peroxide) on THM and HAN formation during subsequent chlorination was also examined. There were significant differences in chloroform (CF), dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) formation between free AAs and short oligopeptides, which was probably ascribed to the presence of peptide bond. Of note, the combined tyrosine (Tyr) in tripeptides (Tyr–Tyr–Tyr) formed more TCAN compared with free Tyr and other combined Tyr in dipeptides, and a novel possible formation pathway of TCAN from Tyr–Tyr–Tyr was proposed. In addition, the effect of three pre-oxidation on DBP formation was different, and their rank order was permanganate>persulfate>hydrogen peroxide. The permanganate is a better choice than persulfate and hydrogen peroxide for controlling AA derived HANs, but this benefit should be weighed against the potential drawback of increased regulated THMs.

Evaluation of disinfection by-product formation potential (DBPFP) during chlorination of two algae species — Blue-green Microcystis aeruginosa and diatom Cyclotella meneghiniana

Microcystis aeruginosa (blue-green alga) commonly blooms in summer and Cyclotella meneghiniana (diatom) outbreaks in fall in the reservoirs that serve as drinking water sources in Southeast China. Herein, an evaluation of disinfection by-product formation potential (DBPFP) from them during chlorination should be conducted. Five DBPs including trichloromethane (TCM), trichloronitromethane (TCNM), dichloroacetonitrile (DCAN), 1,1-dichloropropanone (1,1-DCP) and 1,1,1-trichloropropanone (1,1,1-TCP) were monitored. The formation potential of TCM and TCNM was enhanced with the increase of reaction time and chlorine dosage, whereas that of DCAN, 1,1-DCP and 1,1,1-TCP increased first and then fell with continuing reaction time. M. aeruginosa showed higher DBPFP than C. meneghiniana, the yield of DBPs varied with components of algal cells. The DBPFP order from components of M. aeruginosa was cell suspension (CS)≈intracellular organic matter (IOM)>extracellular organic matter (EOM)>cell debris (CD), which indicated that IOM was the main DBP precursors for M. aeruginosa. The yields of DBPs from components of C. meneghiniana were in the order of CS>IOM≈CD≈EOM, suggesting that three components made similar contributions to the total DBP formation. The amount of IOM with higher DBPFP leaked from both algae species increased with the chlorine dosage, indicating that chlorine dosage should be considered carefully in the treatment of eutrophic water for less destroying of the cell integrity. Though fluorescence substances contained in both algae species varied significantly, the soluble microbial products (SMPs) and aromatic protein-like substances were the main cellular components that contributed to DBP formation for both algae.