Halonitromethane drinking water disinfection byproducts: chemical characterization and mammalian cell cytotoxicity and genotoxicity

Halonitromethanes are drinking water disinfection byproducts that have recently received a high priority for health effects research from the U.S. Environmental Protection Agency (EPA). Our purpose was to identify and synthesize where necessary the mixed halonitromethanes and to determine the chronic cytotoxicity and the acute genotoxicity of these agents in mammalian cells. The halonitromethanes included bromonitromethane (BNM), dibromonitromethane (DBNM), tribromonitromethane (TBNM), bromochloronitromethane (BCNM), dibromochloronitromethane (DBCNM), bromodichloronitromethane (BDCNM), chloronitromethane (CNM), dichloronitromethane (DCNM), and trichloronitromethane (TCNM). Low- and high-resolution gas chromatography/mass spectrometry (GC/MS) was used to identify the mixed chloro-bromonitromethanes in finished drinking waters, and analytical standards that were not commercially available were synthesized (BDCNM, DBCNM, TBNM, CNM, DCNM, BCNM). The rank order of their chronic cytotoxicity (72 h exposure) to Chinese hamster ovary (CHO) cells was DBNM > DBCNM > BNM > TBNM > BDCNM > BCNM > DCNM > CNM > TCNM. The rank order to induce genomic DNA damage in CHO cells was DBNM > BDCNM > TBNM > TCNM > BNM > DBCNM > BCNM > DCNM > CNM. The brominated nitromethanes were more cytotoxic and genotoxic than their chlorinated analogues. This research demonstrated the integration of the procedures for the analytical chemistry and analytical biology when working with limited amounts of sample. The halonitromethanes are potent mammalian cell cytotoxins and genotoxins and may pose a hazard to the public health and the environment.     

Study on the structure and mutagenicity of a new disinfection byproduct in chlorinated drinking water

The structure of a new chlorinated disinfection byproduct (DBP) in drinking water is studied. The new DBP was prepared through chlorinating its best precursor, and it was extracted and isolated from the chlorination products. Its structure is identified as 2,2,4-trichloro-5-methoxycyclopent-4-ene-1,3-dione (TCMCD) through FTIR, MS, 1H NMR, and 13C NMR spectroscopic analysis and single-crystal X-ray diffraction method. Results of the Ames test with tester strain TA100 indicated that the newly identified DBP TCMCD is a mutagen.     

Occurrence, synthesis, and mammalian cell cytotoxicity and genotoxicity of haloacetamides: an emerging class of nitrogenous drinking water disinfection byproducts

The haloacetamides, a class of emerging nitrogenous drinking water disinfection byproduct (DBPs), were analyzed for their chronic cytotoxicity and for the induction of genomic DNA damage in Chinese hamster ovary cells. The rank order for cytotoxicity of 13 haloacetamides was DIAcAm > IAcAm > BAcAm > TBAcAm > BIAcAm > DBCAcAm > CIAcAm > BDCAcAm > DBAcAm > BCAcAm > CAcAm > DCAcAm > TCAcAm. The rank order of their genotoxicity was TBAcAm > DIAcAm approximately equal to IAcAm > BAcAm > DBCAcAm > BIAcAm > BDCAcAm > CIAcAm > BCAcAm > DBAcAm > CAcAm > TCAcAm. DCAcAm was not genotoxic. Cytotoxicity and genotoxicity were primarily determined by the leaving tendency of the halogens and followed the order I > Br > > Cl. With the exception of brominated trihaloacetamides, most of the toxicity rank order was consistent with structure-activity relationship expectations. For di- and trihaloacetamides, the presence of at least one good leaving halogen group (I or Br but not Cl) appears to be critical for significant toxic activity. Log P was not a factor for monohaloacetamides but may play a role in the genotoxicity of trihaloacetamides and possible activation of dihaloacetamides by intracellular GSH and -SH compounds.     

Biological mechanism for the toxicity of haloacetic acid drinking water disinfection byproducts

The halogenated acetic acids are a major class of drinking water disinfection byproducts (DBPs) with five haloacetic acids regulated by the U.S. EPA. These agents are cytotoxic, genotoxic, mutagenic, and teratogenic. The decreasing toxicity rank order of the monohalogenated acetic acids (monoHAAs) is iodo- > bromo- > chloroacetic acid. We present data that the monoHAAs inhibit glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity in a concentration-dependent manner with the same rank order as above. The rate of inhibition of GAPDH and the toxic potency of the monoHAAs are highly correlated with their alkylating potential and the propensity of the halogen leaving group. This strong association between GAPDH inhibition and the monoHAA toxic potency supports a comprehensive mechanism for the adverse biological effects by this widely occurring class of regulated DBPs.     

Degradation of drinking water disinfection byproducts by synthetic goethite and magnetite

Corrosion of iron pipes leads to the release of ferrous iron, Fe(II), and the formation of iron oxides, such as goethite and magnetite, on the pipe surface. Fe(II), a potent reductant when associated with iron oxide surfaces, can mediate the reduction of halogenated organic compounds. Batch experiments were performed to investigate the kinetics and pathways of the degradation of selected chlorinated disinfection byproducts (OBPs) by Fe(II) in the presence of synthetic goethite and magnetite. Trichloronitromethane was degraded via reduction, while trichloroacetonitrile, 1,1,1-trichloropropanone, and trichloroacetaldyde hydrate were transformed via both hydrolysis and reduction. Chloroform and trichloroacetic acid were unreactive. Observed pseudo-first-order reductive dehalogenation rates were influenced by DBP chemical structure and identity of the reductant. Fe(II) bound to iron minerals had greater reactivity than either aqueous Fe(II) or structural Fe(II) present in magnetite. For DBPs of structure Cl3C-R, reductive dehalogenation rate constants normalized by the surface density of Fe(II) on both goethite and magnetite correlated with the electronegativity of the -R group and with one electron reduction potential. In addition to chemical transformation, sorption onto the iron oxide minerals was also an important loss process for 1,1,1-trichloropropanone.     

Tribromopyrrole,brominated acids,and other disinfection byproducts produced by disinfection of drinking water rich in bromide

Using gas chromatography/mass spectrometry (GC/MS), we investigated the formation of disinfection byproducts (DBPs) from high bromide waters (2 mg/L) treated with chlorine or chlorine dioxide used in combination with chlorine and chloramines. This study represents the first comprehensive investigation of DBPs formed by chlorine dioxide under high bromide conditions. Drinking water from full-scale treatment plants in Israel was studied, along with source water (Sea of Galilee) treated under carefully controlled laboratory conditions. Select DBPs (trihalomethanes, haloacetic acids, aldehydes, chlorite, chlorate, and bromate) were quantified. Many of the DBPs identified have not been previously reported, and several of the identifications were confirmed through the analysis of authentic standards. Elevated bromide levels in the source water caused a significant shift in speciation to bromine-containing DBPs; bromoform and dibromoacetic acid were the dominant DBPs observed, with very few chlorine-containing compounds found. Iodo-trihalomethanes were also identified, as well as a number of new brominated carboxylic acids and 2,3,5-tribromopyrrole, which represents the first time a halogenated pyrrole has been reported as a DBP. Most of the bromine-containing DBPs were formed during pre-chlorination at the initial reservoir, and were not formed by chlorine dioxide itself. An exception wasthe iodo-THMs, which appeared to be formed by a combination of chlorine dioxide with chloramines or chlorine (either added deliberately or as an impurity in the chlorine dioxide). A separate laboratory study was also conducted to quantitatively determine the contribution of fulvic acids and humic acids (from isolated natural organic matter in the Sea of Galilee) as precursor material to several of the DBPs identified. Results showed that fulvic acid plays a greater role in the formation of THMs, haloacetic acids, and aldehydes, but 2,3,5-tribromopyrrole was produced primarily from humic acid. Because this was the first time a halopyrrole has been identified as a DBP, 2,3,5-tribromopyrrole was tested for mammalian cell cytotoxicity and genotoxicity. In comparison to other DBPs, 2,3,5-tribromopyrrole was 8x, 4.5x, and 16x more cytotoxic than dibromoacetic acid, 3-chloro-4-(dichloromethyl)-5-hydroxy-2-[5H]-furanone [MX], and potassium bromate, respectively. 2,3,5-Tribromopyrrole also induced acute genomic damage, with a genotoxic potency (299 microM) similar to that of MX.     

Chemical and biological characterization of newly discovered iodoacid drinking water disinfection byproducts

Iodoacid drinking water disinfection byproducts (DBPs) were recently uncovered in drinking water samples from source water with a high bromide/iodide concentration that was disinfected with chloramines. The purpose of this paper is to report the analytical chemical identification of iodoacetic acid (IA) and other iodoacids in drinking water samples, to address the cytotoxicity and genotoxicity of IA in Salmonella typhimurium and mammalian cells, and to report a structure-function analysis of IA with its chlorinated and brominated monohalogenated analogues. The iodoacid DBPs were identified as iodoacetic acid, bromoiodoacetic acid, (Z)- and (E)-3-bromo-3-iodopropenoic acid, and (E)-2-iodo-3-methylbutenedioic acid. IA represents a new class (iodoacid DBPs) of highly toxic drinking water contaminants. The cytotoxicity of IA in S. typhimurium was 2.9x and 53.5x higher than bromoacetic acid (BA) and chloroacetic acid (CA), respectively. A similar trend was found with cytotoxicity in Chinese hamster ovary (CHO) cells; IA was 3.2x and 287.5x more potent than BA and CA, respectively. This rank order was also expressed in its genotoxicity with IA being 2.6x and 523.3x more mutagenic in S. typhimurium strain TA100 than BA and CA, respectively. IA was 2.0x more genotoxic than BA and 47.2x more genotoxic than CA in CHO cells. The rank order of the toxicity of these monohalogenated acetic acids is correlated with the electrophilic reactivity of the DBPs. IA is the most toxic and genotoxic DBP in mammalian cells reported in the literature. These data suggest that chloraminated drinking waters that have high bromide and iodide source waters may contain these iodoacids and most likely other iodo-DBPs. Ultimately, it will be important to know the levels at which these iodoacids occur in drinking water in order to assess the potential for adverse environmental and human health risks.     

Role of aluminum speciation in the removal of disinfection byproduct precursors by a coagulation process

Humic acid (HA) was extracted and separated into different molecular weight (MW) fractions, then coagulated by aluminum chloride and polyaluminum chloride (PACl). The removal of disinfection byproduct (DBP) precursors and the aluminum speciation variation of the coagulants were investigated in detail. In particular, the role of aluminum speciation in the removal of DBP precursors was discussed. During the coagulation process, AlCl3 hydrolyzed into dominating in situ Al13 species at pH 5.5. The in situ Al13 species exhibited better removal ability for haloacetic acid (HAA) precursors than PACl. At pH 7.5, in situ hydrolyzed Al13 species of AlCl3 decomposed into dimeric Al species. In this case, preformed Al13 of PACl had a high removal ability of HAA precursors. Specially, the greatest reduction of HAA precursors with a low MW (<30 kDa) was through charge neutralization at pH 5.5, and that of HAA precursors in high MW (> 30 kDa) fractions was through adsorption at pH 7.5. Different from HAA precursors, the in situ Al13 species did not have a high removal ability of trihalomethane (THM) precursors. Therefore, PACl exhibited a better removal ability of THM precursors than AlCl3 at different pH values. In the different MW fractions, the greatest reduction of THM precursors was through charge neutralization at pH 5.5.     

Characterization of disinfection byproduct precursors based on hydrophobicity and molecular size

Natural organic matter (NOM) from five water sources was fractionated using XAD resins and ultrafiltration membranes into different groups based on hydrophobicity and molecular weight (MW), respectively. The disinfection byproduct formation from each fraction during chlorination and chloramination was studied. In tests using chlorination, hydrophobic and high MW (e.g., >0.5 kDa) precursors produced more unknown total organic halogen (UTOX) than corresponding hydrophilic and low MW (e.g., <0.5 kDa) precursors. Trihaloacetic acid (THAA) precursors were more hydrophobic than trihalomethane (THM) precursors. The formation of THM and THAA was similar among different fractions for a water with low humic content. Hydrophilic and low MW (<0.5 kDa) NOM fractions gave the highest dihaloacetic acid (DHAA) yields. No significant difference was found for DHAA formation among different NOM fractions during chloramination. Increasing pH from 6 to 9 led to lower TOX formation for hydrophobic and high MW NOM fractions but had little impact on TOX yields from hydrophilic and low MW fractions. Bromine and iodine were more reactive with hydrophilic and low MW precursors as measured by THM or HAA formation than their corresponding hydrophobic and high MW precursors. However, hydrophobic and high MW precursors produced more UTOX when reacting with bromine and iodine.     

Bioanalytical assessment of the formation of disinfection byproducts in a drinking water treatment plant

Disinfection of drinking water is the most successful measure to reduce water-borne diseases and protect health. However, disinfection byproducts (DBPs) formed from the reaction of disinfectants such as chlorine and monochloramine with organic matter may cause bladder cancer and other adverse health effects. In this study the formation of DBPs through a full-scale water treatment plant serving a metropolitan area in Australia was assessed using in vitro bioanalytical tools, as well as through quantification of halogen-specific adsorbable organic halogens (AOXs), characterization of organic matter, and analytical quantification of selected regulated and emerging DBPs. The water treatment train consisted of coagulation, sand filtration, chlorination, addition of lime and fluoride, storage, and chloramination. Nonspecific toxicity peaked midway through the treatment train after the chlorination and storage steps. The dissolved organic matter concentration decreased after the coagulation step and then essentially remained constant during the treatment train. Concentrations of AOXs increased upon initial chlorination and continued to increase through the plant, probably due to increased chlorine contact time. Most of the quantified DBPs followed a trend similar to that of AOXs, with maximum concentrations observed in the final treated water after chloramination. The mostly chlorinated and brominated DBPs formed during treatment also caused reactive toxicity to increase after chlorination. Both genotoxicity with and without metabolic activation and the induction of the oxidative stress response pathway showed the same pattern as the nonspecific toxicity, with a maximum activity midway through the treatment train. Although measured effects cannot be directly translated to adverse health outcomes, this study demonstrates the applicability of bioanalytical tools to investigate DBP formation in a drinking water treatment plant, despite bioassays and sample preparation not yet being optimized for volatile DBPs. As such, the bioassays are useful as monitoring tools as they provide sensitive responses even at low DBP levels.     

离子色谱法同时测定饮用水中5种消毒副产物的不确定度评定

目的 评定离子色谱法同时测定饮用水中5种消毒副产物含量的不确定度。方法 按照GB/T 5750.10-2006《生活饮用水标准检验方法消毒副产物指标》进行饮用水中溴酸盐、二氯乙酸、三氯乙酸、亚氯酸盐、氯酸盐含量的测定。应用测量不确定度评定理论, 分析测量不确定度的来源并对各分量进行不确定度评定, 计算合成标准不确定度和绝对扩展不确定度, 明确对测试结果有重要影响的分量。结果 在95%的置信区间内, 样品中5种消毒副产物溴酸盐、二氯乙酸、三氯乙酸、亚氯酸盐和氯酸盐的含量依次为(2.00±0.075)、(2.04±0.062)、(0.99±0.054)、(12.6±0.35)、(9.41±0.24) mg/L (k = 2)。结论 影响测量不确定度的主要因素是曲线拟合产生的不确定度和由标准溶液引入的不确定度。实验中应该提高标准溶液配制的准确性和标准曲线测定的精密度。     

饮用水中交链孢霉毒素氯消毒副产物鉴定及其毒性作用评价

目的 研究水中交链孢菌酮酸(TeA)和腾毒素(TEN)在氯消毒过程中的反应动力学特征,对产生的氯消毒副产物(DBPs)进行结构鉴定,并对其消毒副产物的细胞毒性进行初步探索。方法 本研究通过实验室模拟其消毒反应过程,研究其反应动力学特征,利用超高效液相色谱-串联四级杆飞行时间质谱(UPLC-Q-TOF/MS)和核磁共振波谱对反应产物进行结构鉴定并初步评价其毒性。结果 TeA氯消毒反应可生成2种氯消毒副产物DBP-188和DBP-240,而TEN氯代反应很慢未观察到氯消毒副产物的产生。反应动力学试验表明TEN与氯的反应速率随着反应体系中氯浓度和pH值的增加而升高。体外毒性预测分析发现TeA的氯消毒副产物经口毒性、发育毒性和致癌性均高于母体。结论 交链孢霉毒素经过氯消毒会产生氯消毒副产物,反应过程受pH值与氯浓度的影响,氯消毒副产物的预测毒性高于母体,细胞试验证明了TeA氯消毒副产物具有一定的细胞毒性。     

顶空-气相色谱法测定5种挥发性消毒副产物在饮用水加热前后的含量变化

目的建立顶空气相色谱法测定生活饮用水在加热前后5种挥发性消毒副产物三氯甲烷、四氯化碳、一溴二氯甲烷、二溴一氯甲烷、三溴甲烷含量的变化。方法取出厂水、末梢水、煮沸的开水、敞口持续煮沸1 min的开水各10 mL于顶空瓶中70℃顶空平衡15 min,取上层气体进样进行气相色谱分析, HP-5毛细管色谱柱分离,电子捕获检测器检测,外标法定量。结果 5种挥发性消毒副产物在不同的浓度下线性关系良好,相关系数为0.9992～0.9996;加标回收率为83.3%～101.8%。其中三氯甲烷在4种样品中检出浓度为0.717～44.9μg/L;四氯化碳、一溴二氯甲烷、二溴一氯甲烷均有不同程度检出,三溴甲烷均未检出。结论经过氯化消毒的自来水煮沸后,挥发性消毒副产物含量大幅降低,其中以开盖持续煮沸1min的开水中含量最低,因此建议饮用自来水需要提前煮沸。     

Development and interpretation of disinfection byproduct formation models using the Information Collection Rule database

Multiple linear regression models were used to examine relationships between water quality, treatment, and disinfection byproduct (DBP) formation in Information Collection Rule field data. Finished water models were specified using a cross-validation approach based on data for 225 free chlorine treatment plants. Turbidity, bromide, temperature, alkalinity, total organic carbon, ultraviolet absorbance at 254 nm, pH, chlorine residual, chlorine consumed, and chlorine contact time were employed as independent variables. Important trends within the trihalomethane, dihaloacetic acid, and trihaloacetic acid classes were observed. Bromide was a significant predictor for all DBP species and its influence changed in sign and magnitude with the extent of bromine substitution. A similar pattern followed by alkalinity suggested it plays an important role as an indicator of natural organic matter hydrophobicity and reactivity. Chlorine consumed and organic precursor variables were significant predictors in almost all DBP species models, exhibiting trends opposite to those for alkalinity and bromide. Temperature was the most significant variable in chloroform and chloral hydrate models and its significance declined with increasing bromine substitution within the trihalomethane class. pH had a strong positive influence on chloroform formation, a negative influence on trihaloacetic acid formation, and no influence on dihaloacetic acid formation.     

Reduction of disinfection byproduct formation by molecular reconfiguration of the fulvic constituents of natural background organic matter

Experiments were performed to assess the effects of treating the fulvic acid fractions of background natural organic matter (NOM) by catalyst-induced oxidative coupling reactions. Changes in the molecular characteristics of the fulvic acids and related disinfection byproduct formation potentials of these important NOM constituents were investigated. The coupling reactions were induced by addition of horseradish peroxidase (HRP) and hydrogen peroxide to aqueous solutions of the fulvic acids (FAs) in semicontinuous flow reactors. Subsequent removal of organic matter by ultrafiltration was found to be markedly enhanced for FA solutions subjected to oxidative coupling treatment. Uniform formation condition tests further indicated that the disinfection byproducts formed upon chlorination of FAs treated via induced oxidative coupling were reduced significantly on a unit carbon basis relative to those formed upon chlorination of their untreated counterparts. Spectroscopic examinations revealed thatthe FA molecules were effectively reconfigured in the oxidative coupling reactions. Substantial conversion of aromatic hydroxyl groups into ether-bonded moieties is evident, and a loss of primary amine groups, probably through conversion into secondary or tertiary amines, was also observed. These conversions apparently result in cross-linking of the natural FA moieties to form stable species of larger sizes, thus rendering them more readily removable by ultrafiltration and less reactive with chlorine. The results of the study may be interpreted as indicating that catalytically induced oxidative coupling reactions of the type conducted in this work can be combined with ultrafiltration to provide an effective scheme for removal of disinfection byproduct precursors.     

Effects of acid stress on Vibrio parahaemolyticus survival and cytotoxicity

For several foodborne bacterial pathogens, an acid tolerance response appears to be an important strategy for counteracting acid stress imposed either during food processing or by the human host. The acid tolerance response enhances bacterial survival of lethal acid challenge following prior exposure to sublethal acidic conditions. Previous studies have revealed relationships between a foodborne pathogen's ability to survive acid challenge and its infectious dose. Vibrio parahaemolyticus is capable of causing gastroenteritis when sufficient cells of pathogenic strains are consumed. This study was designed to characterize acid sensitivities and to compare the effects of sublethal acid exposure (adaptation) on survival capabilities and cytotoxicities of different V. parahaemolyticus strains. Survival of acid challenge by stationary-phase cells differed by up to 3 log CFU/ml among the 25 isolates tested. No differences in acid resistance were found between strains when they were grouped by source (clinical isolates versus those obtained from food). Survival at pH 3.6 for log-phase cells that had been previously exposed to sublethal acidic conditions (pH 5.5) was enhanced compared with that for cells not previously exposed to pH 5.5. However, for stationary-phase cells, exposure to pH 5.5 impaired both subsequent survival at pH 3.6 and cytotoxicity to human epithelial cells. Relative cytotoxicities of nonadapted stationary-phase cells were 1.2- to 4.8-fold higher than those of adapted cells. Sublethal acid exposure appears to impose measurable growth phase-dependent effects on subsequent lethal acid challenge survival and cytotoxicity of V. parahaemolyticus.     

Watershed sources of disinfection byproduct precursors in the Sacramento and San Joaquin Rivers, California

High levels of dissolved organic carbon (DOC) and bromide (Br) in the Sacramento and San Joaquin River waterways are of concern because DOC and Br are organic and inorganic precursors, respectively, of carcinogenic and mutagenic disinfection byproducts (DBPs). The Sacramento and San Joaquin Rivers are the two major rivers supplying water to the San Francisco Bay Delta, but sources and loads of DBP precursors into the Delta are still uncertain. The major objectives of this study were to evaluate both the quantity (DOC and Br fluxes) and the quality (reactivity in forming DBPs) of DBP precursors from the Sacramento and San Joaquin watersheds. Water samples were collected every 2 weeks at up to 35 locations along the Sacramento and San Joaquin Rivers and selected tributaries and analyzed for DOC (4 years), Br (1 year), and ultraviolet absorbance at 254 nm (1 year). Selected water samples were also tested for THM formation potential. Estimated fluxes for the Sacramento River were 39 000 +/- 12 000 Mg DOC year(-1) and 59 Mg of Br year(-1) as compared to 9000 +/- 5000 Mg of DOC year(-1) and 1302 Mg of Br year(-1) for the San Joaquin River. The THM formation potential was higher in the San Joaquin River (441 +/- 49 microg L(-1)) than the Sacramento River (176 +/- 20 microg L(-1)) because of higher concentrations of both organic (DOC = 3.62 +/- 0.14 vs 1.92 +/- 0.09 mg L(-1)) and inorganic DBP (Br = 0.80 +/- 0.07 vs < 0.03 +/- 0.01 mg L(-1)) precursors. The Sacramento River's greater DOC load despite lower DOC concentrations is due to its discharge being about 5 times greater than the San Joaquin River (50 x 10(9) vs 10 x 10(9) L day(-1)). The DOC concentration was significantly correlated with several land-cover types, including agriculture; however, no relationship was found between DOC quality and land-cover at the watershed scale.