A New Group of Disinfection Byproducts in Drinking Water: Trihalo

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A New Group of Disinfection Byproducts in Drinking Water: Trihalo-hydroxy-cyclopentene-diones Yang Pan, Wenbin Li, Aimin Li, Qing Zhou, Peng Shi, and Ying Wang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00798 • Publication Date (Web): 10 Jun 2016 Downloaded from http://pubs.acs.org on June 23, 2016

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State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China S

Supporting Information

Abstract: We report the detection, synthesis, A new group of drinking water DBPs: trihalo-hydroxy-cyclopentene-diones SRNOM + Br + Cl / NH Cl trihalo-HCDs preparative isolation, structure characterization/identification, and formation of a new group of drinking water 100 180.9191.1 213.0 222.9 253.3258.9260.8 281.1 302.7306.8 339.1 347.0 353.2 379.2 0 m/z disinfection byproducts (DBPs) ― 180 200 220 240 260 280 300 320 340 360 380 precursor-to-Br molar ratio of 1:8 + Br tribromo-HCD 8 h, 20 ºC trihalo-hydroxy-cyclopentene-diones FTIR characterization Preparative isolation (trihalo-HCDs). With ultra performance liquid chromatography (UPLC)/electrospray ionization-triple quadruple mass spectrometry analyses (full scans, multiple reaction monitoring, and product ion scans) and high resolution mass spectrometry analyses (full scans), the new group of DBPs was identified with formulae and proposed with structures. However, due to lack of commercially available standard compounds, structure identification of this new group of DBPs was challenging. 2,4,6-Trihydroxybenzaldehyde was found to be a good precursor for the synthesis of the tribromo species (m/z 345/347/349/351) in the new group of DBPs by reacting with bromine at a 2,4,6-trihydroxybenzaldehyde-to-bromine molar ratio of 1:8. With UPLC/Photodiode Array analysis (simultaneous 2- and 3-dimensional operations), the new DBP was determined to have a maximum UV absorption at the wavelength of 280 nm. Through isolation with high performance liquid chromatography/UV-triggered collections followed by lyophilization, the pure standard of the new DBP was obtained. Characterized with Fourier Transformation Infrared Spectroscopy, the pure standard of the new DBP was finally identified to be tribromo-HCD, and thus the new group of DBPs was identified to be trihalo-HCDs. Based on the disclosed structure, formation pathways of tribromo-HCD through reactions of three different precursors and bromine were proposed and partially verified. Moreover, increasing the bromide level in source water shifted the formation of trihalo-HCDs from being more chlorinated to being more brominated; with the increasing contact time from 1 h to 5 d, the formation of trihalo-HCDs kept increasing in chloramination, whereas kept decreasing in chlorination; with the increasing pH from 6.0 to 8.5, the formation of trihalo-HCDs was decreased by ~ 80%. Notably, the concentrations of tribromo-HCD in eight Chinese tap water samples were from below detection limit to 0.53 µg/L. –

16 17 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

O-

Br

O

O

O

O

Br Br

Br Br

CHO OH

2

2

OH

100

16.63

2.5e-1

5.22 8.33

0.0

18

O-

Cl

O

Br Cl

Cl Cl

HO

15

2

O-

O

O

O

2

Cl

24.72

29.12

20.00

40.00

Time

50

0 4000

693.4 606.3

14

O-

%

13

Water:

Yang Pan,* Wenbin Li, Aimin Li,* Qing Zhou, Peng Shi, and Ying Wang

Cl

12

Drinking

1752.3 1710.0

11

in

1604.0

10

Byproducts

3443.5

9

A New Group of Disinfection Trihalo-hydroxy-cyclopentene-diones

% Transmittance

1 2 3 4 5 6 7 8

Environmental Science & Technology

3000 2000 1000 Wavenumbers (1/cm)

1

ACS Paragon Plus Environment


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39

INTRODUCTION

40

Drinking water disinfection is regarded as a significant public health advance in the 20th

41

century,1 which has prevented numerous people from being infected by cholera, typhoid,

42

dysentery, etc.2,3 However, disinfection processes can unintentionally generate disinfection

43

byproducts (DBPs) through reactions of disinfectants (e.g., chlorine, chloramines, chlorine

44

dioxide, ozone, etc.), natural organic matter, anthropogenic contaminants, and halides.4

45

In the 40 years of research, around 600−700 halogenated DBPs have been reported in

46

drinking water,5−8 however, only several of them are under routine monitoring and regulation.9,10

47

A few toxicological and epidemiological studies have pointed out that it is unlikely for the

48

currently regulated DBPs to fully account for the toxicity effects and increased bladder cancer

49

risks resulted from consumption of chlorinated drinking water.4,11,12 Actually, a majority of total

50

organic halogen (TOX) produced in drinking water chlorination has not been well characterized,

51

and the percentages of unknown TOX produced in drinking water treated with other disinfectants

52

were even higher.13,14 Since the unknown part of TOX might contain substantial amounts of toxic

53

compounds as suggested by epidemiological studies,11,15 further exploration of unknown drinking

54

water halogenated DBPs should be of paramount importance.

55

Recently, halogenated DBPs with cyclic structures (including halogenated pyrroles,

56

benzoquinones, hydroxybenzaldehydes, hydroxybenzoic acids, and phenols) have been attracting

57

increasing concerns due to their higher cytotoxicity, genotoxicity, growth inhibition, and

58

developmental toxicity than those with chain structures.16−22 More recently, a group of highly

59

abundant halogenated DBPs was detected in drinking water and chlorinated ballast water, which

60

was tentatively proposed to be trihalo-furoic acids or their trihalo-hydroxy-cyclopentene-diones

61

(trihalo-HCDs) analogues.23−26 This new group of DBPs appeared to have high reactivity as they 2


Page 3 of 27


62

readily decomposed to trihalomethanes and haloacetic acids with an excess of free chlorine.24

63

Thus, they deserved great concern and might be toxicological important.25 However, due to

64

multiple isomers of their molecular formulae and lack of commercially available standard

65

compounds, structure characterization/identification of the new group of DBPs has been impeded.

66

As a result, their formation during various disinfection processes remained unclear.

67

With improving sensitivity, resolution, and separation efficiency, ultra performance liquid

68

chromatography (UPLC) becomes increasingly accepted by chromatographers/researchers.

69

Coupled by electrospray ionization-triple quadruple mass spectrometry (ESI-tqMS), the

70

UPLC/ESI-tqMS has been applied in detection of new DBPs in drinking water.23,24,27,28 Further

71

aided with high resolution MS, accurate molecular formulae of the detected new DBPs could be

72

assigned,25,26,29,30 which could provide important information for structure proposing. Since

73

standard compounds of some new DBPs with proposed structures are not commercially available,

74

they are required to be synthesized and isolated to a sufficient amount in the lab to facilitate

75

structure characterization/identification. Thus, the Waters AutoPurificationTM System should be

76

an ideal choice for preparative isolation of these new DBPs through high performance liquid

77

chromatography (HPLC)/UV-triggered collections, which can provide selective UV-directed

78

fraction collection from multiple samples automatically and reliably.

79

In this study, we report a new group of drinking water halogenated DBPs with cyclic

80

structures, trihalo-HCDs, with focuses on the following aspects: (1) detection, formula

81

identification, and structure proposing; (2) synthesis, preparative isolation, and structure

82

characterization/identification; (3) formation under various disinfection processes.

83 84

MATERIALS AND METHODS 3



85

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Materials. Suwannee River natural organic matter (SRNOM, 2R101N) was provided by the

86

International

87

1,2,4-trihydroxybenzene (99%) were provided by Sigma-Aldrich. 3,4,5-Trihydroxybenzaldehyde

88

(98%)

89

2,4,6-Trihydroxybenzaldehyde (>98%) was purchased from TCI. A NaOCl solution (~ 3000

90

mg/L as Cl2) was prepared by diluting a concentrated NaOCl solution (4.00−4.99% available

91

chlorine, reagent grade, Sigma-Aldrich) and titrated using a standard procedure.31 NH2Cl was

92

freshly prepared before use via a reaction between NaOCl and NH4Cl at an ammonia-to-chlorine

93

molar ratio of 1.25. Organic solvents (methyl tert-butyl ether, acetonitrile, and methanol) at

94

HPLC grade and other chemicals at reagent grade were all provided by Sigma-Aldrich and

95

Merck.

and

Humic

bromine

Substances

(99.5%)

Society.

were

1,2,3-Trihydroxybenzene

purchased

from

J&K

(97%)

and

Chemical.

96

Preparation of Simulated Drinking Water Samples and Collection of Real Tap Water Samples.

97

A series of simulated source water samples were prepared by adding SRNOM (3 mg/L as C),

98

NaHCO3 (90 mg/L as CaCO3), and different levels (0, 0.1, 0.4, 1.0, 2.0, and 4.0 mg/L as Br−) of

99

KBr in ultrapure water. For preparation of simulated drinking water samples, the simulated

100

source water samples were dosed with NH2Cl or NaOCl (5 mg/L as Cl2) at different pH values

101

(6.0, 6.5, 7.5, and 8.5), and kept without headspace in darkness at ~ 20 ºC for various contact

102

times (1, 24, and 120 h). The residual disinfectants in the samples were quenched with a 5%

103

excess of required amounts of Na2SO3.

104

As described later, a new group of DBPs was detected and identified to be trihalo-HCDs in

105

the simulated drinking water samples, and thus factors (including bromide level in source water,

106

disinfectant type, contact time, and pH) that may affect their formation during disinfection were

107

examined with batch experiments. A baseline simulated drinking water sample was defined as: a

108

1 L portion of the simulated source water sample containing 0.4 mg/L KBr as Br− (pH 7.5) was 4


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109

chloraminated by dosing 5 mg/L NH2Cl as Cl2 for 120 h. In each batch experiment, one factor

110

was changed at a time and all other factors were kept the same as those of the baseline sample.

111

Moreover, eight real tap water samples (coded as A–H) were collected from drinking water

112

treatment plants in eight different cities of East China in May 2016. Upon collection of these

113

samples onsite, pH was measured to be from 7.2 to 7.7; disinfectant residuals were determined to

114

be all in the form of free chlorine at concentrations from 0.4 to 1.1 mg/L, which were

115

immediately quenched by 105% of the required amounts of Na2SO3. All the samples were put in

116

an ice bath during transportation by car to the lab, and kept refrigerated (~ 4 ºC) till pretreatment.

117

Pretreatment of Simulated Drinking Water Samples and Real Tap Water Samples.

118

Pretreatment of the simulated drinking water samples and the real tap water samples followed

119

previously reported steps.24 Generally, each 1 L of the water sample was added with diluted

120

H2SO4 (70% v/v) drop by drop with vigorous stirring to pH 0.5 and added with Na2SO4 till

121

saturation. Then, 100 mL methyl tert-butyl ether was mixed with the sample in a 2 L separation

122

funnel for extraction of organics. About 15 min later, the upper layer (~ 75 mL) was moved to a

123

250 mL flask and evaporated at 27 ºC to 1 mL. The 1 mL concentrate was dissolved in 10 mL

124

acetonitrile, which was further concentrated to 0.5 mL. Finally, the 0.5 mL solution was dosed

125

with 0.5 mL ultrapure water and all insoluble substances inside were removed by a 0.45 µm

126

filter.

127

UPLC/ESI-tqMS Analysis. An Acquity UPLC system coupled to a Xevo ESI-tqMS

128

(UPLC/ESI-tqMS, Waters) was employed for analysis of the pretreated samples. The sample

129

injection volume in the UPLC was 5 µL. An Acquity UPLC HSS T3 column (1.8 µm particle

130

size, 2.1×100 mm, Waters) was used for chromatographic separation. A gradient eluent applied at

131

0.4 mL/min was composed of water/methanol, and its composition (v/v) was linearly changed

132

from 95/5 to 10/90 in the initial 8 min, brought back to 95/5 within 0.1 min, and kept stable at 5



Page 6 of 27

133

95/5 for another 2.9 min. The parameters of MS were as follows: capillary voltage, 2.8 kV;

134

desolvation temperature, 400 ºC; source temperature, 110 ºC; desolvation gas flow, 800 L/h;

135

cone gas flow, 50 L/h; cone voltage, 20 V; collision energy, 30 eV; collision gas (Ar) flow, 0.25

136

mL/min.

137

High Resolution MS Analysis. To assign exact molecular formulae of the new group of DBPs,

138

a high resolution MS analysis was conducted with a Hybrid Ion Trap-Orbitrap mass spectrometer

139

(LTQ Orbitrap XL, Thermo Fisher Scientific) through accurate m/z value measurement. The

140

instrument with a heated electrospray interface was set in negative ionization mode, and the

141

parameters were set as: capillary voltage, −10 V; spray voltage, 4 kV; tube lens voltage, −40 V;

142

capillary temperature, 275 ºC; auxiliary gas, 15 au; sheath gas, 45 au; sweeping gas, 0 au.

143

Synthesis of the New DBP with m/z 345/347/349/351. Due to lack of the commercially

144

available standard compound, synthesis of the new DBP with m/z 345/347/349/351 was

145

performed in the lab via the reaction of “precursor + bromine” for its preparative isolation and

146

structure characterization/identification. Four precursors were selected for reaction with bromine,

147

including 1,2,3-trihydroxybenzene, 1,2,4-trihydroxybenzene, 3,4,5-trihydroxybenzaldehyde, and

148

2,4,6-trihydroxybenzaldehyde. A series of solutions containing 40 mg/L of a precursor

149

compound were dosed with bromine at precursor-to-bromine molar ratios of 1:2, 1:4, 1:6, 1:8,

150

1:12, and 1:20, and kept reaction in darkness at ~ 20 ºC for 8 h. The bromine residuals were

151

quenched with a 5% excess of required Na2SO3. Then, pretreatment of the reaction solutions was

152

conducted using the same method as that of the simulated drinking water samples.

153

UPLC/PDA Analysis of the New DBP with m/z 345/347/349/351. UPLC/Photodiode Array

154

(PDA) analysis of the new DBP was carried out with the UPLC system coupled to a Waters

155

Acquity PDA detector. Simultaneous 2- and 3-dimensional operations were applied at a scan 6


Page 7 of 27


156

wavelength range of 220 to 350 nm, suggesting that all UV absorbance values from 220 to 350

157

nm of the new DBP separated by the UPLC at a specific retention time (RT) were recorded. In

158

this way, the wavelength at which the new DBP had the maximum UV absorption was obtained.

159

Preparative Isolation and Structure Characterization/Identification of the New DBP with m/z

160

345/347/349/351. HPLC/UV-triggered preparative isolation of the new DBP was carried out using

161

the Waters AutoPurificationTM System with a Waters 2489 UV/Visible detector. A Waters Atlantis

162

T3 OBD Prep column (5 µm particle size, 19×100 mm) was used for the preparative HPLC

163

separation. To maintain selectivity and separation resolution in the preparative separation as

164

those achieved in the analytical analysis, inlet method of the preparative HPLC was migrated

165

from the analytical UPLC according to the approach provided by Waters Corporation.32 The

166

sample volume for each HPLC injection was 614 µL. The gradient eluent composed of

167

water/methanol (v/v) was applied at 11.8 mL/min, and the composition was changed linearly

168

from 95/5 to10/90 in the first 33.3 min, followed by a change to 95/5 within 0.5 min, and this

169

composition was kept by another 12 min for column re-equilibration. Elution of the new DBP

170

from the preparative column was monitored by UV detection and fraction collection was

171

triggered based on the UV absorbance value at the specific wavelength. The collected fractions

172

of the new DBP from multiple injections were combined to a total volume of 1 L in a single glass

173

vessel, which was analyzed with the UPLC/ESI-tqMS full scan to verify its purity and

174

subsequently reduced to dryness using lyophilization at 5 Pa and –50 ºC for 48 h. The obtained

175

pure standard was characterized by Fourier Transformation Infrared Spectroscopy (FTIR) to

176

determine its main functional groups and structure framework. FTIR analysis of the new DBP

177

was performed by an FTIR spectrometer (Nicolet Nexus 870) with omni sampler in ATR mode,

178

with a scan range between 4000 and 400 cm–1 for 32 scans (resolution: 4 cm−1).

179 7



180

Page 8 of 27

RESULTS AND DISCUSSION

181

Detection, Formula Identification, and Structure Proposing of A New Group of Drinking

182

Water DBPs. Figure 1a shows the UPLC/ESI-tqMS full scan chromatogram of the baseline

183

simulated drinking water sample. The peaks detected from RT 0.5 to 1.0 min and from RT 7.8 to

184

8.5 min should correspond to three dihalo-acetic acids (i.e., dichloroacetic acid,

185

chlorobromoacetic

186

(2,6-dibromo-4-chlorophenol and 2,4,6-tribromophenol), respectively (Figure S1).28 Notably,

187

several dominant peaks were partially overlapped and detected from RT 2.7 to 3.1 min. In their

188

corresponding full scan spectrum, four major ion clusters m/z 213/215/217/219 (isotopic

189

abundance

190

301/303/305/307 (isotopic abundance ratio: 3:7:5:1), and 345/347/349/351 (isotopic abundance

191

ratio: 1:3:3:1) were observed (Figure 1b). The isotopic abundance ratios of the four ion clusters

192

suggested that they should contain 3 Cl, 2 Cl 1 Br, 1 Cl 2 Br, and 3 Br in their structures,

193

respectively. As displayed in Figure 1c−f, RTs of the four ion clusters were 2.74, 2.87, 2.90, and

194

2.98 min, respectively, suggesting that they were not aliphatic (since RTs of aliphatic compounds

195

should be in the domain of 0–2.5 min under the aforementioned UPLC settings).23 In the product

196

ion scan spectra of ion cluster m/z 345/347/349/351 (Figure 1g−j): a loss of 28 indicated the

197

presence of a carbonyl group; a loss of 44 indicated that a CO2 fraction could be lost from the

198

molecular ion. The fragmentation pathways of ion clusters m/z 213/215/217/219,

199

257/259/261/263, and 301/303/305/307 in their product ion scans were similar to that of ion

200

cluster m/z 345/347/349/351. Based on the closely related m/z values, isotopic abundance ratios,

201

RTs, and fragmentation pathways of the four ion clusters, we believed that they should belong to

202

a group of DBP analogues with the same main structure and different combinations of Cl and Br

ratio:

acid,

and

3:3:1:0.1),

dibromoacetic

257/259/261/263

acid)

(isotopic

and

two

abundance

trihalo-phenols

ratio:

9:15:7:1),

8


Page 9 of 27


203

substitutions. In a recent study, compounds with m/z 257/259/261/263, 301/303/305/307, and

204

345/347/349/351 were detected in a chlorinated simulated drinking water sample, and the one

205

with m/z 345/347/349/351 was suspected to be tribromo-HCD.24 More recently, Gonsior et al.

206

reported the detection of compounds with m/z 213/215/217/219, 257/259/261/263, and

207

301/303/305/307 (proposed to be either trihalo-furoic acids or trihalo-HCDs) in a Swedish

208

chlorinated drinking water,25 and a highly abundant compound with m/z 345/347/349/351

209

(proposed to be tribromo-HCD) in chlorinated ballast water.26 However, due to lack of

210

commercially available standard compounds, structure identification of this new group of DBPs

211

remained to be an unsettled problem in these previous studies.

212

Formulae identification was an important step towards revealing the structures of the new

213

group of DBPs, which was accomplished by a high resolution MS analysis of the four ion

214

clusters for obtaining their accurate m/z values. As displayed in Figure 2, the accurate m/z values

215

of the four ion clusters were determined to be 212.8914/214.8884/216.8854/219.1017,

216

256.8408/258.8384/260.8357/262.8327,

217

344.7394/346.7374/348.7354/350.7332, respectively. Calculated with a built-in formula

218

predictor software (m/z value shift within ± 1 ppm), the corresponding molecular ion formulae of

219

the four ion clusters were C5O3Cl3−, C5O3Cl2Br−, C5O3ClBr2−, and C5O3Br3−, with m/z value

220

shifts of 0.65, 0.56, 0.58, and 0.19 ppm, respectively.

221

300.7903/302.7881/304.7858/306.7832,

and

According to the RTs, fragmentation pathways, and molecular formulae of the new group of

222

DBPs,

their

possible

structures

could

only be

trihalo-furoic

acids,

trihalo-HCDs,

223

trihalo-methylfurandiones, trihalo-hydroxypyranones, or trihalo-cyclopentane-triones.

224

Synthesis of the New DBP with m/z 345/347/349/351. For the purpose of structure

225

identification, the standard compound of the new DBP with m/z 345/347/349/351 was aimed to 9



be

227

trichloro-5-methoxy-4-cyclopentene-1,3-dione

228

3,5-dimethoxy-4-hydroxybenzaldehyde with NaOCl; Zhai et al.24 reported that the compound

229

with

230

1,2,3-trihydroxybenzene/1,2,4-trihydroxybenzene with bromine. Based on the above reaction

231

pathways,

232

3,4,5-trihydroxybenzaldehyde, and 2,4,6-trihydroxybenzaldehyde) were selected for reacting

233

with bromine at various precursor-to-bromine molar ratios to optimize synthesis conditions of

234

the new DBP. As illustrated in Figure 3a−f, among the four precursors, 1,2,3-trihydroxybenzene,

235

3,4,5-trihydroxybenzaldehyde, and 2,4,6-trihydroxybenzaldehyde could react with bromine to

236

generate the same compound as that (the new DBP with m/z 345/347/349/351) formed in the

237

simulated

238

2,4,6-trihydroxybenzaldehyde

239

2,4,6-trihydroxybenzaldehyde was selected to react with bromine for the synthesis of the new

240

DBP. As shown in Figure 3g−l, with the increasing bromine dose in the reaction of

241

“2,4,6-trihydroxybenzaldehyde

242

345/347/349/351 (detected at UPLC RT 3.65 min) exhibited a trend of first increasing and then

243

decreasing, peaking at a 2,4,6-trihydroxybenzaldehyde-to-bromine molar ratio of 1:8; moreover,

244

at the molar ratio of 1:8, the peak at UPLC RT 3.65 min contained the pure compound of the new

245

DBP with m/z 345/347/349/351 (impurities were hardly detected). Accordingly, the pretreated

246

reaction

247

2,4,6-trihydroxybenzaldehyde-to-bromine molar ratio of 1:8 was used for preparative isolation of

248

the new DBP with m/z 345/347/349/351.

m/z

in

the

lab.

Gong

345/347/349/351

four

solution

of

water

was

the

synthesis

be

compared

proved

bromine”,

to

generated

the

a

higher

formation

“2,4,6-trihydroxybenzaldehyde

of

+

by

reacting

1,2,4-trihydroxybenzene,

with

have

of

reacting

(1,2,3-trihydroxybenzene,

sample;

+

reported by

could

precursors

drinking

et

al.33

226

249

synthesized

Page 10 of 27

the

new

bromine”

other

precursors,

yield.

Therefore,

DBP with

prepared

at

m/z

the

Preparative Isolation and Structure Characterization/Identification of the New DBP with m/z 10


Page 11 of 27


250

345/347/349/351. Under the optimized condition, a reaction solution was prepared and pretreated

251

for isolation of the new DBP with m/z 345/347/349/351 (Figure 4a). Prior to HPLC/UV-triggered

252

preparative isolation, the new DBP was determined to have a maximum UV absorption at the UV

253

wavelength of 280 nm by UPLC/PDA analysis (simultaneous 2- and 3-dimensional operations)

254

(Figure 4b). When analyzing the pretreated reaction solution of “2,4,6-trihydroxybenzaldehyde +

255

bromine” with the UPLC/PDA at 280 nm, a very intensive peak corresponding to the new DBP

256

with m/z 345/347/349/351 was detected at RT 3.37 min (Figure 4c). For larger-scale isolation of

257

the new DBP with m/z 345/347/349/351, inlet method migration from the analytical UPLC to the

258

preparative HPLC was performed. As can be seen in Figure 4d, by applying the migrated inlet

259

method, acceptable and reproducible preparative separations were achieved by the Waters

260

Atlantis T3 OBD Prep column, and the obtained HPLC/UV chromatogram was very similar to

261

the UPLC/PDA chromatogram (Figure 4c) in terms of selectivity and resolution (regardless of

262

scales). Fraction collection was set up using FractionLynxTM Application Manager and the peak

263

corresponding to the new DBP with m/z 345/347/349/351 (at HPLC RT 16.63 min) was collected

264

(triggered by UV absorbance). After multiple HPLC injections, the collected fractions from all

265

separations were combined in a vessel to a final volume of 1 L, and the purity of the combined

266

solution was verified by the UPLC/ESI-tqMS full scan (Figure 4e). Then, the solution was

267

lyophilized to dryness under 5 Pa and –50 ºC for 48 h, and ~ 10 mg yellow solids of the new

268

DBP suitable for the FTIR characterization were obtained.

269

Figure 5 displays the FTIR spectrum of the new DBP. The broad peak at 3443.5 cm–1 should

270

be assigned to stretching vibration of O–H, suggesting that this DBP contains a hydroxyl group.

271

Two dominant characteristic peaks at 1710.0 and 1604.0 cm–1 should correspond to stretching

272

vibrations of C=O, indicating that this DBP contains two carbonyl groups. The peak at 1752.3 11



Page 12 of 27

273

cm–1 should correspond to stretching vibration of C=C. Several peaks corresponding to

274

stretching vibrations of C–Br were detected at wavenumbers between 600 to 700 cm–1.

275

According to above structural information provided by the FTIR spectrum, the previously

276

proposed structures of trihalo-furoic acids, trihalo-methylfurandiones, trihalo-hydroxypyranones,

277

and trihalo-cyclopentane-triones were excluded, and the new DBP with m/z 345/347/349/351

278

was finally identified to be tribromo-HCD. Logically, new DBPs with m/z 213/215/217/219,

279

257/259/261/263, and 301/303/305/307 should be trichloro-HCD, dichlorobromo-HCD, and

280

chlorodibromo-HCD, respectively.

281

Formation of the New Group of DBPs. Based on the disclosed structure, formation pathways

282

of tribromo-HCD through reactions of the three precursors (1,2,3-trihydroxybenzene,

283

3,4,5-trihydroxybenzaldehyde, and 2,4,6-trihydroxybenzaldehyde) and bromine were proposed

284

(shown in Figure 6), which were partially verified through the successful detection of proposed

285

intermediate compounds I, II, IV, VI, VII, VIII, and X using the UPLC/ESI-tqMS MRM

286

(displayed in Figure S2). Proposed intermediate compounds III, V, and IX were not detected

287

since they were unstable and might be quickly decarboxlyated/hydrolyzed. As illustrated in

288

Figure 6, the formation reactions started with bromine substitutions on the benzene rings of these

289

precursors, followed by multistep oxidation and hydrolysis. Since the 3- and 5-positions of

290

2,4,6-trihydroxybenzaldehyde were activated by both hydroxyl and aldehyde groups, bromine

291

substitutions

292

1,2,3-trihydroxybenzene and 3,4,5-trihydroxybenzaldehyde. Thus, the highest tribromo-HCD

293

yield was achieved by the reaction of 2,4,6-trihydroxybenzaldehyde and bromine, as

294

demonstrated in Figure 3.

295

on

2,4,6-trihydroxybenzaldehyde

were

much

easier

than

those

on

We further studied factors that may affect the formation of trihalo-HCDs during drinking 12


Page 13 of 27


296

water disinfection, including source water bromide level, disinfectant type, contact time, and pH.

297

In a UPLC/ESI-tqMS MRM chromatograph, the peak area of a DBP of a simulated drinking

298

water sample is positively correlated to its concentration.18

299

As displayed in Figure 7a, with the increasing bromide level from 0 to 4.0 mg/L, peak areas

300

of the four new DBPs exhibited diverse trends: trichloro-HCD kept decreasing; dichlorobromo-

301

and chlorodibromo-HCDs first increased and then decreased (reached maximum at the bromide

302

concentration of 0.4 mg/L); tribromo-HCD kept increasing. Moreover, as the bromide

303

concentration increased, initially the most dominant species was trichloro-HCD, which was

304

gradually taken over by the mixed-chlorobromo species, and finally tribromo-HCD became the

305

most abundant one. All these indicate that, increasing the bromide concentration shifted the

306

formation of trihalo-HCDs from being more chlorinated to being more brominated. Similar shifts

307

within a group of DBPs have been reported for trihalomethanes, haloacetic acids, and phenolic

308

halogenated DBPs,28,34,35 however, it is the first time that such kind of shift was proved to exist in

309

trihalo-HCDs. Figure 7b compares the formation of trihalo-HCDs in chloramination and

310

chlorination at contact times from 1 to 120 h. Basically, with the increasing contact time, the

311

peak areas of trihalo-HCDs kept increasing in chloramination, whereas kept decreasing in

312

chlorination. The formation of trihalo-HCDs was higher in chlorination than that in

313

chloramination with a short contact time (i.e., 1 h), whereas it became lower in chlorination than

314

that in chloramination as contact time further increased. This is because that, in chlorination,

315

trihalo-HCDs could be generated very quickly due to the strong oxidation ability of HOCl/OCl–,

316

however, the formed trihalo-HCDs were not stable and could be decomposed during prolonged

317

chlorination; in chloramination, although less trihalo-HCDs were produced with a relatively

318

short contact time, their accumulation with the increasing contact time was allowed since NH2Cl 13



Page 14 of 27

319

was a mild oxidant. As shown in Figure 7c, with the increasing pH from 6.0 to 8.5, peak areas of

320

trihalo-HCDs experienced a dramatic decrease by ~ 80%. The decrease of trihalo-HCDs with the

321

increasing pH might result from base-catalyzed hydrolysis, which matched previous findings that

322

most halogenated DBPs appeared to favor hydrolysis in alkaline conditions.36−38

323

Notably, occurrence of trihalo-HCDs was investigated in the real tap water samples A–H.

324

As shown in Figure S3, trichloro-HCD was the most prevalent species (detected in all the tap

325

water samples), whereas dichlorobromo-, chlorodibromo-, and tribromo-HCDs were detected in

326

six, seven, and five of the eight tap water samples, respectively. With the synthesized standard

327

compound, tribromo-HCD was further quantified in these tap water samples and the baseline

328

simulated drinking water sample using the standard addition method.28,38 The concentrations of

329

tribromo-HCD were from below detection limit to 0.53 µg/L in the real tap water samples and

330

3.94 µg/L in the baseline simulated drinking water sample. According to Figure 7, the

331

concentrations of tribromo-HCD should be even higher in simulated chloraminated drinking

332

water samples with higher bromide concentrations, longer contact times, and lower pH. Such

333

high levels of tribromo-HCD formed in the simulated drinking water samples and real tap water

334

samples suggested that, compared with other emerging drinking water halogenated DBPs with

335

cyclic structures (e.g., halogenated benzoquinones, hydroxybenzaldehydes, hydroxybenzoic

336

acids, and phenols), trihalo-HCDs might occur in drinking water at more abundant levels. 28,37

337

The

successful

detection,

synthesis,

preparative

isolation,

and

structure

338

characterization/identification of trihalo-HCDs provided a novel and effective approach for

339

exploring new DBPs (especially those without commercially available standards) in drinking

340

water. With UPLC/ESI-tqMS and high resolution MS analyses, an exact formula of a new DBP

341

could be assigned. Through optimization of synthesis condition, UPLC/PDA analysis, 14


Page 15 of 27


342

HPLC/UV-triggered preparative isolation, and lyophilization, a pure standard of the new DBP

343

could be obtained, which makes its structure characterization/identification possible by other

344

analytical techniques such as FTIR. Our findings also suggest that chloramination of source

345

water containing higher levels of bromide under less alkaline condition may enhance the

346

formation of trihalo-HCDs (especially the more brominated ones). Regarding the cyclic

347

structures and the high abundance in drinking water of trihalo-HCDs, further evaluation of their

348

toxicity (e.g., cytotoxicity, genotoxicity, developmental toxicity, etc.) should be important for

349

understanding their adverse health effects on human.

350 351

AUTHOR INFORMATION

352

Corresponding Authors

353

*(Pan, Y.) Phone: +86-25-83592903; fax: +86-25-83592903; e-mail: [email protected].

354

*(Li, A.) Phone: +86-25-89680576; fax: +86-25-86269876; email: [email protected].

355

Notes

356

The authors declare no competing financial interest.

357 358

ACKNOWLEDGEMENTS

359

We thank National Natural Science Foundation of China (Grants 51408296, 51290282,

360

51438008) and Natural Science Foundation of Jiangsu Province, China (Grant BK20140607) for

361

providing financial supports to this study. We also thank Prof. Xiangru Zhang from the Hong

362

Kong University of Science and Technology for his useful suggestions.

363 364

REFERENCES 15



365 366 367 368 369 370 371 372

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467

19



Page 20 of 27

468

0

2.50 O

5.00

O- Cl

Cl Cl

Cl

O

Cl

O O Br

1.41

0

3.51

2.50

349 345 351

3.05

0.90 1.45

0

2.50

300

350

m/z

5.535.88

7.47 8.07 9.31 10.15

5.00

7.50

10.00

7.50

347 79

266

143

240

187

345

0 −79 (79Br)

−79 (79Br)

−81 (81Br)

−81 (81Br)

−28 (CO)

268

81

10.00

270

145

189

305 −81 (81Br)

5.00

7.50

3.66

2.50

270

100 (j)

10.00

2.98 1.37

349 347

240 267

0 4.96

2.50

100 (f)

268

−81 (81Br)

1.30

0

−81 (81Br)

−44 (CO2)

2.90

100 (e)

−79 (79Br)

−79 (79Br) −28 (CO)

100 (i)

4.94 5.78 7.35

5.00

−81 (81Br)

−44 (CO2)

379

344 345 347 301

238 237

100 (h)

2.87

100 (d) %

O

−44 (CO2)

%

%

200 250 2.74 100 (c) 2.61

%

Br

%

% 0

%

O O Br

303 257 305 261 301 213 225 307 249 267 281

181

469 470 471 472 473 474

Br

345

−28 (CO)

187

0

O-

O- Br

143

79

Time

10.00

259

100 (b)

0

7.50

O- Cl

O Br

−44 (CO2)

%

6.67

4.54

−79 (79Br)

266 265

100 (g)

%

%

3.01

0.82

−79 (79Br)

8.48 8.37 7.88

100 (a)

81

5.14 6.32 7.22 8.18

5.00

7.50

10.00

Time

0

50

100

−28 (CO)

189 145

150

200

242 269

250

351 350 271 307 323 353

300

350

m/z 400

Figure 1. (a) UPLC/ESI-tqMS full scan chromatogram of the baseline simulated drinking water sample; (b) UPLC/ESI-tqMS full scan spectrum from RT 2.7 to 3.1 min of the baseline simulated drinking water sample; (c−f) UPLC/ESI-tqMS MRM chromatograms of ion clusters m/z 213/215/217/219, 257/259/261/263, 301/303/305/307, and 345/347/349/351, respectively; (g−j) UPLC/ESI-tqMS product ion scan spectra of ion cluster m/z 345/347/349/351.

20


Page 21 of 27


475 Relative Abundance Relative Abundance

100 50 40

(a)

C5O3Cl3− 218.8303 m/z shift: 0.65 ppm

214.8344 214.8884

212.8914

30 218.8710

20 216.8854 10

213.0764

215.1283

Relative Abundance

214

100

258.7321 256.8408

80 60

Relative Abundance

C5O3Cl2Br− m/z shift: 0.56 ppm

258.9241 260.8357

40 261.0761 20 256.9450

100

262.8327

259.8420

258

260

(c)

262

302.7881

C5O3ClBr2− m/z shift: 0.58 ppm

80

304.7858 60 300.7903 301.2378

40 20

302.9140 300

Relative Abundance

218

258.8384

256

302

(d)

304.9118 306.7832

304

346.7374

100

306

348.7354

C5O3Br3− m/z shift: 0.19 ppm

80 60 40

344.7394

20

350.7332

345.0970 344

476 477 478 479 480

216

(b)

219.1017

217.8356

346

347.7407 348 m/z

349.1283 350

Figure 2. (a−d) High resolution MS spectra of ion clusters m/z 213/215/217/219, 257/259/261/263, 301/303/305/307, and 345/347/349/351, respectively, in the baseline simulated drinking water sample.

21



Page 22 of 27

481

100 (c)

5.00

7.50 347

%

345 0 344 346

2.50

100 (d)

5.00 345

2.89 0 344

0

2.50

346

5.00

348

7.50

350

5.00

1.58

3.67 4.91

6.23

2.50

5.00

0.85

6.25

2.50

5.00

%

%

1.65

2.50

5.00

7.50

0

10.00

3.12

0

8.68200

400

m/z 600

10.00 349 345 351

0

8.67200

7.50

m/z 600

400

10.00

3.333.68

2.50

5.00

100 (l)

203

0

5.61 6.23

8.74200

7.50

349 400

m/z 600

10.00

100

%

%

%

100 (f)

349 345 351

100

0.83

8.26

m/z 600

400

10.00

100

4.93 5.60

1.55 2.44

100 (k) 5.96 6.55

8.66200

7.50

3.65

2.98 3.23

0

7.50

5.59

0.85

0

10.00

311 309 313 349

100

m/z 352

100 (e)

0

5.63 6.24

m/z 600

400

10.00

100

2.42

100 (j) 351

7.50

4.04

2.50

0

10.00 349

347

100

m/z 352

350

7.50 %

%

351 348

5.00

0.85

100 (i)

349

200 8.70

%

0

2.36

0

10.00

%

100

3.04

%

%

%

2.50

m/z 352

350

347 0

4.95

351

348

311

5.61

2.50

100 (h)

347

100

2.51

0.85

0

10.00 349

100

4.96

%

2.71

m/z 352

350

7.50

345 0 344 346

0

348

4.05

%

5.00

%

100 (b)

346

%

2.50

351

%

%

% 0

100 (g)

345

0 344

3.14

349

%

347

100

%

100 (a)

0

482 483 484 485 486 487 488 489 490 491 492 493 494

0.86 1.72

2.50

5.97 6.53

5.00

8.27

7.50

10.00

Time

0

0.65 1.77

205

3.37

2.50

0

8.68200

4.82 5.67

5.00

7.50

347 400

10.00

m/z 600

Time

Figure 3. (a−d) UPLC/ESI-tqMS MRM (345→79, 347→79/81, 349→79/81, 351→81) chromatograms and spectra (in dashed line boxes) of the pretreated reaction solutions of “1,2,3-trihydroxybenzene + bromine”, “1,2,4-trihydroxybenzene + bromine”, “3,4,5-trihydroxybenzaldehyde + bromine”, and “2,4,6-trihydroxybenzaldehyde + bromine”, respectively; (e,f) UPLC/ESI-tqMS MRM (345→79, 347→79/81, 349→79/81, 351→81) chromatograms of the baseline simulated drinking water sample and the baseline sample spiked with the pretreated reaction solution of “2,4,6-trihydroxybenzaldehyde + bromine”, respectively; (g−l) UPLC/ESI-tqMS full scan chromatograms and spectra (peak centered at RT 3.6 min, in dashed line boxes) of the pretreated “2,4,6-trihydroxybenzaldehyde + bromine” reaction solutions prepared at 2,4,6-trihydroxybenzaldehyde-to-bromine molar ratios of 1:2, 1:4, 1:6, 1:8, 1:12, and 1:20, respectively. The y-axes of charts (a−d), (e,f), and (g−l) are on the same scales, respectively.

22


Page 23 of 27


495 5.64 3.41

0.83 2.42

0

6.26

4.45

2.50

5.00

AU

5.96 0.77

10.00 280 281

220

5.0 (b)

0.0

7.07 8.67

7.50

5.63

2.39 3.37

2.50

5.00

AU

%

100 (a) 1.56

4.0e-3

341

2.0e-3 0.0

250

7.50

300

nm 350

10.00

AU

1.0e-2 (c) 3.37

0.77 2.39

0.0

2.50

5.0e-1 (d)

5.00

8.558.91

7.50

10.00

Time

AU

16.63

24.72

8.33

0.0

5.97

4.41

10.00

20.00

30.00

40.00 347

100

100 (e)

%

3.13

%

0

Time

345 351 200 8.77

400

m/z 600

0.74 2.11

0

496 497 498 499 500 501 502 503 504 505 506

2.50

5.00

7.50

10.00

Time

Figure 4. (a) UPLC/ESI-tqMS full scan spectrum of the pretreated reaction solution of “2,4,6-trihydroxybenzaldehyde + bromine”; (b) UPLC/PDA simultaneous 2- and3-dimensional scan (wavelength range: 220 to 350 nm) chromatogram and spectrum (peak at RT 3.37 min, in a dashed line box) of the pretreated reaction solution of “2,4,6-trihydroxybenzaldehyde + bromine”; (c) UPLC/PDA 2-dimensional scan (wavelength: 280 nm) chromatogram of the pretreated reaction solution of “2,4,6-trihydroxybenzaldehyde + bromine”; (d) HPLC/UV (wavelength: 280 nm) chromatogram of the pretreated reaction solution of “2,4,6-trihydroxybenzaldehyde + bromine”; (e) UPLC/ESI-tqMS full scan chromatogram and spectrum (peak at RT 3.13 min, in a dashed line box) of the isolated fractions.

23



Page 24 of 27

507 100

0 4000

508 509 510

1710.0

20

3000

2000 Wavenumbers (1/cm)

606.3 498.2

816.0 693.4

1604.0

1752.3

40

1372.2 1240.1 1122.2 1077.7

60 3443.5

%Transmittance

80

1000

Figure 5. FTIR spectrum of the new DBP with m/z 345/347/349/351.

24


Page 25 of 27


511 O

OH OH HOBr HO

OH HOBr HO

Br

Br

Br

HOBr

HO

OH

Br

OH

OH OH

HOBr

HO

CHO OH

HOBr

HO

OH

512 513 514 515 516

OH

Br H2O

Br

Br

HO

OH

O

OH

(Ⅴ)

(Ⅵ)

CHO HOOC Br OH H O HO OH HOBr HO 2

Br

Br OH (Ⅷ)

O OH Br OH –HCO2H Br O Br O Br

Br

Br O (Ⅸ)

OH O Br

(Ⅲ)

HOOC Br Br Br

(Ⅳ)

HO

Br

(Ⅱ)

CHO Br

HO

Br O

(Ⅰ)

CHO

OH HOBr HO

HOBr

OH HO

OH

Br

Br OH

Br

OH H2O HO

Br OH (Ⅶ)

Br OH (Ⅹ)

Figure 6. Proposed formation pathways of tribromo-HCD through reactions of the three precursors (1,2,3-trihydroxybenzene, 3,4,5-trihydroxybenzaldehyde, and 2,4,6-trihydroxybenzaldehyde) and bromine.

25



Page 26 of 27

517 4

10

(a)

3

Peak area

10

2

10

1

10

0

10

0 10

Peak area

10

0.1 0.4 1.0 2.0 Bromide concentration (mg/L)

4.0

4

(b) Chloramination

Chlorination

3

10

2

10

1

10

0

1

24

120 1 Contact time (h)

24

120

4

10

(c)

3

Peak area

10

2

10

1

10

0

10

6.0

518 519 520 521 522

6.5

trichloro-HCD chlorodibromo-HCD

pH

7.5

8.5 dichlorobromo-HCD tribromo-HCD

Figure 7. Peak areas (in log scales) of trihalo-HCDs in the UPLC/ESI-tqMS MRM chromatograms of the simulated drinking water samples prepared with different (a) source water bromide levels, (b) disinfectant types and contact times, and (c) pH values.

26


Page 27 of 27

523


An Author-created Table of Contents Graphic (TOC Art) A new group of drinking water DBPs: trihalo-hydroxy-cyclopentene-diones SRNOM + Br– + Cl2 / NH2Cl Cl

O-

Cl

%

180.9191.1 213.0 222.9

0 180

200 HO

220 CHO OH

253.3

240

260

O

281.1

302.7 306.8

280

300

339.1 347.0 353.2 379.2

320

precursor-to-Br2 molar ratio of 1:8 8 h, 20 ºC

+ Br2

O Br Br

Br Br

258.9 260.8

100

O-

Br

O

O

Br Cl

Cl Cl

trihalo-HCDs O-

Cl

O

O

O

O

O-

340

m/z 380

360

tribromo-HCD

OH

0.0

524

24.72 29.12

20.00

40.00

Time

0 4000

693.4 606.3

50

1752.3 1710.0

5.22 8.33

FTIR characterization 1604.0

2.5e-1

% Transmittance

100

16.63

3443.5

Preparative isolation

3000 2000 1000 Wavenumbers (1/cm)

27


A New Group of Disinfection Byproducts in Drinking Water: Trihalo

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