Characterization of dissolved organic matter derived from atmospheric dry deposition and its DBP formation

Journal Pre-proof Characterization of dissolved organic matter derived from atmospheric dry deposition and its DBP formation Jijie He, Feifei Wang, Tiantao Zhao, Shaogang Liu, Wenhai Chu PII:

S0043-1354(19)31142-X

DOI:

https://doi.org/10.1016/j.watres.2019.115368

Reference:

WR 115368

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Water Research

Received Date: 16 October 2019 Revised Date:

28 November 2019

Accepted Date: 1 December 2019

Please cite this article as: He, J., Wang, F., Zhao, T., Liu, S., Chu, W., Characterization of dissolved organic matter derived from atmospheric dry deposition and its DBP formation, Water Research (2020), doi: https://doi.org/10.1016/j.watres.2019.115368. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

HPI

>100 kDa 10-100 kDa 1-10 kDa <1 kDa

Cl2 Chlorination

Dry deposition

Resin and MW fractionation

TPI Ultrapure water

>100 kDa 10-100 kDa 1-10 kDa <1 kDa

1

NH2Cl Chloramination

MW: Molecular weight HPI: Hydrophilic fraction

TPI: Transphilic fraction HPO: Hydrophobic fraction

HPO

>100 kDa 10-100 kDa 1-10 kDa <1 kDa

Characterization of dissolved organic matter derived from atmospheric dry deposition and its DBP formation Jijie He a, b, d, Feifei Wang c, Tiantao Zhao d, Shaogang Liu e, Wenhai Chu a, b, *.

a

State Key Laboratory of Pollution Control and Resources Reuse, National Centre for International Research of

Sustainable Urban Water System, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, China b

Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, China

c

School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China

d

School of Chemistry and Chemical Engineering, Chongqing University of Technology, Chongqing 400050, China

e

Guangxi Key Laboratory of Chemistry and Engineering of Forest Products, School of Chemistry and Chemical

Engineering, Guangxi University for Nationalities, Nanning 530008, Guangxi, China

* Corresponding author Address: Room 308 Mingjing Building, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Yangpu District, Shanghai, 200092, China Phone: 0086-18721871983; 0086-21-659826 E-mail address: [email protected]; [email protected]

1

Abstract Disinfection by-products (DBPs) precursors can be regarded mainly from the drinking water sources and the water treatment processes. A recent study showed that dissolved organic matter (DOM) in atmosphere is an important precursor source of DBPs through atmospheric wet deposition. However, little information is available on the characteristics of DOM derived from dry deposition particulate matter (PM) and the impact of dry deposition on CX3R-type DBP formation. This study determined whether dry deposition directly contributed the production of DBPs during chlor(am)ination and investigated the mechanism behind the contribution based on the combination of the resin and membrane for fractionating DOM fractions. The results showed that the hydrophilic fraction (HPI) contributed the most DOM and low molecular weight DOM (< 10 kDa) was the main component of HPI. In addition, aromatic proteins and soluble microbial products-like compounds were the dominant fluorescent species in DOM derived from PM, and < 10 kDa transphilic was the most abundant. The concentrations of C-DBPs and N-DBPs in disinfected PM solution were trihalomethanes (THMs) > haloacetic acids (HAAs) > haloaldehydes and haloacetamides > haloacetonitriles > halonitromethanes for both chlorination and chloramination. The main contributors of calculated toxicity are transphilic and hydrophobic in chlorination and chloramination respectively. Dry deposition PM was deduced to contribute DOM and DBP formation after chlorination in surface water, especially THMs and HAAs. These results presented herein provide key information for controlling DBPs from the perspectives of atmospheric dry deposition, especially in the case of heavy air pollution.

Keywords Disinfection; Disinfection by-products (DBPs); Hydrophobicity; Molecular weight (MW); Dry deposition

2

Abbreviations: APs,

Aromatic

proteins;

C-DBPs,

Carbonaceous

disinfection

by-products;

CH,

Trichloroacetaldehyde; Cl2, Chlorine; DCAA, Dichloroacetic acid; DCAL, Dichloroacetaldehyde; DBPs, Disinfection by-products; DCAN, Dichloroacetonitrile; DCAM, Dichloroacetamide; DCNM, Dichloronitromethane; DCM, Dichloromethane; DIN, Dissolved inorganic nitrogen; DOC, Dissolved organic carbon; DOM, Dissolved organic matter; DON, Dissolved organic nitrogen; DWTPs, Drinking water treatment plants; EEM, Excitation-emission matrix; FP, Formation potential;

GC/ECD,

gas

chromatography/electron

capture

detection;

GC/MS,

gas

chromatograph/mass spectrometry; HAAs, Haloacetic acids; HALs, Haloaldehydes; HANs, Haloacetonitriles; HAMs, Haloacetamides; HPI, Hydrophilic fraction; HPO, Hydrophobic fraction; HNMs, Halonitromethanes; ITRV, Integrated toxic risk values; MW, Molecular weight; N-DBPs, Nitrogenous disinfection by-products; NH2Cl, Chloramine; PM, Particulate matter; SMP, Soluble microbial product; SUVA, Specific ultraviolet absorbance; TCAA, Trichloroacetic acid; TCAM, Trichloroacetamide;

TCAN,

Trichloroacetonitrile;

TCM,

Trichloromethane;

TCNM,

Trichloronitromethane; TDN, Total dissolved nitrogen; THMs, Trihalomethanes; TPI, Transphilic fraction.

3

1

1. Introduction

2

With the development of industry and agriculture as well as the increase of population, drinking

3

water treatment plants (DWTPs) are forced to consider exploitation of source water impaired by

4

municipal wastewater effluents or algal blooms (Schwarzenbach et al., 2006; Rodriguez et al.,

5

2009), which are commonly regarded as sources of dissolved organic matter (DOM) (Imai et al.,

6

2003; Lee and Westerhoff, 2006; Dotson et al., 2009). Although the conventional treatment

7

processes (e.g., coagulation-sedimentation-filtration) in DWTPs are able to remove partial DOM,

8

the un-removed DOM has an opportunity to react with disinfectants (e.g., chlorine) to form toxic

9

disinfection by-products (DBPs) (Goslan et al., 2009; Hou et al., 2012; Chu et al., 2013; Gong et al.,

10

2016; Ding et al., 2019). Since the first discovery in the early 1970s (Bellar et al., 1974), DBPs have

11

been intensively reported due to their high toxicity (Richardson et al., 2007; Muellner et al., 2007;

12

Plewa et al., 2008a; Plewa et al., 2010; Han and Zhang, 2018). Trihalomethanes (THMs) and

13

haloacetic acids (HAAs), as carbonaceous DBPs (C-DBPs), are frequently detected in finished

14

water and are strictly limited in regulatory guidelines by US Environmental Protection Agency

15

(USEPA, 2006), World Health Organization (WHO, 2006), and Chinese standards for drinking

16

water quality (GB5479-2006), due to their relative high concentrations (Richardson et al., 2007).

17

Haloaldehydes (HALs) with geno-, cyto- and reproductive toxicities, as the third class of DBPs

18

based on mass concentration, are extensively detected in finished drinking water (Liviac et al., 2010;

19

Jeong et al., 2015). In addition, nitrogenous DBPs (N-DBPs), including haloacetonitriles (HANs),

20

halonitromethanes (HNMs) and haloacetamides (HAMs), have received increasing concern because

21

of their higher cyto- and geno-toxicity than C-DBPs (e.g., THMs) (Muellner et al., 2007a; Plewa et

22

al., 2008a; Plewa et al., 2008b; Wagner and Plewa, 2017). These six classes of DBPs mentioned

23

earlier can be classified as CX3R-type (X = H, Cl, Br, or I) DBPs due to their similar molecular

24

structure, which have been extensively studied in previous studies for their high detection rates,

25

concentrations and toxicities in finished water (Richardson et al., 2007; Chu et al., 2012; Zhang et

26

al., 2017).

27

Atmospheric deposition plays an important role in carbon cycle (Fowler et al., 2009; Kuang et 4

28

al., 2016). Recently, many studies found that the organic matters derived from atmosphere will

29

increase concentrations of DOM in surface water sources through precipitation (Gao et al., 2018;

30

Warner and Saros, 2019; Xing et al., 2019). However, dry deposition, especially particulate matters

31

(PM) deposition, as another way transporting atmospheric organic matters to the surface water

32

sources, may have important implications for the contribution of DOM in water sources. According

33

to a previous study (Jacobson et al., 2000), PM contained abundant organic matters. For instance, Ti

34

et al. (2018) found that the contribution of atmospheric dry deposition to the total DON of Taihu

35

Lake was 1.4%, indicating that dry deposition, especially PM deposition, can be an important

36

source of DOM in surface water sources. Therefore, there is a contact opportunity for DOM in PM

37

and disinfectants during disinfection process. For wet deposition (precipitation), only one study

38

examined the contribution of atmospheric DOM from wet deposition to the formation of DBPs

39

(Hou et al., 2018). However, till now, little has been known about the effect of atmospheric PM from

40

dry deposition on the formation and the toxicity of DBPs, which is necessary to be estimated

41

considering that dry deposition is also an important pathway transporting atmospheric DOM to

42

drinking water sources.

43

DOM is a complex organic mixture with a broad spectrum of molecular weights, functional

44

groups distributions. It is vital to isolate the DOM into more homogeneous groups based on

45

different chemical or physical properties, such as size, structure and functionality, to better

46

understand the formation mechanism of DBPs and finally achieve good control effect. Among

47

various isolation methods, resin fractionation and membrane filtration are the most commonly

48

adopted methods (Chen et al., 2014; Han et al., 2015; Pan et al., 2016; An et al., 2017; Zhang et al.,

49

2018). In the past, resin fractionation and membrane filtration were used respectively for obtaining

50

the hydrophobicity and molecular weight (MW) distribution of DOM in drinking water sources.

51

However, no information is available concerning the combination of resin fractionation and

52

membrane filtration to further fractionate DOM. It is possible to get more detailed information

53

concerning characteristics of DOM and DBPs precursors due to further refine the DOM based on

54

hydrophobicity and MW. This study attempted to apply the combination of resin fractionation and

55

membrane filtration to fractionate DOM from atmosphere PM for the first time. This novelty in this 5

56

study can be seen clearly and detailly in Figure S1 (Supporting information).

57

The objectives of this study were to 1) determine the contribution of atmospheric dry

58

deposition on DOM and the production of DBPs during chlor(am)ination in surface water, 2)

59

investigate the characteristics of DOM fractions from atmospheric dry deposition PM, 3) assess the

60

formation potential (FP) of CX3R-type DBPs (THMs, HAAs, HALs, HANs, HNMs and HAMs)

61

formed from atmospheric dry deposition DOM, 4) evaluate the integrated risk of these CX3R-type

62

DBPs, and the contribution of dry deposition PM to the DBPs toxicity. The results presented herein

63

would provide key information for DWTPs to control DBPs from the perspectives of atmospheric

64

dry deposition, especially in the case of heavy air pollution.

65

66

2. Materials and methods

67

2.1 Chemicals and materials

68

CX3R-type DBPs standard solutions including THMs, HAAs, HALs, HANs, HNMs and HAMs

69

were purchased from Supelco (St LOUIS, Missouri, USA). XAD-4 and XAD-8 resins were

70

purchased from Sigma-Aldrich. A set of stirred Millipore ultra-filtration cells (Model: 8400) and

71

ultra-filtration membranes with molecular size cut-offs at 100 kDa, 10 kDa and 1 kDa were obtained

72

from USA-Millipore. Potassium dihydrogen phosphate (KH2PO4) and dipotassium hydrogen

73

phosphate (K2HPO4) were supplied by Sigma-Aldrich (USA). Sodium hypochlorite (NaOCl) and

74

nitric acid (HNO3) were obtained from Sinopharm Chemical Reagent Co. (Shanghai, China).

75

Methyl tert-butyl ether was purchased from Aladdin Industrial Inc. (Shanghai, China). Other

76

information is available in Supplementary Material. All other chemicals were obtained from

77

Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and were of analytical grade unless

78

otherwise noted.

6

79

2.2. Experimental procedures

80

2.2.1 Natural dry deposition

81

In order to determine the contribution of atmospheric dry deposition on DOM in surface water

82

sources and DBP formation during disinfection, a natural dry deposition experiment was carried

83

out. Three sampling basins filled with 2 L of fresh ultrapure water as parallel samples were placed

84

at the roof of the Mingjing Building, Shanghai for 24 hours to naturally collect the atmospheric

85

dry deposition. Afterwards, the water with atmospheric DOM was stirred by a magnetic stirrer

86

with a speed of 150 r/min to ensure a complete mixing state, and then filtered through 0.45 µm

87

glass fiber filters for water parameters analysis as well as the subsequent disinfection experiment

88

which can be found in section 2.2.3.

89

90

2.2.2 DOM fractionation

91

In order to quickly collect more PM for subsequent research (resin and membrane fractionation),

92

three total PM samplers (ZR-3920C, Junray, Qingdao) were mounted on the roof of the Mingjing

93

Building in the campus of Tongji University (Yangpu, Shanghai, China) and to collect PM. Total

94

PM-derived DOM solutions were prepared as follows: total PM were collected on the quartz

95

microfiber filters with pore diameter of 1.6 µm (1851-090, Whatman, England) and the total mass

96

of PM was approximately 78 mg. Three filters were rinsed using ultrapure water for three times,

97

respectively, and then all the solutions containing isolated particles were transferred into the

98

corresponding beakers, and finally, additional ultrapure water was further added into the beaker

99

until its solution volume reached 1 L. Solution was then stirred by a magnetic stirrer with a speed

100

of 150 r/min to ensure a complete mixing state. The mixing process proceeded for 24 h to

101

guarantee sufficient dissolution of PM-derived DOM. Then, total PM-derived DOM solutions

102

were filtered through 0.45 µm glass fiber filters. Finally, 3 L PM-derived DOM solutions were

103

concentrated to 1 L by a reverse osmosis unit, which can contain the majority of DOM (Zhao et al.,

104

2006; Pressman et al., 2012). Concentrated DOM solution was stored in the dark at 4 °C until use. 7

105

The storage time of all solutions was no longer than 7 days. Characteristics of concentrated DOM

106

solutions derived from PM are presented in Table S1. A portion of concentrated DOM solutions

107

derived from PM was acidified to pH 2 using sulfuric acid and then passed through XAD-8 resin

108

followed by XAD-4 resin. The effluent from the XAD-4 resin was referred to as the hydrophilic

109

fraction (HPI). The fraction adsorbed by XAD-8 resin and subsequently back-eluted from the resin

110

column using sodium hydroxide solution with pH 11 was referred to as the hydrophobic fraction

111

(HPO). The XAD-4 resin retained organic compounds comprising the transphilic fraction (TPI) and

112

were also eluted using the same sodium hydroxide solution in the reverse direction. The pH of the

113

three fractions was adjusted to 7 using sulfuric acid or sodium hydroxide, and the volume of all

114

fractions was adjusted to the initial sample volume using ultrapure water. The detailed hydrophilic

115

fractionation procedure can be found in previous studies (Hua and Reckhow, 2007; Chu et al., 2010;

116

Han et al., 2015). Then, the water samples with different hydrophilicities were fractionated using a

117

400 mL stirred cell (Millipore US) with Millipore ultrafiltration membranes (Amicon, Billerica,

118

MA) with MW cut-offs of 100 kDa, 10 kDa and 1 kDa, respectively. Usually, the threshold value

119

between high and low MW organic matter is 10 kDa (Liu et al., 2012). <1 kDa and > 100 kDa of

120

DOM represent even lower and higher MW organic matter. The detailed MW fractionation

121

procedure can be found in previous studies (Hua and Reckhow, 2007; Chu et al., 2014; Han et al.,

122

2015). Finally, DBP FP tests were carried out for the separated twelve fractions and the details can

123

be found in section 2.2.3.

124

125

2.2.3 DBP FP tests

126

DBP FP tests were performed in 40 mL amber glass volumetric bottles under headspace-free

127

conditions in the dark at a temperature-controlled (25.0 ± 0.5 °C) room, based on the procedure

128

reported in previous studies (Krasner et al., 2004; Zhang et al., 2017). The disinfectant dosages for

129

DBP FP tests were chlorine (Cl2) = 3 × DOC mg/L + 7.6 × NH3-N mg/L + 10 mg/L. The fresh

130

monochloramine (NH2Cl) solutions were prepared in advance following the procedures of Mitch

131

(Mitch and Sedlak, 2002) and NH2Cl dosage = 3 × DOC mg/L. 8

132

133

2.3 Analytical methods

134

Some general parameters, such as UV-Vis, dissolved organic carbon (DOC), DON and specific

135

ultraviolet absorbance (SUVA), can be used to predict the amount and characterization of DOM

136

(Hua et al., 2015). UV absorbance at 254 nm (SUVA254) and 285 nm (SUVA285) were measured

137

using a UV-Vis spectrophotometer (UV-9000S, Metash Instrument, Shanghai) to characterize the

138

aromaticity of DOM, which were calculated by dividing the UV absorbance at 254 nm and 285 nm

139

by solution DOC, respectively. Three-dimensional spectrofluorometry (F-7100 Fluorescence,

140

HITACHI, Japan) has been widely used to characterize different functional groups and sources of

141

DOM (Han et al., 2015; Li et al., 2020). Fluorescence scans (λex: 200-450 nm; λem: 220-550 nm) was

142

performed with 5 nm slits for excitation and emission.

143

DOC and total dissolved nitrogen (TDN) were measured using a TOC analyzer (Shimadzu

144

TOC-VCPH, Japan). The detection limits of DOC and TDN were 0.1 mg/L. Concentrations of

145

different dissolved inorganic nitrogen (DIN) species (i.e. NH3-N, NO3- and NO2-) were measured

146

using their respective HACH test kits with a UV-Vis spectrophotometer (HACH DR6000). The

147

detection limits of NH3-N, NO3- and NO2- were 0.02 mg/L, 0.002 mg/L and 0.1 mg/L, respectively.

148

DON is the difference between TDN and DIN. THMs including dichloromethane (DCM),

149

trichloromethane (TCM), HANs including dichloroacetonitrile (DCAN) and trichloroacetonitrile

150

(TCAN), HNMs including dichloronitromethane (DCNM) and trichloronitromethane (TCNM),

151

HAMs including dichloroacetamide (DCAM), trichloroacetamide (TCAM) and HALs including

152

dichloroacetaldehyde (DCAL) and trichloroacetaldehyde (CH) were detected using gas

153

chromatography/electron capture detection (GC/ECD, QP2010plus, Shimadzu Corporation, Japan).

154

HAAs including chloroacetic acid, dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA)

155

were measured with a gas chromatography/mass spectrometer (GC-MS-QP2020, Shimadzu

156

Corporation, Japan). Detailed information on the analytical methods of these CX3R-type DBPs

157

were presented elsewhere (Hou et al., 2018; Zhang et al., 2019a; Zhang et al., 2019b).

9

158

3. Results and discussion

159

3.1 DBP formation from natural dry deposition

160

The results of DBP formation during the disinfection of ultra-pure water with and without

161

atmospheric dry deposition DOM are shown in Figure 1. As is shown in Figure 1 (a), DOC and

162

DON concentrations evidently increased by 0.71 mg/L and 0.35 mg/L respectively due to 24 h

163

contact with atmosphere. It is difficult to estimate the exact contribution of atmospheric dry

164

deposition to DOM in real surface water sources based on the results of DOC and DON presented

165

in Figure 1. However, considering that usually hydraulic retention time in surface waters, such as

166

lake, river and reservoir, is from a few days to months (Giraldo and Garzón, 2002; Kawara et al.,

167

1998; Soares et al., 2012; Wang et al., 2017), much longer than 24 h in this study, which may

168

cause more organic matters deposition to surface water. Therefore, atmospheric dry deposition is

169

deduced to contribute DOM in surface water to some degree. Figure 1 (b) presents that atmospheric

170

dry deposition resulted in the increase of DBP formation to some degree. Specifically, TCM

171

increased by approximately 50 µg/L as a result of dry deposition and the value for DCAA and

172

TCAA was 10-15 µg/L, whereas other DBPs were minor. According to previous studies (Zhai et al.,

173

2017; Zhang et al., 2017), TCM/DOC ratio was in the range of 10-45 µg/mg in natural surface water,

174

which was less than that from dry deposition PM (53 µg/mg). Evidentially different from the

175

source of DOM in natural surface water: atmospheric PM originates from mainly combustion of

176

biomass and fossil fuel (Seinfeld and Pankow, 2003; Huang et al., 2014; Yao et al., 2016), which

177

may explain why higher TCM/DOC ratio was observed in atmospheric dry deposition PM than

178

nature surface water. To sum up, dry deposition PM was deduced to be a source of DBPs precursors,

179

and it is necessary to study the composition and characteristics of organic matters from dry

180

deposition as well as the formation characteristics of DBPs.

181 182

[Figure 1]

183

10

184

3.2 Characteristics of DOM fractions derived from atmospheric dry deposition PM

185

3.2.1 Hydrophobicity distribution

186

The DOM derived from atmospheric dry deposition PM was fractioned into three fractions: HPI,

187

TPI and HPO. Figure 2 shows the DOC and the DON percentages of each fraction. It can be

188

observed that nearly half of DOC belonged to HPI and 30.6% of DOC was HPO, while only 19.7%

189

of DOC was TPI, which suggests that HPI was the dominant fraction in dry deposition PM. This

190

result is consistent with Yellow River water (Hu et al., 2014). The relatively high percentage of HPI

191

suggests that the DOM derived from atmospheric dry deposition PM mainly originate from

192

anthropogenic sources, which is in agreement with the formation of PM (Yao et al., 2016; Chang et

193

al., 2019). Similarly, HPI accounted for largest proportion (74.1%) of DON but the percentage of

194

TPI and HPO were 6.1% and 10.9% respectively, suggesting that HPI has higher

195

nitrogen-containing organic matters than TPI and HPO (Figure S2), which may cause higher

196

N-DBP formation. Usually, HPI cannot be removed by conventional drinking water treatment

197

processes (coagulation-sedimentation-filtration) owing to low octanol water partition coefficient

198

(Zhao et al., 2009; Wang et al., 2013). Therefore, the hydrophobicity distribution results indicate

199

that probably a large proportion of DOM derived from atmospheric dry deposition PM will react

200

with disinfectants (chlorine, etc.) to form DBPs during the subsequent disinfection process.

201 202

[Figure 2]

203 204

To further investigate the spectroscopic characteristics of DOM derived from PM, the results

205

with respect to fluorescence excitation-emission matrix (EEM) spectra and SUVA254 and SUVA285

206

are shown in Figure 3 and Figure S3, respectively. Figure 3 (a) shows that the most intense regions

207

were aromatic proteins (λex < 250 nm, λem < 380 nm) and soluble microbial product (SMP)-like

208

regions (λex > 250nm, λem < 380 nm), indicating that the fluorescent compounds in PM were mainly

209

APs and SMP-like compounds, which have been regarded as important precursors of HAMs (Chu et

210

al., 2010). This is different with surface water, which mainly exist humic acid and fulvic acid like 11

211

compounds (Graeber et al., 2012). Figure 3 (b)-(d) show that DOM in HPI, TPI and HPO also have

212

the most intense peaks at Ex/Em of 250/340 nm in the regions of APs and SMP-like region, and the

213

second-highest peak at Ex/Em of 330/440 nm in humic acid-like region, which indicate that they

214

had similar DOM compositions. By comparing Figure 3 (b)-(d), it can be gotten that TPI has much

215

higher APs, SMP-like and humic acid-like region contents than HPI and HPO. SUVA254 and

216

SUVA285 commonly represent aromaticity of DOM (Buffle et al., 1982; Krasner et al., 1996). In

217

particular, SUVA285 serves as an indicator of benzene carboxylic acids and phenols (Buffle et al.,

218

1982; Krasner et al., 1996). Figure S3 presents that both SUVA254 and SUVA285 values for TPI are

219

greater than HPI and HPO, indicating that aromatic DOM, such as APs, benzene carboxylic acids

220

and phenols majorly distributed in TPI, which is in agreement with the results of EEM spectra. The

221

latter two fractions show almost the same SUVA254 and SUVA285 values, suggesting that their DOM

222

had similar aromaticity.

223 224

[Figure 3]

225

226

3.2.2 MW distribution of different hydrophobicity fractions

227

The DOM derived from three different hydrophobicity fractions were further fractioned into four

228

MW groups: < 1 kDa, 1-10 kDa, 10-100 kDa and > 100 kDa. Figure 4 presents the MW distribution

229

of different hydrophobicity DOM fractions, and the 'others' shown in Figure 4 represents a small

230

portion of the DOM lost during the fraction process, including residues on ultrafiltration membranes

231

and ultrafiltration devices. For HPI, TPI and HPO, < 1 kDa fraction contributed 41.8%, 25.9% and

232

34.5% DOC, respectively, which were relatively higher than other fractions with > 1 kDa. DOM

233

with >100 kDa MW was greater than 10-100 kDa fraction in high MW organic matter for HPI, TPI

234

and HPO. It is noteworthy that DOM with < 10 kDa in HPI and TPI were greater than 50%. The

235

results indicate that HPI with low MW fraction (< 10 kDa), which is hardly removed by the

236

conventional treatment processes (Zhao et al., 2009), occupied a large proportion of DOM in the dry

237

deposition PM. This is in agreement with many polluted surface water sources (Zhao et al., 2006; 12

238

Rosario-Ortiz et al., 2007).

239 240

[Figure 4]

241 242

Figure 5 shows the EEM spectra for different MW fractions of different hydrophobicity DOM

243

derived from atmospheric dry deposition PM. As presented in Figure 5 (a)-(d), all the MW fractions

244

of HPI have a most intense peak in SMP-like (λex > 250 nm, λem < 380 nm) and APs regions (λex <

245

250 nm, λem < 380 nm). Moreover, the fluorescence intensity increased with the increase of MW,

246

suggesting that high MW organic matter in HPI contained more abundant SMPs and APs

247

compounds than low MW organic matter, which is similar with HPO. Differently, TPI with MW >

248

100 kDa and < 1 kDa included more SMPs and APs compounds than 1-100 kDa. Figure S4 shows

249

SUVA254 and SUVA285 of different MW of different hydrophobicity DOM fractions derived from

250

PM. As for HPI, SUVA254 and SUVA285 values decreased in the following order: [> 100 kDa] >

251

[10-100 kDa] > [< 1 kDa] > [1-10 kDa], suggesting that high MW organic matter (> 10 kDa)

252

contained more aromatic structures and humic compounds than low MW organic matter (< 10 kDa),

253

which is the same with the results of EEM. SUVA254 and SUVA285 values for < 10 kDa fraction in

254

TPI were higher than that of > 10 kDa. SUVA254 and SUVA285 values, apart from 10-100 kDa

255

fraction, were basically the same for the other fractions in HPO, indicating that aromatic structure in

256

TPI and HPO fractions mainly occurred at low and high MW organic matters, respectively.

257 258

[Figure 5]

259 260

3.2.3 The relationship of CX3R-type DBP FP and SUVA

261

A previous study has demonstrated that SUVA254 can be used to predict DBP FP (Hua et al., 2015).

262

Figure S5 presents the correlation of SUVA254 and SUVA285 as well as THMs, HAAs, HALs, HANs,

263

HAMs and HNMs for the different DOM fractions derived from PM after chlor(am)ination.

264

SUVA254 and SUVA285 have similar results, which indicated that SUVA285 can also be used to

265

predict DBP FP and the following discussion is performed with SUVA254. As illustrated in Figure S5 13

266

(a) and (b), THMs shows the strongest correlation (R2 = 0.90 and 0.71 for chlorination and

267

chloramination, respectively) with SUVA254, indicating UV absorbing compounds are the primary

268

precursors to form THMs. HAMs also showed a good correlation with SUVA254 (R2 = 0.70) during

269

chlorination. This indicates that UV absorbing compounds and aromatic carbon containing nitrogen

270

within DOM derived from PM are the primary sources of precursors for HAMs. However, the

271

correlation of HAMs and SUVA254 became weak (R2 = 0.42) during chloramination, which is

272

mainly due to a new source of nitrogen from monochloramine. A generally weak correlation (R2 =

273

0.28, 0.33 and 0.24) was observed between SUVA254 and HALs, HANs and HNMs during

274

chlorination, and HAAs has a poor correlation with SUVA254, which indicated that non-humic

275

substances can contribute a large number of CX3R-type DBPs. For chloramination, a similar result

276

was shown for HALs, HANs and HNMs, while a weak correlation occurred between HAAs and

277

SUVA254 (R2 = 0.47), which may be due to different formation mechanism.

278

279

3.3 C-DBP FP characteristics during chlor(am)ination

280

3.3.1 THMs

281

In order to avoid concentration effects, the DBP FP was normalized by DOC. Figure 6 and Figure S6

282

show the results of three C-DBP FPs of different DOM fractions derived from dry deposition PM

283

after chlor(am)ination. The previous study has demonstrated that the concentrations of C-DBPs in

284

finished drinking water were THMs > HAAs > HALs for both chlorination and chloramination

285

(Goslan et al., 2009), which is consistent with the results from most DOM fractions in this study.

286

This indicates that the composition of the precursors of C-DBPs might be similar in the atmospheric

287

dry deposition PM and drinking water source.

288

By comparing Figure 6 (a) and (b), higher total THM FP was observed for most DOM fractions

289

during chlorination than chloramination, indicating that chloramination generally resulted in less

290

THMs, which is in agreement with the results from natural water disinfection (Hua and Reckhow,

291

2007; Bougeard et al., 2010). It might be explained by that chlorine has higher oxidative ability than

292

chloramine. During chlorination, THM FP was generated by TPI, especially < 10 kDa TPI, which is 14

293

obvious more than other fractions. During chloramination, more THM FP was also observed in TPI.

294

This indicated that TPI was main precursors for generating THM FP during chlor(am)iantion. In

295

addition, Figure S6 (a) and (b) shows that TCM FP was greater than DCM FP in all DOM fractions

296

during chlorination, while the results were opposite during chloramination: DCM FP > TCM FP,

297

which is consistent with a previous research using surface water (Yang et al., 2014). This could be

298

because the oxidizing power of NH2Cl is weaker than Cl2, and it is impossible to further transform

299

DCM to TCM.

300 301

[Figure 6]

302

303

3.3.2 HAAs

304

Figures 6 (c), 6(d), S6 (c) and S6 (d) display the HAA FP of each DOM fraction derived from

305

PM. As shown in Figure 6 (c) and (d), similar to THMs, total HAAs were greater during

306

chlorination than that during chloramination in most fractions. In addition, HAAs mainly formed by

307

1-100 kDa HPO during chlorination, which is almost an order of magnitude higher than other

308

fractions. During chloramination, the majority of HAAs was generated by TPI. As presented in

309

Figure S6 (c) and (d), TCAA was the most main HAAs species during chlorination. Nevertheless,

310

the formed DCAA was more than TCAA for most fractions during chloramination, which is similar

311

with the results of a previous study (Goslan et al., 2009). This could be because the oxidizing

312

capacity of NH2Cl is weaker than Cl2, and it is impossible to further transform DCAA to TCAA.

313

314

3.3.3 HALs

315

The HAL FP for different DOM fractions derived from PM is shown in Figures 6 (e), 6 (f), S6 (e)

316

and S6 (f). Similarly, total HALs were greater during chlorination than that during chloramination in

317

most fractions. As illustrated in Figure 6 (e) and (f), more HAL FP was seen in HPO during

318

chlorination, while HPO did not form HALs during chloramination. As shown in Figure S6 (e) and 15

319

(f), CH FP was higher than DCAL FP during chlorination. In addition, HALs was detectable only in

320

HPI during chloramination, and DCAL was main species, while CH was not detected as a result of

321

below the detection limit.

322

323

3.4 N-DBP FP characteristics during chlor(am)ination

324

3.4.1 HANs

325

Figure 7 and Figure S7 show the N-DBP FPs of different DOM fractions derived from PM after

326

chlor(am)ination. HAN FP of each DOM fraction after chlor(am)ination is shown in Figure 7 (a)

327

and 7 (b), S7 (a) and S7 (b). As shown in Figure 7 (a) and (b), total HANs were greater during

328

chlorination than that during chloramination in most fractions. In addition, as seen in Figure S7 (a),

329

TPI was main precursors of HANs during chlorination and DCAN was main HANs, while no HANs

330

were detected in TPI during chloramination. As shown in Figure S7 (a) and (b), DCAN was

331

dominant HANs species in most fractions, irrespectively of chlorination or chloramination. Further,

332

HANs was only detected in HPI with < 1 kDa fraction during chlorination, but HANs was also

333

produced by other HPI fractions during chloramination, indicating NH2Cl is also an important

334

source of nitrogen in N-DBPs, which was consistent with a previous study (Yang et al., 2010; Shah

335

and Mitch, 2012; Chu et al., 2016). In addition, HPI with highest DON/DOC did not exhibited

336

higher HAN FP (Figure S2), which may be related to the structure of the organic matter and the

337

formation path of HANs.

338 339

[Figure 7]

340

341

3.4.2 HAMs

342

HAM FP formed during chlor(am)ination of different DOM derived from PM is illustrated in

343

Figures 7 (c) and 7 (d), S7 (c) and S7 (d). As shown in Figure 7 (c) and (d), more HAM FP was

344

observed in TPI during chlorination, while more HAM FP was observed in HPI during 16

345

chloramination. As shown in Figure S7 (c) and (d), both DCAM and TCAM were detectable during

346

chlor(am)ination of most fractions, and DCAM FP was much higher than TCAM FP in all fractions,

347

regardless of chlorination or chloramination.

348

349

3.4.3 HNMs

350

The results of HNM FP formed by different DOM fractions derived from PM after chlor(am)ination

351

are displayed in Figures 7 (e), 7 (f), S7 (e) and S7 (f). As shown in Figure 7 (e) and 7 (f), HNMs were

352

only detected in few fractions during chlor(am)ination. Overall, chloramination formed more

353

HNMs than chlorination, which is disagreement with previous studies (Bougeard et al., 2010; Hu et

354

al., 2010), probably because there is a new formation path due to different DOM nature. Further, < 1

355

kDa TPI was major precursors of HNMs during chlorination, while < 1 kDa HPO was major

356

precursors of HNMs during chloramination.

357

In summary, the DOM derived from PM can form HANs, HAMs and HNMs during

358

chlor(am)ination. Among of which, HAMs were the most, followed by HANs and HNMs, which is

359

in disagreement in finished water in real drinking water plants, in which HANs were the most

360

N-DBPs (Richardson et al., 2007; Bond et al., 2011; Chu et al., 2011;Bond et al., 2015).

361

362

3.5 Integrated toxic risk of selected CX3R-type DBPs

363

In the past, Plewa and his colleagues systematically investigated the cytotoxicity and genotoxicity

364

of a range of halogenated DBPs (Plewa et al., 2004; Muellner et al., 2007b; Plewa et al., 2008b). The

365

integrated toxic risk values (ITRV) were calculated to evaluate the comprehensive risk of DBPs

366

based on cytotoxicity and genotoxicity. Figure 8 shows ITRV of eight CX3R-type DBPs (TCM,

367

DCAA, TCAA, DCAN, TCAN, DCAM, DCAM, and TCNM) after chlor(am)ination of DOM

368

fractions derived from dry deposition PM and surface raw water (Zhang et al., 2017) to compare the

369

overall toxicity based on same organic matters level. The ITRV are the reciprocal of the

370

averaged %C½ (cytotoxicity) and the SCGE genotoxic potency (genotoxicity) values, which were 17

371

calculated using Equation (1): n

ITRV =

[ X=1

1 × Cx ] (%C1/2x +Genotoxicity potencyx )× M

(1)

372

where %C1/2X and Genotoxic potencyX are cyto- and geno- toxicity of each DBP compound; M is

373

the relative molecular mass of each DBP compound; CX is the FP of each DBP compound (nM); X is

374

the specific DBP compound. As is shown in Figure 8 (a) and (b), DBPs formed during chlorination

375

and chloramination have similar ITRV, and the main contributors of ITRV are TPI and HPO for

376

chlorination and chloramination respectively. In addition, the ITRV of TCM was obviously higher

377

than that of other CX3R-type DBPs during chlorination. For chloramination, TCNM was the major

378

contributor to ITRV. As is shown in Figure 8 (c), the ITRV of PM solution is higher than that of raw

379

water during chlorination. Much more TCM and TCAA were formed in PM solutions than in raw

380

water during chlorination. All the CX3R-type DBPs but TCAN were observed to be higher in PM

381

solution than in raw water, signifying that the organic matters in dry deposition PM will promote the

382

formation of CX3R-type DBPs in raw water. In summary, the increase in the formation of DBPs

383

derived from dry deposition PM to surface raw water are noteworthy.

384 385

[Figure 8]

386

18

387

4. Conclusion

388

The main conclusions were as follows:

389

(1) Atmospheric dry deposition PM was deduced to contribute DOM and be a source of DBPs

390

precursors in surface water, especially TCM, DCAA and TCAA. Therefore, the increase in the

391

formation of DBPs derived from dry deposition PM to surface raw water are noteworthy.

392

(2) Among dry deposition PM, HPI contributed the most DOM and low MW DOM was the main

393

component of HPI. Fluorescent compounds in PM were mainly APs and SMP-like compounds,

394

and TPI contained more abundant SMPs and APs compounds than HPI and HPO.

395

(3) Among C-DBPs, THMs concentrations were much higher than HAAs and HALs formed

396

during chlor(am)ination. More THMs, HAAs and HALs were formed during chlorination than

397

chloraminationm. It is noteworthy that the main precursor of HAAs formed during

398

chlorination was 1-100 kDa HPO. The N-DBP formation during chlor(am)ination was in the

399

following order: HAMs > HANs > HNMs. Only small MW DOM (< 1 kDa) was the

400

precursor of the formation of HNMs during chlor(am)inaiton.

401

(4) DBPs formed during chlorination and chloramination has similar comprehensive toxicity, and

402

the main contributors of integrated toxicity are TPI and HPO for chlorination and

403

chloramination respectively. The toxicity of TCM formed during chlorination was obviously

404

higher than other CX3R-type DBPs. For chloramination, TCNM was the major contributor to

405

comprehensive toxicity risk.

406

Appendix A. Supplementary data

407

Supplementary data related to this article is available in this appendix.

408

409

Acknowledgements

410

The authors gratefully acknowledge the National Natural Science Foundation of China (Nos.

411

51822808; 51578389; 51778445), the National Major Science and Technology Project of China (No. 19

412

2017ZX07201005), the Shanghai City Youth Science and Technology Star Project (No. 17QA1404400),

413

Shanghai City Youth Top Talent Project, State Key Laboratory of Pollution Control and Resource Reuse

414

Foundation (No. PCRRE16009) and Tongji University Youth 100 program.

415

416

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Figure 1. The effect of natural dry deposition on C and N levels in water (a) and DBP formation

627

during water chlorination (b). Cl2 dosage = 3 × DOC mg/L + 7.6 × NH3-N mg/L + 10 mg/L; pH =

628

7.0 ± 0.2; T = 25.0 ± 0.5 ‐. The left column is blank and the right one is after 24 h dry deposition.

27

629 630

Figure 2. Hydrophobicity distribution of DOM derived from PM. pH = 7.0 ± 0.2; T = 25.0 ±

631

0.5 ‐.

28

632 633

Figure 3. Fluorescence EEM spectra of DOM derived from (a) PM, (b) HPI, (c) TPI and (d) HPO.

634

Solution DOC was adjusted to 2 mg/L. EEM spectra was divided into five regions. pH = 7.0 ± 0.2;

635

T = 25.0 ± 0.5 ‐.

29

636 637

Figure 4. MW distribution of different hydrophobicity fractions of DOM derived from

638

atmospheric dry deposition PM. pH = 7.0 ± 0.2; T = 25.0 ± 0.5 ‐.

30

639 640

Figure 5. Fluorescence EEM spectra of DOM derived from (a) HPI- > 100 kDa, (b) HPI-10-100

641

kDa, (c) HPI-1-10 kDa, (d) HPI- < 1 kDa, (e) TPI- > 100 kDa, (f) TPI-10-100 kDa, (g) TPI-1-10

642

kDa, (h) TPI- < 1 kDa, (i) HPO- > 100 kDa, (j) HPO-10-100 kDa, (k) HPO-1-10 kDa, (l) HPO- <

643

1 kDa. Solution DOC was adjusted to 1 mg/L. EEM spectra was divided into five regions. pH =

644

7.0 ± 0.2; T = 25.0 ± 0.5 ‐.

31

645 646

Figure 6. C-DBP FPs: (a) and (b) THMs; (c) and (d) HAAs; (e) and (f) HALs. Experimental

647

conditions: Cl2 dosage = 3 × DOC mg/L + 7.6 × NH3-N mg/L + 10 mg/L; NH2Cl dosage = 3 × DOC

648

mg/L; pH = 7.0 ± 0.2; T = 25.0 ± 0.5 ‐.

32

649 650 651

Figure 7. N-DBP FPs: (a) and (b) HANs; (c) and (d) HAMs; (e) and (f) HNMs. Experimental

652

conditions: Cl2 = 3 × DOC mg/L + 7.6 × NH3-N mg/L + 10 mg/L; NH2Cl dosage = 3 × DOC

653

mg/L; pH = 7.0 ± 0.2; T = 25.0 ± 0.5 ‐.

33

654 655

Figure 8. The ITRV of DBPs formed by DOM fractions from PM ((a) chlorination and (b)

656

chloramination) and (c) PM and surface raw water (Zhang et al., 2017) during chlorination. DOC

657

= 1 mg/L for PM and surface raw water.

34

Highlights Dry deposition particle was deduced to contribute DOM and DBP formation in water Hydrophilic and low MW DOM contributed the most DOM from dry deposition particle < 10 kDa transphilic contained the most abundant APs and SMP-like compounds The main contributors for DBP toxicity were transphilic for Cl2 and hydrophobic for NH2Cl DBP formation during chlor(am)ination: THMs > HAAs > HALs > HAMs > HANs > HNMs

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: