Monthly survey of N-nitrosamine yield in a conventional water treatment plant in North China

J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S 38 (2 0 1 5 ) 1 42– 1 4 9

Available online at www.sciencedirect.com

ScienceDirect www.journals.elsevier.com/journal-of-environmental-sciences

Monthly survey of N-nitrosamine yield in a conventional water treatment plant in North China Chengkun Wang1 , Shuming Liu1 , Jun Wang1 , Xiaojian Zhang1 , Chao Chen1,2,⁎ 1. School of Environment, Tsinghua University, Beijing 100084, China. E-mail: [email protected] 2. State Key Joint Laboratory of Environment Simulation and Pollution Control (SKLESPC), Beijing 100084, China

AR TIC LE I N FO

ABS TR ACT

Article history:

A sampling campaign was conducted monthly to investigate the occurrence of

Received 28 January 2015

N-nitrosamines at a conventional water treatment plant in one city in North China. The

Revised 5 May 2015

yield of N-nitrosamines in the treated water indicated precursors changed greatly after the

Accepted 7 May 2015

source water switching. Average concentrations of N-nitrosodimethylamine (NDMA),

Available online 15 August 2015

N-nitrosomorpholine (NMOR), and N-nitrosopyrrolidine (NPYR) in the finished water were 6.9, 3.3, and 3.1 ng/L, respectively, from June to October when the Luan River water was

Keywords:

used as source water, while those of NDMA, N-nitrosomethylethylamine (NMEA), and NPYR

N-nitrosamines

in the finished water were 10.1, 4.9, and 4.7 ng/L, respectively, from November to next April

Precursors

when the Yellow River was used. NDMA concentration in the finished water was frequently

Fluorescence excitation–emission

over the 10 ng/L, i.e., the notification level of California, USA, which indicated a considerable

matrix

threat to public health. Weak correlations were observed between N-nitrosamine yield and

Dissolved organic nitrogen

typical water quality parameters except for the dissolved organic nitrogen.

Molecule weight

© 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences.

Correlation

Introduction Chloramines are widely used to restrain the formation of halogenated disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs) (Diehl et al., 2000; Chen et al., 2007). However, the occurrence of N-nitrosodimethylamine (NDMA) and several other N-nitrosamines, which are regarded as emerging DBPs of health concern, have been reported in the drinking water during chloramination in recent decade (Najm and Trussell, 2001; Zhao et al., 2006; Charrois and Arend, 2004; Charrois et al., 2007). A previous survey conducted in North America indicated that the maximum concentration of NDMA in drinking water was 30 ng/L (Barrett et al., 2003). However, NDMA

Published by Elsevier B.V.

concentrations exceeding 100 ng/L were reported in distribution systems in Canada later (Zhao et al., 2006; Charrois et al., 2007). The recent Unregulated Contaminant Monitoring Rule round 2 announced the occurrence data of NDMA in water treatment plants (WTPs) of the United States (US EPA, 2010). About 10% of all samples had the NDMA detected and the highest concentration was as high as 630 ng/L. Besides NDMA, several other N-nitrosamines including N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR), N-nitrosopiperidine (NPIP), N-nitrosodiphenylamine (NDPhA), and N-nitrosodi-npropylamine (NDPA) were also detected in the drinking water (Zhao et al., 2006; Charrois et al., 2007; Planas et al., 2008; Wang et al., 2011, 2013; US EPA 2010). Dissolved organic matter (DOM) was regarded as a significant precursor for NDMA (Gerecke and Sedlak, 2003). However,

⁎ Corresponding author. E-mail address: [email protected] (C. Chen).

http://dx.doi.org/10.1016/j.jes.2015.05.025 1001-0742/© 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

J O U RN A L OF E N V I RO N M EN TA L S CI EN CE S 38 (2 0 1 5 ) 1 4 2– 1 4 9

the DOM, which may contain various components or functional groups, would lead to the formation of different N-nitrosamines in different source waters. Zhao et al. (2008) reported that concentrations of NDMA from 0 to 118 ng/L were produced from seven different surface waters in Canada. A further study conducted by Chen and Valentine (2007) concluded that the hydrophilic fraction and base fraction had a higher NDMA formation potential than the hydrophobic fraction and acid fraction. They also reported the NDMA formation well correlated with the reduction in SUVA272 during the chloramination of Iowa River water. In addition, the occurrence of bromide ion in the water was proven to enhance the formation of NDMA (Luo, 2005). The WTPs with high concentration of NDMA or other nitrosamines generally have their water source contaminated by industrial or domestic wastewater discharge. There were much more precursors for NDMA in wastewater than those in surface water and ground water (Mitch and Sedlak, 2004; Guo and Krasner, 2009; Wang et al., 2014). Therefore, the WTPs with raw water impacted by wastewater discharge or other pollution would produce unacceptable concentrations of NDMA (Gerecke and Sedlak, 2003). The nitrosamine concern also has been increasing in China in recent years. Liang et al. (2009) reported that the NDMA concentration in the distribution system of Shanghai was as high as 78.9 ng/L. Wang et al. (2011) found that the total nitrosamine concentrations in the finished water in 12 WTPs in China were from no detection to 26.3 ng/L, respectively, and NDMA (no detection—20.5 ng/L) and NDEA (no detection— 14.0 ng/L, respectively) were the most abundant. Our previous survey found the existence of NDMA in each of four monitored big cities and the highest concentrations were 3.0 ng/L, 35.7 ng/L, 21.3 ng/L, and 19.7 ng/L, respectively (Wang et al., 2012). If the NDMA standard in Antario, Canada (9 ng/L) or that in California, United States (10 ng/L) were accepted, the previous survey in China indicated that the nitrosamine problem could be more serious than the regulated THMs and HAAs. Many water sources in China have been being impacted by the anthropogenic pollution due to the huge population and the lenient environmental protection policy and administration (Zhang et al., 2011). In addition, many WTPs have to switch their source water because of the seasonal shortage of water resources and the frequent contamination. For the drinking water safety, the change of precursors for N-nitrosamines should be evaluated during the source water switching. Therefore, the objectives of this study were: (1) to detect the yield of N-nitrosamines in a conventional WTP monthly to evaluate the influence of different source waters and (2) to investigate the correlation between N-nitrosamine yield and raw water quality parameters and DOM fractions to find the key characteristics of precursors for N-nitrosamines.

1. Material and methods

143

hydrologic year. The basic water quality of source water is included in Table 1.

1.2. Water treatment plant Design and operating parameters of this WTP are presented in Table 2. The conventional water treatment processes were applied, consisting of pre-chlorination, coagulation, sedimentation, sand filtration, and post-chloramination.

1.3. Water sample collection A set of water samples including raw water, sedimentation effluent, filtration effluent, and finished water in the WTP was collected from May to next April. The sample collection, dechlorination, transport and storage procedure were conducted in accordance with US EPA Method 521. Briefly, the treated water samples for nitrosamines and other bulk water quality detection were collected in amber glass bottles, and dechlorinated with sodium thiosulfate immediately. The water samples for nitrosamine formation potential detection were firstly collected without addition of sodium thiosulfate. All samples were kept on ice during shipment, and held below 6°C, but not frozen, until extraction.

1.4. N-nitrosamines and formation potential analysis Nine N-nitrosamines were analyzed using a modified operation of solid phase extraction and liquid chromatographer plus tandem mass spectrometer (SPE-LC/MS/MS) procedure (Zhao et al., 2006; Wang et al., 2012). An SPE instrument (Model 57044, Supelco Corp., St. Louis, USA) and an LC/MS/MS instrument (Quattro Premier XE, Waters Corp., Manchester, U.K.) were applied in the N-nitrosamine detection. The multiple reactions monitoring transition mode was selected as the quantitative detection in positive-ion mode for each N-nitrosamine. Analyst software MassLynx was used for equipment control and data analysis. A C8 BEH colum (2.1 × 100 mm, 1.7 μm) (Waters, Manchester, U.K.) was employed for separation. The mobile phase was composed of solvent A (acetonitrile) and solvent B (0.05% formic acid in purity water). The solvent gradient consisted of 5% to 10% of solvent A for 1 min, increasing solvent A from 10% to 90% over 5 min, and coming back to 5%, and re-equilibration was carried out before the next injection. The total run time was 8 min. The flow rate was 0.3 mL/min, and the sample injection volume was 10 μL. The procedure for NAFP test was similar to that used in other studies (Mitch et al., 2003; Chen and Valentine, 2007). An excessive dosage of monochloramine (20 mg/L as Cl2) was added into an amber bottle stored in the dark at 25°C. The pH was adjusted to 8 with a 0.02 mol/L phosphate buffer solution. After 7 days, the reaction was quenched by addition of excessive amount of sodium thiosulfate. Then the samples were processed for N-nitrosamine analysis.

1.1. Source waters 1.5. Fluorescence spectroscopy Monthly survey was conducted in traditional WTPs located in North China. Two water sources were used sequentially for this WTP. The Luan River is used from May to October and the Yellow River is used from November to next April in one

Excitation–emission matrix (EEM) fluorescence spectra were measured using a spectrometry (F-7000 Fluorescence Spectrophotometer, Hitachi, Tokyo, Japan). The EEM spectra

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Table 1 – Basic water quality of source water. Sampling date

DOC (mg/L)

UV254 (cm− 1)

SUVA254 (L/mg-m)

NH3-N (mg/L)

NO3-N (mg/L)

NO2-N (mg/L)

DON (mg/L)

pH

T (°C)

May June July August September October November December January February March April

2.54 2.46 3.21 2.95 2.81 2.94 2.74 2.66 2.51 2.58 2.61 2.92

0.057 0.054 0.090 0.078 0.058 0.080 0.054 0.069 0.054 0.061 0.066 0.069

2.24 2.20 2.80 2.64 2.06 2.72 1.97 2.59 2.15 2.36 2.53 2.36

0.083 0.071 0.10 0.091 0.082 0.085 0.12 0.11 0.10 0.09 0.10 0.080

2.48 2.65 2.25 1.78 2.31 1.96 4.04 4.64 4.82 4.21 4.54 4.41

0.003 0.004 0.004 0.007 0.006 0.008 0.064 0.038 0.043 0.039 0.044 0.048

0.18 0.21 0.24 0.25 0.29 0.21 0.39 0.32 0.40 0.36 0.29 0.31

7.6 7.8 8.1 7.9 7.8 7.8 8.0 7.8 8.1 7.7 7.8 7.6

20.1 22.3 26.8 26.4 21.1 16.3 12.4 5.0 5.2 8.1 10.0 15.3

Note: Samples from May to October were the Luan River water and samples from November to next April were the Yellow River water. T: temperature.

were collected with corresponding scanning emission spectra from 250 to 550 nm at 5 nm increments by varying the excitation wavelength from 200 to 400 nm at 5 nm sampling intervals. An EEM of the Milli-Q water was determined and subtracted from EEM of each sample to remove most of Raman scatter peaks. The PMT voltage was maintained at 600 V and the scanning speed was set at 1200 nm/min for this study. Spectra for all samples were analyzed at ambient pH 8 since only minor difference was observed from the results at pH 3, which was used to minimize the effect of metals contained in the water. The EEM data was quantified following the fluorescence regional integration (FRI) technique (Chen et al., 2003). The EEM spectra were divided into five regions, which represent specific component of NOM (Appendix A Table S1).

1.6. Apparent average molecular weight (AMW) analysis A Shimadzu (Japan) HPLC system consisting of 2 LC-20AD pumps, a model SPD-M20A detector and a CTO-10ASvp column oven was used to obtain the molecular size distribution of water samples. Column temperature was 35°C and chromatographic separation was carried out on a PL Aquagel-OH 30 sec column (300 mm × 7.5 mm i.d., 8 μm, Agilent Technologies, Middleburg, Netherlands). The column was calibrated with molecular mass standards of poly styrenesulfonic acid sodium salt standards (Fluka, Sigma-Aldrich, St. Louis, U.S.) from 210 to 32000 Da.

1.7. Other bulk water quality indices Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) of the water samples were measured with a Shimadzu 5000A TOC analyzer. Ammonia was analyzed using the colorimetric phenate method, nitrate was measured by ultraviolet spectrophotometric screening method, and nitrite was measured using colorimetric method (APHA et al., 1995). TDN was measured after all the organic material was converted to nitrate by potassium persulfate under alkaline conditions. Dissolved organic nitrogen (DON) was quantified by equation (Westerhoff and Mash, 2002):       DON ¼ TDN− NO−2 − NO−3 − NHþ 4 : UV254 was measured by a set of UV–Vis spectra (Model: T6, Puxi, Beijing, China). SUVA254 is obtained by equation SUVA254 (L/(mg·m)) = UV254/DOC × 100%.

2. Results and discussion 2.1. N-nitrosamines formation in the WTP The concentrations of N-nitrosamines in different process waters are presented in Fig. 1. According to Fig. 1a, when the Luan River was used as source water, NDMA, NMOR, and NPYR were detected in most of these samples. The highest

Table 2 – Operating and design parameters of the water treatment plant (WTP). Processes Mixing

Flocculation Sedimentation Filtration Clear well

Parameters

Values

Pre-free chlorination Poly-aluminum chloride dosage Retention time GT Retention time Dual media of anthracite/sand bed depth Filtration velocity Chlorine/ammonia Retention time

2.0 mg/L as Cl2 6 mg/L as Al2O3 1.4 min 48276 77 min 350/500 mm 10 m/hr 3–5:1 2.5 hr

Residual total chlorine (mg/L) Break point chlorination

1.2–1.5 1.0–1.2 0.7–1.1 1.8–2.0

145

10 May 8 6 4 2 0 14 July 12 10 8 6 4 2 0 10 September 8 6 4 2 0 RW SE

June

August

October

FE

DE

RW

SE

FE

NDMA NOMR NPYR 12 25 November 10 20 8 15 6 10 4 5 2 0 0 12 8 January 10 8 6 6 4 4 2 2 0 0 8 8 March 6 6 4 4 2 2 0 0 DE RW SE

December

Feburary

Apirl 22, 2011

FE

DE

RW

SE

FE

DE

12 10 8 6 4 2 0 5 4 3 2 1 0 12 10 8 6 4 2 0

N-nitrosamines concentration (ng/L)

N-nitrosamines concentration (ng/L)

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Fig. 1 – N-nitrosamines formation along the water treatment train. (a) Samples collected from the Luan River, (b) samples collected from the Yellow River (note: RW, SE, FE, and DE represent raw water, sedimentation effluent, filtration effluent, and disinfection effluent, respectively. The concentrations of N-nitrosamines are average value of duplicate samples at each sampling location).

the Yellow River was used. This result indicated that the NDMA precursors in the Yellow River water remained a relative higher concentration while the precursors in the Luan River water drastically changed over time. Precursors in source waters and external variables such as pH, disinfectant dosage, temperature, and disinfection contact time would influence the nitrosamine formation in water (Mitch et al., 2003; Zhao et al., 2008). Temperature may play an important role on the formation of NDMA since other variables are almost the same in the WTP. However, Asami et al. (2009) conducted a nationwide survey of NDMA in the drinking water in Japan, and they found that the concentrations of NDMA in winter were a little higher than those in summer. In another study, Mitch et al. (2003) showed that the temperature did not have a large effect on NDMA formation during chloramination of unfiltered secondary activated sludge effluent. Based on the above information, the higher concentrations of N-nitrosamines in the WTP in winter might be attributed to the more precursors contained in the Yellow River.

2.2. Results of fluorescence spectroscopy of organic matter in raw water Fig. 3 shows the EEM spectra of the Luan River water and the Yellow River water. The specific peaks in an EEM spectrum

50 Nitrosamine formation (ng/L)

concentrations of NDMA, NMOR, and NPYR were 12.4 ng/L, 8.6 ng/L, and 4.5 ng/L, respectively. Fig. 1b shows the yield of N-nitrosamines in the finished water when the Yellow River was used. The highest concentrations of NDMA, NMEA, and NPYR were 21.2 ng/L, 9.0 ng/L, and 10.8 ng/L, respectively. Among the detected nitrosamines, NDMA took the majority, which was consistent to the previous detection of N-nitrosamines in the real drinking water in Canada (Charrois and Arend, 2004; Charrois et al., 2007; Zhao et al., 2006) and China (Liao et al., 2014). The nitrosamines formed in the finished water with two sources are also of some difference, i.e., NMOR was only detected after chloramination of the processed Luan River while NMEA was only detected in the treated Yellow River. It was found that concentrations of N-nitrosamines increased along the water treatment process. The occurrence of N-nitrosamines in settling tank effluent suggested that the breakpoint pre-chlorination in this WTP would benefit greatly the formation of N-nitrosamine (Krasner et al., 2013). Moreover, the conventional water treatment process is not effectively to remove the precursors of N-nitrosamines (Wang et al., 2013; Liao et al., 2014). The fairly long contact time, i.e., generally over 2 hr of the chloramine and the residual precursors allowed the higher formation of nitrosamines in the clear well. NMOR used to be regarded more like a contaminant rather than a kind of DBP (Krasner et al., 2013). However, according to Fig. 1a, b, NMOR was only detected twice in very low level in the raw Luan River water while never detected in the Yellow River water. Its concentration increased gradually after the pre-chlorination of the Luan River water. Thus, it is safe to say that NMOR is really a kind of DBP in this case. Fig. 2 compared the formation of total N-nitrosamines in the finished water during one year. The average sum of concentrations of total N-nitrosamines (TNA) in the finished water was 19.8 ng/L from November to next April, while that was 13.9 ng/L from May to October. This result indicated that the WTP would produce more N-nitrosamines when the Yellow River water was used than the Luan River. NDMA accounted for about 21% to 80% of TNA from May to October when the Luan River was used as the source water. The corresponding percentage was about 47% to 62% when

40

TNA NDMA

30 20 10 0

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Fig. 2 – Nitrosamine formation in the finished water (note: the concentrations of N-nitrosamines are average value of duplicate samples at each sampling location).

146

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region I and region II were higher than those in other regions. It indicated that there were abundant aromatic proteins contained in the Luan River water. The weakest fluorescence intensity in region V suggested that there might be little humic acid-like organic matter in this source water. The samples collected from December to next March were from the Yellow River. The fluorescence intensities in region IV and region II were higher than those in other regions indicating that there were more aromatic protein II and soluble microbial products (SMPs) contained in these samples. Overall, there were a large number of aromatic proteins and SMPs but a little humic acid-like in both the Luan River water and the Yellow River water. Holbrook et al. (2005) reported the increased fluorescence intensity in region II and region I indicating that the source water might be impacted by wastewater discharges, and it was regarded as a result of microbially derived organic matter in the natural water. Therefore, the occurrence of large number of aromatic proteins and soluble microbial products in these two rivers indicated that they might have been impacted by the wastewater discharge.

2.3. Molecular weight distribution of organic matter in raw water

Fig. 3 – Fluorescence Excitation–Emission Matrix of raw water from Luan River and Yellow River (samples collected from June to October were from the Luan River, samples collected from December to next March were from the Yellow River). were produced by some specific dissolved organic matter (Coble, 1996; Mcknight et al., 2001). For the Luan River water, the EEM spectra were composed of one major peak located around excitation–emission pair (240 nm, 360–380 nm) which was related to the aromatic proteins. The EEM spectra of the Yellow River water captured two major peaks. One was located around excitation–emission pair (280 nm, 320 nm) which was related to soluble microbial products (Chen et al., 2003). The other peak was located around excitation–emission pair (230 nm, 350 nm) which was related to aromatic proteins in the water. The FRI technique developed by Chen et al. (2003) was used to quantitatively analyze the EEM spectra. Fig. 4 showed the FRI results for samples collected from these two rivers. The integration limits for analysis and the assignment of each region to specific dissolved organic matter were presented in Appendix A Table S1. The samples collected on June to October were the Luan River water. For these samples, the fluorescence intensities in

Apparent average molecular weight (MW) of raw water samples is presented in Fig. 5. The water samples collected on July to October were from the Luan River. These four samples showed a similar MW distribution. The molecular weight fraction <3 kDa was the dominant fraction. The average portions of the molecular weight fraction <1 kDa, 1–3 kDa, 3–5 kDa, 5– 10 kDa, and >10 kDa for these four water samples were about 43.2%, 51.6%, 3.7%, 0.7%, and 0.8%, respectively. The water samples collected on December to next March were from the Yellow River. Similar to the water samples from the Luan River, majority of dissolved organic matter in the Yellow River presented small MW below 3 kDa. For these five water samples, the average portions of the MW fraction < 1 kDa, 1–3 kDa, 3–5 kDa, 5–10 kDa, and > 10 kDa were about 37.2%, 61.3%, 1.1%, 0.2%, and 0.3%, respectively. These results were quite different from that of the Iowa River water reported by Schnoor et al. (1979), which showed that about 80% of the DOM was 1–3 kDa, and only 7% of DOM was < 1 kDa. Previous study conducted by Hua and Reckhow (2007) showed the molecular weight > 3 kDa accounted for about 67% and 82% of total DOC in the water from Springfield and Tampa, respectively. It was reported that the MW distribution of DOM varied from source to source, and the environmental conditions such as vegetation, soil, and wastewater discharge played important roles in the determination of molecular weight distribution of DOM in the natural water (Hua and Reckhow, 2007). The occurrence of abundant low molecular weight DOM in both water samples from the Pearl River, the Huangpu River and lakes in China was also reported by previous studies (Zhao et al., 2006; Xu et al., 2007; Liao et al., 2014), which was mainly attributed to the anthropogenic sources (Zhao et al., 2009). Based on this information, the Luan River and the Yellow River might have been impacted by the anthropogenic activities.

147

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Region I

Region II

35000

Region III

Region IV

Region V

100

30000 80 Percentage (%)

i,n

25000 20000 15000

60

40

10000 20 5000 0

0 Jun

Jul

Sep

Oct Dec Jan Sampling time

Feb

Mar

Jun

Jul

Sep

Oct Dec Jan Sampling time

Feb

Mar

Fig. 4 – Fluorescence regional results for raw water samples collected from Luan River and Yellow River (samples collected from June to October were from the Luan River, samples collected from December to next March were from the Yellow River). (a) Intensity of fluorescence, (b) percentage of fluorescence intensity.

2.4. Correlation of N-nitrosamine formation with basic water quality There were weak correlation between TNA and the most frequently detected NDMA and basic water quality parameters in the finished water, as presented in Table 3. The Pearson coefficients (R2) between NDMA and DOC or UV254 were from 0.30 to almost zero. However, the nitrogenous water quality parameters, such as DON showed a fairly higher correlation with the formation of NDMA and TNA than those of other water quality parameters, as also reported by Lee et al. (2007). Gerecke and Sedlak (2003) also reported a weak correlation between NDMA formation and DOC. The DOC represented the whole organic matter in the source water. However, the major precursors of N-nitrosamines did not exist evenly in the dissolved organic matter as a whole but just some specific component. In previous studies, typical water quality parameters including DOC, UV254, and bromide were always correlated with the formation of C-DBPs (Solarik et al., 2000; Sohn et al., 2001; Sadiq and Rodriguez, 2004; Chen et al., 2011). Besides DOC, UV254 and bromide, it was suggested that nitrogenous precursors including ammonia, nitrite, nitrate, and DON should be contained to predict the formation of NDMA (Chen and Westerhoff, 2010). The importance of ammonia in the formation of NDMA was also reported by Najm and Trussell (2001). More investigations are needed to find the components or fractions of higher contribution to NA precursors and to conduct the correlation analysis.

3. Conclusions Precursors for N-nitrosamines changed greatly with source water switching. There were probably more precursors of N-nitrosamines that existed in the Yellow River than those in the Luan River. The average concentrations of NDMA, NMOR and NPYR in disinfection effluent were 6.9, 3.3, and 3.1 ng/L, respectively from June to October in the Luan River water, while the average concentrations of NDMA, NMEA and NPYR in disinfection effluent were 10.1, 4.9, and 4.7 ng/L, respectively from November to next April in the Yellow River water. The concentration of NDMA is much higher than those of the other N-nitrosamines indicating that there are more precursors of NDMA contained in both rivers. Weak correlations were observed between N-nitrosamine yield and typical water quality parameters except for DON.

>10 kDa

5-10 kDa

3-5 kDa

1-3 kDa

<1 kDa

100 80 Percentage (%)

Mantas and Sedlak (2008) reported that DON with molecular weight below 1 kDa was the main NDMA precursor in the wastewater effluent. Chen et al. (2014) also reported that the fraction with MW less than 1 kDa contributed about 80% of NDMAFP in the tertiary effluent of one wastewater treatment plant in California. Thus, DOM with low molecular weight should be given more attention since it may serve as a significant fraction of precursors for N-nitrosamines.

60 40 20 0

Jun

Jul

Sep

Oct Dec Sampling time

Jan

Feb

Mar

Fig. 5 – Apparent molecular weight distribution of raw water samples from the Luan River and the Yellow River (samples collected from June to October were from the Luan River, samples collected from December to next March were from the Yellow River).

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Table 3 – Correlation analysis (Y = aX + b) between formed nitrosamines and basic water quality. Sample

Time

Dependent variables, Y

Independent variables, X DOC

Luan River

Yellow River

May to Oct

Nov to next Apr

Total

UV254 DON TNA NDMA UV254 DON TNA NDMA UV254 DON TNA NDMA

a

b

R

0.026 0.036 −4.616 −5.211 0.017 −0.242 −13.481 −22.052 0.023 0.014 −4.031 −4.667

−0.004 0.121 22.779 17.641 0.013 0.781 39.606 68.016 0.001 0.194 25.080 18.423

0.891 0.178 0.308 0.266 0.749 0.113 0.161 0.113 0.830 0.002 0.017 0.069

Acknowledgments This research was supported by the National Natural Science Foundation of China (Nos. 51290284 and 21477059) and the Tsinghua University Initiative Scientific Research Program (No. 20131089247).

Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.jes.2015.05.025.

REFERENCES APHA, AWWA, WEF, 1995. Standard Methods for the Examination of Water and Wastewater. 19th ed. APHA, Washington DC, USA. Asami, M., Oya, M., Kosaka, K., 2009. A nationwide survey of NDMA in raw and drinking water in Japan. Sci. Total Environ. 407, 3540–3545. Barrett, S.E., Hwang, C.J., Guo, Y.C., Andrews, S.A., Valentine, R.L., 2003. Occurrence of NDMA in drinking water: a North American Survey, 2001–2002. Proceedings of American Waterworks Association Annual Conference and Exhibition (Anaheim, C.A., USA). Charrois, J.W.A., Arend, M.W., 2004. Detecting N-nitrosamines in drinking water at nanogram per liter levels using ammonia positive chemical ionization. Environ. Sci. Technol. 38 (18), 4835–4841. Charrois, J.W.A., Boyd, J.M., Froese, K.L., Hrudey, S.E., 2007. Occurrence of N-nitrosamines in Alberta public drinking distribution systems. J. Environ. Eng. Sci. 6, 103–114. Chen, Z., Valentine, R.L., 2007. Formation of Nnitrosodimethylamine (NDMA) from humic substances in natural water. Environ. Sci. Technol. 41, 6059–6065. Chen, B.Y., Westerhoff, P., 2010. Predicting disinfection by-product formation potential in water. Water Res. 44, 3755–3762. Chen, W., Westerhoff, P., Leenheer, J.A., Booksh, K., 2003. Fluorescence excitation–emission matrix regional integration to quantify spectra for dissolved organic matter. Environ. Sci. Technol. 37, 5701–5710. Chen, C., Zhang, X.J., Zhu, L.X., He, W.J., Han, H.D., 2007. Comparison of seven kinds of drinking water treatment

DON

UV254 2

2

a

b

R

a

b

R2

0.647 −182.15 −165.81

0.162 22.295 15.138

0.044 0.360 0.202

−18.142 9.955

16.847 5.061

0.034 0.007

3.779 312.27 −8.547

0.062 4.041 10.535

0.011 0.009 0.000

63.018 29.036

3.899 2.798

0.481 0.387

1.379 −126.190 −83.048

0.154 14.823 20.680

0.011 0.032 0.005

64.428 30.869

2.214 1.677

0.474 0.336

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