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wat e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 3 6 9e3 3 7 7
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Occurrence and formation potential ofN-nitrosodimethylamine in ground water and river water inTokyo
Nguyen Van Huy a, Michio Murakami b,*, Hiroshi Sakai a, Kumiko Oguma a, Koji Kosaka c,Mari Asami c, Satoshi Takizawa a
aDepartment of Urban Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japanb “Wisdom of Water” (Suntory), Corporate Sponsored Research Program, Organization for Interdisciplinary Research Projects, The University
of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, JapancDepartment of Water Supply Engineering, National Institute of Public Health, 2-3-6 Minami, Wako, Saitama 351-0197, Japan
a r t i c l e i n f o
Article history:
Received 11 November 2010
Received in revised form
28 January 2011
Accepted 27 March 2011
Available online 5 April 2011
Keywords:
NDMA formation potential
NDMA precursors
Ground water
Chlorination
Chloramination
Disinfection byproducts
* Corresponding author. Tel.: þ81 3 5841 626E-mail address: [email protected]
0043-1354/$ e see front matter ª 2011 Elsevdoi:10.1016/j.watres.2011.03.053
a b s t r a c t
N-nitrosodimethylamine (NDMA), a disinfection byproduct of water and wastewater
treatment processes, is a potent carcinogen. We investigated its occurrence and the
potential for its formation by chlorination ðNDMA� FPCl2 Þ and by chloramination ðNDMA�FPNH2ClÞ in ground water and river water in Tokyo. To characterize NDMA precursors, we
revealed their molecular weight distributions in ground water and river water. We
collected 23 ground water and 18 river water samples and analyzed NDMA by liquid
chromatography-tandem mass spectrometry. NDMA� FPCl2 was evaluated by chlorinating
water samples with free chlorine for 24 h at pH 7.0 while residual free chlorine was kept at
1.0e2.0 mgCl2/L. NDMA� FPNH2Cl was evaluated by dosing water samples with mono-
chloramine at 140 mgCl2/L for 10 days at pH 6.8. NDMA precursors and dissolved organic
carbon (DOC) were fractionated by filtration through 30-, 3-, and 0.5 kDa membranes.
NDMA concentrations were <0.5e5.2 ng/L (median: 0.9 ng/L) in ground water and
<0.5e3.4 ng/L (2.2 ng/L) in river water. NDMA concentrations in ground water were slightly
lower than or comparable to those in river water. Concentrations of NDMA� FPCl2 were not
much higher than concentrations of NDMA except in samples containing high concen-
trations of NH3 and NDMA precursors. The increased NDMA was possibly caused by
reactions between NDMA precursors and monochloramine unintentionally formed by the
reaction between free chlorine and NH3 in the samples. NDMA precursors ranged from 4 to
84 ng-NDMA eq./L in ground water and from 11 to 185 ng-NDMA eq./L in river water. Those
in ground water were significantly lower than those in river water, suggesting that NDMA
precursors were biodegraded, adsorbed, or volatilized during infiltration. The molecular
weight of NDMA precursors in river water was dominant in the <0.5 kDa fraction, followed
by 0.5e3 kDa. However, their distribution was inconsistent in ground water: one was
dominant in the <0.5 kDa fraction, and the other in 0.5e3 kDa. Molecular weight distri-
butions of NDMA precursors were very different from those of DOC. This is the first study
to reveal the widespread occurrence and characterization of NDMA precursors in ground
water.
ª 2011 Elsevier Ltd. All rights reserved.
3; fax: þ81 3 5841 8529..jp (M. Murakami).ier Ltd. All rights reserved.
wat e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 3 6 9e3 3 7 73370
1. Introduction
N-nitrosodimethylamine (NDMA) is a highly water-soluble
N-nitrosamine (WHO, 2008). NDMA had been used as an inter-
mediate in the production of rocket fuel, an inhibitor of nitrifi-
cation in soil, a plasticizer in the manufacture of rubber and
polymers, a solvent in the fiber and plastic industry, an antiox-
idant, a softener of copolymers, and an additive to lubricants
(WHO, 2002). Recently, NDMA was found to be a disinfection
byproduct of chlorination, chloramination (Najm and Trussell,
2001; Choi et al., 2002; Mitch and Sedlak, 2002; Chen and
Young, 2008; Zhou et al., 2009a), and ozonation (Andrzejewski
and Nawrocki, 2007; Andrzejewski et al., 2008; Oya et al., 2008).
Its occurrence in drinking water has been investigated
throughout Canada, the USA (Charrois et al., 2007), and Japan
(Asami et al., 2009). A survey of 20 municipal drinking water
systems in Alberta, Canada, showed concentrations of
<5e100ng/L (Charrois etal., 2007).Anational surveyof Japanese
drinking water treatment plants revealed concentrations in
finished water of<1e10 ng/L (Asami et al., 2009).
NDMA in waters has been causing concern because of its
risk to health. NDMA has been classified as a probable human
carcinogen (B2) by the Integrated Risk Information System
(IRIS) of the United States Environmental Protection Agency
(USEPA, 1987). WHO (2008) has set the guideline value for
NDMA in drinking water at 100 ng/L. Health Canada proposed
a maximum acceptable concentration of NDMA in drinking
water of 40 ng/L (Health Canada, 2010). In Japan, the Ministry
of Health, Labor andWelfare added NDMA to items for further
study in the setting of drinking water quality standards and
adopted the WHO’s guideline value as the target in April 2010.
NDMA likely reaches aquifers owing to its high polarity (log
octanol/water partition coefficient¼�0.57) (Singer et al., 1977)
and moderate biodegradation rate. Zhou et al. (2009b) esti-
mated that 90% of NDMA by mass recharged from surface
water to ground water was biodegraded over 7 years in Los
Angeles, USA. In the USA, the detection of NDMA in ground
water is commonly attributed to its use and release in asso-
ciation with asymmetrical dimethylhydrazine, a rocket fuel
component, at aerospace facilities, or to the infiltration of
effluent from municipal wastewater treatment plants
(Fleming et al., 1996; Gunnison et al., 2000; Zhou et al., 2009b).
The occurrence of NDMA in ground water in Japan has not
been investigated.
The use of groundwater by some sectors such as hospitals,
hotels, and small factories in Tokyo has increased recently.
However, some aquifers in Tokyo are heavily polluted by high
concentrations of NH3 and organic matter (Kuroda et al., 2007,
2008). Nakada et al. (2008) also revealed that ground water in
Tokyo is contaminated by pharmaceuticals and personal care
products, probably owing to leakage from decrepit sewer
pipes, the past practice of sewage disposal underground, and
infiltration by contaminated river water, and estimated that
the average composition of ground water is w1% sewage
across Tokyo. Since NDMA can be formed from precursors
such as dimethylamine and natural organic matter by chlor-
amination or chlorination in the presence of high concentra-
tions of NH3 (Choi and Valentine, 2002;Mitch and Sedlak, 2002;
Gerecke and Sedlak, 2003; Mitch et al., 2003; Chen and
Valentine, 2007), the formation of NDMA after disinfection of
these waters is a matter of concern. It is now required to
investigate NDMA and its potential for formation in ground
water to avoid detrimental impacts to health. AlthoughNDMA
precursors, normally estimated by monochloramine reaction
during 10 days (Mitch et al., 2003), have been measured in
surface water (Gerecke and Sedlak, 2003; Schreiber and Mitch,
2006) and wastewater (Mitch and Sedlak, 2004; Sedlak et al.,
2005; Pehlivanoglu-Mantas and Sedlak, 2006b), there are no
studies of the occurrence of NDMAprecursors in groundwater
over a wide area.
Our research had three aims. First, we investigated the
extent of the occurrence of NDMA in ground water in Tokyo,
comparing the results from river water. Second, we evaluated
the potential for NDMA formation by chlorination
ðNDMA� FPCl2 Þ and by chloramination ðNDMA� FPNH2ClÞ andinvestigated the factors influencing it. NDMA� FPCl2 was
analyzed to mimic a practical chlorination process in Japan.
NDMA� FPNH2Cl was analyzed to estimate total NDMA
precursors. Third, we revealed the molecular weight distri-
butions of NDMA precursors in ground water and river water.
Mitch and Sedlak (2004) investigated their molecular weight
distributions in municipal wastewater using a series of
ultrafiltrationmembraneswith cutoffs of 30, 10, and 3 kDa and
showed a dominant size of <3 kDa. So we used membranes
with cutoffs of 30, 3, and 0.5 kDa. To our knowledge, this is the
first study to reveal the widespread occurrence and charac-
terization of NDMA precursors in ground water.
2. Materials and methods
2.1. Ground water and river water sampling
We collected 23 samples from springs and from private and
public wells in Tokyo from October 2009 to May 2010. During
the daytime we also collected 18 samples from the surface of
5 rivers at 15 locations in Tokyodthe Iruma River (R.I), the Ara
River (R.A1e4), the Edo River (R.E1e3), the Tama River
(R.T1e4), and the Tsurumi River (R.TS1e3) (Fig. 1). Sampling
dates, aquifer type, and basic water quality parameters are
shown in Supplementary Tables S1 and S2.
The samples were filtered through pre-baked GF/F glass
fiber filters (pore size 0.7 mm, Whatman) and divided between
2 glass bottles for NDMA and NDMA-FP measurements.
Sodium thiosulfate, a quenching agent, was added into the
bottle for NDMA measurements. All samples were stored in
the dark at 4 �C before analysis.
2.2. Chemical analysis
2.2.1. ChemicalsNDMA was purchased from Supelco. NDMA-d6 (98%) was
purchased from Cambridge Isotope Laboratories. HPLC-grade
distilled water, formic acid, and acetonitrile were purchased
from Wako Pure Chemical. Methanol and dichloromethane
(DCM) of pesticide residue and PCB analysis grade were
purchased from Kishida. Special grade sodium bicarbonate,
sodium thiosulfate, and sulfuric acid, 1st grade monop-
otassium phosphate, and sodium hypochlorite and sodium
Fig. 1 e Sampling locations.
wat e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 3 6 9e3 3 7 7 3371
hydroxide were purchased from Kishida. Special grade
ammonium chloride was purchased from Wako. Distilled
water was passed through a tC18 cartridge (Waters) to remove
trace levels of NDMA precursors andwas then used to prepare
reagent solutions for NDMA-FP measurements. Monochlor-
amine (NH2Cl) solutions were prepared fresh daily following
Mitch and Sedlak (2002). The monochloramine concentration
was confirmed by the indophenol method using a colorimeter
(HACH).
GW
1807
GW
1808
GW
1904
GW
0402
GW
0907
GW
1204
GW
1207
GW
1401
GW
1402
GW
1406
GW
1801
GW
1806
GW
2102
GW
2103
GW
0303
GW
0307
GW
0308
GW
0404
GW
0502
GW
0905
GW
1206
GW
1213
GW
1810 R
.IR
.A1
R.A
2R
.A3
R.A
4R
.E1
R.E
2R
.E3
R.T
1R
.T2
R.T
3R
.T4
R.T
S1R
.TS2
R.T
S3
0
1
2
3
4
5
6
Confinedaquifer
Unconfinedaquifer River waterSpring
ND
MA
(ng/
L)
Fig. 2 e NDMA concentrations in ground water and river
water.
2.2.2. NDMA analysis by solid-phase extraction and LC-MS/MSNDMA in the filtrate was concentrated by a factor ofw2500 by
solid-phase extraction. To 500 mL of sample, 1 g of sodium
bicarbonate and 5 ng of NDMA-d6 were added. The samples
were passed through an EPA 521 method cartridge (Resprep)
preconditioned with 10 mL DCM, 10 mL methanol, and 20 mL
distilled water. The flow rate was 5mL/min. The cartridgewas
then dried under a gentle stream of nitrogen gas. NDMA was
GW
1807
GW
1808
GW
1904
GW
0402
GW
0907
GW
1204
GW
1207
GW
1401
GW
1402
GW
1406
GW
1801
GW
1806
GW
2102
GW
2103
GW
0303
GW
0307
GW
0308
GW
0404
GW
0502
GW
0905
GW
1206
GW
1213
GW
1810 R
.IR
.A1
R.A
2R
.A3
R.A
4R
.E1
R.E
2R
.E3
R.T
1R
.T2
R.T
3R
.T4
R.T
S1R
.TS2
R.T
S3
0
2
4
6
8
10
12NDMA
NDMA-FP
ND
MA
(ng/
L)
Confinedaquifer
Unconfinedaquifer River waterSpring
Cl2
Fig. 3 e NDMA concentrations between before and after
chlorination.
-2
-1
0
1
2
3
4
5
6
0 50 100 150 200 250
Ground water
River water
Incr
ease
d N
DM
A* (n
g/L)
NDMA precursors (ng-NDMA eq./L)
-2
-1
0
1
2
3
4
5
6
0 5 10 15
Ground water
River water
R.A2GW0502
GW0303In
crea
sed
ND
MA*
(ng/
L)
NH 3-N (mg/L)
a b
* Increase = NDMA-FPCl2 – NDMA.
Fig. 4 e Relationship between increased NDMA due to chlorination and (a) NH3 and (b) NDMA precursors.
*Increase [ NDMA� FPCl2 e NDMA.
wat e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 3 6 9e3 3 7 73372
elutedwith 10mLDCM. The eluate was concentrated to 200 mL
under nitrogen gas. NDMA was separated in an Acquity UPLC
system (Waters) with a BEH C18 column (Waters). The mobile
phase was composed of 0.1% formic acid aqueous solution
(eluent A) and 100% acetonitrile (eluent B). The flow rate was
0.2mL/min at all stages, and the sample injection volumewas
30 mL. NDMAwas detected with an Acquity TQD tandemmass
spectrometer (Waters) operated in electrospray/chemical
ionization positive-ion mode. Multiple reaction monitoring
transitions were m/z 74.9e43.1 (quantification) and m/z
74.9e57.9 (confirmation) for NDMA and m/z 81.0e46.0 for
NDMA-d6. NDMA concentrations were label-recovery
corrected.
The reproducibility and recovery rate were confirmed by
spiking sampleswith 5 ng-NDMA standard in 500mL. The rate
of recovery from distilled water (n ¼ 5) was 116% and the
GW
1807
GW
1808
GW
1904
GW
0402
GW
0907
GW
1204
GW
1207
GW
1401
GW
1402
GW
1406
GW
1801
GW
1806
GW
2102
GW
2103
GW
0303
GW
0307
GW
0308
GW
0404
GW
0502
GW
0905
GW
1206
GW
1213
GW
1810 R
.IR
.A1
R.A
2R
.A3
R.A
4R
.E1
R.E
2R
.E3
R.T
1R
.T2
R.T
3R
.T4
R.T
S1R
.TS2
R.T
S3
0
50
100
150
200
ND
MA
prec
urso
rs
(ng-
ND
MA
eq./L
)
Confinedaquifer
Unconfinedaquifer River waterSpring
Fig. 5 e NDMA precursor concentrations in ground water
and river water.
relative standard deviation (RSD) was 4%. The rate of recovery
from ground water (n ¼ 3) was 83%.
The rates of recovery of NDMA-d6 were 78% from ground
water and 72% from river water. The limit of quantification
(LOQ) was 0.5 ng/L. An operational blank was run with every
batch, and NDMA was normally less than LOQ.
2.2.3. Potential for NDMA-formation by chlorinationðNDMA� FPCl2 ÞNDMA� FPCl2 was analyzed by following the method for the
investigation of disinfection byproducts (Japan Water Works
Association, 2001). Briefly, 570 mL water was buffered with
30 mL 0.2 M monopotassium phosphate at pH 7.0 � 0.2,
chlorinated by free chlorine, and then incubated at 20 �C in the
dark for 24 h. The residual free chlorine was kept at
1e2mgCl2/L. Chlorine was analyzed by the DPDmethod using
a colorimeter. The reactions were halted by the addition of
sodium thiosulfate solution, and NDMA was measured. The
reproducibility was confirmed by using ground water (n ¼ 4;
RSD ¼ 10%). NDMA� FPCl2 in the operational blank ranged
from <0.5 to 0.9 ng/L.
2.2.4. Potential for NDMA-formation by chloraminationðNDMA� FPNH2ClÞNDMA� FPNH2Cl was analyzed according to Mitch et al. (2003).
Briefly, 510 mL water was mixed with 30 mL 0.2 M monop-
otassium phosphate, dosed with 60 mL 20 mM (1400 mgCl2/L)
monochloramine solution at pH 6.8� 0.2, and then incubated
at 20 �C in the dark for 10 days. The residual total chlorine
was analyzed by the DPD method using a colorimeter. The
reactions were halted by the addition of sodium thiosulfate,
and NDMA was measured. The reproducibility was
confirmed by using river water (n ¼ 4; RSD ¼ 4%).
NDMA� FPNH2Cl in the operational blank using distilled water
passed through a tC18 cartridge was 5.4� 0.7 ng/L (arithmetic
mean � standard error; n ¼ 7), whereas those in the opera-
tional blank using Milli-Q water and distilled water were
0
20
40
60
80
100
0 10 20 30 40 50 500
1000
1500
Ground water
ND
MA
prec
urso
rs
(ng-
ND
MA
eq./L
)
Crotamiton (ng/L)
0
50
100
150
200
0 5 10 15 20
Ground water
River waterN
DM
A pr
ecur
sors
(n
g-N
DM
A eq
./L)
TIN (mg/L)
a b
Fig. 6 e Relationship between NDMA precursors and (a) TIN and (b) crotamiton (Kuroda, 2010). (a) Ground water: r2 [ 0.02,
P > 0.1; river water: r2 [ 0.81, P < 0.01. (b) Ground water: r2 [ 0.003, P > 0.1.
wat e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 3 6 9e3 3 7 7 3373
13.9 � 2.6 ng/L (n ¼ 2) and 8.6 � 1.5 ng/L (n ¼ 2), respectively.
Use of the tC18 cartridge reduced NDMA� FPNH2Cl in the
operational blank, indicating that the cartridge removes
trace levels of NDMA precursors in distilled water.
NDMA� FPNH2Cl in the operational blank was not subtracted
from that in ground water and river water, because
a proportion of the NDMA precursors may have come from
the distilled water, even after it had been passed through the
cartridge.
We expected total NDMA precursors in the water samples
to convert to NDMA during the 10 days of chloramination
(Mitch et al., 2003; Mitch and Sedlak, 2004). Therefore, we
considered the increased concentration to represent total
NDMA precursors, and defined the precursors as
NDMA� FPNH2Cl minus initial NDMA. The concentration was
expressed as ng-NDMA equivalent/L (ng-NDMA eq./L).
Under these conditions, monochloramine decays mainly
by disproportionation and other autodecomposition reactions
(Valentine and Jafvert, 1988; Vikesland et al., 1998). The
0
50
100
150
200
0 2 4 6 8 10
Ground water
River water
ND
MA
prec
urso
rs
(ng-
ND
MA
eq./L
)
DOC (mg/L)
Fig. 7 e Relationship between NDMA precursors and DOC.
Ground water: r2 [ 0.16, P [ 0.06; river water: r2 [ 0.47,
P < 0.01.
residual total chlorine concentrations were similar among all
samples except two, and were approximately 9 mgCl2/L,
which was comparable to a previous result (Mitch and Sedlak,
2004). NDMA precursor concentrations were possibly under-
estimated in samples GW0307 and R.A4, which showed
�0.1 mg/L of residual total chlorine.
2.2.5. Other chemical analysesAfter the samples were filtered through CE membrane filters
(pore size 0.45 mm, Advantec), NH3 was analyzed by colorim-
etry using a salicylate method or indophenol blue absorpti-
ometry. After the samples were filtered through PTFE
membrane filters (0.45 mm, ADVANTEC), dissolved organic
carbon (DOC), NO2, NO3, and UV absorbance were analyzed.
DOC was analyzed with a total organic carbon analyzer (TOC-
V, Shimadzu). NO2 and NO3 were analyzed by ion chroma-
tography (761 Compact IC, Metrohm). The sum of NH3eN,
NO2eN, and NO3eN was regarded as total inorganic N (TIN).
UV absorbance at 254, 260, and 272 nm (UV254, UV260, UV272)
was analyzed by spectrophotometer (U-2010, Hitachi).
2.3. Fractionation of NDMA precursors
The NDMA precursors in two ground water samples (GW0905
and GW0907) and two river water samples (R.TS3 and R.T3)
were fractionated by molecular weight by the filtration-in-
series method (Lohwacharin et al., 2009). The samples were
sequentially fractionated through 30-kDa regenerated cellu-
lose (PLTK), 3 kDa regenerated cellulose (PLBC), and 0.5 kDa
cellulose acetate (YC05) membranes (Millipore) in a 2000 mL
Millipore Amicon stirred cell unit.
Before use, all membranes were immersed in distilled
water for 24 h to remove the wetting agent. Distilled water
passed through a tC18 cartridge was then flushed through the
membranes for 30 min to obtain pure water permeability in
a quasi-steady state. Dead-end filtration was operated at
a constant trans-membrane pressure. Constant trans-
membrane pressures of 100, 207, and 401 kPa for the 30-, 3-,
and 0.5 kDa membranes, respectively, were maintained
during fractionation at a constant stirring rate of 100 rpm.
Fig. 8 e Molecular weight distributions of DOC and NDMA precursors. (a) DOC concentration in each molecular fraction.
(b) Molecular weight distribution of DOC. (c) NDMA precursors in each molecular fraction. (d) Molecular weight distribution
of NDMA precursors.
wat e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 3 6 9e3 3 7 73374
After fractionation, water samples were subjected to
NDMA� FPNH2Cl, DOC, and UV absorbance measurements.
3. Results and discussion
3.1. Occurrence of NDMA in Tokyo
In ground water, NDMA was detected in 20 out of 23 samples,
at <0.5e5.2 ng/L, with a median of 0.9 ng/L (Fig. 2). NDMA
probably decreased during infiltration owing to biodegrada-
tion (Zhou et al., 2009b), gaseous diffusion, or volatilization
(Arienzo et al., 2006). In river water, NDMA was detected at 13
out of 15 locations (16/18 samples) at <0.5e3.4 ng/L (median:
2.2 ng/L). Because the river water samples were collected from
the surface during the daytime, direct photolysis of NDMA
might have occurred in these samples (Plumlee and Reinhard,
2007). These results are comparable to those of Asami et al.
(2009), who reported a maximum NDMA concentration in
surface water in Japan of 4.3 ng/L. NDMA concentrations in
ground water were slightly lower than or comparable to those
in river water. The highest concentrations were 5.2 ng/L in
ground water and 3.4 ng/L in river water, or <10% of the WHO
guideline for NDMA in drinking water.
No strong relationships were found between NDMA and
other water quality parameters (Table S3) in groundwater and
river water (Tables S4, S5).
3.2. NDMA� FPCl2
NDMA� FPCl2 concentrations in ground water ranged from
<0.5 to 10.8 ng/L, with a median of 1.8 ng/L (Fig. 3). Those in
river water ranged from 0.7 to 7.8 ng/L (median: 2.3 ng/L).
Concentrations were not much increased (<4.0 ng/L) in most
samples, but increased from 0.6 to 5.2 ng/L in GW0303, from
5.2 to 10.8 ng/L in GW0502, and from 3.3 to 7.8 ng/L in R.A2.
wat e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 3 6 9e3 3 7 7 3375
Samples containing high concentrations of NH3 and NDMA
precursors showed large increases in NDMA by chlorination
(>4.0 ng/L) (Fig. 4). In bench-scale chlorine disinfection
experiments, peak NDMA production occurred near the
theoretical monochloraminemaximum in the sub-breakpoint
region of the disinfection curve (Charrois and Hrudey, 2007).
The increased NDMA in our study was possibly caused by
reactions between NDMA precursors and monochloramine
that was unintentionally formed by the reaction between free
chlorine and NH3 in the samples.
3.3. Occurrence of NDMA precursors
Total NDMA precursors in ground water ranged from 4 to
84 ng-NDMA eq./L, with amedian of 10 ng-NDMA eq./L (Fig. 5).
Total precursors in river water ranged from 11 to 185 ng-
NDMA eq./L (median: 51 ng-NDMA eq./L). Concentrations in
ground water were significantly lower than those in river
water (t-test, P< 0.01). The difference indicates that the NDMA
precursors were biodegraded, adsorbed, or volatized during
infiltration. Although NDMA precursors are degraded only
slightly in wastewater-impacted river water (Schreiber and
Mitch, 2006; Pehlivanoglu-Mantas and Sedlak, 2006a), they
disappeared during the relatively long process of infiltration
into the ground water.
To identify the sources of NDMA precursors in the water,
we investigated the relationships between the precursors and
TIN (Fig. 6a). There was a significant strong relationship in
river water (r2 ¼ 0.81, P < 0.01). This relationship suggests that
NDMA precursors in river water are derived from wastewater
treatment plants, because most N in urban surface waters in
Japan comes fromwastewater treatment plants (Toyoda et al.,
2009; Ohte et al., 2010). In contrast, there was no significant
relationship in ground water (r2 ¼ 0.02, P > 0.1). Since N in
ground water in Tokyo comes from a wide variety of sources,
such as natural soils, fertilizers, and sewage (Kuroda et al.,
2007), we analyzed crotamiton, a conservative marker of
domestic sewage (Nakada et al., 2008). The crotamiton was
analyzed in ground water collected from the same well in
a different year (Kuroda, 2010). There was no significant
relationship (Fig. 6b), suggesting that the major source of
NDMA was not leakage of domestic sewage, or that there is
a large difference in infiltration behavior between NDMA
precursors and crotamiton.
There were weak but significant relationships between
NDMAprecursors and DOC in groundwater (r2¼ 0.16, P¼ 0.06)
and river water (r2 ¼ 0.47, P< 0.01) (Fig. 7), but no relationships
with UV absorbance or specific UV absorbance (SUVA) (Fig. S1).
The arithmetic mean � standard error of the NDMA
precursor-to-DOC ratio was 20� 5 ng-NDMA eq./mg in ground
water and 39 � 5 ng-NDMA eq./mg in river water. Again, this
result indicates that NDMA precursors in ground water were
less abundant than those in river water. After reacting water
samples with monochloramine at 70 mg/L Cl2 for 7 days at pH
7.2 � 0.2, Gerecke and Sedlak (2003) found 1.1 ng-NDMA eq./
mg in ground water (n ¼ 1) and 3.5 � 0.7 ng-NDMA eq./mg in
surface waters (n ¼ 7) in the USA. The NDMA precursor-to-
DOC ratios in our study were approximately one order of
magnitude higher than those of Gerecke and Sedlak (2003),
although the measurement of NDMA precursors differed
between the two studies. Our results indicate that ground
water and river water in Tokyo are heavily contaminated by
NDMA precursors, possibly owing to urban activities.
3.4. Molecular size distributions of NDMA precursors
The distributions of DOC were inconsistent between the two
ground water samples tested (Fig. 8a and b, Table S6). DOC in
GW0907 was distributed substantially in all four fractions:
highest in the <0.5 kDa fraction (45%), followed by 3e30 kDa
(27%), 0.5e3 kDa (21%), and >30 kDa (7%). But DOC in GW0905
was dominant in the >30 kDa (58%) and <0.5 kDa (38%) frac-
tions, and very small in the 3e30 kDa (3%) and 0.5e3 kDa (1%)
fractions. On the other hand, DOCwas similarly distributed in
the two river water samples tested (Fig. 8a and b, Table S6):
dominant in the 3e30 kDa fraction (35%e40%), followed by
0.5e3 kDa (28%e32%), <0.5 kDa (18%e29%), and >30 kDa
(7%e10%).
The distributions of NDMA precursors (Fig. 8c and d, Table
S7) were very different from those of DOC (above) and UV
absorbance (Fig. S2, Tables S8eS10). There were also no clear
relationships between NDMA precursors and SUVA (Fig. S3).
The molecular weight distributions of NDMA precursors were
inconsistent between the two ground water samples tested
(Fig. 8c and d): NDMA precursors in GW0905 were dominant in
the <0.5-kDa fraction (73%), whereas those in GW0907 were
dominant in the 0.5e3 kDa fraction (53%). NDMAprecursors in
both river water samples were dominant in <0.5 kDa fraction
(49%e57%), followed by 0.5e3 kDa (24%e43%). In general,
NDMA precursors were dominantly (>70%) distributed in the
<3 kDa fraction in both groundwater and river water samples.
This result is consistent with the same finding in municipal
wastewater (Mitch and Sedlak, 2004).
4. Conclusions
(1) NDMA concentrations in groundwater ranged from<0.5 to
5.2 ng/L and were slightly lower than or comparable to
those in river water.
(2) NDMA was not greatly increased (<4.0 ng/L) by chlorina-
tion, except in two ground water and one river water
samples. NDMA was increased greatly in samples con-
taining high concentrations of NH3 and NDMA precursors.
(3) Concentrations of NDMA precursors ranged from 4 to
84 ng-NDMA eq./L in ground water and from 11 to 185 ng-
NDMAeq./L in riverwater. Therewereweak but significant
relationships between NDMA precursors and DOC in both
sources, and the NDMA precursor-to-DOC ratios were
20 � 5 ng-NDMA eq./mg in ground water and 39 � 5 ng-
NDMA eq./mg in river water. NDMA precursors in ground
water were less abundant than those in river water, indi-
cating that the NDMA precursors were biodegraded,
adsorbed, or volatized during infiltration.
(4) The molecular weight of NDMA precursors in river water
was dominant in the <0.5 kDa fraction, followed by
0.5e3 kDa. However, their distribution was inconsistent in
ground water: one was dominant in the <0.5 kDa fraction,
and the other in 0.5e3 kDa. Molecular weight distributions
of NDMA precursors were different from those of DOC.
wat e r r e s e a r c h 4 5 ( 2 0 1 1 ) 3 3 6 9e3 3 7 73376
Acknowledgments
This research was partially supported by JSPS Grants-in-Aid
for Scientific Research (22760406, 21860018, and 19360237)
and a CREST project grant for ‘Development of Well-balanced
Urban Water Use System Adapted for Climate Change’ from
the Japan Science and Technology Agency.
Appendix. Supplementary data
Supplementary data related to this article can be found online
at doi:10.1016/j.watres.2011.03.053.
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