심재구
(Jae-Goo Shim)
*
아킬아프잘
(Afzal Aqeel)
**
최보미
(Bo-Mi Choi)
**
이정현
(Jung-Hyun Lee)
*
곽노상
(No-Sang Kwak)
*
임호진
(Ho-Jin Lim)
**†
Copyright © 2016, Korean Society on Water Environment
Key words
Nitrosamine, pH effect, Photodegradation, UV photolysis, Water treatment
1. Introduction
It has been more than 100 years since N-nitrosamines have been studied by the scientific community. N-nitrosamines received much attention when Barnes and Magee discovered the carcinogenic
properties of these compounds (Barnes and Magee, 1954). Moreover, with extensive research, most of N-nitrosamines (i.e., 90% of the total) are now classified as carcinogenic, mutagenic,
and/or teratogenic compounds, which can ultimately cause detrimental effects on human
health (Andrzejewski et al., 2005; Wang et al., 2011; Xu et al., 2010; Zhou et al., 2012). N-nitrosamines primarily target esophagus and liver sites for tumor formation. Other
organs, which can also be affected by N-nitrosamines are bladder, brain, and lungs (Xu et al., 2009a). Therefore, many developed countries established stringent laws for the regulation
of acceptable level of nitrosoamines. Acceptable limit proposed by the Norwegian Public
Health Institute for all N-nitrosoamines is 4 ng/L for drinking water and 0.3 ng/m3 for air (Sorensen et al., 2015; Zhou et al., 2012).
N-nitrosamines cause severe problem in drinking water purification systems and in reprocessing
of waste water to fulfill increasing water demands worldwide (Zhou et al., 2012). High concentration of organic nitrogen in industrial waste water effluents can serve
as precursors for N-nitrosamines in the reaction with disinfectants (Krasner et al., 2009). Consequently, more efficient drinking water treatments are required to achieve the
purity up to safe drinking levels. Recent studies have confirmed that chlorination
and chloramination treatments of drinking water and industrial wastewater result in
the formation of new disinfection by-products of N-nitrosamines (Mitch and Sedlak, 2002; Padhye et al., 2009; Schreiber and Mitch, 2006). N-nitrosopyrollidine (NPYR) and N-nitrosodibutylamine (NDBA) have been included in this new class of emerging disinfection
by-products (Zhou et al., 2012). Charrois et al. (2004) detected NPYR in drinking water both in the water supply system and at the plant,
where chloramination was used for disinfection (Charrois et al., 2004). NPYR has been reported in drinking water distribution systems up to 70.5 ng/L and
up to several hundred ng/L in waste water and municipal sludge, respectively (Krasner et al., 2009; Padhye et al., 2009; Zhao et al., 2006). Wang et al. (2016) investigated 54 drinking water treatment plants and reported that NDBA was one of
the most abundant N-nitrosamines. The occurrence of NPYR and NDBA in aquatic environment is estimated
to be associated with 10-6 cancer risk at 20 ng/L concentration level (Gerrity et al., 2014). Conventional drinking water and waste water treatment plants are not designed to
remove these emerging contaminants (Zhou et al., 2012).
N-nitrosamines are usually soluble in water due to their polar nature. These compounds
are difficult to extract with organic solvents due to their low octanol/water partition
coefficients (Kow). These compounds are not significantly adsorbed on non-polar surfaces. This high
hydrophilicity and low adsorbability of N-nitrosamines contribute to a great risk of ground water contamination. Coagulation
and filtration could not be used for the removal of N-nitrosamines in drinking water facilities due to the above discussed properties.
The majority of N-nitrosamines precursors are also too small in size that could not be removed by coagulation
(Xu et al., 2011). Furthermore, many polymers (e.g., poly-DADMAG, polyamines) used as coagulant in
drinking water treatment plants, could be the source of nitrosamines precursors (Kohut and Andrews, 2003; Wilczak et al., 2003). Miyashita et al. (2009) concluded that nitrosamines cannot be efficiently removed even though nanofilters
and reverse osmosis membranes are used. Nitrosamines cannot be removed from water
by aeration due to low Henry constants, and are also hardly biodegradable (Nawrocki and Andrzejewski, 2011). Previous research groups have distinctly described that nitrosamines exhibit two
absorption peaks (strong at ~230 nm and weak at ~340 nm) when expose to UV light.
Therefore, this property can be exploited for photolytic degradation of N-nitrosamines in water (Andrzejewski et al., 2005; Sorensen et al., 2013; Stefan and Bolton, 2002). Furthermore, photodegradation of nitrosamine results in less harmful products and
conventional plants could also be retrofitted with this technology (Zhou et al., 2012).
Environmental hazards and measurement methods of both N-nitrosamines (i.e., NPYR and NDBA) have been widely studied in previous studies (Gushgari et al., 2016; Kodamatani et al., 2009; Lee et al., 2013; Mahanama and Daisey, 1996; Ngongang and Duy, 2015; Pozzi et al., 2011; Sen et al., 1997; Wang et al., 2011; Zhang et al., 2016; Zhao et al., 2006). However, a few studies were published on treatment methods and degradation pathways
of NPYR and NDBA (Plumlee and Reinhard, 2007; Xu et al., 2009b; Zhou et al., 2012). The pH effects on photodegradation of NDBA have been studied in a mixture of nine
N-nitrosamines in earlier study of Zhou et al. (2012). Therefore, it may have assumed that NDBA will follow the same behaviour alone as
in mixture. To the best of authors’ knowledge, there is no study available where pH
effect on photodegradation of NDBA was individually evaluated. It is important to
evaluate the pH effect on photodegradation of NDBA in individual solution for proper
understanding of kinetics and identification of the degradation products. Therefore,
in this paper, photodegradation of N-nitrosamines in aqueous solution by UV irradiation was carried out and influence
of initial pH was investigated. Furthermore, formation of oxidized products (i.e.,
primarily NO2- and NO3-) was also investigated.
2. Materials and Methods
2.1. Nitrosamines Reagents
N-Nitrosodibutylamine (analytical grade) and N-nitrosopyrrolidine (purity=99%) were purchased from Sigma-Aldrich (St. Louis, MO,
USA). Stock solutions (i.e., 500 mg/L) were prepared in ultra-pure water (>18.3 μΩ-cm)
taken from a Milli-Q water system (Power 1+, Human, Korea). These stock solutions
were stored in the refrigerator before photodegradation experiments and reaction solutions
(i.e., 50 mg/L) were prepared by further dilution with ultra-pure water. Glass bottles
containing stock solutions were properly covered with the aluminum foil to avoid from
light. These stock solutions were kept in the refrigerator and used within 30 days.
Concentrations of stock solutions were rechecked throughout storage period with UV
absorbance calibration. All glassware was cleaned thoroughly by sonicating in deionized
water with a cleaning agent (CIP 100, Steris, USA), then followed by rinsing with
reverse osmosis water in an ultrasonic cleaner (8510R-DTH, Branson, USA) and dried
in a drying oven (SW-90D, Sang Woo, Korea) at 50℃ before use.
2.2. Experimental Procedure
Photodegradation experiments were performed in a cylindrical water jacketed glass
batch reactor under controlled conditions as shown in Fig. 1. Initial pH of the solution was pre-adjusted with 2 M HCl and NaOH using a pH meter
(Orion 4 star, Thermo Scientific, USA) after calibration. Then, 700 mL of 50 mg/L
N-nitrosamine solution was exposed to UV irradiation. A low pressure Hg lamp (GL4WP,
UV Nature, Korea) of 4 W was installed to the reactor. Solution was heated on a hot
plate equipped with magnetic stirrer (HMS100, Yhana, Korea) and a temperature controller
(TZ4ST, Autonics, USA) with a K-type thermocouple to maintain temperature at 40℃.
A fraction collector (2110, Bio-Rad, USA) was installed to collect samples at fixed
intervals. A peristaltic pump (BT 100-2J, Longer Pump, China) was used to transport
reaction solution to the fraction collector. After stabilizing the system, UV-lamp
and peristaltic pump were switched on to start irradiation and drawing sample solution.
Samples were collected in 7 mL vials with 0.5 min interval keeping the flow rate of
10 mL min-1 during first 10 minutes. Afterwards samples were collected in 2.5 min
interval keeping the flow rate of 2 mL/min up to next 20 minutes. Then, every two
consecutive vials were combined in 20 mL amber colored vial to get cumulative volume
of 10 mL for each sample. These collected samples were stored at 6℃ in the refrigerator
for further analysis. Remaining N-nitrosamine solution in the reactor was further degraded for 2 hours before disposal
to ensure complete degradation of nitrosamines for the safety of environment. Samples
were analyzed within three weeks after collection.
Fig. 1.
Experimental design for direct photolysis of N-nitrosamine.
2.3. Analysis
Degradation of N-nitrosamines was monitored by UV-Vis spectrophotometer (8453, Agilent, USA). The
removal of N-nitrosamines was quantified by correlating the absorbance at specific wavelengths.
A rectangular quartz cuvette of 10 mm path length (5061-3387, Agilent) was used for
absorbance measurements between 190-800 nm with 1 nm interval. Every time the cuvette
was washed three times with Milli-Q water and one time with sample solution before
absorbance measurement. Collected samples at different time intervals were diluted
two times with ultra-pure water (LiChrosolv, Merck, USA) before analysis of NO2- and NO3-. Dionex ICS-3000 ion chromatography (Sunnyvale, CA, USA) equipped with self-regenerating
suppressor and conductivity detector was used for the measurement of NO2- and NO3-. Dionex Ionpac AS14 analytical column (I.D. 4 × L 250 mm) coupled to AG14 guard column
(I.D. 4 × L 50 mm) was used in the analysis. The ion analysis unit was operated in
autosuppression mode using an eluent comprised of 3.5 mmol Na2CO3 + 1 mmol NaHCO3 at a flow rate of 1.2 mL/min. The accuracy and precision for the IC analysis was
ensured by placing the repeated set of samples after every 10th sample and standard
sample was added after this repeated set of samples. In order to remove zero error,
blank samples were also placed after each standard sample. The minimum detection limit
of NO2- and NO3- was 8.9×10-3 ppm and 8.3×10-3 ppm, respectively. It was determined as 3 times of standard deviation of blank measurements.
TOC/TN analyzer (Shimadzu, TOC-L CPH, Japan) coupled with autosampler was used for
total organic carbon (TOC) and total nitrogen (TN) of the collected samples after
two times dilution. A multi-point calibration was carried out from a mixed standard
solution of 100 mgC/L TC and 100 mgN/L TN acidified with 0.05 M HCl. The standard
solutions were diluted in the range of 1-50 mg/L (i.e., 1, 2, 5, 10, 25, and 50 mg/L)
and then these were analyzed for TOC and TN. The accuracy was checked and zero error
was removed during the analysis of samples by introducing check standard (5 mg/L)
and blank sample after every 10th sample. The minimum detection limit of TOC and TN
was 7.0×10-2 ppm and 9.4×10-3 ppm, respectively. It was determined as 3 times of standard deviation of blank measurements.
3. Results and Discussions
3.1. UV-Vis Absorption Properties
N-nitrosamines exhibit two primary absorption peaks in UV-Vis range. Absorption spectra
of N-nitrosamines along with UV lamp emission spectra are shown in Fig. 2. The maximum peak intensity was observed at λmax = 234 nm and λmax = 231 nm for NDBA and NPYR, respectively. Crosssectional absorptivity (єmax) at λmax was determined to be 5.94×106 and 4.20×106 cm2/mol for NDBA and NPYR, respectively as shown in Table 1. The strong absorption band is due to π→π* intramolecular charge transfer (Lee et al., 2005; Stefan and Bolton, 2002). Weak absorption bands were observed at λ = 338 nm and λ = 333 nm for NDBA and NPYR,
respectively. The weak absorption band is associated with n→π* transition. These are
consistent with earlier reports of a strong peak at ~230 nm and a weak peak at ~340
nm for N-nitrosamines (Nawrocki and Andrzejewski, 2011; Stefan and Bolton, 2002; Xu et al., 2008).
Fig. 2.
UV-Vis absorption spectra of 50 mg/L nitrosamine solutions at pH6 along with emission
spectrum of UV lamp.
Table 1.
Physicochemical and optical properties of N-nitrosamines at λmax and 254 nm
The homolytic cleavage of N-NO bond in N-nitrosamine is associated with π→π* electronic transition when irradiated under UV
light as shown in R1 below (Lee et al., 2005; Xu et al., 2009). Hydrogen ions present in water attach to the oxygen of nitroso group via hydrogen
bonding. Due to the sharing of electron in hydrogen bonding, N-N bond becomes weaker
to result in degradation of N-nitrosamines. Acidic solutions have large quantities of H+ available for this hydrogen bonding, which could accelerate the degradation of N-nitrosamines.
This photolytic cleavage of N-nitrosamines produces corresponding ammonium radical and nitric oxide. In addition,
the heterolytic cleavage of N-NO bond in nitrosamines is induced by n→π* electronic
transition as shown in R2 below (Lee et al., 2005).
Mechanistic pathways are further described by different research groups. Xu et al. (2010) suggested that homolytic cleavge of N-N bond in NDEA photodegradation resulted in
diethylaminium radical. Two diethylaminium radicals could combine to form diethylamine.
Acid-catalyzed hydrolysis of intermediates resulted in the formation of ethylamine
and aldehyde. When the heterolytic cleavage takes place in the acidic solution, diethylamine
is exposed to favorable conditions for the nucleophile attack. Stefan and Bolton (2002) reported that secondary amines and nitrite ions were produced during photodegradation
in weakly acidic and neutral pH conditions. Chow (1973) showed that acid complex of NDMA (or protonated NDMA) was photodegraded into dimethylamine
and HNO2 by photo-hydrolysis from the heterolytic cleavage of N-NO bonds. Whereas, aminium
radical and . produced by photoelimination from the homolytic cleavage of N-NO bonds.
The interference of absorbance was observed due to byproducts at shorter wavelength
(i.e., λmax). There was a minimal interference for weak peak at λ = 338 nm and λ = 333 nm for
NDBA and NPYR, respectively. This wavelength was selected for the determination of
nitrosamines, because interference at this wavelength was apparently appeared only
at the later part of the reaction. Therefore, the absorbance values of N-nitrosamines during the first 10 min were used to determine the reaction rate constants.
3.2. Effect of pH on kinetics of N-nitrosamines photodegradation
The decay of N-nitrosamines under UV irradiation was studied over a wide range of pH2-10 as shown
in Fig. 3. The photodegradation depends on photon flux and concentration of N-nitrosamine. A uniform photon flux was supposed in the reactor, so reaction rate
should depend only on the concentration of N-nitrosamine. Therefore, reaction rate constants were obtained assuming pseudo-first
order kinetics for the degradation. For more reasonable comparison of rate constants
presented in this study with the literature data, these were normalized to the intensity
of UV lamp and volume of the reactor (i.e., L/W-min). In case of NDBA, degradation
rate constants were 3.26×10-2 L/W-min, 2.38×10-2 L/W-min, 9.98×10-3 L/W-min, 7.53×10-3 L/W-min, and 5.08×10-3 L/W-min at pH2, 4, 6, 8, and 10, respectively. Degradation rate constants increased
with decrease in pH for NDBA. Similar trends for degradation rate constants were observed
in previous studies (Lee et al., 2005; Stefan and Bolton, 2002; Xu et al., 2008; Xu et al., 2010). In case of NPYR, degradation rate constant of 1.14×10-2 L/W-min at pH4 was higher than 9.45×10-3 L/W-min of pH2. Such irregular trend of NPYR is not clearly known. NPYR showed negligible
change in rate constant at alkaline pH. This negligible change in rate constant could
be explained by corresponding similar formation rates of NO2- (i.e., 8.2×10-3 mmol/L-min) and NO3- (i.e., 6.1×10-3 mmol/L-min) at pH8-10 as shown in Table 3. Because, it has been observed that the formation of NO2- and NO3- follow degradation of N-nitrosamines.
Fig. 3.
Photodegradation of nitrosamies (expressed as C/Co) as a function of reaction time at different pH. Reaction rate constants are obtained
assuming pseudo-first order reaction for the first 10 min. a) NDBA b) NPYR.
Table 2.
Kinetic studies comparison of NDBA and NPYR with the available literature, on the
basis of different parameters
Table 3.
Formation rate of NO2- and NO3- along with degradation rate of N-nitrosamines
There are two different explanations about the mechanism of N-nitrosamines photodegradation. The stretching of N-N double bond induces partial
dipole and negative charge at nitroso oxygen, which is a good site for protonation
(Chow, 1973). According to Xu et al. (2010), protonated species of nitrosamines are more photolabile than unprotonated species.
Lee et al. (2005) suggest that acid-catalyzed complex rather than protonated or unprotonated species
are responsible for the photodegradation. Polar character of N-nitrosamines is good explanation to conclude that acidic conditions promote photolability
of nitrosamines through weakening of N-N bonding.
Photodegradation rate constant of NDBA was higher than that of NPYR at all pH values.
Zhou et al. (2012) reported similar trend of rate constants for NDBA and NPYR. The difference in degradation
rate constants might be primarily due to their chemical structures (Ohwada et al., 2001; Salvo et al., 2008). The higher degradation rate of NDBA might be caused by the fact that organic species
produced also affect the dissociation energies such as benzyl radicals clearly contribute
to the C-N bond breakage (Salvo et al., 2008). The lower degradation rate of NPYR might be due to its unique cyclic structure with
high electron density that might tolerate the weakening of N-NO bonding by protonation
via electron donation. The pH effect is caused by the weakening of N-NO bond by increased
protonation at lower pH. This makes NPYR more stable than other straight chain nitrosamines
(i.e., NDBA) (Xu et al., 2009b). Hence, chemical structures might influence degradation rate along with pH effect.
Zhou et al. (2012) showed the influence of various factors (e.g., Initial nitrosamine concentration,
UV intensity, pH, H2O2 dosage, and inorganic anions) on photodegradation of the mixture of nine N-nitrosamines. Rate constants obtained in our study for NDBA and NPYR were much higher
relative to the former study data. These higher rate constants might be due to difference
in experimental design. In our study nitrosamine solutions were directly irradiated
under UV light, while baffles with different helix angles between lamp shade and nitrosamine
solution were used in the former study. On the other hand, competition for available
UV light might be increased for the mixture of nine N-nitrosamines irradiated together in the previous study. Photodegradation rate constant
of NPYR presented in this study (i.e., 4.73×10-3 L/W-min) at pH6 was 3.94 times higher than that of Chen et al. (2015) at pH7 (i.e., 1.20×10-3 L/W-min). The discrepancy can be explained by the fact that photodegradation rate
constant increases with decrease in pH. Solution was kept at a distance of 30 cm from
lamp in their study, whereas UV lamp was submerged in the solution in our study. This
might be another reason for the discrepancy in rate constants.
3.3. NO2-, NO3-, TN, and TOC
Linear regression lines were obtained from the concentration (mmol) and reaction time
(min) data for NO2- and NO3- ions. Slopes of these regression lines were reported as rates (dC/dt) as shown in
Table 3. The influence of pH on TOC, TN, NNitrosamine, NNO2-, NNO3-, and NOthers is shown in the Fig. 5. NNitrosamine, NNO2-, NNO3-, and NOthers denote nitrogen in nitrosamine, nitrogen in NO2-, nitrogen in NO3-, and nitrogen in other compounds, respectively. Concentrations of NNO2- and NNO3- increased gradually with the reaction time during the photolysis of N-nitrosamines. NNO2- concentration was too low to be detected at pH2 in both N-nitrosamines. NO2- might be unstable at strong acidic conditions (Fan and Tannenbaum, 1972) or react to form stable organic compounds (i.e., organic nitrate) (Polo and Chow, 1976). Hydroxide ion concentration might be too low to form nitrite at lower pH (Fan and Tannenbaum, 1972). This may well be another possible reason for low concentration of nitrite at pH2.
Hence, NO2- was present at lower level than NO3- at pH2. Xu et al. (2008) also observed similar results for NDEA photodegradation in strong acidic conditions.
A slight decrease in NNO2- after the complete removal of nitrosamine at lower pH was associated with increase
in NNO3-. NO3- produced by further oxidation of NO2- (Stefan and Bolton, 2002). Yield of NNO2- rapidly increased with increasing pH from acidic to neutral solution and decreased
in alkaline solution. These results are consistent with the previous studies (Xu et al., 2009; Xu et al., 2010). Owing to different patterns in NO2- and NO3- formation, it might be concluded that NO2- and NO3- production were dependent on degradation rates of parent N-nitrosamines along with other control factors. Solution pH might be one of these
factors which influences the yield of NO2- and NO3- (Fan and Tannenbaum, 1972). Higher concentration of NO2- indicates that main degradation pathways (i.e., R1 and R2) were the principal source
of NO2- production under neutral conditions. NO3- formation mechanism has been proposed in a previous study under acidic and alkaline
conditions as shown in R3 and R4 (Lee et al, 2005).
Fig. 4.
Reaction rate constants of NDBA and NPYR at different pH.
Fig. 5.
Time profiles of TOC, TN, NNitrosamine, NNO2-, NNO3-, and NOthers for NDBA.
Fig. 6.
Time profiles of TOC, TN, NNitrosamine, NNO2-, NNO3-, and NOthers for NPYR.
forms as an intermediate and reacts with NO to form peroxynitrile. Peroxynitrile
finally transforms to NO3- by spontaneous isomerization or its reaction with NO2-. NO2- and NO3- formation could also be explained by the following reactions
In this study, NO2- and NO3- formed at comparable levels during initial five minutes of degradation possibly due
to above reactions R5 and R6 at all pH except at pH2. The formation rates of NO2- remained between 4.0×10-4 - 2.0×10-2 mmol/L-min and 8.6×10-4 - 1.2×10-2 mmol/L-min for NDBA and NPYR at pH2-10, respectively. The formation rates of NO3- remained between 4.0×10-4 - 1.2×10-2 mmol/L-min and 6.1×10-3 to 2.6×10-2 mmol/L-min for NDBA and NPYR at pH2-10, respectively. Formation rates of NO2- and NO3- are presented in Table 3. It is evident that mechanistic pathways of UV photodegradation are pH dependent.
Total nitrogen almost remained constant throughout the reaction. Furthermore, it was
observed that the TN concentration was greater than the collective sum of NNitrosamine, NNO2-, and NNO3- throughout the reaction. Hence, it could be concluded that some undetected nitrogen
species also produced. These might be organic (i.e., alkylamines) or inorganic (i.e.,
NH4+) species. The amount of these species has been specified as NOthers in the Fig. 5. The total organic carbon (TOC) also remained at a constant level, suggesting negligible
loss of N-nitrosamines and degradation products from the system. Xu et al. (2009b) identified pyrrolidine as main degradation product of NPYR. Moreover, low molecular
weight aliphatic amines were also identified as further degradation products of NPYR
i.e., (methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine and n-methylethylamine).
In case of NDBA, it could be proposed that n-butylamine would be the main degradation
product. Further low molecular weight degradation products might be similar to those
of NPYR.
4. Conclusions
Degradation rate constants of NDBA and NPYR increased with the decrease in pH between
pH2-10. The pH effect is caused by the weakening of N-NO bond by increased protonation
at lower pH. Overall NDBA degradation rate constants were higher relative to NPYR.
Chemical structures might influence degradation rate along with pH effect. NDBA photodegradations
showed gradual decrease with the increase in pH. The lower degradation rate of NPYR
might be due to its unique cyclic structure with high electron density that might
tolerate the weakening of N-NO bonding by protonation via electron donation. The formation
rates of NO2- remained between 4.0×10-4 - 2.0×10-2 mmol/L-min and 8.6× 10-4 - 1.2×10-2 mmol/L-min for NDBA and NPYR at pH2-10, respectively.The formation rates of NO3- remained between 4.0×10-4 - 1.2×10-2 mmol/L-min and 6.1×10-3 to 2.6×10-2 mmol/L-min for NDBA and NPYR at pH2-10, respectively. Pro ductions of these ions
are also pH dependent. To sum up, the results show that acidic condition is an effective
option for the removal of N-nitrosamines by UV photolysis, because in acidic pH both nitrosamines degraded in
less than 20 minutes. Although, N-nitrosamines have been removed efficiently, detailed analysis of degradation products
is required to suggest this process for drinking water facility. It is remained as
our future study.
Acknowledgements
This work was supported by the Korea Institute of Energy Technology Evaluation and
Planning (KETEP) granted financial resource from the Ministry of Trade, Industry &
Energy, Republic of Korea (No. 20142010201810) through POSCO E&C.
References
(2005), The Hazard of N-nitrosodimethylamine (NDMA) Formation during Water Disinfection
with Strong Oxidants, Journal of Hazardous Materials, Andrzejewski, P., Kasprzyk-hordern,
B., and Nawrocki, J., (2005). The Hazard of N-nitrosodimethylamine (NDMA) Formation
during Water Disinfection with Strong Oxidants, Journal of Hazardous Materials, 176,
pp. 37-45., Vol. 176, pp. 37-45
(1954), Some Toxic Properties of Dimethylnitrosamine, British Journal of Industrial
Medicine, Barnes, J. M. and Magee, P. N. (1954). Some Toxic Properties of Dimethylnitrosamine,
British Journal of Industrial Medicine, 11, pp. 167-174., Vol. 11, pp. 167-174
(2004), Detecting N-Nitrosamines in Drinking Water at Nanogram per Liter Levels Using
Ammonia Positive Chemical Ionization, Environmental Science & Technology, Charrois,
J. W. A., Arend, M. W., Froese, K. L., and Hrudey, S. E. (2004). Detecting N-Nitrosamines
in Drinking Water at Nanogram per Liter Levels Using Ammonia Positive Chemical Ionization,
Environmental Science & Technology, 38(18), pp. 4835-4841., Vol. 38, No. 18, pp. 4835-4841
(2015), Oxidative Degradation of N-Nitrosopyrrolidine by the Ozone/UV Process: Kinetics
and Pathways, Environmental Science & Technology, Chen, Z., Fang, J., Fan, C., and
Shang, C. (2015). Oxidative Degradation of N-Nitrosopyrrolidine by the Ozone/UV Process:
Kinetics and Pathways, Environmental Science & Technology, 38(18), pp. 4835-4841.,
Vol. 38, No. 18, pp. 4835-4841
(1973), Nitrosamine Photochemistry: Reactions of Aminium Radicals, Accounts of Chemical
Research, Chow, Y. L. (1973). Nitrosamine Photochemistry: Reactions of Aminium Radicals,
Accounts of Chemical Research, 6, pp. 354-360., pp. 354-360
(1972), Stability of N-Nitroso Compounds, Journal of Food Science, Fan, T. Y. and
Tannenbaum, S. R. (1972). Stability of N-Nitroso Compounds, Journal of Food Science,
37, pp. 274-276., Vol. 37, pp. 274-276
(2014), Nitrosamines in Pilot-Scale and Full-Scale Wastewater Treatment Plants with
Ozonation, Water Research, Gerrity, D., Pisarenko, A. N., Marti, E., Trenholm, R.
A., Gerringer, F., Reungoat, J., and Dickenson, E. (2014). Nitrosamines in Pilot-Scale
and Full-Scale Wastewater Treatment Plants with Ozonation, Water Research, 72, pp.
251-261., Vol. 72, pp. 251-261
2016, Occurrence of N-Nitrosamines in U.S. Freshwater Sediments Near Wastewater Treatment
Plants, Journal of Hazardous Materials, Gushgari, A. J., Halden, R. U., and Venkatesan,
A. K. (2016). Occurrence of N-Nitrosamines in U.S. Freshwater Sediments Near Wastewater
Treatment Plants, Journal of Hazardous Materials, pp. 1-7., pp. 1-7
(2009), Highly Sensitive Method for Determination of N-Nitrosamines Using High-Performance
Liquid Chromatography with Online UV Irradiation and Luminol Chemiluminescence Detection,
Journal of Chromatography A, Kodamatani, H., Yamazaki, S., Saito, K., Amponsaa-Karikari,
A., Kishikawa, N., Kuroda, N., and Komatsu, Y. (2009). Highly Sensitive Method for
Determination of N-Nitrosamines Using High-Performance Liquid Chromatography with
Online UV Irradiation and Luminol Chemiluminescence Detection, Journal of Chromatography
A, 1216(1), pp. 92-8., Vol. 1216, No. 1, pp. 92-8
(2003), Polyelectrolyte Age and N-Nitrosodimethylamine Formation in Drinking, Water
Treatment, Water Quality Research Journal of Canada, Kohut, K. D. and Andrews, S.
A. (2003). Polyelectrolyte Age and N-Nitrosodimethylamine Formation in Drinking, Water
Treatment, Water Quality Research Journal of Canada, 38(4), pp. 719-735., Vol. 38,
No. 4, pp. 719-735
(2009), Impact of Waste Water Treatment Processes on Organic Carbon, Organic Nitrogen,
and DBP Precursors in Effluent Organic Matter, Environmental Science and Technology,
Krasner, S., Paul, W., Chen. B., Brucee, R., Nam, S., and Gary, A. (2009). Impact
of Waste Water Treatment Processes on Organic Carbon, Organic Nitrogen, and DBP Precursors
in Effluent Organic Matter, Environmental Science and Technology, 43, pp. 2911-2918.,
Vol. 43, pp. 2911-2918
(2005), UV Photolytic Mechanism of N-Nitrosodimethylamine in Water: Roles of Dissolved
Oxygen and Solution pH, Environmental Science & Technology, Lee, C., Choi, W., and
Yoon, J. (2005). UV Photolytic Mechanism of N-Nitrosodimethylamine in Water: Roles
of Dissolved Oxygen and Solution pH, Environmental Science & Technology, 39(24), pp.
9702-9709., Vol. 39, No. 24, pp. 9702-9709
(2013), Analysis of N-Nitrosamines and Other Nitro(so) Compounds in Water by High-Performance
Liquid Chromatography with Post-Column UV Photolysis/Griess Reaction, Water Research,
Lee, M., Lee, Y., Soltermann, F., and von Gunten, U. (2013). Analysis of N-Nitrosamines
and Other Nitro(so) Compounds in Water by High-Performance Liquid Chromatography with
Post-Column UV Photolysis/Griess Reaction, Water Research, 47(14), pp. 4893-4903.,
Vol. 47, No. 14, pp. 4893-4903
(1996), Volatile N-Nitrosamines in Environmental Tobacco Smoke: Sampling, Analysis,
Emission Factors, and Indoor Air Exposures, Environmental Science & Technology, Mahanama,
K. R. R. and Daisey, J. M. (1996). Volatile N-Nitrosamines in Environmental Tobacco
Smoke: Sampling, Analysis, Emission Factors, and Indoor Air Exposures, Environmental
Science & Technology, 30(5), pp. 1477-1484., Vol. 30, No. 5, pp. 1477-1484
(2002), Formation of N-Nitrosodimethylamine (NDMA) from Dimethylamine during Chlorination,
Environmental Science & Technology, Mitch, W. A. and Sedlak, D. L. (2002). Formation
of N-Nitrosodimethylamine (NDMA) from Dimethylamine during Chlorination, Environmental
Science & Technology, 36(4), pp. 588-595., Vol. 36, No. 4, pp. 588-595
(2009), Removal of N-Nitrosamines and Their Precursors by Nanofiltration and Revere
Osmosis, Journal of Environmental Engineering, Miyashita, Y., Park, S. H., Hyung,
H., Huang, C. H., and Kim, J. H. (2009). Removal of N-Nitrosamines and Their Precursors
by Nanofiltration and Revere Osmosis, Journal of Environmental Engineering, 135(9),
pp. 788-795., Vol. 135, No. 9, pp. 788-795
(2011), Nitrosamines and Water, Journal of Hazardous Materials, Nawrocki, J. and Andrzejewski,
P. (2011). Nitrosamines and Water, Journal of Hazardous Materials, 189(1-2), pp. 1-18.,
Vol. 189, No. 1-2, pp. 1-18
(2015), Analysis of Nine N-Nitrosamines Using Liquid Chromatography-Accurate Mass
High Resolutionmass Spectrometry on a Q-Exactive Instrument, The Royal Society of
Chemistry, Ngongang, A. D. and Duy, S. V. (2015). Analysis of Nine N-Nitrosamines
Using Liquid Chromatography-Accurate Mass High Resolutionmass Spectrometry on a Q-Exactive
Instrument, The Royal Society of Chemistry, 7(14), pp. 24-26., Vol. 7, No. 14, pp.
24-26
(2001), Structural Features of Aliphatic N-Nitrosamines of 7-Azabicyclo [2.2.1] heptanes
that Facilitate N-NO Bond Cleavage, Journal of The American Chemical Society, Ohwada,
T., Miura, M., Tanaka, H., and Sakamoto, S. (2001). Structural Features of Aliphatic
N-Nitrosamines of 7-Azabicyclo [2.2.1] heptanes that Facilitate N-NO Bond Cleavage,
Journal of The American Chemical Society, 123(42), pp. 10164-10172., Vol. 123, No.
42, pp. 10164-10172
(2009), Occurrence and Fate of Nitrosamines and Their Precursors in Municipal Sludge
and Anaerobic Digestion Systems, Environmental Science & Technology, Padhye, L., Tezel,
U., and Mitch, W. A. (2009). Occurrence and Fate of Nitrosamines and Their Precursors
in Municipal Sludge and Anaerobic Digestion Systems, Environmental Science & Technology,
43(9), pp. 3087-3093., Vol. 43, No. 9, pp. 3087-3093
(2007), Photochemical Attenuation of N-Nitrosodimethylamine (NDMA) and Other Nitrosamines
in Surface Water, Environmental Science & Technology, Plumlee, M. H. and Reinhard,
M. (2007). Photochemical Attenuation of N-Nitrosodimethylamine (NDMA) and Other Nitrosamines
in Surface Water, Environmental Science & Technology, 41(17), pp. 6170-6176., Vol.
41, No. 17, pp. 6170-6176
(1976), Efficient Photolytic Degradation of Nitrosamines, Canadian Journal of Chemistry,
Polo, J. and Chow, Y. L. (1976). Efficient Photolytic Degradation of Nitrosamines,
Canadian Journal of Chemistry, 56, pp. 997-1001., Vol. 56, pp. 997-1001
(2011), Determination of Nitrosamines in Water by Gas Chromatography/Chemical Ionization/Selective
Ion Trapping Mass Spectrometry, Journal of Chromatography A, Pozzi, R., Bocchini,
P., Pinelli, F., and Galletti, G. C. (2011). Determination of Nitrosamines in Water
by Gas Chromatography/Chemical Ionization/Selective Ion Trapping Mass Spectrometry,
Journal of Chromatography A, 1218(14), pp. 1808-1814., Vol. 1218(, No. 14, pp. 1808-1814
(2008), Synthesis, Structure, and Reactivity of Aliphatic Primary Nitrosamines Stabilized
by Coordination to [IrCl5]2-, Salvo, F. D., Estrin, D. A., Leitus, G., and Doctorovich,
F. (2008). Synthesis, Structure, and Reactivity of Aliphatic Primary Nitrosamines
Stabilized by Coordination to [IrCl5]2-, 27(9), pp. 1985-1995., Vol. 27, No. 9, pp.
1985-1995
(2006), Nitrosamine Formation Pathway Revisited : The Importance of Chloramine Speciation
and Dissolved Oxygen, Environmental Science & Technology, Schreiber, I. M. and Mitch,
W. A. (2006). Nitrosamine Formation Pathway Revisited : The Importance of Chloramine
Speciation and Dissolved Oxygen, Environmental Science & Technology, 40(19), pp. 6007-6014.,
Vol. 40, No. 19, pp. 6007-6014
(1997), Rapid Semi-Quantitative Estimation of N-Nitrosodibutylamine and N-Nitrosodibenzylamine
in Smoked Hams by Solid-Phase Microextraction Followed by Gas Chromatography-Thermal
Energy Analysis, Journal of Chromatography A, Sen, N. P., Stephen, W., and Seaman,
B. D. (1997). Rapid Semi-Quantitative Estimation of N-Nitrosodibutylamine and N-Nitrosodibenzylamine
in Smoked Hams by Solid-Phase Microextraction Followed by Gas Chromatography-Thermal
Energy Analysis, Journal of Chromatography A, 788, pp. 131-140., Vol. 788, pp. 131-140
(2013), Preliminary Studies into the Environmental Fate of Nitrosamine and Nitramine
Compounds in Aquatic Systems, Energy Procedia, Sorensen, L., Silva, E. F. d., Brakstad,
O. G., Zahlsen, K., and Booth, A. (2013). Preliminary Studies into the Environmental
Fate of Nitrosamine and Nitramine Compounds in Aquatic Systems, Energy Procedia, 37(1876),
pp. 683-690., Vol. 37, No. 1876, pp. 683-690
(2015), Photodegradation in Natural Waters of Nitrosamines and Nitramines Derived
From Co2 Capture Plant Operation, International Journal of Greenhouse Gas Control,
Sorensen, L., Zahlsen, K., Hyldbakk, A., Silva, E. F. D., and Booth, A. M. (2015).
Photodegradation in Natural Waters of Nitrosamines and Nitramines Derived From Co2
Capture Plant Operation, International Journal of Greenhouse Gas Control, 32, pp.
106-114., Vol. 32, pp. 106-114
(2002), UV Direct Photolysis of N-Nitrosodimethylamine (NDMA): Kinetic and Product
Study, Helvetica Chimica Acta, Stefan, M. I. and Bolton, J. R. (2002). UV Direct Photolysis
of N-Nitrosodimethylamine (NDMA): Kinetic and Product Study, Helvetica Chimica Acta,
85(5), pp. 1416-1426., Vol. 85, No. 5, pp. 1416-1426
, UVNATURE CO. http://www.uvnature.com/ (accessed Mar. 2016).
(2016), Occurrence and Profiling of Multiple Nitrosamines in Source Water and Drinking
Water of China., Science of the Total Environment, Wang, W., Yu, J., An, W., and Yang,
M. (2016). Occurrence and Profiling of Multiple Nitrosamines in Source Water and Drinking
Water of China., Science of the Total Environment, 551-552, pp. 489-495., Vol. 551-552,
pp. 489-495
(2011), Derivatization Method for Determination of Nitrosamines by GC-MS, Chromatographia,
Wang, X., Gao, Y., and Xu, X. (2011). Derivatization Method for Determination of Nitrosamines
by GC-MS, Chromatographia, 73, pp. 321-327., Vol. 73, pp. 321-327
(2003), Formation of N-Nitrosodimethylamine (NDMA) in Chloraminated Water Coagulated
with DADMAC Cation Polymer, Journal American Water Works Association, Wilczak, A.,
Assadi-Rad, A., Lai, H. H., Hoover, L. L., Smith, J. F., Berger, R., Rodigari, F.,
Beland, J. W., Lazzelle, L. J., Kincannon, E. G., Baker, H., and Heaney, C. T., (2003).
Formation of N-Nitrosodimethylamine (NDMA) in Chloraminated Water Coagulated with
DADMAC Cation Polymer, Journal American Water Works Association, 95(9), pp. 94-106.,
Vol. 95, No. 9, pp. 94-106
(2008), Photodegradation of N-Nitrosodiethylamine in Water with UV Irradiation, Chinese
Science Bulletin, Xu, B., Chen, Z., Qi, F., and Yang, L. (2008). Photodegradation
of N-Nitrosodiethylamine in Water with UV Irradiation, Chinese Science Bulletin, 53(21),
pp. 3395-3401., Vol. 53, No. 21, pp. 3395-3401
(2009), Factors Influencing the Photodegradation of N-Nitrosodimethylamine in Drinking
Water, Environmentmental Science and Engineering, Xu, B., Chen, Z., Qi, F., Shen,
J., and Wu, F. (2009). Factors Influencing the Photodegradation of N-Nitrosodimethylamine
in Drinking Water, Environmentmental Science and Engineering, 3(1), pp. 91-97., Vol.
3, No. 1, pp. 91-97
(2009a), Inhibiting the Regeneration of N-Nitrosodimethylamine in Drinking Water by
UV Photolysis Combined with Ozonation., Journal of Hazardous Materials, Xu, B., Chen,
Z., Qi, F., Ma, J., and Wu, F. (2009a). Inhibiting the Regeneration of N-Nitrosodimethylamine
in Drinking Water by UV Photolysis Combined with Ozonation., Journal of Hazardous
Materials, 168(1), pp. 108-14., Vol. 168, pp. 108-14
(2009b), Rapid Degradation of New Disinfection By-Products in Drinking Water by UV
Irradiation: N-Nitrosopyrrolidine and N-Nitrosopiperidine, Separation and Purification
Technology, Xu, B., Chen, Z., Qi, F., Ma, J., and Wu, F. (2009b). Rapid Degradation
of New Disinfection By-Products in Drinking Water by UV Irradiation: N-Nitrosopyrrolidine
and N-Nitrosopiperidine, Separation and Purification Technology, 69(1), pp. 126-133.,
Vol. 69, No. 1, pp. 126-133
(2010), Comparison of N-Nitrosodiethylamine Degradation in Water by UV Irradiation
and UV/O3: Efficiency, Product and Mechanism, Journal of Hazardous Materials, Xu,
B., Chen, Z., Qi, F., Ma, J., and Wu, F. (2010). Comparison of N-Nitrosodiethylamine
Degradation in Water by UV Irradiation and UV/O3: Efficiency, Product and Mechanism,
Journal of Hazardous Materials, 179(1-3), pp. 976-82., Vol. 179, No. 1-3, pp. 976-82
(2011), Measurement of Dissolved Organic Nitrogen in a Drinking Water Treatment Plant:
Size Fraction, Fate, and Relation to Water Quality Parameters, Science of Total Environment,
Xu, B., Ye, T., Li, D.P., Hu, C.Y., Lin, Y.L., Xia, S.J., Tian, F.X., and Gao, N.Y.
(2011). Measurement of Dissolved Organic Nitrogen in a Drinking Water Treatment Plant:
Size Fraction, Fate, and Relation to Water Quality Parameters, Science of Total Environment,
409(6), pp. 1116-1122., Vol. 409, No. 6, pp. 1116-1122
(2016), Fully Automated Analysis of Four Tobacco-Specific N-Nitrosamines in Main Stream
Cigarette Smoke Using Two-Dimensional Online Solid Phase Extraction Combined with
Liquid Chromatography-Tandem Mass Spectrometry, Talanta, Zhang, J., Bai, R., Yi, X.,
Yang, Z., Liu, X., Zhou, J., and Liang, W. (2016). Fully Automated Analysis of Four
Tobacco-Specific N-Nitrosamines in Main Stream Cigarette Smoke Using Two-Dimensional
Online Solid Phase Extraction Combined with Liquid Chromatography-Tandem Mass Spectrometry,
Talanta, 146, pp. 216-224., Vol. 146, pp. 216-224
(2006), Characterization of New Nitrosamines in Drinking Water Using Liquid Chromatography
Tandem Mass Spectrometry, Environmental Science & Technology, Zhao, Y., Boyd, J.,
Hrudey, S. E., and Li, X. (2006). Characterization of New Nitrosamines in Drinking
Water Using Liquid Chromatography Tandem Mass Spectrometry, Environmental Science
& Technology, 40(24), pp. 7636-7641., Vol. 40, No. 24, pp. 7636-7641
(2012), Factors Affecting Ultraviolet Irradiation/Hydrogen Peroxide (UV/H2O2) Degradation
of Mixed N-Nitrosamines in Water, Journal of Hazardous Materials, Zhou, C., Gao, N.,
Deng, Y., Chu, W., Rong, W., and Zhou, S. (2012). Factors Affecting Ultraviolet Irradiation/Hydrogen
Peroxide (UV/H2O2) Degradation of Mixed N-Nitrosamines in Water, Journal of Hazardous
Materials, 231-232, pp. 43-48., Vol. 231-232, pp. 43-48