Advanced
Formation of Reactive Species Enhanced by H<sub>2</sub>O<sub>2</sub> Addition in the Photodecomposition of N-Nitrosodimethylamine (NDMA)
Formation of Reactive Species Enhanced by H2O2 Addition in the Photodecomposition of N-Nitrosodimethylamine (NDMA)
Environmental Engineering Research. 2013. Mar, 18(1): 29-35
Copyright ©2013, Korean Society of Environmental Engineering
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
  • Received : November 11, 2012
  • Accepted : January 01, 2013
  • Published : March 30, 2013
Download
PDF
e-PUB
PubReader
PPT
Export by style
Share
Article
Author
Metrics
Cited by
TagCloud
About the Authors
Bum Gun Kwon
Department of Bioenvironmental and Chemical Engineering, Chosun College of Science and Technology, Gwangju 501-744, Korea
Jong-Oh Kim
Department of Civil Engineering, Gangneung-Wonju National University, Gangneung 210-702, Korea Abstract
jokim@gwnu.ac.kr
Joong-Keun Kwon
Department of Bioenvironmental and Chemical Engineering, Chosun College of Science and Technology, Gwangju 501-744, Korea
jkkwon@cst.ac.kr
Abstract
This study noted that the actual mechanism of N -nitrosodimethylamine (NDMA) photodecomposition in the presence of H 2 O 2 is missing from the previous works. This study investigated a key unknown reactive species (URS) enhanced by the addition of H 2 O 2 during the photolysis of NDMA with H 2 O 2 , not hydroxyl radicals. In order to provide experimental evidences in support of URS formation, we have mainly used p -nitrosodimethylaniline, methanol, and benzoic acid as well-known probes of ∙OH in this study. Both loss of PNDA and formation of hydroxybenzoic acids were dependent on NDMA concentrations during the photolysis in a constant concentration of H 2 O 2 . In particular, competition kinetics showed that the relative reactivity of an URS was at least identical with ∙OH-like reactivity. In addition, the decay of NDMA was estimated to be about 65% by the direct UV light and about 35% by the reactive species or URS generated through the photolysis of NDMA and H 2 O 2 . Therefore, our data suggest that a highly oxidizing URS is formed in the photolysis of NDMA with H 2 O 2 , which could be peroxynitrite (ONOO - ) as a potent oxidant by itself as well as a source of ∙OH.
Keywords
1. Introduction
N -Nitrosodimethylamine (NDMA) has been an environmentally important issue because of its potential human carcinogen and mutagen [1 - 5] . In particular, NDMA is classified by the United States Environmental Protection Agency (US EPA) as a B-2 carcinogen and an emerging contaminant [5] . For this reason, extensive studies have focused on the effective decontamination technologies of NDMA as well as its formation mechanism [6 - 10] . Recent studies have paid attention to the new routes on unintentional NDMA formation from general water treatment processes such as UV induced photochemistry [11] , chlorination (or chloramination) [12 , 13] , and ozonation [14] . Thus, the chemical mechanism related to NDMA chemistry is one of the most significant.
Until now, various process technologies for NDMA treatment in water have been proposed. Previous studies have evidently shown that UV treatment is the most effective method due to the strong photo-sensitive NDMA [8 , 10 , 15 - 18] . Furthermore, the photo-mechanism for the decomposition of NDMA during UV-based treatment has extensively been studied [6 , 8 , 15 , 16 , 19] . However, in the UV photolysis there are concerns of nitrosamines reformation including NDMA occurrence after UV irradiation [8 , 11 , 20] . Thus, another approach to prevent the reformation of NDMA is necessary.
As an alternative method, the photodecomposition of NDMA has been performed in the presence of H 2 O 2 [10] . The UV/H 2 O 2 process utilizes further oxidation of NDMA by itself and/or NDMA degradation byproducts such as dimethylamine and nitrite as representative NDMA precursors via the hydroxyl radical (∙OH). In this process, H 2 O 2 as a source of hydroxyl radical may be quite useful for controlling NDMA reformation in post-UV treatment [8 , 10 , 20] . According to Sharpless and Linden [10] , the addition of H 2 O 2 in the photo-degradation of NDMA slightly enhanced the performance by using a low pressure Hg lamp, but economic benefit in view of practical engineering effectiveness was little or none. Since their study, however, additional study on the photodecomposition of NDMA in the presence of H 2 O 2 has not been continued. Furthermore, new reactive species and a new mechanism that can be generated from the addition of H 2 O 2 during the photodecomposition of NDMA have not been reported recently, to the best of our knowledge. In particular, the chemistry of reactive species generated from the direct photolysis of NDMA is of considerable significance in water purification research for those mechanistic roles and an important accompanying role of the secondary product [19] . This information is
PPT Slide
Lager Image
Schematic diagram of the continuous flow system for the photolysis of NDMA. PP: peristaltic pump, P1, P2, P3, and P4: inlet ports, KTM: knotted tubing mixer, PR: photo-reactor, GD: glass de-bubbler, D: detector, A/D: A/D converter, PC: personal computer, V1, V2, and V3: valves.
able to contribute to the development of the kinetic computer model for the well-defined or proposed chemistry in the system that provides the best test of the actual engineering data. In this point, a critical component for the kinetic modeling is a description of the kinetics and mechanisms of the reactions for all the chemical species involved in the decay of NDMA. Thus, an understanding of the reaction mechanisms that could take place in the presence of H 2 O 2 is necessary in NDMA photodecomposition.
The objective of this study is to experimentally reveal the formation of unknown reactive species (URS) and its reactivity toward NDMA photo-degradation in the presence of H 2 O 2 . To investigate the formation of URS, this study employed mechanistic probing compounds which are p -nitrosodimethylaniline (PNDA), methanol, and benzoic acid (BA) as well-known probes of ∙OH [21 , 22] . These probes and competition reactions were used to prove that a URS was probably generated from the course of the photo-degradation regarding NDMA. Thus, our study can contribute to understand the reaction mechanism of photochemical NDMA decomposition by means of involved URS.
2. Materials and Methods
- 2.1. Materials
BA, methanol, NDMA, and 30% H 2 O 2 (Sigma-Aldrich, St. Louis, MO, USA) were reagent grade and were used as received from commercial supplies; water was purified with use of an aquaMAX model (Young Lin, Anyang, Korea). The PNDA (99%; Acros Organics, Geel, Belgium) was also used without further purification. To examine competition and subsequent NDMA reactions, all PNDA solutions were prepared by the addition of small amounts of borate buffer solution (pH = 8.75; LabChem, Pittsburgh, PA, USA). The concentration of H 2 O 2 stock solution was determined with the KMnO 4 titration method prior to use. The working solution of H 2 O 2 was prepared daily by diluting the stock solution with water.
- 2.2. Experimental Apparatus and Procedures
Fig. 1 shows a schematic diagram for the experimental apparatus used in this study. The apparatus and experimental procedures employed in the present study are similar to a previous study [19] except for the port of H 2 O 2 solution. All solutions were delivered with a peristaltic pump (PP; BVP-Process IP65 model; Ismatec, Glattbrugg, Switzerland) with polytetrafluoroethylene (PTFE) tubing (i.d. 0.8 mm; Cole-Parmer, Vernon Hills, IL, USA).
As shown in Fig. 1 , water or the H 2 O 2 solution was delivered through port 1 (P1, 0.62 mL/min). At the same time, PNDA solution alone or a mixed solution of NDMA and PNDA or methanol was delivered through port 2 (P2, 0.62 mL/min), which joined with the H 2 O 2 solution or water. A 1 m long knotted tubing mixer (KTM) [23] premixed the solutions of PNDA and NDMA, PNDA only, or a mixture of NDMA/PNDA/H 2 O 2 . During a competition reaction of PNDA and NDMA on ∙OH and/or URS, valve 1 (V1) was opened, while valve 2 (V2) and valve 3 (V3) were closed. In the meantime, during the detection of o - and m -hydroxybenzoic acid isomers (OHBAs) formed from the hydroxylation of BA, V2 and V3 were opened, while V1 was closed. The typical concentrations of NDMA and PNDA were established at molar ratios ([NDMA] o /[PNDA] o ) ranging from 0 to 20 based on 2.0 μM PNDA and 10 μM H 2 O 2 in borate buffer solution.
Then, the premixed solutions were transferred to a quartz coil-type photo-reactor (PR), and these solutions inside the quartz coil-type PR were photolyzed by irradiation from a low pressure Hg lamp (4 W, λ max = 254 nm; Sankyo Denki G4T5, Kanagawa, Japan). The lamp was placed at the inner center of the PR. In this PR, H 2 O 2 is cleaved by absorbed light, producing ∙OH. After mixing in the second KTM, the photolyzed solution containing decayed NDMA and/or PNDA was delivered into a homemade glass de-bubbler (GD), which was placed prior to the detector to remove formed bubbles. The changes in the absorbance signal of PNDA and the fluorescence signal of OHBAs were monitored for reaction times by a UV/Vis spectrophotometer (730D model; Young Lin) and by a fluorometer (474 model; Waters, Milford, MA, USA), respectively. Finally, the detected signal was transferred to a data acquisition system, which consisted of a signal amplifier, analog-to-digital converter, and personal computer.
Additionally, the induction period for photolysis (or competition reaction) was approximately 40 sec, which was based on the absorbance signal, with the total irradiation time less than approximately 3 min. To analyze NDMA, irradiated samples were repeatedly collected into sample vials at constant time intervals throughout repeated experiments.
- 2.3. Competition Reaction of PNDA and NDMA for a URS
A competition reaction was used to identify a URS having ·OH-like reactivity. In this process, ∙OH is produced during the decomposition of H 2 O 2 (reaction 1). ∙OH reacts with PNDA (reaction 2, k 2 = 1.25 × 10 10 M -1 s -1 ), H 2 O 2 (reaction 3, k 3 = 2.7 × 10 7 M -1 s -1 ), and NDMA (reaction 4, k 4 = 3.3–4.3 × 10 8 M -1 s -1 ) [21 , 22 , 24 , 25] . In particular, this study considered a URS generated through reaction 5 during NDMA photolysis in the absence of H 2 O 2 , based on the result of Kwon et al. [19] . Here, HO 2 ∙ and UV do not decompose PNDA [21 , 26] . The concentration of added H 2 O 2 was always constant with 10 μM, which is reasonable to assume that the concentration of ∙OH generated from the photolysis of H 2 O 2 is constant in various concentrations of PNDA and NDMA, respectively.
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
The competition kinetic model for the NDMA and PNDA in this study is Equation 1 (E1) listed below:
PPT Slide
Lager Image
where S o represents the loss rate of PNDA in the absence of NDMA, and S represents the loss rate of PNDA in the presence of NDMA; [PNDA] 0 and [NDMA] 0 in E1 are the initial concentrations. Control experiments consisted of the same mixture and irradiation conditions without the H 2 O 2 . Since k 2 is well-known (reaction 2), the plot of the S o /S vs. [NDMA] o /[PNDA] o should be a straight line with an intercept of 1 and a slope of k 4 / k 2 .
- 2.4. Analyses
NDMA was analyzed by high performance liquid chromatography (2690 Model and PDA 996; Waters) with a μBondapak C18 (3.9 × 300 mm; Waters) employing UV detection at 228 nm. The eluent consisted of water:phosphoric acid = 99:1 (volume %) with a flow rate of 0.8 mL/min [19] . The detection limits of this method was approximately 0.1 μM, based on the signal-to-noise ratio (SNR) = 3.
All absorbance measurements of PNDA were adjusted with borate buffer solution because the maximum extinction coefficient, 32,282/M/cm, of PNDA at 446 nm was observed at pH 8.75 [26] . The concentration of PNDA was determined in a continuous
PPT Slide
Lager Image
Normalized initial rates (r/rmax) of N-nitrosodimethylamine (NDMA) photodecomposition plotted against [H2O2]o/[NDMA]o. Experimental condition: pH, 8.75; and wavelength, 254 nm.
flow by using a UV/Vis spectrophotometer (730D; Young Lin).
To identify the formation possibility of URS and/or ∙OH driven from NDMA photodecomposition with H 2 O 2 , OHBAs as main products of BA trapped ∙OH were determined with a fluorescence detector (474 model; Waters) at 400 nm (emission), which was excited by 320 nm (excitation) [23] . A 0.5 N NaOH solution (pH ≥ 11) was used to enhance fluorescence intensity, as shown in Fig. 1 .
The dissolved oxygen (DO) was measured with a DO meter (SensorLink PCM800; Thermo Scientific Orion, Waltham, MA, USA).
3. Results and Discussion
- 3.1. NDMA Photodecomposition by Reactive Species in the Presence of H2O2
To account for the dependences of reactive species (or URS) and the UV photolysis on NDMA decay in the presence of H 2 O 2 , a series of experiments were carried out over a range of initial NDMA concentrations (6.25–50 μM) at pH 8.75. In each experiment, the relative importance on H 2 O 2 effect during NDMA photolysis was investigated, based on the initial rate (r = - d [NDMA]/ d t) of NDMA photo-decay over [H 2 O 2 ] o /[NDMA] o . To the best of our knowledge, this attempt has not been previously reported in the literature. Here, the maximum initial rate (r max ) during NDMA photo-decay was observed at a molar ratio of [H 2 O 2 ] o /[NDMA] o ≈ 80–100, as shown in Fig. 2 . In addition, the concentration of H 2 O 2 was varied in a wide range depending on the molar ratio of [H 2 O 2 ] o /[NDMA] o , based on a given NDMA concentration. Thus, the normalized initial rate ratio (r/r max ) of NDMA decay on the effect of H 2 O 2 can be determined.
Fig. 2 shows r/r max as a function of [H 2 O 2 ] o /[NDMA] o in a given NDMA concentration at pH 8.75. As shown in Fig. 2 , r/r max was gradually increased with increasing molar ratio of [H 2 O 2 ] o / [NDMA] o , and then it was constant at the molar ratio of [H 2 O 2 ] o /[NDMA] o = 80–100. In particular, the ratio of r/r max without H 2 O 2 at a given NDMA concentration was 0.65, and its ratio at a molar ratio of [H 2 O 2 ] o /[NDMA] o = 80–100 was approximately 1, as shown in Fig. 2 . This result suggests that the ratio of r/r max
PPT Slide
Lager Image
Mechanism of the photolytic pathways for formation of URS during NDMA photolysis in the presence of H2O2. Note that the percentage in parentheses shows the contribution of the reactive species (or URS) and UV photolysis, respectively, on NDMA degradation. NDMA: N-nitrosodimethylamine, URS: unknown reactive species.
is independent of the initial NDMA concentration, but this ratio at above 0.65 is dependent on the initial H 2 O 2 concentration added. In other words, as described in Fig. 3 approximately 65% of NDMA decay was accomplished by the direct photodecomposition of NDMA by UV light, whereas about 35% referred to the effect of reactive species (i.e., ∙OH) and/or URS generated through the photolysis of H 2 O 2 (reactions 1 and 5) and a subsequent unknown reaction(s). This result seems to be similar to that observed by Sharpless and Linden [10] . According to their study, the addition of 2.94 mM H 2 O 2 in the photo-degradation of NDMA lead totely a 30% increase in performance by the low pressure Hg lamp, compared with treatment using UV alone in the absence of H 2 O 2 . Even though the initial rate of NDMA photo-decay was mostly explained by UV photolysis, the addition of H 2 O 2 considerably enhanced direct photolysis of NDMA. This result can be explained by considering the photochemically generated ∙OH and/or URS. Thus, the effect of H 2 O 2 can be quantitatively explained by the reactive species including URS.
- 3.2. Competition Reaction between Probes and NDMA for URS
In this study, a competition reaction was used to identify the reactivity of an URS or reactive species. Reactive species including URS can be produced through NDMA photo-decay in the presence of H 2 O 2 , in which a hydroxyl radical (reaction 1) and URS (reaction 5) are able to competitively react with PNDA and NDMA [19] . Hence, the competition reaction between NDMA and PNDA as a well-known representative probe for ∙OH on an URS was investigated in this study. In this experiment, the concentrations of H 2 O 2 and PNDA were always constant with 10 and 2 μM, respectively, at pH 8.75. As a result, NDMA concentrations
PPT Slide
Lager Image
So/S plotted against [NDMA]/[PNDA]. Experimental conditions: pH, 8.75; [H2O2]o = 10 μM, [PNDA]o = 2 μM; and wavelength, 254 nm. Note that the dashed line is a linear line generally expected in the competition kinetics. NDMA: N-nitrosodimethylamine, PNDA: p-nitrosodimethylaniline.
were varied in a wide range from 0 to 40 μM depending on the molar ratio of [NDMA] o /[PNDA] o .
Fig. 4 presents S o /S as a function of [NDMA] o /[PNDA] o . As shown in Fig. 4 , S o /S was slightly increased into a molar ratio = 1 of [NDMA] o /[PNDA] o , and thereafter, these values were rapidly decreased with an increasing ratio of [NDMA] o /[PNDA] o . At the molar ratio = 20 of [NDMA] o /[PNDA] o , S o /S was 0.62. This result shows that the S of URS generated in the presence of NDMA is much higher with approximately 1.61 times than S o in the absence of NDMA. In other words, the decomposition rate of PNDA was dependent on the initial concentration of NDMA, which
PPT Slide
Lager Image
Fluorescence signal intensity of OHBAs from BA depending on initial NDMA concentration added in the photolysis of NDMA. Experimental conditions: pH, 8.75; [BA]o = 1 mM; and wavelength, 254 nm. Note that the signal intensity of OHBAs (arbitrary unit), which means the fluorescence signal intensity produced from URS during the photo-degradation of NDMA, subtracts the fluorescence signal intensity of H2O2 alone from the total fluorescence signal intensity in the presence of NDMA and H2O2. NDMA: N-nitrosodimethylamine, OHBA: hydroxybenzoic acid, BA: benzoic acid, URS: unknown reactive species.
PPT Slide
Lager Image
N-nitrosodimethylamine (NDMA) photodecomposition depending on methanol added in the photolysis of NDMA. Experimental conditions: pH, 8.75; [H2O2]o = 10 μM; and wavelength, 254 nm.
means a marked increasing PNDA decay rate with increasing initial concentrations of NDMA. This result was unexpected in the competition kinetics under the same condition with 10 μM H 2 O 2 , even though NDMA was strongly photo-labile.
In the general competition kinetics, S in the presence of NDMA should be smaller than S o in the absence of NDMA, and thus S o /S vs. [NDMA] o /[PNDA] o generally produces a linear slope of the rate constant ratio ( k 4 / k 2 ) in E1 [27 , 28] , as is depicted by the bold dashed line shown in Fig. 4 . In our experiment, owing to H 2 O 2 concentration fixed with 10 μM, the concentration of ∙OH generated from reaction 1 could be the same in all cases. Furthermore, PNDA did not react with HO 2 ∙/O 2 - ∙ and the nitric oxide radical (NO∙) generated from NDMA photo-decay, and UV photolysis of PNDA was not observed [21 , 26] . Thus, further enhanced decay of PNDA could stem from URS having an ∙OH-like reactivity during NDMA photo-decay in the presence of H 2 O 2 .
To further examine a URS having ∙OH-like reactivity during the photolysis of NDMA, a series of experiments were performed in the presence of 1 mM BA as a ∙OH probe and in a range of initial H 2 O 2 concentrations (10–1,000 μM). BA is a well-known ∙OH probe ( k = 4.3 × 10 9 M -1 s -1 ) that is able to scavenge ∙OH, producing OHBAs [23] . In this experiment, the signal intensity of OHBAs (arbitrary unit) subtracted the fluorescent signal intensity of H 2 O 2 alone from the total fluorescence signal intensity in the presence of NDMA and H 2 O 2 .
Fig. 5 demonstrates the formation of OHBAs in the photodecay of NDMA. As shown in Fig. 5 , OHBAs produced through reactions between ∙OH and BA were linearly increased with increasing initial concentration of NDMA at a given concentration of H 2 O 2 . This indicates that URS having ∙OH-like reactivity and/or additional ∙OH could be produced by an unknown pathway during the photochemical decay of NDMA, influencing intermediates or other products. Thus, a URS having ∙OH-like reactivity can influence the photolysis of NDMA.
To further examine URS formed during the photolysis of NDMA, methanol was used as an alternative probe for ∙OH, which is able to scavenge ∙OH [29 - 31] . A series of experiments were performed in the presence of H 2 O 2 and at pH 8.75. At this time, the concentration of methanol added was varied in excess ranging from 0 to 50 mM, compared to the concentration of NDMA.
As shown in Fig. 6 , an excess of methanol (50 mM) did not interfere with the photo-decay of NDMA, but, rather, methanol of 30 mM or less improved the photo-degradation of NDMA slightly. Even though ∙OH would be produced in this experiment, most of ∙OH is able to be scavenged by of methanol, producing a hydroperoxyl radical (HO 2 ∙) and HCHO as final products (reactions 6–8) [29] . This result suggests that an URS formed during the photodecomposition of NDMA reacts with NDMA. As a result, the slightly enhanced decomposition of NDMA could result from a URS formed by the photolytic behaviors of NDMA in the presence of methanol.
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
- 3.3. Possible Mechanism of URS formation in the Photodecomposition of NDMA
As shown in Figs. 2 5 , a URS generated from the course of the photo-degradation of NDMA in the presence of H 2 O 2 would be a strong reactive species having ∙OH-like reactivity. To the best of our knowledge, one of the plausible explanations on the URS is additional ∙OH and/or peroxynitrite (ONOO - ), as described in Fig. 3 .
Excited NDMA under UV light irradiation releases NO∙ by photo-elimination from the homolytic cleavage of N-NO bonds (reactions 9–10), and by photo-hydrolysis from the heterolytic cleavage of N-NO bonds (reaction 11) [6 , 16 , 17] . Here, NDMA is photolyzed to dimethylamine (CH 3 = NHCH 3 ) and the aminium radical (CH 2 = + NHCH 3 ∙) which have very weak reactivity [6] . In the initial step, NO∙ and the superoxide anion radical (O 2 - ∙) in an excess of oxygen (DO = 0.39 mM) could undergo a rapid combination reaction to yield the powerful oxidant ONOO - (reaction 12). The generation of NO∙ and the concomitant formation of O 2 - ∙ were confirmed by Chow [6] and by Lee et al. [16] , respectively. Thus, URS as a new reactive species can be related to the formation of ONOO - .
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
In the meantime, HO 2 ∙/O 2 - ∙ formed from reaction 3 and reaction 11 is dependent upon the acid-base equilibrium (reaction 14) [32] . Considering our experimental conditions (pH = 8.75), self-disproportionation by reactions 15–16 ( k 15 = 8.3 × 10 5 M -1 s -1 ; k 16 = 9.76 × 10 7 M -1 s -1 ) will not be occurred. Furthermore, reaction 17 at high pH is negligible due to its small rate constant ( k 17 < 0.3 M -1 s -1 ) [32] . Under our experimental conditions, the disproportionation of HO 2 ·/O 2 - · is too slow to compete with reaction 12. Therefore, the steady-state concentrations of NO∙ and O 2 - · are sufficiently high that ONOO - can be produced by reaction 12 ( k 12 = 4.3 × 10 9 M -1 s -1 ) [33] .
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
PPT Slide
Lager Image
Recent studies have revealed that the decomposition of ONOO - can generate NO 2 ∙ and ∙OH with a 30% yield as well as NO 3 - with a 70% yield [34] , even though the reactivity of ONOO - and its decay pathways have been in dispute [34 - 39] . In addition, according to Koppenol et al. [36] , ONOO - can be a strongly oxidizing compound by itself. Hence, the reactivity of ONOO - is closely intertwined with that of ∙OH, and appears to have significant rivaling to that of ∙OH.
As shown in Figs. 3 5 , at the alkaline pH solution, both loss of PNDA and formation of OHBAs providing experimental evidences in support of URS and/or ∙OH formation were dependent on NDMA concentrations during the photolysis with the constant concentration of a given H 2 O 2 . In particular, as shown in Fig. 6 , an excess of methanol (≤ 30 mM) improved the photodecomposition of NDMA slightly. These results suggest that a highly reactive oxidizing species can be ONOO - by itself or ∙OH. Therefore, our data suggest that, presumably, a highly oxidizing URS is formed in the photolysis of NDMA in the presence of H 2 O 2 , which is ONOO - as a potent oxidant, as described in Fig. 3 .
4. Conclusions
Careful work in this study led to the discovery that a URS generated from NDMA photolysis with a constant concentration of H 2 O 2 added was enhanced with increasing NDMA. The detailed study was performed with competition kinetics and probes for URS. Both loss of PNDA and formation of OHBAs were dependent on concentrations of NDMA during the photolysis of NDMA with 10 μM H 2 O 2 added. In particular, the competition kinetic method demonstrated that the relative reactivity of a URS was identical with ∙OH-like reactivity. These results suggest that a highly oxidizing URS is ONOO - as a potent oxidant by itself as well as a source of ∙OH.
Acknowledgements
This was supported by the National Research Foundation (NRF) grant funded by the Korea government (MEST, 2012- 0005227).
References
Liteplo RG , Meek ME , Windle W 2002 International Programme on Chemical Safety. N-Nitrosodimethylamine. World Health Organization Geneva
Charrois JW , Arend MW , Froese KL , Hrudey SE 2004 Detecting Nnitrosamines in drinking water at nanogram per liter levels using ammonia positive chemical ionization. Environ. Sci. Technol. 38 4835 - 4841
Plumlee MH , Reinhard M 2007 Photochemical attenuation of Nnitrosodimethylamine (NDMA) and other nitrosamines in surface water. Environ. Sci. Technol. 41 6170 - 6176
Plumlee MH , Lopez-Mesas M , Heidlberger A , Ishida KP , Reinhard M 2008 N-nitrosodimethylamine (NDMA) removal by reverse osmosis and UV treatment and analysis via LC-MS/MS. Water Res. 42 347 - 355
U.S. Environmental Protection Agency. 2012 Technical fact sheet N-nitroso-dimethylamine (NDMA). EPA Washington No. EPA-505-F-11-006
Chow YL 1973 Nitrosamine photochemistry: reactions of aminium radicals. Acc. Chem. Res. 6 354 - 360
Mirvish SS 1975 Formation of N-nitroso compounds: chemistry, kinetics, and in vivo occurrence. Toxicol. Appl. Pharmacol. 31 325 - 351
Stefan M , Bolton JR 2002 UV direct photolysis of N-nitrosodimethylamine (NDMA): kinetic and product study. Helv. Chim. Acta 85 1416 - 1426
Mitch WA , Sedlak DL 2002 Formation of N-nitrosodimethylamine (NDMA) from dimethylamine during chlorination. Environ. Sci. Technol. 36 588 - 595
Sharpless CM , Linden KG 2003 Experimental and model comparisons of low- and medium-pressure Hg lamps for the direct and H2O2assisted UV photodegradation of N-nitrosodimethylamine in simulated drinking water. Environ. Sci. Technol. 37 1933 - 1940
Lee C , Yoon J 2007 UV-A induced photochemical formation of N-nitrosodimethylamine (NDMA) in the presence of nitrite and dimethylamine. J. Photochem. Photobiol. A Chem. 189 128 - 134
Chen Z , Valentine RL 2008 The influence of the pre-oxidation of natural organic matter on the formation of N-nitrosodimethylamine (NDMA). Environ. Sci. Technol. 42 5062 - 5067
Mitch WA , Schreiber IM 2008 Degradation of tertiary alkylamines during chlorination/chloramination: implications for formation of aldehydes, nitriles, halonitroalkanes, and nitrosamines. Environ. Sci. Technol. 42 4811 - 4817
Schmidt CK , Brauch HJ 2008 N,N-dimethylsulfamide as precursor for N-nitrosodimethylamine (NDMA) formation upon ozonation and its fate during drinking water treatment. Environ. Sci. Technol. 42 6340 - 6346
Lee J , Choi W , Yoon J 2005 Photocatalytic degradation of N-nitroso dimethylamine: mechanism, product distribution, and TiO2surface modification. Environ. Sci. Technol. 39 6800 - 6807
Lee C , Choi W , Kim YG , Yoon J 2005 UV photolytic mechanism of N-nitrosodimethylamine in water: dual pathways to methylamine versus dimethylamine. Environ. Sci. Technol. 39 2101 - 2106
Lee C , Choi W , Yoon J 2005 UV photolytic mechanism of N-nitrosodimethylamine in water: roles of dissolved oxygen and solution pH. Environ. Sci. Technol. 39 9702 - 9709
Lee C , Yoon J , von Gunten U 2007 Oxidative degradation of N-nitrosodimethylamine by conventional ozonation and the advanced oxidation process ozone/hydrogen peroxide. Water Res. 41 581 - 590
Kwon BG , Kim JO , Namkung KC 2012 The formation of reactive species having hydroxyl radical-like reactivity from UV photolysis of N-nitrosodimethylamine (NDMA): kinetics and mechanism. Sci. Total Environ. 437 237 - 244
Landsman NA , Swancutt KL , Bradford CN , Cox CR , Kiddle JJ , Mezyk SP 2007 Free radical chemistry of advanced oxidation process removal of nitrosamines in water. Environ. Sci. Technol. 41 5818 - 5823
Kraljic I , Trumbore CN 1965 p-Nitrosodimethylaniline as an OH radical scavenger in radiation chemistry. J. Am. Chem. Soc. 87 2547 - 2550
Buxton GV , Greenstock CL , Helman WP , Ross AB 1988 Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (.OH/.O-) in aqueous solution. J. Phys. Chem. Ref. Data 17 513 - 886
Kwon BG , Lee JH 2004 A kinetic method for HO2∙/O2∙-determination in advanced oxidation processes. Anal. Chem. 76 6359 - 6364
Wink DA , Nims RW , Desrosiers MF , Ford PC , Keefer LK 1991 A kinetic investigation of intermediates formed during the Fenton reagent mediated degradation of N-nitrosodimethylamine: evidence for an oxidative pathway not involving hydroxyl radical. Chem. Res. Toxicol. 4 510 - 512
Mezyk SP , Cooper WJ , Madden KP , Bartels DM 2004 Free radical destruction of N-nitrosodimethylamine in water. Environ. Sci. Technol. 38 3161 - 3167
Kwon BG , Ryu S , Yoon J 2009 Determination of hydroxyl radical rate constants in a continuous flow system using competition kinetics. J. Ind. Eng. Chem. 15 809 - 812
Kochany J , Bolton JR 1992 Mechanism of photodegradation of aqueous organic pollutants. 2. Measurement of the primary rate constants for reaction of hydroxyl radicals with benzene and some halobenzenes using an EPR spin-trapping method following the photolysis of hydrogen peroxide. Environ. Sci. Technol. 26 262 - 265
Mabury SA , Crosby DG 1996 Pesticide reactivity toward hydroxyl and its relationship to field persistence. J. Agric. Food Chem. 44 1920 - 1924
Asmus KD , Moeckel H , Henglein A 1973 Pulse radiolysis study of the site of hydroxyl radical attack on aliphatic alcohols in aqueous solution. J. Phys. Chem. 77 1218 - 1221
Hess WP , Tully FP 1989 Hydrogen-atom abstraction from methanol by hydroxyl radical. J. Phys. Chem. 93 1944 - 1947
Zhou X , Mopper K 1990 Determination of photochemically produced hydroxyl radicals in seawater and freshwater. Mar. Chem. 30 71 - 88
Bielski BH , Cabelli DE , Arudi RL , Ross AB 1985 Reactivity of HO2/O2-radicals in aqueous solution. J. Phys. Chem. Ref. Data 14 1041 - 1100
Goldstein S , Czapski G 1995 The reaction of NO∙ with O2-∙ and HO2∙: a pulse radiolysis study. Free Radic. Biol. Med. 19 505 - 510
Goldstein S , Lind J , Merenyi G 2005 Chemistry of peroxynitrites as compared to peroxynitrates. Chem. Rev. 105 2457 - 2470
Beckman JS , Beckman TW , Chen J , Marshall PA , Freeman BA 1990 Apparent hydroxyl radical production by peroxynitrite: implications for endothelial injury from nitric oxide and superoxide. Proc. Natl. Acad. Sci. U S A 87 1620 - 1624
Koppenol WH , Moreno JJ , Pryor WA , Ischiropoulos H , Beckman JS 1992 Peroxynitrite, a cloaked oxidant formed by nitric oxide and superoxide. Chem. Res. Toxicol. 5 834 - 842
White CR , Brock TA , Chang LY 1994 Superoxide and peroxynitrite in atherosclerosis. Proc. Natl. Acad. Sci. U S A 91 1044 - 1048
Gerasimov OV , Lymar SV 1999 The yield of hydroxyl radical from the decomposition of peroxynitrous acid. Inorg. Chem. 38 4317 - 4321
Coddington JW , Hurst JK , Lymar SV 1999 Hydroxyl radical formation during peroxynitrous acid decomposition. J. Am. Chem. Soc. 121 2438 - 2443