EFFECT OF AMINE-BASED WATER TREATMENT POLYMERS ON THE FORMATION OF N-NITROSODIMETHYLAMINE (NDMA) DISINFECTION BY-PRODUCT

Transcription

1 EFFECT OF AMINE-BASED WATER TREATMENT POLYMERS ON THE FORMATION OF N-NITROSODIMETHYLAMINE (NDMA) DISINFECTION BY-PRODUCT A Dissertation Presented to The Academic Faculty by Sang Hyuck Park In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the School of Civil and Environmental Engineering Georgia Institute of Technology April, 2008 COPYRIGHT 2008 BY SANG HYUCK PARK

2 EFFECT OF AMINE-BASED WATER TREATMENT POLYMERS ON THE FORMATION OF N-NITROSODIMETHYLAMINE (NDMA) DISINFECTION BY-PRODUCT Approved by: Dr. Ching-Hua Huang, Advisor School of Civil and Environmental Engineering Georgia Institute of Technology Dr. Mustafa M. Aral School of Civil and Environmental Engineering Georgia Institute of Technology Dr. Boris Mizaikoff School of Chemistry and Biochemistry Georgia Institute of Technology Dr. Amelia E. Taylor SNF Polychemie Inc Dr. Spyros G. Pavlostathis School of Civil and Environmental Engineering Georgia Institute of Technology Date Approved: Jan 7, 2008

3 [To my family]

4 ACKNOWLEDGEMENTS First of all, I always thank God because in him I have been enriched in all my knowledge that enabled me to finish this dissertation. I would like to especially thank Professor Ching-Hua Huang for her unconditional support and excellent guidance during my research. Her endless patience and robust faith in my capabilities made me complete this journey as an experienced researcher. I also want to thank Professor Mustafa M. Aral, Professor Spyros G. Pavlostathis, Professor Boris Mizaikoff, and Dr. Amelia E. Taylor for serving on my thesis committee and providing valuable feedback on my research. I also gratefully acknowledge SNF FLOERGER Corporation for financial support for this research and thank SNF personnel, Mr. Dennis Marroni, Dr. Cédrick Favero, and Dr. Paul Whitwell for their assistance. I am also thankful to my labmate Piti Piyachaturawat who often sat up all night with me to develop analytical methods for our target compounds. Special thanks also go to my co-worker in this project, Shuting Wei and my research group members, Seungjin Lee, Wan-Ru Chen, Amisha Shah, Lokesh Padhye, and Judy Zhang who contributed to make my research more enjoyable and fruitful. I also appreciate Dr. Jaesang Lee, Dr. Doo-Il Kim, Dr. Min Cho, Dr. Yeon Gu Jeong, Dr. Jaehong Kim, Sung Soo Han, and Hoon Hyung who inspired me to keep my life vigorous in research and fun. Dr. Guangxuang Zhu also should be included in my acknowledgement list for his zeal for lab safety and instrument maintenance. In addition to people in my work, there are quite a few people I owe great debts of gratitude. To Joel and Angie Mercer, I offer my sincere gratitude from the bottom of my iv

5 heart for taking care of me like my parents in Korea. I also thank Al and Elaine LaCour for involving me in their ministry from which I became to meet many invaluable friends. I especially thank Professor Emeritus, Virgil C. Smith who has been a church choir member with me and gave me great help for writing this thesis as well as singing bass. My gratitude also goes to lovers of adventure, Tim and Rinda Lieuwen who always provided me great opportunity for having fun in their amusing home. Finally, I can never find enough words to express how grateful I am for the endless support of my family. My parents, Jung Sook Huh and Yi Yong Park, have always kept their unwavering faith in me and funded affluently whole my education. I also thank my sister, Jihyun Park for her dedication toward my family. I am also very grateful for my mother in law who has been praying so sincerely her entire life for our family to walk in the ways of the righteous with the Lord, Jesus Christ. Lastly and foremostly, I really want to express my heartfelt appreciation to my wife of noble character, Hwasook Seo for her unselfish love for me and deep understanding of me as I am. v

6 TABLE OF CONTENTS Page ACKNOWLEDGEMENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS AND ABBREVIATIONS SUMMARY iv xi xiii xvi xviii CHAPTER 1 INTRODUCTION Introduction NDMA Properties and Use NDMA Health Concerns and Exposure NDMA Occurrence in Drinking Water and Wastewater Analysis of NDMA NDMA Formation Mechanisms in Drinking Water and Wastewater N-Nitrosation Chlorinated UDMH Oxidation Pathway Potential NDMA Precursors NDMA Precursors in Wastewater NDMA Precursors in Drinking Water Treatment for NDMA Removal Water Treatment Polymers Amine-based Water Treatment Polymers as Potential NDMA Precursors 28 vi

7 1.9.2 Synthesis of Amine-based Water Treatment Polymers 33 2 RESEARCH OBJECTIVES 38 3 GENERAL SCREENING OF NDMA FORMATION POTENTIAL OF AMINE- BASED WATER TREATMENT POLYMERS Introduction Materials and Methods Materials Experimental Procedures Preparation of Monochloramine Stock Solution Preparation of Chlorine Dioxide Stock Solution NDMA Analysis Dimethylamine Analysis Results Discussion Conclusions 56 4 NDMA FORMATION FROM AMINE-BASED WATER TREATMENT POLYMERS UNDER RELEVANT WATER TREATMENT CONDITIONS Introduction Materials and Methods Materials NDMA Formation Test NDMA Analysis Results and Discussion Coagulated Artificial Water Samples Effect of Alum, Humic Acid, and Bentonite Clay Effluents of Water Treatment Plants Using Polymer 68 vii

8 4.3.4 Coagulated Raw Water Samples and Artificial Water Samples Effect of Polymer Dosage Conclusions 76 5 PROBING MECHANISMS OF NDMA FORMATION FROM POLYAMINE AND POLYDADMAC Introduction Materials and Methods Materials Experimental Procedures for Mechanistic Study NDMA and DMA Analysis DADMAC Analysis Results Effect of Polymer Solution Purification Effect of Polymer Molecular Weight Investigation of Polymer Intermediate Compounds DMA-epi-DMA, ADMA, and DADMAC PolyDADMAC Synthesized with ADMA-spiked DADMAC Effect of ph Kinetics of NDMA and DMA Formation from Polymers Discussion 97 6 EFFECT OF WATER TREATMENT PROCESSES ON NDMA FORMATION FROM AMINE-BASED WATER TREATMENT POLYMERS Introduction Materials and Methods Materials 111 viii

9 6.2.2 Batch Reaction Set up NDMA and DMA Analysis Monochloramine and Chlorine Dioxide Preparation Ozone Experiment UV Experiment Results and Discussion Effect of Sequence of Reagent Addition During Chloramination of Polymers Impact of Pre-oxidation Followed by Chloramination on NDMA Formation Comparison of NDMA Formation Potential of Four Oxidants from the Reactions with Polymers and Dimethylamine Effect of Pre-oxidation of the Polymers on NDMA Formation during Monochloramination Investigation on NDMA Formation Potential of Ozone Through UDMH Oxidation Pathway Effect of UV Exposure Conclusions REDUCING POLYMERS NDMA FORMATION POTENTIAL Introduction Materials and Methods Materials NDMA and DMA Analysis NDMA Formation Potential Test Results and Discussion Polyamine Manufactured with Chain End Capping Evaluation of Polyamine Synthesized with Quat 188 Termination at Different ph and Viscosity 143 ix

10 7.3.3 PolyDADMAC manufactured in Mild Conditions and with Chain End Capping Effect of Ionic Strength Conclusions CONCLUSIONS General Screening of NDMA Formation Potential of SNF Polymers NDMA Formation from Amine-based Water Treatment Polymers under Relevant Water Treatment Conditions Mechanism of NDMA Formation from Polyamine and PolyDADMAC Effect of Water Treatment Processes on NDMA Formation from Amine-based Water Treatment Polymers Strategies to Minimize NDMA Formation Potential of Amine-based Water Treatment Polymer Future Work Further Study of Polymer Breakdown Mechanisms during Oxidation Study of Polymer Behavior at Treatment Plants Flocculation / Coagulation Test with Modified Amine-based Water Treatment Polymers Other Nitrosamines of Concerns 160 REFERENCES 163 VITA 175 x

11 LIST OF TABLES Table 1.1: Physical and chemical properties of N-nitrosodimethylamine 5 Table 1.2: N-nitrodimethylamine (NDMA) data from 179 Ontario water treatment plants ( ) using either chloramines, chlorine, or ozone and chlorine disinfection 9 Table 1.3: N-nitrodimethylamine (NDMA) data from 32 California surface water treatment plants (1999) using either chloramines, chlorine, or ozone and chlorine disinfection. 11 Table 3.1: Residual oxidant s concentration in the polymer solutions after 24 h reactions 48 Table 4.1: Sample list for experiments simulating representative water treatment conditions 58 Table 4.2: NDMA and DMA measurements for chloramination of coagulated and filtered artificial water samples 64 Table 4.3: NDMA and DMA measurements for chloramination of coagulated and filtered artificial water samples (repeated experiments for Table 3.2) 65 Table 4.4: NDMA and DMA measurements for chloramination of SNF synthetic water samples 67 Table 4.5: NDMA formation potential of alum, humic acid and Bentonite clay 69 Table 4.6: NDMA formation in raw water samples that were coagulated followed by filtration or no filtration prior to monochloramination 71 Table 4.7: NDMA formation in artificial water samples that were coagulated followed by filtration or no filtration prior to monochloramination 71 Table 4.8: NDMA formation in artificial water samples that were coagulated with alum and varying dosage of polymer followed by filtration prior to monochloramination 73 Table 4.9: NDMA formation in raw water samples that were coagulated with varying concentration of alum and polymer followed by filtration prior to monochloramination 75 Table 5.1: Polymers sample list for mechanistic study 79 Page xi

12 Table 5.2: Calculated molar ratio of NDMA and DMA 99 Table 6.1: Increased NDMA formation potential of pre-oxidized polyamine and polydadmac solution during monochloramination 123 Table 6.2: NDMA formation potential of pre-ozonated polyamine and polydadmac solution during monochloramination 128 Table 6.3: NDMA formation potential and DMA f of UDMH under oxidation by ozone, chlorine dioxide, sodium hypochlorite, and monochloramine 133 Table 7.1: Polymers sample list 140 Table 7.2: NDMA formed under representative drinking water treatment condition using Quat terminated polymer 147 xii

13 LIST OF FIGURES Figure 1.1: N-nitrosodimethylamine (NDMA) structure 2 Figure 1.2: NDMA formation from UDMH oxidation from Mitch and Sedlak (2002b) 20 Figure 1.3: NDMA formation from chlorinated UDMH oxidation from Schreiber and Mitch (2006b) 20 Figure 1.4: Two pathways of NDMA photolysis in aqueous solution 27 Figure 1.5: Ion exchange resins and polymers that were examined in previous studies 30 Figure 1.6: Synthesis of polyamine 35 Figure 1.7: Synthesis of polydadmac 35 Figure 1.8: Synthesis of cationic polyacrylamide copolymer 37 Figure 1.9: Synthesis of Mannich polymer 37 Figure 3.1: NDMA formation from polymers in reactions with chlorine-based oxidants, nitrite, and nitrate in DI water matrix 47 Figure 3.2: NDMA formation potential of Mannich polymer and DMA mg/l as active ingredient of Mannich polymer was reacted with mm (10mg as Cl 2 /L) of preformed monochloramine for 24 h at ph 7.5 and 23 C 49 Figure 5.1: Effect of polymer purification (by precipitation) on NDMA formation 82 Figure 5.2: Effect of polymer purification (by dialysis) on NDMA formation 83 Figure 5.3: Effect of polymer molecular weight on NDMA formation 86 Figure 5.4: Structure of DMA-epi-DMA 87 Figure 5.5: NDMA formation potential of intermediate compounds 89 Figure 5.6: Monitoring DADMAC concentration under monochloramination 90 Figure 5.7: NDMA formation potential of polydadmac made of ADMA-spiked DADMAC 92 Figure 5.8: Effect of ph on NDMA formation from polymers 93 Page xiii

14 Figure 5.9: Polyamine s NDMA formation and DMA measurement as a function of time 95 Figure 5.10: PolyDADMAC s NDMA formation and DMA measurement as a function of time 96 Figure 5.11: Repeating units of polyamine and polydadmac, respectively 101 Figure 5.12: Fraction of DMA moiety in Polyamine and PolyDADMAC 105 Figure 6.1: Effect of the sequence of free chlorine and ammonium chloride additions on the NDMA formation potential of polyamine 115 Figure 6.2: Effect of the sequence of free chlorine and ammonium chloride additions on the NDMA formation potential of polydadmac 119 Figure 6.3: Comparison of NDMA formation of four oxidants from the reactions with polyamine, polydadmac, and dimethylamine 119 Figure 6.4: The effect of the pre-oxidation of polyamine and polydadmac on their NDMA formation potential during chloramination 121 Figure 6.5: The conceptual understanding of three important factors affecting NDMA formation from polymer solution during chloramination 124 Figure 6.6: The effect of free chlorine dosage on their NDMA formation potential of polyamine during chloramination 126 Figure 6.7: NDMA formation potential test in the reaction of polyamine and different MW polydadmac with ozone 129 Figure 6.8: DMA concentration change during oxidation of 10 mg/l as active ingredient of polyamine and polydadmac by mm (10 mg as Cl 2 /L) of free chlorine, chlorine dioxide, and ozone for 120 min at 23 C and ph Figure 6.9: The effect of the pre-oxidation of dimethylamine on its NDMA formation potential during chloramination 134 Figure 6.10: Effect of UV irradiation on NDMA formation. 10 mg/l as active ingredient of polymers (with or without pre-exposure to UV light) were reacted with 10 mg as Cl 2 /L of preformed monochloramine for 24 h at ph 7.5 and 23 C 137 Figure 7.1: Preparation of chain-end capped polyamine 142 Figure 7.2: NDMA formation of undialized, dialyzed and capped polyamines.10 mg/l as active ingredient of polymers were reacted with 10 mg as Cl 2 /L of preformed monochloramine for 24 h at ph 7.5 and 23 C 144 xiv

15 Figure 7.3: The evaluation of polyamine (PA) terminated with 100% theoretical QUAT 188 at ph 7 and ph 8, increased viscosity linear PA, and increased viscosity linear PA terminated with QUAT Figure 7.4: NDMA formation potential of polydadmac manufactured in mild conditions and with chain end capping 149 Figure 7.5: NDMA formation from polydadmac spiked with varying concentration of DADMAC monomer chloride salt 150 Figure 7.6: Effect of ionic strength on NDMA formation from (A) polymer solutions and from (B) DMA solutions 152 xv

16 LIST OF SYMBOLS AND ABBREVIATIONS Cationic PAM CDHS CLLE CSPE DBP DCM DI water DMA Cationic polyacrylamide copolymer California Department of Health Service Continuous liquid-liquid extraction Cartridge solid-phase extraction Disinfection by-product Dichloromethane Deionized water Dimethylamine DMA-d 6 Dimethylamine-d 6 DMAEA DOC DON EI GC/MS GC/HRMS HAA LLE LVI Mannich polymer MAC MCA Dimethylaminoethyl acrylate Dissolved organic carbon Dissolved organic nitrogen Electron ionization Gas chromatography/ mass spectrometry Gas chromatography/ high resolution mass spectrometry Haloacetic acids Liquid-liquid extraction Large volume injector Aminomethylated polyacrylamide Maximum acceptable concentration Monochloramine xvi

17 MCL MDL NDMA Maximum contaminant level Method detection limit N-Nitrosodimethylamine NDMA-d 6 N-Nitrosodimethylamine-d 6 NDEA NDBA NDPA NMEA NOM NPYR ODWQS PCI Polyamine PolyDADMAC SPE SPME THMs UDMH UV N-nitrosodiethylamine (NDEA) N-nitrosodi-n-butylamine N-nitrosodi-n-propylamine N-nitrosomethylethylamine Natural Organic Matter N-nitrosopyrrolidine Ontario s drinking water quality standard Positive-ion chemical ionization Poly(epichlorohydrin dimethylamine) Poly(diallyldimethylammonium chloride) Solid-phase extraction Solid phase micro extraction Trihalomethanes Unsymmetrical Dimethylhydrazine Ultraviolet xvii

18 SUMMARY In recent years, a compound N-nitrosodimethylamine (NDMA), a probable human carcinogen, has been identified as an emerging disinfection by-product (DBP) since its formation and detection were linked to chlorine-based disinfection processes in several water utilities in the U.S. and Canada. Numerous organic nitrogen compounds present in water may impact the formation of NDMA during disinfection. Amine-based water treatment polymers used as coagulants and flocculants have been suggested as potential NDMA precursors due to the presence of amine functional groups in their structures, as well as the possible presence of dimethylamine (DMA) residues in polymer products. To minimize the potential risk of NDMA associated with water treatment polymers, the mechanisms of how the polymers behave as NDMA precursors and their contribution to the overall NDMA formation under actual water treatment conditions need to be elucidated. This research involved a systematic investigation to determine whether aminebased water treatment polymers contribute to NDMA formation under drinking water and wastewater treatment conditions, to probe the involved reaction mechanisms, and to develop strategies to minimize the polymers NDMA formation potential. The investigation included five research tasks: (1) General screening of NDMA formation potential of commonly used amine-based water treatment polymers, (2) NDMA formation from amine-based water treatment polymers under relevant water treatment conditions, (3) Probing the mechanisms of NDMA formation from polyamine and PolyDADMAC, (4) Effect of water treatment processes on NDMA formation from xviii

19 amine-based water treatment polymers, and (5) Developing strategies to reduce polymers NDMA formation potential. Direct chloramination or chlorination of high doses of polymers in deionized water at longer than typical contact time was used in the general screening of the NDMA formation potential of water treatment polymers and in the studies to identify reaction mechanisms. On the other hand, realistic dosages of chloramines and polymers and contact time were used in simulating representative water treatment conditions to evaluate the contribution of polymers to the overall NDMA formation in real systems. On the basis of the study results, strategies were developed to reduce the NDMA formation potential of amine-based water treatment polymers, which include modification of polymer structures and treatment parameters. xix

20 CHAPTER 1 INTRODUCTION 1.1 Introduction N-nitrosodimethylamine (NDMA) (Figure 1.1) is a yellow oily liquid that is highly water soluble (Table 1.1). It is a probable human carcinogen, as classified by the US Environmental Protection Agency (U.S. EPA), with 10-6 cancer risk level in drinking water at 0.7 ng/l (U.S. EPA, 2002). Historically, concerns about human exposure to NDMA had been mainly related to its occurrence in food, consumer products, and industrial sites because it had been used for several decades in a number of industrial applications and had been produced as a by-product during manufacturing of consumer products and cured food. However, NDMA has recently been identified as an emerging disinfection by-product (DBP) since its occurrence in drinking water supplies in California and Canada was shown to be related to chlorine-based disinfection processes (OMOE, 1998; Choi and Valentine, 2002a, 2002b; Mitch and Sedlak, 2002a, 2002b; Barrett et al., 2003; CDHS, 2006). Due to greater toxicity than other DBPs, NDMA has much stricter advisory guidelines including a notification level of 10 ng/l in California and maximum acceptable concentration (MAC) of 9 ng/l in Ontario compared to the maximum contaminant levels (MCLs) of currently regulated DBPs (e.g., total trihalomethane 80 μg/l) (OMOE, 1998; CDHS, 2000). NDMA is now listed in the second unregulated contaminant monitoring regulation (UCMR2) for drinking water systems in order to determine future regulation by MCLs (U.S. EPA, 2005). 1

21 Figure 1.1 N-nitrosodimethylamine (NDMA) structure 2

22 How NDMA is formed in wastewater and natural water during treatment processes is a highly complex phenomenon and not fully understood. The recent concern of NDMA being a disinfection by-product, however has prompted many studies on the subject which include its sources and occurrence in the aquatic environment, analytical techniques, potential precursors, treatment for removing, and exposure pathways. One major study is to elucidate the major pathways of the NDMA formation mechanism. Up to date it has been shown that NDMA can be produced with the right types of organic-n compounds under suitable conditions in reaction with nitrite or monochloramine. Two pathways, (i) N-nitrosation; and, (ii) formation by oxidation of chlorinated unsymmetrical dimethylhydrazine (UDMH) intermediate, have been suggested for the formation of NDMA with nitrite and monochloramine, respectively (Choi and Valentine, 2002b; Mitch and Sedlak, 2002b). Along with the studies on the mechanisms of NDMA formation under water treatment conditions, there has been significant research interest in identifying precursors of NDMA in water sources (e.g., Mitch et al., 2003a; Gerecke and Sedlak, 2003; Mitch and Sedlak, 2004). Among many potential NDMA precursors, water treatment polymers used as coagulants and flocculants for suspended particle removal have been suspected due to the presence of amine functional groups in their structures, as well as the possible presence of dimethylamine (DMA) residues in polymer products. DMA is a well recognized NDMA precursor and frequently used as a starting reagent in amine-based monomer and polymer production. Results of several recent studies have indicated that certain treatment polymers such as aminomethylated polyacrylamide (Mannich polymer), poly(epichlorohydrin dimethylamine) (polyamine) and poly(diallyldimethylammonium 3

23 chloride) (polydadmac) can contribute to NDMA formation in chlorine-based disinfection processes (Kohut and Andrews, 2003; Mitch and Sedlak, 2004; Najm and Trussell, 2001; Najm et al., 2004; Wilczak et al., 2003). Despite the recent studies, knowledge regarding how water treatment polymers may form NDMA and how much they contribute to the overall NDMA formation in actual treatment plants was severely limited. The purpose of this research was to conduct a systematic investigation to determine whether amine-based water treatment polymers contribute to NDMA formation in water and wastewater treatment plants, understand the NDMA formation potential of polymers at the mechanistic level, and identify factors that will enhance or reduce such a formation. A major goal of this project was to provide scientific basis for strategies in minimizing NDMA formation potential of and thus environmental health risk associated with amine-based water treatment polymers. The literature review provided below should give readers a better understanding of NDMA as an emerging drinking water contaminant and its important precursors, amine-based water treatment polymers. 1.2 NDMA Properties and Use NDMA is an oily yellow liquid of low viscosity which is soluble in water due to its polar characteristic and also soluble in organic solvents such as alcohol and ether. Given its low vapor pressure, Henry s law constant, and octanol/water partition coefficient (Table 1.1), NDMA is not expected to easily evaporate from water or to adsorb onto particles in water or soil. NDMA undergoes photolytic degradation because it strongly absorbs UV light between 225 and 250 nm (Fiz et al., 1993), and is expected 4

24 Table 1.1 Physical and chemical properties of N-nitrosodimethylamine Molecular Weight: Boiling Point: ºC Melting Point: -41 ºC Density/Specific Gravity: at 20 ºC Vapor Density: 2.56 (air = 1) Vapor Pressure: 2.7 mm Hg at 20 ºC Viscosity: Low Henry s law constant (37 C) atm m 3 /mol Log Octanol/Water Partition Coefficient: Solubility: soluble in all common organic solvents & in lipids; very soluble in water, alcohol, and ether; miscible with dichloromethane and vegetable oils Synonyms: dimethylnitrosamine; N-methyl-N-nitrosomethanamine; DMN; DMNA (Merck, 1983; HSDB, 1993) 5

25 to rapidly degrade with a half-life time of 5-30 min when 1 12 ppm NDMA was exposed to sunlight in the ambient atmosphere (ATSDR, 1989; Hanst et al.; Tuazon et al.). Although current production of NDMA is limited to its use as a research chemical, prior to 1976, NDMA was used as an intermediate in the production of 1,1- dimethylhydrazine ((CH 3 ) 2 NNH 2 ), or unsymmetrical dimethylhydrazine (UDMH), a liquid rocket fuel. It was also used as a solvent or an additive in the fiber and plastics industry, a plasticizer for rubber and acrylonitrile polymers, a softener of copolymers, an antioxidant, an additive for lubricants, and nitrification inhibitor in soil (Sittig, 1985; Merck, 1983). 1.3 NDMA Health Concerns and Exposure Since the first discovery was made in 1956 that rats fed with NDMA developed a high occurrence of hepatic tumors (Magee and Barnes, 1956), a significant amount of research has been conducted regarding the carcinogenic behavior of nitrosamines including NDMA. NDMA is reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity in experimental animals (IARC 1978, 1982). Oral administration, inhalation, or intramuscular injection of NDMA into mice and rats induced tumors in their livers, lungs, and kidneys. Although no adequate studies have been reported regarding the relationship between exposure of NDMA and human cancer, NDMA is considered a potent human carcinogen due to similarities of metabolism to reactive intermediates between humans and animals (IARC 1978, 1982; ATSDR, 1989; 6

26 Linjinsky, 1983). The US EPA also classifies NDMA as a probable human carcinogen and has set its 10-6 cancer risk level in drinking water at 0.7 ng/l (U.S. EPA, 1993). Besides occupational exposure to NDMA related to industrial uses, the general population may be exposed to unknown quantities of NDMA through ingestion, inhalation, and dermal contact. NDMA is widespread in a variety of foods including cheeses, soybean oil, meat products, and canned fruit (Sen et al., 1980; Fine et al., 1977), beverages (Scanlan et al., 1980), and tobacco smoke (Spincer and Westcott, 1976), as well as even in the air in certain industrial areas, notably in the rubber and leather tanning industries (Fajen et al., 1979; Brewer et al., 1980). NDMA was also reported to be possibly formed from nitrite or nitrate in the stomach or gastrointestinal tract (Marvish, 1975; Bartsch and Montesano, 1984; Pignatelli et al., 1993). Potential human exposure to NDMA is expected, at levels of a few micrograms per day, from air, diet, and smoking, and its concentrations in aforementioned foods have been ranged between 0 and 85 µg/kg (DHHS, 2005). Although NDMA can be formed in a variety of places, it does not persist in air or water in the open environment because it is rapidly decomposed by sunlight (HEEP, 1980). 1.4 NDMA Occurrence in Drinking Water and Wastewater Since NDMA was first discovered in treated drinking water in Ohsweken, Ontario, Canada, in 1989, it was added to the list of Ontario s Drinking Water Surveillance Program (DWSP) in 1994 for its occurrence survey. The survey results from 179 Ontario water treatment plants during are summarized in Table 1.2 (Charrois et al., 2007). The data are quite extensive and very helpful for understanding NDMA 7

27 occurrence in drinking water. Median NDMA concentrations in effluents from drinking water treatment plants using chlorine as disinfectant were less than 1 ng/l (method detection limit, MDL), while effluents from plants using chloramines and their distribution systems showed median NDMA levels of 1.3 ng/l and 2.2 ng/l, respectively. More than 58% of effluent or distribution system samples disinfected by chlorine showed NDMA concentrations of less than MDL (~1 ng/l); however, a maximum NDMA concentration of up to 66 ng/l of was observed in some of the distribution system samples. Effluent samples treated by chloramines also showed 65 ng/l of maximum NDMA concentration. NDMA was detected in 79% of samples collected from distribution systems treated by chloramines, in contrast to in only 36% of samples from chlorine-treated distribution systems. The above results indicate the stronger tendency of chloramines than chlorine to produce NDMA, and the tendency of increased NDMA concentrations along a distribution system due to slow kinetics of NDMA formation. Notably, the results of surveying 1021 samples between 2000 and 2002 showed that 23 tests from five municipal drinking water treatment plants exceeded Ontario s drinking water quality standard (ODWQS) of 9 ng/l (Charrois, 2007). Among the 23 tests, 15 were from the facilities using chloramines and their NDMA concentrations ranged from 9.3 ng/l to 19 ng/l. In the U.S., California has been the leading state in NDMA research programs since NDMA was detected in drinking water wells in eastern Sacramento County and the San Gabriel Basin in The California Department of Health Service (CDHS) began an NDMA occurrence study in 1999 to determine if NDMA was a possible DBP; the summary of occurrence data is shown in Table 1.3 (CDHS, 2002). The maximum NDMA 8

28 Table 1.2 N-nitrodimethylamine (NDMA) data from 179 Ontario water treatment plants ( ) using either chloramines (21), chlorine (157), or ozone and chlorine (1) disinfection. Data reported represent 3063 NDMA analyses from raw water, treatment plant, and distribution sampling collected through Ontario s Drinking Water Surveillance Program (Charrois et al., 2007). Treatment Sample location Samples (n) Median (ng/l) Min (ng/l) Max (ng/l) Samples < MDL (n) Chlorine Influent 851 <1 < Chlorine Effluent 1429 <1 < Chlorine Distribution 282 <1 < Chloramine Influent 142 <1 < Chloramine Effluent < Chloramine Distribution < Ozone and chlorine Influent 2 <1 <1 <1 2 Ozone and chlorine Ozone and chlorine Effluent 2 <1 <1 <1 2 Distribution 2 <1 <1 <1 2 9

29 concentrations detected were 18 ng/l for chloraminated plant effluents and 16 ng/l for chloraminated plant distribution systems. During , Barrett et al. (2003) conducted a survey of NDMA occurrence in treated waters of 21 North American drinking water treatment plants located in seven U.S. states and four Canadian provinces to expand the occurrence studies to a variety of facilities, especially those suspected as vulnerable to NDMA formation. They analyzed NDMA from quarterly collected samples of treatment plant influent, effluent, and distribution system waters along with water treatment and distribution system parameters. Out of 81 plants, only one influent sample showed an NDMA concentration above the method reporting limit (MRL) ( ng/l), while maximum NDMA concentrations in plant effluent samples and in distribution samples were 30 ng/l and 24 ng/l, respectively. The median NDMA concentration was less than 2 ng/l in a chloraminated drinking water distribution system and less than 1 ng/l in chlorinated one. In an occurrence study in Alberta, Canada, Charrois et al. (2004) reported much higher NDMA concentrations, 180 ng/l from the distribution system and 67 ng/l from finished water samples of one plant using a surface water source and chloramination. An increase in NDMA concentration along the distribution system was also noticeable in this study. Besides NDMA occurrence, 2-4 ng/l of N-nitrosopyrrolidine (NPYR) and 1 ng/l of N-nitrosomorpholine (NMOR) were also detected at the same city in Alberta where the higher NDMA concentration was observed. Schreiber and Mitch also reported the detection of NDMA as well as NMOR along Quinnipiac River, CT, which was impacted by wastewater effluent (Schreiber and Mitch, 2006a). Most of the sampling sites showed concentrations less than 10 ng/l of NDMA, but concentrations greater than 15 ng/l were 10

30 Table 1.3 N-nitrodimethylamine (NDMA) data from 32 California surface water treatment plants (1999) using either chloramines (20), chlorine (7), or ozone and chlorine (5) disinfection. Data reported represent 153 NDMA analyses from raw water, treatment plant, and distribution sampling (Charrois et al., 2007; Original data, CDHS, 2002). Sample Samples Median Min Max Samples < Treatment location (n) (ng/l) (ng/l) (ng/l) MDL (n) Chlorine Influent 11 <1 < Chlorine Effluent 11 <1 < Chlorine Distribution 12 <1 < Chloramine Influent 27 <1 < Chloramine Effluent < Chloramine Distribution < Ozone and chlorine Influent 7 <1 < Ozone and chlorine Effluent 10 <1 < Ozone and chlorine Distribution 10 <1 <

31 measured from two sampling sites located downstream or upstream of wastewater treatment plants. Even higher concentrations of NMOR were detected in range of ng/l. Although the Quinnipiac River is not used as drinking water source, the results indicate nitrosamine persistence within surface water, which can be a major concern for consumers using wastewater-impacted surface water as drinking water sources. Recently, the U.S. EPA proposed the second Unregulated Contaminant Monitoring Regulation (UCMR 2) for monitoring 26 chemicals using nine different analytical methods during , (U.S. EPA, 2005). For screening survey, NDMA is included in UCMR, List 2 with five other nitrosamines: N-nitrosodiethylamine (NDEA), N-nitrosodi-n-butylamine (NDBA), N-nitrosodi-n-propylamine (NDPA), N- nitrosomethylethylamine (NMEA), and N-nitrosopyrrolidine (NPYR). The screening survey will be conducted during a continuous 12-month period between July 2007 and June 2009, quarterly for surface water systems, and twice at 6-month intervals for ground water systems. 1.5 Analysis of NDMA It has been challenging to establish reliable analytical methods for measuring NDMA in water, because the levels of interest for NDMA are very low (ng/l range) and NDMA is highly water soluble compared to other organic water contaminants. The basic analytical procedure to detect low-level NDMA in water consists of extraction, preconcentration, and analysis by gas chromatography mass spectrometry (GC/MS). Extraction techniques used for NDMA analysis are mostly liquid-liquid extraction (LLE) and solid phase extraction (SPE). Based on an isotope dilution GC/MS method, a known 12

32 amount of deuterated NDMA (NDMA-d 6 ) is added as a surrogate standard to the sample prior to extraction in order to calculate extraction recovery during LLE or SPE. Since mass spectrometry can distinguish the different mass-to-charge ratios (m/z) of the parent compound (NDMA) and its isotopic analogue (NDMA-d 6 ), the use of an isotope makes quantification highly accurate by precluding the uncertainty of extraction efficiency associated with the sample matrix. In LLE used earlier in California for NDMA analysis, based on U.S. EPA Method 607 and Method 3510C (U.S. EPA, 1998), NDMA is extracted using dichloromethane (DCM) and a separatory funnel. However, this method has drawbacks of varying extraction efficiency depending on sample matrix and low recoveries especially when used with wastewater effluents. Another difficulty in performing LLE is the poor separation between aqueous and nonaqueous phases due to emulsification caused by surfactant-like constituents in wastewater samples (Mitch and Sedlak, 2003b; Mitch et al., 2003). Alternatively, continuous liquid-liquid extraction (CLLE) according to U.S. EPA Method 3520C (USEPA, 1998) was also used with a larger volume of DCM ( ml) and longer extraction time (approximately 6-18 h) to avoid emulsification problems encountered in wastewater samples during LLE. The CLLE method reportedly yielded extraction efficiencies up to 60% (Mitch et al., 2003). The extract from LLE or CLLE is usually preconcentrated to less than 1 ml by nitrogen blowdown or using rotary evaporator to lower MDL. In addition to the inconvenience coming from labor-intensive procedures in LLE methods, the use and disposal of large volumes of organic solvents render these methods less environmentally friendly for routine sample analysis. 13

33 As an alternative extraction method, solid-phase extraction (SPE) has been used often because it possesses several advantages over LLE such as lower costs, shorter extraction times, accommodation of more samples, ease of practice and optimization. Taguchi et al. (1994) developed a SPE method using a granular carbonaceous adsorbent, Ambersorb 572, which is commercially produced by pyrolysis of highly sulfonated styrene divinyl benzene ion exchange resins. The black spherical bead form of Ambersorb 572 is much easier to handle compared to the powder types of other carbonaceous adsorbent materials or DCM during the extraction. Typically, a few hundred milligrams of Ambersorb 572 are put into water samples with the surrogate standard, NDMA-d 6, and then extraction is conducted on a roller apparatus or shaker platform for 1-2 h. After NDMA adsorbs to Ambersorb 572, it is isolated from water samples by filtration, dried in air, and transferred to an autosampler vial. The vial is filled with 400 µl of DCM which immediately elutes NDMA from the resin. Not only does the above approach greatly reduce the amount of DCM thereby creating a more environmentally friendly method, it also results in a reduction in lowering the method detection limit without a preconcentration step due to the large concentration factor between the water sample and extract. The NDMA extract is then mounted on an autosampler and undergoes GC/MS analysis. With this SPE method combined with GC/High Resolution MS (GC/HRMS), the determination of 1 ng/l levels of NDMA in water samples became possible (Taguchi et al., 1994). However, the Ambersorb resin s fragmentation problem and low recovery remain as shortcomings of this method. As alternative SPE methods, SPE disk or SPE cartridge-packed carbonaceous adsorbent materials are used. Tomkins et al. (1996) employed solid-phase extraction 14

34 using a carbon-based Empore SPE disk which resulted in NDMA recovery as high as 60%. Charrois et al. (2004) developed an SPE column packed with glass wool, Ambersorb 572, and LiChrolut EN. After careful drying of SPE phases, analyte elution was conducted with DCM, followed by preconcentration. With this SPE method combined with GC/MS ammonia positive chemical ionization (PCI), the authors obtained an estimated MDL at 1.6 ng/l with high extraction recovery ( %) for finished and distribution drinking water samples. Solid phase micro extraction (SPME) was also investigated for NDMA analysis in water focusing on its convenience of short analysis time due to the combiantion of extraction and preconcentration using only SPME fibers without solvent (Grebel et al., 2006). However, its MDL for NDMA was more than 30 ng/l, which makes the method unsuitable for the detection of a few ng/l levels of NDMA in drinking water. After extraction and preconcentration, the determination of low-level NDMA concentrations is typically conducted by gas chromatography with high resolution mass spectrometry (GC/HRMS) or tandem mass spectrometry using chemical ionization (GC/CI/MS/MS). GC/MS using traditional electron ionization (EI) with selected ion monitoring (SIM) was also used. However, EI suffers from lack of selectivity and yields nondistinctive fragmentation patterns, resulting in less sensitivity compared to CI. Positive chemical ionization (PCI) uses a softer ionization process resulting in less molecular fragmentation (Prest and Herrmann, 1999). Although methanol gas is commonly used in PCI mode for detecting NDMA in water samples, the selection of alternative reagent gases can increase the sensitivity by allowing selective ionization resulting in reduction of background noise and an increase of analyte response. For 15

35 example, ammonia reagent gas makes adduct formation in the gas phase more favorable to nitrosamine groups, compared to methanol PCI, resulting in increased selectivity for NDMA determination. Utilization of large-volume injection (LVI) can also be applied to lower the detection limit of NDMA in extracted samples. The U.S. EPA method 521 (U.S. EPA, 2004) is the most recent EPA published method for the determination of nitrosamines including NDMA in drinking water by SPE and capillary column gas chromatography with large volume injection and chemical ionization tandem mass spectrometry. A coconut charcoal SPE cartridge is used for extracting nitrosamines and surrogate standards from 0.5 L water samples. Then the cartridge is eluted with a small quantity of dichloromethane followed by concentration with blowdown and addition of an internal standard. A fused silica capillary column of a GC/MS/MS system equipped with a large volume injector (LVI) is used for identifying and quantifying nitrosamines by operating in the chemical ionization (CI) mode. Because a CI reagent gas such as methanol produces a mass spectrum with only one significant ion, the MS/MS mode is used for identification and quantitation. 1.6 NDMA Formation Mechanisms in Drinking Water and Wastewater NDMA s occurrence has been related to industrial wastewater effluents due to industrial inputs and NDMA-contaminated chemicals in manufacturing processes (OCSD, 2002). In addition, formation of NDMA has also been reported at significant levels during chlorine and chloramines disinfection processes in both drinking water and wastewater as reviewed in Mitch et al. (2003b). Currently, two pathways have been proposed to be responsible for most NDMA formation in drinking water and wastewater: 16

36 (i) formation of NDMA via N-nitrosation reaction; (ii) formation of NDMA by oxidation of a chlorinated unsymmetrical dimethylhydrazine (UDMH) intermediate. Details of these two proposed formation mechanisms are discussed as follows N-Nitrosation Since nitrosamines were identified as powerful carcinogens, nitrosation of secondary amines has been thoroughly investigated, with special emphasis on in vivo formation of nitrosamines such as in foods, human stomachs, and water supplies (Williams, 1988). N-nitrosation is the reaction of amines (mostly secondary amines and to a lesser extent tertiary amines) with a nitrosating agent such as nitrous acid which readily decomposes to a nitrosyl cation or forms dinitrogen trioxide in the acidic conditions, as outlined in equations 1.1 and 1.2. However, much stronger acidic conditions are needed to obtain the nitrosyl cation from nitrous acid compared to formation of dinitrogen trioxide. The nitrosyl cation or dinitrogen trioxide then reacts with amines such as dimethylamine to form NDMA as shown in equations 1.3 and 1.4. HNO 2 + H + H 2 O + NO + (1.1) 2HNO 2 N 2 O 3 + H 2 O (1.2) NO + + (CH 3 ) 2 NH (CH 3 ) 2 NNO + H + (1.3) N 2 O 3 + (CH 3 ) 2 NH (CH 3 ) 2 NNO + HNO 2 (1.4) Since the reaction of an amine with N 2 O 3 is usually faster than hydrolysis of N 2 O 3 to nitrous acid, the rate-limiting step becomes the formation of N 2 O 3 that is favored in the 17

37 presence of acid. (Challis and Kyrtopoulos, 1977). Another way to make nitrosating agents is by the addition of non-basic nucleophilic catalysts such as halide ions (Cl -, Br -, I - ) and thiocyanate (SCN - ) (equation 1.5). The reaction rate of this catalytic N-nitrosation was reported to increase as the concentration of halide, such as bromide, was increased (Boyland et al., 1971; Casado et al., 1979). Besides halide and thiocyanate, other examples of catalysis of N-nitrosamine formation were reported in the presence of some alcohols and phenolic compounds (Challis and Challis, 1982; Archer, 1984). HNO 2 + H + + X - X-NO + H 2 O (1.5) This N-nitrosation is believed to be responsible for NDMA occurrence in many foods such as malt grains, fish, dried or canned foods, and, especially, meat products cured with nitrite (Mitch et al., 2003b). Nitrite is used to prevent the growth of Clostridium botulinum, the bacterium that generates botulism toxin (IRAC, 1978). In vivo N- nitrosation also occurs when nitrite enters the acidic environment of the stomach (Sharpley, 1976), and nitrate also can be involved in N-nitrosation because it can be reduced to nitrite by bacteria in the mouth (Preussmann, 1984). However, NDMA formation in water treatment facilities where circumneutral ph and low nitrite concentration are mostly encountered is not well explained by the classical N-nitrosation mechanism since the nitrosyl cation or N 2 O 3 formation in N- nitrosation requires strong acidic conditions. The most rapid N-nitrosation reaction was reported at ph 3.4 where an optimum condition between the demand for protonation of nitrite (pk a of nitrite = 3.35) and the need of unprotonated dimethylamine exists (pk a of 18

38 DMA = 10.7) (Mirvish, 1975). Some studies have reported that N-nitrosation can be catalyzed at circumneutral ph by photochemical reactions (Ohta et al., 1982; Lee and Yoon, 2007b) or by formaldehyde (Keefer and Roller, 1973) and fulvic acid (Weerasooriya and Dissanayake, 1989). More Recently, Choi and Valentine (2003) reported that the formation of NDMA from the reaction of DMA and nitrite can be greatly enhanced by the presence of free chlorine at ph 7. The authors attributed the enhancement of N-nitrosation even at neutral ph to the formation of a highly reactive nitrosating intermediate such as dinitrogen tetroxide (N 2 O 4 ) during the oxidation of nitrite to nitrate by free chlorine Chlorinated Unsymmetrical Dimethylhydrazine (UDMH) Oxidation Pathway Since Najm and Trussel (2001) found that NDMA is a disinfection by-product of chloramination rather than of chlorination from the test of strong anion exchange resins and polydadmac as NDMA precursors, Choi and Valentine (2002a) and Mitch and Sedlak (2002b) proposed that NDMA could be preferably formed via an unsymmetrical dimethylhydrazine (UDMH) intermediate during the reaction of DMA and monochloramine instead of nitrosation pathway (Figure 1.2). The authors showed that the reaction of monochloramine and DMA formed much more NDMA compared to the reaction of nitrite and DMA at the circumneutral ph conditions encountered in drinking and wastewater treatment plants. NDMA formation from UDMH is traced back to earlier studies reporting that NDMA can be produced from oxidation of 1,1-dimethylhydrazine or UDMH by hypochlorite (Brubaker et al., 1985; Brubaker et al., 1987), cupric ions (Banerjee et al., 1984), hydrogen peroxide, and oxygen (Lunn et al., 1991). Contrary to 19

39 Figure 1.2 NDMA formation from UDMH oxidation from Mitch and Sedlak (2002b) Figure 1.3 NDMA formation from chlorinated UDMH oxidation from Schreiber and Mitch (2006b) 20

40 the nitrosation pathway, NDMA formation from UDMH is maximized at neutral and high ph (Lunn et al., 1991), which is consistent with Mitch and Sedlak s (2002b) experiment showing that NDMA formation is maximized at ph 8 from the reaction of DMA and monochloramine. However, NDMA formation mechanisms after the UDMH intermediate -forming step, i.e., the oxidation pathways from UDMH to NDMA were not explicit at that time about how the NH 2 moiety in UDMH converts to the NO moiety in NDMA. Later on, Schreiber and Mitch (Schreiber and Mitch, 2005; Schreiber and Mitch, 2006b) refined the previous UDMH oxidation pathway by revealing the important role of dichloramine and dissolved oxygen with the chlorinated UDMH intermediate rather than UDMH (Figure 1.3). The authors demonstrated that dichloramine plays a major role instead of monochloramine for NDMA formation; there is further evidence of disproportionation of preformed monochloramine to form traces of dichloramine. The chlorinated UDMH intermediate then undergoes further oxidation by dissolved oxygen to form NDMA, which is in competition with oxidation by dichloramine to form other products. The authors proposed that the low concentration of dichloramine solely contributes to NDMA formation via chlorine disproportionation even in typical chloramination conditions in which monochloramine exists as the dominant chloramine species, thereby possibly explaining the low yield of NDMA formation at the treatment plants. 1.7 Potential NDMA precursors Based on NDMA formation mechanisms via both nitrosation and chlorinated UDMH oxidation pathways, not surprisingly, DMA has been demonstrated by many 21

41 studies to be the most effective organic NDMA precursor (e.g., Choi and Valentine, 2002a; Fiddler et al., 1972; Mitch and Sedlak, 2002b). However, the effort to identify other potential NDMA precursors has been continuously conducted because DMA cannot explain all the concentrations of NDMA measured in wastewater and drinking water treatment plants (Mitch et al., 2003a; Gerecke and Sedlak, 2003; Mitch and Sedlak, 2004, Chen and Valentine, 2007). Trimethylamine and dimethylethanolamine, in which a proton is replaced by methyl and ethanol functional groups respectively from dimethylamine, also have been shown to produce NDMA at lower but very comparable yields to that from DMA. The lower yield is attributed to the need to break a C-N bond prior to NDMA formation (Mitch and Sedlak, 2004). According to NDMA precursor tests conducted by Mitch and Sedlak (2004), the presence of DMA functional groups seems to be the prerequisite to be a significant NDMA precursor; and the structural relationship between the DMA functional group and its adjacent group in the precursors is also an important factor to determine NDMA formation potential and rate during chloramination. For example, primary and tertiary amines which do not have DMA functional groups did not form significant levels of NDMA. Dimethylaminobenzene and dimethylamides (e.g., dimethyldithiocarbamate and dimethylformamide) also did not form significant NDMA for short time chloramination (4 hrs), but formed the levels of NDMA comparable to those from DMA and tertiary amine containing the DMA functional group for longer chloramination (10 days). This is because both dimethylaminobenzene and dimethylamides have structures or adjacent groups hindering electrophilic attack of chloramines to form NDMA, and thereby delay the formation of NDMA; but after long time exposure to chloramines, DMA was possibly released and 22