Disinfection By-Products in Drinking Water - ACS Publications

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Chapter 12

Formation of Volatile Disinfection Byproducts from Chlorination of Organic-N Precursors in Recreational Water Jing L i and Ernest R. Blatchley IIΙ School of Civil Engineering, Purdue University, West Lafayette, IN 47907

Volatile disinfection byproducts (DBPs) formed in recreational water can function as respiratory irritants, and may promote asthma. However, little information has been published regarding volatile DBP formation in recreational water settings. In this research, the formation of volatile DBPs resulting from chlorination of four organic-N precursors (creatinine, urea, L-histidine, and L-arginine) was investigated. Trichloramine, dichloromethylamine, cyanogen chloride, and dichoroacetonitrile were identified and quantified as volatile DBPs by membrane introduction mass spectrometry in benchscale experiments involving individual organic precursors and in actual swimming pool water samples. Additional experimentation was conducted for identification of possible reaction pathways to describe the formation of these DBPs from relevant organic-N precursors.

172

© 2008 American Chemical Society In Disinfection By-Products in Drinking Water; Karanfil, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.


173 Chlorination is the most common method used for disinfection of recreational water. Organic-N compounds are major contaminants in swimming pools, and reactions between free chlorine and organic-N compounds are common in recreational water settings. Most of these organic-N compounds originate in sweat and urine, and can result in the formation of undesirable DBPs, including some that are sufficiently volatile to be transferred to the gas phase. For example, trihalomethanes have been reported to be formed during chlorination of materials of human origin (eg., hair, lotion, saliva, skin, and urine) (7) and during chlorination of human urine analogs containing urea, creatinine and citric acid (2). Chlorination of N-containing precursors may also lead to the formation of N-chlorinated DBPs. Moreover, nitrogenous byproducts tend to be more toxic than others (3) A considerable body of anecdotal evidence indicates that some of these compounds can adversely affect human health. For example, childhood asthma could be associated with exposure to chemicals in swimming pools (4). Trichloramine (NC1 ) has been reported to function as an irritant to the eyes and upper respiratory tract, and may contribute to acute lung injury in accidental, occupational or recreational exposures to chlorine-based disinfectants (5, 6). However, little information is available to describe the specific compounds responsible for volatile DBP formation in recreational waters. Additionally, most available literature related to DBPs in recreational waters focus on inorganic chloramines. Little information is available to describe the formation of other volatile DBPs in recreational water settings. The objective of this investigation was to identify volatile DBPs resulting from chlorination of organic-N compounds that are likely to be present in recreational water settings. Four model organic-N compounds, urea, creatinine, L-histidine, and L-arginine, were selected as representative organic pollutants of recreational water (refer to Figure 1). Urea is the major nitrogenous end product of protein metabolism and is the chief nitrogenous component of urine and sweat in mammals. Creatinine is a constituent of perspiration and urine formed from the metabolism of creatine; it is found in muscle tissue and blood and is normally excreted in urine and sweat as a metabolic waste product. L-histidine and Larginine are amino acids that are commonly found in human sweat. Urea, creatinine, and L-histidine are also the primary constituents of "body fluid analogue" (BFA), which has been used as a surrogate mixture of organic-N compounds in previous studies involving chlorination of recreational waters (7, 8). Membrane introduction mass spectrometry (MIMS) was employed to monitor chlorinated DBPs because MIMS has been shown to be a suitable method for analysis of volatile compounds in aqueous samples (P). An important benefit of analysis by MIMS is that it yields quantitative and structural information regarding essentially all volatile DBPs present in the sample, not just a single compound. Therefore, the application of MIMS allowed identification of other volatile DBPs that were produced from chlorination reactions. 3

In Disinfection By-Products in Drinking Water; Karanfil, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

174 Organic-N Precursors H

H N 2

H °V-N

OH ί

11

2

H NCNH 2

CH

NH NH H NCNH(CH ) CHCOOH

Ο

[I ^

ι


V

2

2

2 3

Η 3

Histidine

Arginine

Urea

Creatinine Volatile DBPs Identified in this Study NC1

CH NC1

3

3

Trichloramine

NECCl

2

NECCHC1

2

Dichloromethylamine Cyanogen Chloride

Dich loroaceton itri le

Figure 1. Illustration of the structures of model organic-N compounds and possible volatile DBPs after chlorination.

Materials and Methods All chemicals used in this study, unless otherwise noted, were reagent-grade, purchased from Sigma-Aldrich, and used without further purification. Dilution to target aqueous-phase concentrations was accomplished with distilled, deionized water. Free chlorine stock solutions and standard solutions of inorganic chloramines were prepared in the same manner as described previously (P). Standard solutions of cyanogen chloride (CNC1) were prepared daily from a CNC1 stock solution (2000 mg/L Protocol Analytical Supplies, Inc.). Standard solutions of chloroform (CHC1 ) and dichloroacetonitrile (CNCHC1 ) were prepared gravimetrically from pure compounds. Standard dichloromethylamine (CH NC1 ) solutions were prepared by chlorination of methylamine (CH NH ) at C1:N molar ratio of 2.0; the concentration of CH NC1 was estimated by DPD/FAS titration as apparent dichloramine. All bench-scale chlorination experiments were conducted using a bicarbonate buffer system (120 mg/L as CaC0 ) at pH=7.5. The experiments were carried out in well-mixed, glass-stoppered, 250 mL flasks in the dark. Aliquots of a standardized sodium hypochlorite (NaOCl) stock solution were then added to the flasks. Free chlorine was added over free chlorine to precursor molar ratios (C1:P) ranging from 1.6 to 9.6. 0.01 M HC1 and 0.01 M NaOH were used to adjust the initial pH of the solution to pH 7.5. The reaction vessels were 3

3

2

2

3

3

2

3


2


175 sealed and kept in the dark at room temperature. The concentrations of free and (apparent) combined chlorine were measured by DPD/FAS titration; MIMS was used to measure residual chlorine and volatile DBPs. The MIMS system was based on a modification of an HP 5892 benchtop GC/MS comprising an HP 5972A Mass Selective Detector (MSD) equipped with electron (70 ev) ionization (EI). Mass spectrum scan mode (49 < m/z < 200) coupled with EI was used to identify possible DBPs, while selected ion monitoring (SIM) mode was used for quantification of volatile DBPs. Other details of the configuration and setup for MIMS system and operational conditions can be obtained from reference 9. The concentration of volatile DBPs was determined by comparison of ion abundance measurements with those developed from a series of standard solutions. Ions at m/z 61, 74, 85, 98 and 119 amu were monitored for quantification of CNC1, CNCHC1 , CHC1 , CH NC1 , and NC1 , respectively, and the detection limits of these compounds were 0.003 mg/L, 0.005 mg/L, 0.01 mg/L, 0.01 mg/L as C l , and 0.06 mg/L as C l , respectively. A l l compound identifications by MIMS were confirmed by analysis of standard solutions. Swimming pool water samples were collected from indoor and outdoor swimming pools and stored in screw-capped plastic bottles with minimal headspace. The samples were immediately transported back to the Environmental Engineering Laboratories at Purdue University to allow initiation of MIMS analyses within 1 hour after collection. 2

3

3

2

3

2

2

Results and Discussion Volatile DBP identification in the bench-scale chlorination experiments The chlorination of model organic-N compounds including creatinine, urea, L-histidine and L-arginine were studied individually. At least four volatile DBPs were detected by MIMS during the chlorination of these model organic-N compounds: these included trichloramine, dichloromethylamine, cyanogen chloride, and dichloroacetonitrile (refer to Figure 1). Trichloramine, which functions as an irritant to eyes and the respiratory system, was observed to result from chlorination of all four model organic-N compounds. Also, time-course monitoring of reaction progress suggested that trichloramine may persist for several days if no measure is taken to eliminate it from the solution phase. The health effects of CH NC1 are not known; however, it is characterized by an odor similar to trichloramine. CNC1 is well known to be extremely toxic to humans. CNCHC1 has been identified as an irritant of the respiratory system and skin, and has also been identified as a possible mutagen in humans {10). More 3

2

2


176 generally, given that all of these compounds are volatile, they are expected to diminish air quality around swimming pools, especially around indoor pools.

and NCI3 formationfromchlorination of creatinine


CH3NCI2

Figure 2 illustrates a mixed mass spectrum of volatile DBPs after 24 hours of chlorination of creatinine at pH 7.5. The peak clusters in the spectrum indicate that two different volatile DBPs were generated. Trichloramine was identified by the existence of a peak cluster at m/z 84 (N C1 * ), 86 (Ν 01 θΓ), 88 (N C1 ) at an abundance ratio of 9:6:1, as well as a molecular ion peak at m/z 119 (N C1 ' ). This spectral pattern was in agreement with spectra that were developed from NC1 standard solutions. 35

+

35

37

2

37

#+

2

35

+

3

3

99

100000

80000

100 ,62

101

60000 -I

84 40000

102

20000

103

JJL 50

60

80

70

90

110

100

120

m/z Figure 2. Mass spectrum of a chlorinated sample of an aqueous solution of creatinine after 24 hours. Initial concentration of creatinine = 1.8x10' M; initial Cl:Ρ molar ratio = 5.0 ; initial pH = 7.5. (Reproducedfrom Environ. Sci. Technol. 2007, 41, 6732-6739. Copyright 2007 American Chemical Society.) 4

In addition to the peak clusters described above that were associated with NCb, three additional clusters were observed. The peak clusters located at m/z 98(CH N Cl )-100(CH N Cl Cr )-102(CH N Cl2 ) and 99(CH N Cl )101(CH N Cl cr>103(CH N Cl ), each with abundance ratios of 9:6:1, and m/z 62(CHN Cr ), 63(CH N C1 ), 64(CHN C1* , CH N Cl ), 35

e+

2

35

2

35

37

+

37

2

37

3

3

35

e+

35

2

37

3

ê+

2

e+

2

+

35

2

#+

37

+

35

3


e+

177 37

#+

37

e+

65(CH N C1 ) and 66(CH N Cl ) suggested the formation of N-dichloromethylamine (dichloromethylamine). MIMS analysis of a standard solution of dichloromethylamine confirmed this finding. The formation of trichloramine and dichloromethylamine in chlorination of creatinine was studied at different C1:P molar ratios, ranging from 1.6 to 9.6, with an initial creatinine concentration of 1.8 χ 10" M . In general, roughly 0.1 mg/L trichloramine (as Cl ) was detected by MIMS after 96 hours of creatinine chlorination at C1:P > 3.2. The MIMS measurements indicated dichloromethyl amine concentrations of less than 10 μg/L (as Cl ) after 1 hour chlorination; however, the CH NC1 concentrations increased steadily during the first 24-hour chlorination period, ultimately yielding a concentration of approximately 1.5 mg/L as C l at chlorine to precursor molar ratio 8.0. Time-course measurements of CH NC1 concentration resulting from chlorination of creatinine at different C1:P molar ratios were also studied with a higher initial creatinine concentration (3.6χ 10" M). As shown in Figure 3, the formation of CH NC1 took approximately 20 hours to complete at C1:P molar ratios from 1.6 to 8.0. As the free chlorine concentration increased, the yield of CH NC1 increased as well. The maximum CH NC1 yield was approximately 66% of the initial creatinine. 2

3

5

2


2

3

2

2

3

2

4

3

3

^

2

2

3

2

40-

CN Ο

0

20

40

60

80

100

Reaction time / h

Figure 3. Time-course measurements of dichloromethylamine concentration resulting from chlorination of creatinine at different molar ratios. Experiments were conducted with a creatinine concentration of3.6 χ Î0' M at pH 7.5. (Reproducedfrom Environ. Sci. Technol. 2007, 41, 6732-6739. Copyright 2007 American Chemical Society.) 4



178 Additional experimentation was conducted for identification of reaction mechanisms to describe the formation of each of these DBPs from chlorination of model compounds. Some aspects of these mechanisms can be generalized to other organic-N compounds. A proposed mechanism for formation of dichloromethylamine is illustrated in Scheme 1. The mechanism begins with chlorine substitution, followed by hydrolysis to yield urea and N-chloro-sarcosine as intermediates. Additional chlorine substitution and hydrolysis steps yield the ultimate products of trichloramine and dichloromethylamine. To test the validity of this hypothesized mechanism, an aqueous solution of sarcosine was exposed to free chlorine at C1:P=5, and dichloromethylamine was found as the major DBP. Tachikawa et al (11) demonstrated that urea is generated during the chlorination of creatinine. Chlorination of urea results in formation of dichlorourea; when allowed to stand, dichlorourea has been shown to decompose, yielding trichloramine as a product (12) .

N

°V

0

Τ

-NH ψ CH

_JQC1

Γ

>

k

-NHCI

n

OC1/H 0 2

N

"|

1

*

H C 1

H

3

MU,

71'

Ο NCI CH 3

H0

° H NCNH

7

2

2

+ CH NC1CH C00H 3

Urea

i? H NCNH 2

OCl 2

CH NCICH COOH 3 0

1

2

2

N-chlorosarcosine

_ •

9 C1 NCNC1 2

OC1/H 0 2

•

2

2

H

NC1

2

f ° » CH N=CH ° > CH NH -HCI -HCHO 3

3

2

+

3

2

3

2

C0

"°

C 1

2

»» CH NC1 3

2

Scheme 1. Proposed mechanism for the formation of trichloramine and dichloromethlyamine from chlorination of creatinine.

CNCHCl and CNCl formation from chlorination of L-histidine 2

Volatile DBP formation in chlorination of L-histidine was also investigated, with CNCHC1 , CNCl, and NC1 all being identified by MIMS as volatile DBPs. The initial concentration of L-histidine in these experiments was 1.8 χ 10" M . Approximately 0.2 mg/L (as Cl ) of CNCHC1 and 0.02 mg/L (as Cl ) of CNCl were found to be generated at a molar ratio C1:P = 8.0 after 96 hours of 2

3

5

2

2


2

179 chlorination. Among the organic precursors investigated in this study, L-histidine was found to be the most reactive toward free chlorine, as defined by the rate of free chlorine consumption. The free chlorine concentration decreased steadily over the course of 96-hour chlorination and the CNCHC1 concentration increased. NC1 and CNCl concentrations both increased in the beginning of the reaction, reached a plateau, and then decreased. Roughly 0.22 mg/L of NC1 (as Cl ) formed after 4-hour chlorination of L-histidine, followed by its decay. In general, the reactions between free chlorine and organic-N precursors have been generalized to proceed via electrophilic substitution, in combination with hydrolysis. The reaction between free chlorine and L-histidine is assumed to proceed with an initial chlorine substitution step, followed by dechlorination and decarboxylation to yield a nitrile (13J4). 2

3

3


2

NCI3 formation from chlorination of urea and L-arginine Urea was found to yield relatively high concentrations of NC1 , even at C1:P as low as 1.6. For example, roughly 0.1 mg/L (as Cl ) of NC1 was detected by MIMS after 1-hour chlorination of 1.8 χ ΙΟ" M urea at C1:P = 1.6. This observation was consistent with results from experiments involving high precursor concentrations. No other forms of residual chlorine were evident in MIMS analysis of chlorinated urea samples. Trichloramine was the only DBP identified by MIMS in chlorination of Larginine. No NC1 was detected after 1-hour chlorination of L-arginine at C1:P molar ratios from 1.6 to 9.6, and NC1 was detectable only at C1:P > 6.4. No NC1 was detected at later times. In general, chlorination of all four organic-N precursors yielded volatile DBPs, even at the low precursor concentrations that are believed to be representative of recreational waters. Inorganic chloramine, which was always observed as trichloramine (always in the presence offreechlorine), was found as a common byproduct in all cases. This finding, together with previously published results, suggests that many organic-N compounds can act as precursors to NC1 formation. The formation of trichloramine was strongly dependent on the C1:P molar ratio, the structure of the precursor, and reaction time. 3

2

3

5

3

3

3

3

Analysis of actual swimming pool water samples Volatile DBPs present in samples collected from public recreational water facilities were identified and quantified by MIMS. Table I provides a summary of volatile DBP measurements for samples collected from six public swimming pools. These data are accompanied by measurements of chlorine residuals by DPD/FAS titration.


180 Table I. Volatile DBP measurement in samples of recreational water. Sample"

NClj* (mg/L as Cl )


2

(mg/L)

CNCHC1 * (mg/L)

Free Chlorine (mg/L as Cl^)

Combined chlorine (mg/L as Ci )

CHCI3*

2

c

c

2

A

0.08

0.07

0.01

1.5

1.34

Β

0.07

0.13

0.03

1.95

0.25

C

0.09

0.14

0.01

0.68

1.36

D

0.16 0.1

0.08 0.13

0.02 0.01

6.52 5.92

1.76

Ε

1.28

0.76 1.72 0.07 0.08 0.01 F Α, C, Ε, F: Indoor lap Swimming Pool; B: Outdoor General Use Swimming Pool; D: Outdoor Recreation Park; * Analysis by MIMS; Analysis by DPD/FAS titration SOURCE: Reproduced from Environ. Sci. Technol. 2007, 41, 6732-6739. Copyright 2007 American Chemical Society.

α

c

Three volatile DBPs (chloroform [CHC1 ], trichloramine, and dichloroacetonitrile) were detected and quantified from all six recreational water samples by MIMS. Among them, trichloramine and dichloroacetonitrile were also detected in the chlorination of model organic-N compounds. Dichloromethylamine was detected only in Sample A, and was present at a concentration of 10 μg/L. Interestingly, sample A was collected from a natatorium that is used almost exclusively for lap swimming and swimming competitions. Although no measurements of precursor concentrations of these samples were performed, the use pattern of swimming pool A is consistent with a scenario where a relatively high creatinine concentration is expected, based on excretion of sweat by swimmers. Creatinine was the only precursor in this research that yielded dichloromethylamine as a result of chlorination. However, no CNCl was detected in all swimming pool samples, which may attributed to the short half-life (about 1 hour in the presence of 0.5 mg/L free chlorine, at 25°C, pH 7) of CNCl in the presence offreechlorine (15). More generally, most volatile DBPs that were identified in the experiments with model organic-N compounds were also detected in municipal pool water samples. The data presented in Table I also suggest that the concentration ranges of these volatile products in actual recreational water facilities were relatively narrow, regardless the existing concentrations of free chlorine and combined chlorine. This suggests that these volatile DBPs may be ubiquitous in chlorinated swimming pools, even in well-maintained facilities. These compounds are difficult to eliminate by simple chlorination, even shock chlorination. As a result, additional treatment may be needed in recreational water settings to improve water and air quality, relative to these volatile DBPs. 3


181

Acknowledgments The authors are grateful to the Dupont Experimental Station and NSPF (National Swimming Pool Foundation) for financial support of this research.


References 1. Kim, H.; Shim, J.; Lee, S. Chemosphere, 2002, 46, 123-130. 2. Judd, S. J.; Jeffrey, J. A. Water Res., 1995, 29, 1203-1206. 3. Muellner, M . G. ; Wagner, E. D. ; McCalla, K. ; Richardson, S. D. ; Woo, Y.-T,; Plewa, M . J. Environ. Sci. Technol. 2007, 41, 645-651. 4. Nickmilder M.; Bernard, A. Occup. Environ. Med., 2007, 64, 37-46. 5. Nemery, B.; Hoet, P. H. M.; Nowak, D. Eur RespirJ.,2002, 19, 790-793. 6. Thickett, K. M.; McCoach, J. S.; Gerber, J. M.; Sadhra, S.; Burge, P. S. Eur Respir J., 2002, 19, 827-832. 7. Judd, S. J.; Black, S. Water Res. 2000, 34, 1611-1619. 8. Judd, S. J.; Bullock, G. Chemosphere, 2003, 51, 869-879. 9. Shang, C; Blatchley, E. R. III Environ. Sci. Technol., 1999, 33, 2218-2223. 10. Osgood, C; Sterling, D. Mutation Research 1991, 261, 85-91. 11. Tachikawa, M.; Aburada, T.; Tezuka, M.; Sawamura, R. Water Research, 2005, 39, 371-379. 12. Dowell, C. T. J. Am. Chem. Soc., 1919,41,124-125. 13. Armesto, X . L.; Canle, M . L.; Santaballa, J. A. R Tetrahedron 1993, 49, 275-284. 14. Conyers, B.; Scully, F. E., Jr. Environ. Sci. Technol. 1993, 27, 261-266. 15. Na, C.; Olson, T. M. Environ. Sci. Technol., 2004, 38, 6037-6043.


Disinfection By-Products in Drinking Water - ACS Publications

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