Environ. Sci. Technol. 1991,25, 1160-1164
presence of 1 pM of CoIITSP.
Acknowledgments Many thanks to Dr. Jochen Kraft for the preparation of the catalyst and his valuable contribution in the initial stage of this work. We also thank the reviewers of this article for useful comments and suggestions.
Glossary Col*TSP cobalt(”)-4,4’,4’’,4’”-tetrasulfophthalocyanine S(-11) bivalent sulfur; includes H2S, HS-, S+ Eh sulfide ion specific electrode potential kob8 observed pseudo-first-order rate constant for S(-11) oxidation x wavelength (nm) Ai absorbance referring to species i P order of S(-11) oxidation with respect to Co”TSP Y order of S(-11) oxidation with respect to oxygen K Michaelis-Menten half-velocity coefficient k Michaelis-Menten maximum utilization rate Registry No. CoIITSP, 28802-06-4; H2S,7783-06-4. Literature Cited Sulfide in Wastewater Collection and Treatment Systems;
ASCE Manuals and Reports on Engineering Practice 69; American Society of Civil Engineers: New York, 1989. Thistlethwayte, D. K. The Control of Sulphides in Sewerage Systems; Butterworth Sydney, 1972. Pomeroy, R.; Bowlus, F. D. J. Sewage Works 1946,18,597. Hoffmann, M. R.; Lim, C. H. Enuiron. Sci. Technol. 1979,
(7) Hoffmann, M. R. Enuiron. Sci. Technol. 1977, 11, 61. (8) Hoffmann,M. R.; Edwards, J. 0. Znorg. Chem. 1977, 16, 3333. (9) McArdle, J. V.; Hoffmann, M. R. J . Phys. Chem. 1983,87, 5425. (10) Chen, K. Y.; Morris, J. G. J . Sanit. Eng. Diu., Proc. Am. SOC.Ciu. Eng. 1972, SAI, 215. (11) Weres, 0.;Tsao, L.; Chatre, R. M. Corrosion 1985,41, 307. (12) Dohnalek, D. A.; FitzPatrick, J. A. J.-Am. Water Works Assoc. 1983, 65, 298. (13) O’Brien,D. J.; Birkner, F. B. Enuiron. Sci. Technol. 1977, 11, 1114. (14) Hong, A. P.; Boyce, S. D.; Hoffmann, M. R. Enuiron. Sci. Technol. 1989, 23, 533. (15) Boyce, S . D.; Hoffmann, M. R.; Hong, P. A.; Moberly, L. M. Environ. Sci. Technol. 1983, 17, 602. (16) Leung, K.; Hoffmann, M. R. Enuiron. Sci. Technol. 1988, 22, 275. (17) Weber, J. H.; Busch, D. H. Znorg. Chem. 1965, 4, 469. (18) Baumann, F.; Bienert, B. U.S. Patent No. 2613 128, 1952. (19) Moore, J. W.; Pearson, R. G. Kinetics and Mechanism,3rd ed.; Wiley: New York, 1981. (20) Ellis, A. J.; Golding, R. M. J. Chem. SOC.London 1959,127. (21) Giggenbach, W. Znorg. Chem. 1971, 10, 1333. (22) Giggenbach, W. Znorg. Chem. 1972, 11, 1201. (23) Chen, K. Y.; Gupta, S. K. Enuiron. Lett. 1973, 4, 3, 187. (24) Wilmot, P. D.; et al. J-Water Pollut. Control Fed. 1988, 60, 1264. (25) Bernauer. K.: Fallab. S. Helu. Chin. Acta 1961.44. 1287. (26) Wagnerova, D. M.; Blanck, J.; Veprek-Siska, J. Collect. Czech. Chem. Cornmun. 1982,47, 755.
13, 1406.
Snavely, E. S.; Blount, F. E. Corrosion 1969, 25, 397. Chen, K. Y.; Morris, J. C. Enuiron. Sci. Technol. 1972,6, 529.
Received for review M a y 30, 1990. Accepted February 11,1991. We gratefully acknowledge the financial support of the County Sanitation Districts of Los Angeles County (CDS Contract 2966).
Characterization of Aqueous Humic Substances before and after Chlorination John V. Hanna,t W. David Johnson,$ Robinson A. Querada,+Michael A.
and Lu Xlao-Qlaot
CSIRO Division of Coal and Energy Technology, P.O.Box 136, North Ryde, New South Wales 21 13, Australia, and Department of Physical Chemistry, University of New South Wales, P.O. Box 1, Kensington, New South Wales 2033, Australia
Five aquatic humic substances have been chlorinated and characterized by 13C nuclear magnetic resonance spectrometry and pyrolysis gas chromatography-mass spectrometry. It is shown that methoxyl, phenolic, and ketonic structural groups are more reactive to chlorine than alkyl or carboxyl, which in turn are more reactive than carbohydrates. These results suggest that the choice of aryl, methoxyl, phenolic, and ketonic compounds as models for water chlorination studies are valid, even though it is now known that these structures often are not the most significant structural groups in humic substances.
Introduction The nature of the species present in aqueous chlorine solution has been known for a long time (1-3). Electrophilic attack on organic substances is through Clz,H20C1+, C1,0, or HOC1, depending on reaction conditions. The use of chlorine for water purification has been the subject of extensive investigation due to the discovery of the formation of a number of hazardous organic byproducts such as haloforms (4). The majority of studies have concenCSIRO Division of Coal and Energy Technology. *University of New South Wales. 1160
Envlron. Scl. Technol., Vol. 25, No. 6,
1991
trated on the identification of the byproducts from chlorine exposure of aquatic organic matter (4-13), but there have also been attempts to elucidate the mechanism of chlorination. A number of workers have used model compounds (14-17), e.g., phenols (16),to elucidate mechanism, and while it has been clearly demonstrated that haloforms and other hazardous chlorination products can be formed from these substrates, a major deficiency in this approach is that the model compounds may not resemble aquatic organic matter. Advances in our understanding of the structure of aquatic organic matter have recently been made by the application of the techniques of high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy and pyrolysis gas chromatography-mass spectrometry (18,19). The structure of aquatic organic matter appears to be quite variable, and the relatively low concentration of phenols in many preparations has led to questioning of the idea of these being the sole origin of haloforms (20, 21). The recent Dahlem conference (22) on humic substances recommended that an important research priority should be to characterize the macromolecules composing aquatic humic materials before and after chlorination, and this is the subject of this paper. Humic substances of different structures have been chlorinated and the macromolecular
0013-936X/91/0925-1160$02.50/0
0 1991 American Chemical Society
Table I. Sites from Which Humic Substances Were Isolated and Their Elemental Composition sample no.
location
1 2 3 4
under trees, Tait Homstead under trees, near Myall Lake under trees, near Smiths Lake Neranie South Bay under trees near Myall Lake
5
date Nov Nov Nov Nov July
1989 1989 1989 1989 1989
PH
conductance, d c m
3.74 4.36 3.70 3.79 NDf
42 336 130 303 NDf
humic subst H/Ca H/Cb 1.1 1.0 1.0 1.2 1.1
1.2 1.3 1.7 1.6 1.3
yielde 1.8' 3.6' NIY 77.7d 3.6'
"Before chlorination. *After chlorination. 'As percent of mass air-dried. dAs mg/mL. eFrom estimates of humic and fulvic acid contents (ref 26). 'ND, not determined.
Figure 1. Map of sample collection area, New South Wales, Australia.
structures investigated by pyrolysis gas chromatographymass spectrometry and high-resolution solid-state NMR spectroscopy both before and after chlorination. The results clearly indicate that phenols and ketones are the most labile components of the organic macromolecules, and in addition, an order of reactivity has been established for other structural groups. Experimental Section Sampling Locations. Samples of surface swamp water were collected near shores of Smith Lake and Myall Lake, NSW, Australia. Sample sites are listed in Table I and a map of sample locations is shown in Figure 1. Isolation Procedure. Samples (40 L) were adjusted to pH 2 with hydrochloric acid (6 M) and then passed through a prewashed Amberlite XAD-7 resin (47 cm X 2 cm diameter column) at a flow rate of approximately 1 mL/min until the eluent was a light yellow. The column was washed with dilute hydrochloric acid (1L, 0.1 M) and distilled water until neutral. The adsorbed humic substance was desorbed with 0.1 M sodium hydroxide and the combined eluents were passed through a cation-exchange resin (Amerlite IR-120, protonated form, 30 cm X 1 cm diameter column). The humic substance was isolated by evaporation of the cation-exchange eluate. The chlorinated product was formed by adjusting the pH of the solution of the cation-exchanged free acid to pH 10 with 6 M NaOH and then chlorine gas was passed through the solution for 2 h, in which time the sample turned from dark brown to light yellow. The solution after chlorination had a pH of
1. The pH was adjusted to 4.0 with sodium hydroxide (2 M). The sample was treated in two ways. The sample was passed through a cation-exchange resin as above and also evaporated directly to look for any changes due to selective adsorption. NMR spectra from products prepared by both methods were identical. Solid-state Nuclear Magnetic Resonance. Spectra were obtained on a Bruker CXPlOO instrument operating at 22.5 MHz for carbon. A Doty probe with single air bearing rotors was used. Approximately 300 mg of sample was analyzed by using the cross polarization technique with magic angle (54.7O) spinning (23). Recycle time was 1 s. A 90° pulse of 4 ws was used, contact time was 1 ms, and data were collected in 1K points, zero filled to 4K, and Fourier transformed with a line-broadening factor of 50 Hz to obtain the frequency domain spectrum. Some studies were also carried out using the dipolar dephasing technique (21,23,24)to distinguish protonated and nonprotonated carbon. Pyrolysis Gas Chromatography-Mass Spectrometry. Pyrolysis gas chromatography-mass spectrometry (py-gcms) was carried out in continuous mode using an SGE pyroinjector interfaced directly to a Hewlett-Packard 5970 mass-selective detector with a 5890 gas chromatograph and chemical data system. Chromatography was carried out on a 50-m Hewlett Packard ultra no. 2 capillary column. The samples were introduced as a pellet and pyrolyzed at 610 "C. The capillary column was kept at 30 "C for 2 min after injection, after which the temperature was raised by 4 OC/min to 280 "C. The pyrolysis products were identified by comparison with library spectra.
Results and Discussion Nuclear Magnetic Resonance. The 13C CP/MAS spectra of the humic substances before and after chlorination are shown in Figure 2. There are at least eight observable resonances: 42-46 ppm (alkyl, mainly tertiary and quaternary carbon and carbon attached to electronwithdrawing groups); 55 ppm (methoxy carbon, probably lignin derived); 75-84 ppm (oxygen-substituted aliphatic carbon of carbohydrates); 104-108 ppm [dioxygenated carbon and aromatic protonated carbon of tannins and phenols and aromatic nonprotonated carbon of tannins, identified by dipolar dephasing (24)l;128-133 ppm with a shoulder to high field [carbon-substituted aromatic carbon (aryl-C) with protonated aromatic carbon lying to high field]; 151-153 ppm [oxygenated aromatic carbon of phenols and ethers (aryl-O)];172-177 ppm carboxyl carbon (probably mainly carboxylic acid); 195-199 ppm (ketone carbon, identified by dipolar dephasing). The relative peak heights of these resonances are shown in Table 11. There are some differences and some similarities between the samples. The carboxyl resonance is largest in all the spectra. The aryl-C content is largest for sample 1 (Table 11). The alkyl content is particularly low for sample 1and the carbonyl carbon particularly high for sample 4. Environ. Sci. Technol., Vol. 25, No. 6, 1991
1161
Table 11. Normalized Peak Heights of
NMR Resonances from Humic Substances and Their Chlorinated Derivatives"
sample no.
alkyl
methoxyb
alkyl-0
(42-46)
(55) -
(75-84)
1 2 3 4 5
0.12 0.13 0.13 0.15 0.14
0.10 0.10 0.10 0.10
0.12 0.12 0.12 0.14 0.12
1 2 3 4 5
0.17 0.17 0.16 0.17 0.17
NO NO NO NO NO
0.21 0.21 0.21 0.20 0.19
humic matter chem shift (pprn) dioxy + tannin aryl-C (104-108)
(129-133)
aryl-0
carboxyl
carbonyl
(151-153)
(172-175)
(195-199)
0.12 0.13 0.11 0.13 0.12
0.18 0.19 0.20 0.23 0.19
0.05 0.04 0.05 0.06 0.04
0.07 0.09 0.07 0.08 0.08
0.24 0.24 0.25 0.26 0.26
0.02 0.03 0.02 0.03 0.03
Unchlorinated Substances
NO
0.13 0.13 0.12 0.14 0.13
0.18 0.16 0.17 0.15 0.16
Chlorinated Humic Substances 0.15 0.13 0.14 0.13 0.13
0.14 0.13 0.14 0.13 0.14
"For definitions see text. b N O , not observed. Table 111. Pyrolysis Products of Humic and Fulvic Substances Identified by py-gcms peak no.
compound
possible origin
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
furan methylfuran dimethylfuran pyridine methylbenzene trimethylfuran ethylbenzene dimethylbenzene phenol methylethylbenzene benzofuran indene methylphenol methylbenzofuran methylidene ethylbenzofuran methylnaphthalene benzene
carbohydrate carbohydrate carbohydrate protein protein, lignin carbohydrate protein, lignin lignin carbohydrate, protein, lignin
Table IV. Relative Abundances of Pyrolysis Products from Reconstructed Ion Chromatograms
1
2 3 4 5 6 7 8 9 10 11
protein, lignin
protein, carbohydrate, lignin
Pyrolysis Gas Chromatography-Mass Spectrometry. Table I11 lists the compounds positively identified by py-gcms in the product and their origin after SaizJimenez and de Leeuw (25). A typical py-gcms trace is shown in Figure 3. The relative abundances of these identified pyrolysis products varied between samples (Table IV); nevertheless it is clear that a major product is phenol, which may arise from carbohydrate, lignin, and possibly proteins. The other major products are methylbenzenes from lignin and possibly protein. These results reflect the importance and almost uniform amount of carbohydrate and aryl oxy carbon across the samples as demonstrated by 13CNMR (see regions of chemical shift 75-84 and 151-153 ppm, respectively). Chlorinated Humic Substances. The py-gcms spectra of the chlorinated humic substances differed considerably from those of the starting material. The predominant identified components were chloroform, dichloromethane, tetrachloroethane, chloroethylene, and dichlorobenzene (Figure 3). No obvious differences could be detected in the nature of the other pyrolysis products except the amount of phenol (compound 9) appeared to be reduced and the amount of furan (compound 1) increased. This result is confirmed by the NMR data, which are shown in Table V as percent change in peak height on chlorination, Le., 100(peak height after chlorination - peak height before chlorination)/ (peak height before chlorination). 1182 Envlron. Scl. Technol., Vol. 25, No. 6, 1991
compd re1 abund, 70
sample no.
12 13 14 15 16 17 18 a
1
14 67 10 63 5 17 2 70 100 15 24 14 17 52 + 22a 72 100 81 27 10 38 30 13 12 6
+ 17"
3
2
68 25 29 4
+ 45"
5
4
25 22 10
21 16 12
20 10 5 3
74 10
55 7
100
55 100 43 22 30 33 31 14
+ 32O
50 100 32 32 30 27 22 15 8 12
+
3 14 24" 85 + 26" 100 3 38 18 44 41 24 13 13
Two isomers.
These data quite clearly demonstrate that after chlorination there is a marked reduction in phenols, methoxyl carbon, aryl-C carbon, and ketones (- percent values) and a relative increase in carbohydrate (from which the furan derives) and alkyl carbon (+ percent values). Carbon resonating in the region 104-108 ppm does not appear to change much in percent contribution. A contribution from chlorinated aliphatic carbon might also be expected a t a broad range of chemical shifts in the region 50-100 ppm. Bearing in mind that there is considerably more error in measuring the percent change in ketone and methoxyl functionalities because the signals are small or overlap, these materials appear to be more reactive than oxygenated aromatic carbon, which in turn appears to be more reactive than other types of aromatic carbon. Next comes the complex group of carbons that resonate between 104 and 108 ppm. This consists of reactive tannin carbons and less reactive anchiomeric carbohydrate carbons. The alkyl and carboxyl carbon appear to be of about equal reactivity with carbohydrate carbon the least. These results are in broad agreement with the expected reactivity of chlorine (11) proposed by degradation studies (20). Although the nature of the electrophile is pH dependent, the order of reactivity of functional groups in the humic macromolecules is expected to be similar at different pH's to that studied here. It is probably worthwhile confirming this by studies of
c c
1
400
,
,
300
,
1
,
200
1
100
,
,
1
0
Chemical shift, 6 (ppm)
1
-100
1
1
-200
400
,
1
300
1
200
1
,
~
100
Chemical shift
1
0
6
~
-100
1
~
-200
(pprn)
Flgure 2. I3CCP/MAS spectra of humic material before and after chlorination. Key: (a) sample 1 before chlorination, (b) sample 1 after chlorination, (c) sample 2 before chlorination, (d) sample 2 after chlorination, (e) sample 3 before chlorination, (f) sample 3 after chlorination, (9) sample 4 before chlorination, (h) sample 4 after chiorination, (i) sample 5 before chlorination, (j)sample 5 after chiorination. Table V. Percent Change in Peak Heights" (ppm) o f Signals f r o m Various Functional Groups in Materials on Chlorination
sample no. 42-46 1 42 2 31 3 23 4 13 5 21 a Measured as 100(peak height mined.
NMR Spectra of H u m i c
% change 55 75-84 104-108 129-133 151-153 172-175 195-199 75 15 -22 -42 33 -60 -100 -100 75 0 -19 -46 26 -50 75 17 -18 -36 25 -60 -100 NDb 43 -7 -13 -38 13 -50 -100 58 0 -13 -33 37 -25 after chlorination - peak height before chlorination)/(peak height before chlorination). ND, not deter-
Envlron. Sci. Technol., Vol. 25, NO. 6, 1991
1163
,
1
la)
9
(4) Jolley, R. L., Bull, R. J., Davis, W. P., Katz, S., Roberta,
1.4 x 10E L
(5) (6) (7) (8) (9)
M. H., Jacobs, V. A., Eds. Water Chlorination: Chemistry, Environmental Impact and Health Effects;Lewis: Chelsea, MI, 1985; Vol. 5. Bull, R. J. Environ. Sci. Technol. 1982, 16, 554A. Kringstad, K. P.; Ljungquist, P. 0.;de Soma, F.; Stromberg, L. M. Environ. Sci. Technol. 1983, 17, 553. Quimby, B. D.; Delaney, M. F.; Uden, P. C.; Barnes, R. M. Anal. Chem. 1980,52, 259. Kringstad, K. P.; de Sousda, F.; Stromberg, L. M. Enuiron. Sci. Technol. 1985, 19, 427. Uden, P.; Miller, J. W. J.-Am. Water Works Assoc. 1983,
75, 524. (10) Rook, J. J. J.-Am. Water Works Assoc. 1976, 68, 168. (11) Coleman, W. E.; Munch, J. W.; Kaylor, W. H.; Steicher,
R. P.; Ringhand, H. P.; Meler, J. R. Enuiron. Sei. Technol. Ib)
I CHCL3
2x105
?
0
C 0
1984, 18, 674. (12) Hemming, J.; Holmbom, B.; Reunanen, M.; Kronberg, L. Chemosphere 1986, 15, 549. (13) Fielding, M.; Horth, H. Water Supply 1986, 4 , 103. (14) Boyce, S. D.; Hornig, J. F. Environ. Sci. Technol. 1983,17, 202. (15) Norwood, D. L.; Johnson, D. J.; Christman, R. F.; Hass,J. R.; Bobenrieth, M. J. Environ. Sci. Technol. 1980,14,187. (16) Lin, S.; Llukkonen, R. J.; Thom, R. E.; Bastian, J. G.;
Lukasewycz, M. T.; Carson, R. M. Environ. Sei. Technol.
U
1984, 18, 932. (17) Lin, S.; Lukasewycz, M. T.; Llukkonen, R. J.; Carson, R. M. Environ. Sei. Technol. 1984, 18, 985. (18) Hayes, M. H. B.; MacCarthy, P.; Malcolm, R. L.; Swift, R.
D 3
(19) Time lmin)
Flgure 3. Typical reconstructed ion chromatogram from pyrolysis gas chromatography-mass spectrometry of humic material. (a) Sample 4 befor! chlorinatlon; (b) sample 4 after chlorination. Alkanes are labeled C, the flrst labeled is the C,, homologue. The unknown (7) had hlghest mle of 243 but could not be Identified further.
different pH’s. However, the results presented here clearly support the choice of methoxy aromatics, phenols, and aryl ketones as model compounds for chlorination studies, even though aquatic humic substances are now known to be less aromatic and contain smaller amounts of phenol than previously supposed.
Literature Cited (1) de la Mare, P. B. D. Electrophilic Halogenation; Cambridge University Press: Cambridge, UK, 1976. (2) de la Mare, P. B. D.; OConnor, C. J.; Wilson, M. A. J. Chem. SOC.,Perkin Trans. 2 1975, 1150. (3) Aleta, E. M.; Roberts, P. V. Environ. Sci. Technol. 1986, 20, 50.
1164 Envlron. Scl. Technoi., Vol. 25, No. 6, 1991
(20) (21) (22)
(23) (24) (25) (26)
S. Humic Substances 11-In Search of Structures; J. Wiley and Sons: New York, 1989. Saiz-Jimenez, C. Origin and Chemical Nature of Soil Organic Matter; Delft University Press: Delft, The Netherlands, 1988. Norwood, D. L.; Christman, R. F.; Hatcher, P. G. Enuiron. Sci. Technol. 1987, 21, 791. Leenheer, J. A,; Wilson, M. A.; Malcolm, R. L. Org. Geochem. 1987,11, 273. Horth, H.; Frimmel, F. H.; Hargitai, L.; Hennes, E. C.; Huc, A. Y.; Muller-Wegener, U.; Nieymeyer, J.; Nissenbaum, A.; Sekoulov, I.;Tipping, E.; Weber, J. H.; Zepp, R. G. In Humic Substances and Their Role in the Environment; Frimmel, F. H., Christman, R. F., Eds.; J. Wiley & Sons: New York, 1988; pp 245-256. Wilson, M. A. NMR Techniques and Applications in Geochemistry and Soil Chemistry; Pergamon Press: Oxford, UK, 1987. Wilson, M. A.; Hatcher, P. G. Org. Geochem. 1988,12,539. Saiz-Jiminez, C.; de Leew, J. W. J. Anal. Pyrol. 1986,9,99. Sihombing, R.; Johnson, W. D.; Wilson, M. A.; Johnson, M.; Vassallo, A. M.; Alderdice, D. Org. Geochem. 1991,17, 85.
Received for review September 5, 1990. Revised manuscript received January 25, 1991. Accepted February 18, 1991.
