Environ. Sci. Technol. lQ86, 20, 1050-1055
Registry No. Cu, 7440-50-8; MnOz, 1313-13-9.
Literature Cited
van den Berg, C. M. G. Ph.D. Thesis, McMaster University, Hamilton, Ontario 1979. van den Berg, C. M. G.; Kramer, J. R. ACS Symp. Ser. 1979, 115-132.
van den Berg, C. M. G.; Kramer, J. R. Anal. Chim. Acta 1979,106, 113-120.
Stroes-Gascoyne, S. Ph.D. Thesis, McMaster University, Hamilton, Ontario, 1983. van den Berg, C. M. G. Mar. Chem. 1982, 11, 307-322, 323-342.
McDuff, R. E.; Morel, F. M. M. California Institute of Technology Technical Report EQ-73-02,1973,1974,1975; W. M. Keck Laboratory of Environmental Engineering Science. Loganathan, P.; Burau, R. G. Geochim. Cosmochim. Acta 1973, 37, 1277-1293.
(8) Gabano, J. P.; Etienne, P.; Laurent, J. F. Electrochim. Acta 1965,10,947-963. (9) Schindler, P. W.; Ftirst, B.; Dick, R.; Wolf, P. U. J. Colloid Interface Sci. 1976, 55, 469-475. (10) McKenzie, R. M. Geochim. Cosmochim. Acta 1980, 43, 1855-1857. (11) Davis, J. A. PbD. Thesis, Stanford University, Stanford, CA, 1978. (12) Breeuwsma, A,; Lyklema, J. J.Colloid Interface Sci. 1973, 43,437-448. (13) Sillen, L. G.; Martell, A. E. Spec. Pub1.-Chem. SOC.1961, No. 17. (14) Sillen, L. G.; Martell, A. E. Spec. Pub1.-Chem. SOC.1971, No. 25.
Received for review October 17,1985. Accepted May 29,1986. This research was supported by research grants from the Natural Sciences and Engineering Research Council of Canada and from Environment Canada.
Enhancement of N-Nitrosamine Formation on Granular-Activated Carbon from N-Methylaniline and Nitrite Andrea M. Dietrich, * s t Danlel L. Galiagher,t Patricia M. DeRosa,' David S. Mililngton,5and Francis A. DlGlanot
Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina 275 14, State of North Carolina, Division of Health Services, Raleigh, North Carolina 27602-2091, and Department of Pediatrics, Division of Genetics and Metabolism, Duke University, Durham, North Carolina 27706 Sterile aqueous N-methylaniline solutions were allowed to equilibrate at various nitrite, F-400 granular-activated carbon, and pH levels for 1 week. The aqueous and activated carbon phases were extracted and analyzed for nitrosamines relative to an added internal standard. Selected ion monitoring GC/MS, utilizing continuous monitoring of the NO+ ion (m/z 29.9980) characteristic of nitrosamines, at medium resolution ( R = 2500-3000) was applied to quantitatively measure nitrosamines at picograms per microliter concentrations. This method selected for nitrosamine products only and eliminated interferences from non-nitrosamine reaction products. Results indicate that the presence of granular-activated carbon significantly enhanced the formation of nitrosamine from N-methylaniline (F = 145, p < 0.0001). The amount of N-nitrosomethylaniline formed in the presence of activated carbon was 75 times more than that formed in the absence of activated carbon under the same nitrite, pH, and precursor amine conditions. High nitrite concentrations and low pH values significantly increased the conversion of secondary amine to nitrosamine. Introduction
Granular-activated carbon (GAC) accumulates natural and anthropogenic organic material in addition to inorganic salts, minerals, and microorganisms during water treatment. Chemical and biochemical activity may produce new compounds from those originally present, with possible human health consequences ( 1 , 2 ) . This research investigated the role of activated carbon in mediating the formation of N-nitrosamines from nitrite and secondary amine precursors. N-Nitrosamines are of particular environmental and health importance because, as a class, these compounds possess potent mutagenic and carcino'University of North Carolina. Carolina, Division of Health Services. *Duke University. *State of North
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Environ. Sci. Technol., Vol. 20, No. IO, 1986
genic activity (3). Although secondary amines and nitrite are id in only very low concentrations in water supplies (4, a), GAC may still mediate the formation of N-nitrosamines. Secondary amines can accumulate on GAC over a long period of operation, and nitrite is an intermediate in nitrification, a microbial process that occurs in GAC filters (6). Nitrosamine formation depends on the direct nitrosation of secondary amines (7), although primary and tertiary amines are also potential precursors since they may be converted to secondary amines. The overall reaction is R2NH
+ NOp- + H+
-
RzN-N=O
T H2O
The rate of reaction is first order with respect to the secondary amine and second order with respect to nitrite (8):
rate of formation = k,[R2NH][HN02]2 Direct nitrosation occurs optimally at pH 3.4, the pKa of nitrous acid (9),but another reaction pathway catalyzed by certain carbonyl compounds (including formaldehyde and trichloroacetaldehyde) can produce nitrosamines under neutral and even basic conditions (10). The nitrosating potential of tapwater has been demonstrated when secondary amines are added (11). Whether activated carbon affects nitrosation remains unclear. However, activated carbon has been implicated in the formation of nitrosamines from airborne precursors (12). The occurrence of nitrosamines in a variety of environmental samples has been cited. N-Nitrosamines have been detected in drinking water ( I I ) , industrial wastes (13-15), and water passed through deionizing resins (16-18). This study was designed to investigate the effects of pH and nitrite on the abiotic F400-GAC-mediated nitrosation of N-methylaniline. N-Methylaniline was selected because of its high solubility, low volatility, low pKa, strong adsorption on GAC, and known occurrence in certain drinking water supplies (19). The experimental conditions
0013-936X/86/0920-1050$01.50/0
0 1986 American Chemical Society
were not designed to simulate actual water treatment conditions, which could involve microbial-mediated nitrosation, rather the experiments were designed to investigate conditions which could chemically mediate nitrosation. Experimental Section Materials. N-Methylaniline (MA) was obtained from Aldrich Chemical Co. (Miwaukee, WI); N-nitroso-Nmethylaniline (NNMA) and 3-chloroaniline (CA) were from Sigma Chemical Co. (St. Louis, MO); N-nitrosopyrrolidine (NNPy) was from Fluka Chemical (Hauppauge, NY). Acetone and methylene chloride were purchased from Burdick & Jackson (Muskegon, MI), and distilled, deionized water was prepared in our laboratory. F-400 granular-activated carbon from Calgon Corp. (Pittsburg, PA) was first sieved through a 40/50 mesh, rinsed with tapwater and distilled water, dried at 110 "C, and stored in a desiccator over anhydrous calcium sulfate prior to use. Fisher Scientific reagent grade nitrite and phosphate salts were used. ANOVA Design. A four-way analysis of variance (ANOVA) design was utilized to evaluate the effect of activated carbon on the formation of N-nitrosamines from secondary amines. The variables were pH 7 and 4, nitrite (NaN02 as N) at 0,0.02, and 2.0 mg/L, N-methylaniline at 0 and 100 mg/L, and activated carbon at 0,27, and 52 mg/100 mL (these dosages reduced the initial solution concentration of N-methylaniline by 0% ,75%, and 95%, respectively). Each experiment was performed in 118-mLglass bottles with Teflon-lined caps. The pH 7 buffer was 4 mM KHzP04and 4 mM Na2HP04. The pH 4 buffer was 100 mM NaH2P04and 1.38 mM H3P04. Glass bottles containing preweighed amounts of carbon and solutions of phosphate and nitrite salts were autoclaved prior to use. N-Methylaniline was added aseptically after autoclaving; the final volume per bottle was 100 mL. Each experiment was performed in duplicate. The bottles were wrapped in aluminum foil to prevent photolytic decomposition of nitrosamines (11) and agitated for 1 week in a rotary shaker a t 25 rpm. After this time, the NNMA was measured from extracts of the carbon and aqueous phases. The carbon from each bottle was transferred to a 5-mL glass vial and dried in a vacuum desiccator over P206. Samples containing MA at pH 4 were dried separately from those without MA; however, this was not done for comparable samples obtained in the pH 7 experiment. After 3-4 days, the dried carbon samples were weighed to ensure dryness and determine carbon losses during handling. The solvent extracts of the carbon and aqueous phases were stored in glass vials with Teflon-lined caps at 4 "C. Statistical Analysis. Statistical analysis of the results from the ANOVA design experiment was performed by using the Statistical Analysis System (SAS, release 79.6). To compensate for nonhomogeneity of variance, only the data for the samples with 100 mg/L MA were analyzed, and the data were log (e) transformed prior to statistical analysis. This necessitated that all samples in which no NNMA was detected be set t o a value less than the detection limit so that the numerical transformation could be performed. A value of 0.25 pg was selected (half the effective detection limit; see Results). Preparation of Sample Extracts. Fifty-milliliter aqueous samples were extracted with methylene chloride (3 X 5 mL) and the combined extracts reduced by evaporation to 2 mL. The internal standard, either 3-chloroaniline (CA) for gas chromatography/flame ionization
detection (GC/FID) or N-nitrosopyrrolidine (NNPy) for gas chromatography/mass spectrometry (GC/MS), was added prior to analysis. Dried carbon samples were extracted ultrasonically with acetone (2 mL, then 2 X 1 mL) for 30 min total (10 min for each acetone addition) (20). The combined extracts were filtered through 0.5-pm Millex-RS filters from Millipore Corp. (Bedford, MA) and reduced by evaporation to 2 mL, and the internal standard was added. Recovery Experiments. The recovery of N-nitrosoN-methylaniline (NNMA) from aqueous solution was determined at 50 and 0.5 mg/L NNMA concentrations. Five 50-mL portions of each solution were extracted according to the methylene chloride procedure. The internal standard, 3-chloroaniline (CA), was added in the amounts of 0.20 and 0.002 mg, respectively, to the extracted 50 and 0.5 mg/L solutions (final CA concentration in extracts: 100 and 1mg/L). Analytical standards were prepared in the ranges of 60-140 (100 mg/L CA) and 1-5 mg/L NNMA (1mg/L CA) by serial dilution. The recovery of NNMA from F-400 activated carbon was determined under sterile conditions. Ten replicate samples, each containing 0.5 g of F-400 and 100 mL of a 50 mg/L NNMA solution (5 mg of NNMA total), were equilibrated for 1week. The aqueous phase was decanted and extracted with methylene chloride. The carbon samples were dried and extracted with acetone. An internal standard of 1 mg (500 mg/L) was added. Analytical standards were prepared in the range 20-800 mg/L NNMA. The recovery experiment was analyzed by GC/ FID. Capillary GC/FID Analysis. GC/FID was employed for methods development, recovery experiments, and prescreening samples prior to mass spectrometric analysis. A Varian 3700 capillary GC equipped with an FID and an SGE OCI-2 on-column injector (SGE, Austin, TX) was used. The FID chromatographic conditions were as follow: CAM-15N or DX3-15N column (112-2112 or 122-6312 from J&W Scientific, Rancho Cordova, CA); He carrier at 1mL/min; flame ionization detector at 300 "C; temperature program rate 1-2 pL injected on column at 40 "C for CHzClzand 50 "C for acetone, ramped to 90 "C and then 90-150 "C at 6 "C/min for standards and controls or 90-220 "C at 6 "C/min for samples; Recorder-Cole/Palmer, Model 8376-20, variable attenuation (typically 4 x 10-11 hA/mV). Capillary GC/MS Analysis. The gas chrbmatography/mass spectrometry system consisted of a HewlettPackard 5710A GC with an SGE OCI-2 on-column injector interfaced to a VG Micromass 7070F (double focusing magnetic sector type) mass spectrometer/VG2035F/B data system. Full scanning GC/MS conditions for electron ionization (EI) were electron energy of 70 eV (filament current 200 PA), source pressure of 5 X lo4 Torr, resolution of 1000 (10% valley), scan time of 0.7 s/decade, and mass range of 300-20 amu. A 2-pL sample was injected on a CAM-15N or DX3-15N column with the helium carrier at 1 mL/min and the oven temperature programmed 40-220 "C at 6 "C/min. A GC/MS selected ion detection method was developed for accurate, quantitative measurement of picogram amounts of NNMA. Similar to most nitrosamines, NNMA fragments to produce an intense NO+ ion at m/z 30 (21). This characteristic fragment was utilized to measure NNMA. The NO' ion, mass 29.9980 amu, was selectively monitored with respect to a reference ion (l4Nl5N+*, mass 29.0032 amu) which was continuously present. The resolution was 2500 (10% valley), Envlron. Sci. Technol., Vol. 20, No. 10, 1986
1051
Single ion monitoring (SIM) utilized the peak matching unit of the VG Micromass 7070F. The low mass channel was tuned to 14N15N*+, and the high mass channel continuously monitored the NO+ ion. The output from the amplifier was fed directly to a recorder, and quantitative measurement was based on the peak height ratio of the analyte to its internal standard. Individual nitrosamines were identified on the basis of retention time on a DX315N column. Quantitative Analysis. For both GC/FID and GC/ MS analyses, quantitative measurement consisted of adding a known amount of the internal standard to a known volume of the final extract. Determination of amounts present in individual samples was performed by comparing peak ratios of NNMA/NNPy (internal standard) for the samples to peak ratios generated for standard curves in the appropriate concentration range. The amount of internal standard added and the standard curve range varied for particular groups of samples. For SIM GC/MS analysis, most of the samples containing no carbon, no or 0.02 mg/L added nitrite, and no MA received 1mg/L NNPy. The pH 4 carbon extracts from the samples containing 2 mg/L nitrite and MA were diluted 1:lO prior to GC/MS analysis, and then 50 mg/L NNPy was added to these samples. All other samples received 10 mg/L NNPy. Standard curves were prepared and analyzed in conjunction with the samples. The ranges of the standard curves were 10-100 mg/L NNMA with 50 mg/L NNPy, 1-40 mg/L NNMA with 10 mg/L NNPy, and 0.04-5 mg/L NNMA with 1 mg/L NNPy. All samples were analyzed by SIM GC/MS for the quantitative measurement of NNMA except the pH 4 and pH 7 samples containing no carbon, no added nitrite, and no MA. GC/FID analysis indicated the absence of NNMA in these 1 2 samples. As an additional confirmation, one sample from each of the pH 4 and pH 7 groups was randomly selected and analyzed by SIM GC/MS. Total NNMA, in micrograms, was calculated for each treatment sample by summing the recovery-corrected values of NNMA for the carbon and aqueous phases. Ten replicate 2-pL injections of an acetone blank and low microgram per liter (ppb) solutions of NNMA were analyzed in a random fashion to determine the limit of detection. The limit of detection was defined as the mean response for the acetone blank *3 standard deviations (22). Results and Discussion
Recovery and Preliminary Experiments. The recovery for the 50 mg/L NNMA aqueous solution was 33.4 f 1.34 mg/L (67%) and for the 0.5 mg/L NNMA aqueous solution was 0.42 f 0.07 mg/L (83%). Thus, the mean percent recovery by this method was 75% for the aqueous samples. The recovery from the F4OO-GAC was 0.81 f 0.10 mg, of NNMA (16.3%) with a coefficient of variance of 12.5%; no NNMA was recovered from the aqueous solution, thus indicating that all was adsorbed. This recovery is comparable to the results of Millington and Christman (20), who found similar results for the recovery of aromatic compounds from GAC using a sonication/solvent extraction procedure. Their results for naphthalene, quinoline, and nitrobenzene are as follow: compound
adsorption efficiency to activated carbon
recovery from activated carbon
-naphthalene quinoline nitrobenzene
91%, 98% 91%, 98% 94%, 98%
30%, 30% 6%, 10% 45%, 48%
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Environ. Sci. Technol.. Vol. 20, No. 10, 1986
n Varion 3 7 0 0 G C Corbowox h i n e Deactivated Column 50'C i 900C-6*C/min+22O0C
Figure 1. GCIFID chromatogram for acetone extract of activated carbon from a pH 7 sample containing 100 mg/L N-methylaniline, 2.0 mg/L NaNO, (as nitrogen), and 52 mg of activated carbon. GC Column: CAM, attenuation 2 X lo-'' mA/mV.
I
30 rnin
Flgure 2. GC/FID chromatogram for methylene chloride extract of aqueous solution from pH 7 sample containing 100 rng/L N-methylaniline, 20 mg/L NaNO, (as nitrogen), and 52 mg of activated carbon. GC Column: CAM, attenuation 2 X lo-'' mA/mV.
Recovery from activated carbon utilized sonication/solvent extraction from GAC with three successive solvents: acetone, methylene chloride, and toluene. These results included duplicate samples. When the instrumental limit of detection for the SIM GC/MS is adjusted for 75% recovery from the aqueous phase and 16% from the carbon phase, the effective detection limit for samples is 500 pg/2 pL injected on capillary column or 0.50 pg per sample bottle. Figures 1and 2 present chromatograms for the carbon and aqueous-phase extractions, respectively, of a sample at pH 7 which contained 2.0 mg/L nitrite and 100 mg/L MA. As is evident in these chromatograms, a complex mixture of chromatographable products, including N nitrosomethylaniline, was produced. The concentration of these products was greater in the carbon extracts of samples than in the aqueous extracts. High nitrite concentration and neutral pH increased the number and concentration of the products formed when compared to low nitrite and low pH. Several products were identified as oxidation and degradation products of MA, including aniline, formanilide,
Table I. Results of Experiment at pH 7 with 0 mg/L N-Methylaniline" activated carbon, mg 0
I1
N- Nitroso Methyl Aniline-
27 52
N-Nitroso Pyrrolidine
nitrite (NaNO, as N), mg/L 0.02 2.00
0.00
ND ND 1.27 1.68 0.99 9.80
ND ND ND ND ND 0.97
ND ND 6.90 12.4 3.68 4.00
a Data reported in microgram (pg) of N-nitrosomethylaniline. ND = not detected.
Inject
Time
-
Figure 3. GC/MS selected ion chromatogram ( m / z 29.9980) for acetone extract of activated carbon from a pH 7 sample containing 100 mg/L N-methylaniline, 2.0 mg/L NaN02 (as nitrogen), and 52 mg of activated carbon. N-Nitrosopyrroliine is an added internal standard. GC Column: DX-3.
Table 11. Results of Experiment at pH 4 with 0 mg/L N-Met hylaniline' activated carbon, mg 0
27 52
nitrite (NaN02as N), mg/L 0.02 2.00
0.00
ND ND ND ND ND 4.50
ND ND ND 1.24 ND 0.96
ND ND ND 0.78 ND 0.77
Data reported in micrograms (pg) of N-nitrosomethylaniline. ND = not detected. Table 111. Results of Experiment a t pH 7 with 100 mg/L N-methy lanilhe"
activated carbon, mg IO
20
30
40
0
N-NMA (rng/l)
Figure 4. Standard curve for selected Ion monitoring of N-nitrosomethylaniline (NNMA).
and methylformanilide (identifications based on mass spectral interpretation and library comparison). NNMA was the only detectable N-nitrosamine identified, and its presence was confirmed by comparison for the E1 fragmentation pattern and GC retention time to that of an authentic standard. In addition to reaction products from MA, several contaminants and artifacts such as 4hydroxy-4-methyl-2-pentanone (diacetone alcohol), phthalate esters, and tris(chloroethy1) phosphate were identified in both the samples and controls. The large number and concentration of various chromatographable products and the small amount of NNMA formed under the reaction conditions made it essential that a very selective method by used for the quantitative measurement of N-nitrosomethylaniline. A sample chromatogram using selected ion monitoring GC/MS is shown in Figure 3. Only the analyte and the internal standard, N-nitrosopyrrolidine, are detected. The selected ion monitoring method was linear for the ranges analyzed; a typical standard curve is shown in Figure 4. Results from ANOVA Design. Quantitative analyses of NNMA for the controls (0 mg/L MA) at pH 7 and pH 4 and 100 mg/L MA samples at pH 4 and pH 7 are presented Tables I-IV, respectively. The individual values reported represent the s u m of the mass of NNMA detected in the aqueous and carbon phases. Nearly all of the NNMA (95100%) was recovered from the activated carbon, indicating that NNMA was well adsorbed. The amounts of NNMA detected in the control samples (containing no MA) were less than 1 2 pg, and frequently no NNMA was detected. This indicated that there was
27 52
nitrite (NaN0, as N), mg/L 0.00 0.02 2.00 ND ND 2.30 1.98 5.10 5.50
0.62 ND 3.80 4.40 4.90 7.20
2.80 5.00 87.4 49.8 93.2 95.3
" Data reported in micrograms (pg) of N-nitrosomethylaniline. ND, not detected. Table IV. Results of Experiment at pH 4 with 100 mg/L N-Met hylaniline" activated carbon, mg 0
27 52
nitrite (NaN02as N), mg/L 0.00 0.02 2.00 ND ND 9.18 17.6 10.0 1.05
3.24 3.53 806 275 61.7 75.5
800 864 5300 6550 7300 6980
'Data reported in micrograms (rg) of N-nitrosomethylaniline. ND = not detected.
little MA or NNMA either present on the original F-400 activated carbon and labware or introduced through contamination during analysis. NNMA values reported for the pH 4,0 mg/L MA samples are generally lower than those for the pH 7,O mg/L MA samples. This may have been due to a reduction in cross-contamination by desiccating the pH 4 samples without MA separately from those containing MA whereas all of the pH 7 samples were desiccated together. The 100 mg/L MA samples produced significantly more NNMA than the 0 mg/L MA samples. The formation of NNMA then is clearly related to the presence of the secondary amine and not an artifact of the experimental Environ. Sci. Technol., Vol. 20, No. 10, 1986
1053
design. The amount of NNMA formed at pH 4 was frequently 2 orders of magnitude greater than the corresponding treatment at pH 7 due to the greater amount of nitrous acid at the lower pH. Additionally, a greater number and concentration of oxidation/degradation products other than NNMA formed at pH 7; these competitive reactions could be partly responsible for the lower overall conversion of MA to NNMA at pH 7. Statistical evaluation of the data was performed by using a three-way analysis of variance, considering nitrite, pH, and F-400activated carbon as the parameters for the 100 mg/L MA treatment set. This resulted in the following F statistics for each individual parameter and all possible interactions: parameter PH nitrite carbon pH-nitrite pH-carbon carbon-nitrite pH-nitrite-carbon
F statistic
probability
293 353 145 60.6 8.58 1.88 3.80
0.001 10.0001 10.0001 10.0001 0.0024 0.1583 0.0207
An analysis of variance is used to test for significant differences among sample means. The means in this experiment are the logs ( e ) of the microgram amount of NNMA formed in each sample bottle. The results of this analysis indicate that each of the individual parameters had a significant effect on the quantity of NNMA formed (generally, significant statistical differences are indicated by probability values less than 0.05). Thus, the lowering of pH increased the NNMA formation, the addition of nitrite increased NNMA formation, and the presence of F-400activated carbon increased NNMA formation. The effects of nitrite and pH were expected based on the kinetics and mechanism of the nitrosation reaction. However, this research has additionally demonstrated that the presence of F-400 activated carbon is important in nitrosamine formation. The interaction effects, those with more than one parameter in the ANOVA table, are more difficult tQ explain. The pH-nitrite interaction effect is probably caused by the greater formation rate of the nitrosating agent at lower pH value and higher nitrite concentrations together. The interaction effect between pH and activated carbon may be caused by surface changes on the activated carbon at different pH values or increased adsorption of the nonprotonated amine at more acidic pH values (23). The interaction between the activated carbon and nitrite is not significant, while the three-way interaction cannot be easily interpreted. The design of this experiment permitted the measurement and comparison of amounts of NNMA formed after a 1-week reaction time and did not directly permit the examination of kinetics. Two alternative hypotheses can explain the effect of activated carbon: either activated carbon altered the thermodynamic equilibrium concentrations of reactants and products to favor the nitrosamine product or it catalyticdy increased the rate of the reaction, without interfering with the thermodynamic equilibrium. Both possibilities are discussed below. The literature suggests that the nitrosation reaction is fast (8), and thus, it is possible that a reaction time of 1 week was sufficient to reach an equilibrium concentration of NNMA. Under this assumption, the equilibrium concentrations of NNMA measured in the samples containing activated carbon were higher than in the samples without activated carbon. Therefore, in the presence of activated carbon the equilibrium was shifted toward nitrosamine 1054
Envlron. Scl. Technol., Vol. 20, No. IO, 1986
product. Because MA (the precursor to NNMA) is well adsorbed, it is implied that the nitrosation reaction occurs mostly on the surface. Additional evidence comes from the analytical results that indicated most of the MA, NNMA, and other organic products were recovered from the carbon surface and not from the aqueous phase. The enhancement effect, or the increased nitrosamine formation in the presence of carbon, may therefore be the result of an increased surface concentration or the so-called “mass action” effect. Although an increase in MA concentration caused by adsorption should increase the reaction rate on the basis of the solution-phase rate equation, catalysis theory suggests that increased surface concentration is not responsible for the observed enhancement of reaction rates (24). In these experiments, the overall quantity of NNMA formed was approximately the same for samples containing either 27 or 52 mg of activated carbon. This may suggest a possible catalytic effect in that merely the presence of activated carbon, rather than an increase in surface concentration, caused enhanced formation of nitrosamine. The activated carbon then acts as a catalyst to increase the rate of NNMA formation without changing the final equilibrium, possibly due to a lower activation energy for the amine-nitrosonium ion complex. Such catalytic properties of carbon in industrial processes are well documented, although the catalytic behavior of carbon in aqueous solutions has not been well studied (25). Catalytic activity usually resides in only a small number of active sites on the surface (24). The catalytic behavior of activated carbon is attributed to the presence of oxygenated sites such a carboxyl, lactone, quinone, hydroxyl, or peroxide functional groups. The possibility also exists for metal ion catalysis due to trace impurities of certain metals such as iron or copper in the carbon itself (25). The maximum possible amount of nitrosamine that could form in these experiments was calculated from stoichiometry and compared to the measured amounts. Since nitrite was the limiting reagent, 100 mL of 2.0 mg/L of NaN02 (0.143 mmol/L) solution should form a maximum of 0.0143 mmol, or 1950 pg, of NNMA if nitrosation were complete. Table I11 indicates that, at pH 7, the maximum NNMA formed was only 95.3 pug which is a conversion of 4.8% of amine in the presence of 52 mg of activated carbon. However, Table IV indicates that at pH 4 and 2.0 mg/L NaNOz the maximum NNMA formed was 7300 kg, or 366% of the possible conversion in the presence of 52 mg of activated carbon. Even higher percent conversions were measured when 0.02 mg/L NaNOz was added. Several explanations are possible for these anomalously high conversions. A likely source of error is the correction factor applied for the analytical recovery from carbon. A recovery efficiency of 16.3% was assumed for pH 4 samples, even though the initial recovery experiments were performed at pH 7. Additionally, NNMA was a minor product, and the adsorption properties of the activated carbon would be significantly modified by the presence of the other components in the matrix, which were different at pH 7 and pH 4. Another point to be made is that NNMA formed in the presence of activated carbon at both pH 4 and pH 7 even when no added nitite was present (see Table I11 and IV). The amount of NNMA formed under these circumstances was greater than the control samples presented in Table I and 11. This indicates a residual nitrosation capacity due to the presence of F400-GAC. Although the absolute values of the NNMA production at pH 4 are in doubt, it is still valid to compare NNMA
productions with sample treatment at this pH because all samples were treated identically during extraction and analysis. The results in Table IV show that much more NNMA is produced when activated carbon is present at either level of NaN02,while the controls containing neither NaNOz nor activated carbon show little production of NNMA. Summary
The chemically mediated formation of a N-nitrosamine from a precursor secondary amine and nitrite in aqueous solution is enhanced by the presence of activated carbon. Acidic pH values and high nitrite concentrations further increase the extent of the nitrosation reaction in the presence of activated carbon. The exact mechanism of carbon-mediated enhancement is not known, but the results indicate that the F400-GAC presence of activated carbon is very important. Registry No. MA, 100-61-8; NNMA, 614-00-6. L i t e r a t u r e Cited National Academy of Sciences. Drinking Water and Health; National Academy Press: Washington, DC, 1980; pp 315-323. Voudrias, E. A,; Carson, R. A.; Snoeyink, V. L. Enivron. Sci. Technol. 1985,19,441-449. Singer, B.; Grunberger, D. Molecular Biology of Mutagens and Carcinogens; Plenum: New York, 1983. Milliner, R.; Bowles, D. A.; Rett, R. W. Water Treat. Exam. 1982,21, 318-325. Wegman, R. C. C.; DeKorte, G. A. C. Water Res. 1981,15, 391-394. Rittman, B. E.; Snoeyink, V. L. J.Am. Water Works Assoc. 1984,76,106-114. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 2nd ed.; McGraw-Hill: New York, NY, 1977. Mirvish, S.S.Toxicol. Appl. Pharmacol. 1975,31,325-351. Fishbein, L.Sci. Total Enuiron. 1979,13,157-188. Roller, P. P.; Keefer, L. K. In “N-Nitroso Compounds in the Environment”; Bogovski, P.; Walker, E. D.; Davis, W., Eds.; IARC Publication No. 9;Lyon, France , 1975. Kimoto, W. I.; Dooley, C. J.; Carre, J.; Fiddler, W. Water Res. 1981,15, 1099-1106.
(12) Rounbehler, D.P.; Reisch, J. W.; Coombs, J. R.; Fine, D. H. Anal. Chem. 1980,52,273-276. (13) Fine, D. H.; Rounbehler, D. P.; Rounbehler, A.; Silergleid, A,; Sawicki, E.; Krost, K.; DeMarrais, G. A. Environ. Sci. Technol. 1977,11,581-584. (14) Cohen, J. B.; Bachman, J. D. In “Environmental Aspects of N-Nitroso Compounds”; Walker, E. A.; Griciute, L.; Castegnaro, M.; Lyle, R. E., Eds.; IARC Publication No. 19;Lyon, France, 1978. (15) Richardson, M. L.;Webb, K. S.; Gough, T. A. Ecotoxical. Environ. Safe. 1980,4 , 207-212. (16) Gough, T.A.; Web, K. S.; McPhail, M. F. Food Cosmet. Toxicol. 1977,15,437-440. (17) Fiddler, W.; Pensabene, J. W.; Doerr, R. C.; Dooley, C. J. Food Cosmet. Toxicol. 1977,15,441-443. (18) Angeles, R. M.; Keefer, L. K.; Roller, P. P.; Uhm, S. J. In “Environmental h p e c t s of N-Nitroso Compounds“;Walker, E. A.; Griciute, L.; Castegnaro, M.; Lyle, R. E., Eds; IARC Publication No. 19;Lyon, France, 1978. (19) Cotruvo, J. A.; Wu, C. In Activated Carbon Adsorption of Organics from the Aqueous Phase; Suffet, I. H.; McGuire, M. J., Eds.; Ann Arbor Science: Ann Arbor, MI, 1980;Vol. I, overview. (20) Millington, D. S.; Christman, R. F. “Extraction and Analysis of Organic Compounds Adsorbed on GAC Filter Used in Treatment Plants”; Final Report for U.S. EPA Project No. R808551-01;Washington, DC, 1984. (21) Gough, T. A. Analyst (London) 1978,103(122),785-806. (22) Keith, L.H.; Crummett, W.; Deegan, J., Jr.; Libby, R. A.; Taylor, J. K.; Wentler, G. Anal. Chem. 1983,55,2210-2218. (23) Myers, A. L.; Zolandz, R. R. In Activated Carbon Adsorption of Organics from the Aquous Phase; Suffet, I. H.; McGuire, M. J., Eds.; Ann Arbor Science: Ann Arbor, MI, 1980;Vol. I, Chapter 12. (24) Hassler, J. W.Purification of Activated Carbon, 2nd ed.; Chemical Publishing Co., Inc.: New York, 1974. (25) Cookson, J. T. In Activated Carbon Adsorption of Organics from the Aqueous Phase; Suffet, I. H.; McGuire, M. J., Eds.; Ann Arbor Science: Ann Arbor, MI, 1980;Vol. I. Chapter
18. Received for review August 8,1985.Revised manuscript received April 3,1986.Accepted May 12,1986. This research was supported by the U.S. EPA Office of Exploratory Research, Grant R-809654.
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