Environ. Sci. Technol. 1902, 26, 2218-2227
(4) Mikesell, M. D.; Boyd, S. A. Appl. Environ. Microbiol. 1986, 52, 861-865. ( 5 ) Struijs, J.; Rogers, J. E. A R R ~Environ. . Microbiol. 1989. 55,2527-25311 Kuhn, E. P.; Suflita,J. M. Environ. Sci. Technol. 1989,23, 848-852. Shelton, D. R.; Tiedje, J. M. Appl. Environ. Microbiol. 1984, 48,840-848. DeWeerd, K. A.; Mandelco, L.; Tanner, R. S.; Woese, C. R.; Suflita, J. M. Arch. Microbiol. 1990, 154, 23-30. Dolfing, J.; Tiedje, J. M. FEMS Microbiol. Ecol. 1986,38, 293-298. Dolfing, J.; Tiedje, J. M. Arch. Microbiol. 1987,149,102-105. Dolfing, J. Arch. Microbiol. 1990, 153, 264-266. Mohn, W. W.; Tiedje, J. M. Arch. Microbiol. 1990, 153, 267-271. Thauer, R. K.; Jungermann, K.; Decker, K. Bacteriol. Rev. 1977,41, 100-180. Benson, S. W. Thermochemical Kinetics; 2nd ed.; Wiley: New York, 1976. Stull, D. R.; Westrum, E. F.; Sinke, G. C. The Chemical Thermodynamics of Organic Compounds; Krieger: Malabar, FL, 1987; pp 532-536. Stumm, W.; Morgan, J. J. Aquatic Chemistry, 2nd ed.; Wiley: New York, 1981. Thauer, R. K.; Morris, J. G. In The Microbe 1984, Part 2; Kelly, D. P., Can, N. G., Eds.; Cambridge University Press: Cambridge, England, 1984; pp 123-168. Bosma, T. N. P.; van der Meer, J. R.; Schraa, G.; Tros, M. E.; Zehnder, A. J. B. FEMS Microbiol. Ecol. 1988, 53, 223-229. Weast, E. D., Ed. Handbook of Chemistry and Physics; CRC Press: Boca Raton, FL, 1987. Serjeant, E. P.; Dempsey, B. Zonisation Constants of Organic Acids in Aqueous Solution; IUPAC Chemical Data Series 23; Pergamon: Oxford, England, 1979. Platonov, V. A.; Simulin, Y. N. Russ. J . Phys. Chem. 1983, 57,840-845.
__
(22) Mackay, D.; Shiu, W. Y. J . Phys. Chem. Ref. Data 1981, 10, 1175-1189. (23) Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed.; Interscience: New York, 1978. (24) Reid, R. C.; Prausnitiz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed.; McGraw Hill: New York, 1987: DD 12-26. 206. Vapo; Pressure and Critical Points of Liquids, XIX, Phenol and Derivatives; Engineering Sciences Data Co.: London, 1981. Dean, J. A., Ed. Lunge's Handbook of Chemistry, 11th ed.; McGraw Hill: New York, 1973. Doedens, J. D. In Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd ed.; Kirk, R. E., Othmer, D. F., Mark, H. F., Stander, A., Eds.; Wiley: New York, 1965; Vol. 5, p 325. Xie, T. M.; Dyrssen, D. Anal. Chim. Acta 1984,160,21-30. Cord-Ruwisch, R.; Seitz, H.-J.; Conrad, R. Arch. Microbiol. 1988,149,350-357. Madsen, T.; Aamand, J. Appl. Environ. Microbiol. 1991, 57,2453-2458. Zehnder, A. J. B.; Stumm, W. In Biology of Anaerobic Microorganisms; Zehnder, A. J. B., Ed.; Wiley: New York, 1988; Chapter 1. Robertson, L. A.; Kuenen, J. G. Arch. Microbiol. 1984,139, 351-354. van den 'heel, W. J. J.; Kok, J. B.; de Bont, J. A. M. Appl. Environ. Microbiol. 1987, 53, 810-815. Apajalahti, J. H. A.; Salkinoja-Salonen, M. S. J . Bacteriol. 1987,169, 5125-5130. Dolfing, J. In Anaerobic Biodegradation of Xenobiotic Compounds; Proceedings of an EEC workshop, Copenhagen, Denmark, 22-23 November 1990; Jacobsen, B. N., Zeyer, J., Jensen, B., Westermann, P., Ahring, B., Eds.; Commission of the European Communities, Brussels, 1991; pp 47-64.
Received for review March 13,1992. Revised manuscript received June 17,1992. Accepted June 25, 1992.
Ozonation Byproducts of Atrazine in Synthetic and Natural Waters Craig D. Adarns",' and Stephen J. Randtket:
Department of Environmental Systems Engineering, Clemson University, Clemson, South Carolina 29634, and Department of Civil Engineering, University of Kansas, Lawrence, Kansas 66045 The primary ozonation byproducts of atrazine [2chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] were determined in natural and synthetic waters with a maximum initial atrazine concentration of 15 pg/L. Deethylatrazine [2-amino-4-chloro-6-(isopropylamino)-s-triazine] was the primary byproduct under almost all conditions, with up to seven other degradation products being detected at various conditions. Experiments conducted under conditions which inhibited the autodecomposition of ozone to the hydroxyl radical (e.g., low pH and high alkalinity), produced primarily dealkylation byproducts of atrazine and an amide. Under conditions which favored the production of the hydroxyl radical from ozone (e.g., high pH, low alkalinity, or the presence of H,OJ additional (though minor) reactions included hydrolysis of the C1-C bond to form s-triazine hydroxy analogues. Introduction
In recent years, the use of ozone in water treatment planta in the United States as a disinfectant, as an oxidant, and as a coagulant aid has been increasing, and this trend + Clemson University. f University of Kansas.
2218
Envlron. Sci. Technol., Vol. 26, No. 11, 1992
is expected to continue (I). Among ozone's advantages are its ability to degrade undesirable micropollutanta in municipal water supplies, such as the ubiquitous herbicides atrazine [CIET (Z), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and simazine [CEET, 2-chloro-4,6-(diethy1amino)-s-triazine]. In the midwestern United States and elsewhere, atrazine is used extensively as a preemergent herbicide for crops including corn, sorghum, sugar cane, macadamia nut, and pineapple (3))as well as for weed control on rangeland and along railroads and highways. Atrazine has a water solubility of 33 mg/L (27 OC) and a half-life in soil of from 4 to 57 weeks (4). As a result, atrazine is frequently detected in groundwater and surface-water supplies with concentrations in surface waters near or exceeding the recently promulgated maximum contaminant level (MCL) of 3 pg/L which takes effect in 1992 (5). Previous investigators determined that atrazine undergoes degradation to relatively stable degradation products in soil, in pesticide waste treatment processes, and in water treatment processes. Because deethylatrazine [CIAT, 2-amino-4-chloro-6-(isopropy1amino)-s-triazine], a primary metabolite of atrazine formed in soil (6),is mobile and persistent, it is also observed in water supplies (7). Degradation products of atrazine may also occur
0013-936X/92/0926-2218$03.00/0
0 1992 American Chemical Society
I@ J N - n
I
I
I
H-N
CI
OH
CI
YH. I CH3
H-N
cnPCH)
CH I - CH3
I@ Z N - H CHI CH3
CIET
OIET
CH3
(Atrazine, 2-Chloro-4-ethylarnino6-isopro ylamino-s-triazine, G300.277
CH3
(H droxyatrazine, 2-&hylamino-4-hydroxy6-isopro ylamino-s-triazine, G-340487
CDAT (Deisoprop latrazine amide, 2-Acetamidb-4-amino6-chloro-s-triazine)
CI I
OH
CI
I
I
H-N l @ A y - H
li
CIAT (Deethylatrazine, 2-Amino-4-chloro6-isopropylamino-s-triazine, C-30033)
I
H
CH. CH3
I
fi. CH3
CH . CH3
OUT CH3 (2-Amino-4-hydroxy6-isopropylamino-s-triazine, GS-17794)
CI
‘H3 CDIT (Atrazine amide, 2-Acetamido-4-chloro6-isopropylamino-s-triazine)
on
PH
HO
OH
AH.2 CH3 OOOT
OEAT
CEAT (Deisopmpylatrazine,
(2-Amino-4-ethylarnino-6-hydroxy- (Cyanuric acid, 2,4,6-Trihydroxy-s-triazine, 2-Amino-4-chloro-6-ethylamino- s-triazine, GS-17792)
s-triazine, G28279)
G-28521)
CI
OH
I
OH
I
I
L?A~-~ *N
I
H-N
k
I
H
A
CAAT OOAT OAAT Didealkylated atrazine, (Ammeline, (2-Amino-4,6-dihydroxy-s-triazine, 2-C hloro-4,6-diamino-s-triazine, 2,4-Diarnino-6-hydroxy-s-triazine, GS-35713) G28273) GS-17791)
Flgure 1. Chemical structures of atrazlne and selected degradation products. Compounds may exist In other tautomeric or ionized structures under certaln conditions (2).
during ozonation in water treatment plants. In separate studies, Kuhn (8)and Hulsey et al. (9) monitored the volatile degradation products of atrazine, CIAT, and deisopropylatrazine [CEAT, 2-amino-4-chloro-6-(ethylamino)-s-triazine] and found that substantial conversion of atrazine to these compounds was observed. Studies of the conversion of atrazine to nonvolatile degradation products using ozone in water treatment processes have not previously been reported. The structures of selected s-triazine compounds are presented in Figure 1. For the oxidation of many organic substrates in water and wastewater treatment processes, the hydroxyl radical, ‘OH, has been shown to be a much stronger and less specific oxidant than ozone itself, leading potentially to different degradation pathways and byproducts for the organic substrate (10-12). Hydrogen peroxide catalyzes the formation of the hydroxyl radical and other free radicals from m n e in the aqueous phase via a well-understood autodecomposition cycle (13-16).Systems which promote the generation of hydroxyl radicals for oxidation purposes
(e.g. HzO2/O3or UV/03) are referred to as advanced oxidation processes (AOPs) (17).Researchers studying the treatment of atrazine-laden wastewaters (with atrazine concentrations of more than 10O00 times the promulgated MCL) have observed that a suite of byproducts is formed during oxidation by ozone (18)and with a UV/03 AOP (19). It should be noted that, in UV/03 processes, photolysis rather than oxidation by ozone or the hydroxyl radical may be the primary mechanism for chemical reactions. The toxic degradation products of atrazine and other herbicides are not currently regulated in the United States, although it may be anticipated that selected toxic ozonation byproducts of atrazine will eventually be regulated. European Community (EC) directives on drinking water already have a limit on “pesticides and related products” of 0.1 pg/L separately and 0.5 pg/L in total (20). Therefore, it is important to determine the extent to which atrazine is simply chemically modified while retaining its s-triazine ring structure during removal by ozonation. Environ. Sci. Technol., Voi. 26, No. 11, 1992 2219
Further, it is important to determine the identity of the primary ozonation byproducts of atrazine and the conditions under which they form, for future studies regarding their public health implications and, if necessary, their control. The objectives of this research were as follows: (1)to determine the primary ozonation byproducts and degradation pathways for atrazine in ozonation processes at concentrations typically found in drinking water and (2) to determine the effect of process parameters (e.g., pH, alkalinity, temperature, aqueous ozone concentration, and HzOzaddition) on the speciation of atrazine's ozonation byproducts. An additional objective of this research was to determine the effect of process parameters on the oxidation rate for the reaction of atrazine with ozone in natural waters; these results are presented elsewhere (21). Materials and Methods Materials. The atrazine standard (99%)was purchased from Supelco (Bellefonte, PA). The CEAT (99%), CIAT (98%),2-chloro-4,6-diamino-s-triazine (CAAT, go%), hydroxyatrazine (OIET, 97 %), 2-amino-4-hydroxy-6-(isopropy1amino)-s-triazine (OIAT, 95%), and 2-amino-4(ethylamino)-6-hydroxy-s-triazine (OEAT, 95%) standards were provided at no charge from the Ciba-Geigy Corp. (Greensboro, NC). The atrazine amide [CDIT, 2-acetamido-4-chloro-6-(ethylamino)-s-triazine] and deisopropylatrazine amide (CDAT, 2-acetamido-4-amino-6chloro-s-triazine)standards were provided at no charge by the US.Department of Agriculture (PesticideDegradation Laboratory,Agricultural Research Service, Beltsville, MD), Because the exact concentrations of the amide standards were not known precisely, nominal concentrations of the CDAT were estimated using the response factors of adjacent s-triazine compounds on the high-pressure liquid chromatogram. This should be a good assumption because most of the UV absorbance of this molecule may be attributed to the resonance structure of the ring. The high-pressure liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS) internal standards were metribuzin and phenanthrene-dlo, respectively, and were EPA reference standards. Atrazine and monodealkylated s-triazine standards were prepared in pesticide-grade methanol (Burdick and Jackson, Muskegon, MI). The nonvolatile standards were prepared in reagent water (Milli-Q Reagent Water System; Millipore Corp., Bedford, MA) and methanol. Methods for Ozone. Aqueous ozone concentrations were measured using the indigo method, standard method 4500 (22). Gas-phase ozone was measured using the iodometric method, standard method 422 (23). Characterization of Natural Waters. The natural waters were characterized with respect to dissolved organic carbon (DOC), turbidity, and alkalinity using the standard methods 5310C, 2130, and 2320B (22), respectively. Atomic absorption was used to measure calcium and magnesium by standard method 3111B, and iron, manganese and aluminum were measured by standard method 3113 (22). Analysis for s -Triazines. The solid-phase extraction (SPE) procedure was completely automated and used a Waters Millilab workstation 1A (Millipore Corp., Waters Chromatography Division, Bedford, MA). In the extraction procedure for HPLC analysis, the cartridge (CIS Sep-Pak Plus Environmental; Millipore Corp.), was prepared with methanol, ethyl acetate, and water prior to extracting a sample voIume of 50 mL. The cartridge was then eluted with methanol (Fisher Scientific, Springfield, NJ), and the eluent was spiked with the internal standmd 2220
Environ. Sci. Technol., Vol. 26, No. 11, 1992
and then reduced in volume to approximately 250 pL for HPLC injection. Each set of 14 water samples that was extracted typically included two blank samples and two standard samples with known concentrations of atrazine and its degradation products. Prior to extraction, the pH of each water sample was adjusted to between 6.7 and 7.3 so that the octadecyl-water partitioning coefficients for these compounds were constant. This resulted in reproducible partitioning between the aqueous and solid (organic) phases, and therefore, the extracted mass of each compound on the solid-phase medium was proportional to the concentration of that specific compound in the water phase. The coefficients of determination (R2)for the resulting 8-10 point standard curves for all standards analyzed by HPLC were greater than 0.99. The Waters HPLC system (Millipore Corp.) used in this study consisted of a quaternary pump system (Model 600E Powerline), a C-8 NovaPak reverse-phase column, a variable-wavelength detector (Model 490) set to 230 nm, an auto injector (Model 700), and a Baseline workstation (Model 810). The binary gradient system (50 mM ammonium acetate, pH 7.2) was ramped from 10:90 to 7030 (v/v) (methanol/water) with a 30-min cycle time. For confiiational of nonvolatile degradation products, a CPS Hypersil-CN HPLC column (24) (Keystone Scientific, Inc., Bellefonte, PA) and the same binary gradient method was used, which resulted in a different order of elution of the s-triazine compounds. Additional confirmation of OIET in a natural water sample from the Kansas River was performed using a Vestec Model 201A thermospray/LC/MS system (25)after fraction collection from the Waters HPLC. The massselective detector (MSD) conditions were as follows: electron multiplier voltage, 1600 V; control temperature, 115 "C; tip temperature, 211 "C; block temperature, 285 OC; 30-ms dwell time. Confirmation of volatile degradation products utilized a SPE plus GC/MS method. The same SPE extraction procedure was used for the GC/MS confirmation samples as for the HPLC samples except the cartridge was a CIS Sep-Pak Plus (Millipore Corp.) and was eluted with ethyl acetate (into which the analytes partitioned), and the internal standard was phenanthrene-d,,. GC/MS analyses utilized a Hewlett-Packard (HP) 5890A gas chromatograph (Palo Alto,CA), an HP-1fused-silica capillary column with a dimethylpolysiloxane stationary phase (12.5 m X 0.2 mm X 0.33 pm film thickness) and an HP 5970A MSD operated in selected-ion-monitoringmode. The column conditions were as follows: carrier gas, helium (1 mL/min); temperature ramp, 50-250 OC (6 OC/min). The MSD conditions were as follows: electron multiplier voltage 300 V above autotune; ionization voltage, 70 eV; ion source temperature, 250 "C; interface temperature, 280 "c; 50-ms dwell time. Because the extraction efficiencieswere greater for the less soluble compounds, their quantitation and detection limits reported were lower than for the more soluble compounds, For the four most soluble compounds &e., C U T , CDAT, OEAT, and OIAT) the limits were as follows: not detected (ND) 10.3 pg/L; and 0.3 I trace (T) 5 0.5 pg/L. For the five least soluble compounds (i.e., atrazine, CDIT, CEAT, CIAT, and OIET), the limits were as follows: ND k'cIAT [0.0014 L/ (pmol-min)]. No measurable ozonation byproducts were detected for CIAT under these conditions, including CAAT or OIAT. Ozonation of CEAT resulted in the formation of two products, CAAT and an amide, CDAT. The ozonation of OIET resulted in OIAT as the predominant byproduct with lesser amounts of OEAT. pH and Alkalinity Experiments. A series of experiments were performed in the flow reactor with synthetic waters to determine the effects of pH and total carbonate alkalinity. The experimental matrix included nine experiments with pH held constant, at 5, 7, and 9 with all combinations of total carbonate alkalinities of 0.5,1.0, and 5.0 mM added to the feed as sodium bicarbonate. Temperature and aqueous ozone concentration in these experiments were held constant at 20 "C and 1.0 mg/L, respectively. Three feed rates were used that corresponded to HRTs of 4.1, 8.3, and 16.7 min. In the experiments at pH values of 5 and 7, CIAT was the predominant ozonation byproduct (Table I). At pH 9, however, the concentration of an unknown byproduct was also significant and surpassed CIAT in the experiment with a total carbonate alkalinity of 1 mM (100 mg/L as CaC03). Other ozonation byproducts formed included CAAT, CEAT, OIAT, and OIET. Measurable concentrations of CDAT or OEAT were not formed in these experiments. At pH 5 there were only two byproducts besides CIAT measured above trace levels: CEAT and CAAT. These experiments at pH 5 showed that even at high alkalinity (Le., strong radical trapping) substantial dealkylation oc2222
Envlron. Scl. Technol., Vol. 20, No. 11, 1992
curred, resulting in the formation of three dealkylation byproducts. Additionally, molar balances were greater than 90% in these experiments at pH 5 for all of the alkalinity concentrations (0.5,1.0, and 5.0 mM) and HRTs (4.2, 8.3, and 16.7 min). Because ozone itself was the primary oxidant present, it may be concluded that the ozone readily cleaves the alkyl groups from the secondary amine groups of atrazine. In experiments using Fenton's reagent, Plimmer et al. (29) showed that the hydroxyl radical can also deethylate and deisopropylate atrazine and related s-triazines. At pH 7 and 9, the primary degradation pathway was still via dealkylation. However, low concentrationsof three other compounds were measured in addition to the dealkylation byproducts measured at pH 5: OIET, OIAT, and an unidentified byproduct. As shown in Table I, the measured concentrations of the hydroxy analogues were always low, less than 0.5 pg/L. Several results suggest that the formation of OIAT occurs through deethylation of OIET and not through hydrolysis of CIAT. First, ozonation of CIAT alone (at pH 7 and 1 mM total carbonate allralinity)did not result in the formation of any detectable ozonation byproducts, although 32% removal of CIAT was achieved. Second, ozonation of OIET alone resulted primarily in the loss of the ethyl group to form OIAT. To a much lesser degree, the isopropyl group was cleaved resulting in low concentrations of OEAT. Third, the only occurrences of OIAT at greater than trace levels (in the experiments on pH and total carbonate alkalinity) wree concurrent with quantifiable concentrations of OIET. The conclusion that OIAT (or its tautomer) is formed
via deethylation of OIET and not the hydrolysis of CIAT is not consistent with the mechanistic pathway proposed by Legube et al. (30),although these researchers stated that the product may have been OIET instead of OIAT. Legube et al. performed their experiments at atrazine concentrations of 22-44 mg/L and used for GC/MS after derivatization by diazomethane for analysis. Hydrogen Peroxide/Ozone. The effect of H202 addition on speciation of atrazine's ozonation byproducts was studied at four ratios of H202to aqueous ozone: 0.0,0.4, 1.0, and 1.6 (w/w). Optimum H202-to-aqueousozone ratios have been shown by several workers to typically be in the range 0.4-0.6 (w/w) due to stoichiometric considerations (12,27, 31). In these experiments, the aqueous ozone concentration was constant at 0.3 mg/L as ozone. The feed was spiked with approximately 10 pg/L of atrazine and was buffered with 10 mM sodium phosphate. The feed rate was held constant at 0.3 and 0.6 L/min with corresponding HRTs of 16.7 and 8.3 min. In the experiment at a Hz02-to-ozoneratio of 0.0, a feed rate of 0.15 L/min was also used in addition to 0.3 and 0.6 L/min. Two samples were taken at each feed ratio as described above. Feed samples were also obtained and analyzed in duplicate. The addition of Hz02caused a significant enhancement of atrazine decomposition during ozonation (Figure 3). With no H202added, the primary degradation product was CIAT, followed by CEAT, CAAT, and CDAT. These same compounds also were measured with a H202/03ratio of 0.4 (w/w), although the reaction rate was significantly enhanced. CDAT was the primary degradation product measured at all HRTs with H202/03ratios of 1.0 and 1.6 (w/w). Molar balances of 11-4370 were obtained on the measured compounds when H202was added as compared with 84-100% when H202was not added. Extended Contact Time. Experiments performed in the batch reactor with synthetic water buffered with 50 mM sodium phosphate were used to determine the pathways and byproducts resulting from ozonation of atrazine for extended reaction times. These experiments were in semibatch mode; that is, the ozone concentration was held constant while the s-triazine concentrations varied with time. After the desired aqueous ozone concentration and temperature were obtained, the reactor was spiked with atrazine to a predetermined concentration. Samples were removed periodically from 0.5 to 40 min to measure the concentrations of atrazine and its degradation products over time. As in the flow reactor, sample bottles contained sodium sulfite to immediately quench residual ozone. Experiments were conducted a t pH values of 5, 7, and 9 with aqueous ozone concentrations of 0.82, 0.87, and 0.3 mg/L, respectively. The results showed that, at pH 5 and 7, CDAT was the primary measured degradation product resulting from the ozonation of atrazine for extended contact times of 30-40 min while other byproducts predominated at shorter contact times (Figure 4). At pH 9, however, the oxidation of atrazine was so extensive that at a contact time of 40 min a molar balance of only 3% was obtained compared with 69 and 81% at pH values of 5 and 7, respectively. The hypothesized nature of the s-triazines unaccounted for is presented below with the discussion on degradation pathways. It should be noted that appreciable concentrations of CDAT only occurred under conditions more severe than would typically occur during water treatment. Additionally, CDAT was detected only in experiments in which there was little or no total carbonate alkalinity. Therefore,
10
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0 40
Flgure 3. Mean atrazine and byproduct Concentrations for hydrogen peroxide/ozone ratios of 0.0,0.4, 1.O, and 1.6 (w/w). The aqueous ozone concentration was 0.29-0.31 mg/L. The coefficient of variation for duplicate samples separated by 1 HRT was 4.1 % .
CDAT may not be a significant byproduct of the ozonation of atrazine in natural waters under typical water treatment conditions. Temperature. The effect of temperature on speciation was studied in the flow reactor using synthetic water in a series of experiments conducted at 15, 20, and 25 "C. The reactor liquid had a pH of 7 and was buffered with Environ. Sci. Technol., Vol. 26, No. 11, 1992 2223
Table 11. Natural Water Feed Characteristics atrazine conc (fig/L) raw water spiked feed
source Clinton Reservoir Perry Reservoir Kansas River (no dilution) Kansas River (dild 50%) Kansas River (dild 67%) Missouri River
1.7 5.0 2.6 1.3 0.9 ND" WO.1 pg/L)
10.2 11.4 3.8 4.7 4.8 5.2
DOC (mg/L as C) 5.7 6.8 7.3 3.7 2.4 4.0
total carbonate alk (mg/L as CaC03)
turbidity
(NTU)
128
1.0
131 258 129 86 200
3.5 14.0 7.1
" Not detected. 12
4\
10
Table 111. Range of Process Parameters for Natural Water Experiments PH5
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3
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0
0
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20
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50
Figure 4. Atrazine concentration for batch reactor experiments at pH 5, 7, and 9 with aqueous ozone concentrations of 0.82, 0.87, and 0.30 rng/L, respectively. The concentrations of hydroxyatrazine and 2arnln~ydroxy-8isopropy~s-triazine were always less than 0.2 and 0.5 MglL, respectively.
10 mM sodium phosphate. In each temperature experiment, samples were taken at three different HRTs after obtaining steady-state conditions. Mean molar balances to 75,66, and 62% were obtained at HRTs of 8.3,16.7, and 33.3 min, respectively. The effect of temperature on speciation was negligible with regard to the measurable byproducts. Natural Waters. A series of experiments were performed in the flow reactor to determine the oxidation 2224
aq ozone conc (mg/L)
pH
temp ("C)
Clinton Reservoir Perry Reservoir Kansas River Kansas River (dild 50%) Kansas River (dild 67%) Missouri River
0.76-1.09 0.12-1.27 0.96-1.40 1.31 0.58-0.97 0.87-1.15
6.1-8.2 5.8-7.8 7.2-8.2 6.8 5.8-7.4 6.6-7.5
15.9-22.2 14.4-21.7 17.5-23.3 18.9 16.1-23.3 16.7-20.6
pathways and primary ozonation byproducts resulting from the ozonation of four different natural waters fortified with atrazine to a maximum feed concentration of 11.4 pg/L. Each of these waters was characterized using the methods described previously. Approximately 200-L natural water samples were obtained from four locations: Clinton Reservoir below the spillway (at the intake to the Clinton Water Treatment Plant in Lawrence, KS), the Slough Creek arm of Perry Reservoir (Jefferson County, KS), the Kansas River (at the intake to the Kansas River Water Treatment Plant in Lawrence, KS), and the Missouri River (at the intake to the Leavenworth, KS, Water Works). The Missouri River results are from the confluence of rivers originating in Nebraska, Iowa, North Dakota, South Dakota, and Minnesota. The water samples were collected through PTFE hoses using a submersible centrifugal pump discharging into two 125-L polypropylene reservoirs carried in a van. Each of these samples, except that from the Missouri River, was centrifuged in-line to reduce the turbidity by about 80% using a flowthrough centrifuge. In addition to using the Kansas River water undiluted, it was also diluted 50 and 67% with reagent water for additional variability in the feed characteristics. The feed characteristics of these waters are described in Table 11. Each water was ozonated over a range of process conditions, including variations in pH, temperature, HRT, and aqueous ozone concentration (Table 111). The results are presented in Table IV. Some of the natural waters used contained CIAT and/or OIET at detectable concentrations. CIAT has been identified as the primary mobile and persistent metabolite of atrazine resulting from the application of atrazine to soil at normal application rates (6). Therefore, a portion of the atrazine applied to crop land (or for nonagricultural uses) is found in water supplies as CIAT and not atrazine. The result, from an ozonation byproduct perspective, is that a large fraction of the atrazine-derived byproducts is funneled into the pathway involving CIAT. The results of the CIAT ozonation experiment, however, showed that the ozonation byproducts of CIAT were not detectable by the analytical methods used in this experiment. Results of the standard HPLC analyses indicated that OIET was present in the source waters from Clinton Reservoir, Perry Reservoir, and the Kansas River. The
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Deisopropylatrazine Deisopropylatrazine amide
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3
4 7
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4
source
Environ. Scl. Technol., Vol. 26, No. 11, 1992
Table IV. Experimental Conditions, Mean Atrazine and Byproduct Concentrations, and Molar Balances' molar balances std nom
test feed 1
2 3 4 5
1 2
3 4 5 6 7
conc (rg/L) T HRT [O,l pH ("C) (mid (mg/L) CIET OIET CIAT unknown CEAT OIAT' CDAT CAAT OEAT (%) (%) Clinton Reservoir 100 100 ND ND ND ND 1 1 NDb ND 10 70 86 1 1 ND ND 1 0 3 1 3 0.8 8.2 22.2 8.5 1 ND 46 56 ND T 1 0 2 ND 2 0.8 8.2 22.2 16.8 79 91 1 ND ND 1 1 1 3 ND 1.1 5 6.1 22.2 16.7 1 ND 92 105 T ND 1 1 3 ND 6 0.8 6.1 16.2 16.7 102 102 ND ND ND ND 1 1 2 ND 8 0.8 6.2 15.9 8.6 Perry Reservoir 100 100 ND ND ND ND 1 ND ND 2 11 62 1 ND 54 ND T 1 1 3 ND 3 1.0 7.8 21.7 16.7 72 85 1 ND 1 ND 1 3 1 1 4 0.9 8.3 7.8 21.7 T ND 79 85 1 ND 1 1 3 ND 6 0.9 5.8 17.2 16.7 72 72 1 ND ND ND 1 0 3 ND 5 0.7 7.2 14.4 16.7 T 80 84 ND ND ND 1 3 1 1 0.7 6 8.3 7.2 14.6 1 87 99 ND 1 ND 1 1 3 0 1.2 7 8.3 6.4 17.2 1 1 ND 73 83 ND 1 3 ND 1 5 1.3 6.4 17.2 16.7
Kansas River 1
2 3 4 67% dilution 5 6 7 8 50% dilution 9
1 2 3 4
2 2 5 2 3 3 3 5 2
0 ND 0 0 T 0 ND ND T ND 0 T
5 3 3 2 2
ND ND ND ND ND
4
no dilution 8.2 8.2 7.2 7.2
23.3 21.7 17.8 17.5
17.1 8.5 4.2 17.1
1.0 1.0 1.4 1.2
7.4 7.4 5.8 5.8
23.3 21.7 16.1 16.1
16.8 4.2 8.3 16.7
0.6 0.7 1.0 0.9
6.8
18.9
8.4
1.3
6.6 16.7 6.6 16.7 7.5 20.6 7.5 20.6
18.5 8.3 8.3 16.7
1.1
1.2 0.9 0.9
1 1
1 1 1 1 I ND 1 1 1 1 ND 1
ND 0 1 0 0 ND 0 0 0 0 1 1
ND T ND ND T ND ND ND ND ND ND T
ND T ND ND T ND ND ND ND T ND T
ND 1 1 T ND ND ND ND ND ND ND ND
ND T ND ND T ND ND ND ND ND ND ND
81 72 100 71 89 92 94 100 78
100 74 101 99 78 100 75 93 104 94 100 86
0
ND 0 0 0
ND
0
ND ND ND ND ND
ND ND ND ND ND
ND ND ND ND ND
ND ND ND ND ND
100 79 80 77 64
100 79 82 85 64
ND 0 1 1
0 ND 0 0 1
ND ND 0
Missouri River ND ND 1 ND 1 T 1 1
100 59 67
The coefficient of variation for duplicate samples separated by 1 HRT wm 3.8%. ND, not detected.
presence of OIET was confirmed in each water by using a second HPLC method and additionally in a KansasRiver water sample by LC/MS. OIET is a primary degradation product of atrazine applied to the soil resulting from the soil-catalyzed hydrolysis of the chlorine in the 2-position of the s-triazine ring (32-34). Because OIET binds tightly to soil, it is less mobile than atrazine and other byproducts (35). Possible sources of the OIET in these water supplies include (1)mobilization of OIET, Le., desorption from the soil in the field and subsequent transport in solution in surface water of groundwater; (2) transport on soil sediment and subsequent desorption into the water supply (i.e., river or reservoir); and (3) chemical, biochemical, or photochemical degradation of atrazine in the water supply. Although further research is required to determine which of these mechanisms predominates, the effect of the OIET in the feed was to increase the fraction of atrazine byproducts funneled into the degradation pathway involving OIET. Therefore, increased concentrations of OIET and OIAT were observed in the flow reactor effluent samples when OIET was present in the feed. Degradation Pathways. The proposed degradation pathways for the ozonation of atrazine are presented in Figure 5. Despite the strong oxidizing power of ozone, the primary ozonation byproducts of atrazine (e.g., CIAT and CEAT) are not oxidized byproducts of atrazine; Le., CIAT is in as reduced an oxidation state as atrazine itself. Although the literature on the ozonation of atrazine does not
address this issue, the explanation is that the side-chain leaving group is oxidized by ozone and not the portion of the molecule that contains the s-triazine ring. Bailey (36) concluded that the mechanism of the reaction of alkyl amines and ozone proceeded through the formation of an ozone adduct. According to Bailey, this adduct reacts via one of four reactions, one of which is oxidation of the alkyl side chain to form an amino alcohol intermediate. This intermediate may then form other byproducts through further reactions including (36) (1)cleavage of the C-N bond resulting in the loss of the oxidized alkyl group and (2) reaction with another ozone molecule to form an amide. It is speculated that reactions of ozone leading to the formation of CIAT, CEAT, and CAAT may include the first of these mechanisms and that the formation of CDAT may involve the second of these mechanisms. These possible mechanisms must be viewed with caution, however, because the mechanisms reported by Bailey (1)were primarily in organic solvents while this study was conducted solely in the aqueous phase (albeit often at conditions where ozone was the primary oxidant) and (2) did not specifically address the reaction of ozone and aromatic/aliphatic secondary amines or s-triazines. It is hypothesized that hydrolysis of atrazine primarily resulted from reaction with the hydroxyl radical and not with ozone itself because, in the synthetic water experiments on pH and alkalinity, OIET and OIAT only occurred at conditions favoring hydroxyl radical production. Envlron. Sci. Technol., Vol. 26, No. 11, 1992 2225
H-N
N-
H
H-N
I
\
(Atrazine)
\
\
H-N
N-H H
I
H-N
.
CH CHI
N-
I
CH.CHI
CEAT (Deisopropylatrazine)
H
CH.CH1
OIET "1 (Hydroxyatrazine)
/ /
\ \
/
H-
H-N
H-N H
CAAT (2-Chloro-4,6-diamino-s-trazine)
CDAT (Deiaopropylatrarine amide)
C H i CH,
OEAT (Z-Amino-4-ethyIamino. 6-hydroxy-a-hiazine)
I
I cn.cn3
ki 1
OIAT (!2-Amino-l-hydmxy6-isopropylemino-s-ra~n0)
Figure 5. Proposed mJor( d i d arrows) and minor (broken arrows) degradation pathways for the ozonation of atrazine In water treatment processes
(2).
Kearney et al. reported, for a W/ozonation AOP used to treat atrazine wastewater, the degradation pathway for atrazine was to OIET, OIAT, and OEAT and then am(19). meline (OAAT, 2,4-diamino-6-hydroxy-s-triazine) Atrazine, however, has been shown to undergo rapid photodechlorination(37,38),and thus photolysis may have been the sole mechanism involved in UV/ozonation process study. A study (29) of the oxidation of atrazine by the hydroxyl radical generated by Fenton's reagent did not attempt to analyze for the hydroxy analogues of atrazine and, therefore, did not address this issue. It is emphasized that while OIET and OIAT were observed in low concentrations at certain conditions, this pathway was always trivial relative to the primary degradation pathway, that is, via dealkylation of atrazine. It is hypothesized that the oxidation of atrazine by ozone, by the hydroxyl radical, and by photocatalysis does not lead to appreciable mineralization or cleavage of the s-triazine ring. This hypothesis is based on work by Legub6 et al. (30),Plimmer et al. (291,Kearney et al. (181, and Pelizzetti et al. (39)in which the primary agenta used to oxidize atrazine (and other s-triazines) were ozone; the hydroxyl radical (via Fenton's reagent);ozone, the hydroxyl radical, and photolysis; and photocatalysis, respectively. It is further hypothesized that the terminal oxidation product for these processes is OOOT based on the work by Legub6 et al., Kearney et al., Pelizzetti et al., and Ollis et al. (40). It is thus proposed that the lack of closure of some molar balances in this study resulted from the presence of s-triazines such as OOOT, ammelide (OOAT, 2-amino-4,6-dihydroxy-s-triazine), and O U T , which were not quantifiable by the analytical methods that were used in this study. It should be noted that while the s-triazine ring has been reported to be somewhat resistant to biooxidation (41), several authors have established that the s-triazine ring can be biochemically oxidized by certain microbial strains leading to complete mineralization (42-44). As in the case of chemical oxidation, the biooxidation pathways for striazine herbicides have also been reported to funnel through OOOT (45). AttemDts (using HPLC, GC/MS, and LC/MS) a t identify&g the unl&own byproduct listed in Tables I and 2226
Envlron. Scl. Technol., Vol. 28, No. 11, 1992
IV were not successful. Using HPLC, however, it was confirmed that ita identity was not CDIT, OAAT, OOAT, OOOT, or any of the listed s-triazines (Tables I and IV). Additional research is required to establish and confirm the ultimate fate of atrazine and the identity of all of its degradation byproducts produced at specific process conditions.
Conclusions The primary ozonation byproducts of atrazine were determined under a variety of conditions. The primary ozonation byproduct in both synthetic and natural waters was CIAT, which occurred at significant concentrations relative to atrazine. CIAT is also the primary mobile and persistent metabolite of atrazine occurring from agricultural application of atrazine. Other ozonation byproducta identified included CEAT, CAAT, OIAT, CDAT, and an unknown compound. Pathways for the generation of these byproducts are proposed based on the experimental results of this study as well as those of previous studied. It is hypothesized that other s-triazine compounds that are not detectable by the analytical methods used in this study make up most of the unaccounted moles in the molar balances determined. Identification of ozonation byproducts that occur in significant concentrations relative to a regulated parent compound is important from a public health standpoint because a process such as ozonation may not remove, but only chemically modify, the parent compound to compounds of different (and possibly unknown) toxicity and effects. Although the EPA does not currently regulate the ozonation byproducta of atrazine, these compounds may be regulated in the future. The implications of byproduct formation for water utilities treating atrazine-bearing waters are potentially significant. Acknowledgments
This work was performed while C.D.A. was a doctoral student at the University of Kansas. We thank Mr. Daniel Katz (Pure Water Corp., Kansas City, KS) for providing the ozone generation equipment used in the laboratory study.
Registry No. CIET, 1912-24-9; OIET, 2163-68-0; CDAT, 115339-34-9;C U T , 6190-65-4; OIAT, 19988-24-0; CDIT, 83364152; CEAT, 1007-289;OEAT, 7313-54-4; OOOT, 108-80-6; CAAT, 3397-62-4; OAAT, 645-92-1; OOAT, 645-93-2.
Literature Cited (1) Chang, S. D.; Singer, P. C. J. Am. Water WorksAssoc. 1991, 83 (3), 71-79. (2) The nomenclature developed by A. M. Cook and R. Htitter, (J. Agric. Food Chem. 1981,29,1135-1143) is used herein to identify s-triazine compounds. The structures of selected compounds are shown in Figure 1. (3) Herbicide Handbook of the Weed Science Society of America, 4th ed.; Weed Science Society of America: Champaign, IL, 1979; pp 32-36. (4) Cohen, S.; Creeger, S.; Carsel, R.; Enfield, C. In Treatment and Disposal of Pesticide Waste;American Chemical Society: Washington, DC, 1984; pp 297-325. (5) U.S. Environmental Protection Agency. Fed. Reg. 1991, 56 (20), 3552. (6) Adams, C. D.; Thurman, E. M. J. Environ. Qual. 1991,ZO (3), 540-546. (7) Thurman, E. M.; Goolsby, D. A.; Meyer, M. T.; Kolpin, D. W. Environ. Sci. Technol. 1991,25, 1794-1796. (8) Kuhn, W. (Technical Direktor, Engler-Bunte-Institute der Univ. Karlsruhe, DVGW-Forshngsstelle, RichardWillstiitter-Allee, 5, D-7500 Karlsruhe, 1, Germany). Presented a t a seminar in the Department of Civil Engineering, University of Kansas, Nov 1989. (9) Hulsey, B. A.; Long, B. W.; Adams, C. D. Proceedings from the 1990 Spring Conference of the International Ozone Association: Pan-AmericanCommittee;1990, International Ozone Assoc.: Shreveport, LA. (10) Stirling,C. J. M. Radicals in Organic Chemistry;Oldbourne Press; London, 1965. (11) Hoign6, J.; Bader, H. Water Res. 1976, 10, 377-386. (12) Glaze, W. H.; Kang, J.; Chapin, D. H. Ozone Sei. Eng. 1987, 9,335-352. (13) Forni, L.; Bahnemann, D.; Hart, E. J. J. Phys. Chem. 1982, 86,255-259. (14) Staehelin, J.; Hoign6, J. Environ. Sci. Technol. 1982,16, 676-681. (15) Biihler, R. E.; Staehelin, J.; Hoign6, J. J. Phys. Chem. 1984, 88,2560-2564. (16) Staehelin, J.; Hoign6, J. Enuiron. Sci. Technol. 1985,19, 1206-1213. (17) Glaze, W. H.; Kang, J. J. Am. Water Works Assoc. 1988, 80 (51,57-63. (18) Kearney, P. C.; Muldoon, M. T.; Somich, C. J.; Ruth, J. M.; Voaden, D. J. J. Agric. Food Chem. 1988,36,1301-1306. (19) Kearney, P. C.; Zeng, Q.; Ruth, J. C. In Treatment and Disposal of Pesticide Waste;American Chemical Society: Washington, DC, 1984; pp 195-209. (20) Carney, M. J. Am. Water Works Assoc. 1991,83 (6), 48-55. (21) Adams, C. D.; Randtke, S. J. J. Am. Water Works ASSOC., in press. (22) Standard Methods for the Examination of Water and Wastewater, 17th ed.; APHA, AWWA, and WEF Washington, DC, 1989.
(23) Standard Methods for the Examination of Water and Wastewater, 16th ed.; APHA, AWWA, and W E F Washington, DC, 1985. (24) Bristow, P. A,; Brittain, P. N.; Riley, C. M.; Williamson, B. J. Chromatog. 1977,131, 57-64. (25) Analysis was performed by Dr. Karl Shorno, senior staff scientist, Higuchi Biosience Centers of Excellence, University of Kansas, Lawrence, KS. (26) Sokal, R. R.; Rohlf, F. J. Biometry: The Principles and Practice of Statistics in Biological Research, 2nd ed.; W. H. Freeman and Co.: New York, 1981; pp 52-60. (27) Trancart, J. Znt. Ozone Assoc. News 1990, 18 (5), 7-8. (28) Levenspiel, 0. Chemical Reaction Engineering, 2nd ed.; John Wiley and Sons: New York, 1972; pp 101-107. (29) Plimmer, J. R.; Kearney, P. C.; Klingbiel, U. I. J. Agric. Food Chem. 1971,19,572-573. (30) Legube, B.; Guyon; S.; Dor6, M. Ozone Sci. Eng. 1987,9, 233-246. (31) Bellamy, W. D.; Hickman, G. T.; Mueller, P. A.; Ziemba, N. Res. J. Water Pollut. Control Fed. 1991, 63, 120-128. (32) Armstrong, D. E.; Chesters, G.; Harris, R. F. Soil Sci. SOC. Am. Proc. 1967,31, 61-66. (33) Skippr, H. D.; Gilmour, C. M.; Furtick, W. T. Soil Sei. Soc. Am. Proc. 1967,31,653-656. (34) Obien, S. R.; Green, R. E. Weed Sci. 1969, 509-514. (36) Helling, C. S. Soil Sci. SOC.Am. Proc. 1971,35,737-743. (36) Bailey, P. S. Ozonation in Organic Chemistry. Vol. ZZ, Nomlefinic Compounds: Academic Press: New York, 1982: pp2oQ-201. (37) Pape, B. E.; Zabik, M. T. J. Agric. Food Chem. 1970,18, 202-207. (38) Hapeman-Somich, C. J. In Pesticide Transformation
Products: Fate and Significance in the Environment; Somasundaram, S., Coats, J. R., Eds.; ACS Symposium (39) (40) (41) (42) (43) (44) (45)
Series 459; American Chemical Society: Washington, DC, 1991; pp 133-147. Pelizzetti, E.; Maurino, V.; Minero, C.; Carlin, V.; Pramauro, E.; k b i n a t i , 0.;Tosato, M. L. Environ. Sci. Techml. 1990, 24, 1559-1565. Ollie, D. F.; Pelizzetti, E.; Serpone, N. Enuiron. Sci. Techml. 1991,25, 1522-1529. Kaufman, D. D.; Kearney, P. C. Residue Rev. 1970, 32, 235-265. Wolf, D. C.; Martin, J. P. J. Environ. Qual. 1975, 4 (l), 134-139. Cook, A. M.; Htitter, R. J. Agric. Food Chem. 1981, 29, 1135-1143. Cook, A. M.; Beilstein, P.; Grossenbacher, H.; Hutter, R. Biochem. J. 1985,231,25-30. Cook, A. M. FEMS Microbiol. Rev. 1987,46, 93-116.
Received for review October 29, 1991. Revised manuscript received March 23,1992. Accepted July 9,1992. Major support for this research was provided by the Kansas Water Resources Research Institute (Allocation 14-08-0001 -G1563) and the Ciba-Geigy Corp. (Greensboro,NC). Additional support was provided by the University of Kansas Department of Civil Engineering through the Spahr-Bore1 Fellowship and by a research grant from the University of Kansas General Research Fund (Allocation 3140-xx-0038).
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