Environ. Sci. Techno/. 1995,29, 2083-2089
Degradation of Atrazine by Feaon's Reagent: Condition Optimization and Product
(5,6),TiOzWlight (7),H~OzWlight (8),andFe3+Wlight (9).In most cases, reaction kinetics and product identities are well documented. Fenton's reagent (Fez+and H202) also produces HO' and initiates atrazine alkylamino side chain oxidation and/or dealkylation as follows (9-13):
+
+
Fez+ H,O, = Fe3+ HO' SCOTT M. ARNOLD, WILLIAM J. HICKEY,* AND ROBIN F. HARRIS Environmental Toxicology Center and Department of Soil Science, University of Wisconsin-Madison, Madison, Wisconsin 53706
Atrazine [2-chloro-4-( ethylamino)-6-( isopropylamino)s-triazine] degradation by Fenton's reagent (FR) was determined as a function of reagents' concentration and ratios and pH in batch treatments. The optimal mixture, 2.69 mM (1:l) FeS04:H202, completely degraded [2,4,6-14C]atrazine (140pM) in 5 3 0 s primarily t o 2-chloro-4,6-diamino-striazine (CAAT, 23%) and 2-acetamido-4-amino-6-chloro-s-triazine (CDAT, 28%). Chloride release of 55 f 9% indicated that dehalogenated s-triazines accounted for the balance of 14C. Higher FR concentrations lowered CDAT concentrations, but CAAT and the dehalogenated s-triazines persisted. Atrazine degradation decreased from 99% at pH 3 to 37% at pH 9. Thus, FR can rapidly degrade atrazine, but post-treatments may be necessary to eliminate residual chloro-s-triazines like CDAT and CAAT.
Introduction Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-striazine] accounts for 12% of the pesticides used in the United States (1). It is classified as a possible human carcinogen by the U.S. EPA (2),and most human exposure is from the consumption of contaminated groundwater. Atrazine's resistance to microbial degradation, slow hydrolysis, low vapor pressure, and moderate aqueous solubility enhance its potential for contaminating groundwater (3). High atrazine levels can occur in groundwaters underlyingsoils in which atrazinewas improperly disposed or spilled (4). Technologies that eliminate atrazine from wastes would obviate unnecessary introductions of the chemical into the environment and reduce the risk of groundwater contamination. Atrazine degradation has been studied in several hydroxyl radical (HO')generating systems including ozone * Corresponding author address: Department of Soil Science, University of Wisconsin-Madison, Madison, WI 53706-1229; Telephone: (608)262-9018;Fax: (608)265-2595;E-mail address: wjhickeytWms2.rnacc.wisc.edu. Contribution 275,Environmental Toxicology Center, University of Wisconsin-Madison. +
0013-936x195/0929-2083$09.00/0
B 1995 American Chemical Society
HO' HO'
+ HO-
+ Fez+= HO- + Fe3+
+ RNHCH,CH,
= H,O
+ RNHC'HCH,
(1)
(2) (3)
+ RNHC'HCH, = RNHC(OO')HCH, (4) R"C(OO')HCH, + Fez+ + H+ = R"C(OOH)HCH, + Fe3+ (5) RNHC(OOH)HCH, = R"C(O)CH, + H,O (6) 0,
(RNHCH,CH, = atrazine) The main advantageof Fenton's reagent (FR) over other HO' systems is its simplicity: the chemicals are commonly available and inexpensive, and there is no need for special equipment like W lamps, complex reaction vessels, Ti02 particles, or ozone generators. Because of its simplicity, FR has the potential for widespread use in treating atrazine wastes. But compared to other HO' systems, little information exists detailingatrazinedegradationby FR. Plimmer et al. (14) tested a single FR mixture and identified three dealkylatedatrazineproducts with chlorodiamino-s-triazine (2-chloro-4,6-diamino-s-triazine) as the apparent treatment end point. No information was provided on system optimization, reaction rates, or occurrence of dehalogenated andlor oxygenated atrazine degradation products. Our objective was to determine the effects of different reaction conditions on the efficacy of FR for degrading atrazine. Atrazinedegradation and product formation rates were determined as a function of FeS04 and H202 concentrations and ratios and solution pH. System performance was evaluated by high-pressure liquid chromatography (HPLC), mass spectrometry, and material balances tracking [2,4,6-14C]atrazineand chloride.
Experimental Section Chemicals. Nonlabeled atrazine (CIET)was certified 99% pure and purchased from Chem Service (West Chester, PA), [2,4,6-l4C1Atrazine(19.4 pCi mg-', 97%), deethylatrazine (2-amino-4-chloro-6-(isopropylamino)-s-triazine; CIAT, 99%), deisopropylatrazine (2-amino-4-chloro-6-(ethylamino)+triazine; CEAT, 98%),chlorodiamino-s-triazine(CAAT, go%), hydroxyatrazine (2- (ethylamino)-4-hydroxy-6(isopropy1amino)-s-triazine;OIET, 98%), 2-amino-4-(ethylamino)-6-hydroxy-s-triazine (OEAT, 9593, and 2-amino4-hydroxy-6-(isopropylamino)+triazine (OUT,97%)were provided by Ciba-Geigy Corporation (Greensboro, NC). Table 1 lists the structures, common names, chemical names, and abbreviationsof identifiedatrazine degradation products produced by FR. Acetonitrile (Baxter; McGaw Park, IL) and KH2P04solution (Manufacturing Chemicals Inc.; Cincinnati OH) were filtered and degassed before use
VOL. 29. NO. 8, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 12083
TABLE 1 Chemical Structures, Names, and Abbreviation8 of Atrazine and Fenton's Reagent-Generated Degradatdn Products structure
common name
chemical name
abbreviatiin
atrazine
2-chloro-4-(ethylamino)-6(isopropy1amino)-s-triazine
ClET
atrazine amide
deethylatrazine
simazine amide
deisopropylatrazine
hydroxyatrazine amide
2-acetamido-4-chloro-6-
(isopropy1amino)-s-triazine
2-amino-4-chloro-6-
(isopropy1amino)-s-triazine
2-acetamido-4-chloro-6-
(ethylamiflo)-s-triazine
CDlT
ClAT
CDET
2-amino-4-chloro-6(ethy1amino)-s-triazine
CEAT
2-acetamido-4-hydroxy-6-
ODlT
(isopropy1amino)-s-triazine
deisopropylatrazine amide
2-acetamido-4-amino6-chloro-s-triazine
CDAT
chlorodiamino-s-triazine
2chloro-4,6-diaminos-triazine
CAAT
ammeline
2,4diamino-6-hydroxys-triazine
OAAT
in HPLC. FeS04 was purchased from Fisher Scientific,and H202(30% solution) was from Mallinckrodt (Paris, KY). Concentration and Ratio Effects of Peso4 and Hz0~. Ratios (FeS04:H202)of 1:1, 1:100, and 2:l were examined at concentrations from 0.1 to 25 mM. Solutionsof FeS04 (50 mM) and atrazine (135,uM in distilled deionized H20) were mixed in 150-mLErlenmeyer flasks, and HO' production was initiated by adding 50 mM H202. The aluminum foil-wrapped flasks were incubated for 24 h on a rotary shaker at 200 rpm (25 d= 1 "C). Samples (0.5 mL) were mixed with methanol (0.5mL) to quench the reaction and centrifuged (10min; 3200 rpm),and the supernatantswere analyzed by HPLC. pH Effects. Atrazine solutions (140 ,uM in distilled deionized H20) were buffered with 100 mM ICHzPO4 at pH 3-9 and treated with 0.73, 1.42, and 2.69 mM 1:l FeS04: HzOZ. The flasks were incubated for 24 h, and samples were analyzed by HPLC as described above. The pH was stable within 1 pH unit following each treatment. AtrazineDegradationand ProductFormation Kinetics. Twenty-five milliliters of an atrazine solution (132 pM in 2084 1 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 8, 1995
distilled deionized H20)was treated with FR concentrations of0.49mM 1:lOOFeS04:H202 and 1.06-2.69 mM 1:l FeS04: H202. The reactions were quenched at selected times during a 24-h incubation by mixing 0.5 mL of the sample with 0.5 mL of methanol, and the solutionswere prepared for HPLC analysis as described above. "C Mass Balance. Ten milliliters of [2,4,6-14C]atrazine (0.063pCi mL-l, 140pM)was incubated with 2.69 mM 1:l FeS04:H202 and 0.49 mh4 1:lOOFeS04:H202in serum bottles sealed with Teflon-lined rubber septa and aluminum crimp tops. After 24 h, the vials were flushed with air (25 mL min-l) for 1 h to collect volatile organics and l4CO2. Triplicate samples (40 1L) of the reaction mixture were analyzed by HPLC, and compounds absorbing at 220 nm were collected in scintillation vials. Radioactivity was determined by counting the samples in 10 mL of carbon 14 cocktail (R. J. Harvey Instrument Co., Hillsdale, NJ) on a Rackbeta Model 1209 liquid scintillation counter (LKBWallac, San Francisco, CAI. Chloride Analysis. Chloride was determined using an Orion Model 94-17B chloride ion-specific electrode and
Model 90-02 double junction reference electrode (Orion Research Inc., Boston, MA) connected to a Beckman Q 72 pH meter (Fullerton,CAI. Samples (25mL) were quantified using a standard curve established from 28 to 563 pM C1-. Analysis for Atrazine and Transformation Products. HPLC UV analysis and fraction collection were conducted on a Hewlett Packard 1050 system (PaloAlto, CAI equipped with a variable wavelength U V detector (220 nm) as described elsewhere (15). Five-point calibration curves were run for atrazine, CUT, CEAT, CAAT, OIET, OIAT, and OUT, which had detection limits of 0.24, 0.24, 0.14, 0.29, 0.63, 0.39, and 0.77 pmol L-l, respectively. 2-Acetamido4-chloro-6-(isopropylamino) +triazine (CDIT), 2-acetamido-4-chloro-6-(ethylamino) +triazine (CDET),2-acetamido-4-hydroxy-6-(isopropylamino)+triazine (ODIT),and 2-acetamido-4-amino-6-chloro-s-triazine (CDAT) were quantified using a response factor, which was the ratio of the UV (220nm) response to 14Cactivityinfraction-collected peaks. This gave better concentration estimatesthanusing the absorbance of closely eluting standards as suggested by Adams and Randtke (6). Details of transformation product identification are given in Arnold et al. (15).
1001,
A
30
a 20 10 0
0
0.5
2.5
B
Results and Discussion Peso4 and Hz02 (1:l) Concentration Effects on Atrazine Degradation. At 0.73 mM, FR generated a complex s-triazine mixture containing residual atrazine and 15 oxidation products. Seven major products were identified by HPLCIESIMSIMS (Table 1): CDIT, CIAT, CDET, CEAT, ODIT, CDAT, and CAAT (15). At 1.42 mM FR, atrazine was completelytransformedto a mixture of dealkylatedproducts including CDIT, CIAT, CEAT, ODIT, CDAT, CAAT, and five unknowns. Reaction mixtures were totally depleted of CDIT, CIAT, CEAT, and ODIT by increasing FR concentrations to 2.69 mM (Figure 1A). But CDAT, CAAT, and six minor unidentified atrazine derivatives persisted at FR concentrations up to 25 mM (data not shown). Moreover, CDAT and CAAT were consistently the major products generated by FR treatment of atrazine at concentrations ranging from 5 to 140 pM. Further FR treatment was ineffective in degrading CDAT and CAAT because of the low reactivity of these oxidized products toward HO’. In sequential batch treatments of atrazine using 2.69 mM FR, CDAT was reduced from 23.4% to 10.7%, and CAAT was increased from 29.8% to 36.7% of the initial atrazine concentration. However, the sum of chloro-s-triazines products decreased by only 5.8%. Thus, sequential batch treatment was ineffective in degrading the remaining chloro-s-triazines: the mixture containing CDAT, CAAT, and minor unknowns represented the terminal end products resulting from “complete” FR treatment of atrazine. Effects of FeS04:H202 Ratio and pH on Atrazine Degradation. Reaction efficiency can be interpreted by atrazine loss, product formation, etc. Because remediation of atrazine-containing wastes necessitates complete degradation of atrazine and toxic intermediates (Le.,chlorinated products), reaction efficiency is evaluated here in terms of chlorinated product depletion. According to eqs 2 and 3, loweringthe FeS04:H202 ratio should improve the reaction’s efficiencybecause there would be less FeZ+ competingwith atrazine for HO’. At lower FeS04:H202ratios, a “complete” treatment was achieved with lower Fe2+concentrations as compared to the 2.69 mM (1:l) treatments, but increasing the HZOZconcentration 100-fold lowered the reaction’s efficiency (from a remediation standpoint) since larger
1 1.5 2 1:l (mM) FeSO, : H,O,
1 :lo0 (mM) FeSO, : H202
C
E
E
40 30
a 20 10 0 0
0.5
1 1.5 2 2:l (rnM) FeSO, : HO ,,
2.5
FIGURE 1. Effect of FeSOdHzO, concentretion ratios on atrazine (135 pM) degradation and formation of selected products aftar 24-h incubation. Panel A, 1:l (mM); panel 6, 1:lW (mM); panel C, 2 1 (mM). Legend: ClET W, CDIT (0). CIAT (01,CDET (01,CEAT (A), ODIT (A), CDAT (01,CAAT (6).
amounts of the chlorinated products (CDAT and CAAT) remained compared to the 1:l FR treatments (cf. Figure lA,BI. Using excess H202 may have favored dealkylation, thus decreasing dechlorination. The unidentified products generated in the 1:lOO FR treatment were similar to those detected in the 1:l FR treatment (see Table 2). Increasing Fez+levels lowered reaction efficiency,presumablybecause excess Fe2+reacted with HO; at an FeS04:Ha02concentration ratio of 2:1, atrazine and the alkylated products remained at FR concentrations up to 5.38 mM FeS04and 2.69 mM H202 (Figure 1C). In unbuffered solutions, the final pH varied from 3.5 to 2.4 depending on the amount of Fe2+added. In buffered solutions using 2.69 mM 1:l FR, atrazine degradation decreased from 99% at pH 3 to 37% at pH 9 (Figure 2). FR efficiency declined with increasing pH, probably by oxidation of Fe2+to Fe3+and subsequent precipitation of the Fe3+ as oxyhydroxide complexes, decreasing the Fe concentration in solution (16). The effectiveness of atrazine degradation decreased significantly as pH was increased above 5.5 in the 2.69 mM 1:1FR treatment. Using 1.42mM 1:l FR, atrazine degradation efficiencydecreased at pH 5.0 and between pH 3.0 and pH 5.0 for 0.73 mM 1:l FR. VOL. 29, NO. 8, 1995 /ENVIRONMENTAL SCIENCE &TECHNOLOGY
2086
TABLE 2
Mass Balance for Fenton’s Reagent Treatment
14C
percent of initial radioactivity’ HPLC fraction rk (inin)* FeS04 (mM)
H202 (mMJ
2.69 0.49
2.69 49.0
l4COZ
volatilized
2.3
0.1 0.1
0.0 0.0
10.4
0.0
3.5
4.5
5.9
6.5
6.6
7.3
7.4
7.6
balanceC
total
14.9 7.8
23.4 38.2
27.8 24.8
1.6
1.7 3.9
3.9
2.6
0.0
5.4
0.0
1.0 1.0
18.6 7.7
94.7 99.3
a Based on liquid scintillation counting of HPLC fractions. initial “C activity was 0.063 pCi mL-’ for both treatments. HPLC fractions 4.5 and 5.9min were identified as 2-chloro-4,6-diamino-s-triazine and 2-acetamido-4-amino-6-chloro-otriazine. All other fractions were unidentified. Activity
collected between peaks. 100,
I
90 -
I
70 -
80
t
T
0
3
50 PH
6 Time (h)
9
E
FIGURE2. Effectof pH and Fenton‘s reagent concentrationon atrazine (140 pM) degradation. Legend: 0.73 mM (1:l) hS04:H202(m), 1.42 mM (1:l) FeS04:H20~(e),2.69 mM (1:l) FeSO4:H202 (A). 30
Atrazlne Degradation and Product Formation Rates. Atrazine (132 pM) degradation rates were examined over the range of 1.06-2.69 mM FR (1:l). Using 1:l treatment ratios, rapid atrazine degradation precluded calculation of degradation rates. In the 1.06 mM treatment, atrazine was depleted 98%in 530 s; degradation of the residual atrazine was slow; and at 24 h, 1%of the initial amount remained. Using FR treatments of 21.42 mM FeS04 and H2O2,atrazine was degraded to below detection limits in 530 s. In the 2.69 mM FeS04and H202 treatment, the identified atrazine transformation products accounted for 5 (28,291.Dechlorination of the alkylated s-triazines was a major mechanism of atrazine degradation by FR; however, it was not complete. From a remediation standpoint, this is important because the chlorinatedproducts are consideredas toxic as atrazine (2). Therefore, FR may best be used in combination with microbial treatments to degrade the residual terminal products. Preliminary results have shown that the chlorinated compounds are readily degraded by bacterial pure cultures (30).
Aebowledjareats HPLCIESIMSIMS was done by Rasmy Talaat (Hazelton Wisconsin Inc., Madison,WI).HRIEIIMS and GUMS data was provided by CorneliusHop (Departmentof Chemistry, University of Wisconsin-Madison). This work was funded by the University of Wisconsin-Madison College of Agricultural and Life SciencesHatch project number 3581 [to R.F.H.). Author-Supplied Registry Numbers: CIET, 1912-24-9; CDAT, 115339-34-9; CIAT, 6190-65-4; CDIT, 83364-15-2; CDET, 142179-76-8; CEAT, 1007-28-9;W T , 3397-62-4; OIET, 2163-68-0, OIAT, 19988-24-0; OEAT, 7313-54-4; OAAT, 645-92-1.
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formation Products: Fate and Significance in the Environment; Somasundaram, L., Coats, J. R., Eds.; ACS Symposium Series 459;AmericanChemicalSociety: Washington, DC, 1991;pp254273. (3) U.S.EPAOffice of Pesticide Programs. EnvironmentaZFact Sheet; Atrazine Label Amendments: Washington, DC, Jan 23, 1990. (4) Wisconsin Department of Agriculture, Trade and Consumer
Protection (WDATCP). Environmental impact statement: Proposed 1992amendments to rules on the use ofpesticidecontaining atrazine; WDATCP: Madison, WI, 1991. (5) Hapeman-Somich, C. J.; Gui-Ming, Z.; Lusby, W. R.; Muldoon, M. T.; Waters, R. J. Agric. Food Chem. 1992, 40, 2294-2298. (6) Adams, C. D.; Randtke, S. J. Environ. Sci. Technol. 1992,26,22182227. (7) Pelizzetti, E.; Maurino, V.; Minero, C.; Carlin, V.; Parmauro, E.; Zerbinati, 0.;Tosato, M. L. Environ. Sci. Technol. 1990,24,15591565. (8) Beltrfin, F. J.; Ovejero, G.; Acedo, B. Water Res. 1993, 27, 10131021. (9) Larson, R. A.; Schlauch, M. B.; Marley, K. A. J. Agric. Food Chem. 1991, 39, 2057-2062. (10) Fenton, H. J. H. J. Chem. SOC.1894, 65, 899-910. (11) Keamey, P. C.; Muldoon, M. T.; Somich, C. J.; Ruth, J. M.;Voaden, D. J. J. Agric. Food Chem. 1988, 36, 1301-1306. (12) Masten, S. J.; Davies, S. H.R. Environ. Sci. Technol. 1994, 28, 180A-185A. (13) Pelizzetti, E.; Minero, C.; Carlin, V.; Vincenti, M.; Parmauro, E.; Dolci, M. Chemosphere 1992, 24, 891-910. (14) Plimmer, J. R.; Kearney, P. C.; Klingebiel, U. I. J. Agric. Food Chem. 1971, 19, 572-573. (15) Arnold, S. M.; Talaat, R. E.; Hickey, W. J.; Harris, R. F. J. Mass Spectrom. 1995, 30, 452-460. (16) Bohn, H. L.; McNeal, B. L.; O'Conner, G. A. Soil Chemistry;John Wiley and Sons: New York, 1985; pp 21-65.
(17) Legube, B.; Guyon, S.; Dore, M. Ozone Sci. Eng. 1987, 9, 233246. (18) Erikson, L. E.; Lee, K. H. Crit. Rev. Environ. Control 1989, 19, 1-13. (19) Pignatello, J. J. Environ. Sci. Technol. 1992, 26, 994-951. (20) Bielski, B. H. J.; Cabelli, D. E.; Arudi, R. L.; Ross, A. B. J. Phys. Chem. Ref: Data 1985, 1 4 , 1041-1100. (2 1) Frimer, A. A. In Oxygen Radicals in Biologyand Medicine;Simic, M. G., et al., Eds; Plenum Press: New York, 1988; pp 29-38. (22) Sipes, I. G.; Gandolfi, A. J. In CIlsarett and Doull's Toxicology: The Basic Science of Poisons; Amdur, M. O., Doull, J., Klaassen, C. D., Eds; McGraw-HiU, Inc.: New York, 1991; pp 88-126. (23) Larson, R. A.; Weber,E. J. ReuctionMechanisms inEnvironmental Organic Chemistiy CRC Press, Inc.: Boca Raton, FL, 1994; pp 130-132. (24) Potter, J. F.; Roth, J. A. Hazard. Waste Hazard. Mater. 1993, 10, 15 1- 170. (25) Kearney, P. C.; Zeng, Q.; Ruth,J. C. In Treatment and Disposal
of Pesticide Waste; American Chemical Sociem: Washington, DC, 1984; pp 195-209. (261 Paue, B. E.; Zabik, M. T. I. W c . Food Chem. 1970,18,202-207. (27) Hapeman-Somich, C. J. Inpesticide Transformation Products: Fate and Significance in the Environment; Somasundaram, S., Coats, 1. R., Eds;ACS Symposium Series 459; American Chemical Society: Washington, DC, 1991; pp 133-147. (28) Sun. Y.; Pignatello, J. J. Agric. Food Chem. 1992, 40, 322-327. (29) Sun, Y.; Pignatello, I. J. Agnc. Food Chem. 1993, 41, 308-312. (30) Arnold, S. M.;Hickey, W. J.; Harris, R. F. In Absfracfs of the 94th General Meeting of the American Sociery for Microbiology;ASM: Washington, DC, 1994; p 255.
Received for review January 10, 1995. Revised manuscript received April 28, 1995. Accepted April 28, 1995.@
ES950010D @
Abstract published in Advance ACS Abstracts, June 15, 1995.
VOL. 29. NO. 8, 1995 I ENVIRONMENTAL SCIENCE &TECHNOLOGY
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