Hydrogen

Environ. Sci. Technol. 2000, 34, 430-437

Degradation of Atrazine into Ammeline by Combined Ozone/ Hydrogen Peroxide Treatment in Water S Y L V I E N EÄ L I E U , L U C I E N K E R H O A S , A N D JACQUES EINHORN* Unite´ de Phytopharmacie et Me´diateurs chimiques, INRA, Route de Saint-Cyr, 78026 Versailles Cedex, France

The aqueous ozone treatment of atrazine [2-chloro-4(ethylamino)-6-(isopropylamino)-s-triazine] in the presence of hydrogen peroxide was reinvestigated using a new tandem solid-phase extraction procedure which includes a C18 reverse phase support and a strong cation exchanger. In this way, both chlorotriazines and the more polar hydroxytriazines could be analyzed to establish total molar balances of degradation products vs the initial pesticide in the 45-55% range. In all the experimental conditions examined (treatment rates, pH, and eventual presence of carbonates), ammeline (2,4-diamino-6-hydroxy-s-triazine) was found as the major end-product (20% at pH 8). 2-Chloro4,6-diamino-s-triazine was produced competitively, and the ratio between both products was dependent on the hydroxyl radical content. A number of new intermediates were identified i.e. amino-aldehydes and a carbinolamine. The carbinolamine functionality is of great interest since being involved in the dealkylation process of the triazinic amino groups.

Introduction Several monitoring programs have been conducted to determine the presence of pesticides in surface waters. Atrazine appears as one of the most commonly detected in Europe and North America (1, 2) with concentrations frequently reaching the µg/L level due to its persistence and mobility properties. Atrazine is widely used as a pre- and early post-emergent herbicide in maize and also for industrial weed control (3). The EEC drinking water directive 80/778 sets as maximum contaminant levels of 0.1 µg/L for a single pesticide and 0.5 µg/L for the sum of the pesticides. Owing to the frequently high concentrations encountered, there is a need for an efficient treatment during drinking water production to respect the EEC rules. In this context, chemical degradation generally appears as a decisive step. Ozone is a powerful oxidant that can react in water directly with chemicals (E° ) 2.07 V) or generate radical species such as OH• which is much more reactive (E° ) 3.06 V) (4). Ozone by itself does not allow a high elimination rate for atrazine (5, 6), but the treatment efficiency can be increased when used in association with UV (7) or hydrogen peroxide (810). Both methods constitute so-called “Advanced Oxidation Processes” (AOPs) (11). Atrazine degradation products have been analyzed by various extraction and characterization techniques. Liquid/ * Corresponding author phone: (33)-1-30 83 31 20; fax: (33)-1-30 83 31 19; e-mail: [email protected]. 430

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liquid extraction has often been used, but this technique is costly and applicable only to the less polar compounds (e.g. corresponding to the first oxidation steps) (12). Thus, solidphase extraction is preferable (10, 13) although in some studies aqueous solutions may be analyzed directly if initial concentrations are high (14, 15). Gas chromatography-mass spectrometry (GC-MS) is classically used to identify and/or quantify chlorotriazines of any kind (10, 13) but would require appropriate derivatization in the case of the less volatile degradation products (e.g. hydroxytriazines in general) (12, 14). High performance liquid chromatography coupled to mass spectrometry performed in the conventional way (LCMS) or in tandem (LC-MS-MS) using either thermospray (1618) or electrospray as an interface (19, 20) is universal since compatible with most atrazine degradation products in a wide range of polarities. According to the previous studies, atrazine degradation by ozone alone or coupled with hydrogen peroxide may be achieved through various processes (10, 12, 14, 15) which include dealkylation of the amino groups, formation of amides, and hydroxylation (via deamination and/or dechlorination). It is stated that no ring opening occurs, and cyanuric acid has been detected in some conditions as the most oxidized product (12, 14). A large number of intermediates have been identified so far using various AOPs (10, 12-15), and the degradation kinetics of atrazine has been shown to be dependent on parameters such as treatment rates, pH, and the presence of radical scavengers (10, 21). The effect of temperature has been studied less: a negligible influence on the byproduct content has been observed (10) and there have been contradictory results on the kinetics (21, 22). Although a lot of data have been accumulated so far, there is generally a lack of information regarding the polar compounds that are produced as reflected by the low mass molar balances reported. This may be caused to some extent by the possible lack of efficiency of the extraction and/or analysis procedures being used. Most reported studies on the subject have been conducted using the C18 reverse phase for SPE followed by HPLC analysis therefore limiting the investigations to the most hydrophobic molecules. Thus, the aim of the present study was to extend our knowledge as to the triazinic compounds that can be encountered under advanced oxidation conditions. Besides using a combination of GC-MS and LC-MS (or MS-MS) methods for analysis, considerable improvement of the extraction step was obtained by utilizing a new tandem solid-phase extraction procedure (23). This procedure which combines a C18 reverse phase support and a strong cation exchanger in two successive steps allowed detection of ammeline as the major end-product in many conditions as well as several intermediates including a number of compounds identified herein for the first time.

Materials and Methods Chemicals. The nomenclature developed by Cook and Hu ¨tter (24) and complemented elsewhere (15, 25) is used herein to identify s-triazine compounds: A amino, C chloro, D acetamido, E ethylamino, F formamido, I isopropylamino, O hydroxy, and T triazine ring. We introduce further L for isopropanalamino and N for ethylcarbinolamino. Atrazine (>98%, CIET, 2-chloro-4-(ethylamino)-6-(isopropylamino)s-triazine), deethylatrazine (99.9%, CIAT, 6-amino-2-chloro4-(isopropylamino)-s-triazine), deisopropylatrazine (99.8%, CEAT, 6-amino-2-chloro-4-(ethylamino)-s-triazine), 2-chloro4,6-diamino-s-triazine (96.9%, CAAT), hydroxyatrazine (99.9%, OIET, 2-(ethylamino)-4-hydroxy-6-(isopropylamino)-s-tri10.1021/es980540k CCC: $19.00

 2000 American Chemical Society Published on Web 12/31/1999

azine), hydroxydeethylatrazine (99.9%, OIAT, 2-amino-4hydroxy-6-(isopropylamino)-s-triazine), hydroxydeisopropylatrazine (99.9%, OEAT, 2-amino-4-(ethylamino)-6-hydroxys-triazine), and ammeline (99.6%, OAAT, 2,4-diamino-6hydroxy-s-triazine) were obtained from Promochem (Strasbourg, France). Ammelide (OOAT, 2-amino-4,6-dihydroxys-triazine) was a gift from Ciba-Geigy (Basle, Switzerland). Cyanuric acid (98%, OOOT, 2,4,6-trihydroxy-s-triazine) was purchased from Janssen (Geel, Belgium). Solid-Phase Extraction. Solid-phase extraction (SPE) was performed at ambient temperature (20-23 °C) according to a new tandem procedure (23). Five hundred milligrams of C18 bonded-silica and SCX (strong cation exchanger, propylbenzensulfonic acid binding) Bond-Elut cartridges (Varian, Harbor City, CA) were used sequentially. Before sample application, the C18 and SCX cartridges were conditioned separately with 5 mL of methanol and then with 5 mL of water (C18) or 5 mL of HCl 10-2 M (SCX). The ozonated sample solutions (200 mL) were percolated at 5 mL/min flow rate through successively the C18 and (after acidification with 0.2 M HCl to pH 2) the SCX cartridges. The latter was rinsed with 1 mL of water before elution. Elution was generally performed using 2 mL of methanol for the C18 cartridges and by three successive fractions (2, 5, and 2 mL, respectively) of 0.1 M ammonium acetate in water/acetonitrile 75/25 v/v at apparent pH 8.6 for the SCX support. Most compounds relevant to the SCX extraction were recovered in the first two fractions. In this study, the cartridges were used once. Using this tandem procedure, recoveries were estimated as follows for 250 mL solutions (50 µg/L, four replicates): (i) quantitative recovery on C18 only for CIET and OIET (97.5 ( 3.9% and 96.5 ( 1.0%, respectively) or on SCX only for OAAT (98.1 ( 0.1%, with ca. 1% being found on C18), (ii) quantitative recovery using both supports for CIAT, CEAT, and OIAT (respectively 92.7 ( 3.5%, 34.4 ( 3.9%, and 23.2 ( 1.3% on C18 and 4.0 ( 2.7%, 63.2 ( 2.4%, and 76.0 ( 3.2% on SCX), and (iii) partial extraction for CAAT (2.7 ( 0.1% and 51.1 ( 0.4%, respectively, on C18 and SCX) and OOAT (40% on SCX). According to these data, our reported yields after ozonation might be affected (lowered by ca. a factor 2) only for CAAT and OOAT and should thus be considered as apparent (or pessimistic) yields. HPLC-UV. HPLC-UV analysis was performed with a Waters equipment (Bedford, MA), including an automatic injector model 717, a 600-MS pump, and a 991-MS photodiode array detector. The C18 extracts were analyzed on a 250 × 4.6 mm i.d. Nucleosil 100-5 C18 AB column (MachereyNagel, Du ¨ ren, Germany) using 10/90 and/or 25/75 acetonitrile/ammonium acetate buffer (50 mM) at 0.8 mL/min. The SCX extracts were analyzed with (i) the same C18 column with 10/90 acetonitrile/ammonium acetate and (ii) a 250 × 4.6 mm i.d. benzensulfonic cationic exchanger Nucleosil 100-5 SA column (Macherey-Nagel) with 5% acetonitrile and 95% 40 mM ammonium acetate pH 3.5 adjusted with acetic acid. The latter conditions are particularly appropriate for the most polar compounds (i.e. ammeline, ammelide, ...). Cyanuric acid could be directly (without SPE concentration) analyzed using a 250 × 4.6 mm i.d. quaternary ammonium anionic exchanger Nucleosil 100-5 SB column (MachereyNagel) with a 25 mM phosphate buffer (pH 7.3). Quantitations were obtained by peak integration at 220 nm (5-20 µL sample injections) with the calibration done using external standards. When standards were not available, the response factors were adapted from compounds of similar nature (chloro- or hydroxytriazines as determined by the UV spectra) and retention times. Mass Spectrometry. Mass spectra were obtained on a Nermag R30-10 (Quad Service, Poissy, France) triple quadrupole instrument equipped with a Delsi 200 gas chromatograph. EI-GCMS was carried out under the following source conditions: 180 °C temperature, 100 µA filament current, 70

SCHEME 1. Reactor for Aqueous Ozonation of Atrazine in the Presence of Hydrogen Peroxide

eV electron energy. NH3 (N45, Air Liquide, Paris, France) or ND3 (99.75%, Eurisotop, Gif-sur-Yvette, France) was used as reagent gas for CIMS using 95 eV electron energy, 120 °C source temperature, and 10-4 Torr pressure in the source housing. Samples were introduced via a 25 m × 0.32 mm i.d. CP-Sil 8 CB column heated from 150 to 275 °C (10 °C/min) or by the DCI probe. LC-MS was performed using a Vestec (Houston, TX) thermospray interfaced to the triple quadrupole analyzer. Postcolumn delivery of 0.1 M ammonium acetate (0.6 mL/min) was achieved by an additional Waters 590 pump. Optimal temperatures for tip and source block were determined (26) as 240 and 250 °C, respectively, for a 300 V repeller voltage. Alternatively, an electrospray source (Analytica, Brandford, CT) was used for ionization (LC-ESIMS). The instrument was coupled with a Varian 9012 HPLC (Harbor City, CA), and samples were injected through a 50 µL injection loop onto a Kromasil C18 (250 × 4 mm) column using 1 mL/min flow rate with 1/22 delivered to the electrospray. Acquisition was done in the full scan mode (110-300 Th mass range and 0.5-1.3 s/scan). For MS-MS experiments, collisionally induced dissociation (CID) was achieved with Ar at 4 × 10-2 Torr and 25 eV collision energy. Ozonation Procedure. Atrazine treatment was carried out on 5-L LC-grade water solution (0.46 × 10-5 mol/L) at ambient temperature (20-23 °C). Ozone was produced from air (4.2 × 10-5 mol/L) by a Degremont ozone generator (RueilMalmaison, France) and introduced continuously (1 L/min) through a glass frit at the bottom of the 10-L batch reactor equipped with a recirculation loop including a PTFE singleplunger pump (Scheme 1). Hydrogen peroxide (Sigma, St. Louis, MO) was introduced at 2 mL/min (11.8 × 10-5 mol/ min in the “standard” conditions). All surfaces in contact with ozone and with the solution were made of glass, PTFE, or stainless steel. Concentration of ozone in the gas phase was measured continuously at the inlet by a single-beam UV spectrophotometer (BMT 961 Messtechnik, Berlin, Germany). Ozone and hydrogen peroxide concentrations in the liquid phase were measured periodically, respectively by the carmin-indigo (27) and the Eisenberg (28) methods. Two hundred milliliter ozonated samples were taken regularly, treated by 0.1 M sodium thiosulfate in excess (2 mL) to stop the reaction, and extracted by the tandem SPE procedure before being analyzed. Sodium thiosulfate did not modify the extraction yields as was shown using solutions of standards spiked with the reagent. VOL. 34, NO. 3, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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Results and Discussion 1. Identification of the Atrazine Degradation Products (ADPs). A number of chlorotriazines with an acetamide function have already been reported, and MS criteria have been proposed (15) for their identification. Less common structures such as formamides and deschlorotriazines have also been reported in some solvent compositions (25). In the present study, GC-EIMS or LC-MS were used to analyze the C18 extracts obtained through our tandem SPE procedure, whereas the SCX extracts (aqueous medium and more polar compounds) had to be examined differently (DCI-MS or LCMS). The search for hydroxytriazines was done by applying a specific LC-MS-MS strategy (18) which led to the identification of OIET (only traces), OIAT, OEAT (traces in some cases), and finally OAAT (ammeline) as the major compound in many conditions. Besides compounds already known, three were found in C18 extracts as new ozonation products of atrazine: CNIT (carbinolamine), CLET, and CLAT (amino-aldehydes). These compounds might be respectively a key intermediate in some pathway of the O3/H2O2 degradation of the pesticide or indicate new (but minor) routes. Some ADPs remain unknown and are called “Un” (from U1 to U4). Two compounds were found to contain an aminoaldehyde group. The first one which we named CLET had the same molecular weight (MW 229) as that of the amides CDIT and CDDT but differed substantially from these ADPs (GC retention time and MS behavior). The presence of an N-ethyl group was demonstrated in the EI spectrum by the presence of intense ions at m/z 201/203 (40% relative intensity for m/z 201) and m/z 200/202 (90% relative intensity for m/z 200) corresponding to [M - C2H4]+• and [M - C2H5•]+ ions, respectively. These ions might have a second origin e.g. [M - CO]+• and [M - CHO•]+ which would indicate when taking into account the +14 u increase of MW vs that of the native pesticide the occurrence of a NH-CH(CH3)CHO substituent. The molecular weight was assigned by GC-CIMS (with NH3 as reagent) which yielded ions at m/z 230/232 (MH+) and 196 ([MH - Cl + H]+). MS-MS experiments were performed to confirm the proposed structure. According to the CID product ion spectra obtained for MH+ (35Cl and 37Cl containing ions studied individually), the following daughter ions were considered and interpreted: m/z 212/214 [MH H2O]+, 202/204 [MH - CO]+, or [MH - C2H4]+ and 152 [MH - HNdCCl-NH2]+. Ions at m/z 160/162 and 132/134 ([ClCdN-C(dNH)NH-CH(CH3)CHO]+ and [Cl-CdN-C(dNH)NH-C2H5]+, respectively) and their complementary ions m/z 99 and 71 ([NC-NH2-CH(CH3)CHO]+ and [NC-NH2C2H5]+) were also present as well as [Cl-CdN-C(dNH)NH2]+ at m/z 104/106. Finally losses of HCl were observed from ions m/z 160/162 and 132/134 at m/z 124 and 96, respectively. All these interpretations were in agreement with the MS-MS behavior of chlorotriazines (16-18). They also agreed with the shifts being induced when replacing NH3 by ND3 which allows H/D exchange of the mobile hydrogens (35Cl MDD+ ion): MDD+ at m/z 233 (+3u thus indicating two exchangeable H), ions initially at m/z 160, 132, 99, and 71 being shifted by +2u. The second amino-aldehyde (CLAT, MW 201) was closely related to the first one since it contained the same new substituent. The intense EIMS ions at m/z 172/174 (base peak) and 173/175 (41% relative intensity) specifically corresponded in this case to [M - CO]+• and [M - CHO•]+. Again structure assignment was found in accordance with a number of fragment-ions appearing in the CID spectrum of the (35Cl) MH+ ion: m/z 184 [MH - H2O]+ and 174 [MH - CO]+ on one hand and 160 [MH - H2NCN]+ (and subsequent ions by loss of CO (m/z 132) or HCl (m/z 124)), 104 and 99 in common with CLET. 432

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FIGURE 1. Evolution of the total molar balances or partial balances (ADPs extracted on C18 support or on SCX cation exchanger) during O3/H2O2 treatment of atrazine in the standard conditions (a) or at pH 8 (b). A compound of MW 231 (CNIT) and its corresponding methylated form of MW 245 (met-CNIT) were also found. Their structures were rather delicate to establish due to their unstability. Both compounds could be detected in the same HPLC chromatogram (respectively at 10.05 and 29.8 min on Nucleosil C18 AB with 50 mM NH4Ac H2O/CH3CN 76/24 v/v), and their proportions were found to strongly correlate with the solvent used for elution from the C18 SPE cartridge (MeOH vs acetonitrile favoring the methylated compound). As the met-CNIT peak was well separated, it was collected by semipreparative HPLC (same conditions as above without NH4Ac). After elimination of most organic solvent under vacuum (T ) 30 °C) and concentration on a C18 reverse phase, LC-ESI-MS analysis surprisingly showed a mixture of three compounds: met-CNIT (MH+ at m/z 246/248), CNIT (MH+ at m/z 232/234), and CIAT (MH+ at m/z 188/190). The spectra of both met-CNIT and CNIT exhibited abundant fragmentions at m/z 214/216 corresponding to [MH - MeOH]+ or [MH - H2O]+, respectively, and at m/z 188/190 (loss of C2H4OH or C2H4OCH3 from MH+). This behavior (confirmed by CID experiments) and the easy conversion of CNIT into its methylated form by methanol treatment (and inversely) or into CIAT by hydrolysis likely via an intermediate imine were highly in favor of a carbinolamine structure derived from the ethylamino group (NHCH(OH)CH3) for CNIT (or NHCH(OCH3)CH3 for met-CNIT). The observation of a carbinolamine structure was consistent with the expected reactivity of secondary amines through oxidation with O3 (29). A carbinolamine was also suggested to occur (although not observed) as intermediate during the UV/TiO2 treatment of atrazine (13). 2. Influence of the Ozonation Conditions on Atrazine Degradation. Standard Conditions. Our standard condi-

FIGURE 2. Product profiles of the degradation of atrazine during O3/H2O2 treatment in the standard conditions (4.2 × 10-5 mol/min O3 and 11.8 × 10-5 mol/min H2O2): C18 extract (a) and SCX cation exchanger extract (b). tions corresponded to introduction rates (see Experimental Section) of ca. 4.2 × 10-5 mol/min O3 and 11.8 × 10-5 mol/ min H2O2 in an initial 0.46 × 10-5 mol/L solution of atrazine at pH 6 (nonbuffered). The results are presented in Figures 1a and 2 (means of two experiments). The relative standard deviations can be estimated for any ADP as 1% for [C]/[CIET]o > 10% and 10-20% for 1% < [C]/[CIET]o < 10%. Ninety-one percent of atrazine reacted after 15 min of treatment, and it disappeared after 30 min. According to Figure 1a, the total of the ADPs extracted on the C18 support presents a maximum at 15 min (equivalent to 44% of initial atrazine) and rapidly decreases to be only 4% at 60 min. On the contrary, the amount extracted on SCX (Figure 1b) increases during the first 60 min (but mostly after 15 min) to reach a plateau (ca. 45%). When taking into account both extracts, the molar balance appears to remain remarkably high (ca. 45%) within the 2 h treatment (at least 4-fold the atrazine disappearance time) as compared to results reported in similar studies (10, 30). The delay between the product profiles obtained from the two extraction supports clearly indicate two generations of ADPs: (i) a first generation of moderate polarity directly originating from atrazine (C18) and (ii) a second one comprising more polar compounds and thus being produced through further degradation (SCX). Extraction on C18 leads to three major products at 15 min reaction (Figure 2a): CIAT and CEAT (11.4 and 4.7%, respectively) formed by monodealkylation and the amide CDIT (14.6%). Except for CNIT (3.8%), other ADPs extracted on this support do not exceed 1-2%. Among them, the amide CDAT is detected, but its abundance is very low (ca. 1%) although Adams and Randtke (10) observed its accumulation when operating in a similarly low (e.g. < 1) O3/H2O2 molar ratio.

FIGURE 3. Product profiles of the degradation of atrazine during O3/H2O2 treatment (4.2 × 10-5 mol/min O3 and 2.9 × 10-5 mol/min H2O2): C18 extract (a) and SCX cation exchanger extract (b). In the SCX extracts (Figure 2b), the compounds found are either the complement of ADPs partially extracted on C18 (e.g. CEAT) or new compounds such as CAAT and ammeline OAAT which reach a plateau at 6% (90 min) and 16% (60 min), respectively. Some unknown compounds are also produced but their relative abundances decrease (cf. U1 and U2) after exhibiting a maximum in the 60-90 min period. Therefore, these unknowns might be intermediates in the formation of the accumulating CAAT and OAAT (particularly for the latter). In contrast, the unknown U4 whose abundance increases rather within the second hour of the reaction could correspond to an alternative pathway (and not to a third generation product as will be demonstrated later). Effect of the O3/H2O2 Ratio. While the O3 introduction rate was unchanged (4.2 × 10-5 mol/min), the H2O2 rate was reduced to 2.9 × 10-5 mol/min (instead of 11.8 × 10-5 mol/ min). This new O3/H2O2 (ca. > 1) molar ratio is considered to be optimal regarding the degradation rate of atrazine in pure or natural waters (8). In fact the comparison with the previous experiment (standard conditions) shows that the C18 extract composition vs reaction time is not very different, except that the maximum yields appeared lower at 15 min (Figure 3a) for the main products CDIT, CIAT, and CEAT. Moreover, the disappearance of atrazine seems to occur similarly ( NaHCO3 experiment > standard one (e.g. 6.2, 1.7, and 0.4, respectively). This change in the repartition of both compounds might thus be related to the OH• radical content (33) and/or pH value (carbinolamines being less stable under low pHs). It VOL. 34, NO. 3, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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should be noted that the OAAT/CAAT ratio reflecting the relative importance of the dechlorination/hydroxylation process seems to be also favored by an increase in the OH• concentration if we consider the higher final ratio obtained under basic conditions vs that of the standard ones (3.5 and 2.6, respectively). Regarding the specific decomposition pathways of the amino groups, the following may be suggested. The degradation of the ethylamino substituent would lead concurrently either to an amide (acetamide or to a lesser extent formamide) or to the primary amine through a common carbinolamine intermediate. This mechanism is similar to that proposed by Bailey (29) to explain the decomposition of secondary amines in the presence of O3 only (eqs 1-4):

cation exchanger used as a complementary phase removed from the treated aqueous solutions the most polar compounds that were produced from further degradation i.e. CAAT, OAAT and a number of unknowns (intermediates and/ or competitors). The use of this combination of phases is extremely important in ozonation studies to obtain sufficiently high molar balances vs the initial pesticide content, thus enabling the most appropriate interpretation of the data. In some of the studied ozonation conditions, ammeline OAAT was formed in yields approaching 20% which represented almost 4-fold more than CAAT production. The OAAT/CAAT ratio might be considered as a criterion to adjust the process parameters when the less toxic atrazine byproducts (e.g. hydroxytriazines) are required.

RNH-CHOH-CH3 + O3/OH• f RNH-COCH3 (acetamide) (1)

Acknowledgments

RNH-CHOH-CH3 - H2O f RNdCH-CH3 T RNH-CHdCH2 (2) RNdCH-CH3 + H2O f RNH2 + OdCH-CH3

(3)

RNH-CHdCH2 + O3 f RNH-CHO (formamide) (4) In the case of the isopropylamino group, again an amide and a primary amine might be considered as produced in parallel but through a different sequence (eqs 5-7):

RNH-C(CH3)OH-CH3 - H2O f RNdC(CH3)2 T RNH-C(CH3)dCH2 (5) RNH-C(CH3)dCH2 + O3 f RNH-COCH3

(6)

RNdC(CH3)2 + H2O f RNH2

(7)

Oxidation leading to the amino-aldehyde form as was observed in the present study results certainly from a minor process since compounds containing such a substituent were found as traces. More remarkable was the occurrence of a carbinolamine compound (CNIT, possibly isolated as metCNIT) particularly under the less drastic O3-only reaction conditions. Identifying such a compound for the first time in this context proves the necessary involvement of carbinolamines as intermediates in the dealkylation process of the substituted amino groups of triazinic pesticides. CAAT which was found unreactive in the presence of the O3/H2O2 system should be an end-product. Further, the relatively slow degradation rate of OIET in the same conditions and its quasi-absence (as well as that of its monodealkylated products) during ozonation treatment of atrazine minimize the role of this compound in the formation of ammeline OAAT. Consequently, hydroxylation leading to OAAT, which appears by far as the most abundant hydroxytriazine in any conditions, should occur on intermediate(s) of the CIET (atrazine) f CAAT transformation. Nsubstituents of these may not be amide(s) which were considered as rather difficult to degrade in similar conditions (15). It is also probable that most of them were not extracted and thus analyzed using our SPE procedure if we consider the significant lack of compounds extracted once the parent pesticide has disappeared (Figure 1, standard and pH 8 conditions). Scheme 2 summarizes the degradation pathways of atrazine as suggested by the present study. The tandem SPE procedure carried out herein has proved its high efficiency as a tool to study the reactivity of atrazine during ozonation by the O3/H2O2 system. The first C18 reverse phase support, although used in previous studies, enabled us to identify for the first time a number of chlorinated byproducts e.g. amino-aldehydes and a carbinolamine. The 436

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The authors wish to thank M. Stobiecki (Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland) for his participation when carrying out the ozonation experiments. J. P. Duguet and O. Wable from Lyonnaisedes-Eaux are warmly acknowledged for helpful discussions. INRA and Lyonnaise des Eaux are thanked for cosupporting the doctoral thesis fellowship of Sylvie Ne´lieu.

Literature Cited (1) Pereira, W. E.; Rostad, C. E. Environ. Sci. Technol. 1990, 24, 1400. (2) Mu ¨ ller, S. R.; Berg, M.; Ulrich, M. M.; Schwarzenbach, R. P. Environ. Sci. Technol. 1997, 31, 2104. (3) Seiler, A.; Brenneisen, P.; Green, D. H. Water Supply 1992, 10, 31. (4) Hoigne´, J.; Bader, H. Water Res. 1976, 10, 377. (5) Montiel, A.; Welte, B.; Franchet, C.; Legrand, S. Water Supply 1989, 7, 213. (6) Duguet, J. P.; Wable, O.; Richard, Y.; Toffani, G.; Dalga, N. Water Supply 1992, 10, 105. (7) Beltra`n, F. J.; Garcia-Araya, J. F.; Acedo, B. Water Res. 1994, 28, 2165. (8) Paillard, H.; Brunet, R.; Dore´, M. Water Res. 1988, 22, 91. (9) Duguet, J. P.; Bernazeau, F.; Mallevialle, J. Ozone Sci. Eng. 1990, 12, 195. (10) Adams, C. D.; Randtke, S. J. Environ. Sci. Technol. 1992, 26, 2218. (11) Glaze, W. H.; Kang, J. W.; Chapin, D. H. Ozone Sci. Eng. 1987, 9, 335. (12) Legube, B.; Guyon, S.; Dore´, M. Ozone Sci. Eng. 1987, 9, 233. (13) Pelizzetti, E.; Maurino, V.; Minero, C.; Carlin, V.; Pramauro, E.; Zerbinati, O.; Tosato, M. L. Environ. Sci. Technol. 1990, 24, 1559. (14) Kearney, P. C.; Muldoon, M. T.; Somich, C. J.; Ruth, J. M.; Voaden, D. J. J. Agric. Food Chem. 1988, 36, 1301. (15) Hapeman-Somich, C. J.; Gui-Ming, Z.; Lusby, W. R.; Muldoon, M. T.; Waters, R. J. Agric. Food Chem. 1992, 40, 2294. (16) Voyksner, R. D.; McFadden, W. H.; Lammert, S. A. In Applications of New Mass Spectrometry Techniques in Pesticides Chemistry; Rosen, J. D., Ed.; Wiley: New York, 1987; Chemical Analysis, Vol. 91, Chapter 17. (17) Abia´n, J.; Durand, G.; Barcelo´, D. J. Agric. Food Chem. 1993, 41, 1264. (18) Ne´lieu, S.; Stobiecki, M.; Kerhoas, L.; Einhorn, J. Rapid Commun. Mass Spectrom. 1994, 8, 945. (19) Molina, C.; Durand, G.; Barcelo´, D. J. Chromatogr. A 1995, 712, 113. (20) Cai, Z.; Cerny, R. L.; Spalding, R. F. J. Chromatogr. A 1996, 753, 243. (21) Adams, C. D.; Randtke, S. J. J. Am. Water Works Assoc. 1992, 84, 91. (22) Beltra`n, F. J.; Garcia-Araya, J. F.; Acedo, B. Water Res. 1994, 28, 2153. (23) Ne´lieu, S.; Stobiecki, M.; Einhorn, J. J. Chromatogr. A, in press. (24) Cook, A. M.; Hu ¨ tter, R. J. Agric. Food Chem. 1981, 29, 1135. (25) Ne´lieu, S.; Kerhoas, L.; Einhorn, J. Intern. J. Environ. Anal. Chem. 1996, 65, 297. (26) Ne´lieu, S.; Stobiecki, M.; Sadoun, F.; Virelizier, H.; Kerhoas, L.; Einhorn, J. Analusis 1994, 22, 70. (27) Bader, H.; Hoigne´, J. Ozone Sci. Eng. 1982, 4, 169. (28) Eisenberg, G. M. Ind. Eng. Chem. 1943, 15, 327.

(29) Bailey, P. S. Ozonation in Organic Chemistry II: Nonolefinic compounds; Academic Press: New York, 1982; Organic Chemistry Vol. 39. (30) Arnold, S. M.; Hickey, W. J.; Harris, R. F. Environ. Sci. Technol. 1995, 29, 2083. (31) Beltra´n, F. J.; Garcı´a-Araya, J. F.; AÄ lvarez, P. M.; Rivas, J. J. Chem. Technol. Biotechnol. 1998, 71, 345. (32) Staehelin, J.; Hoigne´, J. Environ. Sci. Technol. 1982, 16, 676.

(33) Hapeman, C. J.; Karns, J. S.; Shelton, D. R. J. Agric. Food Chem. 1995, 43, 1383.

Received for review May 25, 1998. Accepted November 10, 1999. ES980540K

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