Environ. Sci. Technol. 1994, 28, 2207-2277
Formation and Transport of Deethylatrazine and Deisopropylatrazine in Surface Water E. M. Thurman,’ M. T. Meyer, M. S. Mllls, L, R. Zlmmerman, and C. A. Perry
U S . Geological Survey, 4821 Quail Crest Place,
Lawrence, Kansas 66049
Donald A. Goolsby
U S . Geological Survey,
Denver Federal Center, Building 25, Denver, Colorado 80225
Field disappearance studies and a regional study of nine rivers in the Midwest Corn Belt show that deethylatrazine (DEA;2-amino-4-chloro-6-isopropylamino-s-triazine) and deisopropylatrazine (DIA; 2-amino-4-chloro-6-ethylaminos-triazine) occur frequently in surface water that has received runoff from two parent triazine herbicides, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and cyanazine (2-c hlor o-4-et hy lamino-6-methylpropionitrileamino-s-triazine). The concentration of DEA and DIA in surface water varies with the hydrologic conditions of the basin and the timing of runoff, with maximum concentrations reaching 5 pg/L (DEA + DIA). Early rainfall followed by a dry summer will result in an early peak concentration of metabolites in surface water. A wet summer will delay the maximum concentrations of metabolites and increase their runoff into surface water, occasionally resulting in a slight separation of the parent atrazine maximum concentrations from the metabolite maximum concentrations, giving a “second flush” of triazine metabolites to surface water. Replicated field dissipation studies of atrazine and cyanazine indicate that DIA/DEA ratios will vary from 0.4f 0.1 when atrazine is the major triazine present to 0.6 f 0.1 when significant amounts of cyanazine are present. A comparison of transport time of DEA and DIA from field plots to their appearance in surface water indicates that storage and dilution are occurring in the alluvial aquifers of the basin.
Introduction
Agricultural practices may cause widespread degradation of water quality in the midwestern United States (13). Approximately three-fourths of all preemergent herbicides used in the United States are applied to row crops in a 10-state area, called the Corn Belt ( 4 ) . Because many herbicides are relatively water soluble, they may leach into groundwater ( 2 , 5 ) as well as be transported in surface runoff ( 6 , 7 ) . Monitoring studies of surface water (2,3,7-IO), including the Mississippi River (8),have shown widespread detection of herbicides, such as atrazine and its dealkylated metabolites (deisopropylatrazine and deethylatrazine). Furthermore, these same compounds are frequently detected in groundwater (5, 11, 12). Health standards for drinking water have been set by the U.S. Environmental Protection Agency for atrazine at 3.0 pg/L (maximum contaminant level or MCL) and for simazine at 4 pg/L, and a health advisory level (HAL) has been set for cyanazine at 1.0 pg/L. Propazine currently has been removed from the market in the United States (Ciba Geigy Corp.). These are the major triazine herbicides currently used for weed control in corn (Zea mays L.) and sorghum (Sorghum bicolor L.) cultivation (4). In the This article not subject to U S . Copyright.
European Community, the health advisoryfor each triazine herbicide and metabolite is 0.1 pg/L for a total of 0.5 pg/L in groundwater. However, in the United States, health advisory levels have not been set for triazine metabolites, and the possibility of summing parent and metabolites to meet the MCL may be considered [the state of Wisconsin has set a limit of 3.0 pg/L for the sum of atrazine, DEA, and DIA in groundwater; Wisconsin Ground-Water Act 410 (1983), Rule under the law, Enforcement Standard, Chapter NR 140, Wisconsin ADM CODE (199111. Thus, the appearance of two important triazine metabolites (deisopropylatrazineand deethylatrazine)in surface water and groundwater is important in affecting the health standards of at least four parent triazines (atrazine, simazine, propazine, and cyanazine). Because deisopropylatrazine and deethylatrazine are common metabolites of these four triazines, it is important to examine their formation, degradation, and transport fromsoil into surface water. Many studies have examined dealkylation reactions of these triazines (13-311, including recent work of the authors on the formation of DEA from atrazine and propazine and the formation of DIA from atrazine and simazine (11,30,31). Several field dissipation studies have noted the presence of DIA from cyanazine degradation (24-26), but DIA has not been reported in surface runoff from field plots. Nor has there been a regional view of the occurrence and transport of DEA and DIA in surface water and their relationship to the parent triazines. Therefore, the objectives of this research are as follows: (a) to present runoff patterns of DIA and DEA from field disappearance studies of atrazine, (b) to corroborate the formation and runoff of DIA from cyanazine with a field disappearance study, and (c) and to report on the sources and amount of DIA and DEA in surface water at the regional scale, based on nine storm-event studies and new interpretations from published regional surveys of parent triazines (2,3). The combination of these three objectives gives an explanation for DIA/DEA ratios in surface water of the Midwest and shows a “second flush” of herbicide metabolites (DIA and DEA) that occurs periodically when hydrologic conditions allow for a midsummer runoff. Furthermore, these results may help in the decisions for establishingdrinking water standards for the triazines and their dealkylated metabolites. Experimental Methods
Field Dissipation Studies. Four field dissipation studies of atrazine, cyanazine, propazine, and simazine have been conducted at the same site, the Kansas River Valley Experimental Field Site (Topeka, KS) from 1989 to 1992. One of the two atrazine studies of 1989 was published by Adams and Thurman (II), which dealt with
Published 1994 by the American Chemical Society
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atrazine and deethylatrazine transport in the vadose zone. The simazine and propazine study of 1990 was published by Mills and Thurman (31) and dealt with metabolite movement in both surface water and groundwater. The second atrazine study of 1989 addressed surface water and groundwater transport of atrazine from silt- and clayloam soils. The experimental conditions from that study will be presented here along with the cyanazine and atrazine field dissipation study of 1992. The second atrazine study of 1989 ran from May until harvest in November 1989. Two Eudora silt-loam plots (65m2)and two clay-loam plots (65 m2)were planted with corn (Zea mays L.), and atrazine (AAtrex Nine-0, Ciba Geigy Corp.) was applied at 2 kg/ha on the four plots. In the 1992 study, replicate Eudora silt-loam plots (65 m2) were planted with corn (Zea mays L.), and cyanazine (Bladex, Dupont Corp.) was applied to both a t 2 kg/ha. On a third plot of the Eudora silt-loam, atrazine (AAtrex Nine-0, Ciba Geigy Corp.) was applied at 2 kg/ha as a comparison plot to the 1989 atrazine study. In the two studies, both sprinkler-applied irrigation and natural precipitation maintained crop growth. All herbicides were applied prior to the planting of corn. The herbicides were incorporated to various depths (0 and 5 cm) in the 1989atrazine study as part of a larger experiment on the effect of tillage practice on groundwater quality (32). In the 1992 study of atrazine and cyanazine, the herbicides were slightly incorporated (3-5 cm) to prevent wind drift of the herbicide from one plot to the next. The silt-loam had a particle-size distribution of 44-63 % silt, 26-5092 sand, and 5-21 % clay, and the clay-loam was 50-60% silt, 4-25% sand, and 16-3593 clay (32). The pH of the soil was in the range of 6.8-7.8 for both soils. The organic carbon content of the silt-loamwas 0.99 % ,0.69%, and 0.22% at 15, 30, and 45 cm, respectively; the organic carbon content on the clay-loam was 0.63%, 0.21% , and 0.17% at 15, 30, and 45 cm, respectively. Each plot had a 1% slope and was isolated from the other plots by perimeter berms and flashing. In all studies, suction-cup lysimeters (5-cm diameter; Soil-Moisture Equipment, Santa Barbara, CA) were used to sample soil pore water. The lysimeters were placed a t depths of 30,60,90, and 120 cm and were sampled following every precipitation or irrigation event and monthly during the dry harvest season. Soil cores were collected from one location near the center of each plot using a split-tube samples (CME CO., St. Louis, MO) before application, after application, and then monthly. Soil cores were separated into 15-cm intervals to a depth of 1-m, placed in polypropylene bags, and frozen until analyzed. Samples of surface runoff drained into a bucket that was level with the field surface at the end of each plot, which was pumped continuously into a 380-L storage tank using a sump pump. The volume of runoff was recorded, and a 4-L sample of water and suspended sediment was collected after each event for measurement of surface runoff losses from the plot. River Basin Studies. Samples for herbicide analysis were collected at six rivers and three streams during AprilAugust 1990 (Figure 1). The river sites included the Cedar River (Iowa), the Delaware River (Kansas), the Huron River (Ohio),the Iroquois River (Illinois),the Sangamon River (Illinois),and the West Fork of the Big Blue River (Nebraska). Three small streams were also sampled: Old Mans Creek (Iowa),Roberts Creek (Iowa),and Silver Creek (Iowa). Two sites, the Sangamon River and the West Fork 2288
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of the Big Blue, were resampled from March 1991to April 1992. Automatic samplers were installed at existing U.S. Geological Survey streamflow-gaging stations. The samplers were equipped with Teflon-lined intake tubing from the pump to the stream and were capable of collecting at least 24 samples between visits and were programmed to collect a sample every other day during non-runoff periods. When precipitation occurred, samples were collected at 3-8 h time intervals. All samples were filtered on-site through 1-pm glass fiber filters using a peristaltic pump. Filters were first leached with at least 200 mL of distilled or deionized water followed by 25-50 mL of the sample. The filtrate was collected in a 125-mL amber glass bottle that had been precleaned and baked. All samples were stored on ice or refrigerated until analysis in the laboratory. Laboratory analyses consisted of microtiter plate enzyme-linked immunosorbent assay for triazine and chloroacetanilide herbicides and confirmation by gas chromatography/mass spectrometry. Only the GUMS analysis of atrazine, cyanazine, DIA, and DEA are presented in this paper, which consists of approximately 400 samples for the 1990 sampling and approximately 250 samples for the 1991-92 sampling (33). Reconnaissance Studies. Herbicide concentrations were reported in a published survey of herbicides from 149 surface water sites across the Midwest by the authors (2,3). The survey was undertaken in 1989 and repeated a t 55 sites in 1990. There were five sampling rounds, beginning with a preherbicide application 1989, postapplication 1989, harvest 1989, preapplication 1990, and postapplication 1990. New information from this study is presented on DEA and DIA from the 1989 and 1990 periods. The samples were analyzed by gas chromatography/mass spectrometry as described below. Analysis. Methanol (Burdick and Jackson, Muskegon, MI), ethyl acetate, and isooctane (Fisher Scientific, Springfield,NJ) were pesticide-grade solvents. Deionized water was charcoal filtered and glass distilled prior to use. Atrazine, cyanazine, propazine, and simazine were obtained from Supelco (Bellefonte, PA); terbuthylazine standards were obtained from the U.S. EPA (U.S. Environmental Protection Agency) Pesticide Chemical Repository (Research Triangle Park, NC); and the triazine metabolites, deethylatrazine and deisopropylatrazine, were obtained from Ciba Geigy Corp. (Greensboro, NC). The cartridges (Sep-Pak from Waters, Milford, MA) contained 360 mg of 40-pm c18 bonded silica. Standard solutions were prepared in methanol, and phenanthrenedlo (U.S. EPA, Cincinnati, OH) was used as an internal GC/MS quantitation standard. The methods of Thurman et al. (34) and Meyer et al. (35) were used for herbicide analysis, which consists of using a Waters Millilab Workstation (Milford, MA) for solid-phase extraction with cartridges. Each 123-mL water sample was spiked with a surrogate standard, terbuthylazine (2.4 ng/pL, 100 pL) and pumped through the cartridge at a rate of 20 mL/min by the robotic probe. Analytes were eluted with ethyl acetate and spiked automatically with phenanthrene-dlo (500 pL of 0.2 ng/ pL). The extract was evaporated automatically by a Turbovap (Zymark, Palo Alto, CA) at 45 "C under a nitrogen stream to 100 pL. Automated GC/MS analyses were performed on a Hewlett Packard Model 5890 GC (Palo Alto, CA) and a
EXPLANATION
Studv
8 LOCATION OF SAMPLING SITE,
aAND RIVER DRAINAGE BASIN FOR STORM-RUNOFFSTUDY
1 -IROQUOIS RIVER, ILL. 2. SANGAMON RIVER, ILL 3 . SILVER CREEK, ILL. 4 . CEDAR RIVER, IOWA 5 -OLD MANS CREEK, IOWA 6 - ROBERTSCREEK, IOWA 7 DELAWARE RIVER, KANS. 8 -WEST FORK BIG BLUE RIVER. NEBR. 9 -HURON RIVER, OHIO
-
lndex~map Figure 1. Location of study area, hydrologic units. and sites sampled during 1990 and 1991 In the mMwestern UnHed States. 5970A mass selective detector (MSD). Operating conditions were as follows: ionization voltage, 70 eV; ion source temperature, 250 "C; electron multiplier, 2200 V; direct capillary interface at 280 "C, tuned daily with perfluorotributylamine; dwell time, 50 ms. Separation of the herbicides was carried out using a HP-112-m fused-silica capillary column (Hewlett Packard, Palo Alto, CA), 0.2 mm in diameter with a methyl silicone stationary phase, 0.33 pm thick. Helium was used as the carrier gas at a flow rate of 1mL/min and a head pressure of 35 kPa. The column temperature was held at 60 O C for 1min and then increasedat6"C/minto2lOoCwbentherunisterminated. Injector temperature was 280 "C. Quantification of the base peak of each compound was based on the response of the 188 ion of the internal standard, phenanthrene-dlo. Confirmation of the compound was based on the presence of the molecular ion and one to two confirming ions with aretention time matcbof *0.2% relative tophenanthrenedio (34). A rigorous quality assurancelquality control program (which included analysis of 10% blank samples, 10% duplicate samples, 5 % spiked samples at 1pg/L, 1% blind samples, and 1% double-blind samples) was used to assure the accuracy of the results. The detection limit and quantitation limit was 0.05 pg/L for allcompounds,except cyanazine,whichwas0.2 pg/L. Alllaboratoryblankswere free of herbicide or metabolite, and recoveries of spikes
*
varied from 90 to 110 10%. The variation of the duplicates was *5% at one standard deviation. The correlation coefficients of the standard curves were 0.998 f 0.002. Any samples greater than 10 pg/L were diluted and reanalyzed. Results and Discussion
DIA and DEA in Runoff from Field Plots. The four parent triazines (atrazine, cyanazine, simazine, and propazine) may form two important dealkylated metabolites, DIA and DEA (Figure 2). Figure 2 was summarized from published studies (13-31), including recent work of the authors on atrazine, propazine, and simazine degradation usingfield disappearancestudies (11,30,31).Several field studies have noted the presence of DIA from cyanazine degradation in soil and tile drainage (24,25);however, a runoff study of cyanazine and DIA bas not been reported, nor has the amount of DIA produced relative to cyanazine been documented. Therefore, duplicate runoff plots were examined in this study to determine if DIA formed from cyanazine and occurred in surface runoff. Figure 3 shows the replicated patterns of cyanazine disappearanceand the formation of DIA on the cyanazine plots. DIA occurred within the first week of application of herbicide, which shows that it is possible to degrade cyanazine to DIA by loss of the isopropylcyano group. Envlron. Sd.Technol.. VoI. 28, NO. 13. I994 2289
CI
/C"3
Deisopropylatrazine
'lH5
Deethylatrazine :CH CH3
Flgure 2. Pathways for degradation of various triazines to DEA and DIA. Field Plot 1
Fieid Plot 2
50 40
r 4.96
30
20 10
0
r-7
deisopropylatrazine
deisopropylatrazine
r2=0.94
t
0
r 4.94
1
20
40
60
80 100
0
20 40
60
80 100
Days After Application Flgure 3. Cyanazine and DIA runoff from the Eudora silt-loam field plots.
This result corroborates with the earlier soil and tile drainage studies of Sirons et al. (24)and Muir and Baker (25). The concentration of cyanazine was greatest in the first runoff event (30-40 pg/L) and then decreased exponentially to the HAL of 1.0 pg/L in approximately 463 days on both plots (Figure 3). The concentration of DIA increased gradually, with peak concentration in runoff occurring approximately 20 days after application or the second runoff event (each sample point represents a runoff event). DIA accounted for 2% of the herbicide runoff during the first runoff event and increased to 25 % -35 % for subsequent events. Several 14Cstudies of cyanazine degradation in soil (28, 29) have reported DIA as a metabolite that accounts for 5-10% of the total 14C radioactivity compared to cyanazine. The runoff studies 2270
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shown in Figure 3 are in agreement with these previous findings. Atrazine runoff to surface water was determined on an adjacent plot in 1992 (for comparison to cyanazine under similar soil and hydrologic conditions) and on four plots of the same farm in 1989. Figure 4A shows the runoff pattern for the parent atrazine for both years. Concentrations were over 1000 pg/L during the first runoff event from two soils (silt and clay, non-incorporated herbicide 19891, 300-500 pg/L from two soils (silt and clay, incorporated herbicide 19891, and 80 pg/L in the incorporated silt-loam soil from the 1992 atrazine experiment. The parent compound shows an exponentially decreasing curve for the surface runoff and a rapid disappearance from surface soil. The incorporation of herbicide significantly reduced the concentration in runoff from both the siltloam and the clay-loam soils. Figure 4B shows the DEA runoff patterns for the same plots. The plots with the least incorporation had the highest concentrations of DEA. Note that both the nonincorporated silt and the clay-loam had initial DEA concentrations of 28 and 39 pg/L, respectively. The concentrations from the incorporated plots (silt-loam and clay-loam) were only 8 and 1 2 pg/L, respectively, on the first event. The 1992 atrazine study had the most incorporation and the least concentration at only 5 pg/L. These results indicate that tillage practice (incorporated versus non-incorporated) affects runoff concentrations during the first event of both parent and metabolite. Furthermore,the degradation of atrazine to DEA is rapid in soil with the production of DEA within one day of application (the application mixture of herbicide was free of metabolite by G U M S analysis). All of the plots show an increase in DEA concentration that occurs later than in the parent compound. For example, three of the plots peaked within 12 days (or the second runoff event), one of the plots with incorporation of herbicide peaked at 20 days (or the third runoff event), and the other a t 30 days (or third runoff event). These results suggest that although the degradation of atrazine is quite rapid in soils, there is an optimum time between 10 and 20 days (second or third runoff event) for the combination of degradation and runoff to give the maximum concentration of DEA.
2000
Y
-
1000
Clay Non Incorp. 89 Silt Incorp. 89 Silt Non Incorp. 89 Clay Incorp. 89 Silt Incorp. 92
0 0
20
40
80
60
Days
-
I Clay Non Incorp. 89
_t_
0
20
Silt Incorp. 89 Silt Non Incorp. 89 Clay Incorp. 89 Silt Incorp. 92
40
60
80
Days Figure 4. Atrazlne (A) and DEA (B) runoff from the Eudora silt-loam and clay-loam plots for 1989 and 1992.
The runoff disappearance half-life of atrazine and cyanazine may be estimated from a plot of concentration versus time, such as shown in Figures 3 and 4. The slope of the natural log of concentration versus time is related to the disappearance half-life (time for 50%of the chemical to disappear from the soil plot) by the following equation (36):
tl,2 = 0.6931k where k = the slope of the plot of In concentration versus time.
The atrazine plots of 1989had disappearance half-lives in surface runoff from approximately 5-9 days (Table 1) and compared closely to the atrazine study of 1992 with a half-life of approximately 8 days. The two cyanazine plots were similar with half-lives of approximately 8 days. These disappearance half-lives in runoff will be a function of the amount and timing of rainfall on the plot as well as the type of tillage practice which affects runoff (7).By comparison, decomposition half-lives of atrazine in soil are reported from 60 to 120 days (24-26, 37, 38) and of cyanazine from 5 to 30 days (24-26). Thus, the removal of parent compound from surface soil by runoff may be considerably faster than the degradation of parent compound to metabolite in soil. Because the mass of DEA is dependent on initial atrazine concentration (production of DEA is a first-order reaction), the peak in DEA runoff must occur relatively quickly (within 10-30 days or two or three rain events) because runoff is rapidly lowering the concentration of parent compound in the surface soil. The atrazine study of 1989 gave considerably larger concentrations of atrazine (Figure 4A) in the initial runoff events than the 1992atrazine/cyanazine study. This major difference in concentration was caused by the incorporation used (application rates were 2 kglha for both studies). The study of 1992incorporated atrazine to a greater depth, and 7 days elapsed before the first runoff event, which decreased concentrations considerably. However, both studies show that DEA peaked in concentration from 10 to 30 days after application of the parent herbicide (second or third runoff event). Because the two experiments varied in runoff pattern and soil type (both clay and silt loams at different locations on the farm), these results are not surprising. Caution must be used in extrapolating actual amounts of herbicide in runoff to regional scale studies. However,ratios of metabolites and parent compounds are useful in understanding runoff patterns. For example, the DEA to atrazine ratio (DAR) increased from
