contamination of groundwater by triazines, metolachlor and alachlor

Journal of Contaminant Hydrology, 15 (1994) 73-92 73 El~vier Science Publishers B.V., Amsterdam

Contamination of groundwater by triazines, metolachlor and alachlor*

W.F. Ritter a, R.W. Scarborough b and A.E.M. Chirnside c

aDelaware Agricultural Experiment Station, University of Delaware, Newark, DE 19717, USA bAgricultural Engineering Department, University of Delaware, Newark, DE 19717, USA

~College of Agricultural Sciences, University of Delaware, Newark, DE 19717, USA

(Received December 9, 1991; revised and accepted July 19, 1993)

ABSTRACT

The movement of triazines (atrazine, simazine, cyanazine), metolachlor and alachlor were studied in continuous irrigated corn in an Evesboro loamy sand soil. Both no-tillage and conventional tillage treatments were used.

Atrazine and simazine were detected in the groundwater more frequently than cyanazine and metolachlor. Alachlor, atrazine and simazine moved rapidly to the groundwater if sufficient rainfall occurred shortly after they were applied. Alachlor concentrations ranged from 4.0 to 15.0 ppb and atrazine concentrations ranged from < 1.0 to 54 ppb. Metolachlor was detected in the groundwater more frequently than cyanazine. Metolachlor concentrations range from < 1.0 to 12.0 ppb and cyanazine concentrations ranged from < 1.0 to 29.0 ppb. There was no large differences in pesticide movement between conventional tillage and no-tillage.

INTRODUCTION

The three most common herbicides used on corn are atrazine, alachlor and metolachlor. In 1990, > 26- 106 kg of active ingredient of atrazine were used on corn in the U.S.A., and > 16- 106 kg of alachlor and metolachlor were used (DDA, 1991). Groundwater contamination by pesticides has become a national issue. Conservation tillage, which generally requires the application of herbicides, has increased tremendously in the past 10 years. With reduced runoff and increased infiltration, conservation tillage may increase the leaching of herbicides to groundwater.

In 1984, a cooperative research program, funded by the USDA North- east Pesticide Impact Assessment Program, was established involving Penn-

* Published as Miscellaneous Paper No. 1426 of the Delaware Agricultural Experiment Station.

0169-7722/94/$07.00 ~ 1994 Elsevier Science Publishers B.V. All rights reserved.

74 W.F. ~ITTER ET AL.

sylvania State University, University of Maryland, University of Delaware and Cornell University to evaluate the leaching and runoff losses of pesticides from commercially planted corn as influenced by tillage systems, soil structure and regional variation. This paper summarizes results obtained in Delaware.

LITERATURE REVIEW

Spalding et al. (1980) found alachlor in 2 out of 14 irrigation wells sampled in the Central Platte region of Nebraska, U.S.A., in concentrations that ranged from 0.018 to 0.071 ppb. The area has silt loam soils and an unconfined aquifer with the depth of groundwater ranging from 6 to 10 m. Atrazine was the most widely used herbicide in the area followed by alachlor. Most wells in the area had nitrate concentrations above 10 mg L -1 N.

Junk et al. (1980) in another study in the Platte River region of Nebraska, detected alachlor in one out of 35 samples above 0.02 ppb. For this study, monitoring wells were installed to a depth of 15 m in a 62-km 2 area. The one well where alachlor was detected was influenced by infiltration of overland runoff from up-slope irrigation ditches. The data collected by Junk et al. (1980) suggest that the vertical transport of alachlor through the vadose zone is more dependent on site-specific parameters than that of atrazine.

Hallberg (1985) reported alachlor concentrations as high as 16.6 ppb in the Big Spring Basin groundwater of northeast Iowa, U.S.A. The Big Springs Basin is a karst area, but most of the pesticides reach the aquifer with the infiltration water and not in pesticide-carrying surface waters flowing through sinkholes. Hallberg (1985) also detected alachlor in 13% of the wells sampled from alluvial aquifers or Pleistocene aquifers that occur throughout the state. Most of these samples were taken from public water supply wells. The maximum concentration of alachlor detected in these wells was 0.7 ppb.

In Wisconsin, U.S.A., alachlor was detected in 47 of 377 samples with 21 samples exceeding the health advisory limit of 2.0 ppb (Holden, 1986). Par- sons and Witt (1988) in their survey of state regulatory agencies, report that alachlor has been detected in the groundwater in 16 U.S. states. Out of a total of 5016 wells analyzed for alachlor 142 wells had detectable concentrations of alachlor. Only one well was above the health advisory limit of 2 ppb.

Atrazine probably has been detected more widely in groundwater than any other herbicide. Junk et al. (1980) measured atrazine concentrations as high as 88 ppb in groundwater samples in Nebraska. Peak concentrations were observed at the end of the irrigation season in shallow wells down- gradient from irrigated fields. The vertical and areal distributions of atrazine were closely associated with those of nitrate nitrogen. Spalding et al. (1979)

CONTAMINATION OF GROUNDWATER BY TRIAZINES, METOLACHLOR AND ALACHLOR 75

also reported finding atrazine in the water under irrigation fields in Merrick County, Nebraska.

Hallberg (1985) reported that in the Big Springs watershed, the flow- weighted mean atrazine concentrations for groundwater discharge increased steadily from 1981 to 1985. Maximum concentrations of atrazine in the groundwater from 1981 to 1985 ranged from 2.5 to 10.0 ppb. According to EPA (1988) data atrazine has been detected in the groundwater in 13 U.S. states.

Pionke et al. (1988) detected atrazine, simazine and cyanazine in groundwater in an agricultural watershed in Pennsylvania, U.S.A. The soils on the watershed ranged from coarse textured to fine textured. Atrazine was detected in 14 out of 20 wells ranging in concentration from 0.013 to 1.1 ppb. Simazine was detected in 35% of the wells at concentrations ranging from 0.01 to 1.7 ppb and cyanazine was only detected in one well (0.09 ppb).

Brinsfield et al. (1987) studied pesticide leaching on no-tillage and conventional tillage watersheds on a silt loam Coastal Plain soil in Maryland, U.S.A. Over a three-year period atrazine was detected in the groundwater more frequently than simazine, cyanazine or metolachlor. Pesticides were detected more frequently in the groundwater on the no-tillage watershed than the conventional tillage watershed.

Dillaha et al. (1987) found atrazine had the highest mean concentration of 20 pesticides detected in the groundwater on an agricultural watershed with a Rumford loamy sand soil in Virginia, U.S.A. The average concentration of 129 samples was 0.46 ppb with concentrations ranging from 0 to 25.6 ppb.

Southwick et al. (1988) found 0.038% of the atrazine was lost by leaching within 78 days after it was applied in Louisiana, U.S.A., through tile drains. Steenhuis et al. (1988) found atrazine in the groundwater one month after it was applied in conservation tillage, but did not detect any atrazine in the groundwater in conventional tillage until late fall. They concluded atrazine moved to the groundwater under conservation tillage by macropores that were connected to the surface, but under conventional tillage most of the atrazine was adsorbed in the root zone.

Zacharias et al. (1991) found metolachlor leached rapidly in a Suffolk sandy loam soil (coarse-loamy, siliceous, thermic - - Typic Hapludult) shortly after it was applied in Virginia, U.S.A. Statistical tests showed it moved deeper in the no-tillage as compared to conventional tillage.

EXPERIMENTAL METHODS

Field study

In 1984 three plots (0.5 ha) were established on a site at the University of

76 W.F. R ITI 'ER ET AL.

TABLE 1

Soil properties for Evesboro soil

Depth Organic (cm) matter

(°/o)

CEC Sand Silt Clay Hydraulic (meq/100 g) (%) (%) (%) conductivity

(cm hr- 1)

X SD X SD X SD X SD X SD X SD

0-30 1.5 0.4 3.3 0.6 72 7.1 17 4.1 11 2.0 16.0 7.8 31-60 0.7 0.2 2.6 0.9 77 9.2 9 6.1 14 5.7 11.0 3.1 61-90 0.2 <0.1 2.8 0.6 78 10.4 7 4.1 15 6.5 16.3 1.3 91-120 0.1 <0.1 2.1 0.8 64 11.1 14 7.4 22 6.5 -

121 150 0.1 <0.I 4.0 1.2 55 12.1 20 6.9 25 7.2 -

= not data.

Delaware Research and Education Center located near Georgetown, Dela- ware, U.S.A. The plots were planted to no-tillage corn. Atrazine was applied pre-emergence at rates of 1.12, 2.24 and 4.48 kg ha -1 . Alachlor was applied to all three plots pre-emergence at a rate of 2.24 kg ha - l . The atrazine and alachlor were applied on April 27.

In 1985, a conventional tillage plot was also established. The other plots were maintained in no-tillage corn. Atrazine was applied pre-emergence to the no-tillage plots at rates of 1.12, 2.24 and 4.48 kg ha -1, and to the conventional tillage plot at a rate of 2.24 kg ha -1. Cyanazine, simazine and metolachlor were also applied pre-emergence to all plots at rates of 1.68, 2.24 and 1.68 kg ha -l , respectively. The same treatments were used in 1986 as 1985. The herbicides were applied April 23 in 1985 and May 23 in 1986. All herbicides were applied as liquid concentrate formulations. Cyanazine was an emulsifi- able concentrate.

Because of very little slope and the high permeability no runoff occurred on the plots. The plots were located in an Evesboro loamy sand soil (mesic, coated, typic quartzipssament). Soil properties are presented in Table 1. A total of 5 samples were taken in 1984 before the experiments began from the plot area at 30-cm intervals to a depth of 150 cm. The corn was irrigated with solid set sprinkler irrigation on a 9.2-m spacing.

The plots were used in the 1970's for a poultry manure experiment so monitoring wells had been installed for that experiment. For the pesticide experiment, three monitoring wells were sampled in each plot. The monitoring wells were installed to a depth of 3.1 m and constructed from 2.5-cm galvanized steel pipe. The well points were constructed from stainless steel. All monitoring wells in the plots were installed by the driving method. Five background wells were installed outside the plots. These wells were con-


structed from 3.25-cm polyvinylchloride (PVC) pipe with a screen length of 1.5 m and a slot size of 0.25 ram. The background wells ranged in depth from 4.6 to 15.3 m and were installed by the auger-drilling method.

All monitoring wells were sampled monthly with a battery-operated peristaltic pump. The wells were pumped dry and allowed to recharge before a sample was collected. All samples were frozen until they were analyzed. Soil samples were taken 4 or 5 times in 1985 and 1986 to a depth of 150cm at 30-cm intervals with a 76-mm bucket auger. Five individual cores were taken from each plot and composited for analysis. All soil and water samples were analyzed by the New York Agricultural Experiment Station Pesticide Residue Laboratory at Geneva, New York, U.S.A.

Air temperature, rainfall, pan evaporation, relative humidity, wind speed, solar radiation and soil temperature data were collected with an automated weather station at the Research and Education Center. Soil- water content data were collected during the growing season using a neutron probe.

Aquifer characteristics

The principal aquifer system beneath the plots consists of the sands of the Columbia Formation. The aquifer varies in thickness from 27 to 61 m. Depth to the water table generally ranges from 1.5 to 3.1 m. The transmissivity is

994 m 2 day 1. The annual average recharge ranges from 305 to 381 mm (Sundstrom and Pickett, 1969).

Analytical methods

Water samples were thawed at room temperature, then vacuum filtered through glass fiber filters (Gelman ® AE, 0.45-#m pore size). The residue was retained for analysis of attached pesticides. Cls Sep-Pak®'s (Waters Associ- ates, Milford, Massachusetts, U.S.A.) were placed on inverted Luer tips of a vacuum manifold and activated with 5 ml HPLC (high-performance liquid chromatographic) -grade methanol followed by two 5-ml H20 rinses. Syringe barrels (30 ml) were fitted to the upper end of the Sep-Pak®'s and 100 ml of the filtered sample were drawn through at a rate of 3-4 ml min -1. Alter loading was complete, Sep-Pak'~>s were dried by air aspiration for 5 min, then placed in -20°C storage.

Soil samples were thawed then air dried and ground (#20 mesh) and mixed. Subsamples (50 g) were extracted for 30 rain on a mechanical shaker in 100 ml of 90% MeOH. A 50-ml aliquot of each suspension was poured into

78 W.F. R I T T E R E T A L .

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Fig. 1. Rainfall and irrigation for 1984.

a centrifuge tube. After centrifuging for 8 rain at 2400 rpm and a force of 8g, 20 ml of supernate liquid were removed and diluted with 200 ml of H20. This solution was then loaded onto a C18 Sep-Pak ® as described earlier, then placed in -20°C storage.

After thawing at room temperature, the samples were eluted from the Sep-Pak ® into a glass stoppered centrifuge tube with 2 ml of HPLC-grade benzene. The benzene was removed by evaporation in a warm water bath under a gentle stream of high-purity N2 gas. Dry residues were redissolved in 1 ml of chlorothalonil-spiked (0.1 #g m1-1) HPLC-grade benzene.

Capillary chromatographic analyses were performed using either Tracor ® Model 365 or 540 gas chromatographs equipped with 63Ni electron capture detectors. Splitless injections of 1 #1 were made on bonded phase (SGE ®, SE- 54) 25-m columns (0.22-mm I.D.; 0.25-m phase thickness) using He carrier gas at 32-35 cm s 1 with N2 as the column and detector makeup gas. Tempera- ture programming involved injection with a 3-min hold at 130°C, 7°C min -1 to 210°C and 7-min hold to 2500C, and final 5-min hold. The minimum detection limit using these methods for water samples and soil samples was 1 ppb for atrazine, simazine, cyanazine and metolachlor, and 0.1 ppb for alachlor.

Soil particle size was analyzed by the hydrometer method and cation- exchange capacity (CEC) by the ammonium acetate method. Soil organic matter was analyzed by the Walkley-Black wet combustion method (ASA, 1982). The hydraulic conductivity was measured in the laboratory on undis- turbed soil cores by the constant-head permeameter method (ASA, 1986).

C O N T A M I N A T I O N OF G R O U N D W A T E R BY T R I A Z I N E S , M E T O L A C H L O R A N D A L A C H L O R

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R E S U L T S A N D D I S C U S S I O N

Pesticide recovery

Recovery efficiencies for spiked water samples for atrazine, simazine, cyanazine, alachlor and metolachlor averaged 92%, 86%, 90%, 95% and 99%, respectively. None of the data reported in the paper are corrected for extraction efficiency. Water samples were spiked with 10 ppb of herbicide. Forty-eight soil samples were analyzed three times over a period of a year to demonstrate the reproducibility of the analytical methods and to obtain an idea of the effectiveness of the freezer storage conditions. There was good reproducibility of the samples for all five herbicides and it appears very little degradation occurred while the samples were frozen. For the majority of the 48 samples, the reproducibility was within ±10%.

Rainfall and irrigation

Rainfall and irrigation data are presented in Figs. 1-3. In 1984 and 1986 considerable rainfall occurred shortly after the herbicides were applied. Spe- cifically, in 1984, 67 mm occurred before the first sampling data, which was 24 days after the herbicides were applied. A total of 47 mm of rainfall occurred

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within 12 days after the herbicides were applied. There was very little irrigation water applied in 1984.

In 1985, April was extremely dry with only 9 mm of rainfall, so soil-water content was low when the herbicides were applied. No rainfall occurred until 10 days after the herbicides were applied when 17 mm was received. It was 25 days after the herbicides were applied before over 25 mm of rainfall occurred, which reduced the chances for rapid leaching.

In 1986, May was relatively dry with only 25 mm of rainfall. The herbicides were not applied until May 23. Rainfall did not occur until the third week following application when 65 mm of rainfall occurred.

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Fig. 4. Alachlor concentrations in groundwater for 1984.

iiiiiiiiii

1986

. . . . . . . . . . . . . . . Plot C

' ' ' ' 1

CONTAMINATION OF GROUNDWATER BY TRIAZINES, METOLACHLOR AND ALACHLOR 8 |

Alachlor

The groundwater data for alachlor are summarized in Fig. 4. Alachlor was detected in the groundwater in all 9 monitoring wells 24 days after it was applied with concentrations ranging from 0.2 to 2 ppb. Fifty-nine days after application, the highest concentration was 15 ppb. All of the alachlor plots were in no-tillage. Alachlor was not used in 1985 or 1986.

The concentrations of alachlor in the groundwater gradually decreased and after 159 days no detectable concentrations of alachlor were found. Alachlor was detected again in the groundwater 180 days after application at concentrations ranging from < 0.1 to 1.0 ppb. Concentrations 216 days after it was applied ranged from < 0.1 to 3.0 ppb. Alachlor has a short half-life and over 90% will dissipate in 40-70 days (Stewart et al., 1975) so you would not expect to detect it in the groundwater 180 days after it was applied. Alachlor may have been leached to the subsoil near the water table shortly after it was applied and did not degrade rapidly in the subsoil. Pothuluri et al. (1990) found the half-life for alachlor in the surface layer of a Coastal Plain soil was 23 days under aerobic conditions but had a half-life of 100 and 144 days in the subsoil of the vadose zone. Alachlor was also detected in several of the background wells located outside of the plots in the direction of groundwater flow from the plots 200 days after it was applied at concentrations ranging from 0.1 to 0.2 ppb. Based upon the slope of the water table and the transmissivity of the aquifer, water under the plots probably moves at a rate of 0.2 0.3 m day -1 (Sundstrom and Pickett, 1969). Given the distance to the background monitoring wells from the plots, alachlor that was leached to the groundwater shortly after it was applied could have moved to these wells within 130-150 days. No alachlor was detected in the background wells or wells located within the plots 263 days after it was applied.

The concentration decreased to below detectable levels because of a dilution effect or because the alachlor degraded in the groundwater. Probably the alachlor was diluted below detectable levels because of the high transmissivity of the aquifer. Pothuluri et al. (1990) found the half-life of alachlor in aquifer material was 320-324 days under aerobic conditions and 337 553 days under anaerobic conditions. Probably very little degradation occurred once the alachlor reached the aquifer. The rapid movement of the alachlor to the groundwater shortly after it was applied was probably by macropore flow. A dye study on the no-tillage plot indicated rapid movement through root holes and worm holes. A food coloring dye was detected in the groundwater at a depth of 2.2 m, 6 hr after the dye was applied at the surface and after ~ 7.6 cm of water infiltrated into the soil profile. Further evidence of preferential flow was obtained in an experiment to quantify the variability of flow paths in the vadose zone on the plots in 1988 under no-tillage and conventional tillage.

82 W.F. R I T T E R ET AL.

Bromide tracer and an organic dye were applied at a slow rate on the soil surface and collected at a depth of 1 m using 4-pan lysimeters. The resultant flow occurred through fingers in an unstable flow pattern (Hagerman et al., 1988). Other researchers have also found pesticides will leach rapidly to the groundwater if large rainfall events occur shortly after they are applied. Tru- man and Leonard (1991) found through 50 years of simulation with GLEAMS © that conditions existed where pesticide losses by percolation for short half-life pesticides varied significant from long-term means. Large rainfall events occurring within one pesticide half-life after pesticide application were respon- sible for extremes in simulated pesticide losses by percolation, especially for short half-life pesticides (< 10 days). Isensee et al. (1990) found that rainfall timing relative to pesticide application was critically important to pesticide leaching. They found a prolonged rain (48 mm) immediately after application caused cyanazine and atrazine concentrations of ~ 200 ppb in the shallow groundwater on a Hatboro silt loam soil (fine-loamy, mixed, nonacid, mesic - - Typic Fluvaquent).

The amount of water required to displace pesticides to the water-table aquifer can be calculated using the model by Rao et al. (1976). The amount of water, I (cm), needed to piston displace a solute from the surface to the groundwater is:

I = DOFc R (1)

where D is the depth of pesticide movement (cm); OFC is the average soil water content at field capacity; and R is the solute retention factor. R is defined as:

R = 1 + (Pb + Kd/OFc) (2)

where Pb is the soil bulk density (g cm-3); and Kd is the soluble adsorption coefficient.

Using Kd-values from the literature the amount of water required to move alachlor, atrazine, simazine and metolachlor a depth of 200 cm in the plots in the experiment would be 190, 120, 150 and 110 cm, respectively (Wilkerson and Kim, 1986).

Atrazine

The groundwater data for atrazine are summarized in Fig. 5. Plots A (1.12 kg ha-l), B (2.24 kg ha -1) and C (4.48 kg ha -l) were in no-tillage (NT), and plot D (2.24 kg ha -1) was in conventional tillage (CT). In 1984, atrazine was detected in 5 out of the 9 monitoring wells 24 days after it was applied. After 59 days, the atrazine concentration in one of the monitoring wells was 54.0 ppb on the plot where atrazine was applied at a rate of 4.48 kg ha -1.

Higher atrazine concentrations were detected in the groundwater on the


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1.12- and 4.48-kg-ha-I plots than on the plot where the atrazine application rate was 2.24 kg ha 1. After reaching a peak 59 days after the atrazine was applied, the atrazine concentrations slowly decreased in the groundwater and no atrazine was detected 200 days after application, except for one well that had an atrazine concentration of 2.0 ppb, 305 days after application. In 1985, atrazine was not detected in the groundwater until 183 days after application. Soil-water content was much lower in 1985 than 1984 when the atrazine was applied and during the first 24 days following application. In 1984, 47 mm of rainfall occurred within 12 days after the atrazine was applied and in 1985 only 20 mm of rainfall occurred the first 24 days. Fig. 1 indicates 135 mm of rainfall occurred the last week of May in 1984, which probably caused the high atrazine concentrations in the groundwater 59 days after the atrazine was applied. In 1985, > 40 mm Of rainfall occurred during each of the last two weeks in May which leached some of the atrazine below the top 15 cm as indicated by the soil samples. Soil samples were taken 17, 63, 92 and 171 days after application in 1985. On the no-tillage plot 17 days after application, where 2.28 kg ha 1 of atrazine was applied, atrazine was found at the 15- 30-, 60-90- and 120-150-cm depths at concentrations of 5.0, 5.0 and 13.0 ppb, respectively. On the conventional tillage plot, atrazine was found at the 15- 150-cm depth at concentrations ranging from 5.0 to 28.0 ppb. Sixty-three days after application atrazine was found at all depth intervals from 15 to 150 cm on the 2.24-kg-ha -1 no-till plot at concentrations ranged from 1.0 to 6.0 ppb. On the conventional tillage plot concentrations ranged from < 1.0 to 10.0 ppb at the 15 150-cm depth. Based upon soil sampling, it appears, the atrazine moved slowly through the soil profile in 1985 to the groundwater and macropore flow was not a factor. The soil data also indicated atrazine degraded very slowly in the subsoil in 1985. The average atrazine concentration on the 2.24-

84 W.F. R I T T E R ET AL.

kg-ha -1 no-tillage plot at the 30-150-cm depth was 5.0 ppb, 163 days following application and was 3.5 ppb, 171 days after application. Degradation rates under conventional tillage were similar.

A first-order degradation rate obtained from a linear regression analysis of the atrazine soil data for the 0-30-cm depth for 1985 gave a half-life of 60 days for the no-tillage and 84 days for the conventional tillage. These values will be lower than those reported for laboratory half-lives because the field derived degradation half-life values will include additional pathways such as leaching and plant uptake (Hornsby et al., 1990). Zacharias et al. (1991) obtained field half-life values for atrazine of 101 and 147 days for no-tillage and conventional tillage, respectively. They include the degradation rate from 0- to 150-cm depth in their half-life calculations. Probably atrazine degrades more slowly in the subsoil so their half-life values should be larger since they had considerable leaching below the 15-cm depth.

In 1986 atrazine was detected in the groundwater during the winter and early spring months and shortly after it was applied in 1986. Some of the atrazine detected in the groundwater for the samples taken 24 days after it was applied in 1986 may have been from the 1985 atrazine application since atrazine was detected in late April before planting in nearly all of the monitoring wells. Atrazine concentrations were higher in the groundwater on the conventional tillage plot than the no-tillage plots for the first two samplings after atrazine was applied in 1986. Twenty-four days after the atrazine was applied the average concentration in the groundwater under conventional tillage was 10.7 ppb while the concentrations in the 9 wells in the no-tillage plots ranged from < 1.0 to 4.0 ppb. Soil-water content at the time the herbicides were applied in 1986 was greater than in 1985 but was lower than in 1984. During the third week following the herbicide application, 65 mm of rainfall occurred. This rainfall may have caused some leaching of atrazine to the groundwater by macropore flow, since the dye studies as discussed in the alachlor section indicate macropore flow conditions can occur. Rainfall pat- terns in 1986 were similar to 1984 shortly after application but initial soil- water content was lower in 1986. Soil samples taken in 1986, 17 days after the atrazine was applied, indicated atrazine had moved through the top 150 cm of the soil profile on all plots. Concentrations ranged from 3.0 to 17.0 ppb at the 30 150-cm depth on the 2.24-kg-ha -1 no-tillage plot and from 3 to 15 ppb at the 30-150-cm depth on the conventional tillage plot (Fig. 6). A total of 0.085 kg ha-~ of atrazine was recovered in the 30-150-cm depth in the 2.24-kg-ha-1 no-tillage plot and 0.073 kg ha -1 was recovered in the conventional tillage plot. There was no significant difference in the atrazine concentrations by the t-test at the 5% level between conventional tillage and no-tillage. Forty-eight days after the atrazine was applied the atrazine concentrations at the 30-150- cm depth decreased to < 1.0 ppb in both the no-tillage and conventional

CONTAMINATION OF G R O U N D W A T E R BY TRIAZINES, METOLACHLOR AND ALACHLOR 8 5

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tillage treatments. The atrazine was either degraded or was leached below the 150-cm depth. It was probably leached to greater depths since atrazine was detected in the groundwater under both conventional tillage and no-tillage 47 days after application.

The soil sampling data for 1986 for the surface layer (0-30 cm) gave half- lifes of 151 days for the conventional tillage, and 57 and 62 days for the 4.48- and 2.24-kg-ha -1 application rate no-tillage plots, respectively. The soil data for the other no-tillage plot had a low regression coefficient, so no half-life was estimated. The no-tillage half-life values were similar to 1985. The conventional tillage half-life was greater in 1986.

Atrazine was detected in several of the background monitoring wells in 1986 but not in 1985 or 1984. Concentrations ranged from 1.0 to 3.0 ppb. It was detected in the background wells that were located below the plots in the direction of groundwater flow more frequently. Atrazine detected in the other background wells may have come from other fields located on the research center.

There was no clear difference between atrazine application rate and atrazine concentration in the groundwater. Atrazine was detected more frequently in the groundwater of the 4.48-kg-ha -1 application rate. In 1984, atrazine concentrations were higher in the groundwater of the 4.48-kg-ha ] plot but were similar for the 1.12- and 2.24-kg-ha -1 application rates. In 1986, atrazine concentrations were greater in the soil profile at the 30 150-cm depth

86 W . F . R I T T E R E T A L .

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~ ' ~ , / " "?'~" ~ - : ~ - ' X , ~ ~- ' -~- . . . . . - " '4 - J ' ~ , , , , , , , , , , , i , , , , , , , , , , , i , , , , , , , , , ~ , 1

1 9 8 4 1 9 8 5 1 9 8 6

. . . . . . . . . . . . . . . . . . . . Plot A . . . . . . . . . . Plot C

Plol B . . . . . . . . . . . Plot D

Fig. 7. Simazine concentrations in groundwater for 1985 and 1986.

for the 4.48-kg-ha -I application rate than the 2.24-kg-ha -1 application rate, and the 2.24-kg-ha -1 application rate concentrations were greater than those of the 1.12-kg-ha -1 rate.

Simazine

Simazine was detected in the groundwater on all plots in 1985 and 1986 as indicated by Fig. 7. Although atrazine was not detected in the groundwater until 183 days following application, low concentrations of simazine were detected in several of the wells 39 days after it was applied. Concentrations ranged from < 1.0 to 2.0 ppb. The highest simazine concentrations occurred during the winter of 1986. Simazine concentrations were higher in the groundwater on the no-tillage plots A and B than the conventional tillage plot (D) or plot C. Simazine was detected very infrequently in the groundwater on plot C (no-tillage) which received the same treatment as plots B and C. Simazine movement to the groundwater in 1985 showed the same general pattern as atrazine movement with the highest concentrations occurring during the winter of 1986. In 1986, simazine was detected in the groundwater on plots A, B and D, 24 and 47 days after it was applied. Forty-seven days after it was applied, it was detected in 5 out of 12 monitoring wells. Concentrations ranged from < 1.0 to 10.0 ppb. Some of the simazine in the groundwater may have been from the 1985 application, since simazine was detected in the groundwater in April before the 1986 application in 6 out of 12 wells. Concentrations for the April sampling ranged from < 1.0 to 27.0 ppb. Sima- zine concentrations increased in the groundwater on plots A and C during the


Soncentrat,on - (ppb)

i

8

"5

4 5 ~

6 0 -

7 5 ~

9 0 -

105

120 -

135

150

0 20 4,0 60 88 I I I I I I I I

, /C"

/ i / ,

/

/ '

46

100 <20 I 1 I I

E> ~ 17 Days NT

+ ~ 17 Oays CT

t ~ - - . - - ~ 48 Days NT

---~ 4,8 Days CT

Fig. 8. Simazine concentrations in soil in 1986.

fall of 1986. In 1985 and 1986, simazine concentrations were above the EPA (1989) health advisory of 4 ppb for 20 samples.

In 1985, simazine was detected in the soil profile from 0 to 150 cm 17 days after it was applied on the conventional tillage and no-tillage. Concentrations on the conventional tillage plot ranged from 5.0 to 16.0 ppb at the 30-150-cm depth and ranged from < 1.0 to 10 ppb on the no-tillage plots. Simazine was also detected at the 30-150-cm depth in the soil profile shortly after it was applied in 1986 on both the conventional tillage plot and no-tillage plots (Fig. 8). Forty-eight days after application, very little simazine was detected in the soil profile below the 30-cm depth on all four plots. There was no significant difference at the 5% level by the t-test of simazine concentrations in the soil under conventional tillage and no-tillage.

The first-order degradation rates obtained from a linear regression analysis of the soil data for each plot indicated the half-life for simazine for no- tillage varied from 45 to 104 days in 1985 and 1986. The average half-life for no-tillage was 55 days. The average half-life for conventional tillage for the two years was 35 days. The California Department of Food and Agriculture lists simazine as a leacher with a half-life of 55 days (Wilkerson and Kim, 1986).

Simazine was detected in two of the background wells. Concentrations ranged from < 1.0 to 2.0 ppb. One of the background wells where simazine was detected was above the plots and the other well was below the plots in the direction of groundwater flow.

8 8 W.F. RITTER ET AL.

Concentration - (ppb)

0 20 40 60 80 100 120

O~,j~ i ~ ' ~ ~ J ' J ' ~ '

15 "/* '-+ ................... s--- ,+. ......

4 5 f ~ , ....... 602~' / - u---~ 17 Days - NT

v

~_ 75 + .... -- 17 Days - CT

1 o 9 0 . . l i ~, a /.8 Days - NT

! 0 5 ~ i ,~ . . . . . -e 48 Days - CT

120

!35 ~

150

Fig. 9. Metolachlor concentrations in soil in 1986.

Metolachlor

Metolachlor was not detected in the groundwater as frequently as atrazine or simazine. Thirty-nine days after metolachlor was applied in 1985, it was detected in two of the three monitoring wells in the conventional tillage plot but was not detected in any of the no-tillage monitoring wells. The concentrations ranged from < 1.0 to 3.0 ppb. One-hundred and eighty-three days after metolachlor was applied, it was detected in the groundwater beneath all plots. Metolachlor movement followed the same pattern as atrazine and simazine movement in 1985. In 1986, metolachlor was only detected 10 times in the groundwater out of a total of 74 samples. None of the samples had concentrations above the EPA (1989) health advisory of 100 ppb. Meto- lachlor was detected a total of 10 times in the background wells in 1985 and 1986. Concentrations ranged from 1.0 to 3.0 ppb. Some of the metolachlor in the background wells may have originated from other plots on the research center.

Metolachlor concentrations in the 0 150-cm depth of the soil profile for plot B (no-tillage) and plot D (conventional tillage) 17 and 48 days after it was applied in 1986 are shown in Fig. 9. Metolachlor concentrations were higher in the conventional tillage plot at all depths then the no-tillage plot 17 days after the metolachlor was applied. Metolachlor concentrations in the soil profile for the other two no-tillage plots (A and C) were similar to plot B. No metolachlor was detected in the soil profile from 0 to 150 cm in March

CONTAMINATION OF GROUNDWATER BY TR1AZINES, METOLACHLOR AND ALACHLOR 89

1986 before the herbicide was applied. The metolachlor concentration in the 0-30-cm depth was much greater on the conventional tillage plot than the no-tillage plot. Probably some of the herbicide was intercepted by the corn residue on the no-tillage plots. The concentration pattern was similar for the other herbicides on the no-tillage and conventional tillage plots.

The average half-life for metolachlor for 1985 and 1986 for no-tillage was 48 days and for conventional tillage was 45 days. The California Department of Food and Agriculture classifies metolachlor as a leacher with a half-life of 44 days (Wilkerson and Kim, 1986).

Cyanazine

The herbicide was not detected in any of the monitoring wells in 1985 or 1986 before the 1986 application in May. Cyanazine was detected in one of the monitoring wells in the conventional treatment 24 days after it was applied in 1986. The concentration was 29.0 ppb. Twenty-three days later the concentration decreased to 4.0 ppb. Cyanazine was not detected in any other monitoring wells in 1986. Cyanazine was detected in the background wells in 1984, but not in 1985 or 1986. The concentrations in 1984 ranged from < 1.0 to 1.0 ppb.

The soil data indicated cyanazine moved below the root zone in the conventional tillage plot in 1985 shortly after it was applied. Concentrations at the 30 150-cm depth ranged from 2.0 to 8.0 ppb, 17 days after it was applied. Concentrations on the no-tillage plots ranged from < 1.0 to 1.0ppb. In 1986, cyanazine moved through the profile in both the no-tillage and conventional tillage treatments shortly after it was applied. Concentra- tions in the soil profile for plots B and D are presented in Fig. 10. On the conventional tillage plot, concentrations ranged from 1.0 to 4.0 ppb at the 30- 150-cm depth 17 days after the cyanazine was applied. Concentrations on the no-tillage plots ranged from < 1.0 to 4.0 ppb at the 30-150-cm depth. Kanwar (1991) also found cyanazine moved rapidly to shallow groundwater, if heavy rainfall occurred shortly after it was applied. Cyanazine concentrations in the water were above 4 ppb 40 days (June 13) after it was applied but decreased to below 1 ppb in July.

SUMMARY AND CONCLUSIONS

The movement of atrazine, simazine, cyanazine, metolachlor and alachlor were studied in continuous irrigated corn in an Evesboro loamy sand

90 w.v. RITTER ET AL.

r

[ :3

0

15

30

45

60

75

90

105

120

135

150

Concentration (ppb)

2O 40 I I I I

i ,.,./,.,. . /

/ . ,./'

60 8O 100 120 I I I I I I I I

u - - - ~ 17 Days - NT

+ ......... + 17 Days - CT

~ 48 Days - NT

. . . . --~ 48 Days - CT

Fig. 10. Cyanazine concentrat ions in soil in 1986.

soil. Both no-tillage and conventional tillage treatments were used. Atrazine was applied pre-emergence to no-tillage plots at rates of 1.12, 2.24 and 4.48 kg ha 1 from 1984 to 1986, and to a conventional tillage plot at a rate of 2.24 kg ha -I in 1985 and 1986. Alachlor was applied pre-emergence to all plots in 1984 at a rate of 2.24 kg ha - l , and cyanazine, simazine and metolachlor were applied to all plots in 1985 and 1986 at rates of 1.68, 2.24 and 1.68 kg ha -1, respectively.

Atrazine and simazine were detected in the groundwater more frequently than cyanazine and metolachlor. The frequency of herbicide detections was directly related to the half-life of the herbicide. There was no large difference in pesticide transport between conventional tillage and no-tillage. There was no significant difference between the two tillage systems at the 5% level by the t-test.

The research indicates pesticides may move to shallow groundwater by macropore flow in the sandy soils of the U.S. Mid-Atlantic states if large amounts of rainfall occurs shortly after they are applied. The pesticides will probably decrease to non-detectable concentrations in the shallow groundwater with time because of dilution. No pesticides of the type used in this research were detected in municipal or private wells in Sussex County, Dela- ware, during the EPA (1990) pesticide survey. The frequency of the four herbicides detected in the groundwater was directly related to the soil half- life of the herbicide.

C O N T A M I N A T I O N O F G R O U N D W A T E R BY T R I A Z I N E S , M E T O L A C H L O R A N D A L A C H L O R 91

REFERENCES

ASA (American Society of Agronomy), 1982. Methods of Soil Analysis, Part 2. Chemical and Microbiological Properties, by A.L. Page, R.H. Miller and D.R. Keeney (Editors), Am. Soc. Agron., Madison, WI, 2nd ed., 1159 pp.

ASA (American Society of Agronomy), 1986. Methods of Soil Analysis, Part 1. Physical and Mineralogical Methods, by A. Klute (Editor), Am. Soc. Agron., Madison, WI, 2rid ed., 1188

PP. Brinsfield, R., Staver, K. and Magette, W., 1987. Impact of tillage practices on pesticide

leaching in Coastal Plain soils. Am. Soc. Agric. Eng., St. Joseph, MI, Pap. No. 87-2631, 20 pp.

DDA (Delaware Department of Agriculture), 1991. Delaware Agri Facts AF-10-91, May 31, 1991. Del. Dep. Agric., Dover, DE, 5 pp.

Dillaha, T., Mostaghimi, S., Reneau, R., McClellan, P. and Shanholtz, V., 1987. Subsurface transport of agricultural chemicals in the Nomine Creek watershed. Am. Soc. Agric. Eng., St. Joseph, MI. Pap. No. 87-2629, 8 pp.

EPA (Environmental Protection Agency), 1988. Pesticides in ground water data base 1988 interim report. Off. Pest. Prog., U.S. Environ. Prot. Agency, Washington, DC, 71 pp.

EPA (Environmental Protection Agency), 1989. Health advisory summaries. Environ. Prot. Agency Off. Water, U.S. Environ. Prot. Agency, Washington, DC, 110 pp.

EPA (Environmental Protection Agency), 1990. National pesticide survey state sampling results. Off. Pest. Toxic Substances, U.S. Environ. Prot. Agency, Washington, DC, 22 pp.

Hagerman, J.R., Pickering, N.B., Ritter, W.F. and Steenhuis, T.S., 1988. In situ measurement of preferential flow. Proc. Am. Soc. Civ. Eng. 1989 Natl. Water Conf., July 17 20, 1989, Newark, DE, pp. 116 126.

Hallberg, G., 1985. Agricultural chemicals and ground water in Iowa: Status report 1985. Coop. Extens. Serv., Iowa State Univ., Ames, IA, Circ. CE-2158q, 21 pp.

Holden, P., 1986. Pesticides and Ground-Water Quality: Issues and Problems in Four States. National Academic Press, New York, NY, 127 pp.

Hornsby, A.G., Rao, P.S.C. and Jones, R.J., 1990. Fate of aldicarb in the unsaturated zone beneath a citrus grove. Water Resour. Res., 26:2287 2302.

Isensee, A.R., Nash, R.G. and Helling, C.S., 1990. Effect of conventional vs. no-tillage on pesticide leaching to shallow ground water. J. Environ. Qual., 19:434 440.

Junk, G., Spalding, R. and Richard, J., 1980. Areal, vertical and temporal differences in ground water chemistry, II. Organic constituents. J. Environ. Qual., 9:479 482.

Kanwar, R., 1991. Preferential movement of nitrate and herbicides to shallow ground water as affected by tillage and crop rotation. In: T.J. Gish and A. Shirmohammadi (Editors), Proceedings of National Symposium on Preferential Flow, December 16 17, 1991, Chi- cago, IL. Am. Soc. Agric. Eng., St. Joseph, MI, pp. 328 337.

Parsons, D. and Witt, J., 1988. Pesticides in ground water in the United States of America: A report of a 1988 survey of State Lead agencies. Oreg. State Univ., Agri. Chem. Dep., Corvallis, OR, 16 pp.

Pionke, H., Glotfelty, D., Lucas, A. and Urban, J., 1988. Pesticide contamination of ground water in the Manhantango Creek watershed. J. Environ. Qual., 17:76 84.

Pothuluri, J.V., Moorman, T.B., Obenhuber, D.C. and Wauchope, R.D., 1990. Aerobic and anaerobic degradation of alachlor in samples from a surface-to-groundwater profile. J. Environ. Qual., 19:525 530.

Rao, P.S.C., Davidson, J.M. and Hammond, L.C., 1976. Estimation of nonreactive and reactive solute front locations in soils. In: W.F. Fuller (Editor), Residue Management by

92 w F. KITTER ET AL.

Land Disposal. U.S. Environ. Prot. Agency, Washington, DC, EPA-600/9-76-015, pp. 235- 242.

Southwick, L., Willis, G., Bengston, R. and Lormand, T., 1988. Atrazine in subsurface drain water in southern Louisiana. Proc. Am. Soc. Civ. Eng., Irrig. Drain. Div. Conf., Lincoln, NE, pp. 580-586.

Spalding, R., Exner, M., Sullivan, J. and Lyon, P., 1979. Chemical seepage from a tailwater recovery pit to adjacent ground water. J. Environ. Qual., 8:374 383.

Spalding, R., Junk, G. and Richard, J., 1980. Pesticides in ground water beneath irrigated farmland in Nebraska. J. Pest. Monit., 14:70-73.

Steenhuis, T., Paulsen, R., Richard, T., Staubitz, W., Andreini, M. and Surface, J., 1988. Pesticide and nitrate movement under conservation and conventional tilled plots. Proc. Am. Soc. Civ. Eng., Irrig. Drain. Div. Conf., Lincoln, NB, pp. 587-595.

Stewart, B., Woolhiser, D., Wischmeir, W., Caro, J. and Frere, M., 1975. Control of water pollution from cropland, Vol. 1. A manual for guideline development. Agric. Res. Serv., U.S. Dep. Agric., Washington, DC, Rep. No. ARS-H-5-1, 109 pp.

Sundstrom, R.W. and Pickett, T.E., 1969. The availability of ground water in eastern Sussex County. Water Resour. Cent., Univ. of Delaware, Newark, DE, 123 pp.

Truman, C.C. and Leonard, R.A., 1991. Effects of pesticide, soil and rainfall characteristics on potential pesticide loss by percolation - - A GLEAMS simulation, Trans. A.S.A.E. (Am. Soc. Agric. Eng.), 34: 2461-2468.

Wilkerson, M.R. and Kim, K.D., 1986. The Pesticide Contamination Act: Setting specific numerical values. Calif. Dep. Agric. Food, Environ, Monit. Pest. Manage., Sacramento, CA, 21 pp.

Zacharias, S., Heatwole, C.D., Mostaghimi, S. and Dillaha, T.A., 1991. Tillage effects on fate and transport of pesticides in a Coastal Plain soil, II. Leaching. Am. Soc. Agric. Eng., St. Joseph, MI, Pap. No. 91-2544, 19 pp.

contamination of groundwater by triazines, metolachlor and alachlor

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