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Groundwater residues of atrazine, alachlor, and cyanazine under no-tillage practices
Chemosphere, Vol.17, No.i, Printed in Great Britain
GROUNDWATER
pp
165-174,
1988
0045-6535/88 $ 3 . 0 0 + .OO Pergamon Journals Ltd.
RESIDUES OF ATRAZINE, UNDER NO-TILLAGE
ALACHLOR,
AND CYANAZINE
PRACTICES
Allan R. Isensee *I, Charles S. Helling I, Timothy J. Gish I, Philip C. Kearney l, C. Benjamin Coffman I, and Wuji Zhuang 2 Ipesticide (T.J.G.),
Degradation
of Agriculture,
Beltsville,
2Analytical Republic
Laboratory
and Weed Science Laboratory
(C.S.H., A.R.I., (C.B.C.),
and P.C.K.),
Agricultural
Hydrology Laboratory
Research Service, U.S. Department
MD 20705
Laboratory,
Chinese Academy of Agricultural
Sciences,
Beijing,
People's
of China.
ABSTRACT Groundwater from no-till corn plots treated with atrazine, alachlor, and cyanazine was analyzed for residues of these herbicides over a 3-year period. Detectable levels of atrazine, alachlor, and cyanazine were found in 75, 18, and 13% of the recovered samples, respectively. Maximum residue levels were 5.9, 3.6, and 1.0 ~g L-! for atrazine, cyanazine, and alachlor, respectively. Rapid vertical transport to the shallow unconfined groundwater (ca. | m depth), as well as substantial lateral subsurface flow, was indicated.
INTRODUCTION Contamination concern.
of well water supplies
A review in 1984 (2) indicated
in 18 states.
By 1985 these reported
in 23 states (3).
by leaching pesticides that 12 pesticides
cases increased
Some of the reports of groundwater
contamination
at sites where highly soluble pesticides
soils.
concern is that low concentrations
A greater
ditions.
Three corn production
methyl)acetanilide], cyanazine
in shallow aquifers
atrazine
herbicides,
are explainable
are applied
of less soluble
(and per-
to very permeable
but widely used pesti-
alachlor
[2-chloro-4-(ethylamino)-6-(isopropylamino)-_s-triazine],
in 5 states at residue
leaching was shown to be largely responsible
residues
for low-level
in groundwater.
165
in Nebraska (15). atrazine
and
fall into this
ranges of 0.3-3 Dg L -I (3).
pattern of atrazine has been tied to groundwater
con-
[2-chloro-2',6'-diethyl-_N-(methoxy-
[2-chloro-4-(cyano-l-methylethylamino)-6-ethylamino-~-triazine],
in groundwater
in groundwater
found in groundwater
under a wide range of edaphic and climatic
category since they are widely used and have been detected detected
had been detected
to 17 pesticides
haps predictable)
cides are being detected
has become a national
residues
Atrazine has been The leaching Direct downward detected
in
166
groundwater throughout
the irrigated corn production areas of the Platte River Valley.
Groundwater samples taken from 41 monitoring wells in this same area contained from 0.01-8.3 ~g L -| (]5). samples
In another Nebraska survey (8), atrazine was detected
in 64 water
from monitoring wells and surface water and ranged from <0.01-88 ~g L-I.
Areal and
vertical distribution of atrazine in the soil profile were closely associated with that of nitrate,
which was measured as an indicator of deep percolation.
Alachlor has been reported in groundwater samples in Maryland,
Iowa, Nebraska, and
Pennsylvania at residue levels of 0.1-10 ~g L -] and cyanazine in Iowa and Pennsylvania at 0.1-I Ng L -1 (3). (10).
Alachlor and cyanazine are both less persistent
in soil than atrazine
Soil thin-layer chromatography studies indicate that all three herbicides have similar
mobilities
(6).
A laboratory leaching study found no difference in the mobility of cyanazine
and atrazine in two soils (9). zine if differences
Thus, alachlor and cyanazine should leach as deeply as atra-
in persistence were not a factor.
The widespread adoption of conservation tillage practices has further intensified the concern over pesticide movement with a concomitant
to groundwater.
Conservation tillage reduces surface runoff,
increase in water infiltration
[paradoxically,
however,
from fields under conservation tillage may contain higher concentrations
the runoff water
of pesticides (|3)].
This greater water infiltration coupled with higher pesticide usage on conservation tillage (12) has raised questions about residue levels in groundwater.
The objective of this study was to measure the persistence and movement
to groundwater
of
atrazine, alachlor, and cyanazine for 3 years following annual application to no-till corn plots.
METHODS AND MATERIALS
Site Description.
No-till cornfield plots were established at the Beltsville Agricultural
Research Center in 1981.
The experimental
design was a randomized complete block with treat-
meats replicated four times; plots measured 3 . 1 X
7.5 m.
The original intent of this investi-
gation was to study the influence of continuous corn and continuous herbicide treatment on crop growth and weed flora in a conservation tillage system (1). rates, which were normal, have been described previously (7). established in plots representative atrazine + alachlor,
All herbicide
of combination treatments of atrazine + cyanazlne,
and cyanazine + alachlor,
plus several untreated plots (Fig.
well consisted of a 5.1-cm (~) aluminum tube installed to a depth of 1.1-1.4 m. were encountered at different depths between plots and became a depth-limiting installation of wells.
treatments and
In December 1983, wells were
L).
Each
Gravel layers factor for
Two off-site control wells, designated Control North (CN) and Control
South (CS), were installed
in May 1985 prior to treatment (Fig.
Teflon tube for sampling, and were kept sealed and capped.
|).
The wells contained a
167
Sampling and Analysis.
Groundwater samples were taken at pre- and post-treatment
during 1984, 1985, and 1986.
Wells were pumped dry I-3 days before sampling.
samples (300-500 mL) were vacuum filtered 50 mL dichloromethane.
follows:
then concentrated
Hexane (50 mL) was added,
and stored at 4°C.
extract was dried with anhydrous sodium sulfate, to ca. [ mL under reduced pressure (temperature
then evaporated
the extract was transferred
methanol in toluene.
into l-L separatory funnels and extracted 3X with
The dichloromethane
2-3 mL toluene was added, <50°C).
intervals
Groundwater
to ca. l mL.
to a mini Florisil
This elutate was concentrated
column,
Cleanup was carried out as then eluted off with 3% (v/v)
to ca. l mL for gas chromatographic
assay
The three herbicides were analyzed with a Hewlett Packard Model 5880A gas
chromatograph having a nitrogen-phosphorus
(N-P) detector and fitted with a fused silica
capillary column [12.5 m X 0.2 mm (i.d.)] coated with dimethyl silicone phase (HP 19091-60312). Limit of detection was 0.I ppb (~g L -l) for 1984 and 1986 samples and 0.5 ppb for the 1985 samples (which were done by another laboratory). (atrazine),
99% (alachlor), 99 + 9% (cyanazine)
12% (alachlor), and 87 + 9% (cyanazine)
Confirmation.
Extraction efficiencies were
for 1984 samples and 99 + 11% (atrazine), 89 +
for 1985 samples.
The identity of atrazine detected
use of gas chromatography-mass
I09 + 9%
spectrometry (GC-MS).
in groundwater samples was confirmed by An aliquot was injected into 30-m X
0.25-mm (i.d.) fused silica capillary column coated with SE-30 and temperature programmed 90-200°C at 5°C min -1.
The mass spectrometer,
from
a Finnigan 4021 with an Incos data system,
was operated in the electron impact mode, with an electron energy of 70 eV and a source temperature of 250°C.
Alachlor and cyanazine residue levels were too low for GC-MS confirmation.
RESULTS AND DISCUSSION
The plot location of the wells,
the elevation of the soil surface at each well head, the
elevation of the groundwater surface in each well, and the herbicide treatments are shown in Fig. I.
The average slope over the length of the plot (Well 37 to Well 24) is 0.9% while the
slope across the plot varies from 1.3 to 1.9% (Wells 37 to I, 43 to 7, and 48 to 24).
Thus,
during major rainfall events, runoff should flow diagonally in a southeast direction across the plot. vations.
The groundwater surface in the wells approximately parallels
the soil surface ele-
Vector analysis indicates that subsurface water flow is also toward the southeast.
Monthly precipitation (including irrigation) patterns are shown in Fig. 2. (87.6-94.7 cm).
for 1983-1986 at the no-till site
These varied widely, but the yearly totals for 1984-1986 were similar
Much more precipitation (137,3 cm) fell in 1983, well above the 15-year
average of II0 cm in Beltsville.
Atrazlne residues in groundwater samples taken in 1984-1986 are shown in Table
I.
The
range in atrazine residues for both the treated and untreated plots was 0-5.9 pg L -I (excluding the high values from Plot 48, 1984). values reported by Cohen et al. (3).
These concentrations
are in the same range of
The relatlvely high residue level in untreated plots
(some equal to or in excess of treated plots) is likely due to the small plot size and to
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J F M A M J J A S 0 N D J F M A M J J A 8 0 N DJ F M A M J J A 8 0 N DJF 1983
Figure 2.
1984
M A M J J A 8 0 N D
1985
1986
Monthly precipitation for 1983-1986 at the no-till site.
Irrigation,
in 1984
and 1986, is shown as dotted areas.
gravel at~ sand layers located subsurface water movement (untreated)
1.1-1.4 m below the surface.
Under these conditions,
from a treated to an untreated plot may occur.
is located adjacent and downgradient
to several atrazine-treated
and contained high residue levels during all three sampling years. tently higher concentration of atrazine in the downgradient
rapid
The well in Plot 29 plots (Fig.
In addition,
CS well water (compared
well) provides further evidence of subsurface water movement (Table I, Fig. I).
to the CN
There is some
evidence, especially in the 1985 data (Table I), that a plume of atrazine-contaminated water may quickly reach the CS well, peaking in concentration by ca. 70 days. atrazine-treated
I)
the consis-
ground-
Wells in
plots may have reached peak concentration at ca. 30 days, so sampling at 18
and 41 days would have missed such peaks.
The implication is that lateral subsurface mobility
in this shallow groundwater is very rapid, possibly 0.6 m day -I.
For 1985 and 1986,
the highest atrazine concentrations were obtained shortly after treat-
ment and then decreased with time. inadequate
(The residue pattern for 1984 was unclear due to an
number of samples after 1984 pesticide treatment).
The rapid transport
of small
amounts of atrazine to a depth of I m or more is probably associated with the occurrence and amount of rainfall and irrigation between treatment and sampling.
Macropores
have been shown to rapidly conduct water to depths of I m or more in well-
textured soils during major rainfall events (14), and we had suggested (4) that macropore water flow was associated with atrazine redistribution in soll following
the 1984 application.
As shown in Table II, there was a major rainfall event (3.2 cm) 2 and 6 days after treatment in 1986 and 1985, respectively.
Thus, it seems likely that the relatively high residues in
groundwater on Day 163 (1986) and Day 168 (1985) were transported down macropores by the 3.2-cm rainfalls (Table I). post-treatment
In contrast, many of the wells were either dry during the first
sampling in 1984 (Day 184) or contained small residues.
The rainfall
pattern
0.2
2.8
1.1
-
-
.
.
.
.
.
1.2
-
0.4
-
0.5
-
.
0.6~0_.3
0.8
0.8
-
.
-
1.8
0.6
-
0.3
-
-
-
-
. -
-
-
0
0
-
3.4
0.5
-
0.5
-
0
-
-
0
0
0.6+0.5 +0
-
0.9
0
0
149
+0
.
.
1.2
1.7
0.8
0.4
1.2
0.2
0.6~0_.5
0.6
.
.
0.9
219
0.6~.6 1.0~O.7 0.9~O.6 0.7_40.4 0.9+_1.8 1.5+1.7
.
.
1.2
11.9 e
0.2
.
-
184
0
.
.
-
17.2 e
.
0.4
158
1.1+1.3
0.5
0
1.8
3.8
0
0.7
0
1.6
1.1+1.0
1.3
0
0.7
1.4
1.4
0.7
0
168
1.9
0.8+1.0
0.6
0
0
2.5
0
1.1
0
CLimit of detection was 0.i ppb for 1984 and 1986 and 0.5 ppb for 1985. fAverage residue levels + standard deviation.
dNo sample,
0.4
0.I
0.2
2.0
1.1
1.6
0.7
-
1.8+1.8
1.0
0.8
|.2
0.6
2.0
5.9
1.4
163
0.340.5 0.940.7
0
0
0
0.7
0
0.9
0
I.I
0.1+0.3
0~
0
0
0
0
0
0
253
1.0+I.0
0.5
0.I
0.3
2.9
0.9
1.8
0.4
-
1.4+1.2
0.5
4.1
1.2
0.5
! .3
1.3
1.0
191
19~6 c
0.440.5
0.3
0.2
0.1
1.5
0.4
0.I
0.3
-
1.3+1.2
1.2
4.0
1.3
0.5
0.9
1.0
0.5
228
0.4+0.4
0.2
0
1.0
0.3
0.I
0.6
0.1
0.7
eValu~s not included in the average calculations.
0.3+0.1
0.1
-
0.4
0.1
0.2
0.4
0.3
322
bAtrazine was applied at the rate of 2.8 kg/ha.
0.8+0.9
0.4
0
0
2.4
0.6
1.3
0
1.3
0.2+0.4
0.9
0
0
0
0
0.7
0
214
days a
0.6+0.5
1.2
0
0.9
1.0
0
0.9
0
191
1985 e
Ssfnpling t i m e - J u l i a n
.
.
.
1.7
1.6
1.5
0.6
0.1
0.6
I.I
.
0.1
130
1984c
aplots were treated on Julian days 159, 150, and 160 for 1984, 1985, and 1986, respectively,
CS
-
~
43
~ m e
0.I
-
16
22
Untreated
.
67
0.5
0.8_+0.5 f 1.5+_1.2
1.4
+
24
~anaz~e
.
0.5
Machlor
1
7
+
48
Atr~me
-
95.0 e
42
Alachior
_d
37
+
34
0.6
33
#
Plot
Atrazine Residues (pg L-l) in Groundwater under No-till Corn Plots
Atrazine
Treatment b
Table I.
171
Table II.
Occurrence
and Amount (cm) of Rainfal~ after Herbicide Treatment
1984
1985
Day a
cm
Day
cm
Day
2 (161)
0.4
[ (151)
0.6
2 (162)
3.2
1.5
6 (156)
3.2
3 (163)
Sampling
16 (175)
0.5
9 (159)
0.8
22 (183)
2.0
31 (191)
Sampling
20 (179)
2.5 b
22 (181)
2.4
24 (183)
Sampling
between treatment
18 (168)
application
Sampling
(and Julian day).
these may not have been sufficient
Even the larger water inputs 20 and 22 days posttreatment the upper profile. combination
The decrease
of reduced
Four groundwater treatment
concentrations was confirmed
in atrazine
water flowing
apparently
of atrazine
(Table I).
by its mass spectrum.
in from adjacent
and root interception untreated
Samples
that reflected
from one plot, #48, contained
The identity of atrazine Major fragments
175 (6%),
(16%) and 58 (100%).
the molecular
contamination
(but declining) initial
for three samplings.
sampling,
into the borehole
and it is possible then.
to a combination
samplings.
Furthermore,
in comparable
precipitation
residues
mobility
should,
Laboratory
two months before
surface soil may have fallen
Perhaps
in groundwater
residue from such
the high residues were due
of an unusually
permeable
plot.
There
taken in winter and spring
during the last quarter of 1983 was much greater than
later periods (Fig. 2), so more leaching
unique to Plot 48, since we consistently and pesticide
This fragmenta-
atrazine.
show that the expected groundwater
of factors involving winter sampling
is evidence (5) for maximum herbicide
ion.
approximately
that atrazine-contamlnated
a source is much lower than the observed 95 ppb, however.
intensi-
in Plot 48, since they remained high
Wells were established
Our calculations
from Plot 48
relative
173 (17%), 71 (13%), 68
to that of a library spectrum of reference
is an unlikely cause for the high residues
unusually high
in groundwater
and their corresponding
The mass peak at m/z 215 represents
and possible
areas.
ties were m/z 217 (12%), 215 (51%), 202 (12%), 200 (70%),
tion pattern was identical
flow.
served only to recharge
samplings were made in 1984 (Julian days 34-158)
in 1983 or earlier.
events
to cause macropore
residues with time is probably caused by a
leaching due to surface dissipation
by uncontaminated
pesticide
blrrigation.
and sampling in 1984 (Table II) shows that three smaller rainfall
at 6- to 8-day intervals;
dilution
cm
I0 (169)
aDays after herbicide
occurred
1986
therefore,
encountered
is expected.
The soil factor may be
gravel at a shallow depth there; water
be relatively high.
72
Table
III.
Alachlor
Residues
(pg L -I)
in G r o u n d w a t e r
Sampling Treatment b
Plot
under N o - t i l l
time - Julian
C o r n Plots
daya
1985
1986 191
228
322
0.3 0 0.2 0.I
0 0 0 0
0 0 0 0
0 0 0 0
1.0 0 0 0
0.5 0.I 0
0 0 0
0.4 0 0.2
0 0 0 0
0 0 0
0 0 0
0 0 0.2
0 0 0
0.4 0.3 0.2
0 0
0 0 0 0
0 0 0 0
0.2 0.2 0.2 0.1
0 0.i 0.2 0
0 0.7 0 0
0 0 0 0
no.
149
168
191
214
253
Alachlor + Atrazine
33 37 42 48
-c -
0 0 0 0
0 -
0 0 0 0
0 0 0 0
Alachlor + Cyanazine
16 22 39 43
-
0 0 0 1.0
0 0
0 0 0 0
Atrazine + Cyanazine
1 7 24
-
0 0 0
0 0 0
Untreated
29 36 CN CS
-
0 0 0 0
-
163
a p l o t s were treated on J u l i a n dais 150 and 160 for 1985 and 1986, respectively. b A l a c h l o r was applied at 2.8 kg ha(1985) and in 1986 at 2.2 and 0.0 kg ha -I in Plots 16-43 and 33-48, respectively.
Table
IV,
Cyanazlne
Residues
(pg L -I)
in G r o u n d w a t e r
Sampling Treatment b
Plot 149
Cyanazine + Alachlor
16 22 39 43
-c 0 0
Cyanazine + Atrazine
1 7 24
Atrazine + Alachlor
33 37 42 48
Untreated
29 36 CN CS treated applied
168
C o r n Plots
time - J u l i a n day a
1985
no.
aplots w e r e b c y a n a z l n e was
under N o - t i l l
1986 191
228
322
191
214
253
163
3.4 0 0 3.6
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0
0 0 0.1
0.3 0 0
0 0 0 0.|
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0.I 0.2 0.2
0 0
0
0
0
0
0
0
0
0.1
0
-
0
0
0
0
0
0
0
0
0 0
0 0
0 0
0 0
0 0
0.1 0
0.1 0.1
0.7 0.2
0 0
0 0
0 0 0 0
0 0 0 0
0 0 0 0.7
0 0 0 0
0 0 0 0
0 0 0 0
0.2 0 0 0
0 0 0 0
on J u l i a n days 150 and 160 for at the rate of 2.2 kg ha -I.
1985 and
1986,
respectively.
173
Alachlor and cyanazine
residues
in groundwater
in Tables III and IV, respectively. 1986 than 1985, probably because 0.5 ppb in 1985. concentration
In general,
previously
Both herbicides
taken in 1985 and 1986 are shown
were detected much more frequently
more frequently
(1986, Table IV).
reported
The amounts we found were within the range
(3) for alachlor
(0.I-I0 ppb), and only two samples were
(0.I-I ppb).
same concentration
from both treated and untreated plots,
subsurface
water movement
(and little
to
and at slightly higher
above the range for cyanazine in samples
in
the lower limit of detection was 0.i ppb in 1986 compared
alachlor was detected
than was cyanazine
of concentrations
samples
Both herbicides
further degradation)
were found in approximately indicating
the
that
had occurred.
CONCLUSIONS
Shallow unconfined atrazine
(for 3 years),
groundwater
averaged
test of pesticide sis, discussed
groundwater alachlor,
under continuous
and cyanazine
only about 0.9 m, the plots were considered
leaching potential,
elsewhere
the groundwater
dissipation
analyses
transport
either herbicide
With a few exceptions,
the typical herbicide
concentrations
far lower than the "suggested or alachlor
(700 ppb) (II).
management
has specifically
comparative
investigation
0-0.3 ppb, and cyanazine health-advisory
application.
soils data in that alachlor and cyanazine
the odds of detecting
0.2-1.8 ppb, alachlor
when significant
during the first few weeks after pesticide
seem to support
severe
Soil core analy-
of atrazine
greatly reduced
atrazine
soil.
for
Because depth to
to be a relatively
at least for a medium textured
(4, 7) showed early vertical
rainfall events (ca. 2-3 cm) occurred However,
no-till corn plots was monitored
(each for 2 years) residue.
in this groundwater
0-0.2 ppb.
concentrations"
in groundwater.
were
These concentrations
reported for atrazine
are
(150 ppb)
We cannot judge from our present study whether the use of no-till altered pesticide
leaching and persistence
behavior,
but such a
is currently in progress at Beltsville.
ACKNOWLEDGMENTS
We thank the Shell Development and analyses assistance
Company, Modesto,
of the 1985 groundwater
samples.
in sample collection and analysis,
California
for performing
We also thank Michael A. Doherty, and Dr. John M. Ruth, USDA,
the extraction USDA,
for
for mass spectral
analysis.
LITERATURE CITED I.
Coffman,
2.
Cohen,
C. B., and J. R. Frank.
S. Z., S. M. Creeger,
"Treatment and Disposal ACS Symp. Set. No. 259.
Weed Sci. Soc. Am. Abstr.
25:26 (1985).
R. F. Carsel, and C. G. Enfield.
of Pesticide Wastes,"
Krueger,
Am. Chem. Soc., Washington,
pp. 297-326.
In
R. F. and J. N° Seiber,
D.C.
(1984).
Eds.
174
3.
Cohen, S. Z., C. Eiden, and M. N. Lorbes. pp. 170-196. I n "Evaluation of Pesticides in Ground Water," W. Y. Garner, R. C. Honeycutt, and H. N. Nigg, Eds. ACS Symp. Ser. No. 315.
4. 5.
Am. Chem. Soc., Washington,
Gish, T. J., W. Zhuang, Hallberg, Nonpoint
7.
C. S. Helling,
D.C.
EPA 440/5 85-001.
C. S.
Helling,
C. S., W. Zhuang,
Residue Rev. 32:175-210
Junk, G. A., R. F. Spalding,
9.
Majka, J. T., and T. L. Lavy. Nash, R. G.
11.
National
Research Council. D.C.
Chemosphere.
J. Environ.
Weed Sci. 25:401-408
Chemistry of Herbicides,
Vol. I," R. Grover,
Ed.
"Drinking Water and Health, Vol. I."
Storch, W . J .
64( ):35-59, April 9 (1986).
14.
Thomas, G. W., and R. E. Phillips.
15.
Wehtje, G., L. N. Mielke, J. R. C. Leavitt,
Chem Engin. News
(1984). 13
July
CRC
Nat. Acad. Sci.,
(1977).
13.
Germany
(1980).
In press.
Soil Soc. Am. J. 51:410-415
in
Qual. 9:479-483
(1977).
Sauer, T. J., and T. C. Daniel.
(Received
on
Protection Agency,
This issue.
12.
13:507-513
In "Perspective
U.S. Environmental
(1986).
(1970).
and J. J. Richard.
In "Environmental
Boca Raton, Florida.
Washington,
pp. 109-114.
38:251-259
T. J. Gish, C. B. Coffman, A. R. Isensee, P. C. Kearney,
and M. D. Woodward.
8.
Press,
Geoderma
(1985).
Helling.
D. R. Hoagland,
LO.
and P. C. Kearney.
G. R., R. D. Libra, and B. E. Hoyer. Source Pollution."
Washington, 6.
D.C. (1986).
1987)
(1987).
J. Environ. Qual. 8:149-152 and J. S. Schepers.
(1979) J. Environ Qual.
GROUNDWATER
pp
165-174,
1988
0045-6535/88 $ 3 . 0 0 + .OO Pergamon Journals Ltd.
RESIDUES OF ATRAZINE, UNDER NO-TILLAGE
ALACHLOR,
AND CYANAZINE
PRACTICES
Allan R. Isensee *I, Charles S. Helling I, Timothy J. Gish I, Philip C. Kearney l, C. Benjamin Coffman I, and Wuji Zhuang 2 Ipesticide (T.J.G.),
Degradation
of Agriculture,
Beltsville,
2Analytical Republic
Laboratory
and Weed Science Laboratory
(C.S.H., A.R.I., (C.B.C.),
and P.C.K.),
Agricultural
Hydrology Laboratory
Research Service, U.S. Department
MD 20705
Laboratory,
Chinese Academy of Agricultural
Sciences,
Beijing,
People's
of China.
ABSTRACT Groundwater from no-till corn plots treated with atrazine, alachlor, and cyanazine was analyzed for residues of these herbicides over a 3-year period. Detectable levels of atrazine, alachlor, and cyanazine were found in 75, 18, and 13% of the recovered samples, respectively. Maximum residue levels were 5.9, 3.6, and 1.0 ~g L-! for atrazine, cyanazine, and alachlor, respectively. Rapid vertical transport to the shallow unconfined groundwater (ca. | m depth), as well as substantial lateral subsurface flow, was indicated.
INTRODUCTION Contamination concern.
of well water supplies
A review in 1984 (2) indicated
in 18 states.
By 1985 these reported
in 23 states (3).
by leaching pesticides that 12 pesticides
cases increased
Some of the reports of groundwater
contamination
at sites where highly soluble pesticides
soils.
concern is that low concentrations
A greater
ditions.
Three corn production
methyl)acetanilide], cyanazine
in shallow aquifers
atrazine
herbicides,
are explainable
are applied
of less soluble
(and per-
to very permeable
but widely used pesti-
alachlor
[2-chloro-4-(ethylamino)-6-(isopropylamino)-_s-triazine],
in 5 states at residue
leaching was shown to be largely responsible
residues
for low-level
in groundwater.
165
in Nebraska (15). atrazine
and
fall into this
ranges of 0.3-3 Dg L -I (3).
pattern of atrazine has been tied to groundwater
con-
[2-chloro-2',6'-diethyl-_N-(methoxy-
[2-chloro-4-(cyano-l-methylethylamino)-6-ethylamino-~-triazine],
in groundwater
in groundwater
found in groundwater
under a wide range of edaphic and climatic
category since they are widely used and have been detected detected
had been detected
to 17 pesticides
haps predictable)
cides are being detected
has become a national
residues
Atrazine has been The leaching Direct downward detected
in
166
groundwater throughout
the irrigated corn production areas of the Platte River Valley.
Groundwater samples taken from 41 monitoring wells in this same area contained from 0.01-8.3 ~g L -| (]5). samples
In another Nebraska survey (8), atrazine was detected
in 64 water
from monitoring wells and surface water and ranged from <0.01-88 ~g L-I.
Areal and
vertical distribution of atrazine in the soil profile were closely associated with that of nitrate,
which was measured as an indicator of deep percolation.
Alachlor has been reported in groundwater samples in Maryland,
Iowa, Nebraska, and
Pennsylvania at residue levels of 0.1-10 ~g L -] and cyanazine in Iowa and Pennsylvania at 0.1-I Ng L -1 (3). (10).
Alachlor and cyanazine are both less persistent
in soil than atrazine
Soil thin-layer chromatography studies indicate that all three herbicides have similar
mobilities
(6).
A laboratory leaching study found no difference in the mobility of cyanazine
and atrazine in two soils (9). zine if differences
Thus, alachlor and cyanazine should leach as deeply as atra-
in persistence were not a factor.
The widespread adoption of conservation tillage practices has further intensified the concern over pesticide movement with a concomitant
to groundwater.
Conservation tillage reduces surface runoff,
increase in water infiltration
[paradoxically,
however,
from fields under conservation tillage may contain higher concentrations
the runoff water
of pesticides (|3)].
This greater water infiltration coupled with higher pesticide usage on conservation tillage (12) has raised questions about residue levels in groundwater.
The objective of this study was to measure the persistence and movement
to groundwater
of
atrazine, alachlor, and cyanazine for 3 years following annual application to no-till corn plots.
METHODS AND MATERIALS
Site Description.
No-till cornfield plots were established at the Beltsville Agricultural
Research Center in 1981.
The experimental
design was a randomized complete block with treat-
meats replicated four times; plots measured 3 . 1 X
7.5 m.
The original intent of this investi-
gation was to study the influence of continuous corn and continuous herbicide treatment on crop growth and weed flora in a conservation tillage system (1). rates, which were normal, have been described previously (7). established in plots representative atrazine + alachlor,
All herbicide
of combination treatments of atrazine + cyanazlne,
and cyanazine + alachlor,
plus several untreated plots (Fig.
well consisted of a 5.1-cm (~) aluminum tube installed to a depth of 1.1-1.4 m. were encountered at different depths between plots and became a depth-limiting installation of wells.
treatments and
In December 1983, wells were
L).
Each
Gravel layers factor for
Two off-site control wells, designated Control North (CN) and Control
South (CS), were installed
in May 1985 prior to treatment (Fig.
Teflon tube for sampling, and were kept sealed and capped.
|).
The wells contained a
167
Sampling and Analysis.
Groundwater samples were taken at pre- and post-treatment
during 1984, 1985, and 1986.
Wells were pumped dry I-3 days before sampling.
samples (300-500 mL) were vacuum filtered 50 mL dichloromethane.
follows:
then concentrated
Hexane (50 mL) was added,
and stored at 4°C.
extract was dried with anhydrous sodium sulfate, to ca. [ mL under reduced pressure (temperature
then evaporated
the extract was transferred
methanol in toluene.
into l-L separatory funnels and extracted 3X with
The dichloromethane
2-3 mL toluene was added, <50°C).
intervals
Groundwater
to ca. l mL.
to a mini Florisil
This elutate was concentrated
column,
Cleanup was carried out as then eluted off with 3% (v/v)
to ca. l mL for gas chromatographic
assay
The three herbicides were analyzed with a Hewlett Packard Model 5880A gas
chromatograph having a nitrogen-phosphorus
(N-P) detector and fitted with a fused silica
capillary column [12.5 m X 0.2 mm (i.d.)] coated with dimethyl silicone phase (HP 19091-60312). Limit of detection was 0.I ppb (~g L -l) for 1984 and 1986 samples and 0.5 ppb for the 1985 samples (which were done by another laboratory). (atrazine),
99% (alachlor), 99 + 9% (cyanazine)
12% (alachlor), and 87 + 9% (cyanazine)
Confirmation.
Extraction efficiencies were
for 1984 samples and 99 + 11% (atrazine), 89 +
for 1985 samples.
The identity of atrazine detected
use of gas chromatography-mass
I09 + 9%
spectrometry (GC-MS).
in groundwater samples was confirmed by An aliquot was injected into 30-m X
0.25-mm (i.d.) fused silica capillary column coated with SE-30 and temperature programmed 90-200°C at 5°C min -1.
The mass spectrometer,
from
a Finnigan 4021 with an Incos data system,
was operated in the electron impact mode, with an electron energy of 70 eV and a source temperature of 250°C.
Alachlor and cyanazine residue levels were too low for GC-MS confirmation.
RESULTS AND DISCUSSION
The plot location of the wells,
the elevation of the soil surface at each well head, the
elevation of the groundwater surface in each well, and the herbicide treatments are shown in Fig. I.
The average slope over the length of the plot (Well 37 to Well 24) is 0.9% while the
slope across the plot varies from 1.3 to 1.9% (Wells 37 to I, 43 to 7, and 48 to 24).
Thus,
during major rainfall events, runoff should flow diagonally in a southeast direction across the plot. vations.
The groundwater surface in the wells approximately parallels
the soil surface ele-
Vector analysis indicates that subsurface water flow is also toward the southeast.
Monthly precipitation (including irrigation) patterns are shown in Fig. 2. (87.6-94.7 cm).
for 1983-1986 at the no-till site
These varied widely, but the yearly totals for 1984-1986 were similar
Much more precipitation (137,3 cm) fell in 1983, well above the 15-year
average of II0 cm in Beltsville.
Atrazlne residues in groundwater samples taken in 1984-1986 are shown in Table
I.
The
range in atrazine residues for both the treated and untreated plots was 0-5.9 pg L -I (excluding the high values from Plot 48, 1984). values reported by Cohen et al. (3).
These concentrations
are in the same range of
The relatlvely high residue level in untreated plots
(some equal to or in excess of treated plots) is likely due to the small plot size and to
O0 ~0 r-4
0
Og
Or'
09
08
OOL
0,~1.
Ot,~-
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'SlTam jo u o i a v a o I aold
(V) 3NIZV~IV
aa;aelaa
" a o I d Lq (seaav. p ~ p e q s ) ]uam~.eaaa ~)pTo.~qjBq pue
aaa~mpunoa# pue TTOS aqa ~o s u o ; a e ^ a l a
(0) 3NIZVNV),,O
[Plll I
q a e e am s a a e j a n s
" s a o I d IOaauoa p~ae~aaun saues~ad~a
~''---°..
'Ilam
0
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09
ooL
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O~t
09L
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=
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O"
J F M A M J J A S 0 N D J F M A M J J A 8 0 N DJ F M A M J J A 8 0 N DJF 1983
Figure 2.
1984
M A M J J A 8 0 N D
1985
1986
Monthly precipitation for 1983-1986 at the no-till site.
Irrigation,
in 1984
and 1986, is shown as dotted areas.
gravel at~ sand layers located subsurface water movement (untreated)
1.1-1.4 m below the surface.
Under these conditions,
from a treated to an untreated plot may occur.
is located adjacent and downgradient
to several atrazine-treated
and contained high residue levels during all three sampling years. tently higher concentration of atrazine in the downgradient
rapid
The well in Plot 29 plots (Fig.
In addition,
CS well water (compared
well) provides further evidence of subsurface water movement (Table I, Fig. I).
to the CN
There is some
evidence, especially in the 1985 data (Table I), that a plume of atrazine-contaminated water may quickly reach the CS well, peaking in concentration by ca. 70 days. atrazine-treated
I)
the consis-
ground-
Wells in
plots may have reached peak concentration at ca. 30 days, so sampling at 18
and 41 days would have missed such peaks.
The implication is that lateral subsurface mobility
in this shallow groundwater is very rapid, possibly 0.6 m day -I.
For 1985 and 1986,
the highest atrazine concentrations were obtained shortly after treat-
ment and then decreased with time. inadequate
(The residue pattern for 1984 was unclear due to an
number of samples after 1984 pesticide treatment).
The rapid transport
of small
amounts of atrazine to a depth of I m or more is probably associated with the occurrence and amount of rainfall and irrigation between treatment and sampling.
Macropores
have been shown to rapidly conduct water to depths of I m or more in well-
textured soils during major rainfall events (14), and we had suggested (4) that macropore water flow was associated with atrazine redistribution in soll following
the 1984 application.
As shown in Table II, there was a major rainfall event (3.2 cm) 2 and 6 days after treatment in 1986 and 1985, respectively.
Thus, it seems likely that the relatively high residues in
groundwater on Day 163 (1986) and Day 168 (1985) were transported down macropores by the 3.2-cm rainfalls (Table I). post-treatment
In contrast, many of the wells were either dry during the first
sampling in 1984 (Day 184) or contained small residues.
The rainfall
pattern
0.2
2.8
1.1
-
-
.
.
.
.
.
1.2
-
0.4
-
0.5
-
.
0.6~0_.3
0.8
0.8
-
.
-
1.8
0.6
-
0.3
-
-
-
-
. -
-
-
0
0
-
3.4
0.5
-
0.5
-
0
-
-
0
0
0.6+0.5 +0
-
0.9
0
0
149
+0
.
.
1.2
1.7
0.8
0.4
1.2
0.2
0.6~0_.5
0.6
.
.
0.9
219
0.6~.6 1.0~O.7 0.9~O.6 0.7_40.4 0.9+_1.8 1.5+1.7
.
.
1.2
11.9 e
0.2
.
-
184
0
.
.
-
17.2 e
.
0.4
158
1.1+1.3
0.5
0
1.8
3.8
0
0.7
0
1.6
1.1+1.0
1.3
0
0.7
1.4
1.4
0.7
0
168
1.9
0.8+1.0
0.6
0
0
2.5
0
1.1
0
CLimit of detection was 0.i ppb for 1984 and 1986 and 0.5 ppb for 1985. fAverage residue levels + standard deviation.
dNo sample,
0.4
0.I
0.2
2.0
1.1
1.6
0.7
-
1.8+1.8
1.0
0.8
|.2
0.6
2.0
5.9
1.4
163
0.340.5 0.940.7
0
0
0
0.7
0
0.9
0
I.I
0.1+0.3
0~
0
0
0
0
0
0
253
1.0+I.0
0.5
0.I
0.3
2.9
0.9
1.8
0.4
-
1.4+1.2
0.5
4.1
1.2
0.5
! .3
1.3
1.0
191
19~6 c
0.440.5
0.3
0.2
0.1
1.5
0.4
0.I
0.3
-
1.3+1.2
1.2
4.0
1.3
0.5
0.9
1.0
0.5
228
0.4+0.4
0.2
0
1.0
0.3
0.I
0.6
0.1
0.7
eValu~s not included in the average calculations.
0.3+0.1
0.1
-
0.4
0.1
0.2
0.4
0.3
322
bAtrazine was applied at the rate of 2.8 kg/ha.
0.8+0.9
0.4
0
0
2.4
0.6
1.3
0
1.3
0.2+0.4
0.9
0
0
0
0
0.7
0
214
days a
0.6+0.5
1.2
0
0.9
1.0
0
0.9
0
191
1985 e
Ssfnpling t i m e - J u l i a n
.
.
.
1.7
1.6
1.5
0.6
0.1
0.6
I.I
.
0.1
130
1984c
aplots were treated on Julian days 159, 150, and 160 for 1984, 1985, and 1986, respectively,
CS
-
~
43
~ m e
0.I
-
16
22
Untreated
.
67
0.5
0.8_+0.5 f 1.5+_1.2
1.4
+
24
~anaz~e
.
0.5
Machlor
1
7
+
48
Atr~me
-
95.0 e
42
Alachior
_d
37
+
34
0.6
33
#
Plot
Atrazine Residues (pg L-l) in Groundwater under No-till Corn Plots
Atrazine
Treatment b
Table I.
171
Table II.
Occurrence
and Amount (cm) of Rainfal~ after Herbicide Treatment
1984
1985
Day a
cm
Day
cm
Day
2 (161)
0.4
[ (151)
0.6
2 (162)
3.2
1.5
6 (156)
3.2
3 (163)
Sampling
16 (175)
0.5
9 (159)
0.8
22 (183)
2.0
31 (191)
Sampling
20 (179)
2.5 b
22 (181)
2.4
24 (183)
Sampling
between treatment
18 (168)
application
Sampling
(and Julian day).
these may not have been sufficient
Even the larger water inputs 20 and 22 days posttreatment the upper profile. combination
The decrease
of reduced
Four groundwater treatment
concentrations was confirmed
in atrazine
water flowing
apparently
of atrazine
(Table I).
by its mass spectrum.
in from adjacent
and root interception untreated
Samples
that reflected
from one plot, #48, contained
The identity of atrazine Major fragments
175 (6%),
(16%) and 58 (100%).
the molecular
contamination
(but declining) initial
for three samplings.
sampling,
into the borehole
and it is possible then.
to a combination
samplings.
Furthermore,
in comparable
precipitation
residues
mobility
should,
Laboratory
two months before
surface soil may have fallen
Perhaps
in groundwater
residue from such
the high residues were due
of an unusually
permeable
plot.
There
taken in winter and spring
during the last quarter of 1983 was much greater than
later periods (Fig. 2), so more leaching
unique to Plot 48, since we consistently and pesticide
This fragmenta-
atrazine.
show that the expected groundwater
of factors involving winter sampling
is evidence (5) for maximum herbicide
ion.
approximately
that atrazine-contamlnated
a source is much lower than the observed 95 ppb, however.
intensi-
in Plot 48, since they remained high
Wells were established
Our calculations
from Plot 48
relative
173 (17%), 71 (13%), 68
to that of a library spectrum of reference
is an unlikely cause for the high residues
unusually high
in groundwater
and their corresponding
The mass peak at m/z 215 represents
and possible
areas.
ties were m/z 217 (12%), 215 (51%), 202 (12%), 200 (70%),
tion pattern was identical
flow.
served only to recharge
samplings were made in 1984 (Julian days 34-158)
in 1983 or earlier.
events
to cause macropore
residues with time is probably caused by a
leaching due to surface dissipation
by uncontaminated
pesticide
blrrigation.
and sampling in 1984 (Table II) shows that three smaller rainfall
at 6- to 8-day intervals;
dilution
cm
I0 (169)
aDays after herbicide
occurred
1986
therefore,
encountered
is expected.
The soil factor may be
gravel at a shallow depth there; water
be relatively high.
72
Table
III.
Alachlor
Residues
(pg L -I)
in G r o u n d w a t e r
Sampling Treatment b
Plot
under N o - t i l l
time - Julian
C o r n Plots
daya
1985
1986 191
228
322
0.3 0 0.2 0.I
0 0 0 0
0 0 0 0
0 0 0 0
1.0 0 0 0
0.5 0.I 0
0 0 0
0.4 0 0.2
0 0 0 0
0 0 0
0 0 0
0 0 0.2
0 0 0
0.4 0.3 0.2
0 0
0 0 0 0
0 0 0 0
0.2 0.2 0.2 0.1
0 0.i 0.2 0
0 0.7 0 0
0 0 0 0
no.
149
168
191
214
253
Alachlor + Atrazine
33 37 42 48
-c -
0 0 0 0
0 -
0 0 0 0
0 0 0 0
Alachlor + Cyanazine
16 22 39 43
-
0 0 0 1.0
0 0
0 0 0 0
Atrazine + Cyanazine
1 7 24
-
0 0 0
0 0 0
Untreated
29 36 CN CS
-
0 0 0 0
-
163
a p l o t s were treated on J u l i a n dais 150 and 160 for 1985 and 1986, respectively. b A l a c h l o r was applied at 2.8 kg ha(1985) and in 1986 at 2.2 and 0.0 kg ha -I in Plots 16-43 and 33-48, respectively.
Table
IV,
Cyanazlne
Residues
(pg L -I)
in G r o u n d w a t e r
Sampling Treatment b
Plot 149
Cyanazine + Alachlor
16 22 39 43
-c 0 0
Cyanazine + Atrazine
1 7 24
Atrazine + Alachlor
33 37 42 48
Untreated
29 36 CN CS treated applied
168
C o r n Plots
time - J u l i a n day a
1985
no.
aplots w e r e b c y a n a z l n e was
under N o - t i l l
1986 191
228
322
191
214
253
163
3.4 0 0 3.6
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0
0 0 0.1
0.3 0 0
0 0 0 0.|
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0.I 0.2 0.2
0 0
0
0
0
0
0
0
0
0.1
0
-
0
0
0
0
0
0
0
0
0 0
0 0
0 0
0 0
0 0
0.1 0
0.1 0.1
0.7 0.2
0 0
0 0
0 0 0 0
0 0 0 0
0 0 0 0.7
0 0 0 0
0 0 0 0
0 0 0 0
0.2 0 0 0
0 0 0 0
on J u l i a n days 150 and 160 for at the rate of 2.2 kg ha -I.
1985 and
1986,
respectively.
173
Alachlor and cyanazine
residues
in groundwater
in Tables III and IV, respectively. 1986 than 1985, probably because 0.5 ppb in 1985. concentration
In general,
previously
Both herbicides
taken in 1985 and 1986 are shown
were detected much more frequently
more frequently
(1986, Table IV).
reported
The amounts we found were within the range
(3) for alachlor
(0.I-I0 ppb), and only two samples were
(0.I-I ppb).
same concentration
from both treated and untreated plots,
subsurface
water movement
(and little
to
and at slightly higher
above the range for cyanazine in samples
in
the lower limit of detection was 0.i ppb in 1986 compared
alachlor was detected
than was cyanazine
of concentrations
samples
Both herbicides
further degradation)
were found in approximately indicating
the
that
had occurred.
CONCLUSIONS
Shallow unconfined atrazine
(for 3 years),
groundwater
averaged
test of pesticide sis, discussed
groundwater alachlor,
under continuous
and cyanazine
only about 0.9 m, the plots were considered
leaching potential,
elsewhere
the groundwater
dissipation
analyses
transport
either herbicide
With a few exceptions,
the typical herbicide
concentrations
far lower than the "suggested or alachlor
(700 ppb) (II).
management
has specifically
comparative
investigation
0-0.3 ppb, and cyanazine health-advisory
application.
soils data in that alachlor and cyanazine
the odds of detecting
0.2-1.8 ppb, alachlor
when significant
during the first few weeks after pesticide
seem to support
severe
Soil core analy-
of atrazine
greatly reduced
atrazine
soil.
for
Because depth to
to be a relatively
at least for a medium textured
(4, 7) showed early vertical
rainfall events (ca. 2-3 cm) occurred However,
no-till corn plots was monitored
(each for 2 years) residue.
in this groundwater
0-0.2 ppb.
concentrations"
in groundwater.
were
These concentrations
reported for atrazine
are
(150 ppb)
We cannot judge from our present study whether the use of no-till altered pesticide
leaching and persistence
behavior,
but such a
is currently in progress at Beltsville.
ACKNOWLEDGMENTS
We thank the Shell Development and analyses assistance
Company, Modesto,
of the 1985 groundwater
samples.
in sample collection and analysis,
California
for performing
We also thank Michael A. Doherty, and Dr. John M. Ruth, USDA,
the extraction USDA,
for
for mass spectral
analysis.
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