Sulfonylurea, Sulfonamide, Imidazolinone, and Other Pesticides
Introduction
A potential cause for the decline in some herbicide
concentrations in Midwestern streams during spring and early summer
runoff events is a shift to the use to other herbicides. Sulfonylurea
(SU), sulfonamide (SA), and imidazolinone (IMI) herbicides are relatively
new classes of chemical compounds that function by inhibiting the
action of a plant enzyme and stopping plant growth. These compounds
generally have low mammalian toxicity. Plants demonstrate a wide range
in sensitivity to SUs, SAs, and IMIs (fig. 1) with over a 10,000 fold
difference in observed toxicity levels for some compounds. They are
applied either pre- or post-emergence to crops at 1/50th or less the
rate of other common herbicides. The amount of cropland treated by
SU's, SA's, and IMI's has nearly tripled since 1990 to more than 60
million acres in 1997 (fig. 2). Little is known about the occurrence,
fate, or transport of these herbicides in surface water or ground
water in the United States.
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Figure 1. EC50
concentrations in micrograms per liter for selected imidazolinone,
sulfonamide, sulfonylurea, and other herbicides on five aquatic
plants. |
Figure 2. Acres
of corn, soybeans, or wheat treated with imidazolinone, sulfonamide,
and sulfonylurea herbicides, 1990-1998, in 11 Midwestern States. |
Objectives and Methods
To gain an understanding of the occurrence of
16 sulfonylurea (SU), sulfonamide (SA), and imidazolinone (IMI) herbicides
in an unbiased yet economical manner, a Cooperative Research and Development
Agreement (CRADA) between the U.S. Geological Survey (USGS) and DuPont
Agricultural Products was developed. In 1998, 210 water samples
were collected during post-application runoff events at 75 surface-water
and 25 ground-water sites shown on figs. 3 and 4 (2 from each
surface-water site, 1 from each well). These samples were analyzed
for 16 SU, SA, and IMI herbicides by USGS Methods Research and Development
Program staff using high-performance liquid chromatography/mass spectrometry.
Samples were also analyzed for 46 other pesticides or degradation
products by gas chromatography/mass spectrometry at the USGS National
Water Quality Laboratory.
Figure 3. Surface-water sites sampled in 1998 pesticide
reconnaissance.
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Figure 4. Ground-water sites sampled in 1998
pesticide reconnaissance. |
Discussion and Results
The distributions of concentrations for 16
SU, SA, and IMI herbicides in Midwestern streams, reservoir outflows,
and wells are shown in figure 5-7. At least 1 of the 16 SU, SA,
or IMI herbicides was detected at or above the method-reporting
limit (MRL) of 0.010 micrograms per liter (ug/L) in 82 percent of
133 stream samples. Imazethapyr was detected most frequently (69
percent of samples) followed by flumetsulam (62 percent of samples)
and nicosulfuron (51 percent of samples) (fig. 5). At least one
SU, SA, or IMI herbicide was detected at or above the MRL in 6 of
8 reservoir samples and flumetsulam, imazethapyr, and imazaquin
were each detected in 5 samples (fig. 6). At least one SU, SA, or
IMI herbicide was detected at or above the MRL in 5 of 25 ground-water
samples (fig. 7). Imazethapyr was detected most frequently (4 samples)
followed by flumetsulam and imazaquin (3 samples each).
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Figure 5. Sulfonylurea, sulfonamide, and imidazolinone
herbicide concentrations and percent detections at or above
the MRL (0.01 ug/L) in 133 stream samples. |
Figure 6. Sulfonylurea, sulfonamide,
and imidazolinone herbicide concentrations, and percent detections
at or above the MRL (0.01 ug/L) in 8 reservoir outflow
samples. |
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Figure 7. Sulfonylurea, sulfonamide, and imidazolinone
herbicide concentrations, and percent detections at or above
the MRL (0.01 ug/L) in 25 ground-water samples. |
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Results of analysis for 46 other pesticides are also available
(WRIR
00-4225 pdf file). At least 1 of the 46 pesticides was detected
at or above the MDL in every stream sample (134), every reservoir
outflow sample (10) , and 15 of 23 ground-water samples. Acetochlor,
atrazine, deethylatrazine, cyanazine, and metolachlor were all detected
in 90 percent or more of the stream samples. Acetochlor, alachlor,
atrazine, deethylatrazine, cyanazine, metolachlor, metribuzin, and
simazine were all detected in 90 percent or more of reservoir outflow
samples. Atrazine, deethylatrazine, and metolachlor were detected
in 57 percent or more of the ground-water samples.
Because they have similar chemical properties, much lower application
rates, and a shorter history of use, SU, SA, and IMI herbicides
were expected to occur at fraction (about 1/100th) of the concentrations
of other herbicides such as atrazine and metolachlor. The distributions
of imazethapyr, flumetsulam and nicosulfuron to atrazine and metolachlor
ratios from pre- and post-emergence stream and reservoir outflow
samples are shown on figure 8. These ratios are generally smaller
in pre-emergence samples than post-emergence sample. This relation
was expected as the majority of atrazine and metolachlor is applied
before crops emerge and the majority of SU, SA, and IMI herbicides
are applied after crops emerge.
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Figure 8. Ratios of imazethapyr, flumetsulam and nicosulfuron
concentrations to atrazine and metolachlor concentrations in
pre- and post-emergence stream and reservoir outflow samples. |
References:
Scribner, E.A.; Goolsby, D.A.; Thurman, E.M.; Battaglin,
W.A., U.S. Geol. Surv. OFR 98-181, 1998.
Meister, R.T., Farm Chemicals Handbook 97, Meister Pub. Co., Willoughby,
OH, 1997.
Peterson, H.G.; Boutin, C.; Martin, P.A.; Freemark, K.E.; Ruecker,
N.J.; Moody, M.J., Aquatic Toxicol. 1994, 28:275-292.
Battaglin, W.A., Furlong, E.T.; Burkhardt, M.; Peter, C.J., in
Proceedings of the NWQMC National Conference, USEPA, 245-256, 1998.
Battaglin, W.A.; Furlong, E.T.; Peter, C.J., USGS Fact Sheet FS-046-98,
1998.
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