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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.

Figure 1 showing EC50 concentrations in micrograms per liter for selected imidazolinone, sulfonamide, sulfonylurea, and other herbicides on five aquatic plants. Figure 2 showing acres of corn, soybeans, or wheat treated with imidazolinone, sulfonamide, and sulfonylurea herbicides, 1990-1998, in 11 Midwestern States.
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 showing surface-water sites sampled in 1998 pesticide reconnaissance.

Figure 3. Surface-water sites sampled in 1998 pesticide reconnaissance.

Figure 4 showing ground-water sites sampled in 1998 pesticide reconnaissance.
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).

Figure 5 showing sulfonylurea, sulfonamide, and imidazolinone herbicide concentrations and percent detections at or above the MRL (0.01 μg/L) in 133 stream samples. Figure 6 showing sulfonylurea, sulfonamide, and imidazolinone herbicide concentrations, and percent detections at or above the MRL (0.01 μg/L) in 8 reservoir outflow samples.
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.
Figure 7 showing sulfonylurea, sulfonamide, and imidazolinone herbicide concentrations, and percent detections at or above the MRL (0.01 &#956g/L) in 25 ground-water samples.
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.  

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.

Figure 8 showing ratios of imazethapyr, flumetsulam and nicosulfuron concentrations to atrazine and metolachlor concentrations in pre- and post-emergence stream and reservoir outflow samples.
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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