|Currently, little is known about the occurrence, fate, or transport of sulfonylurea (SU), sulfonamide (SA), and imidazolinone (IMI) herbicides in surface water or ground water in the United States. To gain an understanding of the occurrence of these 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 (DuPont) has been developed. As a result of this cooperative effort, the USGS will (1) collect data that can be used to assess the presence of twelve SUs, three IMIs, and one SA in water resources of the midwestern United States; and (2) develop an analytical method for SUs, IMIs, and SAs that is similar in terms of analyte coverage and method detection limits to other pesticide methods currently used nationally by USGS programs. Additionally, DuPont will be able to (1) fill a gap in data regarding the environmental occurrence of SU herbicides, (2) support research comparing the environmental occurrence of SUs with that of other herbicides, and (3) promote environmental stewardship in the use of their products.|
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|Figure 1. Estimated acres of corn, soybeans, or wheat treated with selected sulfonylurea, sulfonamide, and imidazolinone herbicides, 1990-96, in midwestern States.|
Over the last 20 years, a generation of low application rate herbicides have been developed that act by inhibiting the action of a key plant enzyme, resulting in stopped growth and eventual plant death. The enzyme that these herbicides act upon is specific to plants and they are reported to have very low toxicities in mammals or other animals (Brown, 1990; Meister, 1997). SU, SA, and IMI herbicides are three compound classes that act in this manner. Crops that can be treated with SUs, SAs, and IMIs include barley, corn, cotton, durum wheat, peanuts, rice, soybeans, sugar beets, canola, spring wheat, and winter wheat. These herbicides are gaining in popularity among farmers. The total corn, soybean, and wheat acreage on which 9 SUs, 1 SA and 2 IMIs were applied in eleven midwestern States (Iowa, Illinois, Indiana,Kansas, Kentucky, Minnesota, Missouri, Nebraska, Ohio, South Dakota, and Wisconsin) from 1990 through 1996 is shown in figure 1 (U.S. Department of Agriculture, 1991-97). In 1996, the area treated exceeded 59 million acres. For comparison, atrazine, a triazine herbicide, was used on 44.2 million acres of corn in the same 11-State area, in 1996. Although applied over comparable areas, SU, SA, and IMI herbicides typically are applied at much lower rates than other commonly used herbicides classes. For example, in 1996, in the same 11-State midwestern area, an estimated 23,200 tons of atrazine and 19,360 tons of metolachlor were applied to cropland, while the estimated use of 9 SUs, 1 SA, and 2 IMIs was only 1,150 tons (U.S. Department of Agriculture, 1997).
Plants demonstrate a wide range in sensitivity to SUs, SAs, and IMIs with over a 1000-fold difference in observed toxicity levels for some compounds. The concentration in water in the soil zone is the toxicologically relevant concentration. Because SUs, SAs, and IMIs are active at very low concentrations they can cause a problem with plant vigor in some crop rotations even when only 1 percent or less of the originally applied material remains. Little non-target crop stress is expected from soil water concentrations below 0.1 µg/L (micrograms per liter, or part per billion). Less is known about the effect of these compounds on noncrop plant species, but a concentration of 1.0 µg/L in water appears to be a threshold for possible native aquatic plant toxicity (U.S.Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division, Tox One-Liner Database, written commun., 1997).
The CRADA outlines tasks and products that are expected from both parties. The tasks listed as DuPont's responsibilities under the CRADA include (1) providing the USGS National Water Quality Laboratory (NWQL) with the written materials and guidance needed to develop and validate an analytical method for detecting selected SUs, SAs, and IMIs in water samples at a quantification limit of 0.1 µg/L, (2) providing technical consultation to the NWQL on analytical methods adaptation and development, and (3) providing data on the physical and chemical properties and toxicity of SUs and their degradation products. The tasks listed as USGS responsibilities include (1) developing and executing a work plan for the first year of the project focusing on sample collection (with samples going to a laboratory chosen by DuPont) and analytical methods development, (2) validating the performance of the analytical method provided by DuPont as part of an Association of Official Analytical Chemists (AOAC) method validation process, (3) modifying the DuPont method, if feasible, to improve sensitivity to a point were it is comparable with the sensitivity of other analytical methods currently offered by the NWQL for other classes of pesticides and to include other labile pesticide parent compounds and degradation products of SUs, SAs, and IMIs, (4) developing a work plan for 1998 focusing on a multi-state intensive reconnaissance to determine the frequency and magnitude of SU, SA, and IMI detections in water samples, and (5) publishing reports that interpret the results from samples collected and analyzed by the USGS in 1998.
The CRADA also outlines any constraints or limitations that are placed on the information exchanged, results obtained, or data generated by the CRADA activity. The subject CRADA specifies that the USGS and DuPont will be allowed to freely publish the results of this study within the limitations of section 7.4.2 (a section of the General Provisions). This section states that the USGS and DuPont agree to confer and consult at least 30 days prior to either party's submission for publication of subject data. The CRADA also states that the USGS and DuPont will be allowed to review and comment upon, but not censor any data, interpretations, or reports resulting from the CRADA activity. For publication purposes, data generated from samples analyzed by the NWQL will be reported as USGS data and data generated by analyses by DuPont or by any laboratory selected by Dupont will not be reported as USGS data.
External oversight and technical review of analytical methods development, work plan development, study design, and data interpretations are provided by the Interagency Method and Data Comparability Board (MDCB). The MDCB and the National Water-Quality Monitoring Council (NWQMC) were chartered in 1997 under the Federal Advisory Committee Act. The Council's charge is to implement a nationwide strategy to improve water-quality monitoring, assessment, and reporting, and to oversee activities of the MDCB. The Board's charge is to identify, examine, and recommend monitoring approaches that facilitate collaboration and yield comparable data and assessment results. Board members come from Federal, State, tribal, and private organizations and have a mix of interests and expertise. Oversight by the MDCB of the activities associated with this CRADA provides an external review by a group with diverse perspectives.
The USGS will commit time and personnel for work plan development, analytical methods development, sample collection, sample analysis, data interpretation, and reports preparation. DuPont will commit time and personnel for analytical methods development support, sample analysis, reviews of work plans, and reviews of data interpretations. DuPont will also commit financial support for sample collection and analysis, for a portion of analytical methods development, and for some costs associated with the external oversight (travel and meeting costs).
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|Figure 2. Location of surface-water and ground-water sites sampled in 1997.|
The first phase of CRADA sampling activity was initiated in summer and fall 1997. Approximately 50 samples were collected by USGS personnel from 40 sites (20 streams and 20 wells) (fig. 2). These samples were sent to researchers at the National Soil Tilth Laboratory (chosen by DuPont) for analysis. Sampling activities in 1998 will focus in the areas of highest herbicide use (fig. 3). The 1998 study plan calls for the collection of 150-200 samples from 100 sites. These samples will be analyzed at the NWQL using both the DuPont method and the modified method for at least the 16 analytes listed in table 1 plus any additional herbicides or herbicide degradation products added to the target analytes list by the method modifications. Water from all or selected samples collected in 1998 will be sent to DuPont for confirmatory analysis. Water from all samples collected in 1998 will also be analyzed for selected other pesticides. Where possible, samples will be collected in conjunction with planned USGS activities in order to reduce sample collection costs.
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|Figure 3. Estimated 1992 county-level use of (a) imazethapyr and (b) nicosulfuron.|
--By William A. Battaglin, Edward T. Furlong, and C. John Peter
Meister, R.T., 1997, Farm chemicals handbook'97: Willoughby, Ohio, Meister Publishing.
Rodriguez, M. and Orescan, D.B., 1996, Analytical method for the quantitation and confirmation of selected sulfonylurea, imidazolinone, and sulfonamide herbicides in surface water using electrospray LC/MS: DuPont Report No. AMR 4118-96.
U.S. Department of Agriculture, 1991-1997, Agricultural chemical usage--1990-1996 field crops summary: Washington, D.C., USDA, National Agricultural Statistics Service, (published annually).
For further information, contact:
William A. Battaglin
U.S. Geological Survey
Box 25046, MS 406, Denver Federal Center
Denver, CO 80225
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Web version by: Genevieve Comfort
Last Modified: 20MAY1998