Environmental Health - Toxic Substances Hydrology Program

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Management Practices a Factor in Herbicide Declines

Farm field with tractor applying herbicides
The U.S. Geological Survey (USGS) Toxic Substances Hydrology Program studied the runoff of pesticides in midwestern agricultural fields such as this one as part of the Midcontinent Herbicide Reconnaissance. Photo Credit: Dana W. Kolpin, USGS.

Data collected from over 50 Midwestern streams in 1989, 1990, 1994, 1995, and 1998 indicate that there has been some decline of the high herbicide concentrations observed in Midwestern streams during the spring planting season.

  • High concentrations of herbicides occur during spring rainstorms just after herbicides have been applied to agricultural fields.
  • Concentrations of several of the most commonly used herbicides, including alachlor, atrazine, and metolachlor have declined, but the concentrations of acetochlor have increased dramatically since its first use in 1994 (figure 1).
  • In some cases, as with alachlor (figure 2), the downward trend in concentrations is associated with a decrease in the total application amount.
  • With atrazine, however, the downward trend (figure 3) in concentrations is not associated with a decrease in total application amounts, suggesting that changes in farming and best management practices, or other factors, are affecting the concentration.
  • The concentrations of herbicide degradates in samples collected in 1998 were relatively high when compared to their parent compounds. More information on the 1998 reconnaissance is available.

References

Battaglin, W.A., and Goolsby, D.A., 1999, Are shifts in herbicide use reflected in concentration changes in Midwestern Rivers?: Environmental Science and Technology, v. 33, p. 2917-2925.

Scribner, E.A., Battaglin, W.A., Goolsby, D.A., and Thurman, E.M., 1999, Changes in herbicide concentrations in Midwestern streams in relation to changes in use, 1989-98, in Morganwalp, D.W., and Buxton, H.T., eds., U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Charleston, South Carolina, March 8-12, 1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems: U.S. Geological Survey Water-Resources Investigations Report 99-4018B, p. 313-322.

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