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Information on this page was adapted from numerous sources including: (1) U.S. Geological Survey Water-Resources Investigations Report 00-4225 by William Battaglin, Edward Furlong, and Michael Burkhardt, titled "Concentration of Selected Sulfonylurea, Sulfonamide, and Imidazolinone Herbicides, Other Pesticides, and Nutrients in 71 Streams, 5 Reservoir Outflows, and 25 Wells, in the Midwestern United States, 1998", (2) and article in the journal Science of the Total Environment titled "Changes in herbicide concentrations in Midwestern streams in relation to changes in use, 1989-1998" by E.A. Scribner, W.A. Battaglin, D.A. Goolsby, and E.M. Thurman, (248: 255-263 (2000)) and (3) poster presentations prepared by William A. Battaglin, for the 1998 Fall American Geophysical Union (AGU) meeting and the 2001 Fall SETAC meeting.

Potential Toxicity of Pesticides in Midwestern Rivers

We evaluate the potential toxicity of 5 classes of pesticides using concentrations from water samples collected from Midwestern streams during early summer runoff events in 1989 and 1998. Toxicity index values, calculated as the concentration divided by the acute toxicity estimate (LC50 or EC50), were summed by pesticide class. Results indicate that some samples had probable toxicity to duckweed and green algae, but few are suspected of having significant toxicity to bluegill sunfish or frogs.

Evidence for Declining Herbicide Concentrations

Herbicide concentrations in Midwestern streams are affected by climate, soils, agricultural practices, and herbicide use within the associated basins. The USGS sampled 52 Midwestern streams during post-application runoff in 1989, 1990, 1994, 1995, and 1998 with the intent of measuring peak pre-emergence herbicide concentrations of alachlor, atrazine, cyanazine, and metolachlor were significantly smaller in 1998 than in 1989/90.

Occurrence of Herbicide Degradation Products

Our understanding of the effects of herbicides on humans and ecosystems is incomplete because most studies ignore herbicide degradation products. Some degradates are as toxic as their parent, but little information is available on herbicide degradate occurrence or toxicity. This data shows that in midwestern streams, herbicide degradates occur frequently and at similar concentrations as the parent herbicides.

Sulfonylurea, Sulfonamide, Imidazolinone, and Other Pesticides

Information on more of the ~875 registered pesticide active ingredients is needed to better quantify the total load carried, and relative abundances of pesticides in Midwestern rivers. Sulfonylurea (SU), Sulfonamide (SA), and imidazoline (IMI) herbicides are relatively new classes of herbicides. Little is known about the occurrence, fate, or transport of these herbicides in surface water or ground water in the United States. In 1998, 210 water samples were collected during post-application runoff events at 75 surface-water and 25 ground-water sites. The samples were analyzed for 16 SU, SA, and IMI herbicides by HPLC/MS and 47 pesticides or degradation products by GC/MS.