Pesticides in Midwestern Rivers, 1989-2002
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.
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