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Central Columbia Plateau - Yakima River Basin NAWQA Study -- Publications

Are Agricultural Pesticides in Surface Waters of the Central Columbia Plateau?

YES. Many agricultural pesticides are present at very low concentrations. No pesticides were found at concentrations above regulatory drinking water standards, but some were at concentrations that exceeded guidelines for the protection of aquatic life (freshwater-chronic criteria) or health advisories for drinking water.

[Map showing land use in the Central Columbia Plateau] Land-use map of the Central Columbia Plateau (GIF, 85460 bytes)

Surface-water sites representing four drainage basins with different farming practices were sampled by the U.S. Geological Survey as part of its National Water-Quality Assessment Program. Samples were taken one to five times a month from March 1993 through May 1994. Detections of pesticides usually, but not always, were related to pesticides used on crops in the drainage basins.

Of the 84 compounds targeted for analysis, 45 compounds were detected. No pesticides were found at concentrations that exceeded U.S. Environmental Protection Agency (USEPA) maximum contaminant levels for drinking water, but concentrations of dieldrin and alpha-HCH exceeded their USEPA health advisories for drinking water. Five pesticides were at concentrations that could adversely affect aquatic life.

Table 1.--Pesticides that exceeded freshwater-chronic criteria
          for the protection of aquatic life

				Number of samples that exceed criteria at:
Pesticide (trade name)	  EL68D		Crab Creek	Upper Crab	Palouse
 			  Wasteway	Lateral		Creek		River

Chlorpyrifos (Lorsban)	   3		 3		--		--
Azinphos-methyl (Guthion)  3		12		 1		--
Carbaryl (Sevin) 	   0		 2		 0		--
Diazinon (several)	   3		 1		--		 1
Triallate (Far-Go)	  --		--		 1		 3

(Any use of trade, product, or firm names is for descriptive purposes only
and does not imply endorsement by the U.S. Geological Survey.)


Maximum concentrations of detected pesticides

Table 2.--Maximum concentrations of detected pesticides.
Displays the table in-line in your browser as text. The table has
13 columns and 45 rows, plus notes. It includes data on herbicides
and insecticides. The table is also available as a PostScript file (66905 bytes).

Why are some pesticides found more often than others?

Agricultural pesticide use is often a factor that explains detection frequencies, but not always. Application rates, which may influence detection frequencies, are difficult to determine. Non-agricultural use may help explain detections of some pesticides. Other factors influencing detection rates include (1) analytical methods with different limits of detection, (2) the rate at which different pesticides break down in water and soil environments, and (3) the ability of pesticides to dissolve and be transported by water. For example, atrazine, the most commonly detected pesticide, has a very low detection level, dissolves readily in water, and breaks down very slowly in water, but its agricultural usage rate is less than 5 percent of the total herbicides applied in the drainage basins sampled.

Application rates--Irrigated agriculture (GIF, 23062 bytes) [graphs showing application rates at two sites]

Application rates--Dryland agriculture (GIF, 22188 bytes) [graphs showing application rates at two sites]

Variations in the frequency of detections

Variations in the frequency of detections in both the dryland and irrigated basins were observed. Herbicides are detected more often than insecticides in both the irrigated and dryland basins. Herbicides are applied in greater amounts than insecticides in the dryland drainage basins. Some herbicides, triallate and MCPA, for instance, were detected only in the dryland drainage basins. Terbacil and pendimethalin are two herbicides that were detected only in the irrigated drainage basins.

Variations of concentrations

Variations of concentrations of pesticides in surface waters sometimes provide clues about how the pesticides are transported to surface- water systems. Highest concentrations of some pesticides were observed during or shortly after their application period. Pesticides enter surface waters in runoff from fields and through the ground-water system.

Highest concentrations of pendimethalin were detected
during or shortly after the period when it is typically applied.

[graph of pendimethalin concentrations, GIF, 7760 bytes]Concentrations of pendimethalin (GIF, 7760 bytes)

The presence of atrazine during low streamflows
(November to mid-March) indicates that the ground
water is one source of atrazine to the surface water.

[graph of atrazine concentrations, GIF, 8611 bytes]Concentrations of atrazine (GIF, 8611 bytes)

Detections of gamma-HCH (Lindane) coincide
with periods of surface runoff.

[graph of gamma-HCH concentrations, GIF, 6103 bytes]Concentrations of gamma-HCH (GIF, 6103 bytes)

A note on quality assurance

In June 1996 the USGS National Water Quality Laboratory completed adjustments to the pesticide data base from schedules 2001/2010 and 2050/2051 covering sample dates from 1992 through February 29, 1996. Corrected method detection limits (MDLs) were assigned to nondetect values and E (estimate) codes were assigned more consistently. Also, all dimethoate values were deleted from the data base due to this compound's poor performance in analytical tests. While making these adjustments to the data base, it was discovered that some compounds detected at very low concentrations had been inadvertently reported as nondetections. These are now reported as detections. This most frequently occurred for the following compounds: desethylatrazine, dieldrin, simazine, propargite, disulfoton, and linuron.

USGS Fact Sheet 241-95
Prepared by R.J. Wagner, J.C. Ebbert, and L.M. Roberts
July, 1996


Anderson, J.E., and Gianessi, L., 1995, Pesticide use in the Central Columbia Plateau: Washington, D.C., National Center for Food and Agricultural Policy, misc. pagination.

Nowell, L.H., and Resek, E.A., 1994, Summary of National Standards and Guidelines for pesticides in water, bed sediment, and aquatic organisms and their applications to water-quality assessments: U.S. Geological Survey Open- File Report 94-44, 115p.

Wagner, R.J., Ebbert, J.C., Roberts, L.M., and Ryker, S.J., in press, Agricultural pesticide applications and observed concentrations in surface waters from four drainage basins in the Central Columbia Plateau, Washington and Idaho, 1993-94: U.S. Geological Survey Water-Resources Investigations Report 95-4285, [about 50] p.

For further information, contact:
Project Chief
1201 Pacific Ave., Suite 600
Tacoma, WA 98402
Phone:(253) 593-6530 ext 2687; -6514 fax

Suggested citation:
Wagner, R.J., Ebbert, J.C., and Roberts, L.M., 1995, Are agricultural pesticides in the surface waters of the Central Columbia Plateau?: U.S. Geological Survey Fact Sheet 241-95, on line at <URL>, accessed October 17, 1997.

For a paper copy of this report, send Email to

Central Columbia Plateau - Yakima River Basin NAWQA Study
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