USGS Fact Sheet 022-98
Download this fact sheet as a PDF file (811 KB)
Download a free copy of
Occurrence of Cotton Pesticides in Surface Water
of the Mississippi Embayment
By E. Michael Thurman, Lisa R. Zimmerman, Elisabeth A. Scribner, and Richard H. Coupe Jr.
This fact sheet introduces a study of the nonpoint-source occurrence of pesticides in water
of the cotton-growing areas of the Southern United States with special emphasis on the
Mississippi Embayment (fig 1). This study is being conducted by the U.S. Geological Survey (USGS)
Organic Geochemistry Research Group, which investigates the fate and transport of agricultural
chemicals in the environment. The purpose of this fact sheet is to give an overview of the
cotton-growing areas of the United States, to provide usage data for cotton pesticides in the
United States, to present information on the types of pesticide compounds and concentrations
that have been found thus far in the Mississippi Embayment, and to discuss current areas of
cotton pesticide research.
Table of Contents
Contamination of water in the Midcontinental United States from pesticide application to row
crops (corn and soybeans) has been a major water-quality issue during the past decade. Perhaps
equally important to water quality in the Southern United States is the application of
pesticides to cotton, which receives three to five times greater application of pesticides per
acre than does corn or soybeans. In spite of the greater use of pesticides, few regional
water-quality studies have addressed pesticide occurrence in water of the Southern United
Cotton-growing areas of the United States (fig 1) extend from the East
Coast (The Carolinas) to the Mississippi Embayment, the Texas High Plains, and the arid
deserts of the Southwest (Arizona and California). These areas of the country have different
climate, precipitation, and soil types, which result in different weed and insect pressures,
as well as different runoff potentials; therefore, pesticide-usage, runoff, and leaching
patterns are often different. Because of these considerations, the types and amounts of
pesticides applied may vary considerably throughout the cotton-growing areas. For example,
fluometuron is a cotton herbicide used primarily in Mississippi and in the eastern coastal
2; Battaglin and Goolsby, 1995) but is little used in other cotton-growing areas.
The geographic usage information displayed in figure 2 can be useful for designing regional water-quality
surveys and for methods-development strategies for a compound such as fluometuron. Another
method to visualize cotton pesticide usage in the United States is the bar graph shown in
figure 3. The compounds shown
account for nearly all of the pesticides used in cotton-growing areas (Gianessi and Anderson,
1995). The three most-used pesticides are herbicides (monosodium methylarsonate, trifluralin,
A major area for cotton production in the United States is the Mississippi Embayment
(figs. 1 and
4). The area consists of parts of Arkansas,
Kentucky, Louisiana, Mississippi, Missouri, and Tennessee. Rainfall amounts of as much as 60
inches per year and relatively flat, only slightly permeable soils characterized by large
runoff volumes and low relief are typical of this area. Major pesticides used in the area
include monosodium methylarsonate, fluometuron, cyanazine, pendimethalin, methyl parathion,
Surface-water samples were collected at 64 sites in the Mississippi Embayment from
January-December 1996 in conjunction with the USGS National Water-Quality Assessment (NAWQA)
Program. The locations of the sampling sites are shown in figure 4. Fixed sites were sampled weekly for 1 year, and reconnaissance
sites were sampled one time. Samples were filtered through glass-fiber filters (1.0 micron)
and stored on ice until analyzed at the USGS laboratory in Lawrence, Kansas.
Water samples were extracted and analyzed by gas chromatography/mass spectrometry (GC/MS) for
the detection and quantitation of the major cotton pesticides. The method consists of using
solid-phase extraction (SPE) for the isolation of the compounds followed by elution with ethyl
acetate (an organic solvent) and analysis by gas chromatography with identification by mass
spectrometry using selected ion detection (Thurman and others, 1990). The detection limit was
0.05 µg/L (micrograms per liter) for all herbicides and 0.01µg/L for all
In addition to the standard approach of GC/MS for chemical analyses, other methods for the
evaluation of pesticides in the aquatic environment are being used. Enzyme-linked
immunosorbent assay (ELISA) has been developed for fluometuron (Strategic Diagnostics, Inc.,
Newark, Delaware). This immunoassay is portable, provides rapid results, and is less expensive
than conventional methods. Initial analyses have shown very good correlation between GC/MS and
Three general factors are important in defining transport, fate, and toxicity of pesticides in
the aquatic environment (fig.
5). Pesticide usage, such as illustrated in figures
2 and 3, provides basic
source information. Chemical structure affects the physical properties and, thus, the
persistence and mobility of the pesticides. Site hydrology determines runoff and leaching
potentials. Evaluation of all factors will enable improved understanding of the processes of
nonpoint-source contamination and of the occurrence of cotton pesticides in surface and ground
The major herbicides and their metabolites that have been detected in surface water of the
Mississippi Embayment are shown in figure 6.
The most-detected compound was fluometuron with a mean concentration of 2.1 µg/L, a
median of 0.40 µg/L, and a maximum of 50 µg/L (fig. 6). The demethyl metabolites, demethylfluo-meturon and demethylnorflurazon,
were also commonly detected.
n general, cotton pesticides are soluble in water, from 0.3 to 1,000 mg/L (milligrams per
liter). Experience from studies in the corn- and soybean-growing areas of the United States
indicates that at a water solubility greater than 5 mg/L compounds are readily carried by
surface runoff and occur in surface water. Cyanazine, fluometuron, and norflurazon have water
solubilites greater than 5 mg/L. On the other hand, pesticides such as pendimethalin and
trifluralin (fig. 3) have a
solubility less than 1 mg/L and generally are not detected in surface runoff in the
Mississippi Embayment. These low-solubility compounds are tightly bound to soil and are not
readily transported to ground water. The pesticide-contaminated soil may be eroded at a later
time and may be carried by streams as part of the suspended load along with the pesticides
bound to the sediment. Analytical methods are currently (1998) being developed by the USGS to
determine how pendimethalin and trifluralin are bound to soil.
The seasonal distribution of total herbicides is shown in figure 7. Cotton has a long growing season,
almost 6 months, and herbicides may be applied throughout that period. Total concentrations
are highest from May to August when they may reach 100 µg/L. During the nongrowing
season, total herbicide concentrations average approximately 1 µg/L.
Insecticides were also detected in the surface water of the Mississippi Embayment, although
not as frequently and at much lower concentrations than the herbicides.
Figure 8 shows the detections of the insecticides monitored. Dicrotophos was the most
frequently detected (35 percent). It is a highly soluble (1,000 mg/L water solubility)
organophosphate insecticide that is used extensively (nearly 0.7 million pounds annually in
the cotton-growing areas, see fig.
3. Methyl parathion was detected next most frequently, with 18 percent detections. It is
the most-used insecticide in the cotton-growing areas, with more than 3.3 million pounds
applied annually (fig. 3).
However, because it is a volatile insecticide, it is detected less frequently and at lower
concentrations in surface water than dicrotophos, which is much less volatile. The third
most-detected compound was profenofos at 12 percent detections. This organophosphate
insecticide is used nearly three times as much as dicrotophos, yet it is found in lower
concentrations and less frequently. Apparently the shorter half-life of profenofos (about 7
days versus 10 to 15 days for dicrotophos) permits it to be more rapidly decomposed in soil,
and as a result, the parent compound occurs less frequently in surface water.
Of the organochlorine insecticides that were detected (fig. 8), endosulfan was detected most
frequently (3 percent) and in the highest concentrations. This result is consistent with the
fact that endosulfan is the only organochlorine that is still used legally in cotton-growing
areas. Organochlorine insecticides, especially DDT, were used intensively on cotton during
past years; therefore, more detailed monitoring by the USGS is underway for DDT and its
metabolites using passive sampling methods, such as semipermeable membrane devices (SPMDs).
Work with SPMDs shows that DDT and other organochlorine insecticides are present in surface
water at detectable levels (Bastian and others, 1997).
d Additional research by the USGS in the cotton-growing areas includes development of a
bacterial-growth assay using the luminescent organism Vibrio fischeri. Results from
this analytical method are being compared with pesticide concentrations determined by chemical
analysis to identify the relations among chemical application and spatial and temporal
variations in water quality. These bacterial-growth assays also have the potential to identify
interactions between the many organic compounds found in surface and ground water of
Also, passive samplers are being tested by the USGS for the determination of some of the most
insoluble insecticides, including DDT and its metabolites and the pyrethroids. The passive
samplers include SPMDs and SPE disks. These methods are being used on both air and water
samples from the Mississippi Embayment.
Methods are also being developed by the USGS using high-performance liquidchromatography/mass
spectrometry (HPLC/MS) for the analysis of insecticides and their metabolites. The
organophosphorus insecticide metabolites will be analyzed using this method. These metabolites
may be mobile in surface and ground water; therefore, methods to analyze these compounds are
needed in cotton-growing areas.
Lastly, pesticides in other cotton-growing areas of the United States, including Texas,
Arizona, and California, are being examined more extensively.
- Bastian, K.C., Thurman, E.M., Kleiss, B.A., Coupe, R.H., Jr., Huckins, J.N., and
Petty, J.D., 1997, Comparison of pesticide concentrations in semipermeable membrane devices
and fish tissue from the Mississippi Delta: Abstract and poster presentation at the 18th
Annual Meeting of the Society of Environmental Toxicology and Chemistry, San Francisco,
California, November 16-20, 1997.
- Battaglin, W.A., and Goolsby, D.A., 1995, Spatial data in geographic information
system format on agricultural chemical use, land use, and cropping practices in the United
States: U.S. Geological Survey Water-Resources Investigations Report 94-4176, 87 p.
- Gianessi, L.P., and Anderson, J.E., 1995, Pesticide use in U.S. crop production--
National data report: Washington, D.C., unpaginated.
- Thurman, E.M., Meyer, Michael, Pomes, Michael, Perry, C.A., and Schwab, A.P., 1990,
Enzymed-linked immunosorbent assay compared to gas chromatography/mass spectrometry for the
determination of triazine herbicides in water: Analytical Chemistry, v. 62, p. 2043- 2048.
Richard Rebich, Mississippi Delta Management Systems Evaluation Areas, Jackson, MS; Dr. David
Shaw, Mississippi State University, Starkville, MS; Jim Huckins, Biological Resources Division
of USGS, Columbia, MO; and Betsy Beal, Office of Pesticide Programs, U.S. Environmental
Protection Agency, Washington, D.C.
The use of firm names in this fact sheet is for identification purposes only and does not
constitute endorsement by the U.S. Geological Survey.
Chad Bastian, Richard Coupe, Ken Hostetler, Smiley Irelan, Jason Kish, Clydeen Logan, Chris
Robertson, Elisabeth Scribner, E. Michael Thurman, and Lisa Zimmerman.
For more information please contact:
E. Michael Thurman
U.S. Geological Survey
4821 Quail Crest Place
Lawrence, Kansas 66049