E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 5/94
TRADE OR OTHER NAMES
Trade names for products containing the compound include Oust Weed
Killer and DPX 5648. It is compatible with other herbicides but is
incompatible with alkaline materials (1).
Sulfometuron methyl is a General Use Pesticide (GUP).
Sulfometuron methyl is a broad spectrum urea herbicide. It is used
for the control of annual and perennial grasses and broad-leaved weeds in
non crop land. It also has forestry applications where it is used to
control woody tree species. It is applied either postemergent or
preemergent. It works by blocking cell division in the active growing
regions of stem and root tips (meristematic tissue).
Sulfometuron methyl is a slightly toxic compound. Products containing
this compound require the signal word CAUTION on their labels. The acute
oral toxicity of the compound is very low. The LD50 of sulfometuron methyl
in rats is greater than 5,000 mg/kg (2). One study showed an LD50 greater
than 17,000 mg/kg (2). The acute dermal (skin exposure) toxicity of the
compound is also low. The LD50 values for exposure through the skin ranges
from over 2,000 mg/kg in female rabbits to over 8,000 mg/kg in male rabbits
(the highest doses tested, respectively). The compound is not a skin
irritant or a skin sensitizer (2).
The acute inhalation LC50 is above 5.3 mg/l in rats indicating its
slightly toxic nature (1).
Several toxic effects have been seen with chronic exposure to
sulfometuron methyl in rats. At low doses, relative to the compounds LD50
(50 mg/kg), the rats experienced a reduced red blood cell count, and an
increase in liver weight (2). In this study rats were fed the compound in
their food for a year.
In another study conducted over much shorter periods of time (90
days), rats had increased white blood cell counts (leukocytes) at the
highest dose tested (250 mg/kg). In a two year feeding study, no effects
were noted below 50 mg/kg (1).
No reproductive related effects were noted in rats fed up to 500 mg/kg
sulfometuron methyl in their diets (1). The test was conducted over two
successive generations of offspring.
In one rat study and two rabbit studies, the mothers were fed moderate
to high doses (up to 750 mg/kg) of sulfometuron methyl. No birth defects
were noted in their respective offspring (2). No maternal or fetal effects
were noted in rabbits fed up to 300 mg/kg, however, rats fed 250 mg/kg in
their diets exhibited lower maternal and fetal body weights (11, 12).
There is little likelihood that the compound would pose a significant
teratogenic risks to humans under normal conditions.
The compound was not mutagenic in a variety of tests conducted on
Salmonella cells and Chinese Hamster Ovary cells (5, 6, 7). Thus it is
unlikely that the compound would pose a mutagenic risk to humans at low
No carcinogenic effects have been detected in either rats or mice at
low to moderate doses of sulfometuron methyl (8, 9).
As was noted above, one of the chronic effects of this compound is the
increase in liver weights at relatively low doses (50 mg/kg) over a one
year time period (2).
Sulfometuron can cause eye irritation but the condition usually clears
within several days following exposure (2).
Fate in Humans and Animals
Sulfometuron is readily absorbed through the gastrointestinal tract
and is rapidly broken down and removed from the organism. Half lives of
the compound in rats ranged from 28 to 40 hours depending on the dose (16
mg/kg and 3000 mg/kg respectively). The compound did not accumulate in the
rats that were studied (10).
Effects on Birds
Sulfometuron is practically non-toxic to birds. The acute oral LD50
for mallards is greater than 5,000 mg/kg (1). Another dietary study with
mallard ducks also showed a similar result (LC50 greater than 5000 ppm)
Effects on Aquatic Organisms
The compound is slightly toxic to freshwater fish. Its LC50 in
rainbow trout and in bluegill sunfish is greater than 12.5 mg/l (1). While
the compound may not present a significant threat to adult aquatic
organisms, the embryo hatch stage of fathead minnow may be at particular
risk from the presence of the compound at a low concentration of 0.71 mg/l
(3). Fish kills have been reported for sulfometuron methyl but have not
been fully evaluated to rule out other causes (4).
A test with the water flea, Daphnia magna, indicated that the compound
was practically non-toxic to this species. The LC50 for sulfometuron
methyl in the water flea was greater than 1,000 mg/l (the highest
concentration tested) (3).
No bioaccumulation was noted in a test with bluegill fish when exposed
for 28 days at 1 mg/l (4). The compound was not detected in the muscle nor
the viscera of the fish.
Effects on Other Organisms (Nontarget species)
Because sulfometuron methyl is toxic to a number of plants and is non-selective,
the use of the compound on non-croplands, including rights-of-way
and along ditch banks, may endanger both terrestrial and aquatic plant
Breakdown of Chemical in Soil and Groundwater
Sulfometuron methyl is broken down in soil by the action of
microorganisms and by the chemical action of water (hydrolysis). In silt
loam soil, half of the initial amount of the compound degraded within 30
days. These values indicate that the compound is slightly persistent in
soil (4). In several field dissipation studies half of the initial
applied amount of the compound remained for 1 to 3 weeks depending on soil
type and vegetation cover (14, 15).
Under anaerobic soil conditions, the compound persists slightly longer
though the half-life is still rather short (up to 8 weeks). The compound
is also broken down through the action of sunlight (photolysis) (4).
Information on the rapid disappearance of the compound and slight
potential to move through soils indicate that the compound does not pose a
threat to groundwater.
Breakdown of Chemical in SurfaceWater
In well aerated acidic water, the compound is broken down relatively
quickly with a half-life of about 10 days. In more alkaline water, half of
the initial amount of the compound was lost within 8 months. This
indicates that acidity plays an important role in the degradation of the
compound. Under non-oxygenated (anaerobic) conditions in water sediments
the compound had a half-life of several months (4). The compound is only
slightly soluble in water; however, its solubility increases with
increasing alkalinity. The compound has the potential to be transported by
run-off water during intense storms soon after field application.
PHYSICAL PROPERTIES AND GUIDELINES
Sulfometuron methyl is an off-white solid compound with a molecular
weight of 364.4 g/mol. The compound is odorless (4).
|Common name: ||sulfometuron methyl
|Chemical name: ||2-(4,6-dimethylpyrimidin-2-ylcarbamoylsulfamoyl) benzoic acid
|Solubility in water: ||6.4 mg/l (pH 5) @ 25 degrees C and 244 mg/l (pH 7) @ 25 degrees C
|Solubility in solvents: ||3,300 mg/kg in acetone; 1,800 mg/kg in acetonitrile; 137 mg/kg in ethanol; 37 mg/kg in xylene (all @ 25 degrees C)
|Melting point: ||193-194 degrees C (13)
|Vapor pressure: ||negligible at 25 degrees C
|Specific gravity: ||1.48
|Partition coefficient (octanol/water) (log): ||0.84
|Adsorption coefficient: ||NA
|Chemical Class/use: ||urea; sulfonylurea herbicide
Du Pont Agricultural Products
Walker's Mill, Barley Mill Plaza
P.O. Box 80038
Wilmington, DE l9880-0038
Telephone: (800) 441-7515
Emergency: (800) 441-3637
Review by Basic Manufacturer:
Comments solicited: April, 1993
Comments received: May, 1993
The Agrochemicals Handbook: Third Edition. (1991). The Royal Society
of Chemistry, Unwin Brothers Ltd., Surrey, England.
U.S. Environmental Protection Agency. (1990). Office of
Pesticides/HED/SACB Tox Oneliners. Oust, MRID Nos. 244195, 245515.
U.S. Environmental Protection Agency. (1984). Oust Herbicide
(Sulfometuron methyl). Environmental Effects Branch. Washington, D.C.
Environmental Fate and Effects Division. (1992). Pesticide
Environmental Fate One Liner Summaries. Sulfometuron methyl.
DuPont Chemical Company. (1979). Mutagenic Activity in the
Salmonella/Microsome Assay (Ames Test). Unpublished study,
May 21, 1979. MRID No. 93206031.
DuPont Chemical Company. (1981). Chinese Hamster Ovary Cell Assay for
Mutagenicity. Unpublished study, January 26, 1981. MRID No. 93206032.
DuPont Chemical Company. (1981). In Vitro Cytogenetics Mutagenicity
Evaluation of H-13647-03 in an In Vitro Cytogenetic Assay Measuring
Chromosome Aberration Frequencies in Chinese Hamster Ovary (CHO) Cells.
Unpublished study, November 17, 1981. MRID No. 00146846.
DuPont Chemical Company. (1984). Long-Term Feeding Study in Rats
with Benzoic Acid, 2-[[[[(4,6-Dimethyl-2-Pyrimidinyl)Amino]Carbonyl]-
Amino]Sulfonyl]-, Methyl Ester (INT-5648). Unpublished study, December 27,
1984. MRID No. 00146849.
DuPont Chemical Company. (1987). Oncogenicity Study with INT-5648,
Long -Term Feeding Study in Mice. Unpublished study, September 28, 1987.
MRID No. 41273602.
DuPont Chemical Company. (1989). Metabolism of Sulfometuron Methyl in
Rats. Unpublished study, February 3, 1989. Not submitted to the EPA.
DuPont Chemical Company. (1990a). Teratogenicity Study by Diet in the
Rat with Benzoic Acid, 2-[[[[(4,6-Dimethyl-2-Pyrimidinyl)Amino] Carbonyl]-
Amino]Sulfonyl]-, Methyl Ester . Unpublished study. July 16, 1990. MRID
DuPont Chemical Company. (1990b). Teratology study in rabbits,
Benzoic Acid, 2-[[[[(4,6-Dimethyl-2-Pyrimidinyl)Amino] Carbonyl]-Amino]
Sulfonyl]-, Methyl Ester . Unpublished study, July 16, 1990. MRID No.
Brennan, D.E. (1990). Sulfometuron methyl: Physical and Chemical
characteristics. DuPont Chemical Company. Unpublished study. MRID No.
Anderson, J.J. (1981). Terrestrial Field Dissipation Study of 14C-
DPX-T5648 in Delaware, North Carolina, and Mississippi. DuPont Chemical
Company. Unpublished study. MRID No. 00094840.
Trubey, R.K. (1991) Field Soil Dissipation of Oust(R) Herbicide.
DuPont Chemical Company. Unpublished study.