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Sulfometuron-methyl

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).

REGULATORY STATUS

Sulfometuron methyl is a General Use Pesticide (GUP).

INTRODUCTION

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).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

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).

CHRONIC TOXICITY

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).

Reproductive Effects

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.

Teratogenic Effects

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.

Mutagenic Effects

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 exposure levels.

Carcinogenic Effects

No carcinogenic effects have been detected in either rats or mice at low to moderate doses of sulfometuron methyl (8, 9).

Organ Toxicity

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).

ECOLOGICAL EFFECTS

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) (1).

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 species (3).

ENVIRONMENTAL FATE

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).

Exposure Guidelines:

RfD: NA
HA: NA
ADI: NA
PEL: NA

Physical Properties:

Common name: sulfometuron methyl
CAS#: 74222-97-2
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

BASIC MANUFACTURER

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

REFERENCES

  1. The Agrochemicals Handbook: Third Edition. (1991). The Royal Society of Chemistry, Unwin Brothers Ltd., Surrey, England.
  2. U.S. Environmental Protection Agency. (1990). Office of Pesticides/HED/SACB Tox Oneliners. Oust, MRID Nos. 244195, 245515.
  3. U.S. Environmental Protection Agency. (1984). Oust Herbicide (Sulfometuron methyl). Environmental Effects Branch. Washington, D.C.
  4. Environmental Fate and Effects Division. (1992). Pesticide Environmental Fate One Liner Summaries. Sulfometuron methyl.
  5. DuPont Chemical Company. (1979). Mutagenic Activity in the Salmonella/Microsome Assay (Ames Test). Unpublished study, May 21, 1979. MRID No. 93206031.
  6. DuPont Chemical Company. (1981). Chinese Hamster Ovary Cell Assay for Mutagenicity. Unpublished study, January 26, 1981. MRID No. 93206032.
  7. 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.
  8. 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.
  9. DuPont Chemical Company. (1987). Oncogenicity Study with INT-5648, Long -Term Feeding Study in Mice. Unpublished study, September 28, 1987. MRID No. 41273602.
  10. DuPont Chemical Company. (1989). Metabolism of Sulfometuron Methyl in Rats. Unpublished study, February 3, 1989. Not submitted to the EPA.
  11. 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 No. 93206029.
  12. 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. 93206030.
  13. Brennan, D.E. (1990). Sulfometuron methyl: Physical and Chemical characteristics. DuPont Chemical Company. Unpublished study. MRID No. 41672802.
  14. 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.
  15. Trubey, R.K. (1991) Field Soil Dissipation of Oust(R) Herbicide. DuPont Chemical Company. Unpublished study.