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A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Primisulfuron-methyl

Trade and Other Names: Trade names include Beacon, CGAA 136872, Rifle, and Tell. Primisulfuron-methyl may be found in mixes with other herbicides such as 2,4-D, dicamba, cyanazine, bromoxynil, and atrazine.

Regulatory Status: Primisulfuron-methyl is a practically nontoxic compound in EPA toxicity class IV. Labels for products containing it must bear the Signal Word CAUTION. Primisulfuron-methyl is a General Use Pesticide (GUP).

Chemical Class: substituted urea

Introduction: Primisulfuron-methyl is a selective post-emergence herbicide used to control grassy and broad leaved weeds in crop and non-crop applications. It is the methyl ester of primisulfuron, and is similar in its toxicological and environmental fate characteristics. Primisulfuron-methyl is available in wettable powders and water dispersible granules in water-soluble packets.

Formulation: Primisulfuron methyl is available in wettable powders and water dispersible granules in water-soluble packets.

Toxicological Effects:

• Acute toxicity: Primisulfuron-methyl is practically non-toxic by ingestion, with a reported oral LD50 of greater than 5050 mg/kg in rats [4,8]. Via the dermal route, it is moderately to practically nontoxic, with a dermal LD50 of greater than 2010 mg/kg in rats and rabbits [4,7]. Slight skin irritation was observed in rabbits after dermal application of primisulfuron-methyl, but it did not cause skin sensitization in male guinea pigs [4,15]. In rabbits, primisulfuron-methyl caused slight eye irritation that cleared within 3 days after contact [15]. The 4-hour inhalation LC50 for primisulfuron-methyl is greater than 4.8 mg/L in rats, indicating slight toxicity by this route [4].
• Chronic toxicity: Doses of 125 mg/kg/day administered in the diet to dogs over a 1-year period produced decreased body weight gain, anemia, increased liver weight, and thyroid hyperplasia (abnormal growth) [15]. Rats fed dietary doses of about 180 mg/kg/day over 90 days showed effects similar to those noted in dogs, as well as spleen weight increases [24]. In another study, doses of 480 mg/kg/day in rats over 18 months produced increased incidence of tooth disorders, chronic nephritis (kidney damage), and testicular atrophy [4]. In two 18-month studies in mice, testicular atrophy, chronic nephritis, and increased tooth and bone disorders were seen at doses of 180 mg/kg/day and 360 mg/kg/day, respectively [4].
• Reproductive effects: Changes in the function of the testes were noted in rats fed high doses (250 mg/kg/day) of primisulfuron-methyl over two generations. There was also a decrease in the body weight of the offspring. No compound-related effects on reproduction were noted at doses below 50 mg/kg/day [15]. Testicular atrophy was seen in rats in chronic studies (see above), which could result in reproductive effects. The available data suggest that reproductive effects in humans due to primisulfuron are not likely under normal circumstances.
• Teratogenic effects: No teratological effects were seen in offspring of rabbits given doses of up to 600 mg/kg/day. In one study of rats, delayed skeletal development and lack of ossification was seen in offspring of pregnant rats given doses of 500 mg/kg/day, while in another, 100 mg/kg/day produced incomplete ossification of the pubic bone [15]. The available evidence suggests that primisulfuron-methyl is not teratogenic except at very high doses.
• Mutagenic effects: Primisulfuron-methyl did not cause mutations in extensive testing. These tests included the Ames assay with and without metabolic activation, the Chinese hamster ovary cell culture, chromosomal aberration assay, and the rat liver cell unscheduled DNA synthesis assay [4,15]. This indicates that this compound is not mutagenic.
• Carcinogenic effects: In an 18-month study, mice that were fed doses of 180 mg/kg/day showed increased liver tumors, but this same dose level failed to produce the same effect in the same species in another investigation over the same period [4,15]. No carcinogenic activity was seen in rats fed up to about 450 to 500 mg/kg/day [4]. The available data suggest that primisulfuron is not carcinogenic.
• Organ toxicity: Target organs identified in animal studies include the liver, kidneys, spleen, and testes, as well as the skeleton.

• Fate in humans and animals: Nearly all of a single dose (level not noted) of primisulfuron-methyl fed to rats was excreted unchanged in the feces and the urine within 9 days [15]. Relatively low concentrations were identifiable in the feces and urine of rats, goats, and chickens fed the compound [15].

Ecological Effects:

• Effects on birds: Primisulfuron-methyl is practically nontoxic to wildfowl. Both bobwhite quail and mallard ducks show a high tolerance for the compound. The 5-day dietary LC50 for primisulfuron-methyl in both these species was in excess of 2150 ppm [4]. In addition, mallards fed moderate amounts of the compound showed no adverse effects on reproduction at the highest dose tested (500 ppm in their diet) [15].
• Effects on aquatic organisms: Primisulfuron-methyl is only slightly toxic to freshwater fish, aquatic organisms, and marine (estuarine) shrimp. The reported 96-hour LC50 values are greater than 48 mg/L in bluegill, and greater than 13 mg/L in rainbow trout [4,15]. The compound is practically nontoxic to the freshwater invertebrate Daphnia magna [15].
• Effects on other organisms: Primisulfuron-methyl is nontoxic to honey bees [5,6].

Environmental Fate:

• Breakdown in soil and groundwater: Primisulfuron-methyl is of low to moderate persistence in the soil environment, with a field half-life of from 4 to 60 days. A representative value is estimated to be about 30 days. Aerobic conditions enhance the breakdown in soils [4,15]. Losses due to volatilization and photodegradation are negligible [4]. Acidic conditions will accelerate the breakdown process. Primisulfuron-methyl is poorly sorbed to most soils and is soluble in water and thus may be mobile [25]. However, in field tests, no primisulfuron-methyl was detected below 9 inches of the surface [15].
• Breakdown in water: Primisulfuron is resistant to hydrolysis in alkaline and neutral solutions [15]. Anaerobic conditions will increase persistence. A half-life of 22 days at a pH of 5 has been reported [7].
• Breakdown in vegetation: It is rapidly absorbed by plants and translocated throughout the plant roots and foliage [4]. The herbicide works by blocking cell growth in the active growing regions of the plant (meristems) and by blocking photosynthesis [15]. Primisulfuron-methyl application to crops grown previously on the same land resulted in detectable amounts in wheat, soybeans, sugar beets, corn, and lettuce [4].

Physical Properties:

• Appearance: Primisulfuron-methyl is a colorless, crystalline solid under normal conditions [7].
• Chemical Name: 2-[4,6-bis(difluoromethoxy)pyrimidin-2-ylcarbamoylsulfamoyl]benzoic acid [7]
• CAS Number: 113036-87-6
• Molecular Weight: 468.30
• Water Solubility: 70 mg/L @ 20 C [7]
• Solubility in Other Solvents: s.s. in acetone, cyclohexane, isopropanol, methanol, and xylene [7]
• Melting Point: 203.1 C [7]
• Vapor Pressure: 0.000001 mPa [7]
• Partition Coefficient: 0.1987 [7]
• Adsorption Coefficient: 50 (estimate) [25]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: Not Available
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Ciba-Geigy Corporation
P.O. Box 18300
Greensboro, NC 27419-8300

• Phone: 800-334-9481
• Emergency: 800-888-8372
  

References:

References for the information in this PIP can be found in Reference List Number 9