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TRADE OR OTHER NAMES: Trade names for products containing imazethapyr include Contour, Hammer, Overtop,
Passport, Pivot, Pursuit, Pursuit Plus, and Resolve (205, 223, 207).
REGULATORY STATUS: Imazethapyr is a general use pesticide with a toxicity classification of III (slightly toxic).
Check with specific state regulations for local restrictions which may apply. Products containing imazethapyr must bear the
signal word "Caution" on their label (223). It is currently being tested on alfalfa, clover and other crops in the U.S. and is
being sold on these commodities outside the U.S. (207).
CHEMICAL CLASS: imidazole compound
INTRODUCTION: Imazethapyr is an imidazole compound used as a selective herbicide. It is applied preplant
incorporated, preemergence, at cracking, and postemergence. The compound controls weeds by reducing the levels of three
branched-chain aliphatic amino acids, isoleucine, leucine and valine, through the inhibition of aceto-hydroxyacid synthase, an
enzyme common to the biosynthetic pathway for these amino acids. This inhibition causes a disruption in protein synthesis
which, in turn, leads to an interference in DNA synthesis and cell growth. The compound is used to control grasses and
broadleaved weeds including barnyardgrass, crabgrass, cocklebur, panicums, pigweeds, nightshade, mustard, smartweed,
velvetleaf, jimsonweed, foxtails, seedling johnsongrass, lambsquarters, morningglory and others. Tolerant crops include
soybeans, peanuts, dry and edible beans, peas, alfalfa and imidazolinone resistant/tolerant corn. Additional research is being
conducted on other leguminous crops (205, 223, 207). Imazethapyr comes in aqueous concentrate formulations. It is also
formulated and may be combined with other herbicides (223, 207).
- Acute Toxicity: The amount of a chemical that is lethal to one-half (50%) of experimental animals fed the material is
referred to as its acute oral lethal dose fifty, or LD50. The acute toxicity of the technical and formulated products are as
- Technical: The acute oral LD50 for technical imazethapyr was reported to be >5000 mg/kg for rats. The acute
inhalation LC50 for rats exposed to imazethapyr is 3.27 mg/L. The dermal LD50 for rabbits exposed to technical
imazethapyr was >2000 mg/kg. It was found to be slightly irritating to the rabbit eye, with complete recovery in 7
days. The technical material was found to be slightly irritating to the skin of male rabbits (325, 327).
- Pursuit formulation: The oral LD50 of the 2 lb/gallon liquid formulation of imazethapyr was also >5000 mg/kg
for the rat and rabbit. The LC50 was >2.67 mg/L. The dermal LD50 was >5000 mg/kg. The liquid formulation
was non-irritating to the rabbit eye and skin (205, 223, 207, 325, 327).
- Pursuit DG formulation: (70% dispersable granule) The oral LD50 of the granular formulation was >5000
mg/kg for the rat and >2000 mg/kg for the rabbit. It resulted in moderate irritation to the rabbit eye, with
complete recovery in 14 days. It showed slight skin irritation to the rabbit with complete recovery in 72 hours
(205, 223, 327).
- Chronic Toxicity: 90-day dietary subchronic toxicity studies in rats and dogs had a No Observable Effect Level
(NOEL) of 10,000 ppm, the highest dose tested (205). A 1-year feeding study in dogs fed diets containing of 0, 1,000,
5,000, or 10,000 ppm reported a NOEL of 1,000 ppm (25 mg/kg/day) (5).
- Reproductive Effects: A two-generation reproduction study in rats fed dietary levels of 0, 1,000, 5,000, or 10,000 ppm
reported a NOEL for systemic and reproductive effects of 10,000 ppm (500 mg/kg/day, the highest dose tested)(326).
- Teratogenic Effects: A developmental toxicity study in rats fed dosage levels of 0, 125, 375, and 1,125 mg/kg/day,
reported a maternal toxicity NOEL of 375 mg/kg/day and a developmental toxicity NOEL of greater than 1,125
mg/kg/day, the highest dose tested (326). A developmental toxicity study in rabbits fed dosage levels of 0, 100, 300, and
1,000 mg/kg/day reported a maternal toxicity NOEL of 300 mg/kg/day and a developmental toxicity NOEL of greater
than 1,000 mg/kg/day, the highest dose tested (326).
- Mutagenic Effects: A mutagenic test with Salmonella typhimurium was negative; an in vitro chromosomal aberration
test in Chinese hamster ovary cells was positive without metabolic activation but at dose levels that were toxic to the
cells and negative with metabolic activation; an in vivo chromosomal aberration test in rat bone marrow cells was
negative; and a DNA synthesis study in rat hepatocytes was negative (205, 326).
- Carcinogenic Effects: An 18-month carcinogenicity study with mice fed diets containing 0, 1,000, 5,000, or 10,000
ppm with no carcinogenic effects observed under the conditions of the study at levels up to and including 10,000 ppm
(1,500 mg/kg/day, the highest dose tested) and a systemic NOEL of 5,000 ppm (750 mg/kg/day) (326). A 2-year chronic
toxicity/carcinogenicity study in rats fed diets containing 0, 1,000, 5,000, or 10,000 ppm with no carcinogenic effects
observed under the conditions of the study at levels up to an including 10,000 ppm (500 mg/kg/day, the highest dose
tested) and a systemic NOEL of 10,000 ppm (500 mg/kg/day, the highest dose tested) (326).
- Organ Toxicity: No information was found.
- Fate in Humans and Animals: No information was found.
- Effects on Birds: Study results reported the acute oral LD50 for mallard ducks and bobwhite quail to be >2150 mg/kg
body weight. The 8-day dietary LC50 for the same species was >5000 ppm (205).
- Effects on Aquatic Organisms: Study results reported the 96-hour LC50 for channel catfish to be 240 mg/l, 420 mg/l
for bluegill sunfish, and 340 mg/l for rainbow trout. The 48-hour LC50 for the aquatic crustacean Daphnia magna (water
flea) was >100 mg/l (205).
- Effects on Other Animals (Nontarget species): The contact LD50 for honey bees was >100 microgram/bee(205).
- Breakdown of Chemical in Soil and Groundwater: The formulated product does not leach through the soil. It is
weakly to moderately adsorbed and is not lost from the soil through volitilization. Soil microorganisms do not appear to
play a significant role in the degradation of the formulated product (205).
- Breakdown of Chemical in Surface Water: No information was found.
- Breakdown of Chemical in Vegetation: The formulated product is readily absorbed through the roots and foliage. It is
translocated in both xylem and phloem tissues and accumulates in growing points (205, 207).
PHYSICAL PROPERTIES AND GUIDELINES
- Appearance: Technical imazethapyr is an off-white to tan solid with a slightly pungent odor. The formulated product is
a clear dark brown liquid with a musty odor. The formulated product is corrosive to zinc, mild steel, brass, copper, and
aluminum (205, 207). Thermal decomposition products may include toxic oxides of carbon and nitrogen (325).
- Chemical Name: 2-[4.5-dihydro-4-methyl-4-(1 -methylethyl)-5-oxo-lH-imidazol- 2-yl]-5-ethyl-3-pyridinecarboxylic
- CAS Number: 81335-77-5
- Molecular Weight: 289.3
- Water Solubility: (distilled) 0.14 g/ml at 25 degrees C (205, 325)
- Solubility in Other Solvents: Soluble in dimethyl sulfoxide, methanol, methylene chloride; moderately soluble in
acetone and 2-propanol; slightly soluble in toluene; very slightly soluble in heptane (205, 325).
- Melting Point: 169 to 173 degrees C (336 to 343 F) (205)
- Vapor Pressure: <1 x 10 to the minus 7 mmHg at 60 degrees C (140 F) (205)
- Partition Coefficient: Not Available
- Adsorption Coefficient: 11 at pH 5, 31 at pH 7, and 16 at pH 9
- ADI: 0.25 mg/kg body weight/day (326)
- MCL: Not Available
- RfD: Not Available
- PEL: Not Available
- HA: Not Available
- TLV: Not Available
American Cyanamid Co.
One Cyanamid Plaza
Wayne, NJ 07470-8426
- Fax: 201-831-2570
- Telephone: 201-831-2000
- Emergency: 201-835-3100
References for the information in this PIP can be found in Reference List Number 10
DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide
product label/ing or other regulatory requirements. Please refer to the pesticide product label/ing.