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TRADE OR OTHER NAMES: Trade names for products containing imazaquin include Ala-Scept, Scepter, Squadron,
Tri-Scept, and Partner (205, 223).
REGULATORY STATUS: Imazaquin 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 imazaquin must bear the signal
word "Caution" on their label (223).
CHEMICAL CLASS: imidazole compound
INTRODUCTION: Imazaquin is a imidazole compound used as a selective, pre- and postemergence herbicide. It controls
weeds by inhibiting the acetohydroxy acid synthase enzyme responsible for the production of valine, leucine and isoleucine.
Activity is first seen in the growing points of susceptible plants where amino acid demands are greatest. The compound is
used to control grasses and broadleaved weeds including cocklebur, pigweeds, prickly sida, nightshade, mustard,
smartweed, ragweed, velvetleaf, jimsonweed, foxtails, seedling johnsongrass, lambsquarters, sicklepod, morningglory and
others. Crops include soybeans, turf and ornamentals (205, 207). When imazaquin is applied to soil, susceptible weeds
emerge, growth stops and the weeds either die or are not competetive with the crop. When applied postemergence,
adsorption occurs through both the foliage and roots, growth stops and the weeds either die or are not competitive with the
crop. When applied preemergence, rainfall or irrigation is necessary to activate imazaquin (324). Imazaquin comes in
emulsifiable concentrate and dispersable granule formulations. It is also formulated with other herbicides (207).
- Acute Toxicity: Imazaquin is relatively nontoxic by oral, dermal and inhalation routes, nonirritating to slightly irritating
to the eye and skin and not a dermal sensitizer. 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. Acute test results indicate toxicity
categories III and IV as follows: The acute oral LD50 for rats exposed to imazaquin is >5000 mg/kg, toxicity category
IV (205, 223, 207, 323, 324). The acute inhalation toxicity for rats is >5.7 mg/L, toxicity category III (323, 324). The no
effect level in rats is >10,000 ppm which is equivalent to 831 mg/kg of body weight/day (205). The acute dermal LD50
for rabbits exposed to imazaquin is >2000 mg/kg, toxicity category III (323, 324). An acute dermal sensitization study in
guinea pigs found imazaquin not to be a sensitizer (323, 324). Primary dermal and eye irritation studies found imazaquin
to be mildly irritating and nonirritating, respectively. Both are toxicity category IV (323, 324). The acute oral LD50 for
female mice was reported to be 2363 mg/kg (205, 223, 207).
- Chronic Toxicity: The NEL for dogs and rats exposed to imazaquin was 1000 ppm and 5000 ppm, respectively. The
dermal LD50 for rabbits was >2000 mg/kg (205). Studies of chronic exposure to imazaquin included a 21-day dermal
study in rabbits with a no-observed-effect level (NOEL) of 1,000 mg/kg/bwt/day, the highest dose tested; a 90-day
feeding study in rats supporting a NOEL of 10,000 ppm (or 800 mg/kg/bwt/day), the highest does tested; a 2-year oral
dietary study in Sprague-Dawley (SD) rats tested at levels of 1,000, 5,000 and 10,000 ppm with a NOEL of 10,000 ppm,
the highest dose tested, or 500 mg/kg/bwt/day (323, 324). A 1-year dietary toxicity study in beagle dogs tested at 0, 200,
1,000 and 5,000 ppm with a NOEL of 1,000 ppm and a LOEL of 5,000 ppm with decreased body weight gain, skeletal
myopathy, slight anemia, bone marrow hyperplasia, increased serum levels of SGOT, DSGPT and CPK and increased
relative liver weights (323, 324).
- Reproductive Effects: A three-generation reproduction study in SD rats tested at levels of 1000, 5000 and 10,000 ppm,
with a NOEL of 10,000 ppm (1000 mg/kg/bwt), the highest dose tested (323, 324).
- Teratogenic Effects: A teratology study in rats tested at 0, 250, 500 and 2,000 mg/kg/bwt/day with a teratogenic NOEL
of >2,000 mg/kg/bwt/day, a fetotoxic NOEL of 500 mg/kg/bwt/day, a fetotoxic lowest-observed-effect level (LOEL)
2,000 mg/kg/day with a slight decrease in fetal weight and reduced ossification, a maternal toxicity NOEL of 500
mg/kg/bwt/day, and a maternal toxicity LOEL of 2,000 mg/kg/bwt/day with salivation, alopecia lethargy, flaccidity, and
8 percent mortality (323, 324). A teratology study in New Zealand white rabbits tested at levels of 100, 250, and 500
mg/kg/day, with a teratogenic NOEL of 500 mg/kg/day, an embryotoxic NOEL of 500 mg/kg/day, a maternal NOEL of
250 mg/kg/day, and a maternal lowest effect level (LEL) of 500 mg/kg/day with decreased weight gain (323, 324).
- Mutagenic Effects: An Ames test for mutagenicity was negative (323).
- Carcinogenic Effects: An 18-month oncogencity study in the CD-1 mouse tested at levels of 250, 1000 and 4000 ppm,
with a NOEL of 1000 ppm (150 mg/kg/bwt) and a LEL of 4,000 ppm resulted in decreased body weight gain in females
- Organ Toxicity: No information was found.
- Fate in Humans and Animals: A single low-dose metabolism study in rats showed that imazaquin was almost entirely
excreted in 48 hours; urine - 94%, feces - 4% (324).
- Effects on Birds: Imazaquin is practically non-toxic to birds when used as recommended. The avian acute oral toxicity
(LD50) for mallard ducks and bobwhite quail is greater than 2150 ppm. The avian dietary toxicity for the same species is
greater than 5000 ppm (205, 324).
- Effects on Aquatic Organisms: Imazaquin is practically non-toxic to fish when used as recommended. The acute
toxicity values (LC50) for fish exposed to imazaquin are: >280 ppm for rainbow trout; >420 ppm for bluegill sunfish;
and >320 ppm for channel catfish (205, 324). The aquatic invertebrate toxicity (LC50) value for Daphnia magna is >280
- Effects on Other Animals (Nontarget Species): Imazaquin is non-toxic to honeybees at 100 ug/bee. Imazaquin is
non-toxic to wildlife when used as recommended (205, 324).
- Breakdown of Chemical in Soil and Groundwater: The movement of imazaquin in the soil is limited. The compound
is nonvolatile. Loss from photodecomposition is minor. Thus, the resultant average persistance is season long or not
more than 4-6 months when used at recommended rates (205, 324). Imazaquin readily breaks down via microbial
breakdown in the soil. It is decarboxylated slowly to CO2, as well as degraded to the major metabolite CL 266,066 and
at least six minor metabolites (324).
- Breakdown of Chemical in Surface Water: Imazaquin is stable to hydrolysis at pH 3 and 5 and has an aqueous
hydrolytic half-life of 5.5 months at pH 9 (324).
- Breakdown of Chemical in Vegetation: Imazaquin is absorbed rapidly through roots and foliage and translocates
through both the xylem and phloem. Tolerant plants such as soybeans metabolize the active ingredient quickly.
Susceptible plants either do not metabolize or slowly metabolize imazaquin (205, 324).
PHYSICAL PROPERTIES AND GUIDELINES
- Appearance: Imazaquin technical is a tan solid with a slightly pungent odor. The formulation is a clear reddish, brown
solution with a strong sweet, nutty odor (205). Imazaquin is a liquid at room temperature (223).
- Chemical Name: 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2- y1]-3-quinolinecarboxylic (205)
- CAS Number: 81335-37-7
- Molecular Weight: 311.3
- Water Solubility: at 25 degrees C 0.06 g/100 ml (60 ppm) (205, 223)
- Solubility in Other Solvents: at 25 degrees C
- DMF: 6.8 g/100 ml
- Methylene chloride: 1.4 g/100 ml
- Methanol: 0.5 g/100 ml
- Acetone: 0.3 g/100 ml
- Ethanol: 0.3 g/100 ml
- Toluene: 0.04 g/100 ml
- Heptane: 0.02 g/100 ml (205)
- Melting Point: 219-224 degrees C (205, 223)
- Vapor Pressure: <2 x 10 to the minus 8 mmHG at 45 degrees C (205)
- Partition Coefficient: Not Available
- Adsorption Coefficient: Not Available
- ADI: 0.25 mg/kg/body weight/day (323, 324)
- 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.