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: 6/96
TRADE OR OTHER NAMES
Trade names for products containing imazaquin include Ala-Scept, Scepter,
Squadron, Tri-Scept, and Partner (1, 2).
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 (2).
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 (1, 3).
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 comes in emulsifiable concentrate and dispersable granule
formulations. It is also formulated with other herbicides (3).
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 (1, 2, 3, 4, 5). The acute inhalation toxicity for rats
is >5.7 mg/L, toxicity category III (4, 5). The no effect level in rats is
>10,000 ppm which is equivalent to 831 mg/kg of body weight/day (1).
The acute dermal LD50 for rabbits exposed to imazaquin is >2000 mg/kg,
toxicity category III (4, 5). An acute dermal sensitization study in guinea
pigs found imazaquin not to be a sensitizer (4, 5).
Primary dermal and eye irritation studies found imazaquin to be mildly
irritating and nonirritating, respectively. Both are toxicity category IV
The acute oral LD50 for female mice was reported to be 2363 mg/kg (1, 2, 3).
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 (1).
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 (4, 5).
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 (4, 5).
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 (4, 5).
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 (4, 5).
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
An Ames test for mutagenicity was negative (4).
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 (4, 5).
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% (5).
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 (1, 5).
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
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 (1, 5).
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 (1, 5).
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 (5).
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 (5).
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 (1, 5).
PHYSICAL PROPERTIES AND GUIDELINES
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
(1). Imazaquin is a liquid at room temperature (2).
|NOEL: ||25 mg/kg/body weight/day (4, 5)
|ADI: ||0.25 mg/kg/body weight/day (4, 5)
|CAS #: ||81335-37-7
|Chemical name: ||2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-y1]-3-quinolinecarboxylic (1)
|Chemical Class/Use: ||imidazole compound used as a selective, pre and postemergence herbicide (3)
|Specific gravity: ||bulk density - 0.39 g/ml untapped, 0.43 g/ml tapped (technical), 1.0-1.1 g/ml (formulation) (1)
|Solubility in water: ||at 25 degrees C 0.06 g/100 ml (60 ppm) (1, 2)
|Solubility in other solvents:
at 25 degrees C
|DMSO: ||15.9 g/100 ml
|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 (1)
|Melting point: ||219-224 degrees C (1, 2)
|Decomposition temperature: ||219-224 degrees C (1)
|Vapor pressure: ||<2 x 10 to the minus 8 mmHG at 45 degrees C (1)
|Kow: ||2.2 (5)
American Cyanamid Co.
One Cyanamid Plaza
Wayne, NJ 07470-8426
Review by Basic Manufacturer:
Comments solicited: April, 1995
Comments received: not received
Herbicide Handbook of the Weed Science Society of America. 1989. Sixth
edition. Champaign, IL.
Farm Chemicals Handbook. 1995. Meister Publishing Co. Willoughby, OH.
Thomson, W.T. 1993. Agricultural Chemicals. Book II: Herbicides.
Thomson Publications, Fresno, CA.
U.S. Environmental Protection Agency. 1986. Pesticide Tolerances for
Imazaquin. Federal Register. Vol. 51, No. 63. Rules and Regulations.
Wednesday, April 2, 1986.
U.S. Environmental Protection Agency. March 20, 1986. Pesticide Fact
Sheet Number: 83. US EPA, Office of Pesticide Programs, Registration Div.,