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Imazaquin

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).

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 (2).

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 (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 (5).

Imazaquin comes in emulsifiable concentrate and dispersable granule formulations. It is also formulated with other herbicides (3).

TOXICOLOGICAL EFFECTS

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 (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 (4, 5).

The acute oral LD50 for female mice was reported to be 2363 mg/kg (1, 2, 3).

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 (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).

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 (4, 5).

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 (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 (4, 5).

Mutagenic Effects

An Ames test for mutagenicity was negative (4).

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 (4, 5).

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% (5).

ECOLOGICAL EFFECTS

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 (1, 5).

The aquatic invertebrate toxicity (LC50) value for Daphnia magna is >280 ppm (5).

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).

ENVIRONMENTAL FATE

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).

Exposure Guidelines:

NOEL: 25 mg/kg/body weight/day (4, 5)
ADI: 0.25 mg/kg/body weight/day (4, 5)

Physical Properties:

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)

BASIC MANUFACTURER

American Cyanamid Co.
One Cyanamid Plaza
Wayne, NJ 07470-8426
Fax: 201-831-2570
Telephone: 201-831-2000
Emergency: 201-835-3100

Review by Basic Manufacturer:

Comments solicited: April, 1995
Comments received: not received

REFERENCES

  1. Herbicide Handbook of the Weed Science Society of America. 1989. Sixth edition. Champaign, IL.
  2. Farm Chemicals Handbook. 1995. Meister Publishing Co. Willoughby, OH.
  3. Thomson, W.T. 1993. Agricultural Chemicals. Book II: Herbicides. Thomson Publications, Fresno, CA.
  4. U.S. Environmental Protection Agency. 1986. Pesticide Tolerances for Imazaquin. Federal Register. Vol. 51, No. 63. Rules and Regulations. Wednesday, April 2, 1986.
  5. U.S. Environmental Protection Agency. March 20, 1986. Pesticide Fact Sheet Number: 83. US EPA, Office of Pesticide Programs, Registration Div., Washington, DC.