imazaquin (Scepter) Herbicide Profile 3/86
CHEMICAL FACT SHEET FOR:
FACT SHEET NUMBER: 83
DATE ISSUED: MARCH 20, 1986
1. DESCRIPTION OF CHEMICAL
- Generic Name: 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-
imidazol-2-yl]-3-quinoline carboxylic acid
- Common Name: imazaquin
- Trade Name: Scepter
- EPA Shaughnessy Code: 128821
- Chemical Abstracts Service (CAS) Number: None
- Year of Initial Registration: 1986
- Pesticide Type: Herbicide
- Chemical Family:
- U.S. and Foreign Producers: American Cyanamid
2. USE PATTERNS AND FORMULATIONS
- Application sites: Soybeans
- Methods of application: Scepter may be applied preplant incorporated,
preemergence, or postemergence. In southern locations only,
two applications are possible: an initial preplant incorporated or
preemergence treatment followed by a postemergence treatment.
- Application rates: Ground or aerial application rates are 2 oz.
a.i./A. Ground applications are in 10 or more gallons of water
per acre, and aerial applications are in 5 or more gallons of
water per acre. Where two applications are permitted, no more
than 0.25 lb. a.i./A per season may be applied.
- Types of formulations: 95% technical grade and 17.3% active
ingredient liquid concentrate end-use product.
- Usual carriers: Water
3. SCIENCE FINDINGS
- Physical state: solid
- Color: light tan
- Odor: none
- Melting point: 219-224 degrees C
- Solubility: 60 ppm at 25 degrees C
- Octanol/water partition coefficient: 2.2
- pH: 3.8 (slurried into 100 ml of de-ionized water at 23 degrees C)
- Acute effects: Imazaquin is relatively nontoxic by oral, dermal,
and inhalation routes, non-irritating to slightly irritating to
the eye and skin, and not a dermal sensitizer. Acute test results
indicate Toxicity Categories III and IV as follows:
- Acute oral toxicity (rat): Greater than 5,000 mg/kg, Toxicity
- Acute inhalation (rat): Greater than 5.7 mg/L, Toxicity Category
- Acute dermal (rabbit): Greater than 2,000 mg/kg, Toxicity
- Acute dermal sensitization (guinea pig): Not a sensitizer
- Primary dermal irritation (rabbit): Mildly irritating, Toxicity
- Primary eye irritation (rabbit): Non-irritating, Toxicity
- Subchronic effects: Tests indicate no systemic toxicity at the
highest dose tested (HDT).
- 21-day dermal (rabbit): No-Observed-Effect-Level (NOEL) = 1,000
- 90-day feeding study (rats): NOEL greater than 10,000 ppm or
- Chronic effects: Tests indicate no oncogenic or teratogenic
potential and no reproductive toxicity at HDT, and negative
activity in five mutagenicity studies.
- 1-year dietary toxicity study (beagle dogs): NOEL = 1,000 ppm.
Lowest-Observed-Effect-Level (LOEL) = 5,000 ppm
- 2-year oral dietary (rat): NOEL = 10,000 ppm (HDT) or 500
- 18-month oncogenicity (mouse): NOEL = 1,000 ppm (150 mg/kg).
Lowest Effect Level (LEL) = 4,000 ppm
- 3-generation reproduction (rat): NOEL = 10,000 ppm (1,000
- Teratology (rabbits): Teratogenic NOEL = 500 mg/kg/day.
Embryotoxic NOEL = 500 mg/kg/day. Maternal NOEL = 250 mg/kg/day.
Maternal LEL = 500 mg/kg/day
- Teratology (rats): Teratogenic - NOEL > 2,000 mg/kg/day.
Fetotoxic - NOEL = 500 mg/kg/day, LOEL = 2,000 mg/kg/day.
Maternal toxicity - NOEL = 500 mg/kg/day, LOEL = 2,000 mg/kg/day.
- Single low dose metabolism study (rats): Almost entirely
excreted in 48 hours, urine 94% and feces 4%.
- Mutagenicity (Ames test): negative
- Dominant lethal test (rats): negative
- In vitro cytogenetics (CHO): negative
- Unscheduled DNA synthesis (rat hepatocytes): negative
- CHO/HGPRT point mutation: negative
- Major routes of exposure: Dermal and inhalation.
Physiological and Biochemical Behavioral Characteristics
- Foliar absorption: Absorption occurs through both the foliage
- Mechanism of pesticidal action: When applied to soil,
susceptible weeds emerge, growth stops, and the weeds either die
or are not competitive 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.
- Metabolism in plants and animals: The nature of the residue in
plants and animals is adequately understood for the use of
imazaquin on soybeans. The parent compound is the residue
compound of concern. The residue analytical method is adequate
for the determination of residues in soybeans and for enforcement
- Imazaquin is stable to hydrolysis at pH 3 and 5, and has an
aqueous hydrolytic half-life of 5.5 months at pH 9. It is slightly
soluble in distilled water, 60 ppm at 25 degrees C.
- Absorption and leaching: Additional field dissipation studies
must be submitted to further define the leaching potential of
- Microbial breakdown: Imazaquin is decarboxylated slowly to CO2,
as well as degraded to the major metabolite CL 266,066 and at
least 6 minor metabolites.
- Loss from photodecomposition and/or volatilization: Volatilization
does not occur.
- Resultant average persistence: Imazaquin should not persist
beyond 4 to 6 months.
- The following test results indicate that imazaquin is practically
nontoxic to avian species, finfish, aquatic invertebrates, and
- Avian acute oral toxicity (mallard duck and bobwhite quail):
> 2,150 ppm
- Avian dietary toxicity (mallard duck and bobwhite quail): > 5,000
- Fish acute toxicity: rainbow trout, > 280 ppm; bluegill sunfish,
> 420 ppm; and channel catfish, > 320 ppm.
- Aquatic invertebrate toxicity (Daphnia magna): > 280 ppm
- Honeybee: Nontoxic at 100 ug/bee
- List of crops and tolerances (40 CFR 180.426): Soybeans at 0.05
parts per million.
- Results of tolerance assessment: The Accepted Daily Intake (ADI),
based on the 1-year dog feeding study (NOEL of 1,000 ppm or 25
mg/kg/day) and using a 100-fold safety factor, is calculated to be
0.25 mg/kg/day. The Maximum Permissible Intake (MPI) for a 60-kg
person is calculated to be 15 mg/day. The Theoretical Maximum
Residue Contribution (TMRC) for use on soybeans is calculated to
be 0.0007 mg/day, which accounts for 0.00 % of the ADI (0.25 mg/
Summary Science Statement
Scepter has been found to be acceptable for the proposed use. It
is relatively nontoxic by the oral, dermal, and inhalation routes,
non-irritating to slightly irritating to the eye and skin, and it
is not a dermal sensitizer. Hazard to nontarget organisms is
considered to be minimal.
4. SUMMARY OF REGULATORY POSITION AND RATIONALE
- The Agency has conditionally accepted the use of this chemical on
- The Agency has reviewed the data submitted and, with the exception
of field dissipation studies, found these data to be adequate for
the proposed use of this chemical. The proposed use of this
chemical, prior to completion of repeated field studies, is not
expected to result in any adverse effects to humans or the environment
and will fill a need for a herbicide to control weeds in soybeans.
- Use restrictions: none
- Unique label statements: none
5. SUMMARY OF MAJOR DATA GAPS
164-1 Field Dissipation Studies (Soil). due March, 1988.
6. CONTACT PERSON AT EPA
Robert J. Taylor (PM-25)
U.S. EPA (TS-767C)
401 M Street S.W.
Washington, DC 20460
DISCLAIMER: THE INFORMATION PRESENTED IN THIS CHEMICAL INFORMATION FACT
SHEET IS FOR INFORMATIONAL PURPOSES ONLY AND NOT TD BE USED TO FULFILL
DATA REQUIREMENTS FOR PESTICIDE REGISTRATION AND REREGISTRATION.