imazapyr, isopropylamine salt Herbicide Profile 9/85
CHEMICAL FACT SHEET FOR
FACT SHEET NUMBER: 63
DATE ISSUED: JULY 24, 1984
DATE UPDATED: SEPTEMBER 5, 1985
1. DESCRIPTION OF CHEMICAL
- Generic Name: 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1-H-imidazol
- Common Names: Cl 243,997 and AC 243,997
- Trade Name: Arsenal
- EPA Shaughnessy Code: 128829
- Chemical Abstracts Service (CAS) Number: 81334-34-1
- Year of Initial Registration: 1984
- Pesticide Type: Herbicide
- Chemical Family: imidazolinone
- U.S. and Foreign Producers: American Cyanamid Company
2. USE PATTERNS AND FORMULATIONS
Application sites: Noncropland areas such as railroad, utility, and pipeline
rights-of-way, utility plant sites, petroleum tank farms, pumping
installations, fence rows, storage areas, non-irrigation ditch banks, and
other similar areas.
Types of formulations: Aqueous solution of isopropylamine salt.
Types and methods of application: End-use product may be applied either
preemergence or postemergence to the weeds. In most situations, the preferred
method is postemergence application. Product is mixed with water and applied
as a spray.
Application rates: 0.5 to 1.5 lbs. acid equivalent per acre, depending on weed
species and degree of infestation.
Usual carriers: Water. Drift control agent and foam reducing agent may be
added if needed.
3. SCIENCE FINDINGS
- Physical state: powder
- Color: white to off-white
- Odor: slight acetic acid odor
- Melting point: 169-173 degrees C
- Bulk density: 13.1 lb./cubic foot
- Solubility: 1.0 to 1.5% in water at 25 degrees C
- Dissociation constant: pk1 = 1.9, pk2 = 3.6
- Octanol/water partition coefficient: 1.3
- pH: 3-3.5 as 1% solution in water at 25 degrees C
- Stability: stable at 25 degrees C for at least 18 months
Acute toxicology results:
- Acute oral toxicity (rat): > 5,000 mg/kg, Toxicity Category III.
- Acute dermal toxicity (rabbit): > 2,000 mg/kg, Toxicity Category
- Primary eye irritation (rabbit): Toxicity Category III
- Primary skin irritation (rabbit): Toxicity Category IV
- Acute inhalation toxicity (rat): > 5.1 mg/l (nominal),
> 1.3 mg/l (gravimetric), Toxicity Category III.
- Dermal sensitization (guinea pig): Technical material is not a skin
Chronic toxicology results:
- 21-day dermal (rabbit): Systemic NOEL is 400 mg/kg/day (HDT). The NOEL
for skin is 400 mg/kg/day (HOT).
- Teratology (albino rat): NOEL for teratogenicity and fetotoxicity is
1,000 mg/kg/day. The NOEL for maternal toxicity is 300 mg/kg/ day.
The LEL is 1,000 mg/kg/day, with salivation occurring in 6 of 22 females.
- Teratology (albino rabbit): Test material was not teratogenic or fetotoxic
at dosages up to 400 mg/kg/day (HOT). The maternal toxic NOEL is 400
- Mutagenicity: Technical material was not mutagenic in the Ames assay.
- Metabolism (rat): The half-life of the technical was less than one day.
There was no significant radiolabeled compound detected in tissue
Major routes of exposure: Mixers, loaders, and applicators would be expected
to receive the most exposure via skin contact and inhalation.
Physiological and Biochemical Behavioral Characteristics
- Foliar absorption: The product is absorbed by roots and foliage.
- Translocation: The product translocates readily following absorption, and
is distributed between roots and foliage.
- Mechanism of pesticidal action: The herbicide prevents the production of
the amino acids valine, leucine, and isoleucine. Once the levels of these
amino acids decrease, protein synthesis slows down and growth stops. The
growing points of target plants die first. Mature, green tissue is not as
- Adsorption and leaching in basic soil types: The technical material has a
moderate leaching potential. The adsorption coefficient (K) ranges from 1.7
in a clay loam soil (4.0% organic matter) to 4.9 on a silt loam soil (4.0%
organic matter). The adsorbed material will desorb from soil.
- Loss from photodecomposition: Technical material will photodegrade in
aqueous solution with a half-life of 2.5 to 5.3 days (12 hours of
- Fish acute toxicity (rainbow trout): > 100 mg/l
- Fish acute toxicity (bluegill sunfish): > 100 mg/l
- Fish acute toxicity (channel catfish): > 100 mg/l
- Aquatic invertebrate toxicity (Daphnia magna): > 100 mg/l
- Avian acute oral toxicity (bobwhite quail): > 2,150 mg/kg
- Avian acute oral toxicity (mallard ducks): > 2,150 mg/kg
- Avian dietary toxicity (bobwhite quail): > 5,000 ppm
- Avian dietary toxicity (mallard ducklings): > 5,000 ppm
Summary Science Statement
Results of acute toxicity studies indicate Toxicity Category III. Chronic
studies present no evidence of unacceptable health hazards resulting from
proposed use. Ecological effects data indicate that the technical acid is
practically nontoxic to avian and aquatic organisms. Additional fish and
wildlife studies are required on the salt formulation. Several data gaps
exist in environmental fate.
4 SUMMARY OF REGULATORY POSITION AND RATIONALE
Use, formulation, manufacturing process, or geographical restrictions:
Do not use on food or feed crops. Do not apply to ditches used to transport
irrigation water. Do not apply where runoff water may flow onto agricultural
land, as injury to crops may result. Keep from contact with fertilizers,
insecticides, fungicides, and seeds. Do not apply or drain or flush equipment
on or near desirable trees or other plants, or on areas where their roots may
extend, or in locations where the chemical may be washed or moved into contact
with their roots. Do not use on lawns, walks, driveways, tennis courts, or
similar areas. Prevent drift of spray to desirable plants. Do not use in
Unique label warning statements: Physical and Chemical Hazards: Spray
solutions of Arsenal should be mixed, stored, and applied only in stainless
steel, fiberglass, plastic, and plastic-lined containers.
Do not mix, store, or apply Arsenal or spray solutions of Arsenal in unlined
steel (except stainless steel) containers or spray tanks.
5. SUMMARY OF MAJOR DATA GAPS
The following studies are to be done with the end-use product: Avian single
dose oral LD50 (one test), avian dietary LC50 (two tests, waterfowl and upland
game bird), acute toxicity test for freshwater fish (two tests, warm water and
cold water species), acute toxicity test for freshwater aquatic invertebrates
A waiver of above studies will be considered if data are supplied that fulfill
one avian dietary study, one freshwater fish study, and an aquatic
invertebrate study, and demonstrate equivalent toxicity levels to the
Environmental fate: Non-guideline study (application of 14C Arsenal to
weeds), fish accumulation study, and field dissipation study (if field crop
uses are proposed in the future).
6. CONTACT PERSON AT EPA
Robert J. Taylor
Product Manager (25), TS-767C
Environmental Protection Agency
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 TO BE USED TO FULFILL DATA
REQUIREMENTS FOR PESTICIDE REGISTRATION AND REREGISTRATION.