United Ststas Office of Pattlddat and Toxic Sufactaneei
Environmental Protection Office of Pestiade Program* (TS-766C)
Agency Washington, DC 20460
xe/EPA Pesticide
Fact Sheet
Name of Chemical: Hybrex
Reason for ISSUanCe: New Chemical Registration
Date Issued: April 1986
Fact Sheet Number: 85
1. Description of chemical
Generic name: Potassium l-(4-chlorophenyl)-l,^-dihydrc~6-methyl-l4-
oxopyridazine-3-carboxylate
Common name: (ISO) Fenrldazone-potassium
Trade name: Hybrex
EPA Shaughnessy code: 119001
Year of Initial registration: 1986
Pesticide type: Hybridizing agent
Chemical family: dihydro-oxopridizlne
U.S. and foreign producers: Rohm and Haas
2. Use patterns and formulations
Application sites: wheat hybridizing agent (a chemical which allows
production of hybrid plants; in this particular case, through allowing
easier cross-pollination of normally self-pollinating species of
plant such as wheat).
Hybrex® detrimentally affects the pollen produced by treated wheat
plants so that they cannot be self-pollinated, but must rely instead
on a different untreated variety of wheat to supply the pollen. The
offspring is a hybrid wheat variety.
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Method of Application: Apply between the initiation of
jointing and fl-ag lea? tip emergence stages of growth.
Apply no later than 50 days before harvest with a ground.
rig, as a roliar spray in enough water to cover foliage.
Application Rates: Use 2 to 10 pints (0.5 to 2.5 lb active
ingredient) per acre with up to lj quarts of surfactant per
100 gallons of spray mixture.
Types of Pormulatlons: Liquid concentrate end use product
21.97% active ingredient.
Usual Carrier Water, with surractant.
3. SCIENCE FINDINGS
Summary Science statement- Hybrex has been round to be
acceptable for the proposed use and all data requirements
have been met. It is relatively non—toxic by the oral,
dermal an inhalation routes, mildly irritating to the
skin and causes corneal opacity at hours when
exposed to the eyes. Hazard to nontarget organisms
is considered to be minimal.
Chemical Characteristics:
Physical State- Aqueous solution
Color: Deep red to red/brown
Odor: Slight xylene odor
Boiltng Point: 100.2 °C
Molecular Weight- 302.76
So 1 ub iii ty:
Solvent Soluhility I
Distilled water, pH 5.0 1.97 + 0.10 g/l00 ml
Distilled water, pH 6.9Y l.Llu ÷ 0.H g/lOO ml
Methanol 7.02 ± 0.05 g/lOO ml
Absolute ethanol 0.2 147 + 0.OLO g/100 ml
Ethyl cellosolve 1.892 ± .002 g/lt0 ml
Dimethyl sulfoxide 0.670 + .039 g/lOO ml
Acetonitrile 200 t 90 mg/kg
Mixed xylenes < 61 mg/kg -
!/ Mean- value ± standard deviattorf of dujilicate
determinations. -
b/ This mixture was quite viscous: the sdlubflity
would be expected to be still higher at pH 9.
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Unusual Handling Characteristics:
No special handling needed.
Toxicology Characteristics
Acute effect : Hybrex Is relatively non—toxic by oral, dermal
and inhalation routes, mildly irritating to the skin and
causes corneal opacity at 21 hours when exposed to the eyes.
Acute test results Indicate Toxicity Categories Ti. IlL
and iv !! as follows
Acute oral toxicity (mouse)
Greater than 500 ppm (75 mg/kg/day)
Toxicity Category IV
Acute oral toxicity (rat)
Greater than 500 ppm (25 mg/kg/day)
Toxicity Category IV
Acute oral toxicity (mouse)
Greater than 2000 ppm (300 mg/kg/day)
Toxicity Category IV
Acute dermal toxicity (rabbit)
Greater than 5 g/kg
Toxicity Category III
Acute inhalation toxicity (rat)
Greater than 20.2 mg/i
Toxicity Category IV
Primary eye irritation (rabbit)
Corneal opacity at 2 hours
Toxicity Category II
Primary dermal irritation (rabbit)
Mildly irritating
Toxicity Category IV
1/ Precautionary labeling for: 1/ Toxicity Category II- Causes
e e irritation. Do not get in eyes, on skin, or clothing. Harmful
it swallowed. C appropriate first aid statement required ); -
Toxicity Category III- Harmful if swallowed. Avoid contact
with skin eyes or clothing. In case of contact immediately
flush eyes or skin with plenty of water. Get medical attention
If irritation persists; and Toxicity Category IV— No precautions
are required.
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Subchronic effects: Tests indicate sys-temic effects at_the
lowest dose tested (LDT).
1 i-Day dose finding study: No-observed-effect level (NOEL)
(rat) 6250 ppm (312.5 mg/kg/day)
90—Day feeding study (rat) NOEL less than 500 ppm (LDT)
(25 mg/kg/day)
Chronic effects: Tests indicate no oncogenic or teratogenic
potential and no reproductive toxicity, and only weak
mutagenicity In mouse lymphoma cells with three negative
mutagenicity studies reported.
1—year dietary toxicity : NOEL (62.5 mg/kg/day)
study (beagle dogs)
2—year rat feeding study NOEL 300 ppm (15 mg/kg/day)
No oncogenic effects observed.
18-month rat feeding study: NOEL 2,000 ppm (300 mg/kg/day)
No oncogenic effects observed.
3—generation reproduction : NOEL 100 ppm, (5 mg/kg/day)
study (rat) for systemic effects, ( 5
mg/kg/day) for reproductive
effects.
Teratology (rabbit) : NOEL (1,000 mg/kg/day),
fetal toxicity NOEL (100
mg/kg day), maternal toxicity
NOEL (100 mg/kg/day).
Teratology (rat) : NOEL 10,000 ppm (500 mg/kg/day).
fetal toxictty NOEL 0,000 ppm
(1,500 mg/kg/day), teratogenic
‘JOEL 30,000 ppm (1,500 mg/kg/day).
Mutagenicity Ames test : Negative
Mutagenicity Cytogenic : Negative
Mutagenicity Mouse Lymphoma cells:
Weakly mutagenic at 1250 g/ml
under both activated and non-
activated test conditions.
Mutagenicity in vitro transformation:
Negative
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The Acceptable Daily Intake (ADI)
NOEL of (15.0 mg/kg/day)
Major Routes of Exposure: Dermal, inhalation
Physiological and Biochemical Behavoiral Ch racterist1cs:
Foliar Absorption: Absorption occurs through the
foliage.
Translocation: The material Is translocated to the
fruiting parts from the foliage.
Mechanism of Action: Hybrex® detrimentally affects the
pollen produced by treated wheat plants so that they
cannot be self—pollinated but must rely instead on a
different untreated variety of wheat to supply the
pollen. The offspring is a hybrid wheat variety.
Persistence: Hybrex is not persistent In plants or animals.
Metabolism In plants and animals: The nature of the
residues In plants and animals is adequately understood
for the use of hybrex on wheat. The parent compound
and Its decarboxylated metabolite (2% plants, 1% or less
In animals) are the residues of concern. The residue
analytical method Is adequate for the determination
of residues In wheat and for enforcement purposes.
Environmental Characteristics: Hybrex is stable to hydrolysis
at pH 5.0 and 6.9. It is soluble In distilled water at
l.l4Li to 1.97 g/l0O ml.
Absorption and leaching in basic soil types: Hybrex is
strongly adsorbed, and not very mobile in soil.
Microbial breakdown: Hybrex Is decarboxilated slightly,
however the parent compound stays relatively intact
and Is strongly adsorbed to soil particles.
Loss from photodecompositlon and volatilization:
Photodecomposition is very slight and volatilization
does not occur.
Resultant average persistence: Hybrex should not persist
beyond 52 days.
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Ecological Characteristics: The following test results indicate
that Hybrex is practically nontoxic to avian species,
F infish, aquatic invertebrates and honeybees.
Hazards to Birds
Aviari acute oral toxicity: Greater than 5,000 ppm.
(mallard duck and bobwhite quail)
Avian dietary toxicity: Greater than 5,390 ppm.
(mallard duck and bobwhite quail)
Hazards to Fish
Fish acute toxicity:
Bluegill sunfish 141.3 ppm
Rainbow trout 266.5 ppm
Fathead minnow 43.7 ppm
(fathead minnows were very young)
Aquatic invertebrate toxicity
Daphnla magna 188.0 ppm
Honeybees:
Nontoxic to honeybees.
Tolerance Assessment:
List of Crops and Tolerances
Commodity Parts per million
Wheat grain Z40 .0
Wheat straw 25.0
Meat and meat
byproducts (except
kidney and liver) of
cattle, goats, hogs,
horses, and sheep. 0.05
Pat f cattle, goats,
hogs, horses, and..sheep. 0.05
K-ldney and liver
of cattle, goats.-
hogs. horses-, and
sheep.
1.00
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Pat Jne .t and meat
byproducts of poultry. 0.30
Eggs 0.05
Milk 0.05
1 L Summary of Regulatory Position and Rationale :
Position: The agency has accepted the use of this pesticide
for the production of hybrid wheat seed.
Rationale: The agency has reviewed the data submitted
and found these data to he adequate for the
proposed use of this pesticide. The proposed
use of’ this pesticide is not expected to
result in any adverse effects to humans or
the environment and will fill a need for
producing large quantities of hybrid wheat
seed.
Use Restrictions: or use by Rohm and Haas company or
or under the direct supervision of
their representative only.
Unique label statements: See use restrictions above.
5. Summary of major data gaps :
None.
6. Contact Person at EPA
Robert J. Taylor (PM—25)
U.S. Environmental Protection Agency (TS-767C)
I Ol M Street, SW.
Washington, DC 201460
(703) 557—1800
DISCLAIMER:
The information presented in this Chemical Information Fact
Sheet is for informational purposes only and may not be used to
fulfill data requirements for pesticide registration and
reregistration.
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