United Slates Office of Pesticides
Environmental Proteciion and Toxic Substances
Agency (H7501C) 540/FS-91-137
S-EPA Pesticide
Fact Sheet
Name of Chemical: uithiopyr
Reason for Issuance: Registration
Date Issued: June is, 1991
Fact Sheet Number: 223
1. DESCRIPTION OF CHEMICAL
Generic Name: 3,5-Pyridinedicarbothioic acid,
2-(difluoromethyl)-4-(2-methylpropyl)-
6-(trifluoromethyl)-S,S-dimethyl ester
Common Name: MON-72UU, MON-15100 and Dithiopyr
Trade Names: Dimension" Turf Herbicide
EPA Shaughnessy Code: 128994-1
Chemical Abstracts Service (CAS) Number: 97886-45-8
Year of Initial Registration: 1991
Pesticide Type: Herbicide
Chemical Family: Pyridine
U.S. Producer: Monsanto Company
2. USE PATTERNS AND FORMULATIONS
Application sites: Terrestrial non-food sites.
Preemergence and early postemergence for selective
control of crabgrass and other susceptible annual
grasses and broadleaf weeds in established lawns
and ornamental turf.
Types of formulations: The two end-use products
are liquid emulsified suspensions of the active
ingredient; with nominal concentrations of 12.7%
(MON 15151 EC Herbicide) and 13.2% (MON 15104 EC
Herbicide). Acute toxicity studies were with
formulatons containing 12.5%, and were within the
limits of variation for these products.
Amount and Method of Application: A single application
of 0.5U Ib. active ingredient per acre per season is
claimed for both preemergence and postemergence
selective weed control in the culture of turf.
Ground spray application of an aqueous suspension
is the only method of application registered.
-------
~ 2 —
Carrier: Water
3. SCIENCE FINDINGS
Summary Science Statements:
Adequate toxicological, product chemistry, ecological
effects, environmental fate and ground water
data have been submitted and reviewed to support the
conditional registration of dithiopyr for use as a
preemergence and postemergence herbicide in the culture
of ornamental turf grasses. Technical dithiopyr is class-
ified as a Toxicity Category IV pesticide and is labeled
with the signal word "CAUTION", based on a battery of 6
acute studies.
Dithiopyr was non-mutagenic and in developmental
toxicity studies it did not appear to be a potential
developmental toxicant. Ecological effects data character-
ize dithiopyr as practically nontoxic to birds on subacute
dietary and acute oral bases. Toxicological data
demonstrate that it is of low acute toxicity to mammals.
A subchronic 90-day feeding study in rats indicated
a no observable effect level (NOEL) of 0.662 mg/kg/day.
At the 6.62 mg/kg/day there was an increase in organ
weights and diffused hepatocellular swelling. It has
little to no potential for ground water contamination.
It is stable to hydrolysis in neutral and mildly
alkaline solutions. At pH 9 it had a half-life of
1053 days based on first order kinetics. Photode-
gradation in water could contribute significantly
to the overall degradation of dithiopyr in the
environment. Photodegradation of dithiopyr on soil
is insignificant. Therefore, photodegradation on soil
will not contribute significantly to its degradation
in the environment.
Chemical Characteristics:
Physical State: Solid, crystalline
Color: Chemically Pure: White
Technical Grade: Yellow to Burnt Yellow
Odor: Sulfurous
Melting Point: 65-67° C
Density: 1.413 gm/cm3 at 25° C (typical)
-------
-3-
Molecular Weight 401.4
Solubility Solvent at
Parts per Million: Water 1.38 20° C
Grams per 100 ml: Hexane < 3.30 25° C
Toluene > 25.00 25° C
Acetone > 33.30 25° C
Diethyl
ether > 50.00 25° C
Ethanol > 12.00 25° C
Methylene
chloride > 50.00 25° C
Vapor Pressure: 4.0 x 10~6 mm/Hg at 25°C
Dissociation Constant: Not required, Dithiopyr is not
an acid
Octanol/Water Partition Coefficient: P = 5.625 x 104
pH: (in non-aqueous solvent): 4.152
Stability
Less than 1% change in assay was observed after 14 days
of exposure to sunlight, 14 days of exposure to Cu, Zn
and Fe, 14 days of exposure to a temperature of 50° C.
The formulated end use product (MON-15151 EC Herbicide)
was stable stored 12 months at 68 and 80°F. Only
a change of 0.37% in quantity of active ingredient
occurred.
Toxicology Characteristics:
Acute Toxicity ( 90.9%, Technical, MON-7200/MON 15100)
Acute oral toxicity (rats and mice): LD$Q > 5000 mg/kg,
Toxicity Category IV.
Acute dermal toxicity (rat): LD5Q > 5,000 mg/kg,
Toxicity Category IV.
Primary dermal irritation (rabbit): Slight erythema
but no edema within 0.5 hours. No effects by 72 hours.
Toxicity Category IV.
Primary eye irritation (rabbit): No corneal opacity;
irritation reversible within 24 hours.
Toxicity Category IV.
Acute inhalation toxicity (rat): LCso > 5.89 mg/L for
-------
-4-
males and females (nose exposure only).
Toxicity Category IV.
Dermal sensitization (guinea pig): Not a dermal
sensitizer by the Buehler method.
Acute Toxicity (12.5% a.i., Dimension Turf Herbicide, MON-15151)
Acute oral toxicity (rats): L-DSQ = 4100 mg/kg for males
and 3/000 for females.
Toxicity Category III.
Acute dermal toxicity (rats): No deaths,
>5000 mg/kg, Category IV.
Primary dermal irritation (rabbit): Severe dermal
irritation. Superficial (epidermis) necrosis,
clearing within 14 days. Category II.
Primary eye irritation (rabbit): Corneal corrosion
reversible with 21 days, and possibly within 7 days;
corneal opacity reversible within 7 days.
Category II.
Acute inhalation toxicity (rat): LCso = 11 mg/L *
for males. LCso = 8-9 mg/L for females.
Category IV.
Dermal sensitization (guinea pig): Positive for dermal
sensitization by Buehler method.
Acute Toxicity (12.5% a.i., Dimension Turf Herbicide, MON-15104)
Acute oral toxicity (rat): LDso > 5000 mg/kg for males
and females. Toxicity Category IV.
Acute dermal toxicity (rabbit): LD$Q > 5000 for males
and females. Toxicity Category IV.
Primary dermal irritation (rabbit): Very slight or slight
irritation at 72 hours, clearing within 10 days.
Toxicity Category IV.
Primary eye irritation: (rabbit): No corneal opacity;
irritation reversible within 24 hours. Toxicity
Category IV.
Acute inhalation toxicity (rat): LCso > 3.4 mg/L for males
and > 4.5 mg/L for females. Toxicity Category III.
-------
-5-
Dermal sensitization (guinea pig): Not a dermal sensitizer
by the Buehler method.
Subchronic Toxicity
A 21-day dermal study in rats was conducted using
levels of 0, 50, 500 and 1,000 mg/kg/day. Limited
to transient mild irritation occurred in all dose
groups. Incidence was generally dose-related and
higher in females than in males. The NOEL was
500 mg/kg/day and the LEL was 1000 mg/kg/day.
In a rat developmental toxicity study there were no develop-
mental effects at 1000 mg/kg/day (HDT). Maternal effect
was decreased food consumption. The NOEL for this
effect was 300 mg/kg/day and the LEL was 1000 mg/kg/day.
In a rabbit developmental toxicity study there were no develop-
mental effects at 1000 mg/kg/day (HDT). Maternal effect
was reduced body weight gain. The NOEL for this
effect was 500 mg/kg/day and the LEL was 1000 mg/kg/day.
In a 90-day subchronic study in rats a NOEL of 0.662
ing/kg/day was indicated based on an LOEL of 6.62 mg/
kg/day in females. The effect was an increase in
organ weight and diffused hepatocellular swelling.
Mutagenicity
The following mutagenicity studies indicated that
Dithiopyr is not mutagenic at doses tested:
- Ames Assays for mutagenicity with Ames (TA) strains of
Salmonella typhimurium LT2 were found negative
for reverse gene mutation (his" to his"*") at limit
of solubility (3,000" _ug/plate) with or without activation.
- Ames Assays for mutagenicity with Ames (TA) strains of
Salmonella were found negative for reverse gene mutation
(his~ to his+) at 5,000 ucf/plate with or without
activation.
- Gene mutation at the HGPRT locus in Chinese
hamster ovary cells exposed with or without activation
up to cytotoxic dose levels: (300 u_g/ml/-S9; 30 \ag/ral/+S9) .
- Structural chromosome aberrations in Chinese hamster
lung cells exposed to the limit of solubility
(0.33 and 1.0 mM).
-------
-6-
- Unscheduled DNA synthesis (UDS) in primary rat
hepatocytes (HPC), as measured by silver grain counts
indicative of DNA damage/repair.
Mechanism of Pesticidal Action;
Dithiopyr is a mitotic inhibitor of normal cell
division of susceptible plants. The formation and
function of microtubulin is inhibited. Susceptible plant
roots are stunted and fail to function in the presence
of dithiopyr. Plants do not grow and develop through
their normal cycle of vegetative growth followed by
reproduction (flowering and seed setting). Susceptible
plants react to dithiopyr in such a way as to be
less competitive.
Environmental Characteristics:
Hydrolysis: Dithiopyr does not hydrolyze in neutral
solutions and only slowly in alkaline solutions
(pH 9). At pH 9 it has a half-life of 1053 days
based on first order kinetics. Data indicate
that ester hydrolysis, which appears to be the
hydrolysis pathway for dithiopyr/ will not be |
a significant route of degradation of dithiopyr ^
in the environment.
Photodegradation: The half-life of dithiopyr in
sunlight was 17.6 and 20.6 days for nonsen-
sitized and humic acid solutions/ respectively.
The parent material comprised 24.5% of the
applied radioactivity. The half-life of dithiopyr
in soil was determined to be 444.3 days. Based
on the data dithiopyr is classified as photo-
stable in or on soil. These findings indicate
that photodegradation in water could contribute
significantly to the overall degradation of
dithiopyr in the environment. In water dithiopyr
can be expected to degrade to a mixture of normal
acid/ reverse acid, and lesser amounts of polar
compounds upon exposure to sunlight. Photodegrad-
ation of dithiopyr on soils is insignificant.
Therefore/ photodegradation on soil will not
contribute significantly to its degradation in
the environment.
Aerobic Soil Metabolism: In aerobic soil maintained
under laboratory conditions/ dithiopyr degraded
to the normal acid/ reverse acid and diacid. The
maximum concentrations of degradates were reached
at 6-12 months post-treatment.
-------
-7-
Anaerobic Soil Metabolism: An anaerobic aquatic metabolism
is required and will be submitted as a condition of
registration.
Field Dissipation: Dissipation occurs in the field
with vegetation coverage with a half-life of between
17 and 61 days depending on soil composition/
weather conditions and formulation applied. Three
major metabolites of dithiopyr (the normal acid,
reverse acid and diacid metabolites) are formed
and dissipated within 365 days.
Leaching, Adsorption/Desorption: Vertical mobility
of dithiopyr and its acid metabolites through
soil, even in conditions highly susceptible to
herbicide leaching, was found not to exceed 24 inches
and was often not more than 9 to 12 inches. At
a use rate of U.5 Ib/A of dithiopyr, metabolites could
be observed at only barely or nondetectable levels.
Residues should not persist beyond the growing season
and would not be expected to vertically move to a
significant extent in soil.
Potential to Contaminate Ground Water: The low solubility
in water and its high tendency to bind to soil
prevents dithiopyr from being carried downward
through soil. Dithiopyr has a low potential for
leaching into ground water. Surface water con-
tamination from soil containing dithiopyr would
be expected.
Ecological Characteristics
Avian Studies: Dithiopyr is practically non-toxic
to birds based on the following studies:
Single Dose Oral Toxicity:
Mallard duck with 90% Technical:
> 2250 mg/kg
Subacute Dietary Toxicity:
Mallard duct with 90% Technical:
LDso > 5620 ppm
Bobwhite quail with 90% Technical:
LD50 > 5620
Avian Reproduction: A study is required as a condition
of registration.
-------
-8-
Aquatic Organisms: The following data indicate that
dithiopyr is highly toxic to freshwater fish and
aquatic invertebrates:
Fish Acute Toxicity:
Bluegill sunfish, LCso = 0.47 mg/L
Rainbow trout, LCso = 0.46 mg/L
Early Life-stage Toxicity:
Rainbow trout, NOEC = 0.052 mg/L
Freshwater Invertebrates:
A supplemental study indicates that the 48 hour
LCso based on nominal concentration is greater
than 5.6 ug/L. An acceptable study is required
as a condition of registration.
Endangered Species Hazards:
Based on available data, the conditionally registered
use-pattern of dithiopyr is unlikely to pose a hazard to
endangered aquatic and avian species. There may
be some hazard to endangered plant species from
runoff and movement of the products from treated turf
areas.
4. Summary of Regulatory Postion and Rationale
Available data provide adequate information to support
the conditional registration of Dimension* Turf
Herbicide (MON-15151), Dimension* Turf Herbicide
(MON-15104) and MON-15100, that were first conditionally
registered June 18, 1991 under Section 3 of the Federal
Insecticide, Fungicide and Rodenticide Act as amended.
Use, Formulation, Manufacturing Process or
Geographic Restrictions: Aerial applications of
dithiopyr products are not permitted. All products
must bear the precautionary statement: "This pesticide
is toxic to fish." End-use products must bear the
use precaution: "During mixing and loading wear chemical
resistant gloves. Wash non-disposable gloves throughly
with soap and water before removing".
Conditional registration will expire on July 31, 1994.
5. Summary of Data Gaps
Toxicology Data:
1. Dermal Penetration Study (Guidelines Ref. No. 85-2),
Data are due July 18, 1992.
-------
-9-
Exposure Data:
1. Worker Exposure Studies (Upgrade the passive
dosimetry study and the biological monitoring
study). Data are due September 18, 1993.
Ecological Effects Data:
1. Acute LCso Freshwater Invertebrate Study, EPA Ref.
Guidelines 72-2. Data are due March 18, 1992.
2. Avian Reproduction with a Waterfowl and Bobwhite
Quail, EPA Ref. Guidelines 71-4. Data are due
July 18, 1993.
3. Acute LCso Estuarine/Marine Organisms Studies,
EPA Ref. Guidelines 72-3, identified as:
o 96-hour LCso f°r an estuarine marine fish
o 96-hour LCso for a shrimp species
o Either a 48-hour embryo larvae study or a
96-hour shell deposition study with oyster.
Data are due July 18, 1992.
4. Aquatic Invertebrate Life-Cycle Study, EPA Ref.
Guidelines 72-4. Data are due September 18, 1992.
5. Nontarget Area Phytotoxicity :
Tier II: o Seed germination/seedling emergence,
EPA Ref. Guideline 123-1
o Vegetative vigor, EPA Ref. Guideline
123-1
o Aquatic plant growth, EPA Ref. Guide-
lines 123-2.
Tier III: o Terrestrial Field1, EPA Ref. Guidelines
124-1
o Aquatic field2, EPA Ref. Guidelines 124-2
I/ Required if a 25 percent or greater
detrimental effect was found in 1 or more
plant species in corresponding test of
previous tier.
2/ Required if a 25 percent or greater
detrimental effect was found on any
plant species in the corresponding test
of the previous tier.
Data are due March 18, 1992.
-------
-10-
Environmental Fate and Ground Water Data:
1. Anerobic Aquatic Metabolism Study, EPA Ref. Guide-
lines 162-3. Data are due September 18, 1993.
2. Field Dissipation Study, Bare Ground, EPA Ref.
Guidelines 164-1. Data are due September 18, 1993,
6. Contact Person at EPA
Joanne I. Miller
Product Manager 23
Fungicide-Herbicide Branch
Registation Division (H-7505C)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street SW
Washington, DC 20460
Office Location and Telephone Number
Room 237, Crystal Mall Building #2
1921 Jefferson Davis Highway
Arlington, VA 22202
(703) 557-1830
DISCLAIMER: The information presented in this Pesticide Fact
Sheet is for informational purposes only and may not be used
to fulfill data requirements for pesticide registration and
reregistration.
-------
-------
vvEPA
United States
Environmental Protection Agency
Office of Pesticide Program (H7504C)
PMSD, Information Services Branch
401 M Street, SW
Washington. DC 20460
First-Class
Postage and Fees Pan
EPA
Permit No G-35
Official Business
Penalty for Private Use S300
4
------- |