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>EPA Pesticide
Fact Sheet
Name of Chemical: Tebuthiuron
Reason for Issuance: Registration Standard
Date Issued: JUL 31 1987
Fact Sheet Number: 137
!• Description of Chemical
Chemical Name: N-f5-(1,l-dimethylethyl)-l,3,4-thiadiazol-
2-yl)-N,N'dimethylurea
Common Name : Tebuthiuron
EPA Shaughnessy Code: 105501
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Chemical Abstracts Service (CAS) Number: 34014-18-1
Year of Initial Registration: 1974
Pesticide Type: Herbicide
Producers: Elanco Products Company, Division
of Eli Lilly and Company
2- Use Patterns and Formulations
Type of pesticide: A relatively nonselective,"soil-actived1
herbicide for the control of broadleaf weeds, grasses and
brush in noncrop areas, and for spot treatment of woody
brush on rangelands. It is readily absorbed through roots
of broadleaf i^eeds, grasses and brush.
»
Pests controlled: Broadleaf weeds, grasses and brush.
Terrestrial uses: food crop (rangelands and pastures),
noncrop areas (airport runways, fencerows, firebreaks,
industrial sites, paved surfaces, and highway, railroad
and utility rights-of-way ).
Aquatic Uses: ditchbanks.
Predominant uses: Terrestrial noncrop areas
Mode of activity: Photosynthesis inhibitor
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Formulation: (95% a.i.) technical; 1%, 2%, 3%, & 5% granular;
10%, 13.8%, 15.2%, 20%, 30.5%, 40% pelleted/ tableted; 80%
wettable powder; 85% flowable concentrate; and 0.36%
soluble concentrate/liquid.
Method of application: Applied as broadcast or band by
ground or aerial equipment, spot treatment, drop zone or
drip zone treatment or grid pattern treatment.
Application rates: Terrestrial food and nonfood crops:
0.5 to 4.Olb. a.i. per acre, 1-4 grams a.i. per 100 sq.
ft., 1 gram ai. per inch of trunk diameter or 0.25 to
0.50 gram a.i. per ft. of plant height. Terrestrial
noncrop areas and aquatic nonfood crop areas: 1 to 16
lb. a.i. per acre; 0.13 to 0.14 lb. a.i. per 1,000 sq.
ft.; 0.1 lb. or 0.1 oz. a. i. per 2-4 inch of trunk diameter;
1 to 10 oz. finished spray per 2 to 4 inch of stem
diameter; 0.5 oz. a.i. per 1 to 2 inch of stem diameter.
3. Science Findings
Tebuthiuron has low acute toxicity by inhalation in rats,
and is Category III by this route. Toxicity Category III.
Subchronic feeding in rats and chronic feeding in dogs
indicate only mild effects on the liver, kidneys, gonads,
spleen, prostate and thyroid gland. No compound related
histological effects were seen.
A rat multigeneration study showed no adverse effects on
reproductive performance per Se; although parent females
in the high dose group failed to gain weight as those
in the lower doses and control group in the pre-mating phase
of the study.
The Agency is concerned about the potential for ground
water contamination by tebuthiuron, based on tebuthiuron’s
ability to resist environmental degradation and its
relatively high mobility (leachability) in a variety of
soils. The Agency has determined that additional data
are needed to characterize the potential for tebuthiuron
to enter ground water.
* Toxicity categories are based on the acute toxicity of
the chemical (LD 50 or LC 50 values) and are used to
determine the appropriate signal word and precautionary
language for product labeling. Category I II requires
the signal word CAUTION and precautions against swallow-
ing, inhaling, or contact with the skin and eyes, along
with appropriate first aid instruction.
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Terrestrial, avian and aquatic vertebrates and invertebrates
are not susceptible to Tebuthiuron, and it does not pose a
hazard to them. However, numerous endangered or theatened
plant species are at ri8k from the range and pastureland
uses of tebuthiuron and products released for shipment
after Feburary 1, 1988, and which recommend such uses
must bear Endangered Species Labeling.
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Chemical Characteristics :
Physical State: Crystalline solid
Color: Colorless, white
Melting Point: 159 to 161° C
Solubility: (at 25° C in mg/mL) 60 in acetonitrile; 70
in acetone; 170 in methanol; 20 in ethanol;
250 in chloroform; 60 in methyl cellosolve;
3.7 in benzene; 6.1 in hexane; and 2.5 in water.
Vapor Pressure: 2 x i06 mintig at 25° C
Octanol/Water Partition Coefficient: 61 (Log K = 1.79)
Stability: Stable
Acute Toxicology
Acute oral No valid studies.
A study is required.
Acute dermal No valid studies.
A study is required.
Acute Inhalation (rat) 3.696 n /L;
Toxicity Category III.
Primary Eye Irritation No valid studies.
A study is required.
Primary Dermal Irritation No valid studies.
A study is required.
Dermal Sensitization No valid studies.
A study is required.
Chronic Toxicology
Oncogenicity The oncogenic potential of
tebuthiuron cannot be deter—
mined from the available
study. Studies are required.
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Reproduction Reproductive effects NOEL=
(Rat) 400 ppm (20 mg/kg bwt/day)
systemic NOEL=100 ppm (5.0 mgI
kg bwt/day)
Chronic Feeding
(Beagle Dog) 1- year study.
(NOEL) = 25.0 mg/kg bwt/day.
Mutagenicity Not mutagenic in Ames assay
with or without metabolic
activation. Only slight signs
of mutagenicity in a mouse
lyniphoma assay.
Chromosomal Aberration Data limited but negative;
additional data required.
Metabolism Technical tebuthiuron and/or its
metabolites appear in the milk of
lactating rats. General metabolism
data are not available, but the
data are required.
Physiological and Biochemical Behavioral Characteristics
Foliar and Root Absorption - Tebuthiuron is absorbed through
roots, less so through the foliage.
tiechanisin of Pesticidal Action - Phytotoxicity symptoms
suggest that tebuthiuron inhibits photosynthesis.
Environmental Characteristics
Degradation
Tebuthiuron did not undergo significant degradation at p11 5,
7 and 9 at 25° C in 64 days and is considered stable in sterile
water.
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Preliminary data indicate that tebuthiuron is also quite stable
under aerobic and anaerobic soil conditions. Tebuthiuron only
degraded from 8 ppm to 5.7 ppm after 273 days (half life > 1
year) when incubated in loam soil at 25° C and was reported to
degrade in an identical soil under anae’robic conditions with
a half-life of >48 weeks. Similarly, irradiation with an
artificial light that did not quite simulate sunlight resulted
in only 42% decomposition after 15 days.
Tebuthiuron appears stable to biological and chemical degrada-
tion under environmental conditions and can be considered
persistent.
Leaching
Preliminary data indicate that tebuthiuron is mobile to very
mobile in loam, loamy sand, and lakeland sand soils and
slightly mobile in silty loam soil. Kd values of lower than
2 were reported for clay, sandy loam and sand soils.
About 40% of residues of a 30 days sandy loam aged tebuthiuron
were found in the leachate.
Based on the above information, tebuthiuron has the potential
to leach through a variety of soils and contaminate
groundwater. Tebuthiuron was flagged as a ground-
water contaminant through the GWDCI (Groundwater Data Call
In) screen and has been found in shallow groundwater in
Texas. Tebuthiuron will be further analyzed in the Agency’s
National Pesticides in Well Water Survey.
Existing data which were submitted in response to a Ground-
Water Data Call-In have been found to be inadequate to full-
fill Agency guidelines requirements. Therefore, additional
data are necessary to fully characterize cebuthiuron’s ability
to contaminate ground water.
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Ecological Characteristics
As a dietary administration, tebuthiuron is no more than
slightly toxic to birds, however, avian dietary
data are not complete. Avian reproductive studies show that
tebuthiuron has no effect on reproduction at dietary levels
up to 100 ppm.
Tebuthiuron is practically non-toxic (acutely) to fish
and aquatic invertebrates. A fi8h early life-stage study
gives a MATC (Maximum Allowable Toxic Concentration) between 9.3
and 18 mg/i based on impaired growth. Aquatic invertebrates show
significant reductions of growth and fecundity at 44 mg/i.
TheMATC for aquatic invertebrates is between 21.8 and 44.2ppm.
In 1972 tebuthiuron was conditionally registered for control
of brush in rangeland in Texas and Oklahoma. As a requirement
of the registration the registrant was requested to perform
a field monitoring study which would better define this
chemical’s actions in aquatic and terrestrial environments.
Instead of a single monitoring study, several studies (EPA
Accession No. 246373) were submitt d by the registrant to
fulfill the conditional requirement. While each study had
several deficiencies that would preclude their applicability
for singley satisfying the requirement, the series of studies
were considered sufficient to satisfy the monitoring condition
of the 1979 registration. In 1982, in response to a request
for the addition of 17 states to the tebuthiuron registration,
the Agency requested that the regi8trant continue (into a
second year) the monitoring of water and hydrosoil at four
study sites. The Agency is now requiring that these data be
submitted to support the registration of tebuthiuron.
Because of tebuthiuron’s extreme persistence, these monitoring
data are still necessary to determine the long-term availability
of the chemical for runoff into aquatic systems and the likeli-
hood of long-term buildup of tebuthiuron in the soil. Monitor-
ing data are being required through this Registration Standard.
If information from past monitoring is not available or is
determined to be unsatisfactory, a new monitoring study will
be required.
Although tebuthiuron is not expected to pose a hazard to
endangered or theatened terrestrial or aquatic animal species,
its use on range and pastureland will pose a hazard to endan-
gered or threatened plant species.
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Products containing tebuthiuron with range and pasture uses
which are released for shipment after February 1, 1988 must
bear Endangered Species Labeling.
Endangered Species Labeling for non-crop, wide area, and
general indoor/outdoor treatments is deferred until completion
of the analysis by OES and the Agency of the non-crop uses.
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Results Of Tolerance Assessment
Tolerances are established for residues of the herbicide tebu-
thiuron and its metabolites containing the dimethylethyl thia-
diazole moiety in or on the following raw agricultural commodi-
ties:
Commodities Tolerance(ppm)
Cattle, fat 2
CatUe,*mbyp 2
Cattle, meat 2
Goat, fat 2
Goat, mbyp 2
Coat, meat 2
Grass, hay 20
Grass,rangeland,forage 20
Horse,fat 2
Horse,mbyp 2
Horse,meat 2
Milk 0.3
Sheep, fat 2
Sheep, mbyp 2
Sheep, meat 2
The most recent Provisional Acceptable Daily Intake (PADI) is
0.017 mg/kg bwt/day based on the 5.0 mg/kg bwt/day systemic
NOEL derived from the most sensitive study, (the reproductive
NOEL was greater than 20 mg/kg bwt/day, the highest dose
tested), and using an uncertainty factor of 300 (the 300-
fold uncertainty factor is used because a chronic rodent study
is missing).
*Mbyp “meat by product”
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4. Summary Of Regulatory Position And Rationale
Summary of Agency Position: The Agency is requiring regis-
trants of Tebuthiuron to submit additional data as identi-
fied in the Registration Standard and summarized in the
following section. The Agency will not establish any new
food use or register any significant new uses until adequate
data are available to fully assess tebuthiuron.
Unique Warning Statements Required on Labels: Unique labeling
is not imposed in the Registration Standard. Endangered
species labeling, however, is required for rangeland and
pastureland. This labeling is addressed in Pesticide
Registration Notice (PR) 87-4 dated May 1, 1987.
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Summary of Data Gaps
Data
Product Chemistry
Due
6 to 15 Months
Residue Chemistry
Nature of Residues (Metabolism)
Residue Analytical Method
Storage Stability
Environmental Fate
18 Months
15 Months
6 Months
Photodegradation (water/soil)
Metabolism (Anaerobic/aerobic soil)
Leaching and Adsorption/Desorption
issipation (Soil/Aquatic)
ccumulation in Fish
Soil, Long Term
Irrigated Crops
Toxicology
Acute Dermal
Acute Oral
Primary Eye Irritation
Primary Derma]. Irritation
Dermal Sensitization
Chronic Toxicity (Rodent)
Oncogenicity (Rat and Mouse)
Teratogenicity (Nonrodent)
General Metabolism
Mutagenicicy (Chromosomal
Abe rrat ions)
Other Genotoxic Effects
Wildlife and Aquatic Organisms
9 Months
27 Months
12 Months
27 Months
39 to 50 Months
50 Months
39 Months
9 Months
9 Monts
9 Months
9 Months
9 Months
50 Months
48 to 50 Months
12 Months
24 Months
12 Months
12 Months
Nontarget Insect Testing
Avian Dietary LC5O
Field Monitoring (Special Studies)
Phytotoxicity
9 Months
12 Months
36 Months
9 Months
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5. Contact Person at EPA
Robert J. Taylor, PM 25
Registration Division (TS-767C)
U.S. Environmental Protection Agency
401 M Street SW.
Washington, DC 20460
(703) 557—1800
DISCLAIMER: The information presented in this Pesticide
Fact Sheet is for information purposes only and may not be
used to fulfill data requirements for pesticide registration
and teregistration.
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