United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508W)
EPA-738-F-94-006
April 1994
RF.D. FACTS
Pesticide
Reregistration
Tebuthiuron
All pesticides sold or distributed in the United States must be
registered by EPA, based on scientific studies showing that they can be used
without posing unreasonable risks to people or the environment. Because of
advances in scientific knowledge, the law requires that pesticides which
were first registered years ago be reregistered to ensure that they meet
today's more stringent standards.
In evaluating pesticides for reregistration, EPA obtains and reviews a
complete set of studies from pesticide producers, describing the human
health and environmental effects of each pesticide. The Agency imposes
any regulatory controls that are needed to effectively manage each
pesticide's risks. EPA then reregisters pesticides that can be used without
posing unreasonable risks to human health or the environment.
When a pesticide is eligible for reregistration, EPA announces this and
explains why in a Reregistration Eligibility Decision (RED) document. This
fact sheet summarizes the information in the RED for tebuthiuron.
Use Profile Tebuthiuron is a relatively nonselective, soil activated herbicide that
acts by inhibiting photosynthesis. It is used to control broadleaf and woody
weeds, grasses and brush on feed crop sites (pasture and rangeland) and a
variety of non-food crop sites including airports/landing fields, outdoor
industrial areas, non-agricultural rights-of-way, fencerows, hedgerows,
uncultivated areas/soils, and under paved roads and sidewalks in areas
where no future landscaping is planned. Primary uses include rangeland
and near railroads and other industrial facilities.
Single active ingredient formulations include granular,
pelleted/tableted, wettable powder, water dispersible granules, and technical
grade/solid products. Three multiple active ingredient formulations
(granulars) also are registered. All formulations may be applied as
broadcast, banded or spot treatments using ground equipment. The
pelleted/tableted formulations also may be applied using aerial equipment.
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Regulatory
History
Human Health
Assessment
Tebuthiuron was first registered as a pesticide in the U.S. in 1974.
EPA issued a Registration Standard for tebuthiuron in July 1987 (NTIS
#PB87-231866), which identified the potential for groundwater
contamination as well as hazards to endangered plant species from use of
tebuthiuron on pasture and rangeland, and which required additional generic
data.
In 1988, EPA issued a Ground Water Data Call-In which required a
small scale retrospective ground water monitoring study. A 1991 Data Call-
in required residue chemistry studies on residues in meat and milk. In
1992, the technical producer stopped supporting the only aquatic use site
(ditchbanks).
Currently, 12 pesticide products are registered which contain the
active ingredient tebuthiuron.
Toxicity
In acute toxicity studies, tebuthiuron is moderately toxic by the oral
route. It has been placed in Toxicity Category II for this effect in rats,
rabbits and cats, and in Category III for mice and dogs. (Category I
indicates the greatest degree of acute toxicity and IV the least.)
Tebuthiuron is practically non-toxic by the dermal route (Toxicity Category
IV), and only slightly toxic by the inhalation route (Toxicity Category III).
The pesticide is not a dermal irritant, causes only slight irritation to the eyes
(Toxicity Category IV), and is not a dermal sensitizer.
Tebuthiuron does not appear to cause any adverse developmental or
reproductive effects. Based on an acceptable carcinogenicity study in rats
and two supplemental carcinogenicity studies in mice, in which no
compound-related carcinogenic effects were observed, tebuthiuron is
classified as a Group D carcinogen (not classifiable as to human
carcinogenicity). The available data indicate that tebuthiuron does not
appear to be mutagenic.
Dietary Exposure
Tolerances or maximum residue limits are established for residues of
tebuthiuron on grass hay and forage; in the meat of cattle, goats, horses and
sheep; and in milk (see 40 CFR 180.390). A reduction in the grass hay and
forage tolerance from 20 ppm to 10 ppm is recommended since residues do
not typically exceed the lower value.
EPA's worst-case exposure estimates indicate that the overall U.S.
population is exposed to 9% of the Reference Dose (RfD) or amount
believed not to cause adverse effects if consumed daily over a 70-year
lifetime. Non-nursing infants (up to 1 year old) are exposed to 32% of the
RfD, and children age 1-6 are exposed to 21% of the RfD. The effect of
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concern is depressed body weight gain, as observed in a rat reproduction
study.
This worst-case estimate of tebuthiuron's chronic dietary risk assumes
that residues are at tolerance level and that 100% of all commodities are
treated. Actual exposure is less, and dietary risks are considered minimal.
Occupational and Residential Exposure
Pesticide handlers (mixers, loaders and applicators) may be exposed to
tebuthiuron during normal mixing and loading operations, to mists during
spray applications, and to dusts during application of solid formulations.
This exposure is by inhalation and to the skin. However, tebuthiuron is of
sufficiently low toxicity that exposure monitoring data are not required.
The potential for post-application exposure is low due to the nature of the
registered use sites. Again, since the pesticide is of relatively low toxicity,
post-application/reentry data are not required.
Human Risk Assessment
Although tebuthiuron is moderately toxic by the oral route, it is only
slightly toxic by inhalation and is practically non-toxic through the skin. It
is not a skin irritant or sensitizer, and causes only slight irritation to the
eyes. Tebuthiuron does not appear to cause developmental or reproductive
effects, to be mutagenic or to cause cancer.
People may be exposed to residues of tebuthiuron in meat or milk.
The dietary risk from this exposure, however, appears to be minimal.
Occupational pesticide users (mixers, loaders and applicators) also may be
exposed to tebuthiuron by inhalation and through the skin. The risks of this
exposure again are considered minimal due to the pesticide's low toxicity.
Environmental Environmental Fate
Assessment Tebuthiuron is persistent and mobile and can leach to ground water, as
indicated by a small-scale retrospective ground water study. It is resistant to
biological and chemical degradation, and its principle route of dissipation in
the environment appears to be mobility. Transport to ground water through
leaching and to surface water through run-off are likely as a result of
tebuthiuron's persistence and low adsorption to soil. Tebuthiuron has been
detected in ground water in Texas and California. The Agency is concerned
about the potential for ground water contamination from registered uses of
tebuthiuron.
Ecological Effects
Tebuthiuron is practically nontoxic on an acute basis to birds, fish and
aquatic invertebrates, but is slightly toxic to mammals. Current registered
uses of tebuthiuron should not pose a hazard to terrestrial or aquatic
organisms. However, tebuthiuron may pose a significant risk to on- and
off-site endangered terrestrial, semi-aquatic, and aquatic plant
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Additional Data
Required
Product Labeling
Changes Required
species and may also have adverse effects on other off-site non-target plants.
Ecological Effects Risk Assessment
Application of tebuthiuron to rangeland (the most typical use pattern)
exceeds the Agency's high level of concern for nontarget terrestrial and
aquatic plants. Each application of tebuthiuron compounds this hazard due
to the pesticide's extremely long half-life. By reducing the maximum
application rates and limiting the frequency of applications to once every
three years, EPA expects to reduce the risk to non-target plants.
All registered uses of tebuthiuron pose a significant risk to off-site
endangered terrestrial, semi-aquatic and aquatic plant species. Further, all
endangered species in certain use areas, such as rangelands and rights-of-
way, are likely to be jeopardized as they may receive direct applications of
tebuthiuron. EPA may require additional labeling and use modifications
when implementing the Endangered Species Protection Program.
EPA is requiring additional generic confirmatory data for tebuthiuron
including two product chemistry studies (Preliminary Analysis and
Analytical Methods to Verify Certified Limits). The Agency also is
requiring product-specific data including product chemistry and acute
toxicity studies, revised Confidential Statements of Formula, and revised
labeling for reregistration.
All tebuthiuron end-use products must comply with EPA's current
pesticide product labeling requirements, and the following:
Worker Protection Standard (WPS) - The current registered uses of
tebuthiuron do not include uses associated with the production of an
agricultural plant on/in any farm, forest, nursery, or greenhouse. Thus,
tebuthiuron, as currently registered, does not fall within the scope of the
Worker Protection Standard for Agricultural Pesticides and the requirements
of PR Notice 93-7, "Labeling Revisions Required by the Worker Protection
Standard (WPS)," and PR Notice 93-11, "Supplemental Guidance for PR
Notice 93-7," concerning the Agency's labeling regulations for worker
protection statements (40 CFR 156, subpart K) are not applicable to
tebuthiuron end-use products at this time.
Personal Protective Equipment (PPE) Requirements
Registrants must compare the following PPE requirements with those (if
any) on their current labeling and retain the more protective. Labeling must
bear the following minimum PPE requirement:
"Applicators and other handlers must wear:
—Long sleeved shirt and long pants
—Shoes plus socks"
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In addition, gloves are required if the product is in Toxicity Category I, II,
or III for acute dermal toxicity or skin irritation potential. The glove
statement must be one of the following:
— "Waterproof gloves" for dry formulations or for formulations where
water is the only solvent;
— "Chemical-resistant gloves" for all other formulations.
See PR Notice 93-7 for additional guidance on glove selection.
Ground Water Label Advisory - Due to its persistence and mobility in the
environment, tebuthiuron end-use products must bear the following Label
Advisory:
"This chemical is known to leach through soil into ground water
under certain conditions as a result of registered (rangeland and non-
crop) uses. Use of this chemical in areas where soils are permeable,
particularly where the water table is shallow, may result in ground-
water contamination".
"A shallow water table is defined as depth to water table of 30 feet or
less. Permeable soils include, but are not limited to sandy soils."
Additional use restrictions will be required for areas vulnerable to ground
water contamination, once these areas are identified (within 4 months after
issuance of this RED).
Use Rates and Number of Applications - The following maximum
application rates and number and frequency of applications must be included
in the Directions for Use section of the label, to reduce the potential for
ground water contamination and the risks to non-target plants:
• Granular, Pelleted/Tableted, and Water Dispersable Granules (Dry
Flowable) Formulations
For vegetation control by broadcast (aerial and ground equipment) and
banded applications: The maximum label rate and frequency of
application is 1-2 Ibs ai/a once every three years for vulnerable areas
(where soils are sandy and depth to water table is shallow) as
identified in the specific soil series labeling supplement. For all other
areas, may be applied one time in a 3 year period at rates up to 4 Ib
ai/A; however, no more than 6 Ib ai/A may be applied in two
consecutive treatments in any 6 year period.
Spot Treatments (hand-held equipment): May be applied at rates up to
the equivalency of 6 Ib ai/A when needed.
• Wettable Powder Formulation
For vegetation control by broadcast and banded applications (ground
equipment): The maximum label rate and frequency of application is
1-2 Ibs ai/a once every three years for vulnerable areas (where soils
are sandy and depth to water table is shallow) as identified in the
specific soil series labeling supplement. For all other areas, may be
applied one time in a 3 year period at rates up to 4 Ib ai/A; however,
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no more than 6 Ib ai/A may be applied in two consecutive treatments
in any 6 year period.
For total vegetation control and maintainence of bare ground by
broadcast and banded applications (ground equipment): may be
applied one time per year at rates up to 4 Ib ai/A; however, no more
than 6 Ib ai/A may be applied in any 3 year period.
Spot treatments (hand-held equipment): may be applied at rates up to
the equivalency of 6 Ib ai/A when needed.
Other Labeling Requirements (Environmental Hazard Statement)
Granular and Pelleted/Tableted Formulations
"In case of spills, collect, cover or incorporate granules/pellets spilled
on the soil surfaces to prevent contamination to water. Do not apply
to water, or to areas where surface water is present or to intertidal
areas below the mean high water mark. Do not contaminate water
when disposing of equipment washwaters or rinsate".
Wettable Powder and Water Dispersable Granular (Dry Flowable)
Formulation
"Do not apply to water, or to areas where surface water is present or
to intertidal areas below the mean high water mark. Do not
contaminate water when disposing of equipment washwaters or
rinsate".
Regulatory
Conclusion
Based on reviews of the generic data for the active ingredient
tebuthiuron, EPA has determined that tebuthiuron products, labeled and
used as specified in this Reregistration Eligibility Decision, will not pose
unreasonable risks or adverse effects to humans or the environment.
Therefore, products containing tebuthiuron for all registered uses are
eligible for reregistration.
Products that contain tebuthiuron as the sole active ingredient will be
reregistered once the required confirmatory generic data, product specific
data, revised Confidential Statements of Formula and revised labeling are
received and accepted by EPA. Products which also contain other active
ingredients will be reregistered after the other active ingredients are
determined to be eligible for reregistration.
For More EPA is requesting public comments on the Reregistration Eligibility
Information Decision (RED) document for tebuthiuron during a 60-day time period, as
announced in a Notice of Availability published in the Federal Register. To
obtain a copy of the RED document or to submit written comments,
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please contact the Pesticide Docket, Public Response and Program
Resources Branch, Field Operations Division (7506C), Office of Pesticide
Programs (OPP), US EPA, Washington, DC 20460, telephone
703-305-5805.
Following the comment period, the tebuthiuron RED document will be
available from the National Technical Information Service (NTIS),
5285 Port Royal Road, Springfield, VA 22161, telephone 703-487-4650.
For more information about EPA's pesticide reregistration program,
the tebuthiuron RED, or reregistration of individual products containing
tebuthiuron, please contact the Special Review and Reregistration Division
(7508W), OPP, US EPA, Washington, DC 20460, telephone
703-308-8000.
For information about the health effects of pesticides, or for assistance
in recognizing and managing pesticide poisoning symptoms, please contact
the National Pesticides Telecommunications Network (NPTN). Call toll-
free 1-800-858-7378, from 8:00 am to 6:00 pm Central Time, Monday
through Friday.
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