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Terbacil - Herbicide Profile 8/89

EPA Pesticide Fact Sheet
Name of Chemical:     TERBACIL
Reason for Issuance:  REGISTRATION STANDARD (SRR)
Date Issued:  August 1989
Fact Sheet Number: 206
                    1.  DESCRIPTION OF CHEMICAL
- Generic Name:  3-tert-butyl-5-chloro-6-methyluracil
- Common Name:  Terbacil
- Trade and Other Names:  5-chloro-3-(1,1-dimethylethyl)-6-
  methyl-2,4(1H,3H)-pyrimidinedione, Sinbar, DuPont Herbicide 732, and
  Geonter.
- EPA Shaughnessy Codes:  012701
- Chemical Abstracts Service (CAS) Number: 5902 51-2
- Year of Initial Registration:  1966
- Pesticide Type:  Herbicide
- Chemical Family:  Uracils
- U.S. Producers:  E.I. duPont de Nemours Company, Inc.
                   2. USE PATTERNS AND FORMULATIONS
- Application sites:  Terrestrial food crops.
- Types and Methods of Application:  Tractor mounted spray boom to soil
  surfaces and small emerged weeds.  Aerial application.
- Application Rates:  0.4 to 8.0 lb active ingredient per acre
- Annual Usage:  290,000 - 610,000 pounds
- Types of Formulation:  Wettable powder
                         3. SCIENCE FINDINGS
Chemical Characteristics of the Technical Material
- Physical State:  Crystalline solid
- Color:  White
- Odor:  None
- Molecular Weight and Formula:  216.7
- Boiling Point:  Terbacil is a solid at room temperature
- Vapor Pressure:  4.7 x 10-7 mm Hg at 29.5 degrees C
- Density:  1.34
- Solubility in various solvents:  Water, xylene, and dimethylformamide
Toxicology Characteristics
- Acute Oral:  1082 mg/kg (rat) Toxicity Category III
- Acute Dermal:  >5000 mg/kg (rabbit) Toxicity Category III
- Primary Dermal Irritation:  No irritation demonstrated
- Primary Eye Irritation:  slight eye irritation (conjunctiva)
- Dermal Sensitization:  Not a dermal sensitizer
- Acute Inhalation:  >4.4 mg/liter/4 hours (Toxicity Category III)
- Subchronic dermal (2 day):  > 5000 mg/kg. No toxic signs.
- Subchronic Oral (90-day):  No Observed Effect Level (NOEL) of
  5 mg/kg/day.
- Chronic Oral dog (2-year):  NOEL of 1.25 mg/kg/day.
- Oncogenicity:  Data Gap.
- Teratogenicity (rat):  Not teratogenic.  Maternal NOEL was 62.5
  mg/kg/day. Teratogenicity NOEL > 250 mg/kg/day.
- Teratogenicity (rabbit):  Not teratogenic. Maternal and embryotoxicity
  NOEL was 200 mg/kg/day. Teratogenicity NOEL was 600 mg/kg/day (highest
  dose tested).
- Reproduction:  No observed effects with a NOEL of 62.5 mg/kg/day
  (highest dose tested).
- Mutagenicity:  Non-mutagenic in assays tested.
- Metabolism:  Data Gap.
- Major route of exposure:  Dermal
Physiological and Biochemical Characteristics
- Mechanism of Pesticidal Action:  Stops photosynthesis
- Metabolism and Persistence in Plants and Animals:  The available data
  are not adequate to assess the nature of terbacil in plants or in
  animals.
Environmental Characteristics
- Terbacil is stable to hydrolysis and photodegrades slowly in water.
- It has a potential to contaminate ground water particularly in areas
  with sandy soil surfaces.
- It leaches slower in fine textured soils and also in soils having
  higher organic contents.
- It does not accumulate to significant levels in bluegill sunfish.
- Residues resulting from multiple applications of terbacil persisted or
  2 years following the final application.
- Preliminary data indicate that terbacil is extremely persistent with
  half-lives of 520 days aerobically and 178 days anaerobically.
Ecological Characteristics
- Avian acute toxicity: >2250 mg/kg (Quail). Practically Non-toxic.
- Avian dietary toxicity: >5000 ppm (Mallard duck,). Practically Non-
  toxic.
- Freshwater fish acute toxicity:
        102.9 ppm (Bluegill sunfish)  Practically Non-toxic.
         46.2 ppm (Rainbow trout)  Slightly Toxic
- Marine fish acute toxicity: Data Gap
- Freshwater invertebrate toxicity:  65 ppm (Daphnia).  Slightly toxic.
- Marine invertebrate toxicity:  >4.9 ppm Oyster).  Moderately toxic
                                  4 ppm (Shrimp).  Slightly toxic
TOLERANCE ASSESSMENT
   Tolerances have been established for residues of Terbacil in a
variety of raw agricultural commodities (Refer to 40 CFR 18.2  for
listing of tolerances.  Terbacil's tolerances have been reassessed using
the Tolerance Assessment System (TAS).  The TAS chronic exposure
analysis estimates average daily exposure for the overall U.S.
population and each of the 2 populations subgroups and compares these
estimates to the acceptable daily intake (ADI) calculated for terbacil.
   The Theoretical Maximum Residue Contribution (TMRC) for the overall
U.S. population is estimated to be 0.001594 mg/kg/day, which occupies
approximately 12% of the ADI.  The two most highly exposed subgroups are
non-nursing infants, less than 1 year old (TMRC= 0.008122 mg/kg/day or
62% of the ADI), and children, 1-6 years of age (TMRC= 0.004361
mg/kg/day or 34% of the ADI).
                4 SUMMARY OF REGULATORY POSITIONS
   This review of terbacil is the second intensive evaluation of the
compound.  In its original Registration Standard, issued in 1982, the
Agency summarized the available data supporting the registration of
terbacil and concluded that additional data were needed to fully
evaluate the pesticide.
   The Agency has since received and reviewed the data and has revised
its scientific and regulatory conclusions relative to these data.
- Terbacil will not be placed in Special Review at this time.
- The Agency will impose a ground water contamination advisory statement
  to reduce point source contamination.
- The Agency is requiring the following testing on all terbacil end-use
  products:  acute oral, acute dermal, primary eye, primary skin, dermal
  sensitization, and acute inhalation if appropriate.
- The Agency will not establish a reentry interval for terbacil beyond
  the minimum reentry interval (sprays have dried, dusts have settled
  and vapors have dispersed).
- The Agency will require updated worker safety and protective equipment
  statements for end-use products containing terbacil.
- The Agency is requiring a rotational crop statement on all terbacil
  labels which may involve rotation to crops other than those currently
  registered (refer to section IV.D for specific wording).  In addition
  residue data are required for representative crops from any crop group
  which could be rotated from alfalfa, sainfoin, and mint.
- Existing Tolerances for Terbacil per se should be amended to include
  metabolites A, B, and C, as specified in 40 CFR 180.209 (b).
- The Agency will revoke tolerances associated with the commodities
  sainfoin (hay), sainfoin (forage), and pears.
- The Agency will revise the tolerance for residues in or on peaches to
  0.2 ppm for combined residues of terbacil and its metabolites.
- The Agency will impose label restrictions against the feeding and
  grazing of sugarcane forage and spent hay to livestock or require the
  development and submission of data in support of tolerances for
  residues in or on sugarcane forage and spent hay.
- The Agency has determined that grasses grown for seed is a food use.
  Therefore, data depicting residues of terbacil in or on members of the
  grass forage, fodder and hay group are required.
- The Agency will not propose group tolerances for terbacil.
- The Agency will not grant any significant new food or feed uses for
  terbacil until the required residue chemistry and toxicology studies
  have been submitted and reviewed.
- The Agency has identified certain data that will receive priority
  review when submitted;
Section 158.340 Toxicology
  83-1 Chronic Oral Feeding (Rat)
  83-2 Oncogenicity (Rat and Mouse)
Section 158.290 Environmental Fate
  162-1 Aerobic Soil Metabolism
  162-2 Anaerobic Soil Metabolism
  163-1 Leaching Adsorption/Desorption
  164-5 Soil, Long Term (field)
Section 158.490 Wildlife and Aquatic Organisms
  72-3 Estuarine and Marine Testing (Fish)
  122- Tier I Nontarget Area Phytotoxicity
Section 158.240 Residue Chemistry
  171-4 Metabolism in Plants & Livestock
                     5. REQUIRED UNIQUE LABELING
A. Groundwater Advisory Statements
B. Environmental Hazards Statement
D. Reentry Statement
E. Feeding and/or Grazing Restrictions
F. Rotational Crop Statement
                    6. SUMMARY OF MAJOR DATA GAPS
                                           TIMEFRAME RANGES
Toxicology                                  12-48 Months
Environmental Fate/Exposure                 12-48 Months
Ecological Effects                             24 Months
Residue Chemistry                           24-48 Months
Product Chemistry                           12-24 Months
                   7.   CONTACT PERSONS AT EPA
Product Specific Inquiries:
Robert J. Taylor
Product Manager (25)
Fungicide Herbicide Branch
Registration Division (H-7505C)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street, S.W.
Washington, D.C.  20460
Office location and telephone number:
Room 245, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA  22202
(703) 557-1800
Reregistration Document Inquiries:
Donna M. Williams
Review Manager
Reregistration Branch
Special Review and Reregistration Division (H-7508C)
Environmental Protection Agency
401 M Street, S.W.
Washington, D. C.  20460
Office location and telephone number:
Room 1124, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA  22202
(703) 557-0639
DISCLAIMER:  The information in this Pesticide Fact Sheet is a summary
only and is not to be used to satisfy data requirements for pesticide
registration and reregistration.  The complete Registration Standard for
the pesticide may be obtained from the National Technical Information
Service.  Contact the Review Manager listed above for further
information.