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Diflubenzuron - Chemical Fact Sheet 9/85

                          CHEMICAL FACT SHEET FOR:
                            DIFLUBENZURON (DIMILIN)



                      1.  DESCRIPTION OF CHEMICAL

- Generic Name:  N-[[(4-chlorophenyl)amino]carbonyl]-2,6-difluoro-

- Common Name:  diflubenzuron
- Trade Names:  Dimilin, Vigilante
- EPA Shaughnessy Code:  108201
- Chemical Abstracts Service (CAS) Number:  35367-38-5
- Year of Initial Registration:  1976
- Pesticide Type:  benzamine chitin inhibitor
- Chemical Family:  substituted urea
- U.S. and Foreign Producers:  Duphar B.V.

                    2.  USE PATTERNS AND FORMULATIONS

- Application sites:  agricultural crops (cotton and soybeans), forests
  (woodland trees and shrubs, including Christmas trees), ornamentals
  (commercial nursery), pasture (flood irrigated areas in California
  only), greenhouse (mushrooms).
- Type of formulation:  25 WP

                           3.  SCIENCE FINDINGS

Chemical Characteristics

- Physical state:  solid
- Color:  white
- Odor:  none
- Boiling point:  N/A
- Melting point:  210 to 230 degrees C
- Flammability:  N/A
- Solubility in water:  at 20 to 25 degrees C 0.2 mg/l.  There are no
  unusual handling characteristics.

Toxicological Characteristics

- Acute oral, rat:  >4,640 mg/kg, Toxicity Category IV
- Acute dermal, rabbit:  >4,000 mg/kg, Toxicity Category III
- Acute inhalation, rat:  >2.88 mg/L, Toxicity Category III
- Chronic toxicological results:
  - Rat chronic feeding:  NOEL = 40 ppm (2 mg/kg) bwt/day for met-
    and sulphemoglobin formation.
  - Rat oncogenicity:  Not oncogenic to male and female rats under
    the conditions of the study; highest dose tested 10,000 ppm
    (500 mg/kg bwt/day).
  - Mouse oncogenicity:  Not oncogenic to male and female mice under
    the conditions of the study; highest dose tested 10,000 ppm
    (500 mg/kg bwt/day).
  - Rat teratology:  Not fetotoxic or teratogenic to rats at levels
    up to 4 mg/kg bwt/day, the highest dose tested.
  - Rabbit teratology:  Not fetotoxic or teratogenic to rabbits at
    levels up to 4 mg/kg bwt/day, the highest dose tested.
  - 3-generation rat study:  No adverse effects on reproductive
    performance at 160 ppm (8 mg/kg/day), the highest dose tested.
  - Gene mutation:  At rates up to 1,000 ug/plate, there was no
    evidence of changes in spontaneous revertant frequency or any
    mutagenic effect.
  - Sheep 13-week feeding study:  No treatment-related effects were
    observed on food consumption, body weight gain, hematological
    parameters, or urinalysis at 10,000 mg diflubenzuron/kg in the
  - Dog 13-week feeding study:  No histopathological changes were
    reported attributable to feeding diflubenzuron at rates up to
    160 ppm in the diet.

Physiological and Biochemical Behavioral Characteristics

- Translocation:  The available plant metabolism data show that
  diflubenzuron, when foliarly applied in doses approximating those
  registered or proposed for use on citrus, soybeans, and cotton,
  will undergo very little, if any, translocation from treated areas.
  Additional metabolism data are needed to support the established
  mushroom tolerance.
- Mechanism of Pesticidal Action:  Diflubenzuron interferes with
  arthropod chitin formation, thus disrupting the development of a
  new cuticle in preparation for molting of the exoskeleton.  Exposed
  insect larvae continue to feed and otherwise develop normally until
  growth makes it necessary to shed the old cuticle.  The old
  exoskeleton is shed, after which the growing insect swells by
  taking air into the respiratory system, expanding the body, and
  stretching the already formed, elastic new cuticle before it
  hardens.  Insects exposed to diflubenzuron die while trying to
  molt, since the new cuticle is not properly formed.
- Metabolism and Persistence in Plants and Animals:  The metabolism
  of diflubenzuron in plants has been adequately described for
  higher plants following foliar treatments.  The available animal
  metabolism studies indicate that no residues will transfer to the
  fat, kidney, or meat of ruminants at 5 ppm of the total diet.
  Residues do occur in milk and liver.

Environmental Characteristics

  Due to rapid binding with soil particles and organic matter and
  breakdown by soil biota, groundwater contamination problems are
  unlikely.  In aerobic soil, radiolabeled diflubenzuron with a
  particle size of approximately 2 microns had a half-life of less than
  2 weeks at 20 degrees C.

Ecological Characteristics

- Avian oral acute toxicity:  >5,000 mg/kg for bobwhite quail and
  mallard duck.
- Avian dietary toxicity:  >20,000 ppm for bobwhite quail and mallard
- Fish acute toxicity:  >25 ppm for yellow perch; >50 ppm for brook
  trout; >100 ppm for rainbow trout, channel catfish, and bluegill
  sunfish; >500 ppm for fathead minnow.
- Freshwater invertebrate acute toxicity:  560 ppb for Chironomus
  sp., 16 ppb for Daphnia magna, 30 ppb for Gammarus pseudolimnaeus.
- Estuarine/marine organism acute toxicity:  2.06 ppb for mysid
  shrimp; 0.64 ppm for grass shrimp; >130 ppm for oyster larvae;
  255 ppm for mummichog; >1,000 ppm for Uca pugilator, Carcinus
  maenus, Anodonta sp., and Mercenaria mercenaria.
- Honeybee acute toxicity:  >114.8 micrograms per bee (relatively
- Based on these studies, diflubenzuron is of low toxicity to birds,
  finfish, and honeybees, but is extremely toxic to aquatic
  invertebrates.  Therefore, additional studies are required to
  complete a hazard assessment for aquatic invertebrates.

Tolerance Assessment

- Sufficient data are available to determine that the established
  tolerances for residues of diflubenzuron (OFB) in or on the
  following commodities are adequate:  cottonseed, pasture grass,
  soybeans, soybean hulls, soybean soapstock, milk, eggs, and the
  meat, fat, and meat byproducts of cattle, goats, hogs, horses,
  sheep, and poultry.  However, additional data are required for
  complete elucidation of the nature of the residue in mushrooms to
  support the established tolerance in mushrooms.
- The Theoretical Maximum Residue Concentrate (TMRC) for diflu-
  benzuron is 0.0352 mg/day based on a 1.5-kg diet.  The PADI is
  0.011 mg/kg/day based on a 1.5 kg/day diet.  The tolerances
  established add up to 2.9% of the PADI.

Summary Science Statement

- Diflubenzuron has demonstrated a low toxicity to mammals through
  the oral, dermal, and inhalation routes.  The Agency has
  determined that diflubenzuron is not an oncogen or a teratogen.
- The Provisional Allowable Daily Intake (PADI) of diflubenzuron is
  0.02 mg/kg/day.  This is based on a NOEL of 40 ppm (2 mg/kg/day)
  on met- and sulphemoglobin formation in rats.  The tolerances
  established add up to 2.9% of the PADI.
- Diflubenzuron disrupts the normal molting of insects and other
  invertebrates by interfering with the disposition of chitin.


- The Agency has determined that it should continue to allow the
  registration of diflubenzuron. However, because of gaps in the data
  base, additional data are required as specified in the tables.
  Additional tolerances and label changes will be considered as
  applications are submitted.
- Because of toxicity to crab, shrimp, and other aquatic invertebrate
  animals, diflubenzuron is classified as a restricted pesticide for
  use on forests and field crops.  Cautionary statements are required
  on the label warning of hazards to aquatic invertebrates.
- The only geographic limitation for use of products containing
  diflubenzuron is for control of mosquitoes in temporarily flooded
  areas of pastures in central California.  The primary concern with
  these mosquitoes breeding in wastewater from irrigation projects is
  their potential for carrying diseases affecting humans.

                    5.  SUMMARY OF MAJOR DATA GAPS

- Toxicology:  Chronic feeding study in a non-rodent species (dog,
  l-year), acute eye irritation study in rabbits, other mechanisms of
  mutagenicity.  The dog feeding study has been submitted and is
  under review.
- Environmental Safety:  Avian reproduction studies, freshwater
  invertebrate acute LC50, estuarine/marine organism acute LC50,
  freshwater invertebrate life cycle, estuarine invertebrate life
- Residue Chemistry:  Metabolism in mushrooms, metabolism in cattle,
  poultry, and swine

                    6.  CONTACT PERSON AT EPA

Timothy A. Gardner (PM-17)
Insecticide-Rodenticide Branch (TS-767)
U.S. Environmental Protection Agency
401 M Street S.W.
Washington, DC  20460