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dicamba (Banvel) Herbicide Profile 10/83

                            CHEMICAL FACT SHEET FOR: 
.                                   DICAMBA
FACT SHEET NUMBER: 08
DATE ISSUED: OCTOBER 17, 1983
                         1. DESCRIPTION OF CHEMICAL
- Generic Name:  3,6-dichloro-o-anisic acid
- Common Name:   dicamba
- Trade Names:   Banvel, Banex, Brush Buster, Mediben, Velsicol 58-CS-11
- EPA Shaughnessy Number:  029802
- Chemical Abstracts Service (CAS) Number: 1918-00-9
- Year of Initial Registration:  1967
- Pesticide Type:  Herbicide
- Chemical Family:  Benzoic Acid
- U.S. and Foreign Producers:  Velsicol Chemical Corporation
                     2. USE PATTERNS AND FORMULATIONS
- Application sites: corn, small grains, grain sorghum, asparagus,
  sugarcane, pastures, rangeland and agricultural seed crops, noncrop
  sites, forest lands, lawns and ornamental turf.
- Types of formulations: diethanolamine, monoethanolamine,
  dimethylamine and sodium salts as soluble concentrates or granulars.
- Types and methods of application: Applied by aerial or ground spray,
  invert system, tree injection, or granular equipment. Dicamba is
  applied preplant, preemergence, or postemergence.
- Application rates:
  - 1/4 pound active per acre to grain sorghum
  - 1/8-1/2 pound active per acre to small grains, asparagus
  - 1/4-3 pounds active per acre to sugarcane
  - 1/2-8 pounds active per acre to pasture, range, and noncropland
  - 1/4-1 pound active per acre to turf and grass seed crops
- Usual carriers: water, fluid and dry fertilizer, oil in water
  emulsions, clay or vermiculite
                         3. SCIENCE FINDINGS
Chemical Characteristics
- It is a light tan slightly phenolic crystalline solid. It is stable
  to oxidation and hydrolysis and melts at temperatures between 90-100
  degrees C. Dicamba is nonflammable and does not present any unusual
  handling hazards.
Toxicological Characteristics
- Acute Toxicology Results:
  - Oral LD50 in rats: 2.74 mg/kg body weight, Toxicity Category III
  - Dermal LD50 in rats: >2,000 mg/kg, Toxicity Category IV
  - Inhalation LC50 in rats: >200 mg/l, Toxicity Category IV
  - Eye irritation in rabbits: Induced corrosiveness of conjunctival
    tissues and corneal injury which was reversible in 72 hours. In a
    recent study, eye damage was irreversible and pannus was observed.
    Toxicity Category I.
  - Dermal Irritation: slight dermal irritation.
- Chronic Toxicology Results:
  - Teratology in rabbits: NOEL of 3.0 mg/kg/day for maternal
    toxicity; not teratogenic.
  - Teratology in rats: Teratology NOEL s 400 mg/kg; maternal
    toxicity NOEL 5 160 mg/kg.
  - Three-generation reproduction study in rats: No evidence of
    toxicity among the rats from any of the generations in the study.
    No test article related effects were evident for any reproductive
    indices examined. NOEL of 25 mg/kg/day.
  - 90-day subchronic feeding study with rats: The NOEL is 250
    mg/kg/day. LEL was 500 mg/kg/day (slight decrease in comparative
    body weight gains and food consumption and evidence of reduced
    glycogen storage).
- Major Routes of Exposure:
  - Dermal and inhalation exposure to humans may occur during
    application, particularly via splashing during dilution, mixing,
    and loading. Application by aircraft increases the potential for
    exposure of humans, livestock, and wildlife due to spray drift and
    ventilation.
- Risk Assessment and Contaminants:
  - The manufacturing process for dicamba has potential of resulting
    in traces of 2,7-dichlorodibenzo-p-dioxin as a contaminant. It is
    present at levels up to 50 ppb (parts per billion). The more
    toxic dioxin isomer, 2,3,7,8-tetra-chlorodibenzo-p-dioxin, has not
    been found at the limit of detection (2 ppb) of the method and is
    not expected as an impurity in dicamba.
  - Dicamba products formulated with the dimethylamine salt have the
    potential of adding a dimethylnitrosamine (DMNA) contaminant.
    Nitrosamine levels in the dimethylamine formulations are expected to
    be less than 1 ppm. The risk levels for the dicamba products
    with the nitrosamine contaminant are in the 1 x 10 to minus 7 to 1 x
    10 to minus 8 range.
  - The benefits outweigh the risks associated with the nitrosamines.
    The performance of the dicamba-containing herbicides is such that
    they are viable alternatives to the suspended uses (home lawns,
    pastures, ditchbanks and forests) of silvex and 2,4,5-T.
Physiological and Biochemical Behavioral Characteristics
- Foliar absorption:  Readily absorbed by leaves.
- Translocation:  Dicamba is absorbed by leaves and is readily moved
  to other plant parts.
- Mechanism of pesticidal actions: Exhibits properties of an auxin-like
  plant growth regulator.
- Plant metabolism: Rapidly absorbed and metabolized almost entirely
  into soluble metabolites and insoluble plant products (celluloses).
- Animal metabolism: Some dicamba is demethylated to the metabolite,
  3.6-dichloro-2 hydroxybenzoic acid. Most dicamba is excreted
  rapidly in urine as the free and/or conjugated form
Environmental Characteristics
- Adsorption and leaching in basic soil types:
  - Dicamba (free acid and dimethylamine salt) is adsorbed to peat,
    but not appreciably adsorbed to soils ranging from heavy clay to
    loamy sand.
  - Dicamba is readily mobile in soils ranging from clay to loamy
    sand.
- Microbial breakdown:
  - Under aerobic conditions in soil dicamba degrades with half-lives
    ranging from 1-6 weeks, depending on soil texture. Degradation
    rates are slowed by decreasing temperatures (<20 degrees C) and
    decreasing soil moisture below field capacity.
- Loss from Photodecomposition and/or volatilization:
  - Phytotoxic dicamba (free acid) residue's are photodegraded in water
    to nonphytotoxic levels.
  - Dicamba is volatile with losses of 60% in glass flow tubes and 49%
    from thin films. Data from sterile and nonsterile soil samples
    indicate that larger losses of dicamba are due to metabolism
    rather than to volatilization.
- Resultant average soil persistence:
  - Dicamba has a half-life of 1 to 6 weeks. It may be leached out of
    the zone of activity in humid regions in 3 to 12 weeks. Dicamba
    may persist longer under conditions of low soil moisture and
    rainfall.
Ecological Characteristics
- Avian oral LD50: >2,510 mg/kg (practically non-toxic)
- Avian dietary LC50: > 10,000 ppm (practically non-toxic)
- Aquatic invertebrates LC50: >100 mg/l (practically non-toxic)
- Cold water fish LC50: 135.3 mg/l (slightly toxic)
- Warm water fish LC50: >1,000 mg/l (practically non-toxic)
- Available data indicate that dicamba is practically non-toxic to
  fish and wildlife and unlikely to directly affect these organisms.
- Use patterns of the chemical do not present any problem to
  endangered species.
Tolerance Assessments
- Crops and tolerances:
  - 0.1 ppm on sugarcane, sugarcane fodder, and sugarcane forage
  - 0.2 ppm on meat, fat and meat byproducts (except liver and kidney)
    of cattle, goats, hogs, horses, and sheep
  - 0.3 ppm on milk
  - 0.5 ppm on barley grain and barley straw; corn fodder, forage, and
    grain; oat grain and oat straw, and wheat grain and wheat straw.
  - 1.5 on kidney and liver of cattle, goats, hogs, horses, and sheep.
  - 2.0 ppm on sugarcane molasses (food/feed additive tolerance)
  - 3.0 ppm on asparagus, sorghum fodder, forage and grain
  - 40.0 ppm on grasses, hay; grasses, pasture; grasses, rangeland.
- Results of tolerance assessment:
  - The available residue data support the existing tolerances.
  - Tolerances on sorghum milling fractions, poultry and eggs may be
    required once requested residue data and poultry feeding are
    submitted.
  - Based on a NOEL of 600 ppm (rat subchronic study) and a 2,000-fold
    safety factor, the existing tolerance utilizes 37.58% of the PADI.
Problems Known to Have Occurred With the Use of the Chemical
- Based on the Pesticide Incident Monitoring System (PIMS) report, most
  reported incidents with dicamba involve phytotoxicity to adjoining
  crops because of drift.
Summary Science Statement
- Dicamba appears to pose little acute toxicity or environmental hazard.
  The major problem appears to be the potential for a
  dimethylnitrosamine (DMNA) contaminant in the dimethylamine
  formulations. The level of DMNA is expected to be below 1 ppm, and the
  risk level for dicamba with DMNA is 10-7 to 10-8 range.
           4. SUMMARY OF REGULATORY POSITION AND RATIONALE
- Use classification: general use
- Summary of risk/benefit review:
  - The risk level for dicamba products containing DMNA is in the 10-7
    to 10-8 range. The Agency considers that the benefits outweigh
    the risk associated with the nitrosamines. The product
    performance of dicamba-containing herbicides is such that they are
    viable alternatives of several of the suspended uses of silvex and
    2,4,5-T, such as for home lawns, pastures, along ditchbanks and
    brush control in pastures.
- Use restrictions:
  - Dicamba may not be used in any way which contaminates irrigation
    ditches or water for domestic purposes.
- Unique label warning statement:
  - Crops for which dicamba is not registered may not be planted in
    dicamba-treated fields.
                     5. SUMMARY OF MAJOR DATA GAPS
- Residue data on poultry, eggs, and sorghum
- Milling fractions
- Poultry feeding study
- Hydrolysis
- Photodegradation
- Laboratory metabolism studies
- Mobility
- Field dissipation studies
- Accumulation studies
- 90-day feeding (nonrodent)
- Chronic feeding/oncogenicity (2 species)
- Mutagenicity test
NOTE: All the data gaps listed here are to be filled by October 1987.
                       6. CONTACT PERSON AT EPA
Robert J. Taylor
Environmental Protection Agency (TS-767C)
401 M St., SW
Washington, DC 20460
(703) 557-1800
DISCLAIMER:
THE INFORMATION PRESENTED IN THIS CHEMICAL INFORMATION FACT SHEET
IS FOR INFORMATIONAL PURPOSES ONLY AND NOT TO BE USED TO FULFILL
DATA REQUIREMENTS FOR PESTICIDE REGISTRATION AND REREGISTRATION.