United State* Office of Pesticide* end Toxic Substances
Environmental Protection Office of Pettlade Programs (TS-766C)
Agency Washington, DC 20460
v>EPA Pesticide
Fact Sheet
Name of Chemical: DICAMBA.
Reason for Issuance:
Date Issued: Oct. 17, 1983
Fact Sheet Number: 8
1. Description of Chemical;
Generic name: 3,6-dicbloro-o-anisic acid
Common name: Dicamba
Trade Names: Banvel, Banex, Brush Buster, Mediben, Velsicol 58-CS-ll
EPA Shaugnnessy 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, sugar-
cane, 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 sorgbuc
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;
Summary Science Statement:
Dicamba appears to pose little acute toxicity or environmental
hazard. The major problem appears to be the potential for a
dimethylnitrosamine (DNNA) contaminant in the dimethylamine
formulations. The level of DMNA is expected to be beicw 1 PP*
and the risk level for dicamba with DNNA is 10~7 to 10~8
range.
-------
—2—
Chema.ca.l Characteristics:
It is a light tan slightly phenolic crystalline solid. It is stable
to oxidatior and hydrolysis and melts at temperatures between 90-
100•C. Dieamba is nortflkm, ble and does not present any unusual
handling hazards.
Toxicology Characteristics:
Acute Toxicology Results:
Oral LD 50 in rats: 2.74 mg/kg body weight, Toxicity
Category III
Dermal LD 50 in rats >2,000 mg/kg, Toxicity Category IV
Inhalation LC 50 in rats: >200 mg/i, Toxicity Category IV
Eye irritation in rabbits: Induced corrosiveness of con—
unctival tissues and corneal injury i .cn was reversible
in 72 hours. In a recent study eye ti t ge 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 teratogeru.c.
Teratology in rats: Teratology NOEL — 400 mg/kg;
maternal toxicity NOEL — 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 eviden: for any reproductive indices
examined. NOEL of 25 mg/kg/day.
90-day subchronic feeding study with rats: Tne NOEL
is 250 mg/kg/day. LEL was 500 mg/kg/day (slight de-
crease in comparative body weight gains and food con-
sumption and evidence of reduced glycogeri storage).
Major Routes of Exposure:
Dermal and inhalation exposure to hum&nB may occur
during application, particularly via splashing during .lu-
tion, izing and loading. Application by aircraft increases
the potential for exposure of huiw s, livestock, and wild-
life due to spray drift and ventilation.
-------
—3—
Risk Assessment and Cont* ‘santa:
The manufacturing process for dicamba has potential of
resulting in traces of 2, 7 —dichlorodbenzOPdiOz1.fl as a
contaminant. It is present at level. up to 50 ppb (parts
per billion). The more toxic dioxir’ isomer, 2,3,7 ,8—tetra-
chlorod.thenzo—p-diOXifl , has not been found at the limit of
detectiam (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 (D10U 1 ) conta -
nant. Nitros 4 v’e levels in the dimethylamine for ’ etions
are expected to be less h* t 1 ppm. The risk lave].s for the
dicamba products with the attrosamins contaminant are in the
1 x i0 to 1 x range.
The benefits outweigh the risks associated with the nitro-
s ’ es. The performance of th. dice a cont iT ing herbicides
is such that they are viable alternatives to the suspended
uses (home lawns, pa. tures, ditchbanks and forests) of silvex
and 2,4,5—T.
Physiological and Biochemical Behavioral Characteristics:
Foliar absorption: Readily absorbed by leaves.
Translocatiorl: Dicamba is absorbed by leaves and is readily
moved to other plant parts.
Mechan.tem of pesticidal actions: chibits properties of an
auxi ’-like plant growth regulator.
Plant metabolism: Rapidly absorbed and metabolized almost
entirely into soluble metabolites and insoluble plant products
(celluloses).
nim&l metabolism: Some dicamba is demethylated to the mete-
bolite, 3,6 —dichlorO-2hydroXybeELZOiC acId. Most dicumba 1.8
excreted rapidly in urine as the free and/or con)ugated
form.
Environmental Characteristics:
AdsorptIon and leaching in basic soil types:
Dicamba (free acid and dimethylamine salt) i adsorbed
to peat, but not appreciably adsorbed to soils ranging
tram heavy clay to loamy sand.
-------
—4-
Dicamba is readily mobile .ri soils anca .ng from clay to loamy
sand.
Microbial breakdown:
Under aerobic conditions in soil dicamba degrades with half-lives
ranging from I to 6 weeks depending on soil texture. Degradation
rates are slowed by decreasing teaperatures (<20C) and decreasing
soil moisture below field capacity.
Loss from Photodecc.position and/or volatilization:
Phytotoxic dicamba (free acid) residues are photodegraded in
water to nonphytotoxic levels.
Dieamba is volatile with losses of 60% in glass flow tubes and
49% from thin films. Data from sterile and nonaterile soil
samples indicate that larger losses of dicamba are due to metabolism
rather than to volatilization.
Resu.ltant average soil persistence:
Dic-amba nas a half—life of I to 6 weeks. It may be leached out
of the zone of activity in h .id regions in 3 to 12 weeks.
Dicamba may persist Longer under conditions of low soil iature
and rainfall.
Ecoloaical aracteristics:
Avian oral LD 50 >2,510 mg/kg (practically non—toxic
Avian dietary LC 50 > 10,000 p (practically non—toxic)
Aquatic invetebrates LC 50 100 mg/l (practically non-toxic)
Cold water fish W 50 — 135.3 mg/i (slightly toxicity)
Warm water fish “ so >1,000 mg/i (practically non—toxic)
Avaiiable data indicate that dicamba is practically non-toxic to
fish and wildiife and unlikely to directly affect these organisms.
Use patterns of the chemical do not present any prok lea 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 byproducta (except liver and
kidney) of cattle, goats, hogs, horses and sheep
0.3 ppm on milk
-------
—5—
0.5 p a 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 pps on sugarcane molasses (food/feed additive tolerance)
3.0 pp. on asparagus, aorght fodder, forage and grain
40.0 pp. on grasses, bay; grasses, pasture; grasses, rangeland.
Results of tolerance assessment:
The available residue data support the existing tolerances.
Tolerances on aorghta milling fractions, poultry and eggs may be
required once requested residue data and poultry feeding are
submitted.
Based on a NOEL of 600 pp. (rat subchronic study) and a 2,000—fold
safety factor, the existing tolerance utilizes 37.58% of the PADI.
Problems which are kn n to have occurred with the use of the chemical:
Based on the pesticide Incident )bnitoriflg System (Pill’s) report,
most reported incidents with dicamba involve phytotoxicity to
adjoining crops because of drift.
4. Si ary of Regulatory Position and Ratioss!! ’
Use Classification: Gen•ral Use
s ary of risk/benefit review:
The risk level for dicamba products containing DIQIA is in the
to 10-8 range. The Agency considers that the benefits outweigh
the risk associated with the nitrosamines. The product performance
of djcamba-COfltaifliflg 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 ditcbbanks and brush
control in pastures.
Use Restrictions:
Dicambe ay not be used in any way which contaminates irrigation
ditches or vatsr for domestic purposes.
Unique label warning statement:
Crops for which dicamba is not registered may not be planted in
dicaaba-treat.d fields.
-------
—6—
5. Su ary of Data Gaps and Dates When These Gaps Are tobe Filled :
Residue data on poultry, eggs, and sorghi October 1987
Milling fractions October 1987
Poultry feeding study October 1987
Hydrolysis October 1987
Photodegradation October 1987
Laboratory etaboliaa studies October 1987
Pbbi lity October 1987
Field dissipation studies October 1987
Accumulation studies October 1987
90—day feeding (Nonrodent) October 1987
Chronic feeding/oncogenicity (2 species) October 1987
Mutagenicity test October 1987
6. Contact person at EPA :
Robert J. Taylor
Environmental Protection Agency (TS—767C)
401 N St. S W.
Washington, DC 20460
(703) 557—1SOC
------- |