United States Office of Pesticides and Toxic Substances
Environmental Protection Office of Pesticide Programs (TS-766C)
Agency Washington. DC 20460
540/FS-88-114 I
v>EPA Pesticide
Fact Sheet
Name of Chemical: 2,4-Dichlorophenoxyacetic Acid (2,4-D
Reason for Issuance: Registration Standard
Date Issued: September 1988
Fact Sheet Number: 94.2
DESCRIPTION OF CHEMICAL
Generic Name: 2,4-Dichlorophenoxyacetic Acid
Common Name: 2,4-D (includes parent acid as well as salt,
amine and ester derivatives)
Trade Name: 2,4-D is available under a large selection of
trade names, most often formulated as an inorganic salt,
amine or ester.
EPA Chemical Code: 030001 (Acid)
Chemical "Abstracts Service (CAS) Number: 94-75-7 (Acid)
Year of Initial Registration: 1948
Pesticide Type: Herbicide; Plant Growth Regulator.
Chemical Family: Chlorinated phenoxy
U.S. and Foreign Producers: 2,4-D technical products are
manufactured by a large number of companies, both U.S.
and foreign.
Registered Uses: Terrestrial, food and nonfood; aquatic,
food and nonfood; domestic; and forestry.
Predominant Uses: Postemergent weed control in agricultural
crops (approximately 57 percent of total usage; over 45
percent of total usage is on wheat and corn; 20 percent
of total usage on pastures and rangelands; other major
crops are sorghum, other small grains, rice and
sugarcane); the remainder is used on noncrop areas, with
a small amount used as a plant growth regulator (in
filberts, citrus and potatoes).
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Formulation Types Registered: Granular; amine and ester
liquids; aerosol spray (foam).
Methods of Application: Aerial and ground equipment,
knapsack sprayers, pressure and hose-end applicators,
and lawn spreaders.
SCIENCE FINDINGS
Summary Science Statement: The Agency's Office of Pesticide
Programs (OPP) has classified 2,4-D as a Group D oncogen
(not classifiable as to human carcinogenicity) because
existing data are inadequate to assess the carcinogenic
potential of 2,4-D. Accidental human poisoning with
2,4-D, which resulted in severe neurotoxicity, has been
reported; adequate neurotoxicity studies are not
available. While published data indicate that 2,4-D may
be teratogenic, an acceptable rat teratology study is
negative; a study in rabbits is needed.
2,4-D is often formulated as various esters and amines.
These formulations may affect the physical
characteristics, biological activity and environmental
fate of the-parent compound. Data are needed on each
ester and amine before the Agency can completely assess
2,4-D.
Although laboratory data demonstrate that 2,4-D is
mobile in soils, its potential to contaminate
groundwater is limited by its rapid rate of degradation
and uptake by target plants. However, residues of 2,4-D
have been detected in groundwater, mostly from point
sources, such as mixing, loading and disposal.
Certain formulations of 2,4-D are highly toxic to fish
and/or aquatic invertebrates. Other formulations, for
which the Agency has data, are in the range of
moderately toxic to practically nontoxic to nontarget
organisms. The Office of Endangered Species has issued
biological opinions indicating that certain endangered
species may be in jeopardy from the use of 2,4-D.
Chemical Characteristics (Acid):
Physical state - Flakes, powder, and crystalline powder
and solid
Color - White to light tan
Odor - Phenolic to odorless
Melting point - 135-142°C
Boiling point - 160°C at 0.4 mm Hg
Solubility - Soluble in acetone, ethanol, aqueous
alkali, alcohols, diethyl ether, ethyl ether,
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isopropanol, methyl isobutyl ketone, most organic
solvents; insoluble in benzene, petroleum oils
Vapor pressure - 0.4 mm Hg at 160°C
Stability - Stable to melting point
Toxicology Characteristics (Acid, except as noted):
Acute Toxicity:
2.4-D Acid -
Oral (rat): 639 mg/kg (males); 764 mg/kg (females);
Toxicity Category III1
Inhalation (rat): 1.79 mg/L; Toxicity Category III
Dermal Sensitization (guinea pig): Not a sensitizer.
2f4-D Sodium Salt -
Oral (rat): 876 mg/kg (males); 975 mg/kg (females);
Toxicity Category III
Dermal (rat): >2000 mg/kg; Toxicity Category III
Diethanolamine Salt (Manufacturing-Use Product) -
Oral (rat): >2000 mg/kg (males); 1605 mg/kg
(females); Toxicity Category III
Dermal (rabbit): >2000 mg/kg (males and females);
Toxicity Category III
Inhalation (rat): >3.8 mg/L; Toxicity Category III
Primary Eye (rabbit): Severe irritation and corneal
ulcer not resolved 21 days post-treatment;
Toxicity Category I
Primary Dermal (rabbit): No signs of dermal
irritation; Toxicity Category IV
Dermal Sensitization (guinea pig): Not a dermal
sensitizer.
Butoxyethyl Ester -
Oral (rat): 866 mg/kg; Toxicity Category III
1For a description of Toxicity Categories, see 40 CFR 156.10
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Dermal (rabbit): >2000 mg/kg (females: 1829 (mg/kg
(males); Toxicity Category III
Inhalation (rat): >4.6 mg/L; Toxicity Category III
Primary Eye (rabbit): Very mild eye irritation resolved
in 72 hours; Toxicity Category III
Primary Dermal (rabbit): Very slight erythema cleared
in 72 hours; Toxicity Category III.
Dermal Sensitization (guinea pig): Was a sensitizer in
two tests and not a sensitizer in a third
test.
Isooctvl Ester -
Oral (rat): 982 mg/kg (males); >720 <864 mg/kg
(females); Toxicity Category III
Dermal (rabbit): >2000 mg/kg; Toxicity Category III
Isobutvl Ester -
Oral (rat): 700 mg/kg (males); 553 mg/kg (females);
Toxicity Category III
Dermal (rabbit): >2000 mg/kg; Toxicity Category III
Isopropvl Ester -
Oral (rat): 640 mg/kg (males); 440 mg/kg (females);
Toxicity Category II
Dermal (rabbit): >2000 mg/kg; Toxicity Category III
Inhalation (rat): >4.97 mg/L; Toxicity Category III
Primary eye (rabbit): All irritation cleared at 4
days;:Toxicity Category III
Primary dermal (rabbit): No irritation at 72 hours;
Toxicity Category IV
Dermal Sensitization (guinea pig): Nonsensitizer
Subchronic Toxicity: No acceptable data are available on
2,4-D. The requirement for subchronic oral studies on
the acid is waived because chronic studies are required;
a subchronic dermal study is required. Subchronic
studies are required for the esters and amines.
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Chronic Toxicity:
Oncogenicity (rats): No observed effects level (NOEL)
for systemic effects - 1 mg/kg/day; lowest observed
effects level (LOEL) for systemic effects - 5
mg/kg/day; further evaluation needed to determine
if maximum tolerated dose was reached.
Oncogenicity (mice): NOEL for systemic effects - 1
mg/kg/day; LOEL for systemic effects - 15
mg/kg/day; further evaluation needed to determine
if maximum tolerated dose was reached.
Teratology (rats): Fetotoxicity (delayed ossification)
LOEL 75 mg/kg/day and NOEL 25 mg/kg/day; Maternal
toxicity NOEL 75 mg/kg/day (highest dose tested).
Reproduction (rats): NOEL 5 mg/kg/day.
Major Routes of Exposure: The major route of exposure is
dermal; respiratory exposure is negligible.
Physiological and Behavioral Characteristics:
Foliar Absorption: 2,4-D is absorbed through the roots
and/or leaves depending upon the type of
formulation. A rain-free period of 4 to 6 hours
usually is adequate for uptake.
Translocation: Following foliar absorption, 2,4-D
translocates within the phloem, probably moving
with the food material. Following root absorption,
it may move upward in the transpiration stream.
Translocation rate is influenced by the growth rate
of the plant. Accumulation occurs principally at
the rapid growth regions of shoots and roots.
Mechanism of Pesticide Action: 2,4-D acid stimulates
nucleic acid and protein synthesis affecting the
activity of enzymes, respiration and cell division.
Broadleaf plants exhibit malformed leaves, stems
and roots.
Environmental Characteristics:
Absorption and Leaching: 2,4-D is mobile to highly
mobile in five soil types. Based on available
data, aged 2,4-D residues are only slightly mobile.
Microbial Breakdown: 2,4-D degrades rapidly in aerobic
silty clay and loam soil systems.
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Bioaccumulation: Available data indicate a low
potential for 2,4-D to accumulate in fish.
Resultant Average Persistence: In aerobic silty clay
and loam soils, 1.9-2.2 percent of applied 2,4-D
remained at 51 days post-treatment; in four other
soils, only 0.7-2.5 percent remained at 150 days
post-treatment.
Environmental Fate and Surface and Groundwater
Contamination Concerns: Although laboratory data
demonstrate that 2,4-D is mobile in soils, its
potential to contaminate groundwater is limited by
its rapid rate of degradation and uptake by target
plants. However, residues of 2,4-D have been
detected in groundwater, mostly from point
sources, such as mixing, loading and disposal.
Exposure of Humans and Nontarget Organisms: Accidental
human poisoning with 2,4-D, which resulted in
severe neurotoxicity, has been reported. Reports
have been received concerning off-target movement
of 2,4-D resulting in damage to crops or other
desirable plants.
Exposure during Reentry Operations: Based on available
data, 2,4-D products are of low toxicity (Toxicity
Categories III and IV). Because of these low levels
of toxicity, reentry is not a concern.
Ecological Characteristics (detailed information can be
obtained from the Registration Standard):
Avian Toxicity: Acceptable data indicate that 2,4-D
acid can be characterized as moderately toxic to
practically nontoxic to avian species on an acute
basis. Butyl ester can be characterized as
practically nontoxic on an acute and chronic basis.
Fish Toxicity: Acceptable data indicate that 2,4-D acid
and certain of its salts, esters and amines can be
characterized in the range of moderately toxic to
practically nontoxic to fish. However, the
compounds N-oleyl-1,3-propylenediamine salt, N,N-
dimethyloleyl-linoleylamine, butyl ester,
butoxyethanol ester and propylene glycol butyl
ether ester can be characterized as highly toxic to
fish, based on the following toxicity values:
N-oleyl-l,3-propylene-
diamine salt 0.3 ppm (bluegill sunfish)
0.8 ppm (channel catfish)
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N,N-dimethyloleyl-
linoleylamine
Butyl ester
Butoxyethanol ester
Butoxypropyl ester
Propylene glycol
butyl ether ester
0.64 ppm (rainbow trout)
0.49-2.82 ppm (cutthroat trout)
0.5-2.8 ppm (lake trout)
0.4-0.96 ppm (rainbow trout)
0.29-0.3 ppm (bluegill sunfish)
0.65 ppm (rainbow trout)
0.76-1.2 ppm (bluegill sunfish)
3.3 ppm (fathead minnow)
0.78-1.35 ppm (channel catfish)
5.4 ppm (rainbow trout)
0.33-2.8 ppm (cutthroat trout)
0.39-2.93 ppm (lake trout)
0.95-1.44 ppm (rainbow trout)
0.56-0.67 ppm (bluegill
sunfish)
Freshwater Invertebrates Toxicity: Of those compounds
for which the Agency has data, reported toxicity
values indicate that the compounds can be
characterized as slightly toxic to practically
nontoxic, excepted as noted below. The compounds
set forth below have toxicity values which
characterize them as highly toxic to-aquatic
invertebrates.
Dimethylamine
Isooctyl ester
0.15 ppm (grass shrimp)
0
5 ppm (waterflea)
Butoxyethanol ester 1.7-6.4 ppm (waterflea)
2.2 ppm (seed shrimp)
2.6 ppm (sow bug)
0.44-6.1 ppm (side swimmer)
0.39-0.79 ppm (midge)
Propylene glycol
butyl ether ester 0.1-14 ppm (waterflea)
0.42 ppm (seed shrimp)
Estuarine and Marine Organisms Toxicity: Acceptable
data are available only for the butoxyethano1 ester
which report toxicity values of 5.0 mg/L (longnose
killifish), 2.6 mg/L (Eastern oyster) and 5.6 mg/L
(brown shrimp), which indicate that the material is
moderately toxic to estuarine and marine organisms.
Effects on Plants: Limited plant protection studies are
available. In a spray drift study, two application
methods were compared as to quantity and pattern of
deposition. No difference was found between the
amine derivatives (diethanolamine and
dimethylamine). With these amines, drift was
observed beyond 225 feet from the site of
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application. No residues, attributable to drift,
were found when applied postemergent to wheat or
corn.
The toxicity of butoxyethanol ester was tested on
four species of algae. Toxicity values ranged from
75 mg/L to 150 mg/L.
Nontarget Insects: There is sufficient information to
characterize 2,4-D as relatively nontoxic to honey
bees, when bees are exposed to direct treatment.
Potential Problems Related to Endangered Species: The
Office of Endangered Species has determined that
certain uses of 2,4-D may jeopardize the continued
existence of endangered species or critical habitat
of certain endangered species.
Tolerance Assessment:
Tolerances Established: Tolerances and food and feed
additive regulations have been established for
residues of 2,4-D in a variety of raw agricultural
commodities and meat byproducts (40 CFR 180.142),
and in processed food (40 CFR 185.1450) and feed
(40 CFR 186.1450).
Results of Tolerance Assessment: A provisional
acceptable daily intake (PADI) of 0.003 mg/kg/day
for 2,4-D acid has been established based on a two-
year rat feeding study. Compound-related effects
were observed in the kidneys of both male and
female rats. The LOEL was 5 mg/kg/day and the NOEL
was 1 mg/kg/day. An uncertainty factor of 100 was
used to account for the inter- and intraspecies
differences. An additional uncertainty factor of 3
was used since there is no dog study available and
no information available that indicates the dog is
less sensitive than the rat.
Reported Pesticide incidents: Based on the Pesticide
incident Monitoring System files, covering the period
1966 to 1979, reports were received concerning the off-
target movement of 2,4-D in unspecified formulations,
esters and amines. The incidents involved drift from
aerial (173 reports) and ground (104 reports)
applications, as well as volatilization and drift (35
reports) and resulted in damage to off-target crops or
other desirable plants.
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SUMMARY OF REGULATORY POSITION AMD RATIONALE
Summary of Agency Position: OPP has classified 2,4-D as a
Group D oncogen (not classifiable as to human
carcinogenicity). EPA is, however, requiring additional
data, including additional information on oncogenicity
and teratogenicity and neurotoxicity studies, for
further evaluation of 2,4-D. Data are being required on
the ester and amine formulations of 2,4-D as well as on
the acid. EPA will not establish any significant new
food use tolerances or register any significant new uses
at this time.
Additional data are needed to thoroughly evaluate the
ecological effects of 2,4-D and its potential to
contaminate groundwater.
EPA is developing a program to reduce or eliminate
exposure to endangered species from the use of 2,4-D to
a point where use does not result in jeopardy, and will
issue notice of any labeling revisions when the program
is developed. Endangered species labeling is not
required at this time.
Unique Warning Statements Required on Labels:
Manufacturing-Use Products; "Do not discharge effluent
containing this product into lakes, streams, ponds,
estuaries, oceans, or public waters unless this
product is specifically identified and addressed in
an NPDES permit. Do not discharge effluent
containing this product to sewer systems without
previously notifying the sewage treatment plant
authority. For guidance, contact your state Water
Board or Regional Office of the EPA."
End-Use Products;
Aquatic Uses. "Drift or runoff may adversely affect
nontarget plants. Do not apply directly to water
except as specified on this label. Do not
contaminate water when disposing of equipment
washwaters."
Nonaauatic Uses. "Drift or runoff may adversely affect
nontarget plants. Do not apply directly to water
or wetlands (swamps, bogs, marshes, and potholes).
Do not contaminate water when disposing of
equipment washwaters."
End-Use Products - Certain Formulations; End-use
products containing the following formulations must
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contain the above environmental precautions
modified to indicate that the product is toxic
either to fish or aquatic invertebrates:
Toxic to Fish - N-01eyl-l,3-Propylenediamine salt
N,N-Dimethyloleyl-Linoleylamine
Butyl ester
Butoxylethanol ester
Propylene glycol butyl ether ester
Toxic to Aquatic Invertebrates - Dimethylamine
Isooctyl ester
All End-Use Products; The following statements are
required in the use directions for all end-use products:
Liquid Formulations; "This product can reach
groundwater from mixing and loading. To minimize
groundwater contamination from spills during
mixing, loading and cleaning of equipment, take the
following steps:
"Mixing and Loading; When mixing, loading or
applying this product, wear chemical resistant
gloves. Wash nondisposable gloves thoroughly with
soap and water before.removing.
"The mixing and loading of spray mixtures into the
spray equipment must be carried out on an
impervious pad (i.e., concrete slab, plastic
sheeting) large enough to catch any spilled
material. If spills occur, contain the spill by
using an absorbent material (e.g, sand, earth or
synthetic absorbent). Dispose of the contaminated
absorbent material by placing in a. plastic bag and
following disposal instructions on this label.
"Triple rinse empty containers and add the rinsate
to the mixing tank.
"Cleaning of Equipment; When cleaning equipment,
do not pour the washwater on the ground; spray or
drain over a large area away from wells and other
water sources."
Granular Formulations; "This product can reach ground-
water from improper handling. To minimize ground-
water contamination from spills during loading and
cleaning of equipment, take the following steps:
"Handling; When handling this product, wear
chemical resistant gloves. Wash nondisposable
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gloves thoroughly with soap and water before
removing. If spills occur, collect the material
and dispose of by following disposal instructions
on this label.
"Cleaning of Equipment; When cleaning equipment,
do not pour the washwater on the ground; spray or
drain over a large area away from wells and other
water sources."
End-Use Products - Certain Food/Feed Uses. Labels for
products registered for certain food/feed uses must
contain revised use directions pertaining to
appropriate preharvest, pregrazing and preslaughter
intervals; allowable range of diluent; and/or
maximum seasonal application rate and/or number of
applications.
SUMMARY OF MAJOR DATA GAPS. The following data are required
for 2,4-D acid. The Agency is also requiring data on each
individual ester and amine of 2,4-D. Specific requirements
are detailed in the Data Tables, Appendix I of the
Registration Standard, which can be obtained from the Product
Manager listed below.
Study Due Date - From
Date of Standard
Product Chemistry 6-15 months
Residue Chemistry: 18-24 months
Plant and animal metabolism
Analytical methods
Residue studies
Toxicology: . 9-50 months
Primary Eye and Dermal Irritation
21-Day Dermal
Chronic Toxicity (nonrodent)
Teratogenicity (rabbit)
Mutagenicity
Metabolism
Special Dermal (Neurotoxicity)
Reserved: Oncogenicity (two species)
Ecological Effects: 9-18 months
Avian Dietary
Aquatic Organism (freshwater fish
and invertebrates; estuarine
and marine organisms; accumulation)
Phytotoxicity (Tier II)
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Study
Due Date - From
Date of Standard
Environmental Fate: 9-50 months
Hydrolysis
Photodegradation (water, soil,- air)
Metabolism (anaerobic soil; aerobic
and anaerobic aquatic)
Leaching and Adsorption/Desorption
Volatility (lab and field)
Dissipation (soil, aquatic and forestry)
Accumulation (confined rotational
crops; irrigated crops; fish
and aquatic nontarget organisms)
Spray drift
CONTACT PERSON AT EPA; Mr. Richard Mountfort
Product Manager (Team 23)
Fungicide-Herbicide Branch
Registration Division (TS-767C)
Office of Pesticide Programs, EPA
Washington, DC 20460
Telephone: (703) 557-1830
nTSfT.ATMF.R! The information in this Pesticide Fact Sheet is
a summary only and may not be used to fulfill data
requirements for pesticide registration and reregistration.
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