2,4-D (Dacamine, Weed-B-Gon) Herbicide Profile 9/88
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.
USE PATTERNS AND FORMULATIONS
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).
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 degrees C.
Boiling point - 160 degrees C at 0.4 mm Hg.
Solubility - Soluble in acetone, ethanol, aqueous alkali, alcohols, diethyl
ether, ethyl ether, isopropanol, methyl isobutyl ketone, most organic
solvents; insoluble in benzene, petroleum oils.
Vapor pressure - 0.4 mm Hg at 160 degrees 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 III
(For a description of Toxicity Categories, see 40 CFR 156.10.)
Inhalation (rat): 1.79 mg/L; Toxicity Category III
Dermal Sensitization (guinea pig): Not a sensitizer.
2,4-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
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.
Isooctyl Ester -
Oral (rat): 982 mg/kg (males); >720 <864 mg/kg (females); Toxicity
Category III
Dermal (rabbit): >2000 mg/kg; Toxicity Category III
Isobutyl Ester -
Oral (rat): 700 mg/kg (males); 553 mg/kg (females); Toxicity Category III
Dermal (rabbit): >2000 mg/kg; Toxicity Category III
Isopropyl 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.
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.
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-1,3-propylene-
diamine salt 0.3 ppm (bluegill sunfish)
0.8 ppm (channel catfish)
N,N-dimethyloleyl-linoleylamine
0.64 ppm (rainbow trout)
Butyl ester
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)
Butoxyethanol ester
0.65 ppm (rainbow trout)
0.76-1.2 ppm (bluegill sunfish)
3.3 ppm (fathead minnow)
0.78-1.35 ppm (channel catfish)
Butoxypropyl ester
5.4 ppm (rainbow trout)
Propylene glycol butyl ether ester
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 0.15 ppm (grass shrimp)
Isooctyl ester 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 butoxyethanol 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 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.
SUMMARY OF REGULATORY POSITION AND 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."
Nonaquatic 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 contain the above environmental precautions
modified to indicate that the product is toxic either to fish or aquatic
invertebrates:
Toxic to Fish - N-Oleyl-1,3-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 groundwater from improper
handling. To minimize groundwater contamination from spills during loading and
cleaning of equipment, take the following steps:
"Handling: When handling this product, wear chemical resistant gloves.
Wash nondisposable 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 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)
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
DISCLAIMER: 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.
Disclaimer: Please read
the pesticide label prior to use. The information contained at this web
site is not a substitute for a pesticide label. Trade names used herein
are for convenience only; no endorsement of products is intended, nor is
criticism of unnamed products implied. Most of this information is historical
in nature and may no longer be applicable.
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