2,4-D Mode of action and properties

20 MODE OF ACTION:

All formulations

Foliar absorbed with minor root absorption, translocated, post-emergent.

Uptake and translocation:

High concentrations may cause leaf burn and poor translocation leading to poor weed control. Translocated both up and down from the site of application to sources of active growth.

Physiological effects:

Causes twisting, swelling and splitting of soft stems and abnormal growth of leaves often resulting in cupping and inter-veinal chlorosis. Flowers are often deformed and seed viability may be affected. These symptoms may occur at very low dose rates.

21 SELECTIVITY:

Most grasses are tolerant to 2,4-D. Woody plants have lower tolerances and soft broad leaved species are generally susceptible to rates around 1 kg a.e./ha.

The sodium salt formulation is generally more selective than the amine formulations which are generally more selective than the esters formulations. For example 2,4D amine is registered for use in oats whereas the esters are not registered because they cause too much crop damage.

22 DISEASE AND INSECT EFFECTS:

No specific effects relating to different formulations.

23 PLANT SYMPTOMS:

Sensitivity to 2,4-D depends on the species, formulation, stage of growth and rate. The table below summarises the effects of the most efficacious formulations on the most sensitive species.
SpeciesGrowth stageFormulationEC25
g a.e. /ha
NOEC
g a.e./ha
Sorghum (Monocot)Seedling2,4-D DMAS (amine)2917
Onion (Monocot)Seedling2,4-D IPE (ester)116.3
Mustard (Dicot)Seedling2,4-D DEA (amine)50<50
Lettuce (Dicot)Seedling2,4-D IPE (ester)0.90.53
Onion (Monocot)Vegetative2,4-D acid<8.4<8.4
Corn (Monocot)Vegetative2,4-D IPE (ester)22628.2
Tomato (Dicot)Vegetative2,4-D DEA
(amine)
3.32.2
Lettuce (Dicot)Vegetative2,4-D IPE (ester)6.81.4

Table adapted from EPA 738-R-05-002, June 2005



For cereals the ester formulations are less damaging to the crop pre planting than the amine formulations.

SECONDARY EFFECTS:

24 TOXICITY:

Summary:

The 2,4-D herbicides are generally of low toxicity to mammals, birds and bees. Toxicity to aquatic organisms depends on the formulation and can be highly toxic. The ester formulations are generally more toxic to aquatic life than the amine formulations.

Details:

Poison schedule: S5.

Mammalian toxicity: Low toxicity.



Acute oral: LD50 [For comparison table salt is 3000 mg/kg]
ChemicalToxicity LD50Toxicity category
2,4-D acid639 mg/kg (rat)III
DEA salt735 mg/kg (rat)III
DMA salt949 mg/kg (rat)III
IPA salt1646 mg/kg (rat)III
TIPA salt1074 mg/kg (rat)III
IPE ester1250 mg/kg (rat)III
BEE ester 866 mg/kg (rat)III
EHE ester 896 mg/kg (rat)III

Table adapted from EPA 738-R-05-002, June 2005



Acute dermal: LD50
ChemicalToxicity LD50Toxicity category
2,4-D acid>2000 mg/kg (rabbits)III
DEA salt>2000 mg/kg (rabbits)III
DMA salt 1829 mg/kg (rabbits)III
IPA salt>2000 mg/kg (rabbits)III
TIPA salt>2000 mg/kg (rabbits)III
IPE ester>2000 mg/kg (rabbits)III
BEE ester>2000 mg/kg (rabbits)III
EHE ester>2000 mg/kg (rabbits)III

Table adapted from EPA 738-R-05-002, June 2005



Skin: Primary irritation
ChemicalClassCategory
2,4-D acidNA 
DEA saltslight skin irritantIII
DMA saltslight skin irritantIV
IPA saltslight skin irritantIV
IPE esterslight skin irritantIV
TIPA saltslight skin irritantIV
BEE estervery mild irritantIV
EHE esternot a skin irritantIV

Table adapted from EPA 738-R-05-002, June 2005



Skin: Sensitisation
ChemicalClass
2,4-D acidnot a dermal sensitizer
DEA saltnot a dermal sensitizer
DMA saltNA
IPA saltNA
TIPA saltnot a dermal sensitizer
IPE esternot a dermal sensitizer
BEE esternot a dermal sensitizer
EHE esterNA

Table adapted from EPA 738-R-05-002, June 2005



Eye:
ChemicalClassCategory
2,4-D acidsevere eye irritantI
DEA saltsevere eye irritantI
DMA saltsevere eye irritantI
IPA saltsevere eye irritantI
TIPA saltsevere eye irritantI
IPE esternot an eye irritantIV
BEE esternot an eye irritantIII
EHE esternot an eye irritantIII

Table adapted from EPA 738-R-05-002, June 2005



Vapour inhalation:
ChemicalToxicity LC50Toxicity category
2,4-D acid>1.79 mg/L (rat)III
DEA salt>3.5 mg/L (rat)IV
DMA salt>3.5 mg/L (rat)IV
IPA salt =3.1 mg/L (rat)IV
TIPA salt=0.78 mg/L (rat)III
IPE ester>4.97 mg/L (rat)IV
BEE ester=4.6 mg/L (rat)IV
EHE ester>5.4 mg/ (rat)IV

Table adapted from EPA 738-R-05-002, June 2005



Chronic oral toxicity: NOEL 5 mg/kg/day for two years rats and 30 mg/kg/day for rabbits.

Acute dietary toxicity: NOEL 25-67 mg/kg/day.

Not carcinogenic, mutagenic or teratogenic in animal tests. (i.e. has not caused cancer or reproductive problems).

Acceptable Daily Intake (ADI):



Other Species:

Birds: LD50 = 415 to >1000 mg a.e./kg. Moderately to practically non toxic. The acid, amine and ester formulations have similar toxicity. Chronic NOEC for birds is 992 ppm for 2,4-D acid formulation.

Fish: toxicity LC50 >80.24 to 2244 mg a.e./L for acid and amine formulations and >0.1564 to 14.5 mg a.e./L for ester formulations.

NOEC of 14.2 to 63.4 mg a.e./L for 2,4-D acid, 2,4-D DEA and 2,4-D DMAS and

0.0555 to 0.0792 mg a.e/L for 2,4-D BEE and 2,4-D EHE based on larval fish survival for the fish full life cycle studies.

2,4-D amine and acid formulations are practically non toxic to freshwater and marine fish. The ester formulations are slightly to highly toxic to fish.

2,4-D acid, DMA and EHE are practically non toxic to tadpoles.

Invertebrates: LC 50 = 25 to 830 mg a.e./L for freshwater and marine invertebrates for 2,4-D acid and amine formulations. That is slightly toxic to practically non-toxic to freshwater marine invertebrates.

LC50 = 2.2 mg a.e./L for the 2,4-D IPE to 11.88 mg a.e./L for the 2,4-D EHE or slightly toxic to moderately toxic for freshwater invertebrates. Marine invertebrates were more variable with LC50 >0.092 to >66 mg a.e./L for the 2,4-D esters or highly toxic to practically non-toxic.

Chronic toxicities for freshwater and marine invertebrates for 2,4-D acid, DEA, DMAS and BEE

Bees: Practically non toxic. LD > 10 ug/bee. Moderate doses have impaired brood production.

Arthropods: toxicity.

Earthworms:

25 TOXICITY SYMPTOMS:

26 FIRST AID:

If SWALLOWED: Depends on the formulation. For amines and salts induce vomiting. For esters give a glass of water and do NOT induce vomiting. See a doctor.

If in EYES: Irrigate with plenty of water. Amine and salt formulations are more irritating than ester formulations.

If on SKIN: Rinse with plenty of water, remove contaminated clothing, wash with soap and water.

If INHALED: Remove patient to fresh air. See a doctor.

Advice to doctor: Treat symptomatically.

2,4-D Comparative Data

27-35 2,4-D Fate, Properties & Regulations