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 ae/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.

27 ENVIRONMENTAL FATE:

Half life in soil: 2,4-D EHE 1-14 days with an average of 2.9 days. It degrades more slowly on foliage and leaf litter. 2,4-D acid has a aerobic soil half life of 6.2 days.
Half life in water: Less than 24 hours in aquatic environments for 2,4-D EHE, BEE and IPE. Probably longer in clean water. 2,4-D acid has an aerobic half life of 15 days and an anaerobic half life of 41-333 days.
2,4-D acid is stable to abiotic hydrolysis with a half life of 1-2 years.
It has an EPA classification for soil mobility that ranges from intermediate to very mobile. Usually very low mobility in field studies even though laboratory solubility studies indicate 2,4-D is potentially mobile. Rapid degradation in the soil and removal from soil by plant uptake minimizes leaching under realistic application conditions.
Ground water contamination: Significant ground water contamination not likely but it has been detected in ground and surface waters in the US and Canada. Rarely detected more than 500 mm deep in soils.
Accumulation in milk and tissues.
pH stability:
Photolysis rate: 2,4-D acid half life (DT50) was 12.9 days in water at pH 5 and 68 days in soil. In air exposed to UV the half life was 13 days for 2,4-D butyl ester as a liquid and gas.
Hydrolysis half life: Stable to abiotic hydrolysis.
Biodegradation rate: 2,4-D acid half life is 6.9 days in aerobic soils and 15 days in aerobic aquatic environments. 2,4-D amine and salt formulations are similar. 2,4-D esters form the 2,4-D acid with a half life of about 3 (1-10) days then follow the acid degradation pathway with a half life of about 7 days. Most field studies show an apparent half life of 1.7 - 13 days with an average of 5 days in moist soils. In dry soils the half life is much longer because most of the breakdown is due to microbial activity. The half life in grass and thatch was < 7 days on average. The half life in natural water is 1-2 weeks but may be only a few days in rice paddies.
2,4-D degrades through several low toxicity intermediates to carbon compounds, CO2, water and chlorine or HCl.

28 REGISTERED CROPS:

See HerbiGuide Species Solution tab.

29 REGISTERED WEEDS:

See HerbiGuide Species Solution tab.

30 REGULATION AND LEGAL:

UN number: See below.
Dangerous goods class:
Hazchem code:
NOHSC classification:
Proper shipping name:
Packaging group:
EPG:
CAS numbers: See below.

Phenoxy Properties:

Active ingredient (PC Code) Color Physical StateMelting Point/Boiling PointDensity/Specific GravityOctanol/Water Partition Coeff. Vapor PressureSolubility
2,4-D acid (030001)white solid crystalline m.p. 138-141 C s.g.=1.416 at 25 CLog KO/W 0.001 M sol'n
pH 5 2.14
pH 7 0.177
pH 9 0.102
1.4 x 10-7 mm Hg at 25 Cwater = 569 mg/L at 20 C
2,4-D Na salt (030004)white powder m.p. 200 C bulk = 42.2 lb/ft3 at 25 C N/A 2; salt dissociates to acid in water N/A 2; salt dissociates to acid in water water = 4.5 g/100 mL at 25 C
2,4-D DEA salt (030016) cream powderm.p. 83 Cbulk = 0.762 g/cm3 at 25 C2.24 x 10-2 at 25 C<1 x 10-7 mm Hg at 25 Cwater = 806 mg/g at 25 C
2,4-D DMA salt (030019) amberaqueous liquidm.p. 118-120 C (PAI)s.g. = 1.23 at 20 CN/A; salt dissociates to acid in water<1 x 10-7 mm Hg at 26 Cwater = 72.9 g/100 mL at 20 C (pH 7)
2,4-D IPA salt (030025) amber aqueous liquidm.p. 121 C (PAI)s.g. = 1.15 at 20 CN/A; salt dissociates to acid in water N/A; salt dissociates to acid in water water = 17.4 g/100 mL at 20 C (pH 5.3)
2,4-D TIPA salt (030035)amberaqueous liquid m.p. 87-110 C (PAI)s.g. = 1.21 at 20 C N/A; salt dissociates to acid in water N/A; salt dissociates to acid in water water = 46.1 g/100 mL at 20 C (pH 7)
2,4-D methyl ester     1.55 x 10-3 mm Hg 1296 
2,4-D ethyl esterclear brownliquid    0.25-1.39 x 10-3 mm Hg 4 
2,4-D IPE
(030066)
Isopropyl ester
pale amberliquid b.p. 240 C s.g. = 1.252 at 25 C253.8 ± 44.4 (temp N/A) Variable3 10.5 x 10-3 to 3.98 x 10-6water = 0.023 g/100 mL
2,4-D butyl esterclear brownliquid    4.05 x 10-4 mm Hg 
2,4-D iso-octyl ester liquid   1.72 x 10-5 mm Hg 
2,4-D BEE (030053)dark amber liquidb.p. 89 C s.g. = 1.225 at 20 Clog = 4.13-4.17 at 25 C2.4 x 10-6 mm Hg at 25 Cwater = insoluble
2,4-D 2-EHE (030063)dark amber liquidb.p. 300 C s.g. = 1.152 at 20 Clog = 5.78 (temp N/A)3.6 x 10-6 mm Hg (temp N/A)water = 86.7 ppb

Adapted from EPA (2005) Table 2, company MSDS and peer reviewed papers.
1 Data assembled from EPA data.
2 N/A = Not available.
3 Variable values e.g. http://www.inchem.org/pages/pds.html, Flint et al. (1968) has 1.4 x 10-3 mm Hg, Jensen & Schall (1966) has 4.6 x 10-5 mm Hg, EPA (2005) has 5.3 x 10-6 mbar = 3.98 x 10-6 mm Hg, FAO (1978) has 10.5 x 10-3 mm Hg at 25°C, Mullison and Hummer (1949) has 1.2 x 10-3 mm Hg at 26.6 0C.
4 Mullison and Hummer (1949) have 0.86 x 10-3 mm Hg at 26.6 0C.

Active ingredient (PC Code) Molecular weightEmpirical formulaCAS numberHenry's Law constant
2,4-D acid (030001)221.0C8H6Cl2O394-75-71.76 x 10-12
2,4-D Na salt (030004)243.03C8H5Cl2NaO3

2702-72-9 
2,4-D DEA salt (030016) 326.18C12H17Cl2NO55742-19-8 
2,4-D DMA salt (030019) 266.13C10H13Cl2NO32008-39-1 
2,4-D IPA salt (030025) 280.04C11H15Cl2NO35742-17-6 
2,4-D TIPA salt (030035)412.31C17H27Cl2NO632341-80-3 
2,4-D BEE (030053)321.20C14H18Cl2O41929-73-3 
2,4-D 2-EHE (030063)333.27C16H22Cl2O31928-43-4 
2,4-D IPE
(030066)
263.12C11H12Cl2O394-11-1 
2,4-D ethyl ester249.09C10H10Cl2O3533-23-3 
2,4-D butyl ester277C12H14Cl2O394-80-4 



Oil solubility:
Soil organic carbon absorption coefficient (Koc): 31.2-470.9 mL/g.
Soil DT50 aerobic 20 C - 1.7 days.
Soil DT50 anaerobic 20 C - 333 days (aquatic study).
Hydrolysis: 1-2 years sterile water pH 7 buffered.
Photolysis water DT50 13 days (artificial sunlight)
Photolysis soil DT50 68 days

Dissociation constant: pKa
Odour - Amine and salt formulations tend to be of low odour and the ester formulations generally have a strong odour.
pH -
Flammability: Amines and salts are generally not flammable. Ester formulations are generally flammable because they are mixed with flammable hydrocarbons.

32 COMMENTS:

2,4-D decreases nitrate reductase in the plant and this results in an increased nitrate level. In some plants, such as Capeweed, Radishes, Turnips, and Canola, this may reach toxic levels.

33 REFERENCES:

Ashton, F.M. and Crafts, A.S. (1981) Mode of Action of Herbicides. (Wiley-Interscience publication).

Kearney, P.C. and Kaufman, D.D. (1976). Herbicides. Chemistry, degradation and mode of action. Vol 1 & 2.

EPA 2005.

Piper and Moore (2007). Organic acid herbicides : Volatility and side reactions.

Acknowledgments:

Collated by HerbiGuide. For more information see www.herbiguide.com.au or phone 08 98444064.