2,4-D Mode of action and properties

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.

Species	Growth stage	Formulation	EC25 g a.e. /ha	NOEC g a.e./ha
Sorghum (Monocot)	Seedling	2,4-D DMAS (amine)	29	17
Onion (Monocot)	Seedling	2,4-D IPE (ester)	11	6.3
Mustard (Dicot)	Seedling	2,4-D DEA (amine)	50	<50
Lettuce (Dicot)	Seedling	2,4-D IPE (ester)	0.9	0.53
Onion (Monocot)	Vegetative	2,4-D acid	<8.4	<8.4
Corn (Monocot)	Vegetative	2,4-D IPE (ester)	226	28.2
Tomato (Dicot)	Vegetative	2,4-D DEA (amine)	3.3	2.2
Lettuce (Dicot)	Vegetative	2,4-D IPE (ester)	6.8	1.4

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]

Chemical	Toxicity LD50	Toxicity category
2,4-D acid	639 mg/kg (rat)	III
DEA salt	735 mg/kg (rat)	III
DMA salt	949 mg/kg (rat)	III
IPA salt	1646 mg/kg (rat)	III
TIPA salt	1074 mg/kg (rat)	III
IPE ester	1250 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

Chemical	Toxicity LD50	Toxicity 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

Chemical	Class	Category
2,4-D acid	NA
DEA salt	slight skin irritant	III
DMA salt	slight skin irritant	IV
IPA salt	slight skin irritant	IV
IPE ester	slight skin irritant	IV
TIPA salt	slight skin irritant	IV
BEE ester	very mild irritant	IV
EHE ester	not a skin irritant	IV

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

Skin: Sensitisation

Chemical	Class
2,4-D acid	not a dermal sensitizer
DEA salt	not a dermal sensitizer
DMA salt	NA
IPA salt	NA
TIPA salt	not a dermal sensitizer
IPE ester	not a dermal sensitizer
BEE ester	not a dermal sensitizer
EHE ester	NA

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

Eye:

Chemical	Class	Category
2,4-D acid	severe eye irritant	I
DEA salt	severe eye irritant	I
DMA salt	severe eye irritant	I
IPA salt	severe eye irritant	I
TIPA salt	severe eye irritant	I
IPE ester	not an eye irritant	IV
BEE ester	not an eye irritant	III
EHE ester	not an eye irritant	III

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

Vapour inhalation:

Chemical	Toxicity LC50	Toxicity 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 State	Melting Point/Boiling Point	Density/Specific Gravity	Octanol/Water Partition Coeff.	Vapor Pressure	Solubility
2,4-D acid (030001)	white	solid crystalline	m.p. 138-141 C	s.g.=1.416 at 25 C	Log 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 C	water = 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	powder	m.p. 83 C	bulk = 0.762 g/cm3 at 25 C	2.24 x 10-2 at 25 C	<1 x 10^-7 mm Hg at 25 C	water = 806 mg/g at 25 C
2,4-D DMA salt (030019)	amber	aqueous liquid	m.p. 118-120 C (PAI)	s.g. = 1.23 at 20 C	N/A; salt dissociates to acid in water	<1 x 10^-7 mm Hg at 26 C	water = 72.9 g/100 mL at 20 C (pH 7)
2,4-D IPA salt (030025)	amber	aqueous liquid	m.p. 121 C (PAI)	s.g. = 1.15 at 20 C	N/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)	amber	aqueous 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 ¹²¹³
2,4-D ethyl ester	clear brown	liquid				0.25-1.39 x 10^-3 mm Hg ⁴
2,4-D IPE (030066) Isopropyl ester	pale amber	liquid	b.p. 240 C	s.g. = 1.252 at 25 C	253.8 ± 44.4 (temp N/A)	Variable³ 10.5 x 10^-3 to 3.98 x 10^-6	water = 0.023 g/100 mL
2,4-D butyl ester	clear brown	liquid				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	liquid	b.p. 89 C	s.g. = 1.225 at 20 C	log = 4.13-4.17 at 25 C	2.4 x 10^-6 mm Hg at 25 C	water = insoluble
2,4-D 2-EHE (030063)	dark amber	liquid	b.p. 300 C	s.g. = 1.152 at 20 C	log = 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^-6mm 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 weight	Empirical formula	CAS number	Henry's Law constant
2,4-D acid (030001)	221.0	C8H6Cl2O3	94-75-7	1.76 x 10^-12
2,4-D Na salt (030004)	243.03	C8H5Cl2NaO3	2702-72-9
2,4-D DEA salt (030016)	326.18	C12H17Cl2NO5	5742-19-8
2,4-D DMA salt (030019)	266.13	C10H13Cl2NO3	2008-39-1
2,4-D IPA salt (030025)	280.04	C11H15Cl2NO3	5742-17-6
2,4-D TIPA salt (030035)	412.31	C17H27Cl2NO6	32341-80-3
2,4-D BEE (030053)	321.20	C14H18Cl2O4	1929-73-3
2,4-D 2-EHE (030063)	333.27	C16H22Cl2O3	1928-43-4
2,4-D IPE (030066)	263.12	C11H12Cl2O3	94-11-1
2,4-D ethyl ester	249.09	C10H10Cl2O3	533-23-3
2,4-D butyl ester	277	C12H14Cl2O3	94-80-4

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.