2,4-D LV Ester Mode, Toxicity, Fate, Properties & Regulations

20 MODE OF ACTION:

Post-emergent. Disrupts cell growth and elongation. Multiple sites of action.

Uptake and translocation:

Foliar absorbed with virtually no root absorption.

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.

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.

Residual Life and Breakdown:

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.

Crop effects are usually only noticeable if applied at the incorrect growth stage and/or excessive rates.

Plant roots absorb polar (salt and amine) forms of 2,4-D most readily and leaves absorb non polar (ester) forms most readily. Salt formulations have negligible vapour pressure are the safer to use in close proximity to sensitive plants whereas ester formulations are generally safer prior to planting susceptible crops.

Crop tolerance:

Varietal sensitivities:

Applying 2,4-D to wheat before the completion of ear development may lead to yield loss and head deformities. Some varieties complete ear development at an earlier growth stage than others. The earliest timing for 2,4-D application therefore depends on the variety as indicated below


VarietyGrowth StageLeaves on the main stem.
AjanaZ155
AmeryZ166
AroonaZ166
ArrinoZ166
BladeZ166
BrooktonZ177
CadouxZ166
CalingiriZ177
CammZ166
CannaZ155
CarnamahZ166
CorriginZ166
CranbrookZ177
CunderdinZ177
DaggerZ177
EraduZ166
GamenyaZ166
GuthaZ155
HalberdZ166
KalannieZ155
KulinZ155
MacheteZ177
NyabingZ166
PerenjoriZ177
SpearZ177
StilettoZ177
TamminZ177
TincurrinZ155
WestoniaZ155
WilgoyneZ166

Effect on Clover Species:

Clover tolerance increases at later growth stages and at 460 mL/ha damage is often acceptable with many clover varieties. Selectivity in Clover pastures is due mainly to shading by taller growing species. Don't apply to clovers before the 4 leaf stage. It is generally not as safe as 2,4-D amine, MCPA 250 and 500. MCPA is generally preferred where clover damaged needs to b minimized.

Effect on Medic Species:

Medics are very sensitive to 2,4-D. Rates above 100 mL/ha generally damage Medics.

Effect on Lucerne:

Death of seedlings or established plants very common especially at low rates of herbicides and even if leaf growth is at a minimum when sprayed. Cutting/grazing prior to spraying can reduce damage but damage is usually unacceptable and severe. Herbicide drift onto lucerne can cause damage.

Effect on Native Plants:

Most native plants will tolerate low levels of 2,4-D and drift is not expected to cause significant long term effects on roadside trees or vegetation if reasonable care is taken to avoid exposure.

23 PLANT SYMPTOMS:

Initial symptoms are usually apparent in 3-7 days and include twisting of soft stems, cupping of leaves and erection of rosette leaves. Malformed growth may take weeks to develop. Death of young plants usually occurs within a month. Older and more woody plants may take several months to die.

It usually disrupts flowering and seed production or viability.

The table below summarises the effects of 2,4-D esters on the most sensitive species tested.
SpeciesGrowth stageFormulationEC25
g a.e. /ha
NOEC
g a.e./ha
Onion (Monocot)Seedling2,4-D IPE (ester)116.3
Lettuce (Dicot)Seedling2,4-D IPE (ester)0.90.53
Corn (Monocot)Vegetative2,4-D IPE (ester)22628.2
Lettuce (Dicot)Vegetative2,4-D IPE (ester)6.81.4
Table adapted from EPA 738-R-05-002, June 2005



For sensitive species like Lettuce and Tomato, rates around 3 mL/ha of 2,4-D ester can cause symptoms.

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

SECONDARY EFFECTS:

Sugar contents of sprayed plants normally increase within a week of spraying and this may make the plants more palatable to herbivores including sheep and insects. This may cause stock problems if toxic plants are present.

24 TOXICITY:

Summary:

Harmful if swallowed. May cause sensitisation by skin contact.

2,4-D ester is generally of low toxicity to mammals, birds and bees. It can be highly toxic to some aquatic organisms.

Details:

Poison schedule - S5.

Mammalian toxicity - Moderate.

Acute oral LD50 - 720-982 mg/kg (rats, 2,4-D 2EHE), [For comparison table salt is 3000 mg/kg]

Acute dermal LD50 - >2000 mg/kg (rat, 2,4-D 2EHE).

Skin - Mild skin irritant. Prolonged contact may cause skin sensitisation.

Eye - Not an irritant

Vapour inhalation - LC50 - >5.4 mg/L air (rat, 2,4-D 2EHE).

The weight of evidence indicates that it is not carcinogenic or mutagenic but some animal studies have shown effects.

Data indicates that it is not teratogenic and has no reproductive effects.

Acceptable Daily Intake (ADI) - 0.01 mg/kg/day.

Chronic oral toxicity NOEL - 1 mg/kg/day for two years.

Chronic effects: Repeated absorption of large amounts of 2,4-D may damage the liver and kidneys.

Other Species -

Birds - Not toxic. LD50 >663 mg/kg (Mallard Ducks)

Fish - Moderate toxicity. LC50 (96 hour) >0.24 on inland silverside to 20 mg/L on bluegill sunfish for 2,4-D 2EHE technical.

Invertebrates - Moderate toxicity. EC50 (48 hour) 5.2 mg/L (Daphnia magna) for 2,4-D 2EHE technical.

Bees - Not toxic. LD50 >100 ug/bee.

Algae - Low toxicity. EC50 (120 hour) >30 mg/L on Selenastrum capricornutum for 2,4-D EHE technical .

25 TOXICITY SYMPTOMS:

Inhalation of the solvents may cause headache, nausea and intoxication.

Swallowed - Ingestion of large amounts may cause headache, nausea, lethargy, motor weakness and incoordination. (16 g.a.e. consumed over 32 days by humans has caused these effects). Chronic overexposure may present a risk to the liver and kidneys.

Skin - High or prolonged exposure may cause defatting, dermatitis and sensitisation.

Eyes - May irritate eyes. Prolonged exposure may cause damage to eyes.

26 FIRST AID:

If SWALLOWED: Do NOT induce vomiting for small ingested quantities of less than a tablespoon. Give a glass of water. For large ingestions consider vomiting on medical advice but take care to avoid vomit entering lungs. Do not give anything by mouth to a semi conscious patient. Concentrate is considered harmful if swallowed. See a doctor.

If in EYES: Irrigate with plenty of water. See a doctor if symptoms develop or persist.

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 if symptoms develop or persist.

Advice to doctor: Treat symptomatically. Product contains hydrocarbon solvents. Aspiration of vomit into the lungs can cause bronchopneumonia and pulmonary oedema or pulmonary pneumonitis.

Contact the Poisons Information Centre on 131126.

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 - Does not accumulate. Not metabolised in the body. Excreted within a few days in urine.

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.

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.

Spray drift may cause damage.

28 REGISTERED CROPS:

See HerbiGuide Species Solution tab.

29 REGISTERED WEEDS:

See HerbiGuide Species Solution tab.

30 REGULATION AND LEGAL:

CAS number - 1928-43-4

UN number - 3082 (sea transport)

Hazchem code: NA.

NOHSC classification: Hazardous.

Land transport:

Dangerous goods class: Not a dangerous good

Sea transport:

Proper shipping name: ENVIRONMENTALLY HAZARDOUS SUBSTANCE, LIQUID, N.O.S. (contains 2,4-D 2 ethyl hexyl ester)

Class:

Packaging group - Class 9. Packaging group III

EPG -

Restricted spraying areas apply in some states.

A permit is required for spraying between 15th September and 15th April in Tasmania.

31 PROPERTIES:

Empirical formula: C16H22Cl2O3 (2,4-D 2-EHE).

Water solubility at 25 C. - Disperses in water;

Oil solubility -

Octanol:Water ratio at 25 C LogPow - 5.78 for 2,4-D 2-EHE.

Soil organic carbon absorption coefficient (Koc) 31.2-470.9 mL/g.

Vapour Pressure at 25 C. - 0.48 mPa (2,4-D 2-EHE)

Dissociation constant - pKa

Melting point - -5 C.

Boiling point - >200 C (2,4-D 2-EHE).

Molecular weight - 333.27 (2,4-D 2-EHE).

Colour - Clear brown liquid.

Odour - aromatic solvent odour.

Bulk density -

Specific gravity - 1.11

pH -

Flammability - Non flammable. Concentrate is combustible. May emit toxic fumes on burning.

Flashpoint > 65 deg C. Combustible.

May react violently with strong oxidising agents

Shelf Life: 5 years.

(When Stored under Ideal Conditions)

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

Shelf Life: 5 years.

(When Stored under Ideal Conditions)

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.

Nufarm MSDS (September, 2005).

Acknowledgments:

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