2,4-D Ester 800 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:It 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.
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
|Variety||Growth Stage||Leaves on the main stem.|
Effect on Clover Species:Clover tolerance increases at later growth stages and at 350 mL/ha light but acceptable damage occurs with many clover varieties. 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:Rates above 100 mL/ha generally damage Medics. Rates of 100 mL/ha on barrel medic cv Paraggio, Sephi, Cyprus and Parabinga; gamma medic cv Paraponto; snail medic cv sava; spineless burr medic cv Circle Valley and Serena and strand medic cv Harbinger cause minimal to light but acceptable damage.
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.
22 DISEASE AND INSECT EFFECTS:Vascular diseases usually reduce the translocation of 2,4-D and may reduce efficacy. Leaf diseases may reduce the leaf area available for 2,4-D absorption and consequently reduce efficacy.
Low levels of insect damage may increase the absorption of 2,4-D increasing efficacy but also increasing the risk of crop damage. High levels of defoliation by insects may reduce efficacy due to decreased leaf area to collect spray droplets compared to the size of the plant.
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 woodier plants may take several months to die.
The table below summarises the effects of 2,4-D esters on the most sensitive species tested.
Table adapted from EPA 738-R-05-002, June 2005
|Species||Growth stage||Formulation||EC25 |
g a.e. /ha
|Onion (Monocot)||Seedling||2,4-D IPE (ester)||11||6.3|
|Lettuce (Dicot)||Seedling||2,4-D IPE (ester)||0.9||0.53|
|Corn (Monocot)||Vegetative||2,4-D IPE (ester)||226||28.2|
|Lettuce (Dicot)||Vegetative||2,4-D IPE (ester)||6.8||1.4|
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.
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: Low.
Acute oral LD50: 2,4-D ester 620-900 mg/kg (rat). 2,4- D acid 699 mg/kg (rat), [For comparison table salt is 3000 mg/kg]
Acute dermal LD50: >2000 mg/kg (rabbit).
Vapour inhalation: LC50 >1.79 mg/L air 4 hour (rat).
Chronic oral toxicity: NOEL 1 mg/kg/day for two years.
High doses have caused reproductive effects in test animals.
Data indicates that 2,4-D has low teratogenic potential or is not teratogenic.
Several studies investigated 2,4-D as a carcinogen with varying results. At normal exposure levels it is not expected to be carcinogenic.
Acceptable Daily Intake (ADI): 0.01 mg/kg/day.
Other Species: Birds: toxicity.
Fish: Moderate toxicity LC50 5-62 mg/L (Bluegill sunfish). 62-153 mg/L (Rainbow trout).
Invertebrates: Slightly to moderately toxic to freshwater invertebrates. Practically non toxic to highly toxic to marine invertebrates (EPA, 2005)
Bees: Not toxic. Moderate doses have impaired brood production.
25 TOXICITY SYMPTOMS:Prolonged exposure with skin may cause defatting and secondary dermatitis.
Inhalation of the solvents may cause headache, nausea and intoxication.
Absorption of 2,4-D may cause lethargy and incoordination.
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.
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. It is rarely detected more than 500 mm deep in soils.
Accumulation in milk and tissues - Does not accumulate. It is not metabolised in the body and excreted in urine within a few days.
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:CAS numbers: 533-23-3.
UN number: 3082.
Hazchem code: None allocated.
Dangerous goods class: Not a dangerous good for land transport.
Proper shipping name: None allocated.
Environmentally hazardous substance, liquid, NOS, (2,4-D).
Packaging group: III
31 PROPERTIES:Empirical formula: C10H10Cl2O3 (2,4-D ethyl ester). C12H14Cl2O3 (2,4-D butyl ester).
Water solubility: Forms an emulsion with water.
Octanol:Water ratio: LogPow = at 25 C at pH 5;
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
Vapour Pressure: 1.39 x 10-3 mm Hg for 2,4-D ester. (0.5 kPa for solvent).
Vapour density: >1.
Dissociation constant: pKa
Melting point: -5 C.
Boiling point: 183-210 C (solvent).
Molecular weight: - 249 (2,4-D ethyl ester). 277 (2,4-D butyl ester).
Colour: Clear brown.
Odour: Solvent odour.
Specific gravity: 1.29.
Flash Point; 96 C.
Flammability limit LEL: Lower 0.9%, Upper 6%.
May emit toxic fumes of hydrogen chloride and phosgene if burnt.
Exposure to strong oxidising agent may cause violent reactions.
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 (June, 2002).
Farmoz MSDS (November 2003)
Acknowledgments:Collated by HerbiGuide. For more information see www.herbiguide.com.au or phone 08 98444064.