IDENTIFICATION
Common name: 2,4-D
Other name: 2,4-D (BSI, E-ISO, (m) F-ISO, WSSA); 2,4-PA (JMAF)
Iupac name: (2,4-dichlorophenoxy)acetic acid
Chemical abstracts name: (2,4-dichlorophenoxy)acetic acid
Type: Herbicide
CAS RN: [94-75-7]
M.F.: C8H6Cl2O3
Mol Wt: 221.0
PHYSICAL CHEMISTRY
Form (appearance): Composition: Tech. is ≥96% pure.
Colorless powder, with a slight phenolic odour.
M.P.: 140.5℃
S.G.: 0.7-0.8
Solubility. In water 311 (pH 1), 20031 (pH 5), 23180 (pH 7), 34196 (pH 9) (all in mg/l, 25℃). In ethanol 1250, diethyl ether 243, heptane 1.1, toluene 6.7, xylene 5.8 (all in g/kg, 20℃); in octanol 120 g/l (25℃). Insoluble in petroleum oils. Mono-n-butylamine salt: In water 18 g/l (30℃).
2, 4-D-dimethylammonium:In water 3 kg/l (20℃).Soluble in alcohols and acetone. Insoluble in kerosene and diesel oil.
2, 4-D-2-ethylhexyl : In water 0.086 mg/l (25℃). Miscible with most organic solvents.
Stability: 2,4-D is a strong acid, and forms water-soluble salts with alkali metals and amines. Hard water leads to precipitation of the calcium and magnesium salts, but a sequestering agent is included in formulations to prevent this. Photolytic DT50 (simulated sunlight) 7.5 d.
2, 4-D-2-ethylhexyl: Hydrolysis DT50<1 h. Stable to light, DT50>100 d. Stable at 54℃.
Henry: 1.32 × 10-5 Pa m3 mol-1 (calc.)
2, 4-D-2-ethylhexyl : 1.8 Pa m3 mol-1 (calc.)
KowlogP: 2.58-2.83 (pH 1), 0.04-0.33 (pH 5)
2, 4-D-2-ethylhexyl : 5.78 (25℃)
Pka: 2.73
APPLICATION
Formulation types: EC; GR; SP; SL
Biochemistry: Synthetic auxin (acting like indolylacedc acid).
Mode of action: Selective systemic herbicide, Salts are readily absorbed by the roots, whilst esters are readily absorbed by the foliage. Translocation occurs, with accumulation principally at the meristemadc regions of shoots and roots. Acts as a growth inhibitor.
Uses: Post-emergence control of annual and perennial broad-leaved weeds in cereals, maize, sorghum, grassland, established turf, grass seed crops, orchards (pome fruit and stone fruit), cranberries, asparagus, sugar cane, rice, forestry, and on non-crop land (including areas adjacent to water), at 0.28-2.3 kg/ha. Control of broad-leaved aquatic weeds. The isopropyl ester can also be used as a plant growth regulator to prevent premature fruit fall in citrus fruit.
Phytotoxicity: Phytotoxic to most broadqeaved crops, especially cotton, vines, tomatoes, ornamentals, fruit trees, oilseed rape and beet.
Compatibility: Compatibility depends upon the particular formulation.
MAMMALIAN TOXICOLOGY
Reviews: FAO/WHO 77, 79, 80, 82 (see part 2 of the Bibliography). Toxicity and hazards to man, domestic animals and wildlife have been reviewed (J. M. Way, Residue Rev., 1969, 26, 37).
/IARC ref. 15, 41; class chlorophenoxy herbicides classified as 2B, based on epidemiology of production. More recent evidence (M. Kogevinas et al., Am. J. Epidemiot., 145(12), 1061 (1997)) relates this to dioxin contamination of early production. Not relevant to current processes.
Oral: Acute oral LD50 for rats 639-764, mice 138 mg/kg.
Skin and eye: Acute percutaneous LD50 for rats >1600, rabbits >2400 mg/kg. Skin and eye irritant (rabbits). Not a skin sensitiser (guinea pigs).
Inhalation: LC50 (24 h) for rats >1.79 mg/l.
Noel: (2 y) for rats and mice 5 mg/kg b.w.; (1 y) for dogs 1 mg/kg b.w.
ADI: (JMPR) 0.01 mg/kg b.w. [1997] (environmental assessment); 0.01 mg/kg b.w. [1996] (sum of 2,4-D and its salts and esters, as 2,4-D).
Water GV 30 μg/l (based on ADI).
Toxicity: WHO (a.i.) It; EPA (formulation) II
EC hazard: Xn; R22| Xl; R36/37/38: (for salts and esters, Xn; R20/21/22)
ECOTOXICOLOGY
Birds: Acute oral LD50 for wild ducks >1000, Japanese quail 668, pigeons 668, pheasants 472 mg/kg. LC50 (96 h) for mallard ducks >5620 mg/l.
Fish: Acute oral LD50 for wild ducks >1000, Japanese quail 668, pigeons 668, pheasants 472 mg/kg. LC50 (96 h) for mallard ducks >5620 mg/l.
Daphnia: LC50 (21 d) 235 mg/l.
Algae: EC50 (5 d) for Setenastrum capricornutum 33.2 mg/l.
Other aquatic spp. EC50 (14 d) for Lemna gibba 0.58 mg/l.
Worms: LC50 (7 d) 860 mg/kg; NOEC (14 d) 100 g/kg.
Bees Not toxic to bees; LD50 (oral) 104.5 μg/bee.
Other beneficial spp. Harmless to Trichogrammia cacoeciae, Poecilus cupreus, Aleochara bilineata.
ENVIRONMENTAL FATE
Plant: EHC 29 (WHO, 1984), 84 (WHO, 1989). EHC 84 concludes that, when used as recommended, 2,4-D does not appear to produce direct toxic effects on any animal species.
In plants, metabolism involves hydroxylation, decarboxylation, cleavage of the acid side-chain, and ring opening.
Animals: In rats, following oral administration, elimination is rapid, and mainly as the unchanged substance. Following single doses of up to 10 mg/kg, excretion is almost complete after 24 hours, although, with higher doses, complete elimination takes longer. The maximum concentration in organs is reached after c. 12 hours.
Soil/Environment: In soil, microbial degradation involves hydroxylation, decarboxylation, cleavage of the acid side-chain, and ring opening. Half-life in soil <7 d. Koc c. 60. For a review of environmental aspects of 2, 4-D, see Environmental Health Criteria 84 (WHO, 1989). Rapid degradation in the soil prevents significant downward movement under normal conditions.
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