IDENTIFICATION
Common name: Pendimethalin
Other name: pendimethalin (BSI, E-ISO, ANSI, WSSA); pendimethaline ((f) F-ISO); penoxalin* (former WSSA name)
Iupac name: N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine
Chemical abstracts name: N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine
Type: Herbicide
CAS RN: [40487-42-1]
M.F.: C13H19N3O4
Mol Wt: 281.3
PHYSICAL CHEMISTRY
Form (appearance): Orange yellow crystals.
Composition: Tech. grade is 90% pure.
M.P.: 54-58℃
B.P.: 4.0 mPa (25℃)
S.G.: 1.19 at 25℃
Solubility.: In water 0.3 mg/l (20℃). In acetone 700, xylene 628, corn oil 148, heptane 138, isopropanol 77 (all in g/l, 26℃). Readily soluble in benzene, toluene, chloroform and dichloromethane. Slightly soluble in petroleum ether and petrol.
Stability: Very stable in storage; store above 5℃ and below 130℃. Stable to acids and alkalis. Slowly decomposed by light. DT50 in water <21 d.
KowlogP: 5.18
APPLICATION
Formulation types: EC; GR; WG.
Biochemistry: Microtubule assembly inhibition.
Mode of action: Selective herbicide, absorbed by the roots and leaves. Affected plants die shortly after germination or following emergence from the soil.
Uses: Control of most annual grasses and many annual broad-leaved weeds, at 0.6-2.4 kg a.i./ha, in cereals, onions, leeks, garlic, fennel, maize, sorghum, rice, soya beans, peanuts, brassicas, carrots, celery, black salsify, peas, field beans, lupins, evening primrose, tulips, potatoes, cotton, hops, pome fruit, stone fruit, berry fruit (including strawberries), citrus fruit, lettuce, aubergines, capsicums, established turf, and in transplanted tomatoes, sunflowers, and tobacco. Applied pre-plant incorporated, pre emergence, pre-transplanting, or early post-emergence. Also used for control of suckers in tobacco.
Phytotoxicity: njury to maize may occur if used as a pre-plant, soil-incorporated treatment.
MAMMALIAN TOXICOLOGY
Oral: Acute oral LD50 for male rats 1250, female rats 1050, male mice 1620, female mice 1340, rabbits >5000, beagle dogs >5000 mg/kg.
Skin and eye: Acute percutaneous LD50 for rabbits >5000 mg/kg. Non-irritating to skin and eyes (rabbits).
Noel: In 2 y feeding trials, rats receiving 100 mg/kg diet showed no ill-effects.
Water GV 20 μg/l (TDI 5 μg/kg b.w.).
Toxicity: WHO (a.i.) III; EPA (formulation) III
EC hazard: Xn; R22
ECOTOXICOLOGY
Birds: Dietary LC50 (8 d) for bobwhite quail 4187, mallard ducks 10388 mg/kg diet.
Fish: LC50 (96 h) for rainbow trout 0.14, bluegill sunfish 0.2, channel catfish 0.42 mg/l.
Worms: Bees LD50 (topical) >50 μg/bee.
ENVIRONMENTAL FATE
Plant: In plants, the 4-methyl group on the benzene ring is oxidised to the carboxylic acid via the alcohol. The amino nitrogen is also oxidised. At harvest time, residues in crops are below the validated sensitivity of the analytical method (0.05 ppm).
Animals: In rats, the major metabolic routes for pendimethalin involve hydroxylation of the 4 methyl and N-1-ethyl groups, oxidation of these alkyl groups to carboxylic acids, nitro-reduction, cyclisation and conjugation (J. Zulian, J. Agric. Food Chem., 1990, 38, 1743).
Soil/Environment: In soil, the 4-methyl group on the benzene ring is oxidised to the carboxylic acid via the alcohol; the amino nitrogen is also oxidised. DT50 in soil is 3-4 mo (A. Walker & W. Bond, Pestic. Sci., 1977, 8, 359). Kd ranges from 2.23 (0.01% o.m., pH 6.6) to 1638 (16.9% o.m., pH 6.8) (H. J. Pedersen et at., Pestic. Sci.,1995, 44, 131).
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