Permethrin

Common name: permethrin; perméthrine
IUPAC name: 3-phenoxybenzyl (1RS,3RS;1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate
Roth: 3-phenoxybenzyl (1RS)-cis-trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate
Chemical Abstracts name: (3-phenoxyphenyl)methyl 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate
CAS RN: [52645-53-1], (formerly [57608-04-5] and [63364-00-1])

PHYSICAL CHEMISTRY
Mol. wt.: 391.3, M.f.: C21H20Cl2O3; Form: Tech. is a yellow-brown to brown liquid, which sometimes tends to crystallise partly at room temperature. M.p.: 34-35 ºC; cis- isomers 63-65 ºC; trans- 44-47 ºC. B.p.: 200 ºC/0.1 mmHg; >290 ºC/760 mmHg. V.p.: cis- 0.0025 mPa; trans- 0.0015 mPa (both 20 ºC). KOW: logP = 6.1 (20 ºC). S.g./density: 1.29 (20 ¯C). Solubility: In water 6x10-3 mg/l (pH 7, 20 ºC). In xylene, hexane >1000, methanol 258 (all in g/kg, 25 ºC). Stability: Stable to heat (2 y at 50 ºC), more stable in acidic than alkaline media with optimum stability c. pH 4; DT50 50 d (pH 9), stable (pH 5, 7) (all 25 ¯C). Some photochemical degradation observed in laboratory studies, but field data indicate this does not adversely affect biological performance. F.p. >100 ºC ('Perigen').

APPLICATIONS
Mode of action: Non-systemic insecticide with contact and stomach action, having a slight repellent effect.
Uses: A contact insecticide effective against a broad range of pests. It controls leaf- and fruit-eating Lepidoptera and Coleoptera in cotton, at 100-150 g a.i./ha, in fruit, at 25-50 g/ha, in tobacco, vines and other crops, at 50-200 g/ha, and in vegetables, at 40-70 g/ha. It has good residual activity on treated plants. It is effective against a wide range of animal ectoparasites, provides >60 d residual control of biting flies in animal housing, at 200 mg a.i. (as EC)/m2 wall or 30 mg a.i. (as WP)/m2 wall, and is effective as a wool preservative, at 200 mg/kg wool. It provides >120 d control of Blattodea, Diptera, Hymenoptera and other crawling insects, at 100 mg a.i. (as WP)/m2, also flying insects.
Phytotoxicity: Non-phytotoxic when used as directed (except that some ornamentals may be injured).
Formulation types: DP; EC; UL; WG; WP; Fumigant; Aerosol.
Compatibility: Mixing with calcium nitrate is not recommended.

MAMMALIAN TOXICOLOGY
Oral: Oral LD50 values of permethrin depend on such factors as: carrier, cis/trans ratio of the sample, the test species, its sex, age and degree of fasting; values reported sometimes differ markedly. Values for a cis/trans ratio of c. 40:60 are: for rats 430-4000, mice 540-2690 mg/kg; with a 20:80 ratio, the LD50 is c. 6000 mg/kg.
Skin and eye: Acute percutaneous LD50 for rats >2500, rabbits >2000 mg/kg. Mild eye and skin irritant (rabbits). Moderate skin sensitiser.
Inhalation: LC50 (3 h) for mice and rats >685 mg/m3 air; (separate study gives >13 800 mg/m3).
NOEL: In 2 y feeding trials, rats receiving 100 mg/kg diet showed no ill-effects.
ADI: 0.05 mg/kg b.w. (for tech., with cis/trans ratios 25:75 to 40:60)
Water GV: 20 ug/l (based on ADI).
Other: No mutagenic, teratogenic, or carcinogenic activity.
Toxicity class: WHO (a.i.) II; EPA (formulation) II ('Ambush'); III ('Outflank')
EC hazard: Xn; R22

ECOTOXICOLOGY
Birds: Typical oral LD50 values for a cis/trans ratio of c. 40:60 are: for chickens >3000, mallard ducks >9800, Japanese quail >13 500 mg/kg.
Fish: LC50 (96 h) for rainbow trout 2.5 ug/l; (48 h) for rainbow trout 5.4, bluegill sunfish 1.8 ug/l.
Daphnia: LC50 (48 h) 0.6 ug/l.
Bees: Toxic to bees. LD50 (24 h) (oral) 0.098 ug/bee; (topical) 0.029 ug/bee.

ENVIRONMENTAL FATE
EHC: Permethrin is not likely to be a hazard to the environment when used as recommended.
Animals: In mammals, there is hydrolysis of the ester bond, hydroxylation, and elimination as the glucoside conjugate.
Soil/Environment: In soil and water, degradation is rapid. DT50 in soil <38 d (pH 4.2-7.7, o.m. 1.3-51.3%).