Form Tech. is a yellow-brown to brown liquid, which sometimes tends to crystallise partly at room temperature. M.p. 34-35°C; cis- isomers 63-65 °C; trans- 44-47 °C B.p. 200 °C/0.1 mmHg; >290°C/760 mmHg V.p. cis- 0.0025 mPa; trans- 0.0015 mPa (both 20 °C) (D. Wells et al., Pestic. Sci., 1986, 17,473) KOW logP = 6.1 (20°C) S.g./density 1.29 (20°C) Solubility In water 6 ?10-3 mg/l (pH 7, 20°C). In xylene, hexane >1000, methanol 258 (all in g/kg, 25°C). Stability Stable to heat (? y at 50°C), 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 °C ('Perigen')
Mode of Action
Non-systemic insecticide with contact and stomach action, having a slight repellent effect.
Reviews FAO/WHO 86, 88 (see part 2 of the Bibliography). See also A. J. Gray & D. M. Soderlund, Chapt. 5 in "Insecticides". IARC ref. 53 class 3 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 >13800 mg/m3).