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Acute and Short-Term Toxicity of Permethrin

Animal Studies

Synthetic pyrethroids, such as permethrin, are some of the least toxic insecticides to mammals, especially when compared with the more com monly used insecticides—organochlorine, organophosphorus, and methylcarbamate. Permethrin appears to be less toxic than other synthetic pyrethroids, such as cypermethrin and fenvalerate (NRCC, 1986). The acute (single dose) oral LD 50 of technical-grade permethrin (purity 90.5-97.2% and consisting of mixtures of cis/trans isomers in various proportions) in animals (rats, mice, guinea pigs, and chickens) is in the range of 0.5-5 g/kg of body weight, depending on the vehicle used for administration. Permethrin is more toxic when formulated with corn oil, dimethyl sulfoxide, and propylene glycol than when in an aqueous suspension (perhaps because of greater solubility of permethrin in organic solvents than in water). Death in animals occurs within 3 days of exposure to permethrin. The cis/trans isomeric ratio also appears to affect toxicity, the cis isomer being more toxic than the trans isomer in animals

Clinical signs of toxicity, when evident, occur within 2 hr and are associated with central nervous system functions. Permethrin belongs to the Type I group of pyrethroids, and exposure to permethrin is associated with tremors (T syndrome), convulsions, irregular breathing and increased respiratory rates, incoordination, ataxia, hyperactivity, prostration, and paralysis. Other signs that have been reported include hyperexcitability to external stimuli, lacrimation, occasional diarrhea, defecation, and urinary incontinence (Ishmael, 1989). Core body temperature is increased when clinical signs are severe. Signs of toxicity can last up to 3 days after acute exposure. None of the major permethrin metabolites shows greater toxicity than the parent compound.

https://www.ncbi.nlm.nih.gov/books/NBK231556/

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