ABSTRACT
Synthetic pyrethroids (SP) possess greater insecticidal activity and lower mammalian toxicity than the organochlorine, organophosphate and carbamate insecticides. Synthetic pyrethroids are esters of specific acids: chrysanthemic acid, halogen-substituted chrysanthemic acid, 2-(4-chlorophenyl)-3-methylbutyric acid, and alcohols. SP are generally metabolized in mammals through ester hydrolysis, oxidation, and conjugation. Metabolites of some pyrethroids form lipophilic conjugates such as cholesterol esters, which are persistent mainly in fat tissues. SP are nervous poisons. They interfere with the ionic permeability of the cell membranes involved with generation and conductance of nerve impulses. Higher doses produce transient damage to the nervous system, such as axonal swelling and breaks and myelin degradation in sciatic nerves. In humans, dermal exposure of deltamethrin, fenvalerate, permethrin, and Cypermethrin causes transient itching and burning sensations in the face, without clinical signs of inflammation. In humans, intoxications are usually very light, and neurological symptoms, such as generalized tremor and seizures, are found only in animals.
