Enhanced Skin Absorption and Fly Toxicity of Permethrin in Emulsion Formulation

Abstract

In the course of developing new formulations for fly control, we examined the skin disposition of insecticide permethrin, using excised pig skin and evaporation/penetration cells. This model has been shown to be predictive of human skin absorption (Reifenrath et al. 1984; Reifenrath and Hawkins 1986). Since permethrin formulations are intentionally applied to the skin of livestock, we also studied the disposition on cattle skin using similar methods. In many cases, dermal absorption studies of pesticides are conducted in simple solvents, such as acetone or ethanol (Shah et al. 1987), and may not be representative of skin absorption from other types of vehicles. Dust formulations of pesticides are frequently used for fly control in livestock. Emulsifiable concentrates (EC) are diluted and water and the resultant emulsion is applied as space sprays to inanimate surfaces as well as to livestock. Therefore, we determined the evaporation and skin penetration characteristics of permethrin in ethanol solution, clay dust (cattle skin only), and emulsion vehicles. Since the evaporation and skin penetration properties of the insect repellent N,Ndiethyl-m-toluamide or DEET have been extensively studied, we included this compound in our study for reference purposes. Finally, as a parallel to the skin absorption measurements, we examined the knock-down ability of permethrin formulations against house flies. Formulations which enhanced mammalian dermal absorption may also have enhanced insect absorption and toxicity. Materials and Methods