Enhancing or blocking effect of fenvalerate on the subsequent percutaneous absorption of pesticides in vitro

The percutaneous absorption of pesticides has been receiving much research attention. However, most work is conducted with single exposures and potential interactions of previous pesticide exposure have received little attention. In the present study, the effect of in vivo pretreatment of the skin with a 3% fenvalerate in ethanol or a 3% parathion in ethanol solution on carbaryl, fenvalerate, lindane, and parathion absorption was studied in vitro using weanling pig skin in a flowthrough diffusion cell system. Concentrations of 40 or 400 microgram/cm2 of carbaryl, fenvalerate, lindane, and parathion in ethanol were applied topically. Environmental conditions of air and perfusate temperature (37 degrees C), relative humidity (60%), flow rate (4 ml/hr), and Kreb's-Ringer bicarbonate buffer with 4.5% bovine serum albumin medium were controlled. The total absorption of these pesticides, both ethanol control and fenvalerate or parathion pretreated, increased proportionally with the dose; however, the absorption efficiency (fraction of applied dose absorbed) decreased as the dose increased. At both doses, fenvalerate pretreatment had little or no effect on carbaryl and fenvalerate absorption; however, parathion absorption was significantly decreased in fenvalerate-pretreated skin (P < 0.05). There was no significant difference (P greater than or equal to 0.05) of parathion absorption between the parathion pretreatment and the fenvalerate pretreatment. Lindane absorption increased at the 40-microgram dose and significantly increased at the 400-microgram dose (P < 0.05) following fenvalerate pretreatment. Carbaryl absorption was higher than other pesticides at the dose of 40 microgram/cm2. Furthermore, comparing ethanol control data with previous results indicates that prolonged skin treatment with ethanol significantly increases parathion absorption (P < 0.05). This study suggests that the absorption data from a single parent compound alone were not adequate to determine the rate of absorption of pesticide under mixture exposure conditions. Pesticide interactions may significantly affect the percutaneous absorption, interpretation, and assessment of risk.