The in vitro percutaneous penetration of chlorpyrifos

Chlorpyrifos is a widely used organophosphate pesticide. In order to study the pharmacokinetics of the penetration of chlorpyrifos through human skin we measured the percutaneous penetration of chlorpyrifos through human skin using an in vitro now through apparatus. The chlorpyrifos was applied to t he skin as a commercial concentrate or as a reference standard dissolved in ethanol. There was a significant difference (P=0.03) between the rate of p enetration from the commercial concentrate (9.0 nmoles cm(-2) h(-1)) and th at from the reference standard (4.9 nmoles cm(-2) h(-1)). Each experiment w as run for 24 h. The recoveries from experiments where chlorpyrifos was app lied to the skin as a commercial concentrate and as a reference standard di ssolved in ethanol were, respectively, in total 91 and 87% of the applied d ose of which 15 and 10% was recovered from the skin, 56 and 66% was recover ed from the surface of the skin and 20 and 11% was recovered from the recep tor fluid. There was a significant: difference in the recoveries from the s kin but there was no significant difference in the recoveries from the surf ace of the skin. We concluded that the majority of a dermal dose of chlorpy rifos was still present at or in the surface of the skin 24 h after applica tion of a dermal dose. Because chlorpyrifos was recovered from the skin aft er 24 h, it is possible that the skin could act as a reservoir and release chlorpyrifos over a longer period. We also conclude that the solvent vehicl e for chlorpyrifos can affect the rate of penetration of the pesticide.