Simultaneous absorption of copper and zinc through human skin in vitro: influence of counter-ion and vehicle.

Abstract

Copper and zinc percutaneous absorptions were assessed in vitro using sliced human skin and both petrolatum and hydrophilic gels as vehicles. Applied quantities were largely in excess for the duration of the experiment (72 h). The absorption of sulphates and chlorides was compared. The cumulated amount recovered in receptor fluid was below 50 micrograms/cm2. The apparent permeability constant values kept in the range of 10(-6) cm h-1, except for ZnCl2 in gel vehicle (2.9 10(-5) cm h-1). With the exception of CuCl2 in gel vehicle, chlorides gave higher absorption rates than sulphates. This can be related to the higher octanol-water partition coefficient of chlorides. Storage within the epidermis was found to be equal to or greater than, and within the dermis equal to or lower than the 72 hour cumulative amount in receptor fluid. No difference was found in this respect between copper an d zinc. This work confirms the poor absorption of electrolytes through normal human skin, whatever the vehicle used.