The percutaneous absorption and skin distribution of lindane in man. II. In vitro studies

1. The absorption of lindane through human skin was assessed in vitro using static diffusion cells with 50% aqueous ethanol as the receptor fluid. Four formulations of lindane were applied, three of which were commercial preparations. The dermal distribution of lindane within the skin was also examined, focusing particularly on any association of lindane to the stratum corneum. The results were then compared with a parellel in vivo study. 2. Two of the formulations contained white spirit as the predominant solvent, and lindane absorption was greatest from these preparations in terms of the percentage of the applied dose (15-25% by 24 h). Absorption was less from an aqueous spray dilution (3% by 24 h), with absorption from acetone being the least (< 1% by 24 h). Similar amounts of lindane penetrated by 24 h for the acetone and white spirit-based applications (approx. 8 micrograms). This supported the in vivo observation that similar plasma lindane levels were recorded following exposure to the acetone solution and the white spirit-based formulation A, although the lindane concentration in acetone was 40-fold higher. 3. For the acetone and water-based preparations, a soap/water swab of the skin surface at 6 h contained the majority of the applied dose (around 75%). Substantial amounts of lindane were recovered in tape-strippings taken at 6 h (representative of stratum corneum content) which were significantly greater than lindane in the remainder of the skin, for the acetone solution and formulation A. This provided a strong indication that lindane had accumulated in the stratum corneum, a property that has been linked with other lipophilic chemicals.