In this study, we determined partition (Ksc/m) and diffusion (Dsc) coefficients of five different polycyclic aromatic hydrocarbons (PAH) migrating from squalane into and through the stratum corneum (s.c.) layer of the skin. Carcinogenic PAH have previously been detected in numerous polymer-based consumer products, especially those dyed with carbon black. Upon dermal contact with these products, PAH may penetrate into and through the viable layers of the skin by passing the s.c. and thus may become bioavailable. Squalane, a frequent ingredient in cosmetics, has also been used as a polymer surrogate matrix in previous studies. Ksc/m and Dsc are relevant parameters for risk assessment because they allow estimating the potential of a substance to become bioavailable upon dermal exposure. We developed an analytical method involving incubation of pigskin with naphthalene, anthracene, pyrene, benzo[a]pyrene and dibenzo[a,h]pyrene in Franz diffusion cell assays under quasi-infinite dose conditions. PAH were subsequently quantified within individual s.c. layers by gas chromatography coupled to tandem mass spectrometry. The resulting PAH depth profiles in the s.c. were fitted to a solution of Fick’s second law of diffusion, yielding Ksc/m and Dsc. The decadic logarithm logKsc/m ranged from −0.43 to +0.69 and showed a trend to higher values for PAH with higher molecular masses. Dsc, on the other hand, was similar for the four higher molecular mass PAH but about 4.6-fold lower than for naphthalene. Moreover, our data suggests that the s.c./viable epidermis boundary layer represents the most relevant barrier for the skin penetration of higher molecular mass PAH. Finally, we empirically derived a mathematical description of the concentration depth profiles that better fits our data. We correlated the resulting parameters to substance specific constants such as the logarithmic octanol-water partition coefficient logP, Ksc/m and the removal rate at the s.c./viable epidermis boundary layer.
