Permeation of 4-Cyanophenol and Methyl Paraben from Powder and Saturated Aqueous Solution through Silicone Rubber Membranes and Human Skin

The objectives were to compare permeation from neat powder and saturated aqueous solution of two model compounds into homogeneous silicone rubber (polydimethylsiloxane) membranes (SRM) and human skin, which is heterogeneous, and to test the common assumption that solid chemicals do not absorb unless liquid is present. The steady-state flux of 4-cyanophenol (CP) through SRM from the powder (0.0684 ± 0.0040 mg/cm2·h) was almost the same as from a saturated solution (0.0789 ± 0.0064 mg/cm2·h, indicating that solid chemicals can absorb without the presence of liquids. The steady-state flux of CP through skin of a single subject was much smaller from the powder (0.0118 ± 0.0064 mg/cm2·h) than from the saturated solution (0.168 ± 0.033 mg/cm2·h). The average flux for powder relative to the saturated aqueous solution was 7.24% in skin compared with 87.2% in SRM for CP and 9.02% in skin compared with 99.9% in SRM for methyl paraben. It is evident that absorption into SRM and skin can occur from powdered chemicals and that surface oils or moisture are unnecessary. However, SRM proved to be a poor surrogate for dermal permeation from powders of CP and MP.