Permeation studies of chlorpyrifos through skin and synthetic membranes to improve the in vitro dermal absorption assay of lipophilic compounds with ethanolic receptors.

The in vitro percutaneous absorption assay is standardized, but the common use of 50 % ethanol in the receptor compartment for lipophilic compounds is questioned. In parallel, the demand for animal-free methodologies is driving the application of synthetic membranes without standardization guidelines. To address these issues, this study investigated the permeation of the lipophilic compound chlorpyrifos using different ethanol-containing receptor fluids with human and pig skin ex vivo, and silicone and STRAT-M® membranes. The results considered several factors, particularly chlorpyrifos solubility and the contact angles between skin models and receptor fluids. Original experimental approaches demonstrated that ethanol from the receptor rapidly crosses to the donor compartment increasing chlorpyrifos diffusivity. Compared to the described in vivo dermal absorption, human skin and STRAT-M® yielded the best predictive permeation parameters. However, high percentage of ethanol in the receptor fluid can lead to an overestimation of percutaneous absorption. Summing up, it is important to carefully determine the concentration of ethanol to be used in the receptor fluid of lipophilic compounds' assays while further research with synthetic membranes is needed prior to their wider adoption.