In vitro assessment of human dermal exposure to emerging bisphenols: Bisphenol E (BPE) and Bisphenol B (BPB)

Bisphenol E (BPE) and bisphenol B (BPB) are emerging as alternatives to bisphenol A (BPA), although information on their toxicity and human exposure remains limited. While not formally classified as such, both compounds are suspected endocrine disruptors. To better evaluate potential occupational exposure, this study investigated their dermal absorption, following OECD guidelines for in vitro experiments. Experiments were conducted using freshly-excised human skin mounted on Franz diffusion cells. Skin samples were exposed for 20 h to radiolabelled BPE or BPB. Time-course analyses were used to determine key toxicokinetic parameters, including steady-state flux, lag time, and skin permeability coefficient (K_p). After exposure, compound distribution and potential skin reservoir effects were assessed by sequential tape-stripping and separation of epidermis and dermis. Permeability coefficients were determined: 4.2 × 10^-3 cm/h for BPE; 3.4 × 10^-3 cm/h for BPB. Approximately 49% of the applied dose of BPE and 36% of the applied dose of BPB were absorbed, whereas 20% and 29%, respectively, were retained in the skin. Overall, the results demonstrate substantial dermal absorption of BPE and BPB and highlight skin retention as a factor contributing to potential prolonged systemic exposure. These data provide important information for regulatory risk assessment.