Effect of Bromine Substitution on Human Dermal Absorption of Polybrominated Diphenyl Ethers

Human dermal absorption of eight mono- to deca-brominated diphenyl ethers (PBDEs) was investigated for the first time using EPISKIN human skin equivalent tissue. Using a standard in vitro protocol, EPISKIN tissues mounted in specially designed diffusion cells were exposed to the target PBDEs for 24 h. Estimated steady-state flux (J_SS) and permeation coefficients (P_app) across the skin increased with decreasing bromine substitution from BDE-153 (P<inf>app</inf> = 4.0 × 10^-4 cm/h) to BDE-1 (P_SS = 1.1 × 10^-2 cm/h). This was accompanied by an increase in the time required to traverse the skin tissue into the receptor fluid (lag time) from 0.25 h for BDE-1 to 1.26 h for BDE-153. P_app values for the studied PBDEs were correlated significantly (P < 0.05) with physicochemical parameters like water solubility and log K_OW. While less brominated congeners achieved faster dermal penetration, higher PBDEs displayed greater accumulation within the skin tissue. The PBDEs thus accumulated represent a contaminant depot from which they may be slowly released to the systemic circulation over a prolonged period. Maximal percutaneous penetration was observed for BDE-1 (∼30% of the applied 500 ng/cm² dose). Interestingly, BDE-183 and BDE-209 showed very low dermal absorption, exemplified by a failure to reach the steady state within the 24 h exposure period that was studied.