Evaluating dermal absorption of perfluorooctanoic acid (PFOA) and implications for other per- and polyfluoroalkyl substances (PFAS).

To date, only four studies directly measured dermal absorption kinetics of perfluorooctanoic acid (PFOA) in human skin. Reported kinetic parameters spanned two to five orders of magnitude, demonstrating the need to determine the causes of variability and identify the most appropriate dermal absorption factors for use in exposure assessments. We evaluated the reliability and physiological relevance of studies that measured PFOA fractional absorption, steady-state flux (J_ss), and dermal permeability coefficient (K_p). We verified whether the reported kinetic parameters were measured under appropriate conditions (i.e., fractional absorption under finite dose conditions, and J_ss and K_p under infinite dose conditions). We recommend the following values measured at the approximate pH of the skin, and in aqueous solvents or relevant consumer product matrices, for use as provisional values in PFOA exposure assessments: 1.6% fractional absorption under finite dose conditions, and 0.132 μg/cm²-hr and 0.000044 cm/h for J_ss and K_p, respectively, under infinite dose conditions. Using the recommended absorption factors, we estimated PFOA exposures in children from soil and water via dermal and ingestion routes. Our results indicate low dermal absorption of PFOA relative to ingestion, and low dermal absorption is expected for per- and polyfluoroalkyl substances (PFAS) with physicochemical properties similar to PFOA.