Transdermal absorption of 13C4-perfluorooctanoic acid (13C4-PFOA) from a sunscreen in a male volunteer - What could be the contribution of cosmetics to the internal exposure of perfluoroalkyl substances (PFAS)?

Per-and polyfluoroalkyl substances (PFAS) are a complex group of man-made chemicals with high stability and mobility leading to ubiquitous environmental contamination and accumulation especially of some long-chain perfluoroalkyl acids (PFAA) in humans. While dietary intake is the main route of exposure, transdermal up-take from cosmetic products usually is considered negligible. However, PFAS are present in a part of these products, and recent epidemiological studies have provided evidence for relevant uptake via this route. The crucial question is whether PFAA in cosmetic products can cross the human skin barrier. A defined amount (110 mu g) of 13C4-perfluorooctanoic acid (13C4-PFOA) was mixed into a sunscreen (30 g) which was applied on the whole skin of a volunteer. The plasma concentrations of 13C4-PFOA were determined in serial blood samples taken over 115 days using UHPLC-MS/MS and 13C2-PFOA as internal standard. After application, 13C4-PFOA plasma levels increased continuously, reaching levels of 3, 56 and 118 ng/L after 6 h, 3 days and 10 days, respectively. A maximum level of 132 ng/L was measured 22 days after application, representing 9.4 % of the PFOA level resulting from the volunteer's background exposure (1400 ng/L, equivalent to 1.4 ng/mL). In the following weeks, the levels slightly decreased with an estimated half-life of 1.8 years. The best estimate for the fraction absorbed may be 1.6 % of the dose, using a volume of distribution of 0.17 L/kg body weight. For PFOA mixed into a sunscreen, this experimental approach demonstrates a significant uptake of a PFAA via transdermal absorption in humans. In the past, some cosmetic products contained relevant PFAA levels as contaminants/ impurities of PFAS added as active ingredients. Depending on these levels and the use (frequency, skin area involved), it is plausible that this route of exposure has contributed to the internal exposure to PFAA, as already suggested by epidemiological observations.