Presence of Perfluorohexanoic Acid in Fluoroelastomer Watch Bands

Many “smart” and “fitness” watch bands are advertised to contain fluoroelastomers, a type of synthetic rubber designed to be resilient against skin oils and sweat. Fluoroelastomers, which are considered a polymeric form of per- and polyfluoroalkyl substances (PFAS), have historically involved the use of shorter-chain PFAS as surfactants in the polymerization process. In this study, 22 watch bands were analyzed across numerous brands and price points for the presence of PFAS. Products were first screened for total fluorine using particle-induced gamma-ray emission spectroscopy on the surface of these bands, and 15 of the 22 watch bands contained total F concentrations >1% fluorine, suggesting the widespread use of fluoroelastomers in this product category. Watch bands then underwent solvent extraction and targeted LC-MS/MS analysis for 20 PFAS. Perfluorohexanoic acid (PFHxA) was the most frequently detected compound with concentrations from <LoD to 16662 ng/g. A subset of six watch bands also underwent direct total oxidative precursor (dTOP) assay to determine the presence of PFAS precursors. The very high concentrations of PFHxA readily extractable from the surfaces of fluoroelastomer watch bands, together with the current limited knowledge on the dermal absorption of PFHxA, demonstrate the need for more comprehensive exposure studies of PFHxA.