The transformation of per- and polyfluoroalkyl substances (PFAS) and the associated challenges of site owners, regulators, and researchers

ABSTRACT: Per- and polyfluoroalkyl substances (PFAS) are chemicals which contain one or more carbon atom and one or more fluorine atom. There are at least 4000 different PFAS which have been incorporated into industrial and commercial products. The carbon-fluorine bond(s) in conjunction with varying functional groups give PFAS unique properties. They have been produced commercially since the 1950s for water/grease resistance and/or surfactant properties, and used in products such as non-stick pans, popcorn bags, water-proof jackets, furniture fabrics, carpets, cosmetics, and aqueous film-forming foam (AFFF). PFAS have been released to the environment for more than 60 years, and the types of PFAS used and released have also changed over this period. Many PFAS bio-accumulate and are toxic. As the scientific understanding of PFAS has evolved, and the types of PFAS used have changed, so has regulatory guidance. The carbon-fluorine bond(s) make PFAS resistant to degradation. PFAS have however been shown to readily transform both in the lab and the field under varying conditions. PFAS transformations in the field, and the evolving understanding of these processes, have created many challenges for site owners. As PFAS transform their physiochemical properties change. This creates challenges for predicting the stability and/or transport of a PFAS source-zone or plume. As analytical methods are developed to assist in detecting and quantifying these transformation products and intermediates, more of the PFAS "dark matter" becomes clear. This presentation will describe some of the practical challenges with respect to PFAS transformations at contaminated sites, but also describe how some of the same challenges are being seen during PFAS remediation projects during both laboratory development and pilot-scale testing.