Optimizing the PFAS puzzle: piecing together a holistic PFAS restoration strategy

Per- and polyfluoro alkyl substances (PFAS) comprise a diverse class of contaminants, which include a range of perfluoroalkyl acids (PFAAs) with varying perfluoroalkyl chain lengths; most notably PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate) and PFHxS (Perfluorhexane sulfonate). PFHxS and PFOS have gained significant attention in the Australia because of the FSANZ Health Based Guidance Values (HBGVs) released 31 December 2016 which derive drinking water of 70 nanograms per liter (ng/L). The PFAAs (including PFOA, PFHxS and PFOS) are the "dead-end" daughter products resulting from biotransformation of thousands of polyfluorinated precursor compounds, which are present in many commercial products such as Class B firefighting foams. The transformation of precursors to PFAAs further complicate the remediation challenges as precursors are not quantified using standard analytical laboratory methods (USEPA method 537); resulting in underestimation of the PFAS mass when using standard analysis. Further, the aerobic biotransformation of precursors to PFAAs creates an ongoing source of PFAAs. As some precursors are cationic (or cation dominated zwitterions), they are less mobile in fine-grained aquifer systems with primarily negatively charged surfaces, and have the potential to remain in the source area. However, these precursors will eventually biotransform over time forming PFAAs as dead-end daughter products, which seem likely to remain in the ecosystem for thousands of years. (author)