Characterization of per- and polyfluoroalkyl substances (PFAS) in willow and poplar and the impact of soil amendments on accumulation rates

Phytoremediation technologies have the potential to be cost-effective solutions for managing per- and polyfluoroalkyl substances (PFAS). In this greenhouse study, we assessed the uptake of PFAS using two plant species commonly used for phytoremediation, Salix miyabeana (willow) and Populus trichocarpa (poplar). We also assessed the impact of a commercially available growth phytohormone (naphthalene acetic acid (NAA)) and a microbial amendment on plant growth and PFAS uptake. Overall, uptake was observed, depending on perfluorocarbon chain length and functional group. After 90 days, the uptake of individual PFAS in plants grown in PFAS contaminated soil ranged from 0.02 % to 35 % dry weight (dw) for willow and 0.4-29 % for poplar. Within plants, short chain PFAS (i.e., C4-7 perfluoroalkyl carboxylates (PFCA) and C-4 perfluoroalkyl sulfonates (PFSA)) primarily accumulated in aboveground biomass, whereas longer chained homologues (C8-14 PFCA, C6-8 PFSA) primarily accumulated in the roots. For hormone and microbial amendments, there were no statistically significant trends for both willow and poplar (p > 0.05). Interestingly, the microbial community composition did not shift based on PFAS exposure but did shift based on plant-species. The PFAS mass balance for willow and poplar after 90 days approached 100 % (p > 0.05) for all PFAS except PFBA, PFPeA, PFOS, and FOSA. These results suggest that while willow and poplar have the potential to extract short chain PFAS from soil, phytoremediation may be more effective at stabilizing PFAS within a given area (i.e., providing hydraulic control) than extracting.