Exploring the Feasibility of Phytoremediation for PFAS Removal from Treated Water

Abstract

The increasing frequency of detecting elevated concentrations of per- and polyfluoroalkyl substances (PFAS), coupled with growing concerns, underscores the urgent need for effective PFAS remediation technologies. Phytoremediation is a potentially promising, cost-effective, scalable, and nature-based strategy to treat large volumes of PFAS-contaminated water in alternative to conventional sequestration techniques. However, there is a knowledge gap in the assessment of a broader range of PFAS compounds, the applicability of terrestrial and aquatic plant species, and the long-term effectiveness under field conditions in current phytoremediation systems. In addition, the strategy of sorbent amendments to the soil to potentially increase the bioavailability of PFAS in the rhizosphere, and thereby possibly stimulating the PFAS uptake in the plant, is poorly understood. This study focuses on the assessment of the technical feasibility of phytoremediation using an experimental setup containing the plant species birch, willow, sunflower, cattail and reed, combined with various sorbent amendments to the soil. These soil-plant systems were designed in the field and greenhouse to explore the uptake and translocation of PFAS compounds in plant tissues and to evaluate the impact of sorbent amendments on PFAS accumulation in the plant. Furthermore, these systems enabled the establishment of mass balances and the calculation of translocation factors (TF: Cleaves/Croots) as well as bioaccumulation factors (BAF: Cplant/Csoil) based on PFAS concentrations in water, soil, and various plant matrices, determined through targeted LC-MS analyses. These factors and mass balances provide new insights into PFAS uptake dynamics and annual removal rates (ARR) of plants in soil–plant systems, supporting the assessment of the technical feasibility of phytoremediation. The TF increased progressively from PFOS (0.5 ± 0.5) to PFOA (1.7 ± 1.4) to PFBA (8.0 ± 8.1) according to the results of this study. This demonstrates higher accumulation in leaves and flowers for short-chain compounds and PFCA’s compared to longer-chain compounds and PFSAs. A possible explanation for this was the limited adsorption in the soil. In addition, sorbents amendments to the soil did not result in a statistically significant effect on PFAS uptake in plants at the EMK site (p = 0.094). A possible explanation for this was the limited adsorption in the sorbent-amended substrates compared to only-sand substrate. The effect of sorbent additives could provide more conclusive results in future sampling rounds involving a lower hydraulic retention time and longer exposure times for the plants. The ARR for ∑PFAS in sunflowers was 0.091 g/ha/yr and 361 g/ha/yr for the field and greenhouse experiments, respectively. These findings highlight the potential that phytoremediation could have in removing PFAS from contaminated water. The differences in ARR between the field and greenhouse experiments can be explained by variations in evapotranspiration, competition with co-contaminants, and possibly by the turbidity of the incoming water. Implementing a pre-filtration system, reducing the discharge loading rate, and installing an aluminum canopy could help to bridge the gap in the ARR between the field and greenhouse experiments.