Graduate Thesis Or Dissertation
 

Hydrophobicity, Anion Exchange, and Phytoaccumulation of Per- and Polyfluoroalkyl Substances (PFAS): Retention and Remediation

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  • Per- and polyfluoroalkyl substances (PFAS) are a group of contaminants of great concern due to their toxicity and ubiquity in the environment. Remediation efforts historically have focused on granular activated carbon (GAC) because of its low maintenance and relatively low cost. However, GAC is not PFAS selective and is especially poor at removing short-chain, less hydrophobic PFAS (e.g. PFBA). As such, alternative remediation methods for water such as anion exchange sorbents and plants are explored. In Chapter 2, we explore the effect of PFAS head group and chain length on their anion exchange (AE) affinity. Liquid chromatography-mass spectrometry (LC-MS) was used in solvent-only conditions, with an anion exchange guard column, to isolate the role of anion exchange for the retention of anionic PFAS. The AE affinity of PFAS decreased with increasing chain length, contrary to what has been previously reported. Average electrostatic potential (EPavg) was computationally derived and found to be positively correlated with chromatographic retention time using an anion exchange guard column. Both anion exchange retention times and EPavg revealed that given the same number of fluorinate carbons, the AE of PFAS was as follows: n:3 FtAs > n:2 FtAs > PFCAs > Sulfonamides ~ n:2 FtSs > PFSAs. In Chapter 3, we evaluate sorbents for the removal of heavy metals and PFAS as co-contaminants in stormwater. Single-point batch experiments revealed that Biochar Basic, a hazelnut derived biohar with cation exchange capacity, was the most efficient at removing heavy metals from field-collected stormwater. RemBindTM, an anion exchange sorbent with GAC components, was the most efficient at removal PFAS from synthetic and field-collected stormwater. Suspended sediment was found to be the component of stormwater with the largest negative impact on sorbent performance, with particularly high negative effects on PFAS removal over heavy metals. To maximize of PFAS, RemBindTM was placed in series after Biochar Basic in the treatment train and demonstrated significantly improved PFAS removal. In Chapter 4, we conducted a greenhouse experiment to compare PFAS removal and transformation by ten native Pacific Northwest plants and soil. We were able to close the PFAS mass balance within 70-130% for eight out of ten plants and the soil control. Sulfonamide transformation occurred in all ten plants as well as the soil control, indicating that the transformation occurs in the soil, independently of plants. Statistically different linear PFOS enrichment was observed in plant leaves, stems, roots, and soil and the percent linear PFOS in plant roots was positively correlated with root mass. Finally, grasses and stemless dicots were observed to be the two most efficient plant groups at removing PFAS from stormwater based on bioconcentration factors (BCFs) and mass accumulation factors (MAF).
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  • This work was supported through the Department of Defense Strategic Environment Research and Development Program (SERDP) Grant ER18-C3-1230.
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  • Pending Publication
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  • 2021-09-21 to 2023-11-04

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