UC Berkeley

This dissertation covers both biological and chemical transformation of per- and polyfluoroalkyl substances (PFAS) as well as their interactions with bacteria and common PFAS co-contaminants. In Chapter 2, I investigate the biotransformation pathway of a PFAS commonly detected in aqueous film forming foam impacted (AFFF) groundwater. Sites impacted by AFFFs can contain co-contaminants that can stimulate biotransformation of polyfluoroalkyl substances. In this chapter, I compare how microbial enrichments from AFFF-impacted soil amended with diethyl glycol monobutyl ether (found in AFFF), aromatic hydrocarbons (present in co-released fuels), acetate and methane (substrates used or formed during bioremediation) impact the aerobic biotransformation of an AFFF-derived six-carbon electrochemical fluorination (ECF) precursor N-dimethyl ammonio propyl perfluorohexane sulfonamide (AmPr-FHxSA). I found that methane and acetate oxidizing cultures resulted in the highest yields of identifiable products (47% and 36%, respectively), including perfluorohexane sulfonamide (FHxSA) and perfluorohexane sulfonic acid (PFHxS). Using these data, I propose and detail a transformation pathway. Additionally, I examined chemical oxidation products of AmPr-FHxSA and FHxSA to provide insights on remediation strategies for AmPr-FHxSA. I demonstrate mineralization of these compounds using sulfate radical and test their transformation using the total oxidizable precursor (TOP) assay. While perfluorohexanoic acid accounted for over 95% of the products formed, I demonstrate here for the first time two ECF-based precursors that produce PFHxS during TOP assay. These findings have implications for monitoring PFAS during site remediation and application of the TOP assay at sites impacted by ECF-based precursors.

In Chapter 3, I test the interference of PFAS with bioremediation of co-contaminants. In source zones where PFAS from AFFF are commingled with co-contaminants such as trichloroethene (TCE) and fuel hydrocarbons benzene, toluene, ethylbenzene, and xylene (BTEX), high concentrations of PFAS could impact bioremediation efforts of these co-contaminants. Bioremediation of chlorinated solvents and BTEX has been practiced for decades, usually incorporating the augmentation of Dehalococcoides for the former, or oxygen sparging to encourage in situ aerobic microbial communities for the latter. In this study, we exposed an anaerobic co-culture containing Dehalococcoides mccartyi strain 195 as well as an aerobic AFFF-impacted enrichment culture to various PFAS to test the inhibition of TCE and BTEX degradation. Specifically, we added 1 or 10 μM of perfluorohexane sulfonic acid (PFHxS), perfluorohexane sulfonamide (FHxSA), n-dimethyl perfluorohexane sulfonamido amine (AmPr-FHxSA), an electrochemical fluorination produced AFFF, or non-fluorinated surfactant control sodium dodecyl sulfate (SDS). We tested the TCE and BTEX degradation, adenosine triphosphate (ATP) production, and metabolites to determine possible mechanisms of PFAS toxicity. We found that the anaerobic dechlorinating co-culture was resistant to individual PFAS inhibitory effects but was impacted by 1,000x diluted and 100x diluted 3M AFFF. The aerobic BTEX-degrading enrichment culture experienced substrate degradation inhibition when exposed to FHxSA and AmPr-FHxSA, but not with PFHxS or SDS. Based on ATP and amino acid data, I hypothesize that main mechanisms are FHxSA permeating the cell membrane, AmPr-FHxSA interferring with proteins, and the AFFF dilutions negatively impacting the cell's ability to produce ATP via the proton motive force.

Finally, in Chapter 4 I explore a possible in situ destruction technique for PFAS and co-contaminant remediation. Military bases and airports are often contaminated by PFAS due to the repeated use of AFFFs from decades of training exercises, equipment testing, and extinguishing of fuel and solvent-based fires. Pump-and-treat coupled to sorption processes is a common ex situ remediation strategy, but is often expensive and requires decades of operation due to long-term diffusion and dissolution of contaminants. Alternatively, in situ chemical oxidation is an inexpensive strategy during which oxidants (e.g., persulfate, hydrogen peroxide) are injected into an aquifer to react with contaminants in situ. Specifically, heat-activated persulfate oxidation (HAPO) creates highly reactive sulfate radicals that can mineralize perfluorocarboxylic acids (PFCAs) and some polyfluoroalkyl substances. Sulfate radicals, however, can be scavenged by groundwater constituents, reducing the efficiency of PFCA transformation. In this chapter, I conduct HAPO experiments under conditions realistic to groundwater aquifers; I test low-temperature HAPO, examine inhibitors of successful PFAS destruction at 40°C, and examine different persulfate dosing regimes. I find that weekly doses of persulfate (50-300 mM) are needed for >95% PFAS destruction in aquifer solid-groundwater slurries and that neutralization after treatment results in the removal of dissolved, mobile metals from the groundwater. This chapter provides practical insights to performing HAPO as an in situ PFAS source zone remediation pilot.