The surfactant properties of perfluorooctanesulfonic acid (PFOS) impact its environmental behavior, especially under high-ionic strength conditions. We observed an apparent PFOS concentration decrease during bench-scale experiments simulating in situ chemical oxidation (ISCO) with heat-activated persulfate that could not be attributed to chemical transformation. Using chloride salts of Na+, K+, Mg2+, and Ca2+, we observed decreasing PFOS concentrations in salt solutions. In solutions initially containing 10 mg/L PFOS, NaCl or KCl (I = 500 mM) decreased PFOS concentrations by >50%; MgCl2 and CaCl2 (I = 1.5 M) decreased PFOS concentrations by 24–29%. In a seawater matrix (I = 0.68 M), the PFOS concentration decreased by 32–76% in solutions with 0.3–55 mg/L added PFOS. The concentration decrease was attributed to the aggregation and enhanced interfacial activity of PFOS. The PFOS surface activity and surface excess were calculated by fitting the Szyszkowski equation to surface tension isotherms, which indicated that the divalent cations (Mg2+ and Ca2+) decreased the critical micelle concentration and increased the saturation of PFOS at the air–water interface more than the monovalent cations (Na+ and K+). In addition to leading to potential under-reporting of PFOS concentrations under conditions relevant to ISCO, our findings have implications for predicting the fate and transport of PFOS in saltwater-impacted zones proximate to contamination sources.

Fungi and laccase mediator systems (LMSs) have a proven track record of oxidizing recalcitrant organic compounds. There has been considerable interest in applying LMSs to the treatment of perfluoroalkyl acids (PFAAs), a class of ubiquitous and persistent environmental contaminants. Some laboratory experiments have indicated modest losses of PFAAs over extended periods, but there have been no clear demonstrations of a transformation mechanism or the kinetics that would be needed for remediation applications. We set out to determine if this was a question of identifying and optimizing a rate-limiting step but discovered that observed losses of PFAAs were experimental artifacts. While unable to replicate the oxidation of PFAAs, we show that interactions of the PFAA compounds with laccase and laccase mediator mixtures could cause an artifact that mimics transformation (≲60%) of PFAAs. Furthermore, we employed a surrogate compound, carbamazepine (CBZ), and electron paramagnetic resonance spectroscopy to probe the formation of the radical species that had been proposed to be responsible for contaminant oxidation. We confirmed that under conditions where sufficient radical concentrations were produced to oxidize CBZ, no PFAA removal took place.