Biotransformation of AFFF Component 6:2 Fluorotelomer Thioether Amido Sulfonate Generates 6:2 Fluorotelomer Thioether Carboxylate under Sulfate-Reducing Conditions

Abstract

The fate of per and polyfluoroalkyl substances (PFASs) in aqueous filmforming foams (AFFFs) under anaerobic conditions has not been well characterized, leaving major gaps in our understanding of PFAS fate and transformation at contaminated sites. In this study, the biotransformation of 6:2 fluorotelomer thioether amido sulfonate (6:2 FtTAoS), a component of several AFFF formulations, was investigated under sulfate-reducing conditions in microcosms inoculated with either pristine or AFFF-impacted solids. To identify the transformation products, we used high-resolution mass spectrometry and employed suspect-screening and nontargeted compound identification methods. These analyses demonstrated that 6:2 FtTAoS was transformed primarily to a stable polyfluoroalkyl compound, 6:2 fluorotelomer thioether propionate (6:2 FtTP). It did not undergo further reactions to produce the perfluoroalkyl carboxylates and fluorotelomer sulfonates and carboxylates that were observed during aerobic transformations. Here, the 6:2 FtTP was recalcitrant to biotransformation, indicating the stability of the thioether group under sulfate reducing conditions. The total oxidizable precursor (TOP) assay was used to assess the presence of other PFASs. Although nearly all of the PFAS mass initially present was recovered from the pristine microcosms, only 67% of the initial PFAS mass was recovered from the contaminated microcosms, suggesting the formation of volatile biotransformation products or those that could not be detected by the TOP assay.

Environmental Sources, Chemistry, Fate, and Transport of Per‐ and Polyfluoroalkyl Substances: State of the Science, Key Knowledge Gaps, and Recommendations Presented at the August 2019 SETAC Focus Topic Meeting

“…Zhang et al 2016). Only minor changes to 6:2 FtTAoS was observed under nitrate-, sulfate-and iron-reducing and methanogenic conditions with the perfluoroalkyl chain remaining intact and no production of FTOH or PFCAs (Field et al 2017;Yi et al 2018). 6:2 FTSA did not undergo any detectable transformation in anaerobic sediment after a 100-d incubation.…”

Aerobic BTEX biodegradation increases yield of perfluoroalkyl carboxylic acids from biotransformation of a polyfluoroalkyl surfactant, 6:2 FtTAoS

“…Glycols such as diethyl glycol monobutyl ether (DGBE, commercially known as butyl carbitol), accounting for up to 20% by weight of AFFF, 13 can be readily degraded by soil microorganisms. 13,14 Other labile organic matter and co-contaminants at AFFF sites, such as benzene, toluene, ethylbenzene, and xylene (BTEX compounds), can also drive the biotransformation. Substrates like BTEX are of particular interest because the aromatic hydrocarbon oxygenases needed for BTEX biodegradation are known to catalyze the oxidation of a wide variety of chemicals.…”

Surface-water/groundwater boundaries affect seasonal PFAS concentrations and PFAA precursor transformations

“…[9][10][11] Some precursors degrade in the environment into terminal PFAA known to be a concern for human health. 12 Biotransformation of precursors can also lead to the formation of persistent intermediate precursors, 13,14 with altered mobility and transformation rates compared to the primary compounds. Prior work has suggested PFAA precursor biotransformation rates are slower in anaerobic environments compared to oxic conditions, and that biotransformation under anaerobic and oxic conditions produces different end-products.…”

“…Prior work has suggested PFAA precursor biotransformation rates are slower in anaerobic environments compared to oxic conditions, and that biotransformation under anaerobic and oxic conditions produces different end-products. [14][15][16] However, impacts of redox gradients and enhanced biological activity, as found at surface-water/groundwater boundaries, on precursor transformation and transport are poorly understood.…”