Sorption linearity and reversibility are implicit in models for the fate and transport of per-and polyfluoroalkyl substances (PFAS). In this study, however, we found that the sorption of cationic and zwitterionic PFAS in natural soils was highly nonlinear. The nonlinearity was so severe that it led to a variation in the coefficient of sorption by several orders of magnitude over the experimental concentration range. This implies a considerable increase in sorption as concentration falls in the natural environment. Sorption of cationic PFAS correlated strongly with the soil organic matter (SOM) content and was reversible in all soils. Sorption of zwitterionic PFAS, on the other hand, displayed concentration-dependent hysteresis in soils with a low SOM content. The irreversibility, which was associated with neither SOM, pore deformation, nor surface complexation, was likely caused by the entrapment of molecules in porous structures within inorganic components of soil aggregates. Furthermore, electrostatic interactions with negatively charged soil constituents and the hydrophobic effect were found to be major sorption driving forces for cationic/zwitterionic PFAS at low and high concentrations, respectively. The maximum electrostatic potential of PFAS ions, computed using density functional theory, was found to be a useful predictor of the sorption of ionic PFAS species.

Per-and polyfluoroalkyl substances (PFAS) are a large group of manmade chemicals that impose emerging environmental concerns. Among them, short-chain per-and polyfluorinated carboxylic acids represent an important subgroup used as building blocks of biologically active chemicals and functional materials. Some are also considered PFAS alternatives, and some could be byproducts of the physicochemical treatment of PFAS. However, little is known about the environmental fate of shortchain fluorinated carboxylic acids (FCAs) and their defluorination/ transformation by microorganisms. To fill the knowledge gap, we investigated the structure−reactivity relationships in the aerobic defluorination of C 3 −C 5 FCAs by activated sludge communities. Four structures exhibited greater than 20% defluorination, with 3,3,3-trifluoropropionic acid being almost completely defluorinated. We further analyzed the defluorination/transformation pathways and inferred the structures susceptible to aerobic microbial defluorination. We also demonstrated that the defluorination was via cometabolism. The findings advance the fundamental understanding of aerobic microbial defluorination and help assess the environmental fate of PFAS. Since some short-chain PFAS, such as 3,3,3-trifluoropropionic acid, are the incomplete defluorination byproducts of advanced reduction processes, their defluorination by activated sludge communities sheds light on the development of cost-effective chemical−biological PFAS treatment train systems.

The recently discovered microbial reductive defluorination of two C 6 branched and unsaturated fluorinated carboxylic acids (FCAs) provided valuable insights into the environmental fate of per-and polyfluoroalkyl substances (PFASs) and potential bioremediation strategies. However, a systematic investigation is needed to further demonstrate the role of CC double bonds in the biodegradability of unsaturated PFASs. Here, we examined the structure-biodegradability relationships of 13 FCAs, including nine commercially available unsaturated FCAs and four structurally similar saturated ones, in an anaerobic defluorinating enrichment and an activated sludge community. The anaerobic and aerobic transformation/defluorination pathways were elucidated. The results showed that under anaerobic conditions, the α,β-unsaturation is crucial for FCA biotransformation via reductive defluorination and/or hydrogenation pathways. With sp 2 C−F bonds being substituted by C−H bonds, the reductive defluorination became less favorable than hydrogenation. Moreover, for the first time, we reported enhanced degradability and defluorination capability of specific unsaturated FCA structures with trifluoromethyl (−CF 3 ) branches at the α/β-carbon. Such FCA structures can undergo anaerobic abiotic defluorination in the presence of reducing agents and significant aerobic microbial defluorination. Given the diverse applications and emerging concerns of fluorochemicals, this work not only advances the fundamental understanding of the fate of unsaturated PFASs in natural and engineered environments but also may provide insights into the design of readily degradable fluorinated alternatives to existing PFAS compounds.

Perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) are two environmentally persistent per- and polyfluoroalkyl substances (PFAS) that have been detected globally in human tissues and fluids. As part of a project investigating the indirect sources of PFOA/PFOS in the environment and engineered systems, this study is concerned with the mechanisms leading to their in vivo generation in terrestrial invertebrates. We demonstrate here the formation of PFOA and PFOS in earthworms (Lumbricus terrestris) from a group of four zwitterionic/cationic polyfluoroalkyl amides and sulfonamides. In bioaccumulation tests, the zwitterionic PFAS compounds were metabolized within 10 days to PFOA/PFOS at yields of 3.4–20.8 mol % by day 21 and several infrequently reported PFAS species for which chemical structures were determined using high-resolution mass spectrometry. Cationic PFAS, on the other hand, were found to be much less metabolizable in terms of the number (n = 2) and yields (0.9–5.1 mol %) of metabolites. Peak-shaped bioaccumulation profiles were frequently observed for the studied PFAS. Residual zwitterionic/cationic PFAS in earthworms were detected at the end of the elimination phase, indicating that not all zwitterionic/cationic PFAS molecules in vivo are available for enzymatic degradation. Finally, the relative importance of different exposure routes (i.e., waterborne and dietary exposure) was investigated.

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