Poly-and perfluoroalkyl substances (PFASs) derived from aqueous film-forming foam (AFFF) are increasingly recognized as groundwater contaminants, though the composition and distribution of AFFF-derived PFASs associated with soils and subsurface sediments remain largely unknown. This is particularly true for zwitterionic and cationic PFASs, which may be incompletely extracted from subsurface solids by analytical methods developed for anionic PFASs. Therefore, a method involving sequential basic and acidic methanol extractions was developed and evaluated for recovery of anionic, cationic, and zwitterionic PFASs from field-collected, AFFF-impacted soils. The method was validated by spike-recovery experiments with equilibrated soil-water-AFFF and analytical standards. To determine the relative importance of PFASs lacking commercially available analytical standards, their concentrations were estimated by a novel semiquantitation approach. Total PFAS concentrations determined by semiquantitation were compared with concentrations determined by the total oxidizable precursor assay. Finally, the described method was applied to two soil cores from former fire-training areas in which cations and zwitterions were found to contribute up to 97% of the total PFAS mass. This result demonstrates the need for extraction and analysis methods, such as the ones presented here, that are capable of quantifying cationic and zwitterionic PFASs in AFFF-impacted source zone soils.

The photochemical production of reactive species, such as triplet dissolved organic matter (3DOM) and singlet oxygen (1O2), contributes to the degradation of aquatic contaminants and is related to an array of DOM structural characteristics, notably molecular weight. In order to relate DOM molecular weight, optical properties, and reactive species production, Suwannee River (SRFA) and Pony Lake fulvic acid (PLFA) isolates are fractionated by sequential ultrafiltration, and the resultant fractions are evaluated in terms of molecular composition and photochemical reactivity. UV– visible measurements of aromaticity increase with molecular weight in both fulvic acids, while PLFA molecular weight fractions are shown to be structurally similar by Fourier-transform ion cyclotron resonance mass spectrometry. In addition, Bray–Curtis dissimilarity analysis of formulas identified in the isolates and their size fractions reveal that SRFA and PLFA have distinct molecular compositions. Quantum yields of 3DOM, measured by electron and energy transfer probes, and 1O2 decreased with molecular weight. Decreasing [3DOM]ss with molecular weight is shown to derive from elevated quenching in high molecular weight fractions, rather than increased 3DOM formation. This work has implications for the photochemistry of waters undergoing natural or engineered treatment processes that alter DOM molecular weight, such as photooxidation and biological degradation.

The North Temperate Lakes Long-Term Ecological Research site includes seven lakes in northern Wisconsin that vary in hydrology, trophic status, and landscape position. We examine the molecular composition of dissolved organic matter (DOM) within these lakes using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) and quantify DOM photochemical activity using probe compounds. Correlations between the relative intensity of individual molecular formulas and reactive species production demonstrate the influence of DOM composition on photochemistry. For example, highly aromatic, tannin-like formulas correlate positively with triplet formation rates, but negatively with triplet quantum yields, as waters enriched in highly aromatic formulas exhibit much higher rates of light absorption, but only slightly higher rates of triplet production. While commonly utilized optical properties also correlate with DOM composition, the ability of FT-ICR MS to characterize DOM subpopulations provides unique insight into the mechanisms through which DOM source and environmental processing determine composition and photochemical activity.

Ultraviolet photochemical reaction of sulfite (SO3 2–) photosensitizer generates strongly reducing hydrated electrons (eaq –; NHE = −2.9 V) that have been shown to effectively degrade individual per- and polyfluoroalkyl substances (PFASs), including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). However, treatment of complex PFAS mixtures in aqueous film-forming foam (AFFF) remains largely unknown. Here, UV-sulfite was applied to a diluted AFFF to characterize eaq – reactions with 15 PFASs identified by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) targeted analysis. Results show that reactivity varies widely among PFASs, but reaction rates observed for individual PFASs in AFFF are similar to rates observed in single-solute experiments. While some structures, including long-chain perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs) were readily degraded, other structures, most notably short-chain PFSAs and fluorotelomer sulfonic acids (FTSs), were more recalcitrant. This finding is consistent with results showing incomplete fluoride ion release (up to 53% of the F content in AFFF) during reactions. Furthermore, results show that selected PFSAs, PFCAs, and FTSs can form as transient intermediates or unreactive end-products via eaq – reactions with precursor structures in AFFF. These results indicate that while UV-sulfite treatment can be effective for treating PFOS and PFOA to meet health advisory levels, remediation of the wider range of PFASs in AFFF will prove more challenging.

. We tested the hypothesis that differences in Hg(II) i sorption and/or uptake rates drive observed differences in methylation rates among Desulfovibrio species. Hg(II) i associated rapidly and with high affinity to both methylating and nonmethylating species. MeHg production by Hg-methylating strains was rapid, plateauing after ϳ3 h. All MeHg produced was rapidly exported. We also tested the idea that all Desulfovibrio species are capable of Hg(II) i methylation but that rapid demethylation masks its production, but we found this was not the case. Therefore, the underlying reason why MeHg production capability is not universal in the Desulfovibrio is not differences in Hg affinity for cells nor differences in the ability of strains to degrade MeHg. However, Hg methylation rates varied substantially between Hg-methylating Desulfovibrio species even in these controlled experiments and after normalization to cell density. Thus, biological differences may drive crossspecies differences in Hg methylation rates. As part of this study, Microbial mercury methylation is the main driver of risk associated with Hg pollution. Methylmercury production is an anaerobic process that occurs in saturated soils and wetlands (26,44,45,53), decaying periphyton mats (1, 14, 31), aquatic bottom sediments (16,27,33,36), and anaerobic bottom waters (56). Early investigations, prior to the advent of modern methylmercury (MeHg) analyses, reported a wide variety of aerobic and anaerobic Gram-positive and Gram-negative bacteria (30,49,55,58) and fungi (55) to be capable of MeHg production. However, subsequent studies with pure cultures have conclusively demonstrated a role only for sulfate-reducing bacteria (SRB) (4,8,11,13,20,23,38,50) and iron-reducing bacteria (FeRB; principally Geobacter spp.) (21, 37), all belonging to the Deltaproteobacteria. Many field studies, using selective microbial stimulants (1, 10, 26, 44, 57), inhibitors (1, 16, 24, 26, 59), and biogeochemical correlates (6,39,40,45), have buttressed the paradigm of SRB and FeRB as the dominant Hg methylators in natural aquatic systems (16,24,59), though recent studies have hypothesized that methanogens may be significant in some systems (31).Only a subset of SRB and FeRB are capable of Hg methylation (11,23,37,50), but why this is the case remains unclear. Early work by Choi and Bartha (13) suggested that Hg methylation was a "metabolic mistake" of SRB utilizing the acetyl coenzyme A (acetyl-CoA) pathway for carbon metabolism. Subsequent studies, however, indicated that Hg methylation capability is not restricted to SRB possessing the acetyl-CoA pathway (20). At present, it is not possible to conclusively identify the methyltransferase or methyl donor in SRB (or other Deltaproteobacteria) responsible for in vivo Hg methylation. Hg methylation occurs intracellularly (23), and significant effort has therefore been devoted to elucidating the mechanism(s) of Hg uptake by Hg-methylating bacteria.Passive diffusion of neutral HgS species has been hypothesized to control Hg uptak...