Microbial Reductive Dechlorination by a Commercially Available Dechlorinating Consortium Is Not Inhibited by Perfluoroalkyl Acids (PFAAs) at Field-Relevant Concentrations

Abstract

Perfluoroalkyl acids (PFAAs) have been shown to inhibit biodegradation (i.e., organohalide respiration) of chlorinated ethenes. The potential negative impacts of PFAAs on microbial species performing organohalide respiration, particularly Dehalococcoides mccartyi (Dhc), and the efficacy of in situ bioremediation are a critical concern for comingled PFAA-chlorinated ethene plumes. Batch reactor (no soil) and microcosm (with soil) experiments, containing a PFAA mixture and bioaugmented with KB-1, were completed to assess the impact of PFAAs on chlorinated ethene organohalide respiration. In batch reactors, PFAAs delayed complete biodegradation of cis-1,2-dichloroethene (cis-DCE) to ethene. Maximum substrate utilization rates (a metric for quantifying biodegradation rates) were fit to batch reactor experiments using a numerical model that accounted for chlorinated ethene losses to septa. Fitted values for cis-DCE and vinyl chloride biodegradation were significantly lower (p < 0.05) in batch reactors containing ≥50 mg/L PFAAs. Examination of reductive dehalogenase genes implicated in ethene formation revealed a PFAA-associated change in the Dhc community from cells harboring the vcrA gene to those harboring the bvcA gene. Organohalide respiration of chlorinated ethenes was not impaired in microcosm experiments with PFAA concentrations of 38.7 mg/L and less, suggesting that a microbial community containing multiple strains of Dhc is unlikely to be inhibited by PFAAs at lower, environmentally relevant concentrations.

Sulfonamide Per- and Polyfluoroalkyl Substances Can Impact Microorganisms Used in Aromatic Hydrocarbon and Trichloroethene Bioremediation

“…PFOS concentrations of 50 mg/L decreased its metabolic rate due to acute toxicity . In contrast, anaerobic dechlorinating mixed cultures were inhibited by PFASs, , although this was not observed with a commercial dechlorinating consortium . High concentrations (i.e., 16 and 32 mg/L) of the precursor fluorotelomer sulfonamido betaine (FtSaB) have been found to inhibit TCE degradation, whereas fluorotelomer thioether amido sulfonate (FtTAoS) (45 mg/L) did not.…”

“…Few studies have examined PFAS effects on prokaryotes. − When aerobic toluene-degrading Rhodococcus jostii strain RHA1 was exposed to a combination of 11 perfluoroalkyl acids (PFAAs) (10 mg/L each for a total PFAS exposure of 110 mg/L), toluene degradation was not impacted by PFASs, but the cells experienced enhanced aggregation as well as upregulation of stress-related genes . In another study, partitioning of PFAAs into bacterial cell membranes and model membranes increased with PFAS chain length .…”

“… 15 In contrast, anaerobic dechlorinating mixed cultures were inhibited by PFASs, 17 , 18 although this was not observed with a commercial dechlorinating consortium. 16 High concentrations (i.e., 16 and 32 mg/L) of the precursor fluorotelomer sulfonamido betaine (FtSaB) have been found to inhibit TCE degradation, whereas fluorotelomer thioether amido sulfonate (FtTAoS) (45 mg/L) did not. It was hypothesized that the positively charged betaine group in FtSaB was in part responsible for this difference 17 as cationic amines are potent antibacterials.…”