Biodegradation of N-Ethyl Perfluorooctane Sulfonamido Ethanol (EtFOSE) and EtFOSE-Based Phosphate Diester (SAmPAP Diester) in Marine Sediments

Abstract

Investigations into the biodegradation potential of perfluorooctane sulfonate (PFOS)-precursor candidates have focused on low molecular weight substances (e.g., N-ethyl perfluorooctane sulfonamido ethanol (EtFOSE)) in wastewater treatment plant sludge. Few data are available on PFOS-precursor biodegradation in other environmental compartments, and nothing is known about the stability of high-molecular-weight perfluorooctane sulfonamide-based substances such as the EtFOSE-based phosphate diester (SAmPAP diester) in any environmental compartment. In the present work, the biodegradation potential of SAmPAP diester and EtFOSE by bacteria in marine sediments was evaluated over 120 days at 4 and 25 °C. At both temperatures, EtFOSE was transformed to a suite of products, including N-ethyl perfluorooctane sulfonamidoacetate, perfluorooctane sulfonamidoacetate, N-ethyl perfluorooctane sulfonamide, perfluorooctane sulfonamide, and perfluorooctane sulfonate. Transformation was significantly more rapid at 25 °C (t(1/2) = 44 ± 3.4 days; error represents standard error of the mean (SEM)) compared to 4 °C (t(1/2) = 160 ± 17 days), but much longer than previous biodegradation studies involving EtFOSE in sludge (t(1/2) ∼0.7-4.2 days). In contrast, SAmPAP diester was highly recalcitrant to microbial degradation, with negligible loss and/or associated product formation observed after 120 days at both temperatures, and an estimated half-life of >380 days at 25 °C (estimated using the lower bounds 95% confidence interval of the slope). We hypothesize that the hydrophobicity of SAmPAP diester reduces its bioavailability, thus limiting biotransformation by bacteria in sediments. The lengthy biodegradation half-life of EtFOSE and recalcitrant nature of SAmPAP diester in part explains the elevated concentrations of PFOS-precursors observed in urban marine sediments from Canada, Japan, and the U.S, over a decade after phase-out of their production and commercial application in these countries.

Highly Elevated Serum Concentrations of Perfluoroalkyl Substances in Fishery Employees from Tangxun Lake, China

“…40,41 The relatively high FOSA to PFOS ratios in shrimp and river snail (Table S5, mean ratio: 0.430 and 0.287, respectively) may indicate that aquatic species feeding on the benthos receive a higher exposure to PFOS precursors which are strongly hydrophobic and primarily partition to the sediments. 42,43 A higher capability in fish species to metabolize PFOS precursors, 44 on the other hand, may explain the shift in FOSA to PFOS ratios at a higher trophic position. Overall, the trends in PFOS and FOSA concentrations between different aquatic species indicate that uptake and metabolism of PFOS precursors 42 may play an important role in the accumulation of PFOS in the Tangxun Lake food web.…”

Methodology for studying biotransformation of polyfluoroalkyl precursors in the environment

“…Dispersive solid-phase extraction (DSPE) methods, initially established for the determination of PFCAs in environmental matrices, were widely adapted in soil, sediment and activated sludge-incubation systems [26,[35][36][37]45]. Specifically, solid samples were first soaked in an organic solvent (methanol, acetonitrile, or methyl tert-butyl ether), then constantly shaken at 150-200 rpm for from several hours up to 5 days and then centrifuged to obtain supernatant.…”

“…The selectivity is not influenced by the presence of organic solvents, such as methanol, acetonitrile and MTBE, which made the purification procedure easily coupled to both DSPE and IPE methods, as mentioned in sub-section 2.2. The protocol was simple and robust for quantitative recovery of fluorotelomers-and EtFOSE-based precursors and transformation products [29,30,[35][36][37]. Zhang et al [46] demonstrated low matrix effects for PFCAs (C5-C10), PFSAs (C4,6,8), FOSAs and FOSAAs in the range -13% to +24% in digested sewage-sludge extract using the Envi-Carb clean-up procedure.…”

Levels, Isomer Profiles, and Estimated Riverine Mass Discharges of Perfluoroalkyl Acids and Fluorinated Alternatives at the Mouths of Chinese Rivers

“…5 This difference could partly be explained by the fact that PFOS precursors have not been completely transformed to PFOS in the environment and might also be predominantly distributed in the air. 42,43 Thus, measurements of PFOS alone would inevitably lead to an underestimation of the total emissions of PFOS equivalents. The total annual riverine mass discharge of PFOS, as well as F-53B, could further be underestimated in this current study since these compounds could also be strongly sorbed to particulate matter in the water column and bottom sediment.…”