Bioremediation of PFAS: Promise and Challenges Yujie Men Ph.D., Assistant Professor December 4, 2020 #SerdpEstcp2020 Outline Part 1: History of microbial cleavage of C–F in organofluorines Part 2: Current research status on PFAS biotransformation Part 3: Implications in biotechnologies for PFAS remediation 2 #SerdpEstcp2020 Part 1: Microbial cleavage of C–F in organofluorines C−F bond and bioavailability • C–F bond: the strongest single bond in nature Bond kJ/mol Bond kJ/mol C‒F 439 C‒C 347 C‒H 414 C‒Cl 331 C‒O 351 C‒N 293 • Microbial cleavage of C–F: thermodynamically feasible, kinetically hindered ∆G0 (kJ/mol) Reaction Defluorination Dechlorination Tetrahalomethane → Trihalomethane + H+ + halide‒ -89 -188 (Dolfing 2003; Parsons et al., 2008) 3 #SerdpEstcp2020 Part 1: Microbial cleavage of C–F in organofluorines Hydrolytic defluorination • Haloacetate dehalogenase (EC 3.8.1.3) • Aerobic bacteria: Pseudomonas spp., Moraxella sp. B, Burkholderia sp. FA1, Aureobacterium sp. strain RH025 • Substrate: monofluoroacetate • No reports on PFAS as substrates - + O O O O O H2O F + H O Aureobacterium sp. F - HO - Strain RH025 O Haloacetate O dehalogenase H O + F Monofluoroacetate Glycolate F 2 H OH (Goldman, 1965&1969; Key et al., 1997; Natarajan et al., 2005; Kurihara et al., 2008) 4 #SerdpEstcp2020 Part 1: Microbial C–F bond cleavage in organofluorines Reductive defluorination • Unknown enzyme(s) • Anaerobic, methanogenic communities • Poor reproducibility • Cometabolism • No follow-up reports since 2000 O O O O F - F - F - - O O O H3C O F F F Trifluoroacetate Difluoroacetate Monofluoroacetate Acetate (Visscher et al., 1994; Key et al., 1997; Kim et al., 2000) 5 #SerdpEstcp2020 Part 1: Microbial C–F bond cleavage in organofluorines Reductive defluorination (cont’d) • Pyruvate dehydrogenase from E. coli • Co-factor: thiamin pyrophosphate (TPP) • Substrate: fluoropyruvate; no reports on PFAS as substrates O O PDH-TPP O - + H O CO + F + CH C O + F CH2 C C O 2 2 3 + H O O - OH O OH OH - F CH2 C C O F CH C C O CO2 F CH C F CH C PDH 2 2 2 S S S S + + + N N N N R1 R2 R1 R2 R1 R2 R1 R2 O O = P P R = H N N R1 O O OH 2 2 TPP Enzymatic? Fluoride elimination OH OH N O Spontaneous? F PDH: pyruvate dehydrogenase CH3 C OH O OH H2O CH3 C CH2 C S S + S (Leung and Frey, 1978; Natarajan et al., 2005) N N+ + R1 R2 N R1 R2 R1 R2 6 #SerdpEstcp2020 Part 1: Microbial C–F bond cleavage in organofluorines Reductive defluorination (cont’d) • Maleylacetate reductase from Pseudomonas sp. Strain B12 • Co-factor: NADH • Substrate: 2 position halogenated compounds; no PFAS reported O O 1 5 + maleylacetate HO C + HO2C + 2NADH + H 2 + 2NAD + F 4 reductase CO H 2 3 CO2H 2 F H 6 H H 2-fluoromaleylacetate HB-enz H B-enz B-enz H F HB-enz O O O 1 5 O HO C HO2C HO2C 2 4 HO2C 2 3 CO H CO H CO H 2 2 F CO2H 2 F H 6 F H H H H H H (Kaschabek et al., 1995) 7 #SerdpEstcp2020 Part 1: Microbial C–F bond cleavage in organofluorines Reductive defluorination (cont’d) • Baker’s yeast • Unknown enzyme(s) • Allyl alcohol dependent • Substrate: 4,4,4-trifluoro acetoacetate; no PFAS reported • 4 position defluorination F O Baker's yeast OH O F O allyl alcohol 2.0g/L F CO Et F CO2Et F CO2Et 2 CO2Et F F F F F OH CO2Et (Bertau, 2001) 8 #SerdpEstcp2020 Part 1: Microbial C–F bond cleavage in organofluorines HF elimination • Spontaneous or enzymatic HF elimination • Possible enzymes • Muconate cycloisomerase • Acyl-coA dehydrogenase type of enzymes • Various fluoroaromatics and some PolyFAS O O COOH -HF COOH COOH COOH ring cleavage TCA cycle F O OH spontaneous +H2O F hydroxylase ring -HF HOOC cleavage HOOC O O F HOOC Muconate (Key et al., 1997; Natarajan et al., 2005) cycloisomerase Can microbes defluorinate perfluorinated9 compounds? #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation PFCA O - PFSA O O - O F F O O F R - O F F n-1 O OH 10 (Wang et al., 2017) #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Biotransformation without defluorination F F Hydrolysis F R F F n-1 Commercial surfactants Precursors in AFFF Polyfluoroalkyl phosphate esters (PAP) O F - F R1 O P O R1, R2 = F O F F Sulfate-reducing condition n-1 R 0 2 fluorotelomers Amide0 hydrolysis Ester hydrolysis F F OH F F F n:2 fluorotelomer alcohol n-1 (Yi et al., 2018) (Lee et al., 2010) 11 #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Defluorination of PolyFAS Fluorotelomer alcohol (FTOH) Aerobic: F F F F F F F F F F F F O PFCA pathway activated sludge F F soil OH OH F F n:3 acid pathway F F F F F F F F F F pure bacteria 6:2 FTCA 6:2 FTOH anaerobic fungi -HF F O O F F F F F O F F F F F O F F F F O F F F F F F F F F F F F F OH OH OH OH OH F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F 5:3 Acid 3-fluoro 5:3 Acid 6:2 FTUCA 5:3 U Acid 5:3 Acid +H2O -HF slow F FF F O O -HF F FF F O O F H F F F F F F NH2 One-carbon F F FF F F F F F FF F 5:3 ketone aldehyde F removal pathway F F F F F 5:3 U Amide 5:2 preferred Total defluorination: 10-20% ketone 2F Stable products F F F F O F F F F OH F F F F OH F F F (Wang et al., 2005, 2011, 2012; Liu OH F F F et al., 2010, 2013; Kim et al., 2012; F F F F F F F F F F F F O F 12 Butt et al., 2014; Tseng et al., 2014; PFHxA 5:2 sFTOH PFPeA Zhang et al., 2019)#SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Defluorination of PolyFAS (cont’d) One-carbon removal pathway for n:3 polyfluoroalkyl acid (activated sludge) F F F F O F F F F F F F F F F OH F OH OH F F F F F F F F F F F O F F F O 5:3 Acid 4:3 Acid 4:3 U Acid 14.2% yield F F O F F F F F F F OH O OH F F F F F F F F F F F F F F F F F O OH F OH F F F F F 3:3 Acid F 4:2 sFTOH PFPeA 5.9% yield F F F F F O 5:3 U Acid 0.9% yield 5:2 FTUCA F F O F +H O OH 2 -HF F F F F PFBA 0.8% yield F F F F O -CO F F F F F F F F F 2 F H F OH OH F F F F F F F F F F F F F F F F F F OH O O alpha-OH 5:3 Acid 5:2 Aldehyde 5:2 FTCA All intermediates: 10.2% yield (Wang et al., 2012) 13 #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Defluorination of PolyFAS (cont’d) Fluorotelomer sulfonate: more recalcitrant than FTOH/FTCA Activated sludge 90-d removal: 36% Pure culture (Pseudomonas sp.) (Sulfur-limiting; FTS as the sole sulfur source) F O F Complete parent compound removal S O 1:1 formation of fluoride F O F F F O O Partial parent compound removal F S 1:1 formation of fluoride O F F F F F F O F F S Partial parent compound removal F O F F F F F O 1.4:1 formation of fluoride 6:2 FTS (Key, 1996; Key et al., 1997) Total product yield: 6.3% 14 (Wang et al., 2011) #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Defluorination of PerFAS • Peroxidase/Laccase-mediated PFOA/PFOS defluorination Enzyme catalyzed oxidative humification reactions (ECOHR) HRP-mediated PFOA removal (6 h): 63% Initiation peroxidase/laccase Total defluorination: <1% Mediator (M) Mediator radical (M•) Laccase-mediated PFOA removal (96 d): 34% Total defluorination: 49% Propagation Laccase-mediated PFOS removal (162 d): 59% Total defluorination: 47% M• + other organic compounds (R) R• Termination • • − • • − F M or R + C7F15COO CnF2n+1 or CmF2mCO2 PFOA Various products • • − • • − M or R + C8F17SO3 CnF2n+1 or CmF2mSO3 PFOS (Luo et al., 2009; 2017; 2018) 15 #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Defluorination of PerFAS (cont’d) • Anaerobic defluorination of PFOA and PFOS by Feammox cultures Acidimicrobium sp. strain A6 (A6) and A6 enrichment 3+ Acidic pH (4.5 – 5) with Fe as the primary electron acceptor and NH3 or H2 as the electron donor PFOA PFOS Products of PFOA: Products of PFOS: PFPeA, PFBS, PFHxA, HFBA PFPeA, HFBA 68 – 75% defluorination of PFOA/PFOS removed (Huang & Jaffé, 2019) 16 #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Defluorination of PerFAS (cont’d) • Microbial reductive defluorination of branched and unsaturated PerFAS A commercialized dechlorinating enrichment culture - - Primary e donor: lactate or H2; the sole e acceptor: PFAS 17 (Yu et al., 2020) #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Defluorination of PerFAS (cont’d) • Defluorination/transformation pathways Red numbers: bond dissociation energy (Yu et al., 2020) 18 #SerdpEstcp2020 Part 2: Current research status on PFAS biotransformation Defluorination of PerFAS (cont’d) • Which are the responsible microorganisms? ? https://doi.org/10.1021/acs.est.0c04483 19 others? #SerdpEstcp2020 Part 3: Implications in biotechnologies for PFAS remediation Current challenges and future directions Challenge 1: Lack knowledge of PFAS-defluorinating enzymes and substrate specificity Direction 1: Identification of defluorinating microorganisms/enzymes Direction 2: Broad screening of defluorinating microorganisms/enzymes and effective PFAS structures Challenge 2: Slow and incomplete defluorination Direction 3: Optimize growth conditions Direction 4: Accelerated/adaptive evolution to select novel biocatalysts Direction 5: Design engineered defluorinating enzymes Covered in SERDP ER20-1541 (Tasks 1-3) 20 #SerdpEstcp2020 Part 3: Implications in biotechnologies for PFAS remediation Application potential • Difficult to be applied alone for PFAS destruction at the current stage • May be a cost-effective option in combination with other treatment approaches in a treatment train system (SERDP ER20-1541 Task 4) Pre-/post-treatment for efficient/deeper defluorination physiochemical Microbial 1 Microbial 2 PFAS Partial Refined Refined Treatment Train defluorination defluorination& defluorination& products mineralization mineralization 21 #SerdpEstcp2020 Part 3: Implications in biotechnologies for PFAS remediation Other implications • A better understanding of the environmental fate of PFAS • Stable end products of various PFAS structures after microbial transformation • Ways to divert persistent end products to more biodegradable ones • A better assessment of PFAS exposure and potential toxicity F F F F F F O F F F F F OH S F O Structure Mobility Toxicity F F F F F F O F O F F F O F F F F OH O F F F F F F F F O F F F OH F F F F F F F F F F F F F O F OH F F F F F F F F F F F F F OH 22 #SerdpEstcp2020 Acknowledgments • M.E.N.