Nothing lasts forever: understanding microbial biodegradation of polyfluorinated compounds and perfluorinated alkyl substances

Laccase based per- and polyfluoroalkyl substances degradation: Status and future perspectives

Per- and polyfluoroalkyl substances (PFAS) with stable carbon-fluorine bonds are used in a wide range of industrial and commercial applications. Due to their extreme environmental persistence, PFAS have the potential to bioaccumulate, cause adverse effects, and present challenges regarding remediation. Recently, microbial and enzymatic reactions for sustainable degradation of PFAS have gained attention from researchers, although biological decomposition of PFAS remains challenging. Surprisingly, laccases, the multi-copper oxidases produced by various organisms, showed potential for PFAS degradation. Mediators play key roles in initiating laccase induced PFAS degradation and defluorination reactions. The laccase-catalyzed PFAS degradation reactions are relatively slower than normal biocatalytic reactions and the low activity of native laccases constrains their capacity to complete defluorination. With their low redox potential and narrow substrate scope, an innovative remediation strategy must be taken to accelerate this reaction. In this review we have summarized the status, challenges, and future perspectives of enzymatic PFAS degradation. The knowledge of laccase-based defluorination and the molecular basis of the reaction mechanisms overviewed in this study could inform future applications of laccases for sustainable PFAS remediation.

Enzymatic Degradation of PFAS: Current Status and Ongoing Challenges

Per- and polyfluoroalkyl substances (PFAS) are often considered the quintessential example of industrial chemical pollution - they are toxic and ubiquitous environmental contaminants that are extremely difficult to degrade. There has been a large research focus on the development of effective and renewable degradation technologies. In comparison to traditional pollutant degradation techniques, such as advanced oxidation processes and electrochemistry, degradation of PFAS using extracellular enzymes offers an eco-friendly solution as enzymes are biodegradable, recyclable and have low energy and chemical requirements. This review outlines the current understanding of extracellular enzymatic degradation of PFAS with a focus on reported results and proposed degradation mechanisms. More importantly, this review highlights limitations that hinder the application of enzymes for PFAS degradation and proposes critical future research that is needed to improve the applicability of this promising remediation strategy.

Phytoremediation of perfluoroalkyl and polyfluoroalkyl substances (PFAS): Insights on plant uptake, omics analysis, contaminant detection and biomass disposal

The unique properties of per- and polyfluoroalkyl substances (PFAS) have driven their pervasive use in different industrial applications, leading to substantial environmental pollution and raising critical concerns about the long-term impacts on ecosystem and human health. To tackle the global challenge of PFAS contamination, there is an urgent need for sustainable and efficient remediation strategies. Phytoremediation has emerged as a promising eco-friendly approach with the potential to mitigate the spread of these persistent contaminants. However, addressing this complex issue requires interdisciplinary cutting-edge research to develop comprehensive and scalable solutions for effective PFAS management. This review highlights recent advancements in the detection, quantification, and monitoring of PFAS uptake by plants, providing a detailed description of PFAS accumulation in several plant species. Besides, the physiological and molecular responses elicited by these pollutants are described. Leveraging omic technologies, including genomics, transcriptomics, and proteomics, provides unprecedented insights into the plant-PFAS interaction. Novel approaches based on artificial intelligence to predict this interaction and up to date disposal and valorization methods for PFAS-contaminated plant biomass, are discussed here. This review offers an interdisciplinary approach to explore what has been discovered so far about PFAS phytoremediation, covering the entire process from contaminant uptake to sustainable disposal, providing a roadmap for future research.

Insights into poly-and perfluoroalkyl substances (PFAS) removal in treatment wetlands: Emphasizing the roles of wetland plants and microorganisms

Poly- and perfluoroalkyl substances (PFAS) are widespread emerging contaminants in aquatic environments, raising serious concerns due to their persistence and potential toxicity to both human health and ecosystems. Treatment wetlands (TWs) provide a sustainable, low-carbon solution for PFAS removal by harnessing the combined actions of substrates, plants, and microorganisms. This review evaluates the effectiveness of TWs in PFAS treatment, emphasizing their role as a post-treatment option for conventional wastewater treatment plants. Mass balance analysis reveals that substrate adsorption was the primary pathway for PFAS removal from TWs, while plant uptake and subsequent harvesting treatments, as well as microbial degradation, contribute substantially to long-term PFAS removal. Comparisons of bioaccumulation factor (BCF) and translocation factors (TF) between wetland and terrestrial plants demonstrate that wetland plants are particularly effective at adsorbing long-chain PFAS and transferring them from roots to aboveground tissues. The diverse environmental conditions within TWs support varied microbial communities, facilitating the evolution of PFAS-degrading microorganisms. Wetland microorganisms demonstrate the capacity to break down PFAS through processes such as head group transformations (e.g., decarboxylation, desulfonation) and defluorination (e.g., elimination, reductive defluorination, hydrolysis, dealkylation). This review emphasizes the crucial role of wetland plants and microorganisms in the sustainable removal of PFAS in TWs, providing insights for the ecological remediation of PFAS-contaminated wastewater.

Long-chain perfluoro carboxylic acids in landfill leachate: Extraction, detection and biodegradation

Landfills serve as major repositories for products containing per- and polyfluoroalkyl substances (PFASs). These compounds have been documented in the resulting leachate, posing a significant threat to both surface water and groundwater quality. Long-chain perfluoro carboxylic acids (LC-PFCAs), which act as precursors to shorter-chain PFCAs, are particularly persistent in the environment. Despite this, data on LC-PFCA's occurrence in landfill leachate is limited, highlighting the need for thorough monitoring and control efforts. This study focuses on the extraction of LC-PFCA using solid-phase extraction (SPE), detection by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and their biodegradation using an autochthonous bacterial community of landfill leachate based on the hypothesis that native bacteria can consume these pollutants. The findings of the study indicate that SPE efficiency and PFCA recovery rates were higher in diluted leachate samples. LC-MS/MS exhibited superior sensitivity and accuracy compared to direct MS injection, with lower detection limits. Throughout the sampling period, perfluoro nonanoic acid (PFNA) and perfluoro decanoic acid (PFDA), were detected in concentrations ranging from 30 to 640 ng/L and 40-510 ng/L, respectively. Further, the native microbial community degraded spiked PFNA and PFDA (1, 10, and 100 mg/L), with efficiencies of 35.26 ± 5.47% and 53.38 ± 6.54%, respectively, and Aeromonas, Proteus, Moheibacter, Pseudochrobactrum, Providencia and Pseudomonas were identified as the most promising genus to degrade LC-PFCAs. Overall, these findings of the study highlight the significance of robust analytical methods for LC-PFCA detection and reveals the promising prospects for PFNA and PFDA biodegradation by pre-existing bacterial communities.

Enriching fluorotelomer carboxylic acids-degrading consortia from sludges and soils

Fluorotelomer carboxylic acids (FTCAs) has drawn increasing attention due to their prevalent occurrence, high toxicity, and bioaccumulating effects. In this study, microbial consortia with sustainable FTCA removal abilities were enriched and characterized from two activated sludges and five soils when no external carbon sources were supplemented. After four generations of enrichment, stable 6:2 FTCA and 5:3 FTCA biodegradation were achieved, reaching 0.72-0.98 and 0.53-1.05 μM/day, respectively. Coupling with 6:2 FTCA biotransformation, fluoride release co-occurred, conducive to approximate 0.19 fluoride per 6:2 FTCA molecule that was biodegraded. In contrast, minimal free fluoride was detected in 5:3 FTCA-amended consortia, indicating the dominance of "non-fluoride releasing pathways". Microbial community analysis revealed the dominance of 13 genera across all consortia. Among them, 3 genera, including Hyphomicrobium, Methylorubrum, and Achromobacter, were found more enriched in consortia amended with 6:2 FTCA than those with 5:3 FTCA from an identical inoculation source, suggesting their involvement in biodefluorination. This study uncovered that microbial consortia can degrade FTCAs without the supplementation of external carbon sources, though with low biotransformation and biodefluorination rates. Further research is underscored to investigate the involved biotransformation pathways and biodefluorination mechanisms, as well as effects of external carbon sources.

Aerobic or anaerobic? Microbial degradation of per- and polyfluoroalkyl substances: A review

The widespread utilization of per- and polyfluoroalkyl substances (PFASs) as "forever chemicals" is posing significant environmental risks and adverse effects on human health. Microbial degradation (e.g., bacteria and fungi) has been identified as a cost-effective and environmentally friendly method for PFAS degradation. However, its degradation efficiency, biotransformation pathway, and microbial mechanism vary significantly under aerobic and anaerobic conditions. This review provides a comprehensive overview of the similarities and differences in PFAS microbial degradation by bacteria and fungi under different oxygen conditions. Initially, the efficiencies and metabolites of PFAS microbial degradation were compared under aerobic and anaerobic conditions, including perfluorinated and polyfluorinated compounds. Additionally, the microbial mechanisms of PFAS microbial degradation were obtained by summarizing key degrading microbes and enzymes. Finally, the comparisons between aerobic and anaerobic conditions in PFAS microbial degradation were provided, addressing the main challenges and proposing future research directions focused on seeking combined biodegradation techniques, exploring novel microbial species capable of degrading PFAS, and confirming complete biodegradation pathways. The understanding of PFAS microbial degradation in aerobic and anaerobic environments is crucial for providing potential solutions and future research efforts in dealing with these "forever chemicals".

Defluorination of various perfluoro alkyl acids and selected PFOA and PFOS monomers by Acidimicrobium sp. Strain A6 enrichment cultures

Per- and polyfluoroalkyl substances (PFAS) have emerged as a diverse class of environmental pollutants, garnering increasing attention due to their various structural types and potential ecological impacts. The impact of select PFAS on environmental microorganisms and the potential for microbial degradation of certain PFAS are timely research topics. In this study, we conducted a series of batch incubation to investigate the effects of C4-C10 perfluoroalkyl carboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs), as well as linear and branched perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) monomers, on the Feammox reaction and Acidimicrobium sp. A6 (A6), a microbe known to degrade PFOA and PFOS. We explored the defluorination ability of A6 cultures with these PFAS, evaluating their response to varying chemical structures. While A6 cultures demonstrated the ability to degrade a wide range of PFAAs (11.5-56.9 % reduction over 120 days), challenges were noted with specific compounds like PFPeA and double-branched PFCAs and PFSAs, which also showed reduced ammonium removal. Additionally, exposure to the selected PFAS resulted in notable shifts in the microbial community within the A6 enrichment cultures, indicating a selective pressure that benefits certain strains (e.g., increased percentages of Acidimicrobium, Paraburkholderia, and Desulfosporosinus in several PFCA, PFSA and PFOA/PFOS monomers enriched cultures). These insights contribute to our understanding of microbial-PFAS interactions and are instrumental in developing bioremediation strategies for PFAS-impacted environments.

Bioelectricity drives transformation of nitrogen and perfluorooctanoic acid in constructed wetlands: Performances and mechanisms

In this study, constructed wetland-microbial fuel cell (CW-MFC) filled with modified basalt fiber (MBF) via iron modification was utilized for treating perfluorooctanoic acid (PFOA) containing sewage. Results showed the significant promotion by bioelectricity on ammonium and total nitrogen by 7.80-8.14 %. Although such enhancement was suppressed by PFOA, higher removal was still observed with closed circuit, and PFOA removal also increased by 9.05 %. Bioelectricity contributed to enrichment of bacteria involved in nitrifying (Nitrospira and Ellin6067), denitrifying (like Thauera and Dechloromonas), iron redox (Geobacter), and sulfate-reducing (Desulfobacter), aligned with up-regulated of functional genes, including amoA, narG , napA, narK, narS, nrfA, sulp and sqr. Enrichment of autohydrogenotrophic and sulfide-oxidizing autotrophic denitrifiers, and nitrate dependent iron oxidation bacteria by bioelectricity all promoted denitrification. Moreover, bioelectricity boosted relative abundance of organic compounds degradation enzymes, such as dehydrogenase, decarboxylase, and dehalogenase, supporting the enhancement on PFOA removal. Generally, PFOA was converted to short-chain perfluorocarboxylic acids (PFCAs) via decarboxylation, hydroxylation, HF elimination, hydrolysis, F- elimination, C-C bond scission, and dehydration in CW-MFC. The final PFCAs-products determined was perfluorobutyric acid. This work estimated feasibility of treating PFOA containing sewage by CM-MFC, and offered new insights on enhancing mechanisms of nitrogen and PFOA conversion.

A review of per- and polyfluoroalkyl substances (PFASs) removal in constructed wetlands: Mechanisms, enhancing strategies and environmental risks

PER: Polyfluoroalkyl substances (PFASs), typical persistent organic pollutants detected in various water environments, have attracted widespread attention due to their undesirable effects on ecology and human health. Constructed wetlands (CWs) have emerged as a promising, cost-effective, and nature-based solution for removing persistent organic pollutants. This review summarizes the removal performance of PFASs in CWs, underlying PFASs removal mechanisms, and influencing factors are also discussed comprehensively. Furthermore, the environmental risks of PFASs-enriched plants and substrates in CWs are analyzed. The results show that removal efficiencies of total PFASs in various CWs ranged from 21.3% to 98%. Plant uptake, substrate absorption and biotransformation are critical pathways in CWs for removing PFASs, which can be influenced by the physiochemical properties of PFASs, operation parameters, environmental factors, and other pollutants. Increasing dissolved oxygen supply and replacing traditional substrates in CWs, and combining CWs with other technologies could significantly improve PFASs removal. Further, CWs pose relatively lower ecological and environmental risks in removing PFASs, which indicates CWs could be an alternative solution for controlling PFASs in aquatic environments.

Phenotypic Plasticity During Organofluorine Degradation Revealed by Adaptive Evolution

A major factor limiting the biodegradation of organofluorine compounds has been highlighted as fluoride anion toxicity produced by defluorinating enzymes. Here, two highly active defluorinases with different activities were constitutively expressed in Pseudomonas putida ATCC 12633 to examine adaption to fluoride stress. Each strain was grown on α-fluorophenylacetic acid as the sole carbon source via defluorination to mandelic acid, and each showed immediate fluoride release and delayed growth. Adaptive evolution was performed for each recombinant strain by serial transfer. Both strains adapted to show a much shorter lag and a higher growth yield. The observed adaptation occurred rapidly and reproducibly, within 50 generations each time. After adaption, growth with 50-70 mM α-fluorophenylacetic acid was significantly faster with more fluoride release than a preadapted culture due to larger cell populations. Genomic sequencing of both pre- and postadapted strain pairs revealed decreases in the defluorinase gene content. With both defluorinases, adaption produced a 56%-57% decrease in the plasmid copy number. Additionally, during adaption of the strain expressing the faster defluorinase, two plasmids were present: the original and a derivative in which the defluorinase gene was deleted. An examination of the enzyme rates in the pathway suggested that the defluorinase rate was concurrently optimised for pathway flux and minimising fluoride toxicity. The rapid alteration of plasmid copy number and mutation was consistent with other studies on microbial responses to stresses such as antibiotics. The data presented here support the idea that fluoride stress is significant during the biodegradation of organofluorine compounds and suggest engineered strains will be under strong selective pressure to decrease fluoride stress.

Occurrence and fate of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in an urban aquifer located at the Besòs River Delta (Spain)

Urban aquifers are at risk of contamination from persistent and mobile organic compounds (PMOCs), especially per- and polyfluoroalkyl substances (PFAS), which are artificial organic substances widely used across various industrial sectors. PFAS are considered toxic, mobile and persistent, and have therefore gained significant attention in environmental chemistry. Moreover, precursors could transform into more recalcitrant products under natural conditions. However, there is limited information about the processes which affect their behaviour in groundwater at the field-scale. In this context, the aim of this study is to assess the presence of PFAS in an urban aquifer in Barcelona, and identify processes that control their evolution along the groundwater flow. 21 groundwater and 6 river samples were collected revealing the presence of 16 PFAS products and 3 novel PFAS. Short and ultra-short chain PFAS were found to be ubiquitous, with the highest concentrations detected for perfluorobutanesulfonic acid (PFBS), trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TFSA). Long chain PFAS and novel PFAS were found to be present in very low concentrations (<50 ng/L). It was observed that redox conditions influence the behaviour of a number of PFAS controlling their attenuation or recalcitrant behaviour. Most substances showed accumulation, possibly explained by sorption/desorption processes or transformation processes, highlighting the challenges associated with PFAS remediation. In addition, the removal processes of different intensities for three PFAS were revealed. Our results help to establish the principles of the evolution of PFAS along the groundwater flow, which are important for the development of conceptual models used to plan and adopt site specific groundwater management activities (e.g., Managed Aquifer Recharge).

Bacterial degradation of perfluoroalkyl acids

Advances in biological degradation of per- and polyfluoroalkyl substances (PFAS) have shown that bioremediation is a promising method of PFAS mineralization; however, most of these studies focus on remediation of more reactive polyfluorinated compounds. This review focuses on the defluorination of the more recalcitrant perfluorinated alkyl acids (PFAAs) by bacteria. We highlight key studies that report PFAA degradation products, specific bacteria, and relevant genes. Among these studies, we discuss trends in anaerobic versus aerobic conditions with specific bacterial species or consortia. This holistic review seeks to elucidate the state of PFAA biodegradation research and discuss the need for future research for environmental application.

Burning question: Rethinking organohalide degradation strategy for bioremediation applications

Organohalides are widespread pollutants that pose significant environmental hazards due to their high degree of halogenation and elevated redox potentials, making them resistant to natural attenuation. Traditional bioremediation approaches, primarily relying on bioaugmentation and biostimulation, often fall short of achieving complete detoxification. Furthermore, the emergence of complex halogenated pollutants, such as per- and polyfluoroalkyl substances (PFASs), further complicates remediation efforts. Therefore, there is a pressing need to reconsider novel approaches for more efficient remediation of these recalcitrant pollutants. This review proposes novel redox-potential-mediated hybrid bioprocesses, tailored to the physicochemical properties of pollutants and their environmental contexts, to achieve complete detoxification of organohalides. The possible scenarios for the proposed bioremediation approaches are further discussed. In anaerobic environments, such as sediment and groundwater, microbial reductive dehalogenation coupled with fermentation and methanogenesis can convert organohalides into carbon dioxide and methane. In environments with anaerobic-aerobic alternation, such as paddy soil and wetlands, a synergistic process involving reduction and oxidation can facilitate the complete mineralization of highly halogenated organic compounds. Future research should focus on in-depth exploration of microbial consortia, the application of ecological principles-guided strategies, and the development of bioinspired-designed techniques. This paper contributes to the academic discourse by proposing innovative remediation strategies tailored to the complexities of organohalide pollution.

Synergistic material-microbe interface toward deeper anaerobic defluorination

Per- and polyfluoroalkyl substances (PFAS), particularly the perfluorinated ones, are recalcitrant to biodegradation. By integrating an enrichment culture of reductive defluorination with biocompatible electrodes for the electrochemical process, a deeper defluorination of a C6-perfluorinated unsaturated PFAS was achieved compared to the biological or electrochemical system alone. Two synergies in the bioelectrochemical system were identified: i) The in-series microbial-electrochemical defluorination and ii) the electrochemically enabled microbial defluorination of intermediates. These synergies at the material-microbe interfaces surpassed the limitation of microbial defluorination and further turned the biotransformation end products into less fluorinated products, which could be less toxic and more biodegradable in the environment. This material-microbe hybrid system brings opportunities in the bioremediation of PFAS driven by renewable electricity and warrants future research on mechanistic understanding of defluorinating and electroactive microorganisms at the material-microbe interface for system optimizations.

Electron bifurcation and fluoride efflux systems implicated in defluorination of perfluorinated unsaturated carboxylic acids by Acetobacterium spp

Enzymatic cleavage of C─F bonds in per- and polyfluoroalkyl substances (PFAS) is largely unknown but avidly sought to promote systems biology for PFAS bioremediation. Here, we report the reductive defluorination of α, β-unsaturated per- and polyfluorocarboxylic acids by Acetobacterium spp. The microbial defluorination products were structurally confirmed and showed regiospecificity and stereospecificity, consistent with their formation by enzymatic reactions. A comparison of defluorination activities among several Acetobacterium species indicated that a functional fluoride exporter was required for the detoxification of the released fluoride. Results from both in vivo inhibition tests and in silico enzyme modeling suggested the involvement of enzymes of the flavin-based electron-bifurcating caffeate reduction pathway [caffeoyl-CoA reductase (CarABCDE)] in the reductive defluorination. This is a report on specific microorganisms carrying out enzymatic reductive defluorination of PFAS, which could be linked to electron-bifurcating reductases that are environmentally widespread.

Surface Science View of Perfluoroalkyl Acids (PFAAs) in the Environment

Per- and polyfluoroalkyl substances (PFAS) constitute a notorious category of anthropogenic contaminants, detected across various environmental domains. Among these PFAS, perfluoroalkyl acids (PFAAs) stand out as a focal point in discussions due to their historical industrial utilization and environmental prominence. Their extensive industrial adoption is a direct consequence of their remarkable stability and outstanding amphiphilic properties. However, these very traits that have made PFAAs industrially desirable also render them environmentally catastrophic, leading to adverse consequences for ecosystems. The amphiphilic nature of PFAAs has made them highly unique in the landscape of anthropogenic contaminants and, thereby, difficult to study. We believe that well-established principles from surface science can connect the amphiphilic nature of PFAAs to their accumulation and transport in the environment. Specifically, we discuss the role of interfacial science in describing the stability, interfacial uptake (air-liquid and solid-liquid), and wetting capability of PFAAs. Surface science principles can provide new insights into the environmental fate of PFAAs, as well as provide context on their deleterious effects on both the environment and human health.

Defluorination of Organofluorine Compounds Using Dehalogenase Enzymes from Delftia acidovorans (D4B)

Organofluorine compounds have been widely used as pharmaceuticals, agricultural pesticides, and water-resistant coatings for decades; however, these compounds are recognized as environmental pollutants. The capability of microorganisms and enzymes to defluorinate organofluorine compounds is both rare and highly desirable to facilitate environmental remediation efforts. Recently, a strain of Delftia acidovorans (D4B) was identified with potential biodegradation activity toward perfluoroalkyl substances (PFAS) and other organofluorine compounds. Genomic analysis found haloacid and fluoroacetate dehalogenases as enzymes associated with Delftia acidovorans. Here, defluorination activity of these enzymes toward different fluorinated substrates was investigated after their recombinant expression and purification from E. coli. Using an electrochemical fluoride probe, 19F NMR, and mass spectrometry to monitor defluorination, we identified two dehalogenases, DeHa2 (a haloacid dehalogenase) and DeHa4 (a fluoroacetate dehalogenase), with activity toward mono- and difluoroacetate. Of the two dehalogenases, DeHa4 demonstrated a low pH optimum compared to DeHa2, which lost catalytic activity under acidic conditions. DeHa2 and DeHa4 are relatively small proteins, operate under aerobic conditions, and remain active for days in the presence of substrates. Significantly, while there have been many reports on dehalogenation of monofluoroacetate by dehalogenases, this study adds to the relatively small list of enzymes reported to carry out enzymatic defluorination of the more recalcitrant disubstituted carbon in an organofluorine compound. Thus, DeHa2 and DeHa4 represent organofluorine dehalogenases that may be used in the future to design and engineer robust defluorination agents for environmental remediation efforts.

Spatial and temporal distribution of perfluoroalkyl substances (PFAS) detected after an aqueous film forming foam (AFFF) spill

In 2015, > 460,000 L of aqueous film-forming foam (AFFF) and fire suppressors containing per- and polyfluoroalkyl substances (PFAS) were used to combat a fire at a petrochemical fuel storage terminal in the Port of Santos (Brazil). Sediments from seven sites were sampled repeatedly from 2 weeks to 1 year after the fire (n = 30). Ʃ15PFAS concentrations ranged from 115 to 15,931 pg g-1 dry weight (dw). Perfluorooctane sulfonic acid (PFOS) was the most frequently detected compound with concentrations ranging from 363 to 4517 (average = 1603) pg g-1dw to <47.1 to 642 (average = 401) pg g-1 dw, followed by perfluorohexanoic acid (PFHxA) (from 38.8 to 219 (average = 162) pg g-1 dw after 15 days and from <20.8 to 161 (average = 101) pg g-1 dw one year later). Together, the hydrodynamics and fire events documented in the region were important features explaining the spread of PFAS.

Defluorination of monofluorinated alkane by Rhodococcus sp. NJF-7 isolated from soil

Microbial degradation of fluorinated compounds raised significant attention because of their widespread distribution and potential environmental impacts. Here, we report a bacterial isolate, Rhodococcus sp. NJF-7 capable of defluorinating monofluorinated medium-chain length alkanes. This isolate consumed 2.29 ± 0.13 mmol L- 1 of 1-fluorodecane (FD) during a 52 h incubation period, resulting in a significant release of inorganic fluoride amounting to 2.16 ± 0.03 mmol L- 1. The defluorination process was strongly affected by the initial FD concentration and pH conditions, with lower pH increasing fluoride toxicity to bacterial cells and inhibiting enzymatic defluorination activity. Stoichiometric conversion of FD to fluoride was observed at neutral pH with resting cells, while defluorination was significantly lower at reduced pH (6.5). The discovery of the metabolites decanoic acid and methyl decanoate suggests that the initial attack by monooxygenases may be responsible for the biological defluorination of FD. The findings here provide new insights into microbial defluorination processes, specifically aiding in understanding the environmental fate of organic semi-fluorinated alkane chemicals.

Superb green cycling strategies for microbe-Fe0 neural network-type interaction: Harnessing eight key genes encoding enzymes and mineral transformations to efficiently treat PFOA

To address time-consuming and efficiency-limited challenges in conventional zero-valent iron (ZVI, Fe0) reduction or biotransformation for perfluorooctanoic acid (PFOA) treatment, two calcium alginate-embedded amendments (biochar-immobilized PFOA-degrading bacteria (CB) and ZVI (CZ)) were developed to construct microbe-Fe0 high-rate interaction systems. Interaction mechanisms and key metabolic pathways were systematically explored using metagenomics and a multi-process coupling model for PFOA under microbe-Fe0 interaction. Compared to Fe0 (0.0076 day-1) or microbe (0.0172 day-1) systems, the PFOA removal rate (0.0426 day-1) increased by 1.5 to 4.6 folds in the batch microbe-Fe0 interaction system. Moreover, Pseudomonas accelerated the transformation of Fe0 into Fe3+, which profoundly impacted PFOA transport and fate. Model results demonstrated microbe-Fe0 interaction improved retardation effect for PFOA in columns, with decreased dispersivity a (0.48 to 0.20 cm), increased reaction rate λ (0.15 to 0.22 h-1), distribution coefficient Kd (0.22 to 0.46 cm3∙g-1), and fraction f´(52 % to 60 %) of first-order kinetic sorption of PFOA in microbe-Fe0 interaction column system. Moreover, intermediates analysis showed that microbe-Fe0 interaction diversified PFOA reaction pathways. Three key metabolic pathways (ko00362, ko00626, ko00361), eight functional genes, and corresponding enzymes for PFOA degradation were identified. These findings provide insights into microbe-Fe0 "neural network-type" interaction by unveiling biotransformation and mineral transformation mechanisms for efficient PFOA treatment.

Maximum desorption of perfluoroalkyl substances adsorbed on granular activated carbon used in full-scale drinking water treatment plants

Activated carbon adsorption is an effective method for removing perfluoroalkyl substances (PFAS) from water. However, the observation that higher concentrations of PFAS are observed after treatment than before (i.e., desorption) is an important, unsolved issue. In this study, to elucidate PFAS desorption and its relationship with PFAS properties, we conducted solvent extraction and long-term desorption experiments using granular activated carbon (GAC) that had been loaded with PFAS in two actual drinking water treatment plants. The amount of PFAS extracted from GAC depended on the depth in the GAC filter; longer-chain and hydrophobic PFAS were present in relatively higher amounts in the shallow part compared to the deep part of the GAC filter, whereas shorter-chain and hydrophilic PFAS were present in relatively higher amounts in the deep part compared to the shallow part. This pattern was probably due to a chromatographic effect by which hydrophilic PFAS adsorbed once, subsequently desorbed, and migrated from the shallow part of the GAC filter to the deeper part. The desorption potential of PFAS to water (i.e., the maximum amount of PFAS desorbed to water per unit mass of GAC) was estimated by conducting long-term bottle-point desorption tests and analyzing the relationship between the equilibrium water-phase concentration of PFAS in a bottle containing GAC and the amount of PFAS desorbed to water per unit GAC mass. The desorption ratio (ratio of desorption potential to loading) was the highest for PFAS for which the logarithm of the octanol/water distribution coefficient (Log DOW) ranged from -1 to 1. The implication was that most of those PFAS removed by GAC were likely to return to the water as the external water-phase concentrations dropped. The decrease of the desorption ratio to 20 % as Log DOW increased suggested irreversible adsorption due to hydrophobic affinity.

Distinctive biotransformation and biodefluorination of 6:2 versus 5:3 fluorotelomer carboxylic acids by municipal activated sludge

Fluorotelomer carboxylic acids (FTCAs) represent an important group of per- and polyfluoroalkyl substances (PFAS) given their high toxicity, bioaccumulation potential, and frequent detection in landfill leachates and PFAS-impacted sites. In this study, we assessed the biodegradability of 6:2 FTCA and 5:3 FTCA by activated sludges from four municipal wastewater treatment plants (WWTPs) in the New York Metropolitan area. Coupling with 6:2 FTCA removal, significant fluoride release (0.56∼1.83 F-/molecule) was evident in sludge treatments during 7 days of incubation. Less-fluorinated transformation products (TPs) were formed, including 6:2 fluorotelomer unsaturated carboxylic acid (6:2 FTUCA), perfluorohexanoic acid (PFHxA), perfluoropentanoic acid (PFPeA), and perfluorobutanoic acid (PFBA). In contrast, little fluoride (0.01∼0.09 F-/molecule) was detected in 5:3 FTCA-dosed microcosms, though 25∼68% of initially dosed 5:3 FTCA was biologically removed. This implies the dominance of "non-fluoride-releasing pathways" that may contribute to the formation of CoA adducts or other conjugates over 5:3 FTCA biotransformation. The discovery of defluorinated 5:3 FTUCA revealed the possibility of microbial attacks of the C-F bond at the γ carbon to initiate the transformation. Microbial community analysis revealed the possible involvement of 9 genera, such as Hyphomicrobium and Dechloromonas, in aerobic FTCA biotransformation. This study unraveled that biotransformation pathways of 6:2 and 5:3 FTCAs can be divergent, resulting in biodefluorination at distinctive degrees. Further research is underscored to uncover the nontarget TPs and investigate the involved biotransformation and biodefluorination mechanisms and molecular basis.

Toward the development of a molecular toolkit for the microbial remediation of per-and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) are highly fluorinated synthetic organic compounds that have been used extensively in various industries owing to their unique properties. The PFAS family encompasses diverse classes, with only a fraction being commercially relevant. These substances are found in the environment, including in water sources, soil, and wildlife, leading to human exposure and fueling concerns about potential human health impacts. Although PFAS degradation is challenging, biodegradation offers a promising, eco-friendly solution. Biodegradation has been effective for a variety of organic contaminants but is yet to be successful for PFAS due to a paucity of identified microbial species capable of transforming these compounds. Recent studies have investigated PFAS biotransformation and fluoride release; however, the number of specific microorganisms and enzymes with demonstrable activity with PFAS remains limited. This review discusses enzymes that could be used in PFAS metabolism, including haloacid dehalogenases, reductive dehalogenases, cytochromes P450, alkane and butane monooxygenases, peroxidases, laccases, desulfonases, and the mechanisms of microbial resistance to intracellular fluoride. Finally, we emphasize the potential of enzyme and microbial engineering to advance PFAS degradation strategies and provide insights for future research in this field.

The "forever" per- and polyfluoroalkyl substances (PFAS): A critical accounting of global research on a major threat under changing regulations

The European Commission's current efforts to launch the largest proposal to restrict per- and polyfluoroalkyl substances (PFAS) in history reflect the dire global plight of PFAS accumulation in the environment and their health impacts. While there are existing studies on PFAS research, there is a lack of comprehensive analysis that both covers the entire research period and provides deep insights into global research patterns, incentives, and barriers based on various parameters. We have been able to demonstrate the increasing interest in PFAS research, although citation numbers are declining prematurely. Policy regulations based on proving and establishing the toxicity of PFASs have stimulated research in developed countries and vice versa, with increasing emphasis on ecological aspects. China, in particular, is investing increasingly in PFAS research, but without defining or implementing regulations - with devastating effects. The separation of industrial and environmental research interests is clear, with little involvement of developing countries, even though their exposure to PFAS is devastating. It, therefore, requires increased globally networked and multidisciplinary approaches to address PFAS contamination challenges.

Biotransformation of fluorinated drugs and xenobiotics by the model fungus Cunninghamella elegans

Some species of the genus Cunninghamella (C. elegans, C. echinulata and C. blaskesleeana) produce the same phase I and phase II metabolites when incubated with xenobiotics as mammals, and thus are considered microbial models of mammalian metabolism. This had made these fungi attractive for metabolism studies with drugs, pesticides and environmental pollutants. As a substantial proportion of pharmaceuticals and agrochemicals are fluorinated, their biotransformation has been studied in Cunninghamella fungi and C. elegans in particular. This article details the methods employed for cultivating the fungi in planktonic and biofilm cultures, and extraction and analysis of fluorinated metabolites. Furthermore, protocols for the heterologous expression of Cunninghamella cytochromes P450 (CYPs), which are the enzymes associated with phase I metabolism, are described.

Distribution characteristics and transformation mechanism of per- and polyfluoroalkyl substances in drinking water sources: A review

Per- and polyfluoroalkyl substances (PFASs) have raised significant concerns within the realm of drinking water due to their widespread presence in various water sources. This prevalence poses potential risks to human health, ecosystems, and the safety of drinking water. However, there is currently a lack of comprehensive reviews that systematically categorize the distribution characteristics and transformation mechanisms of PFASs in drinking water sources. This review aims to address this gap by concentrating on the specific sources of PFASs contamination in Chinese drinking water supplies. It seeks to elucidate the migration and transformation processes of PFASs within each source, summarize the distribution patterns of PFASs in surface and subsurface drinking water sources, and analyze how PFASs molecular structure, solubility, and sediment physicochemical parameters influence their presence in both the water phase and sediment. Furthermore, this review assesses two natural pathways for PFASs degradation, namely photolysis and biodegradation. It places particular emphasis on understanding the degradation mechanisms and the factors that affect the breakdown of PFASs by microorganisms. The ultimate goal is to provide valuable insights for the prevention and control of PFAS contamination and the assurance of drinking water quality.

Emergence of per- and poly-fluoroalkyl substances (PFAS) and advances in the remediation strategies

A group of fluorinated organic molecules known as per- and poly-fluoroalkyl substances (PFAS) have been commonly produced and circulated in the environment. PFAS, owing to multiple strong CF bonds, exhibit exceptional stability and possess a high level of resistance against biological or chemical degradation. Recently, PFAS have been identified to cause numerous hazardous effects on the biotic ecosystem. As a result, extensive efforts have been made in recent years to develop effective methods to remove PFAS. Adsorption, filtration, heat treatment, chemical oxidation/reduction, and soil washing are a few of the physicochemical techniques that have shown their ability to remove PFAS from contaminated matrixes. However these methods also carry significant drawbacks, including the fact that they are expensive, energy-intensive, unsuitable for in-situ treatment, and requirement to be carried under dormant conditions. The metabolic products released upon PFAS degradation are largely unknown, despite the fact that thermal disintegration methods are widely used. In contrast to physical and chemical methods, biological degradation of PFAS has been regarded as efficient method. However, PFAS are difficult to instantly and completely metabolize through biological methods due to the limitations of biocatalytic mechanisms. Nevertheless, cost, easy-to-operate and environmentally safe are some of the advantages over its counterpart. The present review comprehensively discusses the occurrence of PFAS, the state-of-the science of remediation technologies and approaches applied, and the remediation challenges. The article also focuses on the future research directions toward the development of effective methods for PFAS-contaminated site in-situ treatment.

Spatiotemporal successions of N, S, C, Fe, and As cycling genes in groundwater of a wetland ecosystem: Enhanced heterogeneity in wet season

Microorganisms in wetland groundwater play an essential role in driving global biogeochemical cycles. However, largely due to the dynamics of spatiotemporal surface water-groundwater interaction, the spatiotemporal successions of biogeochemical cycling in wetland groundwater remain poorly delineated. Herein, we investigated the seasonal coevolution of hydrogeochemical variables and microbial functional genes involved in nitrogen, carbon, sulfur, iron, and arsenic cycling in groundwater within a typical wetland, located in Poyang Lake Plain, China. During the dry season, the microbial potentials for dissimilatory nitrate reduction to ammonium and ammonification were dominant, whereas the higher potentials for nitrogen fixation, denitrification, methane metabolism, and carbon fixation were identified in the wet season. A likely biogeochemical hotspot was identified in the area located in the low permeable aquifer near the lake, characterized by reducing conditions and elevated levels of Fe2+ (6.65-17.1 mg/L), NH4+ (0.57-3.98 mg/L), total organic carbon (1.02-1.99 mg/L), and functional genes. In contrast to dry season, higher dissimilarities of functional gene distribution were observed in the wet season. Multivariable statistics further indicated that the connection between the functional gene compositions and hydrogeochemical variables becomes less pronounced as the seasons transition from dry to wet. Despite this transition, Fe2+ remained the dominant driving force on gene distribution during both seasons. Gene-based co-occurrence network displayed reduced interconnectivity among coupled C-N-Fe-S cycles from the dry to the wet season, underpinning a less complex and more destabilizing occurrence pattern. The rising groundwater level may have contributed to a reduction in the stability of functional microbial communities, consequently impacting ecological functions. Our findings shed light on microbial-driven seasonal biogeochemical cycling in wetland groundwater.

Comparative hepatotoxicity of novel lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, ie. HQ-115) and legacy Perfluorooctanoic acid (PFOA) in male mice: Insights into epigenetic mechanisms and pathway-specific responses

Lithium Bis(trifluoromethanesulfonyl)imide (LiTFSI ie. HQ-115), a polymer electrolyte used in energy applications, has been detected in the environment, yet its health risks and environmental epigenetic effects remain unknown. This study aims to unravel the potential health risks associated with LiTFSI, investigate the role of DNA methylation-induced toxic mechanisms in its effects, and compare its hepatotoxic impact with the well-studied Perfluorooctanoic Acid (PFOA). Using a murine model, six-week-old male CD1 mice were exposed to 10 and 20 mg/kg/day of each chemical for 14 days as 14-day exposure and 1 and 5 mg/kg/day for 30 days as 30-day exposure. Results indicate that PFOA exposure induced significant hepatotoxicity, characterized by liver enlargement, and elevated serum biomarkers. In contrast, LiTFSI exposure showed lower hepatotoxicity, accompanied by mild liver injuries. Despite higher bioaccumulation of PFOA in serum, LiTFSI exhibited a similar range of liver concentrations compared to PFOA. Reduced Representative Bisulfite Sequencing (RRBS) analysis revealed distinct DNA methylation patterns between 14-day and 30-day exposure for the two compounds. Both LiTFSI and PFOA implicated liver inflammatory pathways and lipid metabolism. Transcriptional results showed that differentially methylated regions in both exposures are enriched with cancer/disease-related motifs. Furthermore, Peroxisome proliferator-activated receptor alpha (PPARα), a regulator of lipid metabolism, was upregulated in both exposures, with downstream genes indicating potential oxidative damages. Overall, LiTFSI exhibits distinct hepatotoxicity profiles, emphasizing the need for comprehensive assessment of emerging PFAS compounds.

Enzymatic defluorination of a terminally monofluorinated pentyl moiety: oxidative or hydrolytic mechanism?

Fluorination of organic compounds plays an important role in the chemical and pharmaceutical industry and is often applied in order to improve physicochemical parameters or modify pharmacological properties. While oxidative and reductive defluorination have been shown to be responsible for the metabolic degradation of organofluorine compounds, the involvement of hydrolytic mechanisms catalyzed by human enzymes has not been reported so far. Here, we investigated the enzymatic defluorination of terminally monofluorinated aliphates with [1-(5-fluoropentyl)-1H-indol-3-yl]-1-naphthalenyl-methanone (AM-2201) as a model substance. We performed in vitro biotransformation using pooled human liver microsomes (pHLM) and human recombinant cytochrome P450 (CYP) assays. In order to elucidate the underlying mechanisms, modified incubation conditions were applied including the use of deuterium labeled AM-2201 (d2 -AM-2201). Identification of the main metabolites and analysis of their isotopic composition was performed by liquid-chromatography coupled to time-of-flight-mass-spectrometry (LC-QToF-MS). Quantification of the metabolites was achieved with a validated method based on liquid-chromatography-tandem-mass-spectrometry (LC-MS/MS). CYP 1A2 mediated defluorination of d2 -AM-2201 revealed an isotopic pattern of the defluorinated 5-hydroxypentyl metabolite (5-HPM) indicating a redox mechanism with an aldehyde as a plausible intermediate. In contrast, formation of 5-HPM by pHLM was observed independently of the presence of atmospheric oxygen or co-factors regenerating the redox system. pHLM incubation of d2 -AM-2201 confirmed the hypothesis of a non-oxidative mechanism involved in the defluorination of the 5-fluoropentyl moiety. So far, enzymatically catalyzed, hydrolytic defluorination was only described in bacteria and other prokaryotes. The presented data prove the involvement of a hydrolytic mechanism catalyzed by human microsomal enzymes other than CYP. Significance Statement Elucidating the mechanisms involved in the enzymatic detoxification of organofluorine compounds is crucial for enhancing our understanding and facilitating the design and development of drugs with improved pharmacokinetic profiles. The carbon-fluorine bond possesses a high binding energy, which suggests that non-activated fluoroalkanes would not undergo hydrolytic cleavage. However, our study provides evidence for the involvement of a non-oxidative mechanism catalyzed by human liver enzymes. It is important to consider CYP-independent, hydrolytic defluorination, when investigating the pharmacokinetic properties of fluorinated xenobiotics.

Defluorination as the key trait to gauge the biodegradability of fluorinated pollutants in environmental microbial communities

Research on microbial defluorination is largely centred on controlled experiments using axenic or well defined microbial inocula. These approaches serve a relevant purpose in the field, offering fundamental biochemical and mechanistic insights on the intricacies of biological defluorination. However, they fail to account for the effective contribution of environmental microbial communities in the recycling of fluoroorganic pollutants, a highly relevant perspective from an environmental risk assessment standpoint, while also missing an important outlook on how community-wide dynamics can leverage the breakdown of C─F bonds in these recalcitrant compounds. With that in mind, this chapter provides experimental and methodological insights on the study of microbial defluorination in wild environmental communities, using this critical catabolic step as the de facto endpoint to evolve, select and cultivate microorganisms with improved defluorination performances.

Recombinant Pseudomonas growing on non-natural fluorinated substrates shows stress but overall tolerance to cytoplasmically released fluoride anion

IMPORTANCE

Society uses thousands of organofluorine compounds, sometimes denoted per- and polyfluoroalkyl substances (PFAS), in hundreds of products, but recent studies have shown some to manifest human and environmental health effects. As a class, they are recalcitrant to biodegradation, partly due to the paucity of fluorinated natural products to which microbes have been exposed. Another limit to PFAS biodegradation is the intracellular toxicity of fluoride anion generated from C-F bond cleavage. The present study identified a broader substrate specificity in an enzyme originally studied for its activity on the natural product fluoroacetate. A recombinant Pseudomonas expressing this enzyme was used here as a model system to better understand the limits and effects of a high level of intracellular fluoride generation. A fluoride stress response has evolved in bacteria and has been described in Pseudomonas spp. The present study is highly relevant to organofluorine compound degradation or engineered biosynthesis in which fluoride anion is a substrate.

Electron-bifurcation and fluoride efflux systems in Acetobacterium spp. drive defluorination of perfluorinated unsaturated carboxylic acids

Enzymatic cleavage of C-F bonds in per- and polyfluoroalkyl substances (PFAS) is largely unknown but avidly sought to promote systems biology for PFAS bioremediation. Here, we report the reductive defluorination of α, β-unsaturated per- and polyfluorocarboxylic acids by Acetobacterium spp. Two critical molecular features in Acetobacterium species enabling reductive defluorination are (i) a functional fluoride efflux transporter (CrcB) and (ii) an electron-bifurcating caffeate reduction pathway (CarABCDE). The fluoride transporter was required for detoxification of released fluoride. Car enzymes were implicated in defluorination by the following evidence: (i) only Acetobacterium spp. with car genes catalyzed defluorination; (ii) caffeate and PFAS competed in vivo ; (iii) models from the X-ray structure of the electron-bifurcating reductase (CarC) positioned the PFAS substrate optimally for reductive defluorination; (iv) products identified by 19 F-NMR and high-resolution mass spectrometry were consistent with the model. Defluorination biomarkers identified here were found in wastewater treatment plant metagenomes on six continents.

Genome-Wide Expression Analysis Unravels Fluoroalkane Metabolism in Pseudomonas sp. Strain 273

Pseudomonas sp. strain 273 grows with medium-chain terminally fluorinated alkanes under oxic conditions, releases fluoride, and synthesizes long-chain fluorofatty acids. To shed light on the genes involved in fluoroalkane metabolism, genome, and transcriptome sequencing of strain 273 grown with 1,10-difluorodecane (DFD), decane, and acetate were performed. Strain 273 harbors three genes encoding putative alkane monooxygenases (AlkB), key enzymes for initiating alkane degradation. Transcripts of alkB-2 were significantly more abundant in both decane- and DFD-grown cells compared to acetate-grown cells, suggesting AlkB-2 catalyzes the attack on terminal CH3 and CH2F groups. Coordinately expressed with alkB-2 was an adjacent gene encoding a fused ferredoxin-ferredoxin reductase (Fd-Fdr). Phylogenetic analysis distinguished AlkB that couples with fused Fd-Fdr reductases from AlkB with alternate architectures. A gene cluster containing an (S)-2-haloacid dehalogenase (had) gene was up-regulated in cells grown with DFD, suggesting a possible role in the removal of the ω-fluorine. Genes involved in long-chain fatty acid biosynthesis were not differentially expressed during growth with acetate, decane, or DFD, suggesting the bacterium's biosynthetic machinery does not discriminate against monofluoro-fatty acid intermediates. The analysis sheds first light on genes and catalysts involved in the microbial metabolism of fluoroalkanes.

Structural insights into hydrolytic defluorination of difluoroacetate by microbial fluoroacetate dehalogenases

Fluorine forms the strongest single bond to carbon with the highest bond dissociation energy among natural products. However, fluoroacetate dehalogenases (FADs) have been shown to hydrolyze this bond in fluoroacetate under mild reaction conditions. Furthermore, two recent studies demonstrated that the FAD RPA1163 from Rhodopseudomonas palustris can also accept bulkier substrates. In this study, we explored the substrate promiscuity of microbial FADs and their ability to defluorinate polyfluorinated organic acids. Enzymatic screening of eight purified dehalogenases with reported fluoroacetate defluorination activity revealed significant hydrolytic activity against difluoroacetate in three proteins. Product analysis using liquid chromatography-mass spectrometry identified glyoxylic acid as the final product of enzymatic DFA defluorination. The crystal structures of DAR3835 from Dechloromonas aromatica and NOS0089 from Nostoc sp. were determined in the apo-state along with the DAR3835 H274N glycolyl intermediate. Structure-based site-directed mutagenesis of DAR3835 demonstrated a key role for the catalytic triad and other active site residues in the defluorination of both fluoroacetate and difluoroacetate. Computational analysis of the dimer structures of DAR3835, NOS0089, and RPA1163 indicated the presence of one substrate access tunnel in each protomer. Moreover, protein-ligand docking simulations suggested similar catalytic mechanisms for the defluorination of both fluoroacetate and difluoroacetate, with difluoroacetate being defluorinated via two consecutive defluorination reactions producing glyoxylate as the final product. Thus, our findings provide molecular insights into substrate promiscuity and catalytic mechanism of FADs, which are promising biocatalysts for applications in synthetic chemistry and bioremediation of fluorochemicals.

Aryl (β,β',β″-Trifluoro)-tert-butyl: A Candidate Motif for the Discovery of Bioactives

The (β,β',β″-trifluoro)-tert-butyl (TFTB) group has received very little attention in the literature. This work presents a direct synthesis of this group and explores its properties. The TFTB group arises when the methyl groups of a tert-butyl moiety are exchanged for fluoromethyl groups. Sequential fluoromethylations result in a decrease of Log P (increasing hydrophilicity), ultimately by 1.7 Log P units in the TFTB group relative to that of tert-butyl benzene itself. A focus is placed on synthetic transformations, conformational analysis, and metabolism of the TFTB group in the context of presenting a favorable profile as a motif for the discovery of bioactives.

Querying the In Vitro Proteome Cysteine Reactivity of 8:2 Fluorotelomer Acrylate

Despite the phase out of legacy per- and polyfluoroalkyl substances (PFAS), fluorotelomer-based polymers (FTP) have been used for many applications, notably textile surface coatings. FTPs are of a health concern due to their breakdown into legacy PFAS and the co-occurrence of fluorotelomer acrylate (FTAC) monomers, of which the latter may potentially react with cellular thiols. To evaluate this hypothesis, we employed fluorous-solid-phase extraction (FSPE), to enrich peptides covalently modified by 8:2 fluorotelomer acrylate (8:2 FTAC) and coupled it to a modified nano-liquid chromatography method for the identification of in vitro protein adducts using bottom-up data-dependent proteomics analysis. Using this method, over 100 unique peptides were detected with 8:2 FTAC modifications, although none of the modified cysteine residues were annotated active site nucleophiles. In parallel, a synthetic C6F13-iodoacetamide (F13-IAM) chemical probe was used to gauge the upper bound of PFAS-thiol reactivity. Over seven hundred peptides were detected with modifications but only 9 of 28 annotated active site cysteines in this dataset were modified by F13-IAM. Further exploration of the impacts of 8:2 FTAC adducts on protein function revealed that 8:2 FTAC modification promotes protein aggregation in vitro. These results suggest that 8:2 FTAC may exhibit significant proteome thiol reactivity and imply a more general mechanism of toxicity of PFAS-induced protein aggregation.

The effects of per- and polyfluoroalkyl substances on environmental and human microorganisms and their potential for bioremediation

Utilised in a variety of consumer products, per- and polyfluoroalkyl substances (PFAS) are major environmental contaminants that accumulate in living organisms due to their highly hydrophobic, lipophobic, heat-resistant, and non-biodegradable properties. This review summarizes their effects on microbial populations in soils, aquatic and biogeochemical systems, and the human microbiome. Specific microbes are insensitive to and even thrive with PFAS contamination, such as Escherichia coli and the Proteobacteria in soil and aquatic environments, while some bacterial species, such as Actinobacteria and Chloroflexi, are sensitive and drop in population. Some bacterial species, in turn, have shown success in PFAS bioremediation, such as Acidimicrobium sp. and Pseudomonas parafulva.

Sequestration of steroidal estrogen in aqueous samples using an adsorption mechanism: a systemic scientometric review

Steroidal estrogens (SEs) remain one of the notable endocrine disrupting chemicals (EDCs) that pose a significant threat to the aquatic environment in this era owing to their interference with the normal metabolic functions of the human body systems. They are currently identified as emerging contaminants of water sources. The sources of SEs are either natural or synthetic active ingredients in oral contraceptive and hormonal replacement therapy drugs and enter the environment primarily from excretes in the form of active free conjugate radicals, resulting in numerous effects on organisms in aquatic habitats and humans. The removal of SEs from water sources is of great importance because of their potential adverse effects on aquatic ecosystems and human health. Adsorption techniques have gained considerable attention as effective methods for the removal of these contaminants. A systemic review and bibliometric analysis of the application of adsorption for sequestration were carried out. Metadata for publications on SE removal utilizing adsorbents were obtained from the Web of Science (WoS) from January 1, 1990, to November 5, 2022 (107 documents) and Scopus databases from January 1, 1949, to November 5, 2022 (77 documents). In total, 137 documents (134 research and 4 review articles) were used to systematically map bibliometric indicators, such as the number of articles, most prolific countries, most productive scholars, and most cited articles, confirming this to be a growing research area. The use of different adsorbents, include activated carbon graphene-based materials, single and multi-walled carbon nanotubes, biochar, zeolite, and nanocomposites. The adsorption mechanism and factors affecting the removal efficiency, such as pH, temperature, initial concentration, contact time and adsorbent properties, were investigated in this review. This review discusses the advantages and limitations of different adsorbents, including their adsorption capacities, regenerative potential, and cost-effectiveness. Recent advances and innovations in adsorption technology, such as functionalized materials and hybrid systems, have also been highlighted. Overall, the bibliographic analysis provides a comprehensive overview of the adsorption technique for the removal of SEs from other sources, serving as a valuable resource for researchers and policymakers involved in the development of efficient and sustainable strategies to mitigate the effects of these emerging contaminants.

Enhanced biodegradation of perfluorooctanoic acid in a dual biocatalyzed microbial electrosynthesis system

The toxic perfluorooctanoic acid (PFOA) is widely spread in terrestrial and aquatic habitats owing to its resistance to conventional degradation processes. Advanced techniques to degrade PFOA requires drastic conditions with high energy cost. In this study, we investigated PFOA biodegradation in a simple dual biocatalyzed microbial electrosynthesis system (MES). Different PFOA loadings (1, 5, and 10 ppm) were tested and a biodegradation of 91% was observed within 120 h. Propionate production improved and short-carbon-chain PFOA intermediates were detected, which confirmed PFOA biodegradation. However, the current density decreased, indicating an inhibitory effect of PFOA. High-throughput biofilm analysis revealed that PFOA regulated the microbial flora. Microbial community analysis showed enrichment of the more resilient and PFOA adaptive microbes, including Methanosarcina and Petrimonas. Our study promotes the potential use of dual biocatalyzed MES system as an environment-friendly and inexpensive method to remediate PFOA and provides a new direction for bioremediation research.

Microbial and thermal treatment techniques for degradation of PFAS in biosolids: A focus on degradation mechanisms and pathways

Per- and polyfluoroalkyl substances (PFAS) are persistent organic chemicals detected in biosolids worldwide, which have become a significant concern for biosolids applications due to their increasing environmental risks. Hence, it is pivotal to understand the magnitude of PFAS contamination in biosolids and implement effective technologies to reduce their contamination and prevent hazardous aftermaths. Thermal techniques such as pyrolysis, incineration and gasification, and biodegradation have been regarded as impactful solutions to degrade PFAS and transform biosolids into value-added products like biochar. These techniques can mineralize PFAS compounds under specific operating parameters, which can lead to unique degradation mechanisms and pathways. Understanding PFAS degradation mechanisms can pave the way to design the technology and to optimize the process conditions. Therefore, in this review, we aim to review and compare PFAS degradation mechanisms in thermal treatment like pyrolysis, incineration, gasification, smouldering combustion, hydrothermal liquefaction (HTL), and biodegradation. For instance, in biodegradation of perfluorooctane sulfonic acid (PFOS), firstly C-S bond cleavage occurs which is followed by hydroxylation, decarboxylation and defluorination reactions to form perfluoroheptanoic acid. In HTL, PFOS degradation is carried through OH^-catalyzed series of nucleophilic substitution and decarboxylation reactions. In contrast, thermal PFOS degradation involves a three-step random-chain scission pathway. The first step includes C-S bond cleavage, followed by defluorination of perfluoroalkyl radical, and radical chain propagation reactions. Finally, the termination of chain propagation reactions produces very short-fluorinated units. We also highlighted important policies and strategies employed worldwide to curb PFAS contamination in biosolids.

A review on simultaneous heavy metal removal and organo-contaminants degradation by potential microbes: Current findings and future outlook

Industrial processes result in the production of heavy metals, dyes, pesticides, polyaromatic hydrocarbons (PAHs), pharmaceuticals, micropollutants, and PFAS (per- and polyfluorinated substances). Heavy metals are currently a significant problem in drinking water and other natural water bodies, including soil, which has an adverse impact on the environment as a whole. The heavy metal is highly poisonous, carcinogenic, mutagenic, and teratogenic to humans as well as other animals. Multiple polluted sites, including terrestrial and aquatic ecosystems, have been observed to co-occur with heavy metals and organo-pollutants. Pesticides and heavy metals can be degraded and removed concurrently from various metals and pesticide-contaminated matrixes due to microbial processes that include a variety of bacteria, both aerobic and anaerobic, as well as fungi. Numerous studies have examined the removal of heavy metals and organic-pollutants from different types of systems, but none of them have addressed the removal of these co-occurring heavy metals and organic pollutants and the use of microbes to do so. Therefore, the main focus of this review is on the recent developments in the concurrent microbial degradation of organo-pollutants and heavy metal removal. The limitations related to the simultaneous removal and degradation of heavy metals and organo-pollutant pollutants have also been taken into account.

Substantial defluorination of polychlorofluorocarboxylic acids triggered by anaerobic microbial hydrolytic dechlorination

Chlorinated polyfluorocarboxylic acids (Cl-PFCAs) derived from the widely used chlorotrifluoroethylene (CTFE) polymers and oligomers may enter and influence the aquatic environment. Here, we report significant defluorination of Cl-PFCAs by an anaerobic microbial community via novel pathways triggered by anaerobic microbial dechlorination. Cl-PFCAs first underwent microbial reductive, hydrolytic, and eliminative dechlorination, and it was the hydrolytic dechlorination that led to significant spontaneous defluorination. Hydrolytic dechlorination was favored with increased Cl-substitutions. An isolated, highly enriched anaerobic defluorinating culture was dominated by two genomes closest to Desulfovibrio aminophilus and Sporomusa sphaeroides, both of which exhibited active defluorination of CTFE tetramer acid. It implies the critical role played by anaerobic non-respiratory hydrolytic dechlorination in the fate of chlorinated polyfluoro-chemicals in natural and engineered water environments. The greatly enhanced biodegradability by Cl-substitutions also sheds light on the design of cost-effective treatment biotechnologies, as well as alternative PFAS that are readily biodegradable and less toxic.

Modeling the kinetics of perfluorooctanoic and perfluorooctane sulfonic acid biodegradation by Acidimicrobium sp. Strain A6 during the feammox process

Per- and polyfluoroalkyl substances (PFAS) are emerging contaminants of concern due to their health effects and persistence in the environment. Although perfluoroalkyl acids (PFAAs), such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are very difficult to biodegrade because they are completely saturated with fluorine, it has recently been shown that Acidimicrobium sp. A6 (A6), which oxidizes ammonium under iron reducing conditions (Feammox process), can defluorinate PFAAs. A kinetic model was developed and tested in this study using results from previously published laboratory experiments, augmented with results from additional incubations, to couple the Feammox process to PFAS defluorination. The experimental results show higher Feammox activity and PFAS degradation in the A6 enrichment cultures than in the highly enriched A6 cultures. The coupled experimental and modeling results show that the PFAS defluorination rate is proportional to the rate of ammonium oxidation. The ammonium oxidation rate and the defluorination rate increase monotonically, but not linearly, with increasing A6 biomass. Given that different experiments had different level of Feammox activity, the parameters required to simulate the Feammox varied between A6 cultures. Nonetheless, the kinetic model was able to simulate an anaerobic incubation system and show that PFAS defluorination is proportional to the Feammox activity.

Enhancement of perfluorooctanoic acid and perfluorooctane sulphonic acid removal in constructed wetland using iron mineral: Performance and mechanisms

Polyfluoroalkyl substance (PFAS) pose a threat to the aquatic environment due to their environmental persistence. The removal of PFAS using constructed wetlands (CWs) has received interest, but the adsorption saturation and limited removal capacity of the substrate is frequently challenging. To enhance the microbial degradation and performance of the substrate, different configurations of iron minerals were used as substrate to remove perfluorooctane sulphonic acid (PFOS) and perfluorooctanoic acid (PFOA) from CWs. The addition of iron minerals resulted in elimination of 57.2% and 63.9% of PFOS and PFOA in the effluent, respectively, which were 35.0% and 36.8% higher than that of control. Moreover, up to 85.4%, 86%, and 85.1% of NH₄⁺, NO₃^-, and phosphorus, respectively, was removed using iron minerals. The enhanced electron transfer in iron mineral-based CWs was confirmed by a 61.2% increase in cytochrome C reductase content and an increased Fe(III)/Fe(II) ratio. Microbial analysis showed that the proportions of microbes with PFAS removal capacity (e.g. Burkholderiae and Pseudomonas), and the key pathways of the TCA cycle and glycolysis were increased in iron mineral-based CW. Based on these findings, we conclude that supplementation with iron mineral could enhance PFOA and PFOS removal in CWs.

Impact of biological activated carbon filtration and backwashing on the behaviour of PFASs in drinking water treatment plants

PFASs are present in surface water, tap water and even commercial drinking water and pose a risk to human health. In this study, the treatment efficiency of 14 PFASs was studied in a large drinking water treatment plant (DWTP) using Taihu Lake as the source, and it was found that the ozone/biological activated carbon (O₃-BAC) process was the most effective process for the removal of PFASs in DWTPs. For the O₃-BAC process, there were differences in the removal of PFASs by BACs (1,4,7,13 years) of different ages. The sterilization experiments revealed that for GAC, its physical adsorption capacity reached saturation after one year, while for BAC with mature biofilms, biosorption was the main mechanism for the removal of PFASs. The abundance of Alphaproteobacteria and Gammaproteobacteria in biofilms was positively correlated with the age of the BAC. The microbial community with higher abundance is beneficial to the biodegradation of organic matter and thus provides more active sites for the adsorption of PFASs. PFASs can leak in the early stage of filtration after backwashing, so it is necessary to pay close attention to the influent and effluent concentrations of PFASs during biofilm maturation after backwashing.

The fate and behavior of perfluorooctanoic acid (PFOA) in constructed wetlands: Insights into potential removal and transformation pathway

Although constructed wetland (CW) technology is widely used to eliminate emerging organic pollutants, the removal pathway of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in CW system have not been fully understood yet. This study aims to deeply probe into the fate and behavior of perfluorooctanoic acid (PFOA) in CW system. Findings indicated that the removal efficiency of PFOA by CW system was 49.69-73.63 % with initial concentrations at 100-1000 μg/L. Substrate was the main "sink" of PFOA into the CWs (46.22-50.83 %), and the plant uptake (1.99-2.48 %) accounted for a small proportion. Transformation products in the effluent of CW systems included a series of short-chain perfluorinated carboxylic acids (PFCAs), hydrogen-containing perfluoroalkanes and other organic fluorides. Activated pathways of xenobiotics biodegradation suggested that enzyme-mediated biochemical reactions might be responsible for the PFOA transformation. The transformation pathway included enzymatic decarboxylation, hydroxylation, hydrolysis, dehydrogenation and dehalogenation, as well as non-enzymatic reactions. These discoveries provide new insights into the in-depth understanding environmental behavior of PFOA in ecosystem and lay the foundation for further ecological remediation.

A review of microbial degradation of per- and polyfluoroalkyl substances (PFAS): Biotransformation routes and enzymes

Since the 1950s, copious amounts of per- and polyfluoroalkyl substances (PFAS) (dubbed "forever chemicals") have been dumped into the environment, causing heavy contamination of soil, surface water, and groundwater sources. Humans, animals, and the environment are frequently exposed to PFAS through food, water, consumer products, as well as waste streams from PFAS-manufacturing industries. PFAS are a large group of synthetic organic fluorinated compounds with widely diverse chemical structures that are extremely resistant to microbial degradation. Their persistence, toxicity to life on earth, bioaccumulation tendencies, and adverse health and ecological effects have earned them a "top priority pollutant" designation by regulatory bodies. Despite that a number of physicochemical methods exist for PFAS treatment, they suffer from major drawbacks regarding high costs, use of high energy and incomplete mineralization (destruction of the CF bond). Consequently, microbial degradation and enzymatic treatment of PFAS are highly sought after as they offer a complete, cheaper, sustainable, and environmentally friendly alternative. In this critical review, we provide an overview of the classification, properties, and interaction of PFAS within the environment relevant to microbial degradation. We discuss latest developments in the biodegradation of PFAS by microbes, transformation routes, transformation products and degradative enzymes. Finally, we highlight the existing challenges, limitations, and prospects of bioremediation approaches in treating PFAS and proffer possible solutions and future research directions.

Fluorotelomer alcohols are efficiently biotransformed by Cunninghamella elegans

Cunninghamella elegans is a well-studied fungus that biotransforms a range of xenobiotics owing to impressive cytochrome P450 (CYP) activity. In this paper, we report the biotransformation of 6:2 fluorotelomer alcohol (6:2 FTOH) by the fungus, yielding a range of fluorinated products that were detectable by fluorine-19 nuclear magnetic resonance spectroscopy (¹⁹F NMR), gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). Upon incubation with the pre-grown cultures, the substrate (100 mg/L) was completely consumed within 48 h, which is faster biotransformation than other fungi that have hitherto been studied. The main metabolite formed was the 5:3 fluorotelomer carboxylic acid (5:3 FTCA), which accumulated in the culture supernatant. When the cytochrome P450 inhibitor 1-aminobenzotriazole was included in the culture flasks, there was no biotransformation of 6:2 FTOH, indicating that these enzymes are key to the catalysis. Furthermore, when exogenous 5:3 FTCA was added to the fungus, the standard biotransformation of the drug flurbiprofen was inhibited, strongly suggesting that the main fluorotelomer alcohol biotransformation product inhibits CYP activity and accounts for its accumulation.