Biotransformation of 6:2 fluorotelomer alcohol by the whole soybean (Glycine max L. Merrill) seedlings

Removal of 48 per- and polyfluoroalkyl substances (PFAS) throughout processes in domestic and general industrial wastewater treatment plants: Implications for emerging alternatives risk control

Wastewater acts as a significant sink and source of per- and polyfluoroalkyl substances (PFAS). This study investigated the occurrence, removal and mass flow of 48 emerging and legacy PFAS in 8 domestic and general industrial wastewater treatment plants (WWTPs) throughout entire treatment processes. In wastewater and sludge, 24 and 26 PFAS were detected, with concentrations of 246-27,100 ng/L and 91.6-214 ng/g, respectively. Predominant substances included 2H,2H-perfluorooctanoic acid (6:2 FTCA), 2H,2H-perfluorododecanoic acid (10:2 FTCA), and perfluorooctanoic acid (PFOA). Novel alternatives such as hexafluoropropylene oxide dimer acid (GenX) were not detected. Removal efficiency of total PFAS was 1-46 % in domestic WWTPs but negative in industrial WWTPs, with one industrial WWTP showing a 27-fold increase due to 6:2 FTCA generation. Median removal efficiency revealed that 9 out of 13 major PFAS decreased after treatment, while 4 increased. PFAS with -CH2- group showed weaker sludge sorption compared to those with perfluorinated carbon chains. Mass flow analysis revealed wastewater is the major fate rather than sludge for emerging PFAS. Increased mass flows of fluorotelomer carboxylic acids (FTCAs) and perfluorobutanesulfonic acid (PFBS) were observed at biochemical treatment and disinfection. The ecological risk assessment using a relative risk ranking model identified higher risks from PFBS, polyfluoroalkyl phosphate mono-esters, and FTCAs. Emerging PFAS pose challenges in removal and greater hazards to ecosystems, necessitating careful evaluation and restriction to address their risk.

Ecological risk of per-and polyfluorinated alkyl substances in the phytoremediation process: a case study for ecologically keystone species across two generations

The potential ecological risk of per- and polyfluorinated alkyl substances (PFASs) in phytoremediation has raised social concerns, promoting a need to better understand their distribution and risks in the recovery process of aquatic plants. Herein, we aim to fill this knowledge gap by investigating the distribution and ecotoxicological effects of PFASs on the structure and function of water-macrophyte-sediment microcosm systems. Among the entire system, 63.0 %-73.1 % PFOA was found in sediments and submerged plants, however, 52.5 %-53.0 % of PFPeA and 47.0 %-47.5 % of PFBS remained in the water under different treatments. PFOA was more bioavailable than the other substances, as demonstrated by the bioaccumulation factors (BAF) with ranges exposed to PFPeA and PFBS. Bioaccumulation PFASs induced plant oxidative stress which generates enzymes to suppress superoxide, and disturbed the processes of lysine biosynthesis, in which allysine, meso-2,6-diaminoheptanedioate, and Nsuccinyl-2-amino-6-ketopimelate were downregulated. PFASs were detected in the propagator (turions) of an ecological restoration species, where short-chain PFASs (70.1 % and 45.7 % for 2 or 20 μg/L PFAS exposure, respectively) were found to spread further into new individuals and profoundly influence ecological processes shaping populations. PFASs significantly enhanced the number of microbial species in the sediment, but the degree of differentiation in the microbial community structure was not significantly different. This study enhances our understanding of the ecological mechanisms of PFASs in the water-macrophyte-sediment systems and potential threats to the recovery process of macrophytes.

Biotransformation of 6:2/4:2 fluorotelomer alcohols by Dietzia aurantiaca J3: Enzymes and proteomics

Per- and polyfluoroalkyl substances (PFAS) are recalcitrant synthetic organohalides known to negatively impact human health. Short-chain fluorotelomer alcohols are considered the precursor of various perfluorocarboxylic acids (PFCAs) in the environment. Their ongoing production and widespread detection motivate investigations of their biological transformation. Dietzia aurantiaca strain J3 was isolated from PFAS-contaminated landfill leachate using 6:2 fluorotelomer sulphonate (6:2 FTS) as a sulphur source. Resting cell experiments were used to test if strain J3 could transform fluorotelomer alcohols (6:2 and 4:2 FTOH). Strain J3 transformed fluorotelomer alcohols into PFCAs, polyfluorocarboxylic acids and transient intermediates. Over 6 days, 80 % and 58 % of 6:2 FTOH (0.1 mM) and 4:2 FTOH (0.12 mM) were degraded with 6.4 % and 14 % fluoride recovery respectively. Fluorotelomer unsaturated carboxylic acid (6:2 FTUCA) was the most abundant metabolite, accounting for 21 to 30 mol% of 6:2 FTOH (0.015 mM) applied on day zero. Glutathione (GSH) conjugates of 6:2/4:2 FTOH and 5:3 FTCA adducts were also structurally identified. Proteomics studies conducted to identify enzymes in the biotransformation pathway have revealed the role of various enzymes involved in β oxidation. This is the first report of 6:2/4:2 FTOH glutathione conjugates and 5:3 FTCA adducts in prokaryotes, and the first study to explore the biotransformation of 4:2 FTOH by pure bacterial strain.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) and nutrients from two constructed wetlands in a city of southeastern China

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a large class of toxic contaminants. Nutrients are closely related to the ecological health of aquatic systems. Both have received widespread global attention. This study investigated the concentrations, compositions, and spatial distributions of PFAS and nutrients in surface water from two constructed wetlands and the nearby drinking water treatment plants (DWTPs). We explored the natural environmental factors and human activities that affect the composition and distribution of pollutants in wetlands and assessed the ability of the DWTPs to remove contaminants. Concentrations of ∑32PFAS varied from 153 to 405 ng/L. Hexafluoropropylene oxide trimer acid (HFPO-TA) was the predominant substance accounting for 45 % of ∑32PFAS concentrations. It might originate from the emissions of indirect sources of PFAS related manufacturers. The detection rate of 6:2 fluorotelomer carboxylic acid (6:2 FTCA) was 100 % with concentrations ranging from 0.915 to 19.7 ng/L 6:2 FTCA might come from the biotransformation of indirect sources in the air. Concentrations of total nitrogen (TN) and total phosphorus (TP) were from 1.47 to 3.54 mg/L, and non-detect (ND) to 0.323 mg/L, respectively. Constructed wetlands could effectively remove PFAS under nutrient stress, however, the removal of PFAS depends on the characteristics of specific compounds and their sources. The removal rates for PFAS and nutrients could be promoted through artificial dredging. But wetland bioremediation could have two opposing effects. On the one hand, plants can take up pollutants from water via roots, leading to pollutant removal and purification. On the other hand, plants may also absorb precursor intermediates from the air through leaves and release them into the water, leading to increased pollutant concentrations. Thirty-two emerging PFAS were identified by high resolution mass spectrum. The drinking water treatment process removed PFAS and nutrients below the drinking water quality standards of China, however, 9 non-target PFAS compounds were still found in tap water. These results provide case support and a theoretical basis for the pollution control and sustainable development of typical ecological wetlands used as drinking water sources.

Emerging and legacy per- and polyfluoroalkyl substances (PFAS) in fluorochemical wastewater along full-scale treatment processes: Source, fate, and ecological risk

The increasing applications of emerging per- and polyfluoroalkyl substances (PFAS) have raised global concern. However, the release of emerging PFAS from the fluorochemical industry remains unclear. Herein, the occurrence of 48 emerging and legacy PFAS in wastewater from 10 fluorochemical manufacturers and mass flows of PFAS in a centralized wastewater treatment plant were investigated. Their distribution and ecological risk in neighboring riverine water were also evaluated. In wastewater from fluorochemical manufacturers, PFAS concentrations were in the range of 14,700-5200,000 ng/L and 2 H,2 H-perfluorooctanoic acid (6:2 FTCA), perfluorooctanoic acid (PFOA), N-ethyl perfluorooctane sulfonamide (N-EtFOSA), and 1 H,1 H,2 H,2 H-perfluorodecanesulfonate (8:2 FTS) were the major PFAS detected. Several PFAS displayed increased mass flows after wastewater treatment, especially PFOA and 6:2 FTCA. The mass flows of PFAS increased from - 20% to 233% after the activated sludge system but decreased by only 0-13% after the activated carbon filtration. In riverine water, PFAS concentrations were in the range of 5900-39,100 ng/L and 6:2 FTCA, 1 H,1 H,2 H,2 H-perfluorodecyl phosphate monoester (8:2 monoPAP), 1 H,1 H,2 H,2 H-perfluorooctyl phosphate monoester (6:2 monoPAP), PFOA, and perfluorohexanoic acid (PFHxA) were the major PFAS detected. PFOA and 6:2 FTCA exhibited comparable hazard quotients for ecological risk. Current wastewater treatment processes cannot fully remove various PFAS discharged by fluorochemical manufacturers, and further investigations on their risk are needed for better chemical management.

Perfluoroalkyl acid precursors in agricultural soil-plant systems: Occurrence, uptake, and biotransformation

Perfluoroalkyl acid (PFAA) precursors have been used in various consumer and industrial products due to their hydrophobic and oleophobic properties. In recent years, PFAA precursors in agricultural soil-plant systems have received increasing attention as they are susceptible to biotransformation into metabolites with high biotoxicity risks to human health. In this review, we systematically assessed the occurrence of PFAA precursors in agricultural soils, taking into account their sources and biodegradation pathways. In addition, we summarized the findings of the relevant literature on the uptake and biotransformation of PFAA precursors by agricultural plants. The applications of biosolids/composts and pesticides are the main sources of PFAA precursors in agricultural soils. The physicochemical properties of PFAA precursors, soil organic carbon (SOC) contents, and plant species are the key factors influencing plant root uptakes of PFAA precursors from soils. This review revealed, through toxicity assessment, the potential of PFAA precursors to generate metabolites with higher toxicity than the parent precursors. The results of this paper provide a reference for future research on PFAA precursors and their metabolites in soil-plant systems.

Using regular and transcriptomic analyses to investigate the biotransformation mechanism and phytotoxic effects of 6:2 fluorotelomer carboxylic acid (6:2 FTCA) in pumpkin (Cucurbita maxima L.)

Although 6:2 fluorotelomer carboxylic acid (6:2 FTCA), which is one of the most popular substitutes for perfluorooctanoic acid (PFOA), has been widely distributed in environments, little is known about its biotransformation mechanism and phytotoxic effects in plants. Here, we showed that 6:2 FTCA could be taken up by pumpkin (Cucurbita maxima L.) roots from exposure solution and acropetally translocated to shoots. Biotransformation of 6:2 FTCA to different carbon chain perfluorocarboxylic acid (PFCA) metabolites (C2-C7) via α-and β-oxidation in pumpkin was observed, and perfluorohexanoic acid (PFHxA) was the major transformation product. The results of enzyme assays, enzyme inhibition experiments and gene expression analysis indicated that cytochrome P450 (CYP450), glutathione-S-transferase (GST) and ATP-binding cassette (ABC) transporters were involved in the metabolism of 6:2 FTCA in pumpkin. Plant-associated rhizobacteria and endophyte also contributed to 6:2 FTCA degradation through β-oxidation. The chlorophyll (Chl) content and genes involved in photosynthesis were significantly improved by 6:2 FTCA. The reductions of antioxidant and metabolic enzyme activities reflected the antioxidant defense system and detoxification system of pumpkin were both damaged, which were further confirmed by the down-regulating associated genes encoding phenylpropanoid biosynthesis, endoplasmic reticulum-related proteins, ascorbate-glutathione cycle and ABC transporters. This study is helpful to understand the environmental behaviors and toxicological molecular mechanisms of 6:2 FTCA in plants.

Degradation of 8:2 fluorotelomer carboxylic acid (8:2 FTCA) by plants and their co-existing microorganisms

8:2 fluorotelomer carboxylic acid (8:2 FTCA), an important precursor of perfluorocarboxylic acids (PFCAs), is widely detected in environment and biotas. Hydroponic exposures were conducted to investigate the accumulation and metabolism of 8:2 FTCA in wheat (Triticum aestivum L.) and pumpkin (Cucurbita maxima L.). Endophytic and rhizospheric microorganisms co-existing with the plants were isolated to investigate their contributions to degrade 8:2 FTCA. Wheat and pumpkin roots could take up 8:2 FTCA efficiently with the root concentration factor (RCF) as 5.78 and 8.93, respectively. 8:2 FTCA could be biotransformed to 8:2 fluorotelomer unsaturated carboxylic acid (8:2 FTUCA), 7:3 fluorotelomer carboxylic acid (7:3 FTCA), and seven PFCAs with 2-8 carbon chain length in plant roots and shoots. Cytochromes P450 (CYP450) and glutathione-S-transferase (GST) activities in plants were significantly increased, while flavin-dependent monooxygenases (FMOs) activities were not changed, suggesting that CYP 450 and GST were involved in the transformation of 8:2 FTCA in plant tissues. Twelve 8:2 FTCA-degrading endophytic (8 strains) and rhizospheric (4 strains) bacterial strains were isolated from root interior, shoot interior and rhizosphere of plants, respectively. These bacteria were identified as Klebsiella sp. based on the morphology and 16S rDNA sequence, and they could biodegrade 8:2 FTCA to intermediates and stable PFCAs.

Mechanisms for the structural dependent transformation of 6:2 and 8:2 polyfluoroalkyl phosphate diesters in wheat (Triticum aestivum L.)

Polyfluoroalkyl phosphate esters (PAPs) are widely used and detected in various environmental media and organisms, but little is known about their behaviors in plants. In this study, the uptake, translocation and transformation of 6:2 and 8:2 diPAP in wheat using hydroponic experiments were investigated. 6:2 diPAP was more easily taken up by roots and translocated to shoots than 8:2 diPAP. Their phase I metabolites were fluorotelomer saturated carboxylates (FTCAs), fluorotelomer unsaturated carboxylates (FTUCAs) and perfluoroalkyl carboxylic acids (PFCAs). PFCAs with even-numbered chain length were the primary phase I terminal metabolites suggesting that they were mainly generated through β-oxidation. Cysteine and sulfate conjugates were the primary phase II transformation metabolites. The higher levels and ratios of phase II metabolites in the 6:2 diPAP exposure group indicated that the phase I metabolites of 6:2 diPAP were more susceptible to phase II transformation than that of 8:2 diPAP, which was confirmed by density functional theory calculation. Enzyme activity analyses and in vitro experiments demonstrated that cytochrome P450 and alcohol dehydrogenase actively participated in the phase Ⅰ transformation of diPAPs. Gene expression analyses showed that glutathione S-transferase (GST) was involved in the phase Ⅱ transformation, and the subfamily GSTU2 played a dominant role.

Degradation and Plant Transfer Rates of Seven Fluorotelomer Precursors to Perfluoroalkyl Acids and F-53B in a Soil-Plant System with Maize (Zea mays L.)

Fluorotelomer precursors in soil constitute a reservoir for perfluoroalkyl acids (PFAAs) in the environment. In the present study, precursor degradation and transfer rates of seven fluorotelomer precursors and F-53B (chlorinated polyfluoroalkyl ether sulfonates) were investigated in pot experiments with maize plants (Zea mays L.). The degradation of fluorotelomer precursors to perfluoroalkyl carboxylic acids (PFCAs) and their uptake spectra corresponded to those of fluorotelomer alcohol (FTOH) in terms of the number of perfluorinated carbon atoms. Short-chain PFCAs were translocated into the shoots (in descending order perfluoropentanoic, perfluorobutanoic, and perfluorohexanoic acid), whereas long-chain PFCAs mainly remained in the soil. In particular, fluorotelomer phosphate diesters (diPAPs) were retained in the soil and showed the highest degradation potential including evidence of α-oxidative processes. F-53B did not degrade to PFAAs and its constituents were mainly detected in the roots with minor uptake into the shoots. The results demonstrate the important role of precursors as an entry pathway for PFCAs into the food chain.

Foliar uptake overweighs root uptake for 8:2 fluorotelomer alcohol in ryegrass (Lolium perenne L.): A closed exposure chamber study

Fluorotelomer alcohols (FTOHs) are a kind of volatile monomers that can be released from FTOH-based products and their ubiquitous occurrence raises concerns for their plant uptake. To study plant uptake pathway, translocation, and transformation characteristics of 8:2 FTOH, ryegrass (Lolium perenne L.) was selected as a model plant for 8:2 FTOH exposure via air and/or soil uptake for 4 weeks in custom-built closed exposure chambers. The bio-degradation of spiked 8:2 FTOH in the soil led to the production of C6-C8 perfluoroalkyl carboxylic acids (PFCAs) and other intermediates, and perfluorooctanoic acid (PFOA) was the main product (54.9%-88.9%). In the ryegrass, foliar uptake of 8:2 FTOH contributed 78.1% ± 3.4% to the total shoot accumulation while PFOA in shoot was mainly from root uptake of PFOA and the further biotransformation of other unmonitored intermediates biodegraded from 8:2 FTOH in the soil (83.7% ± 7.3%). The results in this study provides the first laboratory evidences that foliar uptake of airborne 8:2 FTOH can be a major pathway over root uptake and its subsequent biotransformation contribute to the burden of PFCA accumulation in plants.

Behaviors of 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) in wheat seedlings: Bioaccumulation, biotransformation and ecotoxicity

As a new alternative to perfluorooctane sulfonate (PFOS), 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) has been currently used in industrial and consumer applications, which has been frequently detected in environment media. However, the behaviors of 6:2 FTAB in plants are still unclear. This study investigated the bioaccumulation, biotransformation and ecotoxicity of 6:2 FTAB in wheat (Triticum aestivum L.) by hydroponic exposure. 6:2 FTAB was easily taken up by roots with the root concentration factor (RCF) as high as 94.8, but difficult to be acropetally translocated in the shoots with the translocation factor (TF) as low as 0.058. Two intermediates and six terminal perfluorocarboxylic acid (PFCA) metabolites were detected in roots and shoots. The detected metabolites included 6:2 fluorotelomer sulfonic acid (6:2 FTSA), 6:2 fluorotelomer carboxylic acid (6:2 FTCA), perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluoropentanoic acid (PFPeA), perfluorobutyric acid (PFBA), pentafluoropropionic acid (PFPrA) and trifluoroacetic acid (TFA), and 6:2 FTSA was the main metabolite. 6:2 FTAB significantly reduced the biomass of plant and prevented chlorophyll (Chl) accumulation, while caused no significant change in malondialdehyde (MDA) content. Significant reduction in glutathione (GSH) contents, excess production of reactive oxygen species (ROS), and obvious inhibition of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione-s-transferase (GST) activities were observed, suggesting damage of antioxidant defense systems and failure to detoxication of 6:2 FTAB in wheat. These findings provide important knowledge for the fate of 6:2 FTAB in plants.

Development of a PFAS reaction library: identifying plausible transformation pathways in environmental and biological systems

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are used in many consumer applications due to their stain repellency, surfactant properties, ability to form water-proof coatings and use in fire suppression. The production, application, transport, use and disposal of PFAS and PFAS-treated products have resulted in their wide-spread occurrence in environmental and biological systems. Concern over exposure to PFAS and their transformation products and metabolites has necessitated the development of tools to predict the transformation of PFAS in environmental systems and metabolism in biological systems. We have developed reaction libraries for predicting transformation products and metabolites in a variety of environmental and biological reaction systems. These reaction libraries are based on generalized reaction schemes that encode the process science of PFAS reported in the peer-reviewed literature. The PFAS reaction libraries will be executed through the Chemical Transformation Simulator, a web-based tool that is available to the public. These reaction libraries are intended for predicting the environmental transformation and metabolism of PFAS only.

Occurrence and seasonal distribution of legacy and emerging per- and polyfluoroalkyl substances (PFASs) in different environmental compartments from areas around ski resorts in northern China

Skiing is an important direct input route of per- and polyfluoroalkyl substances (PFASs) to the environment. However, there has been no study on the occurrence of PFASs in Chinese ski area. In this study, 27 neutral PFASs (n-PFASs) and ionic PFASs (i-PFASs), including 4 emerging PFASs, were analyzed in the multimedia samples collected from areas around six ski resorts in Zhangjiakou and Shenyang to investigate the occurrence and seasonal distribution of PFASs. Both i-PFASs and n-PFASs were found in the air (13.2 ± 9.5 pg/m³ and 167 ± 173 pg/m³, respectively) and pine needles [1.44 ± 0.96 ng/g dry weight (dw) and 0.983 ± 0.590 ng/g dw], whereas only i-PFASs were found in the soil (0.755 ± 0.281 ng/g dw) and snow (3.30 ± 2.66 ng/kg). i-PFASs were significantly higher in samples collected around ski resorts than those from rural sites (n = 105, p < 0.05). Significantly higher perfluorooctanoate concentrations were found in the air around the ski resorts in winter (n = 33, p < 0.05). The i-PFASs were stable in the needle, and the short-chain PFASs in the needle could be ascribed to both air and root uptake. More attention should be paid to PFASs emissions in Zhangjiakou with the approaching 2022 Winter Olympic Games.