Stress response and tolerance to perfluorooctane sulfonate (PFOS) in lettuce (Lactuca sativa)

Perfluorobutanoic acid triggers metabolic and transcriptional reprogramming in wheat seedlings

The environmental risks of fluorinated alternatives are of great concern with the phasing out of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate. Here, multi-omics (i.e., metabolomics and transcriptomics) coupled with physiological and biochemical analyses were employed to investigate the stress responses of wheat seedings (Triticum aestivum L.) to perfluorobutanoic acid (PFBA), one of the short-chain per- and polyfluoroalkyl substances (PFAS) and PFOA alternatives, at environmentally relevant concentrations (0.1-100 ng/g). After 28 days of soil exposure, PFBA boosted the generation of OH and O2- in wheat seedlings, resulting in lipid peroxidation, protein perturbation and impaired photosynthesis. Non-enzymatic antioxidant defense systems (e.g., glutathione, phenolics, and vitamin C) and enzymatic antioxidant copper/zinc superoxide dismutase were strikingly activated (p < 0.05). PFBA-triggered oxidative stress induced metabolic and transcriptional reprogramming, including carbon and nitrogen metabolisms, lipid metabolisms, immune responses, signal transduction processes, and antioxidant defense-related pathways. Down-regulation of genes related to plant-pathogen interaction suggested suppression of the immune-response, offering a novel understanding on the production of reactive oxygen species in plants under the exposure to PFAS. The identified MAPK signaling pathway illuminated a novel signal transduction mechanism in plant cells in response to PFAS. These findings provide comprehensive understandings on the phytotoxicity of PFBA to wheat seedlings and new insights into the impacts of PFAS on plants.

Unveiling behaviors of 8:2 fluorotelomer sulfonic acid (8:2 FTSA) in Arabidopsis thaliana: Bioaccumulation, biotransformation and molecular mechanisms of phytotoxicity

8:2 fluorotelomer sulfonic acid (8:2 FTSA) has been commonly detected in the environment, but its behaviors in plants are not sufficiently known. Here, the regular and multi-omics analyses were used to comprehensively investigate the bioaccumulation, biotransformation, and toxicity of 8:2 FTSA in Arabidopsis thaliana. Our results demonstrated that 8:2 FTSA was taken up by A. thaliana roots and translocated to leaves, stems, flowers, and seeds. 8:2 FTSA could be successfully biotransformed to several intermediates and stable perfluorocarboxylic acids (PFCAs) catalyzed by plant enzymes. The plant revealed significant growth inhibition and oxidative damage under 8:2 FTSA exposure. Metabolomics analysis showed that 8:2 FTSA affected the porphyrin and secondary metabolisms, resulting in the promotion of plant photosynthesis and antioxidant capacity. Transcriptomic analysis indicated that differentially expressed genes (DEGs) were related to transformation and transport processes. Integrative transcriptomic and metabolomic analysis revealed that DEGs and differentially expressed metabolites (DEMs) in plants were predominantly enriched in the carbohydrate metabolism, amino acid metabolism, and lipid metabolism pathways, resulting in greater energy consumption, generation of more nonenzymatic antioxidants, alteration of the cellular membrane composition, and inhibition of plant development. This study provides the first insights into the molecular mechanisms of 8:2 FTSA stress response in plants.

Ecotoxicity of perfluorooctanoic acid and perfluorooctane sulfonate on aquatic plant Vallisneria natans

Perfluorinated compounds (PFCs) are persistent organic contaminants that are highly toxic to the environment and bioaccumulate, but their ecotoxic effects on aquatic plants remain unclear. In this study, the submerged plant Vallisneria natans was treated with short-term (7 days) and long-term (21 days) exposures to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentrations of 0, 0.01, 0.1, 1.0, 5.0, and 10 mg/L, respectively. The results showed that both high concentrations of PFOA and PFOS inhibited the growth of V. natans and triggered the increase in photosynthetic pigment content in leaves. The oxidative damage occurred mainly in leaves, but both leaves and roots gradually built up tolerance during the stress process without serious membrane damage. Both leaves and roots replied to short-term stress by activating superoxide dismutase (SOD), catalase (CAT) and polyphenol oxidase (PPO), while peroxidase (POD) was involved under high concentration stress with increasing exposure time. Leaves showed a dose-effect relationship in integrated biomarker response (IBR) values under short-term exposure, and the sensitivity of roots and leaves to PFOS was higher than that of PFOA. Our findings help to increase knowledge of the toxic effects of PFCs and have important reference value for risk assessment and environmental remediation of PFCs in the aquatic ecosystem.

Phosphorus conditions change the cellular responses of Microcystis aeruginosa to perfluorooctanoic acid

Perfluorooctanoic acid (PFOA), a widespread and emerging organic contaminant of aquatic environments, has high bioaccumulation potential and high toxicity. Consequently, major concerns have been raised worldwide regarding the management of this pollutant in aquatic ecosystems. To thoroughly understand PFOA's toxic effects on aquatic organisms, systematic investigations were conducted on the cellular responses of Microcystis aeruginosa to the environmental concentrations of PFOA under various concentrations as well as phosphorus (P) conditions (concentrations and forms). The results showed that P conditions remarkably affected cyanobacterial growth as well as photosynthetic pigment content, triggered oxidative stress to disrupt the function and structure of the cell membrane, and caused changes in the extracellular and intracellular contents of microcystin-LR (MC-LR). Furthermore, PFOA (100 μg/L) was absorbed by cyanobacterial cells through the stimulation of the secretion of extracellular polymeric substances (EPS) by M. aeruginosa. After entering the cyanobacterial cells, PFOA inhibited photosynthesis, reduced P absorption, induced oxidative damage, lead to a loss of cell integrity evident in scanning electron microscope images, and increased mcyA gene expression to promote MC-LR production. Moreover, the limited P concentration and forms conditions led to increased PFOA absorption by cyanobacterial cells, which further upregulated mcyA gene expression and increased the risk of MC-LR diffusion into the aquatic environment. Our present study provided a theoretical basis and new ideas for understanding and addressing safety issues related to the presence of PFOA in aquatic environments with varying nutritional statuses.

Effects of combined exposure of PVC and PFOA on the physiology and biochemistry of Microcystis aeruginosa

Microplastics (MPs) and per- and polyfluoroalkyl substances (PFASs) have drawn significant attention as emerging threats to aquatic ecosystems. There are currently just a few investigations on the combined toxicity of PFAS and MP on freshwater microalgae. In this research, the combined toxicity of polyvinyl chloride (PVC) and perfluorooctanoic acid (PFOA) to Microcystis aeruginosa was investigated. The results indicated that the combination of these pollutants inhibited the growth of M. aeruginosa and promoted the synthesis and release of Microcystin-LR (MC-LR). Individual and combined exposure caused different responses to cellular oxidative stress. Under the Individual exposure of PFOA, when the concentration was greater than 20.0 mg/L, the catalase (CAT) activity increased significantly, and when it was greater than 100.0 mg/L, the malondialdehyde (MDA) content increased significantly, but there is no significant change under combined exposure. PVC and PFOA exposure also caused physical damage to the algal cells and reduced the content of extracellular polymer substances (EPS) based on analysis of cell morphology. Metabolic analysis revealed that carbohydrate metabolism and amino acid metabolism of the algae were affected. The current study offers a fresh theoretical framework for MPs and PFASs environmental risk evaluations.

Plant responses to per- and polyfluoroalkyl substances (PFAS): a molecular perspective

Per- and polyfluoroalkyl substances (PFAS) constitute a large class of toxic manmade compounds that have been used in many industrial and household products. Dispersion of PFAS in the environment has raised concerns because of their persistence and toxicity for living organisms. Both terrestrial and aquatic plants have been shown to take up PFAS from contaminated soil and groundwater, and to accumulate these compounds inside their tissues. Although PFAS generally exert a low toxicity on plants at environmentally relevant concentrations, they frequently impact biomass growth and photosynthetic activity at higher levels. Uptake, translocation, and toxicity of PFAS in plants have been well covered in literature. Although less attention has been given to the molecular mechanisms underlying the plant response to PFAS, recent studies based on -omics approaches indicate that PFAS affects the plant metabolism even a low concentration. The objective of this review is to summarize the current knowledge about the effects of PFAS on plants at the molecular level. Results from recent transcriptomics, proteomics, and metabolomics studies show that low levels of PFAS induce oxidative stress and affect multiple plant functions and processes, including photosynthesis and energy metabolism. These potentially harmful effects trigger activation of defense mechanisms.

Bioavailability, phytotoxicity and plant uptake of per-and polyfluoroalkyl substances (PFAS): A review

Per- and polyfluoroalkyl substances (PFAS) are a group of legacy and emerging contaminants containing at least one aliphatic perfluorocarbon moiety. They display rapid and extensive transport in the environment due to their generally high water-solubility and weak adsorption onto soil particles. Because of their widespread presence in the environment and known toxicity, PFAS has become a serious threat to the ecosystem and public health. Plants are an essential component of the ecosystem and their uptake and accumulation of PFAS affect the fate and transport of PFAS in the ecosystem and has strong implications for human health. It is therefore imperative to investigate the interactions of plants with PFAS. This review presents a detailed discussion on the mechanisms of the bioavailability and plant uptake of PFAS, and essential factors affecting these processes. The phytotoxic effects of PFAS at physiological, biochemical, and molecular level were also carefully reviewed. At the end, key research gaps were identified, and future research needs were proposed.

Plant rhizosphere defense system respond differently to emerging polyfluoroalkyl substances F-53B and PFOS stress

Chlorinated polyfluoroalkyl ether sulfonate (F-53B) and perfluorooctanesulfonate (PFOS) are used and emitted as fog inhibitors in the chromium plating industry, and they are widely detected worldwide. To study the effects of F-53B and PFOS on the rhizosphere defense system, they were added at two levels (0.1 and 50 mg L^-1) to the soil where different plants (Lythrum salicaria and Phragmites communis) were grown. In bulk soils, high concentrations of F-53B/PFOS resulted in significant increases in soil pH, NH₄⁺-N, and NO₃^--N (the effect of PFOS on NO₃^--N was not significant). Moreover, the extent of the effects of PFOS and F-53B on the physicochemical properties of bulk soils were different (e.g., PFOS caused an increase of NH₄⁺-N by 8.94%-45.97% compared to 1.63%-25.20% for F-53B). Root exudates and PFASs together influenced the physicochemical properties of rhizosphere soils (e.g., TOC increased significantly in contaminated rhizosphere soils but did not change in non-bulk soils). Under the influence of F-53B/PFOS, the root exudates regulated by plants were changed and weakened the effect of F-53B/PFOS on microbial community of rhizosphere soil. The rhizosphere defense systems of different plants have both similarities and differences in response to different substances and concentrations.

Fluoro-cotton assisted non-targeted screening of organic fluorine compounds from rice (Oryza sativa L.) grown in perfluoroalkyl substance polluted soil

The toxicity and environmental persistence of perfluorooctanoic acid (PFOA), and perfluorooctane sulfonate (PFOS) are of great concern for food intake in humans. However, PFASs conversion or conjugation to other substances in rice grown on PFASs polluted soil has not been explored clearly. These unknown transformed or conjugated products of PFOA and PFOS could be harmful to human health. The restriction factor in evaluating the possible transformation of PFOA and PFOS is mainly attributed to the lack of an efficient method for screening PFOA and PFOS and their related metabolites. To circumvent this challenge, we established a non-targeted screening method by combining a fluoro-cotton fiber-based solid phase extraction (FC-SPE) and liquid chromatography-high resolution mass spectrometry (LC-HRMS) to monitor the formation of possible organic fluorine compounds from rice (Oryza sativa L.) grown on PFASs. We synthesized fluoro-cotton fibers to serve as the FC-SPE packing material and characterized by field-emission scanning electron-microscope, Fourier transform infrared, and X-ray photoelectron spectroscopy measurements. The optimal extraction conditions for the prepared FC-SPE were investigated. The performance of FC-SPE in LC-MS analysis was validated by linearity, precision, recovery, and matrix effect. Then the FC-SPE combined with LC-HRMS was used to specifically capture organic fluorine compounds from complex matrices via F-F interaction, including rice seedlings grown in PFOA and PFOS polluted soil and soil samples. By the established FC-SPE LC-HRMS method, in total 429 features were found as the possible organic fluorine compounds from rice seedlings grown in PFOA polluted soil among the 1781 features from the rice seedlings. Finally, we employed a¹³C metabolic tracing analysis of organic fluorine compounds in combination with the FC-SPE LC-HRMS method to further identify the features that detected from rice seedlings grown in PFOA polluted soil. The final result indicated that there were not any new organic fluorine metabolites screened out from rice grown in PFOA or PFOS polluted soil.

Perfluorooctanoic acid and perfluorooctane sulfonic acid inhibit plant growth through the modulation of phytohormone signalling pathways: Evidence from molecular and genetic analysis in Arabidopsis

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are the most representative perfluoroalkyl substances that accumulate in the food chain and are harmful to the environment. The uptake, translocation and physiological effects of PFOA and PFOS in plants have been reported in recent years; however, the regulatory mechanisms underlying PFOA- and PFOS-mediated plant growth and development remain largely unclear. Here, using Arabidopsis thaliana as the study material, we showed that both PFOA and PFOS inhibited plant growth; PFOS showed a stronger inhibitory effect on primary root (PR) growth, whereas PFOA exerted a stronger inhibitory effect on photosynthesis. Transcriptome analysis revealed that PFOA- and PFOS-modulated plant growth and development were correlated with the phytohormones auxin and abscisic acid (ABA). Further genetic analyses using mutants related to auxin biosynthesis, receptors and transport and mutants related to ABA biosynthesis and signalling transduction revealed that both PFOA and PFOS inhibited PR growth by modulating auxin biosynthesis and signalling pathways, and the ABA signalling pathway was also involved in PFOS-mediated PR growth inhibition. Collectively, these results shed new light on the molecular mechanisms of PFOA- and PFOS-mediated root system growth and their effects on phytohormone signalling pathways in plants.

Molecular and genetic analyses revealed the phytotoxicity of perfluorobutane sulfonate

Perfluorobutane sulfonate (PFBS) has oily and hydrophobic characteristics similar to those of perfluorooctane sulfonic acid (PFOS), which is an environmental organic pollutant and has gradually become the main substitute for PFOS in industry. Several studies have revealed the potential toxicity of PFBS in animals. PFBS can be taken up and accumulate in plants; however, whether and how PFBS affects plant growth remain largely unclear. A low concentration of PFBS did not affect plant growth, indicating that it had higher environmental safety than other perfluorinated compounds; however, a high concentration of PFBS (>1 mM) markedly inhibited primary root growth in Arabidopsis thaliana. Subsequently, we investigated the molecular mechanisms underlying plant growth mediated by high concentrations of PFBS. First, a genome-wide transcriptomic analysis revealed that PFBS altered the expression of genes associated with phytohormone signaling pathways. Combining physio-biochemical and genetic analyses, we next demonstrated that PFBS reduced the contents of indole-3-acetic acid (IAA) and abscisic acid (ABA), and disrupted the two signaling pathways in plants, finally inhibiting root growth. Moreover, a high concentration of PFBS also inhibited photosynthesis by comprehensively repressing the expression of genes related to the Calvin cycle and the photosynthetic apparatus. Such an understanding is helpful for elucidating the phytotoxicity of PFBS and provides a new strategy for toxicology research on organic pollutants in plants.

Perfluorinated alkyl substances affect the growth, physiology and root proteome of hydroponically grown maize plants

Poly- and perfluorinated alkyl substances (PFAS) are a group of persistent organic pollutants causing serious global concern. Plants can accumulate PFAS but their effect on plant physiology, especially at the molecular level is not very well understood. Hence, we used hydroponically-grown maize plants treated with a combination of eleven different PFAS (each at 100 μg L^-1) to investigate their bioaccumulation and effects on the growth, physiology and their impact on the root proteome. A dose-dependent decrease in root growth parameters was evidenced with a significant reduction in the relative growth rate, fresh weight of leaves and roots and altered photosynthetic parameters in PFAS-treated plants. Higher concentration of shorter PFAS (C < 8) was detected in the leaves, while long-chain PFAS (C ≥ 8) were more retained in roots. From the root proteome analysis, we identified 75 differentially abundant proteins, mostly involved in cellular metabolic and biosynthetic processes, translation and cytoskeletal reorganization. Validating the altered protein abundance using quantitative real-time PCR, the results were further substantiated using amino acid and fatty acid profiling, thus, providing first insight into the altered metabolic state of plants exposed to PFAS from a proteomics perspective.

Perfluorobutanoic Acid (PFBA) Induces a Non-Enzymatic Oxidative Stress Response in Soybean (Glycine max L. Merr.)

Short-chain perfluoroalkyl substances (PFAS) are generally considered to be of less environmental concern than long-chain analogues due to their comparatively shorter half-lives in biological systems. Perfluorobutanoic acid (PFBA) is a short-chain PFAS with the most root–shoot transfer factor of all PFAS. We investigated the impact of extended exposure of soybean plants to irrigation water containing environmentally relevant (100 pg–100 ng/L) to high (100 µg–1 mg/L) concentrations of PFBA using phenotypical observation, biochemical characterization, and transcriptomic analysis. The results showed a non-monotonous developmental response from the plants, with maximum stimulation and inhibition at 100 ng/L and 1 mg/L, respectively. Higher reactive oxygen species and low levels of superoxide dismutase (SOD) and catalase (CAT) activity were observed in all treatment groups. However transcriptomic analysis did not demonstrate differential expression of SOD and CAT coding genes, whereas non-enzymatic response genes and pathways were enriched in both groups (100 ng/L and 1 mg/L) with glycine betaine dehydrogenase showing the highest expression. About 18% of similarly downregulated genes in both groups are involved in the ethylene signaling pathway. The circadian rhythm pathway was the only differentially regulated pathway between both groups. We conclude that, similar to long chain PFAS, PFBA induced stress in soybean plants and that the observed hormetic stimulation at 100 ng/L represents an overcompensation response, via the circadian rhythm pathway, to the induced stress.

Stress response to oxytetracycline and microplastic-polyethylene in wheat (Triticum aestivum L.) during seed germination and seedling growth stages

Much efforts have been devoted to clarify the phytotoxicity of individual contaminants in plants, such as individual antibiotic and microplastic; however, little is known about the phytotoxicity of their combined exposure. Here, we investigated the effects of individual and combined exposure of wheat (Triticum aestivum L.) (Xiaoyan 22) to oxytetracycline (OTC) and polyethylene (PE) microplastics using physiological and metabolic profilings. During the seed germination stage, OTC induced phytotoxicity, as observed through the changes of root elongation, sprout length, fresh weight and the vitality index, with significant effect at the 50 and 150 mg·L^-1 levels; the effect of PE microplastics depended on the OTC level in the combined exposure groups. During seedling cultivation, catalase (CAT) and ascorbate peroxidase (APX), as antioxidant enzyme indices, were sensitive to OTC exposure stress, although OTC was not determined in leaves. Untargeted metabolomics of wheat leaves revealed OTC concentration-, metabolite class- and PE-dependent metabolic responses. Dominant metabolites included carboxylic acids, alcohols, and amines in the control group and all treatment groups. Compared to only OTC treatment, PE reprogrammed carboxylic acid and alcohol profiles in combined exposure groups with obvious separation in PLS-DA. Combined exposure induced fewer metabolites than OTC exposure alone at the 5 and 50 mg·L^-1 levels. The shared metabolite numbers were higher in the OTC groups than in the PE-OTC groups. Pathway enrichment analysis showed a drift in metabolic pathways between individual and combined exposure to OTC and PE, which included glyoxylate and dicarboxylate metabolism, amino acid metabolism and isoquinoline alkaloid biosynthesis. Among metabolites, aromatic acids and amino acids were more sensitive to combined exposure than individual exposure. These results contribute to clarifying the underlying mechanisms of phytotoxicity of individual and combined exposure to OTC and PE.

Exposure routes, bioaccumulation and toxic effects of per- and polyfluoroalkyl substances (PFASs) on plants: A critical review

Per- and polyfluoroalkyl substances (PFASs) are artificial persistent organic pollutants ubiquitous in ecosystem, and their bioaccumulation and adverse outcomes in plants have attracted extensive concerns. Here, we review the toxic effects of PFASs encountered by various plants from physiological, biochemical and molecular perspectives. The exposure routes and bioaccumulation of PFASs in plants from contaminated sites are also summarized. The bioaccumulation of PFASs in plants from contaminated sites varied between ng/g and μg/g levels. The 50% inhibition concentration of PFASs for plant growth is often several orders of magnitude higher than the environmentally relevant concentrations (ERCs). ERCs of PFASs rarely lead to obvious phenotypic/physiological damages in plants, but markedly perturb some biological activities at biochemical and molecular scales. PFAS exposure induces the over-generated reactive oxygen species and further damages plant cell structure and organelle functions. A number of biochemical activities in plant cells are perturbed, such as photosynthesis, gene expression, protein synthesis, carbon and nitrogen metabolisms. To restore the desire states of cells exposed to PFASs, plants initiate several detoxifying mechanisms, including enzymatic antioxidants, non-enzymatic antioxidants, metallothionein genes and metabolic reprogramming. Future challenges and opportunities in PFAS phytotoxicity studies are also proposed in the review.

Anti-oxidant mechanisms of Chlorella pyrenoidosa under acute GenX exposure

GenX, a substitute for perfluorooctanoic acid, has been widely detected in surface water. Due to its bioaccumulation, toxicity and persistence, GenX can cause adverse effects such as oxidative damage on aquatic organisms. To investigate the toxicity of GenX and the anti-oxidant mechanism of algae under acute exposure, the growth, photosynthetic activity and gene expression of Chlorella pyrenoidosa (C. pyrenoidosa) were tested. Results showed that the growth of C. pyrenoidosa was inhibited under acute GenX exposure. The toxicity of GenX increased with time and concentration but was lower than that of the traditional perfluoroalkyl and polyfluoroalkyl substances (PFASs). Furthermore, with the increase of GenX concentration, the production of reactive oxygen species increased, while the level of the anti-oxidant enzyme first increased and then decreased. Changes in photosynthetic parameters also indicated that the photosynthetic system of C. pyrenoidosa was negatively affected by GenX exposure. Transcription analysis revealed that the up-regulation of genes related to the glutathione-ascorbate cycle and photosynthesis is a positive strategy to cope with the oxidative stress caused by acute GenX exposure. Our findings provide new insights into the interactions between emerging PFASs and aquatic organisms at the molecular level.

Endophytic Bacterial Communities of Ginkgo biloba Leaves During Leaf Developmental Period

Plant-specialized secondary metabolites have ecological functions in mediating interactions between plants and their entophytes. In this study, high-throughput gene sequencing was used to analyze the composition and abundance of bacteria from Ginkgo leaves at five different sampling times. The results indicated that the bacterial community structure varied during leaf developmental stage. Bacterial diversity was observed to be the highest at T2 stage and the lowest at T1 stage. Proteobacteria, Firmicutes, Actinobacteria, Chloroflexi, Cyanobacteria, and Bacteroidetes were found as the dominant phyla. The major genera also showed consistency across sampling times, but there was a significant variation in their abundance, such as Bacillus, Lysinibacillus, and Staphylococcus. Significant correlations were observed between endophytic bacteria and flavonoids. Especially, Staphylococcus showed a significant positive correlation with quercetin, and changes in the abundance of Staphylococcus also showed a strong correlation with flavonoid content. In order to determine the effect of flavonoids on endophytic bacteria of Ginkgo leaves, an extracorporeal culture of related strains (a strain of Staphylococcus and a strain of Deinococcus) was performed, and it was found that the effect of flavonoids on them remained consistent. The predicted result of Tax4Fun2 revealed that flavonoids might lead to a lower abundance of endophytic microorganisms, which further proved the correlation between bacterial communities and flavonoids. This study provided the first insight into the bacterial community composition during the development of Ginkgo leaves and the correlation between the endophytic bacteria and flavonoids.

Perfluorooctanoic acid (PFOA) changes nutritional compositions in lettuce (Lactuca sativa) leaves by activating oxidative stress

Perfluorooctanoic acid (PFOA) is a typical persistent organic pollutant commonly detected in ecosystem. Insights into the risks of PFOA in crops, from the perspectives of food nutritional compositions, are sparse. In this study, the physiological responses to PFOA induced oxidative stress were investigated in lettuce (Lactuca sativa) leaves hydroponically exposed to 5 and 50 μg/L PFOA. The effects on photosynthesis and nutritional compositions were characterized. 35.1 and 316.7 ng/g dry weight PFOA were bio-accumulated in lettuce leaves under exposure to 5 and 50 μg/L PFOA, respectively. PFOA led to exposure-dependent over-generation of reactive oxidative species (ROS; H2O2, 8.1%-38.7%; OH, 11.3%-26.4%; O2-, 3.1%-22.8%) in leaves. Both non-enzymatic and enzymatic antioxidants were activated to scavenge ROS. Nevertheless, metabolomics results indicated some nutritional compositions in lettuce leaves were elevated by environmentally relevant concentrations of PFOA. Both primary metabolites, such as carbohydrates in the tricarboxylic acid cycle and amino acids, and secondary metabolites, such as bioactive (poly)phenol and alkaloid compounds, were significantly up-regulated. Leaf net photosynthetic rates were stimulated and intercellular CO2 concentration was decreased. A thorough scheme on the interaction between PFOA and lettuce leaves was proposed as well, to enhance the understanding of PFOA risks in crops.

Perfluorooctane sulfonate decreases the performance of a sequencing batch reactor system and changes the sludge microbial community

The existence of perfluorooctane sulfonate (PFOS) in large quantities threatens environment biosafety. However, the fate of PFOS in a sequencing batch reactor (SBR) system and its influence in system has not yet been revealed. In this study, the fate and behavior of PFOS in an SBR processing system were investigated. Mass balance analyses revealed that PFOS removal was mainly through adsorption. After the reactors were run for 20 days, the PFOS (100 mg/L) removal rate was only 28%. Under the influence of PFOS, the removal rates of chemical oxygen demand (COD) and ammonia nitrogen dropped rapidly from 92, 98% to 23, 35% in the 20th day of system operation, respectively, while, accumulation of nitrite and nitrate was reduced. Compared with the control group, PFOS stimulates microorganisms to secrete more soluble microbial products (SMP) and extracellular polymeric substances (EPS). The adsorption of PFOS and EPS causes sludge bulking and decreases settling. The richness and diversity of microorganisms decreased significantly, affecting the system's removal of COD and ammonia nitrogen. Therefore, the SBR system is not suitable for treating wastewater containing PFOS. It is necessary to remove PFOS through pretreatment to reduce its impact on the SBR system.

Perfluorooctanoic acid (PFOA) caused oxidative stress and metabolic disorders in lettuce (Lactuca sativa) root

Eliminating the critical knowledge gaps of perfluorooctanoic acid (PFOA) effects in planta is the imperative target to accomplish accurate and meaningful exposure-risk assessment in the environment. Here, we investigated the effect of environmentally relevant concentrations of PFOA on the oxidative stress and metabolic regulation in lettuce (Lactuca sativa) root. Under the exposure to 5 and 50 μg/L PFOA for 10 days, 137.5 and 1275.0 ng PFOA/g dry weight were accumulated to roots, respectively. H2O2, the dominant reactive oxygen species, was slightly over-generated by 4.7%-9.5%. No signs of oxidative damage, such as lipid peroxidation, cell membrane integrity and soluble protein content, were observed. To deal with PFOA stress, the activities of ascorbate peroxidase and peroxidase and the contents of glutathione were dose-dependently up-regulated. Partial least-squares discriminant analysis revealed metabolite profiles were significantly altered by PFOA, involving the primary metabolism (e.g., sucrose, glucose, fructose-6-phosphate, methionine, γ-aminobutyric acid), and the biosynthesis of (poly)phenol (e.g., shikimate, naringenin) and alkaloid (e.g., geranyl diphosphate, dopamine). Our findings showed that environmentally relevant concentrations of PFOA significantly perturbed metabolisms in plant roots albeit no remarkable cell damage was induced.