Evaluation of morpho-physiological traits and contaminant accumulation ability in Lemna minor L. treated with increasing perfluorooctanoic acid (PFOA) concentrations under laboratory conditions

Phytoremediation Potential of Azolla filiculoides: Uptake and Toxicity of Seven Per- and Polyfluoroalkyl Substances (PFAS) at Environmentally Relevant Water Concentrations

Environmental contamination of aquatic systems by per- and polyfluoroalkyl substances (PFAS) has generated significant health concerns. Remediation of contaminated sites such as the fire-fighting emergency training grounds that use aqueous film-forming foams is a high priority. Phytoremediation may help play a part in removing PFAS from such contaminated waters. We investigated the potential of the water fern Azolla filiculoides, which is used for phytoremediation of a wide range of contaminants, to uptake seven common PFAS (perfluorobutanoic acid [PFBA], perfluorobutane sulfonic acid [PFBS], perfluoroheptanoic acid [PFHpA], perfluorohexanoic acid [PFHxA], perfluorohexane sulfonic acid [PFHxS], perfluorooctanoic acid [PFOA], and perfluoropentanoic acid [PFPeA]), during a 12-day exposure to environmentally relevant concentrations delivered as equimolar mixtures: low (∑PFAS = 0.0123 ± 1.89 μmol L-1), medium (∑PFAS = 0.123 ± 2.88 μmol L-1), and high (∑PFAS = 1.39 μmol L-1) treatments, equivalent to approximately 5, 50, and 500 µg L-1 total PFAS, respectively. The possible phytotoxic effects of PFAS were measured at 3-day intervals using chlorophyll a content, photosystem II efficiency (Fv/Fm), performance index, and specific growth rate. The PFAS concentrations in plant tissue and water were also measured every 3 days using ultra-high-performance liquid chromatography-tandem mass spectrometry. Treatments with PFAS did not lead to any detectable phytotoxic effects. All seven PFAS were detected in plant tissue, with the greatest uptake occurring during the first 6 days of exposure. After 12 days of exposure, a maximum bioconcentration factor was recorded for PFBA of 1.30 and a minimum of 0.192 for PFBS. Consequently, the application of Azolla spp. as a stand-alone system for phytoremediation of PFAS in aquatic environments is not sufficient to substantially reduce PFAS concentrations. Environ Toxicol Chem 2024;43:2157-2168. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

PFOA accumulation in the leaves of basil (Ocimum basilicum L.) and its effects on plant growth, oxidative status, and photosynthetic performance

BACKGROUND

Perfluoroalkyl substances (PFASs) are emerging contaminants of increasing concern due to their presence in the environment, with potential impacts on ecosystems and human health. These substances are considered "forever chemicals" due to their recalcitrance to degradation, and their accumulation in living organisms can lead to varying levels of toxicity based on the compound and species analysed. Furthermore, concerns have been raised about the possible transfer of PFASs to humans through the consumption of edible parts of food plants. In this regard, to evaluate the potential toxic effects and the accumulation of perfluorooctanoic acid (PFOA) in edible plants, a pot experiment in greenhouse using three-week-old basil (Ocimum basilicum L.) plants was performed adding PFOA to growth substrate to reach 0.1, 1, and 10 mg Kg- 1 dw.

RESULTS

After three weeks of cultivation, plants grown in PFOA-added substrate accumulated PFOA at different levels, but did not display significant differences from the control group in terms of biomass production, lipid peroxidation levels (TBARS), content of α-tocopherol and activity of ascorbate peroxidase (APX), catalase (CAT) and guaiacol peroxidase (POX) in the leaves. A reduction of total phenolic content (TPC) was instead observed in relation to the increase of PFOA content in the substrate. Furthermore, chlorophyll content and photochemical reflectance index (PRI) did not change in plants exposed to PFAS in comparison to control ones. Chlorophyll fluorescence analysis revealed an initial, rapid photoprotective mechanism triggered by PFOA exposure, with no impact on other parameters (Fv/Fm, ΦPSII and qP). Higher activity of glutathione S-transferase (GST) in plants treated with 1 and 10 mg Kg- 1 PFOA dw (30 and 50% to control, respectively) paralleled the accumulation of PFOA in the leaves of plants exposed to different PFOA concentration in the substrate (51.8 and 413.9 ng g- 1 dw, respectively).

CONCLUSION

Despite of the absorption and accumulation of discrete amount of PFOA in the basil plants, the analysed parameters at biometric, physiological and biochemical level in the leaves did not reveal any damage effect, possibly due to the activation of a detoxification pathway likely involving GST.

Detection of Perfluorooctanoic and Perfluorodecanoic Acids on a Graphene-Based Electrochemical Sensor Aided by Computational Simulations

Perfluoroalkyl carboxylic acids (PFCAs) exhibit high chemical and thermal stability, rendering them versatile for various applications. However, their notable toxicity poses environmental and human health concerns. Detecting trace amounts of these chemicals is crucial to mitigate risks. Electrochemical sensors surpass traditional methods in sensitivity, selectivity, and cost-effectiveness. In this study, a graphene nanosheet-based sensor was developed for detecting perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA). Using the Hummer method, graphene nanosheets were synthesized and characterized in terms of morphology, structural ordering, and surface topology. Ab initio molecular dynamics simulations determined the molecular interaction of per- and poly-fluoroalkyl substances (PFASs) with the sensor material. The sensor exhibited high sensitivity (50.75 μA·μM-1·cm-2 for PFOA and 29.58 μA·μM-1·cm-2 for PFDA) and low detection limits (10.4 nM for PFOA and 16.6 nM for PFDA) within the electrode dynamic linearity range of 0.05-500.0 μM (PFOA) and 0.08-500.0 μM (PFDA). Under optimal conditions, the sensor demonstrated excellent selectivity and recovery in testing for PFOA and PFDA in environmental samples, including spiked soil, water, spoiled vegetables, and fruit samples.

Comparative Phytotoxicity of Metallic Elements on Duckweed Lemna gibba L. Using Growth- and Chlorophyll Fluorescence Induction-Based Endpoints

In this study, we exposed a commonly used duckweed species-Lemna gibba L.-to twelve environmentally relevant metals and metalloids under laboratory conditions. The phytotoxic effects were evaluated in a multi-well-plate-based experimental setup by means of the chlorophyll fluorescence imaging method. This technique allowed the simultaneous measuring of the growth and photosynthetic parameters in the same samples. The inhibition of relative growth rates (based on frond number and area) and photochemical efficiency (Fv/Fo and Y(II)) were both calculated from the obtained chlorophyll fluorescence images. In the applied test system, growth-inhibition-based phytotoxicity endpoints proved to be more sensitive than chlorophyll-fluorescence-based ones. Frond area growth inhibition was the most responsive parameter with a median EC50 of 1.75 mg L-1, while Fv/Fo, the more responsive chlorophyll-fluorescence-based endpoint, resulted in a 5.34 mg L-1 median EC50 for the tested metals. Ag (EC50 0.005-1.27 mg L-1), Hg (EC50 0.24-4.87 mg L-1) and Cu (EC50 0.37-1.86 mg L-1) were the most toxic elements among the tested ones, while As(V) (EC50 47.15-132.18 mg L-1), Cr(III) (EC50 6.22-19.92 mg L-1), Se(VI) (EC50 1.73-10.39 mg L-1) and Zn (EC50 3.88-350.56 mg L-1) were the least toxic ones. The results highlighted that multi-well-plate-based duckweed phytotoxicity assays may reduce space, time and sample volume requirements compared to the standard duckweed growth inhibition tests. These benefits, however, come with lowered test sensitivity. Our multi-well-plate-based test setup resulted in considerably higher median EC50 (3.21 mg L-1) for frond-number-based growth inhibition than the 0.683 mg L-1 median EC50 derived from corresponding data from the literature with standardized Lemna-tests. Under strong acute phytotoxicity, frond parts with impaired photochemical functionality may become undetectable by chlorophyll fluorometers. Consequently, the plant parts that are still detectable display a virtually higher average photosynthetic performance, leading to an underestimation of phytotoxicity. Nevertheless, multi-well-plate-based duckweed phytotoxicity assays, combined with chlorophyll fluorescence imaging, offer definite advantages in the rapid screening of large sample series or multiple species/clones. As chlorophyll fluorescence images provide information both on the photochemical performance of the test plants and their morphology, a joint analysis of the two endpoint groups is recommended in multi-well-plate-based duckweed phytotoxicity assays to maximize the information gained from the tests.

Exposure of Lemna minor (Common Duckweed) to Mixtures of Uranium and Perfluorooctanoic Acid (PFOA)

A variety of processes, both natural and anthropogenic, can have a negative impact on surface waters, which in turn can be detrimental to human and environmental health. Few studies have considered the ecotoxicological impacts of concurrently occurring contaminants, and that is particularly true for mixtures that include contaminants of emerging concern (CEC). Motivated by this knowledge gap, the present study considers the potential ecotoxicity of environmentally relevant contaminants in the representative aquatic plant Lemna minor (common duckweed), a model organism. More specifically, biological effects associated with exposure of L. minor to a ubiquitous radionuclide (uranium [U]) and a fluorinated organic compound (perfluorooctanoic acid [PFOA], considered a CEC), alone and in combination, were monitored under controlled laboratory conditions. Lemna minor was grown for 5 days in small, aerated containers. Each treatment consisted of four replicates with seven plants each. Treatments were 0, 0.3, and 3 ppb PFOA; 0, 0.5, and 5 ppb U; and combinations of these. Plants were observed daily for frond number and signs of chlorosis and necrosis. Other biological endpoints examined at the conclusion of the experiment were chlorophyll content and antioxidant capacity. In single-exposure experiments, a slight stimulatory effect was observed on frond number at 0.3 ppb PFOA, whereas both concentrations of U had a detrimental effect on frond number. In the dual-exposure experiment, the combinations with 5 ppb U also had a detrimental effect on frond number. Results for chlorophyll content and antioxidant capacity were less meaningful, suggesting that environmentally relevant concentrations of PFOA and U have only subtle effects on L. minor growth and health status. Environ Toxicol Chem 2023;42:2412-2421. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Research Priorities for the Environmental Risk Assessment of Per- and Polyfluorinated Substances

Per- and polyfluorinated substances (PFAS) are a group of thousands of ubiquitously applied persistent industrial chemicals. The field of PFAS environmental research is developing rapidly, but suffers from substantial biases toward specific compounds, environmental compartments, and organisms. The aim of our study was therefore to highlight current developments and to identify knowledge gaps and subsequent research needs that would contribute to a comprehensive environmental risk assessment for PFAS. To this end, we consulted the open literature and databases and found that knowledge of the environmental fate of PFAS is based on the analysis of <1% of the compounds categorized as PFAS. Moreover, soils and suspended particulate matter remain largely understudied. The bioavailability, bioaccumulation, and food web transfer studies of PFAS also focus on a very limited number of compounds and are biased toward aquatic biota, predominantly fish, and less frequently aquatic invertebrates and macrophytes. The available ecotoxicity data revealed that only a few PFAS have been well studied for their environmental hazards, and that PFAS ecotoxicity data are also strongly biased toward aquatic organisms. Ecotoxicity studies in the terrestrial environment are needed, as well as chronic, multigenerational, and community ecotoxicity research, in light of the persistency and bioaccumulation of PFAS. Finally, we identified an urgent need to unravel the relationships among sorption, bioaccumulation, and ecotoxicity on the one hand and molecular descriptors of PFAS chemical structures and physicochemical properties on the other, to allow predictions of exposure, bioaccumulation, and toxicity. Environ Toxicol Chem 2023;42:2302-2316. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Combined toxic effects of polypropylene and perfluorooctanoic acid on duckweed and periphytic microorganisms

Microplastics and perfluorooctanoic acid coexist in the aquatic environment. Duckweed was exposed to a range of concentrations (0.1-1000 μg L-1) of solutions containing polypropylene (PP) and perfluorooctanoic acid (PFOA) for 14 days to measure their toxicity. The result showed the single and combined PP and PFOA treatments did not significantly influence the growth of duckweed. The greatest PP and PFOA concentrations of combined pollution affect plant chlorophyll. Moreover, the combined treatment of duckweed consistently resulted in increased malondialdehyde (MDA) levels, indicating oxidative damage. As an antioxidant stress response, the combination-treated plants were encouraged to produce superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Meanwhile, 3519 Operational Taxonomic Units (OTUs) were identified in the duckweed rhizosphere. Proteobacteria was the most predominant microbial community. Shannon, Simpson, and Chao1 discovered that microbial communities changed in response to single and combination PP and PFOA treatments, with decreased diversity and increased abundance. In addition, SEM analysis also revealed that the combined treatment significantly phyllosphere microorganisms. The findings of this investigation add to our knowledge of how PP and PFOA affect duckweed and the rhizospheric microorganisms, expanding the theoretical basis for employing duckweed in complex contamination.

Toxic effects of three perfluorinated or polyfluorinated compounds (PFCs) on two strains of freshwater algae: Implications for ecological risk assessments

Perfluorinated or polyfluorinated compounds (PFCs) continue entering to the environmental as individuals or mixtures, but their toxicological information remains largely unknown. Here, we investigated the toxic effects and ecological risks of Perfluorooctane sulfonic acid (PFOS) and its substitutes on prokaryotes (Chlorella vulgaris) and eukaryotes (Microcystis aeruginosa). Based on the calculated EC₅₀ values, the results showed that PFOS was significantly more toxic to both algae than its alternatives including Perfluorobutane sulfonic acid (PFBS) and 6:2 Fluoromodulated sulfonates (6:2 FTS), and the PFOS-PFBS mixture was more toxic to both algae than the other two PFC mixtures. The action mode of binary PFC mixtures on Chlorella vulgaris was mainly shown as antagonistic and on Microcystis aeruginosa as synergistic, by using Combination index (CI) model coupled with Monte Carlo simulation. The mean risk quotient (RQ) value of three individual PFCs and their mixtures were all below the threshold of 10^-1, but the risk of those binary mixtures were higher than that of PFCs individually because of their synergistic effect. Our findings contribute to enhance the understanding of the toxicological information and ecological risks of emerging PFCs and provide a scientific basis for their pollution control.

Joint effects of CuO nanoparticles and perfluorooctanoic acid on cabbage (Brassica pekinensis L.)

Coexisting nanoparticles (NPs) may change plant accumulation and toxicity of perfluorooctanoic acid (PFOA) in soil, but research is very scarce. In this study, cabbage (Brassica pekinensis L.) was exposed to single or combined treatments of PFOA (2 mg/kg and 4 mg/kg) and copper oxide NPs (nCuO, 200 mg/kg and 400 mg/kg) for 40 days. At harvest, biomass, photosynthesis index, and nutrient composition of cabbage, as well as plant accumulation of PFOA and Cu, were measured. Results showed that nCuO and PFOA were adverse to cabbage growth by decreasing chlorophyll contents, inhibiting photosynthesis and transpiration, and interfering with the utilization of nutrient components. Besides, they also affected each other's plant utilization and transmission. Especially, nCuO at a high dose (400 mg/kg) significantly increased the transport of coexisting PFOA (4 mg/kg) content (by 124.9% and 118.2%) to cabbage shoots. The interaction mechanism between nCuO and PFOA is unknown, and more research is needed to evaluate their composite phytotoxicity.

Screening of structural and functional alterations in duckweed (Lemna minor) induced by per- and polyfluoroalkyl substances (PFASs) with FTIR spectroscopy

As a class of common emerging pollutants, per- and polyfluoroalkyl substances (PFASs) and their alternatives have been widely detected in various environmental matrices, exhibiting a great threat to the ecological environment and human health. Nevertheless, changes in biomolecular structure and function of duckweed caused by PFASs and their alternatives remain unknown thus far. Herein, the effects of four PFASs, including two common legacy PFASs (perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA)) and two PFASs alternatives (perfluorobutane sulfonic acid (PFBS) and 1H,1H,2H, 2H-perfluorooctane sulfonic acid (6:2 FTS)) on duckweed (Lemna minor) at biochemical level were investigated with Fourier transform infrared spectroscopy (FTIR). Although no obvious inhibitions were observed in the growth of L. minor with PFASs exposure at three levels of 1 μg L^-1, 100 μg L^-1, and 10 mg L^-1, significant structural and functional alterations were induced at the biochemical level. In response to PFASs exposure, lipid peroxidation, proteins aggregation and α-helix to β-sheet transformation of the protein conformation, as well as changes of DNA conformations were detected. Moreover, alterations in lipid, protein, and DNA were proved to be concentration-related and compound-specific. Compared to the two legacy PFASs (PFOS and PFOA), alternative ones exhibited greater effects on the biological macromolecules of L. minor. The findings of this study firstly reveal structural and functional alterations in L. minor induced by PFASs exposure, providing further understanding of their toxicity effects.

Toxicity of perfluooctane sulfonate (PFOS) and perfluorobutane sulfonate (PFBS) to Scenedesmus obliquus: Photosynthetic characteristics, oxidative damage and transcriptome analysis

With the wide application as an alternative for perfluorooctane sulfonate (PFOS), perfluorobutane sulfonate (PFBS) has been frequently detected in the aquatic environment. However, the aquatic toxicity of PFBS is still poorly understood. The present work studied the aquatic toxicity of PFBS using freshwater algae Scenedesmus obliquus (S. obliquus) as indicator, and the toxicity of PFOS was also examined for comparison. The results showed that PFBS exhibited much lower toxicity to S. obliquus than PFOS. The EC₅₀ value was higher than 1800 mg L^-1 after 7 days of exposure to PFBS. By contrast, a much lower EC₅₀ value of 136.69 mg L^-1 was obtained for PFOS. Photosynthetic efficiency analyzed by chlorophyll fluorescence also verified that PFOS induced a higher toxic effect on the algae than PFBS. The malondialdehyde, catalase and superoxide dismutase results indicate that PFOS exposure led to the accumulation of ROS, which caused oxidative damage to the algae, thereby resulting in the inhibition in the growth and photosynthesis of the algae. Furthermore, transcriptome analysis indicates that the significant down-regulation of key genes related to photosynthesis induced by PFOS was the fundamental mechanism for the inhibition in photosynthetic efficiency and biomass growth of S. obliquus.

Application of duckweed (Lemna sp.) and water fern (Azolla sp.) in the removal of pharmaceutical residues in water: State of art focus on antibiotics

In recent decades, antibiotic residues in the environment have increased, affecting components of biological communities, from bacteria to plants and animals. Different methods have been used to remove these compounds, including phytoremediation with floating aquatic species such as duckweed and aquatic fern, with positive results. This study analyses information about the removal efficiency of drugs, with a focus on antibiotics, using Lemna and Azolla, which will allow a better understanding of phytoremediation processes from the perspective of plant physiology. The physiological processes of macrophytes in an environment with this type of pollutant and the phytotoxic effects on plants at high concentrations are also analysed. The metabolization of toxic compounds occurs in three phases: phase I begins with the absorption of antibiotics and the secretion of reactive oxygen species (ROS); in phase II, the effects of ROS are neutralized and minimized by conjugation with enzymes such as glutathione transferase or metabolites such as glutathione; and phase III culminates with the storage of the assimilated compounds in the vacuoles, apoplast and cell wall. In this way, plants contribute to the removal of toxic compounds. In summary, there is sufficient scientific evidence on the efficiency of the elimination of pharmaceutical compounds by these floating macrophytes at the laboratory scale, which indicates that their application under real conditions can have good results.

Ecotoxicological and genotoxic effects of dimethyl phthalate (DMP) on Lemna minor L. and Spirodela polyrhiza (L.) Schleid. plants under a short-term laboratory assay

The environmental occurrence of phthalates (PAE) is of great concern for the ecosystem and human health. Despite of their recognized toxicity on biota, a lack of knowledge is still present about the effects of PAE on plants. In this scenario, the effects of dimethyl phthalate (DMP) on duckweed plants (Lemna minor L. and Spirodela polyrhiza (L.) Schleid.), two model plant species for ecotoxicological and trophic studies, were investigated. Under a 7-day lab assay, morphological (biometric indicators), physiological (pigment content and photosynthetic performance) and molecular (DNA damage) parameters were studied. No effects were observed at growth and physiological level in both plants at 3 and 30 mg/L DMP. On the contrary, at 600 mg/L DMP, a concentration used for plant acute toxicity studies, a remarkable growth inhibition and pigment content and photosynthetic parameters reduction compared to control were observed in both plants species, particularly in Spirodela. Alkaline Comet assay in 24 h-treated plants revealed a genotoxic damage induced by DMP, particularly relevant in Spirodela. These results described for the first time the adverse effects exerted by DMP on aquatic plants, contributing to highlight the environmental risk associated to the presence of this compound in the aquatic ecosystem.

Plant uptake of perfluoroalkyl substances in freshwater environments (Dongzhulong and Xiaoqing Rivers, China)

This study provides new knowledge on the mobility, behavior, and partitioning of 17 perfluoroalkyl substances (PFASs) in the water-sediment-plant system along the Dongzhulong and Xiaoqing Rivers. The fate of PFASs in these rivers is also discussed. The study area is affected by the industrial production of perfluorooctanoic acid (PFOA). The ∑PFASs in water and sediments close to the industrial discharge were 84,000 ± 2000 ng/L and 2300 ± 200 ng/g dw, respectively, with the concentrations decreasing along the river due to dilution. PFOA was the dominant compound (74-97% of the ∑PFASs), although other PFASs were identified close to urban areas. Principal component analysis and solid-liquid distribution coefficients revealed that long-chain PFASs accumulated in the sediment whereas short-chain PFASs remained in the water all along the river. PFASs were taken up by plants and remobilized to different plant compartments according to shoot concentration factors (SCFs), root concentration factors (RCF), and transfer factors (TFs). Among the four plant species studied, floating plants absorbed high levels of PFASs, while rooted species translocated short-chain PFASs from the roots to the shoots. Therefore, floating species, due to their high uptake capacity and large proliferation rate, could eventually be used for phytoremediation.

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.

Chlorophyll Fluorescence Imaging-Based Duckweed Phenotyping to Assess Acute Phytotoxic Effects

Duckweeds (Lemnaceae species) are extensively used models in ecotoxicology, and chlorophyll fluorescence imaging offers a sensitive and high throughput platform for phytotoxicity assays with these tiny plants. However, the vast number of potentially applicable chlorophyll fluorescence-based test endpoints makes comparison and generalization of results hard among different studies. The present study aimed to jointly measure and compare the sensitivity of various chlorophyll fluorescence parameters in Spirodela polyrhiza (giant duckweed) plants exposed to nickel, chromate (hexavalent chromium) and sodium chloride for 72 h, respectively. The photochemistry of Photosystem II in both dark- and light-adapted states of plants was assessed via in vivo chlorophyll fluorescence imaging method. Our results indicated that the studied parameters responded with very divergent sensitivity, highlighting the importance of parallelly assessing several chlorophyll fluorescence parameters. Generally, the light-adapted parameters were more sensitive than the dark-adapted ones. Thus, the former ones might be the preferred endpoints in phytotoxicity assays. Fv/Fm, i.e., the most extensively reported parameter literature-wise, proved to be the least sensitive endpoint; therefore, future studies might also consider reporting Fv/Fo, as its more responsive analogue. The tested toxicants induced different trends in the basic chlorophyll fluorescence parameters and, at least partly, in relative proportions of different quenching processes, suggesting that a basic distinction of water pollutants with different modes of action might be achievable by this method. We found definite hormetic patterns in responses to several endpoints. Hormesis occurred in the concentration ranges where the applied toxicants resulted in strong growth inhibition in longer-term exposures of the same duckweed clone in previous studies. These findings indicate that changes in the photochemical efficiency of plants do not necessarily go hand in hand with growth responses, and care should be taken when one exclusively interprets chlorophyll fluorescence-based endpoints as general proxies for phytotoxic effects.

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.

Interactions between Lemna minor (common duckweed) and PFAS intermediates: Perfluorooctanesulfonamide (PFOSA) and 6:2 fluorotelomer sulfonate (6:2 FTSA)

Perfluorooctanesulfonamide (PFOSA) and 6:2 fluorotelomer sulfonate (FTSA) are widely present intermediates of per- and polyfluorinated substances (PFAS). Although detected at high concentrations in landfill leachate and groundwater, the interactions of these two compounds with plants have not been investigated much. In this work, uptake of these two PFAS intermediates at 10 and 200 μg/L by Lemna minor (common duckweed) were studied in detail. It was found that the biomass production of L. minor was not impacted negatively by PFOSA and FTSA at concentrations equal to or lower than 200 μg/L. Between these two target compounds, FTSA had much higher concentrations in L. minor when the concentrations and exposure times were the same as those for PFOSA. In addition, this compound at 200 μg/L inhibited the activities of catalase in L. minor significantly compared to the controls. This study indicates that PFOSA with low water solubility has low toxicity to L. minor, while FTSA at high concentration may accumulate in the floating plants and cause adverse effects on plant's antioxidative defense system. Longer-term studies of L. minor with these two and other PFAS are warranted given the important role of this floating plant in the ecosystem.

Insights into the Use of Phytoremediation Processes for the Removal of Organic Micropollutants from Water and Wastewater; A Review

Greater awareness of micropollutants present in water and wastewater motivates the search for effective methods of their neutralization. Although their concentration in waters is measured in micro- and nanograms per liter, even at those levels, they may cause serious health consequences for different organisms, including harmful effects on the functioning of the endocrine system of vertebrates. Traditional methods of wastewater treatment, especially biological methods used in municipal wastewater treatment plants, are not sufficiently effective in removing these compounds, which results in their presence in natural waters. The growing interest in phytoremediation using constructed wetlands as a method of wastewater treatment or polishing indicates a need for the evaluation of this process in the context of micropollutant removal. Therefore, the present work presents a systematic review of the effectiveness in the removal of micropollutants from polluted waters by processes based on plant used. The article also analyzes issues related to the impact of micropollutants on the physiological processes of plants as well as changes in general indicators of pollution caused by contact of wastewater with plants. Additionally, it is also the first review of the literature that focuses strictly on the removal of micropollutants through the use of constructed wetlands.

A critical review of modeling Poly- and Perfluoroalkyl Substances (PFAS) in the soil-water environment

Due to their health effects and the recalcitrant nature of their CF bonds, Poly- and Perfluoroalkyl Substances (PFAS) are widely investigated for their distribution, remediation, and toxicology in ecosystems. However, very few studies have focused on modeling PFAS in the soil-water environment. In this review, we summarized the recent development in PFAS modeling for various chemical, physical, and biological processes, including sorption, volatilization, degradation, bioaccumulation, and transport. PFAS sorption is kinetic in nature with sorption equilibrium commonly quantified by either a linear, the Freundlich, or the Langmuir isotherms. Volatilization of PFAS depends on carbon chain length and ionization status and has been simulated by a two-layer diffusion process across the air water interface. First-order kinetics is commonly used for physical, chemical, and biological degradation processes. Uptake by plants and other biota can be passive and/or active. As surfactants, PFAS have a tendency to be sorbed or concentrated on air-water or non-aqueous phase liquid (NAPL)-water interfaces, where the same three isotherms for soil sorption are adopted. PFAS transport in the soil-water environment is simulated by solving the convection-dispersion equation (CDE) that is coupled to PFAS sorption, phase transfer, as well as physical, chemical, and biological transformations. As the physicochemical properties and concentration vary greatly among the potentially thousands of PFAS species in the environment, systematic efforts are needed to identify models and model parameters to simulate their fate, transport, and response to remediation techniques. Since many process formulations are empirical in nature, mechanistic approaches are needed to further the understanding of PFAS-soil-water-plant interactions so that the model parameters are less site dependent and more predictive in simulating PFAS remediation efficiency.

Evaluation of Multiple Responses Associated with Arsenic Tolerance and Accumulation in Pteris vittata L. Plants Exposed to High As Concentrations under Hydroponics

Chinese brake fern (Pteris vittata L.) is recognized as an arsenic hyperaccumulating plant. Mechanisms underlying this capability and the associated hypertolerance have been described even if not completely elucidated. In this study, with the aim to expand the knowledge on the matter, an experimental trial was developed to investigate an array of responses, at the morphological, physiological, and biochemical level, in P. vittata plants exposed to high As concentrations in a long-term experiment under hydroponics. Results confirmed the ability of fern plants to both tolerate and accumulate a remarkable amount of As, especially in fronds. Notably, in As-treated plants, a far higher As content was detected in young fronds compared to old fronds, with bioaccumulation (BCF) and translocation (Tf) factors in accordance. At the biochemical level, As treatment affected macro and micronutrient, thiol, and phytochelatin concentrations in fronds of treated plants differently than that of the control. Physiological measurements accounted for a reduction in the photosynthetic activity of As-treated plants in the absence of visual symptoms of damage. Overall, the observed As tolerance and accumulation processes were discussed, evidencing how young fronds developed during As treatment maintain their physiological status while accumulating a high As content. Such indications could be very useful to improve the effective utilization of this plant species for phytofiltration of As-polluted water.

Uptake and translocation of perfluoroalkyl acids (PFAAs) in hydroponically grown red chicory (Cichorium intybus L.): Growth and developmental toxicity, comparison with growth in soil and bioavailability implications

Short-chain perfluoroalkyl acids (PFAAs) have shown a high potential for plant (crop) uptake, making them possibly significant contributors to the total dietary exposure to PFAAs. The plant uptake of PFAAs is a complex process that needs better characterization, as it does not only depend on perfluoroalkyl chain length, but also on their polar terminal group, on the plant species and the exposure media. Here, a plant uptake study with nine perfluoroalkyl acids (PFAAs) was carried out under the hydroponic (soilless) exposure conditions. Red chicory was grown in a nutrient solution, spiked with PFAAs mixture at three different concentrations (i.e. 62.5, 125 and 250 μg/L), in order to extend the range of levels tested and reported in the literature so far. Bioaccumulation metrics and transpiration stream concentration factors (TSCFs) were employed for the plant uptake characterization and consequent comparison with the results of soil uptake experiment we previously performed with the same crop. The results showed that calculated root concentration factors (RCFs) increase with PFAA chain length, while the opposite chain length dependence was present for shoots. Plants from two treatments with the highest PFAAs concentrations manifested physiological changes (discoloration, inhibited roots and leaves growth), despite of the used exposure concentrations being much lower than previously published phytotoxicity thresholds. A comparison among RCFs and TSCFs derived from hydroponic and from the soil experiment has emphasized their different magnitudes and PFAAs chain length dependence patterns. They could not be ascribed only to soil sorption as a process decreasing PFAAs bioavailability for plants, but also to developmental differences between the root systems formed in soil and in nutrient solution and to the potential competitive PFAAs sorption to roots in hydroponics. The interchangeable use of bioaccumulation and translocation parameters derived in hydroponic and soil systems would lead to erroneous conclusions and plant uptake predictions.