Genotypic variation and mechanism in uptake and translocation of perfluorooctanoic acid (PFOA) in lettuce (Lactuca sativa L.) cultivars grown in PFOA-polluted soils

Cutting-edge technologies and relevant reaction mechanism difference in treatment of long- and short-chain per- and polyfluoroalkyl substances: A review

Per- and polyfluoroalkyl substances (PFAS) are emerging contaminants. Compared with short-chain PFAS, long-chain PFAS are more hazardous. Currently, little attention has been paid to the differences in reaction mechanisms between long-chain and short-chain PFAS. This pressing concern has prompted studies about eliminating PFAS and revealing the mechanism difference. The reaction rate and reaction mechanism of each technology was focused on, including (1) adsorption, (2) ion exchange (IX), (3) membrane filtration, (4) advanced oxidation, (5) biotransformation, (6) novel functional material, and (7) other technologies (e.g. ecological remediation, hydrothermal treatment (HT), mechanochemical (MC) technology, micro/nanobubbles enhanced technology, and integrated technologies). The greatest reaction rate k of photocatalysis for long- and short-chain PFAS high up to 63.0 h-1 and 19.7 h-1, respectively. However, adsorption, membrane filtration, and novel functional material remediation were found less suitable or need higher operation demand for treating short-chain PFAS. Ecological remediation is more suitable for treating natural waterbody for its environmentally friendly and fair reaction rate. The other technologies all showed good application potential for both short- and long-chain PFAS, and it was more excellent for long-chain PFAS. The long-chain PFAS can be cleavaged into short-chain PFAS by C-chain broken, -CF2 elimination, nucleophilic substitution of F-, and HF elimination. Furthermore, the application of each type of technology was novelly designed; and suggestions for the future development of PFAS remediation technologies were proposed.

Factors influencing the fate of chemical food safety hazards in the terrestrial circular primary food production system-A comprehensive review

Food safety is recognized as a major hurdle in the transition toward circular food production systems due to the potential reintroduction and accumulation of chemical contaminants in these food systems. Effectively managing these hazardous contaminants in a risk-based manner requires quantitative insights into the factors influencing the presence and fate of contaminants in the entire circular food chain. A systematic literature review was performed to gain an up-to-date overview of the known factors and their influence on the transfer and accumulation of contaminants. This review focused on the terrestrial circular primary food production system, including the pathways between waste- or byproduct-based fertilizers, soil, crops, animal feed, and farmed animals. This review revealed an imbalance in research regarding the different pathways: studies on the soil-to-crop pathway were most abundant. The factors identified can be categorized as compound-related (intrinsic) factors, such as hydrophobicity, molecular weight, and chain length, and extrinsic factors, such as soil organic matter and carbon, pH, milk yield of cows, crop age, and biomass. Quantitative data on the influence of the identified factors were limited. Most studies quantified the influence of individual factors, whereas only a few studies quantified the combined effect of multiple factors. By providing a holistic insight into the influential factors and the quantification of their influence on the fate of contaminants, this review contributes to the improvement of food safety management for chemical hazards when transitioning to a circular food system.

Removal of perfluorooctanoic acid (PFOA) in the liquid culture of Phanerochaete chrysosporium

Perfluorooctanoic acid (PFOA) is becoming a concern due to its persistence, bioaccumulation, and potential harmful effects on humans and the environment. In this study, the fungus Phanerochaete chrysosporium (P. chrysosporium) was used to remove the PFOA in liquid culture system. The results showed that the average activities of laccase (Lac), lignin peroxidase (LiP), and manganese peroxidase (MnP) enzymes secreted by P. chrysosporium were 0.0003 U/mL, 0.013 U/mL, and 0.0059 U/mL, respectively, during the incubation times of 0-75 days. The pH of 3 and incubation time of 45-55 days were the optimum parameters for the three enzymes activities. The enzyme activities in P. chrysosporium incubation system were firstly inhibited by adding PFOA and then they were enhanced after 14 days. The maximum removal efficiency of PFOA (69.23%) was achieved after 35 days in P. chrysosporium incubation system with an initial PFOA concentration of 0.002 mM and no veratryl alcohol (VA). Adsorption was not a main pathway for PFOA removal and the PFOA adsorbed in fungi mycelial mat accounted for merely 1.91%. The possible products of PFOA contained partially fluorinated aldehyde, alcohol, and aromatic ring. These partially fluorinated compounds might result from PFOA degradation via a combination of cross-coupling and rearrangement of free radicals.

Development, Evaluation, and Application of Machine Learning Models for Accurate Prediction of Root Uptake of Per- and Polyfluoroalkyl Substances

Machine learning (ML) models were developed for understanding the root uptake of per- and polyfluoroalkyl substances (PFASs) under complex PFAS-crop-soil interactions. Three hundred root concentration factor (RCF) data points and 26 features associated with PFAS structures, crop properties, soil properties, and cultivation conditions were used for the model development. The optimal ML model, obtained by stratified sampling, Bayesian optimization, and 5-fold cross-validation, was explained by permutation feature importance, individual conditional expectation plot, and 3D interaction plot. The results showed that soil organic carbon contents, pH, chemical logP, soil PFAS concentration, root protein contents, and exposure time greatly affected the root uptake of PFASs with 0.43, 0.25, 0.10, 0.05, 0.05, and 0.05 of relative importance, respectively. Furthermore, these factors presented the key threshold ranges in favor of the PFAS uptake. Carbon-chain length was identified as the critical molecular structure affecting root uptake of PFASs with 0.12 of relative importance, based on the extended connectivity fingerprints. A user-friendly model was established with symbolic regression for accurately predicting RCF values of the PFASs (including branched PFAS isomerides). The present study provides a novel approach for profound insight into the uptake of PFASs by crops under complex PFAS-crop-soil interactions, aiming to ensure food safety and human health.

Phytoextraction of per- and polyfluoroalkyl substances (PFAS) and the influence of supplements on the performance of short-rotation crops

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic compounds threatening water quality and food safety worldwide. Phytoremediation is a nature-based, cost-effective, and scalable solution with high potential for treating PFAS-contaminated sites. However, there is a large knowledge gap regarding choice of plant species and methods to enhance performance. This study assessed the PFAS phytoextraction potential of sunflower (Helianthus annuus), mustard (Brassica juncea), and industrial hemp (Cannabis sativa) in a greenhouse experiment, using inorganic fertilizer and a microbial mixture as supplements. PFAS concentrations were measured using UPLC-MS/MS, and bioconcentration factors for different plant tissues and removal efficiency were determined. Perfluoroalkyl carboxylic acid (PFCA) accumulation was 0.4-360 times higher than that of perfluoroalkyl sulfonic acid (PFSA) homologues of similar perfluorocarbon chain length. Inorganic fertilizer significantly (p < 0.001) reduced PFAS concentration in all plant tissues, whereas the microbial mixture tested did not affect PFAS concentration. PFAS uptake ranged from 0.2 to 33% per crop cycle. Overall, the potential number of crop cycles required for removal of 90% of individual PFAS ranged from six (PFPeA) to 232 (PFOA) using sunflower, 15 (PFPeA) to 466 (PFOS) using mustard and nine (PFPeA) to 420 (PFOS) using Hemp. In this study, the percentage of PFAS removal by plants was determined, and an estimation of the time required for PFAS phytoextraction was determined for the first time. This information is important for practical phytoremediation applications.

New Insights into the Accumulation, Transport, and Distribution Mechanisms of Hexafluoropropylene Oxide Homologues, Important Alternatives to Perfluorooctanoic Acid, in Lettuce (Lactuca sativa L.)

Hexafluoropropylene oxide (HFPO) homologues, which are important alternatives to perfluorooctanoic acid, have been frequently identified in crops. Although exposure to HFPO homologues via crops may pose non-negligible threats to humans, their impact on crops is still unknown. In this study, the accumulation, transport, and distribution mechanisms of three HFPO homologues in lettuce were investigated at the plant, tissue, and cell levels. More specifically, HFPO trimer acid and HFPO tetramer acid were primarily fixed in roots and hardly transported to shoots (TF, 0.06-0.63). Conversely, HFPO dimer acid (HFPO-DA) tended to accumulate in lettuce shoots 2-264 times more than the other two homologues, thus resulting in higher estimated daily intake values. Furthermore, the dissolved organic matter derived from root exudate enhanced HFPO-DA uptake by increasing its desorption fractions in the rhizosphere. The transmembrane uptake of HFPO homologues was controlled by means of a transporter-mediated active process involving anion channels, with the uptake of HFPO-DA being additionally facilitated by aquaporins. The higher accumulation of HFPO-DA in shoots was attributed to the larger proportions of HFPO-DA in the soluble fraction (55-74%) and its higher abundance in both vascular tissues and xylem sap. Our findings expand the understanding of the fate of HFPO homologues in soil-crop systems and reveal the underlying mechanisms of the potential exposure risk to HFPO-DA.

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.

Effect of HHCB and Cd on phytotoxicity, accumulation, subcellular distribution and stereoselectivity of chiral HHCB in soil-plant systems

The toxicity of HHCB in the growth and development of plants is well known, but its uptake, subcellular distribution, and stereoselectivity, especially in a co-contamination environment, is not fully understood. Therefore, a pot experiment was performed to research the physiochemical response, and the fate of HHCB in pakchoi when the Cd co-existed in soil. The Chl contents were significantly lower, and the oxidative stress was aggravated under the co-exposure of HHCB and Cd. The accumulations of HHCB in roots were inhibited, and those in leaves were elevated. The transfer factors of HHCB in HHCB-Cd treatment increased. The subcellular distributions were analyzed in the cell walls, cell organelles, and cell soluble constituents of roots and leaves. In roots, the distribution proportion of HHCB followed cell organelle > cell wall > cell soluble constituent. In leaves, the distribution proportion of HHCB was different from that in roots. And the co-existing Cd made the distribution proportion of HHCB change. In the absence of Cd, the (4R,7S)-HHCB and (4R,7R)-HHCB were preferentially enriched in roots and leaves, and the stereoselectivity of chiral HHCB was more significant in roots than leaves. The co-existing Cd reduced the stereoselectivity of HHCB in plants. Our findings suggested that the fate of HHCB was affected by the co-existing Cd, so the risk of HHCB in the complicated environment should be paid more attention.

Perfluorooctanoic acid uptake in the mustard species Brassica juncea

Perfluorooctanoic acid (PFOA), a surfactant, is a member of the perfluoroalkyl acids (PFAAs) family and is a contaminant of emerging concern for human and environmental health. Perfluorooctanoic acid is a persistent organic pollutant, but currently little is known about (a) the potential ecological and toxicological effects of PFOA and (b) how PFOA moves in the environment. This study uses a radiotracer (¹⁴ C-PFOA) to study the uptake and translocation of PFOA in hydroponically grown brown mustard [Brassica juncea (L.) Czern.], a representative crop species. Plants were exposed in quadruplicate over the course of 7 d (with plants sampled on Days 4 and 7) to PFOA concentrations of 0, 1, 5, 10, and 15 mg L^-1 . Uptake was quantified via liquid scintillation counting of samples from the nutrient solution, roots, stems, and leaves. Transfer factors (roots to shoots) ranged from 0.15 to 4.73 kg kg^-1 . Bioconcentration factors (solution to plant) ranged from 0.36 to 62.29 L kg^-1 . Factors were influenced by plant compartment, day sampled, and treatment level.

Insight into the uptake and translocation of per- and polyfluoroalkyl substances in hydroponically grown lettuce

The prevalence of per- and polyfluoroalkyl substances (PFASs) in agricultural soils has raised concerns regarding the health risks associated with the consumption of PFAS-contaminated agricultural products. The present study investigated the uptake and translocation of nine PFASs in lettuce using a hydroponic setting. During the uptake experiments, long-chain PFASs (≥ C8) exhibited greater accumulations in lettuce roots, while short-chain PFASs (≤ C7) manifested preferential transport to the shoots. The average root concentration factors of PFASs were positively correlated with their log Kow values. A significantly negative relationship was found between the average translocation factors of PFASs and their molecular volume. Sorption of long-chain PFASs by lettuce roots was enhanced after heating the roots to increase the cell membrane permeability. The accumulation of perfluorododecanoic acid increased significantly in shoots of lettuce plants without roots as compared to whole lettuce plants. Results of the present study indicate that sorption to root surface tissues and efficiency in passing through the root Casparian strip are two important factors that affect the uptake and distribution of PFASs within plants.

Root Uptake Pathways and Cell Wall Accumulation Mechanisms of Organophosphate Esters in Wheat (Triticum aestivum L.)

The behavior of organophosphate esters (OPEs) in plants has drawn considerable attention because of their adverse effects to biota. However, the root uptake pathways and cell wall accumulation mechanisms of OPEs in plants are still unclear. In this study, the uptake pathways, subcellular distribution, and accumulation mechanisms of OPEs in wheat roots were elucidated. The results demonstrated that the symplast is the major pathway for uptake of both tris(2-chloroethyl) phosphate (TCEP) and triphenyl phosphate (TPHP) in wheat roots. Inhibitor experiments showed that the transmembrane transport of OPEs is a passive uptake process, and aquaporins and carrier proteins contribute to the uptake of OPEs. More than 69% of TCEP was accumulated in cell sap due to its high hydrophilicity, while the hydrophobic TPHP was mainly stored in the root cell wall. The sorption affinity of TPHP decreased gradually following the sequential fractionation of wheat roots, which confirmed the significant contribution to TPHP sorption on wheat roots. A significant positive correlation between the sorption affinity values and the percentage of aromatic carbon was observed (r² = 0.856, p < 0.01), indicating that the accumulation of hydrophobic OPEs in roots does not just depend on lipids alone, but the aromatic moieties of lignin in the cell wall also contribute to OPE accumulation.

A comprehensive review of recent research concerning the role of low molecular weight organic acids on the fate of organic pollutants in soil

Plants exude through the roots different compounds, including, among others, low-molecular weight organic acids (LMWOAs), with a relevant effect on multiple metabolic activities. Numerous studies have revealed their role in improving soil mineral acquisition and tolerance against inorganic pollutants. However, less information is available on how they may alter the fate of organic pollutants in soil, which may cause environmental problems, compromise soil quality and have a detrimental effect on animal and human health. This review intends to cover recent studies (from 2015 onwards) and provide up-to-date information on how LMWOAs influence environmental key processes of organic pollutants in soil, like adsorption/desorption, degradation and transport, without forgetting plant uptake, with obvious environmental and health repercussions. Critical knowledge gaps and future research needs are also discussed, because understanding these processes will help searching effective strategies for pollutant reduction and control in soil.

Removal potential of multiple perfluoroalkyl acids (PFAAs) by submerged macrophytes in aquatic environments: Tolerance of Vallisneria natans and PFAA removal in submerged macrophyte-microbiota systems

Perfluoroalkyl acids (PFAAs) have emerged as a global concern in aquatic environment remediation due to their abundance, persistence, bioaccumulation, and toxicity. To comprehensively understand the removal potential of multiple PFAAs by submerged macrophytes in aquatic environments, systematic investigations into the tolerance of the typical submerged macrophyte Vallisneria natans to 12 typical PFAAs and the removal capacity to PFAAs in V. natans-microbiota systems were carried out. Results showed that although PFAAs could induce the accumulation of hydrogen peroxide and malondialdehyde, V. natans was overall resistant to multiple PFAAs with natural concentrations. Catalase is one of the main strategies of V. natans to alleviate PFAA stress. Microbiota can remove 18.10-30.84% of the PFAAs from the water column. 24.35-73.45% of PFAAs were removed from water in V. natans-microbiota systems. The uptake of plant tissues and the bioaccumulation of microbiota were proposed as the main removal processes. The removal rates were significantly correlated with the perfluorinated carbon atoms numbers (p < 0.05). PFAAs and V. natans increased the relative abundance of Betaproteobacteria, Nostocales, Microscillaceae, Sphingobacteriales, SBR1031, Chlamydiales, Phycisphaerae, Caldilineales, Rhodobacterales, and Verrucomicrobiales. The present study suggested that V. natans can be a potential species to remove multiple PFAAs in aquatic environments, and further providing insights into the PFAAs' remediation.

Diversity of endophytic bacteria in wild rice (Oryza meridionalis) and potential for promoting plant growth and degrading phthalates

Phthalates (PAEs) accumulated in agricultural soils and rice have increased human exposure risks. Microbial degradation could efficiently reduce the residue of organic pollutants in soil and crop plants. Here, we hypothesized that endophytic bacteria from wild rice have the potential for degradation of PAEs and plant growth promoting. The endophytic bacterial community and functional diversity in wild rice (Oryza meridionalis) were analyzed for the first time, and the potential for PAE degradation and plant growth promoting by endophytes were investigated. The results of Illumina high-throughput sequencing revealed that abundant endophytes inhabited in wild rice with Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria being the dominant phyla. Endophytic bacterial diversity and complexity were confirmed by isolation and clustering of isolates. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that endophytes exerted diverse functions such as plant growth promoting, xenobiotics biodegradation, pollution remediation and bacterial chemotaxis. Pure culture experiment showed that 30 isolated endophytic strains exhibited in vitro plant growth promoting activities, and rice plants inoculated with these strains confirmed their growth promoting abilities. Some endophytic strains were capable of efficiently degrading PAEs, with the highest removal percentage of di-n-butyl phthalate (DBP) up to 96.1% by Bacillus amyloliquefaciens strain L381 within 5 days. Synthetic community F and strain L381 rapidly removed DBP from soil (removing 91.0%-99.2% within 10 d and from rice plant slurry (removing 93.4%-99.2% within 5 d). These results confirmed the hypothesis and demonstrated the diversity of endophytic bacteria in wild rice with diverse functions, especially for plant growth promoting and removing PAEs. These multifunctional endophytic bacteria provided good alternatives to reduce PAE accumulation in crops and increase yield.

A switchable sensor and scavenger: detection and removal of fluorinated chemical species by a luminescent metal-organic framework

Fluorosis has been regarded as a worldwide disease that seriously diminishes the quality of life through skeletal embrittlement and hepatic damage. Effective detection and removal of fluorinated chemical species such as fluoride ions (F⁻) and perfluorooctanoic acid (PFOA) from drinking water are of great importance for the sake of human health. Aiming to develop water-stable, highly selective and sensitive fluorine sensors, we have designed a new luminescent MOF In(tcpp) using a chromophore ligand 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine (H₄tcpp). In(tcpp) exhibits high sensitivity and selectivity for turn-on detection of F⁻ and turn-off detection of PFOA with a detection limit of 1.3 μg L⁻¹ and 19 μg L⁻¹, respectively. In(tcpp) also shows high recyclability and can be reused multiple times for F⁻ detection. The mechanisms of interaction between In(tcpp) and the analytes are investigated by several experiments and DFT calculations. These studies reveal insightful information concerning the nature of F⁻ and PFOA binding within the MOF structure. In addition, In(tcpp) also acts as an efficient adsorbent for the removal of F⁻ (36.7 mg g⁻¹) and PFOA (980.0 mg g⁻¹). It is the first material that is not only capable of switchable sensing of F⁻ and PFOA but also competent for removing the pollutants via different functional groups.

A robust In-MOF, In(tcpp), demonstrates sensitive detection of the fluorinated chemical species F⁻ and PFOA via distinctly different luminescence signal change, and effective adsorption and removal of both species from aqueous solution.

Per- and polyfluoroalkyl substances (PFASs) in the soil-plant system: Sorption, root uptake, and translocation

Per- and polyfluoroalkyl substances (PFASs) are ubiquitous in the environment but pose potential risks to ecosystems and human health. The soil-plant system plays an important role in the bioaccumulation of PFASs. Because most PFASs in the natural environment are anionic and amphiphilic (both lipophilic and hydrophilic), their sorption and accumulation behaviors differ from those of neutral organic and common ionic compounds. In this review, we discuss processes affecting the availability of PFASs in soil after analyzing the potential mechanisms underlying the sorption and uptake of PFASs in the soil-plant system. We also summarize the current knowledge on root uptake and translocation of PFASs in plants. We found that the root concentration factor of PFASs for plants grown in soil was not significantly correlated with hydrophobicity, whereas the translocation factor was significantly and negatively correlated with PFAS hydrophobicity regardless of whether plants were grown hydroponically or in soil. Further research on the cationic, neutral, and zwitterionic forms of diverse PFASs is urgently needed to comprehensively understand the environmental fates of PFASs in the soil-plant system. Additional research directions are suggested, including the development of more accurate models and techniques to evaluate the bioavailability of PFASs, the effects of root exudates and rhizosphere microbiota on the bioavailability and plant uptake of PFASs, and the roles of different plant organelles, lipids, and proteins in the accumulation of PFASs by plants.

Distribution, behaviour, bioavailability and remediation of poly- and per-fluoroalkyl substances (PFAS) in solid biowastes and biowaste-treated soil

Aqueous film-forming foam, used in firefighting, and biowastes, including biosolids, animal and poultry manures, and composts, provide a major source of poly- and perfluoroalkyl substances (PFAS) input to soil. Large amounts of biowastes are added to soil as a source of nutrients and carbon. They also are added as soil amendments to improve soil health and crop productivity. Plant uptake of PFAS through soil application of biowastes is a pathway for animal and human exposure to PFAS. The complexity of PFAS mixtures, and their chemical and thermal stability, make remediation of PFAS in both solid and aqueous matrices challenging. Remediation of PFAS in biowastes, as well as soils treated with these biowastes, can be achieved through preventing and decreasing the concentration of PFAS in biowaste sources (i.e., prevention through source control), mobilization of PFAS in contaminated soil and subsequent removal through leaching (i.e., soil washing) and plant uptake (i.e., phytoremediation), sorption of PFAS, thereby decreasing their mobility and bioavailability (i.e., immobilization), and complete removal through thermal and chemical oxidation (i.e., destruction). In this review, the distribution, bioavailability, and remediation of PFAS in soil receiving solid biowastes, which include biosolids, composts, and manure, are presented.

Phytoremediation of poly- and perfluoroalkyl substances: A review on aquatic plants, influencing factors, and phytotoxicity

Poly- and perfluoroalkyl substances (PFASs) are a group of emerging organic contaminants which are persistent to normal physicochemical treatments. The widespread use of PFASs has caused significant environmental issues. The bioaccumulation and distribution of PFASs within plant compartments have revealed great potentials for phytoremediation. In this review, the roles of aquatic plants in the process of PFASs remediation were highlighted. Moreover, there were different underlying mechanisms of PFASs uptake between terrestrial and aquatic plants. On the other hand, a wide range of influencing factors for bioaccumulation and translocation of PFASs within plant compartments are also presented and discussed. In response to exposure of PFASs, corresponding phytotoxic effects has affected the growth and metabolism of plants, which could provide beneficial guides of the phytotoxic tolerance for plant species selection in applications of phytoremediation. Finally, the discussion about whether phytoremediation is a viable option for PFASs removal and further research priorities are suggested.

Role of Rhizospheric Microbiota as a Bioremediation Tool for the Protection of Soil-Plant Systems from Microcystins Phytotoxicity and Mitigating Toxin-Related Health Risk

Frequent toxic cyanoblooms in eutrophic freshwaters produce various cyanotoxins such as the monocyclic heptapeptides microcystins (MCs), known as deleterious compounds to plant growth and human health. Recently, MCs are a recurrent worldwide sanitary problem in irrigation waters and farmland soils due to their transfer and accumulation in the edible tissues of vegetable produce. In such cases, studies about the persistence and removal of MCs in soil are scarce and not fully investigated. In this study, we carried out a greenhouse trial on two crop species: faba bean (Vicia faba var. Alfia 321) and common wheat (Triticum aestivum var. Achtar) that were grown in sterile (microorganism-free soil) and non-sterile (microorganism-rich soil) soils and subjected to MC-induced stress at 100 µg equivalent MC-LR L⁻¹. The experimentation aimed to assess the prominent role of native rhizospheric microbiota in mitigating the phytotoxic impact of MCs on plant growth and reducing their accumulation in both soils and plant tissues. Moreover, we attempted to evaluate the health risk related to the consumption of MC-polluted plants for humans and cattle by determining the estimated daily intake (EDI) and health risk quotient (RQ) of MCs in these plants. Biodegradation was liable to be the main removal pathway of the toxin in the soil; and therefore, bulk soil (unplanted soil), as well as rhizospheric soil (planted soil), were used in this experiment to evaluate the accumulation of MCs in the presence and absence of microorganisms (sterile and non-sterile soils). The data obtained in this study showed that MCs had no significant effects on growth indicators of faba bean and common wheat plants in non-sterile soil as compared to the control group. In contrast, plants grown in sterile soil showed a significant decrease in growth parameters as compared to the control. These results suggest that MCs were highly bioavailable to the plants, resulting in severe growth impairments in the absence of native rhizospheric microbiota. Likewise, MCs were more accumulated in sterile soil and more bioconcentrated in root and shoot tissues of plants grown within when compared to non-sterile soil. Thereby, the EDI of MCs in plants grown in sterile soil was more beyond the tolerable daily intake recommended for both humans and cattle. The risk level was more pronounced in plants from the sterile soil than those from the non-sterile one. These findings suggest that microbial activity, eventually MC-biodegradation, is a crucial bioremediation tool to remove and prevent MCs from entering the agricultural food chain.

Variety-Selective Rhizospheric Activation, Uptake, and Subcellular Distribution of Perfluorooctanesulfonate (PFOS) in Lettuce (Lactuca sativa L.)

Perfluorooctanesulfonate (PFOS) as an accumulative emerging persistent organic pollutant in crops poses severe threats to human health. Lettuce varieties that accumulate a lower amount of PFOS (low-accumulating crop variety, LACV) have been identified, but the regarding mechanisms remain unsolved. Here, rhizospheric activation, uptake, translocation, and compartmentalization of PFOS in LACV were investigated in comparison with those of high-accumulating crop variety (HACV) in terms of rhizospheric forms, transporters, and subcellular distributions of PFOS. The enhanced PFOS desorption from the rhizosphere soils by dissolved organic matter from root exudates was observed with weaker effect in LACV than in HACV. PFOS root uptake was controlled by a transporter-mediated passive process in which low activities of aquaporins and rapid-type anion channels were corrected with low expression levels of PIPs (PIP1-1 and PIP2-2) and ALMTs (ALMT10 and ALMT13) genes in LACV roots. Higher PFOS proportions in root cell walls and trophoplasts caused lower root-to-shoot transport in LACV. The ability to cope with PFOS toxicity to shoot cells was poorer in LACV relative to HACV since PFOS proportions were higher in chloroplasts but lower in vacuoles. Our findings provide novel insights into PFOS accumulation in lettuce and further understanding of multiprocess mechanisms of LACV.

Effect of soil organic matter on the plant uptake of perfluorooctanoic acid (PFOA) and perfluorooctanesulphonic acid (PFOS) in lettuce on granular activated carbon-applied soil

The presence of perfluorooctanoic acid (PFOA) and perfluorooctanesulphonic acid (PFOS) in crops is an important consideration for food safety. The soil organic matter (SOM) content may affect the adsorption potential of PFOA and PFOS in water and soil and their subsequent uptake in crops. To better understand these dynamics, the adsorption and uptake of PFOA and PFOS in lettuce were investigated using granular activated carbon (GAC)-treated soils with varying SOM content. The adsorption potential of GAC was investigated, with maximum adsorption capacities for PFOA and PFOS calculated to be 9.091 mg g-1 and 27.778 mg g-1, respectively. These values decreased to 5.208 mg g-1 and 17.241 mg g-1, respectively, after the addition of 0.04 wt% humic acid. The average plant uptake factor (PUF) in low and high perfluoroalkyl and polyfluoroalkyl acid (PFAA)-contaminated soils with 4.0 wt% SOM was restricted to 0.353 for PFOA and 0.108 for PFOS. The PUFs were approximately two times lower than those for soil with 2.6 wt% SOM. Addition of 1 wt% GAC to the soil successfully reduced the PUF by up to 99.4%, with values of 0.006 (PFOA) and 0.005 (PFOS) in 2.6 wt% SOM-treated soil and 0.079 (PFOA) and 0.023 (PFOS) in 4.0 wt% SOM-treated soil. Although the PUF in the GAC-treated soil was drastically decreased, the PUF of the soil with 4.0 wt% SOM was at least four times higher than that with 2.6 wt% SOM. Therefore, SOM content is an important consideration in the remediation of PFOA- and PFOS-contaminated farmland soil using carbonaceous adsorbent.

Nitrate supply decreases uptake and accumulation of ciprofloxacin in Brassica parachinensis

How nitrate (NO₃^-) fertilization influences ciprofloxacin (CIP) uptake by crops remains unsolved. Here, two Brassica parachinensis cultivars differing in CIP accumulation were cultivated to investigate the effects of NO₃^- supply on CIP uptake and the underlying mechanism. The results showed that NO₃^- supply effectively reduced CIP toxicity and accumulation in the two cultivars, especially in the low CIP cultivar. Moreover, NO₃^- supply induced different mechanisms of coping with CIP stress in the two cultivars through influencing subcellular distribution of CIP. The uptake of CIP by root was demonstrated to be a carrier-mediated, energy-consuming, and proton motive force-dependent influx process. Consequently, a mechanism of nitrate supply decreasing CIP uptake was proposed that uptake of CIP and NO₃- into root cell would compete for the proton motive force and share a common energy source provided by plasma membrane H⁺-ATPase. Besides, regulating the concentration balances of cytoplasmic NO₃- and proton by inhibiting the activities of NRase and two tonoplast proton pumps (V-ATPase and V-PPase) led to opposite effect on CIP uptake, further supporting this inference. Our results provide a novel insight into CIP uptake by plant roots, and improve the strategy of minimizing CIP accumulation in crops for food safety by fertilization management.

Dynamics, thermodynamics, and mechanism of perfluorooctane sulfonate (PFOS) sorption to various soil particle-size fractions of paddy soil

Soil is an important sink for perfluorooctane sulfonate (PFOS) that is a typical persistent organic pollutant with high toxicity. Understanding of PFOS sorption to various particle-size fractions of soil provides an insight into the mobility and bioavailability of PFOS in soil. This study evaluated kinetics, isotherms, and mechanisms of PFOS sorption to six soil particle-size fractions of paddy soil at environmentally relevant concentrations (0.01-1 μg/mL). The used soil particle-size fractions included coarse sand (120.4-724.4 mm), fine sand (45.7-316.2 mm), coarse silt (17.3-79.4 mm), fine silt (1.9-39.8 mm), clay (0.5-4.4 mm), and humic acid fractions (8.2-83.7 mm) labeled as F1~F6, respectively. PFOS sorption followed pseudo-second-order kinetics related to film diffusion and intraparticle diffusion, with speed-limiting phase acted by the latter. PFOS sorption isotherm data followed Freundlich model, with generally convex isotherms in larger size fractions (F1~F3) but concave isotherms in smaller size fractions (F4 and F5) and humic acid fraction (F6). Increasing organic matter content, Brunner-Emmet-Teller surface area, and smaller size fractions were conducive to PFOS sorption. Hydrophobic force, divalent metal ion-bridging effect, ligand exchange, hydrogen bonding, and protein-like interaction played roles in PFOS sorption. But hydrophobic force controlled the PFOS sorption, because its relevant organic matter governed the contribution of the soil fractions to the overall PFOS sorption. The larger size fractions dominated the PFOS sorption to the original soil because of their high mass percentages (~80%). This likely caused greater potential risks of PFOS migration into groundwater and bioaccumulation in crops at higher temperatures and c_e values, based on their convex isotherms with an exothermic physical process.

Uptake and accumulation of per- and polyfluoroalkyl substances in plants

Per- and polyfluoroalkyl substances (PFASs) are a class of persistent organic contaminants that are ubiquitous in the environment and have been found to be accumulated in agricultural products. Consumption of PFAS-contaminated agricultural products represents a feasible pathway for the trophic transfer of these toxic chemicals along food chains/webs, leading to risks associated with human and animal health. Recently, studies on plant uptake and accumulation of PFASs have rapidly increased; consequently, a review to summarize the current knowledge and highlight future research is needed. Analysis of the publications indicates that a large variety of plant species can take up PFASs from the environment. Vegetables and grains are the most commonly investigated crops, with perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) as the most studied PFASs. The potential sources of PFASs for plant uptake include industrial emissions, irrigation with contaminated water, land application of biosolids, leachates from landfill sites, and pesticide application. Root uptake is the predominant pathway for the accumulation of PFASs in agricultural crops, and uptake by plant aboveground portions from the ambient atmosphere could play a minor role in the overall PFAS accumulation. PFAS uptake by plants is influenced by physicochemical properties of compounds (e.g., perfluorocarbon chain length, head group functionality, water solubility, and volatility), plant physiology (e.g., transpiration rate, lipid and protein content), and abiotic factors (e.g., soil organic matters, pH, salinity, and temperature). Based on literature analysis, the current knowledge gaps are identified, and future research prospects are suggested.

Oxalic Acid in Root Exudates Enhances Accumulation of Perfluorooctanoic Acid in Lettuce

Perfluorooctanoic acid (PFOA) is bioaccumulative in crops. PFOA bioaccumulation potential varies largely among crop varieties. Root exudates are found to be associated with such variations. Concentrations of low-molecular-weight organic acids (LMWOAs) in root exudates from a PFOA-high-accumulation lettuce variety are observed significantly higher than those from PFOA-low-accumulation lettuce variety (p < 0.05). Root exudates and their LMWOAs components exert great influences on the linear sorption-desorption isotherms of PFOA in soils, thus activating PFOA and enhancing its bioavailability. Among root exudate components, oxalic acid is identified to play a key role in activating PFOA uptake, with >80% attribution. Oxalic acid at rhizospheric concentrations (0.02-0.5 mM) can effectively inhibit PFOA sorption to soils by decreasing hydrophobic force, electrostatic attraction, ligand exchange, and cation-bridge effect. Oxalic acid enhances dissolution of metallic ions, iron/aluminum oxides, and organic matters from soils and forms oxalate-metal complexes, based on nuclear magnetic resonance spectra, ultraviolet spectra, and analyses of metal ions, iron/aluminum organometallic complexes, and dissolved organic carbon. The findings not only reveal the activation process of PFOA in soils by root exudates, particularly oxalic acid at rhizospheric concentrations, but also give an insight into the mechanism of enhancing PFOA accumulation in lettuce varieties.

Uptake mechanism, subcellular distribution, and uptake process of perfluorooctanoic acid and perfluorooctane sulfonic acid by wetland plant Alisma orientale

Perfluoroalkyl substances (PFASs) are of particular environmental concern due to their environmental persistence and potential toxicity. Phytoremediation may be used to remove PFASs from wastewater. Here we investigated the uptake mechanism, subcellular distribution, and uptake process of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate acid (PFOS) in the wetland plant Alisma orientale by using a series of hydroponic experiments. Active uptake facilitated by water transporters and anion channels was involved in the uptake of PFASs by plant roots. PFOA and PFOS were mainly distributed in the water-soluble fraction (46.2-70.8%) and in cell walls (45.6-58.4%), respectively. The uptake process was proposed as follows: PFOS and PFOA were first distributed in the soluble fraction; a proportion of PFOS and PFOA were adsorbed gradually by the cell wall, and a proportion of PFOS and PFOA in the cell wall passed through the cell wall and plasmalemma and bind with organelles. PFOS and PFOA were transported from the external solution to the vascular bundle of the plant root through both symplastic and apoplastic routes.

Bioaccumulation and Phytotoxicity and Human Health Risk from Microcystin-LR under Various Treatments: A Pot Study

Microcystin-LR (MC-LR) is prevalent in water and can be translocated into soil-crop ecosystem via irrigation, overflow (pollution accident), and cyanobacterial manure applications, threatening agricultural production and human health. However, the effects of various input pathways on the bioaccumulation and toxicity of MCs in terrestrial plants have been hardly reported so far. In the present study, pot experiments were performed to compare the bioaccumulation, toxicity, and health risk of MC-LR as well as its degradation in soils among various treatments with the same total amount of added MC-LR (150 μg/kg). The treatments included irrigation with polluted water (IPW), cultivation with polluted soil (CPS), and application of cyanobacterial manure (ACM). Three common leaf-vegetables in southern China were used in the pot experiments, including Ipomoea batatas L., Brassica juncea L., and Brassica alboglabra L. All leaf vegetables could bioaccumulate MC-LR under the three treatments, with much higher MC-LR bioaccumulation, especially root bioconcentration observed in ACM treatment than IPW and CPS treatments. An opposite trend in MC-LR degradation in soils of these treatments indicated that ACM could limit MC-LR degradation in soils and thus promote its bioaccumulation in the vegetables. MC-LR bioaccumulation could cause toxicity to the vegetables, with the highest toxic effects observed in ACM treatment. Similarly, bioaccumulation of MC-LR in the edible parts of the leaf-vegetables posed 1.1~4.8 fold higher human health risks in ACM treatment than in IPW and CPS treatments. The findings of this study highlighted a great concern on applications of cyanobacterial manure.

Robust Matrix Effect-Free Method for Simultaneous Determination of Legacy and Emerging Per- and Polyfluoroalkyl Substances in Crop and Soil Matrices

Increasing use of emerging per- and polyfluoroalkyl substances (PFASs) has caused extensive concerns around the world. Effective detection methods to trace their pollution characteristics and environmental behaviors in complex soil-crop systems are urgently needed. In this study, a reliable and matrix effect (ME)-free method was developed for simultaneous determination of 14 legacy and emerging PFASs, including perfluorooctanoic acid, perfluorooctane sulfonate, 6 hydrogenous PFASs, 3 chlorinated PFASs, and 3 hexafluoropropylene oxide homologues, in 6 crop (the edible parts) and 5 soil matrices using ultrasonic extraction combined with solid-phase extraction and ultraperformance liquid chromatography-mass spectrometry (MS)/MS. The varieties of extractants and cleanup cartridges, the dosage of ammonia hydroxide, and the ME were studied to obtain an optimal pretreatment procedure. The developed method had high sensitivity and accuracy with satisfactory method detection limits (2.40-83.03 pg/g dry weight) and recoveries (72-117%) of all target analytes in matrices at five concentrations, that is, 0.1, 1, 10, 100, and 1000 ng/g. In addition, the ME of this method (0.82-1.15) was negligible for all PFASs, even considering 11 different matrices. The successful application of the ME-free method to simultaneously determine the legacy and emerging PFASs in crop and soil samples has demonstrated its excellent practicability for monitoring emerging PFASs in soil-crop systems.

Challenges of aqueous per- and polyfluoroalkyl substances (PFASs) and their foreseeable removal strategies

Per- and polyfluoroalkyl substances (PFASs) are artificial refractory organic pollutants which are widely presented in aqueous environment. Due to the unquiet strength of the highly polarized carbon-fluorine bond (C-F) and their hydrophobic/lipophobic feature as well as biological persistence properties, the remediation and treatment of PFASs is a big challenge. Preliminary studies indicate that a few kinds of technical approaches could remove or transfer PFASs, but the effectiveness is not high as expected or limited while most of the techniques are only tested at laboratory scale. A review of existing treatment technologies was thus conducted for the purpose to outlook these technologies, and more importantly, to propose the foreseeable technique. As such, a constructed wetland-microbial fuel cell (CW-MFC) technology was recommended, which is a newly emerged technology by integrating physical, chemical and enhanced biological processes plus the wetland plants function with strong eco-friendly feature for a comprehensive removal of PFASs. It is expected that the review can strengthen our understanding on PFASs' research and thus can help selecting reasonable technical means of aqueous PFASs control.

Rice root exudates enhance desorption and bioavailability of phthalic acid esters (PAEs) in soil associating with cultivar variation in PAE accumulation

Phthalic acid esters (PAEs) is a class of prevalent pollutants in agricultural soil, threating food safety through crop uptake and accumulation of PAEs. Accumulation of PAEs varies largely among crop species and cultivars. Nevertheless, how root exudates affect PAE bioavailability, dissipation, uptake and accumulation is still not well understood. In the present study, desorption and pot experiments were designed to investigate how root exudates from high-(Peizataifeng) and low-(Fengyousimiao) PAE accumulating rice cultivars affect soil PAE bioavailability, dissipation, and accumulation variation. Rice root exudates including low molecular weight organic acids (LMWOAs) of Peizataifeng and Fengyousimiao could enhance desorption of two typical PAE compounds, di-n-butyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP), from aged soil to their available fractions by increasing soil dissolved organic carbon (DOC), thus improving their bioavailability in soil. Peizataifeng produced twice higher amounts of oxalic acid, critic acid and malonic acid in root exudates, and exhibited stronger effects on enhancing desorption and bioavailability of DBP and DEHP than Fengyousimiao. Higher (by about 50%) total organic carbon contents of root exudates from Peizataifeng led to higher (by 10-30%) soil microbial biomass carbon and nitrogen than Fengyousimiao, and thus promoted more PAE dissipation from soil than Fengyousimiao. Nevertheless, higher (by 20-50%) soil DOC and significantly higher PAE bioavailability in the soils planted Peizataifeng resulted in greater (by 53-93%) PAE accumulation in roots and shoots of Peizataifeng than Fengyousimiao, confirming by higher (by 1.82-3.48 folds) shoot and root bioconcentration factors of Peizataifeng than Fengyousimiao. This study reveals that the difference in root exudate extent and LMWOAs between Peizataifeng and Fengyousimiao differentiates PAE accumulation.

Response of cucumber (Cucumis sativus) to perfluorooctanoic acid in photosynthesis and metabolomics

A mechanistic understanding of perfluorooctanoic acid (PFOA) toxicity to plants is essential for future risk assessment of PFOA in agricultural soil. In this study, soil-grown cucumber (Cucumis sativus) was exposed to 0, 0.2, and 5 mg/kg of PFOA for 60 days. At harvest, contaminant accumulation, cucumber biomass, photosynthesis profiles and metabolites were measured. Results showed that PFOA depressed cucumber biomass and accumulated highest in leaves. Photosynthesis analysis revealed that PFOA at both doses reduced the chlorophyll contents and net photosynthesis rate of cucumber leaves. Gas chromatography-mass spectrometry-based non-targeted metabolomics revealed that PFOA induced metabolic reprogramming in cucumber leaves, including up-regulation of phenols (at 0.2 and 5 mg/kg) and down-regulation of amino acids (at 5 mg/kg), indicating disrupted nitrogen and carbon metabolism. Results revealed how PFOA represses plant growth by down-regulating photosynthetic pigments and disturbing the metabolism of carbohydroxides, phenols and amino acids. These findings provide valuable information for understanding the molecular mechanisms involved in plant responses to PFOA-induced stress.

Subcellular distribution governing accumulation and translocation of pesticides in wheat (Triticum aestivum L.)

Root uptake, translocation, and subcellular distribution of six pesticides (dinotefuran, thiamethoxam, imidacloprid, imazethapyr, propiconazole, and chlorpyrifos) with K_ow ranging from -0.549 to 4.7 were investigated in wheat to study transportation and accumulation of pesticides. The root bioconcentration factor (RCF) of pesticides decreased with water solubility (R² = 0.6121) and increased with hydrophobicity (when the pH-adjusted log K_ow > 2, R² = 0.925), respectively. The translocation of neutral pesticides from roots to shoots increased positively with water solubility (R² > 0.6484) but decreased with hydrophobicity (R² > 0.8039). The subcellular fraction concentration factor (SFCF) increased linearly with hydrophobicity of the tested pesticides (R² > 0.958). The log RCF was positively correlated with log SFCF in root cell walls (R² = 0.9894) and organelles (R² = 0.9786). Transportation of the pesticides from roots to stems and stems to leaves was adversely affected by the log SFCF of cell walls and organelles of roots (R² > 0.7997) and stems (R² > 0.6666), respectively. Hydrophobicity-dependent SFCF is a factor governing accumulation of pesticides in roots after uptake and their subsequent upward translocation.

Model-based analysis of the uptake of perfluoroalkyl acids (PFAAs) from soil into plants

Perfluoroalkyl acids (PFAAs) bioaccumulate in crops, with uptake being particularly high for short-chain PFAAs that are constantly transported with transpiration water to aerial plant parts. Due to their amphiphilic surfactant nature and ionized state at environmental pH, predicting the partitioning behavior of PFAAs is difficult and subject to considerable uncertainty, making experimental data highly desirable. Here, we applied a plant uptake model that combines advective flux with measured partition coefficients to reproduce the set of empirically derived plant uptake and soil-partitioning data for nine PFAAs in red chicory, in order to improve the mechanistic understanding and provide new insights into the complex uptake processes. We introduced a new parameter for retarded uptake (R) to explain the slow transfer of PFAA across biomembranes of the root epidermis, which has led to low transpiration stream concentration factors (TSCFs) presented in literature so far. We estimated R values for PFAAs using experimental data derived for red chicory and used the modified plant uptake model to simulate uptake of PFAA into other crops. Results show that this semi-empirical model predicted PFAAs transport to shoots and fruits with good accuracy based on experimental root to soil concentration factors (RCF_dw) and soil to water partition coefficients (K_d) as well as estimated R values and plant-specific data for growth and transpiration. It can be concluded that the combination of rather low K_d with high RCF_dw and the absence of any relevant loss are the reason for the observed excellent plant uptake of PFAAs.

Investigations on the phytotoxicity of perfluorooctanoic acid in Arabidopsis thaliana

Environmental contamination by perfluorooctanoic acid (PFOA) has raised concerns for years. Yet, little information on its phytotoxic effects and underlying mechanisms in higher plants is available. To this end, comparative analyses of the responses to PFOA exposure between shoots and roots in the model plant species Arabidopsis thaliana were performed at the physiological and molecular levels. Our results showed that PFOA exposure reduced Arabidopsis biomass in a dose-related manner, and shoot growth was more sensitive to PFOA than root growth. Consistently, PFOA accumulation and the levels of several metal elements, including Zn, Ca, Cu, and K, in addition to Fe, were more substantially affected in the shoots than in the roots. Transcriptomic analysis further showed that the shoot transcriptional profile was distinguishable from that of roots upon PFOA exposure. Nevertheless, some overlapping genes were present between the shoots and roots, mainly including transporter genes, Fe-deficiency-responsive genes, and oxidative stress-related genes. More importantly, a comparative analysis of ROS-associated genes in combination with other oxidative stress assays pointed out that PFOA triggered certain oxidative stress-associated events more strongly in shoots than in roots. Overall, the results demonstrated that PFOA exposure caused alterations in PFOA distribution, metal element balance, reconfiguration of transcriptomes, and induction of oxidative stress in a tissue-dependent manner in Arabidopsis thaliana.

High ecological and human health risks from microcystins in vegetable fields in southern China

Frequent cyanobacterial blooms in the eutrophic waters produce a variety of toxins such as the monocyclic heptapeptide microcystins, greatly harming aquatic ecosystems and human health. However, little information of microcystins in agricultural fields is known. This field study of three common microcystin variants (MC-LR, MC-RR, and MC-YR) in vegetables (n = 161), soils (n = 161) and irrigation water samples (n = 23) collected from southern China regions affected by cyanobacteria blooms, shows their prevalence with total concentrations up to 514 μg/L water, 187 μg/kg soil (dry weight) and 382 μg/kg vegetable (fresh weight). MC-RR was the primary variant in all types of samples, accounting for 51.3-100% of total microcystin concentrations. Significant concentration-dependent correlations (p < 0.05) demonstrated that microcystin-contained irrigation waters were the major source of microcystin accumulation in both vegetables and soils. Meanwhile, intracellular-microcystins in irrigation water was found to play an important role in microcystins bioaccumulation in vegetables for the first time. Most vegetable samples (≥60%), particularly celery posed moderate or high human health risk via diet based on toxicity equivalents of the microcystins and reference dose for MC-LR (0.04 μg/kg/d), showing high food safety hidden dangers. Soil microcystins, especially MC-RR in 46.4-88.3% of soils could pose high ecological risks. This study highlights the potential high ecological and human health risks of microcystins in the real soil-vegetable systems of areas affected by cyanobacteria blooms, implying the profound significance and urgent need of investigation on microcystins in terrestrial ecosystems.

Negligible effects of TiO2 nanoparticles at environmentally relevant concentrations on the translocation and accumulation of perfluorooctanoic acid and perfluorooctanesulfonate in hydroponically grown pumpkin seedlings (Cucurbita maxima × C. moschata)

Titanium dioxide nanoparticles (TiO₂-NPs) are widely distributed in the environment. It has been demonstrated that TiO₂-NPs could modify the environmental fate and bioavailability of organic pollutants, which affects ecological risks of TiO₂-NPs and organic pollutants. In this study, the uptake, translocation and accumulation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) in pumpkin plants was investigated in the presence of TiO₂-NPs. We reported for the first time the negligible effects of TiO₂-NPs at environmentally relevant concentrations (0.05-5 mg/L) on the uptake and accumulation of PFOA and PFOS in hydroponically grown pumpkin seedlings regardless of root, stem and leaf. This phenomenon was independent of the initial concentrations of PFOA/PFOS and TiO₂-NPs in the exposure solution. Also, seedling mass and contents of chlorophyll and anthocyanin were not affected by the co-exposure. Adsorption tests demonstrated the negligible adsorption of PFOA/PFOS on TiO₂-NPs in the exposure solution. Moreover, uptake of PFOA/PFOS was insensitive to aquaporin inhibitor AgNO₃ but significantly inhibited by niflumic acid (anion channel blocker) and 2,4-dinitrophenol (metabolic inhibitor) whereas Ti concentration in root was not affected by niflumic acid and 2,4-dinitrophenol but significantly decreased by AgNO₃, indicating that transport of PFOA/PFOS and TiO₂-NPs were via different routes into the pumpkin seedling. It was proposed that different pathways by which TiO₂-NPs and PFOA/PFOS transported into the pumpkin seedling and negligible adsorption of PFOA/PFOS on TiO₂-NPs contributed to the negligible effects of TiO₂-NPs on the uptake, translocation and accumulation of PFOA/PFOS in pumpkin seedlings. In total, this work would improve our understanding of the ecological risks of TiO₂-NPs in the environment.

The Kinetics and Mechanisms for Photodegradation of Nitrated Polycyclic Aromatic Hydrocarbons on Lettuce Leaf Surfaces: An In Vivo Study

Insights into the environmental fates of nitrated polycyclic aromatic hydrocarbons (NPAHs) in edible vegetables are of great significance for better evaluating human exposure to NPAHs through the dietary pathway. In this work, a fluorescence quenching method using graphene quantum dots as a fluorescent probe was first applied for the in vivo determination of 9-nitroanthracene (9-NAnt) and 1-nitropyrene (1-NPyr) adsorbed on the leaf surfaces of living lettuce (Lactuca sativa L.) seedlings. Moreover, the photolysis kinetics and mechanisms of the two adsorbed NPAHs were discussed. The photodegradation kinetics followed the pseudo-first-order equation, and the photodegradation half-life of 1-NPyr (7.4 ± 0.2 h) was greater than that of 9-NAnt (2.3 ± 0.1 h). Anthraquinone and pyrenediones were identified to be the main photolytic products of 9-NAnt and 1-NPyr, respectively. Intramolecular rearrangement was the most reasonable mechanism for the NPAH photolysis. The photolysis-driven degradation exhibited a key role in scavenging NPAHs from the vegetable leaf, indicating the reduction of NPAH transportation in the food chain.

Distribution and partitioning of perfluoroalkyl carboxylic acids in surface soil, plants, and earthworms at a contaminated site

A field study was conducted to elucidate distribution and partitioning of perfluoroalkyl carboxylic acids (PFCAs; C7-12) in a terrestrial ecosystem that was contaminated with industrial sources of release. Surface soil (0-6 cm), plants, and earthworms were collected from a field located within a 1-mile radius of a fluoropolymer industry that had been manufacturing fluorochemicals for over five decades. The mean concentrations of ∑PFCAs were 150, 420, 61, 68, and 430 ng/g dry weight (dw) in surface soil, earthworms, grass roots, grass leaves, and tree leaves, respectively. The measured concentrations were higher than those reported for corresponding matrices in other locations worldwide, suggesting that fluorochemical manufacturing operations have contributed to the contamination of this nearby land. Soil and plant tissues consisted mainly of perfluorooctanoic acid (PFOA; C8) (77.3-97.1% of the total PFCAs), whereas longer-chain PFCAs, such as perfluoroundecanoic acid (PFUnDA; C11: 17.6%) and perfluorododecanoic acid (PFDoDA; C12: 31.9%), accounted for relatively higher proportions in earthworms. Spatial distribution of PFCAs at this site suggested that both atmospheric deposition and groundwater recharge have contributed to the sources of contamination. Both earthworm- and grass-accumulated PFCAs from soil with biota-soil accumulation factors and root concentration factors increased with perfluorocarbon chain length. The translocation factors of PFCAs in grass decreased as the number of carbons in the fluorocarbon moiety increased. This field study is appropriate to improve our understanding of partitioning of PFCAs among soil, plants, and earthworms.

Cultivar-Dependent Accumulation and Translocation of Perfluorooctanesulfonate among Lettuce ( Lactuca sativa L.) Cultivars Grown on Perfluorooctanesulfonate-Contaminated Soil

Perfluorooctanesulfonate (PFOS) is a toxic and persistent organic pollutant that can be widely detected in agricultural soils. In this study, two lettuce cultivars with low PFOS accumulation were screened out to reduce the exposure of PFOS to the human body via vegetable consumption. The screened low-PFOS cultivars may help to ensure food safety, despite planting in highly PFOS-polluted soils (1.0 mg/kg), due to their high tolerance to PFOS and 4.4-5.7 times lower shoot PFOS concentration than the high-PFOS cultivars. Protein content and protein-mediated transpiration played key roles in regulating PFOS accumulation in the lettuce cultivars tested. Lower protein content, lower stomatal conductance, and lower transpiration rate resulted in low PFOS accumulation. This study reveals the mechanism of forming low-PFOS accumulation of lettuce cultivars at physiological and biochemical levels and lays a foundation for developing a cost-effective and safe approach to grow vegetables in PFOS-polluted soils.

Mechanism and Implication of the Sorption of Perfluorooctanoic Acid by Varying Soil Size Fractions

Sorption of perfluorooctanoic acid (PFOA), a toxic and persistent organic pollutant, by various size fractions of an agricultural soil at environmentally relevant concentrations was evaluated. PFOA sorption to all fractions involved both film diffusion and intraparticle diffusion with the rate-limiting step by the latter. PFOA isotherm data fitted a linear model. Organic matter (OM), cation exchange capacity, pore volume, and the Brunauer-Emmett-Teller area played key roles in PFOA sorption. The sorption capacity followed the order of humic acid > clay (0.15-4.4 mm) > fine silt (1.9-39.8 mm) > coarse silt (17.3-79.4 mm) > fine sand (45.7-316.2 mm) > coarse sand (120-724.4 mm), opposite to their contributions to overall PFOA sorption due to the influence of their percentage weight in the original soil. Percentage OM content was the dominant factor controlling the fraction contributions to overall PFOA sorption, demonstrating influence of the hydrophobic force on sorption. PFOA should be highly mobile and bioavailable in soil-crop systems due to the low log K_oc values.