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

Distribution, uptake, and daily exposure of per- and polyfluoroalkyl substances in a paddy field: A growth cycle study

Rice, a crucial agricultural commodity, is potentially susceptible to contamination by persistent organic pollutants throughout its entire growth cycle in the field. Per- and polyfluoroalkyl substances (PFASs) have attracted great scientific attention due to their environmental persistence, bioaccumulation potentials, and toxicity. However, the occurrence and behavior of PFASs in the paddy ecosystem have not been confirmed. This study explored the uptake, accumulation, and potential risks of PFASs in the irrigation water, soils and paddy tissues from a typical paddy system at the main stages of rice growth. The total PFAS concentrations in irrigation water and soils were in the range of 62.9 -85.5 ng/L and 45.7 -75.4 ng/g dw. The concentrations of PFASs in paddy tissues followed the order of root>stem>leaf>grain. A minor decrease in PFAS concentrations in paddy tissues with growth time may be attributed to biotransformation and growth dilution. PFAS distribution in soils, irrigation water, and different paddy tissues also showed different patterns with the growing time of paddy. ΣPFCAs and ΣPFSAs were the most prevalent PFASs in all samples, which constituted 65.0 -96.3 % of the total PFASs. In addition, the transfer factor (TF) values from root to stem/leaf/grain decreased as Log KOW increased (Log KOW< 5). Significant correlations between the concentrations and protein contents in paddy grains were observed for most long-chain PFASs. Risk assessments have suggested that the current levels do not pose a health risk to humans, but PFAS alternatives cannot be neglected for food safety and environmental impacts.

Phytodegradation and phytotoxicity of N-ethyl perfluorooctane sulfonamidoethanol (N-EtFOSE) in pakchoi (Brassica chinensis L.) via root and foliar uptake from physio-biochemical and transcriptomic perspectives

N-ethyl perfluorooctane sulfonamidoethanol (N-EtFOSE), a known volatile perfluorooctane sulfonate (PFOS) precursor (PreFOS), has been widely detected in the environment. However, the mechanisms underlying the behaviors and phytotoxicity of N-EtFOSE in plants are unknown. Integrative physio-biochemical and transcriptomic analyses were used to reveal the accumulation, biotransformation, and toxicity of N-EtFOSE in pakchoi (Brassica chinensis L.) through root and foliar exposure experiments. Root uptake from exposure medium and efficient translocation to shoot, and foliar uptake from air and inefficient root transfer of N-EtFOSE were observed. N-EtFOSE was biotransformed into various PreFOSs and ultimately into PFOS, with N-ethyl perfluorooctane sulfonamide (N-EtFOSA) identified as the major intermediate. Enzyme assays and gene expression analyses indicated that this biotransformation was mediated by alcohol dehydrogenase, aldehyde dehydrogenase, cytochrome P450, glutathione S-transferase, and ATP-binding cassette transporters. N-EtFOSE led to inhibition of plant growth, photosynthetic rate, and respiration rate, as well as to lipid peroxidation, oxidative damage and subcellular damage. Transcriptomic analysis revealed that differentially expressed genes (DEGs) mainly relative to plant endogenous phytohormones homeostasis, regulation of photosynthesis and respiration, oxidative stress, and xenobiotic metabolism and detoxification. This study highlighted the degradation and stress response mechanisms of N-EtFOSE in plants, providing important information to evaluate the environmental risks of volatile per/polyfluoroalkyl substances (PFASs).

Differential uptake and translocation of perfluoroalkyl substances by vegetable roots and leaves: Insight into critical influencing factors

Crop contamination of perfluoroalkyl substances (PFASs) may threaten human health, with root and leaves representing the primary uptake pathways of PFASs in crops. Therefore, it is imperative to elucidate the uptake characteristics of PFASs by crop roots and leaves as well as the critical influencing factors. In this study, the uptake and translocation of PFASs by roots and leaves of pak choi and radish were systematically explored based on perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), and perfluorooctane sulfonate (PFOS). Additionally, the roles of root Casparian strips, leaf stomata, and PFAS structures in the aforementioned processes were elucidated. Compared with pak choi, PFASs are more easily transferred to leaves after root uptake in radish, resulting from the lack of root Casparian strips. In pak choi root, the bioaccumulation of C4-C8 perfluoroalkyl carboxylic acids (PFCAs) showed a U-shaped trend with the increase of their carbon chain lengths, and the translocation potentials of individual PFASs from root to leaves negatively correlated with their chain lengths. The leaf uptake of PFOA in pak choi and radish mainly depended on cuticle sorption, with the evidence of a slight decrease in the concentrations of PFOA in exposed leaves after stomatal closure induced by abscisic acid. The leaf bioaccumulation of C4-C8 PFCAs in pak choi exhibited an inverted U-shaped trend as their carbon chain lengths increased. PFASs in exposed leaves can be translocated to the root and then re-transferred to unexposed leaves in vegetables. The longer-chain PFASs showed higher translocation potentials from exposed leaves to root. PFOS demonstrated a higher bioaccumulation than PFOA in crop roots and leaves, mainly due to the greater hydrophobicity of PFOS. Planting root vegetables lacking Casparian strips is inadvisable in PFAS-contaminated environments, in view of their higher PFAS bioaccumulation and considerable human intake.

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

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

Bioaccumulation of PFASs in cabbage collected near a landfill site in China: Laboratory and field investigations

Previous studies found that the bioaccumulation of PFASs in vegetables poses potential risks to the health of residents in local areas near landfills in China. Therefore, our study investigated the uptake of perfluoroalkyl and polyfluoroalkyl substances (PFASs) and their accumulation and distribution in cabbage roots, stems, and leaves under both field and laboratory hydroponic conditions. It was found that the sum of concentration of 15 PFASs (designated as Σ15PFASs) in roots, stems, and leaves ranged from 24.8 to 365 ng/g, 49.2 to 204 ng/g, 11.9 to 115 ng/g, respectively, in the order of roots > stems > leaves, which were generally higher than the range in soil samples (6.07-63.91 ng/g). The dominant compounds in cabbage were PFBA and PFDA in field and hydroponic samples, respectively. The hydroponic experimental results revealed that the sum concentration of 10 PFASs (designated as Σ10PFASs) was the highest in roots, and PFDA was the dominant compound in different cabbage fractions. Bioconcentration factors of short-chain PFBA, PFPeA, and PFBS in hydroponics followed the trend of leaves > stems > roots, indicating that they were readily transported from roots to stems, and then to leaves, with the majority stored in leaves at abundance levels of 53 %, 71 %, and 60 %, respectively. Additionally, the much higher concentration factor for 6:2 FTS in leaves suggested a higher potential health risk than PFOS in terms of dietary consumption of cabbage leaves.

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

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