Direct observation of organic contaminant uptake, storage, and metabolism within plant roots

Combining a tunable pinhole with synchronous fluorescence spectrometry for visualization and quantification of benzo[a]pyrene at the root epidermis microstructure of Kandelia obovata

The adsorption of polycyclic aromatic hydrocarbons (PAHs) by mangrove roots and their transport to chloroplasts is a potentially critical process that reduces the carbon sequestration efficiency of mangroves. Yet the crucial initial step, the distribution and retention of PAHs at the root epidermis microstructure, remains unclear. A novel method with a spatial resolution of 311 nm was developed for visualizing and quantifying benzo[a]pyrene (B[a]P) at the root epidermis microstructure (0.096 mm2) of Kandelia obovata (Ko). This method combined a tunable pinhole in laser confocal scanning microscopy with synchronous fluorescence spectrometry to reduce the auto-fluorescence interference in locating B[a]P and improve quantitative sensitivity. The linear range for the established method was 0.44-50.00 ng mm-2, with a detection limit of 0.063 ng mm-2 and a relative standard deviation of 9.45%. In a 60-day hydroponic experiment, B[a]P was primarily adsorbed along the epidermis cell walls of secondary lateral roots and lateral roots, with retained amounts of 0.65 ng mm-2 and 0.49 ng mm-2, respectively. It was found to cluster and predominantly accumulate at the epidermal cell surfaces of taproots (0.24 ng mm-2). B[a]P might enter inner root tissues through the root epidermal cell walls and surfaces of Ko, with the cell walls potentially being the main route. This study potentially provides a pathway for visualizing and quantifying B[a]P entering inner root tissues of mangroves.

Survival and reproduction tests using springtails reveal weathered petroleum hydrocarbon soil toxicity in boreal ecozone

Survival and reproduction tests were conducted using two native springtail (subclass: Collembola) species to determine the toxicity of a fine-grained (< 0.005 - 0.425 mm) soil from an industrial site located in the Canadian boreal ecozone. Accidental petroleum hydrocarbon (PHC) release continuously occurred at this site until 1998, resulting in a total hydrocarbon concentration of 12,800 mg/kg (soil dry weight). Subfractions of the PHC-contaminated soil were characterized using Canadian Council of Ministers of the Environment Fractions, which are based on effective carbon numbers (nC). Fraction 2 (> nC10 to nC16) was measured at 8400 mg/kg and Fraction 3 (> nC16 to nC34) at 4250 mg/kg in the contaminated soil. Age-synchronized colonies of Folsomia candida and Proisotoma minuta were subject to 0%, 25%, 50%, 75%, and 100% relative contamination mixtures of the PHC-contaminated and background site soil (< 100 mg/kg total PHCs) for 28 and 21 days, respectively. Survival and reproduction decreased significantly (Kruskal-Wallis Tests: p < 0.05, df = 4.0) in treatments of the contaminated site soil compared to the background soil. In both species, the most significant decline in survival and reproduction occurred between the 0% and 25% contaminated soil. Toxicity responses in the two springtails were ascribed to the standardized test design, short lifespans, and high fecundity in both species. This study showed that 25 + years of soil weathering has not eliminated the toxicity of fine-grained PHC-contaminated soil on two native terrestrial springtail species. Adverse effects to springtail health were attributed to exposure to soils dominated by genotoxic PHC Fraction 2 compounds and slow weathering processes due to the cold climate at the site.

Ryegrass uptake behavior and forage risk assessment after exposing to soil with combined polycyclic aromatic hydrocarbons and cadmium

Internalization of chemicals and the forage risks of ryegrass under the combined exposure to PAHs and Cd at environmental concentrations were studied here. The effect of soil pH was also concerned due to the widely occurred soil acidification and general alkali remediation for acidification soil. Unexpectedly, as same as the acid-treated group (pH 6.77), the alkali-treatment (pH 8.83) increased Cd uptake compared with original soil pH group (pH 7.92) for the reason of CdOH+ and CdHCO3+ formed in alkali-treated group. Co-exposure to PAHs induced more oxidative stress than Cd exposure alone due to PAHs aggregated in young root regions, such as root tips, and consequently, affecting the expression of Cd-transporters, destroying the basic structure of plant cells, inhibiting the energy supply for the transporters, even triggering programmed cell death, and finally resulting in decreased Cd uptake. Even under environmental concentrations, combined exposure caused potential risks derived from both PAHs and Cd. Especially, ryegrass grown in alkali-treated soil experienced an increased forage risks despite the soil meeting the national standards for Cd at safe levels. These comprehensive results reveal the mechanism of PAHs inhibiting Cd uptake, improve the understanding of bioavailability of Cd based on different forms, provide a theoretical basis to formulate the safety criteria, and guide the application of actual soil management.

Alien emergent aquatic plants develop better ciprofloxacin tolerance and metabolic capacity than one native submerged species

Antibiotic pollution and biological invasion pose significant risks to freshwater biodiversity and ecosystem health. However, few studies have compared the ecological adaptability and ciprofloxacin (CIPR) degradation potential between alien and native macrophytes. We examined growth, physiological response, and CIPR accumulation, translocation and metabolic abilities of two alien plants (Eichhornia crassipes and Myriophyllum aquaticum) and one native submerged species (Vallisneria natans) exposed to CIPR at 0, 1 and 10 mg/L. We found that E. crassipes and M. aquaticum's growth were unaffected by CIPR while V. natans was significantly hindered under the 10 mg/L treatment. CIPR significantly decreased the maximal quantum yield of PSII, actual quantum yield of PSII and relative electron transfer rate in E. crassipes and V. natans but didn't impact these photosynthetic characteristics in M. aquaticum. All the plants can accumulate, translocate and metabolize CIPR. M. aquaticum and E. crassipes in the 10 mg/L treatment group showed greater CIPR accumulation potential than V. natans indicated by higher CIPR contents in their roots. The oxidative cleavage of the piperazine ring acts as a key pathway for these aquatic plants to metabolize CIPR and the metabolites mainly distributed in plant roots. M. aquaticum and E. crassipes showed a higher production of CIPR metabolites compared to V. natans, with M. aquaticum exhibiting the strongest CIPR metabolic ability, as indicated by the most extensive structural breakdown of CIPR and the largest number of potential metabolic pathways. Taken together, alien species outperformed the native species in ecological adaptability, CIPR accumulation and metabolic capacity. These findings may shed light on the successful invasion mechanisms of alien aquatic species under antibiotic pressure and highlight the potential ecological impacts of alien species, particularly M. aquaticum. Additionally, the interaction of antibiotic contamination and invasion might further challenge the native submerged macrophytes and pose greater risks to freshwater ecosystems.

Root-zone regulation and longitudinal translocation cause intervarietal differences for phthalates accumulation in vegetables

Selecting and cultivating low-accumulating crop varieties (LACVs) is the most effective strategy for the safe utilization of di-(2-ethylhexyl) phthalate (DEHP)-contaminated soils, promoting cleaner agricultural production. However, the adsorption-absorption-translocation mechanisms of DEHP along the root-shoot axis remains a formidable challenge to be solved, especially for the research and application of LACV, which are rarely reported. Here, systematic analyses of the root surface ad/desorption, root apexes longitudinal allocation, uptake and translocation pathway of DEHP in LACV were investigated compared with those in a high-accumulating crop variety (HACV) in terms of the root-shoot axis. Results indicated that DEHP adsorption was enhanced in HACV by root properties, elemental composition and functional groups, but the desorption of DEHP was greater in LACV than HACV. The migration of DEHP across the root surface was controlled by the longitudinal partitioning process mediated by root tips, where more DEHP accumulated in the root cap and meristem of LACV due to greater cell proliferation. Furthermore, the longitudinal translocation of DEHP in LACV was reduced, as evidenced by an increased proportion of DEHP in the root apoplast. The symplastic uptake and xylem translocation of DEHP were suppressed more effectively in LACV than HACV, because DEHP translocation in LACV required more energy, binding sites and transpiration. These results revealed the multifaceted regulation of DEHP accumulation in different choysum (Brassica parachinensis L.) varieties and quantified the pivotal regulatory processes integral to LACV formation.

Effects of Graphene Oxide on Endophytic Bacteria Population Characteristics in Plants from Soils Contaminated by Polycyclic Aromatic Hydrocarbons

Environmental pollution stands as one of the significant global challenges we face today. Polycyclic aromatic hydrocarbons (PAHs), a class of stubborn organic pollutants, have long been a focal point of bioremediation research. This study aims to explore the impact and mechanisms of graphene oxide (GO) on the phytoremediation effectiveness of PAHs. The results underscore the significant efficacy of GO in accelerating the degradation of PAHs. Additionally, the introduction of GO altered the diversity and community structure of endophytic bacteria within the roots, particularly those genera with potential for PAH degradation. Through LEfSe analysis and correlation studies, we identified specific symbiotic bacteria, such as Mycobacterium, Microbacterium, Flavobacterium, Sphingomonas, Devosia, Bacillus, and Streptomyces, which coexist and interact under the influence of GO, synergistically degrading PAHs. These bacteria may serve as key biological markers in the PAH degradation process. These findings provide new theoretical and practical foundations for the application of nanomaterials in plant-based remediation of polluted soils and showcase the immense potential of plant-microbe interactions in environmental restoration.

Migration Patterns and Potential Risk Assessment of Trace Elements in the Soil-Plant System in the Production Area of the Chinese Medicinal Herb Scrophularia ningpoensis Hemsl

Scrophularia ningpoensis Hemsl. holds a prominent place among Chinese medicinal herbs. Assessing the soil-plant system of its origin is crucial for ensuring medication safety. Although some trace elements are essential for the normal functioning of living organisms, exposure to higher concentrations is harmful to humans, so in order to assess the possible health risk of trace elements in the soil-plant system of Scrophularia ningpoensis Hemsl. origin for human assessment, we used non-carcinogenic risk (HI) and carcinogenic risk (CR) for their evaluation. In this paper, the following trace elements were studied in the soil-Scrophularia ningpoensis Hemsl. system: manganese (Mn), iron (Fe), cobalt (Co), zinc (Zn), selenium (Se), molybdenum (Mo), arsenic (As) and lead (Pb). Correlation and structural equation analyses showed that the effect of soil in the root zone on the plant was much greater than the effect of soil in the non-root zone on the plant. The single-factor pollution index (Pi) showed that the soil in the production area of Scrophularia ningpoensis Hemsl. was polluted to a certain extent, notably with Pb showing the highest average Pi values of 0.94 and 0.89 in the non-root and root zones, respectively. Additionally, the Nemerow composite pollution indices (PN) for both zones indicated an alert range. Regarding health risks, exposure to soil in the non-root zone posed higher non-carcinogenic risk (HI) and carcinogenic risk (CR) compared to the root zone, although neither zone presented a significant carcinogenic risk. The potential non-carcinogenic risk (HI) and carcinogenic risk (CR) from consuming Scrophularia ningpoensis Hemsl. leaves and stems were more than ten times higher than that of roots. However, the carcinogenic risk (CR) values for both the soil and plant of interest in the soil- Scrophularia ningpoensis Hemsl. system did not exceed 10-4, and therefore no significant carcinogenic risk existed.

Phenanthrene metabolism in Panicum miliaceum: anatomical adaptations, degradation pathway, and computational analysis of a dioxygenase enzyme

Polycyclic aromatic compounds (PAHs) are persistent organic pollutants of environmental concern due to their potential impacts on food chain, with plants being particularly vulnerable. While plants can uptake, transport, and transform PAHs, the precise mechanisms underlying their localization and degradation are not fully understood. Here, a cultivation experiment conducted with Panicum miliaceum exposed different concentrations of phenanthrene (PHE). Intermediate PHE degradation compounds were identified via GC-MS analysis, leading to the proposal of a phytodegradation pathway featuring three significant benzene ring cleavage steps. Our results showed that P. miliaceum exhibited the ability to effectively degrade high levels of PHE, resulting in the production of various intermediate products through several chemical changes. Examination of the localization and anatomical characteristics revealed structural alterations linked to PHE stress, with an observed enhancement in PHE accumulation density in both roots and shoots as treatment levels increased. Following a 2-week aging period, a decrease in the amount of PHE accumulation was observed, along with a change in its localization. Bioinformatics analysis of the P. miliaceum 2-oxoglutarate-dependent dioxygenase (2-ODD) DAO-like protein revealed a 299 amino acid structure with two highly conserved domains, namely 2OG-FeII_Oxy and DIOX_N. Molecular docking analysis aligned with experimental results, strongly affirming the potential link and direct action of 2-ODD DAO-like protein with PHE. Our study highlights P. miliaceum capacity for PAHs degradation and elucidates the mechanisms behind enhanced degradation efficiency. By integrating experimental evidence with bioinformatics analysis, we offer valuable insights into the potential applications of plant-based remediation strategies for PAHs-contaminated environments.

Polycyclic aromatic hydrocarbon (PAH) accumulation in selected medicinal plants: a mini review

The use of plant-based products in healthcare systems has experienced a tremendous rise leading to a substantial increase in global demand. However, the quality and effectiveness of such plant-based treatments are often affected due to contamination of various pollutants including polycyclic aromatic hydrocarbons (PAHs). Like other plants, medicinal plants also uptake and accumulate PAHs when exposed to a contaminated environment. The consumption of such medicinal plants and/or plant-based products causes negative effects on health rather than providing any therapeutic advantages. Unfortunately, research focusing on PAH accumulation in medicinal plants has received very limited attention. This review discusses a sizable number of literature regarding the concentration of sixteen priority PAH pollutants as recognised by the US Environmental Protection Agency (USEPA) in different medicinal plants. The review also highlights the risk assessment of cancer associated with some medicinal plants in terms of benzo[a]pyrene (BaP) equivalent concentrations.

Persistent polycyclic aromatic hydrocarbons removal from sewage sludge-amended soil through phytoremediation combined with solid-state ligninolytic fungal cultures

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the environment, causing increasing concern because of their impact on soil health, food safety and potential health risks. Four bioremediation strategies were examined to assess the dissipation of PAHs in agricultural soil amended with sewage sludge over a period of 120 days: soil-sludge natural attenuation (SS); phytoremediation using maize (Zea mays L.) (PSS); mycoremediation (MR) separately using three white-rot fungi (Pleurotus ostreatus, Phanerochaete chrysosporium and Irpex lacteus); and plant-assisted mycoremediation (PMR) using a combination of maize and fungi. In the time frame of the experiment, mycoremediation using P. chrysosporium (MR-PH) exhibited a significantly higher (P < 0.05) degradation of total PAHs compared to the SS and PSS treatments, achieving a degradation rate of 52 %. Both the SS and PSS treatments demonstrated a lower degradation rate of total PAHs, with removal rates of 18 % and 32 %, respectively. The PMR treatments showed the highest removal rates of total PAHs at the end of the study, with degradation rates of 48-60 %. In the shoots of maize, only low- and medium-molecular-weight PAHs were found in both the PSS and PMR treatments. The calculated translocation and bioconversion factors always showed values < 1. The analysed enzymatic activities were higher in the PMR treatments compared to other treatments, which can be positively related to the higher degradation of PAHs in the soil.

Emerging organic contaminants in the soil-plant-receptor continuum: transport, fate, health risks, and removal mechanisms

There is a lack of comprehensive reviews tracking emerging organic contaminants (EOCs) within the soil-plant continuum using the source-pathway-receptor-impact-mitigation (SPRIM) framework. Therefore, this review examines existing literature to gain insights into the occurrence, behaviour, fate, health hazards, and strategies for mitigating EOCs within the soil-plant system. EOCs identified in the soil-plant system encompass endocrine-disrupting chemicals, surfactants, pharmaceuticals, personal care products, plasticizers, gasoline additives, flame retardants, and per- and poly-fluoroalkyl substances (PFAS). Sources of EOCs in the soil-plant system include the land application of biosolids, wastewater, and solid wastes rich in EOCs. However, less-studied sources encompass plastics and atmospheric deposition. EOCs are transported from their sources to the soil-plant system and other receptors through human activities, wind-driven processes, and hydrological pathways. The behaviour, persistence, and fate of EOCs within the soil-plant system are discussed, including sorption, degradation, phase partitioning, (bio)transformation, biouptake, translocation, and bioaccumulation in plants. Factors governing the behaviour, persistence, and fate of EOCs in the soil-plant system include pH, redox potential, texture, temperature, and soil organic matter content. The review also discusses the environmental receptors of EOCs, including their exchange with other environmental compartments (aquatic and atmospheric), and interactions with soil organisms. The ecological health risks, human exposure via inhalation of particulate matter and consumption of contaminated food, and hazards associated with various EOCs in the soil-plant system are discussed. Various mitigation measures including removal technologies of EOCs in the soil are discussed. Finally, future research directions are presented.

Novel insights into the mechanism of laccase-driven rhizosphere humification for alleviating wheat 17β-estradiol contamination

Global-scale crop contamination with environmental estrogens has posed a huge risk to agri-food safety and human health. Laccase is regarded as an unexceptionable biocatalyst for regulating pollution and expediting humification, but the knowledge of estrogen bioremediation and C storage strengthened by laccase-driven rhizosphere humification (LDRH) remains largely unknown. Herein, a greenhouse microcosm was performed to explore the migration and fate of 17β-estradiol (E2) in water-wheat (Triticum aestivum L.) matrices by LDRH. Compared to the non-added laccase, the pseudo-first-order decay rate constants of E2 in the rhizosphere solution after 10 and 50 μM exposures by LDRH increased from 0.03 and 0.02 h-1 to 0.36 and 0.09 h-1, respectively. Furthermore, LDRH conferred higher yield, polymerizability, O-containing groups, and functional-C signals in the humified precipitates, because it accelerated the formation of highly complex precipitates by radical-controlled continuous polymerization. In particular, not only did LDRH mitigate the phytotoxicity of E2, but it also diminished the metabolic load of E2 in wheat tissues. This was attributed to the rapid attenuation of E2 in the rhizosphere solution during LDRH, which limited E2 uptake and accumulation in each subcellular fraction of the wheat roots and shoots. Although several typical intermediate products such as estrone, estriol, and E2 oligomers were detected in roots, only small-molecule species were found in shoots, evidencing that the polymeric products of E2 were unable to be translocated acropetally due to the vast hydrophobicity and biounavailability. For the first time, our study highlights a novel, eco-friendly, and sustainable candidate for increasing the low-C treatment of organics in rhizosphere microenvironments and alleviating the potential risks of estrogenic contaminants in agroenvironments.

Novel Insights into the Promoted Accumulation of Nitro-Polycyclic Aromatic Hydrocarbons in the Roots of Legume Plants

Substituted polycyclic aromatic hydrocarbons (sub-PAHs) are receiving increased attention due to their high toxicity and ubiquitous presence. However, the accumulation behaviors of sub-PAHs in crop roots remain unclear. In this study, the accumulation mechanism of sub-PAHs in crop roots was systematically disclosed by hydroponic experiments from the perspectives of utilization, uptake, and elimination. The obtained results showed an interesting phenomenon that despite not having the strongest hydrophobicity among the five sub-PAHs, nitro-PAHs (including 9-nitroanthracene and 1-nitropyrene) displayed the strongest accumulation potential in the roots of legume plants, including mung bean and soybean. The nitrogen-deficient experiments, inhibitor experiments, and transcriptomics analysis reveal that nitro-PAHs could be utilized by legumes as a nitrogen source, thus being significantly absorbed by active transport, which relies on amino acid transporters driven by H+-ATPase. Molecular docking simulation further demonstrates that the nitro group is a significant determinant of interaction with an amino acid transporter. Moreover, the depuration experiments indicate that the nitro-PAHs may enter the root cells, further slowing their elimination rates and enhancing the accumulation potential in legume roots. Our results shed light on a previously unappreciated mechanism for root accumulation of sub-PAHs, which may affect their biogeochemical processes in soils.

Analysis of Petrogenic Hydrocarbons in Plant Tissues: A Simple GC-MS-Based Protocol to Distinguish Biogenic Hydrocarbons from Diesel-Derived Compounds

Diesel contamination of farming soils is of great concern because hydrocarbons are toxic to all forms of life and can potentially enter the food web through crops or plants used for remediation. Data on plant ability to uptake, translocate and accumulate diesel-derived compounds are controversial not only due to the probable diverse attitude of plant species but also because of the lack of a reliable method with which to distinguish petrogenic from biogenic compounds in plant tissues. The purpose of this study was to set up a GC-MS-based protocol enabling the determination of diesel-derived hydrocarbons in plants grown in contaminated soil for assessing human and ecological risks, predicting phytoremediation effectiveness and biomass disposal. To this end, two plant species, Vicia sativa L. and Secale cereale L., belonging to two diverse vascular plant families, were used as plant models. They were grown in soil spiked with increasing concentrations of diesel fuel, and the produced biomass was used to set up the hydrocarbon extraction and GC-MSD analysis. The developed protocol was also applied to the analysis of Typha latifolia L. plants, belonging to a different botanical family and grown in a long-time and highly contaminated natural soil. Results showed the possibility of distinguishing diesel-derived compounds from biogenic hydrocarbons in most terrestrial vascular plants, just considering the total diesel compounds in the n-alkanes carbon range C10-C26, where the interference of biogenic compounds is negligible. Diesel hydrocarbons quantification in plant tissues was strongly correlated (0.92 < r2 < 0.99) to the concentration of diesel in spiked soils, suggesting a general ability of the considered plant species to adsorb and translocate relatively low amounts of diesel hydrocarbons and the reliability of the developed protocol.

Migration of polycyclic aromatic hydrocarbons in the rhizosphere micro-interface of soil-ryegrass (Lolium perenne L.) system

The unclear multi-media and multi-interface processes of polycyclic aromatic hydrocarbons (PAHs) in environments have drawn great concern. Here, 16 controlled PAHs were selected to reveal the differences in the bioavailability and migration of congeners in soil-ryegrass exposure system. The presence of ryegrass in the exposure groups (with newly introduced PAHs) resulted in a decrease in PAHs dissipation (31.3 %) from soil compared to the unplanted groups (43.2 %). The presence of ryegrass inhibited the soil-air exchange process, which has not been widely reported. PAH congeners with less benzene rings (molecular weight < B[a]A) had consistent bioavailability before and after long-term aging, the competition between adsorption/absorption to plants and soil was not strong (RCFs < 3.5), and their migration in the rhizosphere rapidly reached equilibrium. PAH congeners with more benzene rings (molecular weight ≥ B[a]A) adsorbed to soil particles and significantly decreased their bioavailability after long-term aging. Their concentrations in the rhizosphere were stable and lower than bulk soil, revealing their slow equilibrium process in soil. In addition, PAHs with larger molecular weight and KOW showed less migration at the rhizosphere micro-interface. The migration behavior of congeners with close KOW depended on their molecular structure. Congeners with non-symmetric K-region or L-region showed greater migration ability in the rhizosphere. These findings revealed the fate of PAHs, especially different PAH congeners, in the rhizosphere interfaces for the first time, and explored the molecular mechanisms that affect their rhizosphere behaviors, improving the understanding and knowledge of PAHs in the microenvironment, providing new data on evaluating and controlling the environmental risks of PAHs.

Absorption, metabolism and distribution of carbosulfan in maize plants (Zea mays L.)

BACKGROUND

The insecticide carbosulfan is usually applied as a soil treatment or seed-coating agent, and so may be absorbed by crops and pose dietary risks. Understanding the uptake, metabolism and translocation of carbosulfan in crops is conducive to its safe application. In this study, we investigated the distribution of carbosulfan and its toxic metabolites in maize plants at both the tissue and subcellular levels, and explored the uptake and translocation mechanism of carbosulfan.

RESULTS

Carbosulfan was mainly taken up by maize roots via the apoplast pathway, was preferentially distributed in cell walls (51.2%-57.0%) and most (85.0%) accumulated in roots with only weak upward translocation. Carbofuran, the main metabolite of carbosulfan in maize plants, was primarily stored in roots. However, carbofuran could be upwardly translocated to shoots and leaves because of its greater distribution in root-soluble components (24.4%-28.5%) compared with carbosulfan (9.7%-14.5%). This resulted from its greater solubility compared with its parent compound. The metabolite 3-hydroxycarbofuran was found in shoots and leaves.

CONCLUSION

Carbosulfan could be passively absorbed by maize roots, mainly via the apoplastic pathway, and transformed into carbofuran and 3-hydroxycarbofuran. Although carbosulfan mostly accumulated in roots, its toxic metabolites carbofuran and 3-hydroxycarbofuran could be detected in shoots and leaves. This implies that there is a risk in the use of carbosulfan as a soil treatment or seed coating. © 2023 Society of Chemical Industry.

Polycyclic Aromatic Hydrocarbons in Soil and Vegetation of Niger Delta, Nigeria: Ecological Risk Assessment

The Niger Delta, Nigeria, is noted for crude oil exploration. Whereas there seems to be a handful of data on soil polycyclic aromatic hydrocarbon (PAH) levels in this area, there is a paucity of studies that have evaluated soil and vegetation PAHs simultaneously. The present study has addressed this information gap. Fresh Panicum maximum (Jacq) (guinea grass), Pennisetum purpureum Schumach (elephant grass), Zea mays (L.) (maize), and soil samples were collected in triplicate from Choba, Khana, Trans-Amadi, Eleme, Uyo, and Yenagoa. PAHs determination was carried out using GC-MS. The percentage composition of the molecular weight distribution of PAHs, the molecular ratio of selected PAHs for identification of possible sources, and the isomeric ratio and total index of soil were evaluated. Pennisetum purpureum Schumach (elephant grass) from Uyo has the highest (10.0 mg·kg^-1) PAH while Panicum maximum (Jacq) (guinea grass) has the highest PAH (32.5 mg·kg^-1 from Khana. Zea mays (L.) (maize) from Uyo (46.04%), Pennisetum purpureum Schumach (elephant grass) from Trans-Amadi (47.7%), guinea grass from Eleme (49.2%), and elephant grass from Choba (39.9%) contained the highest percentage of high molecular weight (HMW) PAHs. Soil samples from Yenagoa (53.5%) and Khana (55.3%) showed the highest percentage of HMW PAHs. The total index ranged 0.27-12.4 in Uyo, 0.29-8.69 in Choba, 0.02-10.1 in Khana, 0.01-5.53 in Yenagoa, 0.21-9.52 in Eleme, and 0.13-8.96 in Trans-Amadi. The presence of HMW PAHs and molecular diagnostic ratios suggest PAH pollution from pyrogenic and petrogenic sources. Some soils in the Niger Delta show RQ_(NCs) values higher than 800 and require remediation to forestall ecohealth consequences.

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.

Enhanced phytotoxicity of 4-chloro-3-Methyphenol and lindane under sodium and potassium salt stresses

Investigating the uptake of organic pollutants by plants under salt stress is critical for evaluating crop contamination, understanding the mechanism of plant uptake, and implementing phytoremediation. The uptake of a highly phytotoxic contaminant, 4-Chloro-3-Methyphenol (CMP, 45 mg L^-1), from solutions by wheat seedling with or without Na⁺ and K⁺ was studied to illustrate the synergistic effect of salt on phytotoxicity of CMP, using uptake kinetics, transpiration, Ca²⁺ leakage and fatty acid saturation as indicators. The influence of Na⁺ and K⁺ on the uptake of lindane, a relatively low toxic contaminant, from soil was also explored. Under CMP-Na⁺ and CMP-K⁺ exposure, the concentrations of CMP in both root and shoot were lower than those under CMP exposure, as a result of the inhibition of transpiration caused by Na⁺ and K⁺ stresses. Low concentration of CMP did not reveal serious toxicity on cell membrane. No apparent difference of MDA generation in root cells was observed, due to the lethal concentration of CMP. The relatively small variation of Ca²⁺ leakage and fatty acid saturation degree in the root cell under exposure of CMP, CMP-Na⁺ and CMP-K⁺, compared to intracellular CMP content, suggested the enhanced phytotoxicity of CMP induced by salt. Higher MDA concentration in shoot cell under CMP-Na⁺ and CMP-K⁺ exposure compared with that under CMP exposure again showed the synergetic toxicity of CMP. High Na⁺ and K⁺ concentration significantly facilitated the uptake of lindane by wheat seedlings in soils, indicating that it could boost the permeability of cell membrane, thereby increasing the toxicity of linande to wheat seedlings. The short-term effect of low salt concentration on the uptake of lindane was not obvious, but long-term exposure also led to increased uptake. In conclusion, the presence of salt could amplify the phtotoxicity of organic contaminant via several mechanisms.

Uptake, Translocation, and Distribution of Cyantraniliprole in a Wheat Planting System

Cyantraniliprole uptake, translocation, and distribution in wheat plants grown in hydroponics and soil conditions were investigated. The hydroponics experiment indicated that cyantraniliprole was prone to be absorbed by wheat roots mainly through the apoplastic pathway and predominately distributed in the cell-soluble fraction (81.4-83.6%) and ultimately transferred upward to leaves (TF_leave/stem = 4.84 > TF_stem/root = 0.67). In wheat-soil systems, the uptake of cyantraniliprole was similar to that in hydroponics. The accumulation of cyantraniliprole in wheat tissues was mainly affected by the content of soil organic matter and clay, resulting in the increased adsorption of cyantraniliprole onto soils (R² > 0.991, P < 0.01), and was positively related to the concentration of cyantraniliprole in soil pore water (R² > 0.991, P < 0.001). Besides, the absorption of cyantraniliprole by wheat was predicted well by the partition-limited model. These results increased our understanding of the absorption and accumulation of cyantraniliprole in wheat and were also helpful for guiding the practical application and risk evaluation of cyantraniliprole.

Effects of physicochemical properties and co-existing zinc agrochemicals on the uptake and phytotoxicity of PFOA and GenX in lettuce

Even though the potential toxicity and treatment methods for per- and polyfluoroalkyl substances (PFAS) have attracted extensive attention, the plant uptake and accumulation of PFAS in edible plant tissues as a potential pathway for human exposure received little attention. Our study in a hydroponic system demonstrated that perfluorooctanoic acid (PFOA) and its replacing compound, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy) propanoic acid (GenX) displayed markedly different patterns of plant uptake and accumulation. For example, the root concentration factor (RCF) of PFOA in lettuce is almost five times of that of GenX while the translocation factor (TF) of GenX is about 66.7% higher than that for PFOA. The co-presence of zinc amendments affected the phyto-effect of these two compounds and their accumulation in plant tissues, and the net effect on their plant accumulation depended on both the properties of Zn amendments and PFAS. Zinc oxide nanoparticles (ZnONPs) at 100 mg/L did not affect the uptake of PFOA in either lettuce roots or shoots; however, Zn2+ at the same concentration significantly increased PFOA accumulation in both tissues. In contrast, both Zn amendments significantly lowered the accumulation of GenX in lettuce roots, but only ZnONPs significantly hindered the GenX accumulation in lettuce shoots. The co-exposure to ZnONPs and PFOA/GenX resulted in lower oxidative stress than the plants exposed to PFOA or GenX alone. However, both zinc agrochemicals with or without PFAS led to lower root dry biomass. The results shed light on the property-dependent plant uptake of PFAS and the potential impact of co-existing nanoagrochemicals and their dissolved ions on plant uptake of PFOA and GenX.

The association between phenanthrene and nutrients uptake in lotus cultivar 'Zhongguo Hong Beijing'

It has been well documented that polycyclic aromatic hydrocarbon (PAHs) can be taken up from the environment by the plants and translocated into the shoots. However, the mechanisms underlying this process are poorly understood. Nelumbo nucifera L. (lotus) is a highly ornamental aquatic plant known to possess strong phytoremediation capability. In the present study, the association between phenanthrene (Phe) and nutrients, including nitrogen (N) and phosphorus (P), in lotus was investigated. Over 2 years, all eight lotus cultivars tested accumulated Phe to various degrees when grown in PAH-polluted sediment (0.46 mg/kg Phe). Cluster analysis showed N. nucifera 'Zhongguo Hong Beijing (ZHB)' was the one with the highest Phe levels in the leaves and petals in 2 years. The Phe concentrations in the tissues of 'ZHB' were 3.14 mg/kg and 1.63 mg/kg on average in the first and second year, respectively. Interestingly, 'ZHB' was also the cultivar with the lowest N and P levels considering 2 years and tissues. Hydroponic studies further revealed a negative association between the concentrations of Phe and those of N and P in the aerial tissues under 0.5 and 1.0 mg/L Phe treatments in 'ZHB'. Furthermore, the significant reductions of the roots number (72.6%), longest root length (75.8%), and petiolar height (34.6%) in 'ZHB' seedlings exposed to 1.0 mg/L Phe were observed, indicating that Phe retarded the growth of lotus. These results provide a new understanding of the accumulation of Phe in plants and the association with nutrients and enrich the basis of phytoremediation to the contaminated environment.

Elevated urbanization-driven plant accumulation and human intake risks of polycyclic aromatic hydrocarbons in crops of peri-urban farmlands

As an ubiquitous carcinogen, polycyclic aromatic hydrocarbons (PAHs) are closely related to anthropogenic activities. The process of urbanization leads to the spatial interlacing of farmlands and urbanized zones. However, field evidence on the influence of urbanization on the accumulation of PAHs in crops of peri-urban farmlands is lacking. This study comparatively investigated the urbanization-driven levels, compositions, and sources of PAHs in 120 paired plant and soil samples collected from the Yangtze River Delta in China and their species-specific human intake risks. The concentrations of PAHs in crops and soils in the peri-urban areas were 2407.92 ng g^-1 and 546.64 ng g^-1, respectively, which are significantly higher than those in the rural areas. The PAHs in the root were highly relevant to those in the soils (R² = 0.63, p < 0.01), and the root bioconcentration factors were higher than 1.0, implying the contributions of root uptake to plant accumulations. However, the translocation factors in the peri-urban areas (1.57 ± 0.33) were higher than those in the rural areas (1.19 ± 0.14), indicating the enhanced influence through gaseous absorption. For the congeners, the 2- to 3-ring PAHs showed a higher plant accumulation potential than the 4- to 6-ring PAHs. Principal component analysis show that the PAHs in the peri-urban plants predominantly resulted from urbanization parameters, such as coal combustion, vehicle emissions, and biomass burning. The mean values of estimated dietary intake of PAHs from the consumption of peri-urban and rural crops were 9116 ng day^-1 and 6601.83 ng day^-1, respectively. The intake risks of different crops followed the order rice > cabbage > carrot > pea. Given the significant input of PAHs from urban to farmland, the influence of many anthropogenic pollutants arising from rapid urbanization should be considered when assessing the agricultural food safety.

Distribution of phenanthrene in the ospho2 reveals the involvement of phosphate on phenanthrene translocation and accumulation in rice

The intricate mechanisms involved in the acquisition and translocation of polycyclic aromatic hydrocarbons (PAHs) in plants have not been elucidated. Phosphate (Pi) is the bioavailable form of essential macronutrient phosphorus, which is acquired and subsequently assimilated for plant optimal growth and development. Rice phosphate overaccumulator 2 (OsPHO2) is a central constituent of the regulation of Pi homeostasis in rice. In the present study, the role of OsPHO2 in regulating the translocation and accumulation of phenanthrene (Phe) and the involvement of Pi in this process were investigated. The temporal study (1 d-35 d) revealed a significant and gradual increase of Phe accumulation in Pi-deprived roots of wild-type (WT) seedlings. Compared with the WT, the concentrations of Phe were significantly higher in the shoots of ospho2 (OsPHO2 mutant) grown hydroponically with Phe (1.5 mg/L) under +Pi (200 μM) and -Pi (10 μM) conditions. The sap experiment clearly showed the significant increases in levels of Phe in the xylem sap of ospho2 than the WT grown hydroponically with Phe and +Pi. Further, the concentrations of both Phe and P were coordinately higher in the culms and flag leaves of the mutants than WT at maturity in potting soil with LPhe (6 mg/kg) and HPhe (60 mg/kg). However, the concentrations of Phe in the seeds were comparable in the WT and mutants, suggesting a pivotal of OsPHO2 in attenuating Phe toxicity in the seed. In +Phe WT, the relative expression level of OsPHO2 in the shoots was significantly lower, while those of Pi transporters (PTs) OsPT4 and OsPT8 were significantly higher in the roots compared with -Phe. Together, the results provided evidence towards the involvement of Pi in OsPHO2-regulated translocation and accumulation of Phe in rice.

Uptake, translocation, and metabolism of anthracene in tea plants

The origin of 9, 10-anthraquinone (AQ) contamination in tea remains unclear at present. The objective of this study was to test the hypothesis that AQ could be produced from the precursor anthracene in tea plantations. To test this hypothesis, the uptake, translocation, and transformation of anthracene in tea (Camellia sinensis) seedlings using hydroponic experimentation was investigated. Anthracene concentrations in tea tissues rose with increased anthracene exposure, which in the roots were significantly (p < 0.05) higher than those in aboveground parts at the end of the exposure. These results indicated that anthracene tended to be adsorbed into tea seedling via the roots and accumulated largely within roots. The three main pathways of anthracene degradation in tea seedlings were suggested: oxygen was incorporated in the 9^th and 10^th positions of anthracene resulting in AQ (I) and anthrone (II), and naphthalene was formed by ring fission of anthracene via methylanthracene (III). The principal anthracene metabolites were AQ and anthrone. The concentrations of AQ, like anthrone, were markedly elevated in the roots than those in stems throughout the entire exposure period. Moreover, the translocation factors for anthracene and its primary metabolites AQ and anthrone from roots to stems were persistently lower than 0.1, demonstrating a poor translocation from roots to the aboveground regions. However, tea seedlings could take anthracene up from water and translocate it to the leaves. It was a possible risk for AQ contamination in tea leaves continuously exposed to anthracene for long periods of time because tea plants were perennial crops.

Effect of soil contamination with polycyclic aromatic hydrocarbons from drilling waste on germination and growth of lawn grasses

In many studies, grasses were used to increase the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil because they are the most common plant species on the ground level and are quite resistant to contamination with these compounds. One of the main failures in PAH remediation in soil using plant species was the negative impact on germination and seedling growth. The objective of this study was to evaluate grass seed germination and seedling growth affected by drill cuttings to determine the resistance of selected grass species to the impact of PAH and their suitability for an effective phytoremediation of soils contaminated with waste that contain compounds from this group. In the study four grass species: tall fescue (Festuca arundinacea), red fescue (Festuca rubra), perennial ryegrass (Lolium perenne) and common meadow-grass (Poa pratensis). The germination energy of all species decreased as the amount of drill cuttings increased. Among the species studied, the highest germination energy and capacity were found in Lolium perenne (54.1 and 73.2 respectively), and the lowest - in Poa pratensis (16.7 and 23.3 respectively). With an increasing amount of drill cuttings, the root and seedling height were decreased. Festuca arundinacea seedlings were distinctly the highest and had the longest roots (96.7 and 52.7, respectively), while Poa pratensis seedlings showed the significantly slowest seedling and root elongation rate (30.4 and 12.4, respectively). However, the strongest decrease in seedling height and root length compared to the control was observed in Festuca rubra. Based on IC50, the greatest tolerance to the addition of drilling waste to the substrate was found for Festuca arundinacea and Festuca rubra. The conducted investigation indicates that Festuca arundinacea and Lolium perenne are grass species that are least sensitive to drilling waste in the substrate because no significant differences were found in root length and seedling height between the control soil and the soil where a PAH dose of 5% and 10% was applied.

Systemic fungicidal activity of phenazine-1-carboxylic acid-valine conjugate against tobacco sore shin and its translocation and accumulation in tobacco (Nicotiana tabacum L.)

BACKGROUND

Tobacco sore shin caused by Rhizoctonia solani Kühn is a major soil-borne fungal disease of tobacco, gradually causing infected stems to become thin and dry, leading to great losses to China's tobacco industry. Fungicides with phloem mobility are needed for application to foliage to effectively control root or vascular system pathogens. In this study, phenazine-1-carboxylic acid-valine conjugate (PCA-Val) with strong phloem mobility was tested for control of tobacco sore shin. In vitro fungicidal activity, systemicity, and in vivo efficacy of PCA-Val against R. solani in tobacco seedling were evaluated.

RESULTS

In vitro fungicidal activity of PCA-L-Val against R. solani was lower than that of PCA or PCA-D-Val, but the in vivo protective activity and curative activity of PCA-L-Val was the highest among these chemicals tested. The systemicity tests in tobacco seedlings revealed that PCA did not possess phloem mobility, while PCA-L-Val and PCA-D-Val exhibited strong phloem mobility and could be transported and accumulated in the lower part of the seedling as well as throughout the phloem. In addition, we also found that, just like reported hormone amino acid conjugates, PCA-L-Val could be hydrolyzed by tobacco seedlings, to release free PCA.

CONCLUSIONS

The current research results indicated that PCA-L-Val possess good phloem transport in tobacco and promising in vivo antifungal activity against R. solani, which can be used as a phloem-mobile fungicide against tobacco sore shin in production practice.

Uptake and translocation of triadimefon by wheat (Triticum aestivum L.) grown in hydroponics and soil conditions

Residual pesticides in soil may be taken in by plants and thus have a risk for plant growth and food safety. In this study, uptake of triadimefon and its subsequent translocation and accumulation were investigated with wheat as model plants. The results from hydroponics indicated that triadimefon was absorbed by wheat roots mainly through apoplastic pathway and predominantly distributed into the water soluble fractions (66.7-76.0%). After being uptaken by roots, triadimefon was easily translocated upward to wheat shoots and leaves. Interestingly, triadimefon in leaves was mainly distributed in the soluble fraction by 52.5% at the beginning, and gradually transferred into the cell wall by 47.2% at equilibrium. The uptake of triadimefon from soils by wheat plants was similar to that in hydroponics. Its accumulation were mainly governed by adsorption of the fungicide onto soils, and positively correlated with its concentration in in situ pore water (C_IPW). Thus, C_IPW can be suitable for predicting the uptake of triadimefon by wheat from soils. Accordingly, uptake of triadimefon by wheat was predicted well by using the partition-limited model. Our study provides valuable information for guiding the practical application and safety evaluation of triadimefon.

Phytoremediation of formaldehyde by the stems of Epipremnum aureum and Rohdea japonica

Decorative plants can efficiently purify formaldehyde and improve the quality of indoor air. The existing studies primarily revealed that the aerial and underground parts of plants' capacity to purify formaldehyde, while the performance of stems is unclear. A formaldehyde fumigation experiment was conducted on Epipremnum aureum and Rohdea japonica in a sealed chamber. Results showed the stems could remove formaldehyde. The efficiency of removal by the stems of each plant was 0.089 and 0.137 mg∙m^-3∙h^-1, respectively, the rate of purification was 40.0 and 61.6%, respectively. Both were related to plant species and the latter was affected by other factors like exposed area. To further explore the mechanism of phytoremediation, the correlation between the concentration of formaldehyde and CO₂ during the experiment was investigated. Results showed when leaves of plants were exposed to formaldehyde, the concentration of CO₂ increased with the decrease in concentration of formaldehyde, and the change in concentration of CO₂ could be used as an indicator of the degree of decontamination of formaldehyde by the plants.

The potential risks and exposure of Qinling giant pandas to polycyclic aromatic hydrocarbon (PAH) pollution

Rapid industrialization and urbanization have created a substantial urban-rural gradient for various pollutants. The Qinling Mountains are highly important in terms of biodiversity, providing habitat for giant pandas, which are endemic to China and are a widely recognized symbol for conservation. Whether polycyclic aromatic hydrocarbon (PAH) exposure risks regarding in situ animal conservation zones are affected by environmental pollution or even enhanced by the mountain-trapping effect requires further research. Our group carried out a large-scale investigation on the area ranging from Xi'an to Hanzhong across the giant panda habitat in the Qinling Mountains by collecting atmosphere, soil, bamboo, and fecal samples from different sites over a two-year period. The total toxicity of atmospheric PAHs and the frequencies of soil PAHs above effect range low (ERL) values showed a decreasing trend from urban areas to the central mountains, suggesting a distance effect from the city. The proportions of total 5- and 6-ring PAHs in the atmosphere were higher in the central mountainous areas than in the urban areas, while this difference was reversed in the soil. Health risk assessments showed that the incremental lifetime carcinogenic risks (ILCR) of PAH exposure by bamboo ingestion ranged from 2.16 × 10^-4 to 3.11 × 10^-4, above the critical level of 10^-4. Bamboo ingestion was the main driver of the PAH exposure risks. The concentration difference between bamboo and fecal samples provided a reference for the level of PAHs absorbed by the panda digestive system. Since the Qinling Mountains possess the highest density of giant pandas and provide habitats to many other endangered animal and plant species, we should not ignore the probability of health risks posed by PAHs. Monitoring the pollution level and reducing the atmospheric emissions of toxic pollutants are recommended actions. Further detailed research should also be implemented on pandas' health effects of contaminant exposure.

Uptake, translocation and subcellular distribution of chlorantraniliprole and tetrachlorantraniliprole in maize

This study aimed to investigate the uptake, translocation, and subcellular distribution of chlorantraniliprole (Cap) and tetrachlorantraniliprole (Tca) in maize (Zea mays L.) plants using a hydroponic experiment. Tca mainly accumulated in the roots and stems, while Cap showed better acropetal translocation capacity than Tca. The uptake of Cap was positively correlated with Tca uptake, particularly at the effect of plant transpiration force. Transpiration inhibitor treatments significantly reduced the acropetal translocation of Cap and Tca. The absorption of Cap and Tca in the dead and fresh roots showed a good linear relationship and mainly occurred via the apoplastic pathway. Regarding subcellular distribution, the cell wall was the dominant storage compartment for Cap and Tca. In the protoplast, Cap mainly accumulated in cell soluble fractions, while Tca accumulated in the organelles. This study provides information for the accurate application of maize pest management and is of great significance to environmental risk and food safety assessments.

Presence of polycyclic aromatic hydrocarbons among multi-media in a typical constructed wetland located in the coastal industrial zone, Tianjin, China: Occurrence characteristics, source apportionment and model simulation

In-depth understanding and accurately predicting the occurrence and fate of polycyclic aromatic hydrocarbons (PAHs) in constructed wetlands (CWs) is extremely crucial for optimizing the CWs construction and strengthening the risk control. However, few studies have focused on the PAHs among sediment-water-plant and model simulation in CWs. In this study, sediment, surface water and reed samples were gathered and analyzed from a typical CW. The concentrations of 16 PAHs (Σ₁₆PAHs) in sediments, surface water and reeds ranged from 620 to 4277 μg/kg, 114 to 443 ng/L and 74.5 to 362 μg/kg, respectively. The coefficients of variation (CV) were calculated as 0.796, 0.431 and 0.473 for the above three media respectively, indicating that the spatial distribution variation was medium intensity. The fugacity fraction (ff) suggested that sediments might act as the secondary release source of most PAHs. According to the diagnostic ratios and principal component analysis-multiple linear regression (PCA-MLR), PAHs in this CW mainly come from fossil fuels combustion and petroleum leakage. PAHs in sediments showed high ecological risk at water inlet and moderate risk at the other functional zones, while low risks for surface water at all functional zones. Although the human health risk assessment indicated relatively low cancer risk, the health risk still cannot be ignored with the continuous input and accumulation of exogenous PAHs. A mathematical model covering the hydraulics parameters and composition characteristics of the wetland was established, and its reliability was verified. The simulated results obtained by the established model were basically consistent with the measured values. In addition, the total remove efficiency of PAHs in surface water was 40.2%, which calculated by the simulated model. This work provides helpful insight into the comprehension of occurrence and fate of PAHs among multi-media in CWs.

Detoxification of phenanthrene in Arabidopsis thaliana involves a Dioxygenase For Auxin Oxidation 1 (AtDAO1)

Polycyclic aromatic hydrocarbon (PAH) contamination has a negative impact on ecosystems. PAHs are a large group of toxins with two or more benzene rings that are persistent in the environment. Some PAHs can be cytotoxic, teratogenic, and/or carcinogenic. In the bacterium Pseudomonas, PAHs can be modified by dioxygenases, which increase the reactivity of PAHs. We hypothesize that some plant dioxygenases are capable of PAH biodegradation. Herein, we investigate the involvement of Arabidopsis thaliana At1g14130 in the degradation of phenanthrene, our model PAH. The At1g14130 gene encodes Dioxygenase For Auxin Oxidation 1 (AtDAO1), an enzyme involved in the oxidative inactivation of the hormone auxin. Expression analysis using a β-glucuronidase (GUS) reporter revealed that At1g14130 is prominently expressed in new leaves of plants exposed to media with phenanthrene. Analysis of the oxidative state of gain-of-function mutants showed elevated levels of H₂O₂ after phenanthrene treatments, probably due to an increase in the oxidation of phenanthrene by AtDAO1. Biochemical assays with purified AtDAO1 and phenanthrene suggest an enzymatic activity towards the PAH. Thus, data presented in this study support the hypothesis that an auxin dioxygenase, AtDAO1, from Arabidopsis thaliana contributes to the degradation of phenanthrene and that there is possible toxic metabolite accumulation after PAH exposure.

Bioremediation of aromatic hydrocarbons contaminated soil from industrial site using surface modified amino acid enhanced biosurfactant

Surface modified lipopeptide biosurfactant (BS) with enhancement of amino acids was produced using Bacillus Malacitensis. The aromatic hydrocarbons from contaminated soil were removed by BS soil washing process and bioremediation using activated functionalized carbon-BS matrix (AFC-BS). The Central Composite Design (CCD) showed the optimum time100 h; pH 7; temperature 30°C on maximum yield of BS. The amino acid profiling of BS reveals the enhancement of amino acids especially polar amino acids and its importance in the formation of micellar structure for the tight packing of aromatic hydrocarbons from industrial contaminated soil. AFC-BS matrix was implanted directly into the contaminated soil for 28 days and found 61.80 % of Total Petroleum Hydrocarbon (TPH) removal efficiency which is high compared to the AFC treated soil. The compounds were extracted from contaminated soil and AFC-BS matrix, found similar peaks in high performance liquid chromatography, which reveals the ability of BS to remove aromatic contaminants. The soil toxicity was also analyzed by seed germination and found improvement in the growth of seeds. The germination of seeds increased from 60 % to 100 % and the phytotoxicity of root and shoot was reduced from 89.50 %, 88.45 % to12.55 %, 11.87 % respectively.

Biochemical and Metabolic Plant Responses toward Polycyclic Aromatic Hydrocarbons and Heavy Metals Present in Atmospheric Pollution

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are toxic components of atmospheric particles. These pollutants induce a wide variety of responses in plants, leading to tolerance or toxicity. Their effects on plants depend on many different environmental conditions, not only the type and concentration of contaminant, temperature or soil pH, but also on the physiological or genetic status of the plant. The main detoxification process in plants is the accumulation of the contaminant in vacuoles or cell walls. PAHs are normally transformed by enzymatic plant machinery prior to conjugation and immobilization; heavy metals are frequently chelated by some molecules, with glutathione, phytochelatins and metallothioneins being the main players in heavy metal detoxification. Besides these detoxification mechanisms, the presence of contaminants leads to the production of the reactive oxygen species (ROS) and the dynamic of ROS production and detoxification renders different outcomes in different scenarios, from cellular death to the induction of stress resistances. ROS responses have been extensively studied; the complexity of the ROS response and the subsequent cascade of effects on phytohormones and metabolic changes, which depend on local concentrations in different organelles and on the lifetime of each ROS species, allow the plant to modulate its responses to different environmental clues. Basic knowledge of plant responses toward pollutants is key to improving phytoremediation technologies.

The distribution and retained amount of benzo[a]pyrene at the micro-zones of mangrove leaf cuticles: Results from a novel analytical method

Plant leaf cuticles play a critical role in the accumulation and transport of atmospheric polycyclic aromatic hydrocarbons (PAHs). The relationship between the distribution and retained amount of PAHs on the leaf cuticles and the leaves micro-zone structures is still unclear. In this study, a confocal microscopic fluorescence spectral analysis (CMFSA) system with a spatial resolution of 200 nm was established as a direct and noninvasive means to determine the microscopic distribution and quantify the retained amount of benzo[a]pyrene (B[a]P) at Aegiceras corniculatum (Ac), Kandelia obovata (Ko) and Avicennia marina (Am) leaf cuticle micro-zones (0.096 mm²). The linear ranges for the established method were 10-1900 ng spot^-1 for Ac, 15-1700 ng spot^-1 for Ko and 30-1800 ng spot^-1 for Am, and the detection limits were 0.06 ng spot^-1 for Ac, 0.06 ng spot^-1 for Ko and 0.07 ng spot^-1 for Am. Notably, B[a]P formed clusters and unevenly distributed at the leaf cuticles. On the adaxial cuticles, B[a]P was mainly accumulated unevenly along the epidermis cell wall, and it was also distinctively distributed in the secretory cells around salt glands for Ac and Am. On the abaxial leaf cuticles, B[a]P was concentrated in the salt glands and stomata apart from being unevenly distributed in the epidermis cell wall. Moreover, the amount of B[a]P retained presented a negative correlation with the polarity of leaf cuticles, which resulted in the amount of B[a]P retained on the adaxial leaf cuticles being significantly higher than that on abaxial leaf cuticles. Our results provide a potential in situ method for investigating the distribution and retained amount of PAHs at plant leaf surface micro-zones, which would contribute to further studying and understanding the mechanism of migration and transformation of PAHs by plant leaves from a microscopic perspective.

Morphogenic responses and biochemical alterations induced by the cover crop Urochloa ruziziensis and its component protodioscin in weed species

Urochloa ruziziensis, a cover plant used in no-till systems, can suppress weeds in the field through their chemical compounds, but the mode of action of these compounds is still unknown. The present study aimed to investigate the effects of a saponin-rich butanolic extract from U. ruziziensis straw (BfUr) and one of its components, protodioscin on an eudicot Ipomoea grandifolia and a monocot Digitaria insularis weed. The anatomy and the morphology of the root systems and several parameters related to energy metabolism and antioxidant defense systems were examined. The IC₅₀ values for the root growth inhibition by BfUr were 108 μg mL^-1 in D. insularis and 230 μg mL^-1 in I. grandifolia. The corresponding values for protodioscin were 34 μg mL^-1 and 54 μg mL^-1. I. grandifolia exhibited higher ROS-induced peroxidative damage in its roots compared with D. insularis. In the roots of both weeds, the BfUr and protodioscin induced a reduction in the meristematic and elongation zones with a precocious appearance of lateral roots, particularly in I. grandifolia. The roots also exhibited features of advanced cell differentiation in the vascular cylinder. These alterations were similar to stress-induced morphogenic responses (SIMRs), which are plant adaptive strategies to survive in the presence of toxicants. At concentrations above their IC₅₀ values, the BfUr or protodioscin strongly inhibited the development of both weeds. Such findings demonstrated that U. ruziziensis mulches may contribute to the use of natural and renewable weed control tools.

A review on the role of plant in pharmaceuticals and personal care products (PPCPs) removal in constructed wetlands

Pharmaceuticals and personal care products (PPCPs) cause ongoing water pollution and consequently have attracted wide attention. Constructed wetlands (CWs) show good PPCP removal performance through combined processes of substrates, plants, and microorganisms; however, most published research focuses on the role of substrates and microorganisms. This review summarizes the direct and indirect roles of wetland plants in PPCP removal, respectively. These direct effects include PPCP precipitation on root surface iron plaque, and direct absorption and degradation by plants. Indirect effects, which appear more significant than direct effects, include enhancement of PPCP removal through improved rhizosphere microbial activities (more than twice as much as bulk soil) stimulated by radial oxygen loss and exudate secretions, and the formation of supramolecular ensembles from PPCPs and humic acids from decaying plant materials which improving PPCPs removal efficiency by up to four times. To clarify the internal mechanisms of PPCP removal by plants in CWs, factors affecting wetland plant performance were reviewed. Based on this review, future research needs have been identified.

Application of constructed wetlands in the PAH remediation of surface water: A review

Polycyclic aromatic hydrocarbons (PAHs) pose adverse risks to ecosystems and public health because of their carcinogenicity and mutagenicity. As such, the extensive occurrence of PAHs represents a worldwide concern that requires urgent solutions. Wastewater treatment plants are not, however, designed for PAH removal and often become sources of the PAHs entering surface waters. Among the technologies applied in PAH remediation, constructed wetlands (CWs) exhibit several cost-effective and eco-friendly advantages, yet a systematic examination of the application and success of CWs for PAH remediation is missing. This review discusses PAH occurrence, distribution, and seasonal patterns in surface waters during the last decade to provide baseline information for risk control and further treatment. Furthermore, based on the application of CWs in PAH remediation, progress in understanding and optimising PAH-removal mechanisms is discussed focussing on sediments, plants, and microorganisms. Wetland plant traits are key factors affecting the mechanisms of PAH removal in CWs, including adsorption, uptake, phytovolatilization, and biodegradation. The physico-chemical characteristics of PAHs, environmental conditions, wetland configuration, and operation parameters are also reviewed as important factors affecting PAH removal efficiency. Whilst significant progress has been made, several key problems need to be addressed to ensure the success of large-scale CW projects. These include improving performance in cold climates and addressing the toxic threshold effects of PAHs on wetland plants. Overall, this review provides future direction for research on PAH removal using CWs and their large-scale operation for the treatment of PAH-contaminated surface waters.

Phytotoxicity of petroleum hydrocarbons: Sources, impacts and remediation strategies

Extraction and exploration of petroleum hydrocarbons (PHs) to satisfy the rising world population's fossil fuel demand is playing havoc with human beings and other life forms by contaminating the ecosystem, particularly the soil. In the current review, we highlighted the sources of PHs contamination, factors affecting the PHs accumulation in soil, mechanisms of uptake, translocation and potential toxic effects of PHs on plants. In plants, PHs reduce the seed germination andnutrients translocation, and induce oxidative stress, disturb the plant metabolic activity and inhibit the plant physiology and morphology that ultimately reduce plant yield. Moreover, the defense strategy in plants to mitigate the PHs toxicity and other potential remediation techniques, including the use of organic manure, compost, plant hormones, and biochar, and application of microbe-assisted remediation, and phytoremediation are also discussed in the current review. These remediation strategies not only help to remediate PHs pollutionin the soil rhizosphere but also enhance the morphological and physiological attributes of plant and results to improve crop yield under PHs contaminated soils. This review aims to provide significant information on ecological importance of PHs stress in various interdisciplinary investigations and critical remediation techniques to mitigate the contamination of PHs in agricultural soils.

Soil PAHs contamination effect on the cellular and subcellular organelle changes of Phragmites australis Cav

The concentrations of ∑₁₆ priority polycyclic aromatic hydrocarbons (PAHs) for soils, roots, and above-ground parts of reed (Phragmites australis Cav.) were determined on different monitoring plots located near the city of Kamensk-Shakhtinsky, southern Russia, where historically received industrial sewage and sludge. The total PAHs concentration in monitoring soil plots was significantly higher than those in the background site which situated at the distance of 2 km from the contamination source. Accordingly, the maximum accumulation was found for phenanthrene and chrysene among the 16 priority PAHs in most of the plant samples collected in the impact zone. The effects of PAHs' pollution on changes of Phragmites australis Cav. cellular and subcellular organelles in the studied monitoring sites were also determined using optical and electron microscopy, respectively. The obtained data showed that increasing of PAHs contamination negatively affected the ultrastructural changes of the studied plants. Phragmites australis Cav. showed a high level of adaptation to the effect of stressors by using tissue and cell levels. In general, the detected alterations under the PAHs effect were possibly connected to changes in biochemical and histochemical parameters as a response for reactive oxygen species and as a protective response against oxidative stress. The obtained results introduce innovative findings of cellular and subcellular changes in plants exposed to ∑₁₆ priority PAHs as very persistent and toxic contaminants.

Insights into mechanisms involved in the uptake, translocation, and metabolism of phthalate esters in Chinese cabbage (Brassica rapa var. chinensis)

In the present study, the uptake and translocation mechanisms of phthalate esters (PAEs) and their primary mono esters metabolites (mPAEs), and the mechanisms of PAEs metabolism in plants were elucidated. The objectives of this study were to: (i) elucidate the fractionation of PAEs and mPAEs in Chinese cabbage (Brassica rapa var. chinensis) by hydroponic experiment, (ii) investigate the PAEs and mPAEs uptake mechanisms in root by inhibitor experiments, (iii) explain the molecular mechanisms of PAE interactions with the plant macromolecules by proteomics analysis and molecular docking, and (iv) reveal the involvement of carboxylesterase in the plant metabolism of PAEs. The results demonstrated that both the apoplastic and symplastic pathways contributed to the uptake of di-n-butyl phthalate (DnBP), di-(2-ethylhexyl) phthalate (DEHP), mono-n-butyl phthalate (MnBP), and mono-(2-ethylhexyl) phthalate (MEHP) by vacuum-infiltration-centrifugation method. The energy-dependent active process was involved for the uptake of DnBP, DEHP, MnBP, and MEHP. The passive uptake pathways of anion mPAEs and neutral PAEs differ. Aquaporins contributed to the uptake of anion MnBP and MEHP, and slow-type anion channel was also responsible for the uptake of anion MEHP. Molecular interactions of PAEs and macromolecules were further characterized by proteomic analysis and molecular docking. PAEs were transferred via non-specific lipid transfer protein by binding hydroponic amino acid residues. The carboxylesterase enzyme was attributed to the metabolism of PAEs to form mPAEs by using crude enzyme extract and commercial pure enzyme. This study provides both experimental and theoretical evidence for uptake, accumulation, and metabolism of PAEs in plants.

Risk assessment of heavy metals in milk from cows reared around industrial areas in India

This study assessed the health risk associated with exposure to heavy metals through consumption of milk from cows reared around industrial areas in India. Heavy metals, namely Cu, Zn, Cr, Pb, and Cd, were determined in water and forage from four locations as well as in milk produced by dairy cattle raised in these locations, using inductively coupled plasma-mass spectrometry. A quantitative risk assessment using probabilistic approaches was performed to assess the exposure of adults and children to the heavy metals via milk consumption. In milk samples, the highest levels of Cd and Pb were 0.18 mg L^-1 and 0.37 mg L^-1, respectively, which were above the international permissible levels. Possible sources of Pb in the milk could be the industrial by-products and wastes or automobiles exhaust gas. Significant (P < 0.05) positive relationships were found between the concentration of Cu, Cr, Pb, and Cd in milk and in the environmental samples (water or forage). Exposure assessment showed that milk consumers were mostly exposed to Zn, Cd, and Pb, with 63.7%, 51.2%, and 41.2% of children exposed to a dose greater than the references dose for these metals, respectively. Our results suggest that industrial activities lead to possible transfer of heavy metals to cows from their rearing environment (water, plant), which can be accumulated and cause potential health risks to milk consumers. The outcome of this study can be used by policy makers to manage the potential health risk.

Multistage Defense System Activated by Tetrachlorobiphenyl and its Hydroxylated and Methoxylated Derivatives in Oryza sativa

Crops can initiate various defense responses to environmental stresses. The process is often accompanied by extensive transcriptional and metabolic changes to reallocate metabolites. However, it remains unclear how organic pollutants activate the defense systems to reallocate metabolites in crops. The current study demonstrates that three defense systems, including the cytochrome P450s (CYP450s), glutathione S-transferases (GSTs), and phenylpropanoid biosynthesis, were sequentially activated after Oryza sativa was exposed to 2,3,4,5-tetrachlorobipheny l (PCB 61) and its derivatives 4'-hydroxy-2,3,4,5-tetrachlorobiphenyl (OH-PCB 61) and 4'-methoxy-2,3,4,5-tetrachlorobiphenyl (MeO-PCB 61), respectively. Genes encoding CYP76Ms and CYP72As were significantly upregulated after 0.5 h of exposure, followed by the GST-coding gene GSTU48, suggesting that the biotransformation and detoxification of PCB 61, OH-PCB 61, and MeO-PCB 61 occurred. Subsequently, CCR1 and CCR10 involved in phenylpropanoid biosynthesis were activated after 12 h, potentially reducing the oxidative stress induced by PCB 61 and its derivatives. Furthermore, β-d-glucan exohydrolase involved in both phenylpropanoid biosynthesis and starch and sucrose metabolism was significantly downregulated by 7.04-fold in the OH-PCB 61-treated group, potentially contributing to the inhibition of sugar hydrolysis. These findings provide insights into increasing rice adaptability to organic pollutants by reinforcing the enzyme-mediated defense systems, characterizing a novel and critical strategy that enables augmented crop outputs and quality in environments stressed by organic contaminants.

Anthracene induces oxidative stress and activation of antioxidant and detoxification enzymes in Ulva lactuca (Chlorophyta)

In order to analyze whether the marine macroalga Ulva lactuca can absorb and metabolize anthracene (ANT), the alga was cultivated with 5 µM ANT for 0-72 h, and the level of ANT was detected in the culture medium, and in the alga. The level of ANT rapidly decreased in the culture medium reaching a minimal level at 6 h, and rapidly increased in the alga reaching a maximal level at 12 h and then decreased to reach a minimal level at 48 h of culture. In addition, ANT induced an increase in hydrogen peroxide that remained until 72 h and a higher increase in superoxide anions that reach a maximal level at 24 h and remained unchanged until 72 h, indicating that ANT induced an oxidative stress condition. ANT induced an increase in lipoperoxides that reached a maximal level at 24 h and decreased at 48 h indicating that oxidative stress caused membrane damage. The activity of antioxidant enzymes SOD, CAT, AP, GR and GP increased in the alga treated with ANT whereas DHAR remained unchanged. The level of transcripts encoding these antioxidant enzymes increased and those encoding DHAR did not change. Inhibitors of monooxygenases, dioxygenases, polyphenol oxidases, glutathione-S-transferases and sulfotransferases induced an increase in the level of ANT in the alga cultivated for 24 h. These results strongly suggest that ANT is rapidly absorbed and metabolized in U. lactuca and the latter involves Phase I and II metabolizing enzymes.

Reducing phenanthrene uptake and translocation, and accumulation in the seeds by overexpressing OsNRT2.3b in rice

The uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in crops have gained much attention due to their toxicity to humans. Nitrogen (N) is an essential element for plant growth and has also been implicated in the acquisition and acropetal translocation of PAHs. OsNRT2.3b encodes a nitrate (NO₃^-) transporter that is involved in the acquisition and mobilization of N in rice. Here, we investigated whether overexpression of OsNRT2.3b would exert any mitigating influence on the uptake and translocation of phenanthrene (Phe, a model PAH) in transgenic rice (Oryza sativa). The wild-type seedlings exhibited a reduction in plant height, primary root length, and shoot biomass when grown hydroponically in a medium supplemented with Phe. Acquisition of Phe by the roots and its subsequent translocation to shoots increased concomitantly with an increase in Phe concentration in the medium and duration of the treatment. OsNRT2.3b-overexpressing lines (Ox-6 and Ox-8) were generated independently. Compared with the wild-type, the concentration of Phe in Ox-6 and Ox-8 were significantly lower in the roots (47%-54%) and shoots (22%-31%) grown hydroponically with Phe (1 mg/L). Further, the wild-type and Ox lines were grown to maturity in a pot soil under Phe conditions and the concentrations of Phe and total N were assayed in the culms and flag leaves. Compared with the wild-type, in Ox lines the concentration of total N significantly increased in the culms (288%-366%) and flag leaves (12%-25%), while that of Phe significantly reduced in the culms (25%-28%) and flag leaves (18%-21%). The results revealed an antagonistic correlation between the concentration of total N and Phe. The concentration of Phe was also significantly lower (29%-38%) in the seeds of Ox lines than the wild-type. The study highlighted the efficacy of overexpressing OsNRT2.3b in mitigating the Phe toxicity by attenuating its acquisition, mobilization, and allocation to the seeds.

Investigating the plant and air-quality performances of an internal green wall system under hydroponic conditions

Internal green wall systems can be combined with building structures to bring positive impacts on people's quality of life in interior spaces. However, obtaining green wall systems to optimize the performances of these living walls still needs research works. This study was conducted to investigate the plant, and air-quality performance resulted from combining ornamental plants and growing media types in an internal green wall system. The growing media types (mixed based on volume percentage) included cocopeat, perlite, cocopeat + perlite (1v:1v) and cocopeat + perlite + vermicompost (1v:1v:1v). The ornamental species included Peperomia magnoliiaefolia, Kalanchoe blossfeldiana, Aptenia cordifolia, and Carpobrotus edulis. There were significant differences among the plant species and the growing media types for improvement of the plant growth and morphophysiological factors. Organic-rich growing media of vermicompost along with perlite and cocopeat, combined with Aptenia cordifolia as the species can be used to create a horticulturally sustainable internal green wall, and also improve the health index in the building interior environments.

Dynamic distribution and accumulation of PAHs in winter wheat during whole plant growth: Field investigation

A field investigation was conducted to study the dynamic distribution and accumulation of polycyclic aromatic hydrocarbons (PAHs) in winter wheat in the surrounds of a coal-fired power plant. During March to June 2019, various tissues of winter wheat and the corresponding rhizosphere soil were collected for determination of PAHs. A clear spatial downward trend was found in concentration of Σ₁₅PAHs in rhizosphere soil and wheat grain (194-237 μg kg^-1 DM) with the increasing distance from the coal-fired power plant. Moreover, Σ₁₅PAHs concentration in rhizosphere soil (1081 μg kg^-1 DM), root (464 μg kg^-1 DM) and stem (365 μg kg^-1 DM) of winter wheat at regreening stage and leaf (323 μg kg^-1 DM) at anthesis stage were significantly (p < 0.001) higher than that (895, 432, 287 and 265 μg kg^-1 DM) at maturity stage, respectively. From regreening to maturity stage, root concentration factors (RCF) of 3- and 4-ring PAHs exhibited an increasing trend but the 5-ring PAHs showed an apparently downward trend. However, stem concentration factors (SCF) of 3- and 4-ring PAHs showed a decrease trend while the 5- and 6-ring showed first down and then stable trend. There were positive linear relationship between logKow and logSCF at anthesis (r = 0.681, p < 0.05) and maturity stage (r = 0.751, p < 0.05). Based on linear regression analysis, PAHs in grain mainly came from the transfer of vegetative tissues, and the contribution of PAHs from stem and leaf to grain was higher than that from root. In addition, the present study also found that the physicochemical properties of PAHs play a crucial role in transfer of PAHs from root to vegetative tissues and then to grain. The present research provided more comprehensive information on the fate of PAHs in winter wheat and the safety of the agricultural products.

Distribution and Chiral Signatures of Polychlorinated Biphenyls (PCBs) in Soils and Vegetables around an e-Waste Recycling Site

The distribution and composition of polychlorinated biphenyls (PCBs) within soil-plant systems around a notorious e-waste recycling site were investigated. The average total PCB concentrations in rhizospheric soils (RSs) and nonrhizospheric soils (NRSs) were 2160 and 1270 pg g^-1 dry weight (DW), respectively. PCBs were more enriched in RS than NRS for most vegetable species. PCB accumulation in plant tissues varied greatly among plant cultivars, ranging from 4020 to 14 500 pg g^-1 DW in shoots and from 471 to 24 400 pg g^-1 DW in roots. The compositions of PCBs in soil and plants showed that hexa- and hepta-chlorinated PCBs were preferentially accumulated in soils, while tri- and tetra-PCBs were abundant in plant tissues. These results indicated that low-chlorinated PCBs might be prone to accumulation and transfer within plants, which was confirmed by the relationship between the root concentration factor and octanol-water coefficient. The first eluting enantiomers of PCB 84 and PCB 95 were preferentially transferred between the soil and plants, while the stereoselectivity of PCB 136 varied among plant species. A significant difference in enantiomeric fractionation of PCB 84 between the soil and roots indicated that enantiomeric enhancement of PCB 84 occurred during its translocation from soil to root, whereas no such difference was observed in these chiral PCBs during their translocation from the root to the shoot.