Organic Pollutant Penetration through Fruit Polyester Skin: A Modified Three-compartment Diffusion Model

Uptake, accumulation and translocation mechanisms of organophosphate esters in cucumber (Cucumis sativus) following foliar exposure

Organophosphate esters (OPEs) have been frequently detected in crops. However, few studies have focused on the uptake and translocation of OPEs in plants following foliar exposure. Herein, to investigate the foliar uptake, accumulation and translocation mechanisms of OPEs in plant, the cucumber (Cucumis sativus) was selected as a model plant for OPEs exposure via foliar application under control conditions. The results showed that the content of OPEs in the leaf cuticle was higher than that in the mesophyll on exposed leaf. Significant positive correlations were observed between the content of OPEs in the leaf cuticle and their log Kow and log Kcw values (P < 0.01), suggesting that OPEs with high hydrophobicity could not easily move from the cuticle to the mesophyll. The moderately hydrophobic OPEs, such as tris (2-chloroisopropyl) phosphate (TCPP, log Kow = 2.59), were more likely to move not only from the cuticle to the mesophyll but also from the mesophyll to the phloem. The majority of the transported OPEs accumulated in younger leaves (32-45 %), indicating that younger tissue was the primary target organ for OPEs accumulation after foliar exposure. Compared to chlorinated OPEs (except TCPP) and aryl OPEs, alkyl OPEs exhibited the strongest transport capacity in cucumber seedling due to their high hydrophilicity. Interestingly, tri-p-cresyl phosphate was found to be more prone to translocation compared to tri-m-cresyl phosphate and tri-o-cresyl phosphate, despite having same molecular weight and similar log Kow value. These results can contribute to our understanding of foliar uptake and translocation mechanism of OPEs by plant.

Biochar-based asymmetric membrane for selective removal and oxidation of hydrophobic organic pollutants

Hydrophobic organic pollutants (HOCs) in the complex groundwater and soil pose serious technical challenges for sustainable remediation. Herein, an asymmetric membrane (PCAM), inspired by the plant cuticle, was comprised of a top polydimethylsiloxane layer being selectively penetrable to HOCs from complex solution with humic acid, followed by transfer and catalyst layers with biochar pyrolyzed by 300 °C (BC300) and 700 °C (BC700). The PCAM triggered the advanced oxidation of the coming pollutant. The graphitized biochar layer of the PCAM acted as catalysts that induced HOC removal through a non-radical oxidation pathway. Compared to one type biochar membrane, the sequential multi-biochar composite membrane had a faster removal efficiency. The greater uptake and transport performance of multi-biochar composite membrane could be due to the larger pore size and distribution properties of PCAM physicochemical properties and oxidative degradation of peroxymonosulfate. The developed PCAM technology benefits from selective adsorption and catalytic oxidation and has the potential to be applied in complex environmental restoration.

Response of sweet pepper autofluorescence against solar radiation

Shades are adjusted in sweet pepper cultivation, based on solar exposure levels. Pyranometers and photosensitive films have recently been introduced to smart agriculture. However, there are no means of observing biological responses to solar exposure. In this study, we hypothesized that solar exposure levels affect the visible autofluorescence of sweet pepper under 365 nm illumination. To test this hypothesis, we cultivated sweet pepper plants under two exposure conditions, low (half of the normal) and high (the normal). Fluorescence photography (365 nm illumination) revealed that dark-fluorescent peppers only arise when cultivated under high-exposure conditions (0.7-fold decline at emission of 390 nm for high-exposure conditions). Microscopic and spectroscopic observations showed that blue autofluorescence was accompanied by an accumulation of UVB pigments (1.2-factor increase in the absorbance at 300 nm) and epidermal development (1.3-fold thicker cell wall). This study suggests that the autofluorescence of sweet pepper can possibly be used to understand the response of crop to solar radiation at a fruit level in horticulture.

Selective Separation Catalysis Membrane for Highly Efficient Water and Soil Decontamination via a Persulfate-Based Advanced Oxidation Process

The application of sulfate radical advanced oxidation for organic pollutant removal has been hindered by some shortages such as the recycling difficulty of a powered catalyst, the low utilization efficiency of oxidants, and the secondary pollution (including soil acidification) after reaction. Herein, we fabricate a selective separation catalysis membrane (SSCM) for a highly efficient and environment-friendly persulfate-based advanced oxidation process. The SSCM comprises a top polydimethylsiloxane layer which is selectively penetrable to hydrophobic organic pollutants, followed by a catalyst layer with a magnetic nitrogen-doped porous carbon material, targeting the advanced oxidation of the selected pollutants. Compared with the catalyst in powder form, such SSCM devices significantly reduced the dosage of peroxymonosulfate by more than 40% and the catalyst dosage by 97.8% to achieve 80% removal of phenol with the coexistence of 20 mg L^-1 humic acid (HA). The SSCM can extract target pollutants while rejecting HA more than 91.43% for 100 h. The pH value in the receiving solution demonstrated a significant reduction from 7.01 to 3.00. In comparison, the pH value in the feed solution varied from 6.05 to a steady 4.59. The results can be ascribed to the specific functionality for the catalyst anchored, natural organic matter isolation, and reaction compartmentation provided by SSCMs. The developed SSCM technology is beneficial for catalysts reused in remediation practices, saving oxidant dosage, and avoiding acidification of soil and water, thus having tremendous application potential.

Improved plant bioconcentration modeling of pesticides: The role of periderm dynamics

BACKGROUND

There is a continuous need to advance pesticide plant uptake models in support of improving pest control and reducing human exposure to pesticide residues. The periderm of harvested root and tuber crops may affect pesticide uptake, but is usually not considered in plant uptake models. To quantify the influence of the periderm on pesticide uptake from soil into potatoes, we propose a model that includes an explicit periderm compartment in the soil-plant mass balance for pesticides.

RESULTS

Our model shows that the potato periderm acts as an active barrier to the uptake of lipophilic pesticides with high K_OW , while it lets more lipophobic pesticides accumulate in the medulla (pulp). We estimated bioconcentration factors (BCFs) for over 700 pesticides and proposed parameterizations for including the effects of the periderm into a full plant uptake modeling framework. A sensitivity analysis shows that both the degradation half-life inside the tuber and the lipophilicity drive the contributions of other aspects to the variability of BCFs, while highlighting distinct dynamics in the periderm and medulla compartments. Finally, we compare model estimates with measured data, showing that predictions agree with field observations for current-use pesticides and some legacy pesticides frequently found in potatoes.

CONCLUSION

Considering the periderm improves the accuracy of quantifying pesticide uptake and bioconcentration in potatoes as input for optimizing pest control and minimizing human exposure to pesticide residues in edible crops.

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.

Association of fruit, pericarp, and epidermis traits with surface autofluorescence in green peppers

The association of green pepper blue autofluorescence (excitation at 365 nm) with the traits of the fruit, pericarp, and epidermis was investigated.

A protocol for combining fluorescent proteins with histological stains for diverse cell wall components

Higher plant function is contingent upon the complex three-dimensional (3D) architecture of plant tissues, yet severe light scattering renders deep, 3D tissue imaging very problematic. Although efforts to 'clear' tissues have been ongoing for over a century, many innovations have been made in recent years. Among them, a protocol called ClearSee efficiently clears tissues and diminishes chlorophyll autofluorescence while maintaining fluorescent proteins - thereby allowing analysis of gene expression and protein localisation in cleared samples. To further increase the usefulness of this protocol, we have developed a ClearSee-based toolbox in which a number of classical histological stains for lignin, suberin and other cell wall components can be used in conjunction with fluorescent reporter lines. We found that a number of classical dyes are highly soluble in ClearSee solution, allowing the old staining protocols to be enormously simplified; these additionally have been unsuitable for co-visualisation with fluorescent markers due to harsh fixation and clearing. Consecutive staining with several dyes allows 3D co-visualisation of distinct cell wall modifications with fluorescent proteins - used as transcriptional reporters or protein localisation tools - deep within tissues. Moreover, the protocol is easily applied on hand sections of different organs. In combination with confocal microscopy, this improves image quality while decreasing the time and cost of embedding/sectioning. It thus provides a low-cost, efficient method for studying thick plant tissues which are usually cumbersome to visualise. Our ClearSee-adapted protocols significantly improve and speed up anatomical and developmental investigations in numerous plant species, and we hope they will contribute to new discoveries in many areas of plant research.

Dependence of Plant Uptake and Diffusion of Polycyclic Aromatic Hydrocarbons on the Leaf Surface Morphology and Micro-structures of Cuticular Waxes

The uptake of organic chemicals by plants is considered of great significance as it impacts their environmental transport and fate and threatens crop growth and food safety. Herein, the dependence of the uptake, penetration, and distribution of sixteen polycyclic aromatic hydrocarbons (PAHs) on the morphology and micro-structures of cuticular waxes on leaf surfaces was investigated. Plant surface morphologies and wax micro-structures were examined by scanning emission microscopy, and hydrophobicities of plant surfaces were monitored through contact angle measurements. PAHs in the cuticles and inner tissues were distinguished by sequential extraction, and the cuticle was verified to be the dominant reservoir for the accumulation of lipophilic pollutants. The interspecies differences in PAH concentrations cannot be explained by normalizing them to the plant lipid content. PAHs in the inner tissues became concentrated with the increase of tissue lipid content, while a generally negative correlation between the PAH concentration in cuticles and the epicuticular wax content was found. PAHs on the adaxial and abaxial sides of a leaf were differentiated for the first time, and the divergence between these two sides can be ascribed to the variations in surface morphologies. The role of leaf lipids was redefined and differentiated.

Mass transfer of hydrophobic organic chemicals between silicone sheets and through plant leaves and low-density polyethylene

Plant leaves play an important role in the fate of hydrophobic organic contaminants (HOCs) in the environment. Yet much remains unknown about the permeability of leaves by HOCs. In this pilot study we measured (i) the kinetics of mass transfer of three polycyclic aromatic hydrocarbons (PAHs) and six polychlorinated biphenyls between a spiked and an unspiked sheet of polydimethylsiloxane (PDMS) in direct contact with each other for 24 h and (ii) kinetics of mass transfer of two PAHs through leaves and low-density polyethylene (LDPE) in a passive dosing experiment by inserting these matrices between the two sheets of PDMS for 48 h. The kinetics of mass transfer of fluoranthene between PDMS sheets in direct contact were a factor of 12 slower than those reported in the literature. The kinetics of mass transfer of fluorene and phenanthrene through leaves were within the range of those previously reported for 2,4-dichlorophenoxyacetic acid through isolated cuticles. Our results provide a proof-of-concept demonstration that the passive dosing method applied in this study can be used to measure the mass transfer coefficients of organic chemicals through leaves. Key recommendations for future experiments are to load the PDMS at the highest feasible concentrations to avoid working at analyte levels close to the limit of detection, to keep the leaves moist and to minimize potential pathways for contamination of the PDMS sheets by exposure to laboratory air.

A passive dosing method to determine fugacity capacities and partitioning properties of leaves

The capacity of leaves to take up chemicals from the atmosphere and water influences how contaminants are transferred into food webs and soil. We provide a proof of concept of a passive dosing method to measure leaf/polydimethylsiloxane partition ratios (K_leaf/PDMS) for intact leaves, using polychlorinated biphenyls (PCBs) as model chemicals. Rhododendron leaves held in contact with PCB-loaded PDMS reached between 76 and 99% of equilibrium within 4 days for PCBs 3, 4, 28, 52, 101, 118, 138 and 180. Equilibrium K_leaf/PDMS extrapolated from the uptake kinetics measured over 4 days ranged from 0.075 (PCB 180) to 0.371 (PCB 3). The K_leaf/PDMS data can readily be converted to fugacity capacities of leaves (Z_leaf) and subsequently leaf/water or leaf/air partition ratios (K_leaf/water and K_leaf/air) using partitioning data from the literature. Results of our measurements are within the variability observed for plant/air partition ratios (K_plant/air) found in the literature. Log K_leaf/air from this study ranged from 5.00 (PCB 3) to 8.30 (PCB 180) compared to log K_plant/air of 3.31 (PCB 3) to 8.88 (PCB 180) found in the literature. The method we describe could provide data to characterize the variability in sorptive capacities of leaves that would improve descriptions of uptake of chemicals by leaves in multimedia fate models.