Decontamination of sarin in water by designed oxime-clay composites
. APPLIED CLAY SCIENCE 2020
The hydrolysis of the organophosphate nerve agent sarin (GB), is prone to rapid catalytic hydrolysis by oximes. In this study, an oxime-clay composite, based on the adsorption of 2-pyridinealdoxime (2-PAM) to montmorillonite (MMT), was designed as a delivery system of oxime for GB degradation in water. 2-PAM adsorption reached a plateau at similar to 0.5 mmol/g; however, the degree of 2-PAM desorption from composites in water (with and without GB) was not constant and increased with an increase in its initial added concentration. The composites were characterized by SEM, XRD, FTIR-ATR and TGA measurements. We suggest 2-PAM adsorbs in three modes; in a planar orientation while 1. intercalated or 2. directly adsorbed on the external surface, and 3. ``weakly adsorbed'', as a multilayer on the external surface. The removal of GB (40 mu g/ml) in the presence of MMT-PAM composites enhanced dramatically compared to its spontaneous hydrolysis in distilled-, tap- or buffered water e.g., from a half-life time of 2.5 h in tap-water to 0.3 h in a composite suspension (6.4 g clay/l). GB removal was attributed, not to adsorption, but rather to catalytic hydrolysis by released oxime, forming nontoxic compounds. The rate of GB removal was further enhanced by applying composites designed to release higher concentrations of 2-PAM.
Dissolved organic matter adsorption from surface waters by granular composites versus granular activated carbon columns: An applicable approach
. WATER RESEARCH 2020
Many new sorbents have been introduced as an alternative for granular activated carbon (GAC), the most common sorbent for dissolved organic matter (DOM) removal. In the current study, we developed an applicable granular composite based on a flocculant commonly employed for drinking water treatment adsorbed to montmorillonite. DOM adsorption from surface waters, Lake Kinneret and Suwannee River, with low and high specific ultraviolet absorption (SUVA), respectively, by composite and GAC columns, was studied. Adsorption of DOM from Suwannee River was significantly higher by the composite column, in comparison to the GAC column, while an opposite trend was obtained for the adsorption of DOM from Lake Kinneret. In-situ regeneration of the columns with a brine solution was extremely efficient and inefficient for the composite and GAC columns, respectively. Adsorption, of both waters, postregeneration by the composite column was not compromised, while GAC effectiveness decreased. The opposite trend in DOM adsorption from Suwannee River and Lake Kinneret was explained by the different affinities of the sorbents towards various DOM molecules. Distinguishing between different DOM components adsorbed by GAC and the composite was supported by C-13 NMR and direct pyrolysisGC-MS measurements. Furthermore, we demonstrated that the kinetics and adsorption at the equilibrium of five organic molecules to the composite and GAC can be correlated to their chemical-physical properties. Indeed, combining the properties of both sorbents, by integrating them into a single column, yielded higher DOM removal than by the individual columns. Furthermore, since DOM removal by GAC and by the composite, increases, and decreases with temperature, respectively, the integrated column, mitigates the changes in removal, stabilizing the adsorption performance. Such an integrated filter may minimize additional seasonal and water quality fluctuations. (C) 2020 Elsevier Ltd. All rights reserved.
The spontaneous secondary synthesis of soil organic matter components: A critical examination of the soil continuum model theory
. APPLIED SOIL ECOLOGY 2020
The Soil Continuum Model questions the occurrence of any independent natural process of secondary synthesis that generates compounds structurally distinct from plant or microbial metabolites. This review shows that a vast volume of interdisciplinary scientific evidence supports the formation of relevant non-pre-existing complex molecules exhibiting various types of structures. These molecules form during degradation and decay of biological cell components. The spontaneous abiotic and enzymatically catalysed reactions of components of organic residues and of their oxidative decomposition products suggested by state-of-the-art studies are indeed those proposed by most of the classical descriptions of humification. The review also highlights the chemically active role of pedofauna, explaining why the apparently harsh conditions of alkaline extraction of HS cannot be considered un-natural. Many insects and larvae feeding on foliage of plants with a high content of tannins have a midgut pH above 9. Albeit, reducing conditions are often maintained to avoid oxidation, peroxidases are active in the intestinal tract and pass on to feces. Polyphenols are then immediately enzymatically oxidized to their reactive quinone form, once feces are excreted and exposed to oxygen. Implications of our current knowledge on the reactivity of plant components in soil are discussed in relation with the present state of the art research on humic substances. Contrary to claims by the Soil Continuum Model theory, complimentary modern approaches need to be used to understand the complexity of soil organic matter.
Assembly of clay mineral platelets, tactoids, and aggregates: Effect of mineral structure and solution salinity
. JOURNAL OF COLLOID AND INTERFACE SCIENCE 2020
Clay mineral properties, together with solution chemistry, control the assembly of clay platelets into hierarchical structures, including tactoids and aggregates. We studied the effect of salinity on the assembly of kaolinite, illite, and montmorillonite at three critical scales: platelet, tactoid, and aggregate, using cryogenic scanning electron microscopy (cryo-SEM), atomic force microscopy (AFM) and cryo-transmission EM (cryo-TEM), respectively. Cyro-SEM images coupled with original alignment analysis indicate that the degree of aggregate alignment in an ionized solution was significantly higher than in deionized water. Furthermore, upon increasing platelet-platelet bonding energy (montmorillonite > illite > kaolinite), tactoid size increased, packing was less ordered, and aggregate alignment decreased. AFM measurements showed that an increase in ionic-strength caused a decrease in the Young's modulus of the clays, indicating higher tactoid alignment, since, disordered structures, comprising various platelet orientations, are stiffer than highly-aligned structures. We successfully measured distances <1 nm, for both kaolinite and montmorillonite by cryo-TEM, directly demonstrating that increasing ionic-strength reduces platelet-platelet distances. The outcome of this study offers a new approach and methodology to study fundamental colloid-assembly which will trigger future studies investigating additional parameters affecting assembly such as, temperature, solution pH, natural organic matter, and anthropogenic activity. (C) 2020 Elsevier Inc. All rights reserved.
Eco-hydrology and geomorphology of the largest floods along the hyperarid Kuiseb River, Namibia
. JOURNAL OF HYDROLOGY 2020
Flood-fed aquifers along the sandy lower reach of the Kuiseb River sustain a 130-km-long green belt of lush oases across the hyperarid Namib desert. This oasis is a year-round source for water creating dense-tall woodland along the narrow corridor of the ephemeral river valley, which, in turn, supports human activity and fauna including during the long dry austral winters and multi-year droughts. Occasional floods, originating at the river's wetter headwaters, travel similar to 280 km downstream, before recharging these aquifers. We analyzed the flood-aquifer-vegetation dynamics at-a-site and along the river, determining the relative impact of floods with diverse magnitude and frequency on downstream reaches. We find that flood discharge that feeds the alluvial aquifers also affects vegetation dynamics along the river. The downstream aquifers are fed only by the largest floods that allow the infrequent germination of plants; mean annual recharge volume is too low to support the aquifers level. These short-term vegetation cycles of green-up and then fast senescence in-between floods are easily detected by satellite-derived vegetation index. This index identifies historical floods and their magnitudes in arid and hyperarid regions; specifically, it determines occurrences of large floods in headwater-fed, ephemeral Namib streams as well as in other hyperarid regions. Our study reveals the importance of flood properties on the oasis life cycle, emphasizing the impact of drought and wet years on the Namib's riparian vegetation.
Humic acid, dextran, and valeric acid representing macromolecules similar to compounds prevailing in treated wastewater induce soil hydrophobicity
. JOURNAL OF SOILS AND SEDIMENTS 2020
Purpose Organic compounds originating from treated wastewater and soil texture have been reported to be the dominant factors influencing soil hydrophobicity. It is the aim of this investigation to elaborate the role of humic acid, dextran, and valeric acid, representing dissolved organic matter, polysaccharides, and fatty acids, respectively, as well as imitating their activity in inducing soil sub-critical water repellency induced by treated wastewater irrigation. Materials and methods The relationships between three model compounds imitating fractions of dissolved organic matter commonly found in treated wastewater, soil texture in relation to water repellency, were investigated. Three types of organic molecules, five soil mixtures with different specific surface areas, and three different organic compounds, as well as a mixture of the three, were tested. Results and discussion After 14-15 of wetting and drying cycles, low levels (sub-critical hydrophobicity) of water repellency developed in all soil mixtures were subjected to applications of several solutions of organic compounds, in comparison with a freshwater control. The highest degree of water repellency was exhibited by the soil with the lowest clay content (lowest specific surface area) and it decreased with increasing clay content (increasing specific surface area). Conclusions The order of intensity of sub-critical water repellency levels induced by the organic compounds was consistent, yet independent of soil texture. However, soil texture exhibited large influence on soil hydrophobicity in response to the various organic chemicals. Humic acid, the closest in structure to organic matter prevailing in treated wastewater, exhibited the largest effect in inducing soil hydrophobicity.
The importance of aromaticity to describe the interactions of organic matter with carbonaceous materials depends on molecular weight and sorbent geometry
. ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS 2020
Dissolved organic matter (DOM) is ubiquitous in aquatic environments where it interacts with a variety of particles including carbonaceous materials (CMs). The complexity of both DOM and the CMs makes DOM-CM interactions difficult to predict. In this study we have identified the preferential sorption of specific DOM fractions as being dependent on their aromaticity and molecular weight, as well as on the surface properties of the CMs. This was achieved by conducting sorption batch experiments with three types of DOM (humic acid, Suwannee River natural organic matter, and a compost extract) and three types of CMs (graphite, carbon nanotubes, and biochar) with different geometries and surface complexities. The non-adsorbed DOM fraction was analyzed by size exclusion chromatography and preferentially sorbed molecular weight fractions were analyzed by UV/vis and fluorescence spectroscopy. All three sorbent types were found to preferentially sorb aromatic DOM fractions, but DOM fractionation depended on the particular combination of sorbent and sorbate characteristics. Single-walled carbon nanotubes only sorbed the smaller molecular weight fractions (<1 kDa). The sorption of smaller DOM fractions was not accompanied by a preference for less aromatic compounds, contrary to what was suggested in previous studies. While graphite preferentially sorbed the most aromatic DOM fraction (1-3 kDa), the structural heterogeneity of biochar resulted in reduced selectivity, sorbing all DOM > 1 kDa. The results explain the lack of correlation found in previous studies between the amount of aromatic carbon in a bulk DOM and its sorption coefficient. DOM sorption by CMs was generally controlled by DOM aromaticity but complex sorbent surfaces with high porosity, curvatures and functional groups strongly reduced the importance of aromaticity.
Effect of leaching events on the fate of polyhalite nutrient minerals used for crop fertilization
. JOURNAL OF PLANT NUTRITION 2020
Polyhalite is a natural mineral containing potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) and is proposed as a fertilizer source for these essential nutrients. Application of polyhalite is expected to be most relevant in soils where the availability of these nutrients is low: in sandy soils, in highly leached soils, or in areas where crops are irrigated by water with low content of these nutrients or are rain-fed. A controlled lysimeter experiment investigated the efficacy of surface applied polyhalite as a fertilizer supplying K, Ca, Mg and S compared to soluble sulfate salts in two soils (sandy and loamy) with or without simulated rain leaching events through two cycles of cropping. In the first cycle, carrot response and nutrient uptake, transport, and loss through leaching were studied, while in the second cycle the residual effect of the fertilizer was considered on maize without additional fertilizer application or leaching. Polyhalite plus rain led to increased carrot yield due to augmented Ca uptake in sandy soil. In both soils, polyhalite behaved as a prolonged availability fertilizer with more nutrients retained in the top soil layer and not leached below the root zone. The treatments did not affect maize growth or nutrient uptake except for lower K and S uptake in soils where rain had been simulated for the previous crop. We conclude that polyhalite shows potential as a commercial fertilizer to supply K, Ca, Mg, and S nutrients under conditions of dryland agriculture where occasionally leaching by rainfall occurs.
Facile synthesis of carbon-supported silver nanoparticles as an efficient reduction catalyst for aqueous 2-methyl-p-nitrophenol
. MATERIALS LETTERS 2020
A facile technique for preparing the stable Ag nanoparticles (NPs) of 5-19 nm average size, anchored onto the heat-treated melamine-oxalic acid supramolecular complex is demonstrated. The synthesized material is tested for its catalytic efficiency towards reduction of aqueous 2-CH3-p-nitrophenol to aminophenol using NaBH4 as reducing agent at 28 degrees C. The reaction followed the pseudo first-order kinetics with respect to the nitrophenol concentrations, and the reaction rate constant was determined to be greater than the reported literature values. The superior catalytic activity of the catalyst was attributed to the combined roles of the Ag NPs and carbon substrate enriched with nitrogen functional groups. Notably, the prepared catalyst sustained its reactivity even after eight consecutive test runs without leaching of the metal NPs in the reaction mixture. The results clearly indicate the organic complex precursor-based carbon supported Ag NPs to be an efficient catalyst for removal of recalcitrant organic compounds from wastewater by reduction. (C) 2020 Elsevier B.V. All rights reserved.
Spectral induced polarization of clay-oxide hybrid particles
. JOURNAL OF COLLOID AND INTERFACE SCIENCE 2020
The properties of clays and oxides govern many environmental processes, consequently, ongoing effort is invested in developing non-destructive, in-situ analytical tools that reflect these properties. Herein, the physicochemical properties of montmorillonite (MMT) and iron-oxide coated montmorillonite (FeOx-MMT) were characterized using common analytical techniques, and the results were compared to spectral induced polarization (SIP) measurements. FeOx-MMT particles showed a lower CEC, higher pH dependency of the surface charge, and lower suspension stability. Also, the size of the primary particles increased following iron-oxide deposition. SIP measurements over a range of salinities showed that the effective polarization length of the clays was in the order of several microns, suggesting the measurements of aggregates (not primary particles). Moreover, FeOx-MMT particles were more compact than MMT, and their size decreased with increasing salinity due to compaction of the EDL and arrangement of primary particles in the aggregate. The SIP-response to pH changes agreed with zeta potential measurements; at low pH values, MMT exhibited higher polarization due to the higher CEC. However, at a high pH, the differences diminish due to deprotonation of the Fe-OH surface groups. These findings suggest that SIP is a sensitive method that can detect changes in the surface chemistry of soil particles. (C) 2020 Elsevier Inc. All rights reserved.
Synoptic stability and anomalies in NE China inferred from dust provenance of Sihailongwan maar sediments during the past similar to 80 kyr
. QUATERNARY SCIENCE REVIEWS 2020
The paleo-synoptic conditions that prevailed during the past similar to 80 kyr in northeastern China are inferred from the elemental and Sr-Nd isotopic compositions of Lake Sihailongwan Maar sediments. The detrital fraction in the lake sediments is dominated by aeolian input of felsic-rock origin, with little contribution of local volcanic material. Based on the isotopic Sr-Nd composition of the lake core-sediments, we postulate that the deserts of northern China are the main source of allochthonous particles to the lake throughout the past similar to 80 kyr. Northwesterly winds associated with the East Asian winter monsoon and high latitude westerlies are the main carriers of dust from these deserts to the lake. The deserts of central China are an additional minor dust source. The episodic dust input from these deserts results from anomalous dry southwesterly winds. These could be related to either El Nino conditions, or to delays in the onset of the East Asian summer monsoon rains. (C) 2020 Elsevier Ltd. All rights reserved.
Effect of Microwave Radiation on Regeneration of a Granulated Micelle-Clay Complex after Adsorption of Bacteria
. APPLIED SCIENCES-BASEL 2020
Granulated micelle-clay complexes including the organic cation octadecyltrimethylammonium (ODTMA) were shown to be efficient in removal of total bacteria count (TBC) from water. Microwave (MW) heating of granules to restore bacterial removal was investigated. Drying of granules by MW required 20-fold less energy than by conventional heating. When water content of granules approached 10%, or less, their heating period by MW had to be below 1 min, e.g., 30 s, and less, in order to avoid ignition and irreversible structural changes. Structural and thermal properties of MW heated samples were studied by FT-IR spectra and thermo gravimetric analyses (TGA). Inactivation of bacteria in water was more efficient by MW than by conventional oven, or by electric plate. For elimination of bacteria from water, MW heating was at least five-fold more efficient than by conventional heating. The results have established an adequate regeneration procedure by MW heating at durations depending on the remaining percentage of water associated with the granules. Tests of first and second regenerations by MW heating, and HCl washing of columns, were carried out. It was concluded that MW treatment may be chosen for optimal regeneration of the granulated micelle-clay complex as an efficient and low-cost procedure.
Environmental risk dynamics of pesticides toxicity in a Mediterranean micro-estuary
. ENVIRONMENTAL POLLUTION 2020
Pesticides are potentially toxic to aquatic systems, even at low concentration, depending on their individual ecotoxicological properties and their mixture composition. Thus, to evaluate possible ecological stress due to pesticide load, a thorough assessment of the potential toxicity of pesticide mixtures is required. Here we report water discharge and quality data of an eastern Mediterranean micro-estuary (Alexander stream), targeting the temporal distribution of a pesticide mixture. Over 150 water samples were collected during 2 hydrological years representing base-flow and flood conditions. On average, each water sample contained 34 and 45 different pesticides with peak concentrations of 1.4 mu g L-1 of Imidacloprid and 55 mu g L-1 of Diuron during base-flow and flood events, respectively. Pesticide mixtures were potentially toxic to benthic invertebrates and algae during flood events, surpassing the toxicity benchmark with medians of 110% and 155%, respectively. The herbicide Diuron and the insecticide Imidacloprid were the main pesticides responsible for the high potential toxicity during flood events. The falling limb of the flood hydrographs was found to inflict the highest stress on the estuarine environment due to elevated toxicity combined with prolonged residence time of the water. Examination of the potential chronic toxicity of single compounds showed continuous stress for plants, algae, amphibians, crustaceans, insects and fish from nine pesticides. Our data show that the ecosystem of the Alexander micro-estuary is under a continuous chronic stress with acute peaks in potential toxicity during flood events and the period that follows them. We propose that analyzing a small set of flood-tail samples is needed for the evaluation of small estuarine ecosystems risk during the rainy season. From a management perspective, we suggest better control of application practices for Diuron in the watershed to minimize the stress to the estuarine ecosystem. (C) 2020 Elsevier Ltd. All rights reserved.
Involuntary human exposure to carbamazepine: A cross-sectional study of correlates across the lifespan and dietary spectrum
. ENVIRONMENT INTERNATIONAL 2020
Treated wastewater (TWW) is increasingly used for agricultural irrigation, especially in arid and semi-arid regions. Carbamazepine is among the most frequently detected pharmaceuticals in TWW. Moreover, its uptake and accumulation have been demonstrated in crops irrigated with TWW. A previous controlled trial found that urine concentrations of carbamazepine were higher in healthy volunteers consuming TWW-irrigated produce as compared to freshwater-irrigated produce. The aim of the current study was to assess whether carbamazepine is quantifiable in urine of Israelis consuming their usual diets and whether concentrations vary according to age, personal characteristics and diet. In this cross-sectional study, we recruited 245 volunteers, including a reference group of omnivorous healthy adults aged 18-66; pregnant women; children aged 3-6 years; adults aged > 75 years; and vegetarians/vegans. Participants provided spot urine samples and reported 24-hour and ``usual'' dietary consumption. Urinary carbamazepine levels were compared according to group, personal characteristics, health behaviors, and reported diet. Carbamazepine was detectable (>= 1.66 ng/L) in urine of 84%, 76%, 75.5%, 66%, and 19.6% of the reference group, vegetarians, older adults, pregnant women, and children, respectively. Quantifiable concentrations (>= 5.0 ng/L) of carbamazepine were found in 58%, 46%, 36.7%, 14%, and 0% of these groups, respectively (p = 0.001 for comparison of proportions across groups). In adults, higher carbamazepine concentrations were significantly associated (p < 0.05) with self-defined vegetarianism, usual consumption of dairy products and at least five vegetables/day, and no meat or fish consumption in the past 24 hours. This study demonstrates that people living in a water-scarce region with widespread TWW irrigation, are unknowingly exposed to carbamazepine. Individuals adhering to recommended guidelines for daily fresh produce consumption may be at higher risk of exposure to TWW-derived contaminants of emerging concern.
Effects of Time-Dependent Contact Angle on Wettability of Subcritically Water-Repellent Soils
. WATER RESOURCES RESEARCH 2020
Recent studies have indicated that under certain conditions, most soils are water repellent to some degree, which impacts agricultural fields, pastures, forests, grasslands, and turf areas. Soil water repellency originates from amphiphilic molecules that reorient during contact with water. However, models to describe the flow in soils affected by time-dependent contact angle (CA(t)) are still lacking. The current study aims to close this gap. The measured CA(t) for an oleic acid-coated glass surface and a uniform capillary tube indicated that the initial CA was substantially higher for the latter. However, the rate of CA decrease was similar for both cases in spite of the fact that the contact area between the water and the tube wall continuously increases by the capillary rise. This indicates that the amphiphilic molecules reorientation at the vicinity of the contact line rather than at the wetted tube area controls the CA dynamics. A mathematical model for flow in a uniform and sinusoidal capillary tube with CA(t) < 90 degrees that includes model for the reorientation of the amphiphilic molecules was introduced. The model for uniform case was successfully verified by comparison with measured capillary rise in a coated uniform tube. The simulations indicated that nonuniform pore geometry amplifies the effect of CA(t) on the capillary rise dynamics. The stepwise meniscus propagation in the sinusoidal capillary tubes is driven by the time for the meniscus to reach the converging section of the tube. The retardation in capillary rise increases with tube waviness.
Immobilized random peptide mixtures exhibit broad antimicrobial activity with high selectivity
. CHEMICAL COMMUNICATIONS 2020
In the current study, we evaluated the antimicrobial activity of randomly-sequenced peptide mixtures (RPMs) bearing hydrophobic and cationic residues thatwere immobilized on beads. We showed that these beads exhibit high and broad bactericidal activity against various pathogenic bacteria while possessing minimal hemolytic activity.
Relationship between wheat root properties and its electrical signature using the spectral induced polarization method
. VADOSE ZONE JOURNAL 2020
Measuring root properties, the ``hidden half'' of the plant, is challenging due to their heterogeneous and dynamic nature. A promising method for noninvasive mapping of roots and their activity, spectral induced polarization (SIP), has been introduced. However, measurements of root properties together with their SIP responses are missing, limiting the interpretation of a root's SIP signature. In this study, we coupled SIP measurements of roots in hydroponic solution with measurements of root biomass, surface area, and diameter. Furthermore, we monitored the SIP response of roots poisoned by cyanide, which results in depolarization of the root's cell membrane potential. We found a linear correlation between root biomass and surface area, and the low-frequency electrical polarization. In addition, we demonstrate the relationship between root cell membrane potential and root polarization. Based on the results, we suggest that in comparison with the stem-based approach used by other researchers, the polarization in the contact-free method used in this study is related to the external surface area of the root and external architectural structures such as root diameter and root hair. Overall, a direct link between root properties and their electrical signature was established.
Soil Degradation Risks Assessed by the SOTE Model for Salinity and Sodicity
. WATER RESOURCES RESEARCH 2020
Soil salinity and sodicity are serious environmental hazards, with the potential to limit agricultural production and cause destructive soil degradation. These concerns are especially high in dry areas, which often rely on saline and sodic irrigation water to support agriculture. To assess long-term soil degradation risk, we introduce the Salt of the Earth (SOTE) model, which describes the dynamics of soil water content, salinity, and sodicity, as driven by irrigation and rainfall. The SOTE model incorporates how changes in salinity and sodicity affect saturated soil hydraulic conductivity, K-s, on a soil-specific basis. The model was successfully validated against results from a multiyear lysimeter experiment involving different irrigation water qualities and precipitation. We evaluated the impact of shorter rainy seasons on the dynamics of soil degradation in a Mediterranean climate. Critical degradation risk, indicated by reductions in K-s greater than 20%, increased from 0% to 3% when the rainy season was shortened from 130 to 80 days. Alarmingly, when irreversible degradation is allowed for, overall risk increases to 68%. Assessing the effect of irrigation water on different soils textures, we found that while greater clay fractions are usually more susceptible to dispersion, accurate risk assessment hinges on soil water dynamics. SOTE is amenable to large-ensemble simulations of stochastic climatic conditions, for which trends in the statistics of salinization and soil degradation can be identified. As such, SOTE can be a useful land management tool, allowing planners to understand the risk of long-term soil degradation given irrigation practices, soil qualities, and climate conditions.
Copper sulfide nanoparticles suppressGibberella fujikuroiinfection in rice (Oryza sativaL.) by multiple mechanisms: contact-mortality, nutritional modulation and phytohormone regulation
. ENVIRONMENTAL SCIENCE-NANO 2020
The use of nanotechnology to suppress crop diseases is gaining increasing interest in agriculture. Copper sulfide nanoparticles (CuS NPs) were synthesized at 1 : 1 and 1 : 4 ratios of Cu and S and their respective antifungal efficacy was evaluated against the pathogenic activity ofGibberella fujikuroi(bakanae disease) in rice (Oryza sativaL.). In a 2 din vitrostudy, CuS (1 : 1) and CuS (1 : 4) NPs at 50 mg L(-1)decreasedG. fujikuroicolony-forming units (CFU) by 35.7 and 33%, respectively, compared to controls; commercial CuO NPs caused an 18.7% inhibition. In a greenhouse study, treating with both types of CuS NPs at 50 mg L(-1)at the seed stage significantly decreased disease incidence on rice by 35.1 and 45.9%, respectively. Comparatively, CuO NPs achieved only 8.1% disease reduction, and the commercial Cu-based pesticide Kocide 3000 had no impact on disease. Foliar-applied CuO NPs and CuS (1 : 1) NPs decreased disease incidence by 30.0 and 32.5%, respectively, which outperformed CuS (1 : 4) NPs (15%) and Kocide 3000 (12.5%). Notably, CuS (1 : 4) NPs also modulated the shoot salicylic acid (SA) and jasmonic acid (JA) production to enhance the plant defense mechanisms againstG. fujikuroiinfection. These findings provide useful information for improving the delivery efficiency of agrichemicalsvianano-enabled strategies while minimizing their environmental impact, and advance our understanding of the defense mechanisms triggered by the NPs presence in plants.
The Moving-Boundary Approach for Modeling 2-D Gravity-Driven Stable and Unstable Flow in Partially Wettable Soils
. WATER RESOURCES RESEARCH 2020
The moving-boundary approach, which has been successfully used to model stable and unstable 1-D flow in initially dry soils of various contact angles (Brindt & Wallach, 2017 ), was extended here for 2-D flow. The wetting front is the plume perimeter that is partly formed by the capillary driving force, the remaining part by the combined capillary and gravity driving forces. The moving-boundary approach overcomes the limitation of the Richards equation for describing gravity-driven unstable flow with nonmonotonic water-content distribution. According to this approach, the 2-D flow domain is divided into two subdomains with a sharp change in fluid saturation between them-the wetting front (moving boundary). The 2-D Richards equation was solved for the subdomain behind the wetting front for a given flux boundary condition at the soil surface, while the location of the other boundary, for which a no-flux condition is imposed, was part of the solution. The moving-boundary solution was used after verification to demonstrate the synergistic effect of contact angle and incoming flux on flow stability and its associated plume shapes. The contact angle that hinders spontaneous invasion of the dry pores decreases the water-entry capillary pressure, psi(we), while the flux-dependent dynamic water-entry value, psi(wed), is even lower, both inducing water accumulation behind the wetting front (saturation overshoot). This innovative physically based model for the 2-D unsaturated flow problem for an initially dry soil of zero and nonzero contact angle using the moving-boundary approach fulfills several criteria raised by researchers to adequately describe gravity-driven unstable flow.