Formulation of oil-in-water emulsions for pesticide applications: impact of surfactant type and concentration on physical stability

Production and comparison of structural, thermal and physical characteristics of chitin nanoparticles obtained by different methods

This study examined the impact of acid hydrolysis, tempo oxidation, and mechanical grinding on the physical, thermal, and structural properties of α-chitin nanocrystals and nanofibers. The manufacturing methods could influence the diameter, functional groups, and crystal patterns of the resulting nanoparticles. Analysis of the DLS results revealed that the size of acidic nanocrystals were smaller and showed improved dispersibility. The XRD patterns indicated that the chemical and mechanical treatments did not alter the crystalline arrangement of the α-chitin. FT-IR spectra analysis revealed that the chemical and mechanical methods did not affect the functional groups of the nanoparticles. DSC results showed that the nanoparticles had good thermal stability up to 400 °C, and it was found that the nanofibers had better thermal resistance due to their longer length. In the FE-SEM images, the nanoparticles were observed as fiber mats with a length of more than 100 nm. It was also found that the diameter of the nanoparticles was less than 100 nm.

Advanced nanopesticides: Advantage and action mechanisms

The use of various chemical substances to control pests, diseases, and weeds in the field is a necessary part of the agricultural development process in every country. While the application of pesticides can improve the quality and yield of crops, plant resistance and the harm caused by pesticide residues to the environment and humans have led to the search for greener and safer pesticide formulations to improve the current situation. In recent years, nanopesticides (NPts) have shown great potential in agriculture due to their high efficiency, low toxicity, targeting, resistance, and controlled slow release demonstrated in the experimental stage. Commonly used approaches to prepare NPts include the use of nanoscale metal materials as active ingredients (AI) (ingredients that can play a role in insecticide, sterilization and weeding) or the construction of carriers based on commonly used pesticides to make them stable in nano-sized form. This paper systematically summarizes the advantages and effects of NPts over conventional pesticides, analyzes the formation and functions of NPts in terms of structure, AI, and additives, and describes the mechanism of action of NPts. Despite the feasibility of NPts use, there is not enough comprehensive research on NPts, which must be supplemented by more experiments in terms of biotoxicology and ecological effects to provide strong support for NPts application.

Larvicidal evaluation of two novel cationic gemini surfactants against the potential vector of West Nile virus Culex pipiens Linnaeus (Diptera: Culicidae)

The development of insecticide resistance is a serious consequence of the widespread applications of synthetic insecticides. Recent studies have provided alternatives to currently available insecticides. Here, novel cationic gemini surfactants were synthesized to assess their insecticidal activities using laboratory and field strains larvae of Culex pipiens Linnaeus (Diptera: Culicidae). The efficacy of these surfactants was compared to that of clove oil and spinosad. The two surfactants G1 and G2 showed good insecticidal activities in laboratory strain with LC50 0.013 and 0.054 ppm, respectively, relative to spinosad with LC50 0.027 ppm, 48 h posttreatment. Although spinosad showed high efficiency against lab strain, it exhibited a high resistance ratio (RR) of 15.111 and 13.111 toward the field strain at 24 and 48 h posttreatment, respectively. The two gemini surfactants have a good safety profile and low RR (RR <5), which is close to clove oil; however, G1 and G2 presented high activities with 11,043.230 and 2658.648 folds, respectively, compared to clove oil. The treated Cx. pipiens larvae showed severe morphological malformations after treatment with gemini surfactants. The results of this study are promising in terms of developing novel, effective, affordable, and safe approaches for mosquito control strategies to reduce the risk of arbovirus transmission, which remains a global public health threat.

Emulsifying Properties of Rhamnolipids and Their In Vitro Antifungal Activity against Plant Pathogenic Fungi

Rhamnolipids have significant emulsifying activity and the potential to become a component of pesticide emulsifier. Rhamnolipids are usually composed of two main components: mono-rhamnolipids (Rha-C10-C10) and di-rhamnolipids (Rha2-C10-C10). The proportion of di-rhamnolipids in the products ranged between 15% and 90%, affected by the production strains and fermentation process. In this paper, three kinds of rhamnolipid products containing di-rhamnolipids proportions, of 25.45, 46.46 and 89.52%, were used to test their emulsifying ability toward three conventional solvents used in pesticide (S-200, xylene, cyclohexanone) and antifungal activities against five strains of plant pathogenic fungi (Phytophthora capsici, Phytophthora parasitica var.nicotianae, Colletotrichum destructivum, Colletotrichum sublineolum, Fusarium oxysporum). The results indicated that although the CMC of the three rhamnolipids were significantly different, their emulsification properties had no remarkable differences, at a concentration of 10 g/L. However, their antifungal activities were significantly different: the more di-rhamnolipids, the stronger the antifungal activity. This work helps to promote the application of rhamnolipids as pesticides adjuvants.

Mitochondrial dysfunction from malathion and chlorpyrifos exposure is associated with degeneration of GABAergic neurons in Caenorhabditis elegans

Toxicity resulting from off-target effects, beyond acetylcholine esterase inhibition, for the commonly used organophosphate (OP) insecticides chlorpyrifos (CPS) and malathion (MA) was investigated using Saccharomyces cerevisiae and Caenorhabditis elegans model systems. Mitochondrial damage and dysfunction were observed in yeast following exposure to CPS and MA, suggesting this organelle is a major target. In the C. elegans model, the mitochondrial unfolded protein response pathway showed the most robust induction from CPS and MA treatment among stress responses examined. GABAergic neurodegeneration was observed with CPS and MA exposure. Impaired movement observed in C. elegans exposed to CPS and MA may be the result of motor neuron damage. Our analysis suggests that stress from CPS and MA results in mitochondrial dysfunction, with GABAergic neurons sensitized to these effects. These findings may aid in the understanding of toxicity from CPS and MA from high concentration exposure leading to insecticide poisoning.

Comprehensive review of the interfacial behavior of water/oil/surfactant systems using dissipative particle dynamics simulation

A comprehensive understanding of interfacial behavior in water/oil/surfactant systems is critical to evaluating the performance of emulsions in various industries, specifically in the oil and gas industry. To gain fundamental knowledge regarding this interfacial behavior, atomistic methods, e.g., molecular dynamics (MD) simulation, can be employed; however, MD simulation cannot handle phenomena that require more than a million atoms. The coarse-grained mesoscale methods were introduced to resolve this issue. One of the most effective mesoscale coarse-grained approaches for simulating colloidal systems is dissipative particle dynamics (DPD), which bridges the gap between macroscopic time and length scales and molecular-scale simulation. This work reviews the fundamentals of DPD simulation and its progress on colloids and interface systems, especially surfactant/water/oil mixtures. The effects of temperature, salt content, a water/oil ratio, a shear rate, and a type of surfactant on the interfacial behavior in water/oil/surfactant systems using DPD simulation are evaluated. In addition, the obtained results are also investigated through the lens of the chemistry of surfactants and emulsions. The outcome of this comprehensive review demonstrates the importance of DPD simulation in various processes with a focus on the colloidal and interfacial behavior of surfactants at water-oil interfaces.

Halloysite Nanotube-Based Pesticide Formulations with Enhanced Rain Erosion Resistance, Foliar Adhesion, and Insecticidal Effect

The incorporation of green and sustainable nanomaterials in pesticide formation is an effective method to lower the use of conventional pesticides without adverse effects on productivity. Here pesticide Pickering emulsions stabilized by halloysite nanotubes (HNTs) were developed for low cost, less environmental pollution, low toxic effects, and better emulsion stability. HNTs were added to chlorantraniliprole (CAP) emulsions, and good stability was exhibited due to the adsorption and aggregation of HNTs at the interface of CAP oil droplets, forming a three-dimensional network structure that prevented the emulsion from aggregation. In addition, Spodoptera frugiperda was used as a pest model and corn was used as a plant model to explore the washout resistance, insecticidal effect, and biological safety of HNTs-CAP emulsion. After spraying emulsion on corn leaves and washing for 10 min, the HNTs-CAP emulsion (5 wt % HNTs) pesticide residue rate was 2.7 times that of pristine CAP emulsion. When the HNT dispersion concentration was 2 wt %, the larva mortality was 83%, which was 1.5 times that of the CAP emulsion group. These results demonstrated that HNTs-CAP emulsion showed good foliar adhesion, rainfall resistance, and insecticidal effect. The tubular clay-based nanopesticide formulations show potential applications in the control of crop pests with modern agriculture technology.

Surfactant affects the tool use behavior of foraging ants

Surfactants are commonly used in detergents, soaps and agrichemical products. After use, the residual surfactants can be dispersed into environmental compartments, directly or indirectly affecting aquatic and terrestrial organisms. Ants are one of the few insects that are able to make and use tools when foraging for liquid food. However, this unique behavior of ants may be greatly affected by environmental pollutants. Here, we hypothesized that surfactants have adversarial impacts on ant foraging behavior, and tested this hypothesis by investigating the effect of TWEEN 80 (a common nonionic surfactant) on the tool use behavior of black imported fire ants (Solenopsis richteri) when foraging for liquid food (sugar water). Natural pine needles and man-made sponges were provided as tools for ants. The results revealed increasing surfactant concentration induced ants to deposit more tools and caused a higher drowning rate of ants. S. richteri tended to deposit more pine needles and tools of smaller size when exposed to surfactant. Interactions between tool type and surfactant concentration showed significant effects on tool deposition and drowning rate of ants. Addition of surfactant into sugar water increased the drowning rate and reduced the foraging activity and food collection of ant workers, suggesting that surfactant in liquid food can affect the foraging efficiency of ants. However, availability of tools reduced drowning rate and increased sugar water collected compared to without tools. Our results demonstrated that ants can adjust their tool use strategies to manage the foraging risk caused by environmental surfactant, such as increasing the amount and selecting appropriate size of the tools and assembling tools of different structures. Therefore, long-term exposure to surfactants may alter foraging behavior of ants and contribute to evolve new foraging strategy.

Contrasting impacts of mixed nonionic surfactant micelles on plant growth in the delivery of fungicide and herbicide

HYPOTHESIS

Nonionic alkyl ethoxylate surfactants are widely used in agrochemicals to facilitate the permeation of systemic herbicides and fungicides across the plant waxy film. Industrial grade surfactants are often highly mixed and how the mixing affects their interactions with pesticides and wax films remains largely unexplored. A better understanding could enable design of mixed nonionic surfactants for herbicides and fungicides to maximize their efficiency and reduce wastage whilst controlling their impact on plant wax films.

EXPERIMENT

In this study, nonionic surfactants with general structure n-oxyethylene glycol monododecyl ether (C₁₂E_n) were used to form surfactant mixtures with the same average ethoxylate numbers but different hydrophilic-lipophilic balance (HLB) values. Their mixed micellar systems were then used to solubilize a herbicide diuron (DN) and a fungicide cyprodinil (CP), followed by plant wax solubilization upon contact with wax films. These processes were monitored by ¹H NMR and SANS.

FINDING

Pesticide solubilization made surfactant micelles effectively more hydrophobic but subsequent wax dissolution caused pesticide release and the restoration of the micellar amphiphilicity. Nonionic surfactants with lower HLBs form larger nanoaggregates, show enhanced wettability, and have better ability to solubilize and permeate pesticides across the wax film, but may cause significant damage to plant growth. These observations help explain why herbicides applied on weeds would benefit from surfactants with lower HLB values while fungicides require surfactants with HLBs to balance between delivery efficiency and potential phytotoxicity risks.

Fabrication and Characterization of Prochloraz Nanoemulsion against Penicillium citrinum for the Postharvest Storage of Navel Oranges

Nanoemulsions have become extremely popular water-insoluble pesticide delivery systems in recent years. In this study, prochloraz nanoemulsions were obtained by selecting the mixing ratio of surfactants (6:1, 3:1, 2:1, 1:1, 1:2, 1:3, and 1:6), surfactant concentration, and shearing time. The optimal formula was 10 wt % prochloraz, 6 wt % surfactant (2 wt % CO-100 + 4 wt % CO-360) dissolved in 6 wt % hydrocarbon solvent (S-100A), and deionized water replenished to 100 wt %. This formula meets the quality index standards of the Food and Agriculture Organization. Compared with oil-in-water emulsion (EW), the prochloraz nanoemulsion exhibited higher antifungal activity against Penicillium citrinum in vitro (lower LC₅₀ of 1.17 mg L^-1) and in vivo (fewer lesions). In addition, the L02 cells treated with the nanoemulsion had a higher survival rate and lower apoptosis rate at the same concentration. Results showed that the toxicity of the prochloraz nanoemulsion on L02 cells was lower than that of EW. The findings provide an important method for developing an efficient, safe, and environment-friendly nanoemulsion for postharvest fruit storage.

Production, characterization and bio-emulsifying application of exopolysaccharides from Rhodotorula mucilaginosa YMM19

Microbial exopolysaccharides (EPS) are high molecular weight polymers having different sugar residues. EPS have potential applications in different fields, such as medicine, food and environment. Therefore, there is a growing interest in production, characterization and application of EPS from different microorganisms. The present study designed to investigate the production and characterization of EPS from Rhodotorula mucilaginosa YMM19 isolated from Morus nigra L. fruits as well as to examine their potential emulsifying properties. Effect of NaCl concentration, incubation period and pH on the production of EPS was studied. The maximum EPS production by yeast was achieved at 10% NaCl (9741.84 mg/l). The best incubation time for production of EPS was 5 days. Production of EPS decreased under neutral condition and increased at acidic and alkaline condition. The structural feature of EPS was examined by FT-IR and NMR spectral analysis and confirmed the presence of glucose, glucopyranose and galactose. The isolated EPS showed higher emulsification capacity with emulsification activity of 71% and emulsifying index of 60%. The EPS gave strong emulsification for farnesol and was more effective than sodium dodecyl sulphate, a reference emulsifier, in enhancing the herbicidal activity of farnesol against Melilotus indicus under greenhouse condition. The results suggest that the EPS produced by YMM19 strain has a potential to be used as emulsifying agent in pesticide formulations.

Effects of metal nanoparticle-mediated treatment on seed quality parameters of different crops

The increasing population of the world requires novel techniques to feed everyone, which can replace or work along with traditional methods to increase production of agricultural crops. In recent times, nanotechnology is considered as a promising and emerging approach to be incorporated in agriculture to improve productivity of different crops by the administration of nanoparticles through seed treatment, foliar spray on plants, nano-fertilizers for balanced crop nutrition, nano-herbicides for effective weed control, nanoinsecticides for plant protection, early detection of plant diseases and nutrient deficiencies using diagnostics kits, and nano-pheromones for effective monitoring of pests. Further, distinct nanoparticles with unique physicochemical and biological properties are used in agriculture to increase the percentage of seed germination, which is the initial step to increase the crop yield. In the context of agricultural crops, nanoparticles have both positive effects on seed quality parameters, such as germination percentage, seedling length, seedling dry weight and vigor indices, as well as negative impacts of causing toxicity toward the environment. Thus, the aim of this review article is to provide a comprehensive overview on the effects of super-dispersive metal powders, such as zinc, silver, and titanium nanoparticles on the seed quality parameters of different crops. In addition, the drawback of conventional seed growth enhancers, impact of metal nanoparticles toward seeds, and mechanism of nanoparticles to increase seed germination were also discussed.

Development of abamectin-loaded nanoemulsion and its insecticidal activity and cytotoxicity

BACKGROUND

Owing to the advantages of high-efficiency, environmental protection and safety, nanoemulsions have become a highly popular water-insoluble pesticide delivery system in recent years.

RESULTS

In this study, abamectin-loaded nanoemulsion with remarkable physical stability and application performance was obtained by selecting the type and concentration of surfactant and the emulsification method. The optimal formula was 2% abamectin and 5% castor oil polyoxyethylene (EL-40) dissolved in 7.5% hydrocarbon solvent (S-200) made up to 100% with deionized water, which conformed to the quality indicators from the Food and Agriculture Organization (FAO) standards. Droplets on cabbage leaves showed a small dynamic contact angle, which ensured that the resulting nanoemulsion exhibited excellent wettability and diffusivity. Compared with emulsifiable concentrates (EC) and microemulsions (ME), the abamectin-loaded nanoemulsion had the lowest LC₅₀ (0.0686 mg L^-1 ) to third-instar larva of Plutella xylostella, causing the larval body to blacken and shrivel, which improved insecticidal activity. In addition, the abamectin-loaded nanoemulsion had low cytotoxicity. The viability of dendritic cells with added nanoemulsion reached 100% after 2 h, whereas that of cells with EC and ME was lower. After 24 h, the cell viability of dendritic cells with added ME was 0.

CONCLUSION

This research facilitated the design and fabrication of nanoemulsions for water-insoluble pesticide to enhance insecticidal activity, lower cytotoxicity and reduce environmental pollution. © 2020 Society of Chemical Industry.

Coalescence and spreading of drops on liquid pools

HYPOTHESIS

Oil spills have posed a serious threat to our marine and ecological environment in recent times. Containment of spills proliferating via small drops merging with oceans/seas is especially difficult since their mitigation is closely linked to the coalescence dependent spreading. This inter-connectivity and its dependence on the physical properties of the drop has not been explored until now. Furthermore, pinch-off behavior and scaling laws for such three-phase systems have not been reported.

EXPERIMENTS

We investigate the problem of gentle deposition of a single drop of oil on a pool of water, representative of an oil spill scenario. Methodical study of 11 different n-alkanes, polymers and hydrocarbons with varying viscosity and initial spreading coefficients is conducted. Regime map, scaling laws for deformation features and spreading behavior are established.

FINDINGS

The existence of a previously undocumented regime of delayed coalescence is reported. A novel application of the inertia-visco-capillary (I-V-C) scale collapses all experimental coalescence data on a single line while the early stage spreading is found to be either oscillatory or asymptotically reaching a constant value, depending on the viscosity of the oil drop unlike the well documented monotonic, power law late-time spreading behavior. These findings are equally applicable to applications like emulsions and enhanced oil recovery.

Polymer Capsules with Hydrophobic Liquid Cores as Functional Nanocarriers

Recent developments in the fabrication of core-shell polymer nanocapsules, as well as their current and future applications, are reported here. Special attention is paid to the newly introduced surfactant-free fabrication method of aqueous dispersions of nanocapsules with hydrophobic liquid cores stabilized by amphiphilic copolymers. Various approaches to the efficient stabilization of such vehicles, tailoring their cores and shells for the fabrication of multifunctional, navigable nanocarriers and/or nanoreactors useful in various fields, are discussed. The emphasis is placed on biomedical applications of polymer nanocapsules, including the delivery of poorly soluble active compounds and contrast agents, as well as their use as theranostic platforms. Other methods of fabrication of polymer-based nanocapsules are briefly presented and compared in the context of their biomedical applications.

Formulation and Application of Nanoemulsions for Nutraceuticals and Phytochemicals

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Recent trends in research and investigation on nanoemulsion based products is the result of many reasons such as food security as a global concern, increasing demand for highly efficient food and agricultural products and technological need for products with the ability of manipulation and optimization in their properties. Nanoemulsions are defined as emulsions made up of nano sized droplets dispersed in another immiscible liquid which exhibit properties distinguishing them from conventional emulsions and making them suitable for encapsulation, delivery and formulations of bioactive ingredients in different fields including drugs, food and agriculture. The objective of this paper is to present a general overview of nanoemulsions definition, their preparation methods, properties and applications in food and agricultural sectors. Due to physicochemical properties of the nanoemulsion composition, creating nanosized droplets requires high/low energy methods that can be supplied by special devices or techniques. An overview about the mechanisms of these methods is also presented in this paper which are commonly used to prepare nanoemulsions. Finally, some recent works about the application of nanoemulsions in food and agricultural sectors along with challenges and legislations restricting their applications is discussed in the last sections of the current study.

Lipid-based nano delivery of antimicrobials to control food-borne bacteria

Direct application of antibacterial agents into foods gives limited advantages because bioactive ingredients may be partially inactivated, neutralized, or easily diffused when contacting with the food matrix. Hence, the aim of this study is to investigate the application of lipid-based nanocarriers as delivery systems for antibacterial ingredients. In this regard, several types of these carriers such as nanoliposomes, nanoemulsions, solid lipid nanoparticles (SLNs), and nanostructured lipid carriers (NLCs) are explored. This study seeks to cover the important challenges of lipid-based nanocarriers including structures and characteristics, properties, production methods, advantages and drawbacks, and their applications to encapsulate antibacterial compounds effectively, particularly in food systems. However, for more scrutiny inspection of the functionality of lipid-based nanocarriers, we have gathered and discussed the studies related to the antibiotic-loaded lipid-based nanoparticles. Also, the role of such nanocarriers in active packaging systems when combining with edible coatings or films is discussed.

A microcapsule oil dispersion for the controlled release of 1-methylcyclopropene in an open environment

1-Methylcyclopropene (1-MCP) is an important gaseous plant growth regulator. For its application as a gaseous pesticide, the plants with 1-MCP α-cyclodextrin microcapsule granules need to be enclosed in a sealed chamber. To provide a new spray formulation of 1-MCP for open environment application, herein, a novel 1-MCP microcapsule oil dispersion (1-MCP/MCOD) was prepared and characterized. It was found that 1-MCP could stay at higher concentrations for more than 36 hours during the controlled release experiment, and the SEM experiment showed good deposition of the 1-MCP/MCOD spray solution. In addition, the apple harvest application experiments showed that 1-MCP/MCOD could effectively prevent fruit drop at 3 μL L⁻¹ in an open environment. These results not only supply a new 1-MCP/MCOD kind of formulation for the flexible application of the 1-MCP gas in an open environment, but also show that this microcapsule oil dispersion formulation has significant potential in gaseous pesticide applications.

Formulation of 1-MCP/MOOD and controlled release process for application in the open environment.

Nonionic Glycolipids for Chromium Flotation- and Emulsion (W/O and O/W)-Based Bioactive Release

Biosourced surfactants are endeavored as a green alternative to biosurfactants and petrochemical surfactants having industrial utilization. Nine glycolipids with headgroup and chain length variation were derived from renewable resources like vegetable oils, carbohydrates, and amino acids. The concentration-dependent interfacial activity, foamability, wetting power, emulsification power, and solubilization capacities of glycolipids were investigated to provide a structure-activity relationship. Later, the metal flotation and emulsification experiments were performed. In general, for metal flotation, the surfactant should contain a hydrophobic tail, hydrophilic head, and chelating function. In the present investigation, it was observed that the headgroup of a glycolipid can serve as a hydrophilic head as well as perform a chelating function. Moreover, heat energy generated from the sunlight was utilized for metal flotation. Additionally, these glycolipids are capable to form stable sunflower oil-water (W/O and O/W) emulsions. The mechanical and thermal stabilities and hydrophobic chain length dependency of the prepared emulsions at different water volume fractions are explored. Furthermore, encapsulation and release of water-soluble (riboflavin and l-ascorbic acid) and oil-soluble (curcumin and α-tocopherol) bioactives in glycolipid emulsions were monitored. Thus, glycolipids under investigation had shown the possibility for pretreatment of chromium-containing wastewaters and bioactive-loaded emulsions toward the controlled release.