Pesticide residues on vegetables remain a persistent public health concern, particularly in urban households where washing is often the primary method of decontamination. Conventional rinsing methods, such as plain water or vinegar, are limited in their ability to eliminate the full spectrum of pesticide types, especially hydrophobic compounds like organochlorines and ionic residues such as carbamates and organophosphates that adhere strongly to vegetable surfaces.

Advances in nanotechnology and green chemistry provide promising avenues for developing more effective, food-safe cleansing agents. This project formulates an enhanced natural nano-solution using five synergistic components, each selected for its distinct mechanism of action in detoxifying vegetable surfaces:

• Neem extract, rich in phytochemicals such as azadirachtin and nimbin, offers antimicrobial activity and surfactant-like properties to dislodge pesticide residues.
• Activated charcoal, known for its high surface area and porous structure, adsorbs a broad range of non-polar organic pesticide molecules.
• Bentonite clay, a naturally occurring aluminosilicate, swells in water, enabling it to reach into micro-crevices and bind positively charged pesticide ions through ion exchange.
• Citric acid, a mild organic acid, assists in breaking down certain pesticide bonds and alters the surface pH, enhancing solubility and degradation of residue, particularly carbamates.
• Polysorbate 80, a food-grade surfactant, lowers interfacial tension and facilitates emulsification, making it particularly effective in lifting oily or wax-bound residues.

Together, these components form a plant-based, biodegradable nano-wash capable of addressing both polar and non-polar pesticide residues. The solution is tested across a selection of vegetables, each representing distinct surface morphologies, to evaluate its broad-spectrum efficacy in practical household contexts.

Role of Neem Nanoparticles in Surface Decontamination

The phytochemical richness of Azadirachta indica (commonly known as neem) has been a cornerstone of traditional Ayurvedic medicine, natural pest management systems, and biopesticide development. Extracts from neem leaves, seeds, and bark contain a diverse range of biologically active compounds, chief among them azadirachtin, nimbin, nimbidin, salannin, and quercetin. These phytochemicals exhibit a spectrum of bioactivities, including insecticidal, antifungal, antibacterial, antiviral, anti-inflammatory, and antioxidant effects. Of particular interest is azadirachtin, a tetranortriterpenoid limonoid, which disrupts insect molting and reproduction by interfering with ecdysteroid hormone pathways, making it a potent natural insect growth regulator (IGR).

Recent advancements in nanotechnology have enabled the synthesis of neem-based nanoparticles (NNPs), which significantly enhance the bioavailability and surface reactivity of neem-derived compounds. When neem extract is incorporated into nanoparticles using green synthesis methods, often with biocompatible polymers or metal oxides as substrates. It results in superior physicochemical stability, improved dispersion in aqueous media and heightened biological efficacy.

Neem nanoparticles exhibit the following advanced functionalities:

• High Surface-to-Volume Ratio: The nanoscale dimension (typically 20–100 nm) dramatically increases the reactive surface area, enabling intimate contact with micro-quantities of pesticide residues adhering to fruit and vegetable surfaces. This enhances adsorption kinetics and degradation potential.
• Hydrophobic Interactions: Many pesticide residues, such as organophosphates and pyrethroids, are lipophilic and form water-insoluble films on produce. Neem nanoparticles display affinity for such hydrophobic moieties, allowing them to penetrate and disrupt these films, thereby loosening residues that conventional water rinses fail to remove.
• Surfactant-Like Action: The amphiphilic nature of certain neem constituents, when nanosized, imparts surfactant-like behavior. This facilitates emulsification and mechanical detachment of pesticide molecules embedded in cuticular waxes or irregular surface morphologies such as lenticels and stomatal grooves.
• Penetration of Microtopography: The ultra-fine size enables the nanoparticles to infiltrate surface microstructures, such as crevices and pores in vegetable skins, reaching residues inaccessible to larger particles. This improves the thoroughness of detoxification.
• Antimicrobial Efficacy: In addition to chemical detoxification, neem nanoparticles possess potent antimicrobial activity. Studies have shown inhibition zones against coli, S. aureus, and Fusarium spp., attributed to the ability of active compounds to interfere with microbial cell membranes and induce oxidative stress via reactive oxygen species (ROS) generation.
• Stability and Sustained Release: Nanoscale formulation enhances the photostability and thermal stability of bioactives like azadirachtin, which are otherwise susceptible to degradation under sunlight or heat. Certain nanoformulations enable slow and sustained release, prolonging the active window for microbial and pesticide degradation.

Cumulatively, these properties position neem nanoparticles as multifunctional agents in pesticide residue mitigation. They act as detoxifiers, by degrading or dislodging harmful agrochemicals; as penetrants, by accessing residues embedded in surface microstructures; and as bio-protectants, by offering antimicrobial action that further ensures produce safety post-wash.

Role of Bentonite Clay in Adsorptive and Ion-Exchange Cleansing

Bentonite is a naturally occurring clay derived from volcanic ash, predominantly composed of the smectite mineral montmorillonite, an aluminum phyllosilicate with a unique layered structure. It possesses exceptional hydration, swelling, and cation-exchange properties, making it widely used in water purification, pharmaceutical formulations, and environmental remediation. Its structure consists of stacked tetrahedral and octahedral sheets, enabling high surface area and a net negative charge distributed across the platelet surfaces.

Upon hydration, bentonite swells dramatically, absorbing several times its weight in water. This property is critical in forming a gel-like matrix capable of penetrating microscopic depressions, fissures, and grooves on the surfaces of fruits and vegetables. Such gel penetration dislodges and suspends particulate and chemical contaminants, enhancing mechanical cleansing.

The key detoxification mechanisms of bentonite in the context of vegetable cleansing include:

• Swelling-Driven Micro-Infiltration: The expansion of bentonite platelets upon contact with water enables physical access into microcrevices and intercellular spaces of the vegetable’s surface, thereby facilitating the detachment of tightly bound pesticide particles and agrochemical residues.
• Electrostatic Adsorption: Bentonite’s negatively charged surfaces exhibit high affinity for cationic (positively charged) pesticide residues, particularly those from organophosphate and carbamate families, such as malathion and carbaryl. These pesticides often carry quaternary ammonium or phosphonium groups, which are electrostatically attracted to the clay’s surface.
• Ion-Exchange Capability: A hallmark of smectite clays, bentonite’s cation exchange capacity (CEC) allows it to swap benign interlayer cations, such as Na⁺, Ca²⁺, or Mg²⁺, with toxic pesticide-derived metal ions or degradation products. This exchange not only removes harmful ions from the produce surface but also stabilizes them within the clay matrix, minimizing re-release.
• Multimodal Adsorption Spectrum: Bentonite can simultaneously adsorb a wide range of substances, including metal ions, ammonium ions, and organic toxins. This enables it to serve as a complementary agent to activated charcoal, which primarily targets non-polar organic compounds like chlorinated pesticides (e.g., DDT, endosulfan) through van der Waals and hydrophobic interactions.
• Environmental Safety and Biocompatibility: As a GRAS (Generally Recognized As Safe) material, bentonite is non-toxic and inert when used externally. It does not leave harmful residues and can be easily rinsed off after treatment, making it ideal for food decontamination applications.

In synergy with neem-based nanoparticles and activated charcoal, bentonite clay contributes to a tri-modal cleansing mechanism:

1. Biological detoxification via neem’s antimicrobial and pesticidal bioactives,
2. Physical adsorption and microstructure infiltration by bentonite’s swelling clay matrix,
3. Chemical neutralization and broad-spectrum contaminant removal through the combined action of ion-exchange and activated carbon's non-polar affinity.

This holistic approach enhances the efficacy, safety, and coverage of pesticide residue removal systems, especially in environments where multi-class pesticide contamination is prevalent. It is particularly valuable for leafy greens, root vegetables, and fruits with textured or porous surfaces where residues tend to accumulate and resist simple washing techniques.

Role of Citric Acid in pH-Mediated Residue Breakdown

Citric acid (C₆H₈O₇) is a tricarboxylic acid naturally found in citrus fruits and widely used in food preservation, pharmaceuticals, and environmental detoxification. As a weak organic acid, it is characterized by multiple carboxyl groups that not only impart a mildly acidic pH but also allow it to act as a versatile chelating agent and biochemical destabilizer. In the context of decontaminating fruits and vegetables, citric acid plays a critical role in the chemical breakdown, desorption, and solubilization of pesticide residues, particularly those that are pH-sensitive.

Its multi-functional role in the formulation is underscored by the following mechanisms:

• Surface pH Reduction and Hydrolytic Breakdown: Many pesticide classes, especially organophosphates (e.g., chlorpyrifos, parathion) and carbamates (e.g., carbaryl, aldicarb), contain ester or amide linkages that are susceptible to acid-catalyzed hydrolysis. When applied to produce, citric acid lowers the surface pH to ~3–4, creating an environment conducive to breaking labile chemical bonds within these pesticide molecules, converting them into more water-soluble and less toxic breakdown products.
• Chelation of Metal Ions: Citric acid forms stable complexes with divalent and trivalent metal ions such as Fe³⁺, Cu²⁺, and Zn²⁺, which are often present as co-factors in pesticide formulations or bind tightly to soil-derived metal residues on produce surfaces. Chelation disrupts these metal-organic interactions, thereby mobilizing and detaching metal-associated pesticide residues. This is particularly important for chelating metal-chelate based fungicides (e.g., mancozeb, zineb).
• Disruption of Biofilms and Microbial Contaminants: The acidic environment also contributes to antimicrobial action by denaturing proteins and disrupting the metabolic activity of spoilage bacteria and fungi such as coli, Listeria monocytogenes, and Aspergillus niger. Citric acid's pKa values (3.13, 4.76, and 6.40) enable stepwise proton donation, destabilizing microbial cell walls across a broad pH range and helping preserve the produce for longer post-treatment.
• Improved Wettability and Penetration: As a buffering agent, citric acid can also modulate the ionic strength of the solution, reducing surface tension and enhancing the penetration of other actives such as neem nanoparticles and bentonite. This synergistic effect ensures deeper infiltration into microgrooves and textured surfaces, further improving the overall efficacy of pesticide residue removal.
• Environmental and Food Safety Profile: Citric acid is classified as GRAS (Generally Recognized As Safe) by regulatory agencies such as the FDA and EFSA. In rinse-off formulations used for vegetable cleansing, residual citric acid levels are negligible and pose no risk to human health, making it ideal for household or commercial vegetable wash products.

In a multi-agent decontamination system, citric acid complements neem nanoparticles and bentonite clay by acting as a pH modulator, chelator, and microbial inhibitor, adding a chemical cleansing dimension to the existing biological and adsorptive mechanisms. This integration not only expands the range of pesticides targeted (polar and non-polar, metal-complexed and ester-bound) but also ensures that residual microbial load is minimized, thereby enhancing both food safety and shelf life.

Role of Polysorbate 80 in Emulsification and Surface Tension Reduction

Polysorbate 80 (also known as Tween 80) is a non-ionic surfactant derived from sorbitol and oleic acid, widely regarded as safe for food and pharmaceutical use. It is characterized by a hydrophilic-lipophilic balance (HLB) value of ~15, making it highly effective in emulsifying water-insoluble substances. In decontamination systems such as vegetable nano-washes, Polysorbate 80 plays a critical role as a surface-active agent, enabling more efficient contact, lift, and removal of stubborn pesticide residues, especially those with low water solubility.

The surfactant’s core functions in the formulation include:

• Surface Tension Reduction and Wettability Enhancement: Polysorbate 80 significantly lowers the surface tension of aqueous solutions from ~72 mN/m (pure water) to ~30–40 mN/m. This reduction enhances the spreading coefficient of the wash, allowing it to form a thin, uniform film over hydrophobic vegetable surfaces (such as tomatoes, bell peppers, and leafy greens). Better surface coverage ensures improved interaction of active agents, like neem nanoparticles and bentonite clay, with the produce surface, maximizing cleansing efficacy.
• Emulsification of Lipophilic Pesticides: A wide range of persistent pesticides, including organochlorines (e.g., DDT, lindane) and synthetic pyrethroids (e.g., cypermethrin, permethrin), exhibit strong hydrophobicity, which makes them difficult to remove with water alone. Polysorbate 80, due to its amphiphilic nature, encapsulates these oily pesticide molecules within micelles, rendering them miscible in the aqueous phase and thus easier to detach and rinse away. This process is essential in removing residues that form thin, greasy films on vegetable surfaces.
• Stabilization of Multi-Component Formulations: In a complex nano-wash system that includes neem extract (rich in phytochemicals), activated charcoal particles, and bentonite clay, Polysorbate 80 enhances colloidal stability. It prevents phase separation, settling, or aggregation of particles by creating a steric barrier around dispersed solids and droplets. This ensures that the wash remains homogeneous over time, preserving its efficacy during storage and use.
• Facilitation of Bioactive Dispersion: Many neem-derived compounds, such as azadirachtin and nimbin, are partially lipophilic and prone to aggregation in water. Polysorbate 80 improves their solubility and distribution in the aqueous phase, ensuring that their pesticidal and antimicrobial properties are evenly deployed across the washed produce surface.
• Safe Use and Regulatory Approval: Recognized as GRAS by the U.S. FDA and widely used in oral and topical pharmaceutical formulations, Polysorbate 80 is safe when used in small, rinse-off concentrations. It is non-toxic, biodegradable, and non-irritant at the levels required for vegetable cleansing applications.

When integrated into the nano-wash system, Polysorbate 80 functions as a mechanical and chemical enabler, enhancing the delivery, lift, and solubilization capabilities of the wash. Its presence not only allows hydrophilic and lipophilic agents to coexist effectively but also ensures that persistent, oily pesticide films, which would otherwise remain post-washing, are efficiently broken down and removed.

Together with neem, bentonite, activated charcoal, and citric acid, Polysorbate 80 helps create a comprehensive, multi-modal decontamination platform that leverages physical, chemical, and biological cleansing mechanisms for maximum pesticide residue reduction and produce safety.

Integrated Cleansing Mechanism

This enhanced nano-formulation brings together five complementary detoxification strategies:

• Biological action via neem’s nanoparticulate phytochemicals
• Chemical adsorption and ion-exchange through bentonite and activated charcoal
• pH-modulated residue destabilization using citric acid
• Surfactant-driven emulsification and surface tension reduction via Polysorbate 80
• Microstructure penetration and physical lift from the swelling action of clay and dispersive force of nano emulsion

This integrative system enables broad-spectrum removal of both polar and non-polar pesticide residues, while maintaining a biodegradable, food-safe, and environmentally responsible profile.

Materials Used

For Enhanced Nano-Veggie Wash:

• Fresh neem leaves
• Activated charcoal powder
• Bentonite clay
• Citric acid (food-grade)
• Polysorbate 80 (food-grade surfactant)
• Distilled water
• Blender or glass stirrer
• Filter paper or muslin cloth
• Beakers, measuring cylinders

For Testing:

• Fresh vegetables:
  • Smooth-skinned: Tomato
  • Leafy: Spinach
  • Waxy-skinned: Brinjal
• Diluted pesticide solution (0.1% organophosphate)
• Iodine tincture
• Starch powder

Extraction of Botanical Bioactive Agents

Fresh leaves of Azadirachta indica were collected and thoroughly cleansed under distilled water to remove surface particulates. The leaves were then subjected to aqueous thermal extraction under controlled conditions. After a brief period of boiling, the decoction was cooled to room temperature and filtered through a standard laboratory-grade filtration medium to obtain a clear botanical extract rich in phytochemicals. The extract was stored under ambient conditions until further use.

Formulation of Nano-Veggie Wash

To enable optimal adsorption properties, bentonite clay was hydrated in distilled water and allowed to swell under static conditions for a fixed duration. The enhanced wash was formulated by combining the previously extracted neem solution, the hydrated clay suspension, activated carbon powder, a weak organic acid (serving both as a pH modifier and chelating agent), and a food-grade non-ionic surfactant. The mixture was homogenized using high-shear stirring or blending to ensure a stable colloidal suspension with uniform dispersion of particulates and actives. The resulting formulation was visually inspected for stability and stored in sterile containers for application trials.

Preparation of Contaminated Samples

Common edible vegetables with distinct surface characteristics (leafy, smooth-skinned, and porous) were selected for testing. These were uniformly treated with a dilute aqueous solution of a model pesticide compound belonging to the organophosphate class. After application, the samples were air-dried in a contamination-controlled environment to simulate real-world surface adsorption conditions prior to washing.

Washing Protocol and Experimental Grouping

The contaminated vegetables were divided into three experimental groups:

• Test Group: Washed with the nano-formulated cleansing solution.
• Control Group 1: Washed with distilled water.
• Control Group 2: Washed with an acidic aqueous solution commonly used in domestic settings.

Each vegetable sample was gently scrubbed and rinsed with the assigned solution for a fixed period under consistent mechanical agitation. All washings were performed under identical conditions to ensure comparability across groups.

Qualitative Detection of Residual Surface Contaminants

A modified starch-iodine assay was prepared to provide a preliminary qualitative indication of surface pesticide residues. A soluble starch solution was prepared via thermal gelatinization and cooled to ambient temperature. An iodine-based colorimetric reagent was diluted to working concentration. Post-wash, surface samples were analyzed using this indicator to assess the presence or absence of oxidizing pesticide residues through observable color change, aiding in comparative assessment of decontamination efficacy.

Testing for Residual Pesticides

• Collect runoff water from each washed sample in a labelled container.
  • In a test tube, mix:
  • 3 mL of starch solution
  • 1 mL of the runoff sample
• 3 drops of diluted iodine solution
  • Observe the colour change:
  • Dark blue = High pesticide residue
  • Faint blue or clear = Low or no detectable residue

1. G) Observation Table

• The Enhanced Nano Neem Wash, comprising a synergistic blend of neem extract, activated charcoal, bentonite clay, citric acid, and Polysorbate 80, consistently demonstrated superior pesticide removal efficacy across all tested vegetable categories. The formulation’s multifunctional approach, combining biological detoxification, adsorptive trapping, pH modulation, and surfactant-enabled solubilization, enabled it to outperform conventional washing methods in both surface decontamination and residue dissolution.
• Tomatoes, characterized by a smooth, hydrophobic skin with relatively few surface microstructures, exhibited near-complete pesticide removal when treated with the nano-formulation. The lack of surface crevices likely facilitated uniform spreading of the wash and maximized contact between active agents and pesticide residues, allowing for efficient emulsification and detachment.
• Spinach, a leafy green with high porosity, stomatal openings, and intricate folds, naturally presented greater challenges for decontamination. However, the nano-wash significantly reduced residue levels, with only faint colouration observed in iodine-starch assays, indicating its ability to penetrate complex surface topologies and neutralize residues embedded within leaf matrices.
• Brinjal (eggplant), which possesses a semi-permeable waxy cuticle, displayed notable resistance to both plain water and vinegar-based washing solutions. This is attributed to the lipophilic nature of common pesticide films, which adhere strongly to waxy surfaces. However, the nano-formulated wash led to a marked improvement in residue removal, suggesting that the combined effect of bentonite’s adsorptive capacity and Polysorbate 80’s emulsifying action enabled the solution to infiltrate and lift hydrophobic residues more effectively than acidic or neutral alternatives.
• Comparative results across all groups reinforced a critical insight: both plain water and vinegar-water solutions were significantly less effective in dislodging pesticide residues, particularly those derived from organophosphates and synthetic pyrethroids. Their limited performance underscores the need for a targeted, multi-functional cleansing system capable of addressing both polar and non-polar contaminants, penetrating micro-irregularities, and ensuring food safety without compromising nutritional or structural integrity.

Safety

All five components used in the enhanced nano-wash, i.e. neem extract, activated charcoal, bentonite clay, citric acid, and Polysorbate 80, are considered safe for human use when applied in the context of a rinse-off vegetable wash. None of the ingredients are toxic in the low concentrations used for this formulation, and all are either naturally derived or commonly used in food, pharmaceutical, or cosmetic applications.

Neem extract is safe externally but should not be ingested in large amounts. Activated charcoal and bentonite clay are inert and non-toxic, However, only food-grade variants should be used for food-contact purposes. Citric acid and Polysorbate 80 are both GRAS (Generally Recognized As Safe) by regulatory authorities such as the FDA and are widely used in the food industry.

As the solution is designed to be rinsed off after use, there is no significant risk of residue ingestion. This ensures the formulation is both effective and food-safe, making it suitable for household and domestic applications.

This study validates the effectiveness of an enhanced, plant-based nano-wash formulation in significantly reducing pesticide residues on fresh vegetables. By combining neem extract, activated charcoal, bentonite clay, citric acid, and Polysorbate 80, the solution harnesses a synergistic mix of biological detoxification, chemical adsorption and emulsification, and physical surface penetration to address a wide range of pesticide chemistries.

Across all vegetable types tested, smooth-skinned (tomato), leafy (spinach), and waxy-surfaced (brinjal), the nano-formulation consistently outperformed both plain water and vinegar in removing pesticide residues, as evidenced by a significant reduction in iodine-starch coloration. The results highlight how each component plays a distinct and complementary role:

• Neem extract contributes phytochemical action and mild biosurfactant properties
• Activated charcoal adsorbs non-polar compounds
• Bentonite clay facilitates ion exchange and micro-surface infiltration
• Citric acid enhances pH-driven residue breakdown, particularly for carbamates
• Polysorbate 80 improves emulsification and removal of lipophilic pesticide films such as organochlorines

The final formulation is biodegradable, food-safe, and low-cost, making it accessible for household use and promising for scalable applications in food safety interventions. Its multi-modal cleansing action demonstrates how green chemistry and nanotechnology can be effectively combined to solve real-world problems in domestic hygiene and public health.

In essence, this project offers a scientifically grounded and environmentally responsible approach to mitigating one of the most persistent challenges in modern food consumption: the safe removal of residual agricultural chemicals from vegetables before they reach the plate.

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