Degradation of Pesticide Residues in Water, Soil, and Food Products via Cold Plasma Technology

Water, soil, and food products contain pesticide residues. These residues result from excessive pesticides use, motivated by the fact that agricultural productivity can be increased by the use of these pesticides. The accumulation of these residues in the body can cause health problems, leading to food safety concerns. Cold plasma technology has been successfully employed in various applications, such as seed germination, bacterial inactivation, wound disinfection, surface sterilization, and pesticide degradation. In recent years, researchers have increasingly explored the effectiveness of cold plasma technology in the degradation of pesticide residues. Most studies have shown promising outcomes, encouraging further research and scaling-up for commercialization. This review summarizes the use of cold plasma as an emerging technology for pesticide degradation in terms of the plasma system and configuration. It also outlines the key findings in this area. The most frequently adopted plasma systems for each application are identified, and the mechanisms underlying pesticide degradation using cold plasma technology are discussed. The possible factors influencing pesticide degradation efficiency, challenges in research, and future trends are also discussed. This review demonstrates that despite the nascent nature of the technology, the use of cold plasma shows considerable potential in regards to pesticide residue degradation, particularly in food applications.


Introduction
According to the United Nations, the world's population is expected to reach 9.8 billion by 2050, and a record high 11.2 billion by 2100 [1].With the increasing global population, the demand for land and other natural resources, including water, food, and agricultural products, will continue to rise [2].To satisfy the rising demand for agricultural products, pesticides have been used to protect plants and crops from pests, insects, fungi, and weeds.In addition to agricultural applications, pesticides are used in human and animal hygiene products such as pet shampoos [3]; moreover, they are incorporated into building materials and boat bottoms to render them insect-resistant [4].Pesticides, used before or after harvesting plants, contain both active and inert ingredients.They can be classified based on the type of pest targeted, such as herbicides, insecticides, rodenticides, and fungicides [5].Pesticide usage has increased worldwide, except in Africa, since the 1990s.In 2020, America was the top contributor to the world's pesticide usage, accounting for more than 50% of the world's total (Figure 1).Pesticides have negative effects on water, soil, and animals [6].Foods contaminated by harmful bacteria, viruses, parasites, or chemical substances, including pesticide residues, are consumed by an estimated 600 million people, which is approximately one-tenth of the world's population, causing common foodborne illnesses and approximately 420,000 deaths annually [8].Pesticides contained in food can accumulate in the human body, leading to chronic diseases.Additionally, polybrominated diphenyl ethers (PBDE), phthalates, bisphenol A (BPA), polychlorinated biphenyls (PCBs), and dioxins, as well as pesticides in the body, result in the generation of endocrine-disrupting chemicals (EDCs), which impair the normal function, biosynthesis, and biotransformation of hormones and the activity of endogenous hormone-metabolizing enzymes [9].Exposure to pesticides can occur via contact with the skin, ingestion, or inhalation, and the severity of health issues can vary depending on the type of pesticide used, the duration and route of exposure, and individual health conditions, such as nutritional deficiencies and healthy/damaged skin [10].The most frequently reported negative effects of pesticide exposure include Parkinson's disease [11], gastrointestinal and respiratory issues [12], neurological issues [13], reproductive issues [14], and endocrine issues [15].In addition to causing health issues, pesticides contaminate water and soil, causing environmental pollution.
Various techniques, such as washing [16][17][18], peeling [19], and thermal [20][21][22] and chemical [23] treatments, are used to remove pesticides in food before cooking.Washing with tap water is the easiest way to remove dust and other particles from food products [24].Although this technique is simple, its efficiency depends on the pesticide concentration and type of washing operation employed [25].Peeling is another method that can easily help remove pesticides because pesticides typically accumulate on the outer surfaces of fruits and vegetables [26].However, this step will also remove some of the important vitamins or nutrients contained in the peels of some fruits and vegetables.Thermal treatments, including boiling, cooking, or sterilization, are used during food processing [25].Although thermal treatment can effectively reduce the concentration of pesticide residues, some of the negative effects include nutritional loss when this method is applied to fruits and vegetables.Chemicals, such as chlorine dioxide, detergent solutions [27], and acetic acid [28], have been used to eliminate pesticide residues from food products.Similar to other conventional techniques, chemicals also affect the environment and human health.The aforementioned techniques are widely used in households owing to their simplicity; however, there are some concerns regarding their resulting environmental, sensory, and nutritional losses in practical applications.Therefore, various other Foods contaminated by harmful bacteria, viruses, parasites, or chemical substances, including pesticide residues, are consumed by an estimated 600 million people, which is approximately one-tenth of the world's population, causing common foodborne illnesses and approximately 420,000 deaths annually [8].Pesticides contained in food can accumulate in the human body, leading to chronic diseases.Additionally, polybrominated diphenyl ethers (PBDE), phthalates, bisphenol A (BPA), polychlorinated biphenyls (PCBs), and dioxins, as well as pesticides in the body, result in the generation of endocrine-disrupting chemicals (EDCs), which impair the normal function, biosynthesis, and biotransformation of hormones and the activity of endogenous hormone-metabolizing enzymes [9].Exposure to pesticides can occur via contact with the skin, ingestion, or inhalation, and the severity of health issues can vary depending on the type of pesticide used, the duration and route of exposure, and individual health conditions, such as nutritional deficiencies and healthy/damaged skin [10].The most frequently reported negative effects of pesticide exposure include Parkinson's disease [11], gastrointestinal and respiratory issues [12], neurological issues [13], reproductive issues [14], and endocrine issues [15].In addition to causing health issues, pesticides contaminate water and soil, causing environmental pollution.
Various techniques, such as washing [16][17][18], peeling [19], and thermal [20][21][22] and chemical [23] treatments, are used to remove pesticides in food before cooking.Washing with tap water is the easiest way to remove dust and other particles from food products [24].Although this technique is simple, its efficiency depends on the pesticide concentration and type of washing operation employed [25].Peeling is another method that can easily help remove pesticides because pesticides typically accumulate on the outer surfaces of fruits and vegetables [26].However, this step will also remove some of the important vitamins or nutrients contained in the peels of some fruits and vegetables.Thermal treatments, including boiling, cooking, or sterilization, are used during food processing [25].Although thermal treatment can effectively reduce the concentration of pesticide residues, some of the negative effects include nutritional loss when this method is applied to fruits and vegetables.Chemicals, such as chlorine dioxide, detergent solutions [27], and acetic acid [28], have been used to eliminate pesticide residues from food products.Similar to other conventional techniques, chemicals also affect the environment and human health.The aforementioned techniques are widely used in households owing to their simplicity; however, there are some concerns regarding their resulting environmental, sensory, and nutritional losses in practical applications.Therefore, various other promising technologies have been developed to improve the effectiveness of pesticide decontamination.
Emerging technologies based on pulsed electric fields (PEFs) [29][30][31], irradiation [32][33][34], high-pressure processing (HPP) [35], ultrasonication [36], ozonation [37,38], and cold plasma have recently been used in the food and agricultural fields for microbial inactivation and pesticide residues degradation.Although quality-related properties, such as nutritional properties, color, texture, and flavor of food, are unaffected by PEF, Gómez et al. [39] summarized the limitations of PEFs in meat and fish processing (e.g., high capital cost; inefficiency of spore inactivation; unavailability of commercial units in many regions of the world; the presence of bubbles, leading to nonuniform treatment, as well as operational problems; and the scarcity of economic and engineering studies regarding the feasibility of the upscaled continuous process).Similarly, the efficiency of pesticide removal by irradiation depends on the surface properties of the food products [25].For instance, size, shape, and homogeneous surface characteristics should be considered to standardize the matrices of the samples [40].The maintenance and system cost, as well as the lack of data on thermophysical properties under pressure, are the main limitations of the HPP technology [41].Moreover, HPP could cause damage such as protein denaturation, color and structure changes, and metal ion release in certain foods [41][42][43].Ultrasonic irradiation is an environmentally friendly technique that can help reduce pesticide residues [44].The efficiency of this technique relies on the power, amplitude, and frequency of the ultrasonic waves [45].Although ozonation is an efficient technique for reducing pesticide residues, consumer acceptability is poor owing to its toxicity [45].Cold plasma is a nonthermal and advanced technology with no adverse effects on agricultural products after treatment.Plasma comprises several reactive species, free radicals, electrons, positive and negative ions, atoms, and molecules in the ground and excited states; the quanta of electromagnetic radiation show unique properties [46].With these numerous reactive species, plasma technology has been employed in various applications such as microorganism decontamination, microbial inactivation, sterilization, and pesticide degradation.In the past few years, many researchers have successfully applied plasma technology for degrading pesticide residues in foods [47], water [48], and soil [49].Plasma-activated water (PAW) is generated by the interaction between cold plasma and water, and it has broad applications [50,51].Many reviews have been published regarding the applications of PAW to various processes in agricultural activities, including microbial inactivation, seed germination, plant growth enhancement, and food preservation, as well as in the removal of pesticide residues [50,52].The various reactive species generated in PAW play the main role in these applications.Without considering the type of working gas used, the following reactions occur during PAW treatment (Equations ( 1)-( 4)) [53]: e e This review provides a framework of the use of cold plasma technology in the degradation of pesticides, including the possible factors influencing the degradation efficiency and related degradation mechanism and degradation products.Moreover, challenges and future trends are also discussed.This review aims to offer useful tools and information for understanding the potential of cold plasma technology in pesticide degradation applications, and the degradation mechanism is further studied.

Types of Nonthermal Plasma
Nonthermal plasma (NTP) is a partially ionized gas comprising various types of atoms, molecules, and ions in excited and ground states, as well as reactive species and free radicals [54].It can be produced through the electrical discharge of carrier gases under low or atmospheric pressure [55].Any type of excitation energy can be used to ionize carrier gases, including air, oxygen, nitrogen, helium, hydrogen, argon, or even their mixtures, into a plasma state [46].The common reactive species produced by nonthermal plasma are reactive oxygen species (ROS), reactive nitrogen species (RNS), and charged particles [56].The concentration of these reactive species depends on the gases and liquids used, the chemical environment, the excitation voltage, and the mode of generation [57,58].Plausible reactions regarding reactive species generation could be established using argon, oxygen, nitrogen, and air as the working gases (Table 1).These reactive species play an important role in various applications such as microbial inactivation, pesticide degradation, and seed germination.When applied to food products or media matrices, nonthermal plasma can be classified into two types: gas discharge and plasma-activated water (or any other solution).
Table 1.Plausible reactions obtained from the interaction between plasma and water molecules when using different working gases.

Argon
Ar

Gas Plasma
As gas plasma or atmospheric-pressure cold plasma (APCP) can be produced at atmospheric pressure, it can overcome most of the drawbacks of conventional cold plasma, such as high investment cost, low processing speed, and the requirement of a vacuum system and special plasma reactor [62].Plasma generation requires an appropriate plasma system that includes a carrier gas, a power source, and electrodes [46].In this section, we discuss the various types of gas plasma discharges operating at atmospheric pressure in terms of the plasma generation method involved, including atmospheric-pressure plasma jet (APPJ) discharge, dielectric barrier discharge (DBD), corona discharge, and gliding arc discharge (GAD).Figure 2 provides an overview of the nonthermal plasma systems used for pesticide degradation.

Atmospheric Pressure Plasma-Jet Discharge
Plasma-jet discharge is a promising technology for many applications, including material treatment [63][64][65], pesticide degradation [66,67], and microbial inactivation [68][69][70].APPJ discharge is one of the most commonly used plasma systems owing to its versatility, low-cost tools, ease of design, and fewer requirements.However, it is unsuitable for largearea treatment because of its uniformity when applied to large areas [71].This plasma system typically comprises a nozzle equipped with two electrodes in different arrangements, such as coaxial or special ring-electrode setups [62].Plasma is produced through the nozzle and expands as a plume [72].The voltage used to ignite the gas ranges from a hundred volts to kilovolts, depending on the gas type and discharge gap.The gases commonly used to produce plasma are air and gas mixtures of argon-oxygen and argon-nitrogen [73].The gas flow rate is another design parameter influencing plasma generation in the APPJ discharge system.Table 2 summarizes the different applications of APPJ and its design parameters.Cold atmospheric plasma jets have been applied to improve the wettability of polypropylene (PP), in which pure argon is used as the working gas [74].The contact angle, which indicates the wettability of the PP surface, decreases with the plasma treatment time.For surface modification via the plasma technology, the gas flow rate and the applied voltage have a considerable impact on the etching process [75].Although various studies have indicated the impact of the plasma process parameters on different applications, the process parameters should be optimized for specific applications.

Atmospheric Pressure Plasma-Jet Discharge
Plasma-jet discharge is a promising technology for many applications, including material treatment [63][64][65], pesticide degradation [66,67], and microbial inactivation [68][69][70].APPJ discharge is one of the most commonly used plasma systems owing to its versatility, low-cost tools, ease of design, and fewer requirements.However, it is unsuitable for large-area treatment because of its uniformity when applied to large areas [71].This plasma system typically comprises a nozzle equipped with two electrodes in different arrangements, such as coaxial or special ring-electrode setups [62].Plasma is produced through the nozzle and expands as a plume [72].The voltage used to ignite the gas ranges from a hundred volts to kilovolts, depending on the gas type and discharge gap.The gases commonly used to produce plasma are air and gas mixtures of argon-oxygen and argon-nitrogen [73].The gas flow rate is another design parameter influencing plasma generation in the APPJ discharge system.Table 2 summarizes the different applications of APPJ and its design parameters.Cold atmospheric plasma jets have been applied to improve the wettability of polypropylene (PP), in which pure argon is used as the working gas [74].The contact angle, which indicates the wettability of the PP surface, decreases with the plasma treatment time.For surface modification via the plasma technology, the gas flow rate and the applied voltage have a considerable impact on the etching process [75].Although various studies have indicated the impact of the plasma process parameters on different applications, the process parameters should be optimized for specific applications.The most frequently applied system for plasma technology is the DBD [81].In this system, a dielectric material, such as plastic, quartz, or ceramic, is coated on the electrodes [82].Air is also used in this system as a barrier to the current, preventing spark generation.The DBD system offers some key advantages, including simple a discharge ignition, the flexibility of using different gas mixtures, a lower gas flow rate requirement, and the possibility of using different electrode geometries and configurations to provide a uniform discharge ignition over several meters [83].However, it requires a high voltage (10 kV) to ignite the plasma, which can be supplied by AC [84].Design parameters, such as the type of roundedged electrodes, dielectric material, and applied voltage, should be appropriately selected to avoid arcing during plasma generation.The system uses typical carrier gases such as atmospheric air, nitrogen, argon, and helium [85].Although the DBD system provides a large-area surface treatment, overcoming the constraints of APPJ discharge, limitations persist, such as the use of flat substrates and a small electrode gap.Moreover, the charge and average current density of the gas are limited owing to electrical breakdown [86].Nevertheless, in the DBD system, the plasma discharge is randomly distributed, and a homogeneous treatment is ensured [87].Table 3 lists the plasma applications through the use of DBD.Xiang et al. [88] inactivated Zygosaccharomyces rouxii in apple juice using DBD plasma; a 5-log reduction of viable Z. rouxii cells in apple juice with a DBD exposure time of 140 s was demonstrated.However, process optimization should be performed to realize an efficient and cost-effective inactivation process in the food industry.Samantaet et al. [89] investigated the effect of DBD plasma on the hydrophobic functionalization of cellulosic fabric, in which the plasma discharge voltage, the gas ratio of the gas mixture, and the gas flow rate significantly affected the fragmentation.This study demonstrated the complexity of plasma applications, which can be controlled by selecting appropriate plasma parameters to achieve the desired functionality.

Corona Discharge
When a high electric current is applied between two electrodes separated by a small gap, corona discharge, which generates small lightning bolts, is generated near the sharpedge electrode [93].The corona discharge system includes a high-voltage supply, electrodes, and sample-treatment chambers.The electrodes used in this system, such as a point, tip, thin wires, or plane with an imposed high voltage, are typically asymmetrical [55,94].The electrodes can be made of copper, ceramic-coated stainless steel, or titanium [95].Air, nitrogen, argon, a mixture of helium and oxygen, or argon and oxygen can be used as the working gas to generate the discharge [96].Corona discharge possesses limitations, as it produces inhomogeneous discharge and has a small treatment area, requiring scale-up operations [97].Furthermore, corona discharge can cause burn spots, discoloration, and oxidation when applied directly to the food surface because the active region is close to the point electrode or is limited to distances of millimeters [87].Therefore, corona discharge is unsuitable for applications that require large-area surface treatments.Table 4 shows its usage in various applications, including the inactivation of virus and foodborne pathogens, nanocomposite coating, shelf-life extension, and the synthesis of carbon nanotubes.

Gliding Arc Discharge
To reduce the temperature to the nonthermal level, GAD is generated by the deposition of a cold, atmospheric-pressure plasma onto surfaces using forced air [102].DC and AC can be used as power sources in GAD to generate near-atmospheric pressure plasma.The plasma system comprises two or more metallic electrodes, along with an AC or DC high-voltage transformer.An electric arc is produced between the electrodes, generating a plasma plume when a high voltage is applied [103].The gliding arc outperforms other types of plasma discharges given its lower current intensity, higher electron density, higher injection flow rate, and lower cost [63,104].Considering the advantages of GAD systems, various applications of this system are summarized in Table 5. Kimet et al. [105] reported that water injection and air flow rates affect the concentration of the hydrogen peroxide produced, while the exposure time of GAD affects bacterial inactivation.

Plasma-Activated Water
PAW can be produced by discharging plasma into a specific amount of water or solution using various plasma sources, including plasma jets, DBD, corona discharge, and GAD [110].DBD is the most widely used plasma source for PAW production [111][112][113][114]. ROS and RNS can be generated by exposing plasma to water, in which the plasma discharge is transferred from the plasma to the liquid at the gas-liquid interface, producing various primary and secondary species that play a crucial role in many applications [115].Two types of RONS are produced in PAW: long-lived species (e.g., hydrogen peroxide (H 2 O 2 ), nitrate (NO 3 − ), nitrite (NO 2 − ), ozone (O 3 )) and short-lived species (e.g., hydroxyl radicals (•OH), superoxide (O 2 − ), singlet oxygen ( 1 O 2 ), nitric oxide (NO•), peroxynitrite acid (ONOO − ), and peroxynitric acid (OONO 2 − )).The generation of these species depends on various parameters, including the gases and liquids used, the chemical environment, the excitation voltage, and the fabrication modes.PAW can be produced using two approaches that rely on the plasma-liquid interaction, i.e., plasma discharge over and under the water surface.The type and concentration of RONS in PAW vary depending on the plasma source, the generation approach, and the operational parameters.The differences between these two approaches lie in the chemical and physicochemical properties of the generated species [50].

Discharge over Water Surface
When plasma is exposed over the water surface, the water composition of the plasma gas-water surface changes [116].The major concern regarding plasma discharge over a water surface is the mass transfer from gas to water.Therefore, the reactor used to mix the gas and water should be optimized [117].Some researchers have overcome this issue by increasing the contact area [118], enhancing the contact time, adding contact regions [119,120], and adjusting the plasma distance [121].In this form of discharge, the energy efficiency is improved through the production of reactive species in the gas-phase plasma, which transfer to the liquid or form at the liquid-gas interface [122].Table 6 presents the applications of PAW, in which plasma discharges over the water surface.The discharge duration for PAW production and the PAW treatment time influence the effectiveness of decontamination [123,124].The longer reaction time between the reactive species and the microbes appears to be a possible reason for this enhancement.According to Kumaret et al. [125], different activated solutions show different effects on the cell viability of pancreatic cancer cells.

Discharge under the Water Surface
In the case of plasma discharge under the water surface, the water and discharge responses have a combined effect, leading to a more powerful reaction and more reactive species [129].As the oxygen content in water is higher than that in air, more oxygen-containing groups are produced, resulting in ROS and free electrons.According to Piskarev [130], the energy required to activate water is less than that required to produce plasma.Moreover, plasma discharge under water provides better results in terms of physicochemical properties, such as the conductivity and oxidation-reduction potential (ORP) [131].A possible reason for the higher efficiency of plasma exposure under water than over the water surface is that a closed system can produce more reactive species in PAW [132].Table 7 lists the application of plasma discharge under the water surface.The gas mixture is one of the parameters influencing the generation of the chemical compounds in PAW.Different gas mixtures or ratios cause different reactive radicals to be generated in PAW [133].In addition to the dissolved substances in PAW, the pH level, electrical conductivity, and oxidative reduction potential are other parameters set for PAW generation [134,135].Liuet et al. [136] found that direct plasma treatment with different feeding gases can produce different degrees of enhancement in the germination of mung beans.Glazing agent on a shrimp [133] Several reports revealed that the parameter settings used to generate both gas plasma and PAW are crucial in almost every application.Therefore, the relevant parameters for plasma generation should be considered and optimized.For instance, Kim, Lee, Puligundla, and Mok [70] investigated the effect of relative humidity on the generation of reactive species (i.e., CO, NO, and NO 2 species).An increase in the relative humidity level was found to improve the efficiency of the corona discharge plasma jet for the inactivation of foodborne pathogens.Panda and Sahu [141] demonstrated that the plasma condition and rate of hydrogen production can be enhanced, depending on the electrode material used in the DBD plasma reactor.They also studied the plasma discharge characteristics by varying the discharge voltage and time, while maintaining a discharge gap of 1.5 mm.

Pesticide Degradation in Cold Plasma
Cold plasma technology, as discussed in the previous section, is an effective and innovative technology for various applications, including pathogen inactivation, seed germination, surface modification, and pesticide degradation.Over four million tons of pesticides have been used annually over the past decade [142].Pesticide usage has significantly affected the quality of water, soil, and air, as well as crop production, causing toxicity, carcinogenicity, and mutagenicity in humans [143][144][145].Kimet et al. [146] adopted APCP to degrade paraoxon and parathion on glass slides.In recent years, the applicability of cold plasma for pesticide degradation in water, soil, and food has been increasingly studied.

Degradation of Pesticide Residues in Water
Water contaminated with pesticide residues in agricultural areas negatively affects the ecosystem [147].Several studies have applied nonthermal plasma to remediate pesticides in wastewater treatment [148].Cold plasma-assisted dissipation of pesticide residues in water has been reported since 2008 [149], and the degradation efficacy has been satisfactory.In most studies, pulsed corona discharge [150,151] and DBD [152][153][154] with a falling water film were adopted for a direct discharge inside, or in contact with, the liquid [148].Table 8 shows the degradation of pesticide residues in water using cold plasma technology.
Cold plasma transforms the chemical structure of pesticides to a structure that is nontoxic or less toxic [155,156].In a previous study, organic micropollutants (atrazine, chlorfenvinphos, 2,4-dibromophenol, and lindane) contaminating a solution were removed using two different nonthermal plasma reactors [157], both of which were based on DBD, with one operating as a planar reactor and the other operating as a coaxial reactor.The efficiency of pollutant removal from water depends on the initial concentrations of the organic matter and mineral salts.Pollutant dissipation increases with increasing plasma treatment time.Huet et al. [158] and Hu, et al. [159] studied other parameters, including the discharge power and air gap distance.Both studies concluded that hydroxyl radicals play the most important role in degrading both pesticides.The effects of various plasma-generated parameters, such as the input power, treatment time, and input voltage, were studied.Ref. [160] found that the degradation efficacy of nitenpyram pesticide improves with increasing input power.In addition, the mineralization of 2,4 dichlorophenoxyacetic acid from an aqueous solution could be enhanced by increasing the plasma treatment time [161].Some studies have also investigated the effects of external factors, such as catalysts, conductivity, and pH, on improving the degradation efficacy.Appropriate amounts and types of catalysts can help improve the degradation process [156,160].Reddy et al. [154] showed that nonthermal plasma combined with cerium oxide catalysts improved the mineralization of endosulfan from an aqueous medium.Similarly, Jović et al. [154] examined four catalytic systems (Mn 2+ /DBD, Co 2+ /DBD, Fe 2+ /DBD, and H 2 O 2 /DBD).A lower pH or an acidic condition were found to result in a greater amount of pesticide degradation in aqueous solutions [161].Ozonation is a promising advanced oxidation process for pesticide dissipation; Bradu et al. [151] treated a solution with a combination of plasma and ozonation reactors and found that the combined treatment resulted in a more effective degradation than did ozonation alone.More recently, microplasma discharge water has been applied to remove organophosphorus and organochlorine pesticides [162].The results revealed that different types of pesticides were degraded via different mechanisms and reactive species.Many pesticides have been investigated in aqueous solutions.The key parameters in these treatments were the mineralization efficiency and solution toxicity.However, different types of pesticides and plasma discharge systems require different configurations of the plasma settings, as well as their optimization.

Degradation of Pesticide Residues in Soil
Soil is known to be an important resource in the agricultural field [164].One of the major threats to soil is the diffusion of pesticides into soil layers, which hinders several of the United Nations Sustainable Development Goals related to the soil environment [165].Pesticide residues in soil can be removed by washing [166] and volatilization [167].However, this causes water and air contamination.Various effective methods, including bioremediation, chemical remediation, and electrokinetic remediation, have been explored to treat soil contaminated with pesticides or other compounds [168].Although these techniques can remediate contaminated soil, some drawbacks remain, such as slow treatment and higher treatment costs.Plant-microbial remediation is one of the most effective methods for dissipating pesticide residues in soil.However, this method is limited when it comes to actual applications due to its high cost [169].Hence, cost-effective cold plasma technology has been examined to remove pesticide residues in soil.p-Nitrophenol (PNP) was removed from contaminated soil using pulsed-discharge plasma combined with TiO 2 [170].Higher quantities of active species, such as O 3 and H 2 O 2 , were observed in the pulse discharge plasma-TiO 2 catalytic system than in a system using plasma only.The improvement was evident from the evolution of the main intermediates over the treatment time.Table 9 summarizes previous studies on the effects of cold plasma on the degradation of pesticide residues in soil.Pulsed corona discharge and DBD have been extensively applied to dissipate pesticide residues in soil.Planar or cylinder-to-plane electrode configurations of the DBD plasma discharge system are typically used, whereas for corona discharge, a multi-needle-to-plate configuration is preferred for soil remediation [171].Wang et al. [166] investigated the effects of several parameter settings of the pulsed corona discharge plasma, including the peak pulse voltage, pulse frequency, gas atmosphere (air, O 2 , Ar, and N 2 ), air flow rate, and pollution time, on the effectiveness of pentachlorophenol (PCP) degradation in soil.These results indicate that the degradation efficiency can be enhanced by increasing the peak pulse voltage or pulse frequency.Similarly, the discharge voltage of atmospheric-pressure DBD plasma also has a positive effect on the degradation efficiency of glyphosate-contaminated soil [172].Although the plasma discharge systems were different, the plasma parameters, such as the voltage, still play an important role and should be optimized before application.Moreover, soil remediation decreased with an increase in the initial pollutant concentration.In the removal of residues from the soil, the ozone is the main active species in the gas form.Other parameters, such as the treatment time and the soil pH, also have a positive effect on pesticide extermination [173].Soil moisture has been found to influence the remediation efficiency of plasma technology [49,172].The latest report by Ref. [174] confirmed the effect of soil moisture on the pesticide degradation efficiency; however, no significant correlation was found with the soil thickness.According to previous studies, the properties of soil, particularly its moisture content, influence the soil remediation process, in which the reaction between the reactive species generated by plasma and water molecules produces strong oxidizing agents including •OH and H 2 O 2 [171].The degradation of trifluralin is feasible, even in thicker soil.The degradation efficiency decreases by 30% with increasing soil moisture.The energy efficiency is up to three orders of magnitude. [174]

Degradation of Pesticide Residues in Food
Food safety, nutrition, and food security are indistinguishably connected.Recently, these have become topics of major concern worldwide.One of the keys to sustaining life and promoting good health is accessibility to sufficient safe and healthy food.Unsafe food containing harmful bacteria, viruses, parasites, or chemical substances results in more than 200 diseases, ranging from diarrhea to cancer [178].Conventional methods, such as heat treatment, chlorine treatment, ultrasound application, and ozonation, have been used to remove pesticide residues from food products.However, these techniques have various negative effects on the physical and chemical qualities of food products, along with environmental impacts.Cold plasma technology is a proven degradation process for pesticide residues found in food products owing to its minimal effects on product quality and attributes.Table 10 presents the applicability of cold plasma for removing pesticide residues from food products.Various types of food, such as blueberries, strawberries, cucumbers, and maize, were examined.Using the O 2 plasma treatment, Bai et al. [179] demonstrated that the chemical structure of pesticides transforms into a structure with less toxic compounds, and this was confirmed by gas chromatographymass spectrometry (GC/MS) analyses.A nontoxic secondary metabolite of chlorpyrifos, 3, 5, 6-trichloropyridinol, was observed after plasma treatment [180].This chlorpyrifos degradation product was less harmful than the parent chlorpyrifos [181].Furthermore, an in-package nonthermal plasma technology was first examined by Misra et al. [182].Strawberries were exposed to a range of pesticides and then treated with the DBD system.The results showed a range of degradation percentages between 45% and 71%, depending on the type of pesticide used.Different types of pesticides have different chemical structures; therefore, the degradation efficiency of the plasma technology differs.The operating parameters of the atmospheric-pressure air DBD plasma system, including the plasma treatment time, discharge power, and initial pesticide concentrations, are other factors affecting the degradation efficiency [183].Cong et al. [184] investigated the efficiency of dielectric barrier discharge on the degradation of malathion and chlorpyrifos in water and on lettuce at different voltages (60, 70, and 80 kV) and different times (30, 60, 90, 120, 150, and 180 s).An optimum treatment condition for pesticide degradation in water was a voltage of 80 kV and a treatment duration of 180 s.Interestingly, ascorbic acid significantly decreased when the long duration required for optimum treatment was applied.Therefore, a shortened treatment duration of 120 s was suggested to maintain the amount of ascorbic acid in lettuce.Several studies have determined the impact of cold plasma on the quality of fresh produce, such as its color, hardness, and sugar percentage.Most studies have shown that cold plasma has minimal undesired effects on food products, and that it can improve some of its chemical qualities [185][186][187].Plasma-activated water, a novel treatment strategy, was applied to reduce phoxim on grapes [139].After a 10 min treatment with PAW prepared for 30 min, phoxim was reduced by 73.60%.The experimental results also revealed that PAW treatment did not significantly affect the quality of the grapes, including color, firmness, sugar, vitamin C, and superoxide dismutase.In contrast, a decrease in the firmness of cherry tomatoes and blueberries was observed.This was the effect of direct treatment with nonthermal plasma on agricultural products, which is attributed to surface softening and mechanical damage, damage to external cells, and an increase in temperature during treatment [188,189].Liu et al. [190] also found that plasma treatment for 60 s at an air flow rate of 1000 mL/min, power of 20 W, and frequency of 1200 Hz can remarkably decrease (p < 0.05) the moisture content of treated corn, while dissipating chlorpyrifos and carbaryl by up to 86.2% and 66.6%, respectively.Some studies have shown that the surface properties of fruits are affected by plasma penetration [191].The analyses of the efficiency of pesticide degradation in grapes and strawberries using PAW showed chlorpyrifos degradation rates of 79% and 69% for grapes and strawberries, respectively, whereas the carbaryl degradation rates were 86% and 73%.Sawangrat et al. [192] adopted a pinhole plasma jet to generate PAW; the carbendazim and chlorpyrifos contained in the solution and on the chili surface was subsequently degraded.For the same plasma configuration, they reported that the pesticide degradation efficiency was higher on the chili surface than in the pesticide solution.However, when fresh produce was treated with PAW, it required an additional drying process after treatment to avoid the wet produce decaying in storage.Overall, the efficiency of pesticide degradation from food products using cold plasma depends on several factors, including plasma configuration, initial concentration of pesticide residue, surface characteristics of food products, and type of pesticide, as well as environmental factors.

Mechanism of Nonthermal Plasma on Pesticide Degradation
For a better understanding of the reactions by which the plasma treatment degrades pesticides, plasma chemistry, such as the produced reactive species and degradation products, should be investigated.Some studies have found that the reactive species components [155] and electron energy [46] are important factors indicating the potential of pesticide degradation.Plasma treatment could produce various high-oxidation-potential reactive species, such as ozone, hydroxyl radical, and hydrogen peroxide, as well as irradiated light and ultraviolet light [48].The presence of these reactive species appears to play a critical role in the degradation mechanism [179].Direct oxidation or several chain reactions that yield H 2 O 2 and the OH radical are the main mechanisms of ROS for pesticide degradation [193].At a high pH, an indirect reaction occurs, whereas a direct reaction is predominant in acidic environments.In acidic environments, a slow reaction between the dissolved ozone and hydrogen peroxide occurs, leading to the formation of the hydroxyl radical.However, these reactions are significantly accelerated at high pH levels.Ozone also leads to oxidation by cleaving double bonds and direct reactions with compounds such as OH, CH 3 , OCH 3 , and NH 2 .A few chemical reactions that may occur during and post-plasma treatment are presented in Equations ( 5)-( 12) [155].
Based on the effect of plasma treatment on pesticide residues, RONS directly attack and react with the pesticide molecules, breaking chemical bonds and forming various chemical reactions that lead to the transformation of pesticide structures into less harmful or harmless compounds under suitable conditions [199].The P=S double bonds in dimethoate are first cleaved via a hydroxyl radical attack.Finally, they are transformed into small harmless compounds containing groups including PO 4 3− , H 2 O, and CO 2 [159].In the application of pulsed corona discharge above the water surface for the degradation of carbofuran and 2,4-dichlorophenoxyacetic acid (2,4-D) [200], the oxidation mechanism initiated by the hydroxyl radical leads to the transformation of carbofuran and 2,4-D to carbamic acid and 2-4-dichlorphenol, respectively.Another crucial property of the degradation pathway is the hydroxylation of the C-O bonds on the benzene ring by the hydroxyl radicals.Ozone, which is a powerful oxidant, can be produced at industrial scales by electrical discharge in oxygen and in air by corona or the DBD discharge system [199].Chamberlain et al. [201] found that the degradation mechanism of pesticides can be attributed to the photolysis reaction by the hydroxyl radicals and oxidation-reduction reactions by ozone and oxygen atoms.Small molecular compounds, including acids, alcohols, amines, and carbonyls, are the by-products of oxidation from the ozone [202].Khan et al. [203] explained the mechanism of diazinon degradation in microplasma discharge water.The various radicals generated in PAW, particularly the oxide of nitrogen and ozone, played various roles in the degradation mechanism.Smaller molecular fragments, including hydroxy diazinon and isopropenyl derivative, were formed through hydroxylation and dehydration reactions, respectively.Unlike other research, this study showed that hydrogen peroxide has a minimal effect on the degradation pathways of diazinon [203].Bennett et al. [204] compared the efficiencies of two plasma systems based on GAD and pinhole plasma discharge.Over 50% of diruron was degraded with pinhole plasma discharge, whereas the GAD was insufficient for diuron degradation.The degradation products of diuron were identified to be 3,4-dichloro-benzenamine, 1-chloro-3-isocyanato-benzene, and 1-chloro-4-isocyanato-benzene through GC-MS; some authors suggested that these degradation products are more harmful to the environment than the parent compound [205].Similarly, Mitrović et al. [155] investigated the effect of a nonthermal plasma needle on the removal of dimethoate from water.According to the high-performance liquid chromatography (HPLC) analysis, one of the degradation products, dimethoate oxo-analogue omethoate, is more harmful than dimethoate.However, the overall toxicity of contaminated water continuously decreases after treatment.Cong et al. [182] proposed a degradation pathway of malathion and chlorpyrifos by DBD plasma (Figure 3).A P=S double bond is first destroyed, and then it is transformed to the P=O double bond in malathion and chlorpyrifos.Subsequently, melaoxon is converted to triethyl phosphate by the cleaving of the P-S bond.Simultaneously, the molecules of malathion can degrade into O,O,S-trimethyl phosphorodithioate, 2-butenedioic acid (Z)-, diethyl ester, 2-butenedioic acid (E)-, and diethyl ester by breaking the C-S bond attacked by active species.For the chlorpyrifos degradation, the oxidation product of chlorpyrifos oxon is further converted into diethyl phosphate, 3,5,6-trichloro-2-pyridinom, and ethyl 3,5,6-trichloropyrid in-2-yl hydrogen phosphate by the cleaving of the C-S bond.From these results, we conclude that the degradation mechanism differs, depending on the pesticides added to a specific food product or media matrix and the specific plasma discharge system used, and should therefore be investigated specifically for each pesticide and system.including hydroxy diazinon and isopropenyl derivative, were formed through hydroxylation and dehydration reactions, respectively.Unlike other research, this study showed that hydrogen peroxide has a minimal effect on the degradation pathways of diazinon [203].Bennett et al. [204] compared the efficiencies of two plasma systems based on GAD and pinhole plasma discharge.Over 50% of diruron was degraded with pinhole plasma discharge, whereas the GAD was insufficient for diuron degradation.The degradation products of diuron were identified to be 3,4-dichloro-benzenamine, 1-chloro-3-isocyanato-benzene, and 1-chloro-4-isocyanato-benzene through GC-MS; some authors suggested that these degradation products are more harmful to the environment than the parent compound [205].Similarly, Mitrović et al. [155] investigated the effect of a nonthermal plasma needle on the removal of dimethoate from water.According to the high-performance liquid chromatography (HPLC) analysis, one of the degradation products, dimethoate oxo-analogue omethoate, is more harmful than dimethoate.However, the overall toxicity of contaminated water continuously decreases after treatment.Cong et al. [182] proposed a degradation pathway of malathion and chlorpyrifos by DBD plasma (Figure 3).A P=S double bond is first destroyed, and then it is transformed to the P=O double bond in malathion and chlorpyrifos.Subsequently, melaoxon is converted to triethyl phosphate by the cleaving of the P-S bond.Simultaneously, the molecules of malathion can degrade into O,O,S-trimethyl phosphorodithioate, 2-butenedioic acid (Z)-, diethyl ester, 2-butenedioic acid (E)-, and diethyl ester by breaking the C-S bond attacked by active species.For the chlorpyrifos degradation, the oxidation product of chlorpyrifos oxon is further converted into diethyl phosphate, 3,5,6-trichloro-2-pyridinom, and ethyl 3,5,6-trichloropyrid in-2-yl hydrogen phosphate by the cleaving of the C-S bond.From these results, we conclude that the degradation mechanism differs, depending on the pesticides added to a specific food product or media matrix and the specific plasma discharge system used, and should therefore be investigated specifically for each pesticide and system.

Conclusions and Future Directions
Pesticide usage is increasing, resulting in chemical residues in the environment.Although several existing techniques can be used to address this issue, they all exhibit potential, along with adverse effects.Owing to its promising efficiency in several applications, including pesticide degradation, the cold plasma technology is currently being extensively studied.Various plasma-generation techniques, including APPJ, DBD, corona discharge, and GAD, have been proposed.These systems can generate plasma in gas or liquid forms.However, not every system is applicable in every scenario.The APPJ is suitable for flat and small samples, whereas the DBD method can be applied to samples with a large surface area.Similar to APPJ, corona discharge, which produces an inhomogeneous discharge, possesses a small treatment area.Recently, GAD has been widely studied in various applications owing to its low current intensity, low cost, high electron density, and high injection flow rate.However, few studies have adopted GAD for pesticide degradation.Therefore, there remain various gaps that should be addressed by the research community.For example, an appropriate plasma generation technique and its optimal setting condition should be verified to obtain the maximum degradation rate regarding specific pesticides and samples.For implementation in a wide range of industries, optimizing cold plasma treatments for specific degradation applications (i.e., pesticides, food products, or solutions) is challenging and should be explored by stakeholders, including researchers.Figure 4 illustrates the factors influencing the pesticide degradation efficiency.This point should be addressed to obtain the most desirable results when plasma treatment is applied to pesticide degradation.Several plasma configuration parameters, such as the discharge time, feeding gas types, treatment time, power, and applied voltage, affect the degradation potential.Factors including the sample properties, pesticide types, and the environment also affect the pesticide degradation efficiency.Therefore, more experimental designs should be adopted to define suitable plasma parameters.Although plasma treatment has been considered a promising technique for pesticide degradation, it does not fully remove pesticides.Hence, its incorporation with other technologies, including microbubbles, UV light, ozone, or shockwaves, may be an alternative to improve the degradation efficiency.Research on cold plasma technology for pesticide degradation in fresh produce is still limited in terms of the penetration depth of plasma-generated reactive species, the effects of cold plasma on quality attributes, and its mechanism, as well as the toxicity of the degradation products.Although some studies have proposed possible pesticide degradation pathways and degraded products, the specific reactive species and their interaction on the pesticide structure are yet to be fully explored.Most studies have shown that hydroxyl radicals and ozone play an important role in the degradation of pesticides.Food safety is another concern associated with this technology; hence, the final by-products and possible side effects of plasma treatment should be considered to gain the trust of consumers.Despite these limitations, this review proves that cold plasma technology exhibits high potential for removing pesticide residues in various samples, particularly in food applications.The potential to upscale and expand cold plasma technology in the food industry should be considered in further investigations.
and grounded electrode: stainless steel Dielectric barrier: quartz tube Gas flow rate: 0.075 L/min Working gas: compressed air

Figure 4 .
Figure 4. Effect of pesticide degradation factors using cold plasma treatment.Author Contributions: P.S. and K.L. conceived the ideas discussed in the article.P.S. wrote the original draft and prepared the figures.P.S. and C.S. performed the literature search and data analysis.K.L., C.S., N.C. and D.B. reviewed and edited the manuscript.All authors have read and agreed to the published version of the manuscript.Funding: This work is supported by the National Research Council of Thailand (NRCT): (N41A640206) and partially supported by Chiang Mai University.Data Availability Statement: Not applicable.

Figure 4 .
Figure 4. Effect of pesticide degradation factors using cold plasma treatment.

Table 2 .
Applications of cold plasma produced by an atmospheric-pressure plasma jet (APPJ).

Table 2 .
Applications of cold plasma produced by an atmospheric-pressure plasma jet (APPJ).

Table 3 .
Plasma application through DBD.

Table 4 .
Plasma application through corona discharge.

Table 5 .
Plasma application through gliding arc discharge.

Table 7 .
Applications of PAW (discharge under the water surface).

Table 8 .
Summary of studies on the degradation of pesticide residues in water using cold plasma technology.

Table 9 .
Summary of studies on the degradation of pesticide residues in soil using cold plasma technology.

Table 10 .
Summary of studies on the degradation of pesticide residues in food using cold plasma technology.