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Pesticides are the main means of production for the prevention and control of pests and diseases in agricultural production. They play an important role in ensuring stable agricultural production, increasing agricultural production, improving the quality of agricultural products, and improving the living standards of farmers. In the past 10 years, the acreage and output of fruits and vegetables in China have grown rapidly. By 2005, the fruit area accounted for 46% of the world's total, and the production accounted for 36.7% of the world's total. The area and yield of apples and pears ranked first in the world for eight consecutive years. Vegetable cultivation area and output ranked first in the world for five consecutive years. However, due to the rapid increase in the impediment of international trade caused by the pesticide pollution of agricultural products, large-scale returns and claims have occurred repeatedly, and some products have even basically withdrawn from the markets of developed countries, which has a tremendous impact on the economy and reputation. The widespread implementation of technical trade barriers with pesticide residues as their main content will often make it easy for China's agricultural products, which have a competitive price advantage in the international market, to fall into an unfavorable situation. In 1998, China's agricultural products worth 7 billion U.S. dollars were returned due to DDT, fenvalerate, dicofol and other pesticide residues exceeding the standard. In 1999, Germany's authoritative pesticide residue testing agency sampled the tea on the German market, exceeding the standard rate of 40. 3%, which caused a serious impact on China's tea exports. In 2001, the Japanese media made a large number of exaggerations on issues such as excessive pesticide residues in vegetables and mushrooms imported from China, which directly impacted the export of agricultural products in China. In order to prevent Chinese spinach from exporting to Japan, in April 2002, it announced that the residual limit of chlorpyrifos in pesticides in spinach was 0.11ppm, which was obviously aimed at China's technical barrier measures and was far more severe than other organophosphorus pesticides in Japanese vegetables. The residue limits (other organophosphorus pesticide residue limits are more than 10 times higher than the "chlorpyrifos"), and greatly exceed the relevant standards of the United States, the European Union and international organizations (the United States, the European Union and the CAC standard is 0. 05ppm).
It can be seen that solving the problem of pesticide residues not only meets the requirements of modern agriculture itself, but also can continuously enhance the competitiveness of China's increasingly fierce international market. Therefore, the study of pesticide residues in fruits and vegetables is an important way to increase farmers' income and solve the "three rural issues."
1 Pesticide Residue Treatment 1.1.1 Physical Methods 1.1.1 Cleaning the surface of the fruit The traditional method of removing pesticide residues is washing with water or washing, or immersing in detergents. Generally, the principle of water solubility and heat insolubility of some pesticides is used. . Kirchhoff [2] found that about 95% of parathion remained on the surface of apples. If the apples are peeled, there is only a very low parathion residue in the processing. It was reported that 43% of captan was removed after the apple was washed, and that 70% to 80% of the captan residue was removed after the apple boiled for 5 minutes or after cooking the sliced ​​and peeled apples. The report also pointed out that washing and then cooking can remove nearly 100% of pesticide residues. According to the report, the residue of captan on the surface of contaminated apple after washing still has 0.42 mg/kg.
The study showed that after 15 minutes of water immersion, the residual pesticide levels on the apple surface were 0. 657 mg/kg of phytozoa, 0. 67 mg/kg of cotton-preserved phosphorus, 0. 488 mg/kg of ketobacillus, and the removal rates were 23 %, 53% and 50%.
1.1.2 Adsorption of activated carbon by activated carbon is toxicologically safe. As long as products of food grade or above are used, it will not cause any harm to the human body. Najm et al. removed 99% of 2,4 5-T, Parathion, Lindane, and Dieldrin with 99% initial concentration of 10 μg/L in beaker and water plant tests. The amount of PAC required for the pesticide was studied. The results show that the water plant test requires much more PAC dosage than the beaker test, and the Frendich adsorption isotherms with an isotherm constant >200 are easily removed by activated carbon. Activated carbon has a strong adsorption effect on methamidophos residues in apple juice concentrate. The activated carbon is added 15%, adsorption is 1min, the diatomaceous earth filter layer thickness is 4mm, and the residue in 50bBrix juice can reach a very low level. 001mg. The effect of removal of pesticides by PAC was compared. The results showed that pH value of the solution had a significant effect on the adsorption of carbamate on activated charcoal, and there was a large adsorption capacity at low pH.
In addition to the above methods for degrading pesticide residues, some methods for applying pesticide degradation to the environment are being gradually applied to the food industry. For example, ultrasonic cleaning has the characteristics of high oscillation frequency and high strength, which accelerates the movement of pesticide molecules, increases the dissolution rate of pesticide molecules, and can solve the problems of slow dissolution and long time consumption of conventional soaked pesticides.
1.2 Chemical Oxidation technology is often an effective means of controlling pesticide contaminants and treating wastewater contaminated with pesticides.
1. 2. 1 Ozone Degradation Ozone reacts with organophosphorus pesticides to produce the corresponding low molecular weight compounds such as acids, alcohols, amines, or corresponding oxides. Ong et al. used chlorine and ozone to treat the fenthion, hydrochloric acid chloride and captan on apple surface and apple sauce. The results showed that the degradation rate of ozone on the above three pesticides was between 29% and 42%. The author believes that the low concentration of ozone (0.25 mg/L) is the main reason why chlorine is not effective in degrading pesticide residues. Hwang et al. used ozone and other oxidants to degrade mancozeb on apples. Only 15% of mancozeb residues remained after 30 minutes of lmg/L ozone water action. Only 3% of 3mg/L ozonated water had acted for 30 minutes. Mancozeb residue. Their other experimental results showed that the optimum pH for ozone degrading mancozeb was 7.0. Ruan et al. studied the effect of ozone and hypochlorite on the degradation of malathion, and pointed out that the effect of ozone degradation is better than that of hypochlorite. At a pH of 7.0, malathion has a maximum ozone degradation rate of 80%.
Kim et al. found that in ozone culture of bean sprouts, ozone can effectively degrade pesticides on sprouts.
Ozone was used to treat residues of pesticides such as pyrethrin in tomatoes, omethoate in cucumbers and cucumbers, and dichlorvos in lentils. The levels of degraded pesticide residues reached internationally accepted standards. Ozone was used to degrade methyl parathion, malathion and cypermethrin in water and achieved satisfactory results. Different concentrations of ozone were used to perform the degradation test of white bacillus. The results showed that ozone could completely degrade white bacteria. Yu Zhanggui used 15~20mg/L concentration of ozone to treat 5 kinds of organophosphorus pesticides used for grain storage, which significantly reduced pesticide residues. Zhang Weihua's experiments show that the longer the treatment time with ozone, the more easily the pesticides in Chinese cabbage are degraded. Taking the Chinese cabbage as the research object, it was pointed out that ozone could significantly promote the degradation of organic phosphorus and pyrethroid pesticides, but the degradation of methomyl was not obvious. Li Qiwan et al studied the effect of ozone on the degradation of pesticide residues in fruits and vegetables such as Chinese cabbage, tomato, pepper, and kidney bean. The results showed that ozone had a strong degradation effect on methamidophos, omethoate, and deltamethrin.
1. 2. 2 Hydrogen Peroxide Degradation The organochlorine pesticide was dissolved in alcohol and tested in milk solution to remove pesticide residues. DDT, chlordane, heptachlor epoxide, BHC, dieldrin, endrin and The degradation rate of aldrin was 33.3%, 31. 2%, 11.2%, 18.0%, 38.3%, 41.2% and 17.0%, respectively. Glaze et al. reported that the mixture of high-pH ozone and hydrogen peroxide can have a good decomposition effect on organochlorine pesticide residues in water. The reason is that ozone decomposes in water while producing cyanide ions. It was reported that when ozone-treated pesticide residues in water (pH, temperature, concentration) were reported, phenylurea could be rapidly and completely degraded in the presence of ozone and hydrogen peroxide combined treatment. In the Orr et al. experiment, it was found that shellfish toxins in fruits and vegetables can be degraded by 10% under both ozone and hydrogen peroxide.
1. 3 Biodegradation In addition to the physical and chemical methods described above for the degradation of pesticide residues, the use of microbiological or enzymatic methods to explore ways to eliminate pesticide residues has also been a hot topic in recent years. For example, the more representative Pseudomonas sp of bacteria can degrade malathion, phorate, dichlorvos, and methyl parathion and other pesticides. So far, the use of microbial or enzymatic methods to discuss the elimination of pesticide residues reported the main research object is organic chlorine, organic phosphorus and carbamate insecticides.
2 The mechanism of synergistic effects of high-voltage rectangular pulsed electric fields In summary, the use of physical, chemical, and biological methods has a certain effect on the removal of pesticide residues. In previous studies, it has been found that the high-voltage pulse discharge technology in water treatment has the synergistic effects of traditional water treatment methods such as high-temperature thermal degradation, photochemical oxidation, liquid cavitation degradation, and supercritical water oxidation. This advanced oxidative physicochemical process is characterized by its high efficiency and non-selectivity. It can rapidly degrade organic contaminants in water and has the function of efficiently killing microorganisms. The basic principle of high-voltage pulse discharge technology is to charge the pulse capacitor through a high-voltage generator, and then close the high-voltage switch. The pulse capacitor discharges through the high-voltage switch and the solenoid coil to generate a high-voltage strong pulse current, thereby establishing a strong pulse magnetic field in the processing chamber. Discharge is formed. In the treatment of high-concentration organic wastewater, some researchers have found that the high-voltage pulse discharge technology is better than the individual effects of each method, so it has excellent removal efficiency of organic pollutants in water, and it has been proved that there are many organic substances that can be degraded, such as phenol, Chlorophenol, trinitrotoluene, acetophenone, indole, rhodamine B, methyl orange, Chicago blue, indigo, direct blue 2B, and reactive red.
In recent years, the author has explored the application of high-voltage rectangular pulsed electric field technology in fruit and vegetable processing. The difference between high-voltage rectangular pulsed electric field technology and high-voltage pulsed discharge technology is that in the former, the electric field acts on substances in the processing chamber, and the latter acts on substances through discharge. . The advantages of high-voltage rectangular pulsed electric field in field strength and pulse width: First, the action time of the rising edge of the rectangular wave is shorter than the exponential wave and sine wave, so the effect of the material is not easy to rise, which is conducive to maintaining the same quality; second, the peak value of the rectangular wave. Easy to control, good regulation of the strength of action; third is to maximize the use of energy. A method for reducing organophosphorus pesticide residues in fruits and vegetables using a high-voltage rectangular pulsed electric field synergistic effect technique is to use an electrode processing chamber to produce high-voltage square wave pulses and ozone to make direct contact with fruits and vegetables, and to utilize the energy of the electric field and the strong oxidizing effect of ozone on organic substances. The destruction of phosphorus pesticide molecules provides a reference for the high-voltage rectangular pulsed electric field technology to be more widely used in the food industry.
3 Conclusion In this paper, the mechanism of high-voltage rectangular pulsed electric field synergistic effect of organophosphorus pesticides in fruits and vegetables was studied. The selection of parameters such as the intensity of the high-voltage pulse electric field, pulse width, frequency, time, the number of pulsed rectangular waves, and the mode of action was investigated. The impact of the degradation characteristics of pesticides was tested and theoretically analyzed. The biomechanical properties and meso-level analysis were used to reveal the mechanism of action and inherent laws, providing a rational analysis of the new technologies for the degradation of organophosphorus pesticides. Basic support.
It can be seen that solving the problem of pesticide residues not only meets the requirements of modern agriculture itself, but also can continuously enhance the competitiveness of China's increasingly fierce international market. Therefore, the study of pesticide residues in fruits and vegetables is an important way to increase farmers' income and solve the "three rural issues."
1 Pesticide Residue Treatment 1.1.1 Physical Methods 1.1.1 Cleaning the surface of the fruit The traditional method of removing pesticide residues is washing with water or washing, or immersing in detergents. Generally, the principle of water solubility and heat insolubility of some pesticides is used. . Kirchhoff [2] found that about 95% of parathion remained on the surface of apples. If the apples are peeled, there is only a very low parathion residue in the processing. It was reported that 43% of captan was removed after the apple was washed, and that 70% to 80% of the captan residue was removed after the apple boiled for 5 minutes or after cooking the sliced ​​and peeled apples. The report also pointed out that washing and then cooking can remove nearly 100% of pesticide residues. According to the report, the residue of captan on the surface of contaminated apple after washing still has 0.42 mg/kg.
The study showed that after 15 minutes of water immersion, the residual pesticide levels on the apple surface were 0. 657 mg/kg of phytozoa, 0. 67 mg/kg of cotton-preserved phosphorus, 0. 488 mg/kg of ketobacillus, and the removal rates were 23 %, 53% and 50%.
1.1.2 Adsorption of activated carbon by activated carbon is toxicologically safe. As long as products of food grade or above are used, it will not cause any harm to the human body. Najm et al. removed 99% of 2,4 5-T, Parathion, Lindane, and Dieldrin with 99% initial concentration of 10 μg/L in beaker and water plant tests. The amount of PAC required for the pesticide was studied. The results show that the water plant test requires much more PAC dosage than the beaker test, and the Frendich adsorption isotherms with an isotherm constant >200 are easily removed by activated carbon. Activated carbon has a strong adsorption effect on methamidophos residues in apple juice concentrate. The activated carbon is added 15%, adsorption is 1min, the diatomaceous earth filter layer thickness is 4mm, and the residue in 50bBrix juice can reach a very low level. 001mg. The effect of removal of pesticides by PAC was compared. The results showed that pH value of the solution had a significant effect on the adsorption of carbamate on activated charcoal, and there was a large adsorption capacity at low pH.
In addition to the above methods for degrading pesticide residues, some methods for applying pesticide degradation to the environment are being gradually applied to the food industry. For example, ultrasonic cleaning has the characteristics of high oscillation frequency and high strength, which accelerates the movement of pesticide molecules, increases the dissolution rate of pesticide molecules, and can solve the problems of slow dissolution and long time consumption of conventional soaked pesticides.
1.2 Chemical Oxidation technology is often an effective means of controlling pesticide contaminants and treating wastewater contaminated with pesticides.
1. 2. 1 Ozone Degradation Ozone reacts with organophosphorus pesticides to produce the corresponding low molecular weight compounds such as acids, alcohols, amines, or corresponding oxides. Ong et al. used chlorine and ozone to treat the fenthion, hydrochloric acid chloride and captan on apple surface and apple sauce. The results showed that the degradation rate of ozone on the above three pesticides was between 29% and 42%. The author believes that the low concentration of ozone (0.25 mg/L) is the main reason why chlorine is not effective in degrading pesticide residues. Hwang et al. used ozone and other oxidants to degrade mancozeb on apples. Only 15% of mancozeb residues remained after 30 minutes of lmg/L ozone water action. Only 3% of 3mg/L ozonated water had acted for 30 minutes. Mancozeb residue. Their other experimental results showed that the optimum pH for ozone degrading mancozeb was 7.0. Ruan et al. studied the effect of ozone and hypochlorite on the degradation of malathion, and pointed out that the effect of ozone degradation is better than that of hypochlorite. At a pH of 7.0, malathion has a maximum ozone degradation rate of 80%.
Kim et al. found that in ozone culture of bean sprouts, ozone can effectively degrade pesticides on sprouts.
Ozone was used to treat residues of pesticides such as pyrethrin in tomatoes, omethoate in cucumbers and cucumbers, and dichlorvos in lentils. The levels of degraded pesticide residues reached internationally accepted standards. Ozone was used to degrade methyl parathion, malathion and cypermethrin in water and achieved satisfactory results. Different concentrations of ozone were used to perform the degradation test of white bacillus. The results showed that ozone could completely degrade white bacteria. Yu Zhanggui used 15~20mg/L concentration of ozone to treat 5 kinds of organophosphorus pesticides used for grain storage, which significantly reduced pesticide residues. Zhang Weihua's experiments show that the longer the treatment time with ozone, the more easily the pesticides in Chinese cabbage are degraded. Taking the Chinese cabbage as the research object, it was pointed out that ozone could significantly promote the degradation of organic phosphorus and pyrethroid pesticides, but the degradation of methomyl was not obvious. Li Qiwan et al studied the effect of ozone on the degradation of pesticide residues in fruits and vegetables such as Chinese cabbage, tomato, pepper, and kidney bean. The results showed that ozone had a strong degradation effect on methamidophos, omethoate, and deltamethrin.
1. 2. 2 Hydrogen Peroxide Degradation The organochlorine pesticide was dissolved in alcohol and tested in milk solution to remove pesticide residues. DDT, chlordane, heptachlor epoxide, BHC, dieldrin, endrin and The degradation rate of aldrin was 33.3%, 31. 2%, 11.2%, 18.0%, 38.3%, 41.2% and 17.0%, respectively. Glaze et al. reported that the mixture of high-pH ozone and hydrogen peroxide can have a good decomposition effect on organochlorine pesticide residues in water. The reason is that ozone decomposes in water while producing cyanide ions. It was reported that when ozone-treated pesticide residues in water (pH, temperature, concentration) were reported, phenylurea could be rapidly and completely degraded in the presence of ozone and hydrogen peroxide combined treatment. In the Orr et al. experiment, it was found that shellfish toxins in fruits and vegetables can be degraded by 10% under both ozone and hydrogen peroxide.
1. 3 Biodegradation In addition to the physical and chemical methods described above for the degradation of pesticide residues, the use of microbiological or enzymatic methods to explore ways to eliminate pesticide residues has also been a hot topic in recent years. For example, the more representative Pseudomonas sp of bacteria can degrade malathion, phorate, dichlorvos, and methyl parathion and other pesticides. So far, the use of microbial or enzymatic methods to discuss the elimination of pesticide residues reported the main research object is organic chlorine, organic phosphorus and carbamate insecticides.
2 The mechanism of synergistic effects of high-voltage rectangular pulsed electric fields In summary, the use of physical, chemical, and biological methods has a certain effect on the removal of pesticide residues. In previous studies, it has been found that the high-voltage pulse discharge technology in water treatment has the synergistic effects of traditional water treatment methods such as high-temperature thermal degradation, photochemical oxidation, liquid cavitation degradation, and supercritical water oxidation. This advanced oxidative physicochemical process is characterized by its high efficiency and non-selectivity. It can rapidly degrade organic contaminants in water and has the function of efficiently killing microorganisms. The basic principle of high-voltage pulse discharge technology is to charge the pulse capacitor through a high-voltage generator, and then close the high-voltage switch. The pulse capacitor discharges through the high-voltage switch and the solenoid coil to generate a high-voltage strong pulse current, thereby establishing a strong pulse magnetic field in the processing chamber. Discharge is formed. In the treatment of high-concentration organic wastewater, some researchers have found that the high-voltage pulse discharge technology is better than the individual effects of each method, so it has excellent removal efficiency of organic pollutants in water, and it has been proved that there are many organic substances that can be degraded, such as phenol, Chlorophenol, trinitrotoluene, acetophenone, indole, rhodamine B, methyl orange, Chicago blue, indigo, direct blue 2B, and reactive red.
In recent years, the author has explored the application of high-voltage rectangular pulsed electric field technology in fruit and vegetable processing. The difference between high-voltage rectangular pulsed electric field technology and high-voltage pulsed discharge technology is that in the former, the electric field acts on substances in the processing chamber, and the latter acts on substances through discharge. . The advantages of high-voltage rectangular pulsed electric field in field strength and pulse width: First, the action time of the rising edge of the rectangular wave is shorter than the exponential wave and sine wave, so the effect of the material is not easy to rise, which is conducive to maintaining the same quality; second, the peak value of the rectangular wave. Easy to control, good regulation of the strength of action; third is to maximize the use of energy. A method for reducing organophosphorus pesticide residues in fruits and vegetables using a high-voltage rectangular pulsed electric field synergistic effect technique is to use an electrode processing chamber to produce high-voltage square wave pulses and ozone to make direct contact with fruits and vegetables, and to utilize the energy of the electric field and the strong oxidizing effect of ozone on organic substances. The destruction of phosphorus pesticide molecules provides a reference for the high-voltage rectangular pulsed electric field technology to be more widely used in the food industry.
3 Conclusion In this paper, the mechanism of high-voltage rectangular pulsed electric field synergistic effect of organophosphorus pesticides in fruits and vegetables was studied. The selection of parameters such as the intensity of the high-voltage pulse electric field, pulse width, frequency, time, the number of pulsed rectangular waves, and the mode of action was investigated. The impact of the degradation characteristics of pesticides was tested and theoretically analyzed. The biomechanical properties and meso-level analysis were used to reveal the mechanism of action and inherent laws, providing a rational analysis of the new technologies for the degradation of organophosphorus pesticides. Basic support.
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