Study On The Variation And Degradation Of Chlorpyrifos Pesticide Residues In Leek Production

Chlorpyrifos,also known as Lesborne,is a cotton insecticide which has been widely used in various fruits and vegetables,particularly for leek,due to its several good factors such as its low toxicity compared with other conventional pesticides,good miscibility,etc.However,there are few studies on chlorpyrifos used for leek,the detection of pesticide residues in leek and the study of common pesticide degradation law are particularly important.In this experiment,the pesticide residues in leek were studied by using the gas phase（GC）technology in accordance with the national standard（GB 2763-2016）.The rule of pesticide residue in leek was studied by taking factors such as the pesticide concentration,pesticide dose and crop picking time system for comprehensive considerations.Ultraviolet irradiation,hydrogen peroxide treatment,ozone water immersion,ultrasonic cleaning,hydrolysis of organic enzymes,pure water,sodium hypochlorite,sodium bicarbonate and surfactant were selected to study the insecticide degradation rule.The main contents and results of the study are as follows:1.To optimize the three single factors of chlorpyrifos pesticide concentration,application volume and harvest time during the application process,the conclusion was drawn as follows:the best condition is whenthe application concentration was 2.0%,the application volume is45L/acre,and the harvest time was 7 days.The results of response surface optimization test are as follows:the best condition is when the application concentration was 2.0%,the application volume was 40.01L/acre,and the picking time was 6.99 days,basically consistent with the recommended value.Compared with 3 controlgroups which are high spraying concentration group,standard spraying concentration group and low spraying concentration group,the verification experiment of chlorpyrifos showed that:on the 7th day,the values of agricultural insecticide residues in the standard spraying concentration group and the low spraying concentration group were alreadybelow the system detection sensitivity（0.05mg/kg）,while the values of high spraying concentration group were still higher than the national standard maximum residue limit（0.1mg/kg）on the 7th day.The agricultural insecticide residue value（0.0662mg/kg）even could be detected on the 8th day.2.Taking the leek sprayed with chlorpyrifos for 3 days as the research object,the degradation rules of chlorpyrifos residues were studied through factors of ultraviolet irradiation,hydrogen peroxide oxidation,ozone water immersion,ultrasonic shock,pure water cleaning,sodium hypochlorite solution immersion,sodium bicarbonate solution immersion and organophosphorase hydrolysis.The conclusion is as follows:（1）When the uv irradiation time was 50-60min,the chlorpyrifos residue was 0.20mg/kg,which is equivalent to the effect of natural decomposition in the field for 4-5days.（2）Hydrogen peroxide could degrade chlorpyrifos residue in leek to a certain extent.8%hydrogen peroxide had the best degradation effect on chlorpyrifos for 9min,and the residuewas0.7082mg/kg,however,the stems and leaves of leek are significantly wilted.（3）After being treated with ozone water,the residue of chlorpyrifos decreased significantly,the degradation effect of chlorpyrifos was best at the combination of 4mg/L and 10min,and the chlorpyrifos residue was 0.4066 mg/kg.（4）When leek is under ultrasonic processingfor 6min,the value of 2.3kW is the best,chlorpyrifos residue was 0.3536mg/kg.（5）The single factor experiment of organophosphatase hydrolysis concluded that:the best condition is achieved when the enzyme concentration was 1.5U/mL,the chlorpyrifos was hydrolyzed by enzyme at pH 9,the temperature was at 30℃,and the time of enzymatic hydrolysis was 15min.The conclusions of the orthogonal experiment are as follows:the effect of enzymolysis time was the biggest,followed by the temperature of enzymatic hydrolysis and pH,the concentration of enzyme had the smallest effect.The conditions of organophosphatase hydrolysis were determined as follows:the enzyme concentration was 1U/mL,pH value was 9,the enzymolysis temperature was at 25℃,and the enzymatic hydrolysis time was 15min.Under this condition,the residual quantity of chlorpyrifos was 0.031mg/kg,within the national standard limit value（0.1mg/kg）.（6）Pure water surface cleaning could remove a small amount of chlorpyrifos residues on the leek,and the higher the water temperature,the better the removal effect,with pure water processingat 30℃for 13 min,value of pesticide residues still was 0.9342 mg/kg.（7）The degradation rate of sodium hypochlorite solution（450mg/L pH4.5）was the highest when the temperature was at 30℃and the immersion time was 8min.（8）Using 1%NaHCO₃ solution to treat leek for 13min at 30℃,the degradation effect of chlorpyrifos residue was relatively good,and the residue was 0.5898mg/kg.（9）The effect of surfactant washing on degradation of chlorpyrifos residue in leek was relatively obvious,and the higher the temperature,the better the removal effect.When the leek was washed for 9min at 30℃,the residue was 0.7441mg/kg.The residue value would no longer change when washing time was more than 11min.