Study On Residual Behavior And Soil Adsorption Behavior Of Pydiflumetofen In Watermelon

Succinate dehydrogenase inhibitors fungicides are the most popular fungicides at present.Pydiflumetofen is the most novel product of this kind of fungicide.It is of great toxicological significance to study its residue analysis method,digestion dynamics and environmental behavior.In this study,several methods for the residue analysis of the pydiflumetofen fungicides in watermelon were established,and the dynamics of the residual degradation of pydiflumetofen in watermelon on the spray mode under different dosage,application time and experimental environment were further studied.The adsorption and desorption behaviors of pydiflumetofen in different soils were studied and the adsorption and desorption characteristics of pydiflumetofen in soil were summarized.The purpose of this study was to provide a reference for the establishment of maximum residue limit of pydiflumetofen in watermelon and environmental safety evaluation.The results of the study are as follows:A high performance liquid chromatography(HPLC)method for the determination of pydiflumetofen residues in watermelon was established.The method has a good linear relationship with the peak area in the range of 0.01-5 mg/L mass concentration,and the correlation coefficient(r)is 0.9999.The recoveries of pydiflumetofen at three spiked levels at 0.02 mg/kg,0.2 mg/kg and 2 mg/kg were 79-84%,with the relative standard deviations of 2.4-3.5%.The limit of quantification of watermelon was 0.02 mg/kg for pydiflumetofen.The results of the method performance study showed this method was suitable for the pydiflumetofen residues detected in watermelon.A dispersive solid phase extraction-dispersed liquid liquid microextraction and high performance liquid chromatography method for the determination of pydiflumetofen residues in watermelon was established.The calibration curves were linear in the range of 0.01-5 mg/L and the correlation coefficient of 0.9999.The recoveries of pydiflumetofen at three spiked levels at 0.01,0.1,1 mg/kg were 89.2-94.5%,with the relative standard deviations of 3.0-8.7%.The limit of quantification of watermelon was 0.01mg/kg for pydiflumetofen.This method function can satisfy the request of this pesticide residue detected.At the mean while,it illustrated that this method was suitable for the pydiflumetofen residue detection in watermelon.A method for the determination of pydiflumetofen residues in watermelon and its soil by ultrahigh performance liquid chromatography tandem mass spectrometry was established.The method has a good linear relationship with peak area in watermelon and its soil in the concentration range of 0.0005-0.5 mg/L,and the correlation coefficient(r)is 0.9992 and 0.9995 respectively.When the concentration of watermelon was 0.005 mg/kg,0.01 mg/kg and 0.05 mg/kg,the average recovery was 72.1%-112.1%,with the relative standard deviation(RSD,n=5)was 8.2%-8.3%,and the recoveries of pydiflumetofen of soil at three spiked levels at 0.01 mg/kg,0.05 mg/kg and 0.1 mg/kg were 91.6%-118.4%,with the relative standard deviations(RSD,n=5)of 1.9%-6%.The limits of quantitation of pydiflumetofen in watermelon and soil were 0.005mg/kg and 0.01 mg/kg.The limits of detection of watermelon and soil were 0.001 mg/kg for pydiflumetofen.Then the study showed the residual degradation dynamics of pydiflumetofen in watermelon and soil under different spraying doses.The results showed that the original deposition of pydiflumetofen in watermelon was lower,the residual amount was 0.0209 mg/kg~0.1415 mg/kg,and the half-life period was between 2.64~26.65 days.It showed that the degradation of pydiflumetofen was fast and the total degradation time was short.The original deposition of pydiflumetofen in the soil was 0.1074mg/kg-0.2478 mg/kg,and the degradation rate could reach more than 50% in the 30 to 45 days after the drug.The half-life period was between 21-69.31 days,and it belonged to low residue pesticide.The adsorption and desorption characteristics of pydiflumetofen in Beijing cinnamon soil,Henan yellow brown soil and Heilongjiang black soil were studied.pydiflumetofen has strong adsorption ability in the three soils,and the adsorption behavior coincidence the Freundlich adsorption isotherm.The order of adsorption ability is Heilongjiang black soil is more able than Beijing cinnamon soil than Henan yellow brown soil.Adsorption mechanism is physical adsorption.Soil organic matter content,cation substitution amount and fpydiflumetofen adsorption coefficient have good positive correlation.Soil pH,soil conductivity and pydiflumetofen adsorption coefficient have a certain negative correlation.The hysteresis coefficient H was higher than 1,which indicated that the desorption of pydiflumetofen in three soils had hysteresis effect.