Residue Dynamics Of 33% Bifenazate-avermectin SC In Citrus And Soil And Its Effect On Quality

A new method for the determination of bifenazate-abamectin in citrus and soil by liquid chromatography coupled with tandem mass spectrometry(LC-MS-MS),and degradation dynamics and final residue of bifenazate-abamectin in citrus and soil was studied,which could provide scientific basis for evaluating the safety of abamectin and bifenazate in environment and establishing secure,reasonable using guideline of abamectin in citrus.Soluble solids,titratable acid and vitamin C were also detected.The results were shown as follows: Bifenazate-Avermectin SC was used to test the residue decline dynamics on citrus and soil.It was detected by optimized QuEChERS combined with LC-MS/MS.The linearity of bifenazate was satisfies between the rangs of 0.001~1.0 mg/L,coefficient of correlation was 0.9988.The linearity of avermectin was satisfies between the rangs of 0.001~1.0 mg/L,and the coefficient of correlation was 0.9992.The limit of detection and the limit of quantification were 0.001 mg/kg and 0.005 mg/kg,respectively.The recoveries of bifenazate in different matrices,including whole fruits,citrus pulp,citrus peel and soil were 85.6%~108.4% with spiking at 0.01 mg/kg?0.1 mg/kg?1.0 mg/kg,the relative standard deviations of bifenazate were 7.2%~12.3%.The recoveries of avermectin in different matrices were 79.6%~106.4% with spiking at 0.01 mg/kg,0.1 mg/kg,1.0 mg/kg,and the relative standard deviations of avermectin were 1.4%~6.8%.The accuracy and precision of the method could meet the requirements for quick qualitative and quantitative analusus.According to degradation dynamics experiments in Chongqing,Hunan and Guangxi in 2015 and 2016,the degradation dynamics indicated that bifenazate-avermectin degraded continuonsly and the curve of degradation dynamics followed the first-order kinetics equation.The half-lives of bifenazate in citrus and soil were 8.6-28.9 d and 5.4-12.8 d,respectively,which indicated that bifenazate should be classified as easily degradable agrochemical.The half-lives of avermectin in citrus and soil were 5.9-15.4 d and 6.2-11.6 d,respectively,which indicated as easily degradable agrochemical,either.The recommended dosage of 33% Bifenazate-Avermectin SC on citrus were 110 mg/kg,the maximum treatment was two times at most and the plastochrone between two treatments was 7 days,and the harvest intervals was recommended at 30 days.The application of high concentration Bifenazate-Avermectin SC on citrus improved the titratable acid and reduced vitamin C and soluble solids to acidity ratio.But it was unclear,it requires increase the amount of sample and the test area.The risk assessment of bifenazate and avermectin dietary intake was carried out and the results shows that the RQc values of bifenazate and avermectin were 61.48% and 13.13% in many kinds of food,respectively.The RQc values of bifenazate and avermectin were 1.348% and 0.373% in citrus.However,both chronic and acute risks of this mixed pesticide in citrus fruits were relatively low to humans irrespective of dosages,frequency of applications,and pre-harvest intervals.It confirmed that the risk of bifenazate and avermectin were acceptable.