Residues And Digestion Dynamics Of Trifloxystrobin In 50% Trifloxystrobin And Difenoconazole In Watermelon And Soil

An optimized QuEChERS method for the simultaneous determination of trifloxystrobin and its metabolite trifloxystrobin acid(GCA321113)residues in watermelon and soil was developed and validated by gas chromatography with electron capture detector(GC-ECD).The method applied to study the terminal residue and dissipation behavior of trifloxystrobin on watermelon and soil.The results could provide guidance for the safe and proper application of trifloxystrobin and difenoconazole(50%,WG)on watermelon.The samples were extracted with acetonitrile(1% formic acid,V:V),evaporated at 45 °C,dissolved in acetone and analyzed by GC-ECD.The limit of quantification(LOQ,S:N =10:1)was 0.01 mg/kg,and the limit of detection(LOD,S:N =3:1)was 0.003 mg/kg.The recoveries of trifloxystrobin in watermelon,pulp and soil were 74.68-87.72%,with RSDs of 0.65-7.56%.The recoveries of trifloxystrobin acid in three matries were 77.49-93.43%,with RSDs of 0.78-9.24%.The results were consistent with the acceptable range.The field experiments of trifloxystrobin and difenoconazole(50%,WG)in watermelon and soil were carried out at three locations in 2015 and 2016.The dissipation dynamics of trifloxystrobin in Guizhou soil followed the first-order kinetics with half-lives of 5.5 and 5.7 days in 2015 and 2016,respectively.There was no maximum residue level(MRL)of trifloxystrobin on watermelon in China,however,the MRL of trifloxystrobin on watermelon were 0.3 mg/kg in European Union.The residual definition of trifloxystrobin includes trifloxystrobin and trifloxystrobin acid and presented as trifloxystrobin.The trifloxystrobin and difenoconazole(50%,WG)formulation was applied at 187.5 g a.i./ha and 281.25 g a.i./ha with 3-4 times sprayings.The re-treatment interval was 7 days.The samples were randomly gathered from each plot at different time intervals(5,7 and 14 days)after the last application.The terminal residue concentrations of trifloxystrobin in watermelon samples were <0.02-0.34 mg/kg,which meant the watermelon samples collected at 14 d after last spraying were safe when the trifloxystrobin and difenoconazole(50%,WG)formulation was applied at 112.5-187.5 g a.i/ha with 3 times sprayings.The study also researched on different soils(Guizhou,Anhui,Tianjin)and sterilization impacted on the dissipation of trifloxystrobin through an indoor simulation experiment.The results showed that the dissipation rates of trifloxystrobin were similarly in three soils,but the dissipation of trifloxystrobin acid in Guizhou soil was slow.The dissipation of trifloxystrobin in nonsterilized soil was faster than that in sterilized soil.