Study On Residue Behaviors And Dietary Risk Assessment Of Pyraclostrobin And Dithianon In Dioscorea Oppsite And Soil

In order to evaluate the safety of 16% pyraclostrobin & dithianon WDG on dioscorea opposite,a field trial about the pesticide on dioscorea opposite was conducted in Henan province and Yunnan province in 2014 and 2015.An analytical method for determination of pyraclostrobin and dithianon residue in dioscorea opposite,soil,dioscorea opposite plant and dioscorea opposite bean was developed in this study.The dissipation dynamic and terminal residue of pyraclostrobin and dithianon in dioscorea opposite and soil were studied,and the dietary risk assessment of pyraclostrobin and dithianon on dioscorea opposite was evaluated.This paper provides a scientific basis for the rational use of 16% pyraclostrobin &dithianon WDG.The results were as follows:(1)A simple and rapid method for determination of pyraclostrobin and dithianon in dioscorea opposite and soil was developed by high performance liquid chromatography.Pyraclostrobin was extracted with acetonitrile,clean-up was performed using NH2 column;When spiked at 0.05,0.5,1 and 20 mg/kg,the average recoveries of pyraclostrobin were from 76.3% to 97.3% with the relative standard deviation(RSD)from 2.9% to 9.1%.Dithianon was acidified with hydrochloric acid,extracted with acetonitrile,salting-out,clean-up was performed using primary secondary amine.When spiked at 0.5,2,5,and 200mg/kg,the average recoveries of dithianon were from 78.1% to 96.1% with the relative standard deviation(RSD)from 0.8% to 9.6%.The recoveries met with the requirements for pesticide residue analysis.(2)The dissipation dynamics of pyraclostrobin and dithianon in dioscorea opposite plant and soil were studied.Dissipation dynamics of pyraclostrobin and dithianon in dioscorea opposite plant and soil in Henan and Yunnan followed the first-order chemical kinetic equationKte C-C(28)0t.The half lives of pyraclostrobin were from 4.3 to 9.9 days in dioscorea opposite plant and from 16.5 to 25.4 days in soil,respectively.The half lives of dithianon were from 3.1 to 6.6 days in dioscorea opposite plant.The degradation speed of Dithianon was fast in soil,so the half lives of dithianon couldn't be calculation.(3)The terminal residues of pyraclostrobin and dithianon in dioscorea opposite,soil and dioscorea opposite bean were studied.As 3 days,7 days,14 days after application,the terminal residue of pyraclostrobin were below 0.05 mg/kg in dioscorea opposite,below 0.12mg/kg in soil and below 0.48 mg/kg in dioscorea opposite bean;the terminal residue of dithianon were below 0.5 mg/kg in dioscorea opposite,soil and dioscorea opposite bean,when applied at the maximum recommended dosage and 1.5 times that of 16%pyraclostrobin & dithianon WDG concentrate with spraying 3 or 4 times at an enterval of 7days.According to the results,the reasonable suggestions were given for the use of 16%pyraclostrobin & dithianon WDG on dioscorea opposite: the dosage was 320 to 400 g a.i./ha,sprayed trice with spraying interval of 7 days.(4)The influence of two kinds of cultivation mode to dissipation dynamic of pyraclostrobin and dithianon in dioscorea opposite plant: the half lives of pyraclostrobin were 5.2 days and 5.7 days in dioscorea opposite plant of no race-building cultivation and race-building cultivation,respectively.The half lives of dithianon were 3.1 days and 6.0days in dioscorea opposite plant of no race-building cultivation and race-building cultivation,respectively.There is little difference between dioscorea opposite plant of no race-building cultivation and race-building cultivation of pyraclostrobin's half life,but the half life of dithianon in dioscorea opposite plant of no race-building cultivation has twice longer race-building cultivation.(5)The dietary intake intake risks of pyraclostrobin and dithianon in dioscorea opposite were studied.Under good agricultural practice,the STMR of pyraclostrobin was0.05 mg/kg,the NEDI of pyraclostrobin was 0.85 ?g?kg-1bw?d-1 for all groups of Chinese residents,the percent ratios to ADI was 44.84%.The STMR of dithianon was 0.5 mg/kg,the NEDI of dithianon was 0.52 ?g ? kg-1bw ? d-1 for all groups of Chinese residents,the percent ratios to ADI was 82.25%.The results indicated that,the residues level of pyraclostrobin and dithianon in dioscorea opposite is in the body acceptable range.