Multiresidue Analysis Of 4 Pyrethroids And Dynamics In Ramie

Ramie is one of traditional economical crops in China. Recently, feed exploitation of ramie is becoming a research hotspot. The pyrethriod pesticides have been widely used in ramie growth. Developed a method for determination of pyrethriod pesticides residues in ramie is significant in guaranteeing ramie quality safety and promoting the development of ramie industry. The research has developed a method for multiresidue analysis of 4 pyrethriod pesticides ?fenpropathrin, lambda-cyhalothrin, beta-cypermethrin, deltamethrin? residues in ramie leaves and soil with QuEChERS-GC, and the residual dynamics and final residues of 4 pyrethriod pesticides in ramie leaves and soil were also studied. The MRL and rational application suggestions in ramie leaves were recommened.The results were as follows:1. A rapid analytical method for simultaneous determination of 4 pyrethriods pesticides in ramie leaves and soil was established based on QuEChERS with GC-uE?CD. The samples were extracted by acetonitrile, eluting the supernate that evaporated in water bath with ethyl acetate, and then purified by primary secondary amine ?PSA?, octadecylsilane chemically bonded silica(C₁₈) and graphitized carbon black ?GCB? as adsorbents. The 4 pyrethriod pesticides residues was analyzed by GC-?ECD and quantified with external standard. The results showed that the average recoveries of the 4 pesticides in ramie at three levels ?0.05mg/kg,0.5 mg/kg and 5mg/kg? were in the range of 86.5%?108.3% with relative standard deviations ?RSD??5.4%. The average recoveries of the 4 pesticides in ramie at three levels ?0.002mg/kg,0.02mg/kg and 0.2mg/kg? were in the range of 89.0%?106.7% with relative standard deviations ?RSD??5.9%.The limits of detection was 0.002mg/kg.2. The dynamics of 4 pyrethriod pesticides in ramie leaves and soil were expounded. The study of residue dynamics indicated that the curve of decline accorded with the first-order kinetics equation, and the half-life of 4 pesticides in ramie leaves and soil were 10.6?15.1 d and 11.0?23.2 d, respectively. The final residues study showed that when spraying for 1?2 successive times at application dosage of 15?112.5 a.i.g/hm² at interval time of 5 d, the final residues of 4 pesticides were in a range of 0.281?4.628 mg/kg in ramie leaves and below 0.002?0.196 mg/kg in soil at 5,10,15,20 d after the last spray.3. The application and dosage during the ramie growth period were suggested:in ramie leaves, the MRL of fenpropathrin is 5 mg/kg and the dosage of 20% fenpropathrin emulsifiable solution is 75 a.i.g/hm² when spraying for 1?2 successive times, and the safety interval period is 5 d; the MRL of beta-cyhalothrin is 2.0 mg/kg and the dosage of 2.5% lambda-cyhalothrin emulsion in water is 15 a.i.g/hm² when spraying for 1?2 successive times, and the safety interval period is 10 d; the MRL of cypermethrin is 5mg/kg and the dosage of 4.5% cypermethrin emulsifiable solution is 22.5 a.i.g/hm² when spraying for 1?2 successive times, and the safety interval period is 5 d; the MRL of deltamethrin is 5mg/kg and the dosage of 25g/L deltamethrin emulsifiable solution is 15 a.i.g/hm² when spraying for 1?2 successive times, and the safety interval period is 5 d.