Residues and decline dynamics of pyrethroid insecticides in tobacco leaf during curing

A GC-MS method was developed for the simultaneous determination of pyrethroid insecticides in tobacco leaf in Shandong,Sichuan,Yunnan,Liaoning and Jiangxi,under the good agricultural practices conditions.Tobacco leaf samples were extracted with acetonitrile and cleaned-up by SPE-PSA,then detected by GC-MS/SIM with external standard method.The average recoveries ranged from 82.9% to 110.9% with relative standard deviations(RSD) from 1.7% to 4.4% in fresh tobacco leaves and from 85.2% to 108.3% with RSD from 2.3% to 5.7% in cured tobacco leaves at 0.01,0.1 and 1 mg/kg,respectively.The limits of quantification(LOQ) of three pyrethroid insecticides were 0.01 mg/kg.The sensitivity and accuracy of the current method was suitable for analysis of target pesticide residues.Dissipation of three pyrethroid insecticides was significant after flue-curing,and the decline rates of lambda-cyhalothrin,beta-cypermethrin and deltamethrin were 78%,89%,91%.The residues of lambdacyhalothrin,beta-cypermethrin and deltamethrin in cured tobacco leaves were determined after two applications at levels of 450-675 g/hm2,600-900 g/hm2 and 450-675 g/hm2,with residues ranged from 0.022-0.50 mg/kg,0.14-0.82 mg/kg and 0.046-0.21 mg/kg in tobacco 14 days after the last application,lower than GRLs(0.5,1 and 1 mg/kg).According to these findings,a prehavest interval of 14 days was recommended.