Residue Dynamics of Pesticides in Head Lettuce and the Impact of Related Factors

The residue dynamics of pesticides including imidaclapaid,propamocarb and procymidone in head lettuce(Lactuca sativa var.capitata L.),was investigated and the impact of pesticide variety,concentration and other outer factors on the pesticides residues were also analyzed,which aimed to improve the safety producing management of head lettuce.Lettuce,"Emperor"variety,was planted in spring openfield,2007,two different doses,recommended dose and two times of recommended dose,of propamocarb,procymidone and imidaclapaidwere were sprayed on the lettuce on June 6th,of which estimated concentration were 1 203.3 mg·kg-1,500.0 mg·kg-1,40.0 mg·kg-1,and 2 406.6 mg·kg-1,1 000.0 mg·kg-1,80.0 mg·kg-1 respectively,the samples were taken at inner day,2 days,6 days and 9 days for detecting the residue of pesticides,and outer factor like temperature and light intensity during experiment were also recorded.The results showed that whatever the spraying dose,any kind of pesticide in this study showed the same characteristic of quick degradation at initial 2 days and last stage(3 days) and gentle degradation at middle stage(4 days).Referring to the Japanese Positive List System(JPLS),for imidaclapaid,the residues of two times of recommended dose was only 1.5 mg·kg-(15.0 mg·kg-1,MRL of JPLS)after 8 hours,suggesting that imidaclapaid had high safety when used in spring openfield production of lettuce;for propamocarb,the residue of recommended dose was 10.7 mg·kg-1 at 6 days,close to MRL 10.0 mg·kg-1 of JPLS standard,and reached 8.4 mg·kg-1 at 9 days,implicating the possible safety intervals of propamocarb was not less than 7 days;for procymidone,whatever the spraying dose,the residue was over MRL 5.0 mg·kg-1 of JPLS standard,suggesting the safety of procymidone need to be more paid attention when used in head lettuce.Statistics showed that outer factors including time,temperature and light intensity had significant difference on the degradation rate of imidaclapaid,propamocarb and procymidone(P0.05)and there were remarkable significant differences(P0.01)among these three pesticides varieties about the impact on the degradation rate,imidaclapaid degraded rapidly,propamocarb was the next and procymidone degraded very slowly.However,there was no significant difference on the degradation rate when different concentrations of pesticides were used(P0.05).