Study On The Enantioselective Translocation And Degradation Of Chiral Insecticide Cycloxaprid And Paichongding In Pak Choi

For a novel potential commercial chiral pesticide, independent study on the fate characteristics and residues of each stereoisomer is essential if the application rates for the pesticide and human exposure are to be reduced. The absorption and translocation of cycloxaprid (CYC) and the degradation of paichongding (IPP) in Pak Choi were studied using 14C-labeling tracer techniques and mass spectrometry. The main results are as following:Stereoselective absorption was observed during root uptake but not during foliar absorption. The mass concentrations (RS/SR) of cycloxaprid in the roots, cotyledons, leaf 1, leaf 2, and leaf 3 were 37.0/16.8,8.3/2.8,11.7/6.5,5.1/4.8, and 8.0/4.7 mg kg-1 (fresh weight), respectively, at 192 HAT at an initial concentration 1.6 mg kg-1. With the foliar application treatment, both acropetal and basipetal transport of absorbed 14C occurred and more than 71.83% of absorbed RS and 82.42% of SR remained in the treated leaf.A facile, reliable method was developed for the identification of metabolites of IPP and CYC in Pak Choi (Brassica campestris L. chinensis). The recoveries ranged from 74.59% to 91.49% for IPP and from 59.04% to 87.40% for CYC. The limits of detection, quantitation, and the linear ranges of IPP were 8.61,28.71,and 10-10000 ng g-1 fresh weight, respectively; the corresponding values for CYC were 9.73,32.46, and 50-50000 ng g-1 fresh weight.The method was applied to detect the metabolites of IPP in pak choi as following: 1a:1-(6-Chloro-pyridin-3-ylmethyl)-5-methoxy-7-methyl-8-nitro-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridine; lb:1-(6-Chloro-pyridin-3-ylmethyl)-5-hydro-7-methyl-8-nitro-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridine; 2a:1-(6-Chlorb-pyridin-3-ylmethyl)-7-methyl-8-nitroso-5-propoxy-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridine; 3a: 1-(6-Chloro-pyridin-3-ylmethyl)-6-hydro-7-methyl-8-nitro-5-propoxy-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridine; 3b:1-(6-Chloro-pyridin-3-ylmethyl)-7-methyl-8-nitro-5-propoxy-1,2,3,7-tetrahydro-imidazo[1,2-a]pyridine. The propose degradation pathway is IPP-1a-1b-1c; IPP-2a-1c; IPP-3a-3b.