Studies on oxamyl : analytical method development and investigation of fate in peach seedlings and corn seeds

摘要

A high performance liquid chromatographic method employingtwo columns connected in series and separated~y·a.switchingvalve has been developed for the analysis of the insecticide/nematicide oxamyl (methyl-N' ,N'-dimethyl-N-[(methylcarbamoyl)oxy]-l-thiooxarnimidate) and two of its metabolites.A variation of this method involving two reverse phase columnswas employed to monitor the persistence and translocation ofoxamyl in treated peach seedlings. It was possible tosimultaneously analyse for oxamyl and its corresponding oxime(methyl-N',N'-dimethyl-N-hydroxy-l-thiooxamimidate}, a majormetabolite of oxamyl in plants, without prior cleanup of thesamples. The method allowed detection of 0.058 pg oxamyl and0.035 p.g oxime. On treated peach leaves oxamyl was found todissipate rapidly during the first two-week period, followedby a period of slow decomposition. Movement of oxamyl or itsoxime did not occur in detectable quantities to untreatedleaves or to the root or soil.A second variation of the method which employed a sizeexclusion column as·the first column and a reverse phasecolumn as the second was used to monitor the degradation ofoxamyl in treated, planted corn seeds and was suitable forsimultaneous analysis of oxamyl, its oxime and dimethylcyanoformamide(DMCF), a metabolite of oxamyl. The methodallowed detection of 0.02 pg oxamyl, 0.02 p.g oxime and0.005 pg DMCF. Oxamyl was found to persist for a period of5 - 6 weeks, which is long enough to permit oxamyl seedtreatmentto be considered as a potential means of protectingyoung corn plants from nematode attack. Decomposition was found to be more rapid in unsterilized soil than in sterililizedsoil.DMCF was found to have a nematostatic effect at highconcentrations ( 2,OOOpprn), but at lower concentrationsno effect on nematode mobility was observed. Oxamyl, on theother hand, was found to reduce the mobility of nematodesat concentrations down to 4 ppm.