183 THIODICARB (154) EMANATION The residue definition for thiodicarb includes thiodicarb, its main metabolite methomyl and methyl hydroxythioacetimidate ("methomyl oxime"). At the 20th Session of the CCPR in 1988 the inclusion of methomyl oxime in the definition was questioned because the oxime is not included in the definition of the residue of methomyl. APPRAISAL Thiodicarb residues in plants consists essentially of thiodicarb and its degradation product methomyl. "Methomyl oxime" is not a significant residue and decomposes to acetonitrile and carbon dioxide. The oxime has been included in the residue definition because it is determined in the analytical method used. Thiodicarb and methomyl are converted by caustic hydrolysis to methomyl oxime, which is determined by GLC with a f lame- photometric detector. The method has been used to analyze for residues in supervised trials. The oxime is also determined in the analytical method used to determine methomyl. Since investigations on the fate of residues of methomyl and thiodicarb in plants show that methomyl oxime is a minor metobolite, its contribution to the total residue is insignificant. If methomyl oxime is present as residue in the crop it is determined when analyzing for residues of methomyl and thiodicarb. For this reason the meeting concluded that methomyl oxime should be included in the definition of residue of methomyl. The meeting recommended that the residue data bases, the residue definitions and the MRLs for methomyl and thiodicarb should be reviewed at a future meeting. RECOMMENDATION The definition of the residue of thiodicarb should remain unchanged.