Oxidative Metabolism and Persistence of Parathion and Malathion on Field-Sprayed Lettuce

Abstract Parathion and malathion, at a rate of 400 g active ingredient/acre, were applied individually to field plots of lettuce. Samples were taken at various intervals after spraying and analyzed by paper chromatography for residues of these compounds and their metabolites. Parathion residues decreased from 1.9 to 0.1 ppm in 4 days; detectable quantities were present up to 15 days. Small quantities of paraoxon and two unidentified metabolites of parathion were detected, at times, up to 2 days after application of parathion. Malathion residues decreased from 11.5 ppm at 4 hours to less than 0.1 ppm at 10 days. Malaoxon and three unidentified metabolites of malathion were detected, at times, up to 2 days after application of malathion.