ANALYSIS AND FATE OF ACEPHATE AND ITS METABOLITE, METHAMIDOPHOS, IN PEPPER AND CUCUMBER

Levels of acephate (Orthene((R))) and its principle metabolite, methamidophos, in/on greenhouse-grown pepper and cucumber fruits and leaves in relation to the applied methamidophos were monitored. Dislodgeable and total residues of acephate and methamidophos were determined by gas-liquid chromatography equipped with a flame ionization detector (GC-FID) and were confirmed by nitrogen phosphorus detector (GC-NPD). The dissipation curves of the residues followed first-order kinetics (R(2)>0.96). Initial residues of acephate on fruits varied between pepper (15.12 ppm) and cucumber (2.16 ppm) Total residues in fruits and leaves determined at intervals following application revealed the greater persistence of acephate on pepper fruits (half-life [t(1/2)] of 6 d) than on cucumber fruits (t(1/2) was 3.7 d). T-1/2 1/2 values for the applied methamidophos were 4.7 and 5.3 d on pepper and cucumber fruits, respectively. Deacetylation of acephate (formation of its metabolite) was detectable 1 d following acephate treatment and reached a maximum of 2.05% of initial acephate residues 3 d after application on pepper fruits. On cucumber fruits, acephate metabolite reached a maximum of 2.12% one wk following application. No acephate residues were detected above the limit of detection of 0.001 ppm in pepper fruits 50 d following acephate application while its metabolite was detectable at that time (detectability limit was 0.0001 ppm).