Fate of [C-14]emamectin benzoate in head lettuce

The fate of [C-14]emamectin benzoate in head lettuce was investigated. Two treatment groups, at a 1 x (0.015 lb of active ingredient/acre) or a 5 x rate, received eight weekly applications. Plants were harvested from 2 h to 10 days after the last application. Total carbon-14 residue in foliage declined from similar to 360 to 80 ppb (1 x) or 1600 to 600 ppb (5 x). Approximately 75-90% of the total carbon-14 residue was extractable with cold solvents. The parent (3-33% of extractable residue) and eight degradates were tentatively identified by HPLC, but the major portion of the extractable residue was an unidentified polar fraction (28-78% of extractable residue). These polar extractable residues were not conjugates and were of a complex nature. Portions of the unextractable residue (equivalent to 5-10% of total residue each) were extractable with hot dimethyl sulfoxide, incorporated into glucose released by acid hydrolyis, or remained uncharacterized as bound residue.