Fate of [C-14]emamectin benzoate in cabbage .2. unextractable residues

Cabbage plants were treated with seven weekly applications of [C-14]emamectin benzoate followed by a final application of [C-14/H-3]emamectin benzoate at two rates; the maximum expected commercial use rate of 0.015 lbs a.i./acre (1x) or an exaggerated rate of 0.075 lbs a.i./acre (5x). Methanol homogenates of cabbage heads were extracted with methanol/water containing ammonium acetate. Approximately 14-26%, or 58-95 ppb for 1x plants and 188-492 ppb for 5x plants, of the total residues remained unextractable. The unextractable residues were characterized by serial treatment with buffer, cellulase, alpha-amylase, pectinase, and protease, solubilization with hot dimethyl sulfoxide (DMSO), and reflux with 0.5 N sodium hydroxide (NaOH). A portion of the amylase hydrolysate was treated with maltase. All samples, including final uncharacterized residues, were analyzed for radioactivity. Selected fractions were assayed for glucose and protein. Generally, recovered radioactivity was released in the following order: protease (23-29%) > DMSO (15-29%) > NaOH (12-18%) > cellulase (9-17%) > buffer (9-16%) > alpha-amylase (7-9%) > pectinase (3-5%). Only about 1% of the initial unextractable residues remained uncharacterized after the procedure. The results suggest incorporation of radioactivity into natural products such as protein, cellulose, lignin, and starch.