Metabolic fate of emamectin benzoate in soil

Aerobic and anaerobic incubation of microbially active soil with [C-14]MAB(1a) resulted in measurable evolution of (CO2)-C-14. Chromatographic and mass spectral analyses of extractable residues demonstrated the degradation of [C-14]MAB(1a) to 8aOH-MAB(1a) and 8aoxo-MAB(1a). The highest levels of 8aOH-MAB(1a) and 8aoxo-MAB(1a) were found at the 60-day incubation interval, comprising about 7 and 3%, respectively, of applied radioactivity. At least eight other residues, more polar than MAB(1a), were also formed at low levels (each <5%). By base extraction, HPLC, and gel chromatography, the unextractable residues were found to be non-avermectin components associated with soil. humic substances. The majority (76-85%) of these unextractable residues were found in fulvic acid fraction while relatively minor amounts remained in humins (9-14%) and high molecular weight humic acids (4-11%). Quantitatively, soil microbial counts were not affected by MAB(1a) treatment. These results demonstrate that emamectin benzoate is biodegradable in soil and will eventually be mineralized to CO2.