Aerobic and anaerobic incubation of microbially active soil with [C-14
]MAB(1a) resulted in measurable evolution of (CO2)-C-14. Chromatograph
ic and mass spectral analyses of extractable residues demonstrated the
degradation of [C-14]MAB(1a) to 8aOH-MAB(1a) and 8aoxo-MAB(1a). The h
ighest levels of 8aOH-MAB(1a) and 8aoxo-MAB(1a) were found at the 60-d
ay incubation interval, comprising about 7 and 3%, respectively, of ap
plied radioactivity. At least eight other residues, more polar than MA
B(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 fu
lvic 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 re
sults demonstrate that emamectin benzoate is biodegradable in soil and
will eventually be mineralized to CO2.