PHOTODEGRADATION OF EMAMECTIN BENZOATE IN AQUEOUS-SOLUTIONS

The half-life of [C-14]4 ''-deoxy-4 ''-(epi-methylamino)avermectin B-1 a (MAB1a) benzoate (1 ppm) photodegradation in buffer (pH 7), natural pond water, and sensitized buffer (1% acetone in pH 7 buffer) determin ed at Three Bridges, NJ (latitude similar to 40 degrees N) during the fall season under natural sunlight was 22, 7, and 1 days, respectively . The half-life of [C-14]MAB1a benzoate (10-12 ppm) photodegradation i n buffer (pH 7) containing 1% (v/v) acetonitrile, ethanol, or acetone as cosolvent under continuous exposure with a xenon lamp was 64.5, 8.5 , or 0.5 days, respectively. The photoisomer 8,9-Z-MAB1a, 8a-hydroxy-M AB1a, and unknown polar residues were found in light-exposed samples o f MAB1a in buffer and natural pond water. In light-exposed sensitized buffer samples, 8a-oxo-MAB1a and MAB1a-10,11-14,15-diepoxide were addi tional products. Very polar residues found in the organic and aqueous phases after extraction increased with time, and their formation follo wed the order sensitized buffer much greater than natural pond water > buffer.