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.