PHOTODEGRADATION OF THE PYRETHROID INSECTICIDE ESFENVALERATE ON SOIL, CLAY-MINERALS, AND HUMIC-ACID SURFACES

Photodegradation of the pyrethroid insecticide esfenvalerate (I) [(2S, alpha-S)-alpha-cyano-3-phenoxybenzyl 2-(4-chlorophenyl)-3-methylbutyrate] on the thin films of intact soil, clay minerals, and humic acid was examined by using a xenon lamp (lambda > 300 nm). Photodegradation studies and reactions with oxidants showed that hydration of the cyano group and ether cleavage in the alcohol moiety were dominant reactions on the surfaces tested. It was strongly suggested that the hydrogen peroxide photochemically produced participated in the hydration reaction and that the ether cleavage proceeded via reaction with hydroxyl radical but not via photonucleophilic substitution by water molecule.