Deltamethrin [(S)-α-cyano-3-phenoxybenzyl (1R,3R)-cis-2,2-dimethyl-3-(2,2-dibromovinyl) cyclopropanecarboxylate] is a powerful pyrethroid insecticide which exhibits very high toxicity to aquatic organisms. Major routes of degradation or dissipation of parent deltamethrin in natural water are chemical and photochemical conversion to a mixture of inactive and active stereoisomers, and hydrolysis with subsequent oxidation of products. Chiral high performance liquid Chromatographic analyses revealed that the parent 1-deltamethrin in natural water in the dark is subject to cis/trans isomerization yielding the α-S, IS eis isomer 2'-deltamethrin, which is inactive against mice and insects. Sunlight photolysis of deltamethrin in natural water is only a partial detoxification step since although it produced the inactive 2'-deltamethrin isomer as well as the inactive α-S, IS trans isomer 4’-deltamethrin, it did produce in addition the α-S, 1R trans isomer 3-deltamethrin, which does retain some activity toward mice, insects and Daphnia magna, albeit less than the parent 1-deltamethrin.

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