Pyrethroid metabolism: studies on cis- and trans-phenothrins, and related epoxide intermediates.

Two synthetic pyrethroids, cis- and trans-phenothrins, undergo an environmental degradation which involves extensive photooxidation on their acidic residue, which contains a double bond. It has been shown that the metabolism of these compounds occurs via epoxidation of the isobutenyl side-chain also with hepatic microsomal preparations. The results did not indicate any formation of epoxide intermediates on the isobutenyl side-chain. Further evidence that metabolism of cis- and trans-phenothrins does not occur via an epoxide intermediate is furnished by the fact that in vitro activity of hepatic microsomal epoxide hydrolase remained unaffected. These findings may be related to the unfavorable steric hindrance of the tri-substituted double bond on the acidic moiety of these pyrethroids.