Elimination and metabolism of permethrin isomers in rainbow trout

Although permethrin, a synthetic pyrethroid insecticide, is highly toxic to fish, its toxicity to mammals is comparatively low. The distribution and metabolism of the cis- and trans-permethrin isomers were studied in rainbow trout to evaluate the role of these parameters in the differential toxicity of permethrin to fish and mammals. Both [¹⁴C]permethrin geometrical isomers were readily taken up and eliminated by rainbow trout. Elimination half-lives for [¹⁴C]permethrin residues in trout tissues, with the exception of fat, were in the magnitude of hours. High concentrations of a polar metabolite were found in bile within 4 hr of cis- and trans-permethrin exposure. Analysis by β-glucuronidase treatment, analytical thin-layer chromatography, and gas chromatography-mass spectroscopy indicated that the metabolite was the glucuronide conjugate of 4′-HO-permethrin. Urine contained a small amount of a polar metabolite that was resistant to hydrolysis by β-glucuronidase but was cleaved to some extent by aryl sulfatase. The relative absence of permethrin hydrolysis products in trout bile and the small amount of radioactivity excreted in urine suggested that the ability of rainbow trout to hydrolyze permethrin, in vivo, was minimal.