Bioconcentration and Metabolism of Pyriproxyfen in Tadpoles of African Clawed Frogs, Xenopus laevis.

Bioconcentration and metabolism of pyriproxyfen uniformly labeled with 14C at the phenoxyphenyl ring were studied using tadpoles of African clawed frog, Xenopus laevis, exposed to water at the nominal concentrations of 3 and 300 ppb for 22 days under the flow-through conditions, with a following 3 day depuration phase. Neither meaningful mortality nor abnormal behavior was observed in control and exposure groups throughout the study. After the rapid uptake to tadpoles, pyriproxyfen was extensively metabolized and excreted, and as a result, steady-state bioconcentration factors and depuration half-lives ranged from 550 to 610 and from 0.34 to 0.54 days, respectively. The metabolites were mostly distributed in the liver or gastrointestinal tract. The major metabolic reactions were hydroxylation at the 4' position of the phenoxyphenyl group and cleavage of the ether linkage, followed by sulfate conjugation.