Quantitative elucidation of maternal-to-fetal transfer of neonicotinoid pesticide clothianidin and its metabolites in mice.

Neonicotinoids (NNs), a widely used class of systemic pesticides, are regarded as exhibiting selective toxicity in insects. However, NNs are suspected of exerting adverse effects on mammals as well, including humans. To date, only adult male animal models have been subjected to general toxicity studies of NNs; fetuses have yet to be considered in this context. Here, we focused on the NN clothianidin (CLO) for the first quantitative LC-MS/MS analysis of maternal-to-fetal transfer and residual property of once-daily (single or multiple days), orally administered CLO and its metabolites in mice. The results revealed the presence of CLO and its five metabolites at approximately the same respective blood levels in both dams and fetuses. In the dams, CLO showed a peak value 1 h after administration, after which levels rapidly decreased at 3 and 6 h. In the fetuses of each group, levels of CLO were almost the same as those observed in the corresponding dams. The present results clearly demonstrated rapid passage of CLO through the placental barrier. However, metabolite-dependent differences observed in blood pharmacokinetics and residual levels. This is the first quantitative demonstration of the presence of CLO and its metabolites in fetal mouse blood.