Effects of the insecticide esfenvalerate on zooplankton in an indoor synthetic model ecosystem.

Effects of esfenvalerate on zooplankton and their recovery potential were studied using an indoor synthetic model ecosystem. Esfenvalerate was applied to the system by direct spiking to overlying water or the introduction of treated slurry soil to imitate drift and run-off exposure. Four zooplankton taxa, Daphnia magna (Cladocera), Heterocypris incongruens (Ostracoda), Cyclops sp. (Copepoda), and Brachionus calyciflorus (Rotifera), were exposed to esfenvalerate with Raphidocelis subcapitata (green alga). In a drift scenario, lower doses (0.02-0.5 µg/L) showed slight or negligible effects, but the results for the highest dose (5 µg/L) indicated direct effects, as remarkable population decreases were observed for three taxa (except rotifera). However, for the latter dose, results of weekly or single (Day-15) zooplankton re-introductions after dosing demonstrated resilient recovery. In a run-off scenario, a nominal dose of 20 µg/L, in which the measured water concentrations remained at 3-6%, had effects similar to those of the high drift exposure scenario for cladocera and ostracoda.

A microarray-based comparative analysis of gene expression profiles in thyroid glands in amphibian metamorphosis: differences in effects between chemical exposure and food restriction.

Tadpoles during metamorphosis are sensitive to chemical exposure as shown in the amphibian metamorphosis assay, which is a method to detect effects of chemicals on the functions of hypothalamus-pituitary-thyroid axis. The present study reports existence of different modes of action between pyriproxyfen (PYR) and 6-propyl-2-thiouracil (PTU) under different feeding conditions based on gene expression profiles (transcriptomics) in the thyroid glands of tadpoles of the African clawed frog, Xenopus laevis. PTU and PYR were exposed to the tadpoles during metamorphosis under normal (fed groups, both of PTU and PRY) and restricted feeding (fasted groups, PTU only) conditions; and effects were compared to control groups. Delayed development based on decreased Nieuwkoop and Faber developmental stage number without any histopathological changes was observed in the control of restricted feeding (control-fasted) group, and the PYR group with reduced food consumption. Clear developmental retardation with typical thyroid histopathological changes was observed in the PTU groups. To find clusters of all samples based on their similarity of expression patterns, hierarchical clustering analysis using selected gene probes was conducted. It revealed gene profiles from samples of the PYR group were quite similar to those of the control-fasted group, followed by the control group with normal feeding (control-fed). The results suggest that key events in the thyroid glands of tadpoles induced by PYR should be quite similar to those of control-fasted, and quite different from those of the PTU groups. Our findings demonstrated the usefulness of transcriptomics, which enabled recognition of the different modes of actions.

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.