The most potent extract was selected for in vivo exposure of Xenopus laevis tadpoles
to analyze the potential effects on development and reproductive biology of amphibians. Tadpoles were
exposed from stage 48 to stage 66 (end of metamorphosis) to aqueous oak leaf extracts covering natural
occurring environmental concentrations of dissolved organic carbon. Gene expression analyses of
selected genes of the hypothalamus–pituitary–gonad and of the hypothalamus–pituitary–thyroid axis
as well as histological investigation of gonads and thyroid glands were used to evaluate endocrine disrupting
effects on the reproductive biology and development.