Is the presence of estradiol benzoate in cow feces environmentally safe?

Estradiol benzoate can be used, among other veterinary protocols, to induce lactation in non-pregnant cows with reproductive failures. However, the use of estrogens in livestock is controversial due to concerns about environmental contamination from hormone residues. The objective of this study was to evaluate the ecotoxicity of estradiol benzoate excreted in cow feces using plant and animal bioassays. Onion and celosia seeds, earthworms (Eisenia fetida), and microcrustaceans (Daphnia magna) were exposed to fecal samples from cows with induced lactation and to aqueous solutions containing estradiol benzoate at 10-100 µg/kg. Exposure to fecal samples did not impair seed germination, earthworm reproduction, or the behavior of either animal bioindicator (P > 0.05) and was associated with increased adult earthworm weight (P < 0.05), according to statistical comparisons of means and measures of dispersion. No effects were observed at any tested concentrations of estradiol benzoate on any response (P > 0.05). These findings indicate that feces from cows treated with estradiol benzoate for lactation induction exerted limited ecotoxicological effects on growth, behavior, and reproduction of plant and animal bioindicators.