Estradiol uptake, toxicity, metabolism, and adverse effects on cadmium-treated amphibian embryos

The exposure of Bufo arenarum embryos to 25 mumol/L 17beta-estradiol (E-2) resulted in 100% lethality within 48 hr, whereas 10 mumol//L E-2 was the no observed effect concentration value for short-term chronic (7 days) exposure. The toxicity profile curves show that lethal effects were proportional to the E-2 concentration and the time of exposure. The E-2 uptake resulted in 20.1 ng E-2/mg embryo at 8 hr posttreatment, but 67.3% of this value was achieved during the first 30 min of incubation with this estrogen. Regarding metabolism, the embryos synthesize estrone (E-1) from E-2 by means of 17beta-hydroxysteroid dehydrogenase. Simultaneous treatments of Bufo arenarum embryos with 1 mg/L Cd2+ and 0.1, 1, or 10 mumol/L E-2 enhanced the lethality exerted by cadmium in 76.7, 80, and 83.3% of embryos, respectively. The results indicate that estrogenic endocrine disruptors could have an adverse effect on amphibian embryos and enhance the toxic effect of Cd on amphibian embryos. This study points to the possibility of using the AMPHITOX test as a screening method for potential endocrine disruption as well as the combined effects of chemical mixtures.