Whole-body autoradiography of 204Tl in embryos, fetuses and placentas of mice.

Whole-body autoradiography was used to study thallium uptake and retention in mice during gestation. Fifteen minutes after an intraperitoneal injection of 50 microCi 204Tl2SO4 into a 15-day pregnant mouse, thallium could be seen within the fetuses. Maximum fetal accumulation occurred 2-4 h after injection, and minimum at the last observation 4 days after injection. The fetal concentration of 204Tl was constantly lower than the placental. Uptake of 204Tl in embryos, fetuses and placentas of mice with gestation ages varying from 5 days to 16 days indicated that thallium crosses the placental barriers throughout gestation. Thallium was retained by the visceral yolk sac placenta during early gestation, by the visceral yolk sac, chorioallantoic placenta and amnion during late gestation. Over a period of time placental transfer and embryonic/fetal retention of small amounts of thallium may be hazardous to the offspring due to the high cumulative toxicity of this metal.