Barry G. Timms of the University of South Dakota School of Medicine and his colleagues studied the effects of very low doses of so-called estrogenic chemicals. Specifically, they studied ethinylestradiol, which is used in oral contraceptives, and bisphenol A, an organic chemical used in the manufacture of plastics, some sealants and the resin lining many tin cans for food storage. The researchers exposed pregnant mice to environmental levels of the two chemicals for five days during the period that corresponds to the 10th week of pregnancy in humans. Male fetuses that developed under these conditions experienced problems with malformation of the bladder and developed more, and larger, ducts in the prostate.
The investigators also subjected a group of mice to high, pharmacological doses of another estrogen chemical that used to be widely prescribed to pregnant women, diethylstilbestrol (DES), and found that it had the opposite effect, inhibiting duct formation. Thus, they argue that results from studies using higher levels of exposure "are not relevant for predicting the effects of exposure to low levels of man-made estrogenic chemicals present in the environment." In addition, because problems in male children of mothers who took DES while pregnant did not become apparent until years later, the team suggests that risk guidelines for ethinylestradiol and bisphenol A should be reevaluated. The findings are published online this week by the Proceedings of the National Academy of Sciences.