A 1976 explosion in an Italian factory rained TCDD over thousands of nearby homes. This unintended byproduct of herbicide manufacture is the most potent dioxin known. A new study finds that men who received large TCDD exposures from the accident have fathered fewer sons than expected. Indeed, the more dioxin a man picked up, the more likely he was to have daughters.
"In New York, Washington, Milan, and throughout the world, 106 males are typically born for every 100 females," observes Paolo Mocarelli of the University of Milano-Bicocca in Italy. He and his colleagues report that after the accident in Seveso, this sex ratio tilted sharply in the other direction. In the men with highest TCDD exposure, only 38 percent of their subsequent children were boys. That's only 62 males per 100 females.