Known largely as a component of rocket fuel, perchlorate is a pollutant that often turns up in soil and water. In dozens of studies, it has perturbed thyroid-hormone concentrations, which can affect growth and neurological development. Data from fish now indicate that perchlorate can also disrupt sexual development.
Some of the changes were so dramatic that scientists initially mistook female fish for males. Several females displayed male-courtship behavior and produced sperm.