By Janet Raloff
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.
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Some of the changes were so dramatic that scientists initially mistook female fish for males. Several females displayed male-courtship behavior and produced sperm.