Update
A new study indicates that some of the same pollutants that apparently cause male fish in the Potomac and Shenandoah rivers to exhibit female characteristics (i.e., intersex characteristics) may also leave them vulnerable to disease and large-scale fish kills. The study, from the U.S. Geological Survey researcher Laura Robertson, injected largemouth bass with estrogen. Those fish were then found to produce lower levels of a hormone called hepcidin that is believed to bolster immune systems. Click here for more information.
Background
In spring 2002, large populations of smallmouth bass and redbreast sunfish were found dead in the South Branch of the Potomac River in West Virginia. Each year since, fish kills of varying severity have occurred in the Potomac River or one of its tributaries.
In 2003, scientists performing necropsies on these fish made a surprising find—many of the dissected male fish contained oocytes (precursors of egg cells normally produced by females) in their testes, a condition known as intersex.
A 2006 study by the U.S. Geological Survey of fish from the Potomac River and various tributaries found intersex in 80% of male bass examined. All samples—those with and without signs of intersex—contained detectible levels of at least one endocrine-disrupting compound.
Endocrine disruptors mimic hormones, and can disturb the body’s normal biological functions. A congressional hearing was held to examine the issue in October 2006, with all participants agreeing that more research was needed to investigate the causes of intersex, the role of endocrine disruptors, and the possible affects of both on human health.