USGS study finds highest rates of intersex fish in the Mississippi River

by Trevor Russell

A recent U.S. Geological Survey study looked at the rate of intersex fish in nine river systems around the nation. In the Mississippi River, near Lake City Minnesota, 73 percent of the smallmouth bass had characteristics of both sexes – the highest recorded rate in the study.

USGS scientists are primarily concerned with male fish with female sex organs. Such feminization is generally thought to be caused by hormone-disrupting chemicals in the environment. These can include endocrine-disrupting pesticides such as Atrazine, PCBs, heavy metals, pharmaceuticals and even household compounds such as shampoos and detergents.

Jo Ellen Hinck, the lead author of the paper and a biologist at the USGS Columbia Environmental Research Center, notes that ...proper diagnosis of this condition in wild fish is essential because if the primary causes are compounds that disrupt the endocrine system, then the widespread occurrence of intersex in fish would be a critical environmental concern.

The study shows that large and smallmouth bass seem to be particularly vulnerable to the chemicals. Scientists found intersex fish in about 33 percent of all sites examined from the Apalachicola, Colorado, Columbia, Mobile, Mississippi, Pee Dee, Rio Grande, Savannah, and Yukon River basins. The Yukon River basin was the only one where researchers did not find at least one intersex fish.

Special Note: On March 20th, 2007 - Friends of the Mississippi River, in partnership with the University of Minnesota & the Mississippi Watershed Management Organization, hosted renowned University of California biologist Dr. Tyrone Hayes.

At this event, Dr. Hayes presented his research demonstrating that Atrazine, the second most widely used herbicide in the world, is a potent endocrine disrupter that can feminize male amphibians at very low concentrations — far below the level considered safe by the US Environmental Protection.

A video of Dr. Hayes' presentation can be found here.

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