Smallmouth Bass In Three Pennsylvania Rivers Show Intersex Traits

Scientists found intersex fish in three river basins in Pennsylvania, a sign that the water may be tainted with chemicals from human activity. Male smallmouth bass with female characteristics — namely, immature egg cells in their testes — were discovered in the drainage areas of the Susquehanna, Delaware and Ohio rivers, according to a new study led by the U.S. Geological Survey (USGS).

Such abnormalities are linked to estrogen-mimicking chemicals, which likely got into rivers and streams from agricultural runoff and human waste, the researchers said. [12 Worst Hormone-Disrupting Chemicals & Their Health Effects]

"The sources of estrogenic chemicals are most likely complex mixtures from both agricultural sources, such as animal wastes, pesticides and herbicides, and human sources from wastewater treatment plant effluent and other sewage discharges," study author Vicki Blazer, a fish biologist with the USGS, said in a statement.

Estrogenic chemicals disrupt the endocrine system, which regulates the release of hormones like estrogen and testosterone, interfering with the fish's ability to reproduce. Bass seem to be especially prone to becoming intersex when exposed to estrogenic compounds, Blazer and colleagues said. Researchers with the USGS previously found intersex smallmouth bass in the Potomac River Basin, similarly linked to endocrine-disrupting chemicals, or EDCs.

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