New Study: Intersex Fish Linked to Endocrine Disruptors

Tuesday, April 16, 2013 - 10:44am

Thanks to the work of Vicki Blazer and other US Geological Survey collaborators, we are beginning to get a clearer picture of what may cause fish health decline and intersex in the Shenandoah River system. Their most recent paper entitled “Chemical Contaminant in water and sediment near fish nesting sites in the Potomac River basin: Determining potential exposures to smallmouth bass” reveals that chemical contaminant exposure plays a key role in intersex development and possibly fish health decline due to lowered immune system function. Shenandoah Riverkeeper worked with USGS during this study to identify individual smallmouth nests and extract spawning fish during the time when fish are reproducing and young fish (fry) are going through sexual differentiation in the presence of these contaminants.

This study uncovered a strong correlation between the hormonal strength of water samples and the presence and severity of the intersex condition (generally when male fish develop eggs in their testes). Additionally, intersex correlated very well with both herbicides and naturally occurring plant hormones in water samples and sediment extracts near smallmouth nests. Chemical contaminants including herbicides, veterinary pharmaceuticals, and biogenic hormones have been detected at fish nesting sites in the Potomac River watershed where endocrine disruption in smallmouth bass (Micropterus dolomieu) was also observed. Two pesticides shared the highest correlation: Atrazine, a known endocrine disrupting compound banned from use in Europe but widely used as an herbicide in crop farming in the Shenandoah Valley, and a pesticide called trans-Nonachlor.

Previous papers by Blazer and others have determined the hormonal strength (levels of estrogen) of our river water correlates strongly with the density of confined animal feeding operations (factory farms known as CAFOs). Also, the prevalence of intersex (measured by the percentage of male smallmouth bass with both male and female sex organs) correlates strongly with the percentage of land use that is agricultural and the density of livestock in the stream basin. Finally the severity of intersex, meaning the number of immature eggs in smallmouth testes, correlates strongly with the presence of things such as poultry houses and sewer treatment plants.

The recent paper concludes that the body of evidence linking common pesticides with intersex and possibly lowered immune system function in fish, is growing rapidly and deserves our careful attention. These studies remind us that we need to make smart choices about the chemicals we use in our own lives, as well as in agriculture and industry. We are dedicated to ensuring protective regulations are developed to safeguard our rivers, communities, and families.


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