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Tackling Fish Endocrine Disruption

USGS scientist dissecting a fish
USGS scientist dissecting a fish to determine possible effects from exposure to endocrine disrupting contaminants

Intersex, the presence of both male and female characteristics within the same fish, is being observed in fish in more streams across the Nation. Intersex is one manifestation of endocrine disruption in fish. Endocrine disruption can result in adverse effects on the development of the brain and nervous system, the growth and function of the reproductive system, and the response to stressors in the environment.  U.S. Geological Survey (USGS) scientists have documented the presence of endocrine disrupting contaminants in rivers and streams across the Nation. Additionally, USGS scientists and others have demonstrated that exposure to endocrine-active contaminants can cause endocrine disruption, which can have ruinous impacts on fish populations. The following are some recent examples of USGS studies on endocrine disruption in fish.

Endocrine Disruption
Exposure to low-levels of some contaminants can cause disruption of endocrine functions in animals, such as reproduction. This is done by modulating, mimicking, or interfering with normal hormonal activity. Examples of endocrine-active contaminants are chemicals such as synthetic hormones, certain pesticides, some pharmaceuticals, detergents degradation products (nonylphenol), and many others.

Selected USGS Information on Endocrine Disruption

  • A study of endocrine disruption in fish in Boulder Creek, Colorado, by USGS and University of Colorado scientists demonstrated how a complex mixture of endocrine-active contaminants in wastewater can have an additive effect on local fish (Vajda and others, 2008). Their paper in Environmental Science and Technology documented that the population of fish downstream of the wastewater discharge from a sewage treatment plant was dominated by females, and 18 to 22 percent of fish exhibited intersex.
  • Another study documented complex effects of fish exposure to nonylphenol, a degradation product of surfactants used in large quantities in commercial and household detergents.  Scientists reported in the journal Aquatic Toxicology that the breading behavior of males exposed to nonylphenol varied significantly with exposure level (Schoenfuss and others, 2008).  Low doses "primed" the males for breeding competition, whereas higher exposures inhibited their breeding behavior.
  • In still another study, USGS scientists along with their colleagues from the West Virginia Division of Natural Resources, U.S. Army Corps of Engineers, and Virginia Department of Game and Inland Fisheries investigated the occurrence of intersex in male smallmouth bass in the Potomac River and its tributaries in Virginia and West Virginia. In an article in the Journal of Aquatic Animal Health the scientists reported a high incidence of intersex in the fish they sampled (Blazer and others, 2007). The occurrence of intersex was particularly high during the spawning season. They also found that higher incidence of intersex occurred in streams draining areas with intensive agricultural production and high population when compared to non-agricultural and undeveloped areas.
  • A team of USGS and West Virginia University scientists investigated the causes of extensive fish kills and impaired fish in the Shenandoah River, Virginia (Ripley and others, 2008). They reported in Environmental Toxicology and Chemistry on a method to assess the health of the immune systems in fish. The method relies on the analysis of proteins and the microscopic evaluation of kidney tissue. Many of the fish studied were unable to manufacture normal disease-fighting white blood cells. The ability to assess immune function in fish will help scientists understand the impact of endocrine-disrupting contaminants in the environment.

More Information

Related Science Features


Blazer, V.S., Iwanowicz, L.R., Iwanowicz, D.D., Smith, D.R., Young, J.A., Hedrick, J.D., Foster, S.W., and Reeser, S.J., 2007, Intersex (testicular oocytes) in smallmouth bass from the Potomac River and selected nearby drainages: Journal of Aquatic Animal Health, v. 19, no. 4, p. 242-253, doi:10:1577/H07-031.1.

Ripley, J., Iwanowicz, L., Blazer, V., and Foran, C., 2008, Utilization of protein expression profiles as indicators of environmental impairment of smallmouth bass (Micropterus dolomieu) from the Shenandoah River, Virginia, USA: Environmental Toxicology and Chemistry, v. 27, no. 8, p. 1756-1767, doi:10.1897/07-588.1.

Schoenfuss, H.L., Bartell, S.E., Bistodeau, T.B., Cediel, R.A., Grove, K.J., Zintek, L., Lee, K.E., and Barber, L.B., 2008, Impairment of the reproductive potential of male fathead minnows by environmentally relevant exposures to 4-nonylphenol: Aquatic Toxicology, v. 86, no. 1, p. 91-98, doi:10.1016/j.aquatox.2007.10.004.

Vajda, A.M., Barber, L.B., Gray, J.L., Lopez, E.M., Woodling, J.D., and Norris, D.O., 2008, Reproductive disruption in fish downstream from an estrogenic wastewater effluent: Environmental Science and Technology, v. 42, no. 9, p. 3,407-3,414, doi:10.1021/es0720661.

Additional References

Barber, L.B., Lee, K.E., Swackhamer, D.L., and Schoenfuss, H.L., 2007, Reproductive responses of male fathead minnows exposed to wastewater treatment plant effluent, effluent treated with XAD8 resin, and an environmentally relevant mixture of alkylphenol compounds: Aquatic Toxicology, v. 82, no. 1, p. 36-46, doi:10.1016/j.aquatox.2007.01.003.

 Chambers, D.B., and Leiker, T.J., 2006, A reconnaissance for emerging contaminants in the South Branch Potomac River, Cacapon River, and Williams River Basins, West Virginia, April-October 2004: U.S. Geological Survey Open-File Report 2006-1393, 28 p.

Hinck, J., Blazer, V., Denslow, N., Echols, K., Gale, R., Wieser, C., May, T., Ellersieck, M., Coyle, J., and Tillitt, D., 2008, Chemical contaminants, health indicators, and reproductive biomarker responses in fish from rivers in the Southeastern United States: Science of the Total Environment, v. 390, no. 2-3, p. 538-557, doi:10.1016/j.scitotenv.2007.10.026.

Lee, K.E., Schoenfuss, H.L., Jahns, N.D., Brown, G.K., and Barber, L.B., 2008, Alkylphenols, other endocrine-active chemicals, and fish responses in three streams in Minnesota--Study design and data, February-September 2007: U.S. Geological Survey Data Series 405, 44 p (plus appendixes).


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