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Chemical Combo and Intersex Fish Found at Smallmouth Bass Nesting Sites

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

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. Although these contaminants are known to originate from a variety of human and animal-waste sources, results of a recent U.S. Geological Survey (USGS) study corroborate previous studies suggesting that seasonal runoff from agricultural activities is an important source of exposure to endocrine disrupting chemicals by smallmouth bass during critical life stages.

In the study, reported in Science of the Total Environment and Environmental Monitoring and Assessment, a team of USGS scientists collected water and bed sediment samples from fish nesting sites and studied fish from these sites where smallmouth bass spawn and build nests in the Potomac River watershed. This study and others help determine the seasonality and sources of chemical exposures contributing to abnormal fish health, such as intersex, observed in this region. Natural-resource managers, scientists, regulators, and others can use the results to inform decisions regarding overall fish health throughout the Chesapeake Bay region.

The Toxic Substances Hydrology, Contaminant Biology, Priority Ecosystems Science, and Fisheries: Aquatic and Endangered Resources Programs of the U.S. Geological Survey supported this study. Funding was also provided by the West Virginia Division of Natural Resources, West Virginia Department of Environmental Protection, Virginia Departments of Game and Inland Fisheries and Environmental Quality, and Maryland Department of Natural Resources.


Kolpin, D.W., Blazer, V.S., Gray, J.L., Focazio, M.J., Young, J.A., Alvarez, D.A., Iwanowicz, L.R., Foreman, W.T., Furlong, E.T., Speiran, G.K., Zaugg, S.D., Hubbard, L.E., Meyer, M.T., Sandstrom, M.W., and Barber, L.B., 2013, Chemical contaminants in water and sediment near fish nesting sites in the Potomac River Basin--Determining potential exposures to smallmouth bass (Micropterus dolomieu): Science of the Total Environment, v. 443, p. 700-716, doi:10.1016/j.scitotenv.2012.09.063.

Blazer, V., Iwanowicz, L., Henderson, H., Mazik, P., Jenkins, J., Alvarez, D., and Young, J., 2012, Reproductive endocrine disruption in smallmouth bass (Micropterus dolomieu) in the Potomac River Basin--Spatial and temporal comparisons of biological effects: Environmental Monitoring and Assessment, v. 184, no. 7, p. 4309-4334, doi:10.1007/s10661-011-2266-5.

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.

Blazer, V.S., Iwanowicz, L.R., Starliper, C.E., Iwanowicz, D.D., Barbash, P., Hedrick, J.D., Reeser, S.J., Mullican, J.E., Zaugg, S.D., Burkhardt, M.R., and Kelble, J., 2010, Mortality of centrarchid fishes in the Potomac drainage--Survey results and overview of potential contributing factors: Journal of Aquatic Animal Health, v. 22, no. 3, p. 190-218, doi:10.1577/H10-002.1.

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.

Iwanowicz, L.R., Blazer, V.S., Guy, C.P., Pinkney, A.E., Mullican, J., and A., A.D., 2009, Reproductive health of bass in the Potomac, USA, drainage--Part 1. Exploring the effects of proximity to wastewater treatment plant discharge: Environmental Toxicology and Chemistry, v. 28, no. 5, p. 1072-1083, doi:10.1897/08-433.1.

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.

Alvarez, D.A., Cranor, W.L., Perkins, S.D., Schroeder, V., Iwanowicz, L.R., Clark, R.C., Guy, C.P., Pinkney, A., Blazer, V.S., and Mullican, J.E., 2009, Reproductive health of bass in the Potomac, USA drainage--Part 2. Seasonal occurrence of persistent and emerging organic contaminants: Environmental Toxicology and Chemistry, v. 28, no. 5, p. 1084-1095, doi:10.1897/08-417.1.

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