Fishy Hormones

Science News Magazine
Week of June 24, 2006; Vol. 169, No. 25, p. 397

To beef up animals quickly, most U.S. cattle ranchers treat their livestock with growth-promoting hormones. Among the more widely used drugs is trenbolone acetate (SN: 1/5/02, p. 10: http://www.sciencenews.org/articles/20020105/bob13.asp), a synthetic anabolic steroid. In April, Environmental Protection Agency scientists reported finding trace concentrations of two breakdown products of this drug in wastes released into a stream by an Ohio cattle feedlot. Now, the scientists show that female fish develop masculine traits when exposed to these testosterone-like breakdown products at the same concentrations seen in those feedlot wastes.

A team led by Gerald T. Ankley of the EPA laboratory in Duluth, Minn., scouted for trenbolone's breakdown products—17-alpha and 17-beta trenbolone—in feedlot wastes. Both occurred at a few parts per trillion (ppt), the group reported in an April supplement to Environmental Health Perspectives.

The alpha metabolite was 5 to 10 times as abundant as the beta metabolite, but preliminary test-tube data had suggested that the alpha form was only one-tenth as potent as the beta.

To the team's surprise, the alpha and beta metabolites proved equally potent in their effects on female fathead minnows. In water with 11 ppt of either metabolite, a concentration comparable to that in the Ohio wastewater, egg production fell to half of normal, the Duluth team reports in the May 1 Environmental Science & Technology. A concentration of about 110 ppt shut down egg production and produced bumps on the females' heads, a trait normally seen only in males.