Hormones that leak into streams from cattle feedlots are altering the sexual characteristics of wild fish, demasculinizing the males and defeminizing the females, according to a newly released study.
The study, which examined minnows in three streams that flow into Nebraska's Elkhorn River, suggests that cattle operations pose a previously unknown effect on the environment. About 30 million head of cattle are raised in U.S. feedlots per year, and nearly all are implanted with growth-promoting synthetic hormones.
A group of scientists from five U.S. institutions, led by the University of Florida at Gainesville, reported "significant alterations in the reproductive biology" of fish immediately downstream from a large Nebraska cattle feedlot.
The male fish had about one-third less testosterone and testes about half as big as unexposed fish upstream, according to the study, which was published last week in the online version of the scientific journal Environmental Health Perspectives [Endocrine Disrupting Effects of Cattle Feedlot Effluent on an Aquatic Sentinel Species, the Flathead Minnow]. The female fish had about 20 percent less estrogen and 45 percent more testosterone than females from the uncontaminated stream, the study found.
In addition, laboratory tests confirmed that feedlot effluent contains a complex and potent mix of androgens, the male sex hormones, and estrogens, the female hormones, said Edward Orlando, the study's lead author who is now an assistant biology professor at St. Mary's College of Maryland.
The scientists said they did not know whether the damage was caused by natural hormones in cattle or by synthetic ones administered to the animals. Either way, their report said, the findings "clearly demonstrate" that effluent from feedlots is hormonally active.
The discovery could fuel ongoing controversies over the safety of growth hormones in beef and increase pressure on the U.S. Environmental Protection Agency to tighten rules for livestock operations.
Cattle-industry representatives, who have long maintained that hormone treatments are safe, called the study an unsubstantiated attack. They disputed whether the effluent came from the feedlots or from septic tanks or sewage plants, which are known to release hormones from human waste into the environment.
"It's very suspicious that they would indicate it is from feedlots, because there are long-standing regulations prohibiting discharge," said Gary Weber, executive director of regulatory affairs at the National Cattlemen's Beef Association. "Feedlots are not allowed (under state and federal laws) to discharge into waters, so that raises the question of where are these materials really coming from?"
However, the scientists said the samples were taken from a site "directly connected to a retention pond" located immediately at the base of a large feedlot, Orlando said. Several spots along the Elkhorn River contained hormones, indicating that "this is not due to one farm in one location," University of Florida co-author Louis Guillette said.
In their report, the scientists said further investigation of livestock farms was "urgently needed if we are to understand the possible adverse effects of these compounds on aquatic ecosystem health." A priority, they said, should be to identify the compounds that altered the fish, and whether they were natural or pharmaceutical.
"Cattle can be treated with any number of chemicals, or chemical combinations, including androgens and estrogens. We do not know what the cattle in this feedlot were treated with or what was in the effluent," said Earl Gray, a reproductive toxicologist at the EPA's health-effects laboratory who was an author of the study. "This is really the first study of this kind, and there are lots of questions but few answers so far."
The European Union has banned U.S. hormone-treated beef. Because nearly all of the funding for the study, $137,000, came from the European Commission, the cattlemen's groups say the researchers may have had an agenda.
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