A study released in early December by a group of scientists shows that hormones leaking into streams from cattle feedlots are altering the sexual characteristics of wild fish.
Edward Orlando, assistant professor of biology at St. Mary's College of Maryland (SMCM), was the leading author in the study that included researchers from five U.S. institutions. The scientists examined minnows in three streams that flow into Nebraska's Elkhorn River. Their findings showed "significant alterations in the reproductive biology" of fish immediately downstream from a large Nebraska cattle feedlot.
The scientists said they do not know whether the damage was caused by natural hormones in cattle or by synthetic ones administered to the animals. Their report states that the findings "clearly demonstrate" that effluent from feedlots is hormonally active, whether it is natural or synthetic. About 30 million head of cattle are raised in U.S. feedlots each year, and nearly all are implanted with growth-promoting synthetic hormones.
Orlando said the scientists took their samples from a site directly connected to a retention pond at the base of a large feedlot. Several spots along the river contained hormones, indicating that "this [result] is not due to one farm in one location." Orlando added that laboratory tests from the study showed that the feed-lot effluent-receiving site contained a complex and potent mix of androgens (male sex hormones), and estrogens (female hormones).
According to the study, published in the online version of the scientific journal Environmental Health Perspectives, the male fish had one-third less testosterone and their testes were about half as big as those of unexposed fish upstream. The female fish had about 20 percent less estrogen and 45 percent more testosterone than females from the uncontaminated stream.
The scientists caution that further investigation of livestock farms is "urgently needed if we are to understand the possible adverse effects of these compounds on aquatic ecosystem health." They say the priority should be to identify the compounds that altered the fish, and "determine whether they were natural or pharmaceutical in origin."
Hormones are used to stimulate growth in cattle and help them produce more meat and less fat. According to a 1999 survey by the U.S. Department of Agriculture, about 99% of the nation's largest, factory-sized cattle feedlots use hormonal implants.
"Cattle can be treated with any number of androgenic or estrogenic chemicals, or combinations of synthetic androgens and estrogens," said Orlando. "We do not know what the cattle in this feedlot were treated with or what was in the effluent. This is really the first study of this kind, and there are lots of questions, but few answers, so far."
This study was conducted on wild fish in Nebraska's Elkhorn River. It is unknown whether the hormones implanted into cattle have any effect on human beings, "but, we do know that human exposure is minimal, given that only trace amounts of these synthetic hormones remain in the meat. In contrast to humans, aquatic wildlife is exposed to an unknown concentration of synthetic and natural hormones excreted by the cattle. We know little about the potential effects of hormone containing effluent from cattle feedlots or other concentrated animal feeding operations on fish and other aquatic wildlife," said Orlando.
Orlando plans similar studies for the tributaries of the Chesapeake Bay. He is currently submitting proposals to various funding sources to conduct research.
SMCM is consistently ranked one of the best public liberal arts colleges in the na-tion by U.S. News & World Report and The Princeton Review. The Washington Post called St. Mary's College of Maryland "a place to get an Ivy League education at a public school price."