By Raloff, Janet
Science News , Vol. 161, No. 1
Each year, U.S. farmers raise some 36 million beef cattle. Farmers fatten up two-thirds of these animals by using hormones.
Many cattle are fed the same muscle-building androgens--usually testosterone surrogates--that some athletes consume. Other animals receive estrogens, the primary female sex hormones, or progestins, semiandrogenic agents that shut down a female's estrus cycle. Progestins fuel meat-building by freeing up resources that would have gone into the reproductive cycle.
While federal law prohibits people from self-medicating with most steroids, administering these drugs to U.S. cattle is not only permissible but de rigueur.
So far, almost all concern about this practice has focused on whether trace residues of these hormones in the meat have human-health consequences. But there's another way that these powerful agents can, find their way into people and other animals. A substantial portion of the hormones literally passes through the cattle into their feces and ends up in the environment, where it can get into other food and drinking water.
Some scientists say that it's time to better manage livestock's hormone-laced waste stream, which has flowed unabated in North America for decades.
As much as anyone, John A. McLachlan knows what's been happening. He first became interested in livestock hormones in the early 1970s, when he learned that farmers were giving the synthetic hormone diethylstilbestrol (DES) to chickens and cattle. This synthetic estrogen chemically castrates male animals, enabling them to grow faster. At the time, McLachlan's own studies at the National Institute of Environmental Health Sciences (NIEHS) used animal models to investigate why DES fostered the development of cancer in daughters of women treated to avoid miscarriages.
While McLachlan wasn't worried about any cancer threat that DES might pose to animals destined for the slaughterhouse, he recalls being very concerned that the animals' excretions were releasing "something like 13 tons of DES a year into the environment." He and others began fearing that the hormones might pose chronic risks to wildlife and people.
Although the Food and Drug Administration (FDA) outlawed veterinary use of DES by the mid-1970s, the provision of other hormones to livestock continued to bother McLachlan. So, he convened a 1980 symposium to explore this and related issues.
For the meeting, he coauthored a paper with the late David P. Rail, then director of NIEHS. "We were prescient," McLachlan now says. He and Rail reasoned that with all the steroid hormones being prescribed not only to livestock but also to people--such as to women for birth control or postmenopausal therapy--excretions of these drugs must be substantial. The economic incentive for farmers to use the hormones--it can amount to a 40-fold return on their investment--is compelling (see box on page 11) and will probably fuel the practice for some time.
"We said we wouldn't be surprised if significant amounts of pharmaceutical [including veterinary] estrogens end up in water," remembers McLachlan, now director of the Center for Bioenvironmental Research, which is administered jointly by Tulane and Xavier Universities, both in New Orleans. Recent data have confirmed that human hormonal drugs do taint rivers and streams--sometimes in amounts that adversely affect fish (SN: 6/17/00, p. 388).
Soon after the 1980 meeting, interest in the environmental fate of livestock hormones faded as researchers got caught up in the discovery that pesticides and other industrial chemicals could mimic and disrupt normal hormone and endocrine action in people and other animals (SN: 7/3/93, p. 10).
Indeed, although he is a biologist specializing in reproduction and hormone-like substances, Bernard Jegou notes that until 3 years ago, he had never heard people discuss excreted livestock hormones.
"Considering that the weakest of these [steroid] growth promoters is probably 100 to 1,000 times stronger in biological activity than the most potent of the [industrial] endocrine disrupters gaining interest, I figured these drugs could pose a real environmental threat," says Jegou, who's the director of research at INSERM (the French Institute of Health and Medical Research) in Rennes. …