Do Cattle Growth Pose an
Hormones Environmental
Risk? Preliminary data suggest that hormoneadulterated runoff REBECCA RENNER
from cattle feedlots could be affecting local fish.
W
hat might some bodybuilders, U.S. beef cattle, and wild fathead minnows from Nebraska have in common? They may be taking anabolic steroids. Preliminary data indicate that wild minnows may be affected by masculinizing hormones from cattle feedlot effluents. The
new data add to a growing concern about the effects of chronic exposure to pharmaceuticals and other bioactive compounds now being found in the environment. Previous U.S. Food and Drug Administration (FDA) environmental assessments have
LOUIS J. GUILLETTE, UNIVERSITY OF FLORIDA
focused on the acute toxic effects of synthetic hormones given to livestock. New compounds and requests for expanded uses of approved compounds may require additional chronic exposure and degradation studies, according to an agency spokesperson. Results from the first national survey of pharmaceuticals, hormones, and other bioactive compounds in U.S. streams were published in the March 15 issue of ES&T (1). Anabolic steroids were not included, but they will be addressed in the future by U.S. Geological Survey (USGS) researchers.
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Anabolic steroid use by athletes is illegal, but each year, millions of cattle in U.S. feedlots are legally given these compounds to promote growth. The result could be significant amounts of steroids in runoff from feedlots. In December 2001, 11.9 million cattle occupied large feedlots—defined as those having more than 1000 animals—according to statistics from the U.S. Department of Agriculture National Agricultural Statistical Service (http://usda.mannlib.cornell.edu/ reports/nassr/livestock/pct-bbc/2001/cofd1201.txt). Almost all of the animals receive low levels of natural and synthetic hormones through pellets implanted in their ears, says Dan Loy, an extension beef specialist at Iowa State University in Ames. The hormones enhance growth so that conversion of feed into meat is more efficient. “They reduce the cost of feeding by at least $20 to $30 a head, which equals or exceeds the total profitability of the animal,” Loy says. Up until now, environmental concerns about the detrimental effects of giant feedlots have focused on their role in the volume of nutrients entering streams and the introduction of antibiotics that could lead to resistant bacteria. Under the Clean Water Act, EPA currently regulates effluent discharges from such lots, although compliance and enforcement of these regulations have been patchy, according to a 1995 General Accounting Office report (2). The agency is under a court-ordered deadline to update its regulations by December 2002. Preparing beef cattle for market is a major activity in Nebraska, and the FDA has acknowledged that hormonally active substances have been detected downstream from several Nebraska feedlots. The agency cautions, however, that the active substances have not been identified, spokeswoman Rae Jones says. Until now, FDA environmental assessments of synthetic hormones have focused solely on acute
effects. According to Jones, concerns about chronic effects on reproduction and development have prompted FDA’s Center for Veterinary Medicine to begin requesting that drug sponsors conduct chronic reproductive studies on Daphnia (water flea) and fish.
BRIAN PRECHTEL, U.S. DEPARTMENT OF AGRICULTURE
Little is known about the environmental fate of natural or synthetic hormones. Nevertheless, there are already inklings that there may be a problem. Last December, University of Florida endocrinologist Lou Guillette told EPA and FDA scientists that he had found native female fathead minnows in waters downstream of several feedlots with male characteristics and male fish with abnormally small testes and almost feminized heads. Waters from these sites also produce androgenic effects in several different in vitro assays, Guillette adds, although, again, the active compounds have not been identified. “Our work is suggestive, not definitive,” he says. At talks at the Society of Environmental Toxicology and Chemistry meeting in Baltimore last November and at the Society of Toxicology meeting in Nashville, Tenn., in March, researchers presented preliminary data raising concerns about one growth promoter, the synthetic androgen trenbolone acetate. EPA scientist Gerald Ankley reported that female fathead minnows exposed to trenbolone acetate for 21 days in the laboratory at concentrations of 30 ng/L developed tubercles, small bumps on the head normally found only on breeding males. Higher water concentrations of trenbolone acetate also significantly decreased egg production, as well as altered other aspects of the fish’s reproductive endocrine function. Ankley cautions that this work is preliminary and does not prove that trenbolone acetate is affecting wild fish. However, he says, the results do compel further investigation. Others point out that these results may not be too surprising, given the potency of trenbolone acetate. In vitro testing by EPA toxicologist Earl Gray has shown that beta-trenbolone, a metabolite of trenbolone acetate, is as active as the androgenic hormone dihydrotesterone, a particularly potent form of the male hormone testosterone. Moreover, fathead minnows appear to be particularly sensitive to trenbolone acetate. West Virginia University of toxicologist Christy Foran studied the effects of trenbolone acetate on Japanese medaka fish. She found that, even for hatchlings exposed at a sensitive developmental stage, reproductive impairment was only detected at concentrations at or above 200 ng/L.
Environmental fate overlooked
TensofmillionsofU.S.beefcattle receive trenbolone acetate, a synthetic grow th-promoting hormone. 196 A
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / MAY 1, 2002
Until now, concern about possible unintended effects of growth hormones has centered on human health. Twelve years ago, the European Union banned growth hormone use in both domestic and imported meat because of worries that these compounds could have
LOUIS J. GUILLETTE, UNIVERSITY OF FLORIDA
UniversityofFlorida endocrinologistLou Guillette caughtw ild fathead minnow sdow nstream ofsome Nebraska cattle feedlots. The minnow sappearto be exposed to androgenic hormones.
human health effects (http://europa.eu.int/abc/doc/ off/bull/en/9604/p103109.htm). The ban, which sparked a trade war, led to considerable research on the possible human health effects of trace residues of growth hormones in meat. But, say scientists, there has been very little research on their environmental effects. In part, this is because it was assumed that bioactive compounds given to animals and humans were inactive when excreted and remained inactive in the environment, says Guillette. This assumption is not entirely true, he adds, and some hormones are excreted unchanged. Conjugating them with sugars in the liver inactivates the rest. However, once in the environment, microorganisms rapidly degrade the sugars, converting the compounds back to their bioactive forms. Little is known about the environmental fate of natural or synthetic hormones. Some estrogens, such as estradiol, are rapidly degraded, whereas others, such as the contraceptive pill’s ethinyl estradiol, are not, says John Sumpter, an endocrinologist at Brunel University in Uxbridge, United Kingdom. Even less is known about androgens. The limited data available show that synthetic androgens are more persistent than their natural counterparts, according to Heinrich Meyer, director of the Technical University of Munich’s Institute of Physiology in Freising-Weihenstephan, Germany. In fact, trenbolone acetate and another synthetic cattle growth hormone, melengestrol acetate, appear to be relatively persistent in the environment under certain conditions, according to published research from Meyer’s group (3). They implanted 41 cattle with trenbolone acetate, then collected and stored the manure that the animals produced under anaerobic con-
ditions. After eight weeks, they had collected ~100 tons of manure containing ~10 ng/g trenbolone acetate. During anaerobic storage, both hormones degraded with a half-life of 260 days. When the manure was spread on fields, the hormones degraded more quickly—trenbolone acetate disappeared in 40 days. The central question raised by these results, says Meyer, is whether steroids are adsorbed to the soil or whether they go into the drainage water. Preliminary results suggest that the answer depends on the soil type, and the group hopes to have more complete results soon. At this point, concentrations of trenbolone acetate and other synthetic hormones in U.S. streams are unknown. USGS researchers measured trenbolone acetate concentrations in streams and rivers as part of its 2000–2001 survey of contaminants of emerging concern, but survey results are not expected until 2003. The recent observations and data suggest that scientists have been blind to the possible effects of growth hormones in the environment. “Once it comes out the tail end of a cow we haven’t been interested,” says Guillette. “Now we need to reconsider our assumptions.”
References (1) Kolpin, D. W.; et al. Environ. Sci. Technol. 2002, 36, 1202–1211. (2) U.S. General Accounting Office. Animal Waste Management and Water Quality; GAO/RCED-95-200BR; U.S. Government Printing Office: Washington, DC, 1995. (3) Schiffer, B.; Daxenberger, A.; Meyer, K.; Meyer, H. H. D. Environ. Health Perspect. 2001, 109, 1145–1151.
Rebecca Renner is an ES&T contributing editor. MAY 1, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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