Source: Michael Fielding, MEATINGPLACE, 5/21/15


Growth-promoting hormones used in beef production are expected to persist in the environment at higher concentrations and for longer durations than previously thought, according to research conducted by an Indiana University environmental scientist and colleagues at universities in Iowa and Washington.

The study focuses on the environmental fate of trenbolone acetate, or TBA, a highly potent synthetic analogue of testosterone, used to promote weight gain in beef cattle. A majority of beef cattle produced in the U.S. are treated with TBA or one of five other growth hormones approved for use in animal agriculture.

“What we release into the environment is just the starting point for a complex series of chemical reactions that can occur, sometimes with unintended consequences,” Adam Ward, lead author of the study and assistant professor in the IU Bloomington School of Public and Environmental Affairs, said in a news release. “When compounds react in a way we don’t anticipate — when they convert between species, when they persist after we thought they were gone — this challenges our regulatory system.”

According to the researchers, the study illustrates potential weaknesses in the American system of regulating hazardous substances, which focuses on individual compounds and often fails to account for complex and sometimes surprising chemical reactions that occur in the environment.

The publication, “Coupled reversion and stream-hyporheic exchange processes increase environmental persistence of trenbolone metabolites,” was published by Nature Communications and is available online. Co-authors are David M. Cwiertny and Colleen C. Brehm of the University of Iowa and Edward P. Kolodziej of the University of Washington (Tacoma/Seattle).
The research that led to the publication is funded by the National Science Foundation and the USDA.

Endocrine disruptors persist in streams
TBA is implanted in the ears of beef cattle. The cattle metabolize the compound to produce 17-alpha-trenbolone, an endocrine disruptor that is chemically close to TBA. The metabolite makes its way to streams and rivers via manure that washes from feedlots or is applied to land as fertilizer.

The compound breaks down rapidly when exposed to sunlight, and regulators once thought this attribute greatly reduced its environmental risk. But a 2013 study by Cwiertny, Kolodziej and others found that the breakdown products reverted back to 17-alpha-trenbolone in the dark. This means that instead of permanent removal in sunlight, the compound would be expected to persist in stream environments, returning to its earlier form overnight in the dark, shallow streambed where stream water mixes with groundwater, known as the hyporheic zone.

Ward and his collaborators set out to learn how much longer trenbolone may persist in the environment because of its unique reactivity, and whether this added persistence matters for aquatic ecosystems. Using mathematical modeling techniques, they show that concentrations of TBA metabolites may be about 35 percent higher in streams than previously thought. And the compounds persist longer, resulting in 50 percent more biological exposure than anticipated.

Even very low concentrations of these powerful endocrine disruptors have been shown to have significant effects on stream life. “These compounds have the potential to disrupt entire ecosystems by altering reproductive cycles in many species, including fish," Ward said. "We expect impacts that extend through the aquatic food web.”

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