Growth Hormone in Cattle More Dangerous Than Previously Thought

By Jane Farrell

Potentially harmful hormones used in beef production are likely to persist for longer in the environment, and at a higher level, than was previous thought, according to new research.

“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,” said Adam Ward, lead author of the study and assistant professor in the Indiana University Bloomington School of Public and Environmental Affairs. “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.”

Numerical simulations performed in this study can help to predict the potential impact of environmental processes on contaminant fate to more effectively understand the potential for these unexpected effects, according to a news release from the university.

The findings were published by Nature Communications.

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.

The compound breaks down rapidly when exposed to sunlight, and regulators once thought this attribute greatly reduced its environmental risk. But a 2013 study found that the compound was more persistent.

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.

“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.”

Studies by the U.S. Geological Survey and other agencies have found endocrine disruptors to be present in many streams, rivers and lakes, and several similar compounds have even been found in drinking water.

While TBA and its metabolites are the focus of the study, Ward said those compounds are representative of many others — suggesting it may be time to update regulatory approaches to better include a wide range of findings from modern research.