Results of a research project from Indiana University, University of Iowa and University of Washington suggest that metabolites of hormones used in cattle implants could persist in the environment longer than previously believed, creating a potential environmental risk.  

Their report, titled “Coupled reversion and stream-hyporheic exchange processes increase environmental persistence of trenbolone metabolites,” was published in the journal Nature Communications.

The researchers focused on trenbolone acetate, (TBA), a synthetic analogue of testosterone used in implants for growth promotion. Cattle metabolize TBA to produce 17-alpha-trenbolone, an endocrine disruptor chemically similar to TBA. The compound breaks down rapidly in sunlight, but the report’s authors cite earlier research showing the components can revert back to 17-alpha-trenbolone in the dark.

If the 17-alpha-trenbolone enters waterways from runoff from feedyards or fields fertilized with manure, the researchers believe the nighttime reversion and persistence of the compound in the dark “hyporheic zone,” where stream water mixes with groundwater, could result in greater environmental exposure. They note that even at very low concentrations, endocrine disruptors such as 17-alpha-trenbolone could have significant effects on stream life.

The research team used mathematical modeling techniques to determine that concentrations of TBA metabolites could 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," says lead author Adam Ward, PhD, from the Indiana University Bloomington School of Public and Environmental Affairs in a university news release. "We expect impacts that extend through the aquatic food web.”