by Natasha Geiling  CLIMATE PROGRESS

Trenbolone acetate, or TBA, is a synthetic growth promoter used extensively in the cattle industry to help cows add muscle mass quickly. Implanted in the ears of over 20 million cows annually, cattle metabolize TBA to create 17-alpha-trenbolone, an endocrine disruptor that can end up in streams or rivers due to feedlot runoff or cattle manure applied to cropland.

For years, regulators weren’t concerned about the environmental risks associated with the compound because 17-alpha-trenbolone breaks down rapidly in sunlight. But a study published Friday in Nature Communications shows that TBA and its metabolite compounds persist in the environment in much higher concentrations — and for much longer — than previously thought, casting doubt on the current regulatory framework’s ability to properly manage risk associated with contaminants in the environment.

“TBA becomes a bit of a canary in a coal mine,” Adam Ward, assistant professor at Indiana University’s School of Public and Environmental Affairs and co-author of the study, told ThinkProgress. “It becomes a test case that demonstrates how a process that we didn’t recognize creates a risk we didn’t know existed.”

When 17-alpha-trenbolone and other TBA metabolites enter into the environment, they’re broken down rapidly by sunlight — but convert back to TBA metabolites in darkness. Ward and his colleagues discovered that this unique reactivity does have an impact on the environment, finding that concentrations of TBA metabolites like 17-alpha-trenbolon may exist in concentrations around 35 percent higher than previously thought. They also found that the TBA metabolites persisted longer in the environment, resulting in 50 percent more biological exposure.

The study also found that the areas with the highest concentration of TBA metabolites aren’t necessarily right next to the release point — sometimes, the worst exposure happens 20 to 25 miles from the site of pollution. “That really challenges how we think about pollution,” Ward said. “It may be that it takes a while for this combination of transport and reaction to produce the worst-case scenario.”

In runoff from feedlots, TBA metabolites have been measured in concentrations as high as 55 nanograms per liter, but even small amounts of endocrine disruptors like 17-alpha-trenbolon have been shown to adversely affect aquatic life. In concentrations as low as 10 nanograms per liter, studies have seen undesirable impacts on fish, including reduced rates of reproduction, skewed sex rations, and disruptions in hormones.

Though the study looked at TBA and its metabolite compounds specifically, Ward stresses that its real contribution is looking at how existing regulatory structure might be incomplete in its ability to deal with chemicals in the environment. The current regulatory system is largely focused on individual chemicals or compounds, forgoing a holistic approach to focus on individual constituents. To better manage the risks associated with chemicals in the environment, Ward says, regulatory bodies need to start thinking about how chemicals interact with the environment.

“The prevailing wisdom on how we manage risk is not complete,” Ward said. “We’ve been so focused on individual compounds that we’ve focused on the trees and not the forest.”

This isn’t the first time a study has discovered something unexpected about the way that TBA and its metabolites function in the environment. Ward has a background in hydrology and environmental transport, and has spent most of his career working on projects that look at how water carries compounds through the environment. In 2013, he met David Cwiertny, an associate professor at the University of Iowa who had just been involved in a study looking at how sunlight does — and does not — breakdown TBA metabolites in the environment.

“When TBA was approved for use, part of that approval was based on the idea that when you expose the compound to sunlight, it breaks down,” Ward said. In sunlight, TBA metabolites have half-lives of between 15 minutes and an hour.

The paper, published in Science in 2013, found that while 17-alpha-trenbolone does break down in sunlight, those compounds revert back to 17-alpha-trenbolone in the dark. The process of reverting back to 17-alpha-trenbolon happens much slower than the initial breakdown — around 100 times slower — but it does happen, meaning that instead of being permanently removed from the environment in the presence of sunlight, 17-alpha-trenbolone can persist in the environment much longer than anticipated.

Ward knew Cwiertny was excited about the study, but wondered whether its findings held true in nature. “I said, ‘You found it in the lab but is it meaningful in the environment? When we scale it up to a stream or a network of streams, do we actually care?”

Friday’s study makes the leap from lab to the environment. To do so, Ward and his co-researchers used mathematical modeling — a relatively new approach to studying emerging contaminants. “If this weren’t such a potent hormone, it would have been ideal to release some into a stream,” Ward said, “but that would be like poisoning the well to understand how the poison works.”

Ward stresses that the study’s findings don’t mean that operations that use TBA — or the companies that produce it — have been negligent. TBA and other growth enhancers help the cattle industry operate more efficiently, using less land and producing fewer greenhouse gases to create the same amount of beef.

“I don’t think the beef producers are doing anything wrong. I don’t think the chemical industry has been doing anything wrong,” Ward said. “No one is at fault, but now that we’ve seen a mistake or an omission or an oversight, it’s time for us to address it.”