Scientists have discovered that the anabolic steroid trenbolone, once thought to break down in sunlight, comes alive again at night and reforms.

It's being called the "vampire steroid."

Trenbolone, which is a steroid given to beef cows on factory farms, does not break down in rivers and streams...as researchers previously thought.

Instead, research released today shows that trenbolone is found in much higher concentrations than thought in water. Scientists thought that the chemical, which is known to damage reproductive processes in fish, broke down in sunlight via a process known as phototransformation.

Not true, researchers have found. At night, trenbolone reassembles. However, water sources are customarily sampled and tested during the day, meaning that trenbolone levels are likely much higher than previously believed.

Trenbolone is a Schedule III controlled substance banned for human use, but approved for use in cattle by the U.S. Food and Drug Administration (FDA).  It is sometimes taken illegally by bodybuilders and can have severe health impacts.

David Cwiertny, one of the study's authors and a scientist at the University of Iowa's Department of Civil and Environmental Engineering, told press that samples need to be measured in a different way to truly understand how trenbolone impacts the environment. Samples should be taken from rivers and streams for 48 hours, he says.

And, he says, trenbolone is likely  "far more persistent than all our models currently predict" in water. "There's a high degree of uncertainty in the existing occurrence data because of the trends we see," Cwiertny said.

Other scientists, such as Bryan Brooks, who serves as director of the Environmental Health Science program at Baylor University and did not take part in the study, were also concerned.

 "Reports from this paper may stimulate rethinking the timing of environmental monitoring and surveillance," Brooks said. "For example, the vast majority of routine water quality monitoring does not examine these unregulated contaminants. And if pharmaceuticals are examined in water bodies, sampling typically occurs during daylight hours and often only examines water samples from the surface of lakes and streams. Such a practice could over- or underestimate risks of various pharmaceuticals."