New regulatory approaches may be needed to assess environmental risks of agricultural growth promoters, and similar human pharmaceuticals, following research that shows a newly found reversion mechanism allows unexpected persistence of the steroidal substances in aquatic environments.

Results of the research will be published in an article in the renowned journal Science - the weekly journal of AAAS, the science society - next month and are available immediately online in Science Express.

"We investigated trenbolone, an anabolic steroid, and found that the photochemical breakdown isn't the end of its life cycle," Ed Kolodziej, co-author of the paper and environmental engineering professor at the University of Nevada, Reno, said. "Our team found that these substances, after a rapid breakdown in sunlight, are capable of a unique transformation in aquatic environments under various temperature and light-cycle scenarios where the process is reversed."

Kolodziej, project leader of a collaborative multi-disciplinary research team that includes the University of Iowa and Truman State, said this newly found mechanism may account for unexplained observations of endocrine disruption in aquatic organisms.

"Right now, I'm not alarmed, just concerned and interested in defining the real ecological risks associated with the widespread use of potent steroidal pharmaceuticals," Kolodziej, who has been studying the effects of these substances on aquatic ecosystems for 12 years, said.

"This implies uncertainty with the current environmental risk assessments or ecotoxicology studies used by regulatory agencies, researchers and pharmaceutical companies."

The team used laboratory and field studies to explore the process. They found that the steroid's chemical compounds, while breaking down as expected in sunlight, never fully disappeared; even in conditions that mimicked surface water, a small percentage of the chemical structure remained after extended sunlight. The remains regenerated themselves at night, in some cases to up to 70 percent of the metabolites initial mass."

"We knew something unique was going on," David Cwiertny, Kolodziej's research partner from the University of Iowa, said. "In daylight, it essentially hides in another form, to evade analysis and detection, and then at nighttime it readily transforms back to a state that we can detect."

The researchers validated the lab results with two experiments in the field - one with water taken from the Iowa River in Iowa City, Iowa and the other from samples taken from a collection pond at a cattle rangeland and research operation in California's Central Valley run by the University of California, Davis.

Trenbolone is a federally approved drug widely used by the beef industry to promote weight gain and to increase feeding efficiency in cattle. The drug, although popular in the bodybuilding and weightlifting communities, and as an athletic performance enhancer, has long been banned for human use, and also is banned for agricultural uses in the E.U.

Trenbolone has been considered safe for ecosystems due to its initially rapid degradation, with studies pointing to an environmental half-life of less than a day. Studies have indicated that low concentrations of these endocrine disrupting environmental steroids affect fish, by reducing egg production of females and skewing the sex of some species.