NEW regulatory approaches may be needed to assess environmental risks of agricultural growth promoters and similar human pharmaceuticals following research that shows that a newly found reversion mechanism allows the unexpected persistence of the steroidal substances in aquatic environments.
Results of the research were published online in the journal 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, multidisciplinary research team that includes the University of Iowa and Truman State, said this newfound 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," said Kolodziej, who has been studying the effects of these substances on aquatic ecosystems for 12 years. "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 regaining up to 70% of the metabolite's 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."
Sunlight is one catalyst for breaking down compounds in the environment. However, in this study, by simulating day and night in the lab, the research team found that the steroid's chemical compounds never fully disappeared in daylight. Moreover, during a simulated night, under typical surface water conditions, some of the compounds regenerated themselves to as much as 60% of the metabolite's initial mass when tracked over a 120-hour period.
More of the drug's mass was regenerated — up to 88% in one highly acidic state (pH 2) — when the water temperature was higher and when it was more acidic or alkaline, the team found.
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 that's 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 European Union.
The U.S. Department of Agriculture, National Institutes of Health and National Science Foundation funded the research through grants.