According to research published on September 27, 2013, in Science, steroid metabolites excreted by beef cattle reassemble themselves in the absence of sunlight, with potentially devastating consequences for aquatic life and human health. Trenbolone acetate (TBA) is an artificial form of androgen, a steroid; many cattle farmers feed it to beef cattle to improve muscle mass -- much the way bodybuilders use steroids. Although environmental risk assessments have been based on the assumption that sunlight completely degrades the metabolites of TBA, scientists in the American Midwest and the Netherlands have just published a paper demonstrating that these metabolites put themselves back together when the sun goes down, in conditions eerily similar to those of Earth's surface waters (pH level of 7, temperature of 77 degrees Fahrenheit).
Commentary by Erik Stokstad in Science accompanying the original research report compares the TBA metabolites to zombies, but Kerry Grens of The Scientist believes that a vampire may be a more apt comparison, due to the regenerative effects of nighttime on the metabolites. Study co-author Edward Kolodziej, interviewed in Nature, explains the significance of the findings: "The assumption is that if it's gone, we don't have to worry about it [...] but we're under-predicting their environmental persistence."
Persistence is the key word: 60% of a sample metabolite regenerated itself in just five days, and this metabolite has the ability to impair fish fertility at a concentration of a few tens of nanograms per liter of water. How much of these endocrine disruptors are out there? Well, a study in 2012 found androgens (typically regarded as "male" hormones) in 35% of freshwater samples. Birth control pills meet the same fate: metabolites excreted by users of hormonal birth control, such as dienogest, have the capacity to re-form in the same way TBA metabolites do. It is likely that the public health community and regulatory bodies vastly underestimate the amount of endocrine-disrupting compounds present in drinking water.