I’m pretty sure Nature is blazing a new B-movie trail with this report on hormone-disrupting chemicals “rising from the dead”:
Environmental scientists have discovered that although these compounds are often broken down by sunlight, they can regenerate at night, returning to life like zombies.
“The assumption is that if it’s gone, we don’t have to worry about it,” says environmental engineer Edward Kolodziej of the University of Nevada in Reno, joint leader of the study. “But we’re under-predicting their environmental persistence.”
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He and his colleague David Cwiertny, an environmental engineer at the University of Iowa in Iowa City, decided to find out whether the breakdown products of endocrine disruptors could be boosting their environmental impact. Their team focused on trenbolone acetate, a synthetic anabolic steroid used as a growth promoter in more than 20 million cattle in the United States each year (this practice is banned in the European Union).
Cattle metabolize the steroid into compounds such as 17?-trenbolone, a potent endocrine disrupter commonly found in agricultural run-off water. In laboratory tests, just a few tens of nanograms of these compounds per litre can skew sex ratios and decrease fertility in fish. Some manufacturers have argued that these metabolites pose little risk in rivers, however, because sunlight breaks them down rapidly.
Kolodziej and his team put solutions of 17?-trenbolone and related compounds through several cycles of light and dark in the laboratory. Although concentrations fell during the simulated daytime, the scientists were surprised to see that levels rebounded during the dark periods. At neutral pH and 25 ºC, it took about five days to regenerate 60% of a sample of 17?-trenbolone from its breakdown products. Higher temperatures or slightly acidic or alkaline conditions accelerated this process.
“I’ve never seen anything like it,” says [Laura Vandenberg, an endocrinologist at the University of Massachusetts in Amherst]. Field biologists usually collect water samples during the day, she says, and nocturnal regeneration “would certainly have the potential to impact those results.”