Researchers find evidence that hormone disruptors reform in the dark

In September 2013 the scientific journals Nature and Science published articles pointing out that EDCs (endocrine disrupting chemicals) may regenerate at night, after being broken down by sunlight during the day.

It was thought that sunlight is effective in destroying EDCs substances, but recent researches demonstrated that although these compounds are often broken down by sunlight, they can regenerate at night. Studies on cattle investigated the behavior of the endocrine disruptor trenbolone acetate, used as a steroid for cattle, during simulated day and night cycles in the laboratory.

Although concentrations fell during the simulated daytime, the scientists saw that levels rebounded during the dark periods. They also note that other steroids with similar chemical structures - including human pharmaceuticals - can regenerate in the same way, including dienogest, an oral contraceptive, and dienedione, an illicit anabolic steroid.

The findings show that risk assessment likely underestimates the environmental persistence of EDCs. As a consequence, scientists suggest prioritizing the assessment of environmental transformation products for risk assessment to make sure that transformation potential is detected.