In an article published September 26, 2013 in the scientific journal Nature, journalist Mark Peplow points out that endocrine disrupting chemicals (EDCs) may regenerate at night, after being broken down by sunlight during the day. According to Laura Vandenberg, endocrinologist at the University of Massachusetts, U.S., this undermines the risk assessment of EDCs, which is based on the assumption that sunlight is effective in destroying the substances. A group of researchers from the University of Iowa, U.S., and the University of Nevada in Reno, U.S., investigated the behavior of the endocrine disruptor 17α-trenbolone, used as a steroid for cattle, during simulated day and night cycles in the laboratory (Qu et al. 2013). They found levels to rebound during the dark periods, with increased product-to-parent reversion seen at higher temperatures or under slightly acidic or alkaline conditions. The researchers surrounding Kolodzeij from the University of Nevada confirmed their findings in a water sample taken from the Iowa River. In their publication, the scientists suggest to prioritize the assessment of environmental transformation products for risk assessment to make sure that transformation potential is detected. The findings show that risk assessment likely underestimates the environmental persistence of EDCs.

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Mark Peplow (September 26, 2013). “Hormone disruptors rise from the death.” Nature doi:10.1038/nature.2013.13831

Qu, S. et al. (published online September 26). "Product-to-Parent reversion of trenbolone: unrecognized risks for endocrine disruption.Science doi. 10.1126/science.1243192.