Product-to-Parent Reversion of Trenbolone: Unrecognized Risks for Endocrine Disruption

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Science  26 Sep 2013:
DOI: 10.1126/science.1243192

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Trenbolone acetate (TBA) is a high-value steroidal growth promoter administered to beef cattle whose metabolites are potent endocrine-disrupting compounds. We performed laboratory and field phototransformation experiments to assess the fate of TBA metabolites and their photoproducts. Unexpectedly, we observed that the rapid photohydration of TBA metabolites is reversible under conditions representative of surface waters (pH 7, 25°C). This product-to-parent reversion mechanism results in unique diurnal cycling and substantial regeneration of TBA metabolites at rates that are strongly temperature- and pH-dependent. Photoproducts can also react to produce structural analogs of TBA metabolites. These reactions occur for structurally similar steroids, including human pharmaceuticals, suggesting that predictive fate models and regulatory risk assessment paradigms must account for transformation products of high-risk environmental contaminants like endocrine-disrupting steroids.

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