A critical review of the environmental occurrence and potential effects in aquatic vertebrates of the potent androgen receptor agonist 17β‐trenbolone

Trenbolone acetate is widely-used in some parts of the world for its desirable anabolic effects on livestock. Several metabolites of the acetate, including 17β-trenbolone (βTRB), have been detected in at low ng/L concentrations in surface waters associated with animal feedlots. The βTRB isomer can affect androgen receptor (AR) signaling pathways in various vertebrate species at comparatively low concentrations/doses. This paper provides a comprehensive review and synthesis of the existing literature concerning exposure to and biological effects of βTRB, with an emphasis on potential risks to aquatic animals. In vitro studies indicate that, although βTRB can activate several nuclear hormone receptors, its highest affinity is for the AR in all vertebrate taxa examined, including fish. Short-term exposures of fish to ng/l water concentrations of βTRB can cause changes in endocrine function, and adverse apical effects in longer exposures during development and reproduction. Impacts on endocrine function typically are indicative of inappropriate AR signaling, such as changes in sex steroid metabolism, impacts on gonadal stage, and masculinization of females. Exposure of fish to βTRB during sexual differentiation in early development can greatly skew sex ratios, while adult exposures can adversely impact fertility and fecundity. To fully assess ecosystem-level risks, additional research is warranted to address uncertainties as to the degree/breadth of environmental exposures and potential population-level effects of βTRB in sensitive species.