Photo Credit: Duncan Hull

Although some endocrine-disrupting chemicals break down rapidly when exposed to sunlight, a new study published in Science shows that they may be able to re-form in dark conditions. Researchers examined metabolized runoff of trenbolone acetate, a synthetic anabolic steroid used as a growth promoter in more than 20 million cattle in the United States each year. The metabolized compound, 17α-trenbolone, has been found to have severe endocrine-disrupting properties. Even in small quantities, this chemical is able to skew sex ratios and decrease fertility in fish. Because this compound breaks down readily in light, it has been argued that it poses relatively low risks to aquatic ecosystems. However, the results of this study call those arguments into question, showing that while 17α-trenbolone and related compounds do break down in the daytime, they are able to regenerate during night periods. In fact, at neutral pH and 25 ºC, it took about five days to regenerate 60 percent of a sample of 17α-trenbolone from its breakdown products, and higher temperatures or slightly acidic or alkaline conditions can accelerated this process. This means that chemicals known to break down when exposed to sunlight may be more persistent in our environment than previously thought.