Date of this Version
There is growing concern about the impact of steroidogenic compounds in aquatic systems. Steroids released into the environment have been shown to sorb to sediments in aquatic environments; however, other studies have suggested that steroids can move through sediment beds, and that fish and other aquatic organisms can facilitate this mobility. In this study, we investigated the effect of sediment-associated 17β-estradiol and 17β-trenbolone on vitellogenin expression in fathead minnows, a ubiquitously distributed freshwater organism. Two natural sediments were selected to represent a diversity of soil properties, one a silty loam and one predominately sand. Sediment contaminated with either 17β-trenbolone or 17β-estradiol was placed in a glass aquarium along with 20 sexually mature female (17β-trenbolone) or male (17β-estradiol) fathead minnows. Both positive (aqueous steroid) and negative (lab water) control experiments were performed. Ten fish were randomly collected from each tank at 7 days with the remaining harvested at 14 days. Livers and gonads were collected from each individual and relative hepatic vitellogenin (Vtg) expression was quantified using ribosomal L8 as a normalization standard. After exposure to 17b-estradiol-contaminated sediments, male fathead minnows exhibited no inappropriate expression of Vtg relative to the negative control group regardless of the sediment type used. By comparison, female fathead minnows exposed to 17β-trenbolone associated with silty loam exhibited Vtg expression that was not significantly different from either the positive or negative control fish at both 7 and 14 days suggesting an intermediate response to the spiked sediment. However, female fathead minnows exposed to 17β-trenbolone associated with sand exhibited no inappropriate expression of Vtg relative to the negative control at 7 days but did exhibit a significant reduction in Vtg at 14 days. Taken together, we observed differential bioavailability for an estrogenic compound (17b-estradiol) and an androgenic compound (17β-trenbolone) when associated with sediment. Additionally, differential bioavailability was observed for 17β-trenbolone depending on sediment type. Liquid chromatography tandem mass spectroscopy was performed on sediment extracts and water samples to evaluate steroid desorption and transformation over the exposure period.
Advisor: Shannon Bartelt-Hunt