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There is growing concern about the biologic effects stemming from steroids in impacted waterways. In aquatic systems, interaction between steroids and sediment influence both contaminant fate as well as subsequent bioavailability to aquatic organisms. The focus of this dissertation research was to gain a better understanding of steroid behavior in aquatic systems based on the physiochemical properties of sediment and to use this knowledge to better understand the biological effects stemming from sediment-associated progesterone exposure. Two natural aquatic sediments, a sand and a silty loam, were selected to represent marked differences in sediments properties. Initially, sorption of 17β-estradiol, estrone, progesterone, and testosterone was evaluated to different size fractions of each sediment to determine the steroid sorption capacity and distribution within the whole sediment. Sorption capacity was influenced more by organic carbon content than particle size; while, interactions between size fractions were found to affect the distribution of steroids within the whole sediments.
In a subsequent study, the sediments were used to evaluate the fate of progesterone and the corresponding alteration of gene expression in a target organism, the fathead minnow (Pimephales promelas), using three steroid-responsive genes; vitellogenin, androgen receptor and estrogen receptor-alpha. When exposed to progesterone spiked sand, fish exhibited significant reductions in the expression of vitellogenin in the 5 and 50 ng/g treatment groups at 7 d and significant reductions in vitellogenin and androgen receptor expression after 14 d in the 50 and 500 ng/g treatment groups. In contrast, fish exposed to progesterone associated with the silty loam sediments did not show a biological response at 7 d and only realized a significant reduction in vitellogenin at 14 d in the 50 and 500 ng/g groups. In both sediments, progesterone degradation resulted in the production of androgens including androsteinedione, testosterone, and androstadienedione, as well as the anti-estrogen, testolactone. Differences in compound fate resulted in organism exposure to different suites of metabolites either in water or associated with the sediment. Results from this study suggest that environmental progestagens will lead to defeminization at environmentally-relevant concentrations, and that exposure is influenced by sediment properties.
Advisor: Shannon Bartelt-Hunt