Graduation Date

Fall 12-15-2017

Document Type


Degree Name

Doctor of Philosophy (PhD)


Environmental Health, Occupational Health, and Toxicology

First Advisor

Alan S. Kolok

Second Advisor

Eleanor G. Rogan


Endocrine disrupting compounds (EDCs) are chemicals that interfere with hormone function and are increasingly detected in aquatic environments, where they elicit adverse effects from exposed organisms. The toxicological effects of EDCs can be described as either activational (reversible) or organizational (irreversible), where the latter are associated with adverse outcomes in reproductive performance of adult fish. However, few studies have investigated the organizational impacts of anti-estrogenic or “defeminizing” EDCs, e.g. agrichemicals or pharmacological agents, in an environmentally-relevant or “sentinel” species. The objective of this study was to investigate the impacts of early-life EDC-initiated changes in estrogenic gene expression on organizational effects in fathead minnows. This was assessed by four experiments in which fathead minnow larvae (fhml) were exposed to defeminizing EDCs, then assessed for organizational impacts. Chapters 2 and 3 described in situ exposure studies conducted at the Elkhorn River Research Station to investigate the impacts of defeminizing agrichemical runoff on the gene expression and growth of fhml. Chapter 4 details the matrix-specific responses of fhml to water and sediments found within agricultural runoff and the subsequent effects on organizational outcomes in adults, including sex ratio, sex characteristics and reproductive performance. In a subsequent study, fhml were assessed for similar organizational effects as adults following the early-life induction of estrogenic genes by exposure to the putative pharmacological anti-estrogen, fulvestrant. Early-life exposure to EDCs produced sex-specific organizational effects in fathead minnows. The early-life induction of estrogenic genes and suppression of androgenic genes contributed to organizational effects in male fathead minnows. In contrast, early-life suppression of estrogenic genes was not associated with organizational effects as adults. Taken together, the results from this study indicate that early-life exposure to defeminizing mixtures of EDCs results in organizational but not adverse impacts in the fathead minnow. The absence of adverse impacts despite the induction of organizational responses suggests that a compensatory response plays an important role in determining the adult outcomes of early-life exposures in fathead minnows.