Vulnerability of Fish Populations in Lakes to Endocrine Disrupting Contaminants

Endocrine disrupting contaminants are chemicals that may interfere with natural hormones in humans and wildlife and produce adverse developmental, reproductive, neurological, and immune effects. These chemicals occur in a variety of everyday products, including pharmaceuticals, plastics, detergents, flame retardants, cosmetics, and pesticides. As these chemicals get discharged into the environment, humans and wildlife are exposed. The U.S. Geological Survey and St. Cloud State University are using this appropriation to study the occurrence of these chemicals in Minnesota's lakes and the degree to which they pose a threat to fish, such as affecting their ability to develop and reproduce.

Overall Project Outcome and Results
Effects of endocrine active compound (EAC) exposure to fish have been assessed predominantly at the molecular to organismal level, leaving questions regarding implications for population sustainability. One EAC, 17 beta-estradiol (E2), is frequently detected in aquatic environments because it is a hormone produced by vertebrates. This study assessed developmental and reproductive effects of E2 exposure on fathead minnows and bluegill sunfish. Continuous, six week exposures were conducted in outdoor tanks to simulate natural lake environments. First generation (F0) fathead minnows and bluegill sunfish were exposed during sexual maturity. Second generation (F1) fathead minnows were exposed during early development, sexual maturity, or both stages. Multiple biomarkers were measured to assess the effects of E2 exposure on fecundity, fish health, and development. Differences in the timing of egg production for both species indicate differences in lifetime fecundity between unexposed and exposed females. Exposure to E2 resulted in lower relative health and reduced expression masculine secondary sexual characteristic expression in F0 fathead minnows. Similar results were not observed in F1 fathead minnows. First generation bluegill sunfish males exposed to E2 had significantly smaller testes compared to controls. Supplemental, laboratory exposures were conducted on a separate fathead minnows cohort to assess reproduction and larval ability to escape a predator threat. Predation tests suggest E2 exposure of the current generation has the greatest effect on larval survival. Larval fathead minnows exposure to E2 in the F2 generation had longer escape responses and lower survival rates when compared to controls. Females exposed to E2 tended to lag behind controls in terms of larvae production after an initial period of similar activity. Results from this study suggest that exposure to E2 (in the absence of other estrogenic compounds) at environmentally relevant concentrations has subtle reproductive and developmental effects on fathead minnows and bluegill sunfish and implications for long-term survival in a predator-rich environment.

Project Results Use and Dissemination
Results from this study feed into an ongoing study assessing septic system discharge to lakes and effects on bluegill fitness (Assessing Septic System Discharge to Lakes, funded by Environment and Natural Resources Trust Fund in 2010).

A manuscript was submitted to the Journal of the American Water Resources Association for inclusion in a special issue on contaminants of emerging concern (originally submitted in February 2013, revised copy submitted in July 2013). A copy of the revised manuscript is included as an attachment to this final report.

Results from portions of this study have been included in two graduate student theses at St. Cloud State University under the supervision of Co-PI, Heiko Schoenfuss.

Results have been presented at the following scientific conferences:
March 2012 - Midwest Society of Environmental Toxicology and Chemistry (Minneapolis, MN)
June 2012 - American Water Resources Association specialty conference on contaminants of emerging concern (Denver, CO)
October 2012 - Minnesota Water Resources Conference (Minneapolis, MN)

This study was discussed in conjunction with similar work in a MPR story that aired on February 20, 2013.

Project Publications:
Fathead Minnow and Bluegill Sunfish Life-Stage Responses to 17 Beta-Estradiol Exposure in Outdoor Mesocosms (PDF - .2 MB)
Master's Thesis: Effect Differences of Estrogenic Exposure Between an Endangered Species and Two Model Species and Across Life Stages (PDF - 2.1 MB)