Endocrine Disruption in Lake Mead

Degradation of water quality in Lake Mead, on the lower Colorado River in Nevada and Arizona, is a matter of public concern because of potential adverse effects on wildlife, and because Lake Mead is the major source of drinking water for about 1.6 million residents of Las Vegas, and about 35 million annual tourists. The National Park Service (NPS) manages the Lake Mead National Recreation Area (LMNRA) which has about 9 million visitors yearly, including 500,000 anglers drawn to its world-class sports fishery. The U.S. Fish and Wildlife Service (FWS) provides management for the federally designated, endangered razorback sucker (Xyrauchen texanus), and for over 180 species of migratory birds that utilize LMNRA surface-waters. These multiple uses demonstrate the vital importance of LMNRA surface-waters, and a strong dependence on the water-quality of these surface-water resources.

Prior studies of Lake Mead indicated the presence of numerous synthetic organic compounds (SOCs) in water, bottom sediments, and fish; and also provided evidence of endocrine disruption in common carp (Cyprinus carpio). These studies determined that SOCs discharging into Las Vegas Wash (LVW), and ultimately into Lake Mead by way of Las Vegas Bay include polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated pesticides, and pharmaceuticals and personal care products. Exposure to these compounds represents potential chronic or acute threats to the health, especially the reproductive health, of aquatic life in LMNRA. Many of these compounds and their metabolites are endocrine-disrupting compounds (EDCs), carcinogens, and toxins. The sources of SOC include urban runoff from lawns, gardens, and golf courses, storm-water runoff, subsurface inflow, and sewage effluent from three municipal wastewater treatment plants.

In 2006, a study funded by the Southern Nevada Public Land Management Act (SNPLMA) was initiated to assess potential effects of chemical stressors on fish in LMNRA. The general goal of this study was to determine if the recent drought in the lower Colorado River and subsequent lowering of the water level in Lake Mead increased the exposure of aquatic biota to environmental contaminants. Data were collected only once during the year (March 2006) and they are now being compared to similar studies conducted in 1995 and 1999-2000. The specific objectives of this work were to assess ecological condition at five sites in LMNRA by examining chemistry of bottom sediments and fish tissues, as well as biomarkers of fish endocrine and reproductive condition. Although these data and interpretations have not yet been completed, preliminary evidence indicates that alterations in male reproductive condition in fish are occurring and that elevated concentrations of fragrance chemicals, polybrominated diphenyl ethers (BDE), and PCBs are found at some of the study sites.

Many unanswered questions concerning SOCs and their potential impacts still remain. For example, the seasonality of male reproductive condition needs to be examined to determine whether differences in condition are due to non-chemical environmental differences between sites. Furthermore, the contribution of treated wastewater effluent to the endocrine- and reproductive-disrupting properties of the lake’s water is uncertain. Finally, the role that flux and transfer of SOCs from and to sediment and through the food chain play in SOC bioavailability as well as the role of resident microbes in breaking down SOC to inert or active metabolites are unknown. The current study is designed to answer these questions.

Objectives

This project has four main components and objectives:

1) field biomarker studies with carp and largemouth bass to assess fish endocrine and reproductive condition,

2) controlled laboratory studies with fathead minnow (Pimephales promelas) exposed to tertiary-treated wastewater effluent to assess the endocrine and reproductive effects of wastewater,

3) studies of food web dynamics, sediment chemistry and microbiology to delineate the historical pattern of deposition and fate and availability of sediment contaminants, and

4) an ecological risk assessment (ERA) to predict risk to the health of the Lake Mead ecosystem.

Results of the field biomarker studies will establish the reproductive condition of fish in the Lake Mead ecosystem over the course of a full year and will expand previous assessments. The effluent exposure studies will provide for a carefully controlled examination of the effect of wastewater effluent on fish reproductive condition and will also allow a comparison between field and laboratory results. The studies of food chain transfer, flux and microbiological transformation of sediment SOCs will provide mechanistic information about sediment as a potential reservoir for contaminants. Data from this study and previous studies will be used for an ERA, which can guide future research directions, and more importantly, identify potential strategies for ecosystem remediation and/or wastewater treatment.

Strategy and Approach

To address Objective 1, fish will be collected from Las Vegas Wash (LVW), Las Vegas Bay (LVB), Overton Arm (OA), and Willow Beach (WB). The first two sites are anticipated to contain the highest levels of municipal contaminants because they carry (LVW) and receive (LVB) municipal effluent from the metropolitan area; OA is relatively uncontaminated and is considered the reference site for this study; and WB is of interest because of its location on the Colorado River downstream of Lake Mead. Fish will be collected using a boat equipped with an electroshocker (LVB, OA & WB) or seine and gill nets (LVW) at four times during the year to cover a full reproductive cycle (March, July, and November 2007, and March 2008). Biomarkers for analysis will include sex steroids (11-ketotestosterone, estradiol-17β), thyroid hormones (triiodothyronine, thyroxine), vitellogenin, gonadosomatic index and parameters of sperm quality (viability, mitochondrial function, motility by computer and unaided eye, DNA integrity and percent spermatogenic stage, sperm count). Whole fish will be analyzed for a suite of pesticides, PAHs, PCBs, and for emerging contaminants including BDEs, musk’s/fragrances, personal care products, and pharmaceuticals.

To address Objective 2, an experiment will be set up at a sewage treatment plant to do a partial life cycle study on fathead minnows (Pimephales promelas) using different concentrations of treated effluent. Endocrine-disrupting effects will be monitored to determine if the effluent has an impact on fish. In addition, a parallel but separate study using ozone-treated effluent will be run side by side with the treated effluent in order to determine if ozonation is effective in degrading SOCs in the waste stream (this study will be funded through the FWS). Biomarker responses measured from Objectives 1 and 2 will be compared with each other and with biomarker results from the previous Lake Mead studies, and analyzed for significant associations with chemical stressors.

To address Objective 3, all trophic levels will be characterized by measuring stable isotopes and constructing a food web model for nutrient (and thus potentially contaminant) transfer. Sediment cores will be collected from LVB with a gravity coring device and analyzed for SOCs and ¹³⁷Cs and ²¹⁰Pb to determine (a) when SOCs were first deposited in sediment and if they have increased over time, and (b) the presence of SOC-degrading microbes. In LVB, contaminant fluxes from sediments will be measured experimentally, thereby mapping compound transfers that increase bioavailability. Cores will be obtained from three locations in a transect close to the outflow of LVW from the inner, middle and outer portions of the bay.

To address Objective 4, bioaccumulation and food chain partitioning based on physical/chemical properties of EDCs will be considered, and models of target species and chemicals of potential concern to will be developed to derive effect threshold concentrations of toxicity relative to site-specific variables.

Relevance and Benefits

The proposed project will address several priority issues in the strategic plan of the USGS including the Water and Biological Resources Disciplines and the Nevada Water Science Center; thereby directly helping to manage water and biological resources of the U.S. The data gained from this project will provide greater understanding of the origin, fate, and toxic effects of SOCs on aquatic wildlife and the food chain in Lake Mead and in the Colorado River below Hoover Dam. This information will also have potential value assessing ecosystem health in other areas with large lakes and reservoirs, especially those in the southwest or those near large metropolitan areas such as the Great Lakes. The ERA model will be useful to other state and federal agencies managing natural resources at Lake Mead and LMNRA. Specific characterization of risks will be made for various types of SOCs for the aquatic biota in this lake ecosystem.

Publications

Publications which were recently released are listed below. A complete list of USGS Nevada WSC Lake Mead publications also is available: Lake Mead Bibliography (PDF)

Rosen, M.R., Goodbred, S.L., and Leiker, T.J., 2007, Use of passive samplers for detecting vertical gradients of organic contaminants in Lake Mead: Nevada Water Resources Association 2007 annual conference, Reno, Nev. February 20-22, abstracts, unpaginated

Rosen, M.R., and Van Metre, Peter, 2007, Use of lacustrine sediments to reconstruct contaminant histories in complex sedimentary environments: 4th International Limnogeology Congress, Barcelona, Spain, July 2007, programme and abstracts book, p. 100

Goodbred, S.L., Leiker, T.J., Patino, Reynaldo, Jenkins, J.A., Denslow, N.D., Orsak, Erik, and Rosen, M.R., 2007, Organic chemical concentrations and reproductive biomarkers in common carp (cyprinus carpio) collected from two areas in Lake Mead, Nevada, May 1999-May 2000: U.S. Geological Survey Data Series 286, 19 p.

Rosen, M.R., Goodbred, S.L., Patino, Reynaldo, Leiker, T.J., and Orsak, Erik, 2006, Investigations of the effects of synthetic chemicals on the endocrine system of common carp in Lake Mead, Nevada and Arizona: U.S. Geological Survey Fact Sheet 2006-3131, 4 p.

Rosen, M.R., Leiker, T.J., and Goodbred, S.L., 2006, Use of passive samplers for detecting vertical gradients and potential sources of organic contaminants to Lake Mead, Nevada, U.S.A.: Geological Society of America Abstracts with Programs, v. 38, no. 7, p. 160