Document Type

Technical Report

Publication Date



U.S. Geological Survey: Branch of Information Services


The Nevada Basin and Range (NVBR) study unit of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program is investigating the status of, trends in, and factors affecting water quality in the Las Vegas area. A principal objective of the investigation is to assess the effects of urbanization on the quality of area water resources.

Las Vegas Wash is the surface-water outlet for the Las Vegas area. The wash transports stormwater runoff, shallow ground-water discharge, and tertiary-treated sewage effluent from the Las Vegas area to Las Vegas Bay of Lake Mead on the Colorado River. Most of the flow—about 96 percent in 1993—transported in the wash to Las Vegas Bay is treated effluent from city and county sewage-treatment facilities. Storm-water runoff, shallow ground-water discharge, and treated sewage effluent from Las Vegas and other urbanized areas in the valley have the potential to affect the water quality of Las Vegas Wash and Lake Mead.

In 1992, NVBR personnel collected bottom-sediment samples from Las Vegas Wash upstream from the discharge of treated sewage effluent and Las Vegas Bay during a survey to determine if synthetic organic compounds (organochlorines and semivolutile industrial compounds) were present. Organochlorines (pesticides and industrial compounds), polycyclic aromatic hydrocarbons (PAH's), phthalales, and phenols were detected at one or both of these sites. Many of these compounds are persistent in the environment, are relatively insoluble in water, and strongly partition into sediment organic material and lipid tissues of organisms.

Compounds referred to as organochlorines include chlorinated pesticides and their metabolites, polychlorinated biphenyls (PCB's), dioxins, and furans. PCB's have been used as plusticizers and hydraulic lubricants, in heat-transfer systems, and as dielectric fluids in electrical capacitors and transformers. Dioxins and furans were produced inadvertently during the manufacture of herbicides and PCB's, and are formed during municipal waste combustion; they are commonly discharged to surface waters in effluents from chemical manufacturing plants, leather tanneries, kraft-pulp mills, wood-processing plants, and sewage-treatment plants.

PAH's originate from natural and human sources. They are produced mainly by high-temperature pyrolylic reactions such as municipal incineration or forest fires, but a few are produced commercially for use in mothballs, pesticides, fungicides, dyes, wetting agents, synthetic resins, cutting fluids, solvents, and lubricants. Phlhalates are used extensively as plaslicizers to manufacture products from polymers of vinyl chloride, propylene, ethylene, and styrene.

Phenols are used in the production of phenolic resins, germicides, herbicides, fungicides, Pharmaceuticals, dyes, plastics, and explosives. Most phenols are not persistent and are highly soluble; however, highly chlorinated phenols are persistent and tend to partition into sediment organic matter and lipids of aquatic organisms.

Interest in environmental contaminants that may affect endocrine systems of animals by causing hormone imbalance, commonly referred to as endocrine disruption, has grown during the past 40 years. A symposium on estrogen in the environment increased the debate about effects of environmental contaminants on endocrine systems. More recently, Colborn and Clement (1992) concluded that many synthetic organic compounds have the potential to disrupt the endocrine systems of animals, including humans; these compounds include organochlorines, PAH's, phthalates, and phenols.

Recent studies have found evidence of endocrine disruption in fish from contaminated ecosystems. Fitzsimons (1990) reported lower sex-steroid hormone levels in male lake trout (Salvelinus namaycush) of Lake Ontario compared with fish from less-polluted sites. Additionally, an inverse relation was found between 11-ketotestosterone and contaminant body burdens in trout from three of the Great Lakes. Male and female white suckers (Catostomus rommersoni) and lake whitcfish (Coregonus clupeaformis) in the vicinity of pulp-mill effluent were found to have depressed gonadal sex-steroid hormones, delayed maturity, lowered reproductive capability, and reduced secondary sex characteristics.

Other studies have measured vitellogenin to assess endocrine disruption. Vitellogenin is an estrogen-induced or dependent egg protein used in the production of egg yolk and normally synthesized by the livers of female egg-laying vertebrates. Male fish have the vitellogenin gene but it is normally suppressed; however, the gene can be activated by exposure to exogenous contaminants or xenoestrogens. Several recent field studies have documented vitellogenin synthesis in carp males from streams affected by sewage effluent.

Histologic abnormalities in gonads offish with endocrine disruption can include multinuclear eggs or the presence of dark, bar-shaped structures in tubules of the testes. Necrosis in tissues of organs can be caused by exposure to a toxicant or a combination of toxicants.

The potentially harmful effects that organochlorines and semivolatile industrial compounds can have on humans and aquatic wildlife prompted the National Park Service (NPS), which administers the Lake Mead National Recreation Area, and the NVBR to begin a cooperative investigation to determine the occurrence and distribution of these compounds in Las Vegas Wash and Lake Mead. Concurrent assessments of the endocrine systems and histology of selected organs in carp (Cyprinus carpio) were made in cooperation with the National Biological Service (NBS), which on October 1, 1996, became part of the U.S. Geological Survey (USGS), and the U.S. Fish and Wildlife Service (USFWS). Although the investigation is currently (1996) ongoing, data were collected in 1995 for Las Vegas Wash, Las Vegas Bay, and Callville Bay. Callville Bay, which is in a part of Lake Mead upstream from Las Vegas Bay, was sampled as a reference site for comparisons with Las Vegas Wash and Bay.

This report presents preliminary results of the 1995 investigation and includes the 1992 sample information.


Aquatic pollution; Environmental monitoring; Environmental protection; Hydrologic data


Biogeochemistry | Desert Ecology | Environmental Indicators and Impact Assessment | Environmental Monitoring | Fresh Water Studies | Natural Resource Economics | Natural Resources and Conservation | Natural Resources Management and Policy | Sustainability | Water Resource Management