USGS Examines Endocrine Disrupting Compounds In Lake Mead

On Oct. 20, the U.S. Geological Survey (USGS) announced it recently released a fact sheet/report describing investigations that have taken place in Lake Mead, Nevada and Arizona, on synthetic organic compounds. The fact sheet also describes new studies that are now underway to assess the potential effects of drought-induced alterations in the hydrology of the lake.

The investigations described in the fact sheet have been a collaborative effort between the USGS, the National Park Service, the U.S. Fish and Wildlife Service, the U.S. Bureau of Reclamation, Texas Tech University, the University of Florida, Gainesville, the University of Nevada - Las Vegas and the Nevada Division of Wildlife.

The studies, conducted in 1995 and 1999-2000, showed that male carp from Las Vegas Bay have low blood levels of androgen and smaller testes compared to male fish from reference sites. The same studies and others also showed the presence of higher levels of synthetic chemicals in water, sediment and fish from Las Vegas Bay compared to reference sites. In addition, commonly used products known as "emerging contaminants," such as triclosan (an antimicrobial drug used in soap), are being accumulated in fish from Las Vegas Bay. Other chemicals found in water, sediment and fish in Las Vegas Bay include organochlorines (e.g., DDT and DDE), polycyclic aromatic hydrocarbons, furans, phthalates, phenols and polychlorinated biphenyls (PCBs). Some of the chemicals present in Las Vegas Bay have been shown by laboratory studies to cause endocrine disruption in male fish.

Since the previous studies of Lake Mead were completed, the southwest region of the United States has been experiencing a drought that has caused current lake levels to be at historic lows. This change in hydrological conditions could potentially exacerbate or change the patterns of contaminant distribution and endocrine disruption in Las Vegas Bay and other sites of the lake. Moreover, municipal dischargers in the Las Vegas Valley are considering plans to divert wastewater from Las Vegas Wash to undetermined locations in Boulder Basin or to the Colorado River below Hoover Dam. Either of these diversions might result in wastewater being introduced for the first time into new parts of the Lake Mead National Recreation Area (LMNRA). New studies are now in place to: assess the potential effects of drought-induced alterations in the hydrology of the lake and provide baseline information to monitor changes in contaminant distribution and potential for endocrine disruption that may occur due to the redistribution of wastewater inflow sites in the Lake Mead and Colorado River ecosystems.

These new studies are wider in geographic and scientific scope and address not only endocrine disruption and the presence and distribution of chemical contaminants, but also contaminant sediment flux and microbiology, food-web dynamics, and wastewater-treatment effects. Such comprehensive studies have never been conducted within the LMNRA.

The fact sheet/report, titled "Investigations of the Effects of Synthetic Chemicals on the Endocrine System of Common Carp in Lake Mead, Nevada and Arizona," is available at http://pubs.usgs.gov/fs/2006/3131.

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