Contaminants in Lake Mead appear linked to gender changes in fish
U.S. Water News Online
LAKE MEAD NATIONAL RECREATION AREA, Nev. -- Something fishy here has been confounding scientists for years.
Male fish are developing female sexual characteristics in Lake Mead and other freshwater sources around the country.
The U.S. Geological Survey recently released a four-page summary of more than a decade of studies linking
wastewater chemicals to those changes. But a scientist who has studied the issue for years complains the report
understated the danger of toxins at Lake Mead and elsewhere.
Tim Gross first aired his concerns seven months ago -- shortly after he was fired by the Geological Survey. The federal
agency says Gross was fired for failing to publish his data. Gross says the federal agency wouldn't let him publish.
Both sides, however, agree on one point. In Lake Mead and other freshwater sites, scientists have found traces of
pharmaceuticals, pesticides, chemicals used in plastic manufacturing, artificial fragrances and other substances linked
to changes in fish and animals.
The USGS report noted that the primary source for chemicals in Lake Mead was the Las Vegas Wash, a man-made
river made up almost entirely of treated wastewater from cities in the Las Vegas Valley.
Lake Mead is the source of 90 percent of Las Vegas' drinking water, and provides water for millions more people in
California. It irrigates many of the winter vegetables produced in the United States. The lake and contamination have
been the subject of intense scrutiny from federal and local scientists.
Gross, a researcher and teacher at the University of Florida, was the lead federal researcher on emerging
contaminants at the lake until he was fired earlier this year by the USGS.
Gross said he was fired because the government didn't like his conclusions that hormone-disrupting chemicals are
prevalent and are affecting the environment in Lake Mead to a greater degree than once suspected.
The agency's Oct. 19 report, which suggests more research is needed, was the product of a new team hired after Gross
was dismissed. It included a summary of research by a number of scientists, but did not include Gross' findings.
"They (federal officials) refuse to let me be involved in the research. They still haven't published the data. They don't
want us to publish," Gross said.
Kimball Goddard, state director of the Nevada-USGS water science center, rejected allegations that data were
He said research data from Gross were not included in the Oct. 19 report because Gross' results were not published.
Gross said the problem is acute in Lake Mead and in other freshwater sites. One element left out of the report was
evidence of sperm failure in fish, he said.
"On a national scale we see alterations in fish," said the scientist, who continues to research hormone-disrupting
chemicals in Florida and other states. He said hormone disruption "is widespread across the United States and is
widespread in Lake Mead."
Gross said his conclusions, shared by other researchers, were not popular.
"The (Southern Nevada) Water Authority doesn't want to hear it. My agency doesn't want to hear it," he said of the
USGS. "The Department of Interior does not want to deal with it. They want to make the argument that there is nothing
to worry about, but common sense just suggests it is not that simple."
Gross said he was concerned that human health could be affected by hormone-disrupting chemicals in Lake Mead.
"There are huge implications, and they're treating it like there's a little preliminary work and the significance of these
effects are unknown," Gross said. "I would disagree with that. They don't discuss the possibility of human exposure. The
potential for that is real, and they don't discuss that."
Goddard said the implications for human health were outside the realm of Geological Survey work.
"The studies that we have been involved in at the USGS are not designed to answer those kinds of questions," he said.
Gross and federal researchers have found sexual abnormalities in carp, bass and the endangered razorback sucker.
The problems are higher in Las Vegas Bay, at the confluence with the wash, than elsewhere in Lake Mead.
Studies documenting sexual abnormalities in fish in the Potomac River -- source of drinking water for millions of people
in the Washington, D.C., area -- raised similar concerns in September. Water officials there said the studies showed no
evidence that drinking water was unsafe, but the studies did not answer the question of potential effects to human
Southern Nevada Water Authority officials maintain that while chemicals from the waste stream flowing through the
sewers and Las Vegas Wash to the lake could affect fish and the environment, drinking water drawn from the lake is
sufficiently treated to eliminate any significant threat to human health.
Shane Snyder, the authority's principal researcher on the issue, said at an Oct. 19 conference of the American Society
of Mechanical Engineers that people are exposed to far higher levels of most hormone-disrupting chemicals in the
environment than from treated drinking water.
He asked rhetorically whether it was good policy to spend "trillions of dollars" removing hormone-disrupting chemicals
from water when such chemicals are present in far larger amounts in the environment.
Snyder said the central question of the "toxicological relevance" of chemicals in tiny quantities -- amounts that were
undetectable just a few years ago -- has yet to be answered.
J.C. Davis, Water Authority spokesman, noted that in Lake Mead the quantities are minuscule -- in the parts per trillion,
a grain of salt in a swimming pool. Treatment processes further degrade, destroy and dilute these chemical compounds
in drinking water.
"Eventually the analytical ability outpaces the health effects," Davis said. "The question is, at what concentration are
these relevant and you have to do something about them?"
He said Snyder will join federal and local researchers in trying to find those answers.
"People in the water industry want to know the answers to the questions we are asking."