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
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
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
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 suppressed.
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
"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 health.
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
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
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."
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