Wetlands park could harm fish in Lake Mead

Friday, Dec. 10, 1999 | 11:15 a.m.

Experts warned local water officials that they will have to carefully monitor a proposed desert wetlands park in the Las Vegas Wash for two metals, mercury and selenium.

Both metals, if concentrated in wetlands designed to slow water flow, could pose a threat to sports fish in Lake Mead, not necessarily people, the scientists said Thursday at the Lake Mead Water Quality Forum.

Wetlands can capture enough elements such as selenium and mercury and concentrate them, causing disruption in reproduction of birds and fish.

Selenium is a gray metal that exists naturally in soils and in people. Most of the selenium streaming down the Colorado River into Lake Mead comes from shale deposits in Wyoming and Colorado and from irrigation runoff, Jerry Miller of the Bureau of Reclamation said.

Lake Mead and its fish contain roughly about half the selenium found in places such as the Great Lakes and Florida.

If kept in balance, selenium forms traps for other toxins that threaten fish and birds, he said.

Selenium comes in trace amounts in vitamin supplements and is believed to counteract the body's deterioration from damaging chemicals and environmental assaults, Miller said. It can block other essential elements used by living cells such as cobalt, copper and zinc.

"In dealing with trace elements, the key is balance," Miller said, urging local water officials to design the 2,000-acre wetlands park to keep the selenium and mercury in check.

Instead of waiting for the marshes to grow and begin clearing pollutants in the Las Vegas Wash that could enter Southern Nevada's water supply six miles downstream in Lake Mead, Miller urged officials to test the waters constantly for selenium.

There are no federal or state standards for selenium, only water quality criteria proposed in 1988 by the U.S. Environmental Protection Agency, the EPA's Mike Schultz said.

No one has reported reproduction problems in water birds or deformed eggs at Lake Mead, unlike the selenium that killed thousands of birds at the Kesterson Wildlife Refuge in California during the 1980s, Miller said.

As for mercury, the heavy metal is known to affect mammal nervous systems. The mercury poisons both humans and wildlife, causing uncontrollable shaking described as "mad as a hatter" syndrome. Hatters used mercury in their trade and frequently showed the effects of being contaminated.

Mercury contamination in Japan during the 1960s wreaked havoc with human health.

While the Food and Drug Administration restricts saltwater fish to a level of 1 part per million of mercury -- comparable to a drop of water in the average swimming pool -- the metal doesn't appear to threaten Lake Mead's fish, James Cizdziel of the U.S. Environmental Protection Agency said.

Cizdziel invented a tool like a paper punch to extract a small sample of fish tissue, saving the rest of the body for further research. He tested muscle, liver and blood in five species of fish in the past year for mercury.

From the 339 fish sampled, Cizdziel discovered that healthy large-mouth bass, channel catfish and striped bass in the Las Vegas Bay had less mercury than those in other parts of the country. In fact, it was half the amount found in Great Lakes fish. That could mean the metal is being diluted, he said.

However, the larger the fish, the more mercury was found.

One catfish liver contained more mercury than any striped bass.

Tilapia, a new lake resident, eats vegetation, so is the safest fish to catch and eat, Cizdziel said.

Officials have never posted a warning against fishing in Lake Mead.