Great Salt Lake cleans itself of natural pollutant

Published June 29, 2009 6:55 am
Environment » The lake breathes out much of the toxic selenium.
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The mineral selenium is changing the notion that the Great Salt Lake is nothing more than a giant puddle.

Yes, some selenium from the runoff that flows into the lake turns it into a depository for waste from the four streams that feed it, like a massive puddle.

But the lake also exhales selenium.

This pour-in-breathe-out cycle, detailed in recent science reports, helps explain how the Great Salt Lake remains healthy for birds, even when it takes in massive quantities of selenium each year.

"We had no idea how the lake regulates selenium," said Bill Johnson, a University of Utah geologist. "Within the uncertainties, there's basically a balance."

Both Johnson and David Naftz, of the U.S. Geological Survey, have studied the lake extensively and have published their surprising findings over the past year. Their findings, they agree, raise many new questions.

Poisonous in large amounts

In the 1980s, selenium contamination at the Kesterson Reservoir in California led to a die-off in birds and deformities and death in livestock.

The mineral is necessary for life, but only in small amounts. Too much selenium is poisonous, causing bird-egg shells to weaken, developing chicks to deform and embryonic birds to become crippled.

Kesterson was declared a toxic waste site in 1987 and later covered over with soil.

Like Kesterson, the Great Salt Lake has no outlets, with selenium leaching from the ground naturally into streams and selenium concentrated in industrial discharges. So, it was logical for scientists to ask if the Great Salt Lake posed the same risk.

Through their research, Naftz and Johnson and their colleagues have learned that the selenium undergoes a chemical transformation in the salty water that allows the surface air to carry it away.

The studies also showed that four streams -- Lee Creek, the Bear River, the Weber and the Farmington Bay outflow --- account for about half of the selenium coming into the lake. Another 24 percent comes from a Kennecott Utah Copper drain.

So far, there's no evidence that selenium is concentrated enough to poison the food and shelter the lake provides to as many as 12 million birds using it as a home or rest stop on their international migration route.

"What we are finding," said Naftz, "is the lake is OK right now."

More study needed

Some of the recent studies suggest more questions.

For instance, the scientists saw selenium increase rapidly, doubling in the water column over 18 months. Is this a long-term trend or just part of a bigger cycle? Naftz and Johnson hope that continued monitoring will answer that over time.

Another oddity is the mystery source that's pumping as much as 1.6 tons of selenium into the lake a year. The U.S. Geological Survey and University of Utah geologists have been awarded additional funding from the state Division of Forestry, Fire and State Lands to study the source of this plume.

"There is something else going into the system," said Johnson, "that we did not catch" in the initial study. That puzzle warrants further research.

The research already has had a practical impact. It helped the Utah Division of Water Quality set its first water-quality standard for the Great Salt Lake, a limit on selenium in mallard eggs that is supposed to be representative of how selenium is affecting all birds that rely on the lake. The U.S. Fish and Wildlife Service has challenged the regulation because it allows for some birds to die, birds that are protected under the Migratory Bird Treaty Act.

Kennecott Utah Copper's discharge permit is up for renewal based on the new loading limits, said water quality Director Walt Baker. Under this new permit, the company would be allowed to put more than three times as much selenium in the lake than its current permit allows. In addition, the company will monitor the number of birds in certain areas, as well as the selenium content in bird eggs.

The state is hoping to fund up to four additional studies: to look at selenium in the food chain, to look at bio-organisms in lake-floor cores, to understand how selenium moves around in the lake and to come up with a master plan for future studies.

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More on selenium:

The Great Salt Lake contains between 5.5 and 8 tons of selenium at any given time and cycles through the lake every three to five years.

About 3,439 pounds come from streams and canals each year.

Between 628 and 2,123 pounds of selenium wind up in sediments annually, 61 pounds are removed from the lake as brine shrimp is harvested, 55 are stirred back up into the water column.

From 2,138 and 4,806 pounds are exhaled into the air after being chemically transformed in the salty water.

The recommended daily allowance of selenium in the diet is 70 micrograms -- slightly more than a grain of table salt.

But consuming more than 400 micrograms of selenium a day over time -- equal roughly seven grains of salt -- can be poisonous, causing hair loss, muscle cramps, nausea, vomiting, diarrhea, joint pain, fatigue, fingernail changes and blistering skin.

Source: U.S. Geological Society



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