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Selenium: A Necessity of Life,
But Not Too Much or Too Little

By Gary Polakovic
The Press-Enterprise

Selenium can be a most unforgiving element.

In the human body, too little makes muscles flaccid, causes infertility and can harm offspring. Too much can result in hair loss, skin lesions, paralysis and monstrous deformities.

The line separating the two is razor thin.

"Selenium has the narrowest band of any toxic chemical between what's safe and what's toxic," said Joseph Skorupa, biologist for the U.S. Fish and Wildlife Service.

Selenium is a micronutrient. People, wild animals and livestock need it in infinitesimally small does to maintain normal body functions.

Steven Sedam-Stone/The Press Enterprise

The U.S. Food and drug Administration se the recommended daily allowance for selenium at 70 micrograms (a microgram is one millionth of one gram) for men and 55 micrograms for women.

In keeping with its schizophrenic nature, the substance becomes toxic for humans at 1,000 micrograms a day. Severe toxicity is believed to occur at about 3,000 micrograms, said Anna Fan, a toxicologist for the California Environmental Protection Agency and a leading authority on selenium poisoning.

One of the worst cases of selenium poisoning occurred in the Humbei Province of China during the 1960s. Residents of three villages routinely ate plants containing 3,000-5,000 micrograms of selenium. They developed brown splotches on their bodies, their fingernails fell out and some suffered sever damage to their central nervous system, Fan said.

Selenium is used to make glass, semiconductors, photovoltaic cells, antifungicide agents, glass and pater. Some power plants emit it.

In nature, it is found in seafood, cereal grains, garlic and certain mushrooms. But more commonly it is imbedded in sedimentary rocks and marine shale deposits laid down by ancient seas that covered the West thousands of years ago.

Irrigation washes it out of the soil and concentrates it in amounts that are deadly to wildlife.

The U.S. Environmental Protection Agency considers selenium so toxic that it says more than 5 parts per billion in water is a threat to aquatic life -- 38 times more stringent than the standard for arsenic.

Through scientifically it belongs to a class of substances called metalloids, selenium has sulfur-like properties that make it especially destructive in the environment.

Selenium replaces sulfur in amino acids, which are the building blocks for protein molecules. Because egg and sperm cells are made up mostly of proteins, selenium scrambles genetic signals in developing embryos "and the whole system goes haywire," Skorupa explained. Birds are more sensitive than mammals.

Hence, chicks with no beaks, eyeballs or feet have been found at selenium-ridden wildlife refuges in California.

Selenium toxicity is especially prevalent in livestock in the northern Plains states. The substance is found in alfalfa and range land weeds.

Selenium poisoning killed U.S. cavalry horses as they crossed the plains in the late 19th century. Accounts of Marco Polo's exploits in Tibet in 1295 mention illness in horses that some experts say was probably selenium poisoning.

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