Selenium: an insidious and persistent toxin

Selenium, an essential nutrient for humans and animals, occurs as a trace element in most soils. Selenium can move into water systems when soil is disturbed by various types of development, or as a byproduct of fossil fuel combustion. When it occurs in higher than normal levels in water, selenium has been shown to cause malformations in fish and other aquatic wildlife.

In an article in the April issue of Aquatic Toxicology, a USDA Forest Service researcher warns that the impacts of selenium on freshwater fish populations may become more widespread as human disturbance increases -- and that long-term effects may be underestimated.

Dennis Lemly, Forest Service research biologist at the Southern Research Station, has spent the last two decades studying the fish in Belews Lake, North Carolina. Created in 1973 to provide cooling water for a large coal-fired power plant, the lake was contaminated by selenium in discharged wastewater.

"Belews Lake represents one of the most extensive and prolonged cases of selenium poisoning of freshwater fish in the United States," said Lemly. "It provides an excellent case study of the insidious and persistent toxicity of selenium to aquatic ecosystems."

As selenium accumulated in Belews Lake, the 20 resident species of fish started showing deformities to the spine, head, fins, and eyes. In 1986, the power plant stopped discharging wastewater into the lake. Natural recovery began, but long-term studies by Lemly and other researchers show that ill effects persist long after the source of pollution is gone.

"Selenium poisoning in fish can be invisible for a time," said Lemly, "because the primary impact is on the egg, which receives the toxin from the mother's diet. When the eggs are hatched, the developing fish metabolize the selenium. Some fish are visibly deformed, but others grow into adult fish that appear healthy yet fail to reproduce. Because there is no apparent fish kill, species can disappe

Contact: Zoe Hoyle
Southern Research Station - USDA Forest Service

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