Why Do Fish Near Coal Plants Have Lower Levels of Mercury?

coal fired power plant photo

Image credit: thewritingzone/Flickr

It makes sense that fish inhabiting waters adjacent to coal-fired power plants would have higher concentrations of bioaccumulating pollutants—most notably, mercury—than those living farther away.

Coal plants are the leading source of mercury pollutants in the air—and most of these pollutants were thought to fall to the ground within 10 kilometers of the plant. A new study, however, has found that fish 30 kilometers from coal plants have higher concentrations of mercury than those only 10 kilometers from the plant. The question is: Why?

large mouth bass photo

The study looked at largemouth bass, a popular sport fish. Image credit: El Frito/Flickr

By analyzing largemouth bass in two different lakes, researchers found that the presence of another compound—selenium—in the lake closest to the power plants was responsible for the unexpected inconsistency.

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Selenium is antagonistic to mercury, meaning that it's high concentration in the lakes 10 kilometers from the power plants pushed the mercury from the fish there. The exact mechanism is not completely understood, but the study showed that selenium and mercury have an inverse relationship in the ecosystem.

Of course, finding lower levels of mercury is a good thing, but the presence of selenium in such concentration—three times the amount found in lakes farther away—is itself a hazard. Such high concentrations are capable of poisoning fish and the animals that consume them.

Still, "this information," as Dana Sackett, lead author of the study, explained, "will inform health and wildlife officials who make determinations about fish consumption advisories and wildlife management decisions."

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Read more about mercury:
Global Warming Not the Only Thing Threatening Polar Bears
The Largest Source of Wastewater Mercury Pollution: Dentists
Permafrost Melting Releases Mercury Into Swedish Lake

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