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updated 8/27/2010 3:59:07 PM ET 2010-08-27T19:59:07

Ever since the banning of the pesticide DDT, which weakened eggshells, bald eagles have been making a comeback in the Great Lakes region.

In Michigan, however, that recovery has been lackluster, and researchers have found one potential reason why: flame retardants and pesticides in the blood of eagle nestlings.

"(Eagles) have recovered mostly, but not to what was expected," said Marta Venier of Indiana University. Venier is the lead author of a paper in the August issue of the journal Chemosphere, which describes a "snapshot" of what is in eagle nestlings' blood in near lakes around Michigan.

Venier and her colleagues were able to collect blood samples of bald eagle nestlings in the Great Lakes region by arduously climbing trees, bagging the large nestlings and carrying them carefully to the ground to draw a small sample of blood. The birds were then returned to their nests angry, but unharmed.

Tests on the blood show that the national symbol of the United States is ingesting flame retardants and pesticides via its food. The chemicals are originally from pesticides or foam padding for furniture and mattresses, which contain a variety of flame retardants.

"Eagles are very vulnerable to chlorinated compounds," said Ronald Hites, also of Indiana University and a co-author of the study. Flame retardants can make up 10 percent of the weight of foam padding, Hites told Discovery News. Because the chemicals spew out every time we sit or lie down on the padding, the same chemicals are also found abundantly in humans, he said.

Discarded furniture in landfills moves the flame retardants into runoff, soil and the air, Hites said. These sources last for decades and make their way to such animals as bald eagles. It's not known if the chemicals are having health effects on the eagles. But they are a suspect, as is habitat loss, in the slowed eagle recovery.

The eagle nestling discovery has broader implications about the way chemicals are produced and used in the United States, said Linda Birnbaum, director of the National Institute of Environmental Health Sciences.

"We shouldn't be making chemicals that don't go away for a long time," Birnbaum told Discovery News. And we should not replace newly banned chemicals with potentially even more dangerous untested chemicals, she said. "There is very little information on their toxicity. It's a problem with our regulatory system."

Some of the substitutes for polyurethane foam, for instance, are now found in human blood and urine. Are they a health threat? Nobody knows.

There is legislation in Congress which would change this, said Birnbaum, if it ever becomes law. In the meantime the bald eagle nestlings should be a matter of concern.

"Just because you don't know anything (about a chemical) doesn't mean you're safe," Birnbaum said.

© 2012 Discovery Channel

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