Researchers say the level of the chemical PFOS in eagles on the Mississippi River is declining.
PFOS, short for perfluorooctane sulfonate, was manufactured by 3M for stain and water-resistant products at a plant on the river until 2002.
The National Park Service first tested eagles for the chemical in 2006. Eagles on the Mississippi River had the highest levels reported anywhere in the world. But a year later, those levels had dropped by more than half.
"If this trend continues I guess it's a hopeful thing, that we've found a contaminant that is very persistent but took it off the market and hopefully it'll decline sufficient to be safe," said ecologist Bill Route, who is working on the project.
Scientists are concerned because PFOS and related compounds stay in the environment long enough to build up, or bio-accumulate, as they move up the food chain.
Some studies have found human health effects, such as low birth weights. But Route says so far his research has not shown health effects on eagles.