Bald eagles are an indicator of environmental health. Eagles dominate local food chains along rivers and lakes. As top predators they retain the highest, most damaging concentration of environmental contaminates. After DDT was banned in the 1970s, many scientists expected eagle populations to make a quick comeback, yet that has not always been the case.
Researchers have been looking at the inability of eagles to prosper in Michigan and along the Mississippi River. They collected blood from four to nine week old nesting bald eagles. Results show that these eagles have high levels of many chemicals in their blood, including DDT, PCBs, PFCs and BFRs.
Researchers looked for DDT and PCBs, chemicals that were banned in the 1970s. These chemicals are known as legacy contaminants due to their long history of harming eagles. They also looked at emerging contaminants including perfluorinated compounds (PFCs) and brominated flame retardants (BFRs). These recently introduced chemicals are found to be widely distributed in the environment, detectable in the blood of wildlife and humans, and their overall health effects are unknown. These chemicals persist within the environment and the organisms that reside there, taking many years to disappear. Due to their persistence, they bioaccumulate in the food chain from prey to predator.
It is not yet known what effect BFRs and PFCs are having on the health of eagles. Certain BFRs are persistent environmental contaminants and accumulate in sediment and animal tissues. These chemicals are also found abundantly in humans. They can disrupt thyroid hormone action and impair neurodevelopment. Recent evidence show that levels of BFRs known as PBDEs in breast milk in North America are as much as 50 times higher than in Europe, increasing from <1 ppb to 200 ppb in the last 25 years.
This study shows a lack of testing on the production and usage of chemicals in the United States. Many chemicals now produced have a very long half-life. And we often replace banned chemicals with untested chemicals that can be just as toxic as or even more toxic than the chemicals they are replacing.
While many bald eagle populations are flourishing, they have only recently been taken off the endangered list. More research needs to be done to determine the long-term persistence of these chemicals and their effects on eagle health and human health.
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