“Egg Test Results”
The eggs that were removed from the nest last year were sent to the lab at the Virginia Institute of Marine Sciences for analysis of potential contaminants. It is important to note that there was no indication of any contamination in these eggs. This test was performed as part of an ongoing effort to assess the presence of contaminants in the environment and their possible effects on birds such as bald eagles.
The tests revealed that the levels of both PCB and DDE were well within acceptable toxicity levels for bald eagles. DDE is a product of the breakdown of the pesticide DDT. DDE persists in the environment for longer then DDT and can have similar effects on the eggs of birds exposed to high levels.
DDT was a commonly used agricultural pesticide and was responsible for crashes in the populations of many predatory birds, as it caused eggshell thinning and failures of nesting attempts. PCB is a chemical that had a wide variety of industrial usages. It entered the environment through improper disposal and leakages. PCB is highly toxic and can have a variety of effects on wildlife. DDT was largely banned in the United States in 1972. PCB production was banned in 1977 although some use continues in enclosed electrical equipment.
Both DDE and PCB persist in the environment and are especially problematic in aquatic ecosystems. The enter the food chain when consumed by micro-organisms and small invertebrates. These are eaten by larger animals as the contamination moves up the food chain, eventually accumulating in top level predators like bald eagles. At each stage of the food chain these chemicals become increasingly concentrated in a process called biomagnification.
Populations of both bald eagles and other fish eating birds like osprey have rebounded since DDT was banned, although in areas of high concentration lingering effects remain.