The Nice Myth: Bald eagles are recovering on Catalina because DDT is gone from the environment.
The Filthy Truth: Actually, DDT (or more correctly it’s byproduct: DDE), will be with us for a very long time to come.
What’s actually happened is that DDT/DDE has broken down enough that the more severe effects that caused reproductive issues in years past are fading. It’s likely that DDE is still causing harm in the environment, but the impacts are now low enough that natural reproduction for bald eagles is possible. The rate of persistence of chemicals like DDT in the environment is often measured in terms of half-lives. A half-life is the amount of time it takes for a chemical to break down by 50 percent. Based on a reasonable estimate of a 15-year half-life -- beginning with 100 kilograms of DDT -- it would break down as follows:
|
Year |
Amount Remaining |
|
0 |
100 kg |
|
15 |
50 kg |
|
30 |
25 kg |
|
45 |
12.5 kg |
|
60 |
6.25 kg |
|
75 |
3.13 kg |
|
90 |
1.56 kg |
|
105 |
0.78 kg |
|
120 |
0.39 kg |
Source: http://www.marietta.edu/~biol/102/2bioma95.html
As you can see, after 40 years, it’s not gone…it’s just present at a lower concentration.
When isn’t an “eagle” an eagle? Read Grand Ole Osprey
