In my science class today, we were talking about how the pesticide DDT ran off lawns into water sources, polluted the water an infected the fish, which were eaten by the eagles, causing them to lay soft-shelled eggs and have decreased reproduction rates.

I have a two part question. First off, how does the DDT cause soft-shelled eggs? I'm big into poultry, so I know how important calcium is in order to lay eggs, since the shell is made of calcium carbonate. So, is there some chemical or substance in DDT that prevents the body from absorbing calcium properly?

Second, how come only eagles were affected? I mean, ospreys and kingfishers along with other birds eat fish as well, but they didn't a huge impact on their population like eagles did. Why is that?

DDT and its metabolite DDE alter hormones, that affect calcium metabolism and can impact reproduction and development of exposed animals. Birds were major victims of the chemicals' effects. They experience reproductive failure as their eggs lacked sufficient calcium, were extremely thin, and shells broke when sat upon by the nesting adult birds. DDT and its metabolites accumulated to the greatest extent in raptors (that is, carnivorous birds that hunt and kill other animals), birds that eat carrion (that is, dead animals) and fish-eating birds. There were drastic declines in populations of these birds that feed at the tops of food chains. Many carnivorous birds (for example, bald eagles, ospreys, and pelicans) were on the brink of extinction before action was taken at the federal level to ban the use of DDT—and eventually other chlorinated hydrocarbons.

and … Birds.html

To add, DTT and a number of its metabolites also act as ‘xenoestrogens’ or ‘endocrine disrupters’ that mimics endogenous estrogen by binding to the classical estrogen receptors (alpha and beta) and estrogen-related receptors.