Not too long ago, humans used a pesticide known as DDT in agriculture to control pests and maintain crops. They didn’t just use a little, they used loads and loads of it. It was hailed as a savior chemical that would eliminate many of the pests that plagued the farming industry. The chemical, which is highly hydrophobic, runs off in heavy rain into streams. It then makes its way into rivers, bays and eventually the ocean. It has a half life of anywhere from two to thirty years, depending on where it is located.
No one noticed any problems with the chemical runoff into bodies of water. It is not as highly toxic to fish and avian species as it is to insects. The problem is, it does biologically magnify. This means the highly hydrophobic DDT will get into the water and get absorbed by plankton. These tiny plankton make up the base of the food chain in many aquatic ecosystems. They in turn are eaten by tiny fish, who are eaten by larger fish and eventually the largest fish or water birds. Animals at each level will consume larger and larger amounts of the chemical as they consume more animals that have absorbed the chemical before them. In this way, the concentration of DDT will magnify as it works its way up the living food chain.
Then in 1962, a scientist named Rachel Carson published a book called Silent Spring. This book suggested that chemicals shouldn’t be added to environments without knowing what effect they would have on the inhabitants of the ecosystems. It turns out that Rachel Carson was correct, the animals that would be most impacted by this pesticide would be those at the top of food chains in marine or estuary ecosystems. The effects of this biological magnification would not be seen right away, but its effects will last far beyond the banning of DDT in the United States.
DDT has very specific properties. It is meant to block sodium channels in insects and will cause immediate death. In other animals, it has other effects. For water birds and birds of prey, the effects are still not entirely understood. It is believed that it may inhibit an enzyme called calcium ATPase that prevents calcium from going from the blood into the eggshell gland. This may be the mechanism by which the egg thickness is diminished.
In New Jersey, the osprey was so devastated that they became an endangered species. There is now a special sanctuary in the marine research preserve to help the osprey breed and become more plentiful. The birds had almost been erased from this area by the thinning of their eggs from DDT. The birds would have a clutch of three to four eggs, but none would hatch because they would be crushed by the nesting birds who were sitting on their eggs. Even as a result of the ban on DDT in 1972, it has still taken a long time for these birds to rebound.
