DDT-Curse or Blessing? The general public first became acutely aware of the impact of human activity on ecology, the study of the interrelationships between plants and animals that live in a particular physical environment, through the book The Silent Spring. Rachel Carson, a marine biologist who worked for the US. Fish and Wildlife Service, wrote The Silent Spring to document the effects of DDT on ecosystems, short for ecological systems. DDT (dichlorodiphenyltrichloroethane) was first used as a pesticide by the Allied troops during World War Il to eradicate typhus-and malaria-causing insects in the South Pacific islands. Unlike many pesticides that are effective at controlling a few species of insects, DDT was the "miracle compound" because it was able to exterminate hundreds of different species of insects. After World War I, its use continued on farms to control agricultural pests, in communities to control mosquitoes, and in the tropics to control malaria and yellow fever. Rachel Carson became aware of the effects of DDT in 1958 when a friend wrote to her about the massive bird kills that resulted on Cape Cod after the land had been sprayed with DDT. For 4 years she investigated the effects of DDT and discovered that significant reductions in the populations of large birds of prey, such as the osprey, per- egrine falcon, and bald eagle, had occurred. Carson wrote, "DDT and other pesticides had irrevocably harmed birds and animals and had contaminated the entire world food supply (Natural Resources Defense Council, 1997). In the years after the book was published, extensive research on the ecological effects of DDT was accomplished. It was discovered that the reductions in bird populations were the result of a failure of the birds to reproduce. DDT degrades into another chemi- cal (DDE), which affects the reproductive hormones causing the thinning of the egg shells. Bats, aquatic invertebrates, and most fish were found to be especially sensitive to DDT. While terrestrial invertebrates are generally not killed by DDT, the chemical accumulates in their tissues. Given the effects of DDT on individual organisms, one can easily envision that effects of DDT on an ecosystem would be significant. As animals eat the terrestrial inverte- brates that have accumulated DDT in their tissues, the chemicals are passed up the food chain. As the numbers of bats, eagles, and falcons decrease, the numbers of their prey, namely insects and rodents, increase. As the small fish, which were found to be especially sensitive to DDT, succumb to its effects, the food supply for larger fish and fish-eating mammals and birds also diminishes, resulting in declines in their popu- lation. By the late 1960s the effects of DDT became well known and in 1970, DDT was banned in Sweden. In 1972, DDT was banned in the United States. In the years since, it is clear that the ecosystems are slowly recovering. For example, in 1963, no bald eagles nested within the state of Illinois (Rubin, 1997). In 1996, there were 20 breeding pairs. The peregrine falcon was considered extinct in New York in the 1970s. In 1996, there were 32 breeding pairs. Unfortunately, the ban of DDT is not without some det- rimental effects. During the 1960s when DDT use was at its greatest, the number of cases of malaria in Sri Lanka was essentially zero. In Sri Lanka, house spraying of DDT