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Since DDT's effects are so severe in nature, many scientists think that it will inevitably exact a toll of man. The National Cancer Institute in Bethesda, Md., has produced evidence incriminating DDT and related pesticides as the cause of tumors of the liver and lungs in mice. When men are consistently exposed to such chemicals, adds the University of Colorado's Dr. David R. Metcalf, there is deterioration of memory and reaction time.
Impaired Effectiveness. The pesticide's defenders consider the dangers vastly exaggerated, although DDT poisoning can cause tremors and convulsion in man. "There isn't anything that doesn't have some toxic effect," insists Vanderbilt University Toxicologist Wayland J. Hayes, a former Public Health Service official and DDT's stoutest supporter. "The toxic effect of mashed potatoes," he adds rather irrelevantly, "is obesity." As proof of DDT's innocence, Hayes and others often point to studies of workers at the Montrose Chemical Corp., the world's largest DDT producer, and federal prisoners who voluntarily accepted daily doses of DDT in Atlanta. In both cases, they say, there was no damage. But other scientists, including Stanford Molecular Biologist Joshua Lederberg, a Nobel laureate, explain that far too little is known about how DDT reacts with other body chemicals to acquit the pesticide so readily.
In spite of its defenders, the use of DDT has already declined sharply. In 1962, when Rachel Carson published Silent Spring, the U.S. produced 167 million Ibs. Last year production slipped to 138 million Ibs., nearly 80% of which was exported. Not only has adverse publicity curtailed the chemical's use; its efficiency has been impaired by the resistance developed by many strains of insects. One scientist estimates that 150 pests formerly controlled by DDT are now immune to it. Nor do scientists expect to produce a new all-purpose bug killer. Instead they are emphasizing more subtle and selective methods of pest control—among them, the breeding of new insect-resistant crops, trapping pests with light and sound, and eliminating insects through sterilization. None of these methods pose anything like the dangers of DDT. The problem is that neither do they promise anything like its effectiveness.
-The others: dieldrin, aldrin, endrin, heptachlor, chlordane and lindane. They are
also sometimes called chlorinated hydrocarbons.