QUESTIONING THE EFFECTS OF DDT
Mr. Katz’s column on malaria and DDT (November) suggests a lack of understanding about the resurgence of malaria and the environmental effects of DDT. Malaria resurgence is a complex issue that has multiple causes, including pesticide resistance of mosquitoes, increasingly drug-resistant malaria, and habitat changes. Those of us who read the science journals of the ‘70s will recall that DDT had many serious environmental effects on raptorial birds. Among our great predatory birds, particularly hawks and eagles, bio-accumulation of DDT in the food chain led to reduced fertility, egg shell thinning and poor survival of nestlings. While PCBs may account for some of the early findings of DDT in widely scattered locations, later definitive studies make it clear that DDT was identified by its breakdown products, DDD and DDE, as well as the parent compound. In the United States, we certainly have many options for controlling malaria that do not require the return of DDT. On a global basis, the implication that the continued use of DDT would have prevented the resurgence of malaria is rebutted by the fact that resistance to DDT was so widespread that its efficacy was already marginal before its decline. DDT is still produced abroad, and those countries that still use it have had not only malaria resurgence, but serious declines in their few remaining raptorial bird species.
Jack B. Gingrich, Ph.D.
Silver Spring, Md.
HARRY KATZ RESPONDS
In response to Jack Gingrich’s letter, please note these references.
In Mosquito News, June 1972, Dr. A.J. Andrews cited a paper from the Journal of Ecology, 1921: “The bald eagle was fast becoming a rare bird in the U.S.” In Science News letter July 43: “Before the widespread use of DDT, decline of eagle population was attributed to wholesale cutting of trees with nesting sites, pollution of streams with sewage and industrial waste (and power lines).” Of 147 eagles found dead in the United States and then examined, only one death was attributed to DDT. The other eagles had been shot or were diseased.
Before 1951, Alaska paid bounties on 100,000 eagles over a 36-year period because they fed on salmon. Before the practice was banned in 1962, 20,000 eagles were shot from small planes for predator control.
The charge of reproductive failures was based primarily on studies in which various bird species were fed gross amounts of pesticide daily for long periods (at just slightly less than the toxic dose). Another factor: since 1872, far more eggs were collected by ornithologists and bird protectionists than were needed for scientific study. Biologist Dr. Gordon Edwards blames, in part, scientific persecution for the decline of California brown pelicans during the 1970 breeding season. In 1971, the National Park Service banned the use of helicopters by scientists because the stress caused thin eggshells and nest desertion.
There are no valid scientific tests which show that DDT, DDD or DDE cause cancer, or that traces affect the environment negatively.
Even the Mrak report which helped doom DDT to extinction admitted, on page 437, that there is reasonable doubt that chlorinated hydrocarbon pesticides found in natural bird food had levels high enough to adversely affect reproduction.
It is true, as Dr. Gingrich claims, that resistance would have diminished the value of DDT for mosquito control. However, we must remember that before World War II, many more soldiers died from mosquitoes and lice than from bullets. The real loss is the demise of chlordane which followed the banning of DDT for the same political (and not scientific) reasons. Termiticides are now far more costly and less persistent than chlordane. Our society is suffering from the “one-in-a-million” obsession of the EPA ruling: cancel the registration if one person in a million could get cancer after 70 years of exposure. However, there is no question that the environment would suffer if excessive dosages are applied, as they were before Silent Spring.
Readers with comments are invited to write: PCT Letters, 4012 Bridge Ave., Cleveland OH 44113. Letters also can be faxed to 216/961-0364, or e-mailed to ljosof@gie.net. Letters may be edited for space or clarity.
Readers are invited to write: PCT Letters, 4012 Bridge Ave., Cleveland OH 44113.
 
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