Laura Erickson's For the Birds

DDT Revisited

From earliest times, humans and birds have suffered from mosquito-borne illnesses. We think of malaria, yellow fever, encephalitis, and dengue as human diseases, but mosquito-borne disease organisms take a huge toll of birds, too. West Nile Virus has killed many orders of magnitude more birds than humans. In Hawaii and other oceanic islands where mosquitoes were introduced during historic times, native human and bird populations have been decimated, and some bird species rendered extinct, because of disease transmission by these blood-sucking pests. Malaria and other horrible diseases have taken a huge toll of human and bird lives, especially in tropical areas where mosquitoes flourish often despite decades of environmental pesticide use.

Many insecticides are known to have serious environmental effects, but the most famous, and perhaps the most controversial even today, is DDT, a persistent, broad-spectrum compound which was often termed the ‘miracle’ pesticide. DDT came into wide agricultural and commercial usage in this country in the late 1940s. During the nest 30 years, approximately 675,000 tons were applied domestically. The peak year for use in the United States was 1959 when nearly 80 million pounds were applied. From that high point, usage declined steadily to about 13 million pounds in 1971, most of it applied to cotton. DDT was also used in many areas to control gypsy moths and the bark beetles that spread Dutch elm disease, failed experiments that did little or nothing to stop or slow the spread of either.

DDT was banned after a long public debate about the role of toxic chemicals in the environment, one side articulated by Rachel Carson in her book, Silent Spring. But even after DDT was proven to have decimated Bald Eagles, Osprey and Brown Pelicans, and extirpated the Peregrine Falcon from eastern North America, destroying their ability to breed by thinning their eggshells, and after DDT killed outright thousands of robins and other songbirds (documented by Dr. George Wallace at Michigan State University and others), the chemical industry continued to deny the connection between outdoor applications of DDT and dead and disappearing birds. Many continue to insist that the DDT and DDE found in human mother’s milk was not at all a health risk to newborns. Of course, science has advanced since the 1960s. In 2001, scientists at the National Institute of Environmental Health Sciences, the National Institute of Child Health and Human Development, the University of North Carolina at Chapel Hill, and the Centers for Disease Control and Prevention found in a study published in The Lancet that elevated levels of DDT’s breakdown product, DDE, were found in the stored blood of mothers recorded as giving birth to premature or low birth weight infants in the 1960s. Pre-term births and low birth weight are major contributors to infant mortality.

Without question, DDT does not belong in the natural environment, where it kills birds and works its way up the food chain to enter our own tissues. But after researching a wide range of data and evidence, I’m starting to believe that DDT should be brought back into use, even in the United States. Of course, DDT should NEVER be applied outdoors, even where malaria is a scourge. Mosquito populations exposed to DDT or other pesticides in the outside environment build up resistances to the toxins much more quickly than do their natural predators, such as dragonflies, which have much longer life cycles and smaller, slower reproductive capabilities. Indeed, DDT’s use in the outdoor environment, for agriculture and other uses, is blamed for the resistance mosquitoes have built up against it, rendering the pesticide ineffective against dangerous malaria vectors in West Africa, Iran, Pakistan, India, Sri Lanka, Greece, Egypt, Central America, and Columbia. But DDT can be useful when applied indoors, on house walls, where it seriously reduces malaria rates for humans. Tomorrow I’ll explain how DDT could be one part of a disease-control program if regulated not by the Department of Agriculture and the EPA but by the Centers for Disease Control and other health agencies, for strict indoor use.