DDT

Which scientist to be trusted? Debate goes on…

By William Shao

SOME studies indicate that the insecticide DDT was—and is—one a chief contributor to some potential ecological disaster. Because of the danger it poses, its uses, and then its production, DDT was banned from one country to another. But Ugandan scientists say it has no effects on the environment and human health.
A Makerere University report released last Wednesday has said that the use of DDT (dichloro-diphenyl-trichloroethane) in fighting malaria has no effect on the environment and human health. Dr Gabriel Bimenya, a University lecturer in the Faculty of Medicine, represented these findings to scientists, policy makers and academicians.
The report said: “Spraying DDT does not create impotence, infertility, and abnormalities especially among women as it was recently alleged by antagonists and environmentalists.”
According to The African newspaper (Nov. 7, 2005), the research team included Professor Wilson Byarugaba, Dr Baterana Byarugaba, Andrew Okwii (all of Medical School) and Dr Myers Lugemwa of Mulango Hospital. Should they be believed?
From historical point of view, DDT, a colorless chemical pesticide, was used to eradicate disease-carrying and crop-eating insects. It was first isolated in Germany in 1874, but not until 1939 did the Swiss Nobel Prize-winning chemist Paul Müller recognize it as a potent nerve poison on insects.
First used heavily in World War II for pre-invasion spraying, DDT was disseminated in great quantities thereafter throughout the world to combat yellow fever, typhus, elephantiasis, and other insect-vectored diseases.
In India, DDT reduced malaria from 75 million cases to fewer than 5 million cases in a decade. Crops and livestock sprayed with DDT sometimes as much as doubled their yields.
With the publication of the American marine biologist Rachel Carson's Silent Spring in 1962, suspicion grew that DDT, by entering the food chain and eventually concentrating in higher animals, caused reproductive dysfunctions, such as thin eggshells in some birds.
Some insect pests also gradually developed DDT-resistant strains whose populations grew unchecked while their natural predators, such as wasps, were being eradicated by spraying. In 1973 DDT was banned in the U.S. except for use in extreme health emergencies. Many other nations have also banned it or placed it under strict control.
Should it now be used? Has its dangerous effect disappeared, or at least diminished? If the scientists who found it harmful years ago were right, then those reports their findings now that it is safe are wrong, and vice versa.
It caused an alarm when it was known that some of the long-lasting pesticides such as DDT were finding their way into humans. Newsweek of January 26, 1970, stated: “American women carry in their breasts milk that has anywhere from three to ten times more of the pesticide DDT than the Federal government allows in dairy milk meant for human consumption.”
Thus, even government officials and scientists were worried. Dr. Charles F. Wurster, biologist at the State University of New York, quoted by the magazine, said: “The danger is no longer debatable; it’s established, scientific fact.” Another scientist who examined the evidence remarked: “I’m scared.”
In 1974, Dr Lorenzo Tomatis of the International Agency for Research on Cancer in France stated: “There is no animal, no water, no soil on this earth which at present is not contaminated with DDT.” In some cases DDT contamination had built up in animals and birds to the point of killing them. Were his findings wrong? If yes, then Dr Gabriel Bimenya and his colleagues are right.
In 1971, Health, Education and Welfare Secretary Robert H. Finch of the United States was worried that If the pesticide DDT were outlawed tomorrow, “…it would take 10 years or longer” to cleanse the nation of effects already caused by the insect killer.”
Early in 1960s, DDT and other pesticides were at first heralded as ‘saviors,’ freeing man from dreaded diseases such as malaria and yellow fever. These pesticides also initially tended to increase crop yields by destroying insects. But in 1970s many governments decided to phase out the use of some of these chemicals. Why?
Because it has been found that they are destroying much animal life, some species being pushed toward extinction. Contamination from DDT has spread earth wide. Traces have been found even in Antarctic animals. Indeed, it has been said that there is no water or land, or life of any kind that has not been affected by DDT. This includes man. And in experiments, heavy doses of pesticides caused serious damage to animals.
These bad effects of what was thought to be for man’s benefit have alarmed authorities. What then can be said of scientific inventions that are deliberately designed to exterminate human life?
Chemicals for warfare have been developed that are so lethal that only a tiny droplet on the skin will cause death. And some of the bacteria that science has cultivated can annihilate entire populations.
Medical World News of February 27, 1970, reported on an experiment where twenty-five fertilized eggs were injected with small amounts of a chemical defoliant widely used in the United States (and in Vietnam). Only fifteen chicks survived. Eleven of the fifteen were crippled and had other defects. In the unhatched chicks serious disorders and deformities were found.
What makes the problem grave is that DDT, and some other pesticides, are not soluble in water. So they accumulate in the organisms that are exposed to them. In time the animal may contain far more pesticide residues in its system than are in the environment. Indeed, it is said that some animals may contain more than a million times as much as their environment!
Pesticides have disturbed what is called “the balance of nature.” An example of this was reported by Dr. Lamont C. Cole of Cornell University, as noted by U.S. News & World Report of November 24, 1969:
“The World Health Organization sent DDT to Borneo to kill mosquitoes. It worked fine. But it didn’t kill roaches, which accumulated DDT in their bodies. Lizards, which lived in the thatched huts, ate the roaches.
“The DDT slowed the lizards. Cats then easily caught the lizards. But the cats died …With the cats gone, rats came, carrying a threat of plague. And, with the lizards gone, caterpillars multiplied in the huts, where they fed on the roof thatching. Then the roofs started caving in.”
What is ironic is that while pesticides have killed insects, these same types of insects have produced strains that are resistant to those pesticides. Thus, more powerful poisons are needed to kill them. But it is said that there is no pesticide that insects cannot eventually handle.
The Makerere scientists do not deny the danger the DDT poses, but the danger, they say, is only at “low levels.” Whether they are right or wrong is not the point I am trying to make. But how and why these scientists contradicts themselves leaves the world intricately puzzled. Which scientists should we trust or not to trust?
“DDT, a pesticide which has been banned in Europe and the US for nearly 30 years, is likely to escape worldwide prohibition because of its effectiveness in eliminating the mosquitoes responsible for one of the world’s biggest killers—malaria,” reported the magazine BBC Wildlife recently.
“Though DDT is a highly toxic compound proven to have a negative impact on wildlife, health campaigners say it is still one of the most important weapons against malaria, a disease which kills more than 2.7 million people a year and leaves up to 500 million chronically ill.”
While supporting a ban on DDT for agricultural purposes, the World Health Organization argues that it should be used for malaria control until a safe and effective alternative can be developed.

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