DDT is an organochlorine insecticide which is a colorless, crystalline solid, tasteless and almost odorless chemical compound.
Formula: C14H9Cl5
IUPAC ID: 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane
Boiling point: 500°F (260°C)
Molar mass: 354.49 g/mol
Melting point: 227.3°F (108.5°C)
Density: 990.00 kg/m³
Recognized as an insecticide by the Swiss scientist Paul Hermann Muller, DDT helped 1 billion people live malaria-free for thirty years after its discovery, thus saving millions of lives. But, according to a study in Environmental Health Perspectives, its “stability, ubiquitous presence, and persistence in the environment, its accumulation in adipose tissues, and its estrogenic properties” make its long-term effects on both humans and wildlife disastrous. The discovery of its toxicity to birds by biologist Rachel Carson in her book Silent Spring led to the banning of DDT in 1972. The book also gave birth to the modern environmental movement.
THE World Health Organisation, Greenpeace, the World Wildlife Fund, the UN environmental programme and its development programme, USAID, and almost all the other international representatives of the great and the good now campaign against DDT. DDT was introduced as an insecticide during the 1940s. In Churchill’s words: “The excellent DDT powder has been found to yield astonishing results against insects of all kinds, from lice to mosquitoes.”
And astonishing they were. DDT was particularly effective against the anopheles mosquito, which is the carrier of malaria, and people once hoped that DDT would eradicate malaria worldwide. Consider Sri Lanka. In 1946, it had three million cases, but the introduction of DDT reduced the numbers, by 1964, to only 29. In India, the numbers of malaria cases fell from 75 million to around 50,000.
Worldwide, malaria has returned with a vengeance, accounting annually for 300 million cases and, sadly, one million deaths, mainly of children.
Other chemicals are available, but they are generally less effective, shorter-acting and – most importantly for the Third World – more expensive. Health effects of DDT exposure are much more contentious than the environmental effects. Carson’s study relied heavily on the carcinogenic effects of DDT but to this day they remain highly speculative. A group convened by the International Agency for Research on Cancer concluded in 1991 that prior studies are inadequate evidence for carcinogenicity in humans. Reports since have focused on DDT’s effect on liver and pancreatic Cancer but have yet to conclusively prove its carcinogenic effects.
DDT is extraordinarily safe for humans. Prof Kenneth Mellanby lectured on it for more than 40 years, and during each lecture he would eat a pinch.
The destruction that Carson described was caused by the agricultural use of DDT as a mass insecticide in vast quantities on crops. But the discriminating application of DDT indoors involves only a tiny, contained, environmentally tolerable, reversible fraction of the dose. That is why some international health (as opposed to environmental) agencies, including Unicef, still support the judicious use of DTT.
“Fraud in science is a major problem.” So begins “DDT: A Case Study in Scientific Fraud” by the late J. Gordon Edwards, Professor Emeritus of Entomology at San Jose State University in San Jose, California. His publications distinguish Edwards as the leading authority on the environmental science and politics of DDT.
In World War I, prior to the discovery of the insecticidal potential of DDT, typhus killed more servicemen than bullets. In World War II, typhus was no problem. The world has marveled at the effectiveness of DDT in fighting malaria, yellow fever, dengue, sleeping sickness, plague, encephalitis, West Nile Virus, and other diseases transmitted by mosquitoes, fleas, and lice.
THE FIRST CHARGE AGAINST DDT was that it causes cancer.
“This is nonsense,” commented pesticide specialists Bruce N. Ames and Thomas H. Jukes of the University of California at Berkeley. (Ames is a professor of biochemistry and molecular biology, world renowned. Jukes, who died a few years ago, was a professor of biophysics and a leader in the defense of DDT.) “Every chemical is dangerous if the concentration is too high. Moreover, 99.9 percent of the chemicals humans ingest are natural… produced by plants to kill off predators,” Ames and Jukes wrote in Reason in 1993.
“Rachel Carson set the style for environmentalism. Exaggeration and omission of pertinent contradictory evidence are acceptable for the holy cause,” wrote Professors Ames and Jukes.
Workers without wearing protective clothing, with nine to 19 years of continuous exposure to DDT in the Montrose Chemical Company which manufactured DDT, never developed a single case of cancer. DDT caused no illness in the 130,000 men who sprayed it on the interior walls of mud and thatched huts, nor the millions of people who lived in them. Professor Edwards in his classroom occasionally ate a tablespoon of DDT to illustrate to his students that it is not harmful. Indeed, DDT is so safe that canned baby food was permitted to contain five parts per million.
“There has never been any convincing evidence that DDT (or pesticide residues in food) has ever caused cancer in man,” concluded Ames and Jukes.
In fact, DDT prevents cancer. “DDT in the diet has repeatedly been shown to enhance the production of hepatic enzymes in mammals and birds. Those enzymes inhibit tumors and cancers in humans as well as wildlife,” wrote Professor Edwards in 1992.
In Africa, anti-malaria mosquito nets go unused by recipients
In 2010 viewers of “American Idol” were urged to donate $10 for an insecticide-treated bed net to save an African child from malaria, the mosquito-transmitted scourge that infects about 300 million people every year, killing nearly 1 million.
The premise behind the idea of treated nets is simple. The netting prevents malarial mosquitoes from biting people while they’re asleep, and the insecticide kills and repels the insects. World health experts say that using the nets can reduce child mortality in malarial regions by 20%.
To date, millions of dollars from international agencies, NGOs and USAID have been spent to get treated nets into the hands of impoverished, sub-Saharan Africans. The inter-agency Roll Back Malaria Partnership is calling for 730 million more.
But, as even the staunchest advocate will admit, the treated nets were not designed with the cultural preferences of the rural African villager in mind. Among other design flaws, their tight mesh blocks ventilation, a serious problem in the hot, humid places where malaria roosts. Minor discomfort might be tolerable in rural African communities desperate for anti-malarial prevention. But, as medical anthropologists have consistently found, because malaria is so common in much of sub-Saharan Africa, and because the overwhelming majority of cases go away on their own, most rural Africans consider malaria a minor ailment, the way that Westerners might think of the cold or flu. Many rural people also believe that malaria is caused not just by mosquitoes but also by other factors such as mangoes, or hard work.
As a result, while we see the treated nets as a lifesaving gift, they see them as a discomfort that provides only partial protection against a trivial illness. Is it any wonder that many use their nets to catch fish or as wedding veils or room dividers — all documented uses of insecticide-treated bed nets? If that sounds ungrateful, think about what would happen if public health officials, concerned about the 41,000 lives that Americans lose every year due to flu, blanketed the United States with anti-viral face masks to be worn during the winter flu season. Donning masks would be a simple, safe and effective measure that could save thousands of lives. But would people wear them?
NetsforLife® works to instill a “net culture”—a community-wide understanding of the protective value of nets and the right way to use and maintain them.
When a net culture is in place, people know how to prevent malaria, when to seek medical treatment and how to access effective treatment. The result: less sickness, fewer deaths and stronger communities.
The CDC Foundation’s Bed Nets for Children Program helps CDC teams working in Kenya and Haiti purchase and distribute insecticide-treated bed nets to help protect children and families from malaria. Malaria is a leading cause of death and disease worldwide. In Africa, a child dies from malaria every 60 seconds.
Study: Mosquitoes change habits to avoid anti-malaria nets
After two African villages started using mosquito nets to fight malaria, the local mosquitoes seemed to change their biting habits to avoid the barriers, according to a French study.
They found that mosquitoes seemed to change their hours of “peak aggression” from 2 a.m. or 3 a.m. to around 5 a.m. three years after nets were put up. And in one village, the proportion of mosquito bites inflicted outdoors rose.
Malaria rates climbing again
Mosquito nets have been credited with spurring big drops in malaria deaths, and a report for the Cochrane Collaboration, an international group that publishes rigorous reviews, estimated that for every 1,000 children protected by an insecticide-treated net, five to six lives would be saved every year.
But in recent years, malaria cases have started to climb again in certain African countries, Corbel said. Experts have mainly been concerned about mosquitoes’ growing resistance to the insecticides used in bed nets and for indoor spraying.