DDT to Return as Weapon Against Malaria, Experts Say
for National Geographic News
|August 1, 2006|
DDT, a notorious symbol of environmental degradation, is poised to make a comeback.
International experts are touting the widely banned pesticide as a best bet to save millions of human lives threatened by malaria.
The disease, which kills mostly children and pregnant women, is largely spread by mosquitoes.
The overwhelming majority90 percentof malaria victims live in Africa, where the disease plagues both human and economic health (Africa facts, maps, more).
In May the U.S. Agency for International Development (USAID) endorsed the use of DDT for indoor antimalarial treatment in the developing world.
The World Health Organization (WHO) is expected to do the same in short order, according to a comprehensive report published in the current issue of the journal Nature Medicine.
The chemical's return is sure to raise some eyebrows, but people on the front lines of the malaria fight generally support the decision.
"It's about 20 years too late, but it's a good thing," said Don Roberts, a professor of tropical public heath at Uniformed Services University of the Health Sciences in Bethesda, Maryland.
"I think it's going to make a huge difference in the health of people at risk of malaria."
From Miracle Pesticide to Notorious Polluter
DDT, or dichloro-diphenyl-trichloro-ethane, was once considered a miracle pesticide. Swiss chemist Paul Müller won the 1948 Nobel Prize in Medicine for discovering its bug-killing properties.
Some 675,000 tons (612,000 metric tons) of DDT were used in the U.S. between 1942 and 1972 (related photo: spraying DDT on a New York beach, 1945).
The pesticide eradicated malaria in the U.S. by 1949 and checked the spread of the disease in many other parts of the world.
DDT likely saved millions of human livesbut there was a hidden environmental cost.
When it was used liberally, the pesticide wreaked havoc on ecosystems and caused reproductive ailments in wildlife.
Because the chemical is fat-soluble, it can be passed along the food chain, steadily accumulating in animal tissue. Studies suggest that a buildup of DDT in predatory birds blocks calcium absorption and causes thinner eggshells.
In the United States the bald eagle became a powerful symbol of the pesticide's problems (related photos: bald eagles, back from the brink).
A dramatic population decline in the 1960s landed the U.S.'s national bird on the U.S. Endangered Species list, an event that was blamed on DDT use.
Overall, DDT's ecological effects were most memorably evoked by Rachel Carson's Silent Springthe bestselling 1962 book that signaled a watershed moment for environmental movements worldwide.
The chemical has been blamed for some human ailments as well, including potential as a cancer risk, although its actual effects are a matter of debate.
Mothers exposed to DDT may have premature births and babies with lower IQs and may also retain the chemical in their breast milk.
Study results vary and some experts say more research is needed to determine what negative impacts DDT has on humans.
The U.S. Environmental Protection Agency banned DDT in 1972, and many other countries banned agricultural use of the chemical in the 1970s and '80s.
The suggested technique for indoor antimalarial use today would be a far cry from the crop-dusting methods of DDT's heyday in the 1950s, experts say.
Very small amounts would be used to treat only house walls, so the probability of human and environmental contamination would be low.
Even small amounts of DDT deliver a lot of bang for the buck as an effective, cheaper, and longer-lasting pesticide, supporters say.
"For duration of activity there is no [competitive] chemical that even comes close to DDT, and of course the duration is a big factor in overall cost," Roberts, of Uniformed Services University, said.
"If you're spraying one time versus four times a year, the cost difference is enormous."
Cost is critical, because malaria typically affects the poorest of the poorlower-income people in developing nations.
DDT also packs a dual-threat capability: It not only kills mosquitoes outright, but it also works as a repellent.
"[Treating house walls] is a perimeter treatment," Roberts explained. "The people you're trying to protect are on the inside of the perimeter, so mosquitoes will come up to that wall, detect the DDT in the vapor phase, and move away from it," Roberts said.
Environmental organizations such as the Sierra Club have acknowledged the chemical's usefulness in saving human life.
"We have not opposed the use of DDT to fight malaria in developing countries," said Ed Hopkins, director of the Sierra Club's environmental quality program.
"Obviously malaria is a serious disease and a public health threat in developing countries. Local public health authorities are in the best position to decide if their countries need to use DDT to fight malaria.
"This is a relatively minor use of DDT compared with agricultural uses," he continued.
"We think it's important for developing countries to be able to protect the health of their citizens, but not to use vast amounts of DDT for growing crops when there are safer alternatives available."
Some experts caution that once the chemical is revived in quantity, DDT may be put to useor misusein agriculture. Robust monitoring will be key to limiting its potential negative effects.
Managing DDT's application to account for insect resistance is another challenge.
Insects are remarkably adaptable, so use of DDT must be carefully monitored and controlled to ensure that the treatments don't enhance insects' genetic DDT resistance.
Despite the potential roadblocks, many health officials have brightened at the prospect of the pesticide's disease-fighting power.
Arata Kochi, director of WHO's Global Malaria Program, is one supporter.
"Quite often in this field politics comes first and science second," he told Nature Medicine. "We must take a position based on the science and the data."
Free Email News Updates
Best Online Newsletter, 2006 Codie Awards
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
|© 1996-2008 National Geographic Society. All rights reserved.|