Few poisons have ridden such a roller coaster through environmental history as DDT.
Once hailed as a miracle pesticide, DDT is outlawed as one of a “Dirty Dozen” chemicals as of Monday even as it stays in use as a controversial spray against malaria-spreading mosquitoes.
The man who discovered its power to kill insects won a Nobel Prize in 1948, while shock at its damage to wildlife awoke a global environmental movement in the 1960s.
Into the 21st century, countries including South Africa and Ethiopia still swear by DDT to combat malaria, which kills a million people a year. They say there is scant evidence that DDT is carcinogenic for humans.
“There is still a role for DDT,” said Jim Willis, head of the U.N. Environment Program (UNEP) chemicals division, estimating that about 25 countries will use DDT under exemptions from the DDT pesticide ban.
DDT is one of 12 industrial chemicals to be outlawed under the U.N.‘s 2001 Stockholm Convention on Persistent Organic Pollutants (POPs), which formally comes into force on Monday after ratification by 50 states.
Although harmful to humans, DDT can substantially reduce the rate of malaria, which kills one African child every 30 seconds, according to U.N. estimates. The disease burdens health budgets and curbs economic growth.
Best known by its initials, dichloro-diphenyl-trichloromethylmethane can suppress the immune system and is infamous for threatening bird populations by thinning eggshells.
NO HEALTH DAMAGE?
“We have seen no conclusive evidence that it (spraying) has any impact on human health. We put very small quantities of DDT on the wall,” said Devanand Moonasar, national malaria program manager of South Africa’s National Department of Health.
“We spray only under the eaves and also inside the houses of traditional mud structures,” he said, adding that spraying was normally done from August to October when mosquitoes are worst.
Still, workers use full protective clothing for spraying, and U.N. warnings about DDT and the rest of the “Dirty Dozen” POPs are stark.
“Of all the pollutants released into the environment every year by human activity, POPS are the most dangerous,” said UNEP chief Klaus Toepfer, adding that the world should hunt for alternatives to DDT to control malaria.
DDT and other POPs including dioxins or pesticides like aldrin or chlordane are found worldwide but build into highest concentrations in the fatty tissues of people in the Arctic and in animals from polar bears to seals.
In the heavily industrialized Northern Hemisphere, the chemicals are swept north by ocean currents and winds and end up lodging in fatty tissues in the apparently pristine Arctic.
“There is a conflict between the interests of the people in the Arctic and those who are living in areas where DDT is used,” said Lars-Otto Reiersen, head of the Arctic Monitoring and Assessment Program.
He said that a main modern source of DDT in the Arctic was Russia - measurements showed that it was still in use there, perhaps as a crop spray. Russia has signed but not yet ratified the POPs convention.
Most western countries banned DDT in the 1970s.
The WWF environmental group said that more efforts should be put into finding less toxic alternatives to DDT in fighting malaria. “It’s still a very dangerous chemical,” said Samantha Smith, director of the WWF’s Arctic program.
Toward the end of World War II, DDT was found to be potent in killing lice that spread typhus among soldiers. Lice-borne diseases had ravaged armies throughout history, including Napoleon’s forces in his ill-fated 1812 march to Moscow.
“Unexpectedly, dramatically, practically out of the blue, DDT appeared as a ‘deus ex machina’,” said Sweden’s G. Fischer in a speech awarding the 1948 Nobel Medicine Prize to Switzerland’s Paul Hermann Muller for his DDT discovery.
But in 1962, U.S. author Rachel Carson made DDT infamous in her landmark book “Silent Spring,” detailing the risks of using industrial chemicals. The book is credited with spurring global environmental awareness.
UNEP’s Willis said there was hope for a world rid of DDT, but that it could take decades.
“Mexico recently stopped using DDT, and they’ve seen at the same time a reduction in malaria rates,” he said.
He said that broader anti-malaria policies included clearing stagnant water where mosquitoes breed, placing nets around beds at night, targeted use of alternative anti-mosquito pesticides and development of new medicines.
Revision date: July 7, 2011
Last revised: by Dave R. Roger, M.D.