A World Wildlife Fund report finds sufficient scientific evidence of hazards to human health and wildlife to justify a global ban on the production and use of DDT. Although banned decades ago in North America because of its links to wildlife declines (such as the near extinction of the bald eagle) and possible risk to human health, DDT is still used to control mosquitoes and other disease-carrying insects in many developing nations.
The report, "Hazards and Exposures Associated with DDT and Synthetic Pyrethroids Used for Vector Control," summarizes the current state of knowledge regarding the health and environmental effects of DDT and its most popular alternative -- synthetic pyrethroids. It dramatically illustrates the persistence and pervasiveness of chemicals such as DDT, which can be sprayed in a village in Africa and end up in the fat of polar bears in the Arctic.
Some of the more recent scientific findings summarized in the report include damage to the developing brain, causing hypersensitivity, behavioral abnormalities and reduced neural signal transmission, and suppression of the immune system resulting in slower response to infections. Investigations in Mexico and South Africa reveal that human breast milk contains DDE (the breakdown product of DDT) at concentrations that exceed the acceptable guidelines for infant intake set by the WHO.
WWF's report was released as representatives from more than 100 nations gathered in Nairobi, Kenya to discuss whether to recommend a global ban on 12 of the most toxic chemicals, including DDT. The chemicals, known as persistent organic pollutants (POPs) because of their long lives, toxicity and ability to travel include chlordane, dieldrin, dioxin and PCBs.
The report notes that most of the millions of tons of DDT that have been produced in the past remain in soil and continue to be redistributed throughout the environment for example, an Oregon (U.S.) orchard still had 40 percent of the original DDT used 20 years later. Although more than 20 years have passed since it was last used in many countries such as the US, Cotton Belt soils are estimated to still release 110 tons of DDT and its metabolites annually into the atmosphere.
When released into the atmosphere, DDT travels thousands of miles to colder areas where it returns to Earth and builds up in body fat of wildlife and humans. "DDT is such a potent chemical that as long as it is used anywhere in the world, nobody is safe," said Clifton Curtis, Director of WWF Global Toxics Initiative.
The report calls for a global ban on the production and use of DDT no later than 2007, and until then for its use only as a pesticide of last resort, to be used when no other disease control mechanisms are available. Even though it is banned in 34 countries and severely restricted in 34 others, DDT is still endorsed by the World Health Organization (WHO) for controlling malaria. However, the last WHO review of DDT's effects came in 1993, well before much of the newly emerging science was released.
There is no longer a question about whether DDT should be banned, only how soon it can happen while still ensuring developing countries access to safe, affordable alternative malaria controls, Curtis said. "The World Health Organization is using outdated data to justify the continued use of DDT -- data that does not take include more recent findings of its effects on behavior, immunity and brain functioning."
Because DDT has been banned or restricted from widespread agricultural use since the 1970s, many of the highest concentrations in humans are now in areas where it is sprayed on the walls and floors of houses to control malaria from mosquitoes and leishmaniasis (a parasitic infection) from sand flies. The report includes a modeling study commissioned by WWF that found up to 82 percent of the DDT applied indoors could eventually escape outdoors.
A WWF report released in June, 1998 demonstrated that alternatives such as chemically treated bednets and environmentally friendly pest control are available and effective. A major goal of the POPs treaty now under negotiation is to make sure that these alternatives are studied for their safety, and that funding is provided to help less affluent nations switch from DDT, as well as other POPs.
In addition to the 2007 phaseout, WWF recommends that the any future government-sponsored testing on DDT and synthetic pyrethroids take into account the extremely low doses that can cause damage to wildlife and human fetuses and embryos, instead of relying solely on high-dose testing. The report also calls on research to focus on the transgenerational effects of DDT on developing nervous systems, immune systems, and behavior.
Finally, WWF stresses the need to apply the precautionary principle in addressing DDT and other POPs. This principle states that action should be taken when there is sufficient scientific evidence to demonstrate that a substance may be harmful -- even if cause and effect relationships have not been fully established scientifically.
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Written by: World Wildlife Fund
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