DDT, short for dichloro-diphenyl-trichloroethane, was first
synthesized in 1874 by German chemist Othmar Zeidler, but it was not until 1939 that Dr Paul Müller discovered its potent
insecticide qualities. DDT was used around the world during the next 20 years to kill disease-bearing
insects such as lice (
typhus) and mosquitos (
malaria). The complete elimination of malaria from North America and Europe during the mid-20th century can be credited largely to DDT.
DDT was also widely used -- in fact badly over-used -- as an agricultural pesticide, and began to accumulate in rivers, soils and animal tissues. Rachel Carson's 1962 blockbuster Silent Spring linked DDT to falling raptor and songbird populations. Her evidence has since been challenged, but the damage was done: there was a massive public backlash against DDT and it was outlawed for use in most developed nations by the mid-1970s. DDT is now popularly believed to be extremely toxic to both humans and animals and has been implicated in particular in breast cancer and the feminising of fish, reptiles and perhaps mammals. In fact, the studies have been contradictory and there is no clear evidence that DDT, even with long-term exposure, has significant negative effects on human health.
DDT has, nevertheless, been characterised as a persistent organic pollutant (other POPs include chlordane, dieldrin and polychlorinated biphenyls) and there is currently a campaign, led by the World Wildlife Fund and others, to ban its use globally.
The proposed United Nations treaty on POPs is facing significant opposition, however, because DDT remains for many developing nations the single most effective and cheapest weapon in the war against malaria.
Malaria is one of the world's deadliest diseases. There are 300-500 million cases each year, 90% of them in Africa, and these result in two and a half million deaths annually, mostly of children. It was the leading cause of death in sub-Saharan Africa until it was recently overtaken by AIDS. The incidence was dramatically reduced by the use of DDT, and has been rising steadily wherever DDT use has been stopped.
Nations which need DDT for malaria control are not obliged to sign up to a global ban, but they have little room to act independently: DDT production facilities have been shut down everywhere but in India and China, with the result that it is now more difficult and expensive to obtain. Donors, under pressure from environmental groups in the richer nations, have also in some cases forbidden the use of DDT as a condition for receiving aid. This paradoxically condemns the populations of countries like Mozambique to further ill-health and poverty -- sick people make bad workers, and foreign investors are understandably reluctant to expose themselves to a disease which carries a significant risk of permanently damaged health or death. DDT seems the lesser of two evils.
Material sourced from www.malaria.org, www.junkscience.com, the World Wildlife Fund, the WHO, the American Council on Science and Health, www.sciencenews.org (Science News Vol 158, No 1, July 1, 2000, p. 12), www.altgreen.com.au and the Centers For Disease Control and Prevention