A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Was Rachel Carson a fraud and is DDT actually safe for humans?

December 13, 2002

Dear Cecil:

Was Rachel Carson a fraud and is DDT actually safe for humans? According to Marjorie Mazel Hecht and [San Jose State University] professor J. Gordon Edwards at www.21stcenturysciencetech.com, DDT is safe and indeed saved and can save human lives, and Rachel Carson's Silent Spring is full of lies. According to them, the banning of DDT was politically motivated and went against the majority of scientific opinion. Yet I consistently hear how dangerous DDT is. What's the truth here?

Cecil replies:

Claiming Silent Spring (1962) is full of lies is a bit harsh. Let's say it contains certain statements at variance with the facts as we now understand them. I'm willing to believe this was a natural result of the fledgling state of environmental science at the time, whereas right-wing conspiracy theorists (who apparently include the parties you mention — Hecht supports crank-for-all-seasons Lyndon LaRouche) see it as evidence of a campaign of deceit by the liberal cabal. We could spend pages debating the details, but the bottom line is this: Soaking the biota in DDT like it was bubble bath, standard practice at the time Silent Spring was written, was a bad thing and Carson was right to condemn it. But refusing to use DDT because of exaggerated fears of environmental damage is, in some circumstances, far worse.

Rachel Carson, a biologist and writer who worked for many years for the U.S. Fish and Wildlife Service, is widely credited with catalyzing the modern environmental movement. Silent Spring was the first popular book to call attention to the dangers of indiscriminate introduction of pesticides and other chemicals into the environment. Carson's principal target was DDT (if you really want to impress the ladies, Craig, tell them it stands for dichlorodiphenyltrichloroethane), a cheap and effective insecticide first employed on a large scale during World War II to control typhus and malaria. After the war DDT was widely used in the United States in agriculture and in mosquito abatement programs.

Part of what made DDT appealing was its broad spectrum — it can kill not just one or two but hundreds of insect species (not to mention various other types of wildlife, especially fish, if you aren't careful about overspraying or runoff into streams). Carson took this fact and ran with it, rhetorically speaking — she claimed that DDT and other pesticides would destroy all living things, and that they should properly be termed "biocides." In the chapter from which Silent Spring takes its title, she paints an apocalyptic picture of an environment bereft of life due to chemical pollution, in which "no birds sing." Among other things, the book claims that DDT interferes with bird reproduction and causes cancer in humans; after its publication the chemical was linked to the thinning of eggshells in some avian species. The Environmental Protection Agency was created in 1970, in no small part due to Silent Spring, and two years later DDT became the first chemical it banned. Most other industrialized nations followed suit, and pressured third world countries to do the same.

Many of Carson's claims were overblown. While DDT is highly toxic to insects and fish and can poison other animals in large enough doses, in moderate amounts it's not especially harmful to birds and mammals, including humans. (Ironically, the EPA's own judge agreed, but was overruled by its chief administrator.) No one has conclusively proved that DDT can give you cancer. The cause of eggshell thinning is likewise poorly understood.

On the other hand, DDT is demonstrably effective at controlling the mosquitoes and other insects that transmit malaria and typhus. Thanks principally to DDT, in the years after World War II malaria was eradicated in the U.S. and sharply curtailed in many tropical countries. Venezuela recorded eight million cases of malaria in 1943; by 1958 that number was down to eight hundred. The World Health Organization estimates that DDT saved 50 to 100 million lives during this period, and that's just counting malaria prevention. In recent years, however, the disease has staged a comeback. Globally it quadrupled during the 1990s, and it's even reappeared sporadically in the United States. The resurgence of malaria is due to a variety of factors, including changes in land use and possibly climate, and some experts say the phasing out of DDT is one of them.

I don't mean to suggest that DDT is benign. On the contrary, it's a potent contact poison, and though it breaks down quickly in sunlight, it's much more persistent in soil and water and accumulates in plants and fatty animal tissues with long-term exposure.

But its drawbacks have to be weighed against its benefits. Malaria currently infects 300 to 500 million people annually, mostly in Africa, and causes as many as 2.7 million deaths. Alternative methods of mosquito control cost more and are less effective. Some 400 scientists and doctors have signed a petition opposing the inclusion of DDT among the 12 persistent organic pollutants (POPs) to be banned under a United Nations treaty now up for ratification, and a few public health experts are campaigning to bring DDT back. DDT isn't a panacea; India, which still uses it, suffered nasty outbreaks of malaria in the 90s, and insects in many parts of that country have become resistant to the chemical. But it remains an important tool, and in a time of rising global pestilence we shun it at our peril.

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