Environment

Carson no 'beacon of reason' on DDT

We disagree with Rob Dunn's view that Rachel Carson's 1962 book on human environmental impacts, Silent Spring, still stands as a “beacon of reason” (Nature 485, 578–579; 2012).

The insecticide DDT (dichlorodiphenyltrichloroethane) was arguably the most successful chemical ever synthesized to control malaria and other insect-borne diseases. However, Silent Spring led to a US ban on DDT use in 1972.

Carson branded DDT as dangerous because of its effects at high doses on experimental rodents and birds. But it was already known that humans experienced no ill effects after consuming 35 milligrams of DDT daily for two years — a dose 1,000 times higher than that received from agricultural exposure. Thousands of pesticides occur naturally in fruit and vegetables and are consumed daily. Around half of these also cause cancer at high doses in rodent tests (B. N. Ames and L. S. Gold Mutat. Res. 447, 3–13; 2000).

DDT is an organohalogen and is concentrated in the food chain, as are many of the organohalogens naturally synthesized by marine and land organisms; some are also found in breast milk (G. W. Gribble Chemosphere 52, 289–297; 2003). But persistence does not equate to harm.

Carson claimed that insect resistance would quickly reduce DDT's effectiveness. But DDT is largely a mosquito repellent, not a toxicant. Repellent resistance has not yet emerged, whereas toxicant resistance is widespread.

Contrary to Dunn's claims and Carson's predictions, the bald eagle had become rare long before DDT, and American robins increased during the 1960s.

At the time of the DDT ban in 1972, 1 billion people were almost malaria-free. Within a few years, malaria cases had risen 10–100-fold. Over 40 years, estimates suggest that there have been 60 million to 80 million premature and unnecessary deaths, mainly children, as a result of misguided fears based on poorly understood evidence.

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Correspondence to Tony Trewavas.

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Trewavas, T. Carson no 'beacon of reason' on DDT. Nature 486, 473 (2012). https://doi.org/10.1038/486473a

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