Better living through chemistry: DDT could save millions of Africans from dying of malaria—if only environmentalists would let it

Reconsidering a Rogue Agent

But over the years, mainstream scientific opinion has absolved DDT of many of its supposed sins. Indeed, the Stockholm Convention partially backfired because it brought to light a slew of studies and literature reviews which contradicted the conventional wisdom on DDT. Like nearly any chemical, DDT is harmful in high enough doses. But when it comes to the kinds of uses once permitted in the United States and abroad, there's simply no solid scientific evidence that exposure to DDT causes cancer or is otherwise harmful to human beings.

Not a single study linking DDT exposure to human toxicity has ever been replicated. In 1993, Mary Wolff, an associate professor at Mount Sinai Medical Center, published a small study linking DDT exposure to breast cancer. But numerous follow-up studies with human subjects--including one large five-study review comparing 1,400 women with breast cancer to an equivalent number of controls--found no evidence for the link. David Hunter, an epidemiologist at Harvard University who ran one of the follow-up studies, says of the breast cancer connection, "the studies have really put that idea to rest." Similarly, various studies have contradicted initial concerns that DDT might cause myeloma, hepatic cancer, or non-Hodgkins lymphoma.

Other reports over the years postulating human toxicity in DDT exposure turned out to be cases of correlation without causation. In its heyday, for instance, DDT was mixed With a variety of dangerous chemicals, sometimes petroleum derivatives. In every anecdote of death or human harm by DDT that Carson related, the Chemical had been dissolved in some other, highly toxic, substance, such as fuel oil, petroleum distillate, benzene hexachloride, or methylated naphthalenes. Such "mixtures with other chemicals or solvents," a 2000 review article in the medical journal The Lancet noted, were responsible for many of the reported deaths from DDT and for other problems like dermatitis. But even these dangers do not extend to public health use, where DDT is dissolved in water and sprayed as a thin film.

That's not to say that DDT is harmless. Matthew Longnecker studied American women who had lived during the period of high DDT use and suggested that high levels of DDT in the bloodstream of pregnant women might cause pre-term delivery and low birthweight, for instance. But public health use doses--two grams per square meter of wall sprayed indoors at most every six months--aren't likely to produce those concentrations. Since DDT is not absorbed through the skin, spraying DDT in houses is unlikely to expose pregnant women--or anyone else--to amounts great enough to pose a danger. And scant evidence suggests DDT gets into the environment in significant amounts when sprayed indoors. According to a WHO report in 2000, "The targeted application of insecticides to indoor walls ... greatly reduces dispersion of the chemicals into the environment. For this reason, the environmental risks from such targeted measures [are] considered minimal"