DDT: Important Messages, Bad Messengers

Forty-four years after Silent Spring, dichloro-diphenyl- trichloroethane (DDT) is front page news again, and as always happens with this compound, critical, finely nuanced issues are being bulldozed into black and white.

War on Insects

The main story, in case you missed it somehow, is that the World Health Organization (WHO) announced that it would start using DDT to control malaria in Africa. This follows a regime change in the WHO’s malaria program, which is now being run by an outspoken public health campaigner named Arata Kochi, who previously ran the WHO’s TB program.

Indoor spraying of DDT, Kochi argues, is an important weapon against malaria, and this circumscribed use of the notorious pesticide has not been proven to cause environmental harm. The Bush administration and prominent Republicans also support the change, representing an unusual convergence of UN and Administration opinions.

The back story is considerably more complicated.

Kochi seems to be a specimen of a familiar type in public health: the “damn the subtleties, full speed ahead” character. There is a place for that approach, but it can easily backfire. Indeed, Kochi was forced off the TB project because he had alienated too many important supporters, and since he took over the malaria project, half of the senior staff has left.

Meanwhile, Bush administration officials and allies seem to be interested in indoor DDT use primarily as a rhetorical tool to put environmentalists on the defensive this election season. In the press release announcing the change, Senator Tom Coburn (R-OK) even takes the opportunity to tar earlier objections to DDT as “junk science and myths,” leaving no doubt about his motivations or his ignorance of recent research.

We’ve been down this road before, and it ended badly last time.

Let’s begin at the beginning. DDT owes its notoriety to American applied research during World War II. At the start of the war, chemists had known how to synthesize the compound for decades, and a few knew of its insecticidal properties, but nobody had tested it rigorously or turned it into a practical product. It seems unlikely that anybody would have, if it hadn’t fallen into the hands of an obscure group of entomologists at the US Department of Agriculture in 1942.

The USDA scientists had recently been drafted into a critical public health project: preventing louse-borne typhus in troops. They worked methodically, testing every chemical they could find to see what would kill lice. Among thousands of other samples, they received a waxy, granular substance from the Geigy corporation in Switzerland. The manufacturer called it Gesarol.

Gesarol did kill lice, and every other insect in the lab, but a crumbly wax doesn’t work well as a delousing treatment, so the USDA crew did the unglamorous but essential job of reformulating it. By 1943, they were producing large quantities of several formulations, including powders and sprays, and they were referring to Gesarol by its generic name, abbreviated DDT.

The USDA scientists promoted DDT only for a few circumscribed uses, including delousing and malaria control. Does this sound familiar? Indeed, the entomologist leading the effort specifically cautioned against spraying the stuff willy-nilly outdoors, arguing as early as 1944 that DDT was “definitely poisonous,” and that its environmental consequences might be bad. I happen to have an archive of his papers sitting in my closet, as he was my grandfather.

Nurse spraying DDT on a hospital bed

That message became unfashionable after the war, when the USDA reverted to its traditional mission of boosting American agricultural yields. Walter E. Dove left the agency, and the USDA started promoting widespread spraying of DDT on crops.

Just as agricultural use was ramping up, the newly constituted WHO also adopted this miracle compound, putting it to use in an ambitious, military-style campaign to eradicate malaria. Not only was it used inside houses, it was also sprayed from aircraft, trucks, and by hand into every conceivable mosquito habitat. If a little was good, more had to be better, and human health trumped all environmental concerns; damn the subtleties, full speed ahead.

The massive doses of DDT soon bred environmental disaster and widespread insect resistance to the pesticide. The more DDT the WHO and the farmers sprayed, the less effect it had, until the leaders of the malaria eradication campaign were forced to surrender, and the farmers were forced onto a treadmill of chemical dependence.

Given this history, it’s easy to understand why malariologists have resisted using DDT again in malaria-endemic areas. But we’re smarter now, so what could go wrong?

For starters, the new campaign will force rich countries to relax bans on DDT-tainted crops. Otherwise, poor African farmers won’t dare let DDT onto their property, for fear that the tiniest bit of cross-contamination could cost them their best foreign customers. Once regulators comply with this change, what’s to keep farmers from using a little cheap DDT here and there to control field infestations? It does work, and poor countries today face the same pressures to boost agricultural yields that the US faced in 1945.

Meanwhile, an overzealous public health worker might decide to use up some extra spray on a few puddles and ponds where mosquitoes are breeding. Higher government officials might also like that idea. Nuance-averse politicians are already paving the way by arguing that the pesticide’s environmental and health risks are overblown, when in fact they continue to reverberate. It might not be long before we’re parachuting cats onto Borneo.

DDT could indeed be an important weapon in combating malaria, but that will require a carefully constructed, fine-grained plan, not another military-style assault backed by science-blind leaders. Used properly, as originally intended and for a narrowly restricted purpose, DDT could be safe for the world. Unfortunately, the world we live in might not be safe for DDT.