DDT's safety record is being unfairly attacked. It remains an essential tool for controlling disease-carrying insects.

The hearings began in August 1971 in a converted ballroom in Washington, D.C. The Environmental Protection Agency, less than two years old, had committed to a full adversarial proceeding to determine whether DDT's registration should be canceled, a process that would run for seven months and produce a record so voluminous that it required a dedicated index. On one side sat lawyers and scientists representing the domestic pesticide manufacturers; on the other, attorneys from the Environmental Defense Fund, the organization that had spent years pursuing the ban through state courts and had finally forced the federal proceeding. Edmund Sweeney, the EPA hearing examiner, presided. The question before him was technical and deeply contested: what the science actually said about DDT's risks to human health and the environment.

The chemical industry's presentation rested on a sharp distinction between what had been demonstrated and what had been extrapolated. Yes, DDT accumulated in fatty tissues. Yes, populations of predatory birds had declined. Yes, laboratory rodents fed extremely high doses of DDT had developed liver tumors. But demonstrating ecological harm to birds was not the same as demonstrating cancer risk to humans; animal studies at doses far beyond any human exposure level did not straightforwardly translate into risk; and malaria, which DDT had helped suppress across tropical regions, killed millions of people per year. Placing DDT in the category of unacceptable risk required a chain of inferences the industry characterized as ideological rather than scientific.

The Environmental Defense Fund's case drew on researchers who had documented the chemical's behavior in the field over fifteen years. DDT's persistence, its half-life in soil could stretch to fifteen years, meant that applications made years earlier were still cycling through ecosystems. Its lipophilic properties caused it to concentrate as it moved up food chains, so that a small application to a field produced measurable concentrations in the fat of birds and fish far from the site. Charles Wurster, a chemist who had been among the founders of the Environmental Defense Fund, testified on the ecological accumulation data. Scientists from the National Cancer Institute testified on the animal carcinogenicity findings. Robert Risebrough, an ornithologist who had been studying the collapse of peregrine falcon populations, detailed the eggshell-thinning mechanism with a precision that the industry's witnesses could not adequately contest.

Edmund Sweeney's decision, issued in April 1972, recommended against canceling DDT's registration. He found the human health evidence inconclusive and the agricultural utility significant. William Ruckelshaus overrode him. In the final order issued June 14, 1972, Ruckelshaus accepted that the ecological evidence alone, the persistence, the bioaccumulation, the documented harm to wildlife, was sufficient to cancel DDT's domestic agricultural registrations. The human carcinogenicity question was addressed not as definitively proven but as an unacceptable level of uncertainty given what was already known.

The year 1971 marks the period when the contested-science framing was at its operational peak, when the industry could plausibly argue in a formal legal proceeding that the evidence was genuinely split. The proceedings generated an enormous record that would be cited for decades as evidence that the scientific case against DDT had once been legitimately uncertain. By the time Ruckelshaus issued his order, the scientific basis for that argument had been substantially eroded. What the hearings had produced, across nine thousand pages and dozens of expert witnesses, was a documentation of what the science actually supported, and what, on examination, turned out to be advocacy dressed as uncertainty.