Quoted from Living Downstream:

What impresses me most is just how much was known about the harmful aspects of this familiar and seemingly harmless substance. As [Rachel] Carson made clear, the scientific case against DDT—even by the late 1950s—was damning. It was not objective science, nor was it blissful ignorance, that created the impression that DDT was somehow both our most lethal weapon against undesirable life forms (“killer of killers,” “the atomic bomb of the insect world”) and a completely benign helpmate. In fact, scientific study after scientific study showed that DDT was failing at both roles. It triggered population explosions in insect pests who evolved resistance and whose natural enemies were killed by the spray. It poisoned birds and fish. It disrupted sex hormones in laboratory and domestic animals. It showed signs of contributing to cancer. By 1951, it had become a contaminant of human breast milk and was known to pass from mother to child.

Nevertheless, people continued using DDT until Carson’s preliminary damning evidence was supplemented with more and more corroborating damning evidence, producing a great accumulation of damning evidence, and its registration was finally revoked in 1972. I find this phenomenon boundlessly fascinating. Across my desk are spread forty years of toxicological profiles, congressional testimonies, laboratory studies, field reports, and public health investigations of toxic chemicals both officially outlawed and officially permitted. Like crossing and recrossing the same field, I move back and forth between Silent Spring and the scientific literature that preceded it, between Silent Spring and the scientific literature published in the decades since. At what point does preliminary evidence of harm become definitive evidence of harm? When someone says, “We were not aware of the dangers of these chemicals back then,” whom do they mean by we?

Steingraber, Sandra. Living Downstream: An Ecologist’s Personal Investigation of Cancer and the Environment (p. 9). Da Capo Press. Kindle Edition.