I remember being quite taken when, as a student, I read Rachel Carson’s 1962 epic Silent Spring. As a biologist, Carson made a compelling case against the synthetic pesticides that had been introduced in the post-World War II era. She maintained that they were responsible for fish kills, pollution of the soil, and reproductive problems in birds. DDT in particular caused thinning of egg shells and led to fewer hatchings. Ospreys, peregrine falcons, and eagles were disappearing, Carson said, and robins were being killed in misguided attempts to eradicate Dutch elm disease by spraying trees with DDT. That’s why there would eventually be no birds to sing: there would be a “silent spring.”

I was impressed by Carson’s book. I thought it was an excellent example of how we cannot always predict the consequences of a chemical intervention and how the introduction of a substance into the environment, although seemingly for all the right reasons, can backfire. Carson made an impassioned plea against putting blind faith in technology, particularly when it came to pesticides such as DDT.

This notorious compound was first synthesized in 1874 by Othmar Zeidler, who combined chloral (which later became known as a “Mickey Finn” after the Chicago bartender who supposedly used it to put his rowdy patrons to sleep), chlorobenzene, and concentrated sulfuric acid to make it. Zeidler was simply interested in making novel compounds for his Ph.D. thesis and never studied DDT further. But in 1939, Paul Muller, working for the JR Geigy Company in Switzerland, did. He was interested in moth repellants and had come across a compound called “diphenyltrichloroethane,” which was somewhat effective. Muller then did a literature search and came upon DDT, a closely related substance. He synthesized it according to Zeidler’s recipe and discovered that it was remarkably toxic to insects. And much to his satisfaction, it seemed not to have any effect on domestic animals or humans. Swiss farmers were thankful. Just a year after Muller’s discovery, DDT was used to wipe out the Colorado potato beetle, which had threatened the country’s potato crop.

By 1945 DDT was being used worldwide on numerous crops. But concerns arose with two discoveries: the chemical’s application caused it to disperse into the air and spread far and wide, and it was showing signs of toxicity in frogs and fish. By the 1950s it was apparent that DDT was building up in the fatty tissues of animals and humans. Eventually, the us Environmental Protection Agency (EPA) stepped in and banned the substance. Rachel Carson had played her role, the environmental movement had begun, and a major problem had been eliminated.

I vividly recall telling this story in class when I first started teaching back in 1973. I thought Rachel Carson had done a great job. True, I had seen references to the use of DDT during the war to wipe out mosquitoes that transmitted malaria, but frankly, I didn’t pay much attention to that. After all, we didn’t have malaria in North America. It never occurred to me that maybe it was because of DDT use. After all, Rachel Carson had made DDT out to be a chemical villain, and the EPA had agreed with her. Being young and somewhat naïve, I didn’t think to check out some of Rachel Carson’s “facts.” When I finally did look into the DDT issue more deeply, I began to realize that the picture Carson had painted was not completely accurate. DDT had another side.

When the Germans retreated from the Italian city of Naples during World War ii, they dynamited the city’s water system. The inhabitants had no water to wash with, and body lice proliferated. The result was an outbreak of Typhus bellicus, or “war typhus,” a disease that in previous wars had killed millions. This time, though, the Allies had an answer. They had DDT. About 1.3 million Neapolitans were dusted with mixture of talcum powder and DDT, and within three weeks the epidemic was stopped in its tracks. But that was only the beginning. DDT turned out to be highly effective against mosquitoes that transmitted malaria. Sprayed on the walls of houses in the tropics, it would keep the insects away for weeks. In Ceylon (now Sri Lanka), where about 2.5 million cases of malaria were recorded annually in the 1950s, regular spraying led to just 31 reported cases in 1962. The world had never seen such a miraculous result.

Coincidentally, 1962 also marked the publication of Rachel Carson’s Silent Spring, in which she described DDT as the “elixir of death.” And she wasn’t referring to insects. Carson was convinced that DDT and other similar pesticides had unleashed a catastrophic plague on the world. In addition to her prediction that wildlife would be affected to the point where no birds would be left to sing in the spring, she claimed that the accumulation of persistent DDT in the bodies of mammals would cause cancer rates to soar. She was certainly right about the persistence and accumulation of DDT. Both it and its major metabolite, DDE, persist in the environment for many years. They are essentially insoluble in water but are very soluble in fat, which means that they accumulate in fatty tissue and build up in the food chain. While plankton in water may have very little DDT, the fish that eat the plankton will have more, and birds that eat the fish more yet. We all have some DDT in our flesh that can be traced back to the massive spraying of agricultural fields and the vast amounts used in insect control efforts prior to 1972, the year when most uses of DDT were banned in North America. Indeed, in 1962, 80 million kilograms of DDT were used worldwide. Carson was absolutely correct when she said that DDT could be found in mountain lakes, in the bodies of polar bears, and at various sites far removed from where it was applied. But its presence is not enough to condemn it as a criminal. What other evidence did Rachel Carson have? Not much.