UC Berkeley professor Elena Conis explores how DDT helped sow science skepticism

The insecticide dichloro-diphenyl-trichloroethane, DDT, was hailed as a miracle bug blaster in the 1940s, then demonized as a wildlife destroyer in the 1960s.The Environmental Protection Agency banned DDT in the United States in 1972, citing concerns it persists in nature, harms wildlife and poses potential human health risks. It was blamed for thinning the eggshells of bald eagles, ospreys and brown pelicans, causing their populations to plummet.

But the World Health Organization in September 2006 declared its support for DDT use indoors in African countries where malaria remains rampant.

Elena Conis, a professor of journalism and history at the University of California-Berkeley and author who writes about public health issues, has written about America’s changing relationship with immunization. She spoke with us about her new book, “How to Sell a Poison: The Rise, Fall and Toxic Return of DDT” (April 2022, Bold Type Books) and how the DDT story colors today’s public debate over health and science. She sees a connection in the DDT story and today’s public doubts about COVID-19 and vaccines.

The conversation has been edited for brevity and clarity.

Q What was the inspiration for your new book?

A I grew up in a time when all we heard of DDT was that it was one of the most toxic chemicals around, how we’d lost all our ospreys and scientists were trying to bring them back and it was because of DDT. Because it was banned, I knew it was bad.

Then experts were saying we needed to bring back DDT in Africa, and I was shocked. It was so fascinating to me that here was a chemical that when it was first developed we thought it was safe, 25 years later we thought it was so toxic it had to be banned, and 25 years after that we thought maybe we need to change our minds on that.

Q How was DDT used in the U.S.?

A We developed it in the Second World War to protect troops from insects that carried diseases. When the war was over, we had a very different disease problem here, which was polio, which was causing bigger and bigger outbreaks after the war. One of the really popular theories was that flies were spreading it.

After the war communities began experimenting with DDT to see if it could stop polio. When a couple of communities sprayed DDT and saw polio outbreaks disappear, others began spraying DDT. Soon, I don’t think there was a single state that wasn’t spraying DDT. We came to believe it was saving us.

Q So how did DDT contribute to science skepticism?

A There are a few things that are so fascinating from the history of DDT that show a pathway to the moment we are living in today, where skepticism in science and mistrust in science and its institutions is so prevalent. There were scientists urging us to move with caution. But they were completely drowned out by other voices saying DDT is fine. ‘Sure it seems to build up in wildlife and human fat but it seems safe so we’re just going to use it.’

It was this pattern of eagerness to set aside warning signals and move ahead with the technology. In time, the scientists who spoke out ended up being right. It was harming populations of birds and animals and was building up in human fat with serous consequences for long-term health.

Q So those warning signals led the U.S. to ban it, but it’s used overseas today?

A In the late 1990s and early 2000s we were increasingly paying attention to high rates of malaria in parts of the globe. And there were a handful of free-market defenders and think tanks who saw in this renewed scientific call for DDT use an opportunity to tell about the hazards of overregulation. They said ‘let’s popularize this narrative that DDT never should have been banned, and that by banning it the U.S. is responsible for malaria deaths in sub-Saharan Africa.’ This was happening at the same time fossil fuel companies were questioning the science behind climate change.

Q You’ve written about the history of vaccination, how does that tie in with all this?

A Skepticism toward vaccines has always been with us. But it really began gaining steam in the 1960s and 1970s when we were developing vaccines against a long list of childhood diseases.

If you know anything about the 1960s and ’70s, it was a time characterized by active social movements. Some of those gave people ideas and language for questioning vaccines, including vaccines against diseases that were considered mild. It wasn’t just the public, but physicians too.

I found that the story of DDT’s ban became a symbolic one to some people. They said, ‘We should move much more slowly and cautiously in approving new vaccines,’ and ‘Why am I vaccinating my child against these diseases that I had as a kid,’ and ‘We haven’t had these vaccines that long — look at DDT, we used it for 20 years before we acknowledged its risks outweighed its benefits.’ It became a parable for people’s vaccine skepticism.

Q We just marked the 60th anniversary of Rachel Carson’s influential book “Silent Spring,” credited with launching the environmental movement and ushering in the U.S. ban on DDT. What are its lessons?

A What’s so fascinating to me about “Silent Spring” today is Rachel Carson took some real risks writing it. She knew there was a lot of skepticism of a link between pesticides such as DDT and cancer. But she also knew there were a whole bunch of scientists who thought there was a connection.