DDT, 13 Years Later

by Brian Dunning
January 2, 2024

This might be the first time you've ever heard me do a followup episode on the same topic as a previous episode, which was "DDT: Secret Life of a Pesticide," episode #230 from 2010. It was about the controversial pesticide DDT — controversial in that while it is a powerful tool for eradicating mosquitoes to reduce human deaths from malaria, it does so at the cost of polluting the environment with a compound that causes birds' eggshells to be too thin, the eggs do not survive, and bird populations are severely impacted. As a result, DDT was banned in most of the world, with exceptions being made for places where malaria deaths were the worst. It turned out to be by far my most controversial episode, well worthy of a revisit, and see if we can figure out what went wrong.

"Humans vs the environment" is a topic that is fraught with pitfalls, especially when you're talking about something of this gravity. This is not building a mall which displaces some frogs; this is saving hundreds of thousands of human lives at the wholesale expense of bird populations. It's a real world example of the trolley problem: to save the humans, you have to kill the birds. Which do you choose? Both alternatives are unacceptable, yet it is the choice we are faced with. Yes, there are newer alternatives to DDT like neonics, but not one is free of harmful environmental side effects.

Such a topic is an emotional one, and I'll state right here at the top that this is where my biggest failing was in that episode: Rather than de-escalating and making a calm and even-handed presentation, my tone was inflammatory throughout. I was emotional when I wrote it, and that's a bad combination. Listen to this example of the language I used in the show:

DDT, while it does have environmental and health concerns like all pesticides, is not known to have ever killed anyone. If we shelve our most effective tools hoping that something perfect will come along that has no potential downside, we'll wait forever, and thousands will continue dying every day. These are the cases where wealthy environmental groups appear to do their best to justify their elitist stereotype, at the expense of brown people.

That was completely uncalled for, and failed the standards I try to uphold. It attacked listeners on the presumption that their solution to the trolley problem would be racist and elitist — which is absurd, especially given that the problem has no right answer. And it wasn't just this one quote; this same basic tone was used throughout the episode. Podcasting pro tip: Don't attack your listeners, especially with something as fallacious and wrongheaded as that was.

There were also two factual errors in the episode that people found, and which I corrected on the transcript. The first concerned Rachel Carson's highly influential 1962 book Silent Spring, which brought to the public's attention the issue of pesticides and their unintended consequences. I said in my episode that her book pointed out that the declines in bird populations associated with aerial spraying of DDT were caused by eggshell thinning. In fact, this mechanism was not yet known, and came out after her book by other researchers. So I corrected that.

The other error was weird, and to understand it, you have to know who Steve Milloy is. Milloy has worked as a coal executive, a lobbyist for fossil fuel and tobacco companies, a Fox News commentator, and was on the EPA transition team in the Trump administration — so by that you can get a pretty good sense of his environmental acumen. Milloy is an extreme climate change denier, and opposed COVID restrictions. Wikipedia's first sentence about him is "Milloy's career has been spent denying the results of science that government agencies rely on for protecting the public." The guy is a real piece of work. The best irony is that his website is called JunkScience.com. He must have been inspired the day he named it.

So here was my error. Right around 1970, the California brown pelican suffered a significant die-off, which many scientists attributed to DDT, while DDT proponents were quick to point out that the real cause was unrelated: an oil spill off Santa Barbara in 1969. The species ranges on the coast from British Columbia to Mexico, and California's Channel Islands are one of their protected breeding grounds. The oil spill, which reached the coasts of all the Channel Islands, was indeed terrible for the local pelicans; but at the same time, the pelicans' eggshells were found to be about 50% thinner and DDT residue was indeed present — although DDT was never used on the Channel Islands, the islands are located right in the target zone of California's agricultural runoff, and DDT stays in the environment for a long time without breaking down; its half life in soil is about 11 years — in water it's 150 years. The pelicans in that part of California had been eating fish contaminated with DDT, and the pelicans' population had been declining for 10 years, so it can hardly be argued that the 1969 oil spill was the real cause. At the lowest point, which was 1970, only 552 nests were made on one of the islands, and only a single chick survived. (Since DDT was banned, these days the brown pelican population is thriving, and DDT residue is no longer found.) My error was bizarre. I tacked on a completely nonexistent third factor: an outbreak of Newcastle Disease, which I said required the culling of "millions" of brown pelicans. If anyone remembers armies of Fish & Game officers going out and shooting millions of pelicans, let me know. I don't remember it. The Newcastle Disease outbreak was real, but it was among poultry on farms, and millions of chickens did indeed have to be killed to eradicate it.

A detailed failure mode analysis, wherein I set out to determine how in the heck I managed to change chickens into pelicans, reveals that this appears to have been one thing I actually did get from Steve Milloy — but I got even that wrong. On a web page of his "100 things you should know about DDT" — a page loaded with so much misinformation it's amazing that it doesn't drop out the bottom of the Internet from its own bloated weight — he said the Newcastle epidemic was spread by infected pelicans migrating from Mexico. But he didn't say the millions of birds culled were pelicans. He also didn't say they were chickens. He said they were birds. From what I can tell, I simply appear to have misinterpreted that — as Milloy no doubt intended. Since his paragraph was all about pelicans, he said "birds" to fool the reader and hide the fact that they weren't pelicans. Evidently I got fooled. And, unusually, I didn't go to outside sources to verify the details of the outbreak. Normally I would, but especially when I was dealing with a source that I knew to be dubious and agenda-driven, it should have been mandatory. So I did blow that one, and I did issue the correction as soon as I learned of the error. No excuse for my error on that — a bizarre piece of nonexistent misinformation, and no basic fact check on it.

But should I even have been looking at his crap website to begin with? I argue that yes, absolutely, it was an important part of my process — despite it clearly having failed in this case. Similarly, in episode #666 on "The Historicity of Jesus Christ", it was necessary for me to study both the arguments in favor of, and opposed to, the idea of Jesus Christ having been an actual historical person. Thus, you'll find in the references section of that online transcript, books by prominent authors who take one side or the other. My job is always to find a conclusion, not to justify a preexisting one. I've always freely admitted that I come into most topics with a certain degree of prejudice; but as setting any prejudice aside is of primary importance to my job, I've gotten pretty good at it. So I take all the views into consideration when I'm trying to learn about a subject. And whether the episode is about Jesus or DDT or the Flat Earth, some of those views are going to be factually wrong. You have to learn what those are so you can make that determination and ultimately get to the real facts of a matter, and be able to explain how you got there. Thus, I am 100% unapologetic for listing Steve Milloy as one of the references for the original DDT episode, as the anti-science perspective is a part of the DDT story. I don't claim to be perfect, but I do claim to at least try to be as comprehensive as I can within the confines of a Skeptoid episode.

Luckily, things have improved since 2010. DDT is still used in a lot of places where malaria is the worst, but all exemptions only allow indoor use. Spraying indoor surfaces every six months is very effective at stopping mosquitoes indoors, where they bite people the most (when they're asleep at night), and largely prevents environmental contamination. Other protections such as insecticide-treated mosquito netting continue to grow in use. New techniques, like genetically engineering mosquitoes to give them natural antibodies against the malaria parasites, are still in the development phase — though there are groups that oppose genetically altering wild animals and it will be politically tricky to put into practice.

But importantly, as of this writing, there are now two malaria vaccines that are approved and are in use in Africa. The first, called RTS,S, requires four doses and reduces hospital admissions from severe malaria by about 30%. Anti-vaccine sentiment runs strong through Africa, and getting four doses into each child is a tall order, so this vaccine has not made as much of a dent as we'd hoped.

The second and newest is called R21. It requires three doses and, in its initial tests, has reduced severe malaria hospitalizations by 74%. Only just within the past few months as of this writing, Ghana, Nigeria, and Burkina Faso have approved the use of R21 in children, and India is building a factory in Ghana to produce it. The World Health Organization has added it to the United Nations procurement list. At least six or seven other malaria vaccines are in various stages of early development. However, the COVID-19 pandemic triggered a lot of studies of vaccine hesitancy in Africa, and it still remains very strong. Combatting this misinformation is going to be crucial to getting the vaccines out there — and hopefully, getting those numbers down from 600,000 children killed per year to zero. The number to remember here is that a child is dying of malaria about every 55 seconds.

Until we can eliminate vaccine misinformation in Africa, DDT is — unfortunately — probably going to continue to play a large role; and may continue to play a reduced role going forward from there. The situation has improved since my 2010 episode, and that's great — but for now, we're going to continue to face the trolley problem — and there's no good answer to that one.

By Brian Dunning
Follow @BrianDunning