Early pesticides were natural but, to be blunt, fucking terrible. 4,500 years ago, Sumerians used sulphur based insecticides to combat mites. A millennium later, arsenic and mercury based pesticides were used in China. Paris Green was also a popular rodenticide and insecticide in the 19th century, but it was also alarmingly good at killing humans.
Then, much to the sadness of aspiring medical students, organic chemistry happened.
One of the early synthetic organic pesticides was dichloro-diphenyl-trichloroethane. The chemist who synthesized it won the nobel prize, and naturally, there was yelling.
You likely know it as DDT.
Today’s Moment of Science… the chemical that saved half a billion lives.
When Swiss chemist Dr. Paul Muller developed DDT in 1939, it was shown to be safe for humans and an unpleasant experience for mosquitoes. It went into popular use in the mid-1940s, shielding entire regions from the world’s deadliest animal. It’s estimated that half a billion lives were spared from malaria and other diseases transmitted via mosquito bites.
Dr. Muller was awarded a Nobel Prize for his work developing the pesticide. After all, DDT was proven safe for humans, it killed mosquitoes, and wasn’t that enough?
Over two decades after it was first synthesized, marine biologist Rachel Carson had concerns about changes to the ecosystem, gravitating to a belief that the changes were caused by the spraying of DDT. Her book, Silent Spring, was widely credited with launching the environmentalist movement. Carson’s opus decried pesticides and the impact of chemicals on the natural world. The title of the book is supposed to refer to the ‘silencing’ of the birds and, in a large sense, the world’s bleak future relying on chemicals.
As a chemist, I would like to remind you that the world is chemicals, and anyone who tells you otherwise is selling something.
We do need to consider the impact of a newly synthesized chemical in the environment. However, Carson’s criticisms weren’t without a heaping dose of bullshit. She made the claim that weeds didn’t grow in healthy soil. She complained about the generation of arsenical pesticides, ignoring that the new safer synthetics like DDT were replacing it. She tried to claim DDT as the acute cause of cancer in the case of a woman who sprayed with DDT and a month later died of leukemia. Of course the public was scared when they read all of this, how could they not have been? This chemical was everywhere and apparently it was out for vengeance on behalf of the little flying bloodsuckers.
The criticisms in Silent Spring were overblown but not unfounded. DDT bioaccumulated in some fish and caused eggshell thinning, leading to death and population decline in some large birds of prey. It’s also a persistent chemical in the environment, still showing up in testing today in areas of Europe where DDT has been banned for years. Though at the time the evidence linking DDT to cancer was lacking, it’s now classified as a group 2A carcinogen, meaning that there’s evidence it can increase risk of some cancers. But to be clear, your coffee contains a group 2A carcinogen, so.
We have to talk about risk, and what choosing to use or not use a substance with some risk entails.
Dr. Muller found, to that point, the safest chemical that could be sprayed around humans to keep mosquitoes in check and prevent the spread of malaria. His discovery saved a number of lives that has unquestionably altered the course of human history. DDT is now only used in a few countries in limited capacity for controlling malaria outbreaks. There are still over 200 million cases of malaria annually, and in 2019 there were over 400,000 fatalities due to malaria.
Was the mistake introducing a persistent environmental toxin, or would it have been a far graver mistake not to prevent all those deadly cases of malaria?
Do any of us understand the true cost of 500,000,000 lives?
This has been your Moment of Science, with no great answers, but a resolute belief that using DDT was the right thing to do.
Thanks for this which has been one of the most reasonable discussions about DDT I have read. The challenge is how do we create a society that can evaluate risks and make decisions?
Again, I honour you for being able to see and share The Big Picture.
Did you check “Silent Spring” to verify? Rachel Carson didn’t ever allege DDT causes cancer (it does, a rather weak carcinogen when by itself, mercifully). I don’t recall and cannot find any place Carson said ‘weeds don’t grow in health soil.’
Carson’s work has been checked and rechecked by top chemists and entomologists and others for decades. 59 years after it was written, every science footnote in “Silent Spring” is still valid. Carson’s work was verified by the President’s Science Advisory Council in 1963, by the Mrak Commission, by the Hilton Commission, by two federal trial courts, by months of hearings at EPA, and by the recovery of the bald eagle and other species.
I calculate that the decline in malaria SINCE the U.S. banned DDT from U.S. farms saved more than 100 million humans, plus bald eagles, osprey, brown pelicans and peregrine falcons, and more.
Short story: Rachel Carson was right about DDT and still is.
Coda: Malaria is, today, at the lowest levels in human history, mostly without DDT. Country by country humans eradicate malaria without DDT.
We were wise to listen to Rachel Carson; we should have listened better and heeded more.
I don’t think you’ve read Silent Spring: https://www.nytimes.com/2007/06/05/health/05iht-sntier.1.6003787.html