Silent Spring and the mixed up story of DDT

Last year I picked up an old copy of The Limits to Growth report from the Club of Rome. It’s a much-maligned book, and I was surprised to find that almost all of the commonly held beliefs about the book are false. You only had to read the book and the controversies evaporated, but several decades of lazy journalism and the internet echo chamber had re-written the history.

Rachel Carson’ Silent Spring is another classic of the environmental canon. It’s considered very influential, making a case against agricultural chemicals and helping  to launch the green movement. It’s also widely criticised.

According to the story, Carson’s polemic against pesticides led to the banning of DDT, which was widely used to control mosquito populations. Because of the risk to birds and wildlife, developing countries were left without a vital tool in the fight against malaria, and millions of people died as a consequence.

The story is told by those who oppose the environmental movement, as an example of how good intentions can go astray, or how greens privilege the natural world over human needs. It’s a tragic story that has been endlessly repeated – here’s a national UK paper telling it. It’s also a myth. Read the book, and you realise the case against Silent Spring is a complete fantasy.

Here are some common misconceptions:

Myth: Rachel Carson called for a ban on pesticides.
“It is not my contention that chemical pesticides must never be used” says the book. Carson’s own argument is that monoculture creates the perfect conditions for insect infestations. Change the way we farm, and pesticides wouldn’t be needed in the first place.

Carson does call for tighter controls on pesticides, and it’s worth remembering that the book was written in a different age. Pesticides were new and relatively unknown, and they were used in remarkably cavalier fashion. In one incident in the book, the town of Detroit is sprayed for beetles – in daylight, without advance notice, by cropdusting planes. A radio announcement later told people that the white dust all over their porches was safe. If it’s hard to imagine dusting down the suburbs from a plane today, it’s partly due to Silent Spring.

Myth: Carson falsely claimed that DDT causes cancer
There is a chapter on cancers in the book, but at no point does Carson claim that DDT causes cancer. She mentions some other pesticides that caused cancers in lab animals, but admits that there is no evidence linking them to human cancers. There are isolated incidents, particularly with those working regularly with the chemicals or those who accidentally get a huge dose, but Carson’s own word is ‘circumstantial’ when it comes to proving anything.
However, DDT was first used for agriculture in 1954, and some cancers can take decades to incubate. Carson, writing in 1960, points out that it’s too early to tell and a link may be found in the future, but she does not claim a link herself.

Myth: DDT was banned because of birds eggs
Most articles mentioning DDT say it makes birds’ eggs thinner. I’m not sure why this has become the key point for so many people, as it’s barely mentioned in the book. What actually happens is that DDT is sprayed to kill insects. Birds eat the insects, and DDT builds up inside the birds until it reaches a toxic level. They then spasm and die. Suburban gardeners noticed dead robins on their lawns, pheasant hunters wondered where their prey had gone. It’s not just birds either – agricultural run-off washes DDT into streams, where it kills fish. Salmon fishermen and shrimp farmers were among those calling for tighter controls. In the UK, a wave of dead foxes made the news. Frogs and squirrels are also killed by DDT at high enough doses.

This is not just bad for the wildlife – it’s counterproductive to the farmers using the pesticides. Why? Because birds or frogs eat insects and keep populations in check. So do predatory insects like wasps or ladybirds, which are killed together with the pests. Eliminate the targeted insect’s natural predators, and you make the problem worse for yourself.

Myth: DDT is the best way to deal with malaria
The common charge here is that DDT is the only proven tool for eradicating malaria. There’s no doubt it’s useful, but by the time the book was published, 28 different species of mosquito had already developed a resistance to DDT and it was already being replaced by alternative products. Carson actually gives a whole chapter to the issue of resistance. “The World Health Organisation has enlisted the help of some 300 scientists in all parts of the world” she writes, “declaring that ‘resistance is at present the most important single problem facing vector-control programmes.’”

This is perhaps the most serious point here. It is the learned resistance to DDT that lead to it being phased out in many parts of the world. In the places where it was first used, such as Sri Lanka, it ceased to be useful within a decade. Today the WHO has a list of 12 recommended pesticides for use in combating pesticides, one of which is DDT.

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Those points all relate specifically to Silent Spring, but there is more to the story. Carson died a few years after writing the book, and the eventual controls on pesticides came a long time later. Those too are seriously misrepresented.

When critics of the environmental movement talk about DDT, they usually claim it was banned in 1972. Then, working backwards, they count the malaria deaths since 1972 and come up with claims that the ban was the “greatest ecological genocide in the known history of man”, as 3 billion and counting puts it. Except that DDT wasn’t banned in 1972. The US banned it for agricultural purposes in 1972. Global restrictions didn’t come until until 2001, and even that wasn’t an actual ban.

In 2001, restrictions came in to control the use of a number of pesticides in agriculture, including DDT. However, DDT was never was banned for disease control. Restrictions were only placed on agricultural use. It remained in use for anti-malaria spraying, and is still in use today in some parts of the world. Here’s a screenshot of the exemption in the UN convention, clearly stating that vector control remains an ‘acceptable purpose’.

Then there are the greens, who lobbied so hard against pesticides. Some did, and there are some groups that still call for an all-out ban on everything. It’s by no means universal. Many environmental groups support the right to spray DDT to control mosquito populations. One group that is regularly mentioned as opposing DDT is Greenpeace, but that’s not their position. “We support the continued use of DDT in malaria control programmes where there are no effective alternatives” says a Greenpeace statement on the matter.

So how did the story get so confused about DDT? That’s an interesting story, and one I don’t have time to explore now. This article in Prospect magazine does a better job than I would. Donald Gutstein also addresses the question in his book Not A Conspiracy Theory, and the chapter on DDT is online here.

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