We’ve covered the world in pesticides. Is that a problem?

August 18, 2013

Pesticides have become an enduring feature of modern life. In 2007, the world used more than 5.2 billion pounds of weed killers, insecticides, and fungicides to do everything from protecting crops to warding off malaria.

And that's led many researchers to wonder what sorts of broader impacts all these chemicals are having. They've helped feed the world, yes, but they may also be causing health problems elsewhere. To that end, the latest issue of Science has a fascinating special section on the world's pesticide use. Here are a few good charts and highlights:

1) Pesticide use is rising almost everywhere, with a few key exceptions:

Note that pesticide sales in North America haven't grown very much — and usage actually seems to be declining in the United States (more on that below). The growth in Europe, meanwhile, is largely driven by a big uptick in sales in Eastern Europe. Meanwhile, sales are more or less stagnant in the Middle East and Africa.

2) There's a surprisingly large variation in how farmers in different countries use pesticides:

Of the 2.4 billion kilograms of pesticides used in 2007, the United States accounted for about 20 percent of the total. But notice that American farmers are relatively sparing in their use of pesticides — using just 2.2 kilograms per hectare of arable land. Compare that with China, where farmers are "less trained" and the figure is more like 10.3 kilograms per hectare.

Of course, the skill level of farmers is just one variable here. The type of crops can matter too. Pesticide use is also particularly high in countries with "valuable crops where pest pressures are high, including Colombian coffee and Dutch tulips." Meanwhile, use is low in Africa largely because of the high cost of pesticides.

3) Chemical pesticides have been quite effective in boosting agricultural yields.

"Long term research plots have shown increases in wheat yield from controlling insects and disease," write David Malakoff and Erik Stokstad. "Gains from plowing fallow fields have been exceeded by the advent of chemical herbicides and fungicides."

4) And insecticides have been invaluable in controlling malaria.

One recent study estimated that the growing use of insecticide-treated mosquito nets prevented the deaths of some 842,800 children between 2001 and 2010. The catch? "Insecticide resistance in the mosquito threatens those gains," the Science issue notes.

5) Yet scientists are starting to discover other problems that might accompany heavy use of pesticides.


Blame pesticides? (Linda Davidson / The Washington Post)

Three long-term cohort studies now suggest that certain chemical pesticides can interfere with brain development in young children. And some experts suspect that a class of pesticides known as neonicotinoids are at least partly responsible for the recent collapse in bee populations (though this is still disputed).

There are other, lesser-known impacts as well. Australia's wheat farmers are now dealing with one of the worst weed infestations in the world — an issue caused in part by overuse of herbicides, which led to resistant weeds. And some 300,000 people kill themselves each year by ingesting pesticides, largely in Asia. That's one third of the world's suicides.

And those are just the effects scientists know about. A notable paper from Heinz-R. Köhler and Rita Triebskorn points out that researchers still don't understand the full impact of many chemicals on broader ecosystems. "Although we often know a pesticide′s mode of action in the target species," they write, "we still largely do not understand the full impact of unintended side effects on wildlife."

6) Pesticides are getting safer in wealthy countries like the United States. But that's not as true in the developing world.

"Developed countries have phased out the more dangerous compounds, such as parathion and other organophosphates," write Malakoff and Stokstad. "After the U.S. Food Quality Protection Act of 1996, several more have been banned altogether, limited to farm use, or further restricted to protect workers or the environment."

But many of these toxic chemicals are still widely used in poorer countries — in part because the more dangerous pesticides tend to be cheaper. "Surveys of farm worker health are scarce," they write, "but it's clear that pesticides cause more harm in the developing word. More toxic chemicals are still used, and basic safety equipment is often lacking."

7) Scientists are developing all sorts of intricate methods to reduce the world's dependence on pesticides, though sometimes simpler solutions work pretty well.

The chart above shows how overall pesticide use in the United States has declined 0.6 percent each year between 1980 and 2007. And it's dropped even faster in corn fields — in part because of the widespread use of Bt corn, a genetically modified breed of corn that's engineered to be toxic to pests. One hitch? There's now some evidence that certain insects are becoming resistant to the Bt corn, especially in areas where it's used heavily. That could lead to a resurgence in pesticide use.

But perhaps researchers will come up with new strategies. The Science issue outlines on some of the other clever ideas in the works: "New synthetic chemicals to protect crops hold the promise of stronger and more specific protection with less collateral damage. And some crops won’t need pesticides at all: Scientists are developing plants whose immune systems can ward off fungal, bacterial, or viral diseases, and they are using RNA interference to help plants fight insects—a new technology that could hit the market before the decade ends."

Then again, sometimes low-tech ideas work pretty well too. One piece points out that a soap-opera-centered campaign in Vietnam helped convince local rice farmers to stop overusing pesticides. And in Australia, farmers are now using non-chemical control techniques, such as burning seeds, to control a massive weed problem that was brought on, in part, by heavy herbicide use.

Related: There's also this free podcast from Science that covers this topic in more depth.

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