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.
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.
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