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May 11, 2009
Rachel Carson’s DDT
Were Rachel Carson living today, she’d be looking at her 102nd birthday
at the end of this month. As she opened up this morning’s newspaper,
she’d see that a movement she helped to inspire is moving toward its
ultimate conclusion of a total, worldwide ban of the insecticide DDT.
Despite hyperventilating attacks, some accusing her of crimes against
humanity on par with Stalin and Pol Pot, Carson never advocated the
abolition of DDT. In fact, the book through which she had her greatest
impact, Silent Spring, lays out that curbing human misery and
suffering is still primary. The secondary goal was to do so in a way
that did not diminish the natural world.
Carson’s solution to insect-borne disease was simple. Rather than
relying on chemistry, we also consider solutions that incorporated
biology. After all, DDT was not tailor-made for the physiology of one
species. For the same reasons it kills mosquitoes, it kills beneficial
insects and works its way up the food chain. The result is a spring
silent due to the absence of songbirds.
Late last week, a group of nations – and there are many of them – where
DDT remains in use moved to make the dream inspired by Carson’s work a
final reality. A pledge was signed by those nations to end the use of
DDT by 2020.
The momentous nature of this step shouldn’t be overlooked. Malaria still
rages in parts of the world, and DDT remains a key component of control
strategies. It is natural to cling to things that have aided us in the
past. What it signals is the growing awareness of the shortcomings of
relying on chemicals like DDT to control disease.
Although some of what Carson wrote about DDT as a threat to human health
has turned out to be more weighted in anecdote than in empirical fact,
some of her other concerns have turned out to be dead on. Among these,
the ability of rapidly reproducing insects to develop resistance to
chemical insecticides is perhaps the most important. In the end, it
hasn’t been cries from the world’s greens that have put DDT on a course
for the ash heap of history, but the ability of mosquitoes to create
multiple generations of insects – each slightly more resistant to DDT
than the one before – in a very short span of time. Meanwhile, insects
and animals that provide a benefit for mankind reproduce much more
slowly, which means ultimately much of the damage down to local wildlife
is in fact concentrated in animals that provide a positive service.
The solution that has evolved over the years was something straight out
of Silent Spring. Rather than looking for that one thing, malaria
control strategies have instead become a smorgasbord of the many. Where
DDT still works without doing too much harm, it remains in use. In other
places, it’s been found that a more effective and affordable strategy is
the use of insecticide-treated nets.
Last week’s agreement was itself crafted based on a five-year study of
DDT-free malaria control in Mexico and Central America. There, cases of
malaria were cut by 60 percent. In addition to the nets and cleaner
living conditions, the biological controls first envisioned by Carson
were applied – bacteria and fish that prey on mosquitoes.
DDT was actually one of a list of chemicals that the United Nations
hopes to stamp out worldwide, but it was given a special waiver. Why?
Well, to make room for the very human goal of reducing misery and
successful, the program means cutting down on horrible disease in a way
that doesn’t demand a trade-off in biodiversity. It will be the result
of a realization that modern chemistry can’t provide silver bullets for
problems older than mankind. Will Carson ultimately get credit for this
broadened way of thinking? First things first: What say we stop calling
her an inhuman monster?
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