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If you’ve heard anything about pesticides,
it’s probably about how toxic they are.
Pesticides, after all, are meant to kill living
things, and you’re a living thing.
It seems like it’d make sense to avoid them.
At the same time, though, pesticides do a
lot of good things for us, like protecting
us from diseases like malaria and typhus,
and increasing the amount of food we can grow.
Most farmers, and yes, even organic farmers,
use them.
Naturally, there’s been a lot of confusion
about these chemicals.
So let’s clear some of that up.
Here's what the science has to say about what
exactly pesticides are, how they work, and
how much you need to worry about their effects
on us and our planet.
You might think of pesticides as primarily
what’s sprayed on your corn or lettuce,
but the first thing to realize is that they’re
actually a /really/ broad category of things.
They’re basically anything that’s used
to kill or control pests, which can be animals,
plants, insects, fungi, and bacteria or other
microbes.
That means the term ‘pesticide’ actually
covers a vast array of products.
It includes herbicides for destroying weeds,
insecticides for getting rid of insects, fungicides
for keeping mold from growing, rodenticides
for poisoning rats and mice, as well as everyday
disinfectants.
So sure, there may be residues on your apple.
But pesticides are also hiding in places you
might not think, like your plastic shower
curtain to prevent mildew, and in paint to
keep bugs in check.
We’ll be focusing on pesticides in agriculture,
though, because that’s one of the largest
sources of exposure for most people.
Much of the modern concern over pesticides
goes back half a century.
Around then, scientists and environmentalists
began to notice problems with some of the
newer synthetic, or man-made, pesticides available
after World War II, including one called DDT.
DDT acts on sodium channels in insect neurons,
forcing them to stay open, and to keep firing.
This causes bugs to spasm and twitch, eventually
paralyzing and then killing them.
DDT was masterful at eliminating the insects
that spread malaria, typhus, and dengue fever,
so much so, that the scientist who discovered
this property won a Nobel prize in medicine
in 1948.
The chemical worked as an insecticide on crops,
too.
But it didn’t come without cost.
Although it’s moderately safe for humans
to handle in low doses, DDT builds up, or
bioaccumulates, in the fat tissues of exposed
animals.
And because the pesticide degrades so slowly
in the environment, it moves up the food chain
in a process called biomagnification.
As a result, birds of prey struggled to reproduce
because their eggshells thinned and broke
more easily.
DDT also proved to be highly toxic to fish
and other aquatic animals.
Basically, it’s not good for ecosystems.
In 1962, Rachel Carson famously sounded the
alarm in her book, Silent Spring, and a decade
later the U.S. government banned DDT for agricultural
use.
In its own way, though, DDT helped to spark
the modern environmental movement.
People started to care more about the chemicals
used to grow their food and how they affected
both our planet and other people.
More care was put into developing and using
pesticides.
And we have gotten a lot better and more careful
with them.
But even today, it’s still not a perfect
system.
Some of the more modern insecticides, such
as the organophosphates, don’t stick around
as much in the environment as DDT, but they’re
sometimes more toxic per application.
Others, like ones called neonicotinoids, improved
on both these fronts.
But they may still be too toxic to certain
species, like bees, that we’d want to keep
around.
Scientists are still debating this.
Herbicides also have their problems.
While insecticides tend to interfere with
the nervous system of insects, herbicides
attack weeds by preventing them from growing.
Often, they do this by preventing photosynthesis,
or by inhibiting enzymes that plants use to
make new cell walls, amino acids, or fatty
acids.
Unfortunately, under certain conditions and
concentrations, some of these are so acutely
toxic to humans that people have used them
to commit suicide.
Others are less dangerous to people and some
other animals, but they can still leach into
groundwater, where they can harm fish.
And even though we’re making progress, other
types of pesticides have their own struggles,
too.
Really, none of these are ideal.
It’d be great if we didn’t have to use
them, and there are strategies people can
use to reduce use.
But when you run into a big problem, like
a massive cockroach infestation in your kitchen,
you’ll be glad they exist.
And, let’s face it.
Pesticides make growing food more cost-effective.
Studies suggest that farmers lose at least
20-40% of their crops to pests, and pesticides
allow growers to keep up on large-scale production.
That means food is cheaper.
It doesn’t just apply to regular produce,
either.
It also applies to the fancy organic stuff.
Many people assume organic food, at least
as it’s legally defined in the US, is grown
completely /without/ pesticides.
But that’s not true.
Organic farmers are supposed to do everything
they can to avoid using pesticides in the
first place, like rotating which crops they
grow.
Because many pests only attack certain crops,
swapping out different plants in your field
can prevent any one of them from gaining a
foothold.
But if those methods fail, and often they
do, organic farmers /are/ allowed to spray
pesticides.
They just can’t be man-made, although there
are a few exceptions.
Perhaps because of this, and because people
generally trust ‘natural’ things over
the ones humans cook up, many consumers have
assumed that synthetic pesticides must be
worse than natural ones.
But that’s only sometimes true.
/Some/ synthetic pesticides are definitely
worse.
But just because something is natural doesn’t
mean it’s better.
Arsenic, of course, is completely natural,
but that doesn’t mean you want to use it.
In fact, before DDT came on the scene, most
American farmers used arsenic-based pesticides.
Now, thankfully, no one is using them to grow
food.
Another example is rotenone, a tropical plant
extract that’s great for killing bugs, since
it gums up their mitochondria.
It’s also 100% natural, but it wreaks havoc
on fish, and has been linked to increased
rates of Parkinson’s disease among farm
workers.
Because of other regulations, American farmers
can’t use rotenone anymore.
But at least right now, it could still be
on some imported organic produce.
Dosage, as toxicologists are constantly reminding
us, is also really important.
Some scientists have pointed out it’s not
always clear-cut which might be better: a
one-time spray of a high-powered synthetic
pesticide, or repeated, larger doses of a
natural one.
The research is still ongoing, but at least
one study in soybeans found that, because
natural pesticides were less effective, using
them ended up actually harming more unintended
targets.
So, the rules, then, are really rather arbitrary
when it comes to synthetic versus natural
pesticides.
Mostly, don’t assume that just because something
is organic, and it’s been grown with natural
pesticides, that you’re better off.
It’s not as clear-cut as you’d hope.
Obviously, all of this isn’t great for consumers,
which includes all of us because we all need
to eat.
But even though we’re still working out
the kinks with modern pesticides, you don’t
need to go and toss out all of your produce
or anything.
The US government carefully monitors the food
supply for excess pesticide residues, so even
if some make it into your groceries, you’re
going to be fine.
The Environmental Protection Agency, or EPA,
sets limits, or tolerances, based on the available
scientific data, for the highest level of
residue that’s still safe.
They also build in a margin of error that’s
at least 10 times, but often 100 times, higher
than what any study has suggested might be
harmful.
And the vast majority, 99.5%, of our food
supply meets that high standard.
So when you hear about certain foods being
full of pesticides, there may be residues
there, but they’re still /well/ below any
known harmful level.
Like, for one pesticide, you’d have to eat
more than 700 times the typical daily apple
consumption to reach the EPA’s already cautious
tolerance level.
Of course, the monitoring program isn’t
perfect.
It doesn’t test all food for all pesticides,
and it also doesn’t test for most organic
ones.
That means comparing an organic apple to a
conventional one isn’t really fair.
It’s kind of like comparing apples to oranges,
so to speak.
Ultimately, this means you don’t actually
know the /total/ level of pesticides on each
piece of your fruit.
To avoid as many pesticides as you can, there
are a few things you can do, though.
Like, you can scrap that outer layer of lettuce,
or wash your fruits and vegetables before
chowing down.
Experts recommend using water, not soap, and
rinsing your produce under a faucet.
The stream of water removes more pesticides
than simply dunking, and rubbing or scrubbing
things like potatoes can get you a deeper
clean.
There’s no evidence, though, that specialty
produce washes do anything that water can’t
do.
Washing won’t remove every last molecule
of pesticide, but does help for most foods.
You can also feel generally better about the
pesticide situation these days.
Even if things aren’t perfect, farmers and
scientists are much more aware of the dangers
of them, and they’ve gotten better about
using them more carefully.
So, as much as people bemoan the good old
days of agriculture, compared with a half
century ago, people are ingesting fewer and
less dangerous pesticides.
Even the most famous ones people love to complain
about aren’t that bad.
One of the most used, and currently hated
herbicides is glyphosate, which may be more
familiar to you as Roundup.
As with any pesticide, it’s not perfect,
but Roundup is /much/ less toxic to people
and the environment than the vast majority
of herbicides.
You don’t want to sit down to a dinner plate
full of it, but all things considered, it’s
not the worst thing out there.
Of course, that’s not to say the situation
is ideal, either.
Farm workers, especially, are still at a much
higher risk for a variety of diseases because
of their increased pesticide exposure.
The long-running Agricultural Health Study
has been tracking the health of people who
apply pesticides for a living for 25 years.
It’s found that certain pesticides are linked
to increased rates of rheumatoid arthritis
and thyroid problems.
But in general, awareness about the possible
dangers of these chemicals, to people and
the planet, means we’re less likely to indiscriminately
use something like DDT before learning more
about it.
Scientists, too, are working on coming up
with new, less toxic options for the future.
One example of these works-in-progress are
a chemical called paldoxins.
They’re considered fungicides, but they
don’t kill fungus directly.
Instead, they help plants fight off the fungus
themselves.
Many plants, especially those in the Brassica
family, which includes things like broccoli
and brussels sprouts, release antimicrobial
compounds to kill their attackers.
The problem is, the fungus have evolved a
way to neutralize those defense compounds.
It produces an enzyme to detoxify the defense.
The idea behind paldoxins is to remove that
counter attack and destroy that fungal enzyme
to make it easier for the crop to win the
battle.
It’s kind of like fixing the match in favor
of King Broccoli.
We don’t know for sure how well these would
work, or how safe they would be.
But because it’s a very specific way of
undermining a certain pest, biologists think
the damage would be pretty much limited to
the fungus they want to keep off their plants.
And it’s hard to imagine how this could
be harmful to humans.
Other scientists are working on using nanotechnology
to do things like control the release of pesticides
and stop them from washing off plants so quickly.
That would allow farmers to use less and still
get the desired results.
Other teams are looking for different ways
to take advantage of the biology of insects,
fungi, and other pests to create more targeted
treatments.
So, hopefully soon, thanks to science, we
can use fewer chemicals on the pesky organisms
out there, and be even smarter about it when
we do use them.
And in the meantime, you probably don’t
need to worry about your salad.
Thanks for watching this episode of SciShow!
Besides pesticides, there are a lot of things
in the health world that can seem a little,
well, fuzzy.
If you’d like to learn more about them,
we recommend one of our sister channels, Healthcare
Triage.
On this channel, Dr. Aaron Carroll explains
healthcare policy, medical research, and answers
a lot of other questions you might have about
medicine, health, and healthcare.
You can check it out at YouTube.com/HealthcareTriage.
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