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If you’ve heard anything about pesticides, it’s probably about how toxic they are. But they make growing food more cost-effective, so when some make it into your groceries, how bad can they be?

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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 bio-accumulates, 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 [♪ OUTRO].