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  • [ intro ]

  • Plastic as we know it has only been widely used

  • since Tupperware was invented in the 1940s,

  • but now it's nearly impossible to go a day without it.

  • And as useful as it is,

  • plastic also causes some serious problems.

  • You've heard about these things, turtles caught in six-pack rings,

  • garbage patches as large as Texas,

  • and beaches with more plastic debris than sand.

  • After all, millions of tons of plastic

  • end up in our oceans every year.

  • But as bad as that sounds,

  • some consequences of plastic pollution might still surprise you.

  • For one, plastics can emit greenhouse gases forever

  • not just during the making and disposing of them.

  • Plastic is basically just a long chain of molecules,

  • and when it's exposed to sunlight,

  • UV radiation starts to break that chain down into smaller molecules

  • like methane and ethylene, in a process called off-gassing.

  • Both of these are greenhouse gases,

  • but methane is especially bad because it's 25 times better

  • at trapping heat in our atmosphere than carbon dioxide.

  • And as plastic breaks down, the problem actually gets worse, not better.

  • Researchers have found that,

  • as more surfaces get exposed,

  • there's a huge increase in the release of gases.

  • For example, a common plastic called LDPE, or low-density polyethylene,

  • releases methane 488 times faster in a powdered form than in pellet form.

  • .

  • To make matters worse,

  • once this off-gassing process begins,

  • it can continue even without sunlight.

  • That's because those first broken bonds make the rest of the plastic more brittle,

  • so it more easily breaks down on its own.

  • Over time, it keeps breaking into smaller and smaller,

  • eventually invisible, particles.

  • And as it does, it releases greenhouse gases into the air.

  • Unfortunately, that's not the end of the story.

  • These indestructible pieces of plastic are also contributing to another modern problem:

  • antibiotic resistance.

  • In a 2020 study out of Northern Ireland,

  • scientists collected bacteria from plastic found along the Irish coastline

  • and tried to kill them with 10 commonly used antibiotics.

  • ...which turned out to be surprisingly hard to do.

  • 98% of the bacteria were resistant to ampicillin,

  • one of the most commonly prescribed antibiotics for things like sinus and ear infections.

  • And 16% of the bacteria were resistant to minocycline,

  • another type of antibiotic.

  • Unfortunately, plastic is a great breeding ground for bacteria,

  • because they will grow on any available surface in the ocean.

  • And many antibiotic-resistant bacteria are already out there

  • plastics just give them more places to flourish.

  • Once again, the problem gets worse as plastics break down,

  • because they create even more surface area for bacteria to colonize.

  • And these bacteria don't just stay way out in the ocean.

  • The same study showed that ocean currents

  • can carry plastic covered in bacteria back into coastal waterways,

  • where different species could ingest them.

  • Unfortunately, another 2020 study found that bacterial growth on marine plastics

  • actually makes these plastics smell like food to sea turtles.

  • So animals could be eating plastic

  • because it smells good rather than because it looks like food.

  • Which is not great.

  • Ingesting plastic covered in antibiotic-resistant bacteria

  • could create health problems for marine animals

  • and also for creatures higher up the food chain, including us.

  • Now, as plastic breaks down,

  • it breaks into smaller and smaller and smaller pieces,

  • and some of the smallest plastics may be capable of doing the most harm.

  • Any plastic that's smaller than a few micrometers is called a nanoparticle,

  • and research has found that these microscopic particles

  • can even pass through biological barriers, such as cell membranes.

  • That means they can enter the bloodstream of animals,

  • pass through the gut lining, and penetrate tissues.

  • They can also accumulate in organs

  • like the liver, kidneys, and intestines.

  • Plastic nanoparticles have even been found to penetrate the blood-brain barrier,

  • a layer of cells that filter harmful substances

  • out of the blood so they can't get into the brain.

  • This seems to be dangerous no matter where you are on the food chain.

  • In a 2017 study out of Sweden,

  • researchers exposed a zooplankton called Daphnia magna

  • to a bunch of plastic nanoparticles.

  • The Daphnia consumed these particles,

  • and scientists found that, while the larger particles didn't seem to affect them,

  • the smallest particles

  • around 50 nanometerswere deadly.

  • Next, to see the effect of the nanoparticles higher up in the food chain,

  • they exposed a group of Daphnia to the plastic nanoparticles again,

  • and then fed them to some fish called Crucian carp.

  • Over the next two months, the carp started to change:

  • They swam slower, explored less of their environment,

  • and lost more weight than the control group.

  • When the researchers analyzed their brains,

  • they found the 53-nanometer particles they had fed to the Daphnia

  • in the fish's brains.

  • And they think these invisible particles changed the carp's behavior.

  • These findings show that plastic nanoparticles can move up the food chain

  • and interfere with the natural function of an ecosystem.

  • And if we ate fish that had ingested nanoparticles,

  • researchers suggest that could even have a direct impact on us.

  • Plastic is everywherein every environment in our planet

  • and it's not going away anytime soon.

  • In some ways, that's great, because plastic can be really useful.

  • But unfortunately, it has some impacts that probably no one was thinking about when they

  • invented Tupperware.

  • Still, the less plastic we use, and the more we understand the consequences,

  • the better we can protect ourselves and our planet's natural ecosystems.

  • Thanks for watching this episode of SciShow!

  • Today is Earth Day!

  • And if you want to learn about ways to make this planet a better, less-polluted place,

  • you might like our video about how engineers and research groups are working on ways to

  • clean up our oceans.

  • You can watch that right after this.

  • [ outro ]

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3 プラスチック汚染の意外な影響 (3 Unexpected Effects of Plastic Pollution)

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    林宜悉 に公開 2021 年 01 月 14 日
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