The Breakdown on Biodegradable Plastics
You may think of the ocean as being full of water, marine life, and not much else. But what about trash? The Great Pacific Garbage Patch is a huge expanse of the Pacific
Ocean that is full of trash. In fact, it’s full of one particular type of trash: tiny bits of plastic. Many tons of plastic have been dropped from ships or washed out to sea from countries all over the world. This plastic has broken down into very small pieces. The currents in the ocean push the plastic into one area and keep it from escaping. Most of the plastic in the Great Pacific Garbage Patch is too small to be easily seen by the naked eye, but it’s definitely there. Scientists estimate that there are about 742,000 bits of plastic per square kilometer of ocean in the Great Pacific Garbage Patch (1.9 million per square mile).
Why is there so much plastic in the Great Pacific Garbage Patch? Well, plastic is durable stuff: it may break into smaller and smaller pieces, but it takes an extremely long time for it to go away completely—so long that nobody’s actually been able to measure how long it takes. The atoms that make it up are still there, making up the simplest unit of plastic.
They may be far out to sea, but these tiny plastic bits can cause big problems for us here on land. Some of the plastic works its way up the food chain when it’s eaten by small organisms in the ocean. The small organisms are eaten by bigger organisms, and so on, until the plastic particles end up in food that humans eat.
Of course, not all of the discarded plastic in the world ends up in the ocean. Other plastic trash ends up in landfills or other places in the environment, where it remains unchanged.
To solve the problem of plastics building up in the environment, scientists have invented biodegradable plastics. Being biodegradable means they can be broken down by natural processes, similar to the way old food breaks down if you leave it alone long enough.
Biodegradable plastics sound pretty great: after all, they break down after just a few months instead of sitting around for hundreds or thousands of years the way regular plastics do. Plastics that just disappear would save a lot of space in landfills and keep the oceans from filling up with even more plastic bits—right?
The answer isn’t so simple. Biodegradable plastics are different from regular plastics because they do break down, but that’s not the end of their story. After all, the atoms that make up biodegradable plastics still exist. When biodegradable plastics break down, they become reactants in chemical reactions and turn into other substances. Some of those substances are harmful and some of them aren’t. But either way, humans need to

deal with them.We know that the atoms in biodegradable plastics don’t just go away because we know they follow the Law of Conservation of Matter. The Law of Conservation of Matter says that matter cannot be created or destroyed. That means all of the matter on Earth already exists, none of it can ever just disappear, and there’s no way to make more. It also means that the products of a chemical reaction contain the same atoms as the reactants. Since all matter is made up of atoms, we know that the atoms in biodegradable plastics can’t just disappear—instead, they rearrange and form new products.
Plastics are made of specific combinations of carbon, hydrogen, and oxygen molecules, and most biodegradable plastics break down when they react with water
(H2O). Since the reactants are made of a certain number of carbon, hydrogen, and oxygen atoms, the products must have exactly the same number of each. After all, the products are made of the same atoms as the reactants—no more and no fewer.
So biodegradable plastics do break down, but their atoms still exist as other substances. And even if they break down into harmless substances, the reactions that cause them to break down can’t just happen under any conditions. They require special circumstances! For example, some biodegradable plastics need temperatures of 60
℃
(140 °F) for ten days straight to break down completely. These kinds of conditions usually happen only at commercial composting facilities, which turn leftover plant matter and other compostable materials into dirt. That means biodegradable plastics won’t break down in landfills or in people’s backyard compost piles. Other types of biodegradable plastic need plenty of water to help them decompose. In cases like these, it’s important to have the right ratio of water to plastic—that is, enough water to decompose the plastic. If there aren’t enough water molecules present to react with every molecule of plastic, the water will run out before all the plastic has broken down, and some of the plastic will be left behind.
Plastic is one of the most common substances in the world, and some people think biodegradable plastic might help us produce less waste, or at least waste that doesn’t stay in our environment as long. That may be true, but the atoms that make up biodegradable plastics don’t go away—just like regular plastic, they’re sticking with us.