Dear Dr. Universe, Why do non-biodegradables take like a billion, zillion years to decay? —Madeline C., age 8
You’re right. It can take a really long time for some things to decay.
If we buried an apple peel in the backyard it might only take a few weeks to break down into the soil. But if we buried a plastic water bottle, it would probably still be there hundreds of years from now.
There are a lot of living creatures in nature that help break down things. In fact, our trash cans are almost like an all-you-can-eat-buffet for tiny creatures called microbes. Well, an almost all-you-can-eat-buffet. There are some things that they can’t really feast on. It all depends on what’s in our trash bins.
For billions of years, microbes have been munching on plants and animals. They’ve also had some help from fellow decomposers, like worms, flies, and fungi.
The environment where they work can also speed up or slow down the process. The conditions of dirt, air, water, temperature, and sunlight can change the speed of decomposition.
These decomposers are pretty great at breaking down a lot of things we find in nature. But they aren’t as good at breaking down some other materials, such as plastic.
To find out why, I visited my friend Shuresh Ghimire, a scientist who studies biodegradables at Washington State University. He is also really curious about finding ways to decrease the amount of plastic waste in our world, particularly on farms.
Plastics were introduced in the 1930s, he explained. Now, that may seem like a long time ago to us. But for microbes that have been around for billions of years, that’s still a pretty new material.
Both an apple peel and a plastic bottle are made up of different kinds of atoms. Those atoms are bonded and held together in different ways. In an apple, the bonds between atoms are pretty weak. Microbes don’t have to use a lot of energy to break them into smaller parts.
But the plastic bottle has really strong bonds—especially where a carbon atom bonds with another carbon atom. It makes the material sturdy, but it also makes it pretty indestructible. Most microbes don’t recognize these bonds as something they can break down, at least not yet.
“There is a possibility that evolution of microbes over many years in the future may enable more of them to recognize bonds in plastics,” Ghimire said.
In fact, a group of scientists in Japan recently discovered a microbe that looks to be pretty good at eating plastic. They might be able to help us manage some of the plastic waste, but we can help, too.
A water bottle might last hundreds of years buried underground or in a land fill, but it could have a new purpose in our own lifetime if we remember to reuse or recycle it.
—Ask Dr. Universe is a science-education project from Washington State University. Send in your own science question at askDrUniverse.wsu.edu/ask.