Walk along almost any beach and you'll spot it: a bottle cap, a scrap of a bag, a tangle of fishing line. Plastic seems to last forever. But how long is forever, really, and how does anyone know?
The short answer is that many common plastics are expected to take hundreds of years to break down. The Ocean Conservancy estimates about 50 years for a foam cup, 400 years for a plastic six-pack holder, 450 years for a disposable diaper, and 600 years for fishing line. These are predictions, though, because plastic hasn't existed long enough for anyone to watch it fully disappear.
A Very Young Material
People have used natural plastic-like materials for a long time. Around 1600 BC, people in Mesoamerica made balls and figurines from natural rubber. In the Middle Ages, treated cattle horn was used for lantern windows.
But the first fully synthetic plastic, Bakelite, was invented in New York in 1907 by Leo Baekeland, who also coined the word plastics. Mass production didn't really take off until the 1940s and 1950s. So the oldest everyday plastics are well under a century old, which is why decomposition times are estimates, not observations.
Why Plastic Hangs Around
Plastics are made of polymers, long chains of molecules, and the breakdown of common plastics is slow. That's exactly why they're so useful. They're tough, light, and resist water, so they don't rot the way wood, paper, or food scraps do. Dozens of types are made today, from polyethylene in packaging to PVC in pipes, which is prized in construction precisely because it's so strong and durable.
Sunlight does slowly damage many plastics, a process called photodegradation. That's why old plastic toys and lawn chairs turn yellow and brittle. Manufacturers often add stabilizers, including ultraviolet absorbers related to the chemicals in sunscreen, to make products last even longer.
It Breaks Up, Not Down
Here's the catch. As plastic weathers, it often doesn't vanish. It crumbles into smaller and smaller pieces. Bits smaller than 5 millimeters, about the size of a pencil eraser, are called microplastics.
Some microplastics come from bigger items like water bottles, bags, and fishing nets breaking apart. Others start out tiny, like fibers shed from synthetic clothing in the wash and dust worn off car tires. Because they're so small, they can enter the food chain at the very bottom.
They even turn up in what we drink. In one study, 93 percent of bottled water samples from 11 brands contained microplastics, and the bottled water had about twice as much as tap water.
The scale is huge. From the 1950s to 2018, the world produced an estimated 6.3 billion tonnes of plastic. Only about 9 percent was recycled and 12 percent burned, with the rest reportedly ending up in landfills or the environment. Studies suggest that 90 percent of seabirds have plastic in their bodies.
Nature Fights Back
There's some hopeful news. In Sakai, Japan, scientists found a bacterium at a bottle recycling site that can break down and feed on PET, the plastic used in many drink bottles. It makes two enzymes that work one after the other to digest it.
So the plastic bottle you toss today may well outlast you. That's a good reason to reuse, recycle, and pick up that stray bottle cap on your next beach walk.
