Why is it so hard to make a biodegradable plastic?
“Biodegradable” sounds like it should be simple — but it’s not. Biodegradable means that biological organisms, like bacteria and fungi, break something down until there’s nothing left but carbon dioxide (CO2), water, and something called biomass (natural material from living things).
The challenge is that the tiny organisms that do the work of breaking materials down need the right temperature, moisture, and oxygen levels to do it. A material that breaks down in a hot, carefully managed compost facility might not break down as well in the ocean, in soil, or in a landfill. So a product can be labeled “biodegradable” but still stick around in the environment for a very long time.
Proving something is biodegradable is harder than you’d think. You might think a plastic spoon disappeared in your compost, but tiny pieces of plastic — too small to be seen by eye — can be left behind. Scientists will typically try to measure how much of the material weight is gone after some time or try to detect how much CO2 is created by the degradation. While these approaches provide a useful clue, they don’t directly look for the leftover fragments and so they may miss how much plastic persists.
There are laboratory standards to help test these materials with consistency, like those from ASTM International and certification programs from TÜV Austria. These set thresholds for how much a material should break down in specific conditions, like industrial composting, in a specific amount of time. But these standards don’t require 100% of the material to disappear. That means a plastic can “pass” the test even if some material remains. And because the tests are done under controlled conditions, they don’t always reflect what happens in the real world.
To understand this challenge, we must remember that plastics are designed to be incredibly durable, which is exactly why they persist in the environment. With biodegradable plastics, scientists are essentially trying to design something with two opposite properties: long-lasting like conventional plastic when we want it, and completely biodegradable when we don’t.
This is a major scientific challenge and one reason many experts emphasize solutions like reduction, reuse, and refill systems, rather than relying on new “biodegradable” plastics to solve the problem. Importantly, these solutions can work now. To learn more about this, check out our report on bioplastics.
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