Biodegradable plastics contain chemical additives that encourage microorganisms to feed on the plastic, using their enzymes to break the plastic’s molecular bonds. These additives work in two main ways: either by attracting microbes to the plastic directly, or by speeding up the plastic’s natural weathering process, which gives a larger, more ragged surface area for the microbes to work on.
Once the microbes have done their work, all that’s left behind is water, carbon dioxide, and methane. The reality is, however, a little more complex, as many biodegradable plastics need particular conditions in order to biodegrade. This typically involves temperatures of over 50°C and the right combination of moisture, air and microbes – meaning that these plastics won’t break down if left in the ocean or on domestic compost heaps.
Meanwhile, some plastics labelled as biodegradable aren’t truly biodegradable but are merely designed to disintegrate into fragments when exposed to air. These plastics never decompose entirely, but leave behind tiny pieces known as microplastics.