The reasons are that not enough was known about the biodegradability of the materials and there were important shortcomings in the test procedures. Some plastics were tested for their biodegradability in freshwater while they biodegrade very slowly in marine habitats. In other words, testing only happened in the labs and not in the oceans. There’s also no clarity and consensus for the time it takes to degrade to be called biodegradable.
This new research may have as consequence that biodegradable labels will no more be equal to environmentally friendly.
Besides the fact that the testing methods were biased and incomplete; there’s another major problem when it comes to biodegradable plastics.
A plastic that biodegrades may disintegrate in smaller plastic particles that can be ingested by marine animals and are harder to manually or mechanically remove from the marine environment. Last element are the chemicals left behind in the ocean after the biodegradation process happened.
The research was commissioned by the UK Department for Food, Environment and Rural Affairs.