Rotting time undermines value of green labels for plastics

A study into such “oxo-degradable” plastics found there was uncertainty over how quickly they broke down or their impact on the natural environment.

The carrier bags, bin bags and flexible packaging, made from common plastics with small amounts of chemicals to speed up their breakdown, are also not suitable for recycling with other plastics, reuse or composting, researchers at Loughborough University have found.

In the wake of the study, Ministers called on the industry not to claim the plastics were better for the environment than more conventional ones.

And the Co-operative said it would not be using carrier bags made from that type of plastic in its stores in future.

Oxo-degradable plastics contain additives to help them degrade into smaller pieces more quickly with the help of heat or light before they then biodegrade.

The report, funded by the Department for Environment, Food and Rural Affairs, said adding the metal compounds to the plastics did not improve their environmental performance and “potentially gives rise to certain negative effects”.

Researchers said it was hard to estimate how long the plastics would take to degrade, though somewhere between two and five years has been suggested if they are left out in the open UK environment.

But they do not degrade in the absence of oxygen so are unlikely to break down in landfill, where much of the plastic would end up.

One claim made for oxo-degradable plastics is they reduce litter as they are biodegradable, but the report said they would still be lying around for several years before this happens.

Concerns remain about the impact the degraded fragments of plastic could have when they are consumed and amass in insects, animals and fish.

The report said there was no evidence either way as to whether this posed a problem for wildlife.

The study warned that consumers may be confused by labelling the products as “biodegradable” and may put them in with compostable materials – even though they take much longer to break down.