Bags made of supposedly biodegradable plastics remain intact and useable three years after being dropped in the sea or buried underground, researchers have found.
The study, carried out by the University of Plymouth's International Marine Litter Research Unit and published in the journal of Environmental Science and Technology, challenges assumptions that switching to biodegradable plastics could reduce ocean-plastic pollution.
"Our results showed that none of the bags could be relied upon to show any substantial deterioration over a three-year period," said Imogen Napper, who co-authored the report.
She said it is therefore "not clear" that biodegradable plastics can help reduce marine litter.
Questions raised about "biodegradable" labels Five types of plastic carrier bag, all widely available on the UK high street, were used for the experiment.
They included a biodegradable bag, an oxo-biodegradable bag, and a compostable bag, as well as a standard plastic bag made of high-density polyethylene.
Each bag was left exposed to the kind of conditions they would encounter if they were discarded as litter, including being left in the open air, buried under soil or submersed in the sea.
The scientists tested the bags at regular intervals, monitoring them for changes in strength, texture and chemical structure.
"This research raises a number of questions about what the public might expect when they see something labelled as biodegradable," s...