Biodegradable plastics offer "no advantage" over conventional plastics in reducing ocean pollution

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.