Researchers at the University of Plymouth’s International Marine Litter Research Unit have revealed that biodegradable, oxo-degradable and conventional plastic bags all remained functional bags despite being in the the soil or marine environment for three years.

The study also tested a compostable bag, which disappeared in the sea after three months, but was still present in soil after 27 months, though it had showed some signs of deterioration. The study has drawn criticism for being “misleading”, however, given that compostable bags are intended to degrade in industrial composting facilities, not the open environment.

Commenting on the study, research fellow Imogen Napper, who led the study as part of her PhD, said: “After three years, I was really amazed that any of the bags could still hold a load of shopping. For a biodegradable bag to be able to do that was surprising. When you see something labelled in that way, I think you automatically assume it will degrade more quickly than conventional bags. But after three years at least, our research shows that might not be the case.”

Professor Richard Thompson, head of the International Marine Litter Research Unit, added: “This research raises a number of questions about what the public might expect when they see something labelled as biodegradable. We demonstrate here that the materials tested did not present any consistent, reliable and relevant advantage in the context of marine litter.

“It concerns me that these novel materials also present challenges in recycling. Our study emphasises the need for standards relating to degradable materials, clearly outlining the appropriate disposal pathway and rates of degradation that can be expected.”

However, trade body European Bioplastics (EUBP) has criticised the University study and said that the University of Plymouth’s research was “misleading”.

EUBP said the bags were designed to degrade in an industrial process and not within the natural environment and they were not designed to reduce littering. It said the report is “misleading” the

EUBP managing director Hasso von Pogrell said: “Plastic products certified to be industrially compostable are no solution for littering. Testing them as if they should be is misleading the public’s perception of the technology.

“It creates the impression of the product lacking in performance, even though the performance in the intended environment has not been tested at all.”

Lucy Frankel, Communications Director at Vegware, which produced the compostable bags for the study, added that the company did not advocate its compostable products as a solution to marine litter pointing out that they must be disposed of in an appropriate facility, not in the environment. She said: “Burying isn’t composting. Compostable materials can compost with five key conditions – microbes, oxygen, moisture, warmth and time. The UK’s industrial composting facilities create these conditions for a living, and Vegware products are accepted and composted at a network of facilities around the UK, as well as some on-site composting solutions. Trade waste collections for Vegware products are now available in around 1,200 UK postcode districts.”

“At Vegware we don’t say ‘biodegradable’ – this vague term has no defined timescale or conditions. What’s more, oxo-degradable plastics are often marketed as ‘biodegradable’, despite the Advertising Standards Authority ruling it was misleading in the case of Ancol’s dog poo bags. Oxo-degradable plastics are being banned by the EU’s Single Use Plastics Directive, but are currently very widespread in carrier bags, clear cups, straws and cutlery – often confusingly marketed as ‘biodegradable’.”

David Newman, BBIA Managing Director, added: “The study shows that compostables will break down in marine environments but that ‘biodegradable’ and ‘oxo-degradables’ will not. This confirms the reason why the EU has announced its ban on oxos, they have no known usefulness, and why using the word ‘biodegradable’ is meaningless and indeed should be made illegal as regards compostable packaging. Either a packaging material biodegrades when composting under the 13432 standard or there is no legal definition. The study proves this.

“Compostables are made to compost. Whilst it may be comforting that they also break down in marine environments, we should not be advocating that compostables are suitable for littering. Compostables should be used to reduce waste, to promote biowaste collections to composting and anaerobic digestion, and to ensure high-quality soil improvers are returned to soil without plastics contamination.

“If we are to define new standards they should be applicable to all plastics, not just to compostables. So, if marine biodegradability becomes an imperative in UK law for the future, we would welcome that as long as all plastic materials are subject to the same standard.”