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Deterioration of compostable bags in the sea happens rapidly, new study finds.

A plastic bag submerged in soil for three years could still hold a full load of shopping (Picture Lloyd Russell, University of Plymouth).

“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.”

Compostable plastic bags can take only three months to completely disappear in the sea and 27 months when put in soil, according to a new study by UK-based University of Plymouth.

The study, carried out by the University of Plymouth’s (@PlymUni) International Marine Litter Research Unit and published in the journal of Environmental Science and Technology, intended to provide insights into the “environmental deterioration” of plastic carrier bags made from different polymer types under littering conditions.

Researchers tested five bags from well-known UK supermarkets, which included two oxo-degradable bags, one fossil non-biodegradable polyethylene bag, one bag marketed as biodegradable and one marketed as compostable. The bags were left exposed to air, soil and sea – environments which they could potentially encounter if discarded as litter.

The study highlighted how the compostable bag completely disappeared from the experimental test rig in the marine environment within three months but, while showing some signs of deterioration, was still present in soil after 27 months.

However, biodegradable, oxo-biodegradable and conventional plastic remained functional bags despite being in the soil or marine environment for three years.

The study maintained that the results showed that deterioration of compostable bags “can be relatively rapid in seawater”. However, it also stated that “more work would be needed to establish what the breakdown products of this deterioration are, such as microplastics or nanoplastics, and to consider any potential environmental consequences”.

In relation to the other bags cited in the study, Richard Thompson, head of the International Marine Litter Unit, said: “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.”

‘Misleading to the public’

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 public.

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.”

EUBP argued the report actually showed the importance of using correct labelling and certification.

The EUBP also criticised online stories and headlines from the University of Plymouth’s report.

EUBP chair François de Bie said: “The study confirms that only certified biodegradable and compostable bags – designed to be collected with the bio-waste and organically recycled in dedicated composting plants – even if mistakenly littered in the environment due to bad habits, have a reduced environmental impact.”

He said that while no plastic bag should end up in the environment, “at least it is clear” that certified compostable ones will not need decades to degrade, as conventional plastic bags.

The initial press release headline from the University of Plymouth about the report put the onus on both biodegradable and compostable plastic bags as “failing to break down” in the natural environment.

Yet, David Newman, managing director of the Bio-based and Biodegradable Industries Association (BBIA), told Bio Market Insights that this headline was later amended to exclude compostable plastic bags from the headline.

He added: “Correspondence between the BBIA and the University of Plymouth showed evidence that there were inaccuracies in the initial University of Plymouth press release. However, this has now been corrected.”

Overall, Newman welcomed the study from the University of Plymouth.

All in all, the University of Plymouth’s study maintained that it was essential that products marketed as biodegradable but intended to go into the natural environment had a “high probability of reaching the appropriate waste stream”.

It added: “This will require availability of a dedicated waste stream, the appropriate infrastructure such as an industrial composting facility and sufficient understanding among consumers to correctly separate their waste accordingly.”

Committee on Climate Change report

Separately, another major report has attracted headlines today. A report from the Committee on Climate Change (CCC) has stated that the UK should lead the global fight against climate change by cutting greenhouse gases to nearly zero by 2050.

The CCC maintains this can be done at no added cost from previous estimates.

Bio-degradable waste streams should not be sent to landfill after 2025, it added. This will require regulation and enforcement, with supporting actions through the waste chain, including for example mandatory separation of remaining waste, the report stated. This would help the biomaterials industry, as compostable bags are normally used to dispose of food waste.


Want to find out more about compostable bags? You may also be interested in reading…

Read: UK compostable packaging market poised for tenfold increase by 2025, new report finds.

Read: AMT Coffee unveils ‘let’s make the change’ bio-compostable cups for Christmas season.

Visit: SynBio Markets (Berlin, 18-19 November 2019) 

NEW!: And available to download issue #14 of the Bio Market Insights Quarterly

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