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Plymouth University admits mistake in compostable plastic claim

The University of Plymouth has admitted a mistake in its press release of a report into how biodegradable and other plastics degrade in the natural environment.

The report from the International Marine Litter Research Unit looked into how biodegradable, oxo-biodegradable, conventional HDPE and compostable plastic bags degraded over time in the marine environment, open air and in the soil.

Many media outlets reported that the bioplastic and compostable bags could still carry bags of shopping after spending three years in sea water and soil. The university now says this is wrong.

The report actually found that the compostable bag completely disappeared in the marine environment within three months, and showed some signs of disintegration after three years in soil, so that it could no longer hold weight without tearing.

The Bio-based and Biodegradable Industries Association (BBIA) accused researchers at the university of removing some of the references to compostable bags within the press release.

A BBIA spokesperson said: “References to compostable bags have now been eliminated everywhere except in one paragraph. The conclusions are very clear that compostable plastic bags biodegrade in marine environments and that they degrade in soil (ie they are no longer able to hold any weight and disintegrate).”

Plymouth University has admitted that the headline on its press release stating that both compostable and bioplastic bags were still intact after three years was wrong. A spokesperson for the external press office at the university said this was “essentially a typo, and it has been corrected”.

The spokesperson added: “Neither the body of the press release nor the academic paper made any mention of the compostable bag being able to hold items after the experiment. And it is not correct to say that there were changes made to the media release to make that clearer.”

They added that it was the press office’s error and the authors of the report were not to blame.

The bioplastics industry pointed out that it has not claimed that compostable bags biodegrade in environments other than industrial composting systems.

The results raise interesting questions about whether the use of compostable plastics is more favourable to the environment compared with other plastics, yet the impact of the compostable material on the marine environment is not known. The study found: “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.”

And it concluded: “For many applications in which plastic carrier bags are used, perhaps durability in the form of a bag that can and is reused many times presents a better alternative to degradability.”


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