Biodegradable plastic bags still able to hold a full bag of shopping after three years

Researchers from the University of Plymouth examined the degradation of five plastic bag materials widely available from high street retailers in the UK.

They were then left exposed to air, soil and sea, environments which they could potentially encounter if discarded as litter.

After nine months in the open air, all the bags had disintegrated into fragments, but this was not the case when left in the soil or marine environments.

The biodegradable, oxo-biodegradable and conventional plastic formulations remained functional as carrier bags after being in the soil or the marine environment for over three years.

This could be especially worrying for marine life which can be badly affected by plastic pollution, as demonstrated in programmes like David Attenborough’s ‘Blue Planet II’.

The compostable bag fared better than the other materials and disappeared completely from the test rig in the marine environment within three months. But even this material was still present in soil after 27 months with signs of deterioration.

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 the most 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.”

In the study, the scientists quoted a 2013 European Commission report that suggested about 100 billion plastic bags were being issued each year, although various governments including the UK have since introduced levies to discourage their use.

The team questioned how effective biodegradable formulations were and whether it is a technology that can be relied upon to help tackle the world’s plastic pollution problem.

Professor Richard Thompson, head of the International Marine Litter Research 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.

“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.”

Tesco recently started a month-long trial to remove plastic packaging from its fresh fruit and vegetables to help reduce plastic waste.