A new study from researchers at the University of Plymouth found that biodegradable and compostable plastic bags are still capable of carrying full loads of shopping after being exposed in the natural environment for three years.
The researchers examined the degradation of five plastic bag materials widely available from high street retailers in the UK, which were then left exposed to air, soil and seas.
These bags were monitored at regular intervals, and deterioration was considered in terms of visible loss in surface area and disintegration, as well as changes in tensile strength, texture and structure.
After nine months in the open air, all the materials had completely disintegrated into fragments.
However, 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.
The compostable bag disappeared from the experimental test rig in the marine environment within three months, but while showing signs of deterioration, was still present in the soil after 27 months.
Researchers from the University’s International Marine Litter Research Unit said that the study created a number of questions.
The most interesting being whether biodegradable formulations can be relied upon to offer an advanced rate of degradation to provide a realistic solution to the problem of plastic waste.
University of Plymouth Head of the International Marine Litter Research Unit Professor Richard Thompson 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.”
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.”