Researchers put a number of biodegradable shopping bags to the test and showed that, in some cases, they can hold a full load years after being left in nature.
Some of the biggest supermarket brands have announced plans to drastically reduce the amount of single-use plastics in their products, including the shopping bags given to customers. Bags described as biodegradable or compostable have been welcomed by campaigners, but they may have a hidden problem.
Researchers from the University of Plymouth have published findings in Environmental Science & Technology that showed five of these so-called greener materials can carry a full shopping load after being exposed to nature for three years.
During the multiyear experiments, the bags were left exposed to air, soil and sea, and monitored at regular intervals. Deterioration was considered in terms of visible loss in surface area and disintegration as well as assessments of more subtle changes in tensile strength, surface texture and chemical structure.
After nine months in the open air, the bags had completely disintegrated into fragments. However, the biodegradable, oxo-biodegradable and conventional plastic materials stayed totally usable after being in the soil or marine environment for three years.
The compostable bag completely disappeared during the marine environment experiment within three months but was still present in the soil after 27 months, with some deterioration.
This study poses a number of questions, according to the researchers, but particularly whether biodegradable bags can be relied upon as a realistic solution to the scourge of plastic litter.
“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,” said Imogen Napper, who led the study. “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.”