According to a new study, published in the journal Environmental Science and Technology, biodegradable plastic bags are capable of carrying full loads of shopping after being exposed in the natural environment for three years.
A carrier bag labeled as biodegradable after three years in the marine environment. Image credit: Napper & Thompson, doi: 10.1021/acs.est.8b06984.
“This research raises a number of questions about what the public might expect when they see something labeled as biodegradable,” said senior author Professor Richard Thompson, Head of the International Marine Litter Research Unit at the University of Plymouth, UK.
“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.”
Professor Thompson and his colleague, Imogen Napper, examined the degradation of five plastic bag materials widely available from high street retailers.
The bags were then left exposed to air, soil and sea, environments which they could potentially encounter if discarded as litter.
They were monitored at regular intervals, and 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, 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 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.
“After three years, I was really amazed that any of the bags could still hold a load of shopping,” Napper said.
“For a biodegradable bag to be able to do that was the most surprising.”
“When you see something labeled 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.”
“Our study emphasizes the need for standards relating to degradable materials, clearly outlining the appropriate disposal pathway and rates of degradation that can be expected,” Professor Thompson said.
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Imogen E. Napper & Richard C. Thompson. Environmental Deterioration of Biodegradable, Oxo-biodegradable, Compostable, and Conventional Plastic Carrier Bags in the Sea, Soil, and Open-Air Over a 3-Year Period. Environ. Sci. Technol, published online April 28, 2019; doi: 10.1021/acs.est.8b06984
