How biodegradable is biodegradable plastic?

Researchers from the University of Plymouth examined the degradation of five plastic bag materials widely available from high street retailers in the UK in natural environments, none of which fully disappeared.

Plastic pollution is a growing problem. Warnings like that there will be more plastic in the ocean than fish by 2050 are commonplace, and most people will be aware of it. Unfortunately, the sad truth is that generally, people will choose immediate convenience over long-term responsibility any day, as was demonstrated by the petition launched to bring back plastic straws after McDonalds in de UK replaced them for more sustainable paper ones.

This trend is one of the reasons why companies and designers are trying to create more sustainable plastic for single use, labelled with terms like oxo-biodegradable, biodegradable, or compostable. Not only are these terms confusing for customers, they hold little meaning if there are no rules about what they describe.

The study conducted by the University of Plymouth found that plastic bags labelled as biodegradable and compostable were still capable of carrying full loads of shopping after being exposed in the natural environment for three years.

The five different materials 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 9 months in the open air, all materials had completely disintegrated into fragments. However, the biodegradable, oxo-biodegradable and conventional plastics remained functional as carrier bags after being in the soil or marine environment after 3 years. The compostable bag completely disappeared in the marine environment, but was still present in the soil after 27 months.

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.”

The study raises question of what to expect when a material is labelled as biodegradable, and it emphasises the need for standards for degradable materials. It also questions the need for single use plastic, biodegradable or not, as a whole. Additionally, it reminds us that manufactures of materials need to take responsibility for their products, ensuring that they either degrade within a reasonable time in any natural environment or can easily be recycled.

Photos: University of Plymouth