How Long Do Biodegradable Bags Really Last?

So-called biodegradable and compostable bags may not provide a tangible environmental benefit over conventional plastic alternatives, according to a new study carried out by the International Marine Litter Research Unit at the University of Plymouth. By testing out five different varieties of bag, the authors concluded that any benefits were negligible.

The compostable bag fared slightly better than its biodegradable counterparts over the three-year course of the study, having decomposed completely in a marine environment in that time and weakened considerably in a terrestrial one. But the allegedly biodegradable bags were still capable of carrying a full bag of groceries even after three years in both environments. The results come after similar revelations about the eco-friendly properties of paper bags (or lack thereof) in comparison to their plastic counterparts.

Claims don’t carry weight

In order to complete the study, the researchers compared how five different types of carrier bag held up when exposed to the natural elements of the sea, the earth and the air. The five varieties tested were a biodegradable bag, two kinds of oxo-biodegradable bag, a compostable bag and a conventional polyethylene plastic bag. None of the items tested had decomposed fully in all three environments at the end of the test period.

The compostable variety fared the best, having disappeared in the marine setting within three months. However, it was present in soil for up to 27 months, at which point it still hung together but would not carry any weight. The other samples had not broken down at all after the three-year testing period and could still function normally with a full load of groceries. Given that there remains the potential for these allegedly superior products to break down into even more dangerous microplastics, it’s doubtful that they pose a more favourable option than conventional plastics.

A persistent problem

Despite the introduction of a charge for all plastic bags in supermarkets in Britain in 2015, the number of bags still being produced and sold is staggeringly high. A survey from Greenpeace found that the top 10 supermarkets in Britain produce a cumulative 1.1 billion conventional plastic bags, 1.2 billion plastic bags for fruit and vegetables and 958 million “bags for life” every single year. The authors of the study argue that 98.6 billion bags were produced for the EU market in 2010 and that that figure has grown by approximately 100 billion every year thereafter.

However, supposedly more environmental alternatives may not even provide the solution that they claim. “After three years, I was really amazed that any of the bags could still hold a load of shopping. For biodegradable bags to be able to do that was the most surprising,” said Imogen Napper, lead author on the paper. “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.”