‘Biodegradable’ plastic bags still carry groceries three years in soil and sea – Australia
30th April 2019

It turns out those ‘biodegradable’ plastic shopping bags might not be as good for the environment as first thought.

A first-of-its-kind study, published in the journal Environmental Science & Technology,  found biodegradable bags were still able to carry shopping after being submerged in soil and water for three years.

 For the study, researchers spent three years running tests on five different types of shopping bags currently offered by popular supermarkets – biodegradable, oxo-biodegradable, compostable, and high-density polyethylene.

A plastic bag subermerged in soil for three years was shown to still be able to hold shopping (University of Plymouth)
A plastic bag subermerged in soil for three years was shown to still be able to hold shopping (University of Plymouth) (Nine Supplied)

“These materials were exposed in three natural environments; open-air, buried in soil, and submersed in seawater, as well as in controlled laboratory conditions,” the report explained.

The bags were checked at regular intervals, with the level of deterioration monitored.

Each of the bags had disintegrated into fragments after exposure to air for nine months, however three of the materials –  including biodegradable bags – were still intact after more than three years buried in soil or left at sea.

In fact, the bags not only remained intact, but could still carry almost 2 kilograms of groceries.


The compostable bags were the friendliest to the environment when left in the sea, breaking down into larger chunks after three months in the marine environment.

However, they could still be found in soil after 27 months – albeit it was unable to hold any groceries.

Researchers questioned whether some of these products should be marketed alongside statements claiming they can be “recycled back into nature” or “plant-based alternatives to plastic”.

The bag was able to hold 2 kilograms of groceries after three years under water.
The bag was able to hold 2 kilograms of groceries after three years under water. (Nine Supplied)

The study also highlighted how the term “biodegradable” can confuse consumers who believe the bag will simply disappear if thrown away. However, researchers insist it’s not an argument against development of biodegradables or compostables.

“Collectively, our results showed that none of the bags could be relied upon to show any substantial deterioration over a three-year period in all of the environments,” the report read.

“It is therefore not clear that the oxo-biodegradable or biodegradable formulations provide sufficiently advanced rates of deterioration to be advantageous in the context of reducing marine litter, compared to conventional bags”

The research comes after Woolworths, Coles and other retailers banned single-use plastic bags in July last year.

The National Retail Association (NRA) estimated 1.5 billion single-use plastic carry bags were eliminated in the first three months following the self-imposed ban.


Even this article could have been written better.  We should not say a item is Biodegradable.   We should be saying ‘Biodegradable under what conditions’.  This would then inform the customer what to expect to have to do with the item if they want to get it to Biodegrade.   Is it compostable that needs to go to a commercial compost facility.   These are not very common.  Is it landfill-biodegradable where it needs to go to a landfill.   This is where most consumers dispose of their rubbish so it makes the most sense.    The Biodegradability rate is years for this process not months.   This is actually beneficial for a landfill that is capturing biogas.  It allows for a steady supply rather than a quick peak then falling off.

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