Nova Scotia·Waves of Change

Q&A: Some biodegradable bags survive years in water, underground

CBC News spoke with a Dalhousie University environmental studies professor about some new research on biodegradable bags that found they aren't necessarily as advertised.

Dalhousie University professor says the best choice for a biodegradable bag is a compostable bag

A Mountain Equipment Co-op customer holds a biodegradable shopping bag at the store in Vancouver, B.C., on Friday, July 18, 2008. The company eliminated single-use plastic bags from the store that year. (The Canadian Press)

Waves of Change is a CBC series exploring the single-use plastic we're discarding, and why we need to clean up our act. You can be part of the community discussion by joining our Facebook group.

In a well-meaning effort to reduce the amount of single-use plastic in the world, some people turn to biodegradable plastic bags. However, new research from the U.K. suggests those bags may not be as environmentally-friendly as they seem.

The research, conducted by the International Marine Litter Research Unit at the University of Plymouth, examined five different kinds of bags, and found that bags that were described as "biodegradable" failed to significantly degrade over a three-year period.

Tony Walker, an environmental studies professor at Dalhousie University in Halifax, said the results show that the only biodegradable bag an environmentally-conscious person should consider using is a compostable bag.

Walker recently spoke to Portia Clark, the host of CBC's Information Morning. The interview has been edited for length and clarity.

I have a feeling I'm going to feel crushed after this conversation since I've been using those so-called biodegradable bags. What did this U.K. study find about them?

It is disheartening, isn't it? Researchers from Plymouth University set about testing five types of bags: two that were labeled as oxo-biodegradable [designed to degrade more quickly into fragments than traditional plastic bags], another was biodegradable, a compostable bag and a conventional plastic bag. They tested them in the marine environment, buried under soil and in the open air at the university campus.

And what happened to them?

The compostable bag actually disappeared virtually immediately within three months in the marine environment. That was genuinely compostable. It was a plant bio-based product.

At the university campus, all of the bags disintegrated into fragments after just nine months [exposed to the air].

Dalhousie University environmental studies professor Tony Walker says compostable bags should be the preferred option for environmentally-conscious people using biodegradable plastic bags. (Submitted by Tony Walker)

But the iconic picture which some of your listeners may have seen on social media in the last couple of days were the biodegradable bags, the oxo-biodegradable bags and the conventional bags. [Those] were all intact after three years in the marine environment and could still hold two kilos of groceries.

What's the difference with what happens to the bags when they're exposed to the air and when they're in a marine environment?

In the air, all the bags disintegrated. So, no matter what type of bag you purchased, they all disintegrated. But of course they don't go away. And I think a lot of people have been lulled into thinking that if they buy a biodegradable bag then it just goes away, but it doesn't. It remains in the environment as smaller pieces of plastics.

So, they're not actually disappearing? They're just in smaller fragments that can still be absorbed by wildlife and by the natural environment?

Exactly. Of the five bag types that they tested, only one was genuinely plant-based and made of natural materials. So for example, I went on the manufacturers' websites and the biodegradable bag made by Exoplastics only contains up to 25 per cent of natural products, which means that over 75 per cent is still petroleum-based. And when they break down, they just make smaller micro plastics that get into the environment. And the same is said for oxo-biodegradable bags as well.

So, really it's only the compostable all plant-based bags that really decompose into a natural state. What does this say about the bans that we're bringing in for example on plastic bags, but also as we move to some of those other alternatives?

The researchers are very skeptical about all these alternatives because unless there's a waste stream that can manage the compostable bags instead of the recyclable high-density polyethylene conventional plastic bags, then I think it's really a non-starter because it causes confusion for consumers and it causes real problems for people doing the recycling or waste management.

Does this mean we just move to a ban on all non-plastic bags?

Well, not necessarily. I've been advocating for a conventional plastic bag ban for quite some time. But what it does mean is that I think we should be considering not just alternatives to plastic bags, but sticking with the cotton bags, so something which is reusable and durable and which will be used time and time again. I think that is the way forward to find an alternative to these single-use items, whether they're conventional plastic or plastic alternatives which, by and large, still contain a lot of plastic polymers.


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