Do Plastic Bag Bans Make A Difference?

Like so many life-cycle assessments, it’s never that simple. The environmental impact of plastic-bag bans is a good news–bad news story.


By Pierre-Olivier Roy

First, the Good News. Cities that have banned consumer plastic bags have seen a decrease in the number of bags found in nature. Abandoned bags are not only an eyesore, they are also detrimental to birds, fish, and other fauna as the bags make their way from cities to oceans—and we definitely don’t need to add to the Great Pacific Garbage Patch.

Now, the Bad News. Despite the local clean-up factor, the environmental benefits of banning plastic bags remain to be seen. A recent life-cycle study from CIRAIG looked at the consequences of banning conventional, single-use, consumer plastic bags (made of high-density polyethylene) from the city of Montreal. The results challenged the conventional understanding of banning these bags.

A key question is what type of bag buyers and sellers use to replace the banned ones. The CIRAIG study looked at the environmental impacts of seven alternatives:

Single-use bags
Oxo-biodegradable bags
Compostable bioplastic bags
Low-density polyethylene bags
Paper bags
Reusable bags
Woven polypropylene bags
Unwoven polypropylene bags
Cotton bags

The human health indicator considers effects such as climate change, human toxicity, respiratory effects due to the inhalation of particles, smog formation, water scarcity, ozone layer depletion, and others. The ecosystem quality indicator theoretically represents the number of species that disappear within a specified area over a year due to different effects such as climate change; land occupation and transformation; ecotoxicity; eutrophication; acidification of terrestrial, aquatic, and marine environments; water scarcity; and others. The fossil fuel depletion indicator represents the quantity of fossil fuels (crude oil, natural gas, coal) that were extracted in order to fulfill life-cycle material and energy requirements of a product, process, or service.

From: Life Cycle Analysis of Shopping Bags in Québec. International Reference Centre for the Life Cycle of Products, Processes, and Services (CIRAIG). 2017.

Results showed that all replacement bags had higher indicator scores for impacts on human health, ecosystem quality, and fossil-fuel depletion. Therefore, by definition, only reusable bags have the potential to be an advantageous switch from single-use consumer plastic bags—and that potential is realized only by reusing the bags many times: as frequently as 9,400 times for cotton bags or a more reasonable 102 times for unwoven polypropylene bags.

The Unintended Consequences

It turns out that those much-maligned conventional plastic bags have very high reuse rates (as much as 77.7 percent), mostly as garbage-bin liners. When they are banned, people buy more conventional, polyethylene garbage bags. And there’s the kicker. While it was already difficult for reusable bags to be advantageous over the banned plastic bags, in this scenario, even if you reuse your reusable bags an infinite number of times, the impacts of using more garbage bags drown out the advantageous environmental effects.

How many times would you have to use each bag to equal the fossil-fuel footprint of a single conventional plastic bag?

5

Oxo Biodegradable

14

Paper

16

Thick Plastic
Low Density Polyethylene

32

Unwoven Polypropylene

195

Cotton

Why? The conventional plastic bag was designed for a single use—it is thin and light, and its life cycle requires little material and energy. Moreover, its reuse as a garbage bag at the end of its life significantly reduces its potential impacts in comparison to the other types of bag, whose material and energy requirements are much higher.

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