Stuff versus Stuff: Which grocery bag does it best?

There’s one shopping choice that you make before you even enter the grocery store: to bring a bag, or not to bring a bag?

In our third edition of Stuff versus Stuff, the MITOS mini-series where we explore the sustainability impact of our everyday product choices, we are examining the grocery bags we use and the impact they have on the environment and our health.

What are the most common choices available to us?
First up is the paper bag. Over the years the humble brown paper bag has been improved with colorful printing and the addition of reinforced handles, but the materials largely remain the same.

Next, there is the plastic bag. Once the darling of shoppers for its flexibility and durability, it has been banned in many parts of the world because that same durability has led to litter in our yards and oceans. This stretchy, thin bag is usually made from high-density polyethylene.

Finally, there is the reusable fabric bag. The bags range from lightweight woven polypropylene to varying thicknesses of cotton to the more rustic jute. For this analysis, we’ll be focusing on a jute bag with a cotton handle. 

Environmental Impact
Let’s start by comparing the energy consumed by the materials of the bags on a single bag basis. A 2012 analysis comparing the three different bags used the polyethylene bag as a benchmark, clocking in at 15g of CO2 equivalents per bag. 

Paper and jute both had a lower material footprint than polyethylene by weight, but more material was required to ensure that the bags stood up to the test of family groceries. Due to this, the paper bag had a footprint of 64g of CO2 equivalents per bag and the jute bag had a footprint of 283g. 

Based on greenhouse gas emissions of material production, the paper bag would require five uses in order to have a lower impact per use than the polyethylene bag, whereas the jute bag would require 19. 

However, this figure varies greatly depending on the weight of the bag and what is factored into the analysis. A full lifecycle analysis conducted for the UK government which considered bag production and likely end-of-life scenarios within the UK came to the conclusion that a common cotton shopping bag would need to be reused 173 times in order to have a lower impact on emissions – that’s taking the bag with you every week for over three years.

Comparing the greenhouse gas emissions of bags on a 1:1 basis might make it seem like plastic is the better way to go, but is it realistic to assume that you only need to use one bag for your weekly groceries?

Capacity of common bag types by weight and volume

The same UK study analyzed the capacity of commonly-available bags by materials and found that reusable bags could hold up to one and a half times more groceries by volume and 18 times more by weight.
This means a load of groceries that requires 6 jute reusable bags might require the capacity of 9 plastic bags, where some might be double-bagged for reinforcement, let’s say totaling 12 plastic bags. If this reflects your weekly groceries, the number of times you would need to use your jute bags to have a lower impact than plastic bags goes down from 19 times to 10.

Beyond greenhouse gas emissions, cloth and paper present an extra concern: the source materials are often bleached, leading to the release of chemicals into the environment. Cotton in particular is known for being a water-intensive crop and the plant material has to be processed heavily before it can be used as a textile. 

The reason why the plastic bag still garners more criticism for its environmental imprint is that we have seen it clogging our beaches, parks, and waterways as litter. Every bag that isn’t recycled has an expected lifespan of several centuries, during which time it will release chemicals into the surrounding environment – whether that’s the water we drink or the soil we grow our food in. Several newer plastic bags have been touted as ‘biodegradable’ but won’t break down quickly in a landfill environment. Even if plastic bags end up in recycling bins, they are likely to be converted into plastic lumber which has more limited end-of-life options. 

What does this really mean for our shopping bag choices? There are many environmental factors for us to think about and it will always come back to how we use and dispose of these products.  Plastic may well have the lowest carbon footprint per bag, but their design often requires us to use more bags and dispose of them almost immediately, where they can have a disastrous impact.

Here are a few things you can consider when thinking about this trade-off: Can you use your grocery bag enough times to reduce its impact? Using a paper bag five times may be difficult, especially for items with a high moisture content, compared to committing to a reusable bag for a longer period of time. 

Will your bags have the best chance possible at a second life? Where possible, we need to reuse our plastic bags as long as we can, recycle our paper bags and donate or repurpose old reusable bags. 

Health Impact
We often focus on the environmental impacts of products and forget that they shape our lives in other ways too. You might want to think about whether your bag choice impacts the way you shop, especially if you have to carry bags for longer distances. Cloth bags tend to have a larger capacity and can handle heavier items, which means that you may end up carrying a heavier load on one side of the body. On the flipside, setting your own limit on shopping by only bringing a set number of bags might just be enough to prevent you from indulging in some impulse purchases which might go to waste and save your wallet in the long run.

Another health question for these unusual times is whether your grocery bags can become a medium to spread viruses. Many people are asking: does the material of your grocery bag make a difference in how long viruses stick around? 

A recent summary of the persistence of coronaviruses on different materials published in the Journal of Hospital Infection suggested that viruses might stick around for a slightly shorter period of time on paper than they would on plastic or cloth – but the time taken before the concentration of the virus was below infectious levels still numbered in days. In short, don’t stress about the material of your grocery bag – if you have concerns about contamination, follow CDC guidelines and disinfect dirty surfaces as well as washing or sanitising your hands.  

Recommendations:

• Try to avoid getting new bags, regardless of the material: Any bag – regardless of material – can be used at the grocery store again if it is in good condition and means you don’t need to pick up another set of plastic or paper bags. And as much as we love picking up new reusable bags through promotions or events, it’s better to say no if you don’t think you’ll use it. 

• Reuse your bags if you can: There are many ways to prolong the life of your bags. Plastic bags can be used to wrap opened foods in the fridge, to pack shoes when travelling or going to the gym, repurposed as bin liners (instead of buying new ones) or for cleaning up dog messes. Paper bags can be used to carry your lunch or even cut up into handy squares of scrap paper for writing notes. Cloth bags can be cut up for shoe polishing rags or, if you’re feeling crafty, converted into beeswax wraps to replace plastic wrap.

• When they can’t be reused, recycle: Check your local recycling program so that you know what will and won’t be accepted. Ensure that anything you put in recycling is free from contaminants like food spills that can ruin the final product.

Ashby M F (2012) Materials and the Environment Chapter 8 ‘Eco-Audits’ 
Environment Agency (UK) (2011) ‘Life cycle assessment of supermarket carrier bags: a review of the bags available in 2006’
Kampf G, Todt D, Pfaender S, Steinmann E (2020) ‘Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents’ Journal of Hospital Infection