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Are cotton bags the most environmentally friendly, or are there bags made from other materials that use up fewer natural resources when they are produced?
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Various studies have shown that the conventional lightweight supermarket plastic carrier bag, certainly reusable although it is classed as disposable, comes out to be the most environment friendly, as long as it is disposed off properly without causing litter or making its way to the marine environment. Cotton bags turn out to be the least environment friendly primarily due to ozone depletion during cotton production.

The Danish Environmental Protection Agency commissioned a life cycle assessment of grocery carrier bags available in Danish supermarkets with the aim to identify the carrier bag with the best environmental performance over a range of environmental impacts.

The table below provides the results as number of reuses needed for a type of bag to provide the same environmental performance of a lightweight supermarket plastic bag. If the reference - lightweight plastic bag - can be reused more than listed, then the number of reuses for the other bags should also be increased proportionally.

Bag typeExampleReuses necessary to have same environmental impact as a lightweight supermarket plastic carrier bag
Lightweight plastic bag with rigid handle0
Lightweight plastic bag1
Recycled plastic bag2
Polyester bag35
Bio-based plastic bag42
Paper (bleached or unbleached) bag43
Woven polypropylene (PP) bag45
Non-woven polypropylene (PP) bag52
Recycled polyethylene terephthalate (PET) bag84
Bag made of multiple materials (plastic, cotton, jute, etc.)870
Conventional cotton bag7,100
Organic cotton bag20,000

A life cycle assessment of supermarket carrier bags conducted by the UK Government had similar results requiring many reuses of paper, more durable PP & cotton bags to have equivalence to global warming potential of a conventional, lightweight carrier bag.

The results of yet another life cycle assessment by the Heartland Institute show that conventional plastic bags use less energy & water during manufacturing, emit fewer global warming gases, less acid rain emissions, and less solid wastes - over both compostable plastic bags and paper bags.

These reports do not consider the effects of littering, including marine litter.

Whatever type of bag is used, the key to reducing the impacts is to reuse it as many times as possible, even for those classed as 'disposable', and where reuse for shopping is not practical, other reuse, e.g. as bin liners, is beneficial. Recycling or composting generally produce only a small reduction in global warming potential.

 

Bibliography

Bisinella V and others, “Life Cycle Assessment of Grocery Carrier Bags” (The Danish Environmental Protection Agency, 2018)

Chaffee C and Yaros BR, “Life Cycle Assessment for Three Types of Grocery Bags - Recyclable Plastic; Compostable, Biodegradable Plastic; and Recycled, Recyclable Paper” (Heartland Institute, June 2014)

Life Cycle Assessment of Supermarket Carrierbags: A Review of the Bags Available in 2006” (GOV.UK, July 2011)

Would Using Biodegradable Plastics Solve the World’s Plastic Problems?” (OneSharedEarth, April 2018)

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Any reusable shopping bag is better than a disposable bag. However, the production of cotton has numerous negative impacts. The World Wildlife Fund states that just 1kg of cotton requires 20,000L of water to produce. Other impacts from cotton farming include soil erosion, and soil/water pollution. Lighter cotton bags use less water to produce, however they still contribute to the pollution caused by chemical fertilisers and pesticides.

Polyester bags are fractionally more environmentally friendly than polypropylene bags. Pablo Paster states that whilst the greenhouse gases emitted in making a 35g polyester bag are equivalent to the manufacturing of 7 disposable plastic bags, polypropylene bags come in slightly higher, at the equivalent of 11 disposable bags.

However, the most environmentally friendly option is to make your own bag out of old fabric. The environmental damage has already been done in producing the material, but upcycling it into a bag prevents it from entering landfill.

Bibliography:

Cole, Lisa, 'What is the most eco friendly shopping bag money can't buy? A Morsbag!', Less Stuff (2017), <https://www.less-stuff.co.uk/eco-shopping-bag-morsbag/>

Paster, Pablo, 'Reusable Shopping Bags: Which is the Greenest of Them All?', Tree Hugger (March 2009), <https://www.treehugger.com/clean-technology/reusable-shopping-bags-which-is-the-greenest-of-them-all.html>

World Wildlife Fund, 'Cotton: Overview' (2020), <https://www.worldwildlife.org/industries/cotton>

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